80 10 13585 https://digitalcollections.lakeheadu.ca/files/original/d56384bb82b7055c0dd8947ef3feb5c3.pdf 6eac8e3073122c599c349c7c53f10d11 PDF Text Text 17TH ANNUAL 17TH A UA INSTITUTE ON LAKE SUPERIOR UPERIOR GEOLOGY MINNESOTA DULUTH, MINNESOTA MAY 5-8,1971 MAY 5-8,1971 1 -4', �TEOINICAL ThGL?J CAL SESSIONS ABSTPACFS ABSTRACfS and FIELD GUIDES GUIDES for the the 17th 17th A\'NU.t\L ANNUAl.. INSTITUTE ON ON L!\.KJ:: LKE SUPERIOR INSTITUTE SUPERIOR GEOLOGY GEOLOGY Sponsored by Sponsored UNIVEPSI1Y ; IIr-,rNESOTA,DULUTI DULUTHI UNIVEPSIfl OF OF IINNESOTA, held at held DULU'fl!, ?IINNESOTA DULUTIl, i'UNNESOTA ..lay 1971 Jay 55 -- 8, 1971 Edited D.ll. Davidson Edited by by D. D.G. Dafoy Darby D.G. J.e. Green J.C. Green J.A. Grant Grant �TABLE OF TABLE OF COYI'EN]7S CONTENTS Page No. Prtge ~~o. INSTITIJTE A!\JDLOCAL IDCAL CCLt1IflEE CCl:IMITTEE INSTI'IlJTE DIRECTORS DIRECRS AND PIJGRAt4 (TflLE of ctpirgwrS pt*R 4S1RfrtCrS) ABSFRACI'S OF OF TECIWICAL TECINICAL SESSIONS ABSTRACTS SESSIONS 11 2 2 77 FIELD FIELD TRIPS Shore Volcanic Group A - North Shore Group (Keweenawan) 73 B - Cross-Section, Precambrian Rocks, Rocks, Minnesota I'brtheastern Northeastern ~tinnesota 97 C - ~Iesabi Mesabi Range Range - Biwabik Taconite US 128 D - Vermilion District 141 �-1-1- 17th 17th Annual INSTITIITE ON LAKE LAKE SUPERIOR SUPERIORGEOLOGY GEOLOGY INSTITUTE ON Sponsored by University of of Minnesota, Minnesota, [*iluth Duluth at Duluth, Duluth, Minnesota May S5 -- 8, 1971 May INSTITUTE BOARD BOARD OF OF DIRECTORS DIRECTORS INSTITUTE Laughlin Steel Steel Corp., * J. IV. W. Avery Avery (Treasurer), (Treasurer), Jones Jones &Laughlin Corp., Negaunee, Negaunee, Michigan. ilichigan. C. C. Reed Reed (Secretary), (Secretary), Michigan J'Hchigan Geological Geological Survey, Survey, ;"Iichigan. Lansing, Michigan. D. M. M. Davidson, Davidson, University University of D. of Minnesota, Minnesota, [Ailuth IW.uth Duluth, Minnesota Minnesota W. J. Hinze, State University, East W. J. Hinze, Michgian Michgian State East Lansing, Lansing, Michigan. A. B. Dickas, Dickas, Wisconsin State Superior, University, Superior, Wisconsin State University, Wisconsin. Wisconsin. G. LaI3erge, Wisconsin Wisconsin State State University, University, Oshkosh, Oshkosh, G. L. U LaBerge, Wisconsin. Wisconsin. U. W. [;1. ],V. Bartley, Bartley, Thunder Thunder Bay, Bay, Ontario Ontario ** R. * Permanent * members menvers LOCAL C(J.·tUTTEE LOCAL CCt1ITrEE Chairman: Coordinating Oiainiian: D. D. M. M. Davison Davison Arrangements Connittee: Committee: R. W. R. W. Marsden C. L.L. Matsch lttsth C. Program Program Comnittee: Coninittee: D. C. D. G. Darby Darby 3. J. C. Green Green Field Trip Committee: Conrrni ttee: J. J. A. Grant Grant A. R. R. 14. W. Ojakangas Ojakangas �-2-2- PROGRAM ~~y 4, 1971 1971 Tuesday, May 5:00 p.m. p.m. Field (North Shore Shore Volcanics) leaves Field Trip Trip A (North Volcanics) leaves Hotel liadisson Hadisson Duluth. Hotel Duluth. Wednesday, May ~,~y 5, 1971 1971 6:00 p.m. p.m. to 7:00 p.m. p.m. 7:00 p.m. 7:00 p.m. to 9:30 p.m. Field Trip A A returns to to Duluth Duluth Institute Registration Registration - Poolside, Hotel Radisson Duluth Radisson Duluth Tnursday, ~hy 6, 1971 1971 Thursday_, May 7:30 a.m. to 12:00 a.m. a.m. Registration, Superior Superior Street StreetFoyer, Foyer,Hotel IbtelDuluth Duluth �-3- SESSION S E S S ION 11 i,lorning ;lorning Thursday, l11Ursday, i.fay 1971 'ay 6,6, 1971 Symposium on Keweenawan Keweenawan Geology Geology—- Lake Superior Region Region Symposium Co-chairmen: Co-chainnen: Jack and Walter Jack Phillips and 1/alter White Page No. No. 8: 45 8:45 J. C. C. Green Green IntroductoryRemarks Remarks Introductory 9:00 IV. White Iv. & Keweenawan lVesterrunost KeweenawanStratigraphy Stratigraphy ofofTYesternimost Michigan Hichigan 71 9:20 N. K. N. K. Ih.xber Huber The Keweenawan KeweenawanGeology Geology Isle Royale, The ofofIsle ;.1ichigan Michigan 31 9:40 II. A. A. Hubbard Hubbard H. Keweenawan Geology Geology of the the Porcupine Porcupine Keweenawan ;"buntains, tuntains, Western Upper Peninsula 30 20 Others ~·,tichigan Uchigan 10:00 J. C. C. Green Green of the theNorth North Shore Shore Voltanic Vo1tanic Stratigraphy of Group Northeast Bay, 1innesota ;··linnesota Group Northeastof of Silver Bay, 10:20 R. R. N. N. Annells Armells Middle ~·liddle Keweenawan VolcanismofofEastern Eastern Lake Keweenawan Volcanism Lake Superior 7 7 10:40 A. P. Jtotsala A. P. Ruotsala Characteristicsof ofSome Some Alteration Alteration Minerals ~tinerals Characteristics Lake Lava Lava Series, Michigan Portage Lake Series, Michigan 59 11 :00 11:00 IV. T. T. Jolly W. Fades Puinpellyite Facies Zeolite and Prehnite Prehnite -- Pumpellyite Zeolite and theKeweenawan Keweenawan Basalts Northern in the Basalts of of Northern :.tichigan The Role Roleof of Volatiles Volatiles Michigan II: II: The 34 11: 20 11:20 T. A. T. A. Vogel Vogel & R.J. R.J. Chemically Zoned Native Copper Chemically Zoned Native Copper and and from White IVhite Pine Pine Michigan Michigan Rohrbacher Chalcocite from 11 :40 11:40 1!. C. C. halls H. Halls G. G. F. F. West \\Test 12:00 12: 00 DON NOON The Isle Royale Royale Fault Fault & The Mjourn for Adjourn for Lunch Lunch There 'vi1l be a lunch lunch meeting meeting of Board of the There will be of the the Board of Directors Directors in the Hotel Radisson Radisson ililuth fuluth—. - location to be be announced. announced. hotel 70 25 �-4- SESSION S E S S ION 22 Afternoon Thursday, Thursday, May 6, ~my 6, 1971 Symposium on on Keweenawan Keweenawan Geology Geology -- Lake Superior Superior Region Region Co-Chairmen: Co-01ainnen: 1:40 1:40 2:00 2:00 2:20 2:20 J. Leone K. Siiis Raymond J. Leone and and Paul K. Sims J. T. T. Mengel, Mengel, Jr.& Jr. Exploration J. Exploration Geology Geology of of Douglas Douglas County, County, R. R. A. A. Hendrickson Hendrickson Wisconsin Wisconsin D. Davidson ,Jr. D. vI. M. Davidson,Jr. Ne,.. View View of of the the Duluth Duluth Complex, Complex, A New A Minnesota B. Bonnichsen B. Bonnichsen in the the Southern Southern Part Part of of the the Hornfelses in Hornfelses Page Page No. No. 47 13 13 11 Duluth Complex, Il1luth Complex,?•linnesota Minnesota 2:40 2:40 M. M. G. G. i4idrey M.ldrey & P. W. W. Weiblen P. Reinvestigation of of "Red "Red Rocks" Rocks" in Reinvestigation in the the Pigeon Pigeon Point Point Area, Minnesota Minnesota 53 53 The Great Logan Logan Paleomagnetic Paleomagnetic Loop Loop The Great 58 58 3:00 3:00 to Coffee Break to 3:20 3:20 3:20 3:20 W. A. Robertson Ibertson W. A. W. F. F. Fahrig Fahrig W. & 3:40 3:40 A. Me.ttis A. 1'-attis Lower Lower Keweenawan Keweenawan Sediments Sediments of of the the Lake Lake Superior Superior Region Region 45 4:00 4:00 D. Myers D. ;"fyers The and Tectonic Tectonic Significance Significance The Sedimentology Sedimentology and of the Bayfield of the Bayfield Group, Group, Wisconsin Wisconsin 54 4:20 4:20 C. Merey G. B. B. ~brey Revised Keweenawan I{evised Keweenawan Subsurface Subsurface Stratigraphy, Stratigraphy, Southeastern Minnesota 50 50 4:40 H. C. Halls H. C. C. F. F. West West C. and Stratigraphy of the the Shallow Shallow Structure Structure and Lake from Seisnic Seismic Refraction Refraction Lake Superior Superior Basin Basin from Measurements Measurements 23 & ******** * * * * * * **** **** ** Evening 7:30 p.m. p.m. Banquet -- Great Hall Banquet Hall - Hotel Radisson Radisson Duluth Duluth - ADDRESS ADDRESS -- Dr. Carl Carl R. R. i\nnhausser Arrmlausser Economic Economic Geology Geology Research Research Unit Unit University University of of Witwatersrand Witwatersrand Johanneshurg, South South Africa Africa Johannesburg, �-5-5— S E S S ION 33 SESSION !trning ~'brning Friday, May 7, Friday, 7, 1971 1971 General General Session Session Co-Chaitnen: Co-Chairmen: Cedric. Cedric. L. L. Iverson Iverson and and J. J. Ka11iokoski Kalliokoski Page It. No. Page 8:40 8:40 F. C. F. C. Tan Tan 4& E. C. Perry, Perry,Jr. Jr. Implications of Carbon Carbon Isotope Isotope Ratio Ratio Variations in in Carbonates Carbonates from from the the Biwabik Biwabik Variations Iron Iron Formation, Formation, Minnesota Minnesota 64 9:00 9:00 S. Viswanathan, S. Viswanathan, Ii. C. C. Perry, E. Perry, Jr. J r. & P. Sims 4 OxygenIsotopic Isotopic Studies Studies of Oxygen of Early EarlyPrecambrian Precambrian Granitic and and Metamorphic Rocks Rocks from from the the Western Giants Range Range Batholith, WesternPart Part of of the Giants Northeastern Minnesota Northeastern Minnesota 66 9:20 G. 1. LaBerge LaBerge G. L. Some Geology of Harathon County County Volcanic of the ?larathon Some 39 Belt P. O. Banks Banks 4~ P. 0. W. Van Sc!llTlUS W. R. R. Van Schmus Rocksof of Iron Chronology of Precambrian Precambrian Rocks chronology L. L. A. A. Prince Prince 4& Geochronology of the the Giants GiantsRange P~ge Granite Granite Geochrono]ngy 57 10:20 G. Klein G. Precambrian Clastic Paleotidal Sedimentation Sedimentation Precambrian Clastic Paleotidal 36 10:40 Pt. ii!inze, Continental Continental Rifts W. Jinze, H. iiavidson,Jr. D. Daviclson,Jr. I). Iv!, & 4 R. Roy 11:00 1\la1an & It C. R. C. Malan 1]. A. A. Sterling D. 9:40 9:40 10:00 G. C. N. . I·ranson Hanson Fj and Dickinson Dickinson and 99 Counties, Michigan Michigan Thoriumin in PreDistribution of Uranium Uranium and and Thorium cambrian Rocks of of the Western cambrian Rocks Western Great Great Lakes Lakes 29 42 42 Region 11:20 20 11: N. 11[. N. Pt. O'Hara 4& w. J. I:inze Hinze Lake nichigan Michigan Aerornagnetic Aeromagnetic Survey Survey 56 56 /u An Aeromagnetic Survey Survey of Southern of the Southern ofMichigan ~lichigan Peninsula of 35 iv. 11:40 11 :40 . R. 1. L. Kellogg Kellogg 4l]" Pt. J. W. J. I-Jinze Hinze 12:00 NWN 12:00 NOON — - Lunch �-6-6- SESSION S E S S ION 44 Afternoon Afternoon 1971 Friday, Friday, I,1ay lay 7, 1971 General Session Co-Chairmen: Co-Chainnen: C. Tychsen 1'chsen Meredith F. E. Ostrom and and Paul C. Page No. Page No. 1:20 1:20 Business of the the Institute Institute &zsiness Meeting Meeting of 1:40 1:40 M. S. S. M. 2:00 2:00 J. Mancuso t,.1.ancuso J. J. J. F. Dimroth & E E. J. Chauvel .J. 2:20 2:20 W. ]Aihling W. fuhling Precambrian Iron Formation Precambrian Formation at at Copper Copper ~·ibuntain, FremontCounty CountyWyoming 1Vyoming Nbuntain, Fremont 18 2:40 E. Frodeston F. Frodeston Some Sedimentary in the the Lower Lower Sonic Sedimentary Structures in Cherty nember Fonnation: Memberofofthe the Bhvabik Biwabik Iron Formation: Cherty The Virginia Virginia Horn The Horn Area Area 32 32 3:00 G. Spencer Spencer G. Chert in Sediments Sediments Chert in 62 3:20 J. Mathersill ~bthersill Limnogeological ofThunder Thunder Bay, Bay, Limnogeological Studies of Lake Superior, Superior, Ontario Lake Ontario 51 3:40 R. Shegelski R. Shegeiski TI1e ofThunder Thunder Bay, Bay, The General General Stratigraphy Stratigraphy of Lake Lake Superior 61 4:00 4: 00 End of Technical End of TecJmical Sessions Sessions Lougheed & Hematite Pseudomorphic After After Biogenic Biogenic Pyrite in the the Negaunee Negaunee Iron Iron Formation Fonnation Pyrite in Textural Facies Facies Analysis of Precambrian Textural Precambrian Cherty Ironstones Ironstones *** * * * **** **** **** ** ** 5:00 5: 00 (Dinner and lodging are included and lodging included in the field field trip trip fee.) fee.) Departure for for Field Field Trips: Trips: Field Field Field Field Field Trip A Trip Trip BB -Trip CC -Trip UD -- North Shore Volcanic Group Volcanic Group Cross-section, Precambrian Rocks Precambrian Rocks Mesabi j\!esabi Range Taconite Range -- Biwabik Biwahik Taconite Vermilion District District Vemiilion Buses will will depart Buses depart from from Hotel Hotel Radisson Radisson Duluth. Duluth. *********** Saturday, nay May 8th, 1971 Saturday, 6:00 to to 7:00 (approx .) (approx.) REThRNOF OFALL ML FIELD RETIJRN FIELD TRIP TRIP BUSES. BUSES. 41 41 15 15 �-7- -7-- KEWEENAWAN VOLCANISM VOLCANISM OF OF EASTERN EASTERN LAKE LAKE SUPERIOR. SUPERIOR. MIDDLE KEWEENAWAN R. N. N. ANNELLS R. Geological Survey Survey of of Canada, Canada, Ottawa. Ottawa. ABSTRACT Following the study of the Michipicoten Island Island Keweenawan flows flows reported reported elsewhere (Annells, (Annells, 1970), srone type type of detailed stratigraphic/petrographic 1970), the same has been carried out on the Keweenawan volcanic rocks study has rocks of the the Mamainse Point, the east shore shore of Lake Lake Superior. Superior. Point, Alona Bay and Cape Gargantua sections on the three east east shore shore sections sections are are mostly mostly made made up up of of inafic mafic olivine—tholefite olivine-tholeiite These three types of texture, accompanied by by aa smaller smaller number number types of medium-coarse medium—coarse ophitic or diabasic texture, of fine—grained fine-grained olivine—poor olivine-poor tholeiite tholeiite flows. flows. Flows of intermediate composition composition found in these these sections sections and and the the flows flows show show little little variation variation in in mineralogy. mineralogy. were not found Small rocks occur occur interbedded interbedded with with the the Small volumes volumes of both basic and acid pyroclastic rocks flows flo\vs in the the lower part of the 14,300 foot foot Mamainse Point section, section, and and conglomerconglomerates partings showing good cross—bedding cross-bedding outcrop in in the the upper upper half half ates with with sandstone partings of this this section and in that that at at Cape Cape Gargantua. Gargantua. Evidence of the simultaneous availability of basaltic and and rhyolitic rhyolitic material material of the is is seen in the Mamainse Matnainse Point Point section; section; plugs, plugs, dykes dykes and and sheets sheets of of fine-grained, fine—grained, often flow—laminated flow-laminated and and autobrecciated leucorhyolite leucorhyolite occur occur at at all all levels levels of of this this one such intrusive sheet was found to section and one to he be composite, composite, having having aa 2—foot 2-foot basal selvage of fine—grained fine-grained basalt and and aa 50—foot 50-foot acid acid upper upper part. part. Fetrographic Petrographic similarities found found in in flows flows of of the the Mamainse Mamainse Point Point and and Cape Cape good basis basis for for lateral lateral correlation correlation of of these these two two Gargantua sequences provide aa good sequences. Near the basal unconformity of theMamainse therlamainse section section there there occurs occurs aa highhighly olivine-tholeiite flow flow crowded crowded with large large plagioclase plagioclase ly distinctive glomerophyric olivine—tholeiite laths concentrated concentrated in spherulitic clusters up laths up to to two two inches inches in in diameter diameter (Ciblin, (Giblin, 1969); aa flow flow of of exactly similar type 1969); type outcrops 40 40 miles NNW NNW along along strike strike near near the the base of the the Cape Gargantua section section (Ayres, (Ayres, 1969). 1969). Both these occurrences are assoBoth these ciated with with aa group group of olivine-tholeiite olivine—tholeiite flows ciated flows rich rich in in large large pseudomorphs pseudomorphs after after \vhich may make up up to to 35 35 per per cent cent by by volume volume of of the the rock rock in in parts parts olivine phenocrysts which of such flows This striking similarity of the flows at at Mamainse Mamainse Point. Point. This the flows flows in in the the levels of the lower levels the Mamainse Point and Cape Gargantua piles piles suggests suggests simultaneous simultaneous effusion of the the same S~le mafic magma supply supply over over aa wide wide area area to to preduce pr~duce lava lava flows flows of of sii,!lar extent to to that that of of the the Greenstone Greenstone Flow Flow of of the the Michigan Michigan Keweenawan. siIIl~Lar extent Point, Alona Alana Bay Bay and and Cape Cape Gargantua Gargantua flo9s f1o'to.{s are are also also petrographical— petrographicalThe Mamainse Hamainse Point, ly similar to olivine—tholeiite flows ly to the the olivine-tholeiite flows forming the the basal part part of of the the Michipicoten Michipicoten Island section and it is possible that that these these latter latter flows, flows, also also cut cut by by acid acid intruintrusions, sions, may represent the the upper part of of an an extensive extensive and and largely largely uniform uniform flood flood babasalt pile whose earliest members rest rest directly directly on on the the Archaean Archaean on on the the east east shore shore of of Lake Superior. Superior. The more highly differentiated differentiated andesite andesite and and rhyolite rhyolite flows flows of of Hichipicoten Island are thus interpreted Michipicoten Island are thus interpreted as as being being of of much much later later extrusion extrusion than than the the A general increase in the deMamainse Point, Point, Alona Alana Bay Bay and and Cape Cape Gargantua Gargantua flows. flows. A flows is gree of alteration alteration of of lava lava flows is apparent apparent as as the the Keweenawan Keweenawan lava lava pile pile is is followed followed downwards of the the Michipicoten Michipicoten Island Island section section to to the the base base of of the the downwards from from the the top top of Mamainse Point Point section. section. Mamainse �-8—8— Some differences differences in general chemistry exist between flows Some flows newly newly analysed analysed from from Island and and Maniainse Mamainse Point the Island Island flows flows the Michipicoten Island Point sections; sections; 36 36 analyses of the tholeiitic trend trend of moderate iron—enrichment iron-enrichment on on an an Nfl MFA plot; plot; aa similar similar plot plot follow a tholeiltic of 46 analyses of Mamainse Point flows flows gives gives aa tholefitic tholeiitic trend trend of of high high iron—enrichiron-enrichment. References; References: Annells, R. N., N., Annells, It. 1970, geology of of Michipicoten Michipicoten Island, Island, 1970, Keweenawan volcanic geology Lake Superior Lake Superior; Program, Program, 16th 16th Ann. Ann. Inst. Inst. on. on. Lake Geol., Thunder Bay, Bay, Ont., May May 1970, 1970, 7. 7. Ceol., Ayres, L. L. D., D., 1969, 31 and 30, 30, Ranges 20 20 and and 19; 19; 1969, Geology of Townships 31 Ontario Dept. Dept. Mines Ceol. Geol. Rept. Rept. 69,38. 69,38. Giblin, P. E., E., Giblin, P. 1969, Prelim. Geol. Geol. Naps Maps 553 553 and and 555. 555. 1969, Ontario Dept. Dept. Mines, Mines, Prelim. �-9—9— CHRONOLOGY OF PRECAMBRIAN ROCKS ROCKS OF OF IRON IRON AND AND DICKINSON COUNTIES, MICHIGAN P.O. P.O. Banks Department of Geology Geology Case Western Reserve University, University, Cleveland, Ohio, 44lO6 44106 and W.R. Van Schmus W.R. Department of Geology Geology University of Kansas, Kansas, Lawrence, Lawrence, Kansas, Kansas, 6604k 66044 U—Pb analyses of cogenetic zircon suites and Rb-Sr whole rock analyses U-Pb from from selected Precambrian Frecambrian units units in Iron and Dickinson Counties, Michigan, suffice to for this classic suffice to establish an internally consistent chronology for area. Stratigraphic nomenclature used herein is adopted from from James et et al. al. (1961). (1961). Zircons from the Norway Lake Gneiss, which underlies the Dickinson Zircons from the Group, 2375 m.y., but Group, yield aa concordia intercept age of approximately 2375 Rb-Sr from the Norway Lake Gneiss do not define define an an Rb-Sr whole whole rock rock analyses analyses from isochron, and the isotopic isotopic composition composition of of Pb Pb from from separated separated feJ.dspars feldspars is isochron, is abnormal. Thus, from the Thus, we we conclude that that the 2375 m.y. m.y. "age" obtained from zircons zircons is is probably the the result result of complex metamorphism and deformation of the Norway Lake Gneiss and does not indicate indicate its its true true absolute absolute age. age. The 2375 m.y. m.y. event event that that affected the the Norway Lake Gneiss may be pre—Dickinson, pre-Dickinson, 2375 thus establishing a possible older limit for for the the age age of of the the Dickinson Dickinson Group. Group. Earlier published zircon analyses suggesting suggesting aa much greater greater antiquity antiquity for for the Dickinson Group etal., Group (2700 (2700 m.y. or more: Aldrich Aldrich et al., 1965) 1965) are are interpreted interpreted to reflect detrital detrital zircon zircon components components in in the thernetasedimentary metasedimentary gneisses. gneisses. The pre—Animikie pre-Animikie Porphyritic Red Granite, Granite, whose whose field field relation relation to to the the Dickinson Group is is uncertain, gives aa zircon zircon conoordia concordia intercept intercept age age of of approximately rock Rb—Sr approximately 2100 2100 m.y. m.y., and whole rock Rb-Sr analyses are also consistent consistent with this We interpret interpret this this age age to be post-Dickinson, thus bracketing this age. age. We the age of the Dickinson Group between 2100 2100 m.y. and, and, perhaps, perhaps, 2400 2400 m.y. m.y. , A single zircon analysis from from the Hemlock Volcanios Volcanics of of the the Animikie Animikie A but the the zircon zircon is is somewhat somewhat discordant, discordant, Series yields a Pb-Pb age of 1985 m.y., but so that that the concordia intercept intercept age is is expected expected to to be be slightly sligh~ly older older at at approximately 2000 2000 m.y. m.y. Rb-Sr whole rock analyses on the the post-Animikie post-Animikie Feavy Peavy Complex Complex yield yield Rb—Sr an age of approximately 1700 m.y. approximately 1700 m.y. However, However, previously published mineral age age determinations determinations on other post—Animikie post-Animikie units units indicate indicate that that the the Animikie Animikie Series is is definitely al., 1965). 1965). Thus, Series definitely older older than than 1900 1900 m.y. m.y. (Aldrich (Aldrich et etal., deposition of the Animikie Series appears to to be be bracketed bracketed in in the the interval interval between 2100 2100 m.y. m.y. and and 1900 1900 m.y. m.y. A A maximum age of 2100 m.y. m.y. for the Animikie Animikie Series, Series, in in conjunction conjunction with with published Rb-Sr data on on the the post—Huronian post-Huronian Nipissing Nipissing Diabase Diabase (2160 (2160 rn.y.) m.y.) and on Huronian 1-luroniansediments sedimentsthemselves themselves(2285 (2285m.y.) m.y.) (Van (Van Schmus, Schmus, 1965; 1965; Fairbairn Fairbairn et al., 1969), 1969), severely severely restricts restricts possible possible correlations correlations between the Animikie etal., Animikie Series and the Huronian formations of the North Shore of Lake Huron. Series Shore of Lake Huron. �—10— -10- References Aldrich, L.T., Davis, Davis, C.L., G.L., and and James, James, FI.L., H.L., 1965, 1965, Ages Ages of of minerals minerals from from metamorphic and and igneous igneous rocks rocks near near Iron Iron Mountain, Mountain, Michigan: Michigan: Jour. Petrology, v. ~ v. 6, 6, pp. pp. +47-472. 447-472. Fairbairn, H.W., H.W., Hurley, Hurley, P.M., P.M., Card, Card, K.D., K.D., and Knight, Knight, C.J., 1969, Fairbairn, Correlation of radiometric radiometric ages ages of ofNipissing Nipissingdiabase diabaseand and1-luronian Huronian CorrelaL on of metasedimen-ts with with Proterozoic Proterozoic orogenic orogenic events in Ontario: Can. metasediments Jour. Earth Sci., Sd., i. Jour. Earth v. 6, pp. Lt89_497. 489-497. James, ILL., H.L., Clark, Clark, L.D., Lamey, C.L., C.L., and Pettijohn, F.J., F.J., 1961, Geology Geology James, L.D., Lamey, U.S. Ceol. of central Dickinson County, County, Michigan: Michigan: U.S. Geol. Surv. Surv. Prof. Prof. 310, 176 176 p. p. Paper 310, Van Schmus, Schmus, R., R., 1965, The geochronology of the Blind River—Bruce River-Bruce Nines Mines area, area, Ontario, Canada: Canada: Jour. Jour. Ceol., Geol., v. v. 73, 73, pp. pp. 755-780. 755-780. �—11--11- HORELSES IN THE DULUTHCOMPLEX, COMPLEX,MINNESOTA MIIESOTA HORNFELSES THE SOUTHERN SOUTHERN PART PART OF OF THE DULUTH Bormichsen Bill Bonnichsen Cornell University Hornfels of feet feet in in Hornfels bodies ranging from less than an inch to thousands of dimensions are abundant in the southern part of the Duluth Complex. They dimensions are were derived from from a wide wide variety of initial rock types, types, many of which occur in the complex footwall. footwall. The The most most abundant abundant types types were derived from argillaceous ceous sediments of the Virginia Formation, Formation, mafic to intermediate volcanic rocks of Keweenawan age and various intrusive rocks indigenous to the complex. rocks complex. Others include iron iron formation, formation, quartzite quartzite and and d.ioritic dioritic rocks rocks from from the the prepreKeweenawan basement basement and. and clastic Keweenawan age. age. elastic sediments sediments of probable Keweenawan Virginia inclusions are are very very similar similar to to metamorphosed metamorphosed footwall footwall Virginia; Virginia; however, the relative relative mineral mineral proportions are hovrever, the the grain grain size size is is larger larger arid and the are slightly different. The silicate mineralogy of argillaceous inclusions inclusions inincludes coexisting cordierite, orthopyroxene, biotite, cludes cordierite, orthopyroxene, biotite, plagioclase and and potassium potassium feldspar. Minor amounts amounts of of pyrrhotite, pyrrhotite, graphite, ilmenite and and traces of chalchalgraphite, ilmenite copyrite and pentlandite are common, but olivine and and Ca pyroxene invariably but olivine pyroxene are invariably absent. Various types types of of relict relict se.imentary sedimentary structures structures are distinguishable distinguishable in all but the smallest smallest of of hornfelsed hornfelsed Virginia Virginia inclusions. inclusions. all inclusions are are characterized characterized by by their lack of of relict Volcanic hornfels inclusions their lack sedimentary structures, local round round to ellipticalplagioclase plagioclase and and Ca pyroxene structures, local to elliptical segregations that probably were segregations were amygdules amygdules and their mineralogy. They consist largely of niagneof plagioclase plagioclase and and Ca pyroxene, and normally contain abundant magnepyroxene, and tite and tite and orthopyroxene (commonly (commonly inverted invertedpigeonite). pigeonite). Olivine, brown brown hornblende, apatite, ilmenite, and and traces traces of biotite biotiteoccur occurininsome some bodies bodies but but none none apatite, ilmenite, graphite, or or more more than than traces traces of of potassium potassium are known knovm to contain cordierite, cordierite, graphite, feldspar. FeO+MgO of various The proportions of of weight weight percent percent 3102, Si0 , Al20~ and. and FeO+MgO 2 types of hornfelses hornfelses and equivalent equivalent rocks rocks are are plotted ploted in in figure figure 11 (Bonnichsen, (Bonnichsen, in prep.). A, B prep. ). The A, B and CC groups are materials from from the the Virginia Virginia Formation, Formation, vlhereas the the D, EE and and FF groups groups are are volcanic volcanic hornfelses homfelses and. and their equivalents. whereas Note Note that, that, although although both both groups groups show show considerable considerable range range in their proportion A12O3. of Si0 the Virginia materials have higher proportion of Al 0 . , SiOa, the Virginia have a higher proportion 2 2 3 The group A unmetamorphosed Virginia and and equivalent hornhomA samples are unmetamorphosed felses from the felses the footwall footwall of of the the complex. complex. The group BB samples are are from from incluinclusions vlithin within the complex. sions complex. Note their depletion in 8i0 relative to the A 5102 the A 2 group. This This suggests suggests that Si02 8i02 was lost from from the inclusions; inclusions; this this loss loss is is accompanied by a similar depletion of K20 ~O in several several samples samples and and suggests suggests loss loss of aa grantic grantic partial partial melt melt during during the the hornfelsip.g hornfelsipg process. process. The group CC samples samples are are from the margins margins of hornfels bodies and and thus thus were in in direct direct contact with with initial the the intrusive intrusive rocks. rocks. Their Their compositions compositions deviate further from from the initial deviate farther values than do those of group B; B; they are considered to be refractory resiresiduals which which had had become become nearly nearly equilibrated equilibrated with vlith the the adjoining adjoiningmagnias. magmas. Part group BBrocks feldspars and and cordierite of the the group rockscontain containtexturally texturallyinterstitial interstitial feldspars which are interpreted interpreted as as recrystallized recrystallized partial partial melts. melts. During the hornfelsing process aa melt melt with ,nth the the composition composition ofofcordierite cordieritearid, and alkali alkali feldspar evidently developed after a granitic fraction had had been been lost. lost. Hornfelses with the group C where this this later type type of melt melt C compositon are considered to have formed formed where had been lost. The formation of granitic dikes dikes and and the the production production of of abundant abundant C pyroxene are the biotite and orthopyroxene orthopyroxene at at the expense of olivine arid and Ca principal effects on the enclosing intrusive intrusive rocks assimilation rocks \vrought wrought by the the assimilation of such partial melts. �—12— -12- Si02 :7 Figure I. 'F A1203 FeO* A 00 E F. c@ 50 to 41203 AI203 V v vV v V vV to to FeOtMgO FeO+ MgO V v Group E consists of hornfelsed. basalts; they they have have bulk bulk compositions compositions that that hornfelsed basalts; show little deviation from from the the compositions compositions of of ordinary ordinary basalts. basalts. Group Group FFrocks, rocks, however, have and Si02 Si02 and and higher higher Ti0 Tb22 and and FeO have lower lower K20 and FeO contents contents than than ordinary hornfelses may have been inbasalts and and have high high Fe/Mg Fe/Mg ratios. ratios. Two of these hornfelses trusive residual residual liquids liquids which which separated separated from from trocto].ite troctolite but but the the other other one one evidently is aa hornfe].sed hornfelsed volcanic rock that that contains contains probable probable relict relictaxnygdules. amygdules. dently is volcanic rock Sample D D is is an magnetite-richbasaltic basaltic rock from an unmetamorphosed unmetamorphosed magnetite-rich from along along the the eastern margin of the complex; its Fe/Mg ratio is is like that of group F. The margin of complex; its Fe/lf~ ratio volcanic rock in group F may initially have had a composition composition similar to that that of sample D. D. If so , it material during during so, it lost lost aa substantial amount amount of granitic granitic material hornfelsing process. the hornfelsing process. in the The abundance and distribution of hornfelsed volcanic rocks in system of southern part of the complex supports the concept that an extensive system Keweenawan flows was present throughout the region and had been laid down Kew"eenawan flOivS was dOim on an erosion erosion surface surface cut cut in in the the Middle Middle Precambrian Precambrian rocks. rocks. The the Theintrusion intrusion of the an Troctolitic Series Series and accompanying crustal extension evidently broke up the volcanic volcanic rocks. rocks. As distributed throughout As a result result the the hornfelses hornfelses are are widely ddely distributed the southern half of of the the complex. complex. Many l~ of of the the large large bodies occur occur as as septum septum betvreen adjacent intrusive intrusive bodies. bodies. The great number of inclusions of various between adjacent types along the the footwall types footwall of the complex indicated that the intruding troctoconsiderable mechanical mechanical strength. strength. Evidently, litic magmas had considerable Evidently, these thesemagmas magmas were mushes were in the the form form crystal-rich crystal-rich mushesduring duringemplacement. emplacement. Ref: Bonnichsen, the Duluth Duluth Complex, Complex, St. st. Bonnichsen, B. B. (in prep.); prep.); The southern part of the Louis and Lake of Minnesota, Minnesota, Lake Counties, Counties, Minnesota; Minnesota; to to be be publ. publ. in in Geology Geolor of Schwartz commemorative volume;P.K. P.K. Sims, Sims, ed. G.M. Schw"artz connnemorative volume; �-13—13— A NEW VIEW OF THE DULUTH DULUTH CO~PLEX, COMPLEX, MINNESOTA A by Donald H. M. Davidson, Davidson, Jr. Jr. University of Minnesota, Duluth Duluth and Minnesota Geological Survey Hinnesota ABSTRACT A B S T R ACT The late Precambrian (Keweenawan) (Keweenawan) Duluth Complex is is a sequence generally discordant intrusive rocks of generally rocks extending extending northeastward northeastward from from Duluth to to 1-loyland, Hovland, Minnesota Minnesotain in a a roughly roughly crescentic crescentic configuration. The the Complex Complex is is bifurcated bifurcated on on the the east east and and south south The outcrop outcrop pattern of the by rocks rocks of the the North Shore Shore Volcanic Volcanic Group. Group. in Table 1, 1, three three rock rock series series (anorthosite, (anorthosite, As may be noted in troctolite—olivine gabbro gabbro and and felsic) troctolite-olivine felsic) constitute the the major petrologic petrologic units of the Complex. units the Complex. Anorthosite series rocks were apparently emplaced as large, crystal-liquid as crystal—liquid masses massesinin ~.,hich whichcumulus cumulusplagioclase plagioclaseisis the the prepredominant mineral. mineral. The anorthositic rocks, which form the central portion dominant rocks, t.,hich of the of the Complex, Complex, have been subsequently intruded intruded by by the the troctolite troctolite series series along the northern and western footwall footwall and and by by the the olivine olivine gabbro gabbro series series to troctolites and to the southeast. The The troctolites and gabbros gabbros are are aa sequence sequence of of genergenerally containing cumulus plagioclase and and olivine olivine and and poik— poikally layered layered rocks rocks containing ilitic pyroxenes. The The basal basal troctolite series dips gently (15°) towards dips gently (15°) towards Lake Superior, Superior, whereas whereas the Lake the attitudes of the the upper upper olivine olivine gabbro gabbro series series vary (e.g. Sawbill vary from northward dips dips of of 40° 40° (e.g. Sawbill Lake Lake area) area) to to southward southward at low Q5°) cLS°) angles angles (e.g. (e.g. along along the the Brule Brule River Prong). Felsic series at rocks are are predominantly granophyric granite which occur rocks occur as as subhorizontal subhorizontal sheet—like masses sheet-like masses above aboveboth bothmargins marginsofofthe theolivine olivine gabbro gabbro series. series. Separate minor arate minor intrusives as the Endion Sill, Sill, the the Beaver Beaver Bay Bay Complex Complex intrusives such as and to be younger than than the the Duluth Duluth Complex, Complex, and the the Hovland Complex appear to whereas only Lie the Gunflint Gunflint Prong Prong Layered Layered Complex Complex appears appears older. older. Petrologic relationships sources derived derived from from the the mantle, mantle, to to relationships suggest suggest multiple magma sources account for account for the the petrogenetic sequence of the the Duluth Duluth Complex. Complex. The Duluth Complex Complex is is coincident coincident with with the the axis axis of of the the Mid—Continent Mid-Continent Gravity High. High. Footwall shearing and the the asymmetric asymmetric position position of of the the Complex Complex with with respect respect to to the the Lake Lake Superior Superior Syncline Syncline suggest suggest Complex Complex emplacenent consanguinous emplacencnt consanguinous with with rifting. riftine. Gravity studies to to date date suggest suggest the Complex thins thins or is absent beneath Lake Lake Superior. Superior. Dominant Complex Complex the N.20E.—N.SOE.) are common fracture trends trends (N.-. (N.-~.90E. or W. W.,, ~.20E.-~.80E.) common throughout throughout 90E. or the Lake regional post—intrusive post-intrusive extension. extension. the Lake Superior area suggesting regional Significant base-metal base—metal mineralization mineralization occurs occurs within within selected Significant troctolite controls afforded afforded by by host host troctolite series series horizons horizons with local ore controls rock lithology and structural settling settling shelves. shelves. Should the proposed funnel the central complex complex be verified, subsurface subsurface funnel configuration configuration of the exploration of the the Southern Complex Complex appears appears warranted. ~varranted. �Table 1. Table 1. Summary of Principal Petrologic Series and Units, Units, Duluth Complex, Complex, Minnesota Late Minor Hinor Intrusive Complexes Felsic Troctolite— TroctoliteDuluth " G hb Duluth Complex CompleX01i Gahbro Ol l.Vl.ne ,cambrian a ro cambrian (l.ltO.2b.y.) (l.10.2b.y.) Endion Sill Sill Er.nst~ W. W. C., G., 1960, 1960, Jour. Jour. Ernst, Beaver Bay Complex Gehman, H. H. M., M., Jr., Jr., 1957, 1957~ Unpub. Unpub. Ph.D. Ph.D. Thesis, Thesis, Univ. Univ. of of Minn. Minn. Konda, T., 1970, 1970, Contr. Contr. Min. Mm. Pet., Konda, T., Pet., Vol Vol 29, 29, p. p. 338—344 338-344 Hovland Complex Hoviand Complex Jones, N., N., 1963 Unpub. Unpub. M.S. M.S. Thesis, Univ. Univ. of Minnesota Granophyric Granite and and Minor Felsic Hinor Intrusives Davidson, D. D. M., Jr., Jr., 1969, 1969, Minn. ~linn. Geol. Geol. Surv. Surv. Misc. Misc. Map Ser., Ser.~ M—7, M-7, M—8 M-8 Grout, F. F., F., and and others, others~ 1959, 1959, Minn. Minn. Geol. Geol. Surv. Surv. Bull. Bull. 39. 39. Grout, F. Grout, F. F., F., and and others, others, 1959, 1959, Minn. Minn. Geol. Geol. Surv. Surv. Bull. Bull. 39. 39. Grout, F. Basal Troctolite Troctolite ,1969, Minn. Minn. Geol. Geol. Surv. Surv. Rept. Rept. Inv. mv. 99 Phinney, W. C. C.,1969~ Phinney, W. 44 Bull. R. B., B., 1964, 1964~ Minn. Minn. Geol. Geol. Surv. Surv. Bull. 44 Taylor, R. Central Anorthosite Early Minor Ninor Intrusive Complexes North ~orth and Anorthosite Inclusions Bonnichsen, Bill, Bill, 1969,30th 1969,30th Annual Annual Min.Sympos.,Univ.Minn.pp.8993 ~lin.Sympos. ,Univ.Minn.pp.89-93 Bonnichsen, ,Univ.Mlnn.pp.89—93 Bonnichsen, Bill~1969~30th AnnualI'lin.Sympos. Hin.Sympos.,Univ.Minn.pp.B9-93 Bonnichsen, Bill,1969,3Oth Annual Misc. Map Davidson, D. D. }[., Jr.~ 1969, Minn. Minn. Geol. Geol. Survey Survey Misc. Hap M., Jr., Ser. 1—7, Ser. H-7~M—8 M-B Sd. Mem. Phinney, W., W., 1966, N.Y. State, State~ Mus. Mus. Sci. Hem. Vol.18, Vol.18, p.135—147 p.135-l47 1966, N.Y. Phinney, 44 Taylor~ R. R. B., B., 1964, 1964, Minn. Minn. Geol. Geol. Survey Survey Bull. Bull. 44 Taylor, Gunflint Prong Prong Sill Sill Babcock~ R.C., R.C., 1959, 1959, Unpub. Unpub. M.S. M.S. Thesis, Thesis, Univ. Univ. Wisc. Wise. Babcock, Brule Lake Sills Bull. 39. Grout and and others, 1959, 1959 ~ Minn. Hinn. Geol.Survey GeoI. Survey Bull. 39. Granoels Granofels Shore Pet., Pet.~ Vol. Vol. 1, 1, p. p. 286—303 286-303 Upper Olivine Gabbro ,e Anorthosite Anorthosite Principal References Principal Unit Series Map Ser. Ser. M—7, D.H., Jr., Jr., 1969, 1969~ Ninn. lorinn. Geol. Geol. Survey Survey Map M-7, N—8 H-B Davidson, D.M., Volcanic Volcanic Group Group Volcanics— VolcanicsUndifferentiated ;-1iddle 'Ii ddle Lower Duluth Complex Early Hinor Minor Early Intrusive Intrusive Complexes Gunflint Gunf lint Prong Layered Complex Complex Nathan~ H., 1969, 1969, Nathan, H., I I Unpub. Ph.D. Thesis, Univ. Unpub. Ph.D. Univ. Minn. Minn. I HI ~I �-15-15— TEXTURAL FACIES IRONSTONES* FACIES ANALYSIS ANALYSIS OF OF PRECAMBRIAN PRECAJfBRIAN CHEItTY CHERTY IRONSTONES* by by Erich Dimroth, Dimroth, Service de Pl'Exploration Erich Exploration geologique des Richesses Richesses Naturelles, Naturelles, Quebec, Quebec, P.Q. P.Q. Ministere des and Jean-Jacques Jean—Jacques Chauvel, Chauvel, Departement de Geologie, Rennes, France France Universite Rennes, Rennes, ABSTRACT A B S T R ACT cherty ironstones ironstones are are very very similar similar to to those those Textures of Precambrian cherty of limestones limestones (Dimroth (Dimroth 1958). 1958). Accordingly the the methods of limestone limestone petrology petrology can be applied in the the study study of of ironstones. ironstones. Ironstones can be be conceived to Ironstones to be composed of textural textural elements. elements. Textural ironstone types are defined by the the kind kind and and proportion proportion of of textural textural elements present. present. Textural facies facies types types compose compose thin thin (3 (3 feet—lOO feet-lOO feet) feet) units; they they are either texturally texturally homogeneous, homogeneous, or or are are comcomstratigraphic units; textural rock rock types types that that form form beds beds alternating alternating in in aa posed of several textural characteristic sequence. sequence. It It is to determine determine the the paleo— paleois generally possible to environment envi~onment in which the the various textural textural facies facies types types formed, formed, and and by by sections, to gain a view of of the the paleogeography paleogeography correlation of of stratigraphic sections, of the depositional basin. of the following following textural textural elements elements in in the the ironstones: ironstones: We distinguish the I I Orthochems — 1. Femicrite: A A past of fine—grained fine-grained iron iron silicate silicate (minnesotaite, (minnesotaite, Femicrite: 1. sti1pnome1ane) from iron iron silicate silicate and and iron iron carbonate carbonate stilpnomelane) or of siderite derived from muds. 2. 2. ~~trix chert; chert: Matrix 3. Cement chert: Cement chert: 3. deposition. Chert deposited as as aa silicagel silicagel matrix. matrix. after Chert that that formed between allochem allochem grains grains after chert and and cement cement chert chert can can be be distinguished distinguished only only in in some some Matrix chert hematite tones. hematite irons ironstones. II IL — Allochems 1. Pellets: particles 0.2 0.2twa. mm. across unsharply unsharply bounded, bounded, Ellipsoidal particles Pellets: Ellipsoidal 1. Pellets are interpreted as aggregated always embedded in matrix chert. Pellets are interpreted as aggregated always embedded in matrix chert. particles. with the premission of the *Published with the Deputy Minister, Department Department of Natural REsources, REsources, Quebec. Quebec. �-16—16— Entraclasts: Fragments of the unconsolidated sediment that 2. Intraclasts: that have been been redeposited. redeposited. Previously (James, (James, 1954) 1954) described from from intra— intra(large intraclasts) intraclasts) and and as as "granules" "granules" (= (= sandformational conglomerates (large sand— size intraclasts). 3. 3. Oolites and and Pisolites. Pisolites. 4. 4. Shards: Shards textures. Two sub—types sub-types predominate Shards are complex textures. (a) (accommodation (a) welded welded and and extremely extremely deformed deformed oolites oolites and and intraclasts intraclasts (accommodation shards). (b) shards fragments of oolites and and (b) shards composed mainly mainly of peeled off fragments shards). intraclasts (exfoliation (exfoliation shards). shards). types are are defined defined by the the combination combination of of textural textural elements elements Textural rock types present. Main types types are: are: I. I. Femicrites: II. II. Matrix Matrix chert: chert: Laminated or ribboned silicate—carbonate silicate-carbonate ironstones. ironstones. Lamina~ed Laminated or ribboned cherts, cherts, generally generally with pellets. pellets. III. intraclastic or or oolitic oolitic ironstones. ironstones. III. Cemented intraclastjc IV. Intraclastic or oolitic rocks with chert chert matrix. matrix. IV. V. Intrafemicrjtes: Intrafemicrites: Intraclasts embedded embedded in in aa femicrite femicrite matrix. matrix. types, particularly containing containing shard shard textures, textures, are are quantitatively quantitatively Some other types, less important. important. The paleogeographic application of the the method will be be demonstrated demonstrated at at the the example of the lower jaspilite member of the the Sokoman Sokoman Ironstone Ironstone in in the the western half of the the Labrador trough trough between between latitudes latitudes 54°45'N 54°45'N and and 55°15'N. 55°l5'N. Close to Close to the the western margin of the trough trough this this stratigraphic stratigraphic unit unit is is thickly bedded bedded finely finely intraclastic intraclastic locally represented by a massive or thickly and oolitic (facies type type 1). 1). Toward o.olitic chert chert cemented cemented hematite hematite ironstone (facies this type grades into into interbedded interbedded oolitic—intraclastic oolitic-intraclastic hematite hematite the east this ironstone with chert alternating with with laminated matrix chert cement cement or or matrix, matrix, alternating chert containing type 2). 2). This type type is is thin thin to to medium medium chert containing hematite hematite (facies (fades type bedded (2—30 (2-30 cm.) em.) andcharacteristically andcharacteristically shows shows lenticular lenticular bedding. bedding. It It grades into aa type type that that contains contains intercalated intercalated beds, beds, 2—100 2-100 cm. ern. thick, thick, basinwards into east the oolitic intra— femicrite (facies (facies type type 3). 3). Farther east intraof laminated femicrite beds are lacking in type clastic beds type 4 and finally finally type type 55 is is composed composed only only of of laminated femicrite femicrite with interbeds of of laminated laminated femicrite femicrite bearing bearing matrix matrix chert. Facies types 33 and 4 are characterized characterized by by siump slump structures structures and and Pacies types structures indicating strong synsedimentary deformation. structures deformation. Toward the the centre centre of the trough types 4 and 3 reappear, and grade into a facies containing of the types 3 reappear, and grade into a facies containing interbeds (2 cm.) em.) intraclasts intraclasts and and pisolites pisolites embedded embedded in in interbeds with very coarse (2 matrix chert chert (facies (facies type type 6); 6); the intraclasts and pisolites were very soft at time of deposition. soft deposition. Facies is tentatively interpreted interpreted as as Facies type 1 is a sand bar facies that that separates separates aa lagoonal lagoonal environment environment (not (not discussed discussed here) farther west from from the the open open basin. basin. Facies Facies type type 22 has has been been deposited deposited here) in the intratidal. intratidal and in the and shallow shallow sub-tidal sub—tidal zone zone in in the the foreshore foreshore of the sand bars. facies and and bars. Types Types 33 and 4 represent represent a relatively relatively deep deep subtidal subtidal facies �-17—17— facies zone zone 55 was was deposited deposited in in aa relatively relatively deep deep basinal basinal environment environment fades (maybe 50-100 m. water depth). Facies type 6 was likely deposited on Fades type 6 was likely deposited (maybe 50—100 m. depth). shallow sub-tidal the centre centre of the the Labrador Labrador sub—tidal shoals that extended in the trough. The coarse intraclastic and pisolitic beds may represent represent storm layers. layers. References: James, II. James, H. L., 1954: Sedimentary of iron iron formation. formation. Sedimentary facies fades of v. 49, 49, p. p. 235—293. 235-293. v. Econ. Geol., Econ. Ceol., Dirmroth, 13., 1968: Dimroth, E., 1968: Sedimentary textures, textures, diagenesis and sedimentary Ironstones. N. N. Jb. Geol. Geol. environment of certain Precambrian Eronstones. Palaeont., Abh. v. 130, 130, p. p. 247—274. 247-274. �—18— -18- IRON FORMATION At COPPER FORMATION AT COPPER PRECAMBRIAN IRON MOUNTAIN, FREMONT COUNTY, COUNTY, WYOMING MOUNTA IN, PREMONT H. Duhling, Jr. Jr. William H. Natural Resources Research Institute Institute University of Wyoming, Wyoming, Laramie ABSTRACT A B S T R ACT iron formation formation is is exposed exposed along along the the south-facing south-facing Precambrian banded iron flanks Shoshoni, in in flanks of of Copper Copper Mountain, Mountain, approximately 15 miles north of Shoshoni, northeastern Frenont Fremont County, County, Wyoming. Wyoming. The Precambrian metamorphic comcomconsists of interlayered interlayered quartzofeldspathic quartzofeldspathic gneisses, gneisses, amphibolites, amphibolites, plex consists amphibole schists, schists, peliric pelitic rocks, rocks, and iron iron formation formation into into which which granite, granite, complex pegmatite, and mafic dikes and sills have been intruded. The pegmatite, sills been intruded. has been metamorphosed to has to the the kyanite-muscovite kyanite-muscovite subfacies subfacies of of the the almanalmandine-amphibolite facies. facies. Sedimentary rocks rocks of Paleozoic or Cenozoic dine-amphibolite the Precambrian Precambrian complex complex on on all all sides. sides. age abut the The mineralogical composition of of the the iron iron formation formation is is very very simple, simple, quartz, and and any any combination combination of of blue-green blue-green hornhornconsisting of magnetite, magnetite, quartz, blend, Magnetite, in blend, grunerite, and and cummingtonite. curnrningtonite. Magnetite, in all degrees of alteration to hematite, hematite, occurs in in thin thin laminae laminae and and fine fine clusters clusters with with angular, angular, sharply embayed boundaries and as very fine fine inclusions inclusions in in quartz quartz and and amphibole grains. grains. Banding is is developed by apparent increase increase in in grain the expense expense of of quartz quartz and and amphibole amphibole grains. grains. size of the magnetite at the The iron formation, formation, interlayered interlayered with amphibolite amphibolite and and quartz-mica quartz-mica schist, is is exposed for for a distance of of about about 66 miles miles over over an an approximate approximate schist, width of of 1000 1000 feet. feet. The strike of of the the formation formation is is NN 80°E 80 0 E and and the the dip dip is to the the south. south. is 70° 700 to Liberation and concentration tests tests indicate indicate the the presence presence of of roughly roughly million iron and 22% 22% silica. silica. The The million tons tons of concentrates concentrates containing 56% iron fine magnetite in in quartz quartz and and amphibole amphibole grains grains and and the the amount of very fine amount interstitial quartz quartz in in the the magnetite-rich magnetite-rich bands bands account account for for amount of interstitial the high high silica content of the the the concentrates. concentrates. l3~ 13¾ Rail comes within ten ten miles of of the the outcrop outcrop area, area, but but Rail transportation comes the nearest markets for a blast furnace furnace feed feed are are over over 240 240 miles miles away. away. the markets for to market, market, high silica silica content, content, low low tonnage, tonnage, and and steep steep The distance to to indicate indicate that that this this iron iron formation formation has has aa questionable questionable dip combine to economic potential. potential. �-19—19— Selected References References 1. 1. Duh1ing, William William H., H., Jr, 1970, 1970, Oxide Oxide facies facies iron iron formation formation in in the the Duhling, Owl Creek Mountains, Mountains, northeastern Fremont Fremont County, County, Wyoming: unpublished MS thesis, thesis, University University of of Wyoming, Wyoming, 92 92 p. p. 2. 2. G1iozzi, James L., L., 1967, 1967, Petrology and and structure structure of of the the Precambrian Precambrian Gliozzi, James rocks the Copper Mountain district, district, unpublished unpublished PhD PhD dissertation, dissertation, rocks of the University of Wyoming, 141 141 p. p. 3. 3. Kopp, S., 1964, 1964, Reconnaissance geology geology of of metamorphic metamorphic strucstrucKopp, Richard S., tures district, Fremont County, County, Wyoming: tures of of the the Copper Copper Mountain Mining district, Compass, v. 43, p. p. 6-20. 6~20. Compass, v. 4. 4. Millgate, Mi11gate, M. M. L., L., Gliozzi, G1iozzi, James James L., L., 1966, 1966, Reconnaissance Reconnaissance of of iron iron forforin the the Copper Copper Mountain Mountain area, area, Fremont Fremont County, County, Wyoming: Wyoming: unpubmation in lished Survey of of Wyoming Wyoming files. files. lished report Geological Survey �-20- Stratigraphy of the North Shore Volcanic Group Northeast of Silver Bay, Minn. by John C. Green University of Minnesota, Duluth Minnesota Geological Survey A B S T RAe T A sequence of flows and flow vPups, totalling about 21,500 feet, makes up the northeast limb of the North Shore Volcanic Group of Keweenawan (late Precambrian) age between Tofte and Grand Portage. Exposures are generally good to excellent along the Lake Superior shore or abandoned wave-cut cliffs, and although cut by several large intrusive bodies and obscured by glacial cover over wide areas, many of these lithostratigraphic units can be traced inland from Lake Superior for many miles. Table 1 shows the informal volcanic units at the northeast limb (top of section at Tofte,base at Grand Portage); Table 2 gives the sequence (less well established because of faulting and intrusion) of the upper part of the southwest limb from Tofte as far as Palisade Head near Silver Bay. The Schroeder basalts at the top of the southwest limb are at least in part equivalent to the Lutsen basalts of the northeast limb. The basal 5,000 feet, near Grand Portage, Minn., have reversed magnetic polarity (Lower Keweenawan) whereas all the rest have normal polarity (Middle Keweenawan). The lowermost 250 feet of lavas on Lucille Island, directly overlying the basal Upper Precambrian Puckwunge Sandstone, are porphyritic melabasalts with abundant olivine and augite phenocrysts, identical to those in the same stratigraphic position at Nopeming, west of Duluth. �—2]— -2J- Table 11 Stratigraphy of (Tofte to Grand Portage) of of of Northeast Northeast Limb Linb (Tofte North Shore Volcanic Group Group (Exclusive (Exclusive of of Interf Interflow low Sediments) Sediments) Approx. Approx. - Thickness() Thickness.J ft.) Lithostratigraphic unit unit Lithic eharacter Character Lithic Top (near Tofte —- Lu Lutsen) Top (near t sen) 1020 -- Lutsen basalts olivine tholeittes tholeiites olivine basalts, olivine 160 160 Terrace Point basalt flow Thomsonite—bearing ophitic Thomsonite-bearing ophitic basalt basalt 310 310 Good Harbor Harbor Bay Bay andesites andesites brown, porphyritic andesite, brown, andesite, trachyandesite 360 flow Breakwater trachybasalt flow brown, columnar, granular trachybasalt 500 Grand I1arais Marais rhyolite flow pink, pink, red, red, gray porphyritic porphyritic rhyolite rhyolite 600 Croftville basalts various fine—grained fine-grained basalts basalts felsites Devil Track felsites aphyric flows aphyric and and porphyritic rhyolite flows Red Cliff basalts amygdaloidal, amygdaloidal, ophitic olivine basalts 1300 Creek felsite felsite Kimball Creek pink to to tan, tan, porphyritic felsite 1800 Marr Island lavas lavas mixed tholeiitic basalt,intermediate, intermediate) tholeiltic basalt, felsic lavas felsic lavas 1000 Brule River basalts granular—diabasic granular-diabasic amygdaloidal amygdaloidal basalts basalts 3500 3500 Brule River rhyolite flow pink pink to gray porphyritic rhyolite Hoviand Hovland lavas lavas mixed porphyritic basalt, basalt, trachybasalt, trachybasalt, rhyolite 200 Red Rock rhyolite flow red, porphyritic rhyolite red, 260 Deronda Bay andesite flow flow gray-brown, gray—brown, aphyric andesite 4500 Grand Portage basalts basalts nixed tholeiitic mixed tholeiitic to to diabasic diabasic basalts basalts Base (at Grand Portage) (at 1020 — 400-900 400—900 4000 21,430 2l~430 (est. ) (est.) �-22—22— Table 22 Stratigraphy of Upper Upper Part of Southwest Limb (Tofte (Tofte to Palisade Palisade Head) Head) of North Shore Volcanic Group to Approx. Thickness Thickness (ft.) (ft.) Lithostratigraphic unit Lithic character character 4000 Schroeder basalts ophitic olivine olivine amygdaloidal, ophitic tholeiites >300 >300 trachybasalt flow flow Manitou trachybasalt red-brown, red—brown, granular trachybasalt to basalt (at Tofte) Tofte) Top (at (more (more of the Schroeder basalts) basalts) >280 >280 Bell Harbor lavas lavas tholeiites, aphyric aphyric quartz tholeiites, trachybasalts >300 Palisade rhyolite rhyolite flow flow gray to pink, pink, porphyritic rhyolite gray to lavas Baptism River lavas mixed lavas, mostly basalts basalts Few 100's �~23-2 3— SHALLOW THE LAXE LAKE SUPERIOR SHALLOWSTRUCTURE STRUCTUREAND ANDSTRATIGRAPHY STRATIGRAPHYOF OF THE FROM SEISMIC SEISMICREFRACTION REFRACTIONMEASUREMENTS MEASUREMENTS BASIN FROM F1.C. Halls Halls and C.?. H.C. G.F. West Geophysics Laboratory, Dept. Dept. of Physics, University of of Toronto. ABSTRACT Between 1966 and 1969 thirty—three thirty-three seismic seismic refraction refraction profiles profiles were obtained in Lake Superior using aa single ship sonobuoy sonobuoy technique technique (Halls (Halls and and West, 1971). 1971). The seismic data have led led to to aa number of of conclusions conclusions concerning concerning the shallow shallow structure structure and and stratigraphy of the late Precambrian Keweenawn basin the that underlies the the lake: lake: that Faults with their bound the (1) their north north side side downthrown downthrown at at least least 1—2 1-2 1cm krn bound the north (1) Isle Royale Royale and and Michipicoten Michipicoten Island. Island. shores of Isle (2) the Keweenawan basin just just southeast southeast of of Isle Isle Royale Royale The northern limb of the (2) appears appears to to have undergone a deformation that that is is perhaps perhaps related related to to movement movement along the the Isle Isle Royale Royale fault. fault. (3) In to the the main basin between Isle Royale and the the Keweenaw Peninsula, In addition addition to (3) there the Slate Islands Islands in in the the there is is aa suggestion of of a smaller one southwest of the part of of the the lake. lake. northern part (4) (4) Cambrian Bayfield—Jacobsville Bayfield-Jacobsville sandstones sandstones appear appear Late Keweenawan or early Cambrian to underlie most of Lake Superior. Superior. Although the the site of the the lake lake is is governed governed to by the the position of the the underlying basin, the the principal principal factors factors determining determining the the size and shape of the the lake depression depression are are the the distribution distribution of of the the Bayfield— BayfieldJacobsville sandstones and their their susceptibility susceptibility to to erosion erosion compared compared with with older older rocks. rocks. (5) For those seismic profiles that have a certain degree of geological geological For those profiles that (5) control, such such as as those between Isle Royale and the control, the Keweenaw Peninsula, refraction refraction agree well with those those estimated estimated (Halls, (Halls, 1969) 1969) from from sasple sample velocities generally agree in the the laboratory. laboratory. One notable exception occurs in in those those profiles profiles measurements in that that lie just off the the Minnesota Minnesota shore. shore. Here velocities of of 55 km/s km/s are are recorded. recorded. These values are typical typical of of Freda—Copper Freda-Copper Harbor Harbor sandstones, sandstones, but but the the presence presence these rocks rocks adjacent to to the the Minnesota coast coast is is discounted discounted on on magnetic magnetic of these evidence. Instead the velocities of S5 km/s are assigned assigned to to the the North North Shore Shore volcanics that that crop crop out out along along the the mainland. mainland. The apparently low velocities of these these rocks rocks compared compared to to those those for for volcanics volcanics between Isle Isle Royale and the the Keweenaw kmfs) can be explained if Peninsula (5.7—6.2 (5.7-6.2 km/s) if the the North Shore Shore sequence sequence contains contains a greater proportion of interflow interflow sediment sediment and/or and/or amygdaloidal amygda10idal flow flow top top material. material. The seismic penetration of the (6) the refraction refraction profiles profiles was was generally generally insufficient insufficient (6) to to record the the Upper Refractor (Berry (Berry and West, 1966) 1966) with velocity 6.7± 6.7± km/s. km/s. However, one profile profile northeast of of Isle Isle Royale Royale recorded recorded aa velocity velocity of of 6.5 6.5 km/s km/s at a depth of of about about 66 km. km. This observation demonstrates the the existence existence of of Upper Upper Refractor—type Refractor-type velocities in the the marginal parts parts of the the Keweenawan basin. basin. �-24—24— References and G.F. G.F. West. West. 1966. 1966. An interpretation of the first first arrival data Berry, M.J. and of the the Lake Superior experiment experiment by by the the time—term time-term method, method, Bull. Bull. Seismol. Seismol. Soc. Amer., 56, Soc. 56, 141—171. 141-171. Halls, H.C. H.C. 1969. 1969. Compressional wave velocities of of Keweenawan rock rock specimens specimens from the Lake region, Can. Can. Jour. Jour. Earth Earth Sci., Sci., 6, ~, 555—568. 555-568. from the Lake Superior region, Halls, H.C. and and G.E. G.F. West. West. 1971. 1971. AA seismic refraction refraction survey in in Lake Lake Superior, Superior, Halls, H.C. Can. Jour. Jour. Earth Earth Sci.(In Sci. (In press). press). Can. �—25— -25- THE THE ISLE ROYALE FAULT FAULT B.C. H.C. Halls and and G.F. G.F. West West Geophysics Laboratory, Dept. Dept. of Physics, University University of of Toronto. Toronto. ABSTRACT A fault bounding the northwest shore of Isle Royale was originally postupostuA fault lated by by Irving Irving and and Chamberlin (1885) lated grounds. However, with (1885) on physiographic grounds. the exception exception of of recent recent aeromagnetic aeromagnetic studies studies (Wold and Ostenso, 1966; Hinze et the and Ostenso, al., 1966) very little extra evidence has been produced as as to to whether the the faiTt faurt al., 1966) really exists. The aeromagnetic data show a linear linear anomaly that that follows follows the the northwest shore of Isle Royale and extends eastward to to Superior Superior Shoal. Shoal. Although the sediments, it the anomaly anomaly indicates indicates aa contact contact between between Keweenawan volcanics and sediments, does or faulted faulted one one (Halls, (Halls, does not not reveal whether the contact is a stratigraphic or Evidence to 1970). to date for the so—called so-called Isle Isle Royale fault fault has therefore therefore been been 1970). rather inconclusive. This lines of evidence that that support support This paper discusses some lines the existence existence of the the fault, fault, in the the light of new magnetic and and seismic seismic data: data: the (1) (1) Seismic data (Halls (Halls and West, West, 1971) 1971) show that that the the uppermost layer that that underlies the channel north of Isle Royale and also the the region region further further northeast northeast underlies the the Slate Islands Islands has has aa velocity velocity of of about about 3.7 3.7 kin/s km/s and toward the and aa thickness of about 1—2 This seismic layer is all but continuous 1-2 km. km. This continuous with witih a similar similar one one in in eastern Lake Lake Superior can be firmly firmly identified identified as as Eayfield—.Jacobsville Bayfield-Jacobsville Superior that can sandstones. These thought to the Isle IsleRoyale Royale channel channel These rocks rocksare are thus thus thought to underlie the and if so, so, their their existence existence necessitates necessitates the the inclusion inclusion of of the the Isle IsleRoyale Royale fault fault with its downthrown downthrown side with its side to to the the north. 1970) show a remarkably (2) Paleomagnetic Books, 1968; 1968; Palmer, Palmer, 1970) Paleomagneticdata data (e.g. Books, consistent pattern pattern for for Keweenawan extrusive extrusive rocks. rocks. Whereas the the lower parts of the the volcanic sequence (such (such as as the Osler and South Range Range lavas) lavas) tend tend to to be be reversely magnetised, the upper parts such as the the Isle Isle Royale Royale and and Portage Portage Lake Lake reversely magnetised, the lavas are are normal. normal. In the the Isle Royale channel channel a linear linear magnetic anomaly anomaly (C (C in in Fig.l), Fig.l), which which is is attributed to to Keweenawan volcanics, is is strongly strongly positive positive with with an attendant minimum to to the the north, north, signifying that that the the volcanics are are normally normally an attendant magnetised. Anomaly CC continues continues beyond beyond the the channel channel to to both both the the east east and and west west where it broadens considerably considerably to to form form anomalies anomalies AA and and DD (Fig.l). (Fig.l). The sharpness and DD together together with the the seismic seismic data that the thevolcanics volcanics of anomalies A,C and data indicate that are overlain Thus north of the postulated Isle by Keweenawan are Keweenawan sedimentary sedimentary rocks. rocks. Thus the Isle If Royale fault buried, normally magnetised, Keweenawan volcanics. Royale fault there there are are buried, volcanics. the Isle Royale 'fault' 'fault' anomaly were due due to to aa stratigraphic stratigraphic contact contact the magnetic Isle between volcanics and and sediments sediments it it would imply imply that that the the sedimentary sedimentary unit unit was was sandwiched between two two thick thick sequences sequences of of normally normally magnet3sed magne~ised volcanics volcanics (i.e. (i.e. the Isle Isle Royale Royale lavas the lavas and those causing anomalies A,C A,C and and D). D). Such a sequence is of course possible but it is not a known feature feature of of Keweenawan Keweenawan stratigraphy. stratigraphy. is of course The only thick thick sedimentary unit unit that that occurs occurs in in the the Keweenawan Keweenawan volcanic volcanic sequence sequence is that is that in Michigan and Wisconsin but it lies lies between the the normal normal and and the the reversely magnetised sequence (e.g. (e.g. Meshref and and Hinze, Hinze, magnetised parts of the volcanic sequence 1970). Thus in 1970). in northern northern Lake Lake Superior Superior aa duplication duplication of of the the normally normally magnetised magnetised volcanics through movement along along the Isle Royale Royale fault fault is is favoured favoured over over aa through movement the Isle stratigraphic sequence of a sedimentary unit between between two two normal normal volcanic volcanic ones. ones. (3) of Fig.l Fig.l shows shows that that the the Isle Isle Royale Royale 'fault' 'fault' anonaly(E) anomaly (E) The magnetic map of (3) A weakening of the gradually assumes a more southerly trend trend toward toward the the west. A the gradually assumes anomaly in this anomaly this direction is more compatible compatible with the the presence presence of of aa fault fault rather rather than aa stratigraphic volcanic-sediment volcanic—sediment contact than contact (Balls, (Halls, 1970). 1970). �—26— -26- (4) Anomaly.C in Fig.l is essentially continuous continuous with aa belt of of prominent prominent the Minnesota shore before before turning turning positive anomalies that extends along much of the south and the Bayfield-Peninsula and terminating terminating in in aa hook-shaped hook—shaped anomaly over the Eayfield—Peninsula (Wold and and Ostenso, 1966). White (1966) (1966) concludes concludes that that this this anomaly is is due due to to volcanics in the upper .part sequence. The volcanics volcanics part of the Keweenawan extrusive sequence. Isle causing causing anomaly anomaly C C should should thus thus be be equivalent, equivalent, at least in part, part, to the Isle Royale lavas. lavas. Again, aa fault fault would be be necessary necessary to to explain explain the the apparent apparent of the the sequence. sequence. duplication of The foregoing foregoing observations therefore therefore all tend to to suggest suggest that that the the Isle Isle Royale fault fault does does exist. exist. A A two—dimensional two-dimensional magnetic model interpretation of the Isle Isle Royale Royale fault fault anomaly anomaly at at its its eastern end (Balls, 1970) suggests that the the (Halls, 1970) fault dips to the fault the south. south. The fault fault is is thus thus of reversad reversed type type as as its its downthrown do'~thrown side is is to to the the north. north. The displacement along along the the fault fault is is at at least least 1—2 1-2 km. km. The reversed nature the fault fault and and its itsincreasing increasingsoutherly southerlytrend trendtoward toward the the west west nature of of the that support the the idea idea initially initially raised Irving Chamberlin (1885) (1885) that (Fig.l) support raised byby Irving andandChamberlin it it is of the the Douglas Douglas fault fault in in Wisconsin. Wisconsin. is an easterly continuation of References Books, K.G. K.G. 1968. 1968. Magnetisation of the lowermost Keweenawan lava lava flows flows in in the the area, USGS Prof. Prof. Paper Paper 600—0, 600-D, 248—254. 248-254. Lake Superior area, Halls, H.C. B.C. 1970. Halls, 1970. Geological interpretation of geophysical data data from from the the Lake Lake Superior region, region, Ph.D. Ph.D. Thesis, University University of of Toronto, Toronto, 203 203 pp. pp. Halls, H.C. B.C. and G.E. West. 1971. Halls, G.F. West. 1971. A A seismic refraction survey in in Lake Superior, Superior, Can. Sci. (In (In press). press). Can. Jour. Jour. Earth Sci. O'Hara, N.W., N.W., Trow, Trow, J.W. J.W. and and Secor Secor G.B. G.B. 1966. 1966. Hinze, W.J., O'Hara, of eastern Lake Superior, Superior, AGU AGU Mono., Mono., 10, la, 95—110. 95-110. Aeromagnetic studies studies Observations on the junction between Irving, T.C. 1885. 1885. Observations Irving, R.D. R.D. and Chamberlin, T.C. the eastern eastern sandstone sandstone and and the the Keweenaw Series Series on Keweenaw Point, Point, Lake the Superior, Bull.US. Bull.US. Geol. Geol. Surv., Surv., 23, ~, 385—498. 385-498. Meshref, W.M. W.J. 1970. Meshref, W.M. and Hinze, W.J. 1970. Geologic interpretation interpretation of of aeromagnetic aeromagnetic data data in in western western Upper Upper Peninsula of Michigan, Michigan, Mich. Mich. Geol. Geol. Surv., Sun., Kept. Rept. of of lxiv., Inv., 12, 25 25 pp. pp. Palmer, B.C. and correlation correlation of of some some Middle Middle Keweenawan H.C. 1970. 1970. Paleomagnetisni Paleomagnetism and rocks, Lake Lake Superior, Superior, Can. Can. Jour. Jour. Earth Earth Sci., Sd., 7, 1410—1436. rocks, 1410-1436. l? White, W.S. W.S. 1966. 1966. Tectonics of the the Keweenawan basin, western Lake Lake Superior Superior region, region, White, USGS Prof. Prof. Paper Paper 525—E, 525-E, 23 23 pp. pp. Aeromagnetic, gravity and sub—bottom Wold, R.J. R.J. and and Ostenso, Ostenso, N.A. N.A. 1966. 1966. Aeromagnetic, sub-bottom studies in western Lake Superior, AGU Mono., Mono., 10, profiling studies Superior, AGU 10, 66—94. 66-94. �FIGURE FI GURE 89° 40' 89°20' 4a"OO' 48°OO' 88°40' $9°0O' THUNDER ---------- I 88°20 B8°0O' 88°00' BAY — ROVE FORMATION — — NORTH SHORE VOLCANICS 47° 50' a + -60$ 600 c1t:) ct=' — E ._—a.—-—ç D I F') N - V y TI V V '-I -...l SCALE V I 6 ••• i n — —, ISLE ROYALE VOLCANICS TI, 1V/ s COPPERHARBOR HARBOR CLASTICS CLASTICS COPPER 89c2O• $9000' _.- X——'-Y— X-·-··Y- 88° 40 ES MILES CONTOURS (X tOO) 100) CONTOURSIN IN GAMMAS GAMMAS 1* 88 0 20' 20' 88° 88 0 00' NORTHERLY LIMIT OF OFKEWEENAWAN KEWEENAWAN VOLCANICS VOLCANICS NORTHERLY LIMIT Total intensity magnetic magnetic map map of o tnt Total intensjty the Isle Isle Royale Royale channel. channel. Survey H. C. C. ILdIs Halls Survey by by N. F. West West in in 1966, 1966, using using aa shipborne proton precession spacing: and C. G. F. spacing: About About 33 miles. miles. N 300 c1:csjt in extreme Profile orientation: N 30 0 W., W.,except extreme northeast where it it is is more more northerly northerly 87°40' I �-28- RELIABILITY OF U-PB AGES OF SPHENE IN NORTHEASTERN MINNESOTA AND NORTHWESTE~~ ONTARIO G. N. Hanson Department of Earth and Space Sciences State University of New York Stony Brook, New York and E. J. Catanzaro Department of Geology Southampton College Southampton, New York A B S T R ACT U-Pb ages have been determined on sphenes from early Precambrian granitic rocks in relatively undisturbed areas and in a thermal aureole. The granitic bodies investigated are the Icarus pluton and the Saganaga tonalite in Ontario and the Linden Syenite and Giants Range Granite in Minnesota. A total of six sphene concentrates were analyzed. One sphene from the Linden Syenite had an unfavorable U/Pb ratio and no age could be calculated. Three sphenes from the Saganaga tonalite, the Icarus pluton, and the Giants Range Granite gave internally concordant U-Pb ages of 2710 ± 30 m.y. 'T'ivo sphenes from the Giants Range Granite and the Linden Syenite were internally discordant, but gave Pb207/Pb206 ages of 2730 and 2740 m.y., respectively. It is suggested that the discordance may be related to a relatively high uranium content in one sphene and to shearing of the host rock in the other. Sphene from near the contact of the Giants Range Granite with the 1100 m.y. Duluth complex gives internally concordant 2700 m.y. ages at 7.4 kilometers from the contact. As the contact is approached the sphene ages become internally discordant suggesting lead loss at 1100 m.y. At about one-half kilometer from the contact, where biotite and hornblende have lost essentially all of their radiogenic argon, sphene still retains about 60% of its radiogenic lead. �-29- CONTINENTAL RIFTS William J. Hinze Dept. of Geology Michigan State Univ. Donald M. Davidson Dept. of Geology Univ. of Minnesota, Duluth Robert F. Roy Dept. of Geology and Geophysics Univ. of Minnesota A B S T R ACT Comparison of late Precambrian, linear, tectonic features transecting the Mid-Continent region of the United States (e.g., the Mid-Continent and Mid-Michigan Anomalies) with relatively recent continental rift zones, such as the East African Rift System, indicates many similarities suggesting a common mode of origin. Hence, a mechanism is proposed for the development of linear Precambrian rifts and subsequent overlying sedimentary basins based upon observed geological and geophysical characteristics of modern rifts. Dissimilarities in stage of development, depth of erosion and geological age are parameters which limit the extent of comparison. Rift formation is initiated by plate splitting and subsequent upwelling of low velocity layer material into the upper mantle along the base of the crust. Although inherently denser than adj acent mantle rocks, the low velocity layer material becomes lighter and therefore rises upon partial melting and fractionation. Uplift of the earth's surface and igneous activity along pre-existing zones of weakness is associated with the vertical rise of this material, while lateral movement results in thinning and rupture of the crust producing extensional rift grabens. Subsequent magmatic activity in the rift zones results in local structural downwarping. Upon cooling, the low velocity layer residuml becomes dense and ultimately sinks into the mantle causing the uplifted rift zone to deflate. The convergent movement of adjacent mantle material into the void produced by the sinking residuum places the crust under compression, thus accounting for not only compressional features associated with rift systems, but the subsequent development of sedimentary basins over rift zones. �—30— -30- Keweenawan Geology of of the the Porcupine Porcupine Mountains, Mountains, upper Peninsula, Peninsula, Michigan Michigan Western Upper Harold A. Hubbard A. Hubbard u. Geological Survey Survey U. S. S. Geological Washington, 0. C. 20242 D. C. 20242 Washington, ABSTRACT The Porcupine Mountains, Mountains, Michigan, are are underlain by by tue the upper upper northwarLl-dipping limb of of an an overturned overturned asymmetric asymmetric anticline, antiline, not northward-dipping limb not aa dome with quaquaversal ~ua~uaversal dios dips as as usually usually shown. shown. The anticline is is faulted near its its axis1 axis, and at the southern margin the mountains mountains middle middle margin of o the diDpi1i to overturned Keweenawan volcanic rocks are thrust over over steeply steeply dipping Keweenawansedimentary sedimentaryrocks. rocks. The rocks, which upper Keweenawan The middle middle Keweenawan Keweenawan rocks, which are younger than Lava Series, can can be be divided divided into intotwo two are younger than the the Portage Porta3e Lake lake lava sequences. The Theolder older se~uence, sequence,which whichincludes inducesmost nostof of the he volcanic se~uences. volcanic of fine-grained fine-grained northward-dipping rocks the mountains, mountains, co:isists consists of rocks in the mafic to to intermediate intermediate lava lava flows flows and and two two interbedded interbedded felsic felsic lava lava flows. flows. southern felsic flow flow is is nonporphyr nonporphyritic The southern itic and and constitutes about half the outcrrp outcrop area. area. The younger younger sequence, se~uence, which which is is present present only only in in the the easternmost part part of of the the mountains, mountains, consists consists of of gently gentlyeastward eastwardand. and easternmost northeastward-dipping fine-grained and aphanitic flows flows overlain by volcanic conElonerate conglomerate and sandstone. The younger sequence se~uence is either either in fault contact or unconformable on on the the older. older. Both Both sequences se~uences are are repeao1L in part in fault slices repeated in in imbricate imbricate fault slices in inthe the southeasteru southeastern part of of the mountains. mountains. A A tear fault separates separates these rocks from the the upper Keweenawan rocks to to the the east. east. In the the Copper Harbor Conglomerate Con81omerate consists consists of of saidstone sandstone the north, north, the interbedded lavas. It appears to be conformable on middle containing interbedded lavas. It appears to be conformable on middle containing Keweenawan lavas in the lake of the Clouds valley. To the south tle Keweenawan lavas in the Lake of the Clouds valley. To the south ofo the mountains, the theupper upperKeweenawan Keweenawan rocks are folded in in an asymmetrical as~nmetrical syncline with with aa steep steep north limb. structural relIef syncline limb. The The structural reliefbets-een between the the size of and the synciline syncline is is more more than than 8000 8000 feet. feet. The size of the the PorcuPorcumountains iid sug3ests that the Keweenawan rocks of pine Mountain of western Mountain structure suggests icichiganwere were strongly st;unly folded in Michigan in post-Freda time, time, and not just just broadly warped. �—31--31- ThE KEWEENAWAN THE OFOFISLE ROYALE, MICHIGAN MICHIGfu~ KEWEENAWNGEOLOGY GEOLOGY ISLE ROYALE, N. King Huber U.S. U.S. Geological GeologicalSurvey Sury Menlo Park, California California 94025 94025 ABSTRACT A B S T R ACT Isle Royale lies on the north limb limb of the Lake Superior syncline, syncline, Royale lies and the the stratigraphic section exposed on the island is correlative correlative with the the much-studied much—studied middle middle Keweenawan Keweenawan Portage Portage Lake Lake Lava Lava Series Series and upper }ZeHr.awan Copper Harbor Conglomerate Cunglomerate on the Keweenaw Peninsula, on Keweenawan on the the south limb of of the the syncline. syncline. Dips of of the the strata strata range range from from less less than than 5Q0; 100 to over 50°; 10° side of of the the they are generally steeper on the north side the south and and average less than 20°. 20°. island than on the less than Exposures on Isle Royale indicate a minimum thickness thickness of of 10,000 10,000 feet for for the the Portage Lake Lava Series at The base feet at this this locality. locality. The baseofoftiiei the series is not exposed. exposed. As on on the the peninsula, the the series series consists consists largely largely of basaltic and andesitic lava flows, flows, with lesser amounts of of interfiow interflow sadiotaoy and tuffaceous rooks. sedimentary rocks. No felsie felsic flows flows are known from outcrops, although one has about outcrops, has been reported from diamond drilling, about 6,200 feet below the the top top of of the the lava lava series. series. The interflow clastic clastic rocks rocks do not not crop generally do crop out, out, and mast most of the individual units are are known only only from diamond drilling. drilling. Within the the lava lava series, series, which probably probably contains contains over a hundred flows flows in the the exposed section, section, certain stratigraphic units units representing flows or groups of flows flows can can be identified identified representing individual lava flows and traced on the basis and and basis of characteristic textures or structures, and relative stratigraphic stratigraphic position. position. Twelve such units have been distinguished distinguished within the the sequence and and provide stratigraphic stratigraphic and and structural structural control control for for geologic mapping. On both the Keweenaw Peninsula and Isle RoyaTh, Royale, the the Copper Copper Harbor Conglomerate is is largely derived from lowermost Keweenawan volcanic source source terranes, shed debris debris into the subsiding Lake Superior basin from from terra as, which shed opposite sides; sides; for for Isle Royale, this would be from from the the North Shore Royale, this Volcanic Group of of Gehman Gehman (1958) (1958) in in Minnesota. Minnesota. The depositional en'i:onment environment Volcano Group is is interpreted as as being one of a combination of fluvial fluvial and and lacustrine lacustrine conditions resulting in piedmont fanglomerates fanglomerates and and playa lake lake or or flood flood conditions plain deposits. deposits, Royale, various various sedimentary features On Isle Isle Royale, features indicate that that the the general direction of sediment transport was easterly, easterly, with aa range range from from northeast to to southeast. In thio this same direction the the Copper Harbor increases in Conglomerate Jr.i-eases in thickness thickness and and in in textural textural and and compositional maturity--namely conglomerate, through through aa mixture of of cobble cobble maturity——namely from a boulder conglomerate, and pebble conglomerates conglomerates and and sandstone, sandstone, to to sandstone sandstoneand andinudstone. mudstone. In a miles this distance of 20 miles this clastic wedge thickens thickens from from aa minimum minimum of of 1,500 feet feet to over 6,000 feet feet between stratigraphic marker horizons; the the top of of the the formation formation is is nowhere nowhere exposed and and the total thickness must be top appreciably greater. greater. �-3232— SOME PRIMA.RY PRIMARY SEDIMENTARY SEDIMENTARY STRUCTURES STRUCTURES IN IN THE SOME THE LOWER LOWER CHERTY CHERTY MEMBER tJfMBER OF OF THE THE BIWABIK IRON FORMATION BI~/ABIK FORMA.TION : VIRGINIA HORN HORN AREA ERIC FRODESEN Department of Geology and Geophysics Geophysics University Wisconsin, Madison, University of \.Jisconsin, Madison, Wisconsin 53706 53706 BSTRACT A B S T R ACT A The writer wri ter discovered di scoverecl and collected collected some some unusual unusua I sedimentary sedimentary oF the the Biwabik structures in the theLower Lower Cherty Cherty Member t-lember of Biwabik Iron Iron Formation Formation addition of at aa locality localitynea;r near the theMidway Midway addition of Virginia, Virginia,Minnesota. Minnesota. Polished Polished and x—radiographs overturned and and disturbed disturbed bedding bedding reresections and x-radiographs reveal reveal overturned sembling convolute—type convolute-type bedding, bedding, load load casts casts with with flame flame structures, structures, and and other structures structures characteristic characteristic of of soft soft sediment sediment deformation. deformation. SmallSmall— other scale cross-bedding cross—bedding and small small local local thrust thrust faults faults also also are are present. present. Recent experiments experi ments on on the the Formation formati on of of contorted contorted structures(McKee s truc tures (Mcl<ee and and Goldberg, show that that convolute—type convolute-type bedding bedding and and small—scale sm~ll-scale thrust thrust Goldberg, 1969) 1969) show faults, simi lar to to those those found in the Biwabik, Biwabik, can be be formed formed by by loading loading similar found in mud which was was deposited deposited on an existing existing slope slope of of 15—20 a semi—cohesive semi-cohesive mud 15-20 degrees. The The preservation of the the fine fine alternating alternatin~ dark dark and and light light laminae, laminae, small—scale small-scale cross—bedding, cross-bedding, and possible possible graded graded bedding, bedding, suggest suggest that that these wave base with only periodic these rocks rocks were deposited below wave periodic current activity. The alternation of the The the laminae laminae is is generally attributed to to seaseasonal changes{Hough, changes(Hough, 1958), or periodic periodic influxes of iron—rich and ironiron— sonal 1950), or influxes of iron-rich and impoverished impoverished layers layers due to to tectonic tectonic activity activity coupled coupled with with isostatic isostatic semi—rigid crust, crust, or or aa cornbina,tion combination oF adjustment of of a. a semi-rigid of the the two two procecess procecess (Cullen, 1963). 1963). Cullen's Cullen's idea idea that (Cullen, that banded iron iron formations formations can can he be rerell garded as as corresponding corresponding to aa syn-orogenic syn—orogenic "flysch "f1ysch' type of deposition deposition type of applications in explaining explaining some some of the structures found may have applications the structures found in in the the Lower Cherty Member. Similar sedimentary sedimentary structures structures are are found found in in the the Lower Member. Similar laminites of of documented flysch facies. The presence presence of ofallochthonous The allochthonous black chert chert pebbles pebbles within within the the beds beds poses poses aa problem as to to mode of of emplacement. Turbidity Turbidity currents, currents, subaqueous subaqueous sliding or or gliding gliding down down aa slope, slope, or or ice mechanisms have have to be ininsliding ice rafting rafting mechanisms to be voked explain their their presence presenceg voked to to exrlain If represent the the products proc'ucts of of chemical chp.mical weathering If iron iron formations formations represent under warm humid conditions in in semi—restricted semi-restricted basins, basins, then then ice ice rafting rafting under is not not aa very very likely is likely possibility. If, If, however, however, the the iron iron formations formations were were �-33—33— deposited rlepositerl in aa cool cool polar pot~rclimate climateasassuggested suggestedby bypaleonagnetic paleomagnetic data data (Symons, 1966),then thenthese thesepebbles pebblesmay may productofofice ice transport. (Symons, 1966), behe thetheproduct structures are are characteristic characteristic of Iff thesc these sedimentary sedimentary structures of the the entire entirefor— formation, and iron iron Formations general, then detailed regional mation, and formations inin ~eneral, then aa detailed regional study study could produce someenlightening enlighteningresults. results. could pro~uce SOMe refer~nces: 1'efercnces: Cul Ten,D•. U.J., 1963, Tectonic Tectonic implications implications of Cullen, J., 1963, of banded banded iron formations: formations: Jour. p.327—392. Jour. Sed. Sed. ret., Pet.,v.33, v.33, p.387-392. Gruner, J.'., Mineralogy andandgeology thethe Mesabi Gruner, J.l !.,l96, 1946, i~ineralogy geologyofof MesabiRange: Range: Office of Iron Range ofthe theComisioner Commisionerofof Iron RangeResources Resources and and t Rehabilitation, rehabilitation, St. Paul, Paul, tlinn. f1inn& 127 ppe 127 Pp. Gundersen, J.N., end Schwartz, 196Z, The geology geologyof of the metaGundersen, J.N., and G.M. G.M. Schwartz, 1962, The metamorphosedRi\-.abik SiwabikIron IronFormation, Formation,Eastern Eastern~lesabi Mesabidistrict, district, morphosed Minnesota:Minn. Minn.Geol. Geol.Sur. Stir. Bull. Bull. 43, Minnesota: 43, 137pp. l37pp. resh_waterenvironment environmentofofdeposition deposition of of PreHough,J.L., J.L., 1958, Yough, 1958, Fresh-water Precambrian iron formations: p. 41t+_1130. cambrian iron formations: Jour. Jour.Sed. Sed. Pet., Pet.,v.28, v.l8, p. 414-430. James, H.L., 1966, Chemistry of of the J~mes, H.L., 1966, Chemistry the iron—rich iron-rich sedimentary sedimentary rocks: rocks: 'J.S).S. Prof. Paper (-4O41, 6lpp. IJ.S.G.S. Prof. Paper 440-Iy" 61pp. Mcee, ~1c:\ee, E.fl., on formation formation of of conE.0., and and M. M. Goldberg, Goldberg, 1969, 1969, Experiments Experiments on torted Bull., v.80, torterl structures structures ininmud: mud: G.S.A. G.S.A. Bull., v.BO,p.23l—24-+. p.23l-244. Symons, P.T.A., 1966, A peleomagnetic paleomagneticstudy study on on the the Gunflint, Gunflint, Mesabi, Symons, ~.T.A., 1966, A Mesabi, and Cuyuna the Lake Lake Superior Superior Region; Region: and Cuyunairon iron ranges ranges in in the Econ. Econ. Geol., Geol., v.G1, v.61,p.p.1336—1361. 1336-1361. hite, \.'hi te, [l.A., [l.A., 1954, Thestratigraphy stratigraphy and 195 1f, The and structure of ofthe theMesabi ~1esabi Minnesota: ]{angc, ta: Minn. Hinn. Geol. Ceoi. Sur. Sur. Bull. Bull. 38, 38, 92pp. 92pp. Range, fHnneso �-34—34— ZEOLITE AND AND PREHNITE—PUELL?ITE PREHNITE-PUMPELLYITE FAdES FACIES IN INTHE THE KEWF.ENAWAN KEHEENAHAN BASALTS OF NORTHERN HICH:LGAN ROLE OF OF VOLATILES VOLATILES OF NORTHERN MICHIGANII: II: THE THE ROLE Wayne WayneT.T. Jolly Jolly ofSaskatchewan Saskatchewan University of Saskatoon, Canada Saskatoon. Canada ABSTRACT A B S T RAe T Keweenawpeninsula, peninsula, ~lichigan, :Iichigan. The lava flows flows of of the the Ke\\'eena,\v Thetholeiitic tholeiitic lava have undergone underone metamorphism of the the zeolite ite have metamorphism of zeoliteand andprehnite—punpelly prehnite-pumpellyite facies. the latter, fractures and upper flow flO\\1 contacts contacts latter, rocks rocks along along fractures facies. In In the been transformed have been transformed to to monomineralic monomineralic rocks rocks (metadomains) (metadomains) corposed composed of either pumpellyite pumpellyite or or epidote, epidote, depending depending on on stratigranhic stratiranhic position of position metadomains are are enriched enriched in in CaO CaO and and /\1')03 A1,O retitive in the pile. These metadomains relative to their their unaltered unaltered basalts basalts through of pre-existlnG pre—exiting plagio— to through albiti.zation albitization of plagioclase. Bulk compositions of the the altered altered parts parts of of the the flows, flows, deduced deduced re through ,veighted weighted averages averages of of the through the rock compositions, compositions, are sinilar similar to to ti1e parental basaits. parental basalts. Thus, Thus, little or no material was was added added from from extraneous extraneous sources. This metamorphic differentiation occurred occurred as as aa result result of of migration of of both both volatile volatile and non-volatile components over short and non—volatile components over Calcium distances through aa fluid fluid pressure pressure gradient zradient with \vi thr'f< r f<P total t l' Calciumalinninum silicates silicates were were formed formed preferentially preferentially near rupture alwninum rup~S~e zones, zones, at its its lowest lowest levels. levels. Theoretical considerations suggest where PP was at differentiation ofofessentially homogeneous that mdamorphic metamorphic differentiation essentially homogeneous bodies bodie~ of of rock thim P l' During the theKeweenawan Ke\\1eenaHan rock may mayoccur occuronly onlywhen whenPf Pfisisless less tian metamorphic event, dehydration. As As aa metamorphic event,the the rocks rocks underwent underwentext~g~rve etensve dehydration. depth from result, secondary phases phases decreases decreases with uith depth result, water content content of of secondary from water—rich or more) more) to water—acor epidote water-rich chlorites chlorites and and zeolites zeolites (1120=12% (H 0=12% or to '\-later-poor 2 (H about 2%). 2%). At lowest exposed levels levels P02 P0 may have have reached reached levels levels (HO0 about 2 2 sutficient sufficient to to subdue formation of pumpellyite in in favor favor of of pistacitic pistacitic epidote. PCOZ was very low 10\\1 during during the the peak peak of of the the metamorphic metamorphic event. event, Co2 �—35— -35AN AN AEROMAGNETIC AEROMAGNETIC SURVEY SURVEY C1" GF THE THE SOUTHKciilJ PENINSULA OF MIOsiIGAN MI~dIGAN PENINSULA OF SOUTHE Richard L. J. Hinze L. Kellogg and William 3. Geology Department of Geology Michigan State University Lansing, Michigan Hichigan East Lansing, ABSTRACT A B S T R ACT Only fragmentary direct information is is available on on the the basement basement complex underlying the Phanerozoic sediments of of the the Michigan Michigan Basin Basin because of the the limi;ed limited and poorly distributed basement basement drill drill tests. tests. To supplement this limited limited information information a a regional regional aeromagnetic survey has has aeromagnetic survey been of of thethe Southern Peninsula. Approximately 17,000 17,000 miles of beenconducted conducted Southern Peninsula. Approximately total magnetic intensity total intensity data data were were recorded recorded along along north—south north-south flight flight lines spaced at lines at three three mile intervals. intervals. A hasement A basement configuration map prepared prepared from from magnetic magnetic depth depth estimates estimates and basement basement drill drill tests and tests confirms that the basement surface surface under under the the Southern Peninsula of Ni Michigan has the the form form of of an an oval oval depression depression reachreachiar has ing aa maximum maximum depth depth of of approximately 15,000 feet ing feet below sea sea level level on on the the western shore shore of of Saginaw Saginaw Bay. Bay. A A basement high underlies the the Howell Howell .Anticilne and Anticline roughly north-south and aa roughly north—southstriking strikingregional regional basement basementtrough trLg plunges into into the boundarypoint poin of of Indiana, Ohio, plunges the basin basinfrom from the thecommon common boundary Ohio, and iIichigan Ilichigan to to the the vicinlty vicinity of 42°30'N. The map map shows a broad basement north\-lest in in the the extreme extreme southwest southwest corner corner of of the the platform striking northwest peninsula. Interpretation of the :esidual =~sidual aeromagnetic aeromagnetic map map in in conjunction conjunction with with geologic and other regional geophysical data seologic and other data from from the the Southern Southern PeiLtsula Peninsula and indicates that that the the basement basement of of the the :1ichigan Hichigan Basin has and adjacent areas indicates geologic history. history. Several Several basement provinces are are defined had a a complex complex geologic basement provinces defined on the basis of magnetic and and isotope isotope of magnetic and gravity gravity anomalies, anomalies, lithologies lithologies and ages of samples obtained from basement drill holes, and extrapolation of samples obtained from basement drill holes, and extrapolation of of known Precambrian geology from the the margin of of the the basin. basin. The Penokean province can be traced from into the can be from northern northern Nichiga Michigan and and Wisconsin Wisconsin into the area the northern the Southern Southern Peninsula. Peninsula. In this area the province province northern portion portion of the is characterized is characterized by east—southeast east-southeast striking striking anomalies. anomalies. Central and southwestern Michigan Michigan isis underlain rocks correlating correlating underlain primarily primarily by by felsic felsic rocks with the the Central Province. Basement rocks in Basement rocks in southeastern southeastern ~lichigan, Michigan, which which strike strike generally generally north—northeast are interpreted as as mafic mafic and and felsic felsic gneisses and north-northeast are interpreted amphibolites. amphiboli tes. They are correlated correlated with the the Grenville Grenville province province which \vhich is bounded on the west is on the west by by aa line line extending extending south-southwest south—southwest from from Saginaw Bay to south to Michigan— to west \vest of the the HowellAnticline HowellAt,ticline and and then then du.e du.e south to the MichiganOhio boundary. A A Keweenawan rift rift zone zone characterized characterized by by mafic mafic intrusives, intrusives~ extrusives and uplifted uplifted gneisses gneisses transects irom the the extrusives transects the the Peninsula from ic.neousactivity activity area to southeastern Traverse Bay Bay area southeasternMichigai Nichigan. Keweenaean Ke\veenmVan igneous mayalso also be be reflected reflected ininthe may thenumerous numerous local local magnetic magnetic anomalies anomalies in -• southwest whichoccur occuralong alongnorthvest norLn'eststriking strikingtrE!lllds treds whith soutlHvest Mi-htgan Nichigan which \vhich the regional pattern. parallel the regional gravity gravity anomaly anomaly pattern. �-36—36— PRECAMBRIAN CLASTIC CLASTIC PALEarIDAL SEDTI1ENTATION PRECAMBRIAN aarna SEDENTATION GEORGE deVRLES KLEIN GEORGE deVRIES Dept. of Geology, Univ.ofofIllinois, Illinois, Urbana, Dept. of Geology, Univ. Urbana, Illinois, Illinois,61801 61801 ABSTRACT ABSTRACT The Lm;er Fine-grained of Scotland Scotland and and The Precanbrian Precrbriari Lower Fine-grained Quartzite Quartzite of both both the Precaubrian Precanbrian Sterling Sterling Quartzite and and Precanbrian Preccmbrian part part of the the Wood Canyon Formation easternCalifornia California and are Wood Canyon Formation of of eastern and Nevada Nevada are characterized by primary primary sedimentazy sedimentary features which are characterized by features which are indicC'ltive indicative of sediment transport and and deposition deposition by bytidal tidal currents. sediment transport currents. Sedimentary structures structureswhich which occur occur in these these formations fonnations are are grouped grouped into sty seven which are produced by seven associ~tions associations which am produced by seven sevenphases phasesofof tidal tidal sediment sediment transport: transport: ASSOCIATION 1: 1: Cross-stratification sets, Cross-stratificationorganized organized into into herringbone herringbone sets, with bipolar-bimodal bipolar—bimodal orientation;parallel parallellaminae; laninae; these these features with orientation; features indicate indicate tidal tidal current current bedload bedload transport transport with with bipolar bipolar reversals reversals of of flow directions directions (Reirieck, flow (Reineck, 1963). 1963). ASSOCIATION 2: Reactivation surfaces:Multimodal Multimodalfrequency frequencydistribdistribASSOCIATION 2: Reactivation surfaces: utions of cross-strata utions cross-strataset setthickness thicknessand andofofdip dipangles; angles;unirnodal unimodal orientation of directional directional current orientation of current structures structures parallel parallel to to basin basin topographic strike; producedbybytime—velocity t:ime-veloci ty assymetry assymetry of of topographic strike; allallproduced tidal tidal current current flow flow (Klein, (Klein, l970a3. 1970a). ASS<X;IATION 3: Interference ripples; superposition ASSOCIATION 3: Interference ripples; superpositionofofcurrent current ripples ripples at 900 crests and at 90 0 and and 1800 180 0 on on crests and slip slipfaces facesofofdunes, dunes,sand sandwaves waves and and internal cross-strata; cross-strata;"B-C" "B-C" sequences sequences ClIf of cross-strata cross-strata overlain overlain by by micro-cross-laninae; highly-variant highly-var! antorientation orientation of of current current ripples; micro-cross-lcminae; all late-stage emergence runoff prior prior to all produced produced by by late-stage emergence runoff to anergence emergence of of an intertidal flat (Klein,1963,1970a,l970b). an intertidal flat ~Klein,1963,1970a,1970b). ASSOCIATION It: 4: Cross-stratification with flasers fla.sers and and clay clay drapes; drapes; Cross—stratification with flaser bedding; flaser bedding; lenticular lenticular bedding; bedding; "tidal "tidalbedding'; bedding"; convolute convolute bedding; all all produced alternation bedding; produced by by al terna.tion of ofbedload bedloadand and suspension suspension sed:imentation associated alternating bedload bedload and and slack-water slack-water sedimentation associated with with alternating tidal current tidal currentflow flow(Reineck (Reineckand andWunderlich,l968a,1965b; Wunderlich,1968a,1968b; Wunderlich, Wunderlich, 1970).• 197Q) ASSOCIATION 5. \lJashout structures, structures,sane sanefilled filled with mUd-chip with mud—chip ASSOCIATION 5. Washout conglanerates; rill casts; all allproduced produced by by tidal tidal scour scour conglctnerates; rill marks; marks;flute flute casts; (Van Straaten,1954; Straaten,l951j; Reineck, (Van Reineck, 1967; Klein,1970a). �—37— -37- ASSOCIATION 6: 6: MUdcracks; Mudc racks; mt intraformational conglanerates; rafo tin ational congicrie rates; birdseye structure; allproduced producedby byexposure exposure and and evaporation (Shinn,1968). stricture; all, Tracks and and trails; trails; burrowing burrowing structures, "escape" ASSOCIATION 7: Tracks structures,"escape burrows; all all produced burrowingorganisns orgaxüausadapted adaptedtotoaa tidal tidal burrows; produced by by burrowing regime (Rhoads,1967; (Rhoads,l967; Remneck 1968). Reineck and others, others, approximatedin in these Precanbrian paleotidal paleotidal ranges can be be approximated ranges can similar to rock units units finn rock from analysis of fining-upward sequences similar date, Late those occurring in in prograding prograding tidal copstlines. COAstlines. To date, Precambrian paleotidal ranges from from 0.3 paleotidal ranges 0.3 to to 13.0 meters meters have been measured. This Late measuitd. This Late Precanbrian Precaubrianpaleotidal paleotidal range rangevariation variation is tidal less than thRn the theknown known variation variation measured measured along along Holocene Holocene tidal ranges fran fran 00 to to 17.5 17.5 meters). meters). Perhaps coasts (variation of tidal ranges Precambri~n range variation is not greatly greatly difforent different is not Precanbripn paleotidal range fran present-day present-day variation. If further work substantiates such Precambrian, it a a limited paleotidal paleotidal range range variation variationfruit fram the Precambrian, poses critical critical problems poses problems for various various geophysical geophysical pxtblms problens that that have have been and age earth-moon systan. systen. beenproposed proposedfor forthe the origin origin and age of of the earth-noon REBERENCES REFERENCES CITED intertidal zone sediments: Jour. Klein, C.deV,1963, G.deV,1963, Bay Bay of of Plindy Fundy intertidal Jour. Sedimentary Sedimenta~ Petrology, Petrology, v. v. 33, 33, p. 844-854 8tb—85t -——,l97Oa, dynanics of intertidal sand ---,1970a, Depositional and dispersal dYnanics sand bars: Jour. Sdimentary S~dimentar,yPetrology, Petrology, v.v.140, 40, p. p. 1095-1127. --—,1970b, Tidal Quartzite -- The Lower ---,1970b, Tidal origin of of aaPrecambrian Precambrian Quartzite Pinc—grairdQuartzite Quartzite (Dalradian) (Dairadian)ofof Isl~; Islay. Scotland: Fine-grained Scotland: Jour. Jour. Sedimentary Sedimentary Petrology, Petrology, v.v.140, 40, p.p.973—985. 973-985. Reineck, H.E., H.E., 1963, un Bereic;h der sudliche Nordsee: Reineck, 1963, Sedimentgefuge Sedimentgefuge im Bereich der Nordsee: Abh. ~enckenbergischen SenckenbergischenNaturfor. Naturfor.Gesells. Gesells. No. 5O5, p. p. 1-138. Abh. No. 505, 1-138. --—,1967,Layered Layeredsediments sediments tidal flats, flats, beaches ---,1967, ofoftidal beaches and and shelf bottoms, p. 191-206: in Lauff, p. 191-206: in Lauff, (hR., G.H., Editor, Editor,1967, 1967,Estuaries: Estuaries:Am. Am. Assoc. Assoc. Adv. Sci. Sci. Pub. Pub. No. No. 83. 83. Reineck, H.E., and WUnderlich, H.E., and Wunderlich,F,F,1968a, 1968a,Classification Classification and and origin origin of flaser 99-1014. fiaserand and lenticular lenticularbedding: bedding:Sedimentology, Sedimentology, v. v. U, ll,p.p. 99-104. ---, &, ---, &, ---, ---,1968b, 1968b, Zeitmessugnen Natur und und ZeitanessugnenananGezeitenschichten: Gezeitenschichten: Natur Musetun, v. Museum, v. 97, 97, p. p. 193—197 193-197 Reineck, H.E., H.E., Dorjes, Dorjes, J, J, Gadow, Garlow, 5, S, and and Hertwick, 0,1968, S3dimentologie, Reineck, 0,1968, Sadiznentologie, Faunenzoniening and Faunenzonierung und Faziesabfolge vor vor der der Ostkuste Ostkuste der der inneren inneren Jeutschen Deutschen Bucht: Bucht: Senck. Senck. Lethaea, Lethaea, v.v.149, 49, p. 261-309 261-309 �-':;8—L8— Rhoads, D.C.,1967, and subtida subtidal D.C.,1967, Biogenic Biogenic reworking reworkingofofintertidal intertidal, and sediments in in Bamstable sediments BarnstableHarbor Harborand and Buzzards Buzzards Bay, Bay, Massachusetts: Massachusetts: Jour. Jour. Geo1or, Geology, 'r. v. 75, p. 461-476. t. b61—L76. E.A.,],968,Practical Practicalsignificance significance of of birdseye birdseye structure structure in in Shinn, E.A.,1968, carbonate rocks: rocks: Jour. Sedimentary Petrology, v. v. 38, carbonate Sedimentar,y Petrology, 38, p. p. 215—223. 215-223. Van Straaten, Van Straaten, L.M.J.U., L.N.J.tJ., 1954, 195h, Sedimentology Sedimento1o'ofof Recent Recenttidal tidal fla.t flat and the thePsamnites Psanmitesdu duC0ndroz Condroz (Devonian): (Devonian): Cleol. Geol. en en deposits and Mijnb., v. i6, Mijnb., v. 16, 25-47. p. 25-217. Wunderlich, F,1970, envirornent ofofthe T1NellenkopfschenWunderlich, F,1970, Genesis and and environment the "Nellenkopfschenschichten Il(Lower sian, EInsian,Rheinian RheinianDevonian) Devonian) at at locus locus typicus typicus in in schichten"(Lower canparison ecinparisonwith withmodern modem coastal environments enviroanents of the Cern GeImclTI n Bay: Bay: Sedimentary Petrology, Petrology, v. 240, Jour. Sedimentar,y 40, p. 102-130. 102-130. �-39—39— GEOLOGYOF OF THE SOME GEOLOGY THE 'ARATHON MARATHON COUNTY COUNTY VOLCANIC VOLCANIC BELT BELT by Gene L. L. LaBerge Wisconsin Geological Survey and and Department of Geology Geology Wisconsin State University Oshkosh, Wisconsin Oshkosh, ABSTRACT ABSTRACT The area east The east of Wausau in Marathon County consists consists largely largely of of rocks which range range in in composition composition from from basaltic basaltic to to rhyolitic. rhyolitic. volcanic rocks The rocks are mainly to the southeast and and the the rhyolitic rhyolitic rocks rocks The basaltic rocks to top of the sequence is northwest: northwest; to the the northwest, northwest, suggesting suggesting that that the the top of the however, however, no no definite definite evidence evidence of of stratigraphic stratigraphic top top \vas was found. fond. Trachytes are a1.. so present edge of of the the napped mapped area. area. Sedimentary are also pr?sent at at the the northwestern northwestrn edge rocks rocks are virtually virtually absent. absent. The volcanic rocks The rocks have been intruded by v;rious various sized masses of of gabbro, and syenite. syenite. There appears appears to to have been been gabbro, diorite, granite, and several ages of granitic intrusion. intrusion. Available radiometric ages ages indicate indicate are late late Middle Niddle Precambrian. Precambrian. that the rocks arc Structurally, the the area is is characterized by at least least two two directions directions Structurally, of large large scale faulting faulting with with niajor major fault faultzones zonestrending trendingapproximately approximately N8O°E to to N60°E. 1180°£ ~~60°E. The \vhich also shows shows up on the aeronagnetic aeromagnetic The faulting, faulting, which up well well on map many of mapcovering coveringthe the area area mainly mainly west west of of Wausau, Wausau,has hasresulted resalted in many of the lithologli units units being in Perhaps the lithologic in fault fault contact. contact. Perhaps the most significant fault zone is is the the N300E N3OF trend fault zone trend whiàh which has has produced produced aa zone zone nearly nearly aa mile mile in the the Eau Eau Claire Claire River River valley in in which mylonite mylonite is is aa major major rock rock wide in This zone truncates type. This truncates the N8O°E—N60°E N800E-N600E trend trend more prevalent prevalent to to the the ,,,,est. west. The current napping project, The current mappins project, funded funded by the the Wisconsin Geological Geological S"rvey, has Survey, revealed significantly significantlymore morevolcanic volcanicrocks rocksthan than shownOLI on has revealed areare shown Weidinan's 1907 map. \veidman's 1907 map. This This has has important importantimplications implicationsfor formineral min al exploration A previously unreported gold prospect, on tion programs. A on which mining attempted about 1920, 1920, is is probably probably the the most most interesting interesting locality locality from from was attempted an economic point point of of view. view. References Dutton, E. (1970) Dutton, C. C. B. E. and and Bradley, Bradley, R. R. E. (1970) "Lithologic, and "Lithologic, Geophysical, and ;·lineral :•lineralCommodity CommodityHaps MapsofofPrecambrian Precambrian Rocks Rocks in in Wisconsin"; Wisconsin"; U.S.G.S. Miscellaneous Geologic InvestigationsMao Map 1-631. Geologic Investigations 1—631. Henderson, J. J. IL, Henderson, R., Tyson, Tyson, ;i). R. (1963) "Aeromagnetic N. S., S., and Page, Page, J. 3. R. (1963) "Aeromagnetic Map of the Wausau Area, Wisconsin"; Map of Wisconsin"; U. U. S. G. G. S. Geophysical Investigations Map Map CP—40l. GP-40l. Laberge, G. U. and l,Jeis, LaBerge, G. 1. L. W. Iv. (1968) Central Weis, L. (1968) "A 'A Greenstone Greenstone Belt Belt if in Central Wisconsin?", Guidebook Guidebook for for 32nd 32nd Annual Annual Tn—State Tri-State Geological Geological Field Field Wisconsin?, Conference. �—40— -40- Weidman, S. S. (1907) (1907) The The Geology Geology of of North North Central Wisconsin; Wisconsin; Wisconsin Geological and Natural History History Survey Survey Bulletin Bulletin 16. 16. Weis, L. W. W. and and LaBerge, LaBerge, C. G. L. 1. (1969) (1969) "Central Wisconsin Volcanic Volcanic Belt," Belt," Weis, L. Guidebook for 15th Annual Institute Institute on on Lake Lake Superior Superior Geology. Geology. �—41— -41- HEMATITE PSEUDOMORPI-1IC AFTER BIOGENIC BIOCENIC HE~1ATITE PSEUDOMORPHIC AFTER PYRITE IN INTHE THENEGAUNEE NEGAUNEE IRON IRONFORMATION FORMATION N. M. S. S. Lougheed and J. J. 3. J. Nancuso Mancuso Bowling Green State University, Green, Ohio 43403 43403 University, Bowling Green, ABSTRACT A B S T R ACT Spherules (limonite), ranging in diameter from from Spherules of of hematite (limonite), 5 microns microns to to 20 20 microns microns but generally of similar size in each each as disseminated disseminated octahedral octahedral crystals crystals particular population, as well as of pseudomorphic hematite occur in in many laminations laminations of of the the Negaunee Negaunee iron formation. formation. Mineral associations associations include include chert, chert, magnetite, magnetite, iron iron carbonate, silicates. A A common associate is is fossil fossil fila— filacarbonate, and iron silicates. A tentative conclusion based on two mat algae. algae. A two microprobe mentous mat Thermal experiments carbon in the filaments. filaments. Thermal analyses indicates indicates carbon in the result considerableremoval removal of the filamentous material suggesting suggesting result ininconsiderable the presence presence of both both amorphous amorphous carbon carbon and and graphite. graphite. Framboidal pyrite with diameters ranging from 55 microns to to 20 20 microns sedi— nlicrons and and pyrite octahedra, octahedra, occurring in two two unconsolidated sediinents with contrasting contrasting environments, environments, one one aa Pleistocene fresh ments with fresh water water lake deposit, deposit, the lake the other a Recent marine tidal tidal lagoon, unequivocally unequivocally demonstrate their their biogenic biogenic origin. origin. Paleozoicanalogs analogsofofsomewhat somewhatsimilar similar lithology lithology to to iron iron formation formation P-Jzoic the following associations: carbonate, biogenic biogenic euhedral euhedral the following associations: chert, carbonate, pyrite, biogenic framboidal pyrite, framboidal pyrite pyrite 55 microns microns to 20 microns microns in diameter, diameter, to 20 sparce euhedral magnetite microflora. magnetite and and fossil fossil microfcunz: microfauna and/or microflora. the biogenic biogenic origin origin of of pyrite. pyrite. They further demonstrate the have A finely laminated A finely laminated chert chertcarbonate carbonatespecimen specimen from from the thePennsylvanian Pennsylvanian formation, Texas, Texas, clearly shows the Dimple formation, the transition transition of of biogenic biogenic pyrite to pseudomorphic hematite hematite (limonite) (limonite) by by oxidation. oxidation. features are These various various features are illustrated by photomicrographs phbtomicrographs to to that the support the the hypothesis hypothesis that the spherules spherules of of hematite (limonite) (limonite) possibly other other hematite hematite in in the theNegaunee Negaunee iron formation formation are pseudomorphic after biogenic biogenic pyrite, pyrite, and together pseudomorphic after together with the the presence presence of the bio~enic bio3enic (in part) genesis of probable probable algal algal mat mat strongly strongly support the (in part) of the Negaunee Negaunee iron formation. of iron formation. and and �—42— -42- DISTRIBUTION OF URANIUM URANIUM AND AND THORIUM THOP.IUM IN PRECAMBRIAN PRECAMBRIAN ROCKS RE GION ROCKS OF OF THE THE WESTERN WESTERN GREAT GREAT LAKE: LAKE: RE3ION by Roger C. Roger C. N~alan and and David Sterling Malan David1_A Sterling ommission, Grand Thiorado U.S. Atomic Energy Energy :::ommission, Grand Junction, Junction,:::olorado U.S. Atomic AE<:::;TRACT AECTRACT 1 Prospecting during during the the 1950 1950's resulted in Prospecting s resulted in the the discovery discovery of of several several uranium and thorium prospects in Precambrian rocks in the westuranium and thorium prospects in Precambrian rocks in the westeconomic deposits ern Great Lakes Lakes region region of of the the United United States. States. No No economic deposits ern Great were delHeated the few few small small exploration efforts that were delineated by by the exploration efforts that were were underunderSince then exploration for for radioradiotaken. Since then there there has has been been very very little little exploration active minerals minerals in active in that that region. region. In Wisconsin Wisconsin and and inin upper upper Michigan, Michigan, Lower, Lower, Middle, PreIn Middle, and and Upper Upper Precambrian silicic cambrian silicic and and hyperalkalic hyperalkalic plutonic plutonic rocks rocks contain contain anomalous anomalous In upper amounts of upper Michigan, Michigan, amounts of disseminated disseminated radioactive radioactive minerals. minerals. In the Middle Middle Precambrian Animikie Series contains uranium uranium veins veins in in the Precambrian Animikie Series contains slate, monazite placers placers in in conglomerate, conglomerate, and and irregular concentraslate, monazite irregular concentrations utanium in iron iron formation adjacent to to slate. tions of of Ul anium in formation adjacent slate. These These prosprospects do do not of uranium uranium or or thorium thorium that that pects not contain contain important important reserves reserves of are at present are economically economically mineable mineable at present but but some some may may contain contain large large long-range, low low-grade resources. long-range, - grade re sources. For Forexample, example, limited limited sampling sampling indicates that that masses masses of indicates of silicic silicic igneous igneous rocks rocks in in northeastern northeastern WisWiscousin may contain contain 50 50 to to lOO 100parts parts per per million consin may million uranium. uranium. This This is is greater than than the the uranium uraniumcontent content in inany any of of about about 250 250 bulk samples greater of igneous rocks rocks that analyzed in in aa recent of igneous that have have been been analyzed recent study study of of the the distribution of uranium rocks in in the the distribution of uranium and and thorium thorium in in Precambrian Precambrian rocks western United United States. potentially great great low-grade low-grade resource resource of of western States. AA potentially thorium may thorium may exist exist in in the the monazite monazite placers placers in inAnimikie Animikie conglomconglomerates in erates in the the Marquette Marquette Range, Range, upper upper Michigan. Michigan. In other other areas areas of of the the world, world, stratiform stratiformuranium uraniumdeposits depositsin inMiddle Middle In Precambrian Precambrian coarse coarse clastic clastic sediments sediments are are of of major major importance. importance. The world's world's greatest resource of uranium is is in The greatest known known resource of uranium in basal '::asal conconglomerates of the Middle Middle Precambrian Huronian Series glomerates of Precambrian Huronian Series in the Elliot Lake Blind River Elliot Lake -- Blind River district district in in southern southern Ontario. Ontario. Important stratiform uranium deposits deposits have have not not been been discovered discovered in in the the stratiform uranium Animikie Series which is in Animikie Series which is in part part correlative correlativewith withthe theHuronian; Huronian; �________ -4343— however, however, limited limited sampling sampling ia L.1. the the iviarquette Ivlarquette Range, Range, upper upper Michigan, Michigan, indicates that anomalous anomalous amounts indicates that amountsofofuranium uraniumare are present present in in coarse coarse clastic facies. Also in the the Animikie Animikie in the Also uranium/thorium uranium/thorium ratios in elastic Blind River Marquette Range and in the Huronian in the Elliot Lake River Marquette Range and in the Huronian in the Elliot Lake -- Blind More study area increase increase in in descending descending stratigraphic stratigraphic positions. positions. More study of of area the distribution of uranium the distribution of uranium and and thorium thorium in in the the Animikie Animikieisis warranted. warnnted. CELECTED REFERENCES :ELECTED REFERENCES T.llsley, ':llsley, C. C.T., T., Bills, Bills, C. C. W. W., Some geoand Pollock, Pollock, J.W. J. W.,, 1958, Some chemical methods of uranium exploration, exploration, in inSurvey Survey of of Raw Raw chemical methods Materials Resources: Materials Resources: United United Nations, Nations, New New York, York, Proc. Proc. Second Second lnternat. Conf. Energy, 1958, v. 2, Internat. Con£. Peaceful Peaceful Uses Uses Atomic Atomic Energy, 1958, v. 2, p. p. 126-130. , James, H. James, H. L., L.,1958, 1958,Stratigraphy Stratigraphyofofpre-Keweenawan pre-Keweenawan rocks rocks in in parts parts of Northern Michigan: Michigan: U. U. E E Geol. Geol. Survey Survey Pro£. Paper314-C, 314-C,42 42 p. p. of Northern Prof. Paper King, J. W., W.,1960, 1960,Report Reportofofexamination, examination,Little Little WolfMining Mining&& MinMinKing, Wolf erals, Inc., erals, Inc.,Anklam AnklamProperty PropertyBig BigFalls, Falls,Waupaca WaupacaCounty, County, WisconWisconsin: file rept. sin: U.S. U. S. Atomic Atomic Energy Energy Comm. Comm. open open file rept. Malan, C., and and Sterling, Sterling, D. Do A., A.,1969, 1969,An Anintroduction introduction to to the the disdisMalan, R. R. C., tribution thorium in in Precambrian Precambrian rocks tribution of of uranium uranium and and thorium rocks including including the the results results of of preliminary preliminary studies studiesin inthe thesouthwestern southwesternUnited United States: States: U.S. U.S. Atomic Atomic Energy Energy Comm. Comm. AEC-RD.-9, AEC-RD-9, 54 54 p., p., open open file. file. Roscoe, Roscoe, S. S. M. M., 1969, 1-luronian Huronian rocks conglomerates rocks and anduraniferous uraniferous conglomerates Canadian shield; shield: Geol. Geol. Survey Survey Canada Paper 68-40. 68-40. in the Canadian , Stead, F. F. W., F. J., Stead, W., Davis, Davis, F. J., Nelson, Nelson, R. R. A., A., and and Reinhardt, Reinhardt, P. P. W., W., 1950, Airborne Airborne radioactivity radioactivity survey survey of of parts parts of 1950, of Marquette, Marquette, DickDickinson, and open— inson, and Baraga Baraga Counties, Counties, Michigan: Michigan:U.S. U. S.Geol. Geol.Curvey :urvey openfile map. file map. Vickers, R. of t>-e te Goodrich Vickers, R. C., C.,1956a, 1956a,Geology Geology and and monazite monazite content content of Goodrich Quartzite, Quartzite, Palmer Palmer area areaMarquette Marquette County, County, Michigan: Michigan: U.S. U. S. Geol. Geo!. Survey Bull. Bull. 1030-F. Survey 1030-F. 1956b, Ai Airborne rborne and and ground groundreconnaissance reconnaissanceofofpart partof of the the ----syenite complex near near Wausau, Wausau, Wisconsin: U.S. syenite complex U. S. Geol. Geol. Survey Survey Bull. 1042-B. �Is.. .c g (/) • lii,Oll.tsdiI ~~ - o o a "'" o I :;= g;;'~~ ~~ ~~ O4! 4 l5S 50565' 8 fl. I 4515 il 0 - V t;%,ir III 1545_C1 •'l'' C E] ~i !: .. ~ (~ ?:t,"t.i. ;'''° Ui,iii,soolli,,t. ltl - ~ ~ u~ C C ~ ~ / I / o o Ul '" ~ I 50 146104Sre,,t.4 dtstil. ~ 15 ~ 0 5, SOlO. 444 isosaStis is C.sbi,en yl.'.!.o.; C154401ltUt,11.pi.o I Slot 05 II S •l 545' !!611 11,41. ~~ ~ ., -:0440,' ~ 0 =;;; fl - Jiddn IIfIJqn,e'd D ii ! :.~ ! I i f : c . 'iii 0 c 0 ~ '" ~ .. --., , I 1 I I I '"." c I I I 1 I Lakes fll*!6441r4!llt 4.11 c ~ 0 . '" Greet n n• . < '. • : 0; .! 3<" Sec horn I-I £!,oe.,, #•flsI 44144!, lId Ut SO IMi ~ i~ — ,__— <D~ • :;;. .i E~ .. ~'ii - ;; : ., co Precambrian, s ! 0.- ;. ~ bi 'I,. - i'I": -,..- ~ <; Map - -- ~i: . ~ i u ";; "0 0 0 GaochronoIoic ~ :;. ~ ood . . I:,':?. : ~~ ;:; Geologic . (I,le,n QIfl4. t15 .44 ~ D I ." ~ I G.n,,oIIzeo ! Kt#,.lIk,Ic,t!ee C $!l afl'I,!L. ;; - '" '" I '" 2 ;.: en. —4 ''6 .; 35 i ! 111111_LI . ~:. I ~ t I •.l.ih C—i,. . A ~ ~ = mj, , -44- ~ ~ ~ ~ .;, I a. II: " C 0 ~ ..J ~ C> ~ . q: u e0 " ~ ~ :E Q. 0 '"u0 C> '" " I ~ ~ c 0 <9 0 "" 0 0 <9 ... 00 ~ ~ �-45—45— LOWER KEWEENAWAN KEWEENAWAN SEDIMENTS THELAKE LAKE SUPERIOk SUPERIOR REGION LOWER SEDHlENTS OFOFTHE REGION Allen F. Mattis Mattis Allen F. Department Department of Geology Geology of Minnesota, Hinnesota, Duluth Duluth University of A B S T RAe T ABSTRACT Lower Keweenawan sediments directly directly underlie underlie the the Keweenawan Keweenawan Studies of the quartz— volcanic series in the the Lake Superior Superior region. region. quartzvoi:anic rich Puckwunge Formation (Minnesota) rich (Minnesota) and the Bessemer Formation Formation (Michigan (Michigan and Wisconsin), Wisconsin), which include thin section petrography, heavy mineral and mineral analysis, and measurement of paleocurrent indicators, indicators, provide provide new new data data analysis, and Keweenawan events. events. on Lower Keweenawan The Puckwunge Formation of Cook Cook County, County, northeastern northeastern Minnesota, Minnesota, from is exposed along along aa 25 25 mile mile belt belt extending extending westward westward from is LT.termittently intermittently exposed Pigeon Point on Lake Lake Superior. Superior. Although the lower contact contact of this this formation is is not exposed, exposed, outcrops of of the the formation formation thicken thicken from from 30 formation feet on Grand Portage Island to to over 100 100 feet feet in in the the westernmost \vesternmost feet of basal conglomerate exposures. Fifteen feet feet-of conglomerate exposed exposed on on Grand Grand Portage Portage exposures. Island contains flat flat chips chips and pebbles of of argillite argillite and and slate, slate, probably probably Island derived from the underlying Rove Rove Formation, Formation, and and rounded rounded pebbles pebbles of of feldspar content quartzite. Thin section examinutioi examination indicates indicates total total feldspar content quartzite. ranges from 20 percent percent in the eastern exposures to only a trace in the western outcrops. Unit Unit quartz is the dominant quartz uype, type, with up up to to Zircon, apatite,and apatite, and 20 percent polycrystalline polycrystalline quartz quartz being beingpreseriI. present. Zircon, with tourmatourma— epidote are the the common common nonopaque nonopaque accessory accessory heavy heavy ininerais, minerals, with line also the outcrop belt. also present in the central portion of the to only a trace in the Nopeming, just just west of of Duluth, Duluth, 25 25 feet feet of of quartzite quartzite and and quartzquartz-At Nopeming, conglomerate are •:->.oosed }T the basal (?) quartzite-pebble are exposed bere&: beneath quatnJte—pebble conglomerate (?) Keweenawn Keweenawan flow over a distance distance of of half half aa mile. mile. In the the sand—sized sand-sized fractions, unit quartz quartz is is the LUe dominant dominant quartz quartz type, tye, with polycrystalline fractions, unit polycrystalline also preseit. present. Zircon is the principal nonopaque accessory heavy quartz also is the amounts of of a;atite apatite and and tourmaline tourmaline present. present. Gravity mineral, with minor amounts and magnetic suggest the the presence presence of of aa tabular, tabular, and magnetic profiles profiles across across the the area na suggest dike—like dike-like mafic body beneath the the Puckwunge exposures exposures at at Nopeming; Nopeming; aa greater degree of recrystallization in in the the lowermos: lowermost sediments sediments may may be be related to related to this this probable intrusive. intrusive. and and The Bessemer :-:ohigai-r BessemerFormation Formationof of Hichigan and Wisconsin lHsconsin is intermittently intermittently exposed :nile belt belt extending extending eastward exposed along along aa 40 mile eastward from from >leflen, ~le~len, Wisconsin. formation is is over 150 The fonnation 150 feet thick thickwhere where both both the the upper upper i-td and lower lower contacts are are visible. visible. A contacts A basal conglomerate contains rounded pebbles pebbles of basal conglomerate contains rounded quartz, qu;E2ite, quartzite, flint, flint, and and jasper jasper in in aa qnartzite rruartzite matrix. matrix. In the the sand—si-:d qunrtz is sand-sized fractions, fractions, unit unit quartz is the dominant dominant quartz type, type, with polycrystalline quartz quartz also also present. present. The average total feidsrar feldspar content content is less than than 10 10 percent. percent. Zircon is is the tlte dominant nonopaque nccesscry accessory h!avy withapatite, apatite, rutile. rutile, and heavy hliner&I, ltlineral, \vith and tourmaline tourmaline also also present. presenL �—46— -46- sediments along both limbs the lower lower IKeweenawan Keweenawan sediments Exposures of the the Lake SuperiorSync:ine Synclinesuggest suggestthe thedeposition depositionofof aa thin thin sheet of the Lake Superior sheet of sediment throughout throughout the region. The cross-bedded, rippie—mariced, ripple-marked, of sediment the region. The cross—bedded, of Hell well rounded well sorted sorted quartz—rich quartz-rich sediment sediment composed composed of rounded grains suggests aa shallow shallow water waterenvironment. environment. Cross-bedding, mark, Cross—bedding,ripple ripple mark, in these these sedimentary sedimentary rocks rocks indicate indicate and parting lineation measurements in sediment transport, transport, with the the sediments sediments a general southerly direction of sediment being derived from the the Pre—Keweenawan Pre-Keweenawan rocks rocks to to the the north. north. Thus, Thus, these these Lower Keweenawan sediments were probably deposited deposited during during the the northward transgression of of aa sea into into the transgression the region, region, and were apparently the the final final region prior to to formation formation of of sediment deposited in the Lake Superior region the Lake Superior Syncline. Syncline. �—47— -47- EXPLORATION GEOLOGY GEOLOGY OF OF DOUGLAS DOUGLAS COUNTY, COUNTY, w::scoNSIN WISCONSIN by Joseph T. T. Mengel, Mcnge1, Jr., Jr., Professor and Ronald A. A. Hendrickson Department of Geology Geology Wisconsin State University, University, Superior, Wisconsin 54880 54880 and and and Natural Natural History History Survey, Survey, Madison Madison 53706 53706 Wisconsin Geological and ABSTRACT A B S T R ACT The oldest bed rock units in Douglas County are are the the Keweenawan Keweenawan basaltic fissure flows flows of the St. St. Croix horst south south of the line lin~ Brule, raple, Wentworth, Wentworth, South Range, Brule, Maple, Range, Pattison State Park, Park, Patzau. Patzau. These flows flows have a N6OE3SS N60E35S attitude along tha the north margin margin of of the the horst and N5OE15S N50E15S along along the the south. south. They are intruded by "red "red rock" .95 b.y. b.y. and and by aa gabbro gabbro mass mass in in 32—48N— 32-48Nin 15-47N-13W,K/Ar l5—47N-13W,K/Ar dated at .95 12W. l2W. flows occur again south of the line Totagatic River— Basaltic flows RiverOunce Creek where the attitude is N4SE3ON N45E30N and and there there are are extensive extensive conglomerate lavas. conglomerate and sandstone interbeds with the lavas. Native copper ides are copper and and copper copper suif sulfides are found found in in ainygdaloidal amygdaloidal horizons and along fractures wherever the the Keweenawan Keweenawan lavas lavas outcrop. outcrop. Almost all lava outcrop is within the the following following limits: limits: (1) A a,uth of of the the line Brule—Patzau A 22 mile wide wide band band south Brule-Patzau (2) (2) A nile wide band north of A 22 mile of the the line line Winnebaujou—St. Winnebaujou-St. Croix River in 43N-14w 44N-13W 43N—14W and 44N—13W (3) (3) 43N-15W The NW half of 43N—1SW (4) (4) The south half of 44N-15W 44N—l5W and SW quarter 44N-14W 44N—14W (5) (5) The NE quarter of 45N—l2W 45N-12W (6) The SE haf half of of 43N—1OW, 43N-lOW. especially especially along along the the valley valley of of Dingle Creek in sections 12 and 13 where an an extensive extensive section is exposed the last last century and a half the properties During the half the properties listed below have all all been the have the locus of shafts and/or test test pits and and drilling drilling for for copper in in the the lavas. lavas. �—48— -48- Location Property Nature NE 12—43N—1OW l2-43N-lOW Weyerhauser Amygdaloid Ainygdaloid and and in assoc. sediments SW 28—43N—1OW 28-43N-lOW Williams Ashbed amygdaloid NW 6—43N—13W 6-43N-l3W Superior Copper Mines C.F. C.F. Irving Mon 5, 5, pI. 25 p1. 25 8—43N—13W SW 8-43N-l3W Copper Mine Dam (? ) Ainygdaloid Amygdaloid (?) SE 34—44N—J.4W SE 34-44N-l4W Nowell (Crotty Brook Arnold) ArnoL) Nowell (Crotty Brook (? ) Anygdaioici Amygdaloid (?) SE 14—44N—13W SE l4-44N-l3W Aac ía Arnold Amygdaloid Amygdaloi<l 7N—liJ NE 31-4 3l-47N-l4W Culligan Amygdaloid SE 28—47N—14W 28-47N-l4W Bardon Amygdaloid Amygdaloid('l) () SW l4-47N-l4W 1447N—14W SW Copper Creek Creek Cc1:ier Amygdaloid NE 8—47N—13W 8-47N-l3W Fond Fond du Lac Lac Amygdaloid SE 2—47N—l3W 2-47N-l3W Starkweather Wisconsin Edwards Zdwards NWdip dip 75 NW NE strike 75 Centerll—47N—13W ll-47N-l3W Amnicon Center Fissure vein vein4—6' 4-6' wide wide Narrow steeply dipping Narrow steeply dipping vein Houghton Amygdalcid Amygdaloid NE 8—47N—12W 8-47N-l2W Badger Amygdaloid Nnygdaloid (?) NW NW 1O—47N—12W lO-47N-l2W Chippewa Fractured Fractured Amygdaloids Amygdaloids St 1O—47N—12W SW lO-47N-l2W Copper King King Amygdaloid (?) (?) Amygdaloid 23--48N--lOW NE 23-48N-lOW Cascade Amygdaloid (?) (?) Miygdaloid NE NE Percival, Jr. Jr. Percival, Amygdaloid NE NE 27-48N-lOW 27—48N—1OW Percival Veinlets ininamygdaloid amygdaloid NW NW 28—48N—1OW 28-48N-lOW Astor Amygdaloid SE 29—48N—12W 29-48N-l2W Mrnicon Amnicon Amygdaloid (?) Mtygdaloid SE SE 34-48N-l3W 34—48N—13W Catlin Amygdaloid 4—47N-12W 4-47N-l2\.J 24-48N-lO\.J 24-48N—lOW �—49— -49- The the The U. U. S. S. Bureau of Mines Mines reported on extensive tests of the Property in 1947 and the the Chippewa Chippewa Property Property in in 1955. 1955. Weyerhauser Property The Keweenawan Oronto Group occupies the the Lake Superior Superior syneline syncline of the Croix River. Resouth of the line lineWinneboujou, Hinneboujou, Solon SolonSprings Springs—- St. Croix Shale, and portedly the the Copper Copper Harbor Harbor Conglomerate, Conglomerate, the Nonesuch Nonesuch Shale, and the the Prospecting in Freda Sandstone units are all present in this area. Prospecting Freda Sandstone units are all present in this area. the the syncline syncline has has centered centered on on attempts attempts to tolocate locatea acopper—bearing copper-bearing facies facies of the the Nonesuch Nonesuch Shale, but but has hasbeen beenhampered hampered by by complete complete absence absence of outcrop except the St. St. Croix River Valley. Valley. except along the lower portion of the Conglomerates in: NWNW NWNW 10— 10Conglomerates have have been reported from exploration tests in: half lO—45N—1OW, 44N-llW, SW corner 3l—44N—1OW, 3l-44N-lOW, WW half 10-45N-lOW, SWSW SWSW l6—45N—llW, l6-45N-llW, NE 27—45N-lOW, NENE 34—45N—llW, 10—46N—llW, NESE 25—46N—11W; NE corner corner 27-45N-lOW, NENE 34-45N-llW,SESE 10-46N-llW, NESE 25-46N-llW; Shale rrom from.near center of 34-47N-llW; Sandstone NE 3-45Nnear thethe center of 34—47N—llw; andand Sandstone fromfrom NE 3—45N— NWSWll-46N-lOW, ll—46N—lOW, W Whalf half 15—47N—1OW, lOW, SW SW 8—46N—lOW, 8-46N-lOW, NWSW l5-47N-lOW, SE SE19—47N—1OW. 19-47N-lOW. Waterwells do estimated 200 200 foot foot depth depth of of sandy sandy Waterwells donot not penetrate penetrate the estimated overburden in this area. overburden in this References Grant, Grant, U. U. S., S., 1901, 1901, Preliminary Preliminary Douglas County, Wisconsin: Douglas 6, 55 p. p. 6, 55 report on the the copper—bearing copper-bearing rocks of report Wisc. Wise. Geol. and and Nat. Nat. Hist. Hist. Surv. Surv. Bull. Bull. Holliday, it. W., Holliday, R. W., 1955, Investigation Investigation of of Chippewa Chippewa copper—nickel copper-nickel prospect prospect near Rockmont, Rockmont, Douglas County, County, Wisconsin: Wisconsin: U.S. Bur. Mines Rept. Rept. U.S. Bur. mv. 5114, Inv. 5114, 11 11 p. p. Irving, R. R. Do, D., 1883, 1883, Copper-bearing Copper—bearIng rocks Irving, rocks of Lake Superior: Superior: Mon. 5, 5, 464 464 p. p. Geo1. Survey Mon. Ceol. U. S. S. U. ,p Smith, N. H. C., 1947, 1947, Copper deposits of Douglas County, County, Wisconsin: U.S. Bur. 4088, 7 7 p. p. Bur. Mines MinesRept. Rept. Inv. mv. 4088, Sweet, F. E. T., 1880, Geology Geology of in T., 1880, of the the western western Lake LakeSuperior Superiordistrict district in Geology of Wisconsin 1873—1879: 1873-1879: Wisconsin Wisconsin Geol. Geol. Survey, Survey, v. v. 4, 4, p. 305-362. 305—362. �-50—50-REVISED KEWEENAWAN KEWEENAWAN SUBSURFACE SUBSURFACE STRATIGRAPHY STRATIGRAPHY SOUTHEASTERN MINNESOTA SOUTHEASTERN B. Morey B. Morey Minnesota Geological Survey Minnesota Geological Survey Minneapolis~ Minnesota Minnesota Minneapolis, G. G. ABSTRACT TheMid-continent Mid—continent Gravity High themajor majortectonic tectonicfeature feature of of the The Gravity High is isthe the Detailed geophysical northern mid-continent mid-continent region. region. Detailed geophysical surveys surveys over over the the 600 600 northern mile-long consists mainly mainly of ofa asequence sequence of babamile—longbelt belt show showthat that the the structure consists saltic lava blocks that are saltic lavaflows flowswhich whichform formsteep—sided steep-sided blocks are an an average average of about about 40 miles wide wide and and several several miles miles thick. Clastic rocks 40 miles rocks occur occur in flanking flanking babaBecause much much of of sins and in grabens grabens and the blocks. blocks. Because sins and andaxial axial basins basins on on top top of of the the structure isis covered rocks, little little is is known the covered by by Paleozoic Paleozoic rocks, knownabout about the the rocks rocks However, the the Paleozoic away outcrop area area around around Lake Lake Superior. Superior. However, awayfrom from their their outcrop cover is is relatively southeastern severaldrill drill holes cover relativelythin thinin in southeasternMinnesota, Minnesota, and and several holes Of particular particular have penetrated considerable thicknesses strata. Of have penetrated thicknesses ofofIceweenawan Keweenawan strata. rocks which whichflank flank and andoverlie overlie the interest here here are are the the sedimentary sedimentary rocks the St. Croix Croix an uplifted upliftedbasalt basaltblock blockin in southeasternMinnesota. Minnesota. horst, an southeastern Keweenawan sandstone shalehave havebeen beenknown known fromthe thesubsurface subsurfacefor for aa Keweenawan sandstone andand shale from Because ofoftheir red color, color,they theyhave havebeen been grouped grouped together together ununhundred years. Because hundred their red der the Red Red Clastic Series, Series, aa"temporary" IItemporaryllname name proposed proposed by der the byHall Hall and and others others in 1912. Mooney Mooney and Geophys. Res., Res., v. v. 75, 75,p.p. 5056-5086) have have 1912. andothers others (1970, (1970, J. J. Geophys. 5056—5086) subdivided number of and concluded concluded that sevsevsubdivided these these rocks rocks into aa number of seismic seismic units, and eral of already named of their theirsubdivisions subdivisionscould couldbebecorrelated correlatedwith with already named formations. formations. A detailed detailed petrographic petrographic study study of Ii,000 4,000 feet feet ofofdiamond diamond drill drillcore corefrom froma number a number thepresence presence leastthree threelithologically lithologically of localities localitieshas hasdemonstrated demonstrated the of of atatleast distinctintervals intervals whichmore—or-less more-or~less correspond correspond to seismic units. Therefore, distinct which to seismic it will be be recommended in prep.) it will recommended (Morey, (Morey, in prep.) that thatthe theterm termRed Red Clastic Clastic Series Series be be abandoned andreplaced replacedby by aa more moresuitable suitable nomenclature. nomenclature. Accordingly, Accordingly, three three abandoned and formations be recognized: recognized: (1) Hinckley Sandstone, Sandstone, a abuff tan rock rock conconformations will will be (1) Hinckley buff to to tan taining 95 (2) Fond du Lac Lac Formation, Formation, consisting consisting of 95 percent percent or or more more quartz. quartz. (2) Fond du intercalated intercalated moderate moderate red red shale shale and and sandstone sandstone containing containing 6o 60 percent percent quartz, 30 30 percent orthoclase, orthoclase, microcline microcline and and sodic sodic plagioclase, plagioclase, and 10 percent percent"granitic" "granitic" percent and 10 rock fragments. fragments. (3) (3) An An as as yet yet unnamed unnamed formation, consisting ofofdark darkreddish— reddishformation, consisting brown mudstone containing plagioclase brown mudstoneand andsandstone sandstone containingvariable variable amounts amountsofofquartz, quartz, plagioclase of intermediate intermediate composition, composition, and and aphanitic aphanitic igneous igneous rock rock fragments. fragments. The The first first two formations are known known from two formations are fromsurface surface exposures, exposures,however howeverthethethird third formation formation is confined sub—surface. confined entirely entirelytotothe the sub-surface. A stratigraphic stratigraphic analysis A analysis indicates indicates that that in in the the flanking flanking basins, basins, the the ununnamedformation formationisisoverlain overlain by by the du Lac LacFormation, Formation,which whichininturn turn is gradanamed the Fond Fond du gradationally tionallyoverlain overlainbybythe theHinckley HinckleySandstone. Sandstone. On the horst, horst,the theunnamed unnamed On top top of of the formation overlies formation overl ies basaltic basalticrocks rocksand and is locallyoverlain overlainbybyHinckley HinckleySandstone; Sandstone; is locally at places, places, aa regolith regolithasasmuch much as as 100 100 feet thick thickseparates separates the the two two formations. formations. Either the the Fond Fond du du Lac Lac Formation Formation was was wasnever neverdeposited depositedonontop topofof the the horst, ororwas removed prior to to Hinckley removed prior Hinckley deposition. Any attempttoto explain explain the the geologic geologic evolution evolution of of this structure Any attempt structuremust must take take thesestratigraphic stratigraphic relationships. into account account these relationships. �-51—51— LIMNOGEOLOGICAL STUDIES OF THUNDER THUNDER BAY, BAY, STUDIES OF LAKE LAKE SUPERIOR, ONTARIO ONTARIO J. S. Mothersil1 Mothersill S. LAKEHEAD UNIVERSITY LAICEHEAD ABSTRACT A B S T R ACT studies were carried carried out out in in Thunder Thunder Bay, Bay, Limnogeological studies Lake Superior during the the 1970 1970 field field season. season. Ponar grab samples and Ph1eger taken at one hundred and forty—seven forty-seven and Phleger cores were taken stations stations on a 1.5 mile grid for geochemical and mineralogical In addition three echo sounding traverses analyses. In three echo traverses were carried out using an an MS MS 26F 26F metric metric echo echo sounder. sounder. Thunder Bay which is partly silled to to the the south south by an an east—northeast trending horst from Victoria Island east-northeast Island to to Spar Spar Island basins. Recent sediments sediments which Island contains contains three separate basins. bay—floor grade from a thin cover the bay-floor thin veneer of of sand, sand, less less than than centimeters thick, thick, to clay—silts, up to 14 33 centimeters to aa sequence of clay-silts, meters thick, thick, in in the the central central parts parts of of the the basins. basins. Tight foldfoldclay-silts in in the the deepest deepest part part of of the the central central ing of the Recent clay—silts basin is probably caused caused by by gravity gravity slumping. slumping. Geochemical investigations the bottom-sediments investigations of of the bottom—sediments show that there appears to towards negative Eh and low pH values in the the to be be aa tendency tendency towards deep—water areas. deep-water areas. In the the vicinity of the Kaministikwia Delta anomalous Eh and pH measurements were recorded recorded which were were anomolous probably caused by industrial pollutants entering entering the the bay bay from from the the Kaministikwia River. River. overlie Pleistocene Pleistocene The Recent sediments unconformably overlie varved sediments of undetermined thickness. The Recent clay— thickness. claythe Pleistocene varved sect±on sectton each each form form aa silt section and the typical thin upper typical syndiagenetic sequence with a relatively thin oxidized zone (initial (initial stage) stage) and and aa lower lower reduced reduced zone zone (early (early burial stage). stage). The oxidized zone zone is is caused caused by by the the dissolved dissolved oxygen in the the trapped trapped waters of of the the upper upper layers layers of of sediment sediment and the the action of of aerobic aerobic bacteria. bacteria. The depletion of oxygen results results in the the underlying reducing reducing zone zone with anaerobic anaerobic and aa sharp sharp increase increase in in pH. pH. conditions and �—52— -52- REFERENCES Bissell, H. H. J., 1959, 1959, Silica in sediments of of the the Upper Upper Paleozoic of the the Cordilleran Cordilleran area. area. Spec. Publ. Spec. Pubi. of Soc. Soc. Econ. Econ. Paleontologists and of and Nineralogists, Mineralogists, 7, pp 150—185. 7, 150-185. Dapples, E. E. C., 1962, 1962, Stage of diagenesis in in the the developdevelopment of sandstones. sandstones. Bull, Bull, Ceol. Soc. Geol. Soc. Am., Am., 73, 73, pp 913—934. 913-934. pp Emery, Emery, K. K. 0. O. and and Rittenberg Rittenberg S. S. C., C., 1952, 1952, Early diagenesis of California Basin sediments in in relation to to origin of oil. Bull. Am. Am. Assoc. Assoc. Petrol. oil. Bull. Petrol. Geologists, Geologists, 36, 36, pp 735-806. pp 735—806. Larsen, C. Larsen, G. and and Chilingar Chilingar C. G. V., V., 1967, 1967, Introduction. Introduction. In In Diagenesis in in sediments. sediments. Univ. Univ. of of Southern Southern California, Los Angeles, Angeles, pp pp 1—17. 1-17. W. H., H., 1942, 1942, The rate of deposition of of sediments: sediments: Twenhofel, W. a major factor connected with aiteration alteration of Jour. Sedimentary sediments after deposition. deposition. Jour. 12, pp pp 99—110. 99-110. Petrology, 12, Changes produced by microC. E., E., 1942, 1942, Changes ZoBell, C. organisms in in sediments sediments after after deposition. deposition. Sedimentary Petrology, 12, 12, pp pp 127—136. 127-136. Jour. �—53— -53- REINVESTIGATIONOF OF "RED "RED ROCKS" REINVESTIGATION ROCKS" IN THE THE PIGIY)N POINT AREA, PIGEON AREA, MINNESOTA MINNESOTA C. M::drey, Jr., and and P. P. W. W. Weiblen Weiblen M. G. Mudrey, Jr., Minnesota Geological Survey Survey and University of Minnesota, Minneapolis ABSTRACT ABSTRACT Keweenawan granitic rocks rocks of reddish reddish color color as as exemplified exemplified by the "red rocks" rocks" of the the Pigeon Point, Cook Cook County, County, area area are are divisible into red quartzites, quartzites, porphyritic red red rocks rocks and and granular granular with this this division division reduces the problem red rocks. rocks. Retnapping Remapping with problem of of excess granophyre abundance associated with the the Pigeon Pigeon Point Point sill. sill. Reddish quartzites quartzites contain abundant recrystallized quartz Reddish quartz iicrstitial sericite—biotite feldspar— with minor minor interstitial sericite-biotite and granophyric feldsparquartz intergrowths. A faint foliation A faint foliationdefined defined by by biotite biotitelinea— lineation and tion quartzite inclusions inclusions and relict relict bedding bedding can be discerned in quartzite found in intermediate rock rock of dioritic dioritic composition. composition. Porphyritic red rock displays euhedral feldspar feldspar phenocrysts in a granophyric quartz—feldspar quartz-feldspar groundmass. groundmass. This rock type cuts Miaro— the Pigeon Point gabbro. Miarothe Rove formation and and intrudes the litic cavities are found filled with calcite and zeolite minerals. cavities zeolite Granular and feldspar feldspar Granular red rock contains granoblastic quartz and tic groundmass groundinassof of quartz quartz and and feldspar feldspar with with minor set in a granophy granophyric minor sericite-biotite and epidote. epidote. sericite—biotite and and rounded grains or sphene and Phase relations relations and overgrowths on quartz suggest suggest that that aa sedimentary parentage is is possible, possible, however intrusive intrusive relations relations on on Pigeon Point require that the granular red rocks rocks must must have have been been a crystal mush. Point area area in in excess excess The abundance of red rock in the Pigeon Point of that to be expected by differentiation has been noted since of that since 1893, the eastern eastern exposures exposures of of 1893, and is is part of a reinvestigation of the Keweenawan rocks rocks in in Minnesota. �—54— -54- THE SEDIMENTOLOGY AND TECTONIC SIGNIFICANCE THE SIGNIFICANCE OF OF THE THE BAYFIELD GROUP, GROUP ~ WISCONSIN HISCONSIN AND MINNESOTA MINNESOTA Wallace Darwin Darwin Myers, Myers~ II II University of Wisccnsin Wisconsin ABSTRACT ABSTRACT A study of the mineralogical and A and physical physical characteristics characteristics of of the the Bayfield Group was made to determine 1) 1) depositional depositional environment, environment, paleogeography, and source terrane paleogeography, terrane during during Bayfield Bayfield time, time, 2) 2) the the of the nature of the contact contact of ofthe theBayfield BayfieldGroup Group with with the the older olderOronto Oronto Group, Group, and and 3) 3) the early of the the Douglas Douglas fault. early history of fault. study included included detailed detailedmapping mapping of of Bayfield Bayfieldand andOronto Oronto Field study Group rocks outcrops, the lithology lithology Group rockstotoestablish establishthe thelocation locationofof all all outcrops, and stratigraphy of of all stratigraphic and stratigraphy all formations, formations, the the geographic geographic and and stratigraphic distribution distribution of of sedimentary structures and the the structural relationships relationships between rock rock bodies. bodies. Analyses of rock rock specimens specimens in in the the laboratory laboratory included 1) 1) petrographic study of the the bulk bulk mineralogy mineralogy and and textural textural characteristics of sandstone specimens, 2) 2) x—ray x-ray diffraction diffraction study study of of the the clay mineralogy of shale beds and and chemical chemical analyses analyses of of the the boron boron conconcentration of the clay mineral illite, 3) 3) x—radiography x-radiography study study of of the the sedimentary structures, structures~ and and 4) 4) internal stratification of selected sedimentary statistical study of directional sedimentary structures. structures. Petrographic studies of Bayfield Bayfield Group Group sandstones sandstones indicate indicate that that constitutes approximately approximately 80 80 percent percent of of framework framework grains, grains, that that quartz constitutes the feldspar population is dominated dominated by microcline, microcline, and and that that Bayfield Bayfield the feldspar Group sandstones sand·stones are are better better sorted sorted and and exhibit exhibit aa higher higher degree degree of of rounding than than the the Freda Freda Sandstone of the the Oronto Oronto Group. Group. The high compositional compositional and and textural textural maturity The high maturity of ofthe theBayfield BayfieldGroup Group suggests that that the suggests the source source area area for forthese thesesediments sediments was was not not aa simple simple volcanic terrane. Petrographic Petrographic data that the the Bayfield Bayfield and and volcanic data indicate indicate that Freda possibly recycling of of the the Freda Freda Freda sandstones sandstoneshad hada asimilar similar source; source; possibly Sandstone was an an important important source source of of sediments sediments during during Bayfield Bayfield time. time. The Tl~ sedimentary structures of the the Bayfield Group are those which are typically developed in fluvial are fluvial environments, environments~ including including trough trough cross— crossbedding, current ripple marks, sandstones, mudcracks, bedding, marks, channel sandstones, mudcracks, and associated structures. structures. The stratification and bed forms forms of the the Bayfield Group are Group are characteristic of those those formed formed in in the the upper upper part part of of the the lower— lowerwith modern alluvial (Harms and and Fahnestock, Fahnestock, 1965). 1965). By analogy ,.,ith alluvial flow regime (Harms channels channels the the general geologic setting of of the the Bayfield Bayfield Group Group can can be be inferred to to have been an alluvial plain plain characterized characterized by by loz—gradient, 100.,-gradient, perennial streams. streams. The strong N40°E N400E trend trend of of trough trough cross— crossmeandering, perennial bedding indicates was from the indicates the the direction of sedimentary transport transport was the southwest to the the northeast. This inference is is supported supported by the the orientation tion of parting lineation and and current current ripple ripple marks. marks. �—55— -55- the Bayfield and and Oronto Oronto Groups Groups is is not not exposed; exposed; The contact of the petrographic data provide~he provide the clearest evidence of the petrographic the nature of of this this boundary. On the the basis of the the high compositional compositional and and textural textural maturity maturity boundary. Group sandstones, exhibited by Bayfield Group sandstones, it it is is suggested suggested that that these these elastics represent represent a new cycle of sedimentation in clastics in the the synclinal synclinal Lake Lake This interpretation is supported by the contrasting Superior basin. basin. This supported the contrasting clay mineralogy mineralogy of the two sequences (illite— clay (illite- and and chlorite—rich chlorite-rich Oronto Oronto rocks, but kaolin—rich rocks, kaolin-rich Bayfield Bayfield rocks). rocks). compelling evidence evidence that:the that: the Douglas Douglas fault fault was was active active There is no compelling during Bayfield time. time. Conglomerates are are known known at at only nittytwo two exposures exposures of the Douglas Douglas fault, the fault, and in each case their their distribution distribution is is restricted restricted to to the zone immediately adjacent the adjacent to to the the fault. fault. Furthermore, Furthermore, the conglomconglomerates do do not not resemble true tectonic conglomerates either erates either texturally texturally or or compositionally. Additional evidence is provided by the the orientation orientation of directional sedimentary structures structures at at the the Douglas Douglas fault fault localities. localities. These structures which include include parting parting lineation and and cross-bedding, cross—bedding, show show structures which no apparent relation to the Douglas fault. to the fault. Thus, Thus, there is no geologic evidence of major faulting faulting during during Bayfield, Bayfield, or or at at least least Orienta, Orienta, time. time. �—f LAKE LAKE MICHIGAN MICHIGAN AEROMAGNETIC AEROMAGNETIC SURVEY SURVEY by W. O'Hara Norbert W. Great Lakes Research Division University of Michigan Arbor, Mi Michigan Ann Arbor, chigan William J. J. Hinze Hinze Department of Geology Michigan State University East Lansing, Lansing, Michigan Michigan E;t ABSTRACT A B S T R ACT The Precambrian Precambrian basement basement complex complex beneath beneath Lake Lake Michigan, Michigan, which which lies lies on the western western and and northern northern flank flankofofthe thePaleozoic PaleozoicMichig.E.n Michigan Basin, Basin, is is only known from a few widely scattered basement drill holes around the scattered drill holes around the perimeter of of the Lake and and aa single single drill drill hole hole -ithin within the Lake Lake on on 3eaver Beaver Nevertheless, the basement geologyof of Lake LakeMichigan MichiganisissignifisignifiIsland. Nevertheless, basement geology cant frameworkofofthe theMidcontinent Midcontinentandand critical to cant to the the Precambrian Precambrian framework is iscritical to the extrapolation extrapolation of ofbasement basement structural structural trends trendsfrom from Lake Lake Superior, Superior, orth— Northinto the fill this ern Michigan, and Wisconsin into theMichigan Michigan Basin. Basin. To To fill thisgap gap an an em Michigan, and aeromagneticsurvey surveyconsisting consistingof of 7,000 7,000 miles miles of of total aeromagnetic total magnetic magnetic intensity were collected along flight traverses separated data were separated by by six six mile mile intervals. intervals. traverses were were flown flown over over northern northern Lake Lake Michigan in aa general northFlight traverses east direction and over southern Lake Lake Michigan in in aa northwest northwest direction. direction. The residual total magnetic intensity map map prepared from from the the collected To general the magnetic data exhibits three regional regional magnetic magnetic positives. positives. In anomalies are related in in aa direct direct manner manner to to gravity gravity anomalies anomalies on on the the periperimeter of the Lake. Lake. The strikes northwest northwest from from the the The southernmost southernmost positive postive :rikes Michigan shore from from +2° 42 0 to 13° 43 0 30'N. 30'N. This anomaly is associated with aa positive and and local local magnetic magnetic positives positives extend— extendsoutheast striking gravity positive icLg across southwestern southwestern Michigan Michigan and northeastern ing across northeastern Indiana Indiana into into Ohio. Ohio. It It is gravity and and magnetic magnetic anomaly anomaly in in northeastern northeastern is on strike with the positive gravity Indiana which has been found found by basement basement drilling drilling to to be be underlain underlain by by basalts basalts similar to Keweenawan flows flows of of the Lake Lake Superior Superior region. region. The central central regional positive, which is made up of several individual anomalies, roughly easteast— anomalies, strikes strikes roughly 450 0 0 t140 The northern components west across ·the Lake between 44 and 45 15'N. The northern components of the l5'N. this anomaly can be traced into into Wisconsin and and across across the southern southern Peninsula Peninsula this of Lchigan except where they are transected by the Mid—Michigan rift Michigan except where they are transected by the Mid-Michigan rift zone. zone. trends are believed to be assrciated with the the Penokean basement basement provprovThese trends associated with ince. A A marked regional magnetic anomaly minimum striking east-west east—west occurs occurs to the north of the regional regional positive. positive. The anomaly is on on strike strike with the the felsic felsic rocks of the Mountain—Amberg Mountain-Amberg area area of of Wisconsin Wisconsin which which is is also also charcharacterized by magnetic magnetic minimums. minimums. The minimum reappears reappears east east of of the the Mid—Michi— Mid-Michigan rift rift zone anomaly and and strikes strikes east—southeast east-southeast across across to to Lake Lake Huron. Huron. The The northern regional positive magnetic anomaly anomaly strikes strikes north—south north-south from from Traverse Traverse where it it bifurcates bifurcates with with one one limb limb extending extending Bay to north of Beaver Island where north—northwest through Lake north-northwest Lake Superior Superiortotothethe Keweenawanbaa basalts Keweenaw Keweenawan alts ononKeweenaw Point. The other limb the eastern eastern portion of of the the Northern Northern Point. limb continues continues into the Peninsula of Michigan and another another segment segment of of this this branch branch connects connects to to the the Keweenawan flows on Mamainse Point. flows on Mamainse Point. In the the Traverse Bay area the regional connects to the positive becomes becomes strongly negative and connects the south with the the midmid— Michigan gravity and and magnetic magnetic anomaly. anomaly. �-57—57— GEOCHRONOLOGY OF THE GIANTS RANGE GRANITE L. A. PRINCE FRECE AND L. A. AND G. G. N. N. HANSON HANSON State University of New York Stony Brook, N. N. Y. Y. 11790 ABSTRACT A B S T R ACT Seven whole rock samples of two—mica, two-mica, foliated foliated quartz ~uartz monzonites monzonites from the central part of the Giants Range Granite, Granite, north of Hibbing, Hibbing, Minnesota, give aa Rb—Sr Rb-Sr isochron isochron age age of of 2670 2670 1) and a 3r87/Sr86 ± 65 m.y. (Rb (Rb 87 x 10yr _1) Sr 87 /Sr 86 initial initial 87 AS A == 1.39 x i0'11 yr ratio ratio of 0.7002 ± 0.0019 0.0019 at at the 95% confidence level. level. Epidote, plagioclase, potassium feldspar, biotite—chiorite, apatite plagioclase, feldspar, biotite-chlorite, apatite and and muscovite separates from one of these whole rock samples give muscovite separates samples give mineral —whole rock ages ranging from 2350 m.y. for epidote -whole ages ranging from 2350 m.y. for epidotetoto26140 2640 m.y. m.y. for muscovite. mineral—whole rock ages muscovite. The lowered mineral-whole ages suggest suggest that at least least one event event occurred after intrusion of the granite, at granite, but that that the individual mineral phases the phases were not completely homogenized homogenized with Sr 87 /Sr 86 ratios. ratios. The 2350 m.y. epidote-rock respect to their 5r87/5r86 m.y. epidote—rock age age probably is is a maximum for the time of the last last event. event. The mineral data provide no conclusive evidence for for the sequence se~uence of of events after intrus on, but are not inconsistent events intrusion, inconsistent with aa regional regional low-grade low—grade metamorphism at around 1600 m.y. This is in agreement with U—Pb U-Pb data data on on sphene sphene This whole rock age is Giants Range Granite which suggest suggest an an age age of of and zircon from the Giants 2700 for hornblende from from the the Giants Giants 2100 m.y. n.y. and also with K-Ar K—Ar ages for Range Granite which generally generally are are 2600—2100 2600-2700 m.y. m.y. These ages ages however are older than most of the Rb—Sr Rb-Sr and and K—Ar K-Ar ages ages for for biotite biotite however are which range from 2260—2630 2280-2630 m.y. m.y. The age of the post-kinematic post—kinematic Linden Linden Syenite Syenite just just to to the the north north also also limits limits the the age ae of the syn— syn?b207_Pb2u6 data on sphene to late—kinematic late-kinematic Giants Giants Range Range Granite. Granite. Pb207_Pb206 sphene and aa Rb-Sr b—Sr mineral—whole mineral-whole rock rock isochron isochron with with an an initial initial ratio ratio of 0.7009£-0.0004 suggest an age for the Linden Syenite Syenite of of about about 0.1009±O.000b 2700 m.y. 2100 m.y. 87 /Sr 86 initial The low Sr initial ratios from from both the the Linden Linden Syenite Syenite Sr87/5r86 and the the Giants Giants Range Granite suggest suggest aa source source with aa low low Rb/Sr Rb/Sr and ratio, perhaps mantle, and and it is is unlikely that appreciable appreciable ratio, perhaps the mantle, mixing with preexisting continental crust crust took place. place. �—58— -58- THE GREAT GREAT LOGAN PALEOHAGNETIC PALEOMAGNETIC LOOP —- THE POLAR THE WANDERING PATH FROM FRaN CANADIAN SHIELD ROCKS ROCKS DURING DURING THE THE HELIKIAN HELIKIAN ERA ERA by W. A. W. A. Robertson }{obertson Geomagnetic Laboratory Energy,Mines Energy,I'Iines & & Resources Resources Ottawa, Ottawa, Ontario w. F. Fahrig H. Geological Survey of Canada Ottawa, Ontario Ottavla, ABSTRACT ABSTRACT Normally magnetized dykes dykes and reversely reversely magnetized sills sills of of Neohelikian age age near the the north west take Superior Superior form form west shore of Lake two distinct distinct paleomagnetic groups groups with mean pole positions of two 179W, 35N, 179\\1, 35N, and 140W, 47N 47i'J respectively. respectively. Thermal and and alternating alternating field field paleomagnetic studies studies and and the study of magnetic properties and opaque opaque minerals minerals indicate that and that directions directions of magnetization of of these rocks were acquired at at the the time time of of their their intrusion. intrusion. Field these rocks evidence indicates indicates that evidence that the the reversely magnetized sills are older than the normally magnetized magnetized dykes than the normally dykes and radiogenic age determinations indicate intrusion between 1000 1000 and and 1100 1100 m.y. m.y. ago. ago. These pole pole positions, positions, together with those for the These the Franklin Franklin intrusions pole pole at at l67E-08N, 167E—08N, assigned age 675 m.y., the intrusions 675 m.y., the Abitibi dykes, the NacKenzie MacKenzie dykes, at at 134W. 134W, 27N, 27N, assigned aged 1150 m.y. m.y. and the Igneous events, at Igneous at 171W, l71W, 4N, 4N, assigned assigned age age 1200 1200 iu.y. m.y. are are used used to to define Logan's Loop, the pole pole took took in in Neohelikian Neohelikian define Loop, the the path path that. that the time to the Canadian Shield. Shield. Other poles well defined defined time relative to magnetically, but less well dated, magnetically, dated, from from rocks rocks of of this this era era fit fit the curve quite well. the of available that the available data data supports supports the the hypothesis hypothesis that the Analysis of relative polarmovement movement that gave rise Logan's Loop Loop was was prerelative polar that gave rise totoLogan's preceded and followed follmved by vis a vis ceded and by polar stability vis vis North America, quite rapid rapid during during the the forforwhereas polar movement may have been quite The depositional environment of Neohelikian the loop. loop. The Neohelikian mation of the rocks of the Canadian Shield should be tested tested against against their their rocks of the probable paleolatitude as probable as indicated by the the 5 key points on Logan's Logan's Loop. �—59— -59- CHARACTERISTICS CHARACTERISTICS OF SOME SOME ALTERATION MINERALS, MINERALS, PORTAGE FJRTAGE LAKE LAKE LAVA LAVA SERIES, SERIES, MICHIGAN MICHIGAN A. A. P. p.RUOTSALA RUOTSALA Michigan Technological University Michigan Technological ABSTRACT Many silicate, carbonate, Many silicate, carbonate, and and oxide oxide minerals minerals are are associated associatedwith with copper mineralization mineralization in the Portage Series and copper in the Portage Lake Lake Lava Lava Series and associated associated conglomerates. complete listing listing was was published published by Butler and and Burbank'. Burbank l • conglomerates. AA complete Amygdule studied by Amygdulezoning zoningpatterns patterns associated associated with with mineralization mineralization were studied 2 Stoiber and and x-ray x-ray diffraction Stoiber and Davidson Davidson .. Chemical and diffraction studies studies are are being being carried out out at atMichigan Michigan Technological Technological University on on a continuing continuing basis. carried basis. In the the past -'n, In past some some of of these these studies studies were weresupported supportedby bythe theCalurnet Calumet Divisi Divisi:::n, Universal Universal Oil Oil Products Products Company. Company. Epidote isis characterized characterized by Epidote by wide wide ranges ranges in in unit unit cell cell dimensions. dimensions. In general, general, epidotes epidotes from from amygdaloids amygdaloids have have larger larger unit unit cell cellvolumes volumes than than those those from conglomerates. congloITlerates. Calcites wide ranges ranges inin trace trace element composition, especially especiaiy Calcites show show wide eleITlent cOlnposition, in Mg, and and Mn. Mn. There is a a positive positive correlation correlation bebeThere is in concentration3 concentratiois of Fe, Fe, Mg, tween Mncontent contentand andcopper copperITlineralization mineralizationininthe theKearsarge Kearsargeamygdaloid, amygaloid, and tween Mn and therefore is potentially potentially useful useful as as an an exploration exploration tool therefore is tool in in the the district. district. 3 in many ITlany forms and at virtually every every stage sh.ge of of the the Chlorite occurs in forms and sequence in alteration sequence in the the district. district. An An interesting interesting occurrence occurrence is is as an essentially pure essentially pure clay clay mineral ITlineral in inthe the fault faultgouge gouge in in the the Allouez Allouez Gap Gap Fault Fault This is and of the the Kingston Kingston Mine4. Mine~. This is one one of of the the few, few, if if not not and hanging hanging wall wall slip of the the only only occurrence occurrence of of pure pure clay clay chlorite chloriteknown, known. It essentially of of It consists consists essentially In ITluch much of ofthe thehanging hangingwall wallslip, slip, chlorite chlorite is is intimately the type Ub lIb polytype5. polytype 5 . In intiITlately absorption properties (plastic and and liquid liquid mixed with hematite. The The water water absorption properties (plastic liITlits) greaterfor for chlorite-hematite chlorite-heITlatite mixtures mixtures than than for for pure pure chlorites, chlorites, limits) are; are greater suggesting the the pas possibility of SOITle some ITlixed mixed layering layering of of chlorite chlorite and suggesting sibility of and hematite. heITlatite. References Cited Cited 1. Butler, Butler, B. B. S., S.,and andW. W.S.S.Burbank Burbank(1929) (1929) The The copper copper deposits deposits of of U. S. Geol. Geol. Surve., Surve., Prof. Prof. Paper Paper144, 144, 238 238 pp. pp. Michigan. U.S. 2. Stoiber, R. E. E.and andE.E.S.S.Davidson Davidson(1959) (1959)Amygdule AITlygdule mineral mineral zoning zoning in Stoiber, R. the Portage the Port age Lake Lake Lava Lava Series, Series, Michigan. Michigan. Econ. Econ. Geo!. v. 54, Geo. v. 1444-1460, p. 1250-1277 and p. 1444-1460. p. 1250-1277 �-60—60— 3. Ruotsala, P., S. S.C. C.Nordeng, Nordeng,and andR. R. 3.J.Weege Weege(1968) (1968) Trace Ruotsala, A. A. P., Trace elements the elements in in accessory accessory calcite -- aa potential exploration tool in the Michigan Copper District. District. Cob. of Mines MinesQuart., Quart., Jour., Jour., Michigan Copper Colo. School School of (International Geochemical Exploration v. 64, 64, p. p. 451-455. 451-455. (International v. Symposium) 4. Ruotsala, Ruotsala, A. A. P. P. (1968) (1968) Clay Clay alteration alteration associated associated with with mineralization mineralization Clays and and Clay ClayMin., Mm., v. in Michigan Copper v. 16, 16, in the Michigan Copper District. District. Clays p. 400-402. p. 400-402. 5. Brown, B. Brown, B. E.,, E., and and S. S. W. W. Bailey Bailey(1962) (1962) Chlorite Chlorite polytypism. polytypism. Am. ,v. 47, Am. Mineral. Mineral.,v. 47, p. p. 819-850. 819-850. �—61— -61- THE THE GENERAL GENERAL STRATIGRAPHY STRATIGRAPHY OF OF THUNDER THUNDER BAY, BAY, LAKE LAKE SUPERIOR SUPERIOR R. J. J. Shegelski LAKE-lEAD UNIVERSITY LAKEHEAD ABSTRACT A B S T R ACT Petrographic studies of the sediments taken from from Thunder Bay Bay combined with x-ray diffractometer analysis have indicated indicated distinct lithologic types in the the bottom sediments sediments of of Thunder Thunder Bay. Bay. Stratitypes in graphic correlation correlation of of thc the bottom bottom sediments sediments from from Thunder Thunder Bay Bay has has the aid aid of of echo echo sounding sounding traces. traces. These traces been developed with the boundaries, nature and thickness indicate the boundaries, thickness of the various litholithofacies. facies. The sediments in in Thunder Thunder Bay Bay can can be be divided divided into into five five categories; categories; (1) (2) Weathered Weathered Varved Clay, (1) Varved Clay, Clay, (2) Clay, (3) (3) Intermediate Intermediate Clay, Clay, (4) Upper Upper Deltaic Sediment, Sediment, (5) Sediment. The Varved (4) (5) Upper Upper Trough Sediment. Clay is overlain is of Post Post Valders Valders glacial glacial origin origin and and is is disconformably discoi:fom*Lj overlain by the Weathered and Intermediate Intermediate Clays. Clays. The latter are are products products of weathering of of the the older older Varved Varved Clay. Clay. The Intermediate Clay is conformably overlain overlain by by Upper Upper Deltaic Deltaic and and Upper Upper Trough Trough Sediment. Sediment • conformably The .T he latter units are sediments sediments derived derived dominantly dominantly from from the the Kaministikwia Kaministikwia River. River. Thin Thin iron iron and and manganese manganese beds beds are are formed formed through through diagenetic diagenetic solution, upward migration, migration, and precipitation at solution, at a chemical chemical interface interface in the Upper Sediments. Sediments. �—62— -62- CHERT IN SEDIMENTS SEDIMENTS by G. G. Spencer Spencer Duluth, Minnesota A B S T R ACT ABSTRACT silica solution solution becomes becomes supersuperAmorphous silica is produced when aa silica some silicates silicates are are dissolved dissolved saturated and a precipitate forms or when some in acids. In the silica is is in a colloidal form and remains remains In either case case the so for long periods of of time. time. Eventually crystallization begins, begins, and heating the substance can speed up the the process to to aa great great extent. extent. In In natural conditions conditions opal opal is is the the first first step step followed followed by by chalcedony chalcedony and and finally cristobalite. All of these finally these forms forms of silica silica have have been been termed termed chert. Chert has·long has long been regarded as a chemical precipitate. Chert precipitate. This is sufficient to to explain explain hot hot spring spring deposits deposits and and hydrothermally hydrothermally view is deposited chert or opal opal near near the the surface. surface. Cooling volcanic waters become supersaturated with silica silica in in solution solution and and amorphous amorphous is is deposited deposited as as a sinter or in in thin thin layers. layers. There are, are, however, many other other environments environments in in which which chert chert is is found found such as: as: a) a) b) c) c) d) d) e) e) f) f) g) black slate with chert lenses or beds limestones limestones with chert nodules or joint joint fillings fillings bedded cherts containing sponge spicules cherts spicules or Radiolaria Radiolaria chert stringers in oxidized sulphides sulphides chert stringers and crusts in fillings of vesicles in in lava lava flows flows agate fillings oxide granules chert chert as as a a matrix for iron oxide opal or chert chert replacing organic matter The author author ascribes chert to to the the decomposition decomposition of of clays, clays, detrital detrital In acid environsilicates, ash or sand grains in in carbonates. carbonates. In silicates, volcanic ash ments alumina alumina and and alkalies alkalies are are removed removed and and aa silica silica gel gel is is left. left. In alkaline waters waters silica is dissolved and and is deposited deposited in in aa more more neutral neutral zone or will replace a dissolving particle such such as as organic organic matter. matter. The relative solubility solubility of of alumina and alkalies compared to relative and alkalies to silica is is the the determining factor. factor. iturata (1946) investigated investigated many many silicates silicates ,vhich which produced gels when i'lurata (1946) \<Then treated with acid. He alumina ratio ratio of 1:1 or or treated with Hefound foundthat that aa silica silica totoalumina 2:3 was Other silicates silicates prpduced was conmion common toto gel forming silicates. Other produced silica gel forming particles larger than than colloidal size or were not not affected affected by by acids. acids. Any particles silicate structure from from which alumina has has been been removed removed is is halfway halfway along along to chert. to becoming chert. In and silicate iron formations formations mixed with ,.,rith quartz, quartz, minerals In carbonate carbonate and become unstable when when the the temperature temperature is is raised raised and is removed from from the the and CO, CO. is point sediment. The ionization ionization of at whicli ,..d lich Doint of \vater water increases increases up up to to 230° 23°CC at silica both in in quartz and silicates becomes hecomes increasingly incren3in~ly soluble. soluble. Sand grains such as as grains in oolites oolites might might dissolve and secondary silicates such �-63—63— minnesotaite and and stilpnonielone stilpnomelone would appear. appear. Chert in this this case case is is minnesotaite clearly clastics clearly diagenetic diagenetic and and came came from from aa breakdown of original elastics even if the the original texture texture remained remained the the same. same. formations would appear to to be be examples examples of of late late Precambrian iron formations they would also contain contain early early diagenetic diagenetic silica silica diagenetic chert although they as well. as Silica content is these rocks because Silica and and iron iron oxide content is higher in these of the the loss loss of carbon dioxide, dioxide, water, water, and small small amounts amounts of of alkalies alkalies in in solution. �—64— -64- IMPLICATIONS OF CARBON ISOTOPE RATIO VARIATIONS IN IN CARBONATES CARBONATES FROM THE BIWABIK BIWABIK IRON FORMATION, FORMATION, MINNESOTA F. C. C. Tan and E. F. E. C. C. Perry, Jr. Jr. Minnesota Geological Survey Survey University of Minnesota Minneapolis, Minnesota 55455 Minneapolis, 55455 ABSTRACT A B S T R ACT Carbon isotope ratios from carbonates of of the the Biwabik Biwabik Iron—formation Iron-formation obtained from core samples of Mesabi Deep Drilling Drilling Project Project (Pfleider (Pfleider and and others, 1968) 1968) show the following significant features. others, features. 13 (1) SC SC13 values values of of carbonates carbonates associated associated with with magnetite magnetite from holes holes (1) 5 and 7 show a range of from —7 -7 to to —19 -19 per nil mil (relative (relative to to aa Cretaceous Cretaceous belemnite standard standard calcite calcite PDB) PDB) in in comparison comparison with with1he he carbonates carbonates from from is strongly correlated the magnetite-free (0 to SC 13 is the magnetite—free horizons horizons (0 to -7 —7 per per mil). mu). with magnetite magnetite content content in in hole hole 7. 7. 13 (2) The Gc SC13 values values of of carbonates carbonates from magnetite and non—magnetite (2) The non-magnetite horizons of hole 2 with one exception, do not show1ignificant horizons of hole 2 with one exception, do not show1~ignificant difference difference range of from in contrast with holes holes 55 and and 7. 7. They exhibit a SC from —7 -7 to to —19 per -19 per mU.. mil. 13 (3) values do do not not show show any any significant significant stratigraphic stratigraphic (3) The The bC C13 values correlation correlation with with tlia the percent iron. iron. (4) between (4) There There appears appears to to be be a correlation between individual members of of the the Biwabik Biwabik Iron—formation. Iron-formation. 13 C1-3 values and the ~C the 13 In explaining the observed correlation between magnetite and and the the 13 values based on our SC our preliminary preliminary results, results, we we proposed proposed (Perry (Perry and Tan, 1970) that that aa diagenetic diagenetic oxidation—reduction oxidation-reduction reaction reaction producing producing permitted exchange exchange between between organic organic carbon carbon and and magnetite from hematite permitted carbonate carbon reservoirs: reservoirs: r 44FeO bFeO +CO 6 Fe 22033 +C + C(organic)~f----~~Fe 33044 + CO 22 (organic) (1) (1) 12 13 C1202 Fec 0 C 0 + FeC3O3 2 3 (2) (2) < 12 13 cC1-3O 0 + + FeC2O3 Fec 0 2 3 recent detailed detailed studies studies have have strengthenI~ strengthen our Our recent our previous previous observaobservavalues (—18 tion on hole 7 but have found anomalously low SC (-18 per per nil) mil) tion from from the the non-magnetite non—magnetite horizons of hole 22 (Lower (Lower Slaty Slaty Unit). Unit). These anomalous values may be related related to to metamorphic metamorphic reactions reactions accompanying accompanying the intrusion of the the the Duluth Complex because hole 22 is is located located near near metamorphic zone zone (1) (1) of French French (1968). (1968). C13 values Our observation that that there is a correlation between ~el3 and the and the individual members of the Biwabik Iron—formation Iron-formation would suggest suggest l3 variations that SC1-3 variations are are depositional depositional or or early early diagenetic diagenetic features features that the the ee and bear no relationship relationship :o ~o the the genesis genesis of of niagnetite magnetite (model (model above). above). The �-65—65— l3 values may be explained by the differences in IC13 bC the variable variable contributions contributions of organic carbon and oceanic bicarbonate to of to the the depositional depositional or or diagenetic environments. environments. 13 SC13 values of We are currently investigating the theoC of co—existing co-existing graphite-tarbonate pairs and oxygen isotope fractionation graphite-carbonate fractionation between between cocoquartz—magnetfte at various stratigraphic existing quartz-magnetite stratigraphic levels levels of of holes holes 22 and 7 to to see if they have different diagenetic diagenetic or metamorphic metamorphic histories. histories. Co—existing quartz—carbonate oxygen isotope Co-existing quartz-carbonate isotope fractionation fractionation In in samples samples from hole 2 compared to that that in in holes 55 and and 77 suggests suggests that that the the post— postdepositional history of these these two two areas areas is is indeed indeed different. different. References rrench, B. B. French, M. , (1968) Progressive contact metamorphism of the M., the Biwabik Biwabik Iron—formation, Mesabi Mesabi Range, Ninnesc:a, Minn. Minn. Geol. Iron-formation, Range, Minnesota, Geol. Surv. Surv. Bull. Bull. 45, 45, Univ. Univ. of Minn., Minneapolis. Ninneapolis. Tan, F. Perry, E. E. C.C., Jr., and Tan, F. C., C., Significance of carbon carbon isotope isotope Perry, , Jr., variations in carbonates from from the the Biwabik Biwabik Iron—formation, Iron-formation, Minnesota. Minnesota. symposiumononthe thegeology geology and and genesis genesis of International symposium of Precambrian Precambrian iron/manganeseformation formationand andore oredeposits, deposits, Kiev, Kiev, 1970 1970 (In (In Press). iron/manganese Pfleider, E. E. P., P.,Morey, Morey, C. G. B., B., and and Bleifuss, Bleifuss, F. R. L. L. (1968) Mesabi deep deep drilling project, project, progress report repo~t no. no. 1, 1, Minnesota Ninnesota section, section,AIME AIME forty— fortymeeting, Dniv. Univ. of Ninn., Minn., Minneapolis. Minneapolis. first first annual meeting, �—66— -66- Oxygen isotopic studies of Early Early Precambrian Precambrian granitic granitic and and metamorphic rocks from from the the western western part part of of the the Giants Range batholith, Northeastern Northeastern Minnesota Minnesota S. Viswanathan, Viswanathan, E.C. s. E.C. Perry, Jr., Jr., and and P.K. P.K. Sims, Sims, Minnesota Geological Survey, University of Minnesota, Geological Survey, University of Minnesota, Minneapolis, Minnesota 55455 55455 ABSTRACT A B S T R ACT objectives: (1) demonstrate that that oxygen oxygen The paper has two main objectives: (1) to to demonstrate isotope geochemistry is a valuable tool tool in in elucidating elucidating granite granite petrogenesis, petrogenesis, provided it is is integrated integrated with with detailed detailed field field and and laboratory laboratory studies, studies, and and (2) to to give give values values for~(018/016)guartz for f(O18/016)qrtz in (2) in the the Early Early Precambrian Precambrian granitic granitic and metamorphic metamorphic rocks, which are rather scarce and rocks, data for wnich scarce in in the the literature. literature. Geologic mapping of of aa 500—square 500-square mile mile area area in in the the western western part part of of the the 2.1 b.y. b.y. old Early Precambrian Giants Range batholith of 2.7 of northeastern northeastern Minnesota has revealed eleven eleven distinct distinct granitic granitic phases phases (Sims (Sims and and others, others, 1970). 1970). Field observations, petrography, petrochemistry, petrochemistry, and and trace trace element element geochemistry suggest that that five five of of the the phases phases are are magmatic, magmatic, four four are are metasomatic, metasomatic,_ and two are anatectic. anatectic. r 18 16 The ~O 10 ratios of quartz separated from from 28 28 rocks, relative relative to to meIo'8/o'6 Standard Mean Ocean are presented presented in in the the accompanying table. Ocean Water Water (SNOW), (SMOW)Jare table. The values are consistent with the the postulated postulated genetic genetic grouping grouping for for the the Early Precambrian granitic succession. succession. The following following conclusions conclusions can can be be drawn from the the data: data: (1) Values of of 9 to to 10 permil are characteristic of relatively (1) Values relatively uncontaminated, probable mantle—derived uncontaminated, mantle-derived granites granites and and granodiorites. granodic~ites. These tharhave been reported for are consistent with the the S(O18/ol6quartz ~(018/016)quartz values values that-have granites, granodiorites, granodiorites, and and tonalites, tonalites, which which range range from from about about plutonic granites, 9 to to about 11 permil (Taylor, (Taylor, 1968, 1968, p.34). p.34). (2) several special special (2) Values Values greater greater than 10 permil require one of several explanations, such such as: as: 18 (a) syntexis of large amounts amounts of of 0018—rich -rich country rocks rocks (a) into a primitive or first—cycle first-cycle granitic granitic magma magma 18 18 (b) co-mingling co—mingling of an 0 -enriched —enriched magma and a primitive (b) or first first cycle granitic magma 18 (c) of 0018_ sediments (c) anatexis of —rich rich sediments �—67— -67- 18 (d) potash metasomatisin metasomatism of of aO'8—rich -rich sediments sediments (d) potash (e) recrystallization (treptomorphisin) (treptomorphism) of of (e) simple recrystallization relatively 018_ 018—rich clastic sediments such such as r ich elastic arkoses and graywackes, which thereby thereby assume assume aa granitic fabric and composition (f) recrystallization recrystallization of of granites granites under under shearing and (f) aplogranites, accompanied by crushing to produce aplogranites, late—tectonic metasomatism in mobile zones late-tectonic (g) post-consolidation post—consolidation eataclasis, cataclasis, and and other other (g) episodes which which facilitate facilitate exchange exchange metamorphic episodes origin and granitic rocks rocks of of magmatic magmatic origin and between granitic between through a pore—fluid pore-fluid medium medium 018_ O'8—rich r ich country rocks through (h) post-consolidation (h) post—consolidation endoblastesis/autometamorphism endoblastesis/autometatOrphism involving 018018—enriched enr iched fluids (i) processes such as imbibition (i) as petroblastesis and imbibition in which the the participants are are O'8—rich 018_r ich sediments sediments and 018-enriched fluids 018—enriched fluids (j) selective (j) selective exchange between granitic intrusions and 018_ host rocks rocks O'8—rich r ich host (k) tectonic tectonic styles styles of of emplacement, emplacement, whether whether synkineinatic, synkinematic, (k) post-kinematic or late—kinematic, late-kinematic, and and post—kinematic 18 (1) early segregation of aO'8—depleted -depleted minerals which (1) in O'8—enrichment 018- enr ichment in in late late granitic granitic differentiates. differentiates. results in (3) in granitic rocks of anatectic origin origin are nearly nearly (3) The The values values observed in identical to to those those of of their their source source rocks. rocks. They are either low or high such granitic granitic rocks rocks were were formed formed from from O'8—poor 018_poor or or depending on whether such OIS_rich 018_r ich sources, respectively. respectively. The values will be grossly grossly different different only only if: if: (i) the the anatectic anatectic melt melt undergoes undergoes subsequent differentiation, differentiation, and (ii) (i) (ii) the the consolidated anatectic melt is subjected to to later later metasomatism metasomatism (see (see data data under "C" "e" and "0 (2)", of of table). table). "D (2)", (4) The main main intrusive phases of (4) The of granites granites and and granodiorites granodiorites of of maginatic magmatic origin have values nearly identical to those of their satellitic phases identical to those of their satellitic phases (sve (sve data under "A" "A" of of table). table). Interestingly, Interestingly, a value of 9.2 9.2 permil permil was obtained for for a leucogranite (satellitic (satellitic late—magmatic late-magmatic differentiate) differentiate) that that transgresses an 018—rich Ol8_r ich metasedimentary host host rock rock having having aa value value of of 12.4 12.4 transgresses perinil. permi!. This result indicates that there indicates that there was was hardly hardly any any oxygen oxygen communication differentiate and and its its alB-rich o8—rich late-magmatic differentiate between the satellitic late—maginatic metasedimentary metasedimentary host host rock. rock. This is is in in sharp sharp contrast contrast to to the the conclusion conclusion of of Shieh and Taylor (1969, (1969, p.353) p.353) who report report that: that: "Samples "Samples from from tiny tiny intrusive intrusive bodies and dikes and from the marginal portions portions of of most most of of the larger plutons 18 /0 16 ratios igneous rocks have unusually high 0 018/016 ratios relative to "normal" "normal" igneous rocks from from �—68— -68- the central portions of plutons. This is interpreted interpreted to to be the the result result of large-scale large—scale oxygen isotopic essentially molten of isotopic exchange exchange between between essentially molten igneous igneous rock and metasedimentary country country rock, rock, either either through through aa medium medium of of aqueous aqueous 1I fluids or or by by contamination contamination with with xenolithic xenolithic blocks blocks of of country country rock. rock." fluids (5) The The sequence: sedimentary (5) sedimentary parent parent ——)' -~ partially partially granitized sediment --~granitic —>-granitic rock progressive sediment rock of of metasomatic metasomatic origin origin reflects a progressive decrease in the 018/016 0 18 /0 16 ratio, and and encompasses encompasses only only aa narrow narrow range range of of 11 to 2 permil, and (6) Global comparisons of oxygen isotopic isotopic ratios ratios from from granitized granitized 18 /0 16 ratios of the sequences should not not be attempted, attempted, unless: unless: Ci) sequences (i) the 0018/016 parent rocks of two widely separated separated granitized granitized sequences sequences are are comparable, comparable, and (ii) their geological settings are nearly identical. (ii) are nearly identical. 18 16 Problems involving a possible time—dependence time-dependence of of the the 018/0 0 /0 16 ratios in in minerals from from specific specific rock—series, rock-series, representing representing the the entire entire geological geological column, column, are under study by one one of of us us (Per;y). (PerJY). Ref e—ences cited References Shieh, Y.N. Y.N. and H.P. Taylor, Shieh, Taylor, Jr. Jr. (1969): Oxygen and hydrogen isotope isotope studies studies in the the Santa Santa Rosa Rosa Range, Range, Nevada Nevada and and other other areas: areas: of contact metamorphism metamorphism in Contr. Mineral. and Petrol., v.20, p.306—356. Contr. Mineral. p.306-356. Sims, P.R. P.K. and and others others (1970): (1970): Geologic Geologic map map of Minnesota, Ribbing Hibbing Sheet Sheet Sims, (scale 1:250,000): 1:250,000): Minn. Minn. Geol. Geol. Survey, University of of Minnesota, Minneapolis. Minneapolis. Taylor, H.P. Jr. Taylor, H.P. Jr. (1968): (1968): The oxygen oxygen isotope isotope geochemistry geochemistry of of igneous igneous rocks: rocks: Contr. Mineral. p.1-71. Contr. Mineral. and Petrol., v.19, p.'—71. Other useful References Allison, 1.5. I.S. (1925): (1925): The The Giants Giants Range Range batholith batholith of of Minnesota: Minnesota: Jour. Jour. Geology, Geology, v.33, p.488—508. p.488-508. v.33, Goldich, S.S. S.S. and others (1961): (1961): The Precambrian Precambrian geology geology and and geochronology geochronology of Minnesota; Minn.Geol. Minn.Geol. Survey Bull.41, University University of of Minnesota, Minnesota, Minneapolis, p.62—65. p.62-65. �-69—69— Table .{'* b(O 18 /0 16 ratios of of quartz in Early Precambrian granitic )SMOW ratios SNOW and metamorphic metamorphic rocks from the western part of the and the Giants Range batholith batholith of Northeastern Minnesota Range (perlil) (perilil) Average (permil) A. Rocks of magmatic origin: origin: (1) Granodiorites Granodiorites (main (1) (main intrusive intrusive phase, phase t two two samples) samples) 9.4 —- 9.9 (2) Leucogranodiorite Leucogranodiorite (satellitic (2) (satellitic phase of of (1), (1). one one sample) sample) 9.7 9.7 9.8 9.8 (3) Granites Granites (main (main intrusive phase, phase t (3) two two samples) 9.5 9.5 —- 9.6 9.6 (satellitic phase phase (4) Leucogranites (satellitic of (3), (3)t two two samples) samples) 9.2 —- 9.6 9.4 10.7 -— 11.4 10.9 10.9 B. Rocks ~~.Rocks of metasomatic origin: origin: (1) (five samples) samples) (1) Granites (five 10.2 (2) Aplogranite (one (2) (one sample) sample) (3) Partially granitized (3) volcanogenic metasediments (three samples) (three samples) 10.4 — 10.4 - 12.5 11.1 11.1 9.2 9.2 —- 10.1 10.1 9.6 9.6 c. C. Rocks of anatectic anatectic origin: origin: (derivatives of relatively relatively alB_poor source rocks) rocks) 0'8—poor source (1) Quartz tonalites (four (four samples) samples) (1) (2) K-feldspathized K—f eldspathized tonalite tonalite (2) (one sample) 12.1 12.1 D. D. Parent volcanogenic metasediments metasediments of: of: (1) B (four (four samples) samples) (1) Group Group B 11.1 — 1l.1 - 12.9 12.2 �—70--70- ZONED NATIVE NATIVE COPPER CrIEHICALLY COPPER AND A<\lD CHALCOCITE CHALCOCITE FROM FRaN CHEMICALLY ZONED WHITE PINE, NICIIIGAN WHITE PINE, MIChIGAN T. A. A. Vogel Geology Department Michigan ~ichigan State State University University East East Lansing, Lansing, Michigan and T. T. J. J. Rohrbacher Staff Geologist Staff \'~ite White Pine Copper Company Pine, Michigan \.Jhite White Pine, tHchigan ABSTRACT A B S T R ACT A the copper ore are minerals at at White ~.Jhite Pine, A microprobe study of the Hichigan, has shown that that zoned copper—mineral copper-mineral grains occur in in the the Michigan, has This zoning is ore-bearing of the the Nonesuch Nonesuch Shale. Shale. This is developed develofled ore—bearing horizons of in the most type of in both both chalcocite chalcocite and and native native copper, copper, and and the most prominent type zoning is zoning is iron enrichment towards to\vards the the edge edge of of the the grain. grain. Some chalcocite grains grains are are highly highly zoned, chalcocite zoned, containing about about four four times times as as as in much iron (at least the edge of of the the grain grain as in the the core. core. least 10%) 10%) on the iron (at Aluminum, magnesium siliconshaH showthe thesame sametype typeofof zoninf, zoning, hut Aluminum, magnesium andand silicon hut are to a lesser extent. are developed to extent. copper grains are also zoned respect to iron, Many native native copper grains arewith also zoned with respect to iron, with the edge of the iron wi th the edge of the grain grain containing containing about about twice t\<7ice as as much much iron (about 1%)asas the the core. an enrichenrich(about 1%) core. All zoned zoned copper copper minerals show show an ment of iron iron towards of the ment of towards the the edge edge of the grain; grain;however, ho\·7ever, both both within ,·7ithin and and between between samples, samples, the the amount amountofofzonin~ zoningand andthe therelative relative proportion proportion This variation zoned to unzoned grains highly variable. varia1)le. This variation does c:oes of zoned to unzoned grainsisis highly not appear to be be controlled controlled by by the the major majorlitholof,ic lithologic variAtions variations in not appear to in the ore ore zone, zone, but but may be controlled controlled by uy subtle differences in lithology or by environmentrttat the the time variations in by variations chemical environment time of of in the local chemical deposition. Any Any j:lotlel modelofof'1re 're Genesis genesis must must take take into account account the the occurrence, occurrence, minerals. distribution and and type distribution type of of zoning in in these these copper copper minerals. �—71— -71- STRATICRAPHY OF KEWEENAWAN KEI.vEENAWAN STRATIGRAPHY OF WESTERNMOST i-JESTERN}[OST MICHIGAN HICHIGAN W. S. Wtite W. S. i-n1i te U. S. Geological u. Survey Agriculture Research Center Center Beltsville, Naryland Beltsville, Maryland E. R. R. Brooks E. Department of Earth and Physical Science Science California State State College College Hayward, California Hayward, H. 3. A. A. Hubbard U. S. S. Geological Survey Survey U. Washington, D.C. D.C. Robert F. Robert F. Johnson 449 Boynton Avenue Berkeley, Berkeley, California J. T. J. T. Wilband iVilband University of Toledo Toledo Uepartment Department of Geology Geology Toledo, Ohio ABSTRACT A B S T R ACT surveysprovide provideaa skeletal skeletal Recent geologic geologic and and aeromagnetic aeromagnetic surveys fracieworkfor forthroughgoing throi:ghgoing stratigraphiccorrelations correlations of framework stratigraphic of the the Keweenawan rocks rocks of westernmost westernmost Michigan. Michigan. The stratigraphy of the the middle and upper Kel.".eenawan Fceweenawan rocksofof the the Keweenaw Peninsula has rocks Keweenaw Peninsula long been known in in great great detail, detail,thanks thanks to tothe thelarge largeamount amount of of drill—hole and drill-hole and surface geologic information. information. The recent recent work perpermits certainty, mits certain certain key key horizons horizons to to be be traced, traced, with with moderate moderate certainty, westward into Wisconsin. Wisconsin. Stratigrapitic relationships relationships for for the the middle middle and and upper upper Keweenawan Keweenawan Stratigraphic rocks best shown rocks are best shown in a longitudinal stratigraphic section section drawn drawn rocks and having along strike of of the the middle middle Keweenawac Keweenawan rocks along the general strike most striking striking base the Nonesuch Nonesuch Shale rlA.tum plane. The The most base of the Shale as as aa datum (1) The predominantly features of such such aa diagram diagram are the the following: following: (1) TIle predominantly features of basaltic Portage Lake Lake Lava Lava Series Series maintains maintains aathickness thicknessofof10,000— 10,000basaltic Portage 12,000 from 1-loughton Houghton to tothe near 12,000 feet feet from theJHack BlackRiver Riverand andisis thinnest thinnest near the Ontonagon Ontonagon River. IItt is isabout about 8000 8000 feet thick thick atatthe theMontreal Montreal River. (2) (2) An An unnamed lenticular unnamed lenticularunit, unit,10,000 10,000feet feetthick thick at at the Liver on Presque Presque Isle River River and and pinching pinchinp, out out near near the the Ontonagon River on the the and the the Montreal Montreal River River on on the the west, west, lies liesabove above the thePortage PortageLake Lake east and Lava Series Series and and below below the the predominantly sediientary sedimentaty Copper Copper Harbor Harbor Conglomerate. to fine— Conglomerate. The The unit is mainly mainly composed composed of fineunit is of thin thin aphanitic to grained andesitic andesitic flows flm,s and and contains contains minor rhyolite rhyolite and and intermediate intermediate rocks, the top. top. It to represent represent accumulation rocks, particularly near the It seems seems to \Vithin fe\.". miles of aa volcanic center south of of the the Porcupino Porcupine within a few center south Mountains. (3) HarborConglomerate Conglomerate less than than 500 500 feet feet f·jountains. (3) The The Copper Copper Harbor is isless thick over over the thick tile thick part of the theunnamed unnamed unit, unit,and and4000—5000 4000-5000 feet thick near the tIle pinchouts pinchouts of of tile theunnamed unnamed unit. combined thickthickthick near unit. (4) The combined ness of of tue tlle three three units units suggests sugr,ests aa strongly strongly asynnetric asymmetric basin, basin, deepening from aa minimum minimum near more than 25,000 25,000 deepening from nearthe the Ontonagon OntonagonRiver River to to more feet between the the next next feet between the Black Blackand andPresque PresqueIsle IsleRivers, Rivers, and and then, then, in in the 15 than 10,000 10,000 feet the 15 miles miles toto the the \Vest, west, thinning thinning rapidly rapidly toto less less than feet at at the Montreal These findinf's findings reinforce reinforce the hontreal River. These the concept concept that that the themiddle middle rather than Keweenawan Ke\VeenaVlan lavas lavas accumulated in separate tectonic tectonic basins basins rather in aa single single large large one. one. the �-72—72— The Ke,,,eenawan lavas, so-called South South Trap Trap The lower lower Keweenawan lavas, !'"hich which form form the the sc—called Range, lie beneath the the Portage Portage Lake Lake Lava Series, Series, from from lie unconfonnably unconforably beneath &hich they differ in in lithology, lithology, metamorphic grade, ("hich they differ grade, and magnetic properties. The feet consists consists predominantly of very properties. The lowennost lowermost 5000 feet thin basalt the next 4000 feet feet mainly to thin basalt flows, flows, and and the next 4000 mainly of aphanitic to The uppermost fine-grained flows flows of intermediate intermediate composition. composition. The uppermost part fine—grained of this sequence is iseverywhere everywhere concealed concealed by by the the Jacobsville JacobsvilleSandstone Sandstone this sequence or deep deep overburden, overburden, but inferred from from gravity gravity and and magnetic magnetic data data or but is is inferred This lower is lC,000 to to consist consist largely largely of of felsic felsic flows. flows. This lower sequence sequence is 10,000 and uncertainty and perhaps perhaps20,000 20,000feet feetthick, thick, the the difference difference reflecting reflecting uncertainty about the location location of about the of the the top. top. The rocksare are more metamornhosedthan than the middle The lower lm"er Keweenawan Keweenm"an rocks more metamorphosed middle Their metamorphic grade appears metamorphic grade appears to to increase increasewestward westl,vard— Keweenmvan. Keweenawan. actinolite is actinolite found in Hisconsin but is is rare rare near near Ironwood. Ironwood. is found Wisconsin but Kenneth Books Hooks has found that that the the lower and middle Keweenaw€n Keweenawan rocks also also differ differ from rocks from one another in in magnetic magnetic direction. direction. In contrast contrast with with the the belts belts of of middle middle and and upper upper Ke,,,eenal,van Keweenawan rocks, roes, In dips of of bedding bedding generally generally decrease decrease !"'ith with stratirraphic dips stratigraphic depth in in the lower Keweenawan Ke\veenawan belt. belt. If If this this represents represents soutlnvard southward thickening thickening rather rather than Lian folding, folding, it it suggests suggests that that the the axis axis of of the the lower Keweenal,van Keweenawan basin lay lay to to the the south. south. �-73—73— THE NORTH SHORE SHORE VOLCANIC GROUP GROUP May 5 and 8, 1971 by Prepared by C. Green John C. University of Minnesota, Minnesota, Duluth Minnesota Geological Survey �—74--74- Croup The North Shore Volcanic Group John C. C. Green Introduction Previous Work Hork and and Acknowledgments. Acknowledgments. Detailed mapping of the Minnesota A. S. E. Sandberg's Sandberg's study study (1938) (1938) of of the the shore of Lake Superior began with A. Grout and Schwartz (1939) section between Duluth Duluth and and Two Two Harbors. Harbors. Grout (1939) and and (1957) studied the the intrusions intrusions and and flows flows in in eastern eastern Lake Lake County; County; Gehman (1957) the lakeshore Two Harbors Harbors and and Split Split Rock Rock Grogan (1940) (1940) mapped the lakeshore between Two River; Schwartz (1949) River; (1949) studied the Duluth Duluth area; area; and and Grout Grout and and others others (1959) (1959) mapped most of of Cook Cook County. County. Most of of the the data data reported reported in in this this account derive from studies by the account the writer who, starting starting in in 1965, 1965, has has mapped the shoreline between Silver Bay and Grand Grand Portage, Portage, with conconsiderable reconnaissance inland (Green, (Green, 1966; 1966; 1968a; 1968a; 1968b; 1968b; 1970). 1970). The report does, however, however, also also lean lean considerably considerably on on Grout Grout ~ etal. report does, al. (1959) (1959) and, for for the Duluth-Two Duluth—Two Harbors area, on and, on Sandberg Sandberg (1938). (1938). The field field studies have have been supported by the studies the Minnesota Geological Geological Survey, Survey, and and most of the laboratory studies have been supported by the National studies the Science Foundation. Sincere gratitude for for this this support is is extended extended to to both agencies. agencies. The writer's ideas ideas have benefitted benefitted from from discussions discussions with many other geologists rocks, esoecia11y esnecially many other geologists concerned concerned with with Keweenawan Keweenffivan rocks, including Bill Jr., H.H.Hubbard, including BillBonnichsen, Bonnichsen, D. D. M. M. Davidson, Davidson, Jr., Hubbard, C. G. B. B. Morey, Horey, W. W. C. C. Phinney, Phinney, ·P. W. Weiblen, and and W. W. S. White. P. W. S. White. Regional Setting. "North Shore has been ~egional Setting. The name "North Shore Volcanic Volcanic Group" Group" has been used used et al. al. (1961) (1961) for by Goldich et for the the lavas lavas and and interbedded sediments of Late Precambrian. rocks, as well Precambrian age in northeastern Minnesota. These rocks, as and sedimentary sedimentary rocks rocks in in the the as all all other Late Precambrian volcanic and district, have traditionally been called"Keweenawad'by called "Ke~veenffiolan" by Lake Superior district, rocks exposed on the general lithic and structural correlation with rocks and paleomagnetic Keweenaw Peninsula of Michigan, Michigan, but recent radiometric and investigations as \-lell indicate that that aa more more precise precise investigations as well as geologic mapping indicate stratigraphic stratigraphic framework framework is is needed needed to to adequately adequately describe describe the the complex complex events and and deposits deposits in in this this area. area. series of Late Precambrian events In (Grand Portage In the the northeast northeast corner corner of of }linnesota Minnesota (Grand Portage area) area) the the lowest lowest Upper Precambrian flows which in flows overlie a thin quartzite (Puckwunge) (Puckwunge) \.;rhich 1.n turn turn overlies, overlies, apparently disconfornably, disconformably, the the shales shales and and graywackes graywackes Of 6f the Middle Precambrian Rove Formation;here hereboth both sequences sequencesstrike strike nearly the Rove Formation; nearly east—west and dip at approximately 10° east-west 100 to to the the south. south. At the the southwest southwest end of the basin immediately west west of miles away), of Duluth (155 (155 miles away), the lowest lowest Upper Precambrian flows flows also conformably conformably overlie thinquartzite quartzite (Puckoverlie aa thin (Puck— wunge?) which there there overlies the the vertically folded slates and metagray— metagraywackes of the the Middle }tiddle Precambrian Thomson Formation, Formation, which is is correlated with the the Rove. Rove. Here the flows flmols strike north and dip dip at at about about 25° 25 0 to the unconformity here here reflects and subsesubseeast. The angular angular unconformity reflects the the diastrophism and quent the Penokean Penokean orogeny, orogeny, which which evidently evidently did did quent erosion associated with the the northeastern northeastern corner corner of of the the state. state. Across the the axis of the the not affect the flows Lake Superior Syncline in northern Wisconsin and Michigan the lowest flows �MINNESOTA \-n I ONTARIO J) I I \ '—-7 - rHCVL AND EARLY PRECAMBRIAN GRAND M AR A IS LEGEND LUTSEN JOFTE uACONITh INTRUSION S i., '\~r KEWEENAWAN INTRUSIONS Wf0J KEWEENAWAN LAVAS "'to FIELD TRIP STOP I -....J U' \Jl I ITLC MARAIS MARAIS ER BAY JBEAVER BAY BAY LAKE SUPERIOR SCALE ° ! •O HARBORS WISCONSIN MINN. 10 20 Miles MICHIGAN 30 40 �—76— -76- conformably overlie aa similar similar quartzite (Uessemer) that in in turn overlies overlies quartzite (Bessemer) Middle Precambrian shale and and graywacke with only only minor discordance. discordance. These quartzites have always been referred to as as Lower Lower Keweenawan, Keweenawan, but but no no radiometric age determinations are are available available and and they they may may be be much much older older than the volcanic volcanic rocks rocks of of the the iCeweenaw Keweenaw Peninsula. The North Shore Volcanic Group is cut The cut by aa. great great variety variety of of intrusive intrusive rocks rocks that are are also also of of Late Late Precambrian Prec&~brian age. age. These range range from from the the great great Duluth Complex, Complex, dominated by anorthositic and and troctolitic troctolitic rocks, rocks, to to smaller sills, sills, stocks, stocks, dLkes, dikes, and irregular plutons of of diabase, diabase, 'crro— ferroabbro, trachybasalt, granocdorite, an gabbro, troctolite, troctolite,syenogabbro, syenogabbro, trachybasalt, granodiorite, and. Someofofthese thesebodies bodiesalso also cut cut the the older graoQphyric, adamellite. Some older rocks rocks grarophyricadanellite. to the to the north, north,northwest northwestand andwest west of ofthe themain mainLate LatePrecambrian Precambrian outcrop outcrop area of Cook Countyand andthe the Thunder BayDistrict District area (e.g. (~.g. the the Logan intrusives intrusives of Cook County Thunder Bay of Ontario). of Ontario). Paleonagnetism and Age. Recent paleomagnetic studies studies (Dubois, Paleomagnetism Recent paleomagnetic (Dubois, 1962; 1962; Beck Deck that two and Lindsley, Lindsley, 1969; 1969; Books, Books, 1968; 1968; Palmer, 1970) 1970) have have shown shmm that two reversals of magnetic polarity occur within reversals 'loTi thin the Late Late Precambrian Precambrian volcanic volcanic rocks of the Lake Superior The 1m-rest lowest strata stnta show 'nor'ial" rocks Superior district. district. The shoYr "normal" (north—seeking) polarity polarity similar to to orientations orientations in the underlying (north-seeking) underlyinp; Middle Precambrian rocks, rocks, but but this this group group of of rocks rocks has has not not been been recognized reconized in Precambrian Minnesota. Keweenawan Books (1y68) (l9~8) has ha.s proposed that the Lover Lower —- Middle ~eweenawan Books boundary be redefined the second reversal where redefined at at the second macnetic magnetic reversal where rocks rocks of normal polarity. The North reversed polarity aresucceeded succeeded by by rocks of' of normal North po]arity are Volcanic Group Groupcontains containsatatthe the ba.se base of of the Shore Volcanic t~e section section atatGrand Grand Portage Portage about 5000 feet feet of lavas lavas tnat that show reversed polarity, and and are are thus thus Lower Lower Keweenawan magnetically defined. defined. The thick wedge of flows Keweenawan asasmagnetically The thick wedge of flows west west of Duluth that underlie ut overlie the Puckwunge Duluth that underlie the theDuluth Duluth Complex Complex but Pucki-runge (?) (?) quartzite have quartzite but on on have not not been beenadequately adequatelytested testedinin the the laboratory, laboratory. hut regional magnetic magnetic maps maps give aa negative negativemagnetic map;neticanomaly anonaly which which implies implies regional reversed polarization. Furthermore reversed polarization. very similar to Furthermorethey theyare arelithically lithically very reversed-polarity lavas of of Grand Grand Portage. Portage. The the reversed—polarity The remainder remainder of of the ::orth North Shore Volcanic Volcanic Group polarity, Grouphas hasnormal normalmagnetic magnetic polarity,similar similar to to the bulk bulk of of the the associated associated intrusive intrusive rocks rocks and and to to the the rocks rocks of the Keweenaw Peninsula. Only available on on rocks rocks Onlylimited limited radiometric radiometric age age determinations determinations are are yet yet available of al. (1961) of the the North North Shore Shore Volcanic Volcanic Group. Goldich Goldich ~~ (1961) found aa !! ~~. 1.1 ±± 0.1 b.y. 1.1 intrusive rocks rocks of of the the Duluth Duluth Complex Complex b.y. age for associated intrusive and K/Ar K/Ar methods, and and Silver Silver and and Green Green (1963) (1963) found found an an isotopic isotopic by Rb/Sr and age age of 1.125 by U/Pb isotopes in in zircons zircons of of both both lavas lavas and and intrusive intrusive rocks rocks and Mellen, Mellen, Wisconsin Wisconsin areas. areas. Paure Faure et al. al. (1969) (1969) determined determined from the Duluth and the age of the Endion sill, sill, which cuts cuts the flows flows at at Duluth, Duluth, as as 1.092 1.092 b.y., b.y., the age and that that of of the the Duluth Duluth Complex Complex .at at Duluth Duluth as as 1.115 1,115 b.y. b.y. by by the theRb/Srmethod. Rb/Srmethod. However, all of these sampled rocks rocks are in areas of normal magnetic However, rr..agnetic polarity polarity, to the the age so no data are available available as as to a~e of the Lower Keweenawan lavas lavas of, of, for for Grand Portage Portage area. area. Hanson and Malhotry (1970) (1970) have recently instance, the Grand a 1.380 b.y. (K/Ar) of aa "Logan "Logan Intrusive' Intrusive" in in southern southern Ontario, Ontario, found a b.y. age (K/Ar) indicate the the possible possible age age span span of of the the Lower Lower Keweenawan. Ke'lveena"ran. Isotopic which may indicate studies over over the the range range of of Upper Upper Precambrian Precambrian rocks rocks iii in the district district are are U/Pb studies currently in in progress. progress. �—77— -77- Structure Structure The Group is is that that of of aa The general structure of the North Shore Volcanic Group great nest of dishes tilted tilted gently gently to to the the southeast into ofmshes into Lake Lake Superior. Superior. endthe thestrata strata at at the strike slightly At the the northeast northeast end the base base strike slightly north north of of west and dip about about 10—12° 10-12° south, south,whereas whereasatat the the southwest southwest end, end, 155 155 miles miles away, they strike north and and dip about 25° east. east. In between the strikes strikes c-raually converge convergealong alongthe theshore shoreof of Lake LakeSuperior Superiorasashigher higher stratigraphic stratigraphic gradually levels are reached, reached, until flows strike to the the shore shore in in the the levels are until the the flows strike parallel parallel to vicinity southwestern vicini ty of ofSchroeder, Schroeder, Torte, Tofte,and andi,utsen Lutseninin southvresternCook Cook County. County. Herethe the highest highest stratigraphic stratigraphic units are the dip Here are exposed, exposed, and and the dip is approxiapproximately 12° to the southeast. southeast. The lavas lavas are The are intruded by a great variety and bulk of intrusive intrusive rocks, rocks, including several large large diabasic diabasic sills sills at at Duluth, Duluth, the the Beaver Beaver Bay Bay Complex, Complex, includim several the 1-iovland andReservation ReservationRiver River diabase diabase complexes complexes and and the the Logan intrusions. the Hovland and intrusions. Where Hhere these intrusions are are discordsnt discordant and and abundant abundant they they have have deformed deformed the the lavas considerably, lavas considerably, with local strongly divergent strikes and and steep steep to to overturned dius. dips. Along with the thick glacial cover inland, inland, they they have have also made made difficult difficult to to impossible impossible the the long-distance long-distance tracing tracing of of stratigraphic major flows or or groups roups of in the the lava lava series. series. Several Several maj or flows of similar similar flows, flovrs, units in however, can be traced inland from the lakeshore for however, can be for at at least least 15 15 to to 25 25 miles. miles. Faulting is COffi.J;lon in the flows flows near the areas of abundant intrusions intrusions (such (such is common as from Silver ~jilver Bay Day to to Little Little:iarais). :'1arais). These faults appear to to be be of of minor as displacement and are are :r.lostly mostly transverse and steeply dipping with no displacement no strongly strongly preferred strike or displacennnt, displacemnnt, but aa few few longer lon~er strike—faults strike-faults have have been been found, one one of which probably extends for found, for at least five five miles. thickness of the has been measured and and estimated estimated by by The thickness of the lava succession has feet between and Split Split ~)andberi!, and Gror-an Grof.\an (l90) (19)j·0) as as 23,148 behreen Duluth Duluth and Sandberg (19::38) (1938) and 23,lB feet Rock complex) by adding Pock River (the (the beginning beginning of of the the Beaver nay Bay intrusive complex) Whether the lakeshore. ~TIether the individual individual flow thicknesses thicknesses intersected along the lakeshore. j.ile at at Split Split Rock Rock River Biver is this conforms to the is not not this conforms the true true thickness of the pile Northeast of the Beaver Bay Complex about 5000 lmovn. Hortheast 5000 feet feet of of lavas lavas are are known. estimated recent mapping to form the lakeshore section section between between 'ilver Silver estimatcd from recent Rortheast of and Lutsen, where Bay and the uppennost flows at 'T'ofte. IJortheast Tofte uppermost flows at °ofte. Bay the flows are are parallel to the shore, lavas totalling about about 16,500 16,500 feet feet the flows have River diabase diabase near near }iovland. Hovland. Below been measured measureddovn downtotothe the Reservation Reservation River have been (northeast of) this is an older section of about 5,000 feet of (northeast of) this is an older section of about 5,000 feet of lavas, lavas, for for total on on this thislimb limb of ofabout about 21,500 21,500 feet. a total Estimate50f volcanic volcanic thicknesses thicknesses by by constructing constructing cross—section cross-section profiles Estimateof profiles give between between 11,000 Tofte, above above the the Duluth Duluth Complex, give 11,000and and18,000 18,000feet feet at at Tofte, depending 20°. Although Although the the average average on ass~~ed assumed dips dips between 12° and 20°. deDendng on is very little control on dips near dip at Tofte is about 12°, there is very little control on dips near the the at Tofte is about 12°, dip flow contacts. contacts. base section as as the thefew fe,., inland inland outcrops outcrops rarely rarelyexpose expose flow base of of the section northeast at at the theCascade Cascade River, River, about about 15,000 15,000 feet feet of of lavas lavas above above Farther northeast of 12°; another the Duluth Duluth Complex Complex are calculated with an average dip of 12°; another are calculated with an average dip lies beneath thick section, section , possibly possibly as much much as thick, here here lies beneath thick as as 5,000 5,000 feet feet thick, '. the Complex. Complex. ~ �—78--78- GenerallDesptiq Description, The North Shore Volcanic Group bears many resemblances, both physically physically and chemically, to plateau lava sequences of various geologic geolo~ic ages. ages. Similarities to the Tertiary Tertiary plateau plateau lavas lavas of of eastern eastern Iceland Iceland are are to the particularly particularly striking. striking. The lavas lavas are almost entirely subaerial, subaerial, showing showing highly vesicular (now (nmr amygdaloidal) amygdaloidal) upper portions and and massive interiors, interiors, and.various various types types of of jointing, jointing, surface surface features, features, and and textures textures depending depending and on their specific composition. composition. Evidence of submarine extrusion extrusion is is almost almost Portage and entirely limited to the at Grand Portage and at the base of the section both at Nopeming, west west of Duluth, the lowest flow Duluth; at at Nopeming, flow is is piflowed pillowed and and on on Portage Island the lowest flow shows shmrs spheroidal spheroidal forms that could could Grand Portage possibly be pillows, but excellent, excellent, thick—rinded, thick-rinded, vesicular vesicular pillows pillows constitute the lakeward side of the island aa few constitute aa flow flow on the few flows flmrs above above of the the section. section. Unequivocal hut but less well—formed well-formed pillows and and the base of pillow-breccia have been seen seen only only rarely rarely higher higher in in the the section. section. These pillow—breccia could or stream stream beds beds on on the the lava lava surface. surface. The could have have formed in local lakes or flows tabular, and since some individual flows flows are are in general tabular, flows or or flow flow groups groups can can be traced along strike for at least 20 miles, the general general impression is is that that of of aa broad, terrain. In contrast contrast broad, rather flat volcanic terrain. to clear to the the situation situation in in eastern eastern Iceland, Iceland, however however (Walker, (Walker, 1964), l96), no no clear evidence of volcanic centers, representing shield or composite evidence composite volcanoes White contemporaneous with the plateau volcanism, has yet been found. found. \'mite contemporaneous (1960) on to some Keweenm-ran (1960) has has drm-rn drawn attenti attention to the the remarkable remarkable extent extent of some Keweenawan flows (especially in Michigan) Michigan) and with ample justification flows justification calls calls them flood basalts. basalts. Interflow sediments of the the section. section. They Interfiow sediments make make up up aa minor minor part (l—3) of -part (1-3%) are principally red, cross—bedded sandstones, that occur sporadically are red,cross-beddedsandstones, sporadically as as beds aa few few inches inches thick thick between flows, flows, but but aa few fe"T local local accumulations accumulations of of over 100 feet feet are are found. found. Conglomerate is is rare. rare. Some Some sand has has filtered down into down into cavities cavities in the upper unper parts of flows, f10vs, and and also also forms forms aa matrix for flow—top breccia for flow-top breccia in in others. others. These sediments appear a.ppear to have been deposited by occasional temporary streams winding across the volcanic surface. There is is little evidence evidence of of erosion. erosion. Pyroclastic deposits deposits are are but welded tuff and mixed sand and extremely scarce, scarce, but and shards shards have been the Cascade IIiver River in Cook County (Johnson reported from the (,Tohnson and and Foster, 1965) 1965) and basaltic to to andesitic flow top breccia, is is present present andesitic breccia, breccia, other than flow in a few localities. , exception of of aa high high potassium potassium content content in in some some oaf mafic With the exception ic and intermediate abundance of of rhyolite, rhyolite, the the compositions compositions of of the the lavas lavas members and the relative abundance are also also very very similar to those those of plateau lava series in Iceland and are and elsewhere. vhere. characteristics and and abundance abundance of of the the Table 1 shows the general characteristics major types. types. The most abundant general type is is olivine olivine basalt 'basalt of of several several varieties; varieties; important, and distinctive variety is is mottled mottled (ophitic), (ophitic), one widespresd, widespread, important, and is is similar similar to to what what has has been called olivine tholeiites in other areas. and areas. Rough columnar These typically have ropy surfaces and and were very fluid. fluid. col~~nar joints are Other olivine olivine basalts basalts are with diabasic are common. common. Other are coarser, coarser, some i-rith and some ,.ith with other other characteristic characteristic textures. textures. In the Tofte—Lutsen Tofte-Lutsen area, area, high in the section, is a group in of olivine base.1ts th abundant, abundant, small basalts "ri with (1-3 phenocrysts or or crystal crystal clots. clots. At section (1—3 nun) mm) bytownite' bytownit&phenocrysts At the base of the section both t at Duluth Duluth and and on on Lucille Lucille Island Island east east of of Grand Grand Portage Portage are are distinctive distinctive basalts basa.lts that contain abundant phenocrysts, 2—3 2-3 mm across, across, of of augite augite and and �_____ ______ TABLE 1 Generalized Characti±ritics Characteristics of of Major Major Lava Lava Types Types of of North North Shore Shore Volcanic Volcanic Group Group ___ ~ I Wt % % Si02 Si0 2 -_ -_. ' --~ ,. --...--.......... I 2 ·~"-··""'''''''·~''-'''''''''''-''''-'''~~··i''''~· Wt %% MgO -..---~.--'.<.~."'-"'.' .. _ ..•,,_'__ "~_ _~ 46-49 1 0.1-0.5 I ~ ~--~·_""""~:~'.....,-'T-'·_.-.~ ~ · I{ Andesite— t"P. Intermediate Andesit~:i Intermediate Trachyandesite Quartz Tr~rtz Latite L~~ Quartz Quartz Tholelite I ~- " - - - - " , .. , . • .~-w••• _ -" ~".~~~ ••• ~.-+,~. Wt %%1(20 K 0 -, Tholei te I Olivine :ic 1 Olivine Characteristic Tholeilte Characteri~~~i~te 4,,52-57 52-57 50—51 50-51 ! 0.6-0.9 ~'~l.·.~ ~ol.AA' .!::..~< 1-,,•• 1,--.' •• _.,,-, 1 ."~.- ~"'-" ·~·~,.._'S...·_"' 5.9:6.8 5. 9-6 . 8 1 I I __ "',.. ,""~ ••• .,J • • • • ~ ~ I • , 1 Very fine— finet Very fine— finegrainS, inter— l grained, inter~ grained, granular. Some pot— { granular. commonly porphyritic (plag., ~ flow structure, ~ phyritic , ..1 augite) (plag., fine oxidationoxidation— i, fine banding Ophitic Occasionally Occasionally porphyritie porphyritic (plagioclase) --------.--.--------!..-----~---~-~t~:~~~~-.-~--+----~ 72—75 72-75 2.8—5.0 2.8-5.0 3.9—6.2 3,.9-6.2 r '_<'~~', 0.9- 1 • 9 ,.,--,~ <J .. _ _ ;· ·",· P _ > ' _ • - . _• •- ~ ~ , " ' _ ••.•• -:... . < - I aphanitic~ . aphanitic, mostly pot— porphyritic (plag., (plag.,. augite, 01.) augite, oh) . . _ _~--~ .- 0.0—0.4 0.0-0.4 ,,,n"~"·.·~,.,-.•~,,·,,,. ,'-~.~ ..,< , .• ~"'_'_, .I •... , < •• ,, ..•, .•--.- .. --. aphanitic aphanitic to to felsitic;aphyric felsitic; aphyric or porphyritic (plag., orthoclase, (plag., ) quartz, mag., pyrox.) pyrox. occas. spherulitic ~.--_ _,--.;,::::~:lt::l~~~.~ . . - — J 62—65 62-65 ._- ! : Thickness, Thickness, feet feet Range '- --.--.,,' j'" -" I ' l \ Textures t ': - 1.9—2.7 1.9-2.7 .•Y. _ _ w .• .• ~yolite ithyolite ..~~~'-~·~~,.. ..,..-".-·.-'''' --..~•...".-.-...."....-.~...,.--~ -"'. ~~-~"~---'-'-'-~---~ _.V·_·__ 1 I 4. 3-5. 9 1. 9-4 . 5 11:9—4.5 ~ ~;~'-<'~~""_ '"-->-"'"'-'~/"""~-"';""'~1--~-'>""'.w.".>--."'-•.,./A~_~C'~~'_"h,,·_, t-'_.,··",._·.·r;.,,·~ . ,..'.,. ".~., !I' __ . Quartz Quartz Latite Latite I' . 50-1300 50—1300 perhaps 3500 3500 1 2 0 ' " · ·_..5 . 0=500 ..·· 50—500 120 — ···------struc~~:-t:=-:-:py--i~c==~=tc=:=::--i·:::=:- -====:-c'oIiIIDo~ .'.. -- ]- -~ >100 <1 to >100 ~." ·I6~46 10—40 ·"' ' 30—150 30-150 ~ -,·--···l 'so 80 - 1 50—240 50-240 ~ i 1". . var:Gibier' varIable 80—200 80-200 - Structures smooth, ropy flow tops oi;ti';;- jointing j vesicular wrinkled scoriaceous rubble scoriaceous, rubbly vesicular, rolled, flow—banded platy, sub—horizontal big columns in thick irejilai tâ ,'~~~~~:~:h~:i~~~~~l ··t-~~~:i~:}~::T.::-t~~~ii,irreg;;i;r-ts~if;~~~;~g;;iarh~~~~;!!~:~~l - sheeted tops[" small, irregular small, 1rregiIar subhorizontal, flows platy .. round stretched 'o"r" or ···... i . stretched, round vesic1es round or 1rregu1ar stretched ...._,··_- . stretched or round round ~ ~--_ ·-··-~·i ~ ~ -14 ,-- ,-- - - ~ . _·--_····_..·. ~."i'----. __ -- -.~~- - - ~~"Q ~ .,~_.-.. '".~-~--'very_fluid Other ! very fluid 1 more viscous ~ brown—weathering brown-weathering I few flow : pink, pink, red, red, or more_viscous contacts exposedt exposed light Characteristics ;omewhat variable variable contacts Characteristics J, pipe amygdules some contain tomewhat light gray gray at at base ~ ~ more more 1(20, K20, ! segregation veins, l segregation veins, i Kspar; ~ vesicle cylinders quartz, agate agate vesicle cylinders ~: quartz, I common in cavities l common in cavi ties' columnar centers ve·si-~i;;~·_ -·--l--·;(;~d·-~-;· 'i;~~g~i~·~+·;t~et"~h'ed --- ~-. -"'-'--- -----..- 1 I i ~ ~~ ---.. -.-.-.. -.. -".. ! - i l··.-,-.----- .- . -.- ---,.. l Ksr I Ij --+;tretch~d· O~.. t"';~~:iche~f I I I I f. ~~~:~·ched·: - " " - . _.. • -,- - �—80— -80- (serpentinized) olivine: olivine: these these are are particularly unusual unusual in (serpentinized) in having ferromagnesian instead of of plagioclase plagioclase phenocrysts. phenocrysts. Another moderately abundant and distinctive distinctive rock rock ty-pe type is tholeiite" which is is is the the "quartz tholeiite fine grained grained and and slightly slightly more more siliceous siliceous and and viscous viscous aphanitic or very fine The quartz—tholeiites than the olivine olivine basalts. basalts. The quartz-tholeiites characteristically characteristically have a rubbly or brecciated top with the highly vesicular vesicular fragments fra~ments set set in in aa matrix of washed-in washed—in red sand sand or or occasionally occasionally calcite calcite and and zeolites. zeolites. They also ~ thick, along subhorizontal subhorizontal also commonly commonly show narrow oxidation bands, bands, 1-3 mm flowage planes. planes. This quartz—tholeiite quartz-tholeiite grades grades into into more more potassium—rich potassium-rich varieties (trachybasalt, (trachybasalt, trachyandesite) that that can can be be distinguished distin~uished only only by chemical analysis and and microscopic study; study; patches of of interstitial interstitial KK feldspar are are present present in these these rocks feldspar rocks but are invisible in in hand specimen. speci~en. Intermediate varieties are are nearly all all porphyritic with plagioclase, plagioclase, augite, ausite, magnetite, and in some magnetite, SOTIe specimens iron—rich iron-rich olivine olivine phenocrysts; phenocrysts; they they have have the compositions of andesites, trachyandesites, and the and intermediate intermediate quartz quartz Most are aphanitic, but one latites. Most one unusual flow, flow, here here called called the the Manitou Manitou trac~ybasalt, is exceptionally thick (at (at least least 300 300 feet) feet) and and granular, granular, traciybasalt, is for 55 miles although it it originally continued continued for an an and can be traced for These flows in both both directions. directions. 'I'hese flows are commonly cOTlJ1!1only brown or unknown distance in red and irregularly jointed jointed or with platy,subhorizontal joints. joints. The felsic The felsic lavas lavas are anomalously abundant abundant for for aa simple simple differentiation differentiation series from aa basaltic basaltic parent parent magma. mae;m.a. They are red, pink, or or light li~ht gray. gray, These flows composition of of quartz quartz latites. lati tes. 'l'hese flows tend to be much and have the composition thicker than the other other types: types: the thickest is is 1300 feet, feet, aa few few miles ~iles east east of Grand Marais; Marais; the 3500' 3500' Brule Flyer River rhyolite rhyolite west of of Hovland Hovland may may be aa lava dome. dome. Their top surfaces are mostly strongly strongly flow—banded, flow-banded, vesicular, vesicular, and. contorted, b~t but not not brecciated, brecciated, and and their their bases bases are are cornmonly commonly flow-banded flow—banded and contorted, brecciated. Spherulites are are occasionally occasionally present. present. Jointing Jointin~ and locally brecciated. ranges across in the thickest flows flows to sub— subranges from large columns 44 feet across horizontal platy joints; joints; small tectonically—produced tectonically-produced parallel fracture fracture sets a a few mID ccooling joint joint fragments fra~ments into into sets mm apart commonly break up the ccooling felsites are are porphyritic, with ,-rith quartz quartz and and small pieces. Most of the felsites feldspar feldspar phenocrysts (oliogclase—andesine (oliogclase-andesine and/or orthoclase) orthoclase) but but some some are only weakly porphyritic porphyritic or or arhyric. aphyric. Poikilitic quartz surrounding are stout stout alkali—feldspar alkali-feldspar laths ("snowflnke ("snowfla1:e texture:) texture';) is is aa common common microscope texture in the thicker thicker flows. flows. Even these siliceous siliceous lavas lavas have have evidently evidently flowed great distance; distance; one one lava lava or or ffow flowed aa great ..J..mr group group can can be be traced traced for for at B.t least 23 miles miles \-lest west from the Devil Track Fiver, least River, Grand Grand Marais (see (see man, Man, fig. 1). fig. 1). Alteration The lavas lavas have been strongly stronlJ,ly but irregularly irrerularl;v affected affected by b;f secondary secondary solutions that have deposited denosi ted low—temmerature lml-temner?ture minerals in in vesicles, vesicles> solutions fractures, and other some of the minerals of fractures, other cavities, cavities, and and -altered altered sot'!.e of the the no fresh fresh olivine divine has lavas themselves. For instance, instance, no has been been detected detected in in any of of the the lavas, lavas, although although it it is is common the intrusive diabases. any co~mon in the diabases. A zonation of of this alteration alteration is is anparent; anparent; at at Duluth Duluth and and at R.t Grand Granel broad zonation of the the ~round~ass groundmass Portage (in (in the lower lower parts parts of of the the lava lava section) section) r'uch ~uch of has been been converted convertedtoto actinolite actinolite (although many larger pyroxene has (althoup::h nan'.' laT£ser aurites aur.j te:=> are unaffected) unaffected) and has been been saussuritized. saussuritized. [ere Iere also andsome SOIne plagioclase plar:ioclase has also the minerals characteristicallyquartz, quartz, prehnite, prehnite, calcite, calcite, the arnygdule amygdule p.dnerals areare characteristically �-81—81— epidote, and chlorite, epidote, chlorite, the the same basic assemblage as as is is found found in in the the Porta~e Lav~ Series Keweenaw Peninsula (Stoiber (Stoiber and and Davidson, Davidson, Portage Lake Lake hava Series on the Keveenaw 1959). In and northeast of Duluth K—feldspar K-feldspar is is also also occasionally occasionally found, found, In arid laumontite becomes becomes abundant. and laumontite in the section section variouS various zeolites, zeolites, Higher in along with vith calcite, caThite, are are dominant dosnant except along except In in the the quartz quartz tholeiites tholeiites and similar agate, crystalline quartz and and chlorite chlorite are are common. common. similar lavas levas where aaate, The most most abundant abundant zeolites The zeolites are are laumontite, stilbite, heulandite, thorrsonite and scolecite scolecite but but analcite, analcite, natrolite, natrolite, mesolite, mesolite, mordenite, thomsonite and apotbvllite have also and apophyllite ~lso been found. Saponite is is common in olivine basalts. Andradite carnets garnets have been discovered in in several several localities localities amydules and andveins veinsfrom froma awide widerange range lavatypes tres (basalts in ~!'lY8dules of of lava (basalts to rhyclites) and and levels levels in rhyolites) in the the sequence, sequence, and and traces traces of ofnative nativecopper copper have have been found foundininseveral severallocalities. localities. Thus the secondary zonation in in the been Thus the secondary zonation :rorth Shore Grout spans spans both both the deeper—level, iTorth Shore 1oThanic Volcanic Group deeper-level, higher—temperatre higher-temperature tyte of the Keweenaw Peninsula and the higher—level, cooler tyte charactertype of the lCe,.,eenaw Peninsula and the higher-level, cooler type characteristic of istic of the the icuer Imler parts partsof ofthe theTertiary Tertiaryplateau plateau lavas lavas of of eastern eastern Iceland Iceland as described upper, zeolite—free is as described by by Walker 'ilalker (1960). (1960). Walker's Halker' s uDper, zeolite-free zone zone is apparently not represented representedinin Hinnesota. innesota. According Accordingtotohis his estinates, estirsates, the apparently not the presently exposed top of the exposed top the section sectionon onthe theLake Lake Sunerior Superior shore shore could could have have been anrrcxirratel'r 5,000 5,000 feet feet below the surface surface during been approximately belm., the during mineralization. Althoughdetailed (tetal led1-Tork workhas hasnot notyet yet been been done, done, no JUthou~h no clear clear cross—cutting cross-cutting relations of' to stratigraph the relations of zeolite zeolite zones zones to stratirr,raphywithin witp_~~ thelavas lavashave havebeen been recocnized. hut reco~nized, but the theevident evidentUpper Upper Precambrian, Precambrian, nostvolcanic postvolcanicunconformity unconformity ;·rhi-chch;;robe.bly Shore must mineralization, wit' probablyfollm.,s followsthe the~Torth lorth Shore must have havepostdated postdated the the mineralization, since it it does since does crosscut the zeolite ZGolite zones. zones. It should be be stressed, It stressed, however, however, that none of the flows flows has has been been entirely entirely in fact, converted to to secondary secondary minerals. In fact, the the plaioclase plagioclaseand and augite augite are are tynic8,11yunaltered unalteredororonly onlylocally locallyaltered altered mostmafic maficand andintermediate intermediate tvicall'r in in most has typically typically rocks. althour:h no no fresh olivine olivine has has been been discovered, discovered. There There h~s rocks, although been sore oxidation oxidation of of the the opsnue minerals, especially especially of of nagnetite, been sor.e opaque minerals, magnetite, and and interrsediate and ni~eonite is iscoirnonly com~only oxidized borders. In many nany intermediate and pi'eonite oxidizedatat its its borders. felsic lavas, plarioclase pladoclasephenocrysts phenocrysts have have been been albitized and/or zeolitized: zeolitized; felsic lavas. albitized and/or Fresh, undevitrified volcanic some could be be deuteric. deuteric. Fresh, volcanic someofofthis this alteration alteration could glass present in in occasional samples, r,lass is is still still present occasional samples,notably notably inina abasalt basaltfrom fromabout about t"m r'liles r10uth of Brule River. River. two miles ,{est west of of the mouth of the the Prule Etnra•iv The Thias of of the ;orth The lavas !.JorthShore ;3horeVolcanic VolcanicGroup Group can can be be conveniently conveniently divided lithostratipTanhic units unitsof ofcoherent coherent petrographic petrographic divided into into several several lithostratir'ranhic character the basis of character nrimarily nrimarily on on the of exposures exposures at or or near nearthe theLake L~ke Superior Superior shore. Hany of these shore. these units can ca,n he be traced traced for for aDoconsiderable considerable distance distance inland, but interruntions and structural structural corwlicatipns complicatiens by by intrusive intrusive bodies bodies inland, buU nterruntions and as well lacial denosits as \·rell -as as ;o;lacial denosi tsprevent prevent the thereconstruction reconstructionof' of aacomplete, complete, conconp • tinuous sequence. ofJoclear tinuous sequenc cleartrend trendofofconnositional compositionalchange chanF':e is isevident evidentfrom from base to top; at the base to top; in in fact, fact,although althou~hthe themost r'lost ferrora-'nesian ferro~arrnesinn lavas lavas occur occur at the base, flows, in in the Tofte—Lutsen area,are areentirely entirely olivine olivine ~ase, the the unnermost u:!Jnermost flmrs, Tofte-Lutsen area, oasalts. It basa,lts. It should 3hould be be kept kent in in rind r;ind also also that that aamajor ma,jor stratigraphic stratigraphic break break. mayoccur occurbeheween the Grand GrandPortap-e Portagelava lavasection section (sho'ing f:lay t"teen the (shO\.,ing reversed reversed magnetic magnetic polo.ri ty) and and the llig-her strnta. polarity) the lhgher strata. qir Table lists the To.ble 22 lists the informal informal stratigraphic strntif.rcmhic units unitsnroposed proposed for for the the northeast limb liMb (Torte (Tofte to toGrand Gr8.nd Portage) Porta,g;e) forth ~JorthShore ;3horeVolcanic Volcanic Group, Group, with "lith estimated thicknesses thicknesses and and ~eneral characters,and and Table Table 33 their estimated general lithic lithic characters, Ltivessimilar sinlar data p:ives data for forthe thesouthwest southwest limb. limb. 'I'his tabledepends depends largely largely This latter latter table on the work (1038) and and Grogan Grogan(1940), (iqito), penclin.Q; pending restudy. restudy. on the "lork of of Sandberrr Sandberr:: (1°38) �—82— -82- Table 22 Stratigraphy of of Northeast Limb (Tofte-Grand (Tofte-Grand Portage) Portage) North Shore Volcanic Group (Exclusive of interflow sediments) (Exclusive of sediments) Approx. Approx • ..IhiCkness(ft. ThigkneaL&Q) Lithostratigraphic Lithostratigraphic unit unit Lithic character character Lutsen basalts divine basalts, olivine basalts. olivine olivine tholeiites tholeiites 160 Terrace Point basalt flow flow thomsonite—bearing ophitic ophitic basalt thomsonite-bearing 310 Good Harbor Bay andesites brown, porphyritic porphyritic andesite, brown. trachyandesite 360 Breakwater trachybasalt flow flow brown, brown, columnar, columnar,granular granular trachybasalt 500 Narais rhyolite Grand Marais rhyolite flow flow pink, red, gray pink, gray porphyritic porphyritic rhyolite 600 Croftville basalts various fine-grained fine—grained basalts Devil Track felsites aphyric and porphyritic rholite rholite fJows flows Red cliff basalts basalts amygdaloidal, amygdaloidal, ophitic olivine basalts 1300 Kimball Creek felsite pink to to tan, tan, porphyritic porphyritic felsite felsite 1800 Marr Island Island lavas tholeiitic basalt, basalt, intermediate, intermediate, mixed tholeiitlc felsic felsic lavas 1000 Brule River basalts granular-diabasic granular—diabasic basalts 3500 Brule River fhyolite fhyolite flow pink to to gray porphyritic porphyritic rhyolite rhyolite (est.) 4000 (est.) Havland lavas Hovland lavas mixed porphyritic porphyritic basalt, basalt, trachybasalt, trachybasalt, rhyolite 200 Red Red Rock rhyolite flow flow red. red, porphyritic porphyritic rhyolite 260 Deronda Bay andesite andesite flow flow gray-brown, aphyric aphyric andesite andesite gray—brown, Grand Portage basalts basalts mixed tholeiltic tholeiitic to to diabasic diabasic basalts basalts Top 'fop 1020 1020 1020 400—900 400-900 4500 Base �—83— -83- Table 33 Generalized Stratigraphy of Southwest Limb (Tofte—Nopeming) (Tofte-Nopeming) North Shore Volcanic Group Group (exclusive (exclusive of interflow sediments) Approx. TbLekness_'ft) Thickness (it) Lithostratigraphic Unit Lithic character Tp 4000 Schroeder basalts ainygdaloidal ophitic ophitic olivine olivine tholeiltes amygdaloidal tholeiites >300 > 300 Manitou trachybasalt flow flow red—brown granular trachybasalt to red-brown to basalt (more of of the the Schroeder basalts) (more > 280 > 280 > 3CC' > 3CO few 100's few — — mostly quartz tholeiites, other other basalts Palisade rhyolite rhyolite flow flow gray to pink, gray to pink, porphyritic rhyolite Baptism River lavas mixed lavas, mostly basalts basalts — Beaver Beaver Bay intrusive complex — basalts, one felsite mixed basalts, felsite River basalts basalts Gooseberry River 3200 — Bell Harbor lavas lavas -- —. LaFayette Bluff, Bluff, Silver Silver Creek Creek Cliff Cliff intrusions intrusions — — — 1025 fine—grained basalts Two Two Harbors fine-grained "melaphyres", "melaphyres", some quartz tholeiites 1615 Larsmont ophitic ophitic basalts basalts amygdaloidal ophitic basalts. amygdaloidal ophitic olivine divine basalts. — — Knife River River diabase intrusion — Knife — — — — — 4930 Sucker River basalts mixed basalts, basalts, mostly ophitic 4400 Lakewood basalts mixed basalts, mostly non—ophitic non-ophitic — 3600 3600 — mixed basalts, basalts, andesites, andesites, felsites felsites Lakeside lavas lavas — diabase sill sill — Endion diabase — Endion — Leif Erickson Park lavas lavas 2560 — Lester River diabase diabase sill sill — Lester — Duluth Complex — Duluth — 2300 Nope'iuingbasalts basalts Nopeming Base Puckwunge Sandstone Sandstone Puckwunge — — mixed basalts, basalts, andesites andesites — porphyri tic meLbasalts, melc.basal ts, diabasic diabasic porphyritic basalts basalts �_____ —84--84- References Beck, M. M. E., Beck, E., and and Lindsley, N. C., 1969, 1969, Paleomagnetism of the the Beaver Beaver Bay Bay N. C., Complex, Minnesota: Jour. Jour. Geophys. Complex, Minnesota: Geophys. Res.,v.74, Res.,v.74, p. p. 2002—2013. 2002-2013. Books, Books, K. K. G., G., 1968, Magnetization of the the Lowermost Lowermost Keweenawan Keweenawan lava lave flows flows in in the Lake Lake Superior area, area, in Geological Survey Research 1968: the 1968: U. U. S. S. Geol. Geol. Prof. Paper 600—n, p. D248—254. Survey Prof. 600-D:-p. D248-254. Dubois, P. P. M., H., 1962, Paleomagnetism and correlation Dubois, correlation of of Keweenawan Keweenawan rocks: rocks: Geol. Sun. Surv. Canada Canada Bull. Bull. 71, 71, 75p. 75p. Geol. Faure, G., G., Chaudhuri, Faure, Chaudhuri, S., S., and Fenton, M. M. D., D., 1969, Ages of of the the Duluth Duluth Gabbro Gabbro Complex and of the Endion Sill, Duluth, Minnesota: Jour. Jour. Geophys. Geophys. Res., Res., v. 74, p. p. 720—725. v. 74, 720-725. Gehman, H. Gehman, H. M., M., 1957, The Beaver Beaver Bay Bay Complex, Complex, Lake Lake Co., Co., Minn.: Minn.: unpub. unpub. Ph.D. Ph.D. Thesis, Univ. Univ. of of iinnesota. Minnesota. Goldich, Goldich, S. S. S., S., Nier, A. A. 0., Baadsgaard, Baadsgaard, Halfdan, Halfdan, Hoffman, Hoffman, J.H., J.H., and and Krueger, Krueger, 11. 1961, The The Precambrian Precambrian geology geology and and geochronology geochronology of of Minnesota: H. tJ., W., 1961, Minn. Minn. Geol. Geol. Survey Survey Bull. Bull. 41, 41, 193 193 p. p. Green, J. Green, J. C., C., 1966, New field field studies studies of of the the Keweenawan Keweenawan lavas lavas of of Minnesota ~linnesota (abs.): Program, 12th 12th Ann. Ann. lnst. Inst. on on Lake Lake Superior Geology, Sault (absJ: Program, Sault Ste. Ste. Marie, Mich., p. p. 9. 9. physical characteristics of Late Precambrian lavas Ch~ical and and physical lavas Cheaical ---of, 1968a, northeastern Minnesota (abs.): (abs.): Amer. Geophys. Geophys. Union Union Trans., Trans., v. v. 49, 49, p.363. p.363. Types and structures of flows , 1968b, Types flows of of the the North North Shore Shore Volcanic Volcanic Group, Group, ---Minnesota (Summary): Program, (Sununary): Program, 14th 14th Ann. Ann. lnst. Inst. on Lake Superior Geology, p. 52-53. p. 52—53. , 1970, Geology of North Shore Volcanic Group, Group, in in Summary Summary of of Fieldwork Fieldwork ----1970, Ed's., Minn. Minn. Geol. Geol. Survey Survey Inf. lnf. Circular Circular 8, 8, p. p. 19—20. 19-20. 1970, Sims Sims and Westfall, Westfall, Ed's., Grogan, R. R. M., M., 1940, 1940, Geology of a part of the Grogan, the Minnesota Minnesota shore shore of of Lake Lake Superior Superior northeast unpub.Ph.D. Ph.D. thesis, thesis, Univ. Univ. of Minn. northeast of of Two ~yo Harbors, Harbors,1-finn.: Minn.: unpub. GrEiut, F. F., F., Sharp, Sharp, R. R. P., P., and Schwartz, G. G. M., N., 1959, 1959, The The geology geology of of Cook Cook Greut, F. Minn. Geol. Geol. Survey Survey Bull. Bull. 39, 39, 163 163 p. p. County, Minn.: Minn. Hanson, C. G. N., N., and and Maihotra, Malhotra, R., R., 1970, 1970, K—Ar K-Ar ages ages of of mafic mafic dikes dikes in in northeastern northeastern Hanson, (abs.): Program, Program, 16th Ann. lnst. on Lake Minnesota (abs.): Ann. Inst. Lake Superior Geology, Geology, Thunder Thunder Bay, Bay, Ontario, p. p. 19. 19. Johnson, C. C. H., and and Foster, Foster, R. R. L., L., 1964, 1964, Contaminated Contaminated Precambrian Precambrian ash—flow ash-flow cuff, tuff, Johnson, Cascade River, River, Minnesota Minnesota (abs.): (abs.): Geol. Geol. Soc. Soc. Amer. Amer. Special Special Paper Paper 82, 82, p. p. 102. 102. Palmer, Palmer, H. H. C., C., 1970, 1970, Paleomagnetism and and correlation correlation of of some some Middle Middle Keweenawan Keweenawan rocks, Lake Lake Superior: 6, p. rocks, Superior: Can. Can. Jour. Jour. Earth Earth Sci., Sci., v. v. 7, 7, No. No.6, p. 1410—1436. 1410-1436. across Keweenawan lavas at Duluth, Minnesota: Sandberg, A. A. E., E., 1938, Section across Minnesota: Geol. Soc. Geol. Soc. Amer. Amer. Bull., Bull., v. v. 49, 49, p. p. 795—830. 795-830. >i. 1949, The The geology geology of the Schwartz, G. G. 1'1., 1949, the Duluth metropolitan area: area: Mfnn. Hinn. Geol. Survey Survey Bull. Bull. 33, 33, 136 136 p. p. Geol. �—85— -85- page 22 Silver, L. L. T., T., and and Green, Green, J. J. C., C., 1963, Silver, 1963, Zircon ages for for Middle Keweenawan rocks rocks of the Amer. Geophys. of the Lake Superior Region (abs.): (abs.): Amer. Geophys. Union Trans., Trans •• v. v. 44, 44, p. 107. p. 107. Stoiber, R. S., 1959, 1959, Amygdule Amygdule mineral mineral zoning in the Stoiber, R. E., E.• and and Davidson, Davidson, E. E. S., Portage Lake lava series, series, Michigan copper district: district: Econ. Econ. Geol. Geol. v. v. 54, 54, p. 1250-1277. p. 1250—1277. Walker, G. G. P. P. L., 1960, 1960, Zeolite zones and dike distribution in relation to the structure basalts of eastern Iceland: structure of the basalts Iceland: Jour. Jour. Geology, v. 68, 68, p. p. 515—528 515-528 1964, Geological investigations in eastern Iceland: Iceland: Bull. Bull. Voic., Vole., v. 27, 27, — - - , 1964, p. 351-363. p. 351—363. �—86— -86- Field Trip Trip A A Field The North North Shore Shore Volcanic Volcanic Group Group Leader: Leader: John C. C. Green Green University of Minnesota, ~finnesota, Duluth are intended intended to give aa broad broad picture picture of of The stops stops described below are to give the the chemical, chemical, petrographic, and and structural varieties varieties of of lavas lavas of of the the Group, Group, some representative exposures of of the the minor minor intrusions intrusions that that cut cut the the flows, flows~ and the general structural characteristics characteristics of of these these Upper Upper Precambrian Precambrian racks. rocks. The area northeast of of Silver Silver Bay, Bay~ where where Green Green has has done done most most of of his his work, work, is is stressed. The trip excludes the the Duluth Complex, Complex, aspects aspects of of which which have have been been or are covered elsewhere (GSA Guidebook, ILSG 1968 Guidebook, Guidebook, and Field Field (GSA 1956 Guidebook, Trip BB of this program). of this program). Many more stops are listed below than will be possible to examinein but they included for examine in a one—day one-day trip, trip, but they are included for the benefit of those those who can can visit or or revisit revisit the the area area at at aa later later time. time. The U.S.G.S U.S.'G.S 7 1/2 minute quadrangle name nameisis given given for for each The stops stops which 7 1/2 minute quadrangle each stop. The which are planned as as a minimal frameworkfor forField Field Trip Trip A are designated planned minimal framework A are designated with with an an asterisk after are listed listed for asterisk afterthe thenumber. number. Mileages Mileages are fordistances distancesbetween between easily identifiable along USUSHighway for easily identifiablepoints points along Highway 61 61 (not (not cumulative cumulative mileage mileage for wholetrip)~ trip), for thethe U.S.A.fCanada whole for travel traveleither eithersouthwest southwest (starting (startingatat u.S.A./Canada or northeast Midway border—- Pigeon River: left—hand left-hand column) column) or northeast atatthe the ~fidwayRoad, Road, border (St. Louis Louis Co. Co. 13), 13),Nopeming, Nopeming,WESt west of of Duluth: Duluth:right—hand right-hand column). column). Mileages are in for side trips tripsoff offHwy Hwy 61 in parentheses parentheses or or not not given. given. All All stops stops are are for side 61 are shown on 1. Descriptions between stops stops are are written written for for southwestward southwestward shown on Fig. Fig. 1. The total total distance travel. The distancecovered covered isisapproximately approximately160 160 miles mileseach eachway. way. travel. stops volcanic volcanic structures are well well preserved. preserved. Visitors Visitors are are At At several several stops structures are destroying them, urged to refrain refrainfrom from loosening, loosening~removing removing or otherwise otherwise them~ urged since they they constitute irreplaceable evidence for for flow flow direction, direction, etc., etc., constitute irreplaceable since and valuable teaching students and teachingfeatures featuresfor for local local students and future future visitors. visitors. and are are valuable GoingGoing SW SW NE 7.4 -0:0 7.4 0.0 3.7 3.7 3.7 Minnesota—Ontario (Pigeon Start of Trip River, Minnesota-Ontario (Pigeon Point, Point, Trip A A -— Pigeon River, Travel SW along flat post—glacial lake bed, Minn. quad.). SW along flat post-glacial bed, — Mich. quad.). Minn. then rise rise along along shoulder shoulder of ofa alarge large NE-trending dike then NE—trending dike of of the Several road Keweenawan road cuts cuts ininMiddle MiddlePrecambrian Precambrian IceweenawanLogan LoganIntrusions. Intrusions. Several Excellent views Rove Formation shales small branch dikes. Excellent views cut by small branch dikes. Rove Formation shales Pigeon from parking rest rest areas areastotothethe Wauswaugoning Bay, Bay, Pigeon easteast overover Wauswaugoning from parking (Rove Fm. Point (thick (thickcomplex complex Keweenawan Keweenawan sill)~ Susy Islands (Rove Fm. and and sill), Susy flo's), Hat Lower Royale(Keweenawan (Keweenawan flows), Hat Point Point Lower Keweenawan Keweenawanflows), flows), Isle Isle Royale with Mount Mount Josephine (Logan dike). Josephine (Logan At Stop 1. Logan Formation (Grand (Grand Portage Portage quad.) quad.) At Logandik~ dike and and Rove Roc Faauction Stop 1. the top of the the rise riseisisa adeep deepcut cuttrirough through the the thick thickKeweenawan Keweenawan the top Farther oint. diabase dike that forms Mt. Josephine and Hat Point. Farther forms Mt. Josephine and flat diabase dike that the are good cuts in the Rove down the highway the southwest are good cuts in the Rove highway to down the Formation which is here dominated by graywacke. which is here dominr4lc-J by graywacke. Formation �—87— -87- Going SW Going NE (At the the base base of of the the slope slope an an interesting interesting detour detour can can be be (At to Grand Grand Portage Chippewa village and bay and made to to the the SE to SE Grand Portage National National Monument. Monument. The base of the Upper Precambrian sequence forms forms Grand Portage Island. Island. Continue out the west end of the the village to to Highway Highway 61). 61). 7.4 7.4 0.0 0.0 14.8 basalts, Grand Portage (Grand Stop 2.* Basal Lower Keweenawan basalts, (Grand At the top of the next rise (at the Junction Portage quad.). the top the rise (at the Junction Portage quad.). of Cook Co. Co. 17) 17) are are low cuts exposing basalts near or at of at the the These basalts base of the Keweenawan reversed reversed polarity polarity sequence. sequence. have aa somewhat somewhat diabasic texture and have been strongly though have though not not completely retrograded to prehnite—pumpellyite prehnite-pumpe11yite facies facies minerals. Amygdules contain weathered agate, Amygdu1es agate, prehnite, and and epidote. epidote. The basal Upper Uppe~ Precambrian sandstone sandstone (Puckwunge) (Puckwunge) underlies underlies the the gentle slope to the the north but is is not exposed exposed at at the the highway. highway. It It can be seen by bushwhacking about about 1/4 1/4 mile to to the the NNW. NNW. It is is aa clean-looking, somewhat feldspathic feldspathic quartz sandstone, sandstone, in in marked marked conconclean—looking,somewhat trast to low sandstones to the the red, red, immature, immature, volcanic volcanic interf interf10w sandstones above. above. The anC all the is underlain lowland beyond beyond is underlainby bythe theRove RoveFm. Pm.,, and the ridges ridges are are held up held up by by large large Logan Logan dikes. 3.0 11.9 Stop Stop 3. 3. Tholeiitic basalt and and porphyry porphyry dike dike (Grand (Grand Portage Portage quad.). quad.). unmaintained little Walk or drive off off Highway Highway 61 61 on on an an inconspicuous, inconspicuous,unrnaintained branch on the lake side to to an an old cabin cabin site site at at aa small small cove cove (1/8 (1/8 mile). On RR (SW) (SW) is the the basal, massive portion portion of of aa fine—grained fine-grained the Lower Keweenawan Grand Grand Portage Portage lavas. lavas. On tholeiitic basalt of the the the L is a thick, thick, compound dike dike of of porphyritic porphyritic trachybasalt trachybasalt that that trends E A large swarm of similar dikes is E into into lake. lake. A is present present in in this studied. They are are unusually unusually rich rich ji in Fe and K. K. this area and is being studied. 3.7 3.7 11.1 Stop 4. 4. Stop Red Rock rhyolite rhyolite (Mineral Center Center quad.). quad.). At Deronda to the the SE SE to to the the breccia—rubble breccia-rubble base base of of Bay the beach leads out to feet) porphyritic porphyritic rhyolite rhyolite flow flow which which is is the the aa thick (over (over 600 feet) uppermost flow found to to show show magnetic reversal reversal by by Books Books (1968). (196 8 ). More scenic exposure can can be seen seen by climbing climbing up up the the ridge ridge and and walking out to to the the point point on on the the open open lake. lake. Less scenic but more accessible exposure is in in a road road cut cut 1/2 1/2 mile mile beyond. beyond. 4.6 10.2 Stop 5. 5. Reservation River Diabase and and abandoned abandoned beach beach ridges. ridges. (Mineral Center quad.) quad.) At the the top top of the the next rise rise is the the eastern edge of the extensive Reservation River River diabase diabase complex: complex: one characteristic phase phase is is exposed exposed here here that that shows shows faint faint banding banding on on sonic surfaces. Lcrge some Large gravel the lowland lowland to to.the northeast, gravel pits pits in n the the northeast, mined out for the the new highway, highway, were large abandoned beaches of late postglacial Lake Lake Superior. Superior. Excellent Excellent smaller, smaller, later ridges can still still be be seen seen on on aa little little track that that goes goes to to the the lake lake shore shore can the base base of of the from the the slope. slope. �—88— -88- Going Going Going Going SW NE SW 9.0 9.0 5.8 10.0 il.8 14.8 --00 0.0 4.0 ----". 0.0 4.8 0r 0.0 0.0 10.6 10.6 Cross Reservation River and out of Grand Portage Indian Indian Slope is is at at contact contact of of Reservation River diabase Reservation. Slope complex and lavas (a (a rhyolite rhyolite here). here). 6.* Hovland porphyry Stop 6.* porphyry lavas. lavas. (Hoviand (Hovland quad.) Opposite aa on the lake side are exposures of a remarkable house the remarkable porphyritic trachyandesite lava flow with platy plagioclase phenocrysts up to 10 cm em across. across. By following following the the low scarp to to the the NE behind aa house (private (private property) two two flows flows can can be be ueen, ~een, the the top top of of the the one being vesicular and showing a slightly uneven crust. lower one crust. These are near the the base of of the the Middle Keweenawan Keweenawan (normal (normal polarity) polarity) lava sequence, sequence, and and are are assigned assigned to to the the Hovland Hovland lavas. lavas. They are are here cut by a large large dike, dike, at at least 22 miles long, long, of brown elinopyroxenephenocrysts, phenocrysts, that that also trachyandesite with with small. small.elinopyroxene crops out across across the the road. road. Highway descends to to old old lake—bed lake-bed flat; flat; then, then, past past Big Big Bay, Bay, rises onto higher higher ground ground of of Hovland Hovland Diabase Diabase complex. complex. Cross Flute Reed River, River, pass pass through village of Hovland at Chicago Bay, Bay, and and up onto aa large large sill—like sill-like body body of of syenogabbro. syenogabbro. Many road road cuts; cuts; some some show good foliation of of plagioclases, plagioclases, dipping dipping gently gently S. S. Syenogabbro, basalt pillow-breccia, pillow—breccia, and rhyolite at Brule Stop 7. 7. Syenogabbro, Brule River (Marr River (Marr Island quad.). Opposite Naniboujou Lodge, Lodge, park in in lot of Judge Hagney tmgney State State Park. Park. Walk up trail, trail, cross rivet river on footbridge, footbridge, Take care and follow fisherman's W bank. bank. Take care -— and follow fisherman's trail and bushwhack up W steep and unstable slope in in places. places. At footbridge footbridge is is medium—grained, medium-grained, foliated syenogabbro of of "Hovland "Hovland diabase diabase complex." complex." This is cut by basalt dike, dike, then gives way to a rather coarse—grained coarse-grained basalt aa later basalt lava with chlorite chloritescraps scrapsand andamygdules. mnygdules. Soon overlain by by Soonthis this is is overlain basaltic—scoriaceous tuff—breccia. basaltic-scoriaceous tuff-breccia. After a short short gap gap in in exposure, exposure, steep bank resumes resumes which is made of basalt pillow—breccia, steep pillow-breccia, with altered volcaniclastic matrix. This is is one of the the few few places places where evidence for evidence for underwater extrusion can can be seen seen in in the the North Shore Shore Volcanic Group (others (others are are on on Grand Grand Portage Portage Island Island and and WWof of Duluth Duluth in the Lower Lmyer Keweenawan). Keweenawan). Farther upstream this this can can be be seen seen to to overlie the altered, altered,flow—banded flow-banded and rled top top of aa very very large porphyricic porphyritic and styi swirled rhyolite the Bride Brule has has cut cut aa deep deep gorge gorge above. above. rhyolite flow through which the Return by fisherman's trail tr~il at at top top of of bank. bank. After crossing After crossing the the Brule (Arrowhead) (Arrowhead) River, River, the the highway rises rises over and cuts cuts through through three three hasalts basalts of of the the Brule Brule River River group, group, then then crosses a porphyritic trachyandesite trachyandesite or or intermediate intermediate quartz quartz latite latite the }larr Island lavas lavas at at Paradise Paradise Beach. Beach. AA few few more low low cuts cuts of of of the Marr Island this mixed group are this are passed passed in in next next 33 miles. miles. 3.8 3.8 5.8 Stop 3•x Stop 8.~ Porphyritic ~arr Island Islan~ Porphyritic intermediate intermediate quartz cuartz latite latite of p Marr lavas one one mile mile past past Cook Co. lavas Co. 14 (Kadunce (Kadunce Creek quad.) quad.) Two large road cuts cuts on N. thick, intermediate intermediate quartz latite latite road N. side of a thick, K 0) plagioclase, ferroaugite, and rare lava (62% (62% SiO Si0 , 4.1% K 0)with with plagioclase, ferroaugite, and rare 2 2 ex-olivine ana magnetie magnetitephenocrysts. phenocrysts. Contacts not exposed. exposed. ex—olivine an , �-89—89-Going SW Going NE 1 1/2 miles to the the west at Kadunce Creek (Kodonce (Kodonce River) River) miles to State Park a thick porphyritic felsite is exposed, especially especial~y in in a deep dl~ep and narrow canyon that begins about 1/8 mile upstream upstream from highway highway -— this this is part of the from the Kimball Kimball Creek Creek felsite felsite group, group, also exposed in Kimball and Cliff creeks farther also farther west. west. Excellent wave—cut cliffs abandoned wave-cut cliffs of of Nipissing Nipissing stage. stage. 7.3 3.2 3.2 Stop 9. 9. Olivine basalts of of Red Red Cliff Cliff series series (Kadunce (Kadunce Creek Creek quad.). quad.). Just past large gravel pit and and creek creek gully, gully, highway highway rises rises onto onto aa series flows totalling totalling between between series of of 5 or 6 ophitic olivine basalt flows 400 and 900 feet feet in thickness. thickness. Amygdules contain contain saponite,laumontite, saponite,laumontite, calcite, quartz, calcite, quartz, and and agate. agate. Plagioclase phenocrysts have floated floated to to top 0.5% K20. K 0. top in some, some, sunk to to bottom bottom in in others. others. 47% Si02 Si0 , 0.5% 2 2 Past Durfee Creek (near (near top of Red Cliff basalts) highway (and (and cliff) pass onto Devil Devil Track Track felsite felsite group, group, here here composed composed Nipissing cliff) of two thick flows. of flows. 9.6 1.0 Stop 10.* Felsite of Devil Track sEries, series, at promontory of of abandoned abandoned Nipissing wave—cut wave-cut cliff. cliff. N N side of highway, 0.85 0.85 miles west of of Pink, nonnon— or weakly porphyritic Durfee Creek (Kadunce (Kadunce Creek Creek quad.). quad.). Pink, rhyolite K20) slabby jointing rhyolite or quartz latite (72% (72% SiO Si0 2 , 5.5% K 0) with with slabby jointing 2 Bushwhack?ng along old cliff to E and faint flow—banding. flow-banding. Bushwhacking E for 1/4 1/4 mile one eventually passes down down into into vesicular, vesicular, locally locally spherulitic spherulitic and flow banded top top of a porphyritic flow flow of of similar similar composition. composition. and flow These two two flows flows total total about about 1020 1020 feet feet in in thickness. thickness. Five Mile (Guano) Rock, Rock, aa mile mile out out in in Lake Lake Superior, Superior, is ~uano) is made of diabase. , 10.6 0.0 0.0 3.7 Track~. upstream Cross Devil Track River. This cuts a deep gorge just upstream felsite flow. flow. Continue on Hwy 61 into Grand Marais, or or in the upper felsite alternatively turn turn off just before rise on small side road alternatively road (Cook (Cook Co. Co. 87) Stop 11. 11. 87) toward toward lake lake to to Croftville settlement and optional Stop (off Hwy 61) 61) (off (1.3) _~~ (0.0) (0.0) (0.45) Stop 11. Spherulitic hasal phase, phase, Grand Marais rhyolite, Croftville Croftville Stop 11. (Grand quad.) Drive about 1.1 mile along Nipissing terrace terrace (Grand Marais Marais quad.) over (about 0.45 mi. from WWend this road). road). over Croftville Croftville basalts basalts (about mi. from end of this Private Property. ?roperty. Ask permission at at the the house hous~ in in birches birches on on lake lake side, beach-back. Slabby, Slabby, spherulitic spherulitic side, exwline examine outcrops outcrops at at modern modem beach—back. red rhyolite rhyolite is is exposed here (73.4% (73.4% SiO SiO , 4.65% K20) K20) that that contains contains red hedenbergie, ex—fayalite and magnetite andesine-oligoclase and rare hedenbergite, ex-fayalite and magnetite andesine—oligoclase and rare Nearby is cross—bedded, calcite—cemented interflow sand. phenocrysts. cross-bedded, calcite-cemented interflow sand. phenocrysts. Strata have been steeply tilted tilted by diabase diabase intrusions. intrusions. Continue on on road until until it it re—joins re-joins Hwy Hwy 61. 61. Croftville road , (0.45) (0.0) (0.0) (2.1) (2.1) Continue SW SW to to Grand Grand Marais. Marais. (off Hwy H'YY 61) 61) Stop 12. 12. Breakwater trachybasalt (Good (Good Harbor Bay Bay quad.). quad.). Drive to E end of Grand Marais harbor. harbor. Tombolo to Coast Coast Guard Guard Station at E here is is made by gravel bar connecting mainland to to resistant resistant island and and ledges ledges of of aa massive, massive, locally locally columnar-jointed, columnar—jointed, porphyritic porphyritic trachybasalt or basalt with small phenocrysts of of plagioclase, plagioclase, augite, augite, trachybasalt and rare olivine. olivine. It 360 feet feet thick. thick. It It is not known It is is about 360 this is is a big flow certain whether this flow or sill; to to the the west is is has has for certain aa sharp, sharp, chilled basal contact contact against against felsite felsite but but its its top top is covered. covered. It It becomes amydgaloidal and zeolitized zeolitized near near contact is �Going SW Going —90— -90- NE its to be be aa flow. flow. As can be seen seen from from its top and is assumed to point, it it forms forms one of the the major major strike—ridges strike-ridges of of vantage point, "Sawtooth Range" Range" to to the the west (as (as does the the big "thomsonite "thomsonite sta~ting Good Harbor Harbor Bay). Bay). The harbor at Grand Marais Harais starting at Good probably eroded from from rhyolite. rhyolite. 3.7 0.0 0.0 9.2 this this the the flm.," flow" is is lint Trail Trail Highway 61 passes corner corner of of harbor, harbor, near near start start of of Gunf Gunflint (Cook Co. Co. 12). (Cook Then highway rises rises to W W past a good norphyritic porphyritic rhyolite rhyolite cut cut (Breakwater trachybasa1t trachybasalt cuesta cuesta ahead), ahead), then then onto higher level (Breakwater down across the the Breakwater Breakwater trachybasalt trachybasa1t and and across across Fall Fall River River back down (Rosebush Creek). About 1 mile past this this creek, low low road road cuts cuts start start in two two thick porphyritic trachyandesite trachyandesite to to andesite andesite flows flows (55% (55% Si02, 5i0 , 2 phenocrysts and and 2.7% K K 0) 0) with small plagioclase and clinopyroxene phenocrysts 2 ahead is vesicular-rubble is held up by Terrace Point vesicuar—rubble tops. Big cuesta ahead Continue across thomsonite-bearing basalt basalt flow. flow. Continue across Cut Cut face (Good (Good thomsonite—bearing Harbor) Creek. Creek. 5.2 3.9 Stop 13.* Thomsonite—bearing low sediments (Good Stop Thomsonite-bearing basalt, basalt, interf interflow (Good Bay quad.). quad.). In this this large road cut one of the major cliff Harbor Bay formers (130') section of formers of of the the "Sawtooth "Sawtooth Range" Range" overlies a thick (130') interf low sediments. The Terrace Point basalt is dominantly a interflow sediments. The Point massive, massive, fine—grained, fine-grained, ophitic basalt that that characteristically characteristically contains contains thomsonite its lengthy exposure (including (including in thomsonite in amygdu1es, amygdules, but hut in its this cut) cut) several several flow units units of of varying character show complex this relations with the major, massive relations massive part part of of the the flow. flow. The interfiow interflow sediment Is is here mainly thin—bedded thin-bedded siltstone siltstone shale, but by walking up up the the bed of of Cutface Cut face Creek Creek at at and silty shale, the bottom bottom of of this hill one passes the this hill passes outcrops of the the basal contact contact the amygdaloidal—scoriaceous amygdaloidal-scoriaceous top top of of of the sediments resting on the an flow and wellan andesite andesite flow and eventually reaches large banks cut into well— bedded sandstone showing abundant ripple ripple marks. marks. 9.2 — 0.0 0.0 16.9 0.5 0 5 16.4 16 4 cuts of the the complex complex upper upper parts parts of of the the Highway 61 passes low cuts Terrace Point flow complex, complex, with big cuesta cuesta on this this flow flow visible visible ahead, ahead, then then at at jct. jct. of of Cook Cook Co. Co. 7 passes into coarse—grained coarse-grained olivine olivine passes into basalt of the the Lutsen Lutsen basalt basalt series. series. Cross Cross Cascade River in State Park. Park. Trail up W W side provides access to to good good river river outcrops outcrops of of Terrace Point thomsonite thomsonite basalt, basalt, the the underlying underlying sandstones, sandstones, and and several andesite flows flows of of the the Good Good Harbor Harbor Bay Bay series. series. Drive past Cascade Lodge. Lodge. Stop 14* Cascade (Deer Cascade olivine olivine basalt basalt of of Lutsen basalt basalt series (Deer Yard Lake quad.). 0.5 miles W. W. of of Cascade Cascade River. River. Shore outcrops of aa thick (100 more), relatively of (100 feet feet or more), relatively coarse—grained coarse-grained olivine basalt this Cascade—Lutsen Cascade-Lutsen area. area. basalt of a distinctive group in this Segregation cylinders cylinders up up to to 6" 6" or so so in Segregation in diameter and segregation lenses lenses or sills can can be be seen seen within within this this flow. flow. Highway continues continues on on long long straight straight stretch roughly parallel parallel to strike of Lutsen basalts, topmost series of the the North North Shore Shore to basalts, topmost Volcanic Group. Group. Pass Pass through Lutsen village (big (big ridges rid?,es to to W held up W up by Leveaux trachybasalt trachybasa1t sill), sill), to to Poplar River. Rive~, �—91— -91- Going SN SW 9.3 Going NE ---7.1 Stop 15. 15. Poflyritic Porphyritic olivine basalts of Lutsen series series (Lutsen (Lutsen Poplar River. River. Watch Hatch your step step -- dangerous. Private land. land. quad.), Poplar Several flows flows of a distinctive ophitic olivine basalt characterized characterized by abundant small small(1—3 (1-3nun) mm) blocky bytownite phenocrysts are are exposed exposed by the Poplar from Poplar River River at at Lutsen Lutsen Resort, Resort, up up through through an an frcrnthe the mouth mouth of the canyon to to the the highway bridge bridge and upstream to left bend impassable canyon (1/10 highway). Take fisherman's fisherman's trail trail on on WWside. side. This (1/10 mile nile from highway). flow Ilprimitive" composition composition (lowest (lowest K, K, highest highest Mg) Mg) ?low type type has has the the most most "primitive' Si02, 0.l2I K20). L bend in river , 0.12% K20). At of the North Shore lavas (1+7% (47% Si0 2 it overlies breccia-rubble breccia—rubble top of aa basaltic andesite andesite flow; flow; red red sand sand has been washed into all the interstices between the lava blocks, has lava a typical situation. situation. 12.3 4.6 Leveaux —- Onion HtIl=Stop 16. Leveaux_ porphyry !411. Eill (Tofte Mtn. trachybasalt trachlbasalt porphyry SWof of Poplar Poplar R.. at slight L quad. ) . 2.5 mi. R•..at L bend cross cross Rollins Rollins quad.). ml. SH Creek and irnediately immediately turn up U. U. S. S. Forest Service gravel road road (No. 336). Continue on it it as as it contours back to SW, then then cuts cuts up up (No. 336). OnionRiver Mvergap gapininbig big ridge ridge held held up up by by aa big big trachybasalt into Onion into porphyry sill. sill. This sill forms forms Leveaux Mtn., the high ridge ridge with a fire tower a fire tower on on it ittotothe theSW, SW, and and comes comes out to the lake lake shore shore to to form the islands at Taccnite Harbor SN of Tofte. Its contacts at Taconite Harbor SH .of Tofte. contacts are are not exposed but it it crosscuts crosscuts the the lavas. lavas. Park as near as as possible possible to the S S corner corner of of the hill hill on on the the NE NE side side of of the the gap, gap, and and bushwKack bush~ack a short distance N n to to· the the steeper, steeper, rocky rocky rise. rise. Here the lower lower part exposed fine—grained, pigeonite-augite pigeonite—augite trachytrachy— of the sill sillis is exposed—- a fine-grained, to trachyandesite. trachyandesite. Farther up up the Glope slope aa bit bit abundant abundant large large basalt to (1 blockylabradorite labradorite phenocrysts phenocrystsappearroruptly; appeartruptly; they appear to (1 cm) cm) blocky to floated. This porphyritic phase forms have floated. forms the upper part of of the the throughoutits its extent. extent. sill throughout 16.9 2.... 0.0 0.0 ---12.1 Continue SW svr past Tofte. pastSawbill SawbillTrail Trail (Cook (CookCo. Co.2)2)atat village village of Tofte. Town Town park park on on lake lake shore 0.3 0.3mi. mi.SW SW of ofEdgewater Edgewater Motel Motel has has good good exposures of of thin-bedded thin—beddedophitic ophiticolivine olivine basalts. basalts. DO DO NOT exposures NOT DESTROY DESTROY FEATURES. These the top top of the section section of the orth NorthShore Shore FEATI.ffiES. Theselie lie at at the Volcanic Group. 10.1+ 10.4 anorthosite in diabase (Tofte Stop 17. 17. Carlton Peak ?lloythosite (Tofte quad.) 1.7 1.7 mi. mi. jet., opposite opposite large large Superior Superior National National Forest Forest SW of Sawbill Trail jct., Sign, Sign, turn up road of Erie Mining Co. Co. to large quarry in in side side of of Carlton Peak, anorthosite xenoliths xenoliths in in Peak, which is held up by massive anorthosite intrusion. Private Property. Property. The The complex complex rela.tions relations a gabbroic intrusion. between the the anorthosite anorthosite and and various various phases phases of of olivine olivine gabbro gabbro are are well well 1.7 exposed. 2.5 9.6 Stop 18. Thin—bedded ophitic olivine tholeiites of Thin-bedded of Schroeder Schroeder 18. basalts, Temperance Temperance River River (Tofte (Tofte quad.). quad.). Park at State Park lots, lots, walk down down trail to bridge near near river river mouth. mouth. Note excellent erosional Several thin flows flows or flow units, with ropy ropy surfaces, surfaces, pipe pipe potholes. anygdules amygdules and lensing lensing shape shape are are well well exposed exposed here. here. If more time is is available, walk up NE side of river above available, above highway to to the the main main gorge gorge where the river river has has cut cut aa very very deep deep and and narrow narrow slot slot with with larger larger into thicker olivine olivine basalts. basalts. Warning: people have have been been potholes into Warning people killed trying trying to to jump jump across. across. Large joint joint columns colUmns visible visible on on trail trail killed cylinders are are present in in thicker thicker flows. flows. and overlooks, overlooks, and vesicle cylinders �—92— -92- Going SW SH Going 3.8 3.8 NE 8.3 8.3 9.14 2.7 Drive SW SI'! through Schroeder and and Taconite Taconite Harbor Harbor (power (power pellet shipping facility of plant and taconite pellet shipping facility of Erie Erie fining Mining Co.) Co.) with occasional occasional low low cuts cuts of of ariygdaloidal amygdaloidal or ophitic olivine olivine tholeiite. tholeiite. Stop 19*. 19*. Thin—bedded Thin-bedded ophitic ophitic olivine olivine tholeiite tholeiite of of Schroeder Schroeder basalts basalts at Sugar Loaf Point (Little at (Little Marais Marais quad.). quad.). Private property. property. Drive down side road (just (just opposite gravel gravel road road from from uphill) uphill) at at Consolidated Consolidated Paper Co. storage and and handling handling facility. facility. Drive down to cove, cove, Co. pulpwood pupwood storage end ask ask permission permission to towalk walk onpoint opoint at and at office. office. Notice great old Walk around pine boom—logs to raft raft pulpwood pulpwood across cross lake. boom-logs used to lake. Halk Excellent exarrioles Sugarloaf Point clockwise clockwise from from end end of of beach. Excellent examples up) and thicker flows flmv units units (6" (6" and up) flo1>ls of ophitic "olivThe " olivine of thin flow tholeiites ,It with ropy ropy surfaces, surfaces, bent bent pipe pipe amyvdules, amye:dules, and and clastic clastic tholeiites," dikes dikes where sand was washed into into open open ;oints joints in in the the tops tops or of flows. flows. not remove or destroy structures! On On the the sides sides of Please do not destroy these thes~_Et~.~ures! the high high knob at the end can the can be seen seen vertical vertical tube—like tube-like concentrations concentrations arnydules ("vesicle of amygdules ("vesicle cylinders") cylinders") in in the massive Massive Imler lower nart tart of the topmost flow. flo",. 11.77 11. 0.14 0.4 12.1 0.0 0.0 11.0 Cross Cook/Lake Cook/Lake County County line. line. Ophitic olivine!-holeii:~s, tholeiites, Ma! !-S.?-chY.Easalt., tracybasalt, and Qphiti c_ olivine ~If~it0l.! strike—fault, Caribou River River (Little (Little ~larais arais quad.) strike-fault, Caribou quad.) Park Caribou Park at Caribou Falls State Park 1°t side of the the hip-;h,.,ray highway and "Talk walk ut Falls lot on the HH side up the (Between the the highway highway and Lake Lake is is private property including trail. (Between typical ophitic falls over typical ophitic olivine olivine basalts). basalts). In In the river riverand and aiocg alonr; the trail are a few outcrops the outcrops of the red red volcanic volcanic breccia breccia and and basalt basalt that underly the "Manitou "lvlanitou trachybasalt," then then at at aa LL bend bend is is the the NE— NEmost outcrop of most of the the trachybasalt. trachybasalt. lis ap]Jroaches the falls falls As the trail anproaches the river has the has cut through aa thick section section of of volcanic volcanic breccia, breccia, nut but aa large strike-fault intervenes between this and and the the typical typical ophitic ophitic large strike—fault olivine thoeiites (flio2=5-.7%, oli vine tholeiites (Si02==45-47%, K the cli f f Torn tt:e :20=o.3_o.5z) 20"'0. 3-0.5%) that form over which the the river river fells. fa.lls. Several flovs, 10-30' each, Several flows, 10—30' each, are visible in the the cliff each with a massive lower part and in and an an amygdaloidal amygdaloidal and and slabbv-jointed top. slabby-jointed These nearly all allthe thelavas lavasbetween between Theseare are typical tynical of nearly 1:ittle arais Little Maraisand andLutsen, Lutsen, the uppermost sequence sequence of of tbe the North North Chore Shore the uppermost Volcanic Group. Group. Stop Stop 20. 20. cli' 2.2 8.8 8.8 Dri ve SW, 8\1, cross cross anitou ~ftanitouRiver, River,'.rhich lIhi ch has Drive has cut cut aa deep deep f!;orge aorge throup;h throu'h drift and olivine basalts (trail in State State Land Land accessible accessible drift (trail up up streaxn stream. in on SW S1:T side via via gravel gravel pit pit road), road). Commercialized has Cornniercializedgonre gorge dmmstrear'l downstrean has falls, sea arches. falls, Continue LW bend at at Little Little I·,farais Marais R. . SH almost to to I? H bend 14.5 4.5 6.5 6.5 Stop 21. 21. Manitou trachsasait (Little Stop !5~j.~.sm !-!_a~J1_x.:!?~a1.!-. (Littlei'larais Marais quad.). quad.). Turn 'I'urndo'.in down road at Ben Fenstad's Fenstad's Resort, Resort. Private ask permission Private nrqperty; property; ask for entry at for at office. office. Continue down to lakeshore, bearing bearinp. left left to to end of driveway dri vevay loop at at fishhouse. fishhouse. here here at B.t the the end end of of the the slit slin is is exposed the base of an 1arre larp,e flow flow of of granular granular trachvbasalt, trachybasalt, at at least least 300' rLles lonp" long, that forns ofth~SDreledges t1roreledges Croa 300' thick and 55 miles forms !'uch much of fro~ breakwater on, HE of M8ni this breaki-mter on, both SW G\l and and tIE tou FLyer. Pi vel". It contains contains Menitou Si022 and 2.3% about 52% 52;~ Si0 K2 (), and and has has labradorite. labradorite, augite, aup.;i te, and and 2.3 K20, and abundant ahundant KK feldspar feldspar and and altered rare olivine phenocrysts and pigeonite piGeoni te in in the the groundviass. groundmass. higher hip:,her in in the flow fIm, it it is is coarser— coarser- �—93— -93- Going SW Going SE HE grained, less less potassic and Its top is grained, and less less porphyritic. porph~ritic. Its is not exoosed. It overlies overlies aa sequence of interLedded eXDosed. It interbedded basalts and red red volcanic volcanic breccia breccia or or conglorierate. conglomerate. high ridge inland is held up by Continue Li ttle 'arais. ~1arais. High Continue S\J SW past Little a thick intrusive diabase sill containing a thick intrusive diabase containin~ some anorthosite blocks. blocks. 8.0 8.0 9.1 9.1 2.6 Stop 22.* .iartz tholeii tholejite—trachybasalt, Kennedy Landing 22. * QJ.artz te-trachybasalt, Kennedy (Finland quad.) quad.) Good cuts for for about about 1/3 mile through throu~h several several typical auartz quartz tholeiites tholeiites to to trachybasalts. trachybasalts. They show the the charcharacteristic fine-grained, fine—grained, aphyric anhyric texture, texture, oxidation lamellae, and acteristic and scoria-rubble feldspar scoria—rubble tops. They contain interstitial alkali feldspar and about about 51-53% 5l—53 5102 and Si02 and and up up to to 2% 2% K20. K20. Red sand, sand, locally cross— crossbedded, fills the interstices between fragments. fragments. Large knob knob bedded, fills is made of the thickest of of these flows. flows. overlooking the bay is 7.8 7.8 Stop 23. in ~y~nogllR..br~; syenoabbro; overturned Anorthosite in 23. ** An_,?rth,?sitE:. ove!:turned lavas l~vas (Illgen City quad.). quad.). After crossing crossing Kennedy Creek Creek come come to to deep deep vertical cut cut in an irregular discordant intrusion intrusion (part (part of of Beaver Beaver Bay complex) Day complex) of altered syenogabbro that contains contains aa great, great, massive massive of rather After examining this, walk block of rather pure pure anorthosite. anorthosite. After examining this, walk or drive SW drive SW downhill cut that sequence of of downhill to to lower cut that is is composed of a sequence several basaltic basaltic lavas lavas with an interflow sediment bed — several - all all of which which have been overturned, overturned, probably as as aa result result of of forceful forceful intrusion intrusion of nearby diabases. These basalts show show aa variety variety of of structures, structures, including at the NE end end some some including some some lobes lobes that that look like pillows and at red scoria,-rubble scoria—rubble that that is is characteristic of the top part of the red fine—grained tholeiites, tholeiites, basaltic andesites, fine-~rained andesites, and trachybasalts. trachybasalts. 11.0 42 0.0 0.0 0.0 It.9 ~ Continue to Ulgen lilgen City, City, ~ Lc•• •with Rte.ito Continue SW to Tith Minc. Minn. Rte. -.l to Ely. Ely. Just .Just to NE are cuts cuts in in quartz tholeiite flows, flows, to to SW SW cuts cuts in in altered rhvolite. rhyolite. 0.45 0.45 4.5 24.* Stop 21~. Palisade .!1~_a~ Head P.s>E1?-~)'Ti pohyritic Stop * ~~~isad~, tic:: rhyolite, rhyolite" Shovel Shovel Point Point (Illgen (Ingert City quad.3. quad.). 0.45 0.b5 mile SW SW of of Illgen Illgen City City jct., jet., or or 0.145 0.45 mile NE of Baptism River, River, search for NE for unmafled unmarked trail leading leading to to shore shore Here is at Shovel Point in at in Baptism Baptism 9. R. State State Park. Park. Here is well exposed the upper-middle upper—middle part of porphyritic rhyolite rhyolite the of the the thick thick (>300'? (>30d: porphyritic (quartz (quartz latite) latite) that that also also forms forms Palisade Palisade Head to to the the SW and the road cuts at at Tllgen III~en City. City. Take care on on clifftop. clifftop. View to SW over underlying lavas ("Baptism ( "Baptism basalts") basalts ") and and some some mafic mafic intrusive intrusive bodies, bodies, to Palisade Palisade Head. Head. Follow trail down dipslope to end end and and corner: view TIE toward overlying overlying quartz quartz tholeiite flows. NE corner: NE toward flows. Return on sa1Ie same trail trail _._----~ Drive Head (big (big hill hill with with Drive 811 SW across across Baptism !liver River to Palisade head radio beacon). 2.1 2.7 (Iliren joint (Tity quad.). quad.), Stop 25. 25. Palisade Drive up up Palisade Head Head rhvolite r1yaUiq. (Illgen City narrow, winding road--C,ju;t'" road (just past--Palisade past Palisade Creek) Creek) to to top top of of cliff cliff next to raOio careful — columns are radio beacon. beacon. ,9areful - joint colwnns are se-narating separating Excellent views from rest of of hill. hill. ~xcellent views to to .N, ~, NE, SE, SE, SW. SW. Ridges to �—94— -94- Goin,:?; GoinI SW Going NE "[IT, NE aie B,Te held up by intrusions intrusions of of Beaver Beaver Bay Bay complex. complex. Up Up N. lakeshore to NE is columnar—jointed columnar-jointed Shovel Point, Point, made made of of same same rhyolite flow, is smoke from Taconite Harbor flow, and far far beyond is plant and and Carlton Canton Peak power plant Peak anorthosite anorthosite knob knob at at Tofte. Tofte. To S across lake lake are are Apostle Apostle Islands Islands and Bayfield Peninsula, Wisc. across Wise. To SW is Reserve Mining Co. Co. taconite plant at at Silver Silver Bay Bay and and humpy humpy Palisades made of thick, por— topography of Beaver Beaver Bay Bay complex. complex. Palisades porrhyolite with quartz quartz and and feldspar feldspar phenocrysts, phenocrysts, flow— flowphyritic rhyolite banded at the base. Return to to highway. highway. 1.9 4.9 0.0 0.0 0.0 0.0 i1.8 14.8 0.4 l.3 14.3 0.14 at Silver Bay, 2.15 ml. mi. to traffic light light at Bay, site of Drive 2.75 Co. 's taconite plant where where about about 100,000 100,000 tons of ' Reserve Mining Co.'s rock from the eastern eastern Mesabi Mesabi Range Range are are processed per day. day. Stop 26. 26. Anorthosite in in diabase diabase of of Beaver Beaver Bay Bay complex, complex, Silver Silver (Silver Bay Bay 15' 15' quad.). quad.). Stop at road cut cut directly directly opposite opposite Bay (Silver the main building taconite plant (after building of of the the Reserve Reserve Mining Mining Co. Co. 's 's taconite (after Here several large blocks of anorthosite the' 2nd lights). anorthosite the traffic lights). 2nd are in the Beaver Beaver Bay Bay are included in diabase, a typical assemblage in complex. Large patches of of interstitital, interstitital, poikilitic poikilitic olivine olivine occur occur in anorthosite. No definite source source for for the the in some parts of the anorthosite. Small red red veins veins and and dikelets dikeletsofof"granoph~y'.(e" "granophe" anorthosite is is known. Small cut the diabase and and anorthosite. anorthosite. across Beaver Beaver River River to to Beaver Beaver Bay. Bay. Continue SW 2.8 miles across 3.2 3.2 11.6 Stop 27. St,up 27. Beaver Beaver Bay ferrogabbro and and Black Black_ Bay_ gabbro (names (names after y ferrogabbro Gebman) Gehman) of Beaver Bay Bay complex complex (Silver (Silver Bay Bay 15' 15' quad.). quad.), Drive or down to shore shore on on gravel gravel road road opposite opposite the the main main restaurant restaurant In tn walk down Beaver Beaver Bay. Bay. Walk E E through woods across little little point point to to shore shore ledges. These are well-foliated ferrogabbro of of the the Beaver Beaver Bay Bay well—foliated ferrogabbro Ferrogabbro, one one of of two similar similar plugs plugs in in this this area. area. On walking NE along the shore, the contact contact with an an enclosing enclosing ring—dike ring-dike of of Black Black Bay Bay Gabhro Gabbro is reached; reached; such rings rings surround both ferrogabbro is ferrogabbro plugs. plugs. It is rather It is inhomogeneous and locally contains very abundant apatite. inhomogeneous apatite. The The ophitic ophitic Beaver River Gabbro can can be seen farther shore below some some farther along the the shore cabins. Return to to highway. highway. - Continue SW through Beaver Bay complex; complex; most outcrop outcrop is of is of coarsely mottled, mottled, ophitic olivine gabbro ("Beaver ("Beaver River River Gabbrot' Gabbro" of of Gehman), Gehman), well well seen seen opposite opposite Kings's Kings's Landing 3 miles miles from from Landing Marina Marina 3 Beaver Beaver Bay. Bay. After 2.2 more miles road road branches to to Split Split Rock Rock Lighthous,buil on Lighthouse,built on anorthosite anorthosite in in diabase. diabase. At Day Hill Hill (parking (parking At Day and 1.0 mile beyond, is and trail), trail), 1.0 is last exposure of Beaver Bay Bay complex. Re—enter volcanics, continue 5.14 5.4 miles to to Gooseberry Gooseberry complex. Re-enter volcanics, continue Falls State Park. Park. 114.8 14.8 0.0 0.0 0.0 13.1 l3.i Stop 28. Stop 28. Smooth—surfaced Smooth-surfaced olivine olivine basalt, Gooseberry Falls Falls State basalt, Gooseberry State Park Park (Split Rock Point quad.). ~Split Rock P6int quad.). Below highway bridge are good exposures, highway bridge are good exposures, in. and between falls, of Columnar—Jointed olivine ln, and between falls, of columnar-jointed olivine basalt basalt lavas lavas with with ainygdalojdal tops, tops, and amygdaloidal and smooth, gently gently billowing billowing surfaces. surfaces. Continue SW through Castle Danger (2.L Continue (2.4 mi.), across Crow Crow Creek Creek ml.), across (a diabasic diabasic intrusion intrusion here (a returns soon soon to to SW SWat here returns at deeply deeply weathered weathered Lafayette Lafayette Bluff), Bluff), through through Encampment Encampment Porest owned old— oldForest(privately (privately owned growth forest with growth forest with summer to to Silver tni~~ summerhomes) homes) SilverCliff Cliff(anothp~ (anoth' +1I41- �Going NE Going SW SW —95— -95- intrusion) to outskirts of Two Harbors. gabbroic intrusion) 12.7 0.5 Stop 29. 29. Quartz tholeiite basalt, Two Harbors city park (Two (Two Stop Just before entering town, Harbors town, turn turn toward toward lake lake at at I:arbors quad.). quad.). Drive past Burlington Wa—Ke—Ya Motel. road to to city city camp camp ground and and Wa-Ke-Ya Burlington road Bay, and up up aa hill. hill. Park at hilltop picnic area, walk walk EE to to shore, shore, Bay, and then S. S. Well exposed contact between amygdaloidal, amygdaloida1, weathered weathered then (ex—laumontite) top of of one basalt and massive basal part of an (ex-laumontite) top analyzed fine—grained, fine-grained, aphyric quartz tholeiite tholeiite (50% (50% 5102, Si02, 0.6% K20). Local thin sand lenses near and and at at contact; contact; traces traces of of Cu have been been found. found. The tholeiite shows shows occasional small small quartz— quartzagate and chlorite amygdules amygdu1es and and typical typical incipient incipient sheeting— sheetingfractures with thin .of this this thick thick thin bands bands of of oxidation. oxidation. Upper Upper zonezone' ,of tholeiite can be examined to to S. S. toward toward power power plant; plant; it it becomes becomes rubbly, vesicular, brecciated, with abundant rubb1y, vesicular, abundant laumontite. laumontite. Return to Hwy 61. 13.1 0.0 0.0 20.6 20.6 20.6 0.0 0.0 0.0 5.9 (3.0) (3.0) (3.0) Continue SW to traffic light in in Two Harbors. Harbors. At west end of town town take express highway highway to to Duluth. Duluth. Many cuts cuts of basalts and minor diabase intrusions. At-about At- about 17.7 11.7 miles Moose Moose Mtn. is is seen seen inland, inland, held up by Lester River diabase sill. sill. At 20 20 miles jct. jet. with old old St. Louis Louis Co. Co. 61), 61), and and at at 20.6 20.6 miles miles Lester Lester River River Hwy 61 (now (now St. either continue continue straight on Hwy bridge. Just beyond, beyond,either Hwy 61 61 (London (London Rd.) Rd.) direct to downtown 6 miles ahead, ahead 9 or or turn turn uphill uphill on on Minn. Minn. 23 23 (60th Ave. Ave. E) E) across ItR tracks to to Superior Superior St; St; go left. (60th RR tracks left. Stop Stop 30. 30. Tischer Creek felsite felsite and and Endion Endion sill, sill, Congdon Congdon Park Park (Duluth quad.). Examine outcrops beneath bridge; then then walk walk up up on WWside side of of creek. creek. There are some some impassable impassable trail that starts on places where you must climb climb up up to to aa bank—top bank-top trail trail on on WWside. side. part of of section cuts cuts through orange, foliated foliated felsite felsite with with Lower part through orange, flow inclusions, Clut by two two flow structure, structure, quartz veinlets, occasional inclusions, out by or three basaltic basaltic dikes. dikes. Upstream at top of of steeper steeper part part of of gorge gorge the stream cuts down into red granophyre top top of of Endion Endion sill. sill. Upcuts gradually gradually down down into into intermediate, intermediate, then then gabbroic gabbroic stream the creek cuts rocks of main part of Endion sill. rocks of Endion sill. At Vermilion Road bridge (second (second bridge above Superior St.) St.) still still in in lower—middle lower-middle part part of of sill; sill; return via trail trail or Congdon Congdon Parkway Parkway on on W. W. side. side. See Ernst, Ernst, 1960. 1960. Continue SW on Superior St. St. over rise rise held held up up by by Endion Endion Sill. Sill. 5.0 5.0 0.9 0.9 5.9 5.9 0.0 0.0 0.0 0.0 11.2 11.2 Stop 31. 31. Basaltic-andesitic interflow sandstone, sandstone, Leif Leif Basaltic—andesitic lavas, interflow Erickson Park, Duluth Duluth (Duluth (Duluth quad.). quad.). At lath 10th Avenue E. E. turn turn off off Superior St. Road at at Leif Leif Erickson Erickson Park. Park. St. toward lake to London Road I Walk over footbbridge footbbridge near near "viking "viking ship" ship' to t shore. shore. Weakly por— porphyritic basalt or basaltic basaltic andesite andesite ledges ledges behind behind stage. stage. Rubbly Rubbly (weathered?) (weathered?) top top to to NE NE is is directly overlain by a thick thick cross—bedded cross-bedded sandstone, that is is cut cut by by aa small small dike dike at at NE NE sandstone, strongly epidotized, that more flows end of beach. Several more flows exposed along shore shore to to SW. SW. anc Superior Superior Street, Street, downtown downtown Duluth. Duluth. Lake Avenue and (approx.) ~approx.) 1L 11-22 approx.)) :approx. o. a 0.0 Drive SW on Hwy 61 past Point of Rocks Rocks through Duluth Complex Thomson Hill Hill to to Nopeming. Nopeming. Turn R R at (St. Douis 13), up Thomson at Midway Midway Road Road (St. Louis ~o. o. 13), drive uphill about 0.9 mi. mi. almost almost to to top top of of rise. rise. �—96— -96- Stop 32. 32. Basal (Puckwunge?) (Puckwunge?) sandstone, basal basalts of of Lower Lower Keweenawan Ke\veena\van ('Grandview ("Grandview Golf Course" locality, locality, Esko Esko quad.). quad.). Drive or walk E E on road toward toward Cloquet Cloquet city city water supply supply tank tank on on hill. Pass low outcrops of vertical Thomson slate slate and and graywacke graywacke (Middle Precambrian: more are exposed (Middle exposed on on rise rise and and roadcuts roadcuts to to N.). At slope, go either RR or LL along along base of of slope slope to to outcrops outcrops N.). At slope, of basal Upper Precambrian quartzite and and conformably conformably overlying mafic, porphyritic basalt with small augite mafic, augite and and altered altered olivine olivine to rocks rocks on Lucille Island Island at at Grand Grand Portage. Portage. phenocrysts identical to Note pillows subtly outlined by small vesicles and and color color zones. zones. �—97-. -97- TO THE GUIDE TO THE PRECAMBRIAN PRECAMBRIAN ROCKS ROCKS OF NORTHWESTERN COOK COUNTY COUNTY AS EXPOSED ALONG ALONGTHE THE GUNFLINT GUNFLINT TRAIL AS EXPOSED Prepared by by Paul Paul W. \~. Weiblen Department of Geology and and Geophysics Geophysics University of Minnesota Hinnesota Minneapolis, Minnesota Minneapolis~ G. B. Horey G. B. Morey Minnesota Geological Survey Survey University of Minnesota Minnesota St. Paul, Minnesota '1. G. Mudrey H. G. Minnesota Geological Survey Survey University of of Minnesota Minnesota St. Paul, Paul, Minnesota �—98— -98- Geology of Northwestern Cook County, County, Minnesota INTRODUCTION An exceptionally complete complete Precambrian section is exposed in the vicinity of the the Cunf Gunflint County. lint Trail Trail in in northwestern northwestern Cook County. Rocks Precambrian age, age , represented by a volcanic Rocks of Early Precambrian succession and the the Saganaga Granite, are are unconformably unconformably overlain by by the the Middle Middle Precambrian Precambrian Animikie Animikie Group,coiLsisting Group, cOllsisting of of A low anglular unconformity the Rove Fotmations. Fo~ations. A the Gunflint and Rove separates strata from from the the nverlying f1verlying Puckwunge Puckwunge separates the t-1iddle Middle Precambrian strata Rocks Formation of Late Precambrian Precambrian age. age. The Logan Intrusive Intrusive Rocks and the Duluth Duluth Complex, Complex, which which intrude intrude and and truncate truncate the the Middle Middle Precambrian Precambrian the strata, strata, comprise comprise the the major major part part of of the the Upper Upper Precambrian Precambrian section. section. However, However, possible remnants remnants of the North Shore Volcanic Group occur at the top of Duluth Complex at Complex rocks. rocks. The geology of the area was summarized in 1959 by Grout and Because geologic mapping mapping since since 1962 has has considerably considerably reBecause revised the the geologic history of the the area, area, and because much of of this this work is is as yet unpublished, unpublished, aa comprehensive comprehensive summary summary is is presented here. This discussion is meant to to provide a framework for the the specific aspects of the the geology geology which which the the chosen chosen stops stops illustrate. illustrate. others. Lower Precambrian Introduction The Lower Precambrian rocks rocks in Cook County are the eastern extension of the Vermilion greenstone greenstone belt belt (Sims (Sims and and others, others, 1971, 1971, has shown that the district contains many in press). Gruner (1941) (1941) has major longitudinal longitudinal faults faults that that divide divide it it into into long long segments segments or or belts, belts, each with distinct distinct characteristics. characteristics. They cannot be connected stratigraphically with each other in in any any simple simple way. way. One segment segment extends from from Gabimichigami Lake Lake across across the the Gunflint Gunflint Trail Trail (Fig. (Fig. 1). 1). It It includes aa metavolcanic assemblage consisting consisting of of metabasalt, metabasalt, metaandesite, tuff, hornblende andesite porphyry, porphyry, metaandesite, agglomerate and tuff, metagraywacke and and slate. the Saganaga Saganaga and intercalated metagraywacke To the north, north, the slate. To Granite has has intruded and and metamorphosed metamorphosed the thevolcanic volcanicsuccession; succession; it it is overlaintotothe thesouth south youngerrocks rocksofofMiddle Hiddleand andLate LatePrecambrian Precambrian is overlain bybyyounger age. �-99—99— The metavolcanic assemblage constitutes constitutes aa homoclinal homoclinal sequence sequence towardwhat whatGruner Grtinerinferred inferredtoto be be the the axis \"hich dips dips southward southward toward which Pillow—topdirections directions of aa southeastward—plunging of southeastward-plunging synclinorium. Pillow-top indicate that thatthe thesequence sequence alsO also becomes becomes stratigraphically stratigraphically younger younger the south. However, However, some pillows pillm"s top top to to the the north north indicating indicating to the folding, but but poor exposure exposure precludes precludes detailed evaluation of the folding, structure. wasthought thoughttoto separate separate the Previously, an an unconformity unconformity was the mafic and rocks; thus thus the thesuccession successionwas was subdivided subdivided mafic and more morefelsic felsic rocks; metabasaltswere werereferred referredtoto as as part part of into two two formations. formations. The The metabasalts of the Ely whereasthe themore morefelsic felsicvolcanic volcanic and andclastic clastic the Ely Greenstone Greenstone whereas rocks \Vere placed placed within within the theKnife KnifeLake LakeGroup. Group. Recent mapping mapping rocks were (Fiorey andothers, others, 19(9) 1969) has has sho\Vn shownthese theset\VO twolithologies lithologies to (i-iorey and to be be other parts parts of district gradational, and gradational, an(~ nappin mapping in other of the the Vernilion Vermilion district (lorey 1968; 1971, (~Iorey and and others, others,1970; 1970;Green, Green, 1970; 107(); Sims Sims and and others, others, 1968; 1971, in press) has shown shm.;n that that specific specific rock rock types types are are not not diagnostic diagnostic particular strati~raphic stratigraphichorizon horizon—i.e., any particular - i.e., lithologic lithologic units units therefore no formal are formal stratigraphic stratigraphic are not not time-stratigraphic time—stratigraphic units units -— therefore used for for these nomenclature is is now no\V used these rocks. rocks. of Descriptive Stratigraphy Descriptive Stratigraphy Volcanogenic Rocks Volcano;;enic Detailed mapping in the Long Island Lake quadrangle, Detailed mappinR in the Lonfl Island Lake quadrangle, reconnaissance reconnaissance as far west \"est as Va>' Fay Lake Lake in the the Cillis GillisLake Lake quadrangle, quadrangle, and and as far Gruner's area have have indicated that the thevolcanigenic volcani8enicsequence sequence Grunerts Hark work in in the area indicated that of approximately 60 percent inetabasalt metabasalt and fragconsists of and associated frag— mental rocks, 30 percent netnandesitic agglomerate, conglomerate, tuff, mental rocks, 30 percent metaandesitic agglomerate, conglomerate, tuff, and flows, and and slate. slate. and flows, and 10 10 percent intercalated intercalatednetagraywacice metagraywacke and mappin rr.appin,~ IjuLLaaLs.st±1psis!; percent ofofthe :i.eta_~~i1.sa-h.~~_?.~(LQ.~sg ..0at~_~.t ro_c±,-s_: Over 95 95 percent themeta— metabasalt is basalt is extrusive; extrusive; there thereare areseveral severaltabular tabularbodies bodiesofofmetadiabase, metadiabase, rLall to too small at aa scale of to show shmv at of 1:24,000. 1:24,000. Nany Manyofof the the metabasalts exhibit pillow exhibit pillm-J structure. The pillows pillo\Vs are are as as much as as three three feet feet in in diameter, but many diameter, manyhave havebeen beendeformed deformedsosothat that they they are are now no\V two two or three three times times as as long lonf, as as they they are are wide. \"ide. Chilled rinds rindsare arewell—developed 1vell-developed and as much much I1Sasone-half inch thick: in and are are as one—half inch thick:typically typicallythey theyare are lighter lighter in color than interiors. Inter-pillm" color than the the dark dar:( green green or ordark darkgreenish—gray fJreenish-Rray interiors. Inter—pillow material locally material locally is iswell welldeveloped developed and and co!nists con~ists of of tuffaceous tuffaceous material material cEtert, chert, or or pillow—rind pillm,,-rind fragments. fragments. Themetabnsalts metaasalts shot: intense retrograde retrograde alteration; alteration; many The shoH intense many thin thin sections sections are nre nearly nearlyopaque. opaque. Recognizable Recognizable minerals include minerals includerelict relict augite augite and anu calcic cnlcic plagioclaso, plagioclase, and and secondary secondary sodic sodic plagioclase, plagioclase, actinolice, chlorite, actinolite, chlorite, epu'ote, epidote, calcite, calcite,quartz, quartz,leucoxene, leucoxene, and opaques. Property of oj C. C. Patrick Ervin Ervi n �—100— -100- The tabular bodies of metadiabase have have aa relict relict poikilitic poikilitic texture texture -— actinolite pseudomorphs after augite -— and a mineralogy much like that that of of the the metabasalts. Thin beds and mineralogically immature immature meta— metabeds of texturally and clastic rocks are locally intercalated intercalated with the the metabasalt. metabasalt. Several beds are crudely graded and have a texture suggestive of a pyroclastic a pyroclastic Most layers, layers, however, however, appear to be epiclastic with with pebblepebble— Most to be origin. to silt-size silt—size clasts of locally derived to derived metadiabase metadiabase in in aa finer—grained finer-grained matrix of chert, chert, plagioclase, plagioclase, hornblende, hornblende, chlorite, chlorite, and and sericite. sericite. Hornblende andesite prophyry and and related related rocks: rocks: There are two two types of hornblende-biotite hornblende—biotlte phenocryst bearing types bearing rocks. rocks. Both are light light greenish—gray greenish-gray in in color. color. One type type lacks lacks internal internal structure. structure. The ground plagioclase, lesser biotite, opaques opaques and and mass consists of plagioclase, lesser amounts amounts of biotite, rare secondary calcite. calcite. The other type type has similar rare quartz and secondary phenocryst and groundmass mineralogy mineralogy but but is is composed composed of of angular angular to to rounded, cobble—s,'ze clasts and and is is inferred inferred to to be be aa volcanic volcanic breccia rounded, cobble-s~ze clasts or agglomerate. Metagraywacke and and slate: slate: In the vicinity of Fay Fay Lake in in the the Gillis Lake quadrangle, quadrangle, the volcanic rocks inter— Gillis the felsic felsic volcanic rocks apparently interfinger, meta— finger, or are infolded with agglomerate agglomerate or conglomerate, conglomerate, metagraywacke, and and slate. slate. Amphibolites: The metamorphic effects of of the the Saganaga Saganaga Granite Granite metabasalts becomes becomes apparent apparent only only within within several several hundred hundred feet feet on the the metabasalts of the contact. contact. Away from from the the contact, contact, the the metabasalt contains incipient hornblende; hornblende; nearer the becomes granular granular incipient the contact, contact, the the rock rock becomes and consists of hornblende and and and calcic calcic plagioclase; plagioclase; at at the the contact, contact, the rock is strongly strongly schistose. schistose. The the The schistosity parallels the granite contact, contact, as does does a well—developed well-developed foliation foliation within within the the granite. granite. Saganaga Granite General General Statement: Statement: The Saganaga Saeanaga Granite Granite (A. (A. Winchell, Hinchell, 1888) 1888) (Fig. 1) 1) is is aa late-kinematic late—kinematic composite intrusion emplaced (Fig. arouno emplaced around 2,700 m.y. m.y. ago in older volcanic rocks rocks and and the the Northern Northern Light Light Gneiss. Gneiss. Inch— Inch- to foot—sized foot-sized inclusions inclusions of of both both rock rock types found in in the the types are are found granite. granite. The main phase, phase, which comprises comprises 85 85 percent of the the outcrop outcrop percent of area, "quartz—eye hornblende—bjotjte area, is is aa medium—graineci medium-grained "quartz-eye" hornblende-biotite tonalite. tonalite. Other Other phases phases include: include: 1) border phase, phase, found found along aloTIC' the the southern southern 1) a border margin of the the batholith margin of batholith and and along along the the base base of of a roof roof"pendant of pendant of the the Northern Northern Light Light Gneiss; Gneiss; 2) 2) aa younger younger fine—grained fine-grained tonali te which ,vhich tonalite lacks conspicuous lacks conspicuous tquartz_eyes?T; "quartz-eyes"; 3) 3) aa coarse—grained coarse-grained biotite—fluorite— biotite-fluoritebearing bearing granodiorite; granodiorite; and and 4) 4) aa quartz—feldspar quartz-feldspar pegnatite pegmatite which which occurs occurs as veinlets as three three feet as veinlets as as much much as feet wide wide in in the main phase. the main phase. �—101--101- Hain Phase: This "quartz eye"-bearing :iain This phase phaseisis aa "quartz eye"bearing tonalite containing 20 20 percent 1-6 percent percent percent quartz, quartz, 60 percent oligoclase, 1—6 microcline, up to 8 percent biotite, 6 percent hornblende, and microcline, to 8 6 percent hornblende, and 1-4 epidote. Other minerals include clino—pyroxene, clino-pyroxene, 1—4 percent epidote. muscovite, chlorite, muscovite, chlorite, sphene, sphene, apatite, apatite, zircon, zircon, calcite calcite and and opaque opaque oxides. Cataclastic deformation of the the tonalite tonalite· is is indicated indicated by by strong undulose extinction and granulation of strong of the the quartz quartz and and abunabundant mortar and mylonite mylonite zones. zones. dant Phase: The border phase is is aa quartz quartz bearing, bearing, hornblende hornblende Border Phase: diorite that that is gradational with the the "quartz—eye" "quartz-eye" tonalite. tonalite. This diorite is well developed along the phase is the southern southern edge edge of of the the batholith batholith in in feet wide, the is as much as as 1000 feet the Long Long Island Island Lake Lake quadrangle quadrangle where it is and Moose Bay area in Ontario where and in the Noose ,,,here it it is is found found along along the the roof pendant of the the Northern Northern Light Light Gneiss. Gneiss. Foliations Foliations underside of a roof rock are everywhere similar, in and in in the the country rock everYWhere similar, in the the border phase and and it is inferred that that the the border phase phase was was produced produced by by partial partial assimilation country rocks of mafic composition composition (Halford, (Halford, 1969). 1969). assimilation of of country Younger Tonalite: Tonalite: A A tonalite characterized characterized by by aa lack lack of of "quartz—eyes," aa fine—grained "quartz-eyes," fine-grained equigranular texture, texture, and and abundant abundant hornblende and biotite biotite crops out in the the Horseshoe Horseshoe Island Island area area of of hornblende crops out Saganaga Lake. Lake. This tonalite tonalite is is not not sheared sheared which ,,,nich indicates indicates that that it the main phase. phase. it was was emplaced after deformation of the Internal Structure: Structure: Linear structural elements marked by an an alignment "quartz eyes" and/or elongate hornblende grains grains are are alignment of 'quartz in the the border border phase. phase. Lineations in in the the border border well developed only in phase plunge gently southeastward. southeastward. In contrast, contrast, lineations in in the the main phase are are random. random. Structure All the minor structural elements elements in in the pre—Saganaga rocks rocks in in All the minor the pre-Saganaga the plunging the Long Long Island Island Lake Lake quadrangle reflect a southeasterly plunging synclinorium. synclinorium. In northwesterly-trending fault fault in addition, addition, a major, major, northwesterly—trending (Lookout Fault, Sims Sims and others, (Lookout Fault, others, 1969) 1969) separates rocks rocks showing showing no no metamorphic effect of of the the Saganaga SaganagaGranite Granitefrorn.those from;those that that do. do. The metamorphic effect fault is is marked marked by by aa topographic low fault 1m" developed in in aa breccia breccia zone zone as much as 50 feet as feet wide. wide. The breccia consists consists of highly sheared metabasalt in aa matrix of massive quartz quartz and and calcite. calcite. Fracture cleavage is is present present throughout the cleavage the area and and commonly commonly parallels parallels the the Fault. Southeastward Lookout Fault. formed by by bedding/ bedding/ Southeastward plunging plunging lineations lineations formed cleavage intersections developed. These lineations intersections are locally well developed. are consistent are consistent in orientation with mineral lineations lineations developed developed in in the amphibolites itself; obviously obviously all all of of these these the amphibolites and in the granite itself; structures tectonic event. event. structures are related to the same tectonic �—102— -102- related to to the the final final The Lookout Fault also apparently was related the Saganaga Saganaga Granite. Granite. Previously it was assumed emplacement of the (Grout, (Grout, 1936) 1936) that that the the granite granite was was emplaced emplaced into into its its present present position via a west\vard westward rotation rotation of about about 700 70° about about aa north—south north-south that the the eastern part part of of the the granite granite and and the the axis. This implies that represent roots roots of the Light Gneiss Gneiss represent the batliolith batholith that thatwere wereonce once Northern Light However,Goldich Goldichand andothers others (1968) as much as 25 miles deep. However, (1968) have have as much as 25 miles deep. that the granite was originally intruded at a shallow depth— suggested that the granite was at a depthan observation more consistent consistent with with the the regional regional Abukurna Abukuma greenschist facies (Mudrey, 1969) to its present present facies metamorphism metamorphism (Mudrey, 1969) -— and brought to relative position position by by dominantly vertical movements along several relative several westerly-trending border faults. faults. The granite—greenstone granite-greenstone contact contact westerly—trending border mapped by Harris (1968) (1968) on the the north shore shore of of Saganaga Saganaga Lake Lake was was interpreted to be the interpreted to be the northern border fault, fault, and it is here inferred inferred that the that the Lookout Fault is is its its southern southern analog. analog. The block block was was emplaced emplaced during during E8~ly E:ly Precambrian The Precambrian time, time, in in as as much as as detritus now found found in the the Knife Knife Lake Lake Group Group of of Gruner Gruner (1941) (19/+1) was derived there has derived from Granite. Although from the Saganaga Saganaga Granite. Although there has been been later t.,as movement on the the Lookout Fault, Fault, it it is is dominantly dominantly aa Lower Lower Precambrian Precambrian structure. MIDDLE ~UDDLE PRECAMBRIAN PRECANBRI!u~ Introduction Gunflint and and '\ove Rove Formations The Animikie Groun Group consisting of the the Gunflint comprises These rocks the entire this area. comprises the entire Middle :oliddle Precanibrian Precambrian inin this area. These rocks unconformably overlie Lower Lm.,er Precambrian rocks rocks and and in in turn turn are are intruded intruded and truncated truncated by gabbroic rocks rocks of Niddle i'·liddle Keweenawan KeweenaT,oJan age. age. The time time of Animilcie !mimikie deposition deposition has has not not been completely completely documented. documented. Hurley and iron— that deposition of the and others (1962) have have suggested suggested that the ironothers (1962) 6 io6 Although this years. formation around 1,900 1,900 ±± 200 xx 10 this K—A K-A formation occurred occurred around age includes age includes an an arbitrary and perhaps unnecessary unnecessary correction correction of of 20 20 percent assumed assumed argon argon loss, loss, it it nevertheless nevertheless has has been been widely widely quoted quoted In contrast, contrast, Faure Faure and and Kovacg Kovac (1969) in the literature. In (1969) obtained obtained aa Rb-Sr age of 1,685 ±± 24 x 10 years years from from the the Rb—Sr tvhole-rock whole—rock isochron age Gunflint Iron—formation. Iron-formation. They interpret interpret this this age age to to be be the the time time of diagenesis, however, similartotoother otherages agesobtained obtainedfrom from rocks rocks however,itit is similar Misra and Faure metamorphosed during the the Penokean orogeny. orogeny. Later Nisra Faure (1970) Iron-formation (1970) showed showed that that argillite argillite from from thr2e three Gunflint Gunflint Iron—formation . .1.7 localities Rb-Sr ages ages that that decrease from from "'.... 1.7 b.y. at the eastern localities have have Rb—Sr end to to 1.2 b.y. b.y. near... near ... the the western.. \vestern ... variation of of . this systematic variation apparent ages may be related to metamorphic effects caused by Keweenawan apparent ages may related to effects caused by Keweenawan . . ".'. Thus there diabase sills. sills •••• there is uriequivical depositional age for for is no no unequivical these rocks. b.y. at the eastern . �-103—10 3— Descriptive Stratigraphy Gunflint Iron—formation Iron-formation The Gunflint Iron—fori:iation crops out out in in aa northeasterly— Iron-formation crops northeasterlytrending belt Superior to trending belt that thatextends extendsfrom fromThunder Thunder Bay Bay on on Lake Lake Superior a point it is point in inMinnesota Minnesota 12 12 miles miles west west of Gunflint Gunflint Lake Lake where where it is truncated by the truncated the Duluth Duluth Complex. Complex. In Canada Canada the iron—formation is In the iron-formation is only slightly, slightly, if at at aF., al:_, metamorphosed and consists of silica, much of of which \"hich is is chalcedonic, chalcedonic, Consequently, Goodwin iron oxides, oxides, iron carbonates, iron carbonates, and and greenalite. greena1ite. Consequently, (1956) recognized six six sedimentary sedimentary facies facies which which serve serve to (1956) recognized to subdivide In Minnesota theoriginal oriina1 the iron-formation fourmembers. members. In Hinnesota the iron—formation into into four nature of metamorphism by the nature of the iron-formation is is -obscured obscured by TIetamorphism the the iron—formation Duluth Complex. The carbonates and greenalite are replaced by Complex. carbonates and greenalite are replaced by amphibole, amphibole, pyroxene, fayalite, and locally by garnet and pyroxene, fayalite, and and other silicates. In In addition, addition, many of the the small—scale small-scale sedimentary sedimentary textures textures have have been been almost completely completely destroyed; destroyed; however larger larger structures, structures, and especially complex bedding bedding relationships relationships are are still still preserved. preserved. Therefore the the four—fold nomenclatural nomenclatural scheme -— originally four-fold in the the Biwabik Biwabik originally outlined in Iron-formation (Wolff, (Holff, 1917) 1917) and and later later extended extended to to the the Gunflint Gunflint Iron— IronIron—formation retained by Morey and others formation (l3roderick, (Broderick, 1920) by 1'1orey and (1969) others (1969) 1920) -— ,vas was retained Accordingly, four because it it emphasizes various bedding aspects. aspects. Accordingly, members are recognized; members recognized; Lower Cherty, Cherty, Lower Lower Slaty, Slaty, Upper Upper Cherty, Cherty, Slaty. Although the do not and Upper Upper Slaty. the boundaries of of these these members members do coincide coincide witll those recognized recognized by by Goodwin Goodwin (1956), (1956) , the with those the two two schemes schemes can be equated equated \vith withonly onlyslight slight difficulty. difficulty. Lo\ver ChertLMemhe.r: Cherty Hember: Lower The Lo,ver is isthin, The Lower Cherty ChtertyNember Member thin, ranging in thickness Feldspathic quartzite quartzite that thickness from from 15 15 to to 45 45 feet. that contains contains feet. Feldspathic granite cobblesisis present present locally locally at at Lie granite and and greenstone greenstone cobbles the base base of of the the formation; these beds beds are are equivalent equivalenttotoGoodwin's CoodHin' s basal basalconglomerate conglomerate formation; member. AA persistent persistent magnetite-rich, magnetite—rich,silicate-bearing silicate—bearingunit unit five five to Feet thick occurs 15 feet occurs within IVithin this thismember member and an excellent and serves serves as as an marker—horizon. marl(er-horizon. :Iost commonly it liesdirectly directly uponbasement basement rocks, rocks, :c'st commonly it lies upon but loc<llly locaii.v it it overlies overlies either eitherthe thefeldspathic feldspathicqtiartzite quartziteorora chert— a chertcemented fragr.ents of cemented conglomerate conglomerate containing contctininr, frctgments algal structllres; in of algal structures; itit in is overlain overlainbyhya massive, a massive,chert—rich, chert-rich,magnetite—poor magnetite,-poor unit about about turn is 15 feet thick. 15 feet thick. ' \ Lower-,:,?-latY---l~~emher: Slaty Member: This This member memberisis8080toto 95 95 feet feet thick. The Lower lOHennost, magnetite-free 10 is a ablack, black,thin—bedded thin-bedded lowermost, nearly nearly magnetite—freo 10feet feet is argillitecomposed conlposcd dominantly dominantly of derived material. It argillite of volcanically volcanically derived It is equivalent equivalent to to the the intermediate InterPlcdi"tc slate slate on on the the 'esahi ;lesabi range range and and to to is the lower the lOh·er tuffaccous tuffaceous shale shale f,icies fD-cLcs ininCanada. l,<ln"da. The beds beds immediately aove the Intermediate .:1iJove tile IntenneJiate slate massive and clierty cherty and and resemble resemble slate are massive the upper upor aert the part of of the the lower LOIver Cherty ;'[e1l1her. This unit passes passes abruptly ahruptly Chcrty :-;ember. ipuird into cherty uith spilrse sparse inagnetite interuTl\!;]rd into cherty si.licate-hci1rini; beds ':lith magnetite inters iJ.icate— carjn beds calated calateJ with \vi til aa few fe\\' thinly—laminated tilinly-la:ninated silicate—rich silicate-rich beds. heels. The The remaining 50 feet is is ai1 thiin—bndciel laminatedrock rockcontaining containingvarious varioussilicates silicates thin-beJded totolill\linated and percent magnetite. and Cro from 20 2C to 35 35 percent map;netite. AA few fe'" cherty-silicate cherty—silicate beds, definitely amount are elefillitely subordinate subordinate in in illllount this interval. interval. are intercalated intercalated in in this �—104— -104- Upper Cherty Cherty Member: Member: There is is a complete complete gradation gradation between between The Upper Cherty the Lower Slaty and and Upper Upper Cherty Cherty Members. Members. Cherty Member, Member, the The lower as defined, is approximately 50 50 feet thick. thick. The 10loJer as presently defined, cherty layers part to lenticular lenticular cherty layers part consists of irregularly bedded to intercalated with thinly—laminated thinly-laminated silicate—rich silicate-rich layers layers that that increase increase in abundance abundance upward. upward. Thin irregular layers of magnetite are are common common in in the cherty beds near the the bottom of of the the member, member, but but become become less less abundant upward. upward. The top top of the the member—equivalent member-equivalent to to Goodwin's Goodwin's abundant upper algal chert facies—is facies-is characterized characterized by by several granular granular chert conglomerate fragments, fragments, chert beds beds containing algal structures, conglomerate and abundant magnetite. Upper Member: The Upper Slaty Slaty Member is is approximately approximately Upper Slaty S1ay Member: Thick lenticular chert chert beds beds with disseminated disseminated few tens tens of of feet, feet, but magnetite characterize characterize the the lower lower few but most most of of the the member consists consists of a thin—bedded thin-bedded to to laminated laminated quartz—silicate quartz-silicate rock rock thinly laminated layersofofgraphitir:: graphiticargillite, argillite, interbedded with with thinly laminated layers and pure chert. chert. The and one onetoto two twoinch inchthick thick beds bedsofof relatively relatively pure upper 10 feet feet is nearly magnetite free free and and consists consists of of limestone limestone and chert interbedded interbedded with with argillite. argillite. 150 feet thick. thick. 150 Rove Formation Rove Formation gradationally overlies The Rove overlies the the Cunflint Gunflint Iron— Ironformation and is intruded by Logan Intrusive formation Intrusive Rocks Rocks and and truncated truncated detailed description of Duluth Complex. Complex. A A detailed of the the formation formation by the Duluth is presented is presentedby byMorey Morey (1969). (1969). In In the the Long Long Island Island Lake, Lake, Gunflint Gunflint Lake, and Hungary Hungary Jack formation Lake, Southlake, and Jack Lake Lake quadrangles, quadrangles, the formation is characterized by by intercalated black to to grayish grayish black, black, locally locally is characterized intercalated black carbonaceous argillaceoussiltstone siltstone and fine-grained carbonaceousargillite, argillite, argillaceous and fine—grained gray\oJacke. In the silt silt sandstone beds becomecoarse— coarsegraywacke. In general the andand sandstone beds become formation. In grained, thicker, thicker, and and more more abundant abundant upward in the formation. tn are several addition, there are several lenses lenses and and irregular irregular bodies bodies of of limelimeaddition, there dolomite, and chert and a number of of calcite—dolomite calcite-dolomite con— constone, dolomite, cretions of of various shapes and sizes, similar cretions similar to to those those described described in the the formation by by Tanton (1931) (1931) and and Moarhouse Moorhouse (1963) (1963) scattered scattered near the the base base of the the formation. formation. Horey deep Morey(1969) (1969)has hassuggested suggestedthat thatdeposition depositionstarted started in aa deep basin in inwhich which fine—grained fine-grained sediment sediment accumulated accumulated under under reducing reducing conditions. The The siltstone siltstone and conditions. andsandstone sandstonebeds beds contain containmany many primary primary sedimentary structures indicative indicative of of turbidite sedimentary structures turbidite deposition. deposition. There is of this this type is also also evidence evidence of of an an increase increase infrequency infrequency of type of of deposition upward in in the the section. section. The graY\oJackes contain abundant abundant framework framework The graywackes grains grains of of quartz, quartz, feldspar feldspar and and Igranitici "granitic"rock rockfragments fragments indicative indicative of a granitic source area. source area. Sedimentary structures including cross— crossbedding and various kinds of of sole sole marks marks indicate indicate that that sediment sediment transport dominantly dominantly was \oJas from from north north to to south. south. These observations observations and the gray\oJacke mineralogy the the graywacke mineralogyled led Horey Morey(1969) (1969)toto conclude concludethat that the source terrane now exposednorth north of of the source area area was was the the Lower Lower Precambrian Precambrian terrane now exposed the outcrdp area of outcrop of the theRove Rove Formation. Formation. �—105— -105- Structure The Animikie SE Animikie strata strata form form aa homocline homocline that that dips dips 10°-15° 1O—l5° SE except where intrusive bodies and and secondary secondary structures structures have have disdisFor example, example, complex folding torted the beds. For torted or disturbed the commonly zones adjacent to to many of of the the Logan Logan commonly occurs occurs in narrow zones Intrusive is most likely related related to to the the forceful forceful ememIntrusive Rocks Rocks and and is the sills into into restricted restricted space. space. There is aa fairly fairly placement of the regular as much as 600 60° near the the Duluth Duluth Complex. Complex. regular increase increase in dip dip to as is most likely likely pre—Duluth pre-Duluth Complex Complex in in age. age. However, this structure is However, in the the Animikie Animikie strata strata inakestecognition makestEcognition of Lack of marker beds in faults northwesterly- and and northerly— northerlyfaults difficult; difficult; however, however, a number of northwesterly— trending faults have been mapped. mapped. trending faults faults have displacements displacements of of less less than than 50 50 feet; feet; however, however, Most faults the Lookout Lookout fault has aa displacement displacement in the the iron—formation iron-formation of fault has of at at least least 200 200 feet. feet. All All faults faults so sofar farrecognized recognizeddisplace displaceLogan Logan Intrusive rocks, Intrusive Complex; thus thus rocks, but but none extend into the Duluth Complex; movement apparently apparently occurred in Middle Middle Keweenawan Keweenawan time time prior prior to to movement of the the Duluth Duluth Complex. Complex. The fault fault pattern is similar emplacement of to 1960; Goodwin, Goodwin, 1960) 1960) near ,.,hat what can to that that in Canada (Moorhouse, (Moorhouse, 1960; be inferred inferred to to be the the northern the Lake northern hinge hinge of of the Lake Superior syncline. syncline. TIlis structure must have formed at least in prior to emplacement part prior to emp1acenen.t This must at least in of the Duluth Duluth Complex. Complex. Hovement during Keweenawan Keweenawan time time duplicates duplicates Movement on the Lookout fault during iron—formationwest westofofthe theGunflint Gunflint Trail, Trail, and the iron-formation and aanortherly— northerlytrending segment of fault separates separatesthe the iron-formation into two two trending segment of the the fault iron—Formation structurally distinct terranes. structurally terranes. East of the Gunflint Trail, Trail, the the rocks dip dip gently southward; southward; accordingly the outcrop area Animikie rocks of relatively wide most of of the apparent of the the iron—formation iron-formation isis relatively wide and and most apparent irregularities mappattern patternresult result fromthe the super-position irregularities ininthethemap from super—position of aa rugged rugged topography on gently—dipping gently-dipping strata. strata. The south side side of fault is is upthrown, upthrown, and and the the Anirnikie Animikie strata on this of the the Lookout fault side outcrop belt. belt. side dip dip steeply and thus form a narrow outcrop A also can can be be recognized. recognized. Just A number of smaller structures also east of Gunflint Trail Trail the the iron—formation iron-formation and of the Gunflint andthe thesills sills are folded into anticline with with a a steeply steeply into a southeasterly plunging anticline dipping north limb limb and a gently dipping dipping south south limb. limb. This structure post-Logan in age has an anticlinal axis which which is obviously post—Logan into the the trace trace of of the the Lookout Lookout Fault. Fault. projects into Metamorphism i'letamorphism In the the Animikie Animikie rocks no textural or or atineralogic mineralogic In rocksthere there is is no evidence for aapervassive metamorphism evidence pervassiveregional regional metamorphism beyond beyond minor minor of the the clay—size clay-size detritral frac'don. The The obvious recrystallization of detritral. fraction. the Animikie strata are are associated in the Animikie strata associated with with the the metamorphic effects in emplacement of the Duluth Complex and Logan Intrusive Rocks of Middle Ke,,,eenawan Keweenawan age. �—106— -106- The contact contact aureole aureole of of the the Duluth Complex has has not been studied in detail in in the the Gunflint Gunflint Trail Trail Area. Area. Preliminary work in in the the Gunflint Iron—formation shows there are a number of metamorphic Iron-formation there are a of facies similar to those those described from from the the Biwabik Bh\Tabik Iron—formation Iron-formation facies by French (1968) (1968) and and Bonnichsen Bonnichsen (1969). (1969). Unmetamorphosed iron— ironformation like that described by Goodwin Good\vin (1956) (1956) is is found found in in Minnesota Hinnesota lint and North Lakes. only in in aa small small area area between between Gunf Gunflint Lakes. There the the iron-formation consists of chert, chert, iron iron carbonates, carbonates, greenalite, greenalite, abundant abundant iron—formation amounts of finely disseminated hematite, and and traces traces of of magnetite. amounts However, lint Lake, Lake, the the iron-formation iron—formation has has been been metamorphosed metamorphosed However, west of of Gunf Gunflint and three three metamorphic zones zones have been distinguished distinguished by hy changes changes in in mineralogy along tI tie strike of the the formation formation toward tm'Jard the the Duluth Duluth Complex. Complex. Zone 1, 1, or slightly metamorphosed iron—formation, iron-formation, occurs occurs in in the the area immediately west of Gunflint Lake. It consists of quartz, iron of Gunflint Lake. It consists quartz, iron carbonates, greenalite, minnesotaite, and carbonates, and stilpnomelane. stilpnomelane. FinelyFinely— divided hematite hematite occurs occurs in the divided the east east end of the zone, ZOne, hut but disappears mid—way in mid-way in it. it. Disseminated Disseminated and and interlocking grains of magnetite are are abundant, especially as abundant, as rims rims around around granules. granules. This part of of the the iron— i ronformation is much like like that that described described by by French French (1968) (1968) in in 'unmetaniorphosed "unmetamorphosed" formation is Biwabik Iron—formation. Iron-formation. Zone 2, moderately metamorphosed iron—formation, Zone 2, or moderately iron-formation, is is about about 1.2 miles wide and extends to to within \vithin 0.3 0.3 miles miles of of the the Duluth Duluth Complex. Complex. GruneriteGrunerite— cummingtonite, hornblende and actinolite, cummingtonite, actinolite, as well as as quartz and magnetite map,netite As in characterize this this zone. zone. As in zone zone 1, 1, much of the the magnetite is is between hetHeen 0.002 and in diameter; and 0.02 0.02 mm in diameter; a a size—range size-range similar to to that that observed in various other other Lake Lake Superior Superioriron—formations. iron-formations. S:'1all-scale pre-metAmorphic Small—scale pre—metamorphic sedimentary structures such such as as granules granules and andoolites oolites are sedimentary structures are partly partly destroyed, destroyed, but primarystructures structuresand andbeddinr, bedding featuresarearelittle little but larger—scale larger-scale primary features affected. Zone 3, or orhighly highlymetamorpl-iosed metan,orphosed iron-formation, iron—formation,occurs occurs adjacent to the and is is characterized the Duluth Duluth Complex Complex and characterizedby bya awholly ",hollymetamorphic metamorphic fabric. The The rock composed chiefly quartz, magnetite, magnetite,iron—rich iron-rich fabric. rock is is composed chiefly of quartz, euliedraloror suhl1edral subliedral grains pyroxenes, and Very commonly, commonly, eultedral (.~rains pyroxenes, and fayalite. fayalite. Very of are poikilitically poikilitically enclosed 'Tithin large large silicate silicate grains; of magnetite magnetite are Ptlclose.d \orithin (~rains; they are of of essentially they are essentially the the same Si1Iile size size as in inthe thelower lOHer grade grade rocks. rocks. However a significantpart partofoftile themagnetite ragnetite is is extensively Hmvever a significant extensively recrystallized, recrystallized, .-:IS and grains as as aa millimeter and grains as much much <18 millimeter in in diameter diiwleter are arc concentrated concentrated along along Actinolite bedding planes. planes. Actinoli bedding te isiscommon cor:lJl1on in magnetite—rich rnagm~ti te-rich layers, layers, and and both prograde and retrograde cummingtonite :Ls±un(lantly oresent. In pro~rade and retro0rrtde cummin;>:tonitc is -:hundnntly nresent. In general this this zone zone is is very very similar similar to tothat thCltdescribed de~;cribedinin thetheJ)unka Dunka!~oiver Piver area on the the I'lesabi :olesabi range ranre by by Bonnichsen nonnicbsen (1)69). (l,)6~l). area on contactt aureole o0 fthe l\Tork on on the contnc theDuluth lluluthComplex Complex in Preliminary work RoveFormation Formationindicates indicates aa complex mixtureofof rock rock tyPes Rove complex mixture tyoes suggesting sUfgcstinR partial melting, and textural textural variations variations due to original original partial meltint, and and mineral mineral and due to Tue met"mop)!losed metamorphosedrocKs rocks :HC are netainorphilari. The inhornogenities and degree degree of of liletamorr1dsr,l. inhoinogenities and commonly layered Individual layers layers commonly layeredane! andhave haveil agranohlastic granoblastic texture. texture. Individual contain; 1) hiotite and contain; 1) cordierite corcJieriteand and Iyperstliene hynersthene with '\Tith minor loinor biotite and ilmenire, ilmenite, hiotite, and plagioclase, hiotite, and ilmanite, ilmenite, J) aur-ite, hypcrsthene, plagioclase, 3) augite, 2) hypersthene, plagioclase ±± minor olivine, ilmentte, or 1+) 4) hvperstliene, plagioclase olivine, biotite, biotite, and "at! ilmeni.t0., hypersthe.ne, contact plagioclase, K—feldspar, andbiotite. hiotite. Calcareous K-feldsrar, and Calcareous beds GeJs near ncar the contact have aa skarn—minera.logy consisting wollastonite,diopsi<le, diopside, tremolite, tremolite, have skarn-mineralogy consisting of of lvollastonitc, fromtile the contflct contact - and piece to and p:arn0.t. Away AI<7ay frol'l nnd from fron plnee to eLace Dlace and 8rossularite grossularite garnet. the the �—10 7— -107- distance varies varies from several tens to several hundreds of feet this from several feet — this distance or may most peletic rocks are are rich rich in in biotite, and and cordierite cordierite may mayor may not be present. present. The Logan Intrusive Intrusive Rocks Rocks also also have have metamorphosed metamorphosed the the Gunf Gunflint lint and Fonnations. The width of the metamorphic aureoles are related related and Rove Formations. to sill sill thicknesses and range from less than to than one foot foot to to more than than 30 30 Gunflint Iron—formation feet. In In the the Gunflint Iron-formation it is difficult difficult to to recognize recognize unique metamorphic assemblages mineral assemblages adjacent adjacent to to sills. sills. In zone 2, 2, mineral assemblages characteristic of zone 3 occurs in assemblages in aureoles around around the the sills. sills. Similarly In in zone zone 1, ininnesotaite, minnesotaite, which which is is characteristic characteristic of of zone 2 to the the sills. sills. metamorphism is found next to In the Rove Formation Fonnation thick thick sills have assemblages assemblages that that can can be be In the assigned to to the the pyroxene—hornfels pyroxene-hornfels facies facies whereas whereas thinner thinner sills sills have have assemblages characterisitc of the assemblages the hornblende—hornfels hornblende-hornfels facies. facies. Locally 1969) and chloritoid (Grant, andalusite (Morey, (Horey, 1969) (Grant, 1971) 1971) have have been been identified identified in certain beds. beds. UPPER PRECAMBRIAN Introduction In northeastern Minnesota two In two units are are recognized recognized in in the the Upper Upper Precambrian: the Lower Lower Keweenawan represented by the Puckwunge the Formation and and the Formation the Middle Keweenawan which consists consists of of the the Logan Logan Intrusive Intrusive Rocks, the the North Shore Volcanic Group (Green, Rocks, (Green, this this volume), and and the the Duluth Complex. Complex. Puckwunge Formation Fonnation The Puckwunge Formation consists consists of conglomerate conglomerate and and sandstone sandstone which unconformably North unconfonnably overlie the Rove Formation Fonnation and underlie the the North Shore Volcanic Group. The type locality was described by N. N. N. H. Winchell Winchell (1897) on Sec. 25, 25, T. T. 64 N., N., R. R. 33 B. E. where about about 18 18 (1897) on the the Stump Stump River in Sec. feet of section is feet is exposed. exposed. Exposures Exposures of of similar similarlithology lithologyare arefuund in frnind in the Grand Portage area (Grout (Grout and and others, 1959). 1959). the If these these isolated exposures are equivalent to to the the Sibley Sibley Series Series If in Canada (Tanton, in (Tanton, 1931) 1931) they represent represent aa period of sedimentation sedimentation around around period of 1376 *± 36 m.y. m.y. ago (Franklin Kustra, 1970) 1970) followed by possible possible 1376 (Franklin and Kustra, followed by uplift and erosion prior to to the the onset onset of of volcanic volcanic activity activity in in Middle Middle Keweenawan time. time. Intrusive Rocks Rocks Logan Intrusive The sills was was applied applied to intrusive The name name Logan Logan sills to tabular, tabular, diabase intrusive rocks in the Rove Formation rocks in the Rove Formation(Lawson,. (Lm"rson, 1893, 1893, p. 48). Similar intrusive p. 48). Similar intrusive in Animikie formations are Animikie and and Lower Lm.,rer Keweenawan Keweenawan formations are currently referred to as Logan referred to as Logan Intrusive Rocks. Rocks. As As now now defined, defined, they they include include sills and dikes of sills and dikes of diabasic diabasicgahhro gabbrowhich which range range in in measured measured age age from from rocks rocks 1300 n.y. ~300 m.y. (hanson (Hanson and and [alhotra, Ha1hotra, 1971) 1971) to to 963 963 m.y. m.y. (Franklin, (Franklin, cited cited Ln Hanless Wanless and In and others, others, 1970, 1970, p. 57). Thus the Logan Intrusive Rocks, Rocks, 57). Thus the Logan Intrusive p. �—108— -108- North Shore Shore Volcanic Group Group may may units of the Duluth Complex, Complex, and the the North have overlapping time—stratigraphic time-stratigraphic relationships. relationships. rocks In County the the predominant exposed volume volume of of the the Logan Logan rocks In Cook County from the sill-like, and and the the present sawtooth smvtooth topography topography results results from the is sill—like, The the inclined inclined sills sills and and Rove Rove Formation. Formation. The differential erosion of the feet sills and sills range range in in thickness thickness from from aa fe\v few feet feet to to over over aa thousand thousand feet and thick sills for several several miles. miles. In In three three sills can be mapped along strike for dimensions dimensions they they form form aa boXtVork boxwork pattern, pattern, their their emplacement emplacement having having been been ~ntro11ed fault plane connections connections between nntrolled by bedding, bedding, joint and possibly fault sills sills but but in in the the Grand Grand Portage Portage in in northeastern northeastern Cook Cook County County area area there there and extent are extent to to the the are major major northwest-trending northwest—trending dikes dikes comparable comparable in in size size and sills (Grout and Schwartz, Schwartz, 1933, P. p. 36—59). 36-59). sills (Grout Early detailed studies the Logan Intrusive studies of of the the petrogenesis petrogenesis of the Rocks were primarily restricted to to the the sill sill on on Pigeon Pigeon Point Point (Bayley, (Bayley, Reinvestigation of 1893; Daly, 1917; 1917; Grout Grout and and Schwartz, Sch\vartz, 1933). 1933). Reinvestigation of these these 1893; Daly, rocks currently in in progress follmving generalized descripdescriprocks is is currently progress and the the following textures, and is based the unpublished work of tion of of textures, and mineralogy mineralogy is based OIl on the of J. A. A. Grant, Grant, E. E. Mathez, Mathez, G. G. B. B. Morey, N. N. Mudrey and and P. P. Weiblen. Weiblen • J. margins, fine— .Texture: T exture: Rock types types include aphyric chilled margins, fine- to medium-grained diabase with ophitic clinopyroxene enclosing plagioclase, medium—grained diabase clinopyroxene enclosing plagioclase, porphyritic diabase with plagioclase plagioclase phenocrysts, phenocrysts, plagioclase plagioclase cumulates, cumulates, margins form sharp contacts and granophyre. Chilled margins contacts with with country country rocks. rocks. Clino— from fine fine to to medium medium toward toward the the center center of of sills. sills. ClinoDiabase grades from remains ophitic even though the the grain size changes changes and enclosed pyroxene remains plagioclase crystals rarely rarely exceed exceed 55 mm rom in in length. length. Plagioclase phenocrysts as 10 10 cms ems long long in in thick thick sills. sills. Diabasic crysts however however are as much as rocks with plagioclase plagioclase phenocrysts phenocrysts grade grade into into accumulations of essentially rocks with accumulations of Such accumulations are found coarse-grained plagioclase. Such found in in the the upper upper coarse—grained plagioclase. to the the parts of some large sills and their origin has been attributed to floating of of plagioclase (Grout floating (Grout and and Schwartz, Schwartz, 1933, 1933, p. p. 50). 50). M1neraly: Minor olivine is found Mineralogy: found in the the lower part of of some Plagioclase as small grains grains enclosed in Plagioclase both both as as phenocrysts phenocrysts and as pyroxene is generally highly highly seriticized. seriticized. Clinopyroxene is is altered altered to to amphibole within single oikocrysts. oikocrysts. The The remnant remnant pyroxene varies varies in composition from pigeonite through augite and has a mottled birefringence which resembles resembles that that of of the the complex complex lunar lunar pyroxenes. pyroxenes. Ilmenite lirnenite and and minor minor magnetite appear at distinct horizons in in some some sills. sills. The is The ilmenite is commonly skeletal. skeletal. Minor interstitial interstitial quartz quartz is is characteristic characteristic of of much of of the the diabase. diabase. Biotite is is ubiquitous ubiquitous in the diahase diabase and texturally appears to appears to be of both igneous and and metamorphic metamorphic origin. origin. Granophyric intergrowths the diabase \vhere intergrowths are are common common in in the the upper upper part part of of the where they impart a pink mottling which can can be be recognized recognized In in hand hand specimen. specimen. Separate impart a Separate o~currences of granophyre in mappable units are rare, rare, except for for the the occurrences Pigeon Point sill (Mudrey P~geon (Hudrey and and Weiblen, Weib1en, 1971). 1971). sills. sills. �-109—10 9— Structure: In Structure: the Duluth Complex truncates the the various various In plan view the along strike strike at at aa low low angle angle (Fig. (Fig. 3). 3). Where exposed, the the Logan sills along base of the Duluth Complex dips gently southward, southward, whereas whereas both both the dips gently country rocks rocks may may dip dip as as much much as as 60° 60° to the south. south. Logan sills and country Drilling in in the the vicinity vicinity of of the the contact contact indicates indicates that that the the base base of of the the Drilling Complex steepens to as much as 60° and levels levels off off to to about about 30° 30° 11 km. km. This structural structural configuration configuration is i down-dip (Johnson, 1970, 1970, p. p. 82). 82). This down—dip (Johnson, zuch like that Mancuso and Dolence (1970) the East much that described by Hancuso (1970) in the ?Iesabi district. They suggested that Mesabi district. that the the emplacement emplacement of the Duluth that area was in part controlled controlled by by aa pre—Complex pre-Complex structure. structure. Complex in that :1inor hydrothermal hydrothermal mineralization mineralization is is found found within within >inera1ization: Mineralization: Hinor the Logan Intrusive Rocks. The mineralization is probably similar similar to to the the important occurrences occurrences the Thunder Thunder Bay Bay silver silver deposits, deposits, but nO no commercially important Island where where aa shaft shaft was was sunk have been found found in in Minnesota. Minnesota. On Susie Island along a fracture zone filled with calcite-barite and lesser amounts along a fracture zone filled with calcite—barite and lesser amounts of of quartz, bornite, bornite, chalcocite, chalcocite, chalcopyrite, chalcopyrite, pyrite, pyrite, covellite covellite and and quartz, malacite, malacite, ore was recovered which which contained 6.22 percent copper and At Loon trace trace amounts of silver silver (Grout (Grout and 1933, p. p. 64). 64). At and Schwartz, Schwartz, 1933, Lake, R. S. Blankenburg Blankenburg has has investigated investigated aa prospect prospect in in aa quartz-calcite quartz—calcite Lake, vein that that contains arsenopyrite with minor cobalt cobalt (Johnson, (Johnson, 1968). 1968). Duluth Complex consists of a variety The Duluth Complex consists of a variety of of anorthositic, anorthositic, troctolitic, troctolitic, granodioritic, and and granophyric granophyric rocks rocks which which crop out in in an an arcuate arcuate belt belt granodioritic, crop out A brief review from the Gunflint Trail (Fig. (Fig. 1). 1). A review of of from Duluth Duluth to to east east of of the the early literature literature and and recent work up to to 1969 1969 is is given given by by Phinney Phinney the of subsequent subsequent mapping and study of of the northeastern (1969). The results results of limb of the the Complex Complex are are presented by by Nathan Nathan (1969), (1969), Morey Horey and and others (1969), Johnson Q970), and Davidson Davidson (1970). (1970). (1969), Johnson a970), and Nathan (1969) mapped aa layered series of sheet—like (1969) mapped sheet-like intrusions intrusions across across the Gunflint, and Hungry Hungry Jack Lake quadrangles (Fig. (Fig. 2). 2). To the Gunflint, South Lake and the west, west, in in the the the Long Island quadrangle, Nathan's Nathan's layered layered series series is is truncated the Tuscarora Intrusion and and other other associated associated rocks. rocks. truncated by by the Nathan Layered Series of Nathan The layered layered series series extends extends from from the the east east edge edge of of the the Hungry Hungry Jack The Jack Lake quadrangle across across the South Lake quadrangle and into into the Gunflint \vhere it it is is truncated truncated by by the the Tuscarora Tuscarora Intrusion. Intrusion. This Lake quadrangle where truncation is is marked by an irregular northwest trending trending scarp scarp (Fig. (Fig. 3). 3). truncation For the most part, part, the the series series consists consists of of aa sequence sequence of of conformable conformable For the most The sheets thicken sheets 15-25° to to the the south. south. The sheets having having a regional dip of 15—25° to west and and are are locally locally interrrupted interrrupted by by minor minor crosscutting stockstock— to the the west and dike—like dike-like bodies. bodies. On the the east side of the Hungry Jack Lake Lake quadrangle aa nortlnvest northwest trending trending fault fault offsets offsets the the series series with with an an unknown unknown quadrangle amount of amount of displacement, displacement, but but as as much much as as 140 140 feet feet of of vertical vertical displacement displacement northeast side side is is inferred of the the northeast inferred (Fig. (Fig. 3). 3). �-110—110— The series consists consists of of troctolitic, troctolitic, gabbroic, gabbroic, and and associated associated felsic rocks. rocks. Several of the major units represent represent uniqud unique occuroccurrences in the the Duluth Complex of oxide—rich rences oxide-rich gabbros gabbros and and two—pyroxene two-pyroxene gabbros. For the most part, fine—grained fine-grained rocks rocks are are not not chilled chilled margins but occur principally as or inclusions inclusions as separate intrusions intrusions or of mappable size. size. Planar orientation of of minerals is is common, cornman, indicating flow flow or or crystal crystal setting. setting. Differentiation resulting resulting from from these processes can be demonstrated within some some units, units, however however the the layered series does not form form aa regular regular stratigraphic stratigraphic sequence. sequence. Intrusive relationships for 27 different units were established for 27 different units established using cross-cutting cross—cutting structures, structs, fine—grained using fine-grainedmargins, margins, inclusions inclusions and thermal effects, effects, the latter being principally aa development development of dark clouded plagioclase near intrusive intrusive contacts, contacts, Nathan (1969, (1969, p. 99). On the basis of field field relationships, relationships, mineralogy, and and composicomposip. 99). tion, tion, Nathan concluded the 27 27 units could could be be combined combined into into eight eight cogenetic cogenetic groups. groups. Detailed rock descriptions and interpretations interpretations are are given given by by Nathan (1969, (1969, p. p. 38—185) 38-185) and are are summarized summarized here here using using his his nomennomenclature. The descriptive rock rock names have have several several textural textural prefixes prefixes clature. that that characterize the primary mineral assemblages. assemblages. AA size size classclassification for these rocks, rocks, based on on visually—estimated visually-estimated mean mean grain grain diameters, is: diameters, is: >10 mm, mm, very coarse—grained; coarse-grained; 4—10 4-10 mm, rnrn, coarse—grained; coarse-grained; 1—4 mm, mm, medium-grained; medium—grained; 1/2—1 1-4 1/2-1 mm, fine—grained; fine-grained; <1/2 <1/2 mm, mm, very very fine— fineA 'granular' grained. fabrics are are recognized. recognized. A "granular" rock has Four basic fabrics grained. If elongate elongate grains grains are present and only equidimensional equidimensiona1 minerals. minerals. If are randomly oriented, the the rock is is "decussate," "decussate," if if the the grains grains define define aligned, the a plane, plane, the rock rock is "foliated," "foliated," and and if if the the grains grains are are aligned, the rock l'lineated. II All rocks rocks are named by the the characterizing characterizing rock is is "lineated." primary mineral assemblage, assemblage, in in order order of of increasing increasing abundance; abundance; the the primary mineral assemblage assemblage refers refers to to early early crystallizing crystallizing phases phases in in Modes are indicated by sub— contrast to to late late interstitial interstitial phases. phases. Modes subIf scripts. If a significant part of the the primary assemblage assemblage was was scripts. transported in the magma the rock rock is is referred referred to to as as an an allocrystallate, allocrystallate, aa cumulate cumulate being a special special case case in in which gravity gravity settling settling has has occurred. occurred. being a Rocks formed formed by crystallization in in place place are are called called autocrystallates. autocrystallates. Rocks Thus a Subscripts are used to to indicate modal composition. composition. Thus a descriptive descriptive Subscripts fine— rock name name for for aa troctolite troctolite formed formed by by gravity gravity settling settling could could he he aa fineinter— grained foliated olivine20—plagioclase70 cumulate with minor 01ivinezo-plagioclase70 cumulate \-lith minor interstitital augite5and augitesand oxides5. oxides S • Group 11 da The oldest unit (da) (da) in in the the layered layered series series now now appears appears in the upper part of the the section section as as dilated dilated septa septa as as It is is 8a fine-grained fine—grained foliated much as as 200 200 feet feet thick. thick. It much cumulate with with minor minor pigeonite9 —plagioclase63 cumulate 01ivine~s-plagioclase63 pigeonite 9 olivine which are and aug1te are also also cumulus cumulus in in the the middle middle of of and aug?e the unit. unit. ~his unit grades grades into into aa 1,000 foot—thick foot-thick his unit the sheet of foliated augite15—pigeonite26 augiteIS-pigeonite26of medium-grained, medium—grained, foliated A very fine—grained piagioclase cumulate (dh). (dh). A fine-grained plagioclase59curnulate S9 ollvine1 —augite27—plagioclase61 rock olivine o-augite27-plagioclaseGl rock (dc) (de) occurs occurs as as sizes near the base of masses o9 ~f various shapes and Slzes of masses the layered layered series. series. Nathan speculated that that it might the represent aa chilled margin of the represent the Group 1 intrusive intrusive rocks. - db db dc de �-111—111— Groip22 Group dg the major part of of the group comprises comprises the major oxide—rich oxide-rich part the This group The main unit layered series. unit (dg) (dg) is a a coarse—grained coarse-grained series. —augite —olivine foliated ilmenite—titanomagnetite foliated ilmenite-titanOmagnetitell-augitel~-olivineI4­ plagioclase cumulate. Within tff~s unit unit fe efollowing followrng plagioclase S66crystallization appears: (1) (1) ilmeniteilmenite— sequence of of5crystallization olivine-plagioclase; (Z) ilmenite—titanomagnetite—olivine— ilmenite-titanomagnetite-olivineolivine—plagioclase; (2) augite—plagioclase; and finally augite-plagioclase; finally (3) (3) apatite—pigeonite— apatite-pigeonitetitanomagnetite-ilmenite-olivine-augite-plagioclase. titanoinagnetite—ilmenite—olivine—augite—plagioclase. dd de Very fine—grained fine-grained foliated foliatedolIvine—oxide—augite—plagioclase olivine-oxide-augite-plagioclase Very plagioclase (dd) and (dd) and fine—grained fine-grained granulo—decussate granulo-decussate augite augite— - plagioclase (de) rocks occur in in unit (de) rocks occur unit dg dg as as inclusions inclusionsasasmuch much as as 400 400 A number of mappable units are across. A are gradational gradational feet across. with (1) at at the the base base of of the the complex, (1) complex, a fine— fine- to coarse— coarsegrained decussate decussate augite—olivine—plagioclase augite-olivine-plagioclase autocrystallate autocrystallate (df) grades into rocks rocks having a texture texture and and mineralogy similar (df) to that unit dg,and may may be the to that in unit the base of the the cumulates cumulates of of Unit df unit dg. dg. Unit df shows sulfide mineralization mineralization similar similar to to unit ttf ttf of of the the Tuscarora Tuscarora Intrusion Intrusion (Johnson, (Johnson, 1970, 1970, p. p. 68). 68). unit dg: dg: unit df df di dj dj dk Groyp3 dm din (2) A fine-grained, fine—grained, olivinezo-plagioclase66-olivine20 olivine2Q—p1agioclase6—o1ivine90 (Z) A cumulate with minor miner augite5-oxide4-pigeon~te4-apatiEel augite —oxide4—pigeonie —apatite1 cumulate with within unit * fine—grained, as aa thin thin sheet sheet ,vitfiin unit dg. dg. (3) (3) A fine-graine4, occurs as autocrystallatee decussate, oxide2 —augite28—plagioclase decussate, oxideZ3-augite2S-plagioclase45 autocrystallat 5 containing minor livine2 olivine and and apatite2 apatite tntrudes intrudes unit dg and and Z z is (4) Unit Unit dg is presumed to to be aa late late differentiate differentiate (di). (di). (4) grades upward into 100—200 grades 100-ZOO foot—thick foot-thick discontinuous discontinuous sheets sheets of coarse—grained, foliated pigeonite4—titanomagnetite4— of coarse-grained, foliated pigeonite -titanomagnetite 4 4 augite6—plagioclase83 cumulatescontaining minor potass~um potassium augite -p1a gioclase cumulates containing minor S3 6 feldspar2 fine—grained granular feldspar and and quartz1 quartz (dj). (dj). A fine-grained granular 2 l plagioclase, quartz, orthoclase orthoclase rock rock (dk) (dk) occurs occurs as as dikes dikes cutting rocks. cutting other Group 22 rocks. Unit din, the upper upper part part of the dm, the the layered layered se•:ies, se~ies, is a 2,000 foot—thick 2,000 foot-thick sheet of coarse—grained coarse-grained decussate decussate pigeonite11—augite24--plagioclase59 pigeonite13-augite24-~lagi~clase59autocrystallates and cumu1aes cumulates containing conta~n~ng minor nanor oxides2, oX~desZ' quartz2 quartz 2 and potassium potassium feldspar1. feldspar . This unit is thought thought to to This unit l have been emplaced along along foliation planes planes and thus thus to have dilated dilated the the earlier earlier units. units. Variations in in grain grain size and and modal mineralogy suggest suggest th.t that this this unit unit may be a multiple intrusion. intrusion. A A related related intrusion intrusion may be be dl c..ll dn do do geonite unit dl, aa inedluin—grained medium-grained decussate decussate pi pigeonite17— 17 augite20—plagioclase50 rock containing augite20-plagioclase60 containing minor oxide, oxide, quartz, which occurs occurs as quartz, and and potassium feldspar, feldspar, ''''hich as a small stock about 1—1/2 1-1/2 miles stock about milesacross acrossininthe the central central part of the Hungry Jack quadrangle. quadrangle. Another related related intrusive granular oxide19— oxide intrusive unit unit is is aa fine-grained fine—grainS granular 19 plagioclase41—augite4 rock (dxi) which occurs occurs as aa plagio~lase4l-a~gite40 rocl~ (dn) 1vhich sheet 6 sheet 6 feet thick tlack anI and 4 mlles the northern miles long in the the part of Souti of the South Lake quadrangle. quadranp;le. Felsic dikes which intrure were given given aa separate separate designation intrude unit unitdcL dm \vere designation (do) (do) and may represent a a late—stage late-stage differentiate of of unit unit dj dj or partially fused fused country country rock rock (Nathan, (Nathan, p. p. 115). 115). �-112—112— Group 44 dp dq Group 55 dr ds Group 66 dt du dw The next intrusive unit unit (dp) (dp) occurs occurs as as aa concordant concordant as 1,200 feet feet thick thick between bet'}7een units units dg dg and and sheet as much as It is is aa fine—grained db. It fine-grained foliated augite32—plagioclase58 augite32-plagioclaseS8 andtrace trace amounts cumulate with olivine3—hypersthene.7 olivine -hypersthene"? and amounts of oxides. Plagioclase augite occur in aa granular oxides. Plagioclase and ~nd augite occur in granular fabric, hyperstheneas as as pheno— hypersthene as oikocrysts, oikocrysts,and andolivine olivine phenocrysts. of late-stage late—stageinterstitial interstitial material crysts. The absence absence of material suggests the suggests the unit unit formed by flow flow or or crystal crystal settling settling with exchange exchange between between the the magma magma and andthe the inner cumulus cumulus melt. Near melt. Near the the top top of of unit unitdp, dp,a 100—foot—thick a 100-foot-thick sheet of medium—grained foliated olivine17—plagioclase83 of medium-grained foliated olivine17-plagioclase83 cumulate gradational with with unit dp. dp. cumulate(dq) (dq)isis gradational In the southwestern lint Lake southwestern part part of of the the Gunf Gunflint Lake quadrang!le quadrangiLe pyroxene-plagioclase and and aa heterogeneous assortment of pyroxene—plagioclase olivine-plagioclase olivine—plagioclase rocks rocks possibly possibly related related to to unit unit tta tta of the Tuscarora Intrusion truncate truncate the the layered layered series. series. of the A typical example is a medium—grained A medium-grained decussate decussate tironals5— tironals S ollvine5—augite 5—plagioclase75 autocrystallate (dr). olivines-augitelS-plagioclase75 autocrystallate (dr). Near the the base base of o the layered series a medium-grained Near medium—grained foliated augite1 —plagioclase77 rock foliated augite17-plagioclase77 rock with minor minor oxide3— oxide 3 pigeonite and olivine oivine (ds) pigeonite? and (ds) is is intruded intruded as as aa sheet sheet 300 feet feet chick hick between 300 between units units df df and and dg. dg. Unit ds ds is is highly altered with montmorillonite montmorillonite after after plagioclase, plagioclase, and and amphibole amphibole and chlorite after after pyroxene. pyroxene. Locally chalcopyrite and and bornite occur within interstitial, chalcopyrite interstitial, altered pyroxene. pyroxene. A number of oxide—rich A oxide-rich stock— stock- and and dike—like dike-like bodies bodies 3/4 miles miles across the Complex Complex across occur near the base of the in the South Lake Lake quadrangle. quadrangle. Nathan recognized recognized four four varieties: varieties: (1) olivine (1) medium-grained medium—grained granular olivine16— oxide73 rocks oxide amount of of plagioclase plagioclasel6 and and 73 rocks with a minor amount augite (dt). augite (dt). The ilmenite andtitanomagnetite anddtanomagnetite occur occur as the latter generally has has exsolved exsolved as primary primary phases; phases; the coarse ilmenite lamellae with intra—titanomagnetite coarse intra-titanomagnetite granules which have in in turn turn exsolved exsolved to to a a fine fine reticulate reticulate intergrowth of magnetite magnetite and and hercynite.(')On hercynite.C)On Little Iron Little Iron Lake in the South Lake quadrangle quadrangle aa medium-grained mediunv-grained granular plagioclase 1—oxide24—olivine gra~ular,plagioclase 1-oxide -olivine (du) rock rock (du) 24 49 having minor hypersttene hyperstLne and hav1ng m1nor 1/2 mile mile and augite augite forms fogs aa 1/2 long composite sheet long sheet within unit dt.G)A coarse--grained coarse-grained unit dt.(3)A granular plagioclase8—oxide23_pjgeonjt2, granular plagioclase -oxide -pigeonite -augite —augite '· i nor8 olivine I' ,23 44 rock rock containing minor m 0 1Vlne occurs as as 24small con t a1n1ng inalldisdi cordant cordant masses in the the South South Lake Lake quadrangle. quadrangle. UI) (4) Two Two occurrences of a coarse—grained occurrences coarse-grained decussate decussate oxide oxide —_ augite31_p1agioc 't l ' 1ase 10mapped a~g1,e3l-~ ag10c autocrystallate (dw) (dw) were wer0mapped S5 autocrystallate within wlth1n unit unlt dg. dg. This unit exhibits an amphibole an amphibole alteration alteration similar similar to to that that in in unit unit ds, ds but but is is conconsidered sidered to to be be part part of of group 5 rocks b;cause of its its group 5 rocks because of large oxide content. content. �-113—113— Groupj dx dy dy dz Group 88 daa dmaa Several fine—grained Several fine-grained decussate rocks occur as as discontinuous thin sheets discontinuous sheets along the base of the the comcomand dikes dikes higher higher in in the the plex and as small stocks and section. represent either either fused fused fractions fractions section. They may represent country rock rock or contaminated contaminated melts, but but all all are are of country They consist to be intrusive. They consist of: of: (1) (1) fine— finethought to grained -augite 2-plagioclase66 grained decussate decussate oxide oxide7—augite2plagioclase66 7 olivine -quarrz and and potassium1 potassluffi 1 rock having minor olivine2—quartz2 2 (2) fine-g~ained fine—grained decussate decussate oxide oxideçfeldspar (dx); (dx); (2) —augite31—plagioclase55 autocrystallate hypersthene -augite -plagioclase autocrystal1ate hypersthone SS (dy); and and (?Y (~t fine—grained fine-g1~inedaugite3—oxide9 augite -oxide g decussate 3 quartz10—orthoclase15—hornblende29—plagioclase34 rock quartzlO-orthoclaselS-hornblende29-p1agioclase34 rock (dz).. (dz) The youngest intrusive unit within the layered series 1—1/2 miles dikes and and stocks stocks as as much much as as 1-1/2 occurs as dikes across the Hungary Jack Lake quadrangle. This unit, unit, across in the inedium-grained granular granular quartzls-alkali quartz18—alkali feldspar feldspar77 aa medium-grained oxide2 (daa), rock ,vitl, (daa) , truncates truncates rock with minor augite and oxide 2 1 unit din. unit dm. Across an an interval at the the inerval over a mile wide at there is is aa prog,ressive progressive increase in end of of unit unit din, dm, there in east end the amount amount of of late stage interstitial material that the that has has a composition similar to to unit unit daa. daa. This unit unit (dmaa) (dmaa) might be aa late late stage stage differentiate differentiate ofofdin. dm. Nathan found however that hm-lever that unit unit dx dx has has been been intruded intruded and and altered altered by by daa. daa. n Therefore, unit daa Therefore, it itisispresumed presumed that thatdin dm was \Vas cold cold when ,vhen unit daa was intruded and that that the the gradational zone zone represents represents melt from daa daa that that was introduced introduced into into unit unit dm. dm. Intrusion and and Associated Associated Rocks Rocks Tuscarora Intrusion In the Long Island quadrangle (Fig. the Long (Fig. 2) 2) a a sequence of rock types common to to other appear in in the other parts partsofofthe theDuluth DuluthComplex Complex appear the following following succession away succession away from the base: (1) (1) aa fine-grained augite from the fine—grained poikilitic augite gabbro (tp), (tp), (2) (2) aa fine-grained (hornfels) (th), (th), fine—grained granoblastic gabbro (hornfels) (3) (ttf-ttm), (4) (4) interlayered interlayered (3) aa finefine— to to medium-grained medium—grained troctolite (ttf—ttm), troctolite and troctolite and poikilitic gabhro gabbro (tta), (tta), (5) (S) anorthositic anorthositic gabbro gabbro (ag), (ag), (6) ferrograndiorite ferrograndiorite (tg), (6) (tg), (7) (gr), and (7) (7) metamorphosed (7) granophyre granophyre (gr), flows (:mv). (kmv). Although the the outcrop pattern suggests aa simple differentiated differentiated layered sequence, the stratigraphic position of units tp, tp, ag, tg and gr layered sequence, the of units ag, tg have not been unequivocally established. established. Hm.;rever, ttm, and and However, units ttf, ttn, are clearly clearly parts a separate troctolite intrusion that that truncates tta are parts of of a part layered series series (Fig. (Fig. 3). 3). part of of Nathan's layered ynits ttm,tL,ad ttf, and tta: The unit of the Tuscarora Intrusion The main unit Units tta: is aa niedium—grained medium-grained troctolite (ttm, Fig. is troctolite (ttrn, Fig. 2), 2), consisting consisting of of 6S-70 65—70 percent and 10-lS 10—15 percent cumulus percent cumulus plagioclase (An (An 56 S-60)' and cumulus divine amouns 09 ol~vine (Fo0). (F~50). Relative amoun~s of poikilitic augite and iron—titanium iron-titanium oxides oXldes varies varles locally. locally. Orthopyroxene mantles olivine and and occurs occurs in in simplectic plagioclase. Biotite biotite is associated with sitaplectic intersrowth intergrowth with plagioclase. tile oxides. Planar orientation of of plagioclase and modal— modalthe iron-titanium iron—titanium oxides. layering are are locally locally well—developed well-developed and and mutually concordant. concordant. mineral layering poikilitic �-114-114— The troctolite grades into The into an an upper upper unit unit which which consists consists of of interlayered poikilitic augite gabbro and and troctolite (Fig. 3). 3). troctolite (Fig. The poikilitic augite augite consists consists of of about about 70 70 percent percent plagioclase plagioclase 15—20 percent augite, (An SO - 60 )' 15-20 augite, 5—10 5-10 percentilmenite percent ilmenite and and is is medium— med1um- to coarse—grained coarse-grained with withwell well developed developedaugite augite orthocrysts orthocrysts as much as 1—1/2" across. The as much as 1-1/2 across. The troctolite \vithin the the layered layered troctolite within interval interval is similar to to that that in in unit unit ttm. ttm. Contacts Contacts between between layers layers are generally generally sharp sharp and and in in general gener& conformable are conformable with with layering layering in in the the troctolite. troctolite. Interlayering of several several inches inches Interlayering occurs on a scale of to to several feet, feet, and is undulatory with wave lengths lengths of of ten to twenty twenty ten to feet feet and amplitudes of two two to to three three feet, but the the gross gross structure structure feet, but is nearly flat—lying. is flat-lying. 11 A belt of fine—grained Unit ttp; ttp: A fine-grained rocks rocks occur occur beneath beneath unit unit ttf. It ttf. It consists consists of fine— fine- to medium—grained medium-grained augite augite troctolite troctolite with 60—70percent percentcumulus cumulusplagioclase plagioclase (An50), with 60-70 (An ), 5-10 cumulus 5—10 percent cumulus 50 olivine percentpoikilitic poikilitic augite, .5—10 ~livin~ (Fo35), (F~35)' 15—20 ~5-20 perce~t augite, 5-10 percent . iron—titanium oxides, minor orthopyroxene-plagioclase orthopyroxene—plagioclase simplect1te. simplecite. 1ron-t1tan1um oX1des, and mlnor As yet the upper contact As contact of tins this unit unit has has not not been been observed observed and and it it is not clear from outcrop data is data if if it it is is aa separate separate intrusion intrusion or the the basal unit of the the overlying overlying rocks. rocks. Johnson (1970, (1970, p. p. 76) 76) concluded concluded from from drill drill core data that that it is is aa separate separate intrusion. intrusion. Unit th: th: Several areas of fine—grained, fine-grained, granoblastic granoblastic gabbro gabbro consisting of 50 to 60 percent short tabular tabular plagioclase, plagioclase, 30 30 to to 40 percent rounded rounded augite, augite, minor minor subhedral subhedral iron—titanium iron-titanium oxides, oxides, olivine, and and blades of biotite are olivine, are exposed exposed on on topographic topographic highs. highs. These rocks however rocks may be a remnant remnant capping over the the troctolite; troctolite; hOlvever there is no noticeable chilling of of the the troctolite troctolite next next to to the the there is hornfels and they they more likely likely represent represent large large inclusions. inclusions. Unit ap; ag: A break in in plagioclase plagioclase content content separates separates A distinct distinct break units tta tta and and ag. ago Unit ag ag — - an anorthositic gabbro— - contains 75 units anorthositic gabbro 75 to contrast to the 85 (in to the 50 50 to to 70 70 percent percent S5percent percentplagioclase plagioclaseAnAn5560 ( 55 60 Plagioclase is phase, and and interinterof is the the only only cumulus cumulus phase, of unit unit tta). tta). Plagioclase stitialminerals, minerals,occurring occurring in invarious various proportions proportions are are augite, augite, stitial olivine, and iron texture. Orthopyroxene olivine, and iron oxides oxidesinin aa poikilitic poikilitic texture. occurs in in siciplectic occurs sil:lplec tic intergrowth intergrm-Jth with W'i th late—stage late-stage plagioclase. associatedwith \'liththe theiron—titanium iron-titanium oxides. oxides. Planar Biotite isisassociated orientation of orientation of plagioclase plagioclase is is developed developed locally. locally. At At the the top top of of unit ag, quartz quartz and and potassium potassium feldspar unit ag, feldsparoccur occurinterstitially. interstitially. Tue flat—lyingoutcrop outcroppattern patternofof the the ferrogranodiorite ferrogranodiorite (tg) The flat-lying (tg) and granophyre concordant with \vithin the the and granophyre(gr) (gr) isis concordant with the the structure structure within troctolite (ttm) troctolite (ttm) and and the the anorthositic anorthositicgalibro gabbro could could be be just just another another part of the layered intrusion. IImvever some field evidence contrapart of the layered intrusion. however some field evidence contradicts this interpretation. interpretation. llornfels Hornfels inclusions inclusions and and sulfide sulfide mineralmineraldicts this ization are are found found in at several several localities localitiesalong along the the contact contact ization in unit unit tta tta at with unit ag. ago Thus the troctolite may be intrusive into the the Thus the intrusive into anorthositicgabbro gabbro as asininthe the GabbroLake Lake quadrangle quadrangle (Green (Green and and anorthositic Gabbro Phinney (1969) (1969)has hasextended extendedthe theolder older anorthositic anorthositic others, 1966). 1966). Phinney gabbro from from the Gabbro Lake quadrangle eastward the Gabbro eastward and and this this extension extension projects toward toward unit unit ag. ago Thus TIluS unit ag ag may be aa thin thin wedge wedge of of an an In this anorthositic gabbro. gabbro. In this case, units units areally extensive older anorthositic fg to the the troctolite troctoliteand and intruded intruded fg and and gr gr could could be either related to the ancirthositic gabbro or or aa differentiated differentiated part into the anorthositic gabbro part of of the the anorthositic gabbro. gabbro. anorthositic �-115—115— Unit f: This unit is restricted Unit fg: restricted to to aa topographically topographically high high area in the southwest corner of the the Long Long Island Island Lake Lake quadrangle quadrangle southwest corner (Fig. 3). 3). It medium-grained ferrogranodiorite which contains (Fig. It isisa amedium—grained ferrogranodiorite which 50 to 60 percent cumulus plagioclase, 10 to 15 percent amphibole, 50 to 60 percent cumulus plagioclase, 10 to 15 percent amphibole, minor clinopyroxene, amounts of potassium minor clinopyroxene, and and varying varying amounts of quartz, quartz, potassium anorthositic feldspar, and magnetite. Contacts with the underlying anorthositic gabbro and overlying granophyre are are gradational gradational over over tens tens of of feet. feet. The former former could replacement by by intrusive intrusiveferrograno— ferrogranocould represent replacement diorite or or differentiation differentiation within within the the anorthositic anorthositic gabbro. gabbro. Further diorite study is needed to the stratigraphic stratigraphic relationships. relationships. is needed to clarify clarify the i the Unit Unit gr: The ferrogranodiorite grades grades into into and is cut The ferrogranodiorite and is cut by by It consists It consists of of quartz, quartz, The texture texture ranges plagioclase, potassium plagioclase, potassium feldspar and and magnetite. magnetite. The ranges from from granophyric granophyrictoto granitoid. granitoid. fine- to medium—grained medium-grained granophyre. fine— granophyre. Unit kmv: kmv: The The granophyre granophyre intrudes intrudesblack black fine-grainedmeta— metafine—grained volcanic rocks whch whch are remnants of ofMiddle Middle volcanic rocks are interpreted interpreted totobeberemnants groundmassisishighly highlyaltered. altered. Acicular Keweenawan The groundmass Keweenawan flows. flows. The blades of ilmenite and plagioclase plagioclase phenocrysts blades ilmeniteare arecommon common and phenocrysts are are clouded similar intruded rocks rocks in layered series. clouded similar to to intruded it'. the the layered series. the the Mineralization: Two Two types types of mineralization are found in Duluth Complex 1m., grade gradecopper—nickel copper-nickel Duluth Complexininthis this area: area: (1) (1) low concentrations are associated associated with with the the basal basal rocks concentrations are rocks of of the the Tuscarora Intrusion and Tuscarora the layered series series intrusions intrusions and several of the (Johnson, 1970), (2) Ilmenite— and and titanomagnetite-rich titanomagnetite—rich rocks (Johnson, (2) Ilmeniterocks occr occur in in several several units units of of Nathan's Nathan's layered layered series. series. With \-lith regard regard to to the the mineralization, the the unpublished unpublished Ph.D. Ph.D. thesis (1970) warrants warrants special special mention. mention. The thesis thesis thesis of of Johnson (1970) summarizes the the results results of summarizes of an an exploration program conducted by the Cleveland—cliffs the Cleveland-Cliffs Iron IronCompany Company and and the Amerada-Hess Amerada—Hess Corporation Company from from 1966 1966 to to 1969. 1969. This program ass~ssed This assessed the economic potential of the base of the Duluth potential of the base of the Duluth Complex in in aa 38 38 km corridor along the Gunflint Trail adjacent adjacent to to the the Boundary Boundary Waters Waters Canoe Canoe Area. Area. The drilling program (10 (10 holes) holes) provides provides an unique opportunity opportunity to to assess assess the the effects effects of of drilling drillingononthe thearea area comparison with with other other inin comparison activities activities such such as as logging logging and and recreation. recreation. More importantly the the rereMore importantly lease lease of of geophysical, geophysical, drill drill core, core, and assay data, data, along along with Johnson's Johnson's study represents represents a study a major contribution by by aa mining company company to to the the concern for for the the environment of the the area. area. The The correlation correlation of of geogeophysical and physical and drill drill core core data, data, discussed below, makes makes possible possible aa discussed below, more accurate accurate evaluation more evaluation of of mineral mineral resources adjacent areas areas resources in in adjacent and in other and in other areas areas of of similar similargeology geology using using less less expensive expensive and and disruptive disruptive preliminary preliminary investigations. investigations. Coç—Nicke1_Iinera1izatjon: ~0J?E.£!:.-Nickel ~'lineralization: Discontinuous gossan Discontinuous areas areas of gossan and visible sulfide and visible sulfide mineralization min~r-;li~-ation ,.,ithin have been been mapped mapped within unit ttf ttf have across the across the Long Long Island Island quadrangle. quadrangle. Similar Similar isolated isolatedexposures exposures have have been found in in unit tta atat the been.found unit tta thecontact contact with with anorthositic anorthositic gabbro. gabbro. The The sulfide assemblage, consisting sulflde assemblage, consisting of pyrrhotite and and minor minor of chalcopyrite cI:alcopyrjte,pyrrhoi, pentlandjte occurs occursinterstitially interstitially to plagioclase pentlandite plagiocla~e and and olivine. Because Because of the size of of the of the smaller smaller grain grain size the troctolite troctolite a a distinct distinct interstitial interstitial texture, texture, like like that thatfound found in the sulfide sulfide mineralization mineralization in in the Kawishiwi in the the iCawishiwi area in the Gabbro area in tQe Gabbro Lake Lake quadrangle, quadrangle, is not apparent apparent ininhand handspecimen. specimen. is not �-116—116— Drilling across across the the quadrangle quadrangle (Johnson, 1969) has has indicated indicated aa Drilling (Johnson, 1969) tabular, tabular, possibly continuous volume of of low low grade grade ore ore (0.3% (0.3% combined combined copper-nickel) about 50 feet thick thick in in the the unit unit ttf. ttf. A A thinner thinner 10—20 10-20 copper—nickel) foot-thick zone, 50—100 50-100 feet feet above above the the lower lower mineralized mineralized zone, zone, has has foot—thick zone, aa higher combined copper—nickel copper-nickel content content that that approaches approaches one one percent percent 84). The mineralization can be correlated3with correlated with a (Johnson, p. 84). the order of 700 x 10 3 ohmcentimeters detectable resistivity anomaly on the in the troctolite (ttf, (ttf, ttm). ttm). Mineralization: The primary titanium titan1um oxide oxide phases phases Titanium Mineralization: ) and titanomagnetite are i].menite ilmenite solid 0 -MgTi0 solid solution solution (Fe (Fe20 —MgTiO -FeTi0 —FeTiO3) 3 3 2 3 (Fe304—Fe (Fe 0 -Fe 2TiO Ti0 4). ). Subsolidus exsoLtion exsolution as fiasresulted resulted in in the the complex complex 3 4 intergrosAhs âescribed intergrowEhs described above. Johnson (1970, (1970, p. p. 87) 87) estimates estimates that that Ti Ti recovered recovered from from ilmenite ilmenite in In unit unit ttf ttf in in the the Tuscarora Intrusion Intrusion could add $1.50 per ton to to sulfide ore ore from from this this unit. unit. The largest titanium concentrations at Little Little Iron Iron Lake Lake in in the the Gunflint Gunflint Lake Lake at exposures in the the South South Lake Lake quadrangle. quadrangle. do not exceed occurrences at the surface do however are in units dt and du quadrangle quadrangle and and other other isolated isolated Unfortunately, most of these Unfortunately, these about 35 feet feet in maximum about dimension. A large low—grade A low-grade titanium titanium resource also is contained within unit dg (Fig. unit (Fig. 3). 3). Oxide—rich Oxide-rich layers as much as as 5 feet feet thick are common, common, although individual layers seem seem too too thin thin and and discontinuous discontinuous to be mined separately. Unit dg should he to be considered considered in its its entirety for commercial evaluation with the the potential of of developing a very large tonnage tonnage of of low—grade low-grade ore. ore. The unit is very heterogeneous and and exposures are scarce and discontinuous, so only widespread field exposures and discontinuous, systematic drilling will reveal reveal which which parts parts have have the the greatest greatest promise. promise. �_____ _____, -117—117— References Cited Bayley, Bayley, W. W. S., S., 1893, The eruptive and and sedimentary rocks on Pigeon Point, their contact contact phenomena: phenomena: U. U. S. S. Geol. Geol. Point, Minnesota, Minnesota, and their Survey Bull. Bull. 109, 109, 121 121 p. p. Bonnichsen, Bill, 1969, 1969, Metamorphic Metamorphic pyroxenes pyroxenes and and amphiboles amphiboles in Bonnichsen, Bill, the Biwabik Iron—formation, Iron-formation, Dunka Dunka River River area, area, Minnesota: Minnesota: Mineralog. Soc. Soc. 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Schwartz, Schwartz, 1933, 1933, The geology geology of of the Rove Rove fonnation in northeastern northeastern Minnesota: Hinnesota: formation and associated intrusives in Minn. Geol. Geo1. Survey Survey Bull. Bull. 24, 24, 103 103 p. p. Gruner, J. J. 14., W., Gruner, 1941, Structural geology of the the Knife Knife Lake Lake area area of of northeastern Minnesota: Minnesota: Geol. Geol. Soc. Soc. America America Bull., Bull., v. v. 52, 52, p. 1577—1642. 1577-1642. p. Halford, C. C. R., R., 1969, 1969, Petrography and structure of the Saganaga Halford, Granite, Saganaga-Northern Light Light Lakes Lakes Area, Area, Minnesota—Ontario: Minnesota-Ontario: Granite, Saganaga—Northern unpub. S. Thesis, of N. N. Y. Y. at at Stony Stony Brook, Brook, 7lp. 71p. unpub. ~1. M. S. Thesis, State Univ. of Hanson, R. Malhotra, Malhotra, 1971, Hanson, G. G. N., N., and R. 1971, K—Ar K-Ar ages of mafic dikes and evidence for low—grade low-grade metamorphism metamorphism in in northeastern northeastern Y.innesota: Hinnesota: Geo1. Soc. Soc. America America Bull., Bull., in in press. press. Geol. Harris, F. F. R., area, District Harris, R., 1968, 1968, Geology af the Saganagons Lake area, of Thunder Bay: Bay: Ont. Onto Dept. Dept. Mines Rept. Rept. 66, 66, 30 30 p. p. P. M., H. H. W. W. Fairbairn, Fairbairn, W. H. H. H. Pinson, Pinson, and and J.J. flower, Hower, 1962, 1962, Hurley, P. Unmetamorphosed minerals the Gunflint fonnation used to to minerals in the Gunflint formation test the age of the the Animikie: Animikie: Jour. Jour. Geol., Geol., v. v. 70, 70, p. p. 489—492. 489-492. Johnson, Johnson, R. R. G., G., 1968, 1968, Copper—Nickel Copper-Nickel mineralization in the the basal Duluth >1. A case study: S. Gabbro complex, complex, northeastern Minnesota: Minnesota: A study: unpub. unpub. M. S. Dniv. of of Iowa, Iowa, 91 91 p. p. Thesis, Univ. - _____, 1970, Economic geology of aa portion portion of of the the basal basal Duluth Duluth Complex, Complex, northeastern northeastern Minnesota: Minnesota: unpub. unpub. Ph.D. Ph.D. Thesis, Univ. Dniv. of of Iowa, Iowa, 136 136 p. p. Lawson, C., 1893, sills of the northwest north\-rest coast of Lawson, A. A. C., 1893, The 1accolithic laccolithic sills Lake Superior: Superior: Ninn. Geol. Nat. Nat. lUst. Hist. Survey Survey Bull. Bull. 8, 8, p. p. 25—48. 25-48. Minn. Geol. Mancuso, D., and J. Dolence, 1970, 1970, Structure of of the Duluth gabbro compic complE Mancuso, J. J. D., J. D. D. Dolence, the Babbitt area, in the area, Minnesota (abst.): (abst.): in 16th Ann. Ann. Inst. Inst. Lake Lake Superior Geol., Geo1., p. p. 27. 27. Misra, Misra, A., A., and G. G. Faure, Faure, 1970, Restudy Restudy of the the age age of of the the Gunflint Gunflint FormaFonnation of of Ontario, Ontario, Canada (absr.): tion (abst.): in Soc. America abstracts abstracts in Geol. Geol. Soc. with programs programs for for 1970, 1970, north—central north-central section, section, v. v. 2, p. 398. 398. 2, p. Hoorhouse, W.W. Moorhouse, W.W., 1960, Gunflint Iron Iron Range in in the the vicinity vicinity of of Port Port Arthur, Arthur, Ontario: Ont. Dept. Ontario: Ont. Dept. Mines, Hines, v. v. ,pt. 7, p. p. 1—40. 1-40. pt. 7, , , ____, 1963, 1963, Concretions from the Animikie of of the the Port Port Arthur Arthur region, region, Ontario: Ontario: Proc. Proc. Geol. Geol. Assoc. Assoc. Canada, Canada, v. v. 15, 15, p. 43-59. p. 43—59. Morey, 1969, The geology of the Middle Precambrian Rove Morey, C. G. B., B., 1969, Fonnation Rove Formation In northeastern Minnesota: in l'linnesota: Ninn. Geol. Survey Special Pub. 7, 62 p. p. Minn. Ceol. Pub. 7, �-119—119— Morey, and P. P. K. K. Sims, Sims, 1970, 1970, Morey, G. G. B., B., J. J. C. C. Green, Green, R. R. W. W. Ojakangas, Ojáangas, and Stratigraphy of the the Lower Lower Precambrian Precambrian rocks theVermilion Vermilion rocks in the Minn. Geol. district, northeasternMinnesota: Minnesota: Minn. Geol. Survey Survey Rept. Rept. district, northeastern Inv. 14, 33 33 p. p. mv. 14, and U. Piorey, G. B., B., P. P. W. \v. Weiblen, D. H. H. Anderson, Anderson, 1969, 1969, Morey, C. J. Papike, and Weiblen, J. J. Geologic map of Long Island Island Lake Lake quadrangle, quadrangle, Cook Cook County, County, Minnesota: Minn. Minn. Geol. Geo1. Survey Survey open open file file map. map. Mudrey, 21. Hudrey, H. G., Light Gneiss, Gneiss, Northern Northern C., 1969, 1969, Petrology of the Northern Light Light Lake, Lake, Thunder Bay district, Light district, Ontario, Canada: Canada: unpub. unpub. M.S. M.S. Thesis, North. Ill. Ill. Univ., Dniv., 66 66 p. p. Thesis, North. Mudrey, >1. r1udrey, H. G., Reinvestigation of of "red "red rocks" rocks" G. , and P. P. hi. N. lveiblen, Weiblen, 1971, Reinvestigation in the in the Pigeon Point area, area, Minnesota (abst.): (abst.): in 17th Ann. Ann. Inst. on Lake Superior lnst. Superior Geol. Geol. Nathan, Nathan, Ii. H. D., portion of of the the Duluth Duluth Complex, Complex, 0., 1969, 1969, The geology of aa portion County, unpub. unpub. Ph.D. Ph.D. Thesis, Univ. Dniv. of of Ninn., Minn., 198 198 p. p. Cook County, Phinney, W. C., 1969a, the Gabbro Phinney, W. C., 1969a, The The Duluth Complex in the Gabbro Lake quadrangle, 11innesota: Minnesota: Minn. quadrangle, Minn. Geol. Geol. Survey Survey Rept. Rept. trw. lnv. 9, 9, 20 20 p. p. Phinney, N. W. C., C., 1969h, 1969b, Geology Geology of of Central Central part part of of Duluth Duluth Complex; Complex; Phinney, P. K. in Summary of Fieldwork Fieldwork 1969: 1969: P. K. Sims and and I. I. Westfall, Westfall, eds.: eds.: t-~inn. Minn. Geol. Geol. Survey Survey Inf. Inf. Circ. Circ. 7, 7, p. 2 18. Sims, P. P. K., B. Morey, R. Sims, K., G. G.B. R. w. l.v. Ojakangas, and N. W. L. L. Griffin, 1968, 1968, Preliminary geologic map of the the Vermilion Vermilion district district and and adjacent adjacent areas, northern ttinneso ta: lirin. Geol. areas, Ninnesota: ;1inn. Geo1. Survey Survey Misc. Map Hap N—S. H-5. Sims, Sins, P. P. 1(., K., G. C. B. B. Morey, Morey, and and J. J. C. C. Green, Green, 1969, 1969, The The potential potential for for ne~v in Minnesota: Ninnesota: 30th Ann. Ann. Mining Hining Symposium, Symposium, new mineral discoveries in Univ. of Uinn., Dniv. ~1inn., p. p. 75—87. 75-87. Tanton, Tanton, T. T. L., L., 1931, 1931, Fort Fort William and and Port Port Arthur, Arthur, and and Thunder Cape mapmap— areas, district, Ontario: Ontario: Geol. CeoI. Survey Survey Canada Canada Mem. Mem. areas, Thunder Bay district, 167, 222 1G7, 222 p. p. Wanless, IL hlanless, R. K., K., IL R. U. D. Stevens, Stevens, G. G. R. and R. R. N. N. Dalablo, Da1abio, 1970, 1970, R. Lachance, Lachance, and Age ages, z\gedetenninations determinations and and geological geological studies studies K-Ar K—Ar is6topic istopic ages, Report 9: 9: Geol. Geol. Surv. Surv. Canada Canada Paper Paper 69—2A, 69-2A, 78 78 p. p. Report Winchell, 1888, Report Winchell, A. A., 18$8, Report of of aa geological survey in ~linnesota Minnesota during the season of 1887: the season of 1887: tlinn. Minn. Geol. 16th Ann. Ann. Geol. Nat. Nat. Hist. lust. Survey, 16th Rept., p. 336—337. 336-337. Rept., p. , 1897, Some· Some new features _____ , 1897, features in the the geology of northeastern northeastern Minnesota: Minnesota: Amer. v. 20, 20, p. p. 41—51. 41-51. Amer. Geologist, Geologist, v. Wolff, \-101ff, J. J. F., F., 1971, 1971, Recent Recent geological geological developments on the the Mesabi Mesabi iron iron developments on range: Amer. Inst. Inst. Min. Mm. Engs., range: Trans. Trans. Amer. Engs., V. 56, p. p. 142—169. 142-169. v. 56, �-120—120— FIELD FIELD TRIP TRIP GUIDE GUIDE TO TO THE THE PRECAMBRIAN PRECAMBRIAN ROCKS, ROCKS, ~UL' i'u.._ •• _ .. _ COOK COUNTY ALONG THE GUNFLINT TRAIL Stop 1 End of Trail Campground -- Main Phase of Saganaga Granite the Saganaga Granite Granite at at this this stop stop is is aa The main phase of the medium—grained medium-grained hornblende—"quartz—eyet' hornblende-"quartz-eye" tonalite tonalite having quartz2o— quartZ20plagioclase (An27)60_lO—hornblende6—microljne3_5 (An27)60-70-hornblende6-microline3_S and and accessory accessory biotite, chlorite, chlorite, epidote, epidote, sphene, sphene, apatite, apatite, allanite allanite muscovite, biotite, and magnetite. magnetite. The apparent lineation of of the the "quartz—eyes" "quartz-eyes" is is 25_300 ENE. 25-30° ENE. This structure is is parodied in in the the hornblende—biotite hornblende-biotite inclusions. inch-sized inclusions related to to These inch--sized inclusions are are probably related the the south south of of Seagull Seagull Lake. Lake. the greenstones to the The bay leading north to Saganaga Lake was The Has considered considered by by Grout (1936) (1936) to to be aa shatter shatter zone. zone. It It is here interpreted as as a fault in the granite. fault the granite. At this stop, aa minor secondary secondary east— eastnortheast and epidote epidote northeast trending foliation is marked by shears and veinlets, and and may be related related to to faulting. faulting. veinlets, Stop 22 Gunf lint Trail Trail near near the the Campground —- Lamprophyre dike in Saganaga Gunflint Granite larnprophyre dike at this stop is is 50 SO feet feet wide, tv-ide, and and can can be be The lamprophyre traced to to the north shore of Saganaga Lake where it it is is found found to to cut cut the northern boundary fault fault (Harris, (Harris, 1968, p. p. 21). 21). This observation the sets aa 10lv-er lower age sets age limit for faulting and uplift uplift to to the the west Hest for for the the Goldich and others (1961, p. 52) date the biotite Saganaga Granite. Granite. (1961, p. S2) date the biotite (KA—70B)fromasmall (KA-70B)from a small island island to to the the north north at at 1.75 1. 7S h.y. b.y. Sundeen (1936) (1936) reviewed reviewed the the petrography petrography of of the the larnprophyre lamprophyre dikes the Saganaga Lake are.a and found biotite, biotite, hornblende, dikes in the Lake area and the mafic phenocrysts in a groundmass of of either either and pyroxene pyroxene as as the plagioclase or This dike dike contains contains plagioclasesoplagioc1ase5— plagioclase or "orthoclase. "orthoclase"11 This pyroxenel5_20—pyroxenei5_20—biotite513 pyroxenelS-20-pyroxeneI5_20-biotiteS_IO and and hornblende5. hornblendes. Accessory Accessory minerals include minerals include quartz, quartz, apatite, apatite, magnetite, chlorite, chlorite, carbonate, carbonate, sphene, pyrite, pyrite, zircon, sphene, zircon, serpentine, serpentine, talc talc and perovskite. perovskite. Stop 3a Stop Saganaga Saganaga Granite Granite -— Border Phase The strongly foliated foliated hornblende diorite diorite exposed exposed at at this this stop stop is typical typical of the border phase of the the Saganaga Granite. Granite. The foliation is of the is defined defined by by aa layering characterized by various proportions is proportions of of dark dark and light minerals; it is is nearly vertical and strikes N70°W. N70oW. Elongate and light minerals; it the foliation foliation plane plane define define an an elongate elongate hornblende needles within the ilneation lineation that that plunges gently gently to to the the east. east. A A transition from the border to the the main phase involving involving an an 'quartz—eye' structure structure increase in quartz - with tv-ith the the development development of of "quartz-eye" -— and aa decrease in hornblende can be seen in in a number of of outcrops outcrops lint Trail Trail to to the on either side of of the the Gunf Gunflint the north of of this this stop. stoP. �—121— -121- Stop 3b 3b Ietabasalt and associated rocks Netabasalt rocks vicinity of of this this stop, stop, vaguely pillowed meta— metaIn the general vicinity basalt thin-bedded to to laminated pyroclastic pyroclastic material material typical typical basalt and thin—bedded of the the mafic the volcanic succession succession are are exposed. exposed. Layering of nafic part of the is is nearly vertical and strikes in in aa northwesterly northwesterly direction. direction. Fracture Fracture cleavage direction cleavage also also is is near near vertical and strikes in a northeasterly direction parallel to to the the trace of the the Lookout Lookout fault. fault. The mafic cut by byconformable conformable layers layers of offine—grained fine-grained mafic rocks rocks are cut graphic feldspar granite. Locally graphic feldspar a thin layer of iron-formation Locally a thin layer of iron—formation overlies the older composed and chert chertunconformably unconformably overlies composedofof magnetite magnetite and rocks. Iron-rich the lower lower part the Cunflint Gunflint Iron—richstrata stratatypical typical of of the part of the Iron—formationare are exposed exposedon on the the steep north—facing Iron-formation north-facing slope immediately immediately to the to the south south of of these theseexposures. exposures. Stopj4 Stop lint Iron-formation Iron—formation Rock Trail Trail—- metamorphosed Gunf Gunflint Along Magnetic Rock Along of Zone 22 Thin-bedded, Thin—bedded, fine—grained, fine-grained, chert—axnphibole—inagnetitebearing chert-amphibole-magnetite-bearing strata assigned to to the upper part of of the the Lower Lower Slaty Slaty member member are are exposed along Magnetic Rock Rock Trail Trail at at this this locality. locality. These exposures are the transition between moderately and and strongly strongly metamorphosed metamorphosed are near the iron-formation; small, poorly developed developed pyroxene pyroxene porphyroblasts porphyroblasts iron—formation; small, can be be seen,pecially seen,especiallyinin moremassive massive beds beds at the the top of of the the thethemore member. Along to the thesouth, south,the theiron—formation iron-formation is Alongthe thepower powerline linetrail trail to locally with beds at 15°. locally deformed deformed with beds dipping dipping northward northward at 15°. Approximately7575feet feetfarther farther to Approximately to the thesouth southa anorthwesterly— northwesterlytrending, medium-grained medium—grained diabase diabase sill sill cuts cuts slaty slaty iron—formatin. iron-formatin. Approximately 200 feet the slaty to Approximately 200 feet to to the the south south the slaty beds beds again dip dip to the south south and coarse-grained, magnetite-rich the and are are interlayered interlayered with with coarse—grained, magnetite—rich cherty beds. beds. On the same knob, knob, algal chert—bearing chert-bearing beds characteristic of the Upper Cherty Member also of also are are exposed. exposed. Stop 55 Along the Kekabeic Kekabeic Trail Trail—- Metamorphosed Gunflint Iron—formation Iron-formation at at Zone 3. The Kekabeic oror less base of of the the Gunflint Gunflint The KekabeicTrail Trailmore more lessparallels parallels the the base Iron—formationand andthe thenorth-facing north—facing slopeimmediately immediately southofofthe thetrail trail Iron-fornlation slope south The iron—formation contains exposures exposures of ofthe theLower Lower Slaty SlatyMember. Hember. The iron-formation everyhas been extensively metamorphosed and now consists where in this this area has of various quartz—cummingtonite—grunerite—fayalite— various assemblages assemblagesofof quartz-cun~ingtonite-grunerite-fayalite­ magnetite and magnetite andquartz—cummingtonite—grunerite—pyroxene—magnetite. quartz-cummingtonite-grunerite-pyroxene-magnetite. �-122—122-are in Test along the the Trail. Trail. IIost Host are iI:. the the lowe.: 10HE;:: Test pits can be seen along magnetite-rich the Lower Lower Cherty Cherty Member. Member. Various sulfides, sulfides, magnetite—rich part of the especially pyrrhotite, the magneti:e. magnetL:e. pyrrhotite, also are associated with the Stop 66 rail cut -— Basal Contact of the dIe Duluth Along the Paulson Mine Mine railcut Complex. Complex The Paulson Mine railcut railcut exposes exposes the the base base of of the the Duluth Duluth Complex Complex from the from the Kekabeic Trail to to the Tuscarora Lodge Lodge road, road, aa distance distance of of about 1—1/4 1-1/4 miles. Contacts between bet\veen beds of of the the Upper Upper Cherty Cherty Memhe: Hembe:.: of the Gui-if Gunflint Iron-formation lint Iron—formationand andfine-grained fine—grained poikilitic poikilitic augite augite troctolite, troctolite, unit unit tp tp of the Duluth Complex, are are exposed exposed at at the the west west end of the the railcut. railcut. Also at the the west end end truncation truncation of of aa thin thin sill sill of the Logan Intrusive Intrusive Rocks Rocks can can he be seen. seen. About half—way half-l'1ay along along the the railcut, railcut, argillite and graywacke of the the Rove Rove Formation Formation are are in in contact contact The contact aureole here is ,-lith the the base base of of the the Duluth Duluth Complex. Complex. The is with narrow with no visible recrystallization recrystallization of of Rove Rove Formation Formation rocks rocks except within a few few feet feet of of unit unit tp. tp. This is inferred to to be aa 100—1,000 feet. reflection of the the thickness thickness of unit unit tp tp 100-1,000 feet. The dip lint and and Rove Rove Formation Formation varies varies from from 15-60° 15—60° to to the the south of the Gunf Gunflint along this part of of the the contact. contact. Stop 7a 7a Scenic overlook overlook on on the the Gunf Gunflint lint Trail above above Gunf Gunflint lint Lake -— Copper— Coppernickel mineralization at at the the base base of of the the Tuscarora Tuscarora Intrusion Intrusion The base of unit unit ttf of the the Tuscarora Intrusion Intrusion is is exposed exposed on on the northeast side lint Trail Trail at the side of of the the Gunf Gunflint the overlook. The fine— fineto mediuin—grairied troctoliteshows shows no no regular regular increase increase in grain medium-grained troctolite grain size size away away from a contact with unit tp tp and and the the upper upper part part of of aa Logan Logan sill. sill. Visible chalcopyrite, chalcopyrite, pyrrhotite, pyrrhotite, pentlandite occur occur interstitial interstitial and olivine olivine in in the the troctolite. troctolite. This is a typical typical to plagioclase and of the example of the copper—nickel copper-nickel mineralization of of unit unit ttf, ttf, which which was was found by by Cleveland-Cliffs Cleveland—Cliffs Iron Company (in found (in five five holes holes along along the the base base of the Complex) to of the Complex) to occur constantly in aa 150 feet feet thick thick interval interval near near the base of unit unit ttf. ttf. The combined nickel—copper nickel-copper content content is is about about the 0.3 percent in this this interval. interval. A A slightly richer richer zone zone 10 10 to to 20 20 feet feet thick was was intercepted about about 50—150 50-150 feet above the the lower lower zone. zone. Stop7b Stop 7b 2000 feet northeast Rocks and 2000 feet northeast of of Stop 7a -— Logan Intrusive Rocks the the Rove Formation Thin bedded argillite is is exposed exposed on on the the north north face face of of aa ridge ridge capped by diabase. diabase. The argillite is recrystallized recrystallized to to aa biotite— biotitean interval interval of of aa few few inches inches at at the the contact. contact. bearing hornfels over an is typical typical of fine— fine- to to medium—grained medium-grained diabase diabase in in thin thin The diabase is sills the lower lower parts parts of of thick thick sills. sills. sills and in the �—123— -123- Stop 88 Northwest arm of Poplar Lake on the the Gunflint Trail At this stop stop typical exposures and and intrusive intrusive relationships relationships of of At this four of Nathads Nathans units units will be be examined. examined. On the the north north side side of of the the unit unit df, df, a fine—grained fine-grained decussate augite—olivine—plagioclase augite-olivine-plagioclase rock rock the Tuscarora Intrusion intrudes (troctolite) similar to unit ttf ttf of the intrudes (troctolite) unit dc, aa very veryfine—grained fine-grained granular granularolivine—augite—plagioclase olivine-augite-plagioclase rock whichmay mayrepresent representa achilled chilled margin marginofof the the oldest rock (gabbro) (gabbro) which unit of About 50 feet (da). About feet north of the the Trail Trail of the layered series (da). at the east end of the northwest arm of Popular Lake, at the east the north~vest Lake, a small small mass of unit dt, dt, aa medium—grained medium-grained granular granular olivine olivine oxide oxide rock, rock, occurs occurs within unit unit dc. dc. A A small isolated exposure of of unit unit ds ds with with uncertain uncertain contact contact relationships occurs occurs between units dc dc and and df df about about 500 500 feet feet Lake and and 400 400 feet feet north north of of the the Gunflint Gunflint Trail. Trail. northwest of Popular Lake South of of the the Gunflint Gunflint Trail there are exposures of of the the large large oxide— oxiderich sheet sheet unit dg (coarse—grained, foliated oxide, augite, olivine, dg (coarse-grained, foliated oxide, augite, plagioclase rock). plagioclase Stop 9 Sto2j Gunflint Trail Trailsouth southofofBear BearClub ClubLake Lake— - Late granitic granitic rocks rocks Cunflint of the theDuluth DuluthComplex Complex Unit daa, daa, a medium-grained quartz-feldspar rock, rock, is is medium—grained granular quartz—feldspar as aa dike on the the north north side side of exposed as dike in in unit unit dm dm on of the the Gunflint Gunflint Trail. Trail. The mainmass massofofdaa daaoccurs occurssouth southofofthe th Trail 1—1/2 The main Trailasasa astock stock 1-1/2 miles miles across. Unit dm, across. dm, aa cumulate cumulate sheet sheet ofofpigeonite—augite—plagioclase pigeonite-augite-plagioclase rockhas hasvisible visibleinterstitial interstitial quartz rock quartz and and alkali alkali feldspar feldspar in in an an This interinteraureole much as wide around daa. This aureole as much as 11 mile mile wide aroundthe the stock stock of daa. stitial material is interpreted as as replacement associated with the intrusion of unit daa. daa. stitial �This page intentionally left blank �"-"'; ADA ~ N A D A c '''L, . ./I '1''''-,t-'-"~)(. _/ <.~~,;t? x" I 'bJ I u : ST. LOUISI St LOUIS ' x. >. )( Ely. xLAKEx Marais X r AN AT ON P LANATION E E XP IKg XX I [+++ + +++J K xx )( xx xx Duluth Duluth Compte. Complell . O~ so' +)" ~~{ SlIver '" ~ '\. Bo.y ~V 0"" .c: U, '9'" <I)", to -" ~~ -c C ..r="c Zo 4? .!:! > 'C :'2 ::;; y.,e a. a :::> ""'" :.;;; 'E E 'c C <X cr INDEX MAP Figure 1 L 0 o 1 I 10 1O 20 ! I C A A L E if s S e 3Orniles 30 miles I ~{ 4? C 2 N V'1 Mci ic intrusive nt, usive rocks Mafic rocks ci rIrirt Shore of North Shore I , 1/7"-: N I // I ? Ettrus,ve Extrusive rocks rocks rongrnq ranging in from olilJine diem. in Composition composition from bosolr totile and basalt to quartz Quartz lotite local rhyolite tocot rt.yolite [02 4cg lite and Argillite cnd Groywocke Groywacke in Cook Rove Fm. includes Rove Fm. in Cook County County C ~ to ond and Vrginio Virginiaand andI horneon Thomson Fm. Fms. St. Louis Louis County .. in in St. County VO S/ I /-' I Lrl ~ ron —Fottitoijon Iron - Formation ncluces Gunflint C u,f tilt in Cook includes Cook County and B'wo bitt in in St. cnd Biwabik Louis County County SI. Louis o l'iitiu Undiv dod ided >lap showing the geologic 1ap of of northeastern northeastern Hinnesota Minnesota showing settinE of Cook County setting County and and the the location location of of Figure Figure 2. 2. C c: ,,=! n .0 E "'C" 4? .t'" a- �I ~) SAGANAGA ISAGANAGA GRANITE 4800730 —H— CANADA ~ + 0 CMATION AN ROVE FORMATION ANO INTRUSIVE ROCKS LOGAN INTRUSIVE ROCKS df L ds — I i-a I-' Gunflint dq tta I dp db dm -~ ag ~f9+ DULUTH WLUTH COMPLEX LAYERED SERIESOF OF NATHAN NATH\ LAYERED SERIES dm + da DIAGRAM BLOCK 0 dgL--------- DULUTH COMPLEX TUSCARORA INTRuSION '~f\ N 0' Trail BLOCK A DIAGRAM DIAGRAM + B • dm + do Quadrangles Studied Field trip hip stop Field stop seA L E Contact o Fault 3 2 4 = t> ~ ~ 5 mi. .~'*'tl) ~~ ",0", " " ~<b s-v G.:J BWCA boundary boundary BWC.A ~ .'" V ~'(§q, c§'t:: ;§ %o3T•3O' Figure 22 Figure I I Generalized geologic map map of part of of northwestern northwestern Cook Cook County. County. The The Gunflit-it Gunflint Iron-formation is is stippled. stippled. Only the the major units units of of the the Layered Layered Series Series of of Iron—formation in the the Duluth Duluth Complex Complex are are shown. shown. The area designated designated df df also also includes includes Nathan in dc,de,dk,ds,du,dy,dx, and dz; similarly ds dc,de,dk,ds,du,dy,dx, ds includes includes dc,de,dg,dk,dt,du,dv,dw; dc,de,dg,dk,dt,du,dv,dw; dg includes dc,dd,dh,di,du,dv,dt, dc,dd,dh,di,du,dv,dt, and dz; dz; dp dp includes dg,dj,and dg,dj,and dq; dq; db db includes includes (Nathan, 1969). da,dd, da,dd, and dm; dm; and and dm dm includes includes da,dd,de,dn,do, da,6j,de,dn,do, and dx. dx. (Nathan, I I I I I I I I I I I I I I I I I -,'" '" "-~~ ","''I 0/' �SAGAN.GA &EANtTS\ MET *VOLC ANICS LGI.JNFLINT lION FM. M El A V Ot C A N I C S FL I N1,\ .106 A N .IOVE ff N. M. dy I t-' tv ---J I in a \ \ 'I.-~-"'----- \\ \ \\ \ , Ii iJlm,l 0 o md 9r \ ------- -, .)l Figure 33 'I ,fg ' , II \ ~ lmile I dm —1900 -1900 / og 1900 C190° 1100 1700 1700 db 1500 I Soc 1500 A B 300FEET FEET 1300 ~1 FfET L_L-----------.... 1 300 300 EE1 diagrams showing showing the the irif inferred Block diagrams erred geologic geologic relationrelationships of of rock units in the ships the Long Island Lake and Gunflint Gunflint Lake quadrangles quadrangles (location Lake (location of diagrams shown in Figure 2). 2). f �-128—12 8— Mesabi Range Magnetite Hesabi Nagnetite Taconite 8, 1971 1971 May 8, by by R. R. W. W. Narsden Harsden Minnesota, Duluth University of Hinnesota, Duluth, Ninnesota Hinnesota �—129— -129- MESABI RANGE RANGEFIELD FIELD TRIP MESABI INTRODUCTION at the Mineinin Virginia, Virginia, The MesabiRange Rangefield fieldtrip trip starts at The Mesabi the Auburn Auburn Mine Minnesota andproceeds proceedsto to the Erie Minnesota and Erie Mine Mine near near Aurora, Aurora, the theReserve ReserveMine Mine at Babbitt and and ends ends at at the the Dunka Dunka Pit theeast eastend endofof MesabiRange Range at Babbitt Pit atat the thethe Mesabi near Birch trip isisdesigned show near Birch Lake. Lake. The The trip designedtoto showthe themetamorphic metamorphic changes changes the Biwabik iron iron formation formation caused caused by by the the intrusion intrusion of of the the Duluth Duluth in the Complex. The trip plan is shown on the index index map. The Mesabi esabi Range The Range trip trip is is made made possible possible by by the the cooperation cooperation of of the the Minnesota Ore Operations, United United States States Steel Steel Corporation, Corporation, the the Erie Erie other inforMining Company and Reserve Mining Company. Maps and and the Reserve and other Leaders for each part of furnished by the the mining mining companies. companies. Leaders mation were furnished the trip are are shown in the trip trip log. log. Stop 1. 1. Stop AUBURN MINE Leader: Wayne L. L. Plummer The accompanying map, section section and description description of the The accompanying map, stratigraphic sequence gives the geologic geologic setting setting of of the the Auburn Auburn Mine. Mine. The unit numbers shown shown on on the the stratigraphic stratigraphic sequence sequence are are painted on on the the rock rock to to aid recognition recognition of the the horizons. The upper part of the Pokegama quartzite and the Cherty, Lower Lower Slaty and 145 3*5 feet feet of the the Upper Upper Cherty Cherty Lower Cherty, members of the Biwabik formation members formation are are exposed. exposed. Oxidized and partly partly leached Biwabik formation is exposed on on the the west west pit wall wall and the Upper Slaty member and leached Virginia pit formations are exposed in north are exposed in the the slump slumpstructure structure at at the north end end of of the the pit. pit. �44 E S C' RESERVE <4 CQ(\ -1 0÷ I I-. f-' w o0 #9 I 1- Os ,Figure .Figure 11 INDEX MAP INDEX MAP OF THE OF THE MESABI DISTRICT DISTRICT,, MINNESOTA MESABI I I �---ex---• I f-' GRANITE Figure 22 Figure MESABI RANGE RANGE IRON FORMATIONS IRON ( BLACK BLACK AREAS AREAS ARE ARE DIRECT—SHIPPING DIRECT-SHIPPING ORE ORE BODIES BODIES)) U) W I-s f-' I �-132—132— AUBURN MINE MINE AUBURN The is isone the The Auburn AuburnMine Nine oneofofa agroup groupofofopen openpits pits located located near the city of Virginia, Minnesota. It city of Virginia, Minnesota. It was was originally developed as asan anunderground underground originally developed mine by the during the and promine by the Minnesota Minnesota Iron IronCompany Company durin?, theperiod periodfrom from1894—1902 1894-1902 and duced 2,143,000 2,143,000tons tons of of ore prior 1902 duced prior totoclosing closingin in 1902when whenownership ownership passed passed to the Oliver Iron Mining Nining Company, Steel 'Cor'CorOliver Iron Company,a asubsidiary subsidiaryofof United United States States Steel poration. Reopened as an poration. an open by Oliver in in 1951, 1951, the mine produced an openpit pit by 11,219,000 tons tons of of ore ore by by the the end end of of 1969 1969 when whenthe themine minehecirne became additional 11,219,000 inactive because the remaining ore is is under under the the approach approach traccs tracks totothe theViridrtia Virr,inia rescreening plant plant located located just just west west of of the the nine. mine. Most of the the crushing and rescreening open pit ore was loaded loaded by by electric electric shovels shovels into into side side dump dump cars cars and and hauled hauled to to the plant by electric locomotives, but in the plant in the the last last few few years, years, ore ore from from the the lower benches benches was was loaded loaded into into trucks, trucks, hauled hauled to to aa stockpile stockpile beside beside the the track track lower in the the upper part of the in the pit and reloaded into into railroad railroad cars. cars. The Auburn Auburn Nine and other former Oliver Iron }Iining Mining Company mines mines on the Mesabi Ran?,e Rance are are the Mesabi Mine now operated by U. S. S. Steel Steel Corporation, Corporation, Minnesota Minnesota Ore Ore Operations. Operations. The rocks rocks exposed in the the mine starting startin~ at at the the bottom bottom are arc the the the lower lower three three members members of of the the Biwabik Biwabik iron iron formation: formation: Pokegama Quartzite and the Lower Cherty, Cherty, Lower Slaty Slaty and and part part of of the the Upper Upper Cherty. Cherty. These dip dip from from degrees to to 20 20 degrees degrees to to the the northwest northwest as as the the formation formatcy lies north 5 degrees lies on on the the north side of the gently southwestward plunging Eveleth anticline and the center center fold known as the fold the Virginia Virginia Horn. Horn. formed in the Biwabik formation formation by removal The Auburn ore body was formed leaving less less of silica from iron bearing rock by leaching ground waters, waters, leaving soluble iron iron Oxides. oxides. The The ore body follows formation for ore body follows drnvn downthe thedip dipof of the the formation for fissure scarcely 50 about 3000 feet. as a aSlr::. small fissure 50 feet feet about 3000 feet. Beginning as at the the southwestern southwestern part part of of the the mine, the the ore ore body gradually gradually widens wide at toward the the northwest into a larger larger trough trough with with aa maximum maximum width width of of about about toward 500 feet. feet. In the the vertical walled fissure fissure at at the the southwestern southwestern end end of of the the mine, mine, the ore the ore extends extends from from slightly slightly above above the the Quartzite Ouartzite (here (here reduced reduced to to aawhite wite sand) feet of the Lower sand) through through 115 115 feet of the Lower Cherty Cherty member, memher, whereas whereas near near the the west west end end of the mine, the ore extends extends to depth of of about about 260 260 feet feet from from the the surface surface of the mine, the ore to aa depth Duetoto the the leaching to contact. Due leaching of to the the Lower Lower Cherty-Lower Slaty contact. silica, ore zones zones are commonly slumped into structures resembling synclinal structures resembling folds. folds. Where slumping occurs adjacent to to taconite taconite walls, walls, sltnp slump faults faults may ii silica, occur. Glacial deposits deposits consisting of reddish—gray—brown reddish-fray-brown till containing containinff numerous boulders boulders of of granite granite and and greenstone greenstone covered covered the the entire entire area area to numerous to aa depth of 10 to to 35 35 feet. feet. years An earth slide in the northwestern bank of the mine several years was stabilized stabilized with with aa rock fill which now covers covers much much of of previously ago was fill which previously exposed exposcd formation formation in in this this area. area. �-133—13 3— I I I I I I I I ROUCHLEAU MINE VIRGIJ1IIA I --l-- I ------ I I I I -j-----t---- ! i I I I " \/Jf'~O~ ~Oo @ V CRUSHER SCREENING -L __ PLANT --- \ \ RIqQ: \ .::>(( \ \ \---_--I \ Figure 33 Figure ~ II1- GEOLOGIC MAP AND VICINITY VTCINITY GEOLOGTC MAPOF OF AUBURN AUBURNMJr~E M:rE AND �-134-134— Table 11 Table STRATIGRAPRIC SEQUENCE G'mATIGRAPHIC SEQUENCE IN THE THEBIWABflC BIWABIK ThON IRONFORMATION FORMATION AUBURN ICIE AUBURN KmE Thickness 'l'h1ckness in feet1 in teet l UPPER CHERTY MEMBER 16.22 Jaspery, algal chert (G 16. Jaspery, conglorieratic conglomeratic and and algal submember I) (a and S $ submember x) 15. 14. 14. 13. 13. 12. 10 (eat.) (est.) Covered Covered interval interval 10 (est.) (eat.) Nodular hematitic chert chert. beds interbedded interbedded with with laminated hematite-eilicate-magnetite beds hematite-silicate-magnetite 48 48 +1' +f Laminatedhematite-uilicate-magnetite heniatite-ailicate-magnetite beds with subordinate Laminated jaspery chert beds Jaspery beds and and lenses 31 Jaspery, conglcaneratic chert beds with subJaspery, conglomeratic chert beds interbedded interbedded with ordinate laminated laminated heinatite-ailicate-magnetite hematite-silicate-magnetite beds beds 28 liberty taconite taconite with magnetite Cherty with thin thinirregular irregular magnetitebeds, beds,mqgfl* magneanddisseminated disseminated 'retite tite mottles mottles and mBgnetite 16_ _--=~ ....,;;1;;,;;6 143 LUiQER $LATY MEMBER3 11. U. 10. silicate magnetite Laminated silicate magnetite taconite taconite with withsubordinate subordinate silicate chert chert lenses lenses silicate Laminated non-magnetic silicate taconite, part. Laminated non-magnetic silicate taconite,fissile fissile in in part. 6' of fissile fissile"intermediate "intermediate slate" slate" at atbottom bottan (a (G and S 6' of submember Q) 6ubmember Q) 101 .....37 3;.;7_--=~ 138 ER LC1WER CHERTY MEMBER LO CHERTY Cherty with irregular irregularrnngnetite magnetite beds. Upper Upper 10' liberty taconite taconite with has silicate rich has dark-colored dark-colored silicate richbeds beds instead instead of ofmagnetite magnetite beds, ng base of lower indefinite beds, mak4 making lower slaty slatysomewhat somewhat indefinite 37 37 8. Mottled with chert "pebbles" and and Mottled silicate-magnetite silicate-magnetite chert with abundant coarse coarse granules. abundant U 11 7. 7. Cherty taconite with with thick thick (i"±) (1 t)magnetite magnetite beds beds and and mottles mottles liberty 84 9. 9. 6. 1f Mottled cherty very irregular irregularmagnetite magnetite Mottled cherty taconite taconite with with thin, thin, very beds. 14 5." Thick jaspery chert beds beds interbedded interbedded with with varying varying proporproporThick 5. tions of of thin, thin,regular regularlaminated lBDlinatedinngnetite-hematite-. magnetite-hemat1te-s1l1cateilicate- carbonate carbonate beds beds.• 66 �-135—135— Thlckneoo Thickne on l feet1 in feet (ConYd) Ldwer Cherty Member Member (Cont'd) Lover Cherty Fflyft, 'rhi c k henicstitic hem~~ti tic chert beJa beis with witb subordinate sulJordinate laminated laminated zonos. Seineclastic elastic sand sand grains grains near zones. Some near bottcn. bottan. Much carbonate. 8a Jaspery, ehert with subordinate Jaspery, conc'lomeratic conglomeratic and algal chert subordinate laminated zones. lnminnted zonea. Sand graino graino common. common. 4:4 2. z. l'lassivechlorit1c chioritic (or (or hematitic) hematitic) sandstone sandstone l-lilsslve 8 8 1. 1. Jaspery, Juapcry, conglomeratic and algal algal 4.. 3. chert 4 4: 236 Total thickness exposed Total, 5I7 Base not exposed Base exposed P0iGAl4A QUARTZ ITE ** ** * ** * * * ** 1. 1. Units 15 and onbank bankbetween betweentruck truckroed road,and andrailroad railroad near entrance Units and 16 measured measured on entrance to pit. pit. Units measured on on SW bank, at at BE end end,ofof pit. pit. Remainder measured. to Units 11 - 5 measured S\rl bank, measured above railroad. above railroad. 2. Unit correspondtoto numbers numberspainted paintedon onthe the walls walls of the Unit nwubers numbers correspond theAtthun Auburn Mine Mine and and are not Intended intended to be a new stratigraphic stratigraphic system. system. 3. 3. exists The lower lower slaty-upper slaty-upper cherty cherty contact contact is 1s not not well—marked, well-marked and and disagreement disagreement exists to its its position. position. as to ** ** ** ** ** * * orebody bodyisis of of the fissure or The Auburn Auburn ore or trough trough type type and and its and its location and 0 W, 400 W, nearly nearly appear to be controlled controlled by set striking strikingabout aboutNN 40 orientation appear to be by aa fracture set at right At the SE of the the mine at right angles angles to to the the strike strikeofofthe theiron ironformation. formation. At SE end. end. of mine the trough is only from the the quartzite quartzite through trough only 50' 50' wide wide and and the theore oreextended extended upward upward from through about about U5' ofofthe At the the northwest end the the trough trough 1s is 500 115' theLower LowerCherty Chertymember. member. At northwest end 500 feet feet wide wide and and ore ore occurs occurs for about about 260 Z60 feet feetfrcmt fran the the Lover Lower Slaty-Lcwer Slaty-Lower Cherty Chertycontact contact to to the Exceflent examples examplesofofore oreslump slumpstructures structurescan canbebeseen seenin in the the ends of the outcrop. Excellent eDds ot pit, pit, especially especiallyatatthe thenorthwest northwestend.. end. �-136— -136- Mine sLown ERIE MINE MINE —- The stops in inthe theErie Erie Mineare are shownon onthe theaccompanying accompanying map. The Erie geologists designate units in in the the Biwabik Biwabik formation formation as follows: A—F A-F G-O G—O P—Q P-Q R—W R-W Leader: Stop 2. 2. Upper Upper Lower Lower Slaty member — - .av. 110' 110' av. Cherty member - avo 185' 185' Slaty member — - av. avo 105' Cherty member — - av. avo 125' Forrest W. W. Boyce Bovee Erie —- Pit 1 West This stop the upper part part of the the Lower Lower Cherty member This stop is is in the (units are are designated TT and and SS layers layers by by Erie). Erie). The Biwabik (units formation is is composed composed of of tine fine Stilpnomelane, Stilpnomelane, I!innesotaite, Minnesotaite, magnetite and cherty quartz and contains bands, mottles quartz and contains bands, mottles and and blotches blotches of' of pink to yellow carbonate. carbonate. Stop 3. 3. Erie Pit 2 West This stop stop is is in in middle to to upper upper part part of of the the Upper Upper Cherty Cherty with the the member and the lower part of the Upper Slaty member (F) (F) with in this this pit pit are algal layer (I) (I) well exposed. exposed. (Units (Units in are designated (Upper Slaty), G, G, H, H, I, I, JJ and and KK by by Erie). Erie). A A diabase sill about about F, (Upper feet in thickness occurs near the bottom of 33 feet of the the exposed exposed iron iron formation in the KK layer. layer. Some green green mottles mottles of of cuminingtonite cummingtonite occur in the I J layer layer and and carbonate carbonate mottles mottles in in the the KK layer. layer. Stop Stop 4. . Erie Pit Pit 33 This stop is in in the western part part of of Pit Pit 33 in T, S. S. and BR of the the Lower Lower Cherty Cherty member. member. The layers in the middle part of rock is a cherty, silicate silicate taconite taconite with with layers layers of of cummingtonite. cummingtonite. Stop 5. Stop 5. Erie Pit Pit 33 This stop stop is is in the the eastern part of pit 33 in the T, CS and R F in about about the the same same stratigraphic stratigraphic layers of the Lower Cherty member in zone as as stop stop 4. 4. Much of the chert in the Biwabik formation formation has has gone to form form actinolite actinolite and and cumniingtonite. cummingtonite. The rock is termed taconite. Locally pyrrhotite occurs occurs in in the the a magnetite-silicate magnetite—sflicate taconite. iron formation. formation. �ERIE MINING COMPANY COMPANY ERIE MINING Of MAP OF E-1835.2 E— 1835 • 2 PLANT 8 MINE AREAS AREAS & MINE LEGEND o CRUSHER CDCOAR COARSE CRUSHER ®FINE FINE CRUSHER CRUSHER ® @ CONCENTRATOR CONCENTRATOR ® .j)PELLET @ PELLET PLANT ® ® ® LOADING LOADING POCIET POCKET ®STOCKPILE STOCKPILE ® CD GENERAL SHOPS SHOPS .1; ADI.IINISTRATION AOMINISTRATION BUILDING S I I-' La) LV ....... I AREA I S Figure 44 Figure Plan of of Erie Pit Plan Erie Pit — �—138— -133- RESERVE MINING COMPANY COMPANY Minil1g Company Company mine mine is is situated situated in in aa zone zone with ~vith aa The Reserve Miniqg considera~le considerable range in mineralogy and texture texture shown shown by by the the Biwabik Biwabik formation. formation. The The Reserve Reserve geologists geologists designate designate units units of of the the Biwabik Biwabik formation as follows: follows: A—G A-G 11—0 H-O P—Q P-Q R-V H—V Stop Stop 6. Upper Upper Lower Lower 100130 av.—120 Slaty member member -— 100'-130' av.-120 Cherty 120—160' av.—140 Chertymember member—- 120-160' av.-140 Slaty member —- 75—120' 75-120' av.'90 av.-90 Cherty member — - 30'-50' av.-30 30'—50' av.—30 Reserve Mine Mine (Peter Mitchell HitcheEMine) Hine) Leader: James James i1. W. Emanuelson Emanuelson This sstop is in This top is in the the western ~ves tern part part of of the the mine, mine, northwest of of Crusher No. No.22 in the the middle middle part partofofthe theUpper UpperCherty Chertymember member in in the J, KK and rock is silicate taconite with J, and L L zones. zones. The The rock is aamagnetite magnetite—- silicate abundant cuznnhingtonite. cummingtonite. Stop Stop 7. 7. Reserve Mine Mine This stop is in same general stratigranhic stratigraphic zone zone as as stop stop 6. 6. with Hith The rock rock is layers from from FF to 00 exposed. exposed. The is aamagnetite—quartz—silicate magnetite-quartz-silicate taconite with and garnet. garnet. There taconite with hedenbergite, hedenbergite, ferro—hypersthene, ferro-hypersthene, and There are local local areas areas of of pegmatite. pegmatite. Stop 8. 8. Dunka Pit The Dunka Erie ['lining Mining Company Company isissituated Dunkapit pit of of the Erie situated near near the eastern end of the Rangewhere wherethe the Bhvabik Biwabik formation formation is eastern end of the Hesabi Nesabi Range by the theDuluth DuluthComplex. Complex. This Hill show show the upper upper This stop will, intruded by part of the part Upper Cherty the Upper Upper Slaty Slaty the Upper Cherty member, member,the thelower lowerpart part of of the member,and and gabbro gabbro of of the member, the Duluth DuluthComplex. Complex. The is composed composed of magnetite, hedenbergite, hedenbergite, The taconite taconite is of quartz, quartz, magnetite, fayalite with with andradite andradite garnet garnet and and locally locallysome some hessingerite hessingerite fayalite The contains suiphides, sulphides, chalcopyrite chalcopyrite and and Thegabbro gabbroininthis this area contains pyrrhotite with pyrrhotite with pentlandite. pentlandite. The iron iron formation formation and andgabbro gabbrowill willbe be observed observedinin the the pit pit and The and in north of of the the pit. pit. in outcrops outcrops north �— -' __I / / ea _I - —— __i SCALE SCALE IN IN MILES MILES —11 4 0 5 2Z 5 / / / / / I I tO / / 'sTrOe,. stnva / I /8 /& 8/~ "E i/l '7 '2OA f/~ STAfiC) "I<c 0: I~ " "/>c / 460 400 / I I I I I (.0 '0 / I I / / / / / - -&try / p -— 2C • 0 SCA.E SC --' AtFtPC i.E iS 5ØS StS?iOeiCO AT iJJ) FT iNT€vSiS SIRS DPI ROADS C IAD DPI F Lint STh YISG co-s5i0$i SHO_ O&nI. ms •PT OLJTLIIA • S Off _ _N PIT Oln'LJNE,I.S - ';"b6 ZC = SCALE ,", 2000' JAN 196~ JQ'I . . . . 10A- I Figure Figure 55 Plan of Plan of Reserve Reserve Mine Mine �lL ERIE ERIE MINING MINING COMPANY COMPANY HOYT PLANT HOYT LAKES LAKES PLANT PLANTSITE TO TO DUNKA DUNKA PIT PIT AREA AREA Figure 6 U, DUNKA PIT BABBITT / ¶ '\ y/ ~ --- C -- 01 \J c:> I I-' ...... o0 .pI RESERVE MINING co. CRUSHER No.2 AREArJ ,, . ., , . , r-. :' ~ l P P L SIT E r-- ) ~ ( I I �—141— -141- of the Metavolcanic— Geology of the Vermilion MetavolcanicMetasedimentary Belt, Belt, Northeastern Minnesota May 8, 1971 Prepared by R. R. \v. U. Ojakangas, Ojakangas, University University of of Ninnesota, iinnesota, Duluth, Duluth, and and Ninnesota Geological Survey P. P. K. Sims, Sims, Minnesota Geological Survey, K. Survey, Minneapolis, Minneapolis, Minnesota C. G. B. Norey, Morey, Hinnesota Minnesota Geological Survey B. Survey Minneapolis, Minneapolis, Minnesota J. J. C. C. Green, Green, University University of of Minnesota, Minnesota, Duluth, Duluth, and Minnesota Geological Survey �—14 2— -142- Guide to Metavolcanicto the the Geology of of the Vermilion Metavolcanic— Belt; Northeastern Minnesota Metasedimentary Belt; INTRODUCTION The The Vermilion district is is a a belt of metavolcanic-metasedimentary metavolcanic—metasedimentary rocks rocks more than 100 100 miles long long and and as as much much as as 20 20 miles miles wide. wide. It is is bordered on on the the north north and and south south by by younger younger granitic granitic batholiths batholiths (Fig. (Fig. 1) 1) of Algoman Algoman (Kenoran) (Kenoran) age. age. The region is typical of Lower Precambrian (>2,500 greenstone—metasediment--granite complexes complexes of of the the Superior (>2,500 m.y.) greenstone-metasediment-granite province. metavolcanic—metasedimentary sequence constitutes a complex The metavolcanic-metasedimentary volcanic pile, pile, characterized characterized by interfingering of lithologies and local local volcanism. Most of the the metasediinents metasediments are composed of of repetitions of volcanism. volcanic detritus, detritus, and probably include volcaniclastic and and epiclastic rocks. Numerous Numerous coeval and younger igneous rocks rocks occur locally within the sequence. sequence. The stratified sequence was metamorphosed and and deformed deformed before before and and during emplacement of the bordering granitic rocks rocks of the the Giants Range and the the Vermilion Vermilion batholith. batholith. Pervasive greensehist greenschist facies facies batholith and assemblages were developed except adjacent to the the intrusive bodies where metamorphism attained aniphibolite amphibolite grade. Deformation consisted consisted of of two two metamorphism attained major foldings foldings and and of of later later faulting faulting on on aa major major scale. scale. STRATIGRAPHY ST RATIGRAPHY The metavolcanic and metasedimentary rocks rocks are are assigned assigned to to five five The oldest oldest formation, (Morey and and others, others, 1970). 1970). The formation, the the Ely formations (Morey is overlain Greenstone overlain Creenstone -— composed mainly of mafic mafic metavolcanic metavolcanic rocks rocks -— is stratigraphically in the west by the Lake Vermilion Formation and locally, locally, the Soudan Iron—formation, Iron-formation, and in the central part by the the Knife Lake Group (Figs. (Figs. 22 && 3). 3). Both the Lake Vermilion Formation and the Knife Lake Group Group are composed mainly of intermediate—felsic the Knife intermediate-felsic pyro— pyroand volcanogenic volcanogenic sandstones. sandstones. The Newton Lake Formation, Formation, clastic deposits and a younger mafic to to intermediate-felsic unit, overlies the a intermediate—felsic metavolcanic unit, Knife Knife Lake Lake Group Group in the the central part part of of the district and interfingers with it to the east (Fig. it (Fig. 3). 3). A A generalized and idealized pre—deformational pre-deformational stratigraphic sequence the western part part of the district is shown in sequence for for the figure 4. 4. Ely Greenstone Greenstone Ely Greenstone, Greenstone, as as redefined redefined (?Iorey (Horey and others, 1970), 1970), is is an The Ely an elongate body of dominantly mafic metavolcanic rocks, rocks, on the the average 2—4 2-4 miles miles wide, wide, that that extends from the vicinity of Tower eastward to to distance of of about about 40 40 miles miles (Figs. (Figs. 22 && 3). 3). Pillowed or or Moose Lake, aa distance lavas and metadiabase dominate dominate the the formation. formation. massive metabasaltic lavas pyroclastic Pillowed lavas of andesitic comnosition, composition, interinediate—felsic intermediate-felsic pyroclastic �-143—14 3— ic—intermediate epiclastic epiclastic deposits, deposits, chert chert and banded deposits, maf mafic-intermediate iron-formation, tuff (?) (?) comprise comprise the the iron—formation, and siliceous carbonaceous tuff remainder. Andesite and and dacite dacite porphyry porphyry are are conmion common hypabyssal hypabyssal intrusive rocks. rocks. The green color of most of of the the rocks rocks is is due due to to abundant secondary chlorite and green amphibole. abundant amphibole. at about The ruaxinul maximum exposed estimated at about exposedthickness thicknessofofthe the Ely Ely is is estimated feet; the are consistently to the 15,000 feet; the tops tops of of separate separate flows flows are consistently to the north, north, as indicated by by pillows. pillows. as indicated Soudan Iron—formation Iron-formation The The Soudan Iron—formation, Iron-formation, the the thickest thickest and and most most continuous continuous banded iron-formation iron—formation in in the the sequence, sequence, extends extends from from Tower Tower and and Soudan Soudan eastward eastward for a a distance of about 16 miles (Fig. (Fig. 2). 2). for In In the the Tower-Soudan Tower—Soudan area area it it is is ov~rlain overlain directly directly by by intermediate— intermediatefelsic volcaniclastic rocks of the felsic the Lake Lake Vermilion Vermilion Formation, Formation, whereas whereas east east (Fig. 2) 2) it it is is overlain directly by at least 7,000 7,000 feet feet of Armstrong Lake (Fig. of metavolcanicrocks rocks with with lenses of mafic—interinediate mafic-intermediate metavolcanic lenses ofofbanded bandediron— ironThus, the formation, which are are assigned assigned to to the the Ely Ely Greenstone. Greenstone. Thus, the Soudan, Soudan, which represents a time—stratigraphic time-stratigraphic unit, unit, is is a useful indicator of the the essential contemporaneity contemporaneity of of intermediate-felsic intermediate—felsic volcanism in the west west essential in the (Lake Vermilion Vermilion Formation) Formation) and and mafic mafic volcanism in the east (Ely (Lake (Ely Greenstone). The Soudan Iron—formation, as redefined 1910), The Iron-formation, as redefined (Morey (Morey and others, others, 1970), consists of several several types of ferruginous ferruginous cherts cherts that consists of types of that are interbedded meta— with fine—grained fine-grained carbonaceous carbonaceous and and sericitic sericitic tuffs tuffs (?) (7) and local metabasalt; all are are intruded intruded by by metadiabase metadiabase and and dacitic dacitic porphyries. porphyries. The thickness thickness of of the the formation formation has has not not been been determined determined accurately accurately because because probably is of complex folding, folding, but probably is less than 1,000 feet. feet. It It should be noted that the in the Ely the iron—formation iron-formation in Ely trough trough (Reid, (Reid, 1956), 1956), which which has has yielded hematite iron iron ore, ore, probably yielded large quantities quantitiesofofhigh—grade high-grade hematite probably is is not equivalent equivalent to to the Soudan Iron—formation. Iron-formation. The high—grade high-grade hematite ores that that were the Soudan Iron—formation Iron-formation at at Soudan (Klinger, (Klinger, ores were mined in the 1956) and and in in the the banded banded iron-formation iron—formation at at Ely Ely (Machamer, 1968) are are 1956) (Machamer, 1968) considered to to have been formed formed by by hydrothermal hydrothermal processes processes (Gruner, (Gruner, 1926). 1926). FO~lation Lake Vermilion Formation In the extreme the district ~Fig. 2), 2), the Lake In the extreme ~~estern western part part of of the district (Fig. Vermilion Formation Formation overlies theEly ElyGreenstone Greenstone or orthe theSoudan Soudan overlies either either the Iron—formation. Until recently these strata were assigned to the Iron-formation. the Knife Lake Lake Group. Group. They were reassigned (Morey (Morey and others, 1970) to to the Lake Vermilion Formation because they the they are not demonstrably concontinuous the Knife tinuous with with strata strata exposed exposed in in the the type type area of of the Knife Lake, Lake, in the eastern part part of of the the district. district. formation which has has been The Lake Vermilion is aa heterogeneous formation divided (Morey (Morey and and others, others, 1970) into four fourinformal informal members — - a fe1dspathic 1910) into members feldspathic quartzite member, member, member, a metagraywacke-slate metagraywacke—slate member, member, a volcaniclastic member, and a mixed metagra~vacke-felsic metagraywacke—felsic conglomerate conglomerate member. member. �—144— -144- The feldspathic quartzite member, member, composed dominantly of -ts volcanogenic minerals and and rock rock fragments fragments of of dacitic dacitic composition, composition, is in at the the fold fold nose nose southwest southwest of of Tower Tower in contact contact with with the the Ely Ely Greenstone Grenstone at (Fig. 2), than the the metagraywacke-slate as indicated indicated (Fig. 2), and and is is older than metagraywacke—slate member, as by graded graded beds. beds. The metagraywacke-slate metagraywacke—slate member, member, which Is is areally area11y the most extensive member, overlies the the Ely Greenstone locally, locally, as as member, directly overlies the south south limb limb of of the the fold fold at at Tower, Tower, but but for for the the most most 'part ,part Is is in in contact contact on the with the the older quartzite. The graywacke graywack~generally generally are well bedded and commonly are are graded; graded; like like the the feldspathic feldspathic quartzite, quartzite, they they consist consist mainly mainly commonly of volcanogenic volcanogenic debris. debris. A A chioritic chloritic facies occurs on on the the shores shores of of the the fades occurs eastern part part of of Lake Lake Vermilion, Vermilion, but but aa biotitic biotitic facies, fades, containing containing scattered scattered amphibole, amphibole, is is dominant dominant elsewhere. elsewhere. The member contains several interbedded lenses of metabasalt that that are are sufficiently sufficiently large large to to be be shown sho\vu on on figure figure 2. 2. The volcaniclastic member is is of interest because it was interp:eted inter~~eted previously to 1903) related to to be mainly aa conglomerate (Clements, (Clements, 1903) to the the Laurentian orogeny. Instead, it it is orogeny. Instead, is dominantly tuff tuff and and agglomerate agglomerate of of dacitic composition, with lesser lesser dacitic dacitic lavas, lavas, banded banded iron—formations, iron-formations s and euxenic black black slates. slates. Locally, Locally, dacite porphyry intrudes the the various rock types. The agglomerates, agglomerates, which which are are interbedded with tuffs, types. The interbedded with tuffs, consist consist cobbles and boulders in a of sub—rounded sub-rounded felsite felsite to to felsite felsite porphyry cobbles and boulders txotic rock fragments, fine-grained matrix of similar similar composition. composition. Exotic fragments, mainly fine—grained iron-formation and greenstone, constitute constitute only only one one or or two two percent of the the iron—formation rock. metagraywacke—felsic conglomerate member, member, which occupies The mixed metagraywacke-felsic occupies an of about about 30 square miles miles on the south limb of the of an area of 30 square the south limb of the fold fold south of Tower, interfingers with and and is is stratigraphically stratigraphically overlain overláin by the meta— Tower, interfingers with the metaIt consists consists of of a graywacke-slate member member (Fig. (Fig. 2). 2). It a maximum of about graywacke—slate 10,000 feet feet of to mafic rocks, felsite felsite flows, flows, several several of felsic felsic to mafic volcaniclastic volcaniclästic rocks, types and metagraywacke metagraywacke (Griffin, (Griffin, 1969; 1969; types of of cong1.omerates conglomerates and agglomerates, and Griffin and Morey, 1969). 1969). The thickness thickness of the the Lake its constituent constituent Lake Vermilion Formation and its members is poorly known because of complex complex folding and faulting faulting and and rather poor exposures. exposures. In the the Tower quadrangle, quadrangle, the quartzite member is estimated to to be the volcaniclastic member is be 1,500-2 1,500—2,000 feet thick and the t OOO feet metagraywacke—slate to be a maximum of about about 4,000—5,000 4,000-5,000 feet feet thick. thick. The metagraywacke-slate to is at at least least 3,000 3,000 feet feet thick thick and and is is probably probably much much thicker. thicker. member is Knife Lake Group Rocks of the Knife Knife Lake Group directly overlie the Ely Greenstone Rocks from the vicinity of Ely, Ely, where the the Knife Knife Lake Lake terminates terminates against against aa fault, fault, from The Knife Group, as eastward to to Moose Moose Lake Lake (Fig. (Fig. 3). 3). The Knife Lake Group, as redefined eastward (Morey consists dominantly of graywacke, gra~vacke, slate, slate, and and (Morey and and others, others, 1970), 1970), consists lava phyllite but includes includes substantial amounts amounts of pyroclastic rocks, rocks, lava flows, and and conglomerates. conglomerates. Gruner (1941, (1941, p. p. 1624) estimated that that the the flows, 15,000 the eastern end of the district district is about 15,000 feet feet Knife Lake near the thick, but this figure may be conservative. conservative. thick, but this �—145— -145- Newton Lake Formation The Newton Lake Lake Formation Formation was was mapped mapped earlier earlier (Clements, (Clements, 1903) 1903) as Ely Greenstone, but has been renamed (Morey as Ely Greenstone, (Morey and and others, others, 1970; 1970; Green, Green, l970)because it is stratigraphically younger 1970)because younger than than the the Knife Knife Lake Lake Group Group (Fig. the north north by by the the Vermilion (Fig. 3). 3). The formation formation is is truncated truncated on the fault and and along along strike to fault to the the northeast by granitic rocks rocks of of the the Vermilion batholjth. batholith. At its its western extremity, extremitYt near near :olf Wolf Lake, Lake, the the is truncated truncated by by aa fault fault (Fig. (Fig. 2). 2). formation is The western western part part of of the Lake formation formation is is composed principrinciThe the Newton Lake pally of of mafic mafic volcanics volcanics and and the the eastern eastern part part of of intermediate-felsic intermediate—felsic pally members,t which interfinger in volcanic members in the the vicinity vicinity of of Newton Newton Lake. Lake. volcanic member member consists consists dominantly dominantly of of metabasalt metabasalt and and metameta— The mafic volcanic andesite and fine—to—coarse—grained fine-to-coarse-grained andesite lavas lavas,t some some of of which are pillowed, and metadiabase and tuff tuff or tuff—breccia. tuff-breccia. Several small bodies of serpen— serpentinized peridotite are are associated spatially with the tinized the metabasalt metabasalt and and metadiabase. Small Small lenses lenses of of siliceous siliceous marble marble and and banded banded iron-formation iron—formation in the the formation. formation. The felsic member, east east of of Newton Newton Lake, Lake t occur locally in is composed composed of of felsic—intermediate is felsic-intermediate volcanics, dominantly dominantly tuff—breccia tuff-breccia deposits and and lesser lesser flows. flows. At places, metabasalt is is interbedded interbedded with the dominantly felsic volcanics. the Intrusive Rocks Five activity are are recognized recognized in in the the Five distinct distinct episodes of intrusive activity region. In In order age, from from oldest to to youngest, youngest, these these are are order of of inferred age, (1) synvolcanic have aa (1) synvolcanic bodies, bodies, including including hypabyssal porphyries, which have metadiabase and and metagabbro, metagabbro, and serpentinized wide range of composition, composition, metadiabase serpentinized peridotite (2) lamprophyres and related related hornblende—bearing hornblende-bearing rocks, rocks, (3) (3) peridotite,t (2) plutonic plutonic rocks rocks of of the the Giants Giants Range Range and and Vermilion Vermilion batholiths, batholiths, which which are are syntectonic, (4) altered diorite—gabbro diorite-gabbro which forms forms large large dikes dikes that that are are syntectonic, (4) post-tectonic, (5) basalt, basalt, which forms forms small, small, discontinuous, discontinuous, scattered scattered post—tectonic, and (5) dikes. In the Saganaga Granite of Winchell (1888) (1888) at at the the eastern eastern In addition, addition, the end of the district (Fig. end (Fig. 1) in age age to to the the 1) is is approximately equivalent in rocks of the rocks the two two batholiths batholiths and and intrudes intrudes the the older older rnetavolcanics metavolcanics (Grout, (Grout, 1929; and Goldich, Goldich, 1970). 1970). 1929; Hanson and The rocks of The plutonic plutonic rocks of the the Vermilion Vermilion and and Giants Giants Range Range batholiths batholiths proprofoundly affected the the volcanic—sedimentary volcanic-sedimentary sequence. sequence. Granitic rocks rocks of of the the foundly on the the south, south, irregularly irregularly intrude intrude the the composite Giants Range batholith, on sequence or are in fault contact contact with it, it, and and have have cut cut out out an an unknown unknown amount amount of section at Where the granite is at the the base base of of the the Ely Ely Greenstone. Greenstone. ~~ere is not in in fault with the the lower-grade lower—grade volcanic-sedimentary volcanic—sedimentary rocks, rocks, it it has has normal normal fault contact contact with to the the older older strata, strata, with with the the development development of of intrusive relationships to amphibolite-facies to the the contact. contact. The Vermilion amphibolite—facies assemblages adjacent to batholith, on on the the north side the district, transects the the upper side of of the district, transects upper stratistrati— graphic part of the the supracrustal sequence. sequence. This leucocratic biotite biotite granite granite includes wide wide zones of abundant inclusions of biotite schist includes zones of schist and and amphibolite amphibolite STRUCTURE The metavolcanic metavolcanic and rocks dominantly constitute a and metasedimentary rocks homoclinal, northward—younging homoclinal, northward-younging sequence sequence in in the the central central part part of of the the district, district, �-146—146-whereas they are faulted in in the the western western and and are both complexly folded folded and and faulted eastern parts. parts. Deformation was not pervasive, pervasive, and and primary primary structures structures Graded bedding and other primary features remain in most of of the the rocks. rocks. Graded features remain in the the graywacke—slate gray\vacke-slate successions, and and pillow pillow structu:es structu::es and and variolites are remarkably well preserved in the mafic metavolcanic remarkably preserved in the mafic metavolcanic rocks. rocks. At places, however, hmvever, a penetrative penetrative deformation, deformation, mainly mainly shearing, shearing, has has obliterated the the bedding. bedding. the western part of the area the the rocks rocks are are complexly complexly folded folded as as In the aa result two distinct episodes of deformation. deformation. The younger folds folds and and result of of two aa pervasive accompanying cleavage largely largely obscure obscure the the older older folds, folds, alalthough though the the older folds folds were important in in determining determining the the distribution distribution of the rocks. rocks. Detailed studies in in the the Tower quadrangle quadrangle and and adjacent adjacent areas areas (Hooper and Ojakangas, Ojakangas, 1971) 1971) indicate that (Hooper and that the metasedimentary strata, strata, and to to aa lesser degree the metavolcanic rocks, rocks, first first were ,,,ere folded folded on on west'iVestThese (F1) folds were tight to isoclinal, had northwest-trending axes. axes. (fo ) folds tvere tight to isoclinal, had northwest—trending l steep axial axial planes, planes, and probably had gentle or steep or moderate moderate plunges. plunges. Major ~lajor fold axes, axes, as as determined by consistently facing fold facing or or opposing opposing tops tops of of beds, beds, were spaced from from 700 700 to to 1,500 1,500 feet feet apart. apart. The younger (F2) (F ) folds, folds, which 2 most of comprise most of the mappable ones, ones, are are strongly strongly asymmetric asymmetrlc and and have have In most most of of the area the (F2) steep axial planes that that trend trend eastward. eastvlard. In (F ) folds folds 2 are dominantly Z—folds, are Z-folds, and the the northwest—trending northwest-trending limbs limbs are are two two or or more more times longer than the southwest—trending southwest-trending limbs; limbs; plunges plunges are are generally generally times of aa pervasive, pervasive, mild, mild, axial axial plane plane cleavage cleavage with with steep. The intersection intersection of In biotitebiotite— and higher—grade to F2 fo fold fold axes. axes. In higher-grade rocks, rocks, bedding is parallel to 2 to the the cleavage—bedding cleavage-bedding intersection. intersection. new minerals minerals are aligned parallel to In joints, In the the Tower Tower area, area, several several nearly nearly vertical vertical structures structures -— faults, faults, joints, and third deformation deformation displace displace the the cleavage cleavage of of the the F2 F and kink bands of a third 2 deformation. High—angle faults High-angle faults of two two trends, trends, longitudinal longitudinal and and transverse, transverse, break break the metavolcanic—metasedimentary sequence the metavolcanic-metasedimentary sequence into into aa number number of of blocks blocks or or segments and separate it in part from from the the marginal batholithic batholithic rocks. rocks. segments The Vermilion fault fault (Sims (Sims and and others, 1968), 1968), aa longitudinal longitudinal fault fault with with an inferred length of 300 300 miles (Sims, (Sims, 1970) 1970) generally generally separates separates the the Vermilion batholith and associated amphibolite facies facies schists schists from from lower— lm"ergrade rocks of of the the district. district. The directioncl the the horizontal horizontal The amount and directionof component of of movement component movement is not known, known, but but possibly possibly is is several several miles. miles. The vertical displacement is inferred to be on the order of a mile, bring displacement is inferred to on the order of a mile, to to bring higher-temperature-facies higher—temperature--facies rocks rocks on on the the north north against against lower-temperaturelower—temperature— facies facies rocks rocks in in the the district. district. Other longitudinal faults, faults, some some of which ,,,hi-ch appear to to be be strands strands from from the the Vermilion fault, fault, slice the the northern part part of the district into of into separate separate segments. segments. The transverse transverse faults faults trend trend northeastward or north—northeastward north-northeastward and have have dominantly dominantly left left lateral lateral displacements; the principal faults displacements; faults of this this Set set have have measureable measureable displacements 3-4 miles (Griffin (Griffin and and Morey, ~1orey, 1969). 19(9). displacements of of about 3—4 The The major faults faults of the area are expressed expressed commonly commonly as as narrow, narrow, Where exposed, linear topographic depressions. depressions. I,'here exposed, they are are seen seen to to of wide zones of crushed crushed and and altered altered rock rock or or of of intensely intensely consist either of silicified and altered altered rocks. rocks. �-147—14 7— Selected References Clements, J. ri., U., 1903, C1e~ents, J. 1903, The Vermilion iron—bearing iron-bearing district district of of Minnesota: Minnesota: U. S. U. S. Geol. Geol. Survey Survey Mon. Hon. 45, 45, 463 463 p. p. Coldich, S. S. S., S., Nier, Nier, A. A. 0., 0., Baadsgaard, Baadsgaard, Ha1fden, Halfden, Hoffman, Hoffman, J. J. H., H., and and Goldich, Krue;er, H. U. The P:ecambrian geology and geochronology Krueger, H. IV., 1961, The P::ecambrian and geochronology of of ilinnesota: dinnesota: [inn. Hinn. Geol. Geol. Survey Survey Bull. Bull. 41, 41, 193 193 p. p. , Green, C., 1970, 1970, Lower Precambrian rocks rocks of of the the Cabbro Gabbro Lake Lake quadquadGreen, J. J. C., rangle, rang1e, northeastern northeastern Minnesota: }1innesota: :--1inn. Geol. Survey, Survey, Spec. Spec. Pub. Pub. Minn. Geol. ser., ser., SP—10, SP-10, 96 96 p. p. Griffin, L., 1969, Embarrass quadrangle, quadrangle, St. St. Louis Louis County, County, Minnesota: Minnesota: Griffin, ,~. U. L., Minn. Ceol. ~Hnn. Geol. Su—vey Su-vey Misc. Misc. Map Hap Sec., Ser., MaD Map M—6. 1'1-6. Griffin, Griffin, U. IV. L., L., and and ?torey, !'forey, G. C. B., 8., 1969, 1969, The The geology geology of of the Isaac Lake Minn. Geol. Survey, quadrangle, quadrangle, St. St. Louis County, County, Minnesota: Hinn. Survey, Special Pub. SP-8, 57 57 p. p. Pub. Ser., SP—B, Grout, F. Grout, F. F., F., 1929, The Saganaga Saganaga granite granite of of Minnesota—Ontario: Minnesota-Ontario: Jour. Jour. Geology, Geology, v. v. 37, 37, p. p. 562—591. 562-591. Gruner, .3. Gruner, J. W., The Soudan Formation and a new suggestion as to to the the U., 1926, The Econ. Geol., v. 21, p. 629—644. oriign of the the Vermilion iron iron ores: ores: Econ. 21, p. 629-644. Cruner, .3. Gruner, J. W., W., 1941, 1941, Structural geolony geology of of the Knife Lake area of northeastern Minnesota: Geol. Soc. Hinnesota: Geol. Soc. America Bull., Bull., v. 52, 52, p. p. 1577—1642. 1577-1642.' Hanson, G. G. N. N. and and Go1dich, Goldich, S. Hanson, S. S., S., 1970, Early Early Precambrian Precambrian geology geology of of the Saganaga-Northern Light Inst. the Saganaga—r4orthern Light Lakes Lakes area, area, Minnesota-Ontario: Minnesota—Ontario: Inst. Sup. Geology, Geology, Proc. 16th 16th Ann. Ann. Mtg., Mtg., Thunder Thunder Bay, Bay, Ontario, Ontario, Lake Sup. p. 18. p. 18. Hanson, C. R., 1971, 1971, K-Ar K—Ar ages ages of of mafic mafic dikes and Hanson, G. N. N. and and >Lalhocra, Nalhotra, R., evidence for low—grade lOVT-grade regional metamorphism metamoJ.Tphism in in northeastern northeastern evidence for :linriesota: Hinnesota: Geoi. Soc. Soc. America Bull. Bull. (in (in press, press, March March issue). issue). Ceol. Hooper, Vermilion [looper,Peter Peter and and Ojakangas, Ojakangas, R. R. W., U., Multiple Multinle deformation deformation in the Vermilion district, Minnesota: district, Hinnesota: Can. Can. Jour. Jour. Earth Earth Sci. Sd. (in (in press, press, April April issue). issue). Klinger, Klinger, F. F. L., L., 1956, 1956, Geology Geology of of the the Soudan Soudan mine mine and and vicinity; vicinity; Guide Guide book book Series, Series, Precambrian ef of northeastern Minnesota: Geol. Geol. Soc. Soc. America, America, Ninneapolis, Heeting, p. p. 120—134. 120-134. Minneapolis, Minnesota Meeting, iachmner, J. F. Machamer, J. F., 1968, Geology the iron are the Geology and and origin of of the ore deposits deposits of of the mine, Vermilion district, Minnesota: Zenith mine, Ninnesota: Minn. Minn. Geol. Geol. Survey Survey Spec. Spec. Pub., SP—2, Pub., SP-2, 56 56 p. p. , Ojakangas, Ojakangas, 11. R. U., W., Sims, Sims, P. & Hooper, P. K., K., & Hooper, Peter, Peter, 1971, 1971, Geology of the Tower Tm.,rer Quadrangle: Quadrangle: !'linn. Geol. Survey Survey (In (In preparation). preparation). Minn. Geol. Reid, 1. I. L., L., 19 1956, l:Zeid, S6, Ceolo1y Geo1of-y of the the Ely Ely Trough: Trough: Guidebook Series, Series, Precambrian of northeastern Minnesota: Geol. of Soc. America, Minneapolis Hinneapolis meeting, meeting, Geol. Soc. i,. 135—148. TJ. 135-148. �—14 8— -148- Sims, P. 1970, Geologic Geologic map map of Minnesota: P. IC., K., 1970, Minn. Geol. Survey Survey Misc. Map Set., Misc. Ser., Map M—l4. M-l4. Sims, Morey, C. Sims, P. P. K., K., Morey, G. B., B., Ojakangas, R. R. W., W., and and Griffin, Griffin, N. W. L., L., 1968, 1968, Preliminary geologic map of of the the Vermilion Vermilion district district and and adjacent adjacent areas, areas, northern Minnesota: Minn. Geol. Geo1. Survey Survey Misc. Misc. Map Map Ser., Ser., Map Map M—5. M-5. Sims, Morey, G. Sims, P. P. K., K., Morey, G. B., B., Ojakangas, R. R. N., W., and and Viswanathan, Viswanathan, S., S., 1971, 1971, (in press), press), Geologic Map of Minnesota, Hibbing (in Hibbing Sheet: Sheet: Minn. Geol. Geol. Survey. Survey. Winchell, H. H. V., V., 1888, 1888, Report Report of of observations observations made made during during the the summer summer Winchell, Minn. Geol. (northern Minnesota); Minnesota): Minn. Geol. Survey Survey Ann. Ann. Rept. Rept. v. v. 16, 16, of 1887 (northern p. p. 395—478, 395-478, map. map. �F L A NJ ATION EXPLANATION cc o C, ~ c~ "-' -'=' ~ E D ° :::) 0C l::~~:1 3: { cC, 0 V ~ 0 ill U "-' ill 3: Duluth Duluth 0:::'" ~f N I Complex a. CO o ~ ~ -0 E -o-'=' -o ::J 0 Virg1nia Vrqinio <..? "'~'l Q... and Formations Rove ill I f-' C « Bv,::uk and Biwabik and Gunflint Gunflinl fornialions Iron — - formations ~ C co o ~+++++J Gions Giants r:''",; ;->~, 'I '] "::~;::::'7·{~::/,--- Range Range Granile Granite Vermilion GronLte Granile , / t,/~'-J = co o — -'=' E Saganaqa Sagona go o S u ~ Granite Q... Q; 3: o ---.J ~Sif epiclastic, volconiclastic undivided epiclastic, volcaniclastic sedlmenlary rocks, extrusive mafic sedimentary rocks, extrusive rocks, and and lhe te igneous rocks, Soudan Iron Iron -—formation tormotion (sit), (sit) mainly greensch;st focies greenschist facies o0................ jO '0 IIoowiiIl 20 I SCALE 5 CAL E 30 Miles 3OMiies J5 E o u 1: "-' & 0::: '0 I �-\0 92°00' 92°45' 90°45' -«) o o co co CANADA "" Area. of <:r p1a.te I I-' lJl o0 °Cook. I + + + + + + + + + + + + + cr + + + + + + + + + + + + Location + + ,'i' ,.'" Map ~qj~ + 'vI;;) (:)~ .",o," ~"r.o~' ~<> ~(:) ",,'0 ::<,,<6 <0(:) 'vC::; ~r:'JQ., 4..':::J'::;''v~ + T + + ., L- ..., L < ,.. "7 .t.. ~ L ? V A 7 90°45' 7 7 1\ ~'" ;, 1'\ \'" L r I< ,o,<> r- ~ L 'e- ~$"~ " "," <§> ~C?it' C)<..J,9.; .~ '<f -,J ,} v'" ~ "o,~ .,.. «J~ ~ ~ ,>'> ,o, »' '" 92°45'00" ~ 92°00' ,,<I;> o,<> ,,1$ '0'" <'¢~~~ ~l>~'v 'v~& <Q~~ J> "", ,'> o,'> ,,«. .J,.<:i <¢",,, o," . . . e,r::),.,."<> .. v'" -~ 'e- '" 92°00'00" ~ Index I "," v'" ~;§' '\:t''''' + Figure 1. 1. Figure 92°00'00" to quadrangles stud ied Generalized the Vermilion (Morey & 1970) Generalized geologic map map of of the Vermilion district, district, Minnesota Minnesota (Morey & (thers, cthers, 1970) i I I I i I I i I I I �C PL LA AN NA ATTI10 N E )C XP ON foijli North of at Vernii/ioii Vermilioll foull I'..... ... '1 Range Granite Range Grande G,onis Glonts Ver ni lion Gronile Bionic Biollle Schisi 5chiSl Newton Lake Lake Farmolion Formal ion Newton undivided undivIded Vif.:::: . ~v.gs. vii Amphibolile Amphibolite —7-———-—vmv vmv vgv YQ vq c LLake oice .2 .D E 3 ~ Q.. 5 .':'.':'." :"> . Verm,tion Vermilion Knit Knife Lake Lake vVm vvm Group (undivided) For molio n Formation vgs, meiagroywocke metagraywacke member member quorrziie vg. quartzite member member v q, vgv, mi xed metogroywacke metagraywacke - felsic felsic vg v, mired I I-' conglomerate member conglomerate member vvtn, vaiconicMsic member member vvm, volcaniclastic bonded iron -- formation vif > banded vlf cmv. dominantly dominantly melobasoli metabasalt and and vmv, metod i a baaso S8 meladiab V1 I-' I - format On Soudan Iron Iron -formation Soudon dominantly domlnontly jaspiiite jospilite, jasper, and cherl chert osper and -- cit Ely Greenstone Greenstone e9, domlnontly menobosoltic metabasaltic eg, dominantly p i ilowed flows and metaandesitic meiaandesitic pillowed and 'nlern,ediate composition and Intermediate composi lIon pyrociostic pyroc lost\c depOsits deposits elf, banded bonded Iron Iron -formation - formation 9it, Corroci, dotled where wiere inferred nte- 'Cd Contact, dotted Vault Faull,• oared dotted where where o '"' 22 inferred 4 5S 6 8 CAL E CAL E loMites �-g 92'30' 92°3 H '7 W R~7W' 9j '45' 92'00' H IS W R~-4VV B. '3"W -0 o Zoo ooZ II"'" "'"II (j) (j) ID f-< f-< Z I'l ton (j) f-< ..4 ,v_t —c a Z zZ (II C -. (j) ID (II Jwtfl okes (j) / I-f-< log1e' b V1 N: t-: 1 'V '< c-..Lake z z (H ft 6 ... : : : Z o(j) · · b H W R t~ 7 7"'V\T Z ,/ ri7' · ·. . . . . .. . .. . . . . . . . . . . · · ·· Figure 2. 2. I .. .. . . . .. . ... .. . . .. .. .. . ............................................................... . 92*30 92'30' I ::::..................... :::::::::::::::: ::::::: ~ . . . .. . 0 a is w 16VV R 0 0 0 -J ~-~-= R . .. 91045 of the the western western part part of Geology of of Vermilion Vermilion district, district, Minnesota Ninnesota (Norey (Norey &&others, others, 1970). 1970). j I I I b -J 92' 92° 15' '5 p o(j) 0 0 n law 8W ~5""N I I I II-' LI I �I I C L AN AT S ON Sc P L A N A T I O N E E X Ou'''''' 1 Cornplt. '-'-' -', - ' , -'" Sno"~OA'" Lo_" "e,,"""O~ StOel und,·•• ded ,,,,I"don Lii LLL G'Qn,'e o~~'O'ed ~(~,~,~ ro. .... ,on La •• formot,on molK: ,Olcon,e nm" mtmatl nh, Itl$,(· ,nl.rmed·"·" .....x:on..: mem!>e< oom'l'Io<"ly fe pyroelau,e (nf,) of ~.c:-"",ermed>o'. ond ,oc.~ ~,m,lc, I.~~.' lIo .. ~ eompc~",on Kn,lt 'm~. dom,nonlly mtlO\l,ay .. o~'. 0"<:1 $101., 'm~. ~m'l'Ianuy m.,'otO~O,1 dom.non", .okon.elo~"t 'oe. 01 '0 ,nr.rmtd,ol. tompo~,"OI'l Ow. Ely .\!. Itl~,~ Gr.el'l~lol'le dJm,nonl" ..,.lotlO$Olh( p,llo".d and .... 'e'm.d'O'. (O""O'O$,I,on Oy'OCIO$I..: d.PO~,I$ ""eloonde~,''': SC £ seA L S. = ~ : 4 t . . . . ;} . . - - 2 - o..._.__ • ~ Ofl<l £E I f-J Ui lJl I G,o"p S.—. La~e hi W ~.,~~...tl - I - F _~M,l~ �- 4 ,e; - - / - - —— — t\ - —— c — —- N .--.--- / / -:- -- 'F !)y/ - / / / 7 Figure 3. 3. I I / G eology of the the central Geology central part part of of the th e Vermilion district , Minnesota M'l.nnesota (Morey Vermilion district, (Morey & & others, others , 1970). 1970). I — I I I �—155— -155- E E w W 0 - C? ...... z::::;. 13 ./ '- /=:::> " ~ / " L:) c=r ' ,;' .. . .• 12 / "/ "- I \ ,;' " .... / / ....... ,;' " "- / / .. j . . .. 0[77: 00 00 .,j . . o 0 " "- "- "/ "- / I 0I- 1. 0 .,.. .,.. ..... •Q ,;' " 6 ..... I' "- ./ ...... Fe1dspathic quartzite quartzite Feldspathic agglomerate Dacite agglomerate I' \. Graywacke-slate Graywacke—slate I I " / / ,;' ./ ... ,;' \. / / \. , " / I' .... Dacite tuff Daci te porphyry Dacite Iron—formation Iron-formation Basalt—andesite Basalt-andesite GENERALIZED AND IDEALIZED IDEALIZED PRE—DEFORMATIONAL PRE-DEFOID1ATIONAL VOLCANIC VOLCANIC PILE, PILE~ WESTERN VERHILION VERMILION DISTRICT of \. / Figure 4. 4. (Not (Not to to scale. \. 3 ,;' ,- \ / \. \ '- \. ,;' 0 0 " Numbers indicate approximate stratigraphic stratigraphic positions positions Numbers field trip stops.) stops.) field trip 2 " �—156— -156- VERMILIONDISTRICT DISTRICT FIELD FIELD TRIP VERMILION INTRODUCTION This field field trip trip is is designed to be a one—day one-day trip, trip, starting starting near near Ely Ely Representative outcrops of most and ending aa few miles west of Tower. few miles west of Tower. of the the major rock rock types types in in the the Vermilion Vermilion district district are are included. included. Most stops are in in the the Lake Vermilion Formation, Formation, the the Ely Ely Greenstone, Greenstone, and and the the Soudan Iron—formation. Iron-formation. None are in the the Knife Lake Lake Group because because good good exposures are not easily accessible; accessible; however, however, the the Knife Knife Lake Lake rocks rocks are are to those those in in the the Lake Vermilion Formation. Forma.tion. similar to Stop 1 Any several roadcuts Any of several roadcuts 2—10 2-10 miles South of Ely Ely on Hwy. Hwy. 1. 1. Giants Range bathalith batholith Most abundant facies in in this this area area ('Farm C'Farm Lake Fades' Facies" of of Green, Green, 1970) 1970) is is medium—grained, medium-grained, porphyritic porphyritic hornblende—biotite hornblende-biotite quartz—poor quartz-pooradainellite adamellite with K-spar phenocrysts. phenocrysts. Hornblende and K—spar K-spar are are commonly con~only aligned aligned in in flow flow pink K—spar structure. Monzonitic, granodioritic, granodioritic, and and dioritic dioritic phases phases also also occur; occur; all all have been cut by shear shear zones zones locally. locally. Stop 22 South of Ely on Hwy 1. Outcrops under powerline pmverline on EE side of Hwy 1, l, 1.4 1. 4 Outcrops under mi. mi. S of junction junction with Hwy Hwy 169. Ely Greens Greenstone tone of a within the Dacitic to to andesitic, andesitic, pillowed lavas characteristic characteristic of a zone zone within the Ely trendsE—W E-W south shapes show show tops face face Greenstone that that trends south of of Ely. Pillow shapes Ely Greenstone are cut These volcanics volcanics are north, as as in in most most of of the the formation. formation. These cut by aplitic north, dikes to the the Giants Giants Range Range batholith; the hidden hidden contact in related to batholith; the contact lies lies in dikes related the the slope slope to to the the southwest, southwest, and and granite granite outcrop outcrop can can be be seen seen near near the the base base of the slope. slope. of Ely. 14. at curve about 0.25 Stop 3 Roadcuts Roadcuts on on Hwy Hwy 169, at 0.25 ml. mi. W. of Ely. StoRj Ely Ely Greenstone of the Creenstone Pillmved metabasalt that that is is typical typical of of the the màflc mafic lavas lavas of the Ely Ely Greenstone Pillowed The pillow structures is exposed in road road cut cut on on north north side of highway. higlmay. The pillow structures have have side of is exposed in somewhat drawn smoothly tops, nearly flat flat bases, and and are are somewhat drawn out out in in smoothly rounded tops, of an vertical an inch inch thick. thick. The The Thechilled chilled rinds rinds are are aa fraction of vertical dimension. The and SE and face U., dip pillmv structures strike strikeapproximately approximately N.20° N. 20° Eo, dip 800 80° SE., face pillow , southeastward. southeastward. The long subparallel to to the the The long dimension dimensionofofthe the pillows pillows is is subparailel in~ersection cleavageand andbedding beddingand andplunge-s plunges steeply steeply northeastward. northeastward. intersection ofofcleavage �—15 7— -157- The exposures are on the the northwest limb limb of of aa tight tight syncline, syncline, the the axis axis The Ely trough contains an through the the Ely Ely trough. trough. trough contains an of which passes through iron—formation that was largely altered to hematite, and which was iron-formation that was was aa substantial source of of direct—shipping substantial direct-shipping hematite ore. ore. On the the south side of highway, fine—to—medium—grained fine-to-medium-grained metadlabase metadiabase is is exposed in road cut and on on hill to to south. south. The metadiabase intrudes and and crosscuts the the pillowed metabasalt. AA contact can can be seen seen in in the the southern southern part part of the tile crest crest of of the the hill. hill. 4. About 2.5 mi. \oJ of Stop 33 on Hwy Hwy 169, turn turn NN (right) (right) on on road road to to Burntside Burntside Stop 4. ml. W Lodge (Co. 88). Continue on road past bridge over Burntside River (Co. 88). Burntside River and and About 1.4 miles past Van Vac road (on (on left). left). About past junction with Van Vac road Stop in about 0.2 miles road, (on curve) curve) on on private private road. road. Stop road, turn left (on north on private road, road, at at curve curve to to right. right. Newton Lake Formation Formation Serpentinized metaperidotite metaperidotite and and associated associated gabbroic gabbroic rocks rocks are are exposed exposed Serpentinized from base of hill northward to from to crest. crest. It is about 150 Serpentinized peridotite is is exposed at base of hill. It 150 feet thick, is nearly black, black, and contains some feet thick, is some poikilitic poikilitic augite. augite. Iniinediately northofofserpentinized serpentinizedperiodite periodite and and apparently apparently gradational gradational Immediately north into it it is is aa coarse-grained coarse—grained hypersthene (?) into (?) gabbro, which grades in turn into a gabbro (higher The gabbro appears to into (higher on on hill). hill). The to have some some crude crude compositional layering and is in part diabasic. diabasic. On crest of hill, hill, part of the the gabbro (or (or diorite) diorite) contains contains coarse, coarse, radiating radiating pyroxene pyroxene crystals, crystals, as much as an as an inch inch long. long. There is some interstitital quartz and feldspar granophyric material in this this phase of the the rock. rock. Pyrite is widely scattered through the the gabbroic gabbroic rocks. rocks. ultramafic-mafic body at this stop is near the the southwestern end of an The ultramafic—mafic at this stop is intrusive sheet that that is about 3.5 3.5 miles long long and and 1,000 1,000 feet feet or or more more thick, thick, and which underlies little little Long Long Lake. Lake. The sheet appears appears to be a differbody, from peridotite at entiated body, at the the base base to to gabbro gabbro at at the the top. top. North of the eastern end end of of Little Little Long Long Lake, Lake, aa small small body body of of serpentinized serpentinized of the eastern peridotite, peridotite, within within metadiabase, metadiabase, is is exposed exposed in in aa roadcut roadcut along along the the Echo Echo Trail. The top top of the body is truncated truncated by by the the Vermilion Vermilion fault. fault. Stop 55 Roadcut about Roadcut about 13.0 13.0 miles miles W W of of Ely Ely and and about about 2.5 2.5 mi. ml. W W of of Eagle's Eagle's Nest Nest Lake road (Co. (Co. 408) 408) on on Hwy H\vy 169. 169. Other outcrops of of similar similar rocks rocks are are also also present along the the highway. highway. Soudan Iron—formation Iron-formation and cross—cutting cross-cutting dacite. dacite. Roadcut Roadcut in Soudan Iron—formation. Iron-formation. A quartz—feldspar quartz-feldspar (dacite) (dacite) A porphyry dike and Ely Creenstone Greenstone are exposed exposed at at east east edge edge of of outcrop. outcrop. The iron-formation is The iron—formation is composed composed of of interlayered interlayered red red and and white white chert chert and and opaque iron iron oxide that plunge oxide layers; layers; it it is is deformed into into drag drag folds folds that plunge 0 500_600 50 -60 0 N.E. Beyond a covered interval interval of of 0.1 0.1 miles miles to to the the east, east,the the �-158iron-formation thin to thick, thick, black, black, red and and white chert chert iron—formation consists consists of of thin beds interlayered with black black argillaceous argillaceous beds beds that that contain contain abundant abundant veins, veins, stringers, and and beds beds of of euhedral euhedral pyrite. pyrite. The beds trend trend about about N.85° and W. N.85° W. and dip dip 80°N. 80 o N. This is representative of the This dacite the felsic felsic volcanic volcanic rocks rocks which apparently provided the the detritus detritus for for most most of of the the sedimentary sedimentary and tuffaceous tuffaceous rocks rocks of the the district. district. Stop 66 Outcrop just W W of Stuntz Bay road road at at crest crest of of Soudan Soudan Hill, Hill, at at the the N, N. edge edge Soudan, 1,000 ft ft E. E. of Soudan Soudan mine. mine. Conserve this this outcrop. outcrop. of village of Soudan, Soudan Iron—formation Iron-formation This is much—visited classic This is a much-visited classic exposure exposure of of folded folded Soudan Soudan Iron—formation Iron-formation comprised of alternating beds of hematite and and jasper. jasper. The nearby Soudan mine was opened opened in in 1884, 1884, and and operated operated continuously continuously until until 1962. 1962, when when it it was was deeded to to the the state state by by U. U. S. S. Steel for for the development of of Tower—Soudan Tower-Soudan State State It was was the the first first iron ore mine in Minnesota; 15.5 million tons Park. It tons of of high grade grade ore ore (63—66% (63-66% Fe) Fe) were were shipped. shipped. Most of the small folds Host folds are the the result result of of the the second second deformation deformation in in the area, and these (F2) the area, (F ) folds folds plunge to to the the east east at at steep steep angles. angles. However, 2 evidence of an earlier set of folds is is provided provided by by structures structures such such as as these in the the sketches below. below. F1 fold axis Fl /" F2 F fold axis axis 2 F F INTERFERENCE INTERFERENCE PATTERNS PATTERNS F1 AND AND F2 l 2 Approximate F1 F FOLD MODIFIED BY BY F2 F 1 DEFORMATION 2 N N 1 H One Foot Foot Approximate Scale Scale �-159—159— Stqpl Several outcrops outcrops on peninsula in Lake Vermilion, east of Several of McKinley Bay, I Bay, E and W W of development development road. road. Lake Vermilion Formation, Lake Formation, Volcaniclastic Member White Hhite dacitic tuff, tuff, white dacitic dacitic agglomerate, agglomerate, black black carbon— carboniferous (?) slate graywacke, all all of of the the volcani— volcaniiferous (?) slate and minor chloritic graywacke, clastic member, are interbedded interbedded in in this this area. area. The westernmost exposures member, are of the the Soudan Iron—formation Iron-formation also occur here. here. Good exposures of the the agglomerate are best reached by boat; therefore, agglomerate boat; therefore, we shall shall only only see see some some large glacial glacial erratics of this rock rock type type which are are virtually virtually in in place. place. The dacitic tuff tuff is is very very difficult difficult (arid (and commonly commonly impossible) impossible) to distinguish from from dacite dacite flows. flows. Study of thin sections is is usually necessary to to resolve resolve the the question. question. It comfort to know that It is is some some thmfort (1903) and numerous other workers had had similar similar difficulties. difficulties. Clements (1903) three main components components —- dacitic The tuff is composed of three dacitic volcanic rock fragments, and volcanic volcanic quartz. quartz. Recrystallization Recrystallization causes causes fragments, plagioclase, and the volcanic volcanic rock fragments the fragments to appear as a fine—grained fine-grained quartz— quartzplagioclase plagioclase matrix. matrix. stop Stop 88 Large mi. WW of of Tower Tower on on Hwy Hwy 169, 169. roadcuts 0.3 mi. Lake Vermilion Fornation, Formation, Felds feldspathic athic Quartzite Quartzite Member Member This is a a limonite—stained limonite-stained exposure of the the conglomeratic conglomeratic facies facies This is of the the feldspathic feldspathic quartzite quartzite member. member. Bedding and clasts clasts are are best observed on the the glaciated surface at at the the western end end of of the the south south roadcut. Pyrite and pyrrhotite are are the the major major sulfides sulfides present, present, and and to have replaced replaced slaty slaty fragments fragments .in ,in the the conglomerate. conglomerate. Most appear to clasts clasts are volcanic rocks, rocks, probably mostly dacitic. dacitic. The matrix is is the strong Stop 10. 10. Note the similar to the feldspathic quartzite of Stop development development of F2 lineation which ~vhich plunges easterly easterly at at about about 600. 60°. ~t.-<?.p_J_ 5t229 Small outcrop SS of thvy Hwy 169, 169, in and across ditch, ditch, 1.1 mi. WW of of Tower. Tower. (optional) Lake Vermilion Vermilion Formation, Lake formation, FeljIiicQuartzite feldspathic ~uartziteMember Member feldspathic quartzite Lapilli (?) in the basal part of of the the feldspathic Lapilli tuff tuff (?) This is the This is the only exposure of this this rock rock type type in in the the immediate immediate it appears appears to area; it to be transitional in in texture texture between between the the dacitic dacitic tuffs and dacitic agglomerates. tuffs ap,glomerates. newiber. melilber. �-160- Note: Stop 10 South of the highway in the woods on West Two Rivers is tte folded western end of the Ely Greenstone. The fold nose points W but the fold plunges E at about 55°. This is an antiformal mass cored by older, mafic volcanics whose fold axis plunges toward the older rocks the wrong way. Some small folds at Stop 11 exhibit the same structure. Roadcuts N & S of Hwy 169, 1.85 mi W of Tower. Lake Vermilion Formation, Feldspathic Quartzite Member Feldspathic quartzite is an unfortunate choice of field terms, as the rock is largely composed of plagioclase and volcanic rock fragments with only minor large quartz grains (see below). Faint bedding and lamination are visible on some parts of the outcrop, and a sericitic phyllite band occurs on the north cut. At the east end of the south cut, felsic volcanic fragments up to an inch in diameter are visible. The 20 ft.-thick dike of diabasic gabbro at the tvest end of the outcrop is the youngest rock in the area. It has a minimum K-Ar age of 1570 m.y., and similar dikes a few miles away have ages of 1520 and 1685 m.y. (Hanson & Malhotra, 1971). The dike exhibi~s excellent chilled contacts and some inclusions of the quartzite. The feldspathic quartzites contain 20-30% plagioclase; 15-30% felsic volcanic rock fragments; 30% fine recrystallized quartz and plagioclase which probably represents, in large part, recrystallized volcanic rich fragments, plagioclase and quartz; 5-10% micaceous matrix; and 5-10% quartz, including some quartz which is definitely of volcanic origin. �—161— -161- -.l1.Long Long roadcut roadcut SSof of Hwy H\vy 169, 169, 2.5 Z. 5rid. mi. WW of Tm.]er. Conserve these these folds. folds. Tower. Conserve Stp_11 _~t...2.E .. jjrwacke—Slate Vermilion_Formation Lake Vermilion Formation, Metagraywacke-Slate Member (The composition Strongly and slate. slate. (The Strongly folded biotitic metagraywacke and this rock is is described at at Stop Stop 12, lZ, where the rocks of this where the rocks are are evenly evenly bedded folding results from two and relatively undeformed.) The The complex folding two deformations, as described in in the the text text accompanying accompanying this this tions, as sketched below and as described Some geologists have speculated that field trip trip log. log. Some that the the folding folding is is soft soft sediment deformation, deformation, rather than than tectonic. tectonic. However, these these stnictures structures are are unique unique in in the the area, area, this this exposure exposure is is located located near near aa major major anticlinal anticlinal axis, well—preserved sedimentary structures axis, and well-preserved structures nearby nearby are are not not chaotic. chaotic. the excellent excellent grading. grading. Note the Approximate N i One Foot F1 F fold fold axis l Approximate Scale ·····e 5Q0 50° axial plunge OVERTURNEJ) F2 FOLD FOLD OV ERTU R.:\IED F2 F1 FOLD F2 CLEAVAGE FOLD ANT) A..~D FZ P2 cleavage fold axis 1 / -7 F F FOLD 1ODIFIED BY fOLD MODIFIED HY FF Z 2 1 DkFORMATION. DEFORMATION. F2 Cleavage FZ ~ o• F 2 cleavage --"EYE STRUCTURE" t1EYE STRUCTURE" DUE DUE TO TO EROSION EROSION OF FOLDS WHICH OF FFI FOLDS I-.THICH WERE I-.TERE DEFOR1€1) DEFORMED BY FOLDS. BY FF FOLDS. Z �-162—162— 'I •. -. C Stop 12;Lposure ExposureNJNWof of bridge bridge across across Pike Pike 169. .r:S'Y (Junction of of Co. Co. 77 Hwy 169. (Junction 77 and ... this outcrop. Please conserve conserve this River on Co. Co. 77, 77, 0.55 0.55 mi mi NN of of River an Hwy 169 is 2.4 miles W of Tower). Hwy 169 is 2.4 miles W of Tower). .;: Lake Lake Vermilion Formation, Formation, Metagraywacke—s]ate Metagraywacke-Slate Member Member This This is is an an exposure exposure of of biotitjc biotitic metagraywacke metagraywacke and and slate, slate having having excellent grading. excellent grading. Two-thirds the 200 200 graywacke beds beds on Two—thirds of the on ~his this exposure are are graded and nine percent of the exposure the 100 beds are are 100 siltstone siltstone beds graded. Beds here here are are thin, graded. Beds thin, but graywacke beds beds are are as as much much as as 12 12 feet feet thick. North—trending kink North-trending kink bands bands were formed formed by by the the latest latest (F (F )) deformation. Small Small scale scale faults faults are are common. A NNE-trending fault with 1000 feet feet A NNE—trending fault with aiout aout 1000 of of left—lateral left-lateral displacement displacement forms the S side forms the side of the river channel at this locality, locality, and extends for this for several several miles miles to to the the north north and and south. south. The biotitic biotitic graywackes graywackes contain contain 10-20% l0—20 plagioclase; The plagioclase; 15-25% 15—25% felsic felsic volcanic rock fragments; 30—50% fine recrystallized rock fragments; 30-50% fine recrystaliized quartz and and plagio— plagioclase which probably represents, clase which represents, in large large part, part, recrystallized volcanic volcanic rock fragments, plagioclase, and rock fragments, and quartz; quartz; 2-5% 2—5% quartz, quartz, and and 10-15% lO—15 biotitic matrix. matrix. Stop 13 Exposures N of Hwy 169 on Co. Co. 77, 77, at Gruben's Resort Resort on Exposures about 10 mi N (Optional) (Optional) Arrowhead Point. Point. Best exposures are are just just EE of of wooden wooden bridge bridge to to Isle Isle of Pines. Pines. Lake Vermilion Vermilion Formation, Formation, Hetagr~acke-Slate Metagrywacke—Slate Member Lake i'lember Exposures Exposures of chloritic graywackes of this locality, pillowed greenstones of this locality, slate. This is near the axis This locality is is an ENE—trending (F2) is an ENE-trending (F 2) anticline, anticline, the the the west although the beds at the fold the west the beds at fold and slates. Both east and west are are interbedded interbedded with the the graywacke— graywackethe Arrowhead Point Point fold. fold. This of the axis axis of of which ,,,hich plunges plunges steeply steeply to to nose are younger to the are younger to the east. east. The 40-50% plagioclase (albite—oligoclase), (albite-oligoclase), The chloritic gra~vackes graywackes contain 40—50% 20—25% felsic volcanic rock fragments, 20-25% felsic volcanic fragments, 10—20% 10-20% chioritic chloritic matrix, matrix, 2—6X 2-6% quartz, quartz, some of of which which is some is definitely of volcanic origin. origin. Roadcuts bet\veen between lanes of Hwy 169 on "Confusion Stop 14 Roadcuts "Confusion Hill" Hill" (the (the Continental Continental (Optional) Divide) N of Virginia and about 23 23 miles WW of of Tower. Tower. (Optional) Divide) about about 3 mi N Giants Giants Range Granite the south edge of the This the complexity complexity of of the the south This exposure illustrates the Giants Range A gray gneiss contaLning containinh ailiphiholite amphibolite gray granite granite gneiss Rangebatholith. batholith. A inclusions cut by by diorite, diorite,and andminor minor pink pink granites granites cut cut the theabove above rocks. rocks. inclusions is is cut At top of of the the exposure exposure between het\\'een the tHO lanes of of the thehichway higlmay are At the the top the ttro remnants of mafic remnants of LOvIer LowerPrecanlHian Precanl,rianthinly thinly bedded bedded sediments sediments (tuffaceous?), (tuffaceous?), mafic lapilli tuffs (?y, and massive massive amphibolites. lapilli tuffs (fl, �� Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1971 Description An account of the resource Institute on Lake Superior Geology. University of Minnesota, Duluth, Minnesota. May 5-8, 1971. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1971 Contributor An entity responsible for making contributions to the resource R.N. Annells P.O. Banks W.R. Van Schmus Bill Bonnichsen Donald M. Davidson Jr Erich Dimroth Jean-Jacques Chauvel William H. Duhling Jr J.C. Green H.C. Halls G.F. West R. Roy Harold A. Hubbard H. King Huber Eric Frodesen Wayne T. Jolly Richard L. Kellogg William J. Hinze George deVries Klein Gene L. LaBerge M.S. Lougheed J.J. Mancuso Roger C. Malan David A. Sterling Allen F. Mattis Joseph T. Mengel Jr Ronald A. Hendrickson G.B. Morey J.S. Mothersill M.G. Mudrey P.W. Weiblan Wallace Darwin Myers Norbert W. O'Hara L.A. Prince G.N. Hanson W.A. Robertson W.F. Fahrig A.P. Ruotsala R.J. Shegelski G. Spencer F.C. Tan E.C. Perry Jr P.K. Sims S. Viswanathan T.A. Vogel T.J. Rohrbacher W.S. White Robert F. Johnson E.R Brooks J.T. Wilband Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/3ecd85424de1d35eb6f0359af1235823.pdf 916dcba45175acb8a04524d427dc4144 PDF Text Text �18th ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY MAY 3-6, 1972 MICHIGAN TECHNOLOGICAL UNIVERSITY HOUGHTON, MICHIGAN PART I. TECHNICAL SESSIONS AGENDA and ABSTRACTS Edited by W. I. Rose, Jr. �AGENDA Tuesday May 2, 1972 8:00 a.m. Field Trip A leaves Michigan Tech Memorial Union Wednesday May 3, 1972 6:00 p.m. 7:0010:00 p.m. Field Trip A arrives back in Houghton. Institute Registration, St. Albert the Great Student Parish, MTU Campus Thursday May 4, 1972 7:3010:00 a.m. 8:00- Registration, Fisher Hall Foyer 12:00 noon General Session I, 135 Fisher Hall 1:305:00 p.m. General Session II, 135 Fisher Hall 7:00 p.m. Banquet and Address, Onigaming Supper Club Friday May 5, 1972 8:0011:00 a.m. 1:30— Penokean Session I, 135 Fisher Hall 4:45 p.m. Penokean Session II, 5:30 p.m. Departure of General Session III, 135 Fisher Hall. Field Trips B and C. from MTU Memorial Union. Saturday May 6, 1972 8:00 p.m. Departure of Field Trip D from MTU Memorial Union 6:00 p.m. Field Trips B, C. and D. arrive back in Houghton. �7 8-12 Paper No. GENERAL SESSION MAY 4, 1972 TECHNICAL SESSIONS I. Time 8:15 a.m. 34 8:0.0 a.m. 8:35a.m. 10:40 a.m. 10:20 a.m. 10:00 a.m. 18 10 8 15 9:00 a.m. 11:00 a.m. 17 6 11:20 a.m. 11:40 a.m. Co-chairmen: Ehrlich 0. Lewan M. G. Mudrey W. Weiblen J. C. Green K. G. Books P. M. T. A. Vogel R. Author(s) Robert C. Reed and Donald M. Davidson, Jr. 135 Fisher Hall (Building #15, See Map) AM Title Introductory remarks, Announcements Based on Lithologic Variation Deposition Model for the Lower Nonsuch Shale Weathering and Metasomatism of the Presque Isle Serpentinized Peridotite, Marquette County, Michigan Break for coffee Petrologic and Structural Aspects of the Gabbro Sill on Pigeon Point, Minnesota Keweenawati Lavasin Minnesota Peleomagnetic Evidence for the Extent of Lower Dimroth W. O'Hara J. Hinze Oray A. Robertson J. A. Kilburg E. N. W. E. W. Upper Precambrian Ely's Peak Basalts Petrology, Structure and Correlation of the Magnetic Reversals and Polar Shifts as Markers in a Proterozoic Time Scale The Eastern Terminus of the Lake Superior Syncline The Labrador Trough — not a Precambrian Plate Boundary �II. GENERAL SESSION 1:30 p.m. 13 4 E. Brown Author(s) Randall J. Weege and Gerald Anderson Title B. Lou gheed Co-chairmen: Iron Segregation in Precambrian Iron Formations: Effects on Sedimentary Compositions S. Geologic compilation and Nonferrous Metals Potential , Precambrian Section, Upper Michigan M. w. w. J. LeAnderson M. Lahr A. Bodwell J. J. Mancuso The Newly Compiled Geological Map of the Precambrian of Upper Michigan P. W. Ojakangas Waupee Volcanics R. Smith H. McNutt Kal 1 iokoski A. Bodwell The Geology of the Garlic River Greenstone Belt R. D. R. P. M. Clifford Cuddy' P. M. Clifford G. Nature Effect of a Rigid° Ultrebasic Sill on Deformation R. Archean Salic Volcanic Rocks at Kakagi Lake, NW Ontario - Their Physical and Chemical J. Lower Precambrian Metavolcanic-Metasedimentary Sequence, Rainy River, Northernmost Minnesota J. L. Berkley Precambrian Geology of a Greenstone Belt in Oconto County, Wisconsin, and Chemistry of the The Geology of the Deer Lake Gabbro-Peridotite Complex, Itasca County, Minnesota Formations Morphology of Magnetite in Precambrian Iron M. 1:30- 5PM Paper No. 1:50 p.m. 2 Time 2:10 p.m. 9 12 2:30 p.m. 3:10 p.m. 16 11 3:30 p.m. 2 2:50 p.m. 3:50 p.m. 19 5 4:10 p.m. 4:30 p.m. In Adjacent Rocks, Kakagi Lake, NW Ontario �III. IV. BANQUET 9:55 •a.m. 27 23 J. Naldrett, University of Toronto 7:00 p.m. May 4, 1972 Relation of Penokean Polyphase Deformation to Regional Metamorphism In the Western Marquette Range, Northern Michigan The Penokean Orogeny Title W. J. S. A. Trent F. Cannon S. S. Goldich Author(s) Co-chairmen Carl E. Dutton and Stephen C. Nordeng Penokean Tectonics in Northern Michigan V. G. G. W. B. Morey L. LaBerge R. Van Schmms Kiasner Three-phase Deformation Associated with the Penokean Orogeny, East Gogebic Range, Michigan 0. Banks Coffee and Discussion Precambrian Rocks in Minnesota Stratigraphic and Tectonic Framework of Middle Lineaments and Mylonite Zones in the Precambrian of Northern Wisconsin Dickinson Counties, Michigan, Part II Chronology of Precambrian Rocks of Iron and Short Break (10-15 minutes) P1. 8-11 A.M. Archean Ultramafic Lavas and Their Associated Nickel Suiphide Deposits" A. Onigaming Supper Club (U.S. 41 South, Houghton) ADDRESS MAY 5, 1972 PENOKEAN SESSION .1 Paper No. 25 Time 8:00 a.m. 24 26 8:50 a.m. 20 8:30 a.m. 9:20 a.m. 10:15 a.m. 28 9:40 a.m. 10:35 a.m. 11:00 a.m. �V. ____ PENOKEAN SESSION 2 and GENERAL SESSION 3 1:30-5:00 p.m. Author(s) J. W. Avery and Robert Seasor Title Geochronology of Precambrian Rocks in the Penokean Fold Belt Subprovince of the Canadian Shield Regional Relationships in the Penokean Province Stratigraphy and Sedimentation of the Espanola Formations an Early Aphebian (Middle Precambrian) Carbonate Unit. Granitic Plutonic Rocks of the Southern Province of the Canadian Shield J. T. Mengel M. E. W. H. G. Haddadin. Booy R. Van Schmus B. Stonehouse M. Young J. A. Robertson S. Goldich J. S. Stuckless Structured Clay Products Industry, Keweenaw Peninsula, Michigan J. Warren S. lvii nnesota-Wi sconsi n E. G. Winter Glacial On ft on the Mesabi Iron Range, Minnesota, Its Characteristics, Origin and Hydrologic Bedrock Morphology in the Vicinity of Portage Subsurface Geology of the Duluth Superior Area, Potential Sources of Raw Materials for the Lake, Keweenaw Peninsula, Michgan 1. Minnesota Ages of Some Precambrian Rocks in East Central Co-chairmen: 31 Paper No. 1:30 p.m. 29 Time 1:50 p.m. 33 30 2:10 p.m. 2:30 p.m. 32 3 2:50 p.m. 3:20 p.m. 21 14 4:00 p.m. 22 3:40 p.m. 4:20 p.m. Signi ficance. p �Paper THE GEOLOGY OF THE DEER LAKE GABBRO—PERIDOTITE COMPLEX ITASCA COUNTY, MINNESOTA John L, Berkley University of Missouri, Columbia ABSTRACT The Deer Lake Gabbro—Peridotite Complex is located in northern Itasca County, Minnesota, three miles southwest of Big Deer Lake. It is intruded into a terrane composed of quartzofeldspathic, tuffaceous metasedimentary rocks and pillowed metabasalts of Lower Precambrian age (Sims, et. al., 1971). In recent years the area has been investigated by several mining companies as a possible source of exploitable nickel deposits. Detailed mapping has revealed that the complex is composed of five, separate, sheet—like, basaltic intrusions, averaging approximately 700 feet in thickness, each, Magma was supplied to the area in chronologically, widely dispersed episodes, allowing time for earlier intrusions to differentiate and lithify before the emplacement of a later sheet above those already present. Observed contacts between any two sills are character— Ized by chilled dolerite against a thin zone of amphibolite, The chilled do].erite is thought to represent the parent magma, while the amphibolite is probably a result of contact metamorphism by the magma, For any given sill within the complex, a sharp contact separates the chilled dolerite from the layered sequence above which consists of, from stratigraphic bottom to top, an augite—hornblende peridotite, diopsidic or augitic pyroxenite, and gabbros of varying compositions. This layered series of rocks is a result of selective crystallization and gravity settling of phases, Typical cumulate—intercumulate textural relations as described by Jackson (1961) from the Stllwater Complex of Montana may be seen in rocks from the peridotite up to and including certain lower gabbro units. Small scale layering structures may occassionally be observed in pyr— oxeniteg and lower gabbros. Figure one shows the ideal sequence of rock types for any particular intrusion within the complex and gives the expected cumulate and intercuinulate phases for each unit, The peridotite is composed of rounded to elongate olivines surrounded poikalitically by augite, hornblende, or both, Evidence of reaction rims may be seen surrounding some olivine crystals. The peridotite grades sharply into a pyroxenit., usually composed predominately of subhedral to euhedral diopside 1 �Paper enclosed by plagioclase, diopsidic overgrowth, or oikocrysta originally of pyroxene composition but now completely altered. With increasing cumulate plagioclase content, the pyroxenite grades gradually into an augite gabbro. Upper units may exhibit a significant quartz content and micrographic intergrowth. Micro— pegatite veins cut many gabbro exposures and pegmatitic material has been observed in certain pyroxenite units as well. Post—intrusive folding in the area has deformed the formerly horizontal sills into a sequence of tightly folded anticlinee and sync].ines with axial traces trending N4OE. The complex plunges to the southwest at an undetermined magnitude. Exposure of the intrusive units is now restricted to a narrow band six miles long and a maximum of about one and one half miles wide. Metamorphic grade does not surpass lower amphibolite or hornblende hornfels facies in the rocks of the complex with most assemblages, including those of the adjacent country rocks, falling into the greenschist fades, REFERENCES CITED Jackson, Everett D.,, 1961, Primary textures and mineral associations in the ultramafic zone of the Stiliwater Complex Montana, U. S. G, S. Prof. Paper 358, 106 pp. Sims, P. K., Morey, G. B., Ojakangas, R. W., and Viswanathan, S., 1971, Geologic Map of Minnesota, Hibbing Sheet: Mimi. Geol, Survey. 1 �FIGURE I. -— — ZONE CONTACT . ZONE ULTRAMAFC ZONE GABBRO ZONES — SINGLE NONE I4ORNBLENDE AUOITE/ PLAGIOCLASE AUGITE OLIVINE- PYROXENE OIKOCRYSTS DIOPSIDE QUARTZ PYROXENE OIKOCRYSTS PLAGIOCLASE PY ROXENE AUGITE QUARTZ PHASES CUMULATE PLAGIOCLASE N ONE N ONE PHASES CUMULATE INTER — INTRUSIVE SHEET. DEER LAKE AMPHIBOLTE DOLERITE PERIDOTITE PYR OX ENI T E GABBRO CUMULATE LOWER GABBRO AUGITE GABBRO AUG ITE BEARING MEMBERS QUARTZ IDEAL STRATIGRAPHIC COLUMN FOR A COMPLEX, MINNESOTA. ETAMORPHICFAdES CONTACT FACIES BORDER SERIES LAYERED GENETIC FACIES �Paper 2 GEOLOGIC COMPILATION AND NONFERROUS METALS POTENTIAL PRECAMBRIAN SECTION, NORTHERN MICHIGAN W. A. Bodwell Michigan Technological University ABSTRACT The geology and nonferrous metal occurences of the PreCambrian section, Northern Michigan, have been compiled at the scale of 1:250,000. The map incorporates considerable new data which has become available since the previous regional map of 1936. Review of the regional geology and mineral associations indicates several geologic environments or conditions considered to have potential for mineral deposition. 1) The effective coverage of past exploration drilling in the Michigan copper district was assessed. From this data, it appears that as much as 80 - 85% of presumed favorable ground is yet to be penetrated by drilling according to criteria developed herein: a) The strata-controlled ore deposit sought has a minimum strike length of 2000 feet. b) Maps showing drill holes were reviewed and all strike segments with 2000 feet or more between drill holes were outlined. These areas were measured by planimeter and compared to total area of the favorable strata. c) All strike segments of greater length constitute untested ground. 2) A series of small felsic porphyry intrusives occurring near the base of Portage Lake lava series appear to have potential for copper sulfide deposits based on analogous features with mineralized felsic porphyry bodies on north limb of the Lake Superior syncline in Ontario. 3) A greenstone belt northwest of Marquette, Michigan exhibits certain characteristics of mineralized greenstone belts of the Canadian shield. The presence of numerous base metal occurrences and one small gold deposit suggest that significant base metal or precious metal depsoits may yet be found. �Paper 3 POTENTIAL SOURCES OF RAW MATERIALS FOR THE STRUCTURAL CLAY PRODUCTS INDUSTRY KEWEENAW PENINSULA, MICHIGAN EMMY BOOY AND MUSA S. HADDADIN Michigan Technological University ABSTRACT The Keweenaw Peninsula of Michigan was explored for potential sites for the establishment of a structural clay products plant. The most favorable location for the establishment of such an industry was in Ontonagon County, in the southwestern portion of the Peninsula. The sedimentary cover overlying the Precambrian to possibly Cambrian bedrock varies rapidly both laterally and vertically because of the conditions of deposition during the Pleistocene. In general, the average particle size decreases from North to South. Otherwise, no consistent variations were observed. Most sediments having suitable properties for raw materials for the structural clay products industry have been mapped as glacial lake sediments. An attempt was made to identify distinctive flora which might provide a mapable criterion for distinguishing between sediments for structural clay products manufacturing and those unsuitable. Although there is variation in floral assemblage with topography (e. g. well vs. poorly-drained areas) there was no distinguishable variation with sediment size. suitable Requirements for suitable materials for structural clay products include good workability, low drying and firing shrinkage, good dry and fired strengths, and good fired color. Most of the samples studied met all criteria for most structural clay products. The mineralogy of the samples did not vary appreciably in major constituents throughout the area sampled. Illite, expandable vermiculite, and chlorite were the dominant clay minerals. Quartz and feldspar were ubiquitous, while minor kaolinite, calcite, and dolomite were present in many samples. Certain fundamental soil mechanics tests were run on the materials in conjunction with the ceramiô tests performed. In general, the samples tested were relatively stable clays to silty clay soils. �Paper 3 In the area studied the most desirable location from the view- points of volume of material available and ease of transportation to markets would be in the area around Ontonagon. Most of the samples studied from this area would be useful for all types of structural clay products. �Paper 4 IRON SEGREGATION IN PRECAMBRIAN IRON FORMATIONS: EFFECTS ON SEDIMENTARY COMPOSITIONS BRUCE E. BROWN Department of Geological Sciences Milwaukee, Wisconsin ABSTRACT According to Ronov's (1964) estimates, cherty iron formations of the pre-Cambrian type were present in the amount of 15% of the total sedimentary rock volume during the time period around 2 b.y. ago. The segrega- tion of iron to this degree would seem to require significant shifts in the iron contents of other types of sediments, particularly shales. A sample mass balance calculation after the manner of Garrels and Mackenzie (1971, p. 242) illustrates this. Using a present day "average igneous rock" (Brotzen, 1966) as a source for limestone, sandstone, and shale, and considering just the total iron percent we have, after Garrels and Mackenzie (1971, p. 242): Average igneous rock Fe oxides in gms/kg 62 limestone shale sandstone 62 4 if one considers a situation where 15% by weight of the sediments are of iron formations containing 30% iron oxides, we must subtract 45 grams of iron oxide to supply this source, leaving only 17% to go into shales and sandstones. The assumption is made that iron normally going into shales (such as might happen during the weathering of a basalt today) has been diverted into iron formations. If this assumption is valid, shales formed during times when iron formations were a significant portion of the sedimentary column, should contain less iron than might otherwise be expected considering possible igneous sources. Since iron is the heaviest common element this might have implication regarding the composition, density and isostatic relationships ofrocks such as granitic gneiss formed by metamorphism of shale. �Paper 5 EFFECT OF A "RIGID" ULTRABASIC SILL ON DEFORMATION IN ADJACENT ROCKS, KAKAGI LAKE, NW. ONTARIO by R. G. Cuddy, P. M. Clifford Department of Geology, McMaster University, Hamilton, Ontario ABSTRACT The greenstones of Kakagi Lake consist of about 7500 metres of basic to acid volcanic rock, and some associated sedimentary rocks. Embedded within this assemblage are "sills" of ultrabasic material Study of the western portion of the Kakagi Lake area shows that the ultrabasic sills have a fold form of class 1-B or 1-C (cv. Ramsay; 1967 pp. 365 ff.), as revealed by thickness, measurement and isogon plots. Petrographic study of one sill (Ridler, 1966) suggests that very little strain has occurred within the sill. The rocks in contact with the sills are with very few exceptions, acid pyroclastic volcanics. They lack significant primary layering and, mechanically, form thick, rather homogeneous units. Cleavage density rises, as does consistency of orientation of cleavage, in the vicinity, and along axial surface continuationsof tight folds in the sills. Conversely, open folds in the sills are adjacent to areas of low cleavage density and locally variable cleavage orientation. In addition, fragments in the pyroclastic rocks, though flattened to lie roughly parallel to cleavage, are poorly oriented within the cleavage, a situation which suggests rather low strains within the cleavage plane compared to the high strains across it, or alternatively, a fluctuation of pyroclast long axes over 1800 in the pre-strain state. Fold axes, few in number, are everywhere of moderate to steep plunges. These features are the product of an early phase of deformation. Subsequent deformation has produced kink folds and en echelon quartz-filled gash arrays. These suggest local orientations of principal axes of stress or strain, apparently not of regional value. It is not clear from our data, or any other data available whether the granites surrounding these rocks are fully responsible for the deformation, or have merely modified a prior fold array whose axial surfaces were aligned east-west. What is clear is the marked effect of the sills with their low ductility compared to the pyroclastic rocks in which they occur. Ramsay, J. G. (1967) Folding and Fracturing of Rocks. Ridler, R. H. (1966) M.Sc. thesis (unpublished) Univ. of Toronto. �Paper 6 THE LABRADOR TROUGH - NOT A PRECAMBRIAN PLATE BOUNDARY Erich Dimroth, Service d'Exploration gologizue, Mjnistre des Richessea naturelles, Qubec ABSTRACT The boundaries between the Precambrian age provinces are the natural location where to look for Precambrian plate boundaries. This is specifically so for the .junction between the Superior and Churchill Provices, which are separated by the Circum-Ungava geosyncline. Deep erosion has removed the whole of the original geosynclinal filling in the sector between Labrador trough and Cape Smith belt, and the relations between the geosynclinal filling and its basement can be studied. Other segments of the Labrador trough are deeply enough eroded to infer the presence of a basement. At the level of the basement (that is between the Labrador trough and the Cape Smith belt) the contact between the Superior of Churchill Provinces appears to be gradational. The Archean gneisses are continuous to Ungava bay, but they give Hudsonian K-Ar ages east of line indicated in Wanless (1969). The Archean gneisses east of the age front appear to have suffered Hudsonian deformation, as indicated by the folded outline of the contact between the basement and the Lower Proterozoic sequence. Beau et al. (1963) noted that the Hudsonian biotite isograd intersects the basement-cover contact, and retrograde metamorphism has been noted in a few basement outcrops visited. It appears therefore that a Hudsonian tectonic, metamorphic and age (K-Ar) front, intersects a uniformly Archean terrain between the Cape Smith belt and the Labrador trough. The northernmost Labrador-trough and the easternmost Cape Smith belt are synclinoria plunging south-southeast and west-northwest. The Lower Proterozoic sequence of both belts, which includes very voluminous oceanic tholeiites rests on the basement gneiss with an absolutely sharp contact (Hardy, 1969; Schimann, 1972). �Paper 6 -2- In the centre of the Labrador trough a very thick sequence of oceanic tholeiite rests on continental red beds and on shallow water sediments (for example sandstone with coarse current cross-bedding, stromatolitic dolomite). Units of stromatoljtjc dolomite, of oolitic iron formation and similar shallow-water deposits is continuously exposed across the whole trough, and, in its east, mantles domes of basement gneiss. There is not a trace of a sheeted gabbro complex, and in fact the source of the basalts is still enigmatic. Only very few and generally thin gabbroic dykes intersect the sedimentary sequence and are the only possible conduits known at present. In the extreme east of the Labrador trough a metamorphosed meta-pelitic sequence, comprising interbeds of orthoquartzite, dolomitic sandstone (now diopsidequartzite), para-aniphibolite, is exposed. Arkoses, arkosic conglomerates, are present here and there and perhaps indicate the presence of occasionally emergent source areas east of the trough. According to Wanless (1970) granitoid gneisses east of the trough give at one locality a K-Ar age of 2160 m.y., that is somewhat older than the Rb-Sr age of the Labrador trough rocks (Fryer, 1971). This seems to confirm the basement nature of at least some granitoid gneisses east of the trough. There appears little doubt that the Labrador trough formed by differential subsidence and that it is not related to a continental margin existing at Lower Proterozoic time. REFER EN C ES Beall, G. H., Hurley, P.M., Fairbairn, H.W., and Pinson, W.H., Jr. (1963), Comparison of K-Ar and Rb-Sr dating in New Quebec and Labrador. Am. J. Sci., V. 261, p. 511-560. Fryer, B. J. (1971), Rb-Gr whole rock ages of Proterozoic Strata bordering the eastern part of the Superior Porvince, Canada. Geol. Soc. Amer., Abs with programs, 3, p. 574-575. �Paper 6 -3- Hardy, R.1(1969), Gologic de la re9ion du lac des Chefs, These de maitrise, non publiee; Ecol Polytechnique. Travaux sur le Department of Natural Resources, Quebec, Report S-126AF, p. 7-10. Schimann, K. (1972), Wakeham Bay In: terrain 1971. Wanless, R. K. (1969), Isotopic age map of Canada. Geol. Surv. Canada, Map No. 1259A. Published with the permission of the Minister of Natural Resources, Quebec. �Paper 7 I DEPOSITIONAL MODEL FOR THE LOWER NONESUCH SHALE BASED ON LITHOLOGIC VARIATION Robert Ehrlich and Thomas A. Vogel Geology Department Michigan State University 48823 East Lansing, Michigan ABSTRACT The White Pine copper deposit is one of the classic strata—bound Not only is the mineralization restricted to a small lower portion of the Nonesuch Shale but the vertical succession of lithologies within the mineralized section is remarkably similar in all parts of This striking similarity in vertical succession has in the the mine. past been used as a basis for assuming wide scale lateral continuity of subunits within the Lower Nonesuch Shale. This in turn led to models of deposition, diagenesis, and ore emplacement in which the layercake The aspect of the lower Nonesuch stratigraphy played a key role. purpose of this report is to integrate the observed lithologic variation into an overall depositional model for the Lower Nonesuch Shale. deposits. The lower fifty feet of the Nonesuch is composed of numerous textural modes such as graded, well—laminated, crudely laminated, fragmental, blebby, massive, etc. Various combinations of these textural elements can be found in varying proportions in each of the formal stratigraphic units and each of these (Domino, Brown Massive, etc.) have extensive lateral continuity whereas the individual textural elements included within each unit are not persistent. These lateral changes arise in three principal ways: (1) abrupt changes apparently resulting gradual and (2) from slumping and sliding of plastic sediments, and continuous changes in lithology within a major stratigraphic unit such as massive units becoming crudely laminated and then graded. Similar lateral variations can be seen with major elements within one formal stratigraphic unit varying laterally into a lithology which is a characteristic of an adjacent stratigraphic unit above or below. Most of the textural elements can be seen in varying proportions in the massive units. When observed in detail, it can be seen that there is a non—random juxtaposition of the elements; that is, certain elements tend to be adjacent to certain others. Figure 1 shows the most probable �Paper 7 PAGE 2 associations between textural elements. Elements adjacent in the diagram tend to be intimately associated with each other on a hand sample scale. Elements far apart on the diagram are rarely seen juxtaposed. Figure 1 Mutual Occurrence of Textural Elements in Massive Units Textural elements relatively closer on diagram occur together more often. ,Massive ———— Crudely Laminated ———— Graded ———— Laminated Fragmental' "Blebby ———— Crudely Laminated In these massive units the textural elements on the left side diagram (e.g., fragmental, massive, blebby) are more abundant than on the right. Because each of these elements, except those on the extremes, is associated with two others, these inter—relationships the basis for the pattern of vertical and lateral variation within massive units. of the those are the A characteristic vertical succession is from bottom to top; massive, crudely—laminated, fragmental, scoured surface, massive, blebby, crudely— laminated, graded, well—laminated. A section such as this is composed of two depositional units, each beginning with a massive textural variety Within each and terminated by a fragmental or laminated variety. depositional unit there are no sharp boundaries as one proceeds from one textural element to another, indicating that the sequence of textural elements arose from a single genetic event. The textural varieties and lateral and vertical relations observed are consistent with a depositional model involving progressive infilling of a depositional basin with coarse, denser materials being deposited over materials of low specific gravity that are mechanically weak. The pattern seen here can be understood if the effects of lateral migration and loci of sedimentation are considered as well as general infilling in the basinward direction. In general terms, the dynamic model consists of coarse—grained material deposited on muds, triggering its accompanying flow components. In the Nonesuch two modes of deposition and transport were involved in most slumps. The uppermost, least consolidated materia],, generally (1) hematite—rich, moved rapidly, partially as suspended material, partially as bonafide turbidity flow, and fanned out into a roughly lobate deposit. �Paper 7 PAGE 3 (2) The slightly more consolidated material underlying this zone, in a more reduced condition, either flowed plastically, more slowly, down the depositional slope with relatively little rotation or, if it was reasonably coherent, behaved as a rotational slump with a well—developed concave upward slip surface. Sediment that has moved further downslope is more laminar and less rotational in nature. This, coupled with longer time involved in transport, allows the previously homogenized sediment to differentiate itself with respect to grain size. The sequence, updip to downdip, is thickest, but of least lateral extent at the updip end, and thinnest (perhaps only one graded bed thick) but most laterally extensive at its downdip extremity where it fans out in an unrestricted fashion. This process model can explain the three dimensional pattern of rock variation and provides an important framework for a discussion of the origin of the other geochemical and petrological variations in the Lower Nonesuch Shale. �Paper 8 PALEOMAGNETIC EVIDENCE FOR THE EXTENT OF LOWER KEWEENAWAN LAVAS IN MINNESOTA by John C. Green Geology Department University of Minnesota, Duluth and Minnesota Geological Survey Kenneth G. Books U. S. Geological Survey Silver Spring, Maryland ABSTRACT Most of the North Shore Volcanic Group of Gehman (1958), from central Duluth northeastward to the diabase complex at Hovland (Fig. 1), is now known to be middle Keweenawan on the basis of its normal magnetic polarity (Books, 1968; Palmer, 1970; new data). Beneath (north of) the Hovland diabase and the southern prong of the Duluth Gabbro Complex in Cook County is a series of lavas, approximately 8,000—10,000 feet thick (the Hoviand and Grand Portage lavas of Green 1971) that were extruded during an earlier period of reversed polarity, and are therefore lower Keweenawan. These two units can be traced for at least 25 and probably 50 miles westward, where they are intruded by the Duluth Gabbro Complex. The Hovland lavas include many porphyritic basalts with platy plagioclase phenocrysts. These two lava units thus correlate with the lithically similar reversed "Traps of the South Range" in the Ironwood area, Michigan—Wisconsin, (Books, 1968) and with the Osler Series of Ontario (Palmer, 1970). The Grand Portage lavas are cut by a dike swarm of basalt and porphyritic basalt that also show reversed polarity and may have been feeders for the porphyritic Hovland lavas. The Grand Portage lavas rest disconformably on the Puckwunge Formation of Schwartz, 1942, an orthoquartzite that overlies the middle Precambrian Rove Slate. Although the samples showed only weak magnetization, new determinations give an unequivocal reversed polarity for the Puckwunge, and support its correlation with the lithically similar Sibley Series sandstones of the Thunder Bay district, Ontario. At the southwest end of the basin also, the Duluth Gabbro Complex intruded between lavas of normal and reversed polarity, i.e. between middle and lower Keweenawan volcanic rocks. New determinations show that most or all of the basalts at Ely's Peak (the wedge of lavas that underlie the Duluth Gabbro Complex west of Duluth) have reversed polarity, and thus correlate with the flows at Ironwood and Grand Portage. The basal pyroxene—porphyritic lavas in this unit bear a very close resemblance to the basal lavas on Lucille and Magnet Islands east of Grand Portage, further supporting this correlation; such lavas are not known from anywhere else in the North Shore Volcanic Group. Samples from the conformably underlying "Nopeining sandstone" and from the lowest flow at the "Grandview Golf Course" locality show weak magnetization and considerable scatter, but normal polarity. What is believed to be the same flow (certainly part of the same unique pyroxene—basalt flow group) 3/4 mile to the south shows reversed polarity. Although these normally polarized samples were taken at least 500 to 800 feet (structural distance) from the base of the Duluth Gabbro Complex and are not visibly recrystallized, even in thin section, it appears likely that the basalt's polarity has been inverted to �Paper 8 normal during contact metamorphism by the Duluth Gabbro Complex. No conclusions can yet be made regarding the original polarity of the sandstone; it may have been normal, thus correlating with the Bessemer Quartzite of Seaman, 1944, beneath the lowest Keweenawart flows at Ironwood, or it may also have been changed from an original reversed state, thus correlating with the Puckwunge and Sibley. Further investigations will be carried out. References Books, K. G., 1968, Magnetization of the lowermost Keweenawan lava flows in the Lake Superior area: U. S. Geol. Survey Prof. Paper 600—D, p. D248—D254. Gehman, H. M.,, Jr., 1958, The petrology of the Beaver Bay Complex [Minn.J [abs.], in Institute on Lake Superior Geology, Apr. 21—22, 1958: Minneapolis, Univ. Minn. Center Continuation Study [19581, p. 1. Green, J. C., 1971, Stratigraphy of the North Shore Volcanic Group northeast of Silver Bay, Minn. [Summary]: Inst. on Lake Superior Geology, May 5—8, 1971: Duluth, Univ. of Minn., Duluth, 1971, p. 20—22. Palmer, H. C., 1970, Paleomagnetism and correlation of some middle Keweenawan rocks, Lake Superior: Can. Jour. Earth Sd., v. 7, No. 6, p. 1410—1436. Schwartz, G. M., 1942, Correlation and imetamorphism of the Thomson Formation, Minnesota: Geol. Soc. America Bull., v. 53, no. 7, p. 1001—1020. Seaman, W. A., 1944, Summary of the geology of the Marquette iron range [Mich.]: Michigan Geol. Survey Prog. Rept. 10, p. 11—17. �a II ntrusjve rocks a L owes af Keene.wen teuas tt44t Kewn.n u&s ktween&u,an Kilo", ee's S )s _______ �Paper 9 THE NEWLY COMPILED GEOLOGICAL MAP OF THE PRECAMBRIAN OF THE UPPER PENINSULA OF MICHIGAN J. Kalliokoski and W. Bodwell Department of Geology and Geological Engineering Michigan Technological University Houghton, Michigan With the retirement of the older staff, the Department of Geology and Geological Engineering found itself in a position of requiring a mechanism whereby it could refamiliarize itself with the Precambrian geology of the Upper Peninsula, in order to identify good field-thesis problems and to become knowledgeable about the mineral potential of the region. The most direct approach seemed to be in compiling all geological data on the most suitable scale. With the help of the Institute of Mineral Research (M. T. U.) and the full cooperation of the Michigan Geological Survey, the U. S. Geological Survey, various mining companies, and land owners, this task has now been completed. The resulting map, "Precambrian Geology of the Upper Peninsula" (M. T. U. Press, Geological Series, Map 2, 1972) is on a scale of 1:250, 000. A second map "Geology of the Marquette-L'Anse Region, Michigan", (M. T. U. Press, Geological Series, Map 1, 1972) shows the available outcrop data for the "Northern Complex" on a scale of 1:62, 500. Both maps, uncolored, show the location of known base metal and precious metal showings. The 1:250, 000 map (released April, 1972) is priced at $3. 00 and the 1:62, 500 map (released in late August, 1972) is $5. 00, both including postage, prepaid. They are available from the Department of Geology and Geological Engineering, Michigan Technological University, 49931. Although the maps are complete in themselves, they represent part of the documentation for an M. S. thesis by W. Bodwell, entitled "Geologic Compilation and Non-ferrous Potential, Precambrian Section, Northern Michigan". Copies of the thesis may be obtained from the Department for the cost of reproduction. �Paper 10 PETROLOGY, STRUCTURE, AND CORRELATION OF THE UPPER PRECAMBRIAN ELY'S PEAK BASALTS JAMES A. KILBURG University of Minnesota, Duluth ABS TRACT The Upper Precambrian Ely's Peak basalts crop out in a north—south trending, wedge shaped belt in the area around Nopeming, southwest of Duluth, Minnesota. These Lower Keweenawan flows overlie the basal Upper Precambrian quartzite in the southwestern portion of the Lake Superior basin. There are about 18 individual flows totaling some 1,200 feet of thickness, the thickest flow being 125 feet thick while the thinnest is less than 10 feet thick. Many of the flows show lateral continuity, for example, one flow is traceable for about three miles along strike. Petrographically, there are three main types of flows. Five of the first six that form the basal portion are dark gray, porphyritic basalts. Of these, four contain euhedral, zoned, single and glomerophorphyritic augite phenocrysts up to 5 mm in diameter. Some ilmenite phenocrysts and some olivine pseudomorphs are also present. The groundmass contains altered plagioclase, magnetite, augite, actinolite, chlorite, and sphene. The sixth flow up from the base is a dark gray, porphyritic basalt with single and glomeroporphyritic plagioclase phenocrysts up to 7 mm in diameter; there are also occasional augite phenocrysts. The groundmass contains altered plagioclase, augite, actinolite, ilmenite, sphene, epi— dote and chlorite. The third type of flow is a dark gray, commonly ophitic, altered basalt. It consists of plagioclase, occasional olivine pseudo— morphs, actinolite after augite, augite, ilmenite, magnetite, epidote, sphene, and chlorite. Structures within the flowsinclude ropy surfaces, vesicular and amygdaloidal tops, straight and bent pipe vesicles, straight cylinder vesicles, columnar joints, and pillows in the basal flow. Several northeast trending basalt dikes cut the flows and have been deeply eroded leaving pronounced lineaments. The whole sequence has undergone regional hydrothermal metamorphism to the high zeolite—low greenschist fades. Minerals present which demonstrate this are actinolite, chlorite, and epidote. The only zeolite present is wairakite which has been discovered probably for the first time in the Lake Superior region. It is the highest temperature zeolite. Intrusion of the Duluth Complex is thought to be responsible for elevating the geothermal gradient and thus, permitting the formation of wairakite. The gabbro intrusion also contact metamorphosed the lavas to a medium grained pyroxene hornfels for a distance of up to one—fifth of a mile from the contact. �Paper 10 Pressures of metamorphism are thought to have been around 2,000 bars, although a range of pressures between 1,500—2,500 bars seems feasible. This pressure was produced by the weight of up to 30,000 feet of overlying Upper Precambrian lavas and Duluth Complex which underlie the North Shore of Lake Superior; however, as little as about 16,000 feet of overburden could have produced the minimum pressures of about 1,500 bars needed for metamorphism. Based on their distinctive petrology and reversed magnetic polarity (Green and Books, 1972), the Ely's Peak basalts appear to correlate with the basal flows at Grand Portage, Minnesota. This implies that the time of deposition at these localities was approximately the same, and the source area from which these lavas were derived was probably the same. �Paper 11 PRECAMBRIAN GEOLOGY OF A GREENSTONE BELT IN OCONTO COUNTY, WISCONSIN, AND CHEMISTRY OF THE WAUPEE VOLCANICS. Melvin M. Lahr University of Wisconsin, Madison, Wisconsin ABSTRACT Detailed mapping has been carried out in the northern half of the Mountain Quadrangle in order to establish the geologic history and evolution of a Precambrian greenstone belt and to determine the nature of volcanism. The sequence of Precambrian events was the following (oldest to youngest): 1. Deposition of the Waupee formation, including flows, agglomerates, tuffs, volcaniclastic sediments, and sandstones. 2. Emplacement of the Macauley intrusive (granodiorite to quartz monzonite). 3. 4. 5. Deformation and regional metamorphism. Deposition of the Baldwin conglomerate. Intrusion of the Hager granite and contact metemorphism of the older rocks. The Waupee formation trends approximately N450E and has a steep dip. Relic graded bedding and cross-stratification indicate that tops of beds are to the northwest. Three lithologic units have been distinguished in the Waupee formation: a basal member consisting of massive flows, volcaniclastic sediments, and minor agglomerates; a middle sandstone member with a subordinate amount of massive flows; an upper thin-bedded tuff member. Pyrrhotite mineralization is concentrated along the boundary between the basal and middle members of the formation. Sedimentary features and volcanic textures have been preserved in the Waupee formation, but recrystallization under conditions of the amphibolite facies has produced the following mineral assemblages: basic volcanic flows: plagioclase-hornblende-clinopyroxene. p1 agi ocl ase-hornbl ende-cummi ngtoni te. quartz-biotite-hornblende-plagioclase+ sedimentary rocks: epidote. quartz -microcline-biotite-mu scovite+ p1 agiocl ase. Contact metamorphism due to intrusion of the Hager granite has been superimposed on the regional metamorphic assemblages, resulting in the appearance of garnet, vesuvianite, scapolite, clinopyroxene, hornblende, and plagioclase in the metavolcanic rocks. In the aluminous metasedimentary rocks the assemblage quartz-plagioclase-alkali feldspar-muscovitebiotite-andalusite+ sillimanite has developed. �Paper 11 Eighteen samples of massive volcanic flows from the Waupee formation were fused and analyzed for nine elements (Si, Al, Ti, Fe, Mn, Mg, Ca, Na, K) by means of an electron microprobe. The majority of samples are basalts (Sio2, 46 to 51%) containing 15 to 20% A1203 and 2.0 to 5.8% Na20 + K20; a few samples are andesiEic, containing up to 6T% Si02. If the chemical compositions of the massive flow rocks have not been modified during regional metamorphism, then the Waupee volcanics can be classified as high-alumina and alkalic basalts. As yet, no tholeiitic basalts have been recognized in this area. The chemistry of the metavolcanic rocks and the nature of associated metasedimentary rocks suggest that the Waupee formation originated in an island ac environment. �Page 12 THE GEOLOGY OF THE GARLIC RIVER GREENSTONE BELT P. James LeAnderson Queen's University, Kingston, Ontario ABSTRACT The Garlic River Greenstone Belt is the Archaen greenstone belt northwest of Marquette, Michigan. It consists of a series of basalt flows, tuffs, greywackes, arkoses and iron formations formerly referred to as the "greenstone" or as Mona Schist. The belt is twenty miles wide along the southern boundary, at the contact with the Marquette Synclinorium, and extends ten miles to the north (See Fig. 1). Discernable tectonic history indicates gentle folding of the flows and sediments, followed by intrusion of quartz monzonite pegmatites, large diabase dikes and finally granodiorite pegmatites.. The flows and sediments were metamorphosed to chlorite schists and amphibolites. The chlorite and chloritic amphibole schists may represent greywackes and/or reworked or waterlain tuffs. The amphibolites are thin bedded or massive; some of the latter have pillows or relict plagioclase laths, indicating a volcanic origin. Felsic volcanics are uncommon, but form a zone of sheared rhyolitic at the east end of the Dead River Basin. Small extrusive bodies of porphyritic dacite are found throughout the chlorite and amphibole schists. tuffs (?) The Arkoses (Gar) occur commonly as thin units in the chlorite and amphibole schists, but are the dominant rock type in two areas near the northwestern boundary of the belt. Iron formation (IF) consists of thin discontinuous lenses of Neither carbonate nor sulfide facies iron formation ntagnetite in arkoses. were found. Two synclines have been mapped trending northwest—southeast and plunging southeast, one in the northwest corner of the belt and the other some six miles to the south in the central part. Additional detailed mapping may reveal other folds. Two large downfaulted basins with lower (Ar) and middle and upper (Amu) Animikie Sediments, partially covered with thick deposits of Pleistocene sand, truncate the northern and western boundaries of the belt. A third smaller basin occupies the center of the belt. In the northern part of the area two ages of felsic intrusives can be distinguished, but this distinction cannot be made southeast of the Dead River Basin. The younger intrusives are predominantly quartz monzonites, and are cut by the second set of intrusives which are weakly metamorphosed, non— porphyritic granodioritea. The felsic intrusives in the southern part are porphyritic granodiorite pegmatites. Diabase dikes consisting of unoxiented subhedral hornblende and plagioclase crystals trend east—west across the regional foliation but are not folded. They appear to belong to one set, intermediate in age between the quartz monzonite and the granodiorite. �2 Paper 12 TFie uniformity of mineral composition of the greenstones and the ubiquitous and commonly complete alteration to chlorite and sericite, makes However, the trend, from determination of the metamorphic grade difficult. predominantly pale green amphiboles to dark blue—green amphiboles, from the center to the margins of the belt, indicates that the metamorphic grade increases in the same direction from the greenschist to the amphibolite facies. Although stratigraphic and time relationships in the belt are unknown the following generalizations can be made, 1) the sediments, tuffs and lavas were deposited in shallow water, possibly subaerially, as indicated by the pillow lavas and oxide facies iron formations, 2) the series of thick and extensive metabasalts, tuffs, greywackes and rhyolites south of the Dead River Basin indicate continuous and voluminous outpourings of lava and pyroclastics, and 3) the thin discontinuous layers of basalt, greywackes, tuffs, dacites, arkoses and iron formations to the north, suggest local eruptions of short duration with frequent erosional breaks. After folding of the greenstones, magma intruded and assimilated the lower units, leading in turn to first stages of development of the The magma spread further into the greenstone and lit—par—lit gneisses (Gu), formed pegmatite dikes and sills in the nose of the northwestern syncline. This was followed by the intrusion of a series of diabase dikes; at this time the metamorphic grade reached it's peak. The area was then covered by Animikie sediments which were folded by the Penokean Event, when the structural basins were formed. The intrusion of Keweenawan dikes, followed by deposition of the Jacobaville sandstone in late Precambrian or early Cambrian times, closed the geological record, with the exception of that attributed to the Pleistocene glaciation. �GENERALIZED GEOLOGIC MAP OF THE GARLIC RIVER GREENSTONE BELT AND of Michigan. PCg Lower Precambrian Garlic River Greenstone Belt Oneiss Complex Pgn, Lower Precambrian where approximately located where approximately northern peninsula Dotted Shoet dashed located complex in the Location map of the Lower Precambrian Garlic River Greenslone Belt and the Gneisx Geologic contacts Faults VICINITY* �Paper 12 COLUMN' GEOLOGIC GENERALIZED C .00 a NE Sandstone Jacobsviile 2 a--I unconformity Dikes Diabase Keweenowan Middle and tAmu) Upper 0 Lower and N (A) Animikie (Aim) Middle 2 Reony Lower 0 Creek (Ar) Formation — Serpentinized Peridotites 2 2 Granodiorites Intrusive contact Metadiabase Dikes Intrusive contact Quartz Monzonites Intrusive contact Gu Gar — IF Z Garlic River 3 Greenstones Gri GIpa GI Gm (G) U Gneiss and Intrusive Complex (Gn) �Paper 12 Based in part on maps by Case, J.E. and Gair, J.. (i5), Gair, J.E. and Thayden, R.E. (1968), Puffett, w.P. (1969) and LeAnderson, P.J. (1969). 1Units with symbols are included on the map with Units without symbols descriptions in the text. are not included on the map due to the scale involved. 2The age is uncertain. They may be post—Anamikie and pre—Keweenewan. 3The stratigraphic succession of the units of the Garlic River Greenstone is indeterminate. BI BLIOG.APHY Case, J.1. and Gair, J.E., 1965, "Aeromagnetic Map of parts of Marquette, Dickenson, Baraga, Alger, and Schoolcraft Counties, Michigan, and its Geo1o'ic Interpretationt', U.S. Geological Survey Geophysical mv. Map GP—467 Gair, J.E. and Thayden, R.E., 1968, "Geology of the Marquette and Sands Quadrangles, Marquette County, Michian", U.S. Geological Survey Professional Paper397 LeAnderson, P.J., 1969, "The Pre—Animikie Greenstone Complex of a small area in Narquete County, "ichignn", Unpub]Jsed Msc. Thesis, Michian State University Puffett, W.P., 1969, "The Reany Creek Formation, Marquette County, Michigan", U.S. Geologicl Survey Bull. 1274—F �Paper 13 MORPHOLOGY OF MAGNETITE IN PRECAMBRIAN IRON FORMATIONS M. S. LOUGHEED and J. 1. MANCTJSO Bowling Green University, Bowling Green, Ohio ABSTRACT The morphology of magnetite in all metamorphic fades of unoxidized Precambrian iron formations in the Lake Superior region is remarkably similar. Particularly noticeable are discrete symmetrical or distorted octahedral crystals of magnetite disseminated within individual lamina of chert. Several other features are noteworthy: 1) the crystal diameters range from sub—micron to over fifty microns; 2) the concentration of crystals in a particular lamina can range from a fraction of a percent to aggregates constituting the entire lamina; 3) the invariant associate of magnetite is chert; 4) the variant associates are iron carbonate and/or iron silicate minerals; 5) the minor but not uncommon associates are minute hematite crystals as disseminated spherical clusters, and pyrite as fram— boids, octahedra, and crystal aggregates generally within laminations of digital stromatolites or in laminations of mat algae. The morphology of magnetite, its variation in grain size, and its relationship to chert (quartz) siderite, iron silicate minerals, pyrite and/or hematite indicate that it is primary and that no chemical interreactions took place during diagenesis or metamorphism even to extremely high grades. �Paper 14 SUBSURFACE GEOLOGY OF THE DULUTH-SUPERIOR AREA, MINNESOTA-WISCONSIN J. T. MENGEL, JR. University of Wisconsin, Superior ABSTRACT Study of about 300 borehole records for the Wisconsin Geological Survey indicates that the Quaternary succession in the western end of the Superior lowland consists of glacial, lake, and river deposits which record stages in the development of Lake Superior which are not presently evident in the high-level shore deposits around the rim of the basin to the west or in deeper water lake deposits to the east. Preliminary interpretation of the sequence suggests two times of deep water red clay accumulation separated by a low water stage during which sands and gravels were laid down across an unconformity. A prominent boulder bed overlies the youngest red clay deposit, suggesting a late pulse of ice development during about Nippissing time. The Duluth Complex forms the north wall of the lowland in the Twin Ports area and is found in borings along St. Louis and Superior Bays, where wells encounter the same lithologies known from surface exposures. Fluvial red clastics - mainly quartzose sandstones with limited amounts of conglomerate and shale - of the Bayfield group are unconformable on the Complex and subcrop beneath most of the plain. Throughout the subcrop the Bayfield Group is identified as a "sandstone" or "brownstone" and an aquifer. Similar red clastics underlie most of the western end of the Superior Basin and are the principal source from which the Ouaternary sediments were derived. Along the base of the South Range the red clastics are cut off by the Douglas Fault which brings the Keweenawan basalt sequence of the St. Croix Horst upward and northward over the sandstones. Basalts crop out locally along the crest of the South Range and subcrop beneath the Quaternary succession southward to the Lake Duluth beaches (elevation about 1070) and beyond. The most notable feature about the configuration of the erosion surface on which the Quaternary succession lies is the buried western extension of the major depression along the northerly shore of Lake Superior (cf. Farrand, 1969). Twenty-five to 50 feet of local relief is present on the bedrock One local high forms a prominent outcrop along the bay front at the foot of 27th Avenue West in Duluth and a belt of subsurface surface everywhere. bedrock highs are known in the northern half of 48N-13W, extending westward into the center of 48N-14W in Wisconsin. �Paper 14 2 A maximum thickness of about 600 feet of sediments are present along the axis of the north shore depression between Fond du Lac and Superior Bay and 100 to 300 feet are present under the plain as far south as the crest of the South Range. Less than a hundred feet of glacial drift overlain by clays and/or sands is present along the crest of the South Range. Glacial drift everywhere overlies the bedrock of the plain. Typically about 25 feet is present except toward the bottom of the north shore depression, where as much as 200 feet is known. The drift ranges from a silty or sandy clay to an argillaceous sand and generally contains gravel and erratic boulders. Clean sand/gravel lenses are presently locally most commonly at or near the base of the drift, and are an important source of ground water when encountered. Lake deposited stiff red clay overlies the drift and is more or less gradational with it. Along the northerly side of the St. Louis River in West Duluth, and beneath the plain to the south of Superior almost the entire Ouaternary succession is medium to stiff red brown clay containing scattered ice rafted pebbles and cobbles. Silty, sandy/gravelly layers, some of which contain small amounts of water are encountered in the clays, most comonly at depths of about 20 to 50 feet below the general level of the plain. At higher elevations i.e., about 900-1000 feet the clays are gradational with sandy materials representing shore reworking of the underlying drift and materials introduced by small tributary streams. Locally the sandy materials extend to lower elevations-lying on top of the clay sequence. Along the St. Louis River the clays are largely replaced in the stratigraphic succession by brown, poorly permeable dense argillaceous silty to sandy deposits which become coarser and cleaner and may contain gravels toward the top of the sequence. These deposits, which reach a maximum thickness of about 200 feet lie on a stiff red clay unit, which in turn rests on glacial drift deposited in the north shore depression. Deep engineering bore control is not adequate to define lateral relationships with the middle part of the clay sequence. It presently appears that there is little or no interbedding of sand and clay either in West Duluth or in Superior, suggesting the possibility of introduction of the sandy materials by ice or in part by turbidity flow or river deposition along the general trend of the north shore depression. The coarseness of the upper part of the sandy sequence, its considerable degrees of sorting, and prominent cross bedding indicate the existence of high energy conditions at the Lakehead prior to deposition of the 15 to 50 foot thick red clay which overlies the sandy unit, forming the surface of the Superior plain. The uppermost clay layer lies on an undulating surface having up to a few tens of feet of relief. Contours on the base of the clay define the north shore depression and indicate slopes toward the depression and toward Lake Superior. The clay dips beneath present water level in Howards Bay and is known beneath the younger sands and gravels of Connors Point and the outer end of Rice's Point. Both of these points are built along �Paper 14 3 the erosional zero edge of the clay as it subcrops under St. Louis Bay, suggesting that this fact may have influenced their construction. The same red clay subcrops beneath the outer end of Minnesota Point and under Wisconsin Point. This uppermost clay rests on a thin sandy or gravelly unit which overlies the main clay sequence in West Duluth and Morgan Park and conditions are similar in Superior. Prominent develop- ment of clays to elevations of about 700 feet on the Duluth hillside may indicate flooding of the plain to this level during development of the clay layer. A later very low water stage, perhaps Ferrand's (1969) Houghton Stage, allowed deep incision of drainage along the north shore depression, exposing the sandy sequence and initiating the present drainage system. A general rise in lake level toward a maximum of about 610 feet during the Nippissing Stage caused the deeper parts of the drainage to become aggraded with sandy materials and subjected the upper red clays to strong wave attack. The rise of the uppermost clay away from the north shore depression made it particularly subject to wave erosion, causing steep bluffs from the central part of the Superior Bay waterfront eastward to the present shore line of the lake. A prominent clay platform was developed offshore from the bluffs. This platform is the floor on which Minnesota and Wisconsin Point are built. It is presently blanketed by twenty to at least 70 feet of clean fine to coarse sand containing small amounts of gravel. A greater thickness of such sandy deposits may lie below present control depth under the central part of Rice's Point and the northerly third of Minnesota Point. A great number of large crystalline rock boulders occur at or near the base of these young sandy deposits under Superior Bay. Maximum boulder size recorded so far is 5 x 6 x 7 feet for one recovered during construction of the Cloquet water line. Large boulders are known throughout the length of the Superior Front Channel and the open lake shore to the southeast, their number, size and wide distribution, together with the existence of a higher lake level more or less following their deposition may suggest a late pulse of ice development. An alternative view is that they are developed by exposure of the top of the sandy unit beneath the upper red clay. This unit is known to contain boulders locally, as in the vicinity of the local bedrock high at the foot of 27th Avenue West in Duluth. However, the fact that boulders lying on a few feet of sand overlie the top of the young red clay under Connors Point suggest that ice transport may be involved. It is quite possible that some of the sand present on south shore beaches comes from exposure of the underlying sands. Much of the modern south shore sand is derived from reworking of the underlying till which is exposed along several drainages as the bedrock surface rises to the east of the Twin Ports. A period of declining lake levels during which water levels dropped from about 610 to perhaps 590 feet, witnessed the sequential development of the lake-head barriers of Grassy Point, Rice's—Connors Points, and Minnesota-Wisconsin Points (cf. Loy, 1963). All are built primarily from materials derived by the erosion of the sandy sequence of the north shore depression by the St. Louis River and by lake activity during the high waters of the Nippissing stage. The eventual decline in water level during the subsequent Algoma stage was low enough �Paper 14 4 to permit development of spruce woods rooted in the sands of what is now Allouez Bay. Later flooding, which is apparently continuing at present (cf. Moore, 1948), has led to development of organic-rich mucks, locally capped by peats as the main sediments above the most recent harbor sands. The upper parts of the organic deposits often contain sawdust, wood fragments and horse manure, a legacy of late 19th century activities in the harbor. Slag, wood derivatives, etc. of more recent origin are also present. Dredging for harbor development and slip construction have largely altered the natural stratigraphic sequence of the young sands and organic materials but the natural bottom contours, sediment types, and shore features can still be studied on the excellent 1861 chart directed by Captain G. C. Meade for the Army Corps of Engineers. REFERENCES Farrand, W. R., 1969, The Quaternary history of Lake Superior: Proc. 12th Ann. Conf. Great Lakes Res., International Assoc. Great Lakes Res., p. 181-197. Loy, W. G., 1963, The evolution of bay-head bars in western Lake Superior: Pub. No. 10, Great Lakes Res. Dir., Univ. Michigan, Ann Arbor. Moore, Sherman, 1948, Crustal movements in the Great Lakes area: Bull. Geol. Soc. Amer., 59, pp. 697-710. �Paper 15 PETROLOGIC AND STRUCTURAL ASPECTS OF THE GABBRO SILL ON PIGEON POINT, MINNESOTA M. G. Mudrey, Jr. and P. W. Weiblen Minnesota Geological Survey and University of Minnesota, Minneapolis Detailed mapping on Pigeon Point, Cook county, Minnesota, discloses petrologic and structural complexities heretofore not reported. The sill on Pigeon Point ranges in composition from a tholeiltic olivine gabbro to ilmenite gabbro, to quartz gabbro, and to potassium feldspar-bearing gabbro. The red granitoid rock above the sill is intrusive in the upper parts of the gabbro, but the origin of these red rocks by differentiation of the gabbro or fusion of the Rove sedimentary rocks is not clear. Analyses of coexisting phases in the gabbrô indicate iron— enrichment during the differentiation history of the sill. Analysis of phases also sets limits on petrogenetic relations to the Logan Intrusive Rocks, and to the Pigeon River Intru— sions of Geul. The Pigeon River Intrusions appear to have a simple direct relation; however the Logan Intrusive Rocks of Geul cannot be directly related by simple fractional crystallization to the sill on Pigeon Point. Since emplacement and cooling of the sill, faulting and fracturing on northwest and east-west trends has occurred. The northwest faulting is marked by barite—calcite veins, and the east—west direction by late olivine diabase dikes. �Paper 16 Lower Precambrian metavolcanic—metasedimentary seguence, Rainy River, northernmost Minnesota Richard W. Ojakangas University of Minnesota, Duluth ABSTRACT A thick metavolcanic—metasedimentary sequence is exposed in northernmost Minnesota, south of the Rainy River and about midway between International Falls and Baudette. The previously undescribed volcanic rocks range In composition from basalt to rhyodacite. Intermediate—felsic tuffs and agglomerates and dacitic flows and hypabyssal intrusions apparently are the dominant rock types. These rocks are intermittently exposed along the edges of two younger 200—400 ft wide diorite—gabbro dikes that trend nearly perpendicular to the northeasternly regional strike of the steeply dipping country rocks. Stratigraphic top determinations are limited to a few pillowed metabasalts. However, the scanty data indicate that the sequence may be as much as 25,000 feet thick. Massive suif ides are present in prospect pits and in drill holes in the western part of the area. References: Fletcher, G. L., and Irvin, T. N., 1955, Geology of the Emo Area: 63rd Annual Report, Ontario Department of Mines, part 5, 36 p. Ontario Department of Nines, 1967, Kenora—Fort Frances Sheet, Geological Compilation Series, Map 2115. �Paper 17 THE EASTERN TERMINUS OF THE LAKE SUPERIOR SYNCLINE ERDOGAN ORAY W. S. HINZE N. W. O'HARA Michigan Purdue University West Lafayette, Indiana Naval Weapons Center China Lake, California State Univ. East Lansing, Michigan ABSTRACT A regional gravity Investigation of the eastern portion of the Northern Peninsula of Michigan was conducted and combined with previously observed gravity stations in the Southern Peninsula of.Michigan, Beaver Island, northern Lake Huron, northern Lake Michigan and the Sault Ste. Marie area of Canada to investigate the eastern terminus of the Lake Superior syncline. The Bouguer gravity anomaly map of the eastern portion of the Northern Peninsula shows three major positive gravity anomalies. One of these anomalies trends southeast from Grand Island in Lake Superior and can traced orthwestby magnetics to the Middle Keweenawan volcanics of This anomaly represents the margin of the western limb of the Lake Superior syncline. Another positive anomaly trends south from Whitefish Point on the south shore of Lake Superior be the Keweenaw Peninsula. and is interpreted as a horst of basalts which can be traced magnetically to the Middle Keweenawan volcanics outcropping on Mamainse Point, Ontario. The eastern limb of the syncline near the eastern edge of the Northern Peninsula is also defined by a positive gravity anomaly. These three positive gravity anomalies which are associated with positive magnetic anomalies merge in the vicinity of Beaver Island in Lake Michigan and mark the termination of the Lake Superior syncline. South of Beaver Island, the Keweenawan basalts continue in a south—trending narrow belt and are expressed by the "Mid—Michigan gravity high". The Bouguer anomaly map indicates two local gravity minimums in the Whitefish Bay area on the south shore of Lake Superior. These are interpreted to result from a thick accumulation of Upper Keweenawan clastic sediments. The results of two dimensional model studies suggest that the Lake Superior syncline in the eastern portion of the Northern Peninsula consists of up to 12,000 feet of basaltic flows overlain by Upper Keweenawan clastic rocks. Two geological models can be fitted to the observed anomalies of the northern tip of the Southern Peninsula of Michigan. The basalts either extend throughout the northern tip of the Southern Peninsula where they are highly faulted into a series of horsts and grabens or they are confined to the Grand Traverse Bay area in which case pre—Keweenawan extrusives and intrusives make up the basement of the northern tip of the Southern Peninsula. �Paper 18 MAGNETIC REVERSALS AND POLAR SHIFTS AS MARKERS IN A PROTEROZOIC TIME SCALE W. A. ROBERTSON Geomagnetic Laboratory Earth Physics Branch Department of Energy, Mines and Resources Ottawa, Canada A B STRACT The construction of a useful Precambrian time-scale Fossils are scarce. Sedimentary basins are widely separated, and deposition rates may have been different from today. Small errors in radiogenic age determinations represent many millions of years. Geologists should consider the help that is presents great difficulties. becoming available from paleomagnetic sources when attempting to divide Precambrian time into useful time units. Difficulties using paleomagnetic methods of dating so far back in time are no greater than those of other methods, and have one unique advantage. The pattern of reversals of the earth's magnetic field is world-wide; it is not diachronous, and any identifiable marker horizon occurs at the same point in time wherever it is found. This is not true of polar-wandering curves, however, which apply only to their own continent. The figure shows a hypothetical reversal pattern for the earth's magnetic field, with time as abacissa. Above and below it are hypothetical movement rates, on the same time scale, of two continents, EG and AS. It is hypothetical for the Proterozoic due to lack of data, but is based on patterns emerging from Phanerozoic time. M intervals are ones of mixed polarity, whereas N and R. are of wholly normal and reversed polarity respectively. Reversal nodes marked X, between wholly normal and wholly reversed polarity intervals provide unambiguous, universal marker horizons. G nodes, where one double polarity inversion took place, give good marker horizons but may be hard to find in rock sequences. The F nodes also yield marker horizons, but may be harder to identify precisely. �Paper 18 -2— At the first and third polarity node the continents are shown as accelerating sympathetically at the time of change of reversal frequency. Further back in time they are shown as independent of each other, and more indern.dent of the polarity rhythm. Whether there are links between motions at the earth's surface and reactions at the core-mantle boundary is still an unsolved problem. In any case, the location of a pole position on the polar wandering curve of the same continent will be a measure of its age. The accuracy will be highest for rocks formed at times of rapid polar movement: conversely if a conti- nent is static relative to the pole for a long interval pole positions will not differentiate ages of rocks formed in that interval Working out the polarity scheme for a Precambrian period is a very big task. Unconformities will leave gaps that have to be filled in from elsewhere. Nevertheless a pattern is : beginning to emerge in the Hadrynian and Helikian (880-1640 m. Y.) of the Canadian Shield, although large gaps remain to be filled. An older normal interval ( 1400 m.y.) appears to be followed by a mixed interval. Then a second normal interval is succeeded by a reversed interval about 1100 m.y. ago (a potential X node). A possibly longer normal interval then appears to be followed by one of mixed polarity. It is still too early to use paleomagnetic nodes as boundaries to help form a Proterozoic time-scale, but new polar wandering and reversal pattern data are accumulating fast, and we would be wise to consider the possibility of using them to help to split the Precambrian into time strati graphic units of wide application. �Ic' 1¼. rr, WORLD -WIDE POLARITY fl C C; 4 S tt. —4 C) fl hi N 1,, z -x *3 �Paper 18 'vv'ORLJ) —WIDE C.Di /tr POLAR IT z rr —4 C) t-j N C' �Paper 18 -2SELECTED REFERENCES Cox, Allan, 1968, Lengths of geomagnetic polarity intervals. J. Geoph. Res. V. 73, p. 3247-60 Cox, A., Doell, R. R., and Dairymple, G. B. 1964, Reversals of the earth's magnetic field, science, V. 144, p. 1537-43. Gough, 0. I., Ondyke, N.D., and McElhinny, M. W., 1964, The significance of paleomagnetic results from Africa. J. Geoph. Res. V. 69, p. 2509-2519. Heirtzler, J. R., Dickson, G. 0., Herron, E.M., Pitman III, W. C., and Le Pichon, X., 1968, Marine magnetic anomalies, geomagnetic field reversals, and motions of the ocean floor and continents, J. Geoph. Res. V. 73, p. 2119-36. Irving, E., and Robertson, W. A., 1969, Test for polar wandering and some possible implications. Res. V. 74, p. 1026-36 J. Geoph. McElhinny, M. W., 1971, Geomagnetic reversals during the Phanerozoic. Science, V. 172, p. 157-9. Minkovitch, D., Opdyke, N.D., Heezen, B. C., and Foster, J. H., 1966, Paleomagnetic stratigraphy, rates of deposition and tephrachronology in North Pacific deep-sea sediments. Earth and plan. Sci. 1st. V. 1, p. 476-92. Robertson, W. A., and Fahrig, W. F. 1971, The Green Logan Paleomagnetic Loop -- the polar wandering path from Canadian Shield rocks during the Neohelikian Era. Can. J. Earth Sci. V. 8, p. 1355-72. Vine, F. J.., 1968, Magnetic anomalies associated with Mid-Ocean Ridges. The History of the Earth's Crust. Ed. R. A. Phinney, p. 73-89. �Paper 19 ARCHAEAN SALIC VOLCANIC ROCKS AT KAKAGI LAKE, NW ONTARIO - THEIR PHYSICAL AND CHEMICAL NATURE by D.R. Smithl R. H. McNutt P. M. Clifford? ABSTRACT At Kakagi Lake, and Archaean (older than ca. 2500 my) supracrustal assemblage has, for its upper portion, salic volcanic rocks, approximately two thousand metres thick. These rocks are somewhat unusual , being almost devoid of outcrop-scale layering in rhyodacitic and andesitic scoriaceous breccias and having limited or crude layering in crystal tuffs. Within the fragmental rocks, there is only poor sorting of size fractions. Moreover, in any given outcrop, the accessory fragments which make up the bulk of the framework are monolithologic. Analysis of variation of maximum fragment size, and framework - matrix ratios reveal a "cryptic° macroscopic layering, not visible in individual outcrops. In addition, there are two, possibly three, areas having both large values of maximum fragment size, and a high framework matrix ratio. These areas are interpreted as projections of emission centres into the present day outcrop plane. Chemical analyses of 23 pairs of fragments and adjacent matrix show that, in general, the fragments are the richer in Si02 and perhaps Na20, with matrix the richer in total Fe and MgO. Discriminant function analysis of our data, using the four oxides mentioned, properly identifies fragments from the matrix in 80% of the samples. These pyroclastic rocks have rather strong caic-alkaline affinities, and tend to be normal or low in K)O. Normatively, matrix is: 33% basaltic, 48% andesiti, 19% dacitic; fragments are: 29% basaltic,29% andesitic, 42% dacitic. These chemical differences are echoed in thin sections. Fragments commonly have polycrystalline quartz aggregates and felspar phenocryst in a felsic background: matrix is markedly chloritic. Alteration is ubiquitous. There are no discernible chemical trends along "strike or upwards through the volcanic pile. This reinforces the evidence from physical properties-considerable thickness, lack of layering, poor sorting, monolithologic fragment 1. Texaco, Calgary, Alberta. 2. Department of Geology, McMaster University, Hamilton, Ontario. �Paper 19 —2- character locally - which indicate a pyroclastic flow origin for these rocks. Presence of a fabric possibly pseudomorphic after shard structure is further support for this interpretation. �Paper 20 Three-phase deformation associated with the Penokean orogeny, east Gogebic Range, Michigan-' by Virgil A. Trent U.S. Geological Survey, Washington, D.C. Abstract Three phases of deformation in the east Gogebic area resulted in tight folding of Precambrian X (Marquette Range Supergroup) strata followed by folding and block tilting of the Precambrian Y (lower Keweenawan) and Precambrian X (Animikie) phase of orogeny. sections during the last The deformationa]. periods are marked by coeval volcanism and by three angular unconforniities. Although the deformations may be widely spaced in time, lithology and structural morphologlj suggest that they are separate phases of a single orogenic episode. Near the east end of the Gogebic Range, Precambrian X (Marquette Range Supergroup) strata lie between tilted metamorphosed Precambrian Z volcanic rocks (lower Keweenawan) to the north and strongly meta- morphosed Precambrian W or X gneiss complex, Algoman Granite of Lawson (l9lL), and volcanic rocks (Keewatin) to the south. Three defoniiational phases can be identified in Precambrian X rocks of the eastern Gogebic Range: -'Work done in cooperation with the Geological Survey Division of the Michigan Department of Natural Resources. 1 �Paper 20 i) The earliest was folding of the Sunday Lake Quartzite, Bad River Dolomite, Palms Formation, and Ironwood Iron- Formation. Mafic lava flows intercalated with the Ironwood Iron-Formation indicate that extrusive volcanic activity preceded folding. The large Wolf Mountain anticline began to form, followed by erosion and Copps Group of Allen and unconformable Barrett (191S) and deposition of the the Tyler Formation. 2) The strongest deformational phase, the Penokean orogeny, as defined by Goldich and others (1961, p. 120-122, i6-i6o), took place at the end of Precambrian X ("Animikie") The this time. Wolf Mountain anticline was more tightly folded during event. Mafic sills, also intercalated with the Ironwood Iron-Formation were intruded syntectonicafly. The northernmost thick sill truncated by the pre-Keweenawan unconformity (Prinz, 1967), appears to be genetically related to flow breccia cropping out along its eastern margin. Erosion of these volcanic rocks, parts of the Tyler and Copps, and older rocks preceded the unconformable deposition of the oldest Keweenawan strata. 3) Post-lower Keweenawan deformation, upon which Blackwelder 638) based his original definition of the Penokean orogeny, warped and the whole Precambrian succession (191)4, p. tilted except for the Jacobsville Sandstone. folding seems to mimic major Penokean The last phase of trends of the preceding folding, especially in the area close to Lake Gogebici. Torsional basement movements related to block tilting probably contributed to the assymetry of the Wolf Mountain anticljrie. 2 �Paper 20 A large Wolf Mountain in the area. flat-lying niass of (T. 147 N., R. 1414 eflipsoidal basalt north of w.) may be the youngest volcanic rock It lies athwart the Precambrian X (.Animikie) structural trend and has not been blocktilted. The youngest major fracture in the area passes nearby, and to the southwest the fracture is filled by a thick mafic dike which I interpret to be the feeder. Two miles to the northeast, this fracture truncates the lower Keweenawan ridge. This field evidence suggests that these ellipsoidal lavas were extruded in post-early Keweenawari time and were perhaps associated with the terminal phase of folding. 3 �Paper 20 References cited Allen, R.C., and Barrett, L.P., l9l, A revision of the sequence and structure of the pre-Keweenawan formations of the eastern iron range of Gogebic (Geol. Michigan: Michigan Geol. Survey Pub. 18 Ser. l), p. 33-61; in part, Jour. Geology, v. 23, p. 689—703. Blackwelder, geologic Eliot, l91L, A summary of the orogenic epochs in the history of North America: Jour. Geology v. 22, no. 7, p. 633-65)4. Goldich, Samuel S., Nier, John H., and Krueger, Alfred 0., Baadsgaard, Halfdan, Harold W., Hoffman, 1961, The Precambrian geology and geochronology of Minnesota: Minnesota Geol. Survey Bull. 141, 193 p. Lawson, A.C., 191)4, A standard scale for the pre-Cambrian rocks of North America: Internat. Geol. Cong., 12th, Canada, 1913, Comptes rendus, p. 31i.9-370. Prinz, W.C., 1967, Pre-Quaternary geologic and magnetic map and sectioriLs of part of the eastern Gogebic iron range, Michigan: U.S. Geol. Survey Misc. Geol. mv. Map 1-1497. 14 �Paper 21 BEDROCK MORPHOLOGY IN THE VICINITY OF PORTAGE LAKE, KEAW PINSULA, MICHIGAN E. J. WARREN Department of Geology and Geological Engineering Michigan Technological University ABSTRACT Portage Lake stretches across the Keweenaw Peninsula of Michigan between Keweenaw Bay and Lake Superior. This circumstance was put to good use by the Indians and later by French voyaguers and Jesuits who used the long sinuous lake as a shortcut in their travels along the south shore of Lake Superior. Modern shipping uses the same shortcut, now known as the Keweenaw Waterway. Portage Lake has a maximum depth of about 50 feet located On the other hand, Torch in the main body of the lake. Lake, which is connected to Portage Lake by Torch Bay and a dredged ship channel, was once 170 feet deep before it was partially filled by mill tailings from various copper recovery operations. Several geologists have speculated about the origin of these unusual lakes (Martin, 1911; Scott, 1921; Hughes, 1963). However, they were handicapped by their lack of knowledge of the bedrock morphology around and under the lakes. The bedrock morphology was determined from water well and diamond drill logs and by geophysical methods. Seismic refraction profiles were run on land and on the mill tailings in Torch Lake. On the lakes, sparker and air-gun surveys were performed. Unfortunately the sparker survey lacked penetration and the air-gun profiles were rendered nearly useless by excessive reverberation. Gravity profiles were then run over Portage Lake, on ice, in an attempt to extrapolate the land based information. Interpretation of the gravity surveys, now being performed, is hampered by the large regional gravity gradient due to the Keweenaw fault (Bacon, 1966). Preliminary results indicate that both Portage and Torch Lakes lie in a complicated network of buried bedrock valleys. A water well next to the narrow northwest arm of Portage Lake reaches a depth about 380 feet below lake level and a diamond drill hole east of Hancock Michigan reaches bedrock about 280 feet below lake level. Of course, there is no assurance that either of those wells have reached the deepest part of the bedrock valley. �Paper 21 Torch Lake lies in a bedrock valley with a floor 250 feet This valley underlies the pre-. below present lake level. sent Traprock River valley to the north and continues south of Torch Lake into Portage Lake under Torch Bay. The bedrock valley under Torch Lake is also connected to Portage Lake by a bedrock valley 200 feet below lake level which parallels the Keweenaw fault and passes under the town of Dollar :ay. bedrock valley about 150 feet below lake level extends from the southeast part of the main body of Portage Lake out through Portage Fh-itry, curving to the east of the present channel. The deepest bedrock valley, however, extends south of the main body of Portage Lake under the present Sturgeon River valley where a depth L50 feet below present Lake Superior level was found. The southern extension of this deep It is interesting valley still remains to be explored. that this valley has bedrock depths on the same order as the depth of Keweenaw Bay. A bedrock valley 200 feet below lake level branches off the west side of the Sturgeon valley and passes under Otter Lake. It is probable that these buried bedrock valleys were originally a product of stream erosion. It is possible that some glacial overdeepening has taken place also, but this cannot be detexmiined until all the data is compiled and a contour map of bedrock elevations is completed. At any rate, it is apparent that the base level for stream erosion was once considerably lower than the present Lake Superior level. This discovery may have some bearing on the controversy about whether Lake Superior is mainly a result of subaerial erosion, of glacial scour, or of some combination of the two. References Bacon, L. 0., 1966, Geologic Structure East and South of the Keweenaw Fault on the Basis of Geophysical Evidence: The Earth Beneath the Continents, A.G.U. Mon. 10, pt2—55. Hughes, J. D., 1963, Physiography of a Six Quadrangle Area In the Keweenaw Peninsula North of Portage Lake: Unpublished Ph.D. Dissertation, Northwestern Univ., Evanston, Ill., 228 pp. Martin, L., 1911, Physical Geography of the Lake Superior Region: Chapt. IV in U.S.G.S. Mon. LII, The Geology of the Lake Superior Region, p85-l17. Scott, I. D., 1921, Inland Lakes of Miohigan: Mich. Geol. and Biol. Survey, Lansing, Mich., 383 pp. �,, 4/ / / I / / I F I / / ,, 6, LAKE SUPERIOR -¼ SCALE :250000 OF MICHIGAN THE KEWEENAW PENINSULA �Paper 22 GLACIAL DRIFT ON THE MESABI IRON RANGE, MINNESOTA ITS CHARACTERISTICS, ORIGIN, AND HYDROLOGIC SIGNIFICANCE'! THOMAS G. WINTER U. S. Geological Survey ABSTRACT Glacial deposits in the Mesabi Iron Range area consist ments. The basal till occurs in only a small number of mines, but they are scattered across the entire Iron Range. The is dark gray to dark greenish gray and brownish gray, sandy, silty, and is calcardous. The middle till unit, a of three major till units and associated glaciofluvial sedi- till bouldery till, is the thickest and most widespread of the three tills. It is grey, yellow, red, orange or brown, sandy, silty, contains abundant cobbles and boulders, and is non-calcareous. The till was depsoited by the Rainy lobe, which has a minimum age of 14,000 to 16,000 years before present. The surficial till was deposited contemporaneously by two minor sublobes of the same ice lobe about 12,000 years ago. The brown silty till occurs in the western and north-central part of the area. It is light to medium brown, sandy, silty, and calcareous. Red clayey till the south-central part of the area is red to reddish brown, clayey, silty, and calcareous. Stratified fluvial sediments occur within the glacial drift at many places in the Mesabi Iron Range area. These sediments, which are important aquifers, occur extensively between the three main till units. The thickest and most extensive aquifer consists of glaciofluvial sediments that lie between the surficial till and the bouldery till. The thickness of the glaciofluvial sediments is greater than 50 feet in much of the area, and the transmissivity is greater than 100,000 gallons per day per foot at a number of localities. Glaciofluvial sediments underlying the bouldery till occur largely in the western half of the area. These sediments are generally less than 50 feet thick and their transmissivity is generally less than 50,000 gallons per day per foot. Surficial glaciofluvial sediments are a source of ground water for high yield wells only in the eastern part of the area in the general vicinity of the Biwabik bedrock valley. Thickness of these sediments is greater than 100 feet in some places, but their transmissivity is generally less than 50,000 gallons per day per foot. �Paper 22 -2- The glacial drift aquifers can yield as much as 40 mgd (million gallons per day). Assuming that the ratio of area underlain by aquifer to total area is constant for the study area (about 20 percent where mapped in detail), it is concluded that as much as 80 million gallons per day could be developed from glacial drift aquifers without causing excessive water declines and depleting streamfiow. Publication authorized by the Director, U.S. Geological Survey �Paper 23 CHRONOLOGY OF PRECAMBRIAN ROCKS OF IRON AND DICKINSON COUNTIES, MICHIGAN PART II P. 0. Banks Department of GeologyCase Western Reserve University, Cleveland, Ohio 44106 and W. R. Van Schmus Department of Geology University of Kansas, Lawrence, Kansas 66044 Ertensive K-Ar, Rb-Sr, and U-Pb data available for the Precambrian rocks of Iron and Dickinson Counties, Michigan, permit considerable clarification of the chronologic development of this area. The following ares are considered well established (rounded to nearest 25 m.y.): Peavy complex 1900 m.y., Hemlock volcanics 1950 m.y., and Porphyritic Red Granite 2100 m.y. A U—Pb concordia intercept ago of 2575 ni.y. for the Norway Lake gneiss is considered minimal for this unit because of probable multiple secondary events. The pre—Animikie post—Dickinson Granite Bluffs gneiss gives an apnarent Rb—Sr whole rock age of Ca. 2700 m.y. whereas its apparent zircon U—Pb concordia intercept age is ca, 2100 m.y. This anomaly can be explained either by urusual migration of radiogenic Sr or by multi-stage Pb loss. Additional mineral analyses are in progress to resolve the issue. Our previous conclusion (Banks and Van Schmus, ILSG 1971) remains unchanged that the Animikie Series of James et al. is bracketed between 1900 and 2100 m.y. and therefore is not correlatable with the original Huronian of Ontario. Resolving the ae of the Granite Bluffs gneiss will determine whether the Dickinson Group Is or is not a candidate for correlation with the original Huronian. Additirnal data of interest include a Pb/Pb age of 2900 m.y. for detrital zircon from the East Branch arkose, and a suggestion from K—Ar h.ornblende and U-Pb apatite and sphene data that the last major metamorphism in the area occurred 1500—1600 m.y. ago. �Paper 24 PENOKEAN TECTONICS IN NORTifERN MICHIGAN by W. F. CANNON U. S. Geological Survey Washington, 2O242 D.C. ABS TRA CT The major Penokean deformation in northern Michigan occurred between 1.9 and 2.0 b.y. ago. Lower and. middle Precambrian rocks were deformed independently of, and mostly before, regional metamorphism; the deformation took place at low temperatures. The subsequent metamorphism was a low-pressure type in which andalusite was stable over a wide temperature range. The maximum confining pressure is set by the aluminosilicate triple point at about 5 kilobars (about 13 miles burial depth), but the true pressure may have been much less. Structural interpretations must be consonant with mechanisnis of rock deformation possible at low temperatures and low to moderate confining pressures. Lower Precambrian granitic rocks form the basement for the Marquette Range Supergroup in much of northern Michigan. granitic Experimental rock deformation indicates that rocks have very high strength and very low ductility under probable conditions of Penokean deformation, and kinematic interpretations of Penokean deformation must consider the probability of a strong nond.uctile basement; interpretations requiring a weak ductile basement are difficult to reconcile with the probable physical environment of deformation. The first-order regional structures in northern Michigan are uplifts of lower Precambrian rocks with middle Precambrian rocks of the Marquette Range Supergroup in intervening synclinorial basins. A wide divergence of trends for these structures suggests vertical tectonism rather than regional horizontal compression. The lower Precambrian cores of many uplifts are cut by diabase dikes. These dikes are older than the Penokean orogeny, and many are probably associated with mafic intrusive and extrusive rocks in the middle Precambrian section, yet these dikes were not externally deformed during Penokean folding; they remain planar and. largely massive. These relationships substantiate inferences from experimental rock deformation of a strong nonductile basement and strongly suggest that the lower Precambrian rocks remained rigid and were not penetratively deformed d.uring Penokean deformation. The uplifts are interpreted, as fault- bounded blocks of lower Precambrian rocks which were uplifted V The Gogebic Range is excluded from this discussion because of cnp1ications introduced by younger deformation. �Paper 24 along steep faults, many of which are steep reverse faults. The blocks may have moved either as single units or, more likely, with internal adjustments occurring along relatively narrow shear zones and parallel to dike margins. During this phase of deformation, middle Precambrian rocks were passively draped over the fault blocks, forming the presently preserved synclinal structures which occupy the relatively dow'nfaulted segments of the basament. Second-order and, smaller folds in middle Precambrian rocks indicate that these rocks have undergone substantial horizontal shortening, whereas the underlying lower Precambrian rocks have not. Furthermore, the trends of second-order and smaller folds are mostly in west and west-northwest directions and are much more uniform than trends of first-order structures (block uplifts). In some areas, second-order folds cross the trends of first-order structures at high angles. Many of these smaller folds seam to have formed independently of first-order structures, and their genetry requires a thin-skinned compressive deformation which has affected. only the middle Precambrian rocks and not the lower Precambrian basament. Many of these folds may be due to gravity sliding or spreading which, because of relatively uniform fold trends, appears to have occurred in response to a region-wide gradient. This phase of deformation must have occurred before block faulting produced sithstantial structural relief on the contact of lower and middle Precambrian rocks. The suggested sequence of events is: 1) Regional gravity sliding which produced folds in middle Precambrian rocks with west and west-northwest trends but did not deform the lower Precambrian basament rocks. This event was probably associated with early uplift of the depositional basin. 2) Uplift of fault-bounded basament blocks with widely divergent trends, accompanied by passive draping of middle Precambrian rocks and earlier gravity folds into basins or tight synclines between the uplifts. A second set of folds formed in middle Precambrian rocks in areas marginal to the uplifts. �Paper 25 THE PENOKEAN OROGEM S. S. Goldich Northern Illinois University DeKalb, Illinois 60115 ABSTRACT The Penokean orogeny (Blackwe1der, 1914) was redefined by Goldich arid others (1961) as Middle to Late Precambrian event that involved the Anuinikie Group of Minnesota and Ontario and similar rocks that were formerly assigned to the Huronian in Wisconsin and Michigan. Time limits from 1600 to 1800 ni.y. were set for the orogeny; however, Peterman (1966) showed that the metasedimentary rocks of the Cuyiina district were folded 1850 n.y. ago. New data for the Thomson Formation of east-central Minnesota give a minimum age of the folding and metamorphism of 1900 n.y. ago (Stuckless and Goldich, 1972). Thus, the Penokean orogeny is a Middle Precambrian event, using 1800 m.y. as the time boi.]ndary between the Middle and Late Precambrian (Goldich, 1968). Limiting ages have been placed on the type Huronian rocks by dating of the Nipissing Diabase in the Blind River—Bruce Mine area (Van Schmus, 1965) and of the Nipissing Diabase and Gowganda Formation at Gowganda (Fairbairn and others, 1969). The type Huronian rocks are at least as old as 2280 n.y. (Gow— ganda Formation) and were folded at least 2160 m.y. ago (Nipissing Diabase). Fryer (l97l has reported ages of 1800, 1870, and 1790 m.y. for volcanic and metasedimentary rocks from the Belcher Fold Belt, the Labrador Trough, and the Mistassini Lake area. Rb—Sr ages, however, must be used with caution. They do not necessarily date the time of deposition or of a specific metamorphic event. In Minnesota, for example, isochron ages on Aniniikian rocks range from 1900 to 1660 n.y., but all were probably deposited at essentially the same time. Considerable radiometric dating of Middle Precambrian rocks is now in progress. Until the new data from a number of laboratories are published and can be assessed, it is premature to correlate the rocks of widely separated areas of North America. References For references prior to 1969 see Goldich (1968). Fairbairn, H. W., P. M. Hurley, K. D. Card, and C. J. Knight (1969) Correlation of radionietric ages of Nipissing Diabase and Huronian metasedinients with Proterzoic orogenic events in Ontario: Canadian Jour. Earth Sci., v. 6, p. 489—497. Fryer, B. J. (1971) Rb—Sr whole—rock ages of Proterozoic strata bordering the eastern part of the Superior Province, Canada (abs.): Geol. Soc. America Abstracts with Program, v. 3, p. 574—575. Goldich, S. S. (1968) Geochronology in the Lake Superior region: Jour. Earth Sci., v. 5, p. 715—724. Canadian Stuckless, J. S. and S. S. Goldich (1972) Ages of some Precambrian rocks in east-central Minnesota: 18th Annual Institute on Lake Superior Geology, Houghton, Michigan. �Paper 26 RELATION OF PENOKEAN POLYPI-IASE DEFORMATION TO REGIONAL METAMORPHISM IN TI-fE WESTERN MARQUETTE RANGE, NORTHERN MICHIGAN John S. Kiasner Michigan Technological University Houghton, Michigan ABSTRACT Recent work at Lake Michigamme at the western end of the Marquette Trough suggests that some metamorphic minerals began to form during the early stages of Penokean deformation contrary to previous studies (Powell 1970) that suggest that regional metamorphism almost completely postdates deformation. The new studies indicate that metamorphism peaked late in the deforrna.tional sequence as shown on figure 1. F F1 F2 F Deformational events Andalusite Garnet S t.au ro lit e Actinolite Grunerite Biotite Sericite Thermal metamorphism ically shown Chlorite Fabric elements Time Figure 1, Kinematic relationship of metamorphism to deforrnationQ The deformational sequence, characterized by four phases, started with regional soft sediment deformation (F that produced a penetrative N 75° W trending foliation, th8 early stages of which can be identified as slaty cleavage (S ). Selective migration of silica (Williams 1972) during continued deformation (F1) along the early formed slaty cleavage enhanced this cleavage an formed the numerous quartz veins. The F -F1 deformational couplet produced the regional S foliation. ° ) �Paper 26 Crenulation folding (F2) of S1 foliation resulted in the formation of S2 fracture cleavage and formation of lineations (L2) due to the intersection of S1 and S2. The L2 lineations are flat lying because the strike of S2 and S1 are nearly parallel. Kink—banding (S) that affects S0, Si, 2 and L2 characterizes the last eformationai event in the area. Regional thermal metamorphism accompanied the sequence of deformation. The growth of pre-F1 andalusite porphyroblasts (figure 1) indicates that metamorphism started early in the deforinational sequence. It probably peaked between F2 and deformation as indicated by the growth of post-, pre-F2 staurolite porphyroblasts and post-F2 brown biotite and grunerite. Abundant retrograde metamorphism is shown by andalusite and staurolite porphyroblasts that have been replaced by sericite, and by garnet porphyroblasts that have been replaced by chlorite. References James, H. L., 1955, Zones of Regional Metamorphism in the Precambrian of Northern iviichigan, Bull. Geol. Soc. Am., v. 66, p. 1Li55_1483. Powell, C. McA., 1970, Relict Diagenetic Textures and Structures in Regional lVletarnorphic Rocks, Northern Michigan, North- western University Report 20, N.A.S.A. Geol. Test Site No. 126, 35 p. Williams, P. F., 1972, Development of Metamorphic Layering and Cleavage in Low Grade Metamorphic Rocks at Bermagui, Australia, Am. Jr. Sci., v. 272, p. 1—7. �Paper 27 LINEAMENTS AND MYLONITE ZONES IN THE PRECAMBRIAN OF NORTHERN WISCONSIN Gene L. LaBerge Wisconsin Geological and Natural History Survey and University of Wisconsin-Oshkosh ABSTRACT Recent geological mapping in Marathon County by the Wisconsin Geological and Natural History Survey has shown that a number of major zones of shearing cross central Wisconsin. At least 3 directions of major shearing have been recognized: N300_350E, N60°E, and N800E. The N300_350E trend is best developed in the area mapped, but reconnaissance indicates that other directions are impor- tant in other parts of the county. The major shear zones are represented by zones of mylonite and variously sheared rocks up to a mile wide. Because a number of different rock types, ranging in composition from granite to greenstone, have been granulated, mixed, and recrystallized to varying degrees to form the mylonite, the zones are lithologically variable both along and across the strike. However, they are structurally rather uniform, displaying a lensoidal structure on all scales from map scale to thin section. Indeed they seem to be composed of a myriad of overlapping lenses which show different degrees of flattening. Excellent examples of the progressive shearing of a granitic rock to produce a mylonite were observed along several of the shear zones. The best example of a mylonite zone mapped is that along the Eau Claire River in northeastern Marathon County. It has been mapped for a distance of approximately 20 miles, and almost certainly continues an additional 15 miles across the county. Furthermore, it is on a topographic lineament which can be traced across Wisconsin for at least 120 miles. At least 4 other major N300_35oE shear zones cross Marathon County, and some of these also occur on topographic lineaments 100 miles or more long. Numerous stream valleys and other topographic lineaments in northern Wisconsin are oriented approximately N30°E, and these may also represent shear zones. Significantly, the N600E and N80°E directions of shearing are also common trends of topographic lineaments. �Page 27 -2- The origin of these major shear zones is not yet certain; however, the lithologic associations in the area mapped coupled with the major shearing suggest that northern Wisconsin be part of a Precambrian subduction zone. Whatever the explanation of the shear zone, it is evident that they represent a major feature in the Precambrian of the Lake Superior region which has not previously been recognized. �—' • ,1 N ) '\ /-1e N 11 Jv 'F ' r$tt cerJf } i/f woo Fe L'.n /' • I 1r - T1 5 I. L. i11tth1r\ I - / S ibar,) -I 1! I s1o -::; ---(U 'Y t / ZL -I Po (TI ___ I 99 I I L4 Witt41 0)__fl ,NorthJ Lp (r7 aieik / _ f/ : _I LINEAMENTS AND'S POSSIBLE SHEAR ZONES IN MARATHON COUNTY T. L / / U L.—Th&/-T/r /i 7 7--MariTi1a _c) r&rrU 4:;j 29 I :; ____ �Page 27 00 C LIMIT OF OLDER DRIFT —......—LIMIT OF YOUNGER DRIFT S10. LINEAMENTS AND POSSIBLE ShEAR ZONES IN NORTHERN WISCONSIN �Paper 28 STRATI GRAPHIC AND TECTONIC FRAMEWORK OF MIDDLE PRECAMBRIAN ROCKS IN MINNESOTA G. B. MOREY Minnesota Geological Survey St. Paul, Minnesota ABSTRACT Sedimentary strata of Middle Precambrian age in Minnesota predominantly consist of argillite and graywacke with lesser amounts of iron—formation, quartzite, quartzose siltstone, limestone, and dolomite. These strata unconformably overlie folded metasedimentary and igneous rocks approximately 2,700 m.y. old; locally they also appear to unconformably overlie diabasic gabbro or diorite dikes that may be approximately 2,000 m.y. old (Hanson and Malhotra, 1971). Except for an older unnamed dolomite unit in east—central Minnesota, all the sedimentary rocks are assigned to the Animikie Group, a wedge-shaped body that thickens from less than 100 feet in the northern part of the State to at least 15,000 feet in areas 100 miles to the south. The Animikie Group comprises a single depositional event that began with well— sorted clastic detritus characteristic of a stable shelf —— Kakabeka, Pokegama, and Mahnomen Formations ——, passed through a phase of iron—formation deposition —— Gunflint, Biwabik, and Trommald Formations ——, and ended with deposition of fine sand and mud characteristic of a "deep" basin with poor circulation —— Rove, Virginia, Rabbit Lake, and Thomson Formations. Locally, the "deeper" water clastic rocks contain intercalated lava flows, thin to thick beds of pyroclastic material, and layers of carbonate— to sulfide—facies iron—formation. During or subsequent to the time of deposition, the sedimentary rocks in east—central Minnesota were folded —— perhaps more than once —— into numerous large antic lines and syndines that have many second-order folds on their limbs. The major folds are asymmetric, with steeply—dipping to locally overturned north limbs and more gently—dipping south limbs. Fold axes trend within 300 of east, and plunge from horizontal to 300 east. In addition, a part of the Thomson Formation was regionally metamorphosed to at least the lower range (staurolite and garnet) of metamorphic grade in the amphibolite facies; however, definable metamorphic isograds are not everywhere parallel to recognizable structural trends, suggesting that deformation and metamorphism were independent variables in the orogenic scheme for this region. The time of folding is unknown, but the metamorphism on the Cuyuna range has been dated at 1,850 m.y. ago (Peterman, 1966). The Animikie strata in northern Minnesota also were deformed about northeast-trending axes, although the degree of deformation and the metamorphic grade is less pronounced. In addition, these rocks appear to have been subsequently folded about north-northwest—trending axes. Available isotopic data cluster around an age of 1,650 m.y. and these data may reflect a period of mild deformation and metamorphism at that time. A variety of igneous rocks also were intruded into the sedimentary pile in east—central Minnesota. Several discrete events can be recognized, which together with the deformation and metamorphism comprise the Penokean Orogeny. These include (Woyski, 1949; Goldich and others, 1961): (1) pre—tectonic emplacement of small mafic intrusions; (2) syntectonic emplacement (1.78 — 1.63 b.y.) of intermediate—size intrusions of tonalitic to granodioritic composition -- the quartz monzonites at Warman, Isle, and Pierz, the tonalites near Hillman and Freedhem, and the gray granodorite at St. Cloud; and (3) late-tectonic to post—tectonic emplacement (1.73 1 .68 b.y.) of Woyski's "Stearns Magma Series" consisting of the augite—hornblende (red) granite at St. Cloud, the porphyritic quartz monzonte at Rockville, and other similar intermediate to silicic rocks. Lastly,rocks of the Stearns Magma Series are cut by basalt dikes which may have been emplaced during a single period, at least 1,570 m.y. ago (Hanson, 1968). — �Paper 29 GRANITIC PLUTONIC ROCKS OF THE SOUTHERN PROVINCE OF THE CANADIAN SHIELD James A. Robertson Division of Mines, Ontario Ministry of Natural Resources, Toronto *paper presented by permission of the Director, Geological Branch. AB STRACI In Ontario granitic rocks associated with the eastern portion of the Penokean fold belt comprise: (1) Archean basement; (2) early post-Huronian intrusives (= Penokean of Church, 1968), and (3) late post-Huronian intrusive ( Hudsonian of Church). Other authors eg. Stockwell (1964) have used Hudsonian and Penokean interchangeably and have not named the earlier orogenic event. The individual granitic bodies are named on Figure 1. Algoman = Archean (Robertson, 1960) granitic rocks may be divided into massive quartz monzonite and gneissic to migmatitic Bodies of quartz monzonite were formed during the terranes. Early workers placed these Kenoran orogeny circa 2,500 MY. Overprinting bodies with the "young" post-Huronian granites. of age dates becomes pronounced as the Penokean fold belt is approached (Van Schmus, 1965). 1) The Creighton and Murray Granites (Card, 1968; Ginn, 1958) They were intruded prior lie south of the Sudbury Irruptive. to the irruptive and local anomalous cutting relationships The reflect remobilisation of the granite (Hawley, 1962). granites pre-date the regional metamorphism and deformation. Gibbins et al (1971) have obtained 2,200 MY, which suggests that they are earlier than the Nipissing Diabase (2,155 MY Whether they are synchronous with the Van Schmus, 1965). earlier post-Huronian orogenic cycle or with early Huronian volcanism remains an open question (Card et al, 1972). 2) �—2— Paper29 3) The Cutler Batholith (Robertson, 1969; 1970a; Cannon, 1970) lies some eighty miles west of Sudbury and intrudes folded and metamorphosed Huronian sediments and Nipissing Diabase and is itself foliated. Age-dates (Wetherill et al, 1960; Van Schmus, 1965) indicate a minimum age of 1,750 MY with some thermal resetting at 1,350 MY. The Cutler granite is clearly synchronous with the Hudsonian orogeny. The granite is intrusive but may have been derived from Huronian rocks at depth and metasomatism may have been an important factor (Cannon, 1970). The Croker Island Complex (Card, 1965; Robertson, 1970) lies some twelve miles southeast of Cutler and comprises a circular complex of comagmatic mafic to granitic rocks accompanied by a marked magnetic anomaly. The complex postdates regional metamorphism and folding. Age-dates (Van Schmus, 1965) and paleomagnetism studies (Palmer, 1969) indicate 1,445 MY. The complex is clearly late Hudsonian. Similar magnetic anomalies under Manitoulin Island were drilled by Union Carbide. Core of granitic rock resembling that at Killarney was obtained and submitted to Van Schmus for dating. 4) Grenville Front Granites (Card et al, 1971; Frarey and Cannon, 1969; Hnderson, 1967; Quirke and Collins, 1930) are intrusive bodies in the Southern Province adjacent to the Grenville Front. To the northwest these bodies are intrusive but to the southeast they become strongly mylonitised passing into the deeper crustal granite-gneiss complex of the Grenville Province. The mylonite zone marks the Grenville Front. 5) 5a*) The Killarney batholith featured in the classical work of Quirke and Collins (1930) with a minimum age of 1,585 MY comprises porphyritic quartz monzonite. 5b*) The Lake Panache and Eden Lake Intrusives, (Card et al, 1971) range in composition from gabbro-granite with a minimum age of 1,430 M.Y. from mica. 5c*) The Chief Lake Batholith comprises quartz diorite to quartzonzonite marking the northeast continuation of the Killarney granite. Near Coniston, Phemister (in Grant et al, 1962) interpreted the rock as feldspathised sediment. Krogh (1971) indicates an initial age of 1,730 MY with some granites at 1,590 MY - 1,460 MY reflecting early movement on the Grenville Front. *Individual bodies not shown on Figure 1. �Paper 29 — — Conclusion The granitic rocks of the Ontario Sector at the Southern Province may be classified with respect to petrography, mineralogy, chemistry, isotopic composition and they can be fitted into the historical and structural scheme established by regional mapping (Robertson et al, 1969; Card et al, 1972). However, much detailed work on individual bodies remains to be done. References CannQn, W.F. (1970) Plutonic Evolution of the Cutler Area, Ontario; G.S.A., Vol. 81, p. 81-94. Card, K.D. (1965) The Croker Island Complex; No. 14. Bull. Ont. Dept. Mines, Geol. Circ. Card, K.D. (1968) Geology of Denison-Waters Area, District of Sudbury, Ont. Dept. Mines G.R. 60. Card, K.D., Palonen, P.R., and Siemiatkowska, K.M. (1971) Geology of the Louise-Eden Area, District of Sudbury; Ont. Dept. Mines and Northern Affairs, Open File Report 5065. Card, K.D. et al (1972) The Southern Province in Canada in Structural Styles in Canada, in press. Geol. Assoc. Can., Contribution to 24th mt. Cong. Montreal 1972. Church, W.R. (1968) The Penokean and Hudsonian orogenies in the Great Lakes region and the age of the Grenville Front, 14th Annual Ints. on Lake Superior Geology, p. 16-18. �Paper 29 —4— Frarey, M.J., and Cannon, R.T. (1969) Notes to accompany a map of the Geology of the Proterozoic Rocks of Lake Panache. Collins Inlet Map Areas, Ontario. Geol. Surv. Can. Paper 68-63 Gibbons, W.A., McNutt, R.H., and Adams, C.J.D. (1971) Rb-Sr Isotopic Studies of the Murray Granite, Geol. Assoc. Can. Abstracts, Sudbury 1971, p. 27-28. Ginn, RM. (1958) A Study of the Granitic Rocks in the Sudbury Area. Unpublished M0Sc. Thesis, Queen's University. Ginn, R.M. (1961) Geology of Porter Township, Ont. Dept. Mines, Geol. Rept0 No 5. Grant, J.A., Pearson, W.J., Phemister, T.C., and Thomson, J.E. (1962) Geology of Broder, Dill, Neelon and Dryden Townships District of Sudbury, Ont. Dept. Mines GR 9. Hawley, J.E. (1962) The Sudbury Ores: Their Mineralogy and Origin, Can. Mm. Vol. 7, part 1, 1962. Henderson, J.R. (1967) Structural and petrologic relations across the Grenville Province-Southern Province boundary, Sudbury, District of Ontario. Ph.D. Thesis, McMaster University, Ontario. Krogh, T.E. (1971) Isotopic ages along the Grenville Front in Ontario. Assoc. Can. abstracts Sudbury 1971. Geol. Palmer, H.C. (1969) The Paleomagnetism of the Croker Island Complex, Ontario, Canada; Can. Jour. Earth Sci., Vol. 6, p. 213-218. Quirke, T.T., and Collins, W.H. (1930) The Disappearance of the Huronian; Geol. Surv. Can. Mem. 160. Robertson, J.A. (1960) The General Geology of Part of the Blind River Area; Thesis, Queen's University, Kingston. Robertson, J.A. (1969) Geology of the Cutler Map-Area; File Rept. 5026. Robertson, J.A. (l970a) Geology of the Spragge Area; M.Sc. Ont. Dept. Mines, Open Ont. Dept. Mines, Geol. Rept. 76. �—5- Paper 29 Robertson, J.A. (1970) Geology of the Massey Area, Districts of Algoma and Sudbury; Ont. Dept. Mines Open File Rept. 5043. Robertson, J.A., Card, K.D., and Frarey, M.J. (1969) The Federal-Provincial Committee on Huronian Stratigraphy Progress Report; Ont. Dept. Mines, M.P. 31, 26p. Van Schmus, R. (1965) The Geochronology of the Blind River-Bruce Mines Area, Ontario Canada; Jour. Geol., Vol. 73, p. 755-780. Wetherill, G.W., Davis, G.L., and Tilton, G.R. (1960) Age Measurements on Minerals from the Cutler Batholith, Cutler, Ontario; Jour. Geophys. Research, Vol. 65, p. 2461-2466. Structure, metamorphism and Post-Huronian granitic intrusions of the eastern Southern Province. Fig. 1. �Paper 30 REGIONAL RELATIONSHIPS IN THE PENOKEAN PROVINCE H. B. STONEHOUSE Michigan State University ABSTRACT Investigations over the last few years in that area of the Southern Province of the North American Shield known as the Penokean Fold-Belt Subprovince, allow some of the following conclusions to be made:1. 2. Similar sequences of sediments deposited over a period of about 600 my (roughly 2.2 by to 1.6 by ago) are of predominently shallow water origin. Local tectonic activity occurred during deposition of these sediments. 3. Intrusive igneous activity during this period resulted in basic dikes and/or sills; acid intrsives are minor. 4. The regional E-W folding increases in intensity to the 5. Older geological events tend to occur in the eastern part of the region and younger ones in the west. 6. Regional tectonism was most intense at some time before south. the end of the period. Events which took place within this region during this time period are pit into the context of cause-effect relationships and a regional-time pattern; a better geological understanding results. The evidence strongly suggests that the area be re- designated as "The Penokean Province" and that the term "Penokean Orogeny" be replaced by "Penokean Tectonic Sequence". �Paper 31 AGES OF SONE PRECAi4BRIAN ROCKS IN EAST-CENTRAL NINNESOTA J. S. Stuckless Department Northern and S. S. Goldich of Geology Illinois University Illinois 60115 DeKaib, ABSTRACT The McGrath Gneiss, formerly assigned to the Penokean orogeny, l6Oo-lOO m.y. ago, was actually emplaced in a Lower Precambrian terrane during the Algoman orogeny, approximately 2700 m.y. ago. Locally the gneiss is intensively sheared. This phase of the deformation is related to epeirogeny that followed the regional metamorphism of the Middle Precambrian formations. Rb—Sr isochron studies of igneous rocks that were emplaced following folding and regional metamorphism place a minimum age of 1900 m.y. on the Mid- This age is somewhat older than the 1850 m.y. age obtained by Z. E. 'Peterman for the metasedimentary rocks of the Cuyina district and is considerably older than the previous K-Ar and Rb-Sr mica age determinations. The McGrath Gneiss appears to be extensive in east-central Minnesota; hence, it is likely that the Middle Precambrian rocks of Minnesota were all- deposited on an erosion surface developed on an Archean continental crust rather than on oceanic crust. dle Precambrian Thomson Formation. �Paper 32 GEOCHRONOLOGY OF PRECAMBRIAN ROCKS IN THE PENOKEAN FOLD BELT SUBPROVINCE OF THE CANADIAN SHIELD W. R. Van Schmus Department of Geology University of Kansas Lawrence, Kansas 66044 ABSTRACT The Penokean Fold Belt subprovince is that part of the Southern Province consisting of the folded and metamorphosed Middle Precambrian rocks which occur in an E-W trending belt running south of Lake Superior and north of Lake Huron. Included within this belt are strata of the Huronian, Marquette Range, and Animikie supergroups and associated economic deposits. For many years these rocks have been considered possible corre- latives, and the folding, metamorphism, and intrusive activity have been referred to as the Penokean Orogeny. Recent and current field and laboratory studies now show that the orogenic history of this region can not be represented by a single major orogenic episode. Instead, this portion of the North American continental plate was affected by a succession of events over the interval 2.7 to 1.1 b.y. ago. The oldest Proterozoic rocks are apparently those in Ontario, north of Lake Huron. In this area Huronian strata overlie a 2.7 b.y. old basement and are intruded by the 2.16 b.y. old Nipissing Diabase. To the west, in Upper Michigan, the Proterozoic sedimentary and volcanic rocks, the Marquette Range supergroup, are apparently younger, being between 1.90 and 2.05 b.y. old, and thus not correlative with true Huronian rocks. Farther west, in Minnesota, the Animikie rocks may be partly correlative with and partly younger than those in Michigan and Wisconsin. There have been multiple periods of intrusive, metamorphic, and tectonic activity. The oldest Proterozoic deformation apparently occurred about 2.15 b.y. ago in Ontario, affecting the Nipissing Diabase and Huronian rocks. A major episode of igneous, metamorphic, and tectonic activity occurred about 1.9 + 0.1 b.y. ago, affecting most, if not all, of the E-W trending belt from Minnesota to Ontario. This event would appear to be the one most representative of a uPenokean Orogeny.' Subsequent to the main orogenic activity several intrusive and! or metamorphic episodes have occurred, about 1.65, 1.5, and 1.3 b.y. ago. Several of these younger events may be correlated with the Middle Precambrian history of Wisconsin and the rest of the Midcontinent. Finally, much of the area was affected by Keweenawan igneous activity and associated metamorphism 0.9 to 1.2 b.y. ago. �Paper 32 -2- On the basis of present geologic and geochronologic data, it appears reasonable to interpret the Penokean Fold Belt as an orogenic belt developed along the southern edge of the Superior craton about 1.9 billion years ago. The exact nature of this structural belt and its possible relation to arc-trench sequences of present models of plate tectonics must await further work. �Paper 32 SELECTED BIBLIOGRAPHY Aldrich, L. 1., Davis, G. L., and James, H. L., 1965, Ages of Minerals from metamorphic and igneous rocks near Iron Mountain, Michigan: Jour. Petrology, v. 6., p. 447-.472. Banks, P. 0., and Cain, J. A., 1969, Zircon ages of Precambrian granitic rocks, northeastern Wisconsin: 77, 208-220. Jour. Geology, R. , 1971, Chronology of Precambrian rocks of Iron and Dickinson Counties, Michigan (Abs.). 17th Annual Institute on Lake Superior Geology, Duluth, Minn., May. Banks, P. 0. and Van Schmus, W. Bass, M. N., 1959, Mineral age measurements --Wisconsin: Inst. of Washington Year Book, 58, 246-247. Carnegie Dickinson, W. R., 1971, Plate tectonic models of geosynclines: Earth Plan. Sci. Letters, 10, 1965-174. Dott, R. H., Jr., 1969, Isotopic dating of the Baraboo and Waterloo quartzites. 15th Institute of Lake Superior Geology, Oshkosh, Wisc., p.15. Dutton, C. E. , and Bradley, R. E. , 1970, Lithologic, geophysical, and mineral commodity maps of Precambrian rocks in Wisconsin. U. S. Geol. Surv. Map set 1-631, with accompanying pamphlet (15 pp.). Fairbairn, H. W., Hurley, P. M., and Pinson, W. H., 1960, Mineral and rock ages at Sudbury-Bling River, Ontario: Geol. Assoc. Canada Proc., 12, 41-66. Fairbairn, H. W., Hurley, P. M., Card, K. D., and Knight, C. J., 1969, Correlation of radiometic ages of Nipissing diabase and Huronian metasediments with Proterozoic orogenic events in Ontario. Can. J. Earth Sci., 6, pp. 489-497. Faure, G., and Kovach, J., 1969, The age of the Gunflint Iron Formation of the Animikie Series in Ontario, Canada. Geol. Soc. America Bull., 80, 1725-1736. Goldich, S. S., Nier, A. D., Baadsgaard, H., Hoffman, J. H., and Krueger, H. W. , 1961 nology of Minnesota: Krogh T. E. , , The Precambrian geology and geochro- Minnesota Geol. Survey Bull. 41. and Davis, G. L. , 1971, the Grenville Front inter- preted as an ancient plate boundary: Washington Year Book, 70,. 239-240. Carnegie Inst. of Peterman, Z. E., 1966, Rb-Sr dating of middle Precambrian metasedi- nientary rocks of Minnesota. 1031-1044. Geol. Soc. America Bull., 77, Van Schmus, R., 1965, The geochronology of the Blind River-Bruce Mines area, Ontario, Canada: J. Geol., 73, 755-780. Woolsey, L. L., 1971, A Rb-Sr geochronologic study of the Repi.iblic metamorphic node, Republic, Michgn. Unpub. M. S. Thesis, Univ. of Kansas, Lawrence. �Paper 33 STRATIGRAPHY AND SEDIMENTATION OF THE ESPANOIA FORMATION, AN EARLY APHEBIAN (MIDDLE PRECAMBRIAN) CARBONATE UNIT GRANT M. YOUNG Department of Geology University of Western Ontario London, Ontario ABSTRACr The Espanola Formation is unique among Huronian formations in its high carbonate content. It forms part of the Quirke Lake Group, lying between the Bruce Formation (beneath) and the stratigraphically higher Serpent Formation. The Bruce Formation is mainly unstratified sandy polymictic paraconglomerate (tillite) whereas the Serpent Formation consists mainly of cross bedded felspathic quartzites. In the Quirke Lake area the Espanola Formation is divisible into three units, here called, in ascending order, limestone member, siltstone member and dolostone member. Some fifty miles to the southeast these three members can still be recognised but the central, dominantly terrigenous clastic unit, is much thicker. In the southern area there is also an additional thick upper member which displays fining upwards cycles (from conglomerate to mudstone) similar to those attributed to fluvial deposition. In the Quirke Lake area the Espanola Formation contains both intraformational and intrusive breccias. The intrusive breccias are later than some faulting and transect clastic dykes. They are considered to be downward intrusions caused by release of high pore pressure in watersaturated sediments along fissures in the already lithified Espanola Formation. The triggering mechanism for the breccias may have been earth tremors associated with early (pre-Gowganda) earth movements for the breccias appear to be spatially related to areas where there is evidence of disconformable/unconformable relations between the Gowganda Formation and older Huronian rocks. Cross bedding studies, mainly from the highest member of the Espanola Formation in the southern part of the Huronian outcrop belt, reveal a bimodal pattern with dominant modes in the south-west quadrant and towards the E.S.E. Microprobe analyses of the carbonates of the dolostone member showed that the rusty-weathering dolostones are composed of ferruginous dolomite. The Espanola Formation is interpreted as a post-glacial transgressiveregressive cycle (Fig. 1). The limestone and dolostone members are thought to be shallow water deporits while the siltstone member represents a deeper water facies (involving some turbidite transportation). The sandstone member of the southern region is thought to have been laid down from meandering streams which initiated sedimentation of the thick prograding fluvial sequence of the Serpent Formation. �0 .,-4 C. S S SQ '.4 00 00 '0 5 0 FIG. 1, F- LU 0.0 ,-l us C w C. .0 '0 NW I I (turbidite facies) SERPENT FORMATION SPACE - TINE RElATIONSHIPS DURING SEDIMENTATION OF THE ESPMTOLA FORMATION TRANSPORT DIRECTION DOMINANT SEDIMENT UPLIFT AND EROSION REGION OF CONTEMPORANEOW UPLIFT — ESPANCLA Southern limit of SUBS! DEN CE REGION ZONE OF TECTONIC Northern Limit of preserved Huronian ZONE OF TECTONIC TECTONIC HINGE ORMATION SE III • �Paper 34 WEATHERING AND METASOMATISM OF THE PRESQUE ISLE SERPENTNIZED PERIDOTITE, MARQUETTE COUNTY, MICHIGAN M. D, LEWAN Michigan Technological University ABSTRACT Presque Isle Park, Marquette, Michigan is underlain by a mass of peridotite, probably cut by Archean granite and definitely cut by a diabase dike of probable Keweenawan age. The three rock types grade upward into a complex altered zone that has variable thickness and mineralogy, depending upon the rock type it occurs on. This zone is comprised of a lower zone of dolomite-silica. and an upper zone rich in silica, which in turn is unconformably overlain by Jacobsville Sandstone. Data from major element analysis of 42 rocks, qualitative mineralogy determinations by X-ray diffraction, and field observations indicate that the peridotite has undergone three periods of alteration; 1 )early s erpentinization, 2)carbon dioxide meta somatism after emplacement, and 3)weathering after the area was exposed to surface conditions. The granite has also undurgone the same sequence of alteration with the exception that the first period of alteration was illitization. On geological and geochemical grounds the serpentinization and illitization processes could not have been contemporaneous. The forming of the silica rich weathered zone, which is best developed over the granite, is the result of weak acidic meteoric waters dissolving dolomite out of the dolomite-silica zone. Chemical and mineralogical profiles show that the removal of dolomite results in the upward concentration of residual minerals such as quartz, rutile, hematite, chlorite, and illite. The weathered zone was searched for nickel concentrations such as garnierite, but none were found. Field evidence indicates that the weathering and metasomatic alteration post-dates the intrusion of the probable Keweenawan dike and pre-dates the deposition of the Jacobsville Sandstone. Jacobsvifle Sandstone p Basal Conglomerate 8 Silica-Rich weathered zone c ° -— Dolomite-Silica zone , Diagramatical sketch(not to scale) showing the relationship between the rock units on Presque Isle.. � https://digitalcollections.lakeheadu.ca/files/original/a4db2f602031c8a408c608d8cb354236.pdf d677645b5be965a820d9bca69a888cc9 PDF Text Text ������������������������������������������������������������������� https://digitalcollections.lakeheadu.ca/files/original/b5f4086c9db7eb5ddf6d4f37b1ce7c16.pdf b1d42fe2b6fcf5b2fb62b0815cc007f1 PDF Text Text �---'--------......;;===================----------=====--------------==================.,......------'.. i" Michigan Technological University University /- ..-..;// ....::>' /tPl;SID~8;t;.~ /' ~ H'QH~A . _.'~ / ~7'" .:- .-":-'Y._~;---;;;r-;;.,.-;~--?~'-:~ - ----. --:..-- Y.~==-.:,- - _=_ -. ---._ __ HOUGHTON MI 49931 • -2< ' '1'~1J - rf'I 0'">" ~ III! :r::£'(P~ .- _.._. . . . . - .--- - ..- - . - . - . ,{'(}-(~.,c?". 'J<'£:: .f\ --' / (',{,!~,-- -~ .,~~ './ ---~. - -_. - . _ . ' - . N'-c.A ~ ~\ Seaman c···.· -' ••/ / ! --; , . .~r: ~; Mineral Museum . . .. --- (5th (5th floor) Memorial Union Union .. .,~=-'~" ::~::::-~':"'~~~:. .'.~' ~:-- - ----,- ...->--'-" / ~ —- - 1 (3rd floor) \\ / / // / r--. .. - ~f1Y- -. Geology -.—- ~~-::.~;,::;:~:~,:, * -.:• ,/ ..' ~C~ 0 ~.-:_-- - .. --7'- - " " . .. . -.., _ ...:>c.....- ~- // /' --;;.,;-. ---;.. - _~'~..rg;~.'~~~: ~_.-ifi,~.:.'~-': ~-F'i:rPJl' -~... ..e;- . ' ~ ... ?- • -~I)<0.rr - / PORTAGE LAKE / Commuter & DHH -) - _ ... - rv-l\l:rd- ~ (l"ri_,y,> 0 "'-0,,r ~ ( ,'."" f\,:,''''''- Qr4 'b-97? ?•j(4?it ,/7 r-5.jfy ,,, 5' //' - //.'/, /j1'J. HARONAVE' " - - clf i—__._ —__-'" = - - / J/ / ( /— — ,,, 5- --5 —'-_ \ -= 5J( 'n\\ \ 11 v'— r (" r -y"y' AdmInistration BuIlding Administration Building 4 ROTC ROTC BuildIng Building 5 Academic Academic Offices Offices BuIlding Building Electrical Energy Resources Resources Center Center ElectrIcal Energy 7 EERC-AE. Seaman Seaman Mineralogical Mineralogical Museum EERC·A.E. Museum (5th (5th Floor) Floor) 9 Alumni AlumniHouse-MT House-MT Fund Fund Humanities Center Center Arts and Humanities InstItute of of Mineral Mineral Research Research (Benedict (Benedict Lab) Lab) ,39- 'i\ '(! . 12 Institute CivIl-Geology Building Civil·Geology Hall 15 Fisher Hall library Forestry·lnstitute of Wood Research 19 ChemistryMetaurgyBuiing Chemistry·Metaliurgy Building MechanicalEngIneering-Engineering Engineering-Engineering Mechanics 20 Mechanical -3(Y- 24 Student Development Complex Student Development Complex Douglass Houghton Hall (DHH) Daniell Heights Housing -r4-,c' 34 Memorial Union Memorial UnionBuilding Building 37 Wadsworth Wadsworth Hall Hall \L7 -— - - I - - // rr-w-- fç,7 - FOOTBALL FIE LD -, / k/ 1 ' 9c'?1i-' /) J 14 (1 38 West West Coed Coed Hall Hall 38 39 Coed Coed Food Food Service Service 39 East East Coed Coed Hall 4t Central Heatmg Healing Plant 41 42 Physical Physical Plant Plant Storage Storage Building Building 42 Lakeside Laboratory 43 Lakeside 43 44 Storage-Service Storage-Service Building Buiiding (Pool (Pool Cars) Cars) 44 50 Gates Tennis Tennis Center Center 50 Gates 58 U.S. Forest Engineering Laboratory U.S. Forest Engineering A Visitors'Parking Parking Ares Area A Visitors )L. ç- - 9 - 40 Not appearing on on map map: Experimental Mine, Hancock Hancock Ford Forestry Center, Alberta Ford Alberta Keweenaw Research Center Center, Memorial Memorial Airport Airport Mont Ripley Ski Hill, Ripley Portage Lake Golf Course, Course, Houghton Houghton I ',S (\C'l(') '()r l ' r- (( .,.... .-,_ -( ,CY C �FIELD GUIDE TO THE GEOLOGY GEOLOGY OF OF THE THE KEWEENAW PENINSULA, PENINSULA, MICHIGAN BY J. Bornhorst Theodore J. William I. I. Rose, Rose, Jr. Jr William James B. B. Paces Department of of Geology and Geological Engineering Michigan Technological University University Houghton, Houghton, Michigan 49931 FOR SALE SALE AT: AT: E. R. R. Lauren Bookstore, Bookstore, Memorial Union E. Michigan Technological University Houghton, Michigan 49931 Houghton, Prepared as field trip trip guide guide for for the the 29th Annual Institute as aa field Annual Institute on Lake Superior Geology held held at at Michigan Michigan Technological Technolo~ical University on May 11—14, 11-14, 1983. 1983. FIRST EDITION May, 1983 May, COVER PHOTO: Miners Miners at at the the Mine(?) circa circa 1910. 1910. Baltic Mine(?) Michigan Technological University Archives and Copper Country Historical Collections. Collections. �PREFACE — It is presumptuous presumptuous for for us us to put together is based based mainly mainly on on the the work work It is to put together aa book which is of others. We have done so because hundreds of people come to of to the Keweenaw each year to to look look at at geological geological features features and and many many of of them them ask ask us us for for advice. advice. So we've tried to tried to communicate with people people who who are are doing doing serious serious geological geological field field trips. trips. This is is a first first draft of an evolving document, document, which we expect to to continually rerePlease help help us us make make it better by by suggesting changes, changes, finding finding mistakes mistakes and and Please it better vise. telling us what we've we've left left out. out. Starting with Douglass Douglass Houghton almost almost 150 years years ago, ago, dozens dozens of of geologists geologists have have contributed aa mountain of of geological on the the Keweenaw Keweenaw which which makes makes it it contributed geological information information on aa real challenge to to compile this this book. book. The greatest greatest contribution by far far has come come from from Walter Walter S. S. White, White, who who devoted devoted much of of his his professional professional career career to to Keweenawan Keweenawan whose impact geology and whose impact can can be traced traced to to virtually virtually every every page page of of this this book. book. of his his We hope that that we have faithfully faithfully transmitted his his ideas with a a fraction fraction of enthusiasm. ingenuity and enthusiasm. Houghton Houghton 30 March 1983 i1 �TABLE OF CONTENTS Page i PREFACE iii HOW TO USE THIS GUIDE GUIDE iv LIST OF OF STOPS STOPS vlii viii LIST OF MAPS ix LIST OF FIGURES xi LIST OF OF TABLES TABLES INTRODUCTORY NOTES ON THE GEOLOGY OF THE KEWEENAW PENINSULA 11 17 17 ROAD LOG AND STOP DESCRIPTION INDEX TO GEOLOGY ON NAPS MAPS IN IN THE FIELD FIELD GUIDE GUIDE 111 111 112 112 REFERENCES 11i i �HOW TO USE THIS GUIDE To make all the the stops stops listed listed in in this this guide guide would would take take three three days. days. If If you wish to to emphasize certain types types of of stops, stops, we we recommend recommend the the following following subsets: subsets: Suggested Stops Stops Sediments Sediments Volcanic Rocks Mineral Deposits Broad Coverage 5, 6, 8, 8, 9,. 16, 17, 17, 19, 19, 20, 20, 24 24 10, 13, 13, 16, 5, 6, 9, 10, 1, 15, 16, 16, 17, 17, 18, 18, 21 21 1, 3, 3, 11, 11, 12, 12, 13, 13, 14, 14, 15, 2,3,4,7,11,13,17,22,23 2, 3, 4, 7, 11, 13, 17, 22, 23 3, 6, 10, 10, 11, 11, 13, 13, 16, 16, 18, 18, 19, 19, 20, 20, 24 24 3, 6, Be imaginative and make up up your own own subset subset of of stops. stops. stops are are on on or or near near private private land. land. Please respect private property. property. The preMany stops Sent problems of access are minimal, but obviously we could ruin we don't don't sent problems of access are minimal, but obviously we could ruin things things if if we use low profile outdoor principles. principles. AA few few stops stops are are located located ot on old mine dumps. dumps. These can be hazardous, hazardous, especially especially where where bad bad ground ground occurs. occurs. Use common sense. sense. - have north north to to the the top top and and are are 1:24,000 1:24,000(4(4cmcmtoto1 Ikin). km). All maps have road log route on the the maps, maps, while while stars stars mark mark the the stops. stops. follow the the Dots follow Mineral collectors have long long flocked flocked to to the the Keweenaw to to collect its its unusual minerals. minerals. One of the best in the world located at this best mineral museums in world is located at the starting point point of of this field trip. trip. The Seaman Mineralogical Museum, Museum, open from 9:00—4:30 9:00-4:30 weekdays, weekdays, is is housed housed in the the EERC EERC Building, Building, Fifth Floor, in Floor, on on the the Michigan Michigan Tech Tech Campus. Campus. The mineralogical over the the Keweenaw and is collection includes includes samples samples from from all over is aa must for for all all rockhounds. rockhounds. 111 iii �STOPS LIST OF STOPS The following used to to help help you you design design your your own own field field trip trip following list of stops can be used to to see the geology of the the Keweenaw Peninsula. Peninsula. The location location of of stops stops are are shown shown in Figure la. la. The appropriate maps for for each stop and trip trip route are located in Figure Figure lb. lb. — — STOP MAP) (APPROPRIATE MAP) STOP DESCRIPTION STOP 11 (1) (1) Ophitic Scales Creek basalt flow and Keweenaw view, 7th 7th St., St., Houghton. Houghton. Waterway view, 2 2 (1) (1) Secondary minerals in in amygdaloid amygdaloid at at dump dump of of Isle Royale Mine, Dodgeville. Dodgeville. '-" 3 (2) (2) Section through a lava lava flow flow at at South South Range Range quarry. quarry. ....---4 (2) (2) Secondary minerals in in amygdaloid amygdaloid at at dump dump of of Baltic Mine. Mine. 5 5 (3) Glacial deposits on M—26 M-26 south south of of Houghton. Houghton. 6 6 (4) (4) Overlook of Keweenaw Waterway, Waterway, Houghton and the Range towns; towns; Quincy Quincy Hill, Hill, Hancock. Hancock. 7 7 (4 ) (4) Secondary minerals of amygdaloid at at dump dump of of Quincy Quincy Mine. Mine. 8 (6) (6) Flat—lying Flat-lying Jacobsville Jacobsville Sandstone Sandstone along along M—26, M-26, near Dollar Dollar Bay. Bay. 9 9 (7) (7) Hungarian Falls, Falls, near near Hubbell. Hubbell. Keweenaw Fault at Hungarian 10 10 (8) (8) Keweenaw Fault at at Natural Wall Wall Ravine, Ravine, near near Laurium. Laurium. 11 (9) (9) Secondary minerals in amygdaloid at at dump dump of of Wolverine Wolverine Mine. Mine. 12 (9) (9) Ophitic Scales Creek basalt flow, flow, at Scales Creek near Copper City. City. —- 13 ...../13 (9) (9) Lava flows flows of Portage Lake Volcanics and mineralized conglomerate with an excellent ized excellent view view of of the the central part of of the the Keweenaw Keweenaw Peninsula, Peninsula, Bumble— Bumbletown Hill. 14 (12) (12) Ophitic Greenstone flow and vein mineralogy at dump of Phoenix Mine. 15 15 (12) (12) part of of the Portage Lake Lake Section through through the the upper part the Portage Volcanics along along Eagle Eagle River. River. 16 (12) Contact between Portage Lake Volcanics Volcanics and Copper Contact Harbor Conglomerate Conglomerate at at Eagle Eagle River River Falls. Falls. ~. t/ iv �STOPS (Cont'd.) (Contld.) LIST OF STOPS STOP DESCRIPTION STOP (APPROPRIATE MAP) 17 17 (13) through the the upper upper part part of of the the Portage Portage Section through Lake Volcanics along Owl Owl Creek Creek and and amygdaloid! amygdaloid/ vein mineralogy at dump dump of of Copper Copper Falls Falls Mine. Mine. v"J.8 "18 (16) (16) Lava flows of the the Lake Shore Shore Traps Traps at at Esrey Esrey Park. Park. V19 \/19 (17) Overlook of Lake Superior Superior and and the the eastern eastern end end of of the Keweenaw Keweenaw Peninsula and outcrops of Copper the Harbor Conglomerate at at Brockway Mountain. Mountain. flO (17) (17) Copper Harbor Conglomerate Conglomerate at at Dan's Dan's Point. Point. 21 (20) (20) Diorite and granophyre stock stock at at Mt. Mt. Bohemia. Bohemia. 22 (21) Secondary mineralogy of of veins and and conglomerate conglomerate at Delaware Delaware Mine'. Mine~ The Delaware Mine is is open to to tourists for for aa fee. fee. 23 (28) Amygdaloid mineralogy of of dumps dumps at at Osceola Osceola Mine. Mine. 24 (30) at Hancock Hancock campground campground quarry. quarry. Nonesuch Shale at v �I ( I . ···i·9*··..······..·····;:;: ; ~ "'-~'L"'"alre Bailey . Eagle . . . f~~;I~.·.:::::::···:< . . . ""C~~r~·I La e M.,!dO'~ C ............ Delawar~.~.,2 ..'····· ....····· Copper Harbor 20 \ 0 " fifo" 5 IJ Eagle H ...r-nnr :._. _ - .~ .-:--~"::::~tS ~-~. Lak e Fanny Hooe Schlstter('.., •....1 (? ········\···'>... 21 = LakeV ~ Manitou Island Island ........ Phoenix .-:,., <f.2 .~.' i-~ Lake .../ "to A:::;!l\(~~:,..• o Kearsargei..,.J 1 ..i '···12 -< ~. McLain State Park McLain Park .rC"aiun;-~t·'· .f .-.,1.0... ~~ ~~ ~\ o~ C, Laurium 23*/ . Lake Linden ..... .... Scale Scale 1 0o M I 1 1 2 3 4 miles 4miles ~ Freda Atlantic South ~ ~ly ~ '" Painlsdale Pa in ed a le 12 Stopnumber number •2 Stop Figure Figure 1A: 1A: Route Route and and stop stop map map �SU ~~ \\ \ 17 o o~ 13~ ~ 23 o 12 'I-~ ... '" _0_" 27 ./' <~ t-<t-<. -.)~ ~ ~ \ o ~ c., 8 SCALE in in miles 01234 ,.... ji"Wiij o 1 2 ....., 3 p> 4 Dil2 Map number 12 ,.*" I'l + ~ " Figure 1B: 18: *'2 number Stop number Index of of 1:24,000 Index 1:24,000 scale scale maps maps �LIST OF OF NAPS MAPS Page MAP MAP 1 18 MAP MAP 2 22 MAP MAP 33 26 MAP MAP 44 31 MAP MAP 5 35 MAP MAP 6 39 MP MAP 77 42 MAP MAP 88 46 MAP MAP 9 49 MAP 10 MAP1O 60 MAP MAP 11 63 MAP 12 MAP 64 MAP13 MAP 13 71 MAP 14 MAP 74 MAP15 MAP 15 76 MAP 16 MAP 77 MAP17 17 MAP 79 MAP 18 MAP 82 MAP MAP 19 86 MAP2O t-1AP 20 87 MAP MAP 21 88 MAP 22 MAP 91 MAP MAP 23 95 24 MAP24 MAP 96 MAP25 MAP 25 98 MAP26 MAP 26 99 NAP MAP 27 100 MAP MAP 28 104 MAP MAP 29 106 MAP MAP 30 109 viii viii �LIST OF FIGURES Page vi Vi Figure 1: 1: Index map map of of route, Index route, stops and 1:24,000 scale scale maps. maps. Figure 2: 2: Location of the the Mid—Continent Mid-Continent Rift Rift System. System. 2 2 Figure 3: 3: Simplified geologic map, map, cross—section, cross-section, and and strati— stratigraphic column, column, western western Lake Lake Superior Superior region. region. 3 3 Generalized geologic geologic map of of the the western western Upper Upper Peninsula and stratigraphic stratigraphic section section of of the the Portage Portage Lake Volcanics. 4 4 Columnar stratigraphic Section section of of rocks rocks northwest northwest of of the Keweenaw Fault in the Calumet—Ahmeek the Calumet-Ahmeek area. area. 66 rocks Location of silicic to to intermediate intrusive rocks the Portage Lake Volcanics. in the Volcanics. 8 8 Figure Figure Figure Figure 4: 4: 5: 5: 6: 6: 7: 7: Schematic diagram showing interrelationships between northwest of of the major stratigraphic units units northwest the Keweenaw Fault in the the Keweenaw Peninsula. 10 Geologic and structure structure maps of of the the Keweenaw Keweenaw native native copper district. district. 13 and paragenesis of of secondary minerals Distribution and secondary minerals in Volcanics. in the the Portage Lake Volcanics. 14 14 Elemental mobility in in an an idealized idealized lava lava flow flow and and diagrammatic diagra~matic regional model for for metamorphism metamorphism of of the Portage Lake Volcanics. the 16 16 Figure 11: 11: Geologic cross—section cross-section for for Map Map 1. 1. 20 Figure 12: 12: Geologic profile of South Sou~h Range quarry. quarry. 21 21 Figure 13: 13: Speculative ice—marginal ice-marginal positions positions during during the the Wis— Wisconsin ice retreat. retreat. 27 Figure 14: 14: End moraine of the End the Keweenaw Bay Lobe glacier. glacier. 27 Figure Figure 15: 15: Enlarged view of ice—marginal ice-marginal positions. 28 Figure Figure 16: 16: High level drainage drainage through through the the Portage Portage Gap. Gap. 29 29 Figure Figure 17: 17: View from from Portage overlook overlook facing facing south. south. 32 32 Figure Figure 18: 18: Structures of the the Quincy Mine location. location. 36 Figure 19: 19: Geologic cross section section for for Maps Maps 4, 4, 5 and 30. 30. 37 37 Figure Figure 8: 8: 9: 9: Figure 10: 10: ix �Page Figure 20: 20: Relationships of of Jacobsville Sandstone. Sandstone. 40 21: Figure 21: Geologic sketch map of of Hungarian Falls Falls area. area. 44 Figure 22: 22: Wall Ravine. Ravine. Geologic sketch map of of Natural Wall 47 Figure 23: 23: Geologic Geologic map map and cross section, Wolverine Mine and and section, Wolverine arid cross vicinity. 51 Figure 24: 24: Thickness of of the the Kearsarge Kearsarge flow. flow. 52 Figure 25: 25: Paragenesis of secondary minerals in in the Kearsarge amygdaloid. 52 Cross section section of of Kearsarge Kearsarge amygdaloid amygdaloid showing showing the Cross the banding of of mineral assemblages. assemblages. 54 Distribution of quartz, quartz, microcline and high grade ore in in the the Kearsarge Kearsarge amygdaloid. amygdaloid. native copper ore 55 Figure Figure 28: 28: Outcrop map of of the the Allouez—Bumbletown Allouez-Bumbletown Hill Hill area. area. 57 Figure 29: 29: Map and section of the Greenstone flow between Seneca and the the Cliff Cliff Mine. Mine. 61 Figure 30; Figure 3O Map and section section of of the the Greenstone Greenstone flow flow near near Phoenix. Phoenix. 66 66 Figure Figure 31: 31: Stratigraphy of the Portage Lake Volcanics Volcanics above above the the Greenstone flow. flow. Greenstone 68 68 Plot of K20 and P205 content of 106 individual individual Portage Lake Volcanic flows flows in in stratigraphic stratigraphic order. order. 69 69 Schematic cartoon cartoonofdepositional Schematic of depositional environment environment of of the the Copper Harbor Conglomerate. Conglomerate. 83 83 Measured section of Copper Harbor Conglomerate at Dan's Dants cartoon of of the the depositional depositional environment. environment. Point and cartoon 84 84 Geologic map showing andesitic dikes near Mount Bohemia and occurrence occurrence and and paragenesis paragenesis of of secondary secondary and and opaque opaque and in the the dikes. dikes. minerals in 90 90 map and development of Sketch map of the the Keweenaw Keweenaw Fault Fault in in of Deer Deer Lake. Lake. vicinity of 93 93 Figure 26: 26: Figure 27: 27: Figure Figure 32: 32: Figure Figure 33: 33: Figure 34: 34: Figure 35: 35: Figure Figure 36: 36: Figure 37: 37: Figure 38: 38: Schematic illustration of the the funnelling effect on on Schematic illustration of funnelling effect fluids, Kingston Kingston conglomerate. conglomerate. mineralizing fluids, 102 102 Results of gravity gravity measurements across the Bear Lake on Map Map 29. 29. traverse plotted on 108 108 x �LIST OF TABLES Page Table 1: 1: Secondary minerals found found within within the the Portage Portage Lake Volcanics. Volcanics. 11 Table 2: 2: Major—element Major-element composition composition of of the the Kearsarge Kearsarge flow. flow. 51 Table Table 3: 3: Volume percent amygdule minerals from mapped assemblages shown in in Figure 26. 26. 54 Average major—element major-element composition of the the Scales Creek Creek flow. flow. 57 57 Table 4: 4: Table xi �INTRODUCTORY NOTES ON THE GEOLOGY OF THE KEWEENAW PENINSULA PENINSULA General Background The Mid-Continent Mid—Continent Rift Kansas to Lake Superior Superior Rift System extends northeasterly from Kansas to Lake It was was formed and then southeasterly through and through lower lower Michigan Michigan (Fig. (Fig. 2). 2). It formed about 1.1 1.1 to 1.2 b.y. b.y. ago ago (Keweenawan age) by by extensional extensional thinning of the the rigid rigid Precambrian Precambrian to 1.2 (Keweenawan age) thinning of Superior crustal block (Kiasner (Klasner and and others, others, 1982). 1982). Present day crustal thickness thickness the Lake Superior region, region, however, however, is is between between 40 40 and and 50 50 Km, Km, which which is is thicker thicker in the than than adjacent areas areas (Halls, (Halls, 1982). 1982). -— Peninsula is is located located on on the the margin margin of of the the Lake Lake Superior Superior Basin, Basin, The present Keweenaw Peninsula one of of the one the basins within the the Mid—Continent Mid-Continent Rift Rift System System (Fig. (Fig. 3). 3). The volcanic and sedimentary rocks rocks on the northwest side side of of the the Keweenaw Keweenaw Peninsula Peninsula generally generally dip dip toward Lake Superior and include the Portage Lake Volcanics, moderately toward Volcanics, Copper Copper Conglomerate, Nonesuch Shale Shale and and the the Freda Freda Sandstone. Sandstone. The Jacobsville Sand— SandHarbor Conglomerate, stone stone occupies the southeast side side of of much of of the the Keweenaw Keweenaw Peninsula Peninsula and and is is in in fault along the the Keweenaw Keweenaw Fault. Fault. The Jacobs— Jacobsfault contact contact with the Portage Lake Volcanics along ville Sandstone is however, it it is probably slightly younger than the the Freda Sandstone, Sandstone, however, is still most most likely upper Keweenawan in is still in age age (Kalliokoski, (Kalliokoski, 1982). 1982). At some time after the deposition of basin filling filling sediments, sediments, the Lake Superior region was was subjected to compression roughly region roughly normal normal to to the the basin basin axis. axis. These stresses in the the Keweenaw Keweenaw and and Isle Isle Royale Royale Faults, Faults, both both high high angle reverse reverse stresses re~ulted reulted in faults faults near near the margins of the the Lake Superior Superior Basin Basin (Fig. (Fig. 3). 3). This faulting steepened the dips the Peninsula Peninsula and and on on Isle Isle Royale. Royale. Definite age the dips of of strata exposed on both the relationships between between reverse reverse faulting faulting and and deposition deposition of of the the Jacobsville Jacobsville Sandstone Sandstone relationships are unclear: unclear: faulting syn- or wholly post—depositional. post-depositional. faulting may may be partially syn— The Lake Superior Syncline was affected affected by aa regional regional burial metamorphic and/or hydrothermal event. event. Remobilization of many elements, elements, particularly within the the Portage Lake Volcanics, Volcanics, caused lava flow caused strong alteration of of lava flow tops tops and and interbedded interbedded concon— glomeratic units. units. Native copper deposits of the the Keweenaw Peninsula are believed to to formed wholly or in in part the deposition of of the the Freda SandSandhave formed part after after the of much or all of stone (White, (White, 1968). 1968). Paleozoic geologic geologic processes processes were were largely largely atectonic. atectonic. Sediments associated with the the Michigan basin probably once covered the the Keweenaw Peninsula, Peninsula, as evidenced by the the isolated limestone at at Limestone Limestone Mountain Mountain and and Sherman Sherman Hill, Hill, isolated occurrence of of Ordovician limestone about 20 miles south about south of Houghton. The present day landscape of the the Keweenaw Peninsula is strongly strongly influenced by Pleistocene glaciation. is glaciation. Stratigraphy The bedrock geology of the the Keweenaw Peninsula consists of five major stratigraphic units. Portage Lake Volcanics, Volcanics, Copper Harbor Conglomerate, Conglomerate, Nonesuch Shale, Shale, Freda Sandstone and Jacobsville Sandstone Sandstone (Figs. (Figs. 33 and and 4). 4). The accumulated maximum thickness of of these these units units is is over over14,000 14,000in. m. The bedrock in the Keweenaw Peninsula is unconformably capped by a variety of is of glacial glacial deposits. deposits. �2 2 A. o0 -= KM t000 1000 KM ORIENTATIONS ORIENTATIONS OF SEGMENTS SEGMENTS OF THE MIDCONTINENT RIFT RIFT B. ---1\ l. I "----... N670,E N67 E "~ f, , 1. ----,j--, , ~ 0 N38 E( i---~~ ;:'-3~'E \ , 1 j 2: Location of the the Mid—Continent Mid-Continent Rift Rift System. System. A. Major Proterozoic A. Figure 2: rifts of of North North America America (from (from Burke, Burke, 1980). 1980). B. B. Orientation of and Paleozoic rifts individual the Mid—Continent Mid-Continent Rift Rift System System (from (from Kiasner Klasner and and others, others, individual segments of the 1982). �r- lie i ~ " II iA*' I 0 - Nipigon Sand,,,,",,. o JACOBSVILLE-BAYFIELD UP UPTO TO5000'+ 500O I f Cambrian &nd _ latesa: Kewc:etUlwu 49. '9" ONTARIO '\ Coppc:r Harbor Conalomcf1ue -/'-'-, '\;Z~'-S~10' /",-, - ""~O'~';ES o Kewecnaw&.l'l voleank: s.cquence, including Portage Lake Voleanic;s ,- __ ~ FREDA SANDSTONE SANDSTONE UP TO UP 70 12,000'+ 2000+ -1030 Ma (m,n.) IO30Mo(n,n.) 0:: W 0.. 0.. 0 MINNESOTA =:l .,. aa.. :3 :::> 47. 0 o 0:: (.!) (0 « WISCONSIN o I 50 I I o 45~ 45- I .,. I 93" I i ... 10(1 0:: I~"",""ES 100 I $0 ill , I ::2: \~')(Il(')Ll£"1RES I I .,. J 85" « C-) u LU w 0:: aa.. LAKE SUPERIOR REGION—distribution of of selected selected rock units. SUPERIOR REGION-distribution units, o0 —• :° .nç•0 .0 zz I— I- z Z COPPER HARBOR CONGLOMERATE 350' 350 -7000' -7000 zz « ~ I040Mo -1040Ma zz LU w UJ w 3: LU w 0:: o0 0:: 0 o Y: LU W aa.. 11 a.. PORTAGE LAKE PORTAGE VOLCANICS 9000' 9000 -15,000'. -(5,000. ::J I (include unnamed ufl0med (Include formation in west UP) formation west U.P.) VW ·YW ThUNDER BAY THUNDER REGION REGK>N KEWEENAW 1Sl..£ ROYALE [,lK£ SUPt.RIOR S£ ct jjjp LU W 1 .J P£HIN$ULA o co :E~ VERTICAL SCALE VERTICAL EXAGGERATED EXAGGERATED SOUTH RANGE RANGE SOUTH VOLCANICS (North Shore ~ Volcanics) Volconics) G]J t'ostvolcanic rrvludrg Poslvolcamc sodimenbo sc:dimenUry rocks. rocks. including the Copper Copper Harbor Harbor Conglom.::rale Conglomerate the tntrrbnddnd volcanic sedimentary ro<:h. rnck,. InltrbeJded VOIcMic and and seJimcntary nolading the the Portage Portage Lake Lake VolcanICS 'olratncs Including Prevolcanic Pynvolcanic rocks rock, a: indrcale relative relative directions directions Arrows indicate of movement along faults BESSEMER & BESSEMER B BARRON BARRON QUARTZ lIES QUARTZITES LU w ~ LAKE LAKE SUPERIOR SUPERIOR BASIN—cross BASIN--cross section. MIDDLE - I BASEMENT PRECAMBRIAN ,v•°°: I Figure 3: 3: Simplified geologic map, map, cross—section, cross-section, and and stratigraphic stratigraphic column column of of upper upper Precambrian rocks in the western Lake Superior region (map and cross—section from rocks in Lake Superior region (map and cross-section from Huber, column from from Daniels, Daniels, 1982). 1982). Huber, 1975; stratigraphic column w �4 NE SW NATIVE COPPER < aw 2 0 2 •° . .4 EEl > wo 0a—a- .4 F MINES — 2000 —, oo —1 1000 2000 3000 — 4000 5000 €000 — Location at onion within atratigraphic anc lion Aanraalmnln upFnn limIt at apiaatn & aaa'tn Approalmate Figure lawn, lion It at A. Generalized geologic map of upper Precambrian rocks of western Upper 4: B. GeneralPeninsula, Michigan. Hatched area is represented in cross—section in B. ized stratigraphic section of the Portage Lake Volcanics from Victoria to Copper Harbor (modified from Stoiber and Davidson, 1959). The major marker horizons and mines are shown. The dashed and dotted lines represent the approximate stratigraphic limits of secondary epidote and quartz and prehnite respectively. �Portage Lake Volcanics The Portage Lake Volcanics is a succession of more than 200 individual basaltic lava flows with a total thickness of 2500 m to 5200 m (Butler and Burbank, 1929; Huber, 1973; White, 1968) (Fig. 4). White (1960) recognized these volcanics as a thick pile of subaerial tholeiitic flood basalts. They are the product of rift zone magmatism and are comparable to the rift zones of East Africa and Iceland (Basaltic Volcanism Study Project, 1981; Chase and Gilmer, 1973; Green, 1977 and 1982; White 1960 and 1972). Volcanism was apparently controlled mainly by eruptions from fissures located under Lake Superior. The Portage Lake Volcanics are others, 1982). about 1,100 m.y. old (Van Schmus and Most of the lava flows are difficult to follow laterally with confidence. The Scales Creek, Kearsarge and Greenstone flows are the best documented laterally continuous flows. The Greenstone flow can be correlated to Isle Royale (Huber, 1975; Longo, 1982). There are thin conglomerate and sandstone beds throughout the section and these are excellent marker horizons (Fig. 4). The sediment inter— beds in all but the uppermost part of the Portage Lake Volcanics have been given names and are shown on the maps included in this field guide (Fig. 5). The inter— bedded sediments make up approximately 3 to 8% of the formation (White, l971a). The conglomerates of the Calumet area the host rocks for large native copper deposits. The lithology of the conglomerates is dominated by clasts of rhyolitic volcanic rocks (Merk and Jirsa, 1982). The frequency of interbedded sediments increases in Eventually volcanism waned and sediment deposition the upper part of the formation. became dominant, the overlying Copper Harbor Conglomerate. The dominant composition of the lava flows of the Portage Lake Volcanics is tholeiitic basalt. Dikes of mafic and intermediate composition cut the volcanic pile but are as unconmion. a whole Silicjc. volcanic and subvolcanic rocks comprise less than 1% by volume of the exposed Portage Lake Volcanics (Bornhorst, 1975; Grimes, 1977; Robertson, 1974; Robertson and others, 1979). They tend to be in the lower part of the stratigraphic section in the Keweenaw Peninsula (Fig. 6). The composition of volcanic rocks of the Portage Lake Volcanics was affected by both Primary magmatic differentiation has long been igneous and metamorphic processes. recognized both within and between tholejitic flows (Broderick, 1935; Broderick and For example, the Greenstone flow, the thickest Hohl, 1935; Cornwall, l95la and b). individual flow in the formation (Figs. 4 and 5), is chemically stratified due to Copper may have conceninternal differentiation (Cornwall, l951b; Longo, 1983). differentiation trated in the pegmatitic and more importantly in the flow tops. Work by Scofield (1976) demonstrated that copper can also be concentrated in the Rose and Grimes base of individual flows by gravitational setting of magnetite. (1979) showed the existence of three magmatic cycles within the Portage Lake Vol— canics which initiate with basalts that have high incompatible element abundances. The degassing of volatiles during and after eruption in an oxidizing subaerial environment was also important in that it allowed degassing of SO2 (Cornwall, 1951c). This created a sulfur deficient environment which favored the later deposition of native copper. A third pre—metamorphic process was deuteric or diagenic alteration of olivine and glass to hydrous minerals, the most important of which is chlorite. Ljvnat and others (1976) used '3D and '3180 to show that the basalts have undergone extensive isotopic exchange with low—temperature meteoric waters prior to metamorphism/hydrothermal mineralization. After emplacement the volcanic pile was subjected to extensive low—temperature, low—pressure hydrothermal/metamorphic alteraThe Portage Lake Volcanics on the Keweenaw Peninsula are in fact a classic tion. �6 Feet FR EDA SANDSTONE ci ,.,', Lava unit 0 AND fn .. COPPER HARBOR 0 NONESUCH SHALE CONGLOMERATE 0 06 0.-A 0 00 0 12,000 c a 15,000 =- - Lava unit c 000 o — QO 4 00 0 0 0 0-0 •0 0 o00 000 00 0 •2.0 . 00 . 0 0 0 11,000 c 14,000 1. .: PORTAGE LAKE LAVA SERIES Lava unit ci :0 10000 c 13,000 . Figure Columnar stratigraphic section of rocks northwest of the Keweenaw 5: Fault in the Calumet—Ahmeek area (from White and others, 1953). The labels for units within the Portage Lake Volcanics are consistent with those used on the maps in the field guide. �C phc paf T Hancock conglomerate (No. 17) Ashbed flow pp 9000 — -— Pewabic West conglomerate (No. 16) pk Kearsarge flow pv Wolverine sandstone (No, 9) 4000- poc Old Colony sandstone (unnumbered) 3000pg Greenstone flow pa Allouez conglomerate (No. 15) 4 orta - Lak 'r,Icanics ph Houghton conglomerate (No. 14) 7000 pi Scales Creek flow psc 2000 - Iroquois flow —— = pc - conglomerate TI (No. 13) 1000P0 pkc flow Kingston conglomerate (No. 12) Pcc Copper City flow PS 5000 St. Louis conglomerate (No.6) Figure 5 continued. �8 STUDY AREA Lake Superior COPPER HARBOR INDEX MAP OF NORTHERN MICHIGAN EAGLE RIVER Fish Cove I..: LacLo_ atiot Lake Cambrian Jacobsvil le Sandstone Upper Keweenawan Precambrian loge - .-.•. . . 10 Miles Figure 6: Portage Lake Lava Series Intrusive or extrusive body Bedrock geology of the Keweenaw Peninsula showing the location of silicic to intermediate volcanic and subvolcanic rocks (from Robertson, 1975). �9 locality of abundant and widespread low temperature alteration minerals (Table 1). Penetrative deformation did not accompany the metamorphic episode and primary textures are preserved even in the most intensely recrystallized areas. Copper Harbor Conglomerate The Copper Harbor Conglomerate conformably overlies and locally interfingers with the Portage Lake Volcanics (Fig. 3). It varies in thickness from about 100 m to 1800 m. The Copper Harbor Conglomerate is a red—brown basinward—thickening wedge of volcanogenic clastic sediments. These clastic sediments fine distally and up— section. Sandstones are lithic graywackes and conglomeratesare composed of volcanic clasts with a ratio of mafic to intermediate + silicic composition of about 2:1 (Daniels, 1982). Daniels (1982) has interpreted the Copper Harbor Conglomerate as Mafic to intermediate lava flows are a prograding alluvial fan complex (Fig. 7). interbedded in the exposed Copper Harbor Conglomerate (Fig. 5). These lava flows are termed the Lake Shore Traps and occur predominantly within the middle section of the formation. Nonesuch Shale — The Nonesuch Shale is a succession of gray—black siltstone, shale and sandstone which overlies and interfingers with the Copper Harbor Conglomerate (Fig. 3). The Nonesuch has a thickness of between 40 m and 215 m. The Nonesuch was deposited in a reducing, rift—flanking lacustrine environment initiated through disruption of drainages (Fig. 7) (Daniels, 1982). This differs from the over and underlying redbeds that formed in an oxidizing environment. Freda Sandstone The Freda Sandstone is a cyclic succession of red—brown, ferruginous, sandstone The Freda and mudstone overlying and gradational with the Nonesuch Shale (Fig. 3). It is dominantly fluvial in origin with has a maximum thickness of over 3700 m. The top of this greater compositional maturity than the Copper Harbor Conglomerate. formation is not exposed. Jacobsville Sandstone The Jacobsville Sandstone is a red to bleached white succession of coarse—to—fine— grained feldspathic and quartzose sandstone with varying amounts of siltstone, shale and conglomerate which rests in fault contact with the Portage Lake Volcanics in the Keweenaw Peninsula. Elsewhere it can be found overlying Middle Precambrian basement. Jacobsville is probably slightly younger than Freda Sandstone. Jacobsville has a Sandstones are fluvial in origin whereas conmaximum thickness of over 3,000 m. glomerates are believed to be alluvial fan deposits (Kalliokoski, 1982). Structure Structure of the Keweenaw Peninsula is dominated by the Keweenaw Fault (Fig. 4), a high angle reverse fault where older Portage Lake Volcanics are thrust to the Both units are affected by this major northeast over younger Jacobsville Sandstone. the normally flat—lying Jacobsville Sandstone is often strongly tectonic feature: deformed by drag folding near the fault contact and the Portage Lake Lavas are often highly fractured. The Keweenaw Fault cuts off the base of the Portage Lake Volcanic Series along its entire strike length so that the total stratigraphic thickness �__ 10 NONESUCH SHALE DEPOSITION POSSIBLE "LAVA-DAMMED LAKE" MODEL FOR SANDSTONE FREDA STREAM BRAIDED FLUVIAL BASIN MA IN BASIN CENTRAL FLUVIO-DELTAIC 0 00 0 O - LUVIQ°Th 0 o 00 0 o° x0 x 0 0 0 0 PORTAGELAKExVOLCxANICSxxX x O 0 0 x x _— o0xxXxx XXX 0 CONGLOMERATE 0 o_—T 0 ALLUVIAL°PLAIN OCOPPER HARBOR 0 0 x 00 x - x - x : x x tINTERFLOW 0 0 SEDIMENTS X -------- ±±± RELATIVE PAL ED F LO W DIRECTIONS Figure 7: Schematic diagram showing the interrelationships between major stratigraphic units found northwest of the Keweenaw Fault in the Keweenaw Peninsula (from Daniels, 1982). x �:ii Table 1: Secondary minerals found within the Portage Lake Volcanics, Keweenaw Peninsula, Michigan (from Butler and Burbank, 1929; Stoiber and Davidson, 1959; Jolly and Smith, 1972). Widespread Minerals Locally Important Minerals Rare Minerals Laumontite Analcime Apophyllite Prehnite Sericite Atacamite Pumpellyite Orthoclase /Nicrocline Bowlingite Quartz Chalcedony Brucite Epidote Thompsonite Chlorastrolite Albite Natrolite Chrysocolla Chlorite Chabazite Cuprite Hematite Native Silver Faujasite Sphene Sulfides Fluorite Calcite Arsenides Powellite Native Copper Datolite Serpentine Heulandite Stilbite Ankerite Tenorite Sulfates Tourmaline Clay Minerals Whitneyite Wairakiite �12 The regional tectonic as well as the total displacement along the fault is unknown. context of the compressional stresses which caused development of major reverse faults is unknown at the present time, although it is probably unrelated to processes which formed the Mid—Continent rift. — The Keweenaw strata dip moderately northwesterly toward the centr of the Lake This Superior Basin and their dip angles increase toward the base of the section. is in part due to modification attributed to the Keweenaw Fault, but White (1960) has demonstrated syn—depositional downwarpage of the basin. Thus, lava flows and sediments formed wedge—shaped beds thickening basinward such that a relatively constant horizontal datum level was maintained throughout the life of the basin. Smaller scale, post—depositional folds are also present as broad synclines and anticlines (wavelengths from 5 to 10 miles) (Fig. 8). The regional context of these folds is not clearly understood, however, they appear to predate major reverse Late high angle faulting occurred throughout the area and produced several faulting. major offsets of the Keweenaw Fault. This type of fracturing and faulting is partiSignificularly abundant in the upper portion of the section northeast of Mohawk. cant deposits of massive native copper later filled many of these cross—cutting channelways (summarized from White, 1968). Mineralization and Alteration The Keweenaw Peninsula is the location of a dormant billion—dollar copper mining district. From 1845 to 1968 the mines of the Keweenaw native copper district produced about 11 billion lbs. of refined copper (Weege and Pollack, 1971). The major ore producing horizons are geographically restricted to a 45Km long belt within the Portage Lake Volcanics in the Keweenaw Peninsula (Fig. 8a). There is a close relation— ship in both time and space between native copper mineralization and alteration in the Native copper, the principal ore mineral in the Portage Lake Volcanics (Fig. 9). Keweenaw Peninsula, occurs in amygdaloidal and brecciated flow tops, interflow conglomerate units, and fracture systems (Butler and Burbank, 1929; White, 1968 and 197la). The predominant native copper deposits are lenticular blanket—like ore bodies that are found along certain stratigraphic horizons such as the tops of lava flows and conWeege and Pollack (1971) estimated that 58.5 percent of the district glomerate beds. copper production came from flow top ore bodies and 39.5 percent came from conglom— erate ore bodies. The remaining 2 percent of copper production was from fissure (or vein) ore bodies. There are three main varieties of lava flow top recognized in the Keweenaw native 1) fragmental or flow top breccia; 2) nonfragmental! cellular copper district: or vesicular basalt; 3) "scoriaceous" or flow top breccia with a sandy or silty White (1968) estimated that 21 percent of the lava flow tops in the Portage matrix. Lake Volcanics are brecciated (fragmental). These flow tops consist of a rubble of The interstices between fragments and the vesicles are vesicular and massive lava. commonly filled with secondary minerals. Most of the major flow top (amygdaloid) copper ore bodies are of the fragmental type. White (1968) has estimated that uppermost 5 to 20 percent of most individual lava flows is vesicular and contains between 5 and 50 percent vesicles which are commonly filled with secondary minerals. The abundance of amygdules decreases downward and the middle and lower parts of flows The tops of these flows are locally termed cellular are amygdule—free massive basalt. Cellular amygdaloid may have traces of native copper but and often have smooth tops. �1968). White, (from district copper native Keweenaw B. the of Folds amygdaloids. in quartz of limit northwest approximate the is line dotted The amygdaloid. (ashbed) Atlantic 7) and amygdaloid; Royale Isle 6) amygdaloid; Osceola 5) amygdaloid; Pewabic 4) amygdaloid; Baltic 3) amygdaloid; Kearsarge 2) conglomerate; Hecla and Calumet 1) production: of order in number, bold the by identified are deposits Major 1968). White, (from district copper native Keweenaw the of map Geologic A. 8: Figure 3 •l �14 Eagle Harbor Section • o,f4 FEET Top of Portage Lake Lava Seriea I Hancock Congl. 2000 I-Il I Greenstone Flow Allouez Congl. — Houghton Congi. Calumet & Hacla Congl. 0 I - I - 2000 King8ton Congl. PUMPELLY lIE ZONE Kearaarge Amyg, 4000 Scale8 Creek Amyg. 8000 Upper Limit of Zone at Dehydration Gratlot Flow Bohemia Congl. 8000 10,000 Keweenaw Fault - I EPIDOTE ZONE 12,000 Micwcline — Chlorite —— — Epidote — — — — Pumpellyite — — — Prehnite — — — Copper — — — — Datolite — — — — Silver — — — — Ankente — — Quartz — — — — — - Sericite — — — — Colcte — — Arsenides — Sulfides — .-_ — — — — — Albite — — .._ Aduloria — — — — Saponite — — — Laumontite — — Analcime — — Sulfates(barite,anhydrrte, gypsum) Figure 9: A. Distribution of secondary minerals in the Eagle Harbor section of the Portage Lake Volcanics (compiled from Butler and Burbank, 1929; Jolly, 1974; Jolly and Smith, 1972; Stoiber and Davidson, 1959; White, 1968). Location of section is between Copper Falls and Delaware Mines shown in Figure 4. B. Paragenesis of secondary minerals in the flow tops and veins (from White, 1968). Solid black symbols are the more abundant minerals. Secondary minerals shown here are nonmagmatic and not of supergene origin. �15 — A few smooth topped flows show a tendency no ore deposits are only of this type. forming what are locally for the amygduies to be laterally interconnected in bands, important host rock for ore termed "coalescing cellular amygdaloid". This is an "ScoriaceouS" amygdaloid is used locally for flow top breccia at the Quincy Mine. filled with sandy or silty in which interstices between vesicular fragments are mineralized example of The Ashbed amygdaloid is the onl-y significantly detritus. this type. — native copper deposits, Conglomerates interbedded with lava flows are host for major of copper distrifundamental control The particularly in the vicinity of Calumet. Permeability is decreased by conglomerate. bution is the permeability of the host greatly on sedimen— Localization of ore depends abundant fine detrital material. which might bedrock topography tological and environmental factors, such as the conglomthickness of influence location of a stream channel resulting in differing erate. — right deposits are tabular and commonly crosscut the bedding at nearly Large masses of native copper weighing many tons were first angles to strike. the fissure deposits. These deposits are economically much less discovered in types. important than the other Fissure Copper sulfides are a minor constituent of the system, and are found as small veins cutting the flow top native copper deposits, joint—coatings in the conglomerate units, and in association with Mt. Bohemia intrusive (Butler and Burbank, 1929; Copper sulfidesandarsenides are paragenetically Broderick, 1931; Robertson, 1975). Significant copper sulfides with minor late in flow tops and conglomerates (Fig. 9b). native copper also occur at the base of the stratigraphically higher Nonesuch Shale and top of the Copper Harbor Conglomerate (Brown, 1971) at White Pine, approximately 70 Km southwest of most of the discovered mineralization in the Keweenaw Peninsula. The solutions that formed the White Pine deposit may have been related to those which formed the deposits in the Keweenaw Peninsula (Ensign and others, 1968). Vesicular and fragmented flow tops of the Portage Lake Volcanics were prevasively altered by hydrothermal fluids, producing low temperature metamorphic mineral associations occurring as amygduie and vein fillings as well as whole rock replacements in the most permeable hOrizons. The systematic metamorphic zoning varies vertically within the volcanic pile and is equivalent to zeolite, prehnite—pumpellyite facies (Jolly and Smith, 1972; Stoiber and Davidson, 1959), and possibly lower greenschist facies (Fig. 9a). The copper deposits lie stratigraphically within the pumpellyite The copper, in the deposits, may have been leached from dehydrated lava flows zone. (epidote zone) in the deep parts of the pile and migrated up dip and precipitated in the zone of hydration where conditions were sufficiently reducing (Jolly, 1974; Scofield, 1976; White, 1968). These workers and Cornwall and Rose (1957) suggest that most of the copper was probably initially tied up in Fe—Ti oxides and their oxidation released the copper. The oxidation reactions of magnetite to hematite and pumpellyite to epidote may occur along with native copper deposition (Jolly, 1974). The intensity and degree of alteration varies as a function of position within individual flows, position in the volcanic pile, and proximity to cross—cutting fractures (Jolly and Smith, 1972). Local controls, such as pre—alteration composition, appear to govern the assemblages of final alteration products and their major—element compositions. Figure 10 shows a summary of known elemental mobilities and a schematic picture of alteration conditions. �PERMEABILITY LITHOLOGY DIA GNOSTIC MINERALOGY Added to flow top Redistributed within flow Hgh '''''' e'°r : FLOW TOP - FLOW INTERIOR Low , None —r---- Pumpellyite Epidote Metadomain - Ca Al f .. Albitized Basalt Albite Chlorite Unmetamorphosed Basalt Ca—Plagiociase 16 ELEMENT MOBILITY from Outside flow - 114 Na Clinopyrosepe Olivme Si - - 1 H2 Lost from flow top Remained Immobile — K, Fe, Ti, Mg, Zn Cu —w- Cu(s) HO—*-HO 2 (p) 2 Ni Ce) Elements Remained Immobile I. DEPTH 4. TEMPERATURE I Basal chill zone ii Least—altered flow interior lIE Amygdular flow top Arrows denote tluid movement Figure 10: A. Possible elemental mobility pattern in an idealized lava flow in the pumpellyite and epidote zones within the Portage Lake Volcanics (based on chemical data of Jolly and Smith, 1972; Jolly, 1974; Scofield, 1976; Stoiber According to Jolly (1974) Cu and H20 were derived from and Davidson, 1959). the epidote (dehydration) zone and deposited in the pumpellyite (hydration) zone. Diagrammatic regional model for the Portage Lake Volcanics showing local B. thermal/chemical gradients superpositioned on the regional geothermal gradient and showing the movement of fluids along flow tops and bottoms and through frac— tures (modified from Jolly and Smith, 1972; Scofield, 1976). �17 ROAD LOG AND STOP DESCRIPTION Mileage MAP 1 0.0 Assemble at the Memorial Union on University. Begin the field trip the northeast side of the Union. on a kame terrace to the south of the campus of Michigan Technological from the circular drive lqcated on The Michigan Tech campus is located the Portage Lake. 0.1 Right turn. 0.2 Immediately after there is a right turn on to Townsend Drive. Left turn. The Quincy Mine can be seen on the ridge on the skyline. 0.55 Left turn on Agate Street, where we go up the steep hill on the south side of the Portage. We are climbing off of the kame terrace. 0.8 Right turn on Seventh Street. 1.0 STOP 1. Scales Creek flow on Seventh Street, City of Houghton. This stop is marked by a prominent ridge of ophitic basalt, which is an outcrop of the Scales Creek flow, one of the great Keweenawan flows, which can be traced continuously for a strike length of more than 160 Km along the Peninsula. It is about 70 m thick, with an amygdaloidal top which is typically not resistent and a prominent, ridge—forming, ophitic core. The ridge at this site can be followed down hill all the way to Shelden Avenue, where it is covered by glacial deposits. It can be traced across the valley, where it passes through the Ripley School, a prominent brick building across the Keweenaw Waterway. This bearing, about N3OE, is the regional strike of the Portage Lake Volcanics which dip about 500 to the NW. Another clue to the attitude of the rocks is given by the Quincy #2 shaft house on the horizon which heads up an inclined shaft down dip along the amygdaloidal ore bodies of lava flows just over 2000 m higher in the Portage Lake section. Throughout the Portage Lake section between Baltic and Mohawk, most amygdaloidal and conglomerate zones show well developed zeolite and prehnite—pumpellyite facies metamorphism and native Cu mineralization. At this site the amygdaloids just below the Scales Creek flow are strongly mineralized. One mine, the Sheldon Columbian, operated just a few hundred m to the east in the early 1900's. This same horizon is exploited by a series of shafts called Isle Royale Mines, for several km to the SW. Stop 2 is at one of these mine dumps. The most obvious geomorphological feature here is the Keweenaw Waterway, The waterwhose origin was thoroughly investigated by Warren (1981). way formed in a fault zone like many which crosscut the Portage Lake stratigraphy. A bedrock valley, more than 200 m deep formed along the fault as a result of stream superposition through a cover of flat—lying This valley, like others on the Keweenaw, was deepened and sediments. widened by glacial erosion, in a fashion similar to the finger lake The complex glacial deposits, consisting of region of New York State. moraines, terraces, varved clays and gravels were the result of the pattern of ice retreat from the region, which had profound and complex effects on the drainage patterns. �/ 71! /, )- - II 55 NJ/' C ft7 D— G N I - -. IStOP 2• -. // / J /1 /11 i// /1 9SGIS1eYaChASHAFT —/ / Li -- d \\\\ P L - 12 p /_ - K E C •==- — I / I ' H San ds1;i one ••°' - _ji _____ C0LL6E OF MINING AND YE CN0L0G \_y' __________________ 46' SSa 907 si _________ _____ \/ I A 1/ 1059 4 +1 /1 R2 Jdevii1e - - -: . 1M7 --- L . --;•: //r '-4 / A ______ T -- — 10 II /R 567/ -7 0 607 .4- - />7) // -/ t.• I - // - H - — NC - Map4 - , — - •MAP 1 �19 1.1 Left turn on Portage Street. 1.25 Grand Portage Mine dump on left. 1.45 At this spot the Scales Creek ridge is Near the Houghton water tower. slope exposed higher on the south of the Keweenaw Waterway. There are many bald knobs with more or less east—west trending deep glacial grooves on them. To the east of the prominent ridge, there are many mine oprIings from the series of Isle Royale shafts. The Adams Township takes its water supply from these Isle Royale mines which are now filled with water, and this is the source of water for Hancock and several other towns. 1.55 Cross Sharon Avenue and continue on Portage Street east of the City of Houghton fire station. 2.15 Right turn immediately followed by a left turn so we are now on Bridge Street heading south. 3.0 Entering Dodgeville. On the right hand side of the road is one of the prominent Isle Royale mine dumps. 3.2 Center of Dodgeville. If you turn on the road to the right through the Trailer Park, there is access to the Isle Royale mine dumps from Shaft No. 4 and 5. The Isle Royale Mine is described at Stop 2, continue ahead. 3.6 Junction to the Green Acres Road and make 3.7 STOP 2. Isle Royale Shaft No. 6 a right turn. mine dump on the Green Acres Road. The Isle Royale mine worked the top of the Isle Royale flow. Production from the Isle Royale amygdaloid began in 1855, the mine closed in 1948. A total of about 350 million lbs. of refined copper was removed from this mine (Weege and Pollack, 1971). The Arcadian Mine (see Map 4) may also work the Isle Royale amygdaloid. The Isle Royale flow varies in thickness but is about 70 to 150 ft. thick and lies just below the Scales Creek flow discussed in Stop 1. It dips about 50 to 60° to the northwest (Fig. 11). A gentle fold accounts for the curvature of the flow (see Map 1), Isle Royale syncline. The flow from the top down is characterized by fragmental zone, banded amygdaloid, foot inclusion zone, The fragmental zone consists of irregular fragments and massive main trap. of amygdaloid and fine—grained basalt ranging from small grains to tabular The vesicles and spaces between the blocks several feet in long direction. secondary minerals. The banded amygdaloid is an fragments are filled with considerable area. Amygdules are commonly abundant unbroken rock body over zone a banded appearance. Below the fragat certain horizons giving this amygdaloid is the foot inclusion zone which is indemental zone or banded foot inclusion The finite patches or inclusions of amygdaloid basalt. devoid of amygdules (summarized zones grades into massive basalt practically from Butler and Burbank, 1929). �L_, I. _J —, - - Le Vc ific Ss S iac 11: Cross section A—A' on Map 1 (from White, 1956). Labels are as follows for the Pewabic West conglomerate (pp), Creenstone Portage Lake Volcanic Series (P) and its subunits: flow (pg), Allouez conglomerate (pa), Calumet and Mecla conglomerate (pc), Kingston conglomerate (pkc), National sandstone (pn), Kearsarge flow (pk), Wolverine sandstone (pw), Scales Creek flow (psc), Bohemia conglomerate (pb), St. Louis conglomerate (ps), Baltic conglomerate (pbc), and Unnamed conglomerate (pu). Figure P ...vIIIe A' �21 Butler and Burbank (1929) recognized two distinct periods of alteration. The earliest alteration was oxidation which caused the development of This oxidation could essenhematite, which produced reddened basalt. alteration shortly after eruption. tially represent deuteric The second after the period of alteration was probably flows had been tilted. This period was complex and resulted in deposition of native copper. This stage :L divisible into three substages: 1) An early stage of deposition of epidote, pumpellyite quartz, calcite, most of the native copper and minor prehnite, alkali feldspar, and laumontite; 2) an intermediate stage characterized by the development of sericite with quartz, calcite, anhydrite, gypsum and minor barite; 3) a final stage of copper sulfides and arsenical copper accompanied by calcite, sericite, quartz, chlorite, and specular hematite occurring in numerous veinlets. Stoiber (unpubthe following estimate of the lished data) made percentage of alteration the Isle Royale Mine: quartz, 26— minerals on dumps from four shafts of 59; calcite, 5—39; prehnite, 6—32; pumpellyite, 1—17; epidote, 1—10; sericite, 0—12; chlorite, 0—3; K—feldspar, 0—trace. This dump and the ones near Dodgeville are freshly reworked and good specimens of native copper and alteration minerals can be found. 3.9 Junction M—26 at the Copper Country Mall and you are going to make a left turn. MAP 2 5.6 Entering Atlantic Mine. 6.9 Right turn at the sign that says South Range Village Limit and drive about 150 yards into the road and walk to the right through a notch up the hill another 60 meters to Stop 3, the South Range Quarry. NW SE Felsite bed 9 IEE Fragmental amygdaloid i Non-fragmental amygdaloid 190 FEET F(a) Masve basaft PegmatEte layer (a) and zone of thin Figure 12: Geologic profile of the South Range quarry along the northeast wall (from Cornwall, 1951; White, l97lb). Location of the quarry is shown in Map 2, Sec. 17, T54N, R34W. �22 C ;: 52 // p —q w• • . njflfe San .one I �23 STOP 3. South Range Quarry. South Range quarry provides an excellent cross sectional view of a massive to amygdaloid lava flow (Fig. 12) of the Portage Lake Volcanic Series. The base of the section is a conglomerate bed, about 4 m thick; it is exposed This is overlain by an 18 m thick fine— on the main path to the quarry. grained basalt flow, followed by a 42 m thick ophitic basalt flow and finally the lower 17 m of another ophitic basalt flow. The conglomerate is well indurated and consists mostly of pebbles and cobbles of rhyolite with subordinate clasts of basaltic lava set in a sandy matrix of similar composition. The clasts are subangular to sub— The overall character is similar to the Copper Harbor Conglomrounded. This conglomerate is erate which will be seen later in the field trip. one of a number of sedimentary beds which are interbedded with the Portage This particular bed is correlatable with the National Lake lava flows. Sandstone, a marker bed in the Nass—Rockland area. The basalt flow that occupies most the quarry face has features which The characterize the thicker flows of the Portage Lake Volcanics. lower half of the flow is massive basalt, overlain by a zone with progressively smaller pegmatitic layers, topped with cellular amygdaloidal basalt, and at the top a discontinuous layer of flow top breccia (called fragmental amygdaloid). A typical pegmatitic layer, consists of 4 cm to 1.3 m core of green amygdaloidal lava surrounded by a 4—9 cm border zone at the top and bottom. The border zone is composed of a medium to coarse grained aggregate of albite/oligoclase, augite, ilmenite, and magnetite. Pegmatitic layers toward the top of the zone are more amygdaloid. Quartz, prehnite, and a green or red cherty substance occurs in flattened vesicles The pegmatitic layers are products of cooling at the top of the layer. and differentiation as it cooled (description of pegmatitic layers from Cornwall, 1951). Amygdules and interfragmental spaces are filled with Locally the basalt is quartz and prehnite containing traces of copper. intensely epidotized or prehnitized. Outside of the Quarry and to the north are a series of glacially grooved outcrops in which the exposures of the pegmatitic zones are spectacular. Take a right turn on M—26, going into the town of 7.9 Return from Stop 3. South Range. 8.4 At stop sign in South Range, take a left turn. 8.6 Right turn at the church and immediately foiJowed by a left turn as the whole road jogs to the left. 8.7 Entering the town of Baltic. 8.8 Right turn. 9.2 The main road turns to the left, we go to the right on a small paved road driving past a concrete building towards some very large mine dumps. �24 9.4 STOP 4. Baltic Shaft No. 3 Mine Dump. The Baltic, Champion, and Trimountain mines worked the Baltic amygdaloid. Total proThe Baltic Mine opened about 1898, the others opened in 1902. duction from the Baltic amygdaloid was about 1.85 billion lbs. of refined copper which was the third largest producer in the Keweenaw native copper district (Weege and Pollack, 1971). The amygdaloid was developed for about 7 Km along strike and to the 38th level in the Baltic Mine. The Baltic flow is an ophite that varies considerably in thickness but The Baltic amygdaloid in many places is 17 m is around 50—70 m thick. or more in thickness and is composed of fragmental amygdaloid, the average stoping width is about 5—8 m. However, like all fragmental amygdaloids of the district, there are significant variations, e.g. the lode can thin to only a few feet thick composed of trappy or cellular amygdaloid. The lode dips at about 70°NW (summarized from Butler and Burbank, 1929). The abundant minerals associated with copper in the Baltic amygdaloid are Copper sulfides are unusually quartz, pumpellyite, epidote and carbonate. The sulfides characteristically occur in fissures that dip 75 abundant. Most of the copper sulto 900 and strike nearly parallel with the lode. fide in the lode is chalcocite associated with iron—bearing carbonate, there is some bornite and rare chalcopyrite. Native copper is irregularly distributed through the amygdaloid ranging from minute specks to masses weighing several tons. Native copper occurs at the margins of sulfide veins and it may occur with quartz in the center of veins. Sulfides are in general paragenetically late (Fig.9h Introduction) (summarized from Butler and Burbank, 1929). The majority of the dump at this stop is amygdaloid basalt. R. E. Stoiber (unpublished) made the following estimate of the percentages of the seconcalcite, 91; quartz, 5; epidote, 3; dary minerals in the dump as a whole: Paragenetically epidote and chlorite were early minerals; chlorite, 1. calcite, quartz and native copper were intermediate; and copper sulfides Excellent specimens of chalcocite and iron—bearing carbonate were later. can be found on this dump as well as native copper. 9.4 Retrace route in Baltic. 9.9 Stop sign in Baltic, make a left turn to go back in the direction of South Range. 10.1 Right turn, immediately followed at the church by a left turn. 10.3 In the center of South Range, right hand turn off M—26. 10.8 Passing the South Range Quarry, Stop 3. 12.5 M—26 jogs to the right at the center of Atlantic Mine �25 MAP 3 14.7 STOP 5. Glacial Deposit Near Pamida The Keweenaw Peninsula has probably been modified by all of the major glacial episodes of the Pleistocene. During maximum glaciation the entire Keweenaw Peninsula is believed to have been overridden by around 3000 m of ice. The present form of Portage and Torch Lakes is related to the final retreat of the Laurentide ice sheet in the Lake Superior The final glacial advance and stillbasin (shown in Figs. 13 and 15). stand over the Keweenaw Peninsula was made by the Keweenaw Bay Lobe, marked by an end moraine of Wisconsin stage (Fig. 14) (summarized from Warren, 198]). The earliest recognized channel cut by drainage through the Portage Gap area is the Huron Creek channel (Nap 3). The channel is waterworn bedSince there is no delta at the southern end rock due to southward flow. of this channel perhaps the source of water was a large lake where glacial The drainage sediments had time to settle before the water was removed. in Fig. 16 (summarized from pattern through the Portage Gap is shown Warren, 1981). A delta kame is just west of the Huron Creek channel and is the location The sediments, in this dissected knob, show strong of Stop 5 (Map 3). evidence of being deposited by a braided stream closely associated with Extreme variations in grain size and sorting occur within a a glacier. This suggests differing flow regimes during distance of a few meters. Poorly to well—worked unconsolidated sands predominate but deposition. Numerous cut—and poorly sorted pebble conglomerates are also present. Large striated boulders of basalt within fill structures are present. from a nearby glacier. This the gravel and sand must have originated large exposure is capped by a thin (less than one meter) poorly sorted clay till which thickens rapidly to the south; it is about 7 meters thick The later unit may be a flow till(?) at the top of the nearby hill. which slumped off the nearby glacier (description by S. Beske—Diehi and S. Nordeng, Dept. of Geol. & Geol. Engrg., MTU). 15.75 Between Junction of M—26 and US—4l, so turn right on US—4l past the Mobil and Erickson gas stations. 16.2 Excellent outcrop of basalt with exposed amygdaloid on both sides of the road. 16.35 Make a left U—turn back onto US—4l going one way back through the City of 1—loughton. 16.45 Amygdaloidal basalt with pegmatitic zones at Burger King Restaurant, Shelden Avenue, Houghton. This stop is an alternate to the South Range Quarry Stop. Excellent exposures of the cellular amygdaloid and pegmatitic interior of a thin Portage Lake lava flow are found to the west of the restaurant and along Montezuma The flow top is strongly metamorAvenue, just a few steps to the north. phosed with a variety of amygdule minerals of the prehnite—pumpellyite The green color of the basalt is due to the abundance of epidote. facies. Below the amygdaloid the basalt is virtually unmetamorphosed except where thin pegmatite zones cross it. �1I 4 0 6O7 R A T ) —. 4 I '',;ee1cii:.! 1 I 4 G 26 L E — ., �1981). Warren, 1976; Kalliokoski, 14: Figure (from glacier Lobe Bay Keweenaw the of moraine End / / e 80 Kilometers es ii M 0 F 0 Prest, 1975; Huber, (from America North central from retreat ice Wisconsin the during positions ice—marginal Speculative 13: Figure 1969). 46) (Fig. 1257A). Map Canada of Survey Geological 1969, Prest, K. V. (from basin Superior Lake the readvance, or surge, ice major Note Amenca. North central from RETREAT ICE WISCONSIN in H P H B NJ' y,.,. ,.4k,.,b,,,, Sh,,..,,d. K "fl". F 40 U j' ,)" L .• •' 27 �L-\' ii) o 5t - -- - -, - - - -?-- -- S — "0A P E - ( - -' - - .— T -"i /5S5 - S jS ji - !j ' - S -- I _\ S. S SI 5—- - QS.AUL -S-j - -- S - f I -- 1 S -' '< S S I \ /55( S ) - S7 sS S - - // HURP - ( ' )•J / - / At KE - /, .S\ 55 - - : S \_S . I / S 55 / - S S MUWAUKEE - 1 5 / S q S mo0/ S - - S. I :/fj'S.S ,jS/ :-r- S - /5 - \55 I - s - / /- S -S. _S___SS S 5CHICAGO Figure 55 S S S 55S\ /,/ ...5 I 5S / / —-S Enlarged view of ice—marginal positions during Wisconsin ice retreat 15: (from Prest 1969) . Note the major ice readvance in the Lake Superior Basin and withdrawal pattern over the Keweenaw Peninsula. S. �29 LAKE / WfSHBURN // / -.5 / I/ Figure 16: High level drainage through the Portage Gap during the Washburn Stage (from Warren, 1981). �30 16.9 Right turn on US—41/M—26 and crossing the Portage Lake Lift Bridge into Hancock. The bridge was built in 1957, and is designed to accommodate Great Lakes ore boats, who prefer the Keweenaw Waterway route to rounding Keweenaw The present bridge abuts the Hancock side of point in stormy weather. the canal at approximately the site of the old Quincy Mill where the tramway descended Quincy Hill from the mines. MAP 4 17.15 Left turn on TJS—41 into Hancock. 17.35 Right turn and immediately followed by US—41 going to the left but we go straight at 17.4. 17.5 Bear to the left on White Street. 18.0 Junction between White Street and Lincoln Drive which is US—41, we take a right turn. The fenced ground near this locality surrounds an area of recently caved ground, which is thought to be related to shallow stopes of the Hancock Mine. The detection and distribution of such openings is a problem of considerable concern to local authorities, since many mines had shallow workings, since towns grew up adjacent to mines and since maps of the underground workings are incomplete and/or inaccurate. 18.3 Turn off US—41 to the right to the overlook of the Keweenaw Waterway or Portage Lake which is Stop 6. STOP 6. Keweenaw overlook near Quincy Mine. This overlook, near the crest of Quincy Hill, allows a broad overview of all the previous stops and also the best general view of the Keweenaw The features which can be seen are, from east to west (left Waterway (Fig. 17). to right): 1) On the skyline, the knobby terrane of the Huron Mountains, which lie across Keweenaw Bay. The mountains are underlain by the Archean gneisses and granites of the Northern Complex, and are the main source 2) In the forearea for the extensive deposits of Jacobsville Sandstone. ground, underlying the flat topography of Jacobsville Sandstone is clearly The Jacobsville extends from the Keweenaw fault, which crosses visible. the Waterway just east of the Michigan Tech campus, across the Keweenaw The formation is genBay and under the Huron Peninsula (Pointe Abbaye). erally flat—lying, while all of the other rocks of the Peninsula dip north3) Within the town of Houghton several westward toward Lake Superior. ridges of basalt can be traced downhill, the most prominent being the The attitude of the Scales Creek flow horizon, where Stop 1 was made. Portage Lake flows and the alternation of resistent flow interiors and interflow conglomerates with less resistent flow tops makes site investigation work critical for construction projects, to accurately determine For example, depths to bedrock and to make hydrologic interpretations. site investigations of the extensive area south of the main campus, where the Michigan Tech Student Development Complex (visible from the overlook) is now located, provided the focus of several Masterts theses for students in Geological Engineering (Stevens, 1971; Hase, 1973). A �7 dVV i / 28 fl\ / I I // 4 _0 / i I / - 0 "HH< L -' / •/ -- - R - 2Z71L 7t z / r iA .•'.<;:Ir..r /1 // (( I _,_ t! II - r • G I / •0 - / / —: / \\ I. - / I I / • // 2? // / / Wewabic h(' / -.. // ---- / NA2 I II NA6 (CH!GAN 4N/ // A2!,'ll .fl. 1/ 2 A2/ /k' / // P -___-J ;LAK/E / 1 5 !s'c , \/ // , lI i//11 !r/z"v/ >1 - • _ wJI .1 L ./.7:E MaF5 - �View from Portage overlook facing south. Notable features include: 17: 1) Huron Mountains, 2) Flat—lying Jacobsville terrain, 3A) Scales Creek flow ridge, 3B) Student Development Complex, 4A) Houghton water tower at Isle Royale Shaft #1, 4B) Isle Royale dump 114, 4C) Isle Royale dump 115, 4D) Wheelkate Bluff (Trimountain, 5) Highway M—26, 6) Contact between the Portage Lake Volcanics and the Copper Harbor Conglomerate, 7) Houghton County Courthouse, 8) Quincy Smelter, 9) Michigan Technological University Main Campus. Previous stops are located with stars and stop numbers are prefixed with an S. Figure w �33 general map, showing the detailed bedrock geology of the City of Houghton (Holcomb, 1975) is used routinely by developers in the area. 4) On the skyline on the opposite side of the Waterway, beginning at the Houghton water tower a series of mine dumps representing the Isle This marks the Royale lodes can be seen extending into the distance. approximate route of the road between Stops 1 and 2, and shows the The knob on the skyline is Wheel— strike of the Portage Lake Lavas. kate Bluff near South Range which is one of several residual bedrock 5) The divided M—26 highhighs and is located just south of Stop 3. way is visible, traversing the glacial deposits described at Stop 5. 6) To the right, the Waterway traverses the upper contact of the Portage Lake Volcanics and the Copper Harbor conglomerate, Nonesuch Shale and Freda Sandstone. The Stop is the best single locality to observe the Keweenaw Waterway. The Waterway and the peninsula are named for an Indian word for Portage route, but to make the Waterway accessible to Lake Superior shipping, This canal work was necessary at both the northern and southern shores. The geological history of the Waterway was investwas completed in 1873. igated in detail by Warren (1981). This and other major bedrock valleys were formed by stream superposition as ancient rivers eroded through flat— But the valleys lying Paleozoic rocks into the tilted Keweenaw strata. Then the Pleistocene. were greatly deepened by glacial erosion during as the Keweenaw Bay sub—lobe retreated at the end of the Wisconsin glaciation, the Waterway allowed eastward drainage across the Peninsula to lower First, drainage occurred in the Portage Gap lake levels to the east. (between Houghton and Hancock) while a tongue of ice remained in what is As the ice retreated further, the valley now nowwestern Portage Lake. occupied by Portage Lake was formed by eastward drainage of successively Torch Lake was formed lower proglacial lakes in western Lake Superior. by a trapped block of ice which later melted in place to form the lake Warren's study includes a complete bedrock topographic map of basin. the Keweenaw and a series of maps showing the pattern of ice retreat, based on the distribution of glacial deposits. Houghton was named for Douglass Houghton, the geologist who sparked the Michigan copper mining boom by publishing his Michigan State Geologist Houghton was settled in 1852 and is the site of several Report in 1841. historic buildings, the most important of which is the Houghton County Courthouse (1887), a prominent yellow brick building with Jacobsville Sandstone facing and copper roof and a flag pole, on the hill above the main part of town. Hancock was settled in 1859. Across the road and just slightly up hill is Quincy Hill House (1871), the mine manager's house for the Quincy Mine. The Quincy No. 6 mine shaft house dominates the skyline behind the viewpoint. A map of the Quincy operations in its heyday are given in Figure 18. The inclined No. 2 shaft descends at about a 45° angle more than 3 Km (1.7 Km below the surface) making this one of North America'a deepest mines. The surface projection of the area mined is shaded on Map 4. 18.35 Right turn back on US—4l going up the hill. 18.75 Prominent outcrop of basalt with glacial grooves. �34 18.85 Right hand turn would lead to the Quincy Steam Hoist, we're in the center The Quincy Steam Hoist can be now of the Quincy Mine area (Fig. 18). visited during the summer months for a small admission charge. Inside is the largest steam mine hoist in the world. This great machine, invented by Bruno Nordberg and installed in 1920, could lift a 10 ton ore load at a rate of more than 1000 m per minute. The hoist is still in pristine condition and a full museum of the Quincy Mine is maintained inside as well. MAP 4 or 5 On the left hand side, immediately after 19.3 Turn right on Arcadian Road. the turn are some of the Quincy mine dumps, nearest Shaft No. 1. This will be Stop 7. Please respect private property signs and stay within the public right—of—way. STOP 7. Quincy Mine Dumps. The Quincy Mine worked the Pewabic amygdaloid. Production from the Quincy Mine began in 1856 and ended in 1967. Total production from the Pewabic amygdaloid was about 1 billion lbs. of refined copper, ranking fourth in the district (Weege and Pollack, 1971). Lankton and Hyde (1982) give an outstanding illustrated historical account of the history of the Quincy Mining Company which earned the name "Old Reliable" because it paid dividends so regularly. The Pewabic amygdalLoid deposit consists of a group of relatively thin flows. These basaltic flows are A geologic cross section is shown in Figure 19. Some texturally distinctly porphyritic with large feldspar phenocrysts. of the thicker flows have an ophitic texture. The tops of flows in some places are cellular whereas thick flows may be either cellular or fragmental. The amygdaloids of Pewabic flows are characteristically of a type Flows of this type typically have smooth termed ].ocally as coalescing. tops in which individual vesicles are larger than average, reaching an inch or more in diameter. VesiciLes in the same layer may coalesce to form a A series thin, jagged gash with a lateral extent of up to 12 feet or more. of such openings provided an almost continuous path for the flow of mineralizing hydrothermal solutions. Several such layers may occur in the same flow top. Where coalescing is well developed in the Pewabic amygdaloid there may be 2 to 10 layers from 3 to 5 feet thick. There is every gradation from coalesced layers of vesicles to those that show only a moderate tendency to collect in layers (summarized from Butler and Burbank, 1929). quartz is the most abundant secondary mineral assoCalcite is also abundant. ciated with native copper. Pumpellyite, epidote Laumon— and chlorite are common but not abundant and prehnite is present. tite and datolite are common in upper levels but not lower levels (summarized from Butler and Burbank, 1929). In the Pewabic lode, The majority of the dump at this stop is amygdaloidal to massive basalt. Secondary minerals in this dump are mostly quartz and calcite with lesser amounts of pumpellyite followed by epidote. Paragenetically epidote and pumpellyite seem to be early whereas quartz, calcite and native copper formed later. �__ 35 zz .../ ... V I _/ • / V ; /t \ \0. 3/ S Jl 0 I • •90:•.• — —-1 -I - - rj z / z N 7 NM j" , 4 - .v__ /' \ / I �I I J I I I :tI J ''j!J QUill~(CY MJINJE QUIENCY MI[NIE JLOCA1rJION LOCAT lION \ \ I _ ~...:r~, " HOU§JING AND HOUS]LNG AND COMMllJ:NJITY COMMUNIITY§TR1UC1r1UR1E§ STRUCTURES Co C0 f 92O R920 J 4 ClrXi5 Pdence C/zrko ~t.(Jence , 11 ff Metf,adtt Methodi.:;tG'7urd7 07urch 5tootom £7ce Mine O{flce (4 14 frank/in Franklin ichooL ochool. 7 Captaur.5 /ejidence Captalf1'.5 Re.5idence franklin Franklu7 .5dJool, icJ700l; Franklin (5 Old 1.5 Ola FranklU7 FrenkWi Franklif? (r~tl)~?) 1/. -" \..r f6 Pewdbic YcJioal ochoa, 15 Pewabic Qurncy ichoo/ QUI ncy SChool Mesnard" •••• Megn.-d -11' ~~.~~~_'~_'_~I._:-:"~"J' U~ '- ---:, \~~ r::~-,'c?::>' , .LI\D~ r;,~~:::/;:~cpJ I\~ J-1~(" G~' <S-' ;: \ .. /' '';\ '/ b;l ~' / \'1:1\ .. " ',,','1,/, \ .. '\ '~ ,~..- \ L.xe (" ,)'v , 9(8) VI \\,'I ,.~, . ~ :", ~ '\ ,®' ', . . '-<::\::i{,::;::: \ " ;. ';- .-;::~ -~_/. ." ~_. =--" ~ "'Ir)!~;'~~::[ • "' t.-" • "{"l'r J'\ : • ':". '" , "'-I' ~.~·:•. :t :, .~ •. '.. ..y~';" ;.~ ~,,"~ .~'. ~ J ',,- ~~ \0t"\' \", (/. 8 \"~ - • ""'. /\, ~.~., /' ~~. r ;' J 5inir: ,;:.O@ • ~ ••,. : ~~"~ / . .":./ ' ••• 0 ,', .. ';: . 'i' ~.- ---~ -J ' ' : . ' ' \VEl tV _ -- "'';'.', ~I)('I)'''' ~ Z ")~~ [1' •~ ,,' \: % ~~ ,~'-- ,.,~ - "I" ~ ,t; ~~ '~.~~",..~.~ ~ ~'f? ~.~ -':_. , 0®' R, .. , \Uti .. , . \ , ') fiu / " .",.. , j. 1'iin !'~inp ® #~:;~'s;ng- ~ .,. ,I Structures StructuH'.S of the the Quincy quincy 'A~G' .. h ';: ~ 'O6~/-,. '·~., ,., • .. /- • Figure 18: 18: ., . h'. i,; #.. . ~~---;- • II---~' J,:. ~, , •.•" . , . " ,®I'I. • ~ :---.-J.... ~ •. t. .... :;.:( ';:'~:\, ·1 " ~; '0\..;.), "~' " ~~i \.',' ~.~~~'i:::'--~., _~ --' .. i (~,",\~ .. /~.;/~~~,.~~I ,1r,-"\r .. ~,:,./... I -;:'1'" 'i'" . '''i;';~';cl:'' • , ',Ii', l'UI Franklin . , . , - ~ ,I, i/···' d,..... " " -![?'~' ..,.t .... ;l:~ '~~'-i.,~-",:~~"""... 6 -- , ~"" Pr I'is.,J)ir ,I .. >or ", ••h,c c- - - -. ~ (Y~'0'~0\ /~!e ,'" ',' u~ 8~~ _;t:,:~~'c~lL, N~6 ; _ , ' ~', @ ) . . W I Z . - ; - : - N 0 ? '~ -.----"'Cl.\ •• • .•~ . '"".•• , ~i~fr .. r '1'/" "J'II .. P~8bl('. •• ,-b~ ......, ~ ·~".I:.. ,I.', - ~ ,:_~. '~II '\!2~).J .... JuP<V,or"$~ '-~~> J!I ~ -______. ,;.,--::~ r'..... lt~ .•_, ~~_.:.- \ ~ ,\. ,'/ ~.~.~ ..••••·1".::"f! 4-ro CalumBt 4—eoca(umr "J,;t. ..... ~...",~" "~\"'':~'')\~;' ~. ,) , (,/",~ ~:;>{( \ :" ". ~ ':', \.-. " .... .., .. ', 5ord flaije 800rdinq ttouse /lhrth!5 OOX otDre 8. Abrth5 . Ii >;,,~/' (3. Jomei /1 Oa9r and i2w77pany fJ James, H ueaq8r cmcJ Wmp.'3ny Abrths /?;!..5ldence O<zorqe wr7e North::> .iderice •.~ -'9-~_ '., "0'., 6 =- .... ; ••-~ .,. , {i? IS Cat/)olle Olurcfiand arid Priest~ Prtest5 C.ti?olc 07urch /?Q.5idencØ R.e.:;ldence 5 9, :1' .. '. ~ . P<.-~ '.. 10 Clubhouse(öathhou5e) (l3athhouse) (0 Clubh,ue Ooctor:J Lbctcr f(e:,t.(Jence Rejtdene Dipetary DI,::;,oe=ary A9cnt5 f?e.5ldence idence k;Jent::> Z ,~ '. ~ I '----------:.~. ~;J: ~:h ~il!i t:/"2Ie' 1l: ~;H ica(e: ~ :~: 11T .~ "¥' '"F'""'C 'iIi: TT 4a:)}.~ i :1; 1um·:¥:-'.lf-----¥'-------, : r;11.. !I': Vl.U(1 • II] - , .\ I - 0 '~~•• ~ or, 'H~lJof A180 of C,e fuxaon me QlHncyMV74 kocy l.t:>cdctOn.,.no Locacror, a,ri Vte<nuy'(noC1dll} ------....... J0cation (['rom Lankton Lankton and and Tyde, Eyde, 1.982). 1982). location (crom Vnnty ( ~ ! 3 n~ a , l.v 0'> �s S' B- I I n ~l·(!,,.1 7""""- s .., c ~ 7/ 'N' J ~'C' ~ ~ "n",~ " .. .'!>'"<" ~teOa ~~ .".'_ L~ . I .J(VJ ' ~~,~eSUC; p ~ c -''' .c:= <' Copper Harbor Jacobsville -4000' I ., <P: ./ Figure 19: 19: Geological cross cross sectionfromB section from Bto to B' B' on on Map Map 30, 30, B' B' to to B" B" on on Map Map 4, 4, B" B" to to B"' B'" on on Map Map 5. 5. This This cross section section illustrates illustrates the the general general geologic geologic relationships relationships of of the the Keweenaw Keweenaw Peninsula. Peninsula. The successively by the the Copper Harbor Conglomerate, Conglomerate, the the Nonesuch Portage Lake Volcanics are overlain successively Shale and the the Freda Freda Sandstone. Sandstone. The Portage Portage Lake Lake Volcanics Volcanics are are in in fault fault (reverse) (reverse) contact contact with with the the Introduction). Labels for Jacobsville Sandstone Sandstone (see (see Fig. Fig. for the the Portage Portage Lake Lake Volcanics Volcanics (P) (P) younger Jacobsville are follows: Hancock conglomerate (phc), (phc) , Pewabic Pewabic West West conglomerate conglomerate (pp), (pp), Greenstone Greenstone flow flow (pg), (pg), are as follows: Allouez conglomerate Kear— canglomerate (pa), (pa), Calumet and and Hecla Hecla conglomerate conglomerate (pc), (pc), Kingston conglomerate conglomerate (pkc), (pkc), Kearsarge flow flow (pk), sarge (pk), Scales Creek flow (psc), (psc), Bohemia Bohemia conglomerate conglomerate (pb), (pb), St. St. Louis Louis conglomerate conglomerate (ps). (ps). W --.J �38 38 MAP 55 19.5 Entering Coburntown. Coburntown. This is is another one of the the communities that that sprung up around the the Quincy operations, operations, most of the the houses built and owned by by up Several ethnically distinct neighborhoods existed the company. Several existed "on "on the the hill" in in the the early early 1900's. 1900's. In lived on on the the In all all more than 6,000 people lived hill in in 1905. 1905. 20.45 Y in There is a Y in the road, road, we take the right hand branch which is essentially aa straight tially straight road with a sign sign saying saying Arcadian Arcadian Scenic Scenic View. View. 20.7 Passing a radio radio tower tower on on the the right. right. We are now crossing the the Scales Creek flow the top top of the small small ridge ridge (see (see Map Map 5). 5). The Arcadian Mine worked flow at at the an amygdaloid just just below below the the Scales Scales Creek Creek flow. flow. The amygdaloid may corcoran relate with the the Isle Isle Royale Royale amygdaloid discussed discussed at at Stop Stop 2. 2. North of the the road is is Shaft Shaft No. No. 11 of Mine. Stoiber (unpublished (unpublished date) date) of the Arcadian Mine. estimated the percentages of of non—metallic non-metallic secondary minerals in in the dump calcite, from Shaft No. No.11 as: calcite, 43; 43; prehnite, prehnite, 25; 25; quartz, quartz, 16; 16; K—feldspar, K-feldspar, 8; 8; epidote, epidote, 6; 6; pumpellyite, pumpellyite, 1; 1; chlorite chlorite 1; 1; and and laumontite, laumontite, trace. trace. 21.4 see the the largest largest part part of of Portage Portage Lake, Lake, Down to to the the right of of the the road road you you can can see of view is the field field of is basically Keweenaw Bay and the the Huron Huron Mountains. Mountains. Much of the flat—lying flat-lying Jacobsville terrane. terrane. 21.6 Road turns turns to to the the right right and and changes changes to to gravel. gravel. 21.8 descending off off the the Portage Lake Volcanic Volcanic Series Series across across the the Keweenaw We're descending Fault onto Jacobsville Sandstone. Sandstone. 23.0 have aa view of of the the Isle Isle Royale sands sands We are descending the the hill and and we have across Portage Lake in in Houghton. Houghton. These are tailings from the Isle Royale out and and into into Portage Portage Lake. Lake. dumps (Stop (Stop 2) 2) which were brought brought out 23.15 Junction with M—26 M-26 and and take take aa left left turn turn at at the the Portage Pottage Lake Lake Coal Coal Dock. Dock. 23.6 Entering Dollar Bay Bay on on M—26. M-26. MAP 66 25.2 of flat—lying Exposure of flat-lying cross—bedded cross-bedded redbeds of the Jacobsville Sandstone on the left hand side side of of the the road road (northwest (northwest side). side). STOP 8. 8. Jacobsville Sandstone. Sandstone. The Jacobsville Sandstone is a a fluvial fluvial succession of feldspathic feldspathic and quartzose quartzose sandstones, sandstones, conglomerates, conglomerates, siltstones, siltstones, and shales shales up to 1,000 m m thick (Fig. (Fig. 20a). 20a). There are no interbedded lava flows flows or cross—cutting cross-cutting dikes. The Jacobsville Sandstone is separated from the Portage Lake Valcanics Volcanics by the Keweenaw Fault, Fault, aa reverse reverse fault. fault. The Jacobsville Sandstone is is probably upper upper Keweenawan in in age and and may may be slightly younger than the the, Freda Sandstone. Sandstone. Current the Keweenaw Peninsula are to the northeast and east east Current directions directions in the suggests transport transport to to deeper parts parts of aa basin located located northeast of of which suggests Keweenaw Keweenaw Bay Bay (Fig. (Fig. 20b). 20b). West of Lake Gogebic thickness thickness and and current direc— directions tions suggest another deep deep part part to to the the basin. basin. East of Calumet, Calumet, near the the Keweenaw Fault (Stop (Stop 10) 10) the the Jacobsville Sandstone contains boulders of basalt which suggests a topographic topographic high in the the Portage Lake Volcanics north north of the the fault fault during during this this period period of of Jacobsville Jacobsville sedimentation. sedimentation. Metamorphosed �/ / / / ,0 /~(" / / // / .I,/""!' ... /Ci' ,;:"00' / , / /'pP .~ // /' ~ 56 / '-~~~ ..... / -....;,:~. / '086 • /// / //' // 39 // ." // II II II 1070 1070 , -I [ II II II II II II II II H \\ ,\ z , " \ 1068 ,__L_ — . II / / p- \\ H \' \\ \\ ,\. H "\\ ". —--•• , L ' p~~// ~\~. H... if] :=:;\ fr-- t1 16 II II r p N 0~ I~ 0 ,:;1'Q , '....... 0, NA/5Q .............. " II NAI3' II "'NA/5Q "" NA/3' " C'~ II :~<? H 1/ 1 0~ ....... .,,00 933 l ' ':O~ ....... CJO C, / 4, cL '\ 21 / ')0 -"',--- ""'--: ...... , . . . . ; /i /1 ~ ~\ \. 1 "( II II I I-=-- 4 A ~0 ...0 b~ --'~ , NAI7 NAI7 N-,~ Il /I It II J e~ ,~ ,000 ___ OFFSET _— OFFSET -4":t- ~0 14 i-- / KEWEENAW KEWEENAW FAULT FAULT c• \\ II .-:-1r;o.f6=====.=~ 15 N83 22 23 • 630 • : H Mill I,- 1 884 I, 'I ii I II" 'I. 913 / - "'-" '", / \. L )8 s. -T , --"J". /_-9_/ \ Stop8 602 602 \• \ "', - 0 V - II ii I, ou II * , H,;" II ,,'I; / CJ~ / ~O'" // 'so / / j .: // 668 ~ 11~ .~ /;:.~=J- ..--"--1-~~==-~;:./~ -: -- II JI-ij . - - If//// • -, ,... .~ .,;.: -:-- // // II /1I, // '1/ II // II /? /-::-~==;!/ 1, II ,726 26 / "// 11/ /,/ ,,/ ij "7 'l~' ,y 1- . 'l /,'l // 7, ~. /.1 ,'/ /1' ,,;1 ",' - "/ //' 800 :- H •- -j 4-\ Aap5 // / *0 ~0 27 62 // 26 ---- H >, \ "''-\ ,,----"'\ _ _ ;;:."'::- _F1_ \\ '\ \. '. 0,", "1L-B9~ --- ' , _ _ ,Q!=D_ M on pv, '\ ,--- ....—.. —'-.. 7 35 • 1 6 .. . MAP6 ~AAP ,,",, • �____ 40 Sandstone Thickness Current Directions 9400 Geophys. est. (ft.) 597 Weillft.l o 50 I j Km. B. A. I rocks Iron ranges 0 - 0 km mi 30 I 50 so N --...... ,. \ c. C. Figure 20: 20: Relationships of Jacobsville Sandstone Sandstone (from (from Kalliokoski, Kalliokoski, 1982). 1982). of Jacobsville Jacobsville Sandstone with minimum thickness denoted Thickness of denoted by +'. '+'. B. Current in the the Jacobsville Jacobsville Sandstone. Sandstone. C. Location of of Current directions in C. possible source areas iron formation staurolitic metasedimentary possible source areas of of iron formation and and of of staurolitic metasedimentary rocks. A. A. �41 iron-formation quartz-staurolite pebbles pebbles suggest suggest aa source source from from the the iron—formation and quartz—staurolite jacobsville Jacob sville sedimentation sedimentation was was preceded preceded by by aa long period of cratonic stability stability with with little little or or no no volcanic volcanic activity. activity. Erosion was was apparently initiated by late Keweenawan warping along the the mid—continent mid-continent rift rift system. system. The major movements on on reverse reverse faults faults were were after deposition (summarized (summarized from from Kalliokoski, Kalliokoski, 1982). 1982). after Jacobsville deposition southeast southeast (Fig. (Fig. 20c). 20~. sandstones varies from from subarkose subarkose to to quartz quartz sublithic sublithic Lithology of sandstones arenite. There are some some beds of of arkose arkose and and quartz quartz arenite. arenite. Grain size size varies from from fine fine to to coarse. coarse. Quartz grains show show evidence evidence of of volcanic volcanic and and metamorphic origin. origin. Microcline is relatively relatively unaltered unaltered and and plagioclase is is unaltered to to highly altered. altered. Other clasts clasts include: include: volcanic rocks, rocks, schist, the minerals epidote, epidote, biotite, biotite, muscovite muscovite and and chlorite. chlorite. schist, shale and the Sandstone varies in in color color from from red red to to aa cream—white cream-white or or purplish—red purplish-red color. color. The color depends on on the the alteration of of ferromagnesian ferromagnesian minerals minerals and and the the amount of iron oxide deposited deposited as as rims rims on on feldspar feldspar grains. grains. Ripple marked amount of bedding surfaces surfaces and and cross—bedding cross-bedding are are common common in in some some localities. iocalities. Sandstones are fluvial stones fluvial and conglomerates probably represent represent alluvial fan fan deposits (summarized (summarized from from Kalliokoski, Kalliokoski, 1982). 1982). At this this stop stop the the character character of of the the Jacobsville Jacobsville Sandstone Sandstone can can be be seen seen in in The exposures here can be the exposures on the left side of the road. the left side of the road. exposures here can be compared and contrasted to to Jacobsville that that will be seen at Stop 99 and Stop 10. 10. 25.9 the small small town town of of Mason. Mason. Mason was the the site site of company housing Entering the for for the Quincy mill operations operations from from 1890. 1890. 26.5 On the the right right hand hand side side of of the the road road is is an an old old dredge dredge which is is stuck stuck in in in Torch Torch Lake. Lake. This is the the C&H dredge #1, #1, built in in 1913, 1913, bought tailings in by Quincy in by in 1955 1955 and and used used until until 1967. 1967. 26.7 Now we pass pass the the remains remains of of the the main main buildings buildings of of the the Quincy Quincy Mill, Mill, built built in 1890 1890 to to accommodate accommodate steam stamps, required when when the Quincy operation operation in stamps, required the Quincy expanded to to the the Pewabic Pewabic Lode. Lode. 27.0 Along the road on the the left there there are more outcrops of flat—lying flat-lying Jacobsville Sandstone. 27.3 On the right, right, Torch Torch Lake. Lake. 27.7 On the right hand side of the the road road are tailings tailings which have been revegetated. revegetated. These tailings tailings now as we are entering Tamarack City are part of the the mill operation of the the Calumet && Hecla company mines and the the Calumet region region which have major mills located located at at Tamarack Tamarack and and Hubbell. Hubbell. 28.15 On the left hand side of the the road road are the the footings footings from from one of the the Tamarack Mills. MAP 7 28.6 On the right right hand side of the the road road are the the remains remains of a steam steam stamp stamp mill. mill. 28.7 Left turn, turn, going going up up the the hill hill toward toward Stop Stop 9. 9. Follow the paved road road which jogs a little little to to the the left left and and goes goes up up the the hill. hill. �__ _______ p 28 c/ / 5 \\ // ___ __ ___________ // i ''s / / //\ ;o367 /\' // TL 7 TL5 FaLls + 31 f I HIL / -LLVARY EM / 1 \ 36\ 42 MaD88 42 • J Cr C - Lake n en / 'S 'I I, ii' . T I \\\ \ II II II II /7 // 959 'I \ \ \ 12 1Ltp,9 . / mrs 1 \ &çubbell —;: -N ---- .. — •••S" 'so —\N ___--1-_ MapG ( MAP77 MAP \ �43 28.85 Cross the the old Copper Range Range railroad railroad grade. grade. 29.0 Sign indicating indicating Hungarian Hungarian Falls. Falls. This is is the the lower lower part part of of the the falls. falls. Continue going up the the hill, hill, straight straight ahead. ahead. 29.25 Junction of a a four—wheel four-wheel drive drive road road to to the the left. left. Stop and walk Stop here here and towards towards Tamarack reservoir/Hungarian reservoir/Hungarian Falls Falls upper upper part part where where excellent excellent exposures of of Jacobsville Jacobsville Sandstone Sandstone are are found found near near the the Keweeriaw Keweenaw Fault. Fault. STOP 9. 9. Hungarian Falls. Falls. The Keweenaw Hungarian Falls is is located located near near the the Keweenaw Keweenaw Fault Fault (Fig. (Fig. 21). 21). The Fault is reverse fault Volcanics and and Fault is aa reverse fault that that juxtaposes older older Portage Lake Volcanics the In this the younger Jacobsville Jacobsville Sandstone. Sandstone. In this locality, locality, the the Keweenaw Fault presumably dips dips at at a west similar to presumably a high angle to to the west to that that illustrated illustrated in Figure 19, in 19, Stop Stop 7. 7. The The Keweenaw Fault Fault at at the surface surface varies varies from from aa single fault single fault plane to to aa more complex complex fault fault zone, zone, such such as as described described hear near Structural relationship Lac La Belle. relationship of of beds beds near near the the fault fault also varies varies from steepened also steepened dips dips to to folds. folds. In general the the dip of the the In Portage Lake Volcanics and Jacobsville Sandstone Sandstone steepen steepen appropriately appropriately as one approaches the the fault. fault. as At Hungarian Hungarian Falls the At the fault fault contact causes very little little deformation of the Jacobsville Sandstone, the Sandstone, which which is is only only tilted tilted slightly. slightly. To To the west of of the fault fault at this this site site the the Portage Lake Volcanics are unusually shallow shallow If not not viewed in the If the context of of many many other other localities, localities, the the fault fault dipping. might not might not be recognized as such such a a profound feature, feature, and could appear as a a conformable contact. contact. The the fault fault exposure The contrast contrast between between the exposure here here and and that at at the the next next stop stop (Stop 10) at at Hungarian Hungarian Falls Falls is and illusthat (Stop 10) is striking striking and illustrates of rocks rocks along along this this major major feature. feature. trates the the structural variability of The Portage Portage Lake Volcanics near the The the Keweenaw Fault at Hungarian Falls conInterbedded sists of of basaltic lava flows sists flows with interbedded interbedded conglomerate. conglomerate. sediments make make up up aa small small part part of of the of the Portage sediments the stratigraphic stratigraphic section section of the Portage Lake Volcanics Volcanics and and are found found as relatively thin thin widely separated separated beds. beds. However, in the the Keweenaw Peninsula conHowever, here and at some other localities in glomerates glomerates within the Portage Lake Volcanics are either near or at the the fault contact. fault Walking downstream downstream along along the the stream stream to to the the upper upper and and lower lower falls falls allows allows examination of good exposures of Jacobsville Sandstone with cross bedding, of Sandstone bedding, interbedded shaly shaly and and conglomeritic conglomeritic horizons horizons and and many many typical arkosic redred— interbedded typical arkosic bed sedimentary features. features. 29.25 Turn around and and go go back back down down the the hill hill to to Tamarack Tamarack City. City. 29.8 Stop sign. sign. 29.9 Entering Hubbell 30.5 On the right are Calumet & & Hecla mill buildings which have recently recently been taken over over by by Michigan Michigan Tech Tech Ventures Ventures as as aa pilot pilot plant plant location taken location for for small small industries. Torch Lake is is still on the the right with many of the the tailings tailings out in in the the lake. lake. Stamp mill mill remains are straight Stamp straight ahead. ahead. Turn left left on on M—26. M-26. �Ta arack reservoir metal gra Jacobs yule sands tone 100 feet -.- z — fIIs D fault basalt c Ong!omer Figure 21: Geologic sketch map of the Hungarian Falls area (by J.M. Robertson, 1973). Basalt and conglomerate are part of the Portage Lake Volcanics. Note that north is toward the left margin of the page. �45 31.4 Entering the town of Lake Linden. The Houghton County Historical Museum is on the right hand side of the road. The building (1917) was donated by the C&H Company to the Houghton County Historical Society in 1963. Among the best displays are scale models of underground mines and a rich photographic record of the boom copper days. 32.2 Right turn on Ninth Street (the so—called Bootjack Road) in Lake Linden. 32.35 Follow the signs to the Lakes Left hand turn at two blocks after 32.2. This is Gregory Street. Drive—In Theatre. MAP 8 33.3 On the left hand side of the road is the Lake Linden cemetery. The road heads north along the Trap Rock River Valley. On the left hand side of the road at the top of the steep slope is the Keweenaw Fault. On the right hand side of the road is a flat—lying Jacobsville terrane. The Trap Rock River follows another of the glacially eroded, deep bedrock valleys described by Warren (1981). 34.5 Pavement ends. 34.6 The gravel road bears to the right. 34.9 Cross a bridge over the Trap Rock River. 35.0 Left turn at the Trap Rock Schoolhouse. 35.0 Cross the Trap Rock River again. 35.7 Left turn on to another dirt road that begins to go up hill. 36.1 Access to the Cross the railroad grade of the Copper Range railway. Natural Wall ravine for mapping purposes can be gained by walking a couple hundred yards to the left along this railroad grade and then walking along the stream valley up toward the fault line. 36.2 Poor exposures of flat—lying conglomerate beds within the Jacobsville Sandstone on the left hand side of the road. 36.4 Stop by an old wooden sign on the left hand side of the road. 200 meters to the left (south) to the Natural Wall ravine. STOP 10. Walk about Keweenaw Fault at Natural Wall Ravine. The Natural Wall is a bed of sandstone within the Jacobsville which has a near vertical attitude and because it is more resistant, it forms a On the sides of wall which extends outward from the walls of the ravine. the ravine the lithology of the Jacobsville here includes conglomeritic The attitudes of beds in the creek beds, sandstones and shaly horizons. flat—lying to the bottom change from east, to vertical and even locally overturned as the fault is approached. An anticline in the Jacobsville trends parallel to and 300 m east of the fault. West of the fault the Portage Lake Volcanics dip to the WNW at 35—40° (Fig. 22). �__ ______________ 7- II =" 46 -': '-,-; •=/_ rN. '/ - - -- - // _.>c I 0, /ö• - 0 -o ' Co 1 0 ' -, • - (,' I \Pj II '- (O' Cog,' ,,' ,< ' -Co " ,d/ ,-; d' / C 0 // / N' 0- N LU /12'i NN "N\ N • - - p\ -, F / ,,/, - /,,' -\ \\ ci 1 // , MI I, I, - e //4' / ,,,i'</ {7iiir ,,// \-" ,/\ / /IL[=== ci C ' \ —4 'C N ' " I -> (z,I4' , ,,\ k ," ". ,/,, =====' - ) -';tiiiiit V/11 __\\ — , 0- \ i I 17 -I ;3S? __WZZ ii4t - I ' P I - < - - r"N(N - ._:;:_ 4. ITC. - ,, ' 4- 0 - ci / .7 , il? -( _o— Sly) 07 I • — 1 : -I/,wI 0- —_. II 7___ /1/1/7- Co 'C I - ;r' 0 ,/ / - - \. \ ) - -/ // - I t - , NQN ci 0 - �47 . • : -. D / N -V l 'Ii 1 SC LE n thousmds of feet 1) // GN : I CL" HEA G.. 13Wfl1V — I I 11111! 1111 1-II 1111111 U II 111111 Figure 22: Geologic sketch map of the Natural Wall Ravine. Note that north is toward the right margin of the page. 2 �48 37.95 The beginning of pavement, we are entering the town of Laurium. 38.7 Left turn which is followed immediately by a right hand turn at the next stop sign on School Street. 38.8 Turn right. Junction of School Street and Calumet Avenue, which is US—41. This is Calumet, Michigan, the center of the Michigan Copper District, and a site of the Calumet & Hecla headquarters. Here Edwin Huribut discovered the Calumet conglomerate load in the early 1860's and this Greater became the most important ore body in the whole district. Calumet (including Red Jacket, Blue Jacket, Yellow Jacket, Laurium and Among many historic Rambaultown) had a population of 33,000 in 1910. buildings here are the Calumet Theatre (1900) and the C&H Community Library Building (1898). MAP 9 40.0 Entering Centennial 40.3 On the left hand side of the road you can see the Centennial Mine After closing in 1968, this mine was dewatered in the Shaft No. 6. This operation has since been abandoned. mid—l970's by Homestake. The Centennial Mine Shaft Nos. 3 and 6 worked the Calumet and Hecla The ore body lies up dip and northeast from the main ore conglomerate. body in the C&H conglomerate mined by the Calumet and Hecla Mine in the The C&H conglomerate yielded about 4.2 billion lbs. of Calumet area. refined copper, the largest lode in th district and is over one—third of the total production from the Keweenaw native copper district (total district production of about 11 billion lbs.). The C&H lode had the highest average grade in the district of 57 lbs. of Cu per ton of rock treated (Weege and Pollack, 1971). The Calumet and Recla conglomerate can be followed along strike for more Along most of this length it is less than about 1 m thick. than 65 Km. In the Calumet area it averages over 3 m thick and tends to thicken with The bed consists of north trending thicker and thinner zones depth. representing channels. At the Centennial Mine Shaft Nos. 3 and 6 thickness is often less than 3 m and the C&H conglomerate was deposited in The pebbles in conglomerate at Centennial a tributary stream channel. The pebbles in are almost all quartz—feldspar phenocrystic rhyolite. the main channel conglomerate are a quite varied suite of rhyolite and Main and granophyre with some quartz—feldspar phenocrystic rhyolite. tributary channel conglomerates tend to be coarser and contain less fine Outside of the 5—foot thickness contours the material where thicker. bed is usually shaly or sandy. At Centennial, copper mineralization tends to occur in bands with the bed and the intensity is related to the type and amount of interstitial material and location of pinch—outs or Higher grade areas are related to conglomerate with coarse barriers. sand or small pebbles as interstitial material, especially when pebbles Evidence and sand grains are quartz—feldspar phenocrystic rhyolite. also strongly suggests that the mineralized areas follow the axis of stream channels and grade is highest adjacent to the 5—foot thickness contour where the conglomerate bed increases greatly n thickness down These pinch—outs localized ore deposition from mineralizing soludip. Sedimentological relationships are tions that were migrating up—dip. �S. Q. -.7 4i 'J. idO I I, N N k-j: IC 7 /5 "4 -'-—--- —, I( - H I, C. dew b7 �50 important in exploring the conglomerate ore bodies (summarized from Wee and Pollack, 1971). 40.6 Entering Kearsarge, Michigan. 41.1 Stone boat on the 41.3 Right turn onto Water St1 .t just before the Wolverine Market. straight ahead on the main paved road. 41.5 STOP 11 is the Wolverine Mine dumps. There are dumps both on the right and left hand side of the road. The oner on the righL hand side of the road (south), just on the other side of some old buildings, ar somewhat dangerous because of bad ground. Mining in this are.a waS Very shallow (Shaft No. 3). The dumps on the left hand side of the road appear to be (Shaft ice. 2). much safcr Park along the road and walk about 100 in to right hand side of the road. Continue the north. The Wolverine Mine is one of seven different mines that worked the Kear— Centennial, South Kearsarge, &orth Kearsa rge, Ahneek. sarge amygdaloid: Allouez, Mohawk, and Seneca. Production of copper from the Kearsarge amygdaloid began in 1887 and stopped in 1967. About 2.3 billion lbs. of ref -i:ied copper Were produced frccn the Kearsarge amygdaloid making it the second largest producer of the Keweenaw native copper district (Weege and Underground workings are continuous far more than 12 Km Pollack, 1971). and extend down dip as much as 2500 m. The Kearsarge amygdaloid is one of the best documented ore bodies in the district. The Kearsarge flow has been recognized for a distance of around 55 Kit along strike, it lies directly above the Wolverine sandstone. The flow dips between 35 and 40 degt-ees to the northwest (Fig. 23). The interior of the Jt flow is a well developed ophite with a compositi:irI shown in Table 2. has an amygdaloid top that ranges from near zero up to 10 in in thickness. Just below the amygdaloid there is a zone in which the glow is distinctly Abundance and size ol porphyritic with tabular plagioclase phenocrysts. the plagioclase phenocrysts in this zone is variable but they can make up a large percentage of the rock and can be up to 2.5 cm in length. This zone. is probably the result of plagioclise floating during in situ crystallization of the flow. The stratigraphic and textural relRtionships makes this flow wore easiiv recognized than most. The near—surface thickness of the Kearsarge flow clearly shows that the most productive area is where it is thickest (Fig. 24). The flow top in the productive ares is Individual fragments mostly a fragmental amygdaloid (flow top breccia). are generally less than 15 cm in greatest dimension and contain nwnerous small amygdules. The fragmental amygdaloid makes up the uppermost part of the flow grading downward into banded cellular atnygdaloid with arnygdules This grades downward into a zone with fewer abundant at certain horizons. and large amygdules with less tendency to be found in bands and stilt further The amygdaloid top of the Kearsarg flow in downward into massive basalt. the mined area has an average thichness of around 2 rn (summarized from Butler and B'jrbsnk, 1929). �51 I A' A C ln,IIe 4000t1 Figure 23: Geologic map and cross section showing Mine and vicinity (modified from White and others, me Mine Shaft No. 2 dump (see Map 9). Labels are (pi); Calumet and Hecla conglomerate (pc); Osceola merate (pkc); Wolverine sandstone (pw); Old Colony conglomerate (ps). Table 2: Major—element composition of the Kearsarge flow (from Stoiber and Davidson, This is a weighted average exclu1959). sive of the top 12 feet and thus represents a close approximation to the original composition of the flow. the Kearsarge flow, Wolverine 1953). Stop 11 is the Wolver— Iroquois flow, as follows: flow (po); Kingston conglo— sandstone (poc); St. Louis Weight Percent Si02 A1203 Fe203* MgO CaO Na20 1(20 Ti02 MnO H20+ H20— CO2 Total ppm Cu 48.55 16.51 11.54 6.68 9.44 2.82 0.58 1.49 0.18 0.16 2.06 0.63 0.15 100.79 90 �52 300 Thickness 200 feet 100 Top of Wolverine sandstone C) CD 0 CD 0 a CD CD Butler and Burbank, 1929). Figure 24: Thickness of the Kearsarge flow (modified from from This is the near surface thickness along a strike distance of around 35 miles directly to Mandan (Map 20). The thickness is relative to the Isle Royale (Map ) underlying Wolverine Sandstone which is arbitrarily shown as horizontal. Th Chlorite Epidote Microcilne Hematite Prehnite Pumpellyite Quartz Sericite Native Copper Calcite early — TIME late Figure 25: Paragenesis of secondary minerals in the Kearsarge amygdaloid at the Wolverine Mine Shaft No. 2 (Paces and Bornhorst, unpublished data). The relationships are based on a limited megascopic and thin section study of samples from the Shaft No. 2 dump and may be modified slightly as research proceeds. The exact timing of the later minerals are difficult to determine because they do not occur together. �interior. flow Kearsarge the of outcrops find can one dumps 3 and 2 Nos. trace. quartz, and 1; Shaft the of vicinity the In prehnite, 10; epidote, 38; microcline, 51; calcite, minerals: of percentage following the estimated data) (unpublished Stoiber whole, a as dumps 2 and Nos. Shaft the For found. be can copper native with specimens Excellent 1 relationships. paragenetic their and assemblages mineral of variety a see to opportunity the have will you dump 2 No. Shaft Mine Wolverine the At trict. dis- copper native Keweenaw the in bodies ore amygdaloid of complexity the of illustration excellent an is amygdaloid Kearsarge the of area ductive pro- the within minerals amygdule of variation spatial and temporal The Bornhorst). and Paces of data unpublished of addition with 1959 Davidson, and Stoiber from summarized (mostly zones regional the within islands free prehnite and quartz are there that suggests data detailed zones. prehnite and quartz the within lies amygdaloid Kearsarge the Thus, scale regional a On mineralization. copper significant of limit the mark also may microcline of limit The boundary. zone quartz the straddle to appears ore copper richest The zones. mineral the than irregular more much is present copper native of amount The absent. is it until depth with irregularly decreases microcline of amount The depth. increasing with zone quartz the within content quartz in increase irregular an is There zone. quartz the within percent 15 about averages whole a as and depths shallower at percent 10 than less considerably is Quartz 27). (Fig. depth with vary mineralization copper native of grade and minerals amygdule the However, mineralization. copper native of grade the and banding between correlation strict no is There 25). (Fig. samples individual in seen relationships paragenetic the with consistent is This openings. remaining the in calcite of deposition finally and channel the of center the in epidote and quartz by followed channel solution the of parts outer the along first deposited been have would microcline and Chlorite channel. permeable a along moving solution hydrothermal a from minerals secondary of deposition by explained be may banding The 26). Fig. in corner wall hanging (north flow overlying the of base the in found is assemblage last The microcline. ± chlorite—calcite and epidote; ± calcite—microline calcite—epidote; quartz—epidote; microcline; ± calcite ± chlorite layer: amygdular the of top to bottom the mineral major five are from assemblages There bedding. to parallel roughly are bands The Table and 26 (Fig. 3). amygdaloid Kearsarge of bottom to top from minerals amygdule of arrangement banded a is there 3 No. Shaft Mine Ahmeek the In 25). (Fig. chlorite and calcite, copper, native quartz, are minerals formed latest the and minerals formed early are prehnite and microcline epidote, chlorite, Paragenetically spatially. and temporarily both vary assemblages mineral secondary The 1959). Davidson, and Stoiber from (summarized minerals amygdule secondary the with associated occurs copper Native sericite. and laumontite, pumpellyite, prehnite, chlorite, K—feldspar, epidote, calcite, abundant): of amounts lesser and quartz least to (most are whole, a as amygdaloid Kearsarge the in minerals filling space interfragmental and amygdule The plagioclase. replacing pseudomorphically pumpellyite fine—grained of consists basalt lyitized Pumpel— groundmass. cryptocrystalline to fine—grained a in set laths albite euhedral percent 60 about is basalt Albitized pumpellyitization. and albitization alteration: of types two by affected been has basalt top flow The oxidized. well is amygdaloid Kearsarge the in basalt The 53 �54 NORTH SOUTH Ii chlorite-mlcrocline-calcite SCALE Eli:; 10 0 3Oleet 20 copper ,, Contact between Kearsarge amygdaloid and overlying flow bottom Figure 26: Cross section of the Kearsarge amygdaloid showing the banding of amygdule mineral assemblages, Ahmeek Mine, 35th level, 399 to 500 feet south of Shaft No. 3 (from Stoiber and Davidson, 1959). The footwall is the bottom of the Kearsarge flow. Data from the back and walls are projected to a horizontal plane. In one mapped locality Stoiber and Davidson (1959) found a laumontite—quartz—calcite zone. Amygdule mineralogy of the various zones are given in Table 3 below. Table 3: Volume percent of amygdule minerals from mapped assemblages shown in Figure 26 (from Stoiber and Davidson, 1959). Mineral Assemblage Band Chlorite Chlorite— Microcline— Calcite Microcline— Calcite Quartz— Epidote Calcite— Epidote 0—3 45—82 0—47 5—10 0—trace 0—8 0 0 Volume Percent Amydule Filling Chlorite Microcline Calcite Epidote Pumpellyite Quartz 100 0 trace 0 69—74 15—25 0—5 0—1 0 0—6 0—5 1 2 0 2 0 0—1 90—96 0 87 12 0 trace 4—9 1 2 1 �copper SCALE 2 27: 4 SENECA N K (thousands of feet) W Distribution of quartz, microcline and high grade native Microcline present on hachured side of line only -" Lower limit of microcline l?igure A Over 10% quartz on hachured side of line Upper limit of quartz Very high grade copper ore NORTH KEARSARGE AHMEEK MO H ore in the Kearsarge amygdaloid (modified from Stoiber and Davidson, 1959). The Calcite and epidote are present in all zones. Kearsarge amygdaloid dips about 35 to 40 degrees to the northwest. Data from the incline are projected to a horizontal plane. CENTENNIAL WOLVERINE SOUTH KEARSARGE �56 41.5 Continue on the same road and in the same direction as before (.isr), away from Kearsarge. 42.1 There is a dirt road junction to the right, stop here. We are now in the vicinity of Scales Creek, which is the type section of the Scales Creek flow. This Is the sane flow seen at Stop 1, about 14 miles to the south, in Houghton. STOP 12. Scales Creek. This stop gives one an opportunity to look at the Scales Creek flow, a regionally extensive basaltic flow. This is the same unit observed at Stop 1, and it has been traced for more than 150 Km along the Keweenaw. There are outcrops of the Scales Cteek flow on both sides of the main road and along Scales Creek, just to the north and paralleling the road. The Scales Creek flow Is characteristically ophitle. This flow was studied, from drill core northeast of here, by Scofield (1976). The Scales Creek The massive flow has an amygdaloidal top and base and a massive interior. interior of this flow is believed to be for the most part geochemicallv unaltered (Table 4). Mineralogically primary and secondary minerals are present. Modes estimated for the massive interior are plagioclase, 40 percent; pyroxene, 48 percent; olivine, 10 percent; and opaque oxides, 2 percent. Primary plagioclase, pyroxene, and opaque oxides can be found but olivine is pseudomorphically replaced by talc, serpentine, and/or chlorite. In the amygdaloidal flow top no primary minerals are present but all have P]agioclase is been replaced by a suite of secondary alteration products. now albite with some replacement by sericite, chlorite, and puinpellyite; clinopyroxene is replaced by chlorite; olivi.ne is replaced by chlorite, epidote and pumpellyite, and opaque oxides are altered to hematite and sphene. Scofield (1976) has studied these changes in some detail. 42.1 Turn around and retrace route back to US—4l. 42.7 Passing the Wolverine mine dumps, Stop 11. 42.9 Right turn on 115—41 at Wolverine Market. 44.2 Entering the Village of Allouez. We have an excellent view of the southeast side of a prominent ridge. This ridge is held up by the Greenstone flow which is the thickest and volumetrically Largest single flow within the Portage Lake Voicanics. It wili be seen at Stop 14. 44.4 Left turn on a paved road called Bumbletownkoad, just before a Standard gas station. 44.6 Stay on the paved road, bearing right. 44.75 STOP 13. Allouez Conglomerate and flumbletown Hill (Fig. 28). The description of this stop is modified onj.y slightly from White (1971b). The stop begins with a survey of the dumps of the Allouez conglomerate mine (1869—1392, 1300T Cu). �Table 4: Average composition of three samples from the massive part of the Scales Creek flow (from Scofield, 1976). Weight Percent 5i02 47.57 A1203 16.10 Fe203* 12.54 MgO 7.67 CaO 10.00 Na20 2.24 K20 0.29 Ti02 1.43 97.84 Total 0 1000 L Figure 28: Outcrop map of the Allouez—Bumbletown Hill area (White, 197lb). 2000 FEET �58 The lithology of the conglomerate is best studied in the dumps. The largest boulders in this conglomerate are about 2 feet in diameter, and the median size is about 3 inches. A pebble count of boulders mafic rock, more than 8 inches across gave the following results: mostly amygdaloidal, 16 percent; quartz porphyry, 36 percent; feldspar porphyry, 11 percent; granophyre, 37 percent. The greater heterogeneity of this assortment suggests a less restricted source terrane than the one that supplied the Kingston and Houghton Conglomerates in this area; the Kingston, in particular, is made up almost entirely of fragments of quartz porphyry. These dumps are well known to rockhounds as a chryso— colla locality. Thin black veinlets cutting the conglomerate are calcite full of chalcocite dust. From the dump, it is a short walk to the top of the hill, which is an area of exceptionally good exposure and provides an opportunity to see several key units of the Portage Lake Lava Series. One has a unique view of both an area of intensive mining activity and of the general physiography of the Copper Range. From here, on a very clear day, one can see Isle Royale to the northwest. The Huron Mountains lie beyond Keweenaw Bay to the southeast. Bumbletown Hill is on the southwest side of Allouez Gap, a saddle crossing the Copper Range, similar to, but much less prounounced than, the valley at Houghton—Hancock. At this gap, the strike of the lava flows swings, going northeast from about N35°E to N50°E. Fractures and minor faults associated with this bend are probably the reason for the gap. To the northwest, the land slopes off very gradually toward Lake Superior, The southeast as it does through most of the length of the Copper Range. flank of the Copper Range has a steeper slope at the skyline, more or less along the line of the Keweenaw Fault. The low—lying plain between the fault and Keweenaw Bay to the southeast is underlain by flat—lying Jacobs— ville Sandstone. Looking northeast along the strike of the Copper Range, one can see the At Bumbletown cuesta form of the ridge upheld by the Greenstone Flow. Hill, this flow is only 85 m thick; it thickens abruptly to more than 300 m at the near end of the cuesta ridge. To the right of the Greenstone ridge, the more distant hills are upheld by lavas much lower in the section; dips of bedding are steep, and cuesta forms are less pronounced. The amygdaloidal top of the Kearsarge Flow has been the principal producer in this area. The line of shafts along its outcrop is a little more than a mile southeast of Bumbletown Hill, and the bottom levels are almost vertically below the surface trace of the Houghton Conglomerate (see outThis immediate area is unique in that five different and widely crop map). separated layers have been at least modest producers, suggesting a common Stratigraphically highest is the Allouez Conglomerate; plumbing system. dumps of the old Allouez mine (1869—1892, l3,000T copper) lie along the A small headframel200m N65°E of the foot of the hill, 300 m southeast. hilltop is the Allouez No. 3 Shaft, which produced (1944—1964) about l7,000T of copper from the Houghton Conglomerate (No. 14) and 2000T copper from the Iroquois Amygdaloid, 170 m stratigraphically beneath; The large headframe 6200 feet due both were found by diamond drilling. �59 east of the hilltop serves the shaft of the Kingstone Mine; this deposit, discovered in 1962 also by diamond drilling, is in the Kingston Conglomerate (No. 12), 300 m stratigraphically above the Kearsarge Flow. The outcrops on the top and upper slopes of Bumbletown Hill represent a series of andesite flows, some slightly porphyritic. The flows range Unlike the basaltic flows found below the up to 20 m in thickness. Houghton Conglomerate, these flows are not individually very extensive; the map shows two flows pinching out within this small area. As a group, the hilltop are stratigraphically equivalent the flows in the vicinity of whose and lithologically similar to those tops were mined at the Quincy Mine, just north of Hancock. The Greenstone Flow is exposed in a series of outcrops 160—300 m southIts thick amygdaloidal top is exposed at the end east of the hilltop. of a private roadway 200 m south—southeast of the hilltop. Columnar fine—grained basalt and ophitic basalt can be seen in exposures farther down the slope. 45.05 Take a left turn on US—4l and cross into Retrace route back to US—4l. Keweenaw County from Houghton County. 45.9 Entering Ahmeek. 46.25 Junction to Cliff Drive. MAP 10 47.65 49.5 Turn left on Cliff Drive. Passing Seneca Lake on the right hand side of the road. We are driving Along the road are along strike, near the base of the Greenstone flow. several small basalt outcrops mostly on the left side of the road, At this point the Greenstone Flow abruptly thickens to nearly 400 m. It dips northward at about 25° toward the Lake Superior Syncline. This lava flow can be traced along much of the Keweenaw and has been stratigraphically and geochemically correlated with a similar unit on Isle Royale, 90 Km away on the other side of the syncline (see Fig. Thus the areal extent 3a). of this great flow exceeds 5000 and its volume is of the order of 800— 1500 Km3 according to White (1960) and Longo (1983). It rivals the composite Roza flow (Columbia R.) as the largest known lava flow on earth, The Greenstone typically shows spectacularly developed pegmatites, ophitic horizons and columnar jointed areas. A cross section of the Greenstone Flow at this locality and a map of the zone where the flow thickens rapidly The pegmatoid zone is unusually thick in the northern are in Figure 29. part of this map. The ophitic zones of the flow are relatively unaltered portions and Longo (1983) has shown that the composition of these zones are remarkably constant and demonstrated the great chemical similarity of the composition of the Isle Royale and Keweenaw ophitic exposures of The rapid thickening of the Greenstone here was sugthe Greenstone Flow. gested by White (pers. comm., 1982) to be caused by the separation of the upper part of the flow into multiple flow units, which appear to be separate flows. To the north the flow may be a continuous, single flow unit, while to the south it may have been made up of many flow units. �—_ . ,.// ! • • ,•//Moh /7 0 ) / ( - / •1' 2 Io / ) ) �10 I EM 0 7 SCALE 1 mile Figure 29: Map and cross section showing vertical zones within the Greenstone flow between Seneca and the Cliff Mine (from Longo, 1983). I 92 1 2 20 15 225 285 680 (feet) Thickness Vertical Scale: 1"=200' Sub-ophite Pg: 2nd Pegmatoid Zone -Sub-ophite Pg: 1st Pegmatoid Zone LOp: Lower Ophite Pg: 3rd Pegmatoid Zone UOp: Upper Ophite Mel anophyre EM: Columnar Jointed Top of Flow Vesiculated Flow Top �62 MAP 10 and 11 50.0 Crossing the Cratiot River MAP 11 50.6 52.5 We are now driving on the southeast side of a prominent ridge which is held up by the Greenstone Plow. We are at the site of the Cliff Mine which was the first mine in the district. The dumps ind old footings for the mine building are mainly on the 1.eft hand side of the road and the townsite, of which little remains, is on the right hand side of the road. optional stop where one can look at the Greenstone Flow and the Cliff Mine dumps. In this region the Creenatone Flow is mainly ophitic basalt and sometimes shows quite well dev.loped coarse columnar jointing. The Cliff Mine worked the Cliff fissure. The mine operated discontinuously from 1845 to 1887. It produced a tote] of abcwt 38 million The productive portion of the fissure lies under lbs. of refined copper. the Creenstone Flow. The Cliff fissure is nearly at right angles to the attitude of bedding and dips steeply to the east. Most of the mineralization was confined to the fissure although SOL1C amygdaloids were mineralized (Cliff Mine suinmarizedtromsutler and Burbank, 1929). Many large masses of native copper were mined from the Cliff Mine and larger masses weighed up to 100 tons. The large 100 ton mass had to be cut, by hand, into smaller pieces, it could not be blasted (Clarke, 1976). Among the fissures rhr Cliff was the In addition to native copper and silver the followmost productive of silver. caling minerals are found at the Cliff Mine (not in order of abundance): cite, epidote, chlorite, laumontite, prehnite. datolite, thomsonite, chlora— strolite, apophyllite, adularia, gypsum, sphalerite, galena, pyrite and surface oxidation minerals. This is zir 53.1 Tunction of U5—41/M—26. Turn left (north). MAP 12 53.4 Entering Phoenix 54.5 Turn left on a dirt road just before (0.1 mile) the junction between US—41 It is about 100 meters from the paved road to the base of the and M—26. Phoenix Nine dump which is Stop 14. STOP 14. Phoenix Mine and Greenstone Plow. At this stop one can look at the Phoenix Mine dump and the lower ophite of The Phoenix Mine worked numerous veins below the the Creenstone Flow. Greenstone Flow. Like the Cliff Mine discussed at mileage 52.5, the Phoenix t'Iine was one of the. eatltet mines in tze d.Lstrict and opexattd off and cc'. from 1849 to 1917. It produced a total of about 17 million lbs. of refined The Phoenix Mine also worked the Ashbed copper (Butier and Burbank, 1929). ainygdaloid where it is mineralized in the vicinity of vein copper occurrences. The Phoenix Mine dump is notable for halfbreedS (native copper plus native silver) and for spectacular secondary analcite. Other minerals reported in the Phoenix Mine ares (Clarke, 1974a) include: pumpellyite, chlorite, natrolite, chlorastrolite, and apophyllire. �It I -t- /1 -iii - I I - 'I (/ If.-r: V- - I -/2 - // // 'i \ /_ 1;' FJ 'T 'ii L7 I - - C - L -.-. - - -c C: --- - - - // - - -:--- Efri /2- - -- r - -- / -: - • / - : '\-. = — — .1 / (r / . /9GOI H ,/ /7 - - // /I- , / I /2 --r - I ' -I \ C9 �_ oo __ - - 0 '. "/ - ' w. ta - '.;:.' Phoenix Ashbed1.. - Workings ! LI9 -- 0 / - /; 4 - / - r A9i-PhoenIx Mine - K Stop 11' MAP 12 -- �54.6 Flow. Greenstonie the cross and strike to perpendicular drive River. Eagle towards M—26 on left Turn 55.0 flow. the in middle cooling slower the represent which exposures, these on found be can cm 5 to up pyroxenes individual with texture, ophitic coarse Exceptionally road. the of left the to Flow Greenstone the of Outcrops 55.4 River. Eagle along traverse a begin also can one road, the up just 15, Stop At spring. the of periods water high the in done be can't This contacts. flow many at looking River Eagle to way the all here from downstream river the follow can You pools. deep many are there locality this in and road the of site the from m 25 about is River Eagle River. Eagle along seen be can Flow Greenstone the above flows the where stop optional an is This road. the of side hand right the on pull—out a is There 55.7 downstream. or upstream either River Eagle along traverse a begin to possible is it stop this At flow. Ashbed the of north River Eagle in bend sharp very a is There flow. Ashbed the crosses River Eagle locality this In right. the on pull—out road dirt maintained poorly a is There to begin and River Eagle Cross l951b). (l951a, Cornwall by papers in described was Flow Greenstone the of differentiation of petrology and chemistry The Sn Sc 28 Zr Zn Y V Sr 195 259 92 84 14 wt.% ppm 0.14 1.2 0.4 2.1 9.9 7.8 12.8 15.1 46.7 214 104 6 8 186 1680 11 66 Rb Ni Mn La Cu Cr Ba Ti02 K20 Na20 CaO MgO FeO* A1203 Si02 is: (1983) Longo of study from determined Flow, Greenstone unaltered the of composition average The 1877—1887. from 1,000 of population a had which Phoenix, of townsite the of and flow great the of strike the of view a is there Ridge Greenstone the of top the From observed. be all can zones ophitic and subophitic pegmatoid, the cliff the along exposures the following By 30. Figure in shown ophitic lower the is zone ophitic The Flow. Greenstone the of portion ophitic the of exposure spectacular a is there where hill the of top the to climb and ahead Proceed shaft. the above just zones fissure the of one pass then and dump the over up climb must you Flow Greenstone the at look To 65 �1 mIle PHOENIX (Longo, 1983). Figure 30: Section and map of the zonation of the Greenstone flow near Phoenix, Michigan SCALE I 78 540 5 62 8 170 35 25 250 (feet) Thickness I ____. ______ Lower Ophite Vertical Scale: 1"200' Bottom of Flow LOp: Sub-ophite Pg: Pegmatoid Zone _—Pg: Pegmatoid Zone Sub-ophite C' a.' Pegmatoid Lenses with intercalated lenses of ophites and sub—ophites Sub-ophite Pg: Pegmatoid Zone Pg UOp: Upper Ophite Ml: Melanophyric Zone Top of Flow �67 STOP 15. Eagle River Eagle River, Jacobs Creek and Owl Creek each make excellent stream traverses which are regularly mapped as an introductory exercise in the Michigan Tech field camp. At this point, approximately at the Ashbed amygdaloid, a traverse along the stream north to Eagle River allows excellent observations of the upper stratigraphy of the Portage Lake Volcanics. The Ashbed is a very distinctive fragmental amygdaloid traced over a distance of almost 100 Km in outcrop and drill holes. It is the second flow top below the Hancock Conglomerate (Fig. 31 and Map 12). The amygdaloid is a jumble of amygdaloid fragments and interstitial brown, fine—grained detrital material. The secondary minerals filling the amygdaloid are calcite quartz, chlorite and minor epidote. Some vesicles contain minute Exposures of the Ashbed are found both in flecks of Cu (White, 197lb). Small mines were found along this horiroadcut and within the streambed. zon in many places, from Atlantic Mine (near Stop 3) to Copper Falls (Stop 17) The stream traverse to Eagle River traverses the section shown in Figure 31. Among the features seen in the traverse are: 1) excellent sections through individual lava flows showing amygdaloidal tops, and massive melaphyric, 2) Interbedding of sediments glomeroporphyritic or ophitic lower portions. with the lava flows, which becomes more prevalent up section. 3) The occurrences of several dikes which cut the section at low angles. These dikes make up a very small portion of the volume of the section and may be analogous to the dikes described in the Tertiary lavas of eastern Iceland by Walker (1975). If you decide to take this traverse, it's best to to wet feet and the traverse is not advisable in the just resign yourself water. spring because of high The flows just above the Greenstone Flow are compositionally different from Although they are tholeiitic basalt like most of the Portage Lake Lavas. nearly all the PLy, these rocks are distinctly higher in K20 and other inLower in the stratigraphy below the Gratiot compatible elements (Fig. 32). flow another zone of K—enriched basalts occur. This caused Rose and Crimes (1979) to divide the PLV into three cycles of basaltic lavas each of which The cycles may reflect different begins with relatively K—enriched basalts. It is interesting to note that degrees of partial melting or fractionation. one of these cycles begins after emplacement of the Greenstone Flow. 55.9 There is an outcrop of amygdaloidal basalt on the left side of the road. Further off of the road is a rock dump from the Phoenix Ashbed workings (1855—1862, 1913—1917, 400T Cu). 56.6 Entering Eagle River. On the left is the road to Five Mile Point. The stone monument is a memorial to Douglass Houghton who was the first State He did pioneering geologic studies in the Keweenaw Geologist of Michigan. He drowned off Eagle River in 1845. Peninsula. 56.8 Cross Eagle River on the Eagle River Bridge. Park NE of the bridge. �COPPER HARBOR CONGLOMERATE 68 14000 Stratigraphy of Figure 31: the Portage Lake Volcanics above the Greenstone flow in the vicinity of Eagle River and Phoenix, Michigan (from Cornwall and Wright, 1954). Melaphyre Tongue of Copper Harbor conglomerate MelophyreS 13000— Ophihc flows; thickest flow pegmatific Melaphyres flows; thickest flow pegmatitic Melaphyres; thicker flows slightly glorneroporphyritic and ophitic 12000— —Hancock conglomerate (No. 17) gygaloid}t egrained rnelaphyreo, Ashbed porphyritic Melaphyres; thicker flows glomeroporphyritic and pegmatitic melaphyres, porphyritic lomeroporphyritiC flows Upper chill zone Greenstone flow PORTAGE LAKE LAVA SERIES �• .S •5 S .•• S • • • S. S • S S I • S S S. •• S • S •S S S S. S •. •S ::, S S. S. ••S. S • S • •S • S • • 2 S S S • 1(20 3 ' S M-O 5wt% 75 50 - 25— No. S •• • S S :. S S S S S . S • S :S. S. •5 S S • S S S • S S S S • S •:. S 55S • S S S S S S. • .2 S S S S • S .3 P205 I .4 .5 GS wt% top) sampled Figure 32: Plot of K20 and P205 content of 106 individual PLV flows in stratigraphic order (1 in drill holes across the section in the vicinity of Delaware by W. S. White (pers. comm., 1976) and reported GS represents the Greenstone flow horizon, M—0 represents the melaphyre—ophite line, by Rose and Grimes, 1979. a texturally traceable line in the PLV below the Gratiot flow in this area. The stratigraphic position is plotted by flow no. and is not to scale. 75. 50 25 No. S S 1 I �70 STOP 16. Eagle River Falls. The falls occur at the contact between the top of the Portage Lake Volcanics and the base of the Copper Harbor Conglomerate. There are some spectacular If the water is low, like it is potholes that have developed on this face. sometimes in the summer, you can see ropy surfaces on flows at the top of The contact dips about 30° NNW. The contact the Portage Lake Volcanics. relationships suggest very little erosion between the flow and deposition Under the bridge one of the basalt beds of the Copper Harbor Conglomerate. can get a good view of the lithology of the lower part of the Copper Harbor It consists of mostly rhyolite pebble conglomerates but inConglomerate. cludes many sandstone and even some shaley beds. There is an optional route to Eagle Harbor via Sand Dunes Drive given after the Garden City road log. NOTE: Eagle River to Eagle Harbor via Garden City Road MAP 12 56.85 Go straight after crossing the bridge. M—26 goes to the left which is the optional route. Passing in front of the Keweenaw County Courthouse and offices. 57.1 Gitche Gumee Bible Camp, continue on paved road. 57.2 Pavement ends. MAP 13 60.2 This is the Garden City Road. Junction with paved road. Turn left towards Eagle Harbor. 60.3 Cross Jacobs Creek. 60.5 Junction of a dirt road on the left. Continue ahead on paved road. From this road, a short distance to the west, there is access into Jacobs Creek, at the site of the Arnold Mine, along the Ashbed amygdaloid. This is the end of a traverse one can make across the upper part of the Portage It is recommended to begin the traverse at the lower end Lake Volcanics. of Jacobs Creek where it crosses M—26 (Sand Dunes Drive optional route to This is a very tough traverse with many steep and dangerous Eagle Harbor). There are excellent exposures of many individual lava points within it. At the Arnold Mine, one of the nearly conformable flows along Jacobs Creek. Geologic traverses made along massive dikes is exposed in the streambed. ahead), and Jacobs Creek allow Eagle River (Stop 16), Owl Creek (Stop 17 lateral variations in the upper part of the Portage one to look in detail at Lake Volcanics. �\\\\\ 71 — 1 :,, '' \" 'I J• I \\; ' lHwtl 0 . . 4. £L - Coooer Harbor Corg!omes an k ( ' \\ i \\ - MAP 13 I - 11 k I; �72 61.2 On the left is a roadside park with a tower. From the top of this tower there is an excellent view of Isle Royale on a clear day. You can also see some of the ridge—valley topography due to the dipping lava flows and conglomerates in this part of the section. 61.9 Dirt road that slants to the right goes to the old townsite of Copper Falls. Copper Fails was settled in about 1846 and had a population of 500 in 1877. Today there are a handful of residents. 62.2 Cross Owl Creek. 62.3 Road to the right goes upstream to the dumps of the Copper Falls Mine which is part of Stop 17 described below. 62.4 If you follow this road several hundred Road to the left goes downhill. meters, you will reach the 30—mile stampsands which are the tailings dump from the Copper Falls mining operation. From this stampsand you can gain access to the bottom of Owl Creek and can begin a one—hour traverse upIf you continue upstream beyond stream to the bridge along this road. the bridge, you will reach poor rock dumped along Owl Creek from the Copper Falls mining operation. By climbing out of the creek bed, to the east, one can reach a dirt road which will come out on the main road at 62.3 STOP 17. Owl Creek — Copper Falls Mine. Owl Creek is another one of the streams that cut across the upper part of The traverse begins downstream where the base the Portage Lake Volcanics. of the Copper Harbor Conglomerate and top of the Portage Lake VoiLcanics interfinger. There are excellent exposures of interbedded conglomerate! There are sandstone and lava flows along the bed and sides of Owl Creek. several well exposed amygdaloidal flows. The Copper Falls Mining Company worked several fissures and the Ashbed The mine operated from 1847 to 1893. It produced about 18 amygdaloid. million lbs. of refined copper from the Ashbed amygdaloid and about 9 Copper Falls million lbs. from fissures, mostly the Owl Creek fissure was the only mine in the north end of the district above the Greenstorie flow that paid dividends but was not a profitable venture (summarized from Butler and Burbank, 1929). The Owl Creek vein starts near the base of the Copper Harbor Conglomerate and extends through the Portage Lake Volcanic Series, probably into the Greenstone flow. The vein was productive only in the vicinity of the Ash— bed amygdaloid. The Ashbed flows are distinctly porphyritic. The amygda— bid is scoriaceous with a notable clastic component. In some localities The mineralpebbles and boulders of amygdaboid are set in a sandy matrix. ization of the Ashbed amydgdaloid is similar to that found in other amygda— bids in the Keweenaw Peninsula. At the Copper Falls Mine the more abundant minerals are: calcite, quartz, epidote, and pumpellyite. Datolite is abundant in the Ashbed near fissures. Datolite is abundant in fissures Native copper was more abundant toward the top part of such as Owl Creek. the deposit. Other minerals reported in the Copper Falls area include: �73 laumonitite, prehnite, native silver, adularia, analcite, apophylite, faugasite, natrolite, stilbite (summarized from Butler and Burbank, The Copper Falls Mine is stratigraphically one 1929; Clarke, l974b). highest in the Keweenaw native copper district and is near the top of the pumpellyite zone (see Figs. 4b and 9a in the Introduction). MAP 14 63.75 63.85 Crossing Eliza Creek There is a dirt road that goes off to the right. From this dirt road just a few hundred meters up hill you can begin a traverse upstream on Eliza Creek to get the exposures of the Portage Lake Lava flows of this region. 64.9 We are at Eagle Harbor where we join back up with M—26. Turn right on M—26. Eagle River to Eagle Harbor via Sand Dunes Drive (M—26). MAP 12 o At Eagle River Bridge make a sharp left turn, follow M—26. 0.1 Sharp right turn. MAP 13 3.05 Jacobs Creek Falls. From this point one can begin a traverse up Jacobs Creek that ends near the Arnold Mine on the Garden City Road (mileage There are excellent exposures of the upper part of the Portage 60.5). For those who are hardy, the stream Lake Vol.canics along Jacobs Creek. offers virtually continuous exposures through thin pahoehoe flows, especially in the first several hundred meters. This is a steep and rough traverse, and should not be attempted in high water periods. 4.9 Great Sand Bay. 5.9 The Lake Shore Traps form the offshore ridge. The Lake Shore Cat Harbor. Traps are mafic lava flows interbedded with the Copper Harbor Conglomerate. MAP 14 7.8 Right hand turn by the Eagle Harbor Store. 8.0 We are at the Junction of M—26 and Garden City Road Route. Return to Main Road Log Mileage. Stay on M—26. �/ - ( I - - - C..-;. *i . etC r Lake Superior - - '"1 it /// .. ( . / ci' iI - 41" 63gke ':yh ff \ ag H / I 8/AST GUARD O8 \..( GLE HARBOR (32 S ____ - . z-- .. �75 65.0 65.75 MAP 15 66.9 67.5 67.65 The harbor at Eagle Harbor is controlled by the occurrence of units which These are basalt flows which are inter— are called the Lake Shore Traps. bedded with conglomerates of the Copper Harbor Conglomerate and form typiThere are excellent exposures of the Lake Shore cally resistant ridges. Traps that occur at the Eagle Harbor Marina and continuing along the shore through Grand Marais Harbor and into Agate Harbor and eastward through small boat from the Copper Harbor. These are accessible by canoe or winds are on—shore. Marina, but don't try it if the Junction to the left to the Eagle Harbor Marina. Continue ahead on M—26. On the right hand side you can see the offA view of Grand Marais Harbor. shore islands and ridges which are controlled by the occurrence of the Lake Shore Traps. We are driving along a conglomerate ridge. this Road passes along the shores of Lake Bailey on the right hand side of Harbor Conglomerate conglomerate ridge. The ridges throughout the Copper the valleys are underlain by the tend to be held up by the conglomerates, On conglomerate. and shaley members within the more easily eroded sandy The (on the right) is Mount Lookout. the opposite side of Lake Bailey Vol— contact between the Copper Harbor Conglomerate and the Portage Lake canics runs through the back side of Mt. Lookout. sandstone On the left hand side of the road there are exposures of the members of the Copper Harbor Conglomerate. NAP 16 69.1 69.2 69.7 70.0 Crossing the Silver River there are excellent exposures of the Copper Brock— Harbor at this locality and along the left hand side of the road up look at the Copper Harbor way Mountain. This is an optional stop to At Eagle River Falls (Stop 16) one had the opportunity to Conglomerate. At this locality look at the basal beds of the Copper Harbor Conglomerate. of the formation, just bewe are stratigraphically in the more central part (20) one low abundant interbeds of Lake Shore Traps. At an upcoming stop The formation. will get the opportunity to look at the upper part of the of other stops. lithology of the sediments here can be compared to those the summit On the south side of the road at this stop a 3 Km trail leads to in the of Mt. Lookout (Map 15), one of the most spectacular viewpoints contact The summit is located on conglomerate, but very near the Keweenaw. with the Portage Lake Volcanics. Allow at least 1½ hours. this Junction to Brockway Mountai1 Drive. We are going to come back to Go to Park. point but we are going to first take a side trip to Esrey the left on M—26. shallow dipping We are now at the shore of Lake Superior where there are approxilava flows of the Lake Shore Traps. The road follows the shore mately parallel to the strike of the lava flows. STOP 18. Esrey Park. �___ ti del4f SI. dVV\I - - _; 3 3 - I p O4 • . —:- - .. ---— - —-I i20° - — - - _- ____________ — C- ——- S I - .. -. - )) Th of magflet .— Approxtmate posItlOfl °I/ .D - 1ff yi pa qtl V �- /_ \ * I r copper Copper L - _i_=-i j' - _ : - -— rbOr. -- - - - 4-.••• - 20 ,.:—.--—:- — ., Shore TrapS. _—- ,— -A Ashbed I T1ZH hc -.-- e -TiLak •:. ! ngtOmC rate ——-— - catedbY2lrb0 _____ tl / _______ - - _ �78 The rocks cropping Out at Esrey Park are lava flows of the Lake Shore Traps. The Lake Shore Traps consist of a number of lava flows interstratified within the Copper Harbor Conglomerate. The Lake Shore Traps extend from the tip of the Keweenaw Peninsula west and south to just north of Hancock. They lie stratigraphically near the middle of the Copper Harbor Conglomerate. They consist dominantly of mafic flows similar to those of the Some intermediate compositions have also been Portage Lake Volcanics. reported. The Lake Shore Traps represent the waning stages of Keweenawan volcanism in the Keweenaw Peninsula. Several of these flows have been traced offshore by prominent magnetic anomalies. The large outcrop between the parking lot and the lakeshore is the massive interior of a fine grained basaltic flow which strikes approximately parallel to the shore. The flow's amygdaloidal top can be observed along the lakeThe metamorphic grade of these rocks is substantially shore to the east. lower than that of the Portage Lake Volcanic Series, i.e. within the zeolite zone. Note the "fresh" appearance of massive interior basalt (with olivine phenocrysts) and the low temperature amygdaloidal minerals (in order of calcite, chlorite, laumontite quartz, adularia decreasing abundance): and analcite. 70.1 Turn around and head back towards the junction of Brockway Mountain Drive. 70.9 Sharp left turn onto the Brockway Mountain Drive followed by some more exposures of the sandy conglomerate zones within the Copper Harbor Conglomerate. We will drive for several kilometers along a conglomerate ridge with many conglomerate exposures. MAP 17 75.9 At the summit of Brockway Mountain we take a right turn a short distance to the observation site. STOP 19. Brockway Mountain Viewpoint. This high conglomerate ridge reaches an elevation of over 1300 feet and is one of the best known tourist stops in the whole Keweenaw. Excellent views of the ridge and valley topography of the northern shore of the Keweenaw can be had here, because the scrub vegetation allows a 360° panorama. The conglomerate here dips at about 20° to the north. To the west the Lake Shore Traps form prominent drowned ridges in the vicinity of Esrey Park. Lake Bailey (with the small island) and Lake Upsom occupy a topographically low valley of finer grained clastic sediments within the Copper Harbor Conglomerate. Just to the south of Lake Bailey the conglomerate ridge of Mt. Lookout can be seen, marking the contact between The inland the Copper Harbor Conglomerate and the Portage Lake Volcanics. lake almost directly south is Lake Medora, and just beyond the lake is a prominent ridge which marks the stratigraphic position of the Greenstone flow. In the distance, farther to the south across Lake Medora, Mount To the southBohemia (Stop 21) with a fire tower on top can be seen. west a distant ridge with white Air Force tracking buildings on it, marks Gratiot Mountain, which is underlain by andesitic dikes and small rhyolite bodies. To the east, Copper Harbor is visible and Lake Fanny Hooe (see Map 18) which occupies the same stratigraphic horizon as Lake Bailey. Beyond Copper Harbor to the east, East Ridge, a conglomerate ridge, is To the north, on the skyline 65 Km the prominent hill on the skyline. away is Isle Royale, easily visible on a clear day. The skyline of Isle �8- Map 16 _ —-- er — -- —--- i_ I 9 ( - Dans P9int N. _J I Lake Shore Tr,ps 26 __-1 —-- — -—--—- (3 — —c- - — et L - Stop 20 —= - - I /077 — Harbor — - — : 26 - - —- 4 Su;_5Or ILake —t . — ••- -- I -- -i_s -e I'.. —. .---.. - '''c —— — p /1) ( i— ) — -I --_----- ——. — --- - '.— —— —- .•1. .f.. .••\ '.4—.. 2! ..ii&' ) :jt .SM.c14— •Q=__ aSr.'; t .-..'—- — "••• SV,.fl -—__75 :nrftt - —-;. — _ ____ �80 Royale is the Greenstone Ridge, underlain by the Greenstone flow, which is apparently a continuous unit all the way from one side of the syncline to the other. It may be the largest single lava flow on earth, with a volume of more than 1500 Km3 (Longo, 1983). 75.9 MAP 18 79.45 80.5 MAP 17 81.7 83.35 We turn to the right and follow the road straight ahead toward Copper Harbor now going downhill and continuing along the ridge with excellent views all the way down. There is a pull—out on the right hand side of the road to give an excellent Copper Harbor is controlled by view of Copper Harbor and Lake Fanny Hooe. The islands offhsore including the occurrence of the Lake Shore Traps. Porters Island are underlain by lava flows. From the Copper Harbor Marina, with a small boat you can have access to excellent exposures of the Lake Shore Traps along the edges of Copper Harbor. There are exposures of the Copper Harbor Conglomerate along the road descending into Copper Harbor. Junction at M—26, turn left. We come to the shore of the lake again at a place called the Devil's Washtub. If you stop here by the right hand side of the road and take a short walk along the conglomerate along the shore, you come to wave washed exposures of the conglomerate at the Devil's Washtub. STOP 20. Dan's Point. There is a small gift shop observation tower on the right hand side of the road. Walk just a few yards down to the shore of Lake Superior to look at the lithology of the Copper Harbor Conglomerate and the occurrence of stromatolite in well exposed and wave washed exposures. Dan's Point consists of a lakeshore outcrop of Copper Harbor Conglomerate that is characteristic of the upper two—thirds of the formation (sometimes called the Outer Conglomerate). As a whole, the Copper Harbor Conglomerate is a red—brown, basin—ward thickening wedge of volcanogenic clastics which attains a maximum thickness of 1830 m (Daniels, 1982). A coarse conglomerate facies consisting of well—rounded, poorly sorted clasts of mafic to silicic volcanic rock fragments directly overlies and locally interfingers with the lavas of the Portage Lake Volcanics (Elmore, 1981). The conglomerate facies is generally clast—supported and contains a ratio of mafic to silicic intermediate clasts of about 2:1. The Copper Harbor Conglomerate fines both distally and upsection so that sandstone interbeds become more frequent in the upper two—thirds of the formation. Sandstones are predominantly subangular to angular lithic graywackes which exhibit current—ripples, festoon trough—cross beds, parting lineations and dessica— tion features. Laminated crystalgal carbonate horizons are interbedded within the conglomeratic and sandstone facies in the upper two—thirds of the formation. Stromatolites occur as laterally—linked drapes over cobbles, as laterally—linked contorted beds in mudstone—siltstone lenses and as poorly developed mats in coarse sandstone (Elmore, 1981). �81 The depositional environment of the Copper Harbor Conglomerate has been interpreted as a prograding alluvial fan complex (Fig. 33) with proximal— to—distal braided stream and sheet flood facies on coalesced alluvial fans and sand flats (Elmore, 1981; Daniels, 1982). Isolated cryptoalgal carbonate and ooid lenses formed in shallow, medial fan lakes receiving very low rates of sediment influx (temporarily abandoned stream channels) (Elmore, 1981). Paleocurrent indicators suggest sediment transport was from the southeast to northwest indicating that a basin was located toward the center of the rift zone (Daniels, 1982). The stratigraphic section of the "Outer Conglomerate" (that part of the Copper Harbor Conglomerate above the Lake Shore Traps) exposed at Dan's Point consists of about 80—90 ft. of interbedded conglomerates and sandPredominantly clast—supported conglomerate beds consist stones (Fig. 34). of rounded, cobble—to—small boulder—sized clasts with a matrix of coarse sand—sized sub—angular grains cemented with iron oxides. Conglomerate clasts are predominantly felsic volcanics (approx. 70%) with sub—ordinate basalt, pyroclastic, plutonic and metamorphic lithic fragments. Several silty—sandstone interbeds higher in the exposed section exhibit cross— bedding, current lineations, ripple marks, parting lineation and (reduction spots along bedding. In particular one should note the white stromato— lite (genus Colleria) horizon draping cobbles about one—third of the way up the exposed section. Algal growth occurred during a period of depositional quiescence and was halted by an influx of silty material followed by renewed conglomerate deposition. Please do not remove stromatolite from the outcrop. Good specimens can be found in the pebble beach. 83.35 MAP 18 86.65 87.1 Turn around and go back toward Copper Harbor on M—26. To the left is the junction Junction, again, to the Brockway Mountain road. to the Copper Harbor Marina. Continue straight ahead on M—26 to Copper Harbor. Junction between M—26 and US—4l in Copper Harbor. out of Copper Harbor. Turn right on US—41, south Copper Harbor was suddenly a boom town in 1843, following the discovery of Porter's Island was the site of the first governcopper in the vicinity. ment land office and in 1844 Fort Wilkins was built on the shores of Lake Fanny Hooe, to protect the miners from potentially hostile Indians. The lighthouse was built in 18o6. Fort Wilkins is now a state park with campMuch exploration activity took place in the ing facilities and a museum. fort and there are shafts and exploration pits immediate vicinity of the all along the land between Lake Fanny Hooe and the Harbor, mostly from In 1853 and for several decades thereexploration in the 1843—46 period. after mining activity took place south of the fort in a series of workings called the Clark Mine. The mineralization is of the fissure and amygdaloid type and consists of prehnite, epidote, analcite, quartz, laumontite, adularia, microcline, chlorite, datolite, calcite and several copper minerals including chalcocite, cuprite and tenorite as well as native copper. Agates are conspicuous in the amygdaloids here, and the area is well known for datolite collecting. One occurrence of manganese minerals in a fissure The manganese minerals found accounts for the name of Manganese Lake. brannite and manganite, orientite. The Estivant here were pyrolusite, of the Clark Mine lands which were deeded to Pine tract represents a part are now a nature preserve, containing some of the C&H Company in 1942 and Upper Peninsula. the last virgin pine tracts in the �L — -S. Cover P'-.. •.. . •• 963 W.AW __ -S ••. • ••- • . Copper :' - LL$i :;/ I• I /* • -, Shore p-----: •; - Lake tTTTTT+ Copp.r H - 4. • erJiarbr Lake Superior J z. HAYS — .) EXPLORATION Copper I 1 Copper Hao< _ '- .) --- ---- . !/ ;,j. �1982). Daniels, from (modified deposits stromatolitic containing lakes ephemeral shallow and deposits plain flood and stream braided fans, alluvial coalescing showing Conglomerate Harbor Copper the of environment depositional of cartoon Schematic 33. Figure — BAStNwARD 83 �I I I I I — IJj i: (T\ ; oooo00oqo;.ooy %o6,°fJ.. 0o:0 P ooj°Q4 ! I Ili. 9# I t'•' C' T rt CD C) CD CD- CD-. H- H. rtt)Q 0 o CD CD I H.t) H- t CD rl- CD CD H H- Fij 0 H. C -1 CD L) -C-- CO '-'1 CD C) CD CD- CD-. CD o '-1 oCDo CD- d 0 H. C 0 H- H- rrDrtCD '—j H- !10 00 H. H. (I) H- OC) H. rt H C o-r CD CD 0(J) H.H CD- CD CC rtH 00CC CD CD- 0HCD H- H- H- 0 0 rt H. C Hrt rt CDC) C) oCDCDCD CD CC H. 0 o o C)CDH H 0(000 0 C) CD CD OH CQ 0 H. CDHCD CD (I) H. CD rt HO -0 oCD 0 o- H. o H H H. HO 0C) 0 H- CI)—. CD c 00 (DrtC) H H. CD CCCD C CD-. C) CD CD H.CD 0 0 rt rt H- H. CD �85 Keweenaw Point, Horseshoe Harbor, East Bluff and other points of interest can be reached by taking an unmarked dirt road which goes eastward from the end of US—41. This road is rough and poorly maintained and may be followed around to Mandan. Horseshoe Harbor has excellent exposures of the Copper Harbor Conglomerate (Fig. 34). 88.2 MAP 19 91.45 MAP 20 94.3 94.55 MAP 21 97.3 MAP 20 101.4 101.6 Nice exposures of the Copper Harbor Conglomerate to the left of the road as we are going up the hill. Lake Medora on the right hand side of the road, Junction to the left to Mandan. Mandan now is only a few houses, it had 300 residents in 1910. Continue ahead on IJS—41. Road to the left. This is the entrance to the outer portion of the Keweenaw Peninsula, all on poorly maintained dirt roads. To visit Mount Houghton and Keweenaw point, you may exit here. Junction of the road to Lac La Belle, Turn left and continue to Stop 21 at Mt. Bohemia. If you wish to skip this stop, you may jump ahead to mileage 105.45. On the left hand side of the road is a large outcrop of amygdaloidal basalt of the Portage Lake Volcanics. These exposures are flows in the lower part of the formation below the Scales Creek flow (see Fig. 4 and in the Introduction). Dirt road turning off the main road to the left. This is STOP 21 at Mt. Bohemia, It is about one half mile walk up this road to. the summit of Mt. Bohemia; this is a four—wheel drive vehicle road. STOP 21. Mt. Bohemia. An intrusive body of diorite and granophyre crops out on the south slope of Mt. Bohemia. The majority of the intrusive body is a massive, medium— grained, miarolitic diorite. The major constituents of the diorite, are oligoclase and hornblende with lesser amounts of orthoclase, magnetite, uralitized augite, apatite, sphene, quartz, sericite, epidote, chlorite, and calcite. The later are alteration products or are introduced secondary minerals. The central core is a fine— to coarse—grained, miarolitic granophyre. The major constituents of the granophyre are albite, quartz and granophyric intergrowths of quartz and feldspar with lesser amounts of orthoclase, sericite, hornblende, apatite, sphene, magnetite and chlorite. Miarolitic cavities are lined with quartz, albite, calcite, chalcopyrite, and chalcocite (summarized from Cornwall, 1954). The Mt. Bohemia intrusive body yielded a Rb—Sr age of 1,130 ± 35 m.y. (Chauduri and Faure, 1968). The diorite and granophyre at Mt. Bohemia intrude basaltic lava flows of The basalts are slightly the lower part of the Portage Lake Volcanics. metamorphosed at the contact. The intrusive body is cut by the Lac La Belle This fissure is mineralized with fissure which trends north—northwest. copper sulfides, mostly chalcopyrite and bornite and in gangue of calcite, chlorite, and quartz (summarized from Juilland, 1965). �P —— _ ( Dl / 4r? 4 — / p 6 \ / - 'P E4 ' p \ai\ L0 ON pg - - • 0 .•, ) /- .5, - /000 S — J/ .• Map 18 �''' p — • -- :TI 'I -; I ,;.. - - • '------—4\1— _j '/ K __\ / 3Yk. - Flow Sci K * Stop 21 :...' ...P 20 7 — �MAP 21 -— = - - - I —___ I V = 1 = — - -I — E) ) MF35N / —- Rv er // • ' - — t/ I 7-IS --- • • ap23 •• 'P24 Map 20 I a \ I --:- / t Ifft /080/P\ \ ---------- - :\i - .-;: - _ (1 �89 Andesitic dikes are found in the vicini.ty of Mt. Bohemia (Fig. 35a). They average about 5 m in thickness. The dikes intrude flows of the Portage Lake Volcanics, two flow tops are shown in Figure 35a as alpha and beta. The dikes and amygdaloidal flow tops carry copper sulfides. Copper sul— fides in other parts of the district are found typically as fracture fillings. Native copper is typical of amygdaloids. A variety of secondary The and opaque minerals are found in the dikes and flow tops (Fig. 35). paragenetic sequence is consistent with that for the other deposits in the district (compare Fig. 35c and Fig. 9b in the Introduction). Copper sul— The copper and sulfur in this occurrence fides are paragenetically late. is believed to be of direct magmatic origin related to the magma source that produced the andesite dikes and Mt. Bohemia intrusive body. The emplacement of flows, subconcordant faulting and chronologic sequence is: fracturing, dike emplacement, renewed movement along subconcordant breaks, regional low—grade metamorphic/hydrothermal alteration, minor folding and faulting, and sulfide mineralization (summarized from Robertson, 1975) The road Up to the summit of Mt. Bohemia crosses flows of the Portage Lake Volcanics. The diorite and granophyre intrusive complex crops out to the southeast of the summit. Intrusive stocks are not common in the Keweenaw Peninsula, Most of these occur in the lower part of the Portage Lake Vol— canics and are rhyolitic in composition. Mt. Bohemia is the only occurrence of a diorite stock in the Keweenaw Peninsula. OPTIONAL SIDE TRIP TO Lac La Belle Discussion of complex relationships along the Keweenaw Fault and the Keweenawan rhyolite bodies, Go straight ahead (south) towards Lac La O At turnoff to Mt. Bohemia. Belle down hill. O4 Junction of roads to left and right at Lac La Belle. MAP 21 To Bete Grise turn left. (See Map 22) Bete Gi se is located on the shore of Keweenaw Bay on the Keweenaw Fault. Along the shoreline east of the point where the road reaches the shore are several exposures of the Keweenaw Fault which crosses on and off These may be visited in canoe or small boat. Also shore several times. to the east are several of the rhyolite bodies which are chiefly found in the lower part of the Portage Lake Volcanics. Three tenths of a mile north of Bete Grise, four—wheel drive road continues east of the paved road to Smith's Fisheries. The road intersects the Bare Hill Rhyolite body, a shallow Beyond the end of the road at Smith's Fisheries a trail continues intrusive. eastward along the shore to the mouth of the Montreal River. From here one may traverse up river to several falls over fine outcrops of basaltic flows or continue along the shore to the Fish Cove Rhyolite, a compositionally zoned shallow intrusive (Bornhorst, 1975). Inland and not far from Bete Grise is the Mt. Houghton Rhyolite. This is an extrusive rhyolite dome �14 55 495I 18 I /48\ 43/31 \ 'i2 47 32' 46 ._—-- 34 22A7flh777/' _____jB 36< 37 6 I g8 7 25 ffflaTImffl1/7"° 4 50 Lac La Belle Fissure - 60 0 EM DIIHe —-.40 Amygdaloid - °jk \-c'-\ v-s, <j r--,1 64 I 7___2t1 Mt. Boheiat'\ .Oiorite,>vt\ \ __-c 56.54 — 61 FIRE TOWER \ 0 loo2oo Amyqdoloids and dike projected to 1300 elevation - )iogy and drQ hole locations in the Mount Bohemia area (modi - from a preliminary Calumet and ilecla Mining Company map). Secondary minerals MINERAL Chlorite Vesicle- Frocture- fillings fillings in dike matrix 0 Epio'ote Quartz 0 0 0 0 ca/cite 5cr/cite Pumpe//y/te Microc/ine o 0 - o Hem Pyri 1, Cc, su/fides Noth Copper - Common o G Minor Nonpyrogenic 0 Rare 0 —Absent Minerals in the DPis MINERAL Pyrogenic I Deuteric Hydrothermal Supergene Magnet/fe Chlorite Pumpe//ylte 3cr/cite .- 'ucrt Microc/ine Su/idj Cha/capyr,te Ga/eva 5p/,o/er,fe ——— Epidote Colch Hei I, Hematite Z Pyrite —— —— — —— ti ——-—— ——— —— P2 ietic sequence of secondary minra1s in the dikes. Pink born,te Purple born/fe Diqenife Ojucleite Cha/coc/te Hematite I.E Cove/life —-— Paragenesis of opaque minerals in dikes and flow tops at Mount Bohemia. Figure 35: Geologic map showing andesitic dikes near Mount Bohemia and occurrence and paragenesis of secondary and opaque minerals in the dikes (from Robertson, 1975). �Y) 1 I I FauI.' Creek e I', r0 Houghton ,. ,iJ \'_ �92 with prominent flow banding and block and ash flow deposits on its flanks. Mt. Houghton is best approached from the Mandan Road (Map 19). Rhyolites make up less than 1% of the mass of the Portage Lake Volcanics Considerable textural variety of as seen in outcrop on the Keweenaw. rhyolites are found including intrusive and extrusive rhyolite and even But the abundance and variety of rhyolitic boulders small ignimbrites. and cobbles within the interflow conglomerates demands that a large number of rhyolitic source areas must underly the Jacobsville south and east of the Keweenaw Fault. To Gratiot River. Turn right and proceed ahead 1.2 miles on paved road. At the west end of Lac La Belle, in the vicinity of Deer Lake, the rocks south of the Keweenaw Fault are Portage Lake basalts (Fig. 36). These rocks may represent the lowest stratigraphic horizons exposed in the The area has been studied by geological and Portage Lake Volcanics. geophysical methods by DeGraff (1976) and his model for the development It is still of this unusual feature is shown graphically in Figure 36. another example of confusing deformation which is typical of this great A traverse down the Little Gratiot River from the Lac La Belle— thrust. Gay Road crosses many outcrops of the basalts. The fault—bounded, tilted body of Portage Lake Volcanics was defined by dense array of magnetic and gravity profiles and a few key drillholes, The attitude of the beds was altered by the faulting, but the rocks, like the rest of the Portage Lake Volcanics, have normal magnetic polarity. AFTER OPTIONAL SIDE TRIP to Lac La Belle return to main road log. MAP 21 101.6 At Mt. Bohemia turnoff. 105.45 Back at the junction of US—4l, 106.5 Dirt road to the right goes to Stop 22 at the Delaware Mine. on the dirt road and follow the signs to the Delaware Mine. 106.2 STOP 22. Turn around and retrace route back to US—41. Make a left turn towards Mohawk. Turn right Delaware Mine. The Delaware Mine, first known as the Northwest Mine, has had a long and It was operated by various companies from about unprofitable history. The mi:ie mostly worked veins for mass copper. Three shafts 1847 to 1887. were opened in 1881 to mine copper from the Allouez Conglomerate (#1, #2, The Allouez Conglomerate was seen at Stop 13. Total production from #3). the Delaware Mine was about 7.5 million lbs. of refined copper. As with other vein deposits in the Keweenaw, the Delaware Mine is a notable locality for datolite. Other minerals reported from the Delaware Mine poor rock piles include (not in order of abundance): chlorastrolite, prehnite, calcite, laumontite, analcite, chlorite, epidote, native copper and native silver (summarized from Clarke, 1975; Zelenka, 1978). �± \ -L Portage Lake VolcaflaS -o \ •Ro Gay Lee LaBeIle To sete Bo8e N N S S S llasalts and sandstones in a block south of the fault are exposed and overturned. l3asalts and sandstones in a block south of the fault are exposed and dip to the south. Classical fault contact between basalt and sandstone. Sandstone still exposed north of the IKeveenaw Fault. Sketch map of part of the Keweenaw Fault in the vicinity of Deer Lake, where the Figure 36: Portage Lake Volcanics are found south of the Keweenaw Fault. At right successive cross sections show stages in the development of the Keweenaw Fault at Deer Lake as envisioned by DeGraff (1976), P = PLy, J = Jacobsville. 11 \ Portage Lake VolcanicS 1' Mt Bohenja N Prior to faulting. �94 The Delaware Mine is open to tours for tourists during the summer months. It is owned and operated by Jack and Tom Poynter. At this stop one has the opportunity to look at the dumps from the Delaware Mine and to visit (for a fee) the underground workings. 106.35 MAP 23 109.0 Junction of Delaware Mine and US—4l. ahead towards Phoenix. Left turn on TJS—4l and continue Ahead we can see cliffs of the Greenstone flow. contact of the flow. Road nears the basal 110.3 Exposure of one of the flows beneath the Greenstone flow. 111.1 In the To the right one can see the Greenstone ridge in the background. foreground is the ghost town of Central and its associated dump piles. 111.45 Junction of paved roads to the right and left. Continue ahead on US—4l. The road to the left goes to Gratiot Lake and an Air Force Base; road to the right goes toward the ghost town of Central and the Central dump piles. The Central Mine worked a fissure vein striking nearly at right angles to bedding and dipping steeply to the east. The mine operated from 1854 to 1898 and produced about 52 million lbs. of copper. The fissure extends from just below the Greenstone flow to the Kearsarge Conglomerate. A strike fault at the Kearsarge Conglomerate offsets the vein to the west and below this it is not mineralized. The town of Central, settled in 1854, was settled mainly by Cornish immi— Although the area was mostly abandoned after the mine closed, grants. the descendants of these immigrants now living all across the country, hold a yearly reunion in July at the townsite. Later immigrant groups to the copper mining towns included: Italian, German, Croatian and Finnish people. MAP 24 112.8 Continue ahead on US—41. The road to the Junction of road to the right. right connects with an earlier part of this field trip at Jacobs Creek (mileage 60.3). 113.9 Another view of the ENE striking Greenstone flow holding up the prominent ridge. 114.6 Again another excellent view of the Greenstone flow ridge. MAP 12 115.4 Junction of M—26 and US—4l at Phoenix. There is an optional route from Phoenix to Ahmeek via US—41/M—26 given after the Five Mile Point road log. �- - - — ( I (L/ C4 ----i-I - - — .- —::; p- H. p p I 7 -- I I - 07 IL 1 ,. . - —y 24 — jge I — L — '7 :-fi0 L 2O' - J. - 1— y./ :' •O- c. . I 1 �_ ____ ___I de, • •-1-•r ,4. -— ".? ii /ç/)/11 \ I, ( // • ( - I \'\ •H \'\ .i • 1 —--\-- -, __ C _\ \\\ \\ \\ \\ \\ - -- \\ D — i4 i--, - I N -f I j 2 (fl ) \c \ LU — 1 copt 1 2 1 / ( - - C — /7 -- — - ••/// - 1 \\ '.1 1 -. - Map 1. �97 Phoenix to Ahmeek via Five Mile Point (a scenic route along the Lake Superior shore). MAP 12 115.4 Right turn toward Eagle River. 117.4 Left turn on to the road to Five Mile Point. MAPS 25 and 26 On the right hand side of the road is a turn—off to the Five Mile Point 112.2 In the front You must get permission to enter this area. lighthouse. yard of the lighthouse, there is a thin lava flow of the Lake Shore Traps with the Copper Harbor Conglomerate bed above and below it 121.5 MAP 27 126.9 Five Mile Point beach turn—off at the right hand side of the road. Along this beach there are many exposures of the Copper Harbor Conglomerate. Cross the Gratiot River. 128.45 A thin basalt flow, from a position just above the Greenstone flow, forms an outcrop here which displays a well—developed columnar jointing. The Greenstone flow itself shows spectacular columnar jointing in some areas, most notably along the Palisades shown on Isle Royale where columns 2 m In a few areas the colonade/entablature or more in diameter are found. jointing pattern described in Columbia River flood basalts is well— developed in the Greenstone. On the Keweenaw columnar jointed exposures in thin flow sequences are rare, probably because the underlying horizons were not water—saturated when covered by the next lava flow. 128.7 Stop sign. 128.8 Another stop sign. 130.0 Right turn which is immediately followed by a stop sign in front of a Join US—4l with a right turn. Directly ahead at about 11:00 church. This is a shallow mine that worked the Kingston is the Kingston Mine. Total proConglomerate. The Kingston ore body was discovered in 1962. duction was about 20 million lbs. of copper until mining stopped in 1968 The mine was left open as a research operation (Weege and Pollack, 1971). in the late 1970's. Go straight ahead. Turn left followed in block by a right turn. The Kingston Conglomerate is stratigraphically about midway between the It is overlàirt by a Calumet Conglomerate and the Kearsarge amygdaloid. A bedding plane fault separates the over60 m thick ophitic basalt flow. The conglomerate rests on a lying basalt from the Kingston Conglomerate. The Kingston Conglomerate can be traced along scoriasceous amygdaloid. strike for over 100 Km and ranges in thickness from 0.3 to 30 m. In vicinity of the ore body it averages about 13 m. Where the bed is thick it consists of a lower layer of shale and siltstone, 10—15 cm thick and an upper congloineratic layer (summarized from Weege and Pollack, 1971). �MAP 25 M — .', ór 5 :; %0 r - - - 07/ / - / i - V ' 4 ,<' /\ �99 Fivemile Poini 6NDH / TcUAR 'I / / —- I I J Sevenmile / /• !Point V I. '1 C7 7f q Map4-'7 MAP 26 r/ �100 : 2 I? Lake Shon I,> J7 • • ( MAP 27 Ma, •./. / �The Kingston Conglomerate is typical of rhyolite pebble conglomerates. Pebbles are largely subangular to subrounded quartz—feldspar porphyry. Quartz—free porphyritic and nonporphyritic rhyolite pebbles, common in Interstitial sand other conglomerates, are not present in the Kingston. Sandstone composition is similar to the peb— and sand lenses are common. The intensity of mineralization is related to the amount of matrix bles. present which is an indication of the original permeability. The main alteration minerals are kaolinite and chlorite. Introduced calcite and copper are found as fillings in healed fractures, interstitially filling A few individual pebbles are replaced voids and replacing the matrix. Economically important copper is found as rims around clasts by copper. Matrix filling takes place along and as matrix replacement or filling. texture bands parallel to bedding. Epidote and quartz are also found as introduced minerals. Bleached rock is commonly associated with mineralization in the Keweenaw native copper district but is not present in the Kingston ore body. The abrupt thinning of the conglomerate bed localized the ore body with high grade ore nearest the pinch—out (Fig. 37) (summarized from Weege and Pollack, 197; Brumleve, 1976). PHOENIX TO AHMEEK VIA US—4l/M—26. MAP 12 O Continue straight ahead on US—4l/M—26. 0.5 Bear left on US—41/M—26. Junction of US—41 and Cliff Drive. excellent view of the Greenstone flow ridge. Another MAP 10 5.2 Lumber mill on the left side of the road. 6.0 Entering Mohawk. 6.1 On the left hand side of the road are mine dumps from the Mohawk Mine. The Mohawk Mine worked the Kearsarge amygdaloid which is described at Stop 11. 7.0 MAP 9 The hill on the skyline with the four towers on it is Bumbletowfl Hill, the location of Stop 13. 7.9 Junction of US—41/M—26 and Cliff Drive in Ahmeek. 8.0 Junction of US—4l/M—26 and the road from Five Mile Point. RETURN TO MAIN ROAD LOG MILEAGE. 130.0 Junction of US—41/M—26 and the road from Five Mile Point. 134.1 Junction of US—41/M—26 and M—2O3. �-- - - -..-, .— contact - .' ore body footwall -..' N N N N N N N N N N N N - N ' contact ha ngwall •' N N Schematic illustration of the funnelling effect on mineralizing 37: fluids causing localization of ore deposition (modified from Butler and Burbank, 1929 by Brumleve, 1976). Figure basalt ridge -— r .YfJ FI :- I! C �103 There is an optional route from Calumet to Hancock via M—203/Mctain State Park given after the TJS—41/M—26 road log. Calumet to Hancock via US—4l/M—26. 134.1 Continue straight ahead on US—41/M—26. MAP 28 134.8 Flashing light 135.7 Continue straight ahead. center of Calumet. A right turn leads to the The Osceola Mine Shaft No. 13 can be seen on Southern edge of Calumet. Follow the right hand side of the road behind the Holiday gas station. Mileage is not logged the roads on Map 28 if you wish to go to Stop 23. to this stop. STOP 23. Osceola Mine Shaft No. 6. ProThe Osceola Mine worked the Osceola amygdaloid in the Calumet area. duction from the Osceola amygdaloid began in 1879 and continued until 1920 when mining activity stopped. The mine reopened between 1925 to 193L A total of The mine reopened in 1925 and production continued until 1968. about 600 million lbs. of refined copper was removed from this mine which The amygdaloid was ranks fifth in the Keweenaw native copper district. developed for about four miles along strike and to a depth of 4,500 ft. along incline (2,700 ft. vertically) (summarized from Weege and Pollack, 1971). The Osceola flow is an ophitic basalt and varies in thickness from 35 to The thickest part of the flow, near Calumet, has been the most 210 feet. The Osceola flow has been traced from the Cliff Mine to the productive. In the Calumet area the flow strikes N35°E and dips around Arcadian. The top of the flow is a well developed fragmental amygdaloid 37°NW. consisting of well oxidized, reddish, angular fragments of vesicular lava which typically range in size from a few inches up to a foot in diameter. The lode ranged in thickness from 1 ft. up to and sometimes greater than Amygdules and the voids in the brecciated flow top are filled 60 ft. mostly with calcite, epidote, K—feldspar, chlorite, and native copper. Quartz is present in certain areas and there is also minor amounts of The fragmental amygda— prehnite, pumpellylte, laumontite, and analcite. bid is frequently interrupted by sill—like layers of dense basalt which may have been emplaced by injection of lava from the interior of the flow into the solidified, brecciated crust. These dense basalt layers proNative copper vided barriers to the movement of mineralizing solutions. in the Osceola ranges from disseminated to small masses up to an inch in diameter to large masses weighing hundreds of lbs. (summarized from Weege and Pollack, 1971; Butler and Burbank, 1929). The Osceola Shaft No. 6 is at the southwest end of the ore body and was A barrier zone is believed to have the richest part of the deposit. funnelled mineralizing solutions moving up dip resulting in the high Textures and colors characteristic of fragmental copper contents. Stoiber (unpublished data) made amygdaloid can be seen in this dump. secondary minerals in the dump as a an estimate of the percentages of �Map. - S N 104 N -1 I. .H.. t. :: ,'I -- - .1 - I' •r- - I.- •- '\_ &__ - --- - -L /\ . /Q — :1: c-.- , '1 -/1 .1 N s 42 — 1 1 L-4y'-*- - _s / /-N / ' -- -— 5/ --- /ss 0 5, 'r' -x tL - / 7l, — / H -' /,- 26- k_ __,; -I' 'V 081 A LS34 p LS33 5/5 — '3 N Q33 /: A II 1&J - :', — L312 P28 — I �105 whole: calcite, 59; microcline, 29; prehnite, 4; epidote, 1; quartz, 1; These and pumpellyite, laumontite and native copper can be chlorite, 5. found on this dump. Bleaching of the basalt in vicinity of native copper can be seen in individual specimens. 135.7 Continue ahead on US—4l/M—26 towards Hancock. No Maps Until Hancock Turn left on White Street. 145.45 Junction of White Street on the left. 145.9 Right turn on Tezcuco 146.0 Stop sign at Quincy Street. Go straight ahead through this stop sign one more block to Hancock Street where you make a left hand turn. 146.55 Middle of the Portage Lake Lift Bridge. 146.8 Junction of US—4l/M—26. Stay left on US—4l to the left past the Mobil and Erickson gas stations. 148.1 Left hand turn off Townsend Drive back into the Michigan Tech Campus. Street in Hancock. CALUMET TO HANCOCK VIA M—203/McLain State Park. O Junction US—41/M—26 and M—203 on the edge of Calumet. turn on M—203. Make a right hand No Maps Until Near McLain State Park. 0.5 Village Limit of Calumet. 2.5 Junction of road to Calumet Township Waterworks Park. 4.2 Bear right on Y 4.6 Nice view of Lake Superior. MAP 29 6.7 with Continue straight ahead. another paved road. Continue on M—203. Road to the right is Lakeshore Drive which goes to Calumet Township Waterworks Park; road to the left is Salo Road to the Bear Lake Rhyolite. The Bear Lake Rhyolite cuts the Freda Sandstone bedrock. It is the youngest known igneous activity in the Keweenaw Peninsula. The Bear Lake Rhyolite is a minimum of 1054 ± 34 m.y. years old based on a K/Ar age date (White, 1968). 7.0 Exposures of sand dunes on the right. 7.5 Bear Lake on the left hand side of the road. glacial Bear Lake Channel. Cross on top of the filled �_ __ __ 106 /('i2 (/ F •... LVA A K E T;_ r I654 eøx COAST \GUARD 7( -' 715 2 792 ( 77 Lily Pond I' I' IIv,i )_i. = TO Hahc MAP 29 1J 26 . T BI 9 i ---V( / TTi N _ af n== c/ : 25 �107 The Bear Lake Channel (Map 29) represents a deep bedrock valley, the Although the Waterway was dredged extension of the Keweenaw Waterway. to the west of McLain Park, because the distance was less, the Bear Lake Channel is a much more profound feature, with more than 600 feet The definition of this and other similar bedrock valleys to bedrock. is shown by gravity data. One such traverse, plotted on the map, is See also the discussion of the origin of the displayed as Figure 38. Keweenaw Waterway under Stops 1, 5 and 6. 8.4 Entrance to McLain State Park and the other edge of the Bear Lake Channel. Camping facilities are located here. 9.2 Continue on M—203. Road to the right is to the Coast Guard Station; road to the left is the Bear Lake Road, location of gravity traverse. 10.6 Access road to Lily Pond. At this point the End Moraine of the Keweenaw Lobe, a great mass of glacial ice which was stabilized here during the Wisconsin glaciation, is crossed. The The regional distribution of this moraine is plotted in Figure 14. positions of lobes as they retreated at the end of the Wisconsin period are shown in Figure 15. 13.5 High Point Road, continue ahead on M—203. NAP 30 16.1 Cross Swedetown Creek. To the northeast along Swedetown Creek there are If one is interested in looking in more expcsures of Freda Sandstone. detail at the Freda Sandstone, excellent exposures can be found elsewhere. In the local area excellent exposures of Freda Sandstone are present along Redridge/Freda can the shore of Lake Superior between Redridge and Freda. be reached by following the Houghton Canal Road which begins on the west side of Houghton (see Fig. 17). 16.55 Access to Hancock Campground. The Nonesuch Shale is exposed in an abanThis is Stop 24 and doned quarry located just NE of the boat launch. mileage is not logged from the main road to the quarry. STOP 24. Hancock Campground. As a whole, the Nonesuch Shale consists primarily of siltstone with subordinate amounts of shale and sandstone. It can be distinguished from the formations above and below by its generally grayish color. Most Nonesuch Lithologically is a rippled, laminated siltstone with reddish—gray partings. siltstones and sandstones of the Nonesuch are composed of around 30 to 40 The rock fragpercent rock fragments and 60 to 70 percent mineral grains. ments are mostly volcanic with a 2:1 ratio of mafic to silicic + intermediate The Nonesuch is stratigraphically between the composition (Daniels, 1982). Copper Harbor Conglomerate and Freda Sandstone (Fig. 5). It is The Nonesuch crops out around the margin of the quarry at this stop. a fine— to medium—grained, gray to reddish brown sandstone with subordinate interbedded, reddish—brown laminated siltstone and shale (Cornwall and The attitude of bedding here is about N30°E, 25°W. Wright, 1956). �108 BEAR LAKE 9 8 7 6 5 4( I 2 I I 4 6 8 0 12 14 x 0 2 -3 Q) S a) Li Results of gravity measurements across the Bear Lake Figure 38: traverse plotted in Map 29. At top is Bouguer anomaly with regional In the middle the regional trend is subtracted to get the trend. solid line which is compared with the modelled topography (X's). Below is the model of the valley and the density difference of the bedrock (Freda Sandstone) and the valley fill (Warren, 1981). �109 n 'I - • McI31fl State Park / I V I t , .,, -I - .4 • // - -- ( ; c, '-.' / 'ir •i• 0 r -• -•• —;• I• • 30 JI_1_ - - �110 16.7 Hancock Beach. 16.85 Sharp left hand turn on M—203. 17.9 Turn right on the one—way road. Junction M—203 and US—41. US—4l back to the Michigan Tech Campus Edge of Hancock. Follow south �111 INDEX TO GEOLOGY ON MAPS IN THE FIELD GUIDE Map No. — — — Quadrangle Reference 1 Chassell White, 1956 2 South Range, Chassell White & Wright, 1956; White, 1956 3 Chasseli Warren, 1981 4 Chassell, Hancock White, 1956; Cornwall & Wright, 1956a 5 Chasseil, Hancock White, 1956; Cornwall & Wright, 1956a 6 Laurium Cornwall & Wright, l956b 7 Laur ium Cornwall & Wright, l956b 8 Laur ium Cornwall & Wright, 1956b 9 Ahmeek White & Others, 1953 10 Mohawk Davidson & Others, 1955 11 Mohawk Davidson & Others, 1955 12 Phoenix Cornwall, 1954a 13 Eagle Harbor Cornwall & Wright, 1954 14 Eagle Harbor Cornwall & Wright, 15 Delaware Cornwall, l954b 16 Delaware Cornwall, l954b 17 Lake Medora Cornwall, l954c 18 Lake Medora, Fort Wilkins Cornwall, l954c; Cornwall, 1955 19 Lake Medora Cornwall, l954c 20 Delaware Cornwall, 1954b 21 Delaware Cornwall, l954b 22 Lake Medora Cornwall, l954c 23 Eagle Harbor Cornwall & Wright, 1954 24 Eagle Harbor Cornwall & Wright, 1954; Cornwall, l954a 25 Phoenix Cornwall, l954a 26 Phoenix, Mohawk, Ahmeek Cornwall, l954a; Davidson & Others, 1955; White & Others, 1953 27 Ahmeek White & Others, 1953 28 Laurium Cornwall & Wright, 1956b 29 Hancock Cornwall & Wright, 1956a; Warren, 1981 Hancock Cornwall & Wright, 1956a MTU Campus Map (Cover Page) White, 1956; Hase, 1973 1954 �____________ _____________ 112 REFERENCES Basaltic Volcanism Study Project, 1981, Basaltic volcanism on the terrestrial planets: Pergamon Press, Inc., New York, 1286 p. 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Cornwall, H.R. and Wright, J.C., 1954, Bedrock geology of the Eagle Harbor quadrangle, Michigan: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 36. 1956a, Geologic map of the Hancock quadrangle, Michigan: U.S. Geolo— gic'al Survey Mineral Investigations Field Studies Map MT 46. 1956b, Geologic map of the Laurium quadrangle, Michigan: gical Mineral Investigations Field Studies Map MT 47. U.S. Geolo- Oronto Group, MichiDaniels- P.A., Jr., 1982, Upper Precambrian sedimentary rocks: gan—Wisconsin: Geological Society of America Memoir 156, p. 107—133. Davidson, E.S., Espenshade, G.H., White, W.S. and Wright, J.C., 1955, Bedrock geology of the Mohawk quadrangle, Michigan: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 54. DeGraff, J.M., 1976, Structural and age relationships of rocks associated with the Lac La Belle magnetic anomaly, Keweenaw County (M.S. thesis): Michigan Technological University, Houghton, 130 p. 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Green, J.C., 1977, Keweenawan plateau volcanism in the Lake Superior region: Geological Association of Canada Special Paper No. 16, p. 407—422. �_____________ ____________ Green, J.C., 1982, Geology of Keweenawan extrusive rocks; of America Memoir 156, P. 47—55. Geological Society 114 Grimes, J.G., 1977, Geochemistry and petrology of Keweenaw rhyolites and associated rocks, Portage Lake Volcanics, Michigan (M.S. thesis): Michigan Technological University, Houghton, 80 p. Halls, H.C., 1982, Crustal thickness in the Lake Superior region: of American Memoir 156, p. 239—243. Geological Society Hase, H.W., Jr., 1973, Geological—geophysical site investigation of a portion of the Student Development Complex, Michigan Technological University, Houghton County, Michigan (M.S. thesis): Michigan Technological University, Houghton, 35 p. Holcomb, F.W., 1975, Urban Geological Map of the Eastern Half of the City of Houghton, Michigan (M.S. thesis): Michigan Technological University, Houghton, 87 p. Huber, N.K., 1975, The geologic story of Isle Royale National Park: Survey Bulletin 1309, 66 p. U.S. Geological Jolly, W.T., 1974, Behavior of Cu, Zn, and Ni during prehnite—pumpellyite rank metamorphism of the Keweenawan basalts, Northern Michigan: Economic Geology, v. 69, p. 1118—1125. Jolly, W.T. and Smith, R.E., 1972, Degradation and metamorphic differentiation of the Keweenaw tholeiitic lavas of northern Michigan, U.S.A.: Journal of Petrology, v. 13, p. 507—531. Juilland, J.D., 1965, Mineralization of the Mount Bohemia intrusive, Keweenaw County, Michigan (M.S. thesis): Michigan Technological University, Houghton, 78 p. Kalliokoski, J., 1976, End moraine map of northern Michigan—Wisconsin: Technological University Press, Geologic Map Series, Map hA. 1982, Jacobsville Sandstone: 156, p. 147—155. Michigan Geological Society of America Memoir Klasner, J.S., Cannon, W.F. and Van Schmus, W.R., 1982, The pre—Keweenawan tectonic history of southern Canadian Shield and its influence on formation of the mid— continent rift: Geological Society of America Memoir 156, p. 27—46. Lankton, L.D. and Hyde, C.K., 1982, Old Reliable — an illustrated history of the Quincy Mining Company: The Quincy Mine Hoist Association, Inc., Hancock, Michigan, 159 p. Livnat, A., Rye, R.O. and Kelly, W.C., 1976, Stable—isotope and fluid inclusion studies of the Keweenaw copper district, northern Michigan (abs.): Geological Society of America Abstracts with Programs, v. 8, p. 980—981. 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Geological Robertson, J.M., 1974, Major and minor element geochemistry of some late Precambrian dikes, Keweenaw County, Michigan (abs.): Proceedings of the 20th Institute on Lake Superior Geology, p. 27. 1975, Geology and mineralogy of some copper sulfide deposits near Mount Bohemia, Keweenaw County, Michigan: Economic Geology, v. 70, p. 1202— 1224. Robertson, J.M., Grimes, J.G. and Rose, W.I., Jr., 1979, Intermediate and silicic volcanic and subvolcanic rocks of the Portage Lake Volcanics, Michigan (abs.): Geological Society of America Abstracts with Programs, v. 11, p. 255. Rose, W.I., Jr. and Grimes, J.G., 1979, Cyclical compositional changes within flood Geological Society of basalts of the Portage Lake Volcanics, Michigan (abs.): America Abstracts with Programs, v. 11, p. 255. Scofield, N., 1976, Mineral chemistry applied to interrelated albitization, pumpel— lyitization and native copper redistribution in some Portage Lake basalts, Michigan (Ph.D. dissertation): Michigan Technological University, Houghton, 144 p. Stevens, A., 1971, A study of subsurface analysis of the proposed outdoor instruction area, Student Development Complex, Michigan Technological University, Houghton Michigan Technological University, Houghton, County, Michigan (M.S. thesis): 58 p. Stoiber, R.E. and Davidson, E.S., 1959, Amygdule mineral zoning in the Portage Lake Lava Series, Michigan copper district: Economic Geology, v. 54, p. 1250—1277, 1444—1460. Van Schmus, W.R., Green, J.C. and Halls, H.C., 1982, Geochronology of Keweenawan rocks of the Lake Superior region: A summary: Geological Society of America Memoir 156, p. 165—171. Walker, G.P.L., 1975, Intrusive sheet swarms and the identity of Crustal Layer 3 in Iceland: Journal of the Geological Society of London, v. 131, p. 143—161. Warren, E.J., 1981, The bedrock topography of the Keweenaw Peninsula, Michigan (Ph.D. dissertation): Michigan Technological University, Houghton, 169 p. Weege, R.J. and Pollack, J.P., 1971, Recent developments in the native—copper district of Michigan: Society of Economic Geologists, Guidebook for Field Conference, Michigan Copper District, Sept. 30—Oct. 2, 1971, p. 18—43. �__________ ___________ ____________ _____________ White, W.S., 1956, Geologic map of the Chassell Quadrangle, Michigan: gical Survey Mineral Investigations Field Studies Map MF 43. U.S. Geolo- 1960, The Keweenaw lavas of Lake Superior, An example of flood basalts: American Journal of Science, v. 258—A, p. 367—374. 1968, The native copper deposits of northern Michigan: ed., Ore Deposits of the United States, 1933—1967: Metallurgy and Petroleum Engineering, p. 303—325. in Ridge, J.D., American Institute of Mining, l971a, Geologic setting of the Michigan copper district: Society of Economic Geologists, Guidebook for Field Conference, Michigan Copper District, Sept. 30—Oct. 2, 1971, p. 3—17. 1971b, Field Trip A—2 —— Houghton to Calumet via South Range quarry and Society of Economic Geologists, Guidebook for Field Conference, Eagle River: Michigan Copper District, Sept. 30—Oct. 2, 1971, p. 68—75. 1972, Keweenawan flood basalts and continental rifting: Geological Society of America Abstracts with Programs, v. 4, p. 732—734. White, W.S., Cornwall, H.R. and Swanson, R.W., 1953, Bedrock geology of the Ahmeek quadrangle, Michigan: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 27. White, W.S. and Wright, J.C., 1956, Geologic map of the South Range quadrangle, Michigan: U.S. Geological Survey Mineral Investigations Field Studies Map MF 48. 1960, Lithofacies of the Copper Harbor Conglomerate, northern Michigan: U.S. Geological Survey Professional Paper 400—B, p. B5—B8. Zelenka, B.R., 1978, The history of the Delaware Mine: Local Publication, 20 p. �i: r 2' V r 25 1. 4 14 Figure 1B: 15 r 1. 2 in mites SCALE 0 17 I r i 3 4 k12 18 12 i Stop n!Jmher Map number Index of 1:24,OOC caIe 'naps 0 r I 2 29 r 1 �'Freda McLain State Park Atlantic South Painesdale p4 Chassell Eagle rm 4 C, 0 1 4 Scate 2 o4? 3 + 4miteS Copper Harbor 12 Manitou Island Stop number Figure 1A: Route and stop map Michigan Technological University is an equal opportunity educational institution/equal opportunity employer. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1972 Description An account of the resource Institute on Lake Superior Geology. Michigan Technological University, Houghton, Michigan. May 3-6, 1972. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1972 Contributor An entity responsible for making contributions to the resource John L. Berkley W.A. Bodwell Emmy Booy Musa S. Haddadin Bruce E. Brown R.G. Cuddy P.M. Clifford Erich Dimroth Robert Ehrlich Thomas A. Vogel John C. Green Kenneth G. Books J. Kalliokoski James A. Kilburg Melvin M. Lahr P. James LeAnderson M.S. Lougheed J.J. Mancuso J.T. Mengel Jr M.G. Mudrey Jr P.W. Weiblen Richard W. Ojakangas Erdogan Oray W.J. Hinze N.W. O'Hara W.A. Robertson D.R. Smith R.H. McNutt Virgil A. Trent E.J. Warren Thomas G. Winter P.O. Banks W.R. Van Schmus W.F. Cannon S.S. Goldich John S. Klasner Gene L. LaBerge G.B. Morey James A. Robertson H.B. Stonehouse J.S. Stuckless Grant M. Young M.D. Lewan Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/11c9d1d86b50e5a7348f083a877476c3.pdf 671b46482ec80859cddc170b04d8d1d3 PDF Text Text C O O P E R A T I V E EXTENSION E X T E N S I O N PROGRAMS PROGRAMS COOPERATIVE I University U n i v e r s i t yofo fWisconsin—Madison Wisconsin-Madison U n i v e r s i t y of o fWisconsin—Extension Wisconsin-Extension University Nineteenth Annual Annual Nineteenth Lake Superior Superior Geology Geology Institute on Lake May 3-6,1973 3-6,1973 Madison, Madison, Wisconsin Wisconsin I P1 ERTS-1 satellite Photo Far infrared band photographed on August 12, 1972 Sponsored Sponsored by the the Geological and and Natural Natural History History Survey Survey Wisconsin Geological Extension Wisconsin - Extension University of Wisconsin and the Departments of the theUniversity University of of Wisconsin WisconsinSystem System Departments of of Geology of - �Technical Program Program and Abstracts ffor or tthe h e 19th Annual GEOLOGY INSTITUTE ON LAKE SUPERIOR GEOLOGY held held at at Sheraton Inn Inn Madison, Wisconsin May May 3—6, 3-6, 1973 1973 �MADISON PRAIRIE Central South South --Central MADISON, MADISON, WISCONSIN WISCONSIN OREGON OREGON 4 0 SHERATON SHERATON INN INN 1 1 MADISON MADISON INN INN 22 MAYFLOWER MAYFLOWER MOTEL MOTEL 33 44 NATIONAL NATIONAL MOTOR MOTOR INN INN 55 QUALITY QUALITY INN INN 66 Short Short Course Course Dorms: Dorms: 77 MURPHY'S MURPHY'S 88 99 POOLE'S POOLES PARK PARK MOTOR MOTOR INN INN HUMPHRY HUMPHRY HALL HALL JORNS JORNS HALL HALL RESTAURANT RESTAURANT CUBA CUBA CLUB CLUB ROHOE'S ROHDES STEAK STEAK HOUSE HOUSE 10 107777SIRLOIN SIRLOIN STRIP STRIP 11 DEPARTMENT DEPARTMENT of of GEOLOGY GEOLOGY 11 and and GEOPHYSICS, GEOPHYSICS, SCIENCE SCIENCE HALL HALL 12 GEOLOGICAL 12WISCONSIN WISCONSIN GEOLOGICAL and and NATURAL NATURAL HISTORY HISTORYSURVEY SURVEY �19th 1 9 t h Annual Annual Institute I n s t i t u t e of Lake Superior S u p e r i o r Geology Geology Sheraton Sheraton Inn, Inn, Madison, Madison, Wis. Wis. May May 3—6, 3-6, 1973 1973 Sponsored Sponsored by by the t h e Wisconsin Geological & Natural History Survey Survey and and Departments of of Geology, Geology, the t h e University U n i v e r s i t y of of Wisconsin Wisconsin System. System. Individuals Individuals from from the t h e U.S. U.S. Geological Survey, Survey, Department of Geology Geology of of the t h e University University of of Kansas, Kansas, and and the t h e Inland Inland Steel S t e e l Corporation Corporation also a l s o contributed c o n t r i b u t e d greatly g r e a t l y to to arranging arranging the t h e program program and and field f i e l d trips. trips. INSTITUTE BOAFZI OF OF DIRECTORS DIWCTORS INSTITUTE BOARD * J.W. J.W. * * * Avery Avery (Treasurer), ( T r e a s u r e r ) , Jones Jones && Laughlin Laughlin Steel S t e e l Corp., Corp., Negaunee, Negaunee, Michigan. Michigan. R.D. R.D. Reed Reed (Secretary), ( S e c r e t a r y ) , Michigan Michigan Geological Geological Survey, Survey, Lansing Lansing Michigan. Michigan. M.E. M.E. Ostrom, Ostrom, Wisconsin Wisconsin Geological Geological && Natural Natural History H i s t o r y Survey, Survey, Madison, Madison, Wisconsin. Wisconsin. J. J. Kalliokoski, K a l l i o k o s k i , Michigan Michigan Technological Technological University, University, Roughton, Houghton, Michigan. Michigan. D.M. D.M. Davidson, Davidson, Jr., Jr., Dept. Dept. of of Geology, Geology, University U n i v e r s i t y of of Minnesota Minnesota at a t Duluth, Duluth, Duluth, Duluth, Minnesota. Minnesota. M.W. M.W. Bartley, B a r t l e y , Thunder Thunder Bay, Bay, Ontario, Ontario, CANADA CANADA * Permanent Permanent members members * LOCAL LCZALCOMMITTEE CWITTEE M.E. M.E. Ostrom, Ostrom, Conference Conference Chairman Chairman Technical Technical Program Program C. C. Craddock, Craddock, Chairman Chairman B. E. Cameron Cameron C. C. Dutton Dutton G. G. Medaris Medaris G. G. Mursky Mursky Field F i e l d Trips Trips M. M. Roshardt, Roshardt, Coordinator Coordinator W. W . Broughton Broughton C. Dutton C. Dutton A. A. Heyl Hey1 H. H. Klemic Klemic G. G. LaBerge LaBerge G. G. Medaris Medaris P. P. Myers Myers G. G. Mursky Mursky J. J. Ohlson Ohlson L. L. Weis Weis W. W. West West ft. Van Schmus R. Van Schmus 11]. iii Physical P h y s i c a lArrangements Arrangements P. P. Olcott, O l c o t t Chairman , Chairman Short Short Course Course Office Office College College of of Agricultural Agricultural and and Life L i f e Sciences Sciences U n i v e r s i t y of of Wisconsin— WisconsinUniversity Extension Extension �CARL APPRECIATION CARL E. E. DUTTON DIJTTON -- AN APPFZCIATION Carl Dutton's career half C a r l Dutton's c a r e e r in i n geology extends through nnearly early h alf a century, and most of this time his headquarters have been in Science century, of t h i s h i s headquarters in Hall H a l l on the t h e Madison campus campus of of the t h e University U n i v e r s i t y of of Wisconsin. Wisconsin. H has Ree has worked extensively Michigan, Wisconsin, Wisconsin, and Minnesota, Minnesota, and he is e x t e n s i v e l y in i n Michigan, is well Precambrian geologists Superior w e l l known to t o Precambrian g e o l o g i s t s throughout throughout the t h e Lake S uperior meeting, h his t h e occasion of of this t h i s meeting, i s ccolleagues o l l e a g u e s and friends f r i e n d s in in area. On the Madison extend this t h i s appreciation a p p r e c i a t i o n for f o r his h i s many many contributions. contributions. iv �Carl C a r l was was born born in i n Dunkirk, Dunkirk, Ohio, Ohio, on on January January 24, 24, 1904. 1904. H Hee was educated DePauw University University (LA., aatt DePauw (B.A., 1926), 1926), the t h e University U n i v e r s i t y of of Illinois I l l i n o i s (M.A., (M.A., 1928), 1928), and tthe University and he U n i v e r s i t y of of Minnesota (Ph.D., (Ph.D., 1931). 1931). Carl C a r l and and Val Val Dutton Dutton have have two sons professor sons — John, a meteorology p r o f e s s o r at a t Pennsylvania Pennsylvania State S t a t e University, University, and Robert, Robert, aa physician in i n San San Francisco Francisco — and ffive i v e grandsons. They have have H i l l s , just j u s t west w e s t of of the t h e Madison Madison campus, campus, since s i n c e 1946. 1946. llived i v e d in i n Shorewood Shorewocd Hills, Carl C a r l has divided his h i s life l i f e between various v a r i o u s academic positions p o s i t i o n s and the the U.S. Geological Geological Survey, Survey, and and he he iis widely respected respected aas s widely s a tteacher e a c h e r and a ffield ield U.S. geologist. Assistant g e o l o g i s t . He was aa Teaching A s s i s t a n t at a t Illinois, I l l i n o i s , an an Instructor I n s t r u c t o r at at Minnesota, Assistant Minnesota, and and an an A s s i s t a n t Professor P r o f e s s o r at a t Wayne State S t a t e University U n i v e r s i t y and and at a t the the University Hee joined U n i v e r s i t y of of Michigan. Michigan. H joined the t h e U.S. U.S. Geological Geological Survey Survey in i n 1943, 1943, becoming Regional Geologist in i n 1946 1946 and and Research Research Geologist Geologist in i n 1962. 1962. Since has p participated Mineral Resources Resources ccooperative coming to t o Madison he has a r t i c i p a t e d in i n tthe h e Mineral ooperative program of History i s t o r y Survey and the the of the t h e Wisconsin Geological & Natural H U.S. Geological Survey, Survey, he has taught some cclasses e c t u r e d in i n tthe he U.S. taught sane l a s s e s & llectured Department of Geology and and Geophysics, Geophysics, and and he has been a valued counselor and friend f r i e n d to t o many professors p r o f e s s o r s and and students. students. During his Carl h i s stay s t a y at a t the t h e University U n i v e r s i t y of of Minnesota C a r l was introduced intrcduced geological problems of of tthe Canadian S Shield Professors tto o tthe he g e o l o g i c a l problems h e southern Canadian h i e l d by P rofessors Grout, John Gruner, His doctoral dissertation Frank Grout, Gruner, and and George George Schwartz. Schwartz. H is d octoral d issertation on the t h e conglomerates and and structure s t r u c t u r e of of the t h e Ensign Ensign Lake Lake area, a r e a , Cook Cook County, County, Minnesota, Minnesota, under Professor P r o f e s s o r Gruner was the t h e beginning of of his h i s life—long life-long Hee also ffascination a s c i n a t i o n with with the t h e Precambrian. Precambrian. H a l s o became interested i n t e r e s t e d in i n iron iron formations and llater Michigan, eeventually formations a t e r began a rresearch e s e a r c h program in i n Michigan, ventually achieving achieving international i n t e r n a t i o n a l rrecognition e c o g n i t i o n as a s an authority a u t h o r i t y on on iron i r o n ores. o r e s . He He paper on U.S. U.S. iiron ore deposits att tthe Geological gave a paper ron o re d eposits a h e International I n t e r n a t i o n a l Geological Algiers U.N. Committee on Iron Ore Congress in in A l g i e r s in i n 1952, 1952, served on tthe h e U.N. Resources in 1953-54, and spent spent ssix weeks sstudying deposits Resources i n Geneva in i n 1953-54, i x weeks t u d y i n g iron iron d eposits AID I D program in i n Yugoslavia Yugoslavia in i n 1961. 1961. Carl C a r l is i s aa Fellow Fellow of of the the with the the A Society of America America and and sserves Membership S Secretary Geological S o c i e t y of e r v e s as a s tthe h e Membership e c r e t a r y ffor or tthe h e Society S o c i e t y of of Economic Economic Geologists. Geologists. Through the papers and t h e years y e a r s Carl C a r l has has produced prcduced many many papers and geologic geologic maps, maps, has worked worked ffor many y years and only aa few few can can be be mentioned mentioned here, here. lie H e has o r many e a r s in in the district of Michigan Michigan and Wisconsin, Wisconsin, and is co—author t h e Menominee iron iron d i s t r i c t of i s GO-author of USGS P.P. i s also a l s o co—author co-author of of USGS Maps MF—99 MF-99 of P.P. 513 513 and and Map Map 1—466. 1-466. He is MF-l81 on the He and MF-181 t h e bedrock geology geology of of the t h e Cuyuna Cuyuna district, d i s t r i c t , Minnesota. Minnesota. He iis s widely known for f o r aa series s e r i e s of of papers on on iron i r o n ore o r e resources r e s o u r c e s of of the t h e U.S., U.S., some foreign f o r e i g n countries. c o u n t r i e s . He is i s co—author co-author of of USGS USGS P.P. P.P. North America, and and some MF—225 on the ore deposits of tthe River— 570 and Map MF-225 t h e geology and o re d e p o s i t s of h e Iron I r o n RiverCrystal C r y s t a l Falls F a l l s district, d i s t r i c t , Michigan. Michigan. A very important contribution c o n t r i b u t i o n is i s aa series series of llithologic, geophysical, and mineral mineral commodity commodity maps of of Precambrian rocks of i t h o l o g i c , geophysical, Wisconsin, published as These maps are iin n Wisconsin, a s USGS USGS Map Map 1—631. 1-631. a r e aa complete of a available Wisconsin Precambrian, Precambrian, including compilation of v a i l a b l e information on tthe h e Wisconsin including previously unpublished d data numerous field many p r e v i o u s l y unpublished a t a ccarefully a r e f u l l y eextracted x t r a c t e d from numerous field Carl notebooks on hand in i n the t h e files f i l e s of of the t h e State S t a t e Survey. Survey. IIn n aaddition, ddition, C a r l has has written has served as w r i t t e n papers ffor o r several s e v e r a l guidebooks and has a s a leader l e a d e r on many ffield i e l d trips, t r i p s , both formal formal and and informal. informal. Carl i s indeed indeed a gentlemen and aa scholar s c h o l a r in i n the t h e highest highest C a r l Dutton is and aa wonderful wonderful man man tto have aas ttradition, r a d i t i o n , and o have s aa cco1league o l l e a g u e We W e thank thank him him for for his h i s long service s e r v i c e and and numerous contributions c o n t r i b u t i o n s to t o our our profession, p r o f e s s i o n , our our state, state, and our u university; his n i v e r s i t y ; for for h i s enduring interest i n t e r e s t and ccareful a r e f u l work in i n the the Precambrian; for his patient his Precambrian; for h i s generous and p a t i e n t assistance a s s i s t a n c e to to h i s ffellow ellow geologists g e o l o g i s t s in i n the t h e classroom, classroom, the t h e office, o f f i c e , the t h e laboratory, l a b o r a t o r y , and and the t h e field; field; and for his We for h i s cheerful c h e e r f u l optimism, optimism, quiet q u i e t modesty, modesty, and and gently g e n t l y dignity. d i g n i t y . We having C Carl us campus, and w wee hope enjoy and appreciate a p p r e c i a t e having a r l among u s on tthis h i s campus, he remains with with us u s for f o r many many years. years. - - v �TABLE TABLE OF OF EVENTS EVEWTS Wednesday, May 2, 1973 May 2, 1973 7:00—9:00 7:OO-9:OO p.m. p.m. Registration R egistration Conference Smoker (Cash Conference (Cash Bar) Bar) Mezzanine Mezzanine Ballroom North Registration Registration Technical Session S e s s i o n 11 Luncheon Technical Session S e s s i o n 22 Happy Hour (Cash Happy (Cash Bar) Bar) Banquet Mezzanine Ballroom North Ballroom South South Ballroom North Ballroom South South Ballroom South South Technical Session S e s s i o n 33 Luncheon Technical Session S e s s i o n 44 Business Meeting Buses for f o r Field F i e l d Trips T r i p s 22 && 33 leave Sheraton Inn leave Inn Parking Parking Lot Lot Ballroom Ballroom Ballroom Ballroom Thursday, May Thursday, May 3, 3, 1973 1973 8:00—10:00 8:OO-1O:OO a.m. a.m. 8:30—12:00 noon 8:30-12:OO 12:00—1:00 p.m. 12:OO-1:OO p.m. 1:30—5:10 1 ~ 3 0 - 5 : l Op.m. p.m. 6:00—7:00 6:OO-7:OO p.m. p.m. 7:00—8:30 p.m. 7:OO-8:30 p.m. Friday, F r i d a y , May 4, 4, 1973 1973 8:30—12:00 noon 8:30-12:OO 12:00—1:00 12:OO-1:OO p.m. p.m. 1:30—4:45 1:30-4:45 p.m. p.m. 4:45—5:00 4~45-5:00 p.m. p.m. 7:00 p.m. 7:OO p.m. Saturday, Saturday, May 5, 5 , 1973 1973 7:30 a.m. a.m. 6:00 p.m. 10:00 p.m. Bus for leaves f o r Field F i e l d Trip T r i p 11 leaves Sheraton Inn Parking Lot Bus ffor Field or F i e l d Trip Trip 1 1 returns returns Sheraton Inn Parking Lot Field Trip Bus ffor or F ield T r i p 2 returns returns Sheraton Inn Inn Parking Parking Lot Lot Sunday, May 6, 6 , 1973 1973 7:00 7:OO p.m. p.m. Bus for f o r Field F i e l d Trip T r i p 33 returns returns Sheraton Inn Inn Parking Lot vi North South South North North �TECHNICAL TECHNICALPROGRAM PROGRAM - SESSION SESSION 11 — Morning, Morning, Thursday, Thursday, May May 3, 3, 1973 1973 Co—chairmen: Co-chairmen: Alan Alan T. T. Broderick Broderick and and L. L. Gordon Gordon Medaris, Medaris, Jr. Jr. 8:30 M.E. M.E. Ostrom Ostrom Welcoming Welcoming Remarks Remarks 8:40 P.K. P.K. Sims Sims Tectonic Tectonic history h i s t o r y of of Early E a r l y Precambrian Precambrian rocks in the Vermilion district, rocks i n t h e d i s t r i c t , northnortheastern e a s t e r n Minnesota. Minnesota. p. 34—35 34-35 p. 9:05 Edward Edward M. M. Ripley Ripley & & ' Donald Donald M. M. Davidson, Davidson, Jr. Jr. Structural Structural ultramafic ultramafic 9:25 M.S. M.S. Lougheed Lougheed && J.J. J. J. Mancuso Mancuso 9:50 Discussion Discussion of of papers papers evolution e v o l u t i o n of of the t h e Deer Deer complex, Minnesota. complex, Minnesota. p. p. Lake Lake 29 29 The The biogenic biogenic origin o r i g i n of of primary primary minerals minerals in i n Lake Superior Superior Precambrian Precambrian ironironformation. formation. p. 21—22 21-22 p. 10:00 Coffee Coffee break break 10:30 Klaus J. Schultz S c h u l t z && Klaus J. Edward Edward M. M. Ripley Ripley Petrology Petrology of of some some Early E a r l y Precambrian Precambrian differentiated d i f f e r e n t i a t e d ultramafic u l t r a m a f i c bodies bodies in in northeastern n o r t h e a s t e r n Minnesota. Minnesota. p. 32—33 32-33 p. 10:50 M.G. M.G. Mudrey, Mudrey, Jr. Jr. && A.L. A.L. Geldon Geldon AA Lower Lower Precambrian Precambrian lamprophyre lamprophyre pluton pluton near n e a r Ely, Ely, Minnesota. Minnesota. p. 25 25 p. 11:10 John John S. S. Klasner Klasner && Thomas Thomas R. R. Turner Turner Precambrian Precambrian north—south north-south oriented o r i e n t e d faults faults in the western Marquette i n t h e western Marquette district, district, northern n o r t h e r n Michigan. Michigan. p. 17—18 17-18 p. 11:30 Jens F. Touborg Touborg Jens F. 11:50 11:50 Discussion Discussion of of papers papers 12:00 12:OO Adjourn Adjourn 12:00 12:OO Luncheon Luncheon Structural S t r u c t u r a l and and stratigraphical s t r a t i g r a p h i c a l analysis analysis of of the t h e Geco Geco sulphide s u l p h i d e deposit d e p o s i t in in Manitouwadge, Manitouwadge, northwestern northwestern Ontario. Ontario. p. 38-39 38-39 p. Ballroom Ballroom South South vii vii �- SESSIII SESSION 22 — Afternoon, Thursday, May May 3, 3, 1973 1973 Co—chairmen: Co-chairmen: Paul G. G. Schmidt Schmidt and and Greg Greg Mursky Mursky Paul 1:30 M.D. Lewan M.D. Lewan Geochemistry Geochemistry of the the calcium-carbon calcium—carbon dioxide metasomatism dioxide metasomatism at a t Presque Presque Marquette, Michigan. p. 19—20 19-20 IIsle, s l e , Marquette, Michigan. p. 1:50 D.M. Mickelson D.M. Summary l a c i a l geology of of Summary of g glacial north—central Wisconsin. p. 24 24 north-central p. 2:15 E. Wm. Wm. Heinrich E. A n unusual manganese manganese deposit in in An Keweenawan lava, lava, Copper Copper Harbor, Michigan. p. 12 p. 12 2:35 Thomas A. A. Vogel & & Nancy Alyanak "Framboidal" "~ramboidal" chalcocite from White Pine, Michigan. Pine, p. 42 42 p. 2:55 Discussion of papers 3:05 Coffee break 3:35 Roger W. W. Cooper Cooper The Keweenawan volcanics north of of Gogebic range range in i n Wisconsin. Wisconsin. the Gogebic p. P. 99 3:55 John C. C. Green Progress report Progress report of of the t h e Coimuittee Committee on Keweenawan Keweenawan Stratigraphy. Stratigraphy. p. 11 11 p. 4:15 R.J. R. J. Stevenson Stevenson A Keweenawan Keweenawan layered layered mafic intrusion intrusion Finland, Lake near Finland, Lake County, County, Minnesota. Minnesota. p. 36 36 p. 4:35 W.F. W.F. Cannon Cannon High grade magnetite magnetite deposits deposits at High grade at Republic, Michigan: Their bearing Republic, Michigan: Their on the genesis genesisof ofMarquette MarquetteRange Range hard ore. 6-8 hard ore. p. 6—8 5:00 Discussion of papers 5:10 Adjourn 6:00 Happy Ballroom South South (cash (cash bar) Happy hour Ballroom 7:00 Banquet Ballroom South Address by Dr. Cameron Dr. Eugene Cameron ANIM&L, VEGETABLE, VEGETABLE, OR OR M MINERAL? ANIMAL, INERAL ? viii v iii �- Friday, May 4, SESSION SESSION 33 — Morning, Friday, 4, 1973 1973 Co-chairmen: Co—chairmen: Ralph W. Carl E. Dutton Ralph W. Marsden Marsden and and C a r l E. 8:30 Richard Berger Richard and oothers and thers Environmental Environmental geology geology and and land land use planning, Chassel planning, Chassel quadrangle, quadrangle,Houghton Houghton p. 3—4 County, Michigan. p. 3-4 8:50 Ennny Booy & E mmy B00y Ruth J. J. Sobanski Sobanski Engineering geology of of the t h e Military Military Hill H i l l landslides, l a n d s l i d e s , Ontonagon Ontonagon County, County, Michigan. P. 5 p. 5 9:10 C.R. Bentley C.R. Magnetotelluric evidence for f o r lateral lateral variations v a r i a t i o n s of of ccrustal r u s t a l structure s t r u c t u r e in in northern n o r t h e r n Wisconsin. P. 2 2 p. 9:30 F. Touborg Jens F. The Atikokan Iron I r o n Range Range and and its its iron-copper m mineralization. iron-copper ineralization. p. p. 40 9:50 Discussion of Discussion of papers 10:00 Coffee break 10:30 G. G. Mursky Mursky and others others Mineralogical and and chemical studies studies of greenstones in 26-27 of i n Wisconsin. Wisconsin. p. p. 26—27 10:50 W.R. Van W.R. Van Schmus Schmus Geochronology of of Precambrian Rocks iin n eeastern a s t e r n Wisconsin. p. 41 41 p. 11:10 L.G. Medaris, Jr. L.G. Jr. and others others late b a t h o l i t h — a late The Wolf River batholith massif in Precambrian rapakivi r a p a k i v i massif in northeastern n o r t h e a s t e r n Wisconsin. Wisconsin. p. 23 23 p. 11:30 J.L. J.L. Anderson Graphical analysis a n a l y s i s of of portions p o r t i o n s of of the granite the g r a n i t e system with application application biotite—bearing tto o b i o t i t e - b e a r i n g granitic g r a n i t i c melts melts and gneisses. and g neisses. P. p. 11 11:50 Discussion of of papers 12:00 Adjourn 12:00 Luncheon - Ballroom South South ix �- SESSION SESSION 44 — Afternoon, Friday, Friday, May 4, 4, 1973 1973 Co—chairmen: Co-chairmen: Paul C. Paul C. Tychsen Tychsen and and Perry P e r r y Olcott Olcott The ppetrology e t r o l o g y and geochemistry of Round Lake Lake iintrusion, n t r u s i o n , northwestern Wisconsin. p. 30 30 p. 1:30 D.L. D.L. E.N. E.N. Roder & Cameron Cameron 1:50 J.E. Thresher J.E. The formation of of the t h e Pittsville Pittsville (Wisconsin) migmatite. 37 (Wisconsin) p. 37 p. 2:10 Robert A. A. Jenkins Jenkins The geology of of Pembine and and Beecher townships, Marinette townships, M a r i n e t t e County, County, Wisconsin. p. 15—16 15-16 p. 2:30 John M. M. Ohlson Ohison The iron i r o n ore o r e deposits d e p o s i t s at a t Black River Falls, F a l l s , Wisconsin, Wisconsin, geology operations. p. 28 and o perations. p. 28 2:50 Discussion of of papers papers 3:00 Coffee break 3:30 0.H. Dury G.H. Southwest Wisconsin as a s aa duricrusted duricrusted pediplain. p ediplain. p. 10 10 p. 3:50 A.V. A.V. Ileyl Hey1 Mississippi Upper M i s s i s s i p p i valley v a l l e y lead—zinc lead-zinc district. d istrict. p. 13—14 13-14 p. 4:10 S.B. Romberger S.B. Upper Mississippi M i s s i s s i p p i valley v a l l e y base base metal metal deposits: d e p o s i t s : experimental solutions s o l u t i o n s to to p. 31 problems of ore genesis. p. 31 problems of o r e g e n e s i s . 4:30 Discussion of of papers 4:45 Business Meeting Business 5:00 Adjourn 7:00 from parking parking lot. Buses for f o r field f i e l d trips t r i p s 22 and and 3 3 leave l e a v e from lot. x �GRAPHICAL ANALYSIS OF OF PORTIONS GRAPHICAL ANALYSIS PORTIONS OF OF THE THEGRANITE GRANITESYSTEM SYSTEMWITH WITH APPLICATION TO BIOflTE—BEARING GRANITIC MELTS AND GNEISSES APPLICATION TO BIOTITE-BEARING GRANITIC MELTS AND GNEISSES Department of Geology and Anderson, Department of Geology J. LL.. Anderson, Wisconsin, Madison, Wisconsin Wisconsin. Madison, Wisconsin 53706 53706 Geophysics. University University of Geophysics, of ABSTRACT ABSTRACT - phase relations in biotite—bearing modelto to describe describe phase granitic melts ite-bearing granitic melts model analysis SiOy - KA1Si3O8 analysis of ofthe thesystem system SiC2 KAlSi30g NaA1Si1OS — FeO Fe2O3 provides a tentative Hz0 - K2MgSiAL20 1120 provides KgMgfiSifiAlzOzo Graphical Graphical CaAl2Si2O8 CaAl SigOg — — — gneisses. Defining and gneisses. Defining 'FeO' 'FeO' as as an an arbitrary arbitrary combination combination of of FeO FeO and Moreover,it it has specifies the and Fe20 theoxygen oxygen fugacity. Moreover, has been been and Fe20 specifies split the system system into three four comoonent comoonent subsystems necessax necessary to split to of the the components components 110, KMgSi6fl2G20, to evaluate evaluate separately separately the effect of and Quartz, alkali feldspar, and CaAl2Si2Op on the the rest rest of of the the system. system. Quartz, CaAl Si 0 on plagioclase, iotite, magnetite, plagioclgse: !?iotite, magnetite,granitic granitic melt, melt, and and vapor vapor are are the the considered phases. considered phases. Application Apolication of of Schreinemakers' Schreinemakers' rules rules combined combined biotite — magnetite magnetite with with experimental experimental data data on on alkali alkali feldspar feldspar — biotite and of topologies. topologies. The The and crystal—melt crystal-melt equilibria equilibria generates generatesan. an array of system system is is characterized characterized by by degenerate degenerate equilibria, equilibria. - - In In application, application, several several conclusions conclusions can can be be made made which which are are as as 1) degrees of 1 ) Dependent Dependent on on the the number number of of degrees of freedom, freedom, the the KK/Na /N~ Fe/Mg ratios in biotite can and ~ e/~ ratios g in biotite can be be aa function function of of temperature, temperature,total total pressure, potential of water, water, oxygen fugacity, and the pressure, chemical chemical potential oxygen fugacity, the bulk fugacity is buffered and fluid fluid If oxygen oxygen fugacity composition composition of of the the rock. rock. If pressure equals equa total totalpressure, pressure,divariant divariant assemblages assemblages (with (with respect respect to to F) have T and and P) have fixed fixed biotite biotite compositions. compositions. Such Such assemblages assemblages become become T trivariant H20 is not in in excess such as in %O H2O - undersaturated trivariant if if HgO undersaturated additional degree of freedom allows only one of of the two melts, melts. One additional ratios will vary with ratios (i.e., (i.e., Fe/Mg ~e/Mgor or K/Na) K/N~)to to be be fixed. fixed. The other other will the bulk composition the composition of of the the rock, rock. As to which of of the the two two ratios ratios will Another degree degree of of freedom freedom will this is is depends depends on on the the assemblage, assemblage. Another Biotite allow ratiosto tovary varywith withthe thebulk bulkcomposition, composition. 2) 2) Biotite allow both ratios follows: follows: - stability can of partial stability canstrongly stronglyinfluence influencethe thecomposition composition of partialmelts melts derived assemblage quartz—plagioclase—biotite— quartz-plagioclase-biotitederived from from gneisses gneissesofofthe the assemblage of partial partial Ifthe thebiotite biotiteremains remainsstable stablebeyond beyond conditions conditions of magnetite. magnetite. If melting onlytonalitic tonalitic melts can result. result. 3) melting only melts can Alternatively, this this 3) Alternatively, coexist in assemblage assemblage cannot cannot coexist in equilibrium equilibrium with introduced granitic granitic south of Stevens melt. A possible example is an injection gneiss south Point, Wisconsin, where the Point, Wisconsin, the alkali alkali feldspar feldspar in in the granitic granitic veins veins isolated from to is isolated from the the host host rock rock by by plagioclase. plagioclase. LiV) 4) Application Application to ranakivi massifs, such batholith of ranakivi granite granite massifs, such as as the Wolf River River batholith of Topological changes Wisconsin, Wisconsin, is is possible, possible. Topological changes suggesting suggesting feldspar feldspar mantling and replacementofofalkali alkalifeldsoar feldsparby bybiotite biotite exist. exist. mantlinc and the the replacement The feasibility of is being The feasibility ofsuch such explanations explanations is being studied, studied. 1 �MAGNETOTELLURIC EVIDENCE FOR FOR LATERAL LATERAL VARIATIONS OF MAGNETOTELLURIC EVIDENCE OF CRUSTAL STRUCTURE CRUSTAL STRUCTURE IN NORTHERN NORTHERN WISCONSIN WISCONSIN C. R. R. Bentley, Bentley, Department Department of Geology and of Geology and Geophysics, Geophysics,University University of of C. Wisconsin—Madison,Madison, Madison, Wisconsin, Wisconsin, 53706. Wisconsin-Madison, 53706. ABSTRACT ABSTRACT IIff two-dimensional two-dimensional inhomogeneity inhomogeneity iis s the reason reason ffor o r apparent apparent anisotropy anisotropy studies, then of the the pair of iinn magnetotelluric magnetotelluric studies, then one one of of curves curves at a t each each site site should be close to t o that t h a twhich whichwould would be be observed observed over over aa one-dimensional one-dimensional earth. should be close Ontthis On h i s basis, sites s i t e sini nWisconsin Wisconsin can can be be divided divided into i n t o three three geographically geographically The systematic systematic distinct w i t h decidedly decidedly different d i f f e r e naverage t average curves. curves. The d i s t i n c tgroups groups with grouping implies tthat grouping ofof ssites i t e s implies h a t the the differences differences rreflect e f l e c t real real differences differences justvariations variationsin in local near-surface conditions. conditions. the crust, crust, not notjust within the thethe local near—surface That implication boundary That implication isi sstrengthened strengthenedby bythe thefact f a cthat t t h one a t one boundarybetween between groups correspondstto groups corresponds o an an abrupt change change iinn structure structurededuced deduced completely completely independently from from seismic seismic and andgravity gravity data in independently data alone alone (Ocola (Ocola and and Meyer, Meyer, in The two-dimensional two—dimensionalassumption assumption alsoimplies implies tthat press, J.G.R.). press, J.G.R.). The also h a t the the c o r r e c t " curve curve of of each each pair corresponds corresponds t otocurrent t o the the "correct' currentflow flow parallel parallel to current direction directioncorresponding corresponding to t o the the two-dimensional boundary. two-dimensional boundary. Plotting current acceptedcurve curveaat eachs site accepted t each i t e reveals reveals a a parallelism parallelism with withcontours contours ofofBouguer Bouguer gravity anomalies, controlling gravity anomalies, suggesting suggesting tthat h a t the the two—dimensionality two-dimensional i t y control 1ing the the tensor orientation isi snot notnear—surface near-surface aatt all, a l l ,asashas haspreviously previouslybeen been tensor assumed, associatedinstead insteadwith withgross grosscrustal crystal structure. t i sis associated assumed, b ubut 2 �ENVIRONMENTAL GEOLOGY GEOLOGYAND ANDLAND LAND U USE ENVIRONMENTAL SE PLANNING, CHASSELL QUADRANGLE, COUNTY, MICHIGAN QUADRANGLE, HOUGHTON HOUGHTON COUNTY, CHASSELL Richard M. Hamil, Hamil, Department Department of of Geology Geology Richard Berger, Berger, Eniny Emy Booy, Booy, and and Brenton Brenton M. and Geol ogi cal Engineeri ng, Michigan Technol ogi cal University, and Geological Engineering , Mi chi gan Techno1ogi cal University, Houghton, Mi chi gan 49931. Houghton , Michigan ABST RACT ABSTRACT The Chassell ChassellQuadrangle Quadrangle locatedinin the the southeastern southeasternquarter quarter of of the The i s islocated It formerly uutilized I t includes includes land land which which was was formerly t i l i z e d for f o rcopper copper area iiss sparsely o r agriculture. The The area sparselypopulated populatedand andmay may mining as aswell well as as ffor mining evaluation of geological be developmenti ninthe the future. future. An An evaluation geological be expected expected tto o undergo undergo development factors affecting such development factors affecting such developmenthas hasbeen beenmade. made. Keweenaw Peninsula. Keweenaw Peninsula. About 85 85 percent percentof of the the land has About has a a slope less less than than 15 15 percent, percent, with withmore more About one one quarter quarter than than half of of that t h a thaving having aaslope slope less less than than 55percent. percent. About of the the land land ininthe thequadrangle quadranglehas has more more than than 50 50 feet f e e t of ofoverburden, overburden, another another quarter (mostly (mostly overlying overlying the the Jacobsville Jacobsville sandstone sandstone in the the eastern eastern area) area) 30 tto 30 o 50 50 ffeet, e e t , and and the the rest r e s t (mostly (mostly in in the thewesterly westerly areas areas overlying overlying the the Portage Lake Lake Lava Lava flows) flows) between and 30 30 ffeet Portage between 00 and e e t of of overburden. overburden. Most of of these Most these soils loam s o i l s are are classified c l a s s i f i e dasassilty s i l tto y sandy t o sandy loam(USDA (USDA cclassification) l a s s i f i c a t i o n )oro rSM SM or or SC (Unified Soil Soil Classification) SC (Unified Classification)having havinga alow lowshrink—swell shrink-swell potential potential and and There iiss aa prevalent prevalent hardpan hardpan layer good permeability permeability (about (about 2.2 2.2 inches/hour). inches/hour). There good pHofof the the soils s o i l s isi ssomesomeThe pH at a t variable variabledepth depth which which isi sa asandy sandyloam loam or o rSC. SC. The The corrosion corrosion hazard hazardf for metal and andconcrete toncrete iiss low. - 55 ttoo 6.6. The o r metal low. what acid — what 10 percent percentofof the the land There generally aa thin thin topsoil. About There iis s generally About 10 land area area is is Theseare aremostly mostly on on the the floodplains underlain organic ssoils. underlain by by alluvium and and organic o i l s . These of wouldseverely severely thepotential potentialf ofor of rivers rivers which which would r e restrict s t r i c t the r uutilization. tilization. areas are generally classified areas are c l a s s i f i e dasasmarshland. marshland. These Underground water supply providedbybythe theglacial glacial ddrift Underground water supply i sisprovided r i f tand andbedrock. bedrock. Wherethe theglacial glacial ddrift Portage Where r i f tisi sdeep deepand and ini nparts partsofofthe the PortageLake LakeLava Lava series series Jacobsville The Jacobsvi l l esandstone sandstone there there is i s sufficient s u f f i c i e n water t waterfor f o domestic r domestic supplies. supplies. The There are some problemswith with Fe has some problems Fe content has ssufficient u f f i c i e n twater water for f o rdomestic domestic use. use. There in water water from from the the glacial glacialand andJacobsville Jacobsvillesources; sources;septic s e p t itanks c tanksmay maycontaminate contaminate some the shallow shallow aquifers. some ofof the About 80 80 percent percent of of the land theChassell ChassellQuadrangle Quadrangleisi swell—drained. well-drained. About land ini nthe There The Pilgrim, Pike, The Pilgrim, Pike, and and Sturgeon Sturgeon Rivers Rivers drain drain the thearea area tot oPortage PortageLake. Lake. There and during during spring spring thaw flooding permanent marshland marsh1 and and thaw temporary temporary flooding iiss substantial substanti a1permanent occurs iinn many uplandareas areasdue duet otothe theimpermeability impermeability of of the the underlying many upland underlying bedbedoccurs areasdirections directions of of surface drainage ddiffer rock. In some some areas surface drainage i f f e r from from the the drainage drainage patterns at bythe the glacial glacial patterns a t depth depth due due to t o the thepresence presence of of bedrock bedrock ridges ridges masked masked by ddrift. rift. Old mine openings openingsdodonot notappear appeart otobe beaamajor majorhazard hazardinin future planning, Old mine planning, bbut u t shaft locations locations will willhave have to t obe be taken taken into intoaccount. account. 3 �About 20percent percentofof the the land land iiss currently About 20 currentlyowned owned by by large private private organorganExceptffor holdings, most of the land izations. Except o r small small state s t a t e and and municipal municipal holdings, most of land of the the quadrangle quadrangle iis s held held by by small small individual individual landholders. landholders. Current forestryand andfarming fanningwith w i t hpotatoes, potatoes, Current uutilization t i l i z a t i o n isi smostly mostlyini nforestry There iiss less less strawberries, and and dairy dairy products products being being the thedominant dominant crops. crops. There commercial and g h t industrial industrial purposes. purposes. than used ffor o r connnercial than 10 10 percent percent of of the the land used andl ilight Recreational useofof the the land, land, e.g. e.g. hunting snowmobilingi sisf afairly hunting and and snowmobiling irly Recreational use usewill will probably widespread. Future Future use probably include include mining mining and and recreation as as well well as agriculture. Development Development industry willbebep partially as of of industry will a r t i a l l y controlled by by access water which which iiss abundant along the the shores of Portage u t less less access tto o water abundant along shores of Portage Lake Lake bbut accessible in major majorquantities quantities further inland. accessible in inland. 4 �ENGINEERINGGEOLOGY GEOLOGY THEMILITARY MILITARYHILL HILL LANDSLIDES, ENGINEERING OFOFTHE LANDSLIDES, ONTONAGONCOUNTY, COUNTY, MICHIGAN MICHIGAN ONTONAGON EmmyBooy Booyand andRuth RuthJ.3.Sobanski, Sobanski, Department Department ooff Geology Geology and and Geological Geological Emmy Engineering, Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan Michigan 49931. Engineering, Michigan Michigan Technological ABSTRACT The vvalley The a l l e y of o fthe t h eEast EastBranch Branchofo the f t hOntonagon e OntonagonRiver, River,Ontonagon Ontonagon County, County, Michigan i is throughaat hthick Michigan s downcut downcut through i c k sseries e r i e s of o f glacial g l a c i a lake—deposited l lake-deposited clays, clays, Thesecclays have proven provenaa hazard hazardt to tthe h e Ontonagon Ontonagon clays. These l a y s have o construction c o n s t r u c t i o n and and maintenanceoof 45because becauseo foft hthe numerous slopef afailures maintenance f tthe h e U.S. U.S. Highway Highway 45 e numerous slope i l u r e s ooff various sizes are rrepetitive These f afailures i l u r e s are e p e t i t i v e in in various s i z e s abutting a b u t t i n g on on the t h ehighway. highway. These nature, rreflecting nature, e f l e c t i n g variation v a r i a t i o n ini nmoisture moisture content content with w i t h precipitation p r e c i p i t a t i o nand and snowmelt. snowmel t. The nature ooff the clayscauses causes The llayered a y e r e d nature t h e Ontonagon Ontonagon clays s usubstantial b s t a n t i a l v avariability riability in i n the t h e physical p h y s i c a l properties p r o p e r t i e s of o f the t h e mass mass bboth o t h l alaterally t e r a l l y and and vvertically. e r t i c a l l y . IInn general tthe material be cclassified general he m a t e r i a l can can be l a s s i f i e d as as clays c l a y s and and clay—silts c l a y - s i l t s with w i t h fine f i n esand sand percent to contents ranging contents ranging from from less l e s s than than 11 percent t o 14 14 percent. percent. Atterberg those ffor A t t e r b e r g LLimits i m i t s of o f these these materials m a t e r i a l s range range from from those o r inorganic i n o r g a n i c clays clays P l a s t i c limits l i m i t srange range from from of o f low low pplasticity l a s t i c i t y to t o those those of o f high high pplasticity. l a s t i c i t y . Plastic 24 50,.liquid limits l i m i t sfrom from 27 27 to t o 100, 100, and and pplasticity l a s t i c i t yindices i n d i c e s from from 12 12 to t o 58. 58. 24 tto o 5O,Jiquid There appearst otobebenonoc oconsistent of physical There appears n s i s t e n t p apattern t t e r n o of f vvariation a r i a t i o n of p h y s i c a l properties properties of (e.g. at o f the t h e material m a t e r i a l wwith i t h llocation o c a t i o n wwithin i t h i n iindividual n d i v i d u a l sslides l i d e s (e.g. a t toes toes of o f slides slides or o r on on the t h e failure f a i l u r eplace placeata the t t h escarp) scarp)nor n owith r w i t helevation e l e v a t i o above n abovea adatum datum nor nor along along the t h e general general north—south north-south ttrend r e n d of o f the t h ehighway. highway. The nnatural moisture content content ooff these The a t u r a l moisture these failure-prone f a i l u r e - p r o n e materials m a t e r i a l s ranges ranges from from 18 tto percent iin takeni nint hthe 18 o 41 41 percent n samples samples taken e l late a t e Fall F a l l of o f1972. 1972. This T h i s approaches approaches water has observed aatt various times the Free water has been been observed times t h e pplastic l a s t i c llimits i m i t s of o f the t h e soils. s o i l s . Free of water ttable o f year y e a r on on these these slides s l i d e s and and the t h e ground ground water a b l e is i s frequently f r e q u e n t l yextremely extremely close close to Averagep rprecipitation e c i p i t a t i o n i in n tthis h i s area area is i s 34 34 inches, inches, much much oof f iitt t o the t h e surface. surface. Average meltwater iinn the t h e form form of o f snowfall s n o w f a l l whose whose meltwater i s isa as isignificant g n i f i c a n t ffactor a c t o r in i n the the frequent frequent occurrence occurrence ooff Spring Spring sslides. lides. IIttisi sextremely extremely uunlikely n l i k e l y tthat h a t chemical chemical o or r e electrical l e c t r i c a l sstabilization t a b i l i z a t i o n ooff these slopes wwill Surface drainage drainage appears i l l prove prove useful. u s e f u l . Surface appears tto o be be the t h e most most these slopes economic formo fofslope slopec ocontrol economic form n t r o l i in n tthis h i s instance. instance. 5 �HIGH-GRADE MAGNETITE HIGH-GRADE MAGNETITE DEPOSITS DEPOSITS AT AT REPUBLIC, REPUBLIC, MICHIGAN: MICHIGAN: THEIR BEARING ON THE GENESIS O F MARQUETTE RANGE HARD ORE* ORE* OF U.S. Geological Survey, Survey, Washington, D.C. D.C. 20244 20244 W.F. Cannon, U.S. W.F. ABSTRACT ABSTRACT Hard ore (60—65 (60-65 percent Fe) in i n the Marquette Iron Range consists c o n s i s t s of I t characteristicalcharacteristicalconcentrations of specularite, s p e c u l a r i t e , magnetite, and and martite. martite. It thethe Negaunee lly y occurs at a t the thetop topofof NeqauneeIron—formation Iron-formation and and over over a few feet feet grades grades llaterally a t e r a l l y and downward into i n t o jaspilite j a s p i l i t e (30-35 (30-35 percent percent Fe). Fe). Van Hise Hise classic and Leith (1911) (1911) developed the now c l a s s i c concept tthat h a t tthe h e ore was formed by surface weathering and leaching of silica s i l i c a from from the iron-formation iron-formation prior prior to deposition of the unconformably overlying Goodrich Quartzite, and the t o deposition of the unconformably overlying Goodrich Quartzite, and the ore produce tthe o r e was was later l a t e rdeformed deformed and and metamorphosed metamorphosed t to o produce h e present present specularite— speculariterich "This hypothesis hypothesis has has withstood withstood critical c r i t i c aexamination l examinationby bymany many r i c h rock. rock. This geologists; evidence in its support is especially compelling in the eastern geologists; evidence i n i t s support i s especially compelling i n the eastern part p a r t of the t h e Marquette Marquette Range. Range. Boyum (1964) (1964) and Anderson (1968) (1968) have suggested suggested that concept, although although probably probably valid, v a l i d , is i snot not adequate adequate tto o explain explain aall ll t h a t this concept, ffeatures e a t u r e s of of the the ore ore bodies. bodies. M y own leadsme me My ownreexamination reexaminationofofthese these deposits deposits leads to support conclusions. II believe to supportBoyum's Boyum's and and Anderson's conclusions. believe that t h a tmuch much of of the the ore, o r e , especially e s p e c i a l l y specularite—rich s p e c u l a r i t e - r i c h ore, ore, has formed as suggested suggested by Van Van Hise and Leith, magnetite-rich ore (commonly Leith, but that t h a t magnetite-rich (commonly greater g r e a t e r than than 90 90 percent magnetite) has has aa different magnetite) d i f f e r e n t origin. origin. - At the Republic open pit, the jaspilite unit at the top of the Negaunee A t the Republic open p i t , the j a s p i l i t e u n i t a t t h e t o p of the Negaunee Iron-formation Iron-formation iiss presently presentlybeing beingmined. mined. The The jjaspilite a s p i l i t e is i s the the host h o s t rock rock The ffor o r magnetite-rich magnetite-rich hard hardore, o r e which , whichwas waspreviously previouslymined minedunderground. underground. The piti t provides p provides exceptional exceptionalexposures exposures of ofthe t h ehigh—grade high-grade magnetite magnetite ore ore bodies bodies and and ttheir h e i r contacts contacts with with the the surrounding surrounding j jaspilite. aspilite. Three ccritical r i t i c a l features features Three common hard—oredeposits deposits iinn the common t otoaall l l magnetite—rich magnetite-rich hard-ore t h e Marquette Marquette Range Range and and difficult d i f f i c u l ttot oexplain explainby bythe theweathering weathering hypothesis hypothesis are a r e shown shown tthere h e r e bbetter e t t e r than than at other a t any any o t h e r locality. locality. 1) Although Althoughsspecularite alll lhard—ore bodies, magnetite 1) p e c u l a r i t e is i scommon common tto o a hard-ore bodies, magnetite i s the thepredominant predominant mineral n many, a r t i c u l a r l y in i n higher higher grade grade is mineral iin many,pparticularly metamorphic rocks toward toward the the west west end end of of the the Marquette Marquette Range. Range. The magnetite-rich magnetite-rich ore ore contains contains ttextural The e x t u r a l evidence evidence iindicating n d i c a t i n g tthat hat formedaafter it has formed f t e r regional regional deformation. deformation. it a) a) The ore iiss massive, textures are massive, deformational deformational textures a r e absent, absent, and and "The ore magnetite grains aare magnetite grains r e largely l a r g e l y euhedral euhedral and and undistorted. undistorted. b) b) Bodies of massive massiveore ore sharply sharply truncate truncate schistose Bodies of s c h i s t o s e and and crenulated specularite—rich crenulated specularite-rich jjaaspilite. spilite. c c)) The magnetite-rich oreis icommonly s commonlysomewhat somewhat vuggy vuggy and porous, porous, The magnetite-rich ore containing sspecularite, containing p e c u l a r i t e , dolomite, dolomite, and and quartz crystals c r y s t a l s in i n vugs. vugs. 6 �2) 2) Magnetite—rich Magnetite-rich ore ore is i s characteristically c h a r a c t e r i s t i c a l l y associated associated with w i t h quartz quartz veins. (+ dolomite, s u l f i d e ) veins. dolomite, sulfide) ±. ± 3) 3) Although ~ l t h o u g hthe the magnetite—rich magnetite-rich ore ore invariably invariably occurs occurs in i n hematitic hematitic iron—formation iron-formation (jaspilite), ( j a s p i l i t e ) , the the ore o r e bodies are a r e surrounded surrounded by by narrow narrow haloes haloes in i n which which jasper jasper was was converted converted to t o gray gray chert c h e r t or or milky milky quartz quartz and and some some specularite s p e c u l a r i t e was was reduced reduced to t o magnetite, magnetite, i s associated associated i n d i c a t i n g that t h a t the the formation formation of of magnetite-rich magnetite-rich ore ore is indicating with w i t h aa reducing reducing process process rather r a t h e r than than an anoxidizing oxidizingprocess process such such as as weathering. weathering. + The magnetite—richore oreiis s probably probably of of hydrothermal hydrothermal origin o r i g i nand andbecause because The magnetite-rich s the only only recognized recognizedpost postiron—formation iron-formation Penokean regional metamorphism iis Penokean regional metamorphism the fluids f l u i d swere wereprobably probably derived derivedby by dehydration dehydration and and dedethermal event, event, the thermal carbonatization carbonatization of ofthe theiron—formation iron-formation and and underlying underlying rocks rocks during during progressive progressive regional metamorphism metamorphism which which reached reached sillimanite s i l l i m a n i t e grade grade at a t Republic. Republic. regional topt oof thethe Negaunee l o c a l i z a t i o n of of the t h eore o r eatathe t the p of NegauneeIron-formation Iron-formation The localization The might be explained explained through throughthe the buffering buffering aaction might be c t i o n of of the theiron-formation iron-formation on on A s fluids f l u i d s(considered (consideredhere hereasa sF120 H20 for for the oxygen oxygen fugacity h e fluids. f l u i d s . As the fugacity of of tthe CO2 rrich) i c h ) are a r e expelled expelled during during metamorphism metamorphism s i m p l i c i t y but but probably probably also a l s o CO2 simplicity w i l l contact contact first f i r s t the the and pass pass upward upward through through the t h e rock rock section, s e c t i o n , they they will and magnetite-silicate and r e l a t i v e l y reduced reduced magnetite-silicate andmagnetite—carbonate magnetite-carbonate uunits n i t s iin n the the relatively lower lower part p a r t of ofthe theNegaunee Negaunee and and will w i l ltend tendtoward towardan anequilibrium equilibriumoxygen oxygen fugacity determined on figure f i g u r e1,1, determined by by aa buffer b u f f e r curve curve fugacity (f02), ( f o 2 ) ,such such as a s point p o i n t 11on such as curve curve A, A, and and will w i l l contain contain concentrations of ferrous ferrous and and ferric f e r r i c iron iron such A s fluids f l u i d spass passupward upward and and species appropriate appropriate for f o r that t h a tf02 f o 2and andtemperature. temperature. As species contact the jaspilite, whichthe thej jaspilite contact the j a s p i l i t e , a aredox redoxreaction reaction must must occur occur iin n which a s p i l i t e is is partly of sspecularite p a r t l y reduced reduced by by the the conversion conversion of p e c u l a r i t e to t o magnetite magnetite and and the the fluids fluids are bybythethe hematite— a r e oxidized oxidized to toachieve achievean anf07, f o such suchasa point s p o i n2, t 2determined , determined hematiteThe increased increased f02 f of of the t h e fluids f l u i d sand andconsequent consequent B). Tfie magnetite buffer magnetite buffer fcurve urve B). 02 lower species lower ssolitility o l u b i l i t yofofferrous ferrousiron iron speciesand andthe theoxidation oxidationofofsome some ferrous ferrous iron i r o n to t o less l e s s soluble soluble ferric f e r r i c species species results r e s u l t s in i n the the precipitation p r e c i p i t a t i o n of of Textures clearly clearly magnetite. Textures magnetite. indicate i n d i c a t e that t h a t silica s i l i c a was removed removed during during the the wasp precipitated its hydrothermal activity a c t i v i t yand and the themagnetite magnetite presumably presumably was r e c i p i t a t e d iin n its hydrothermal Because t the h e equilibrium equilibriumff02 of the buffered assentlages is of the buffered assemblages i s very very place. Because small atmffor the02 probable small small (10-40 (10-40 to t o10—20 10-20 atm o r the probable conditions conditionsof ofmetamorphism), metamorphism), small volumes of l a r g e volumes volumes of l u i d , and and the t h e system system can can volumes of rock rock can can buffer buffer very very large of ffluid, buffered until u n t i l all a l l hematite hematite in i n the the jaspilite j a s p i l i t e is i s converted converted to t o magnetite. magnetite. remain buffered I propose that t h a t the the magnetite—rich magnetite-rich ore ore has has formed formed by: by: 1) 1) the reduction reduction of hematite to t o magnetite magnetite during duringa ahematite—magnetite hematite-magnetite b u f f e r reaction; reaction; 2) 2) buffer of the precipitation p r e c i p i t a t i o nofofmagnetite magnetitefrom fromhydrothermal hydrothermal (metamorphic) (metamorphic) ffluids l u i d s as a s the the the fluids oxidized during duringt that reaction and and tthe f l u i d s were were oxidized h a t bbuffer u f f e r reaction h e ssolubility o l u b i l i t y of of i r o nwas was decreased. decreased. ferrous iron 7 �2 t HEM. 1 Fe—SILICATE T Figure Figure 1.-— I.-- T—f0 T-f diagram showing e l a t i v e positions p o s i t i o n sofof hematite-magnetite diagram showingrrelative hematite—magnetite 02 buffer buffer curvi curveand and aabuffer buffercurve curvedetermined determined by by the the equilibruim: equilibruim: quartz magnetite == Fe—silicate. F e - s i l i c a t e . Points Points 1 1 and and 22 iillustrated l l u s t r a t e d difdifquartz ++ magnetite ference ference in i n f02 f o2 controlled controlledby by the thebuffered bufferedassemblages assemblages at a t constant constantT. T. The formation ore t oto require e s t r i c t e d set set The formationofof magnetite-rich magnetite—rich oreappears appears requirea ar restricted of of conditions: conditions : 1) must reach 1)Metamorphism Metamorphism must reach a t at l eleast a s t bbiotite i o t i t e grade, grade, although although most most l l large l a r g e ones ones are a r e in i n garnet garnet or o rhigher higher grade. grade. ore bodies bodies and and aall ore 2) 2 ) Iron-formation Iron-formation with mostly ferric f e r r i c iron, i r o n , such as a s jaspilite, j a s p i l i t e , must be physically physically above above iron-formation iron-formation with w i t h abundant abundant ferrous ferrous iron. iron. 3) 3) A stratigraphic s t r a t i g r a p h i c or o r structural s t r u c t u r a l trap t r a p capable of concentrating concentrating the the flow flow of of fluids f l u i d s must must be be present. present. The The Goodrich Goodrich Quartzite Quartzite and and metadiabase metadiabase sills s i l l s and and dikes dikes were were apparently apparently relatively r e l a t i v e l y impermeable, impermeable, and the Negaunee—Goodrich Negaunee-Goodrich contact contact near near anticlinal a n t i c l i n a l crests c r e s t s and and dikedikeand the quartzite q u a r t z i t e intersections i n t e r s e c t i o n s were were favorable favorable loci l o c i for f o rore o r eformation. formation. The absenceofofany anyofof these these tthree The absence h r e e conditions conditions iinhibits n h i b i t s the t h eformation formation of of magnetite-rich magnetite-rich ore. ore. References References Paderson, G . J . , 1968, 1968, The The Marquette Marquette district, d i s t r i c t , Michigan, Michigan, in i n Ridge, Ridge, J.D., J.D., Anderson, G.J., (ed.), (Graton-Sales (ed. ) , Ore deposits of the t h e United United States, S t a t e s , 1933—1967 1933-1967T~raton-Sales Volume), V. 1: 1:New New York, York, Pat. Am. Inst. I n s t . Mining, Metall., Metall., and and Petroleum Petroleum Volume), V. Engineers, Engineers, p. p. 505—517. 505-517. Boyum, B.H., 1964, 1964, The The Marquette Marquette mineral mineral district, d i s t r i c t , Michigan: Michigan: Inst. I n s t . on on Boyum, B.H., Lake Lake Superior Superior Geology, Geology, 10th, l o t h , Ishpeming, Ishpeming, Mich., Mich., May May 1964, 1964, Guidebook, Guidebook, 13 13 p. p Van C.R., and and Leith, Leith, C.K., C.K., 1911, 1911, The The geology geology of of the the Lake Lake Superior Superior Van Hise, Hise, C.R., region: region: U.S. U.S. Geol. Geol. Survey Survey Mon. Mon. 52, 52, 641 641 p. p. * Work Work done doneinicooperation n cooperation with Geological Survey Division, with Geological Survey Division, Michigan Dept. * of of Natural Natural Resources Resources 8 Michigan Dept. �THE VOLCANICS NORTH THE KEWEENAWAN KEWEENAWAN VOLCANICS NORTH OF OF THE THE GOGEBIC GOGEBICRANGE RANGE IN I NWISCONSIN WISCONSIN Roger W. W. Cooper, Cooper, Department Department of o fGeology Geologyand andGeophysics, Geophysics, Roger U n i v e r s i t yofoWisconsin—Madison, f Wisconsin-Madison, Madison, Madison, Wisconsin Wisconsin 53706 53706 University ABSTRACT ABSTRACT The sequencennorth The Keweenawan Keweenawan v ovolcanic l c a n i c sequence o r t h of o f the t h eGogebic GogebicRange Range has has aa total t o t a lthickness thicknessofo more f more than than 35,000 35,000 feet f e e t and and an an attitude a t t i t u d e ofo fabout about This sequence of volcanic flows was investigated NW. T h i s sequence o f v o l c a n i c f l o w s was i n v e stigated N65-75 E, 70-80 N65—75 70—80 NW. to t o determine determine iiff aa stratigraphic s t r a t i g r a p h i c division d i v i s i o nofothe f t h eflows f l o w sinto i n tmappable o mappable units units Four units have been defined on the basis of texture, Four u n i t s have been d e f i n e d on t h e basis o f t e x t ure, c o u l d be be achieved. achieved. could petrographic characteristics, c h a r a c t e r i s t i c s ,and andchemical chemi c a l analyses. analyses. petrographic Unit U n i t 1, 1, which which is i s the t h e basal basal unit, u n i t , consists c o n s i s t s of o fabout about 5000 5000 ffeet e e t of of p i l l o w basalts b a s a l t sand and subalkaline subal k a l i n e basalts. basalts. The The basalts b a s a l t sare aremedium— medium- to to pillow The ttextures e x t u r e s most most common common i nint hthis i s unit unit f i n e - g r a i n e d and and grayish—green. grayish-green. The fine—grained are are intergranular i n t e r g r a n u l a r and and subophitic, s u b o p h i t i c , with w i t hophitic o p h i t itexture c t e x t u rless e l e scommon. s common. Unit U n i t 22 is i sabout about 20,000 20,000 ffeet e e t thick t h i c k and and consists c o n s i s t s of o f flows flows more more alkaline alkaline are aaphanitic The fflows l o w s are p h a n i t i c tto o fine-grained, fine-grained, than those those found U n i t 1. 1. The than found iinn Unit most common common The most t e xtextures t u r e s a are r e i nintergranular tergranular b l u i s h - g r a y to t oreddish-brown. reddish-brown. The bluish-gray Flows ooff rather r a t h e r basic basic and iintersertal n t e r s e r t a l with w i t hmicrophenocrysts microphenocrysts of o f plagioclase. plagioclase. Flows and composition neart hthe bottomo of and f felsic composition near e bottom f t hthe e uunit n i t give g i v e way way tto o intermediate i n t e r m e d i a t e and elsic flows upward. upward. flows Unit p o o r l yexposed exposed but b u t estimated estimated to t o be be 2000 2000 tto o 4000 4000 ffeet e e t thick. thick. U n i t 33 isi spoorly ItI tisi scomposed composed o of f pporphyritic o r p h y r i t i c f felsic e l s i c flows flows that t h a t have have aa ppink i n k t to o sslightly lightly purple abundantphenocrysts phenocrystsoof p u r p l e groundmass groundmass wwith i t h abundant f ffeldspar e l d s p a r and and quartz. Unit by gglacial U n i t 44 is i swidely w i d e l y covered covered by l a c i a l drift d r i f but t b uestimated t estimatedtot obe beabout about The flows appear to be mainly mafic, gray, and usually The flows appear t o be m a i n l y m a f i c , gray, and u sually 10,000 ffeet e e t thick. thick. 10,000 The flows are highly vesicular; pipe The flows are h i g h l y v e s i c u l a r ; p i p e n o t more more than than 20—25 20-25 f efeet e t tthick. hick. not amygdules and e s i c u l a rtops topsare are common. Interbedded Interbedded wwith i t h these these flows f l o w s are are amygdules and vvesicular common. The pebbles pebbles found found sedimentary rocks ranging from sedimentary rocks from conglomerate conglomerate ttoo shale. shale. The interbedded flows and These interbedded and i n these these beds beds are are predominantly predominantly f felsites. e l s i t e s . These in sedimentary beds beds pass pass upward upward into i n t othe t h eCopper CopperHarbor HarborConglomerate. Conglomerate. sedimentary The sequenced idisplays general compositional The Keweenawan Keweenawan v ovolcanic l c a n i c sequence s p l a y s aa general compositional trend upward t r e n d from from subalkaline s u b a l k a l i n e ttholeiitic h o l e i i t i basalts c b a s a l tat s athe t t hbase e base upwardthrough through After the extrusion o f these these the t h e porphyritic p o r p h y r i t i c felsic f e l s i c flows flows of o f Unit U n i t 3. 3. A f t e r t h e e x t r u s i o n of f e l s i cflows flowsthere t h e r eappears appears to t ohave have been been iintermittent n t e r m i t t e n t volcanism volcanism of o f aa felsic more alongwwith more mmafic a f i c nnature a t u r e along i t h eerosion r o s i o n o of f t the h e ffelsic e l s i c flows. flows. 9 �SOUTHWEST WISCONSIN PEDIPLAIN SOUTHWEST WISCONSINAS ASA ADIJRICRIJSTED DURICRUSTED PEDIPLAIN Dury, Departments of GG. . HH. . Dury, o f Geography and and Geology, Geology, The The University U n i v e r s i t y of o f Wisconsin-Madison, Wisconsin-Madison, Science S c i e n c e Hall, H a l l , Madison, Madison, Wisconsin Wisconsin 53706. 53706. ABSTRACT ABSTRACT The Driftless D r i f t l e s s Area of of Southwest Wisconsin and and adjacent adjacent parts p a r t s of of Minnesota, Iowa, Iowa, and and Illinois I l l i n o i s consists c o n s i s t s of o f dissectdissected e d plateau p l a t e a u country c o u n t r y traversed t r a v e r s e d by by the t h e Wisconsin Wisconsin and and MississMississhas iippi p p i Rivers. R i v e r s . IIn n tthe h e ppast, a s t , the t h e area area h a s been described d e s c r i b e d in in terms o of orr more more ppeneplains, terms o of terms f one o e n e p l a i n s , aand/or n d / o r iin n terms f a sseries e r i e s of o f cuestas. cuestas. IIn n aactuality, c t u a l i t y , it i t is i s recognizable r e c o g n i z a b l e as a s aa dissected d i s s e c t e d pedipedithe few residuals that have escaped plain: p lain: the residuals t h a t e s c a p e d planation p l a n a t i o n rise rise ssharply h a r p l y from the t h e summit surface s u r f a c e and and exhibit e x h i b i t typical t y p i c a l pedipedii s widespread, widespread, ment profiles. p r o f i l e s . Evidence of o f deep deep weathering w e a t h e r i n g is On carbonates, the rregardless e g a r d l e s s of o f lithology. l i t h o l o g y . On c a r b o n a t e s , t h e deep deep weatherweathering i n g pprofiles r o f i l e s consist c o n s i s t of o f rotted r o t t e d rock r o c k and and red r e d residuum; residuum; but but part p a r t of o f the t h e latter l a t t e r may have been introduced i n t r o d u c e d subsequently subsequently weathering. tto o deep w e a t h e r i n g . On On arenites, a r e n i t e s , the t h e profiles p r o f i l e s are a r e varyingly varyingly horizonated h o r i z o n a t e d into i n t o pallid, p a l l i d , mottled, m o t t l e d , and and duricrusted d u r i c r u s t e d zones, zones, tthe h e ppallid a l l i d zones zones frequently f r e q u e n t l y showing tthe h e rresults e s u l t s of o f attack attack on q quartz grains, and the crusts ranging from highly uartz grains, the c r u s t s ranging highly fferruginous e r r u g i n o u s to t o highly h i g h l y siliceous. s i l i c e o u s . Crust C r u s t texture t e x t u r e can can be be Ferruginous nodules rreplicated e p l i c a t e d in i n Australian A u s t r a l i a n samples. s a m p l e s . F e r r u g i n o u s n o d u l e s in in Wisconsin pprofiles widely have developed tthe h e Wisconsin r o f i l e s aappear ppear w i d e l y tto o have within w i t h i n bedrock. bedrock. On O n eeither i t h e r side s i d e of of the t h e lower lower Wisconsin river, r i v e r , the the deeply-weathered d e e p l y - w e a t h e r e d and and d.uricrusted d u r i c r u s t e d ssurface u r f a c e defines d e f i n e s aa wide wide of which tthe glacial sshallow h a l l o w vvalley, a l l e y , iinto n t o tthe h e ffloor loor o f which he g lacial ssluiceway l u i c e w a y is i s incised. i n c i s e d . IInvestigation n v e s t i g a t i o n of o f ppossible o s s i b l e comparcompari s in i n proproaable b l e rrelationships e l a t i o n s h i p s for f o r the t h e Mississippi M i s s i s s i p p i trench t r e n c h is Ass could c o u l d bbe e expected, e x p e c t e d , there t h e r e is i s evidence e v i d e n c e that t h a t the the ggress. ress. A weathering was, to deep w e a t h e r i n g was, t o some extent e x t e n t at a t least, l e a s t , aa groundgroundwater and some some thin t h i n crusts c r u s t s appear a p p e a r to t o have have been been w a t e r phenomenon; and ddeposited e p o s i t e d under carbonates c a r b o n a t e s in i n the t h e subsurface. subsurface. Outstanding problems include O u t s t a n d i n g problems i n c l u d e the t h e distribution d i s t r i b u t i o n of o f the the deeply-weathered d e e p l y - w e a t h e r e d surface s u r f a c e in i n glaciated, g l a c i a t e d , in i n addition a d d i t i o n to t o ununglaciated, g l a c i a t e d , areas; a r e a s ; the t h e relationship r e l a t i o n s h i p of o f some some ferruginous ferruginous ccrusts r u s t s tto o ssuiphide u l p h i d e deposition d e p o s i t i o n or o r translocation; t r a n s l o c a t i o n ; and the the off the ttime-stratigraphic i m e - s t r a t i g r a p h i c pposition osition o t h e latest l a t e s t local l o c a l episode episode off deep weathering. o weathering. 10 �PROGRESS REPORT PROGRESS REPORT OF OFTHE THECOMMITTEE COMMITTEEON ONKEWEENAWAN KEWEENAWAN STRATIGRAPHY STRATIGRAPHY C. Green, Green, Geology Department, Department, University of of Minnesota, Minnesota, Duluth, John C. Duluth, Duluth, Duluth, Minnesota 55812 and Minnesota Geological Survey ABSTRACT A BSTRACT An A n informal Committee on Keweenawan Stratigraphy was formed in in February 1973 of p participants 1973 in i n response to t o tthe h e wishes of a r t i c i p a n t s at a t the Symposium Symposium on Late Precambrian Geology of of the t h e Lake Superior Area at a t the Annual Meeting members are a r e George V. V. Cohee, Cohee, Campbell Campbell t h e G.S.A. G.S.A. in i n Minneapolis. Minneapolis. Its members of the Craddock, H. Dott, A. Hubbard, Hubbard, Craddock, Robert H. Dott, John C. C. Green (chairman), (chairman), Harold A. Wm. H. Vs. H. Mcllwaine, McIlwaine, Glenn Glenn B. B. Morey, Morey, and and Walter Walter S. S. White. White. Some Some rather r a t h e r wide differences of of opinion and usage aare by tthe differences r e represented by h e members and because of s i n c e its i t s organization, organization, few few areas a r e a s of complete of the short s h o r t time elapsed since consensus have developed by the t h e mid—March mid-March abstract a b s t r a c t deadline. deadline. name "Keweenawan" The name "Keweenawan" appears appears to t o be be widely widely considered considered as a s applying to, to, not formally defined as, as, aa p provincial supergroup, a ass iif f not r o v i n c i a l llithostratigraphic i t h o s t r a t i g r a p h i c supergroup, part well as a s to t o that that p a r t of of geologic time t i m e when the Keweenawan Supergroup was being formed. formed. It would then be composed composed of of various groups and formations, formations, but many of these stratigraphic s t r a t i g r a p h i c units u n i t s have yet y e t to t o be formally formally defined. defined. An An attempt will w i l l be be made made to t o clarify c l a r i f y their t h e i r stratigraphic s t r a t i g r a p h i c relationships. relationships. wrestling with with tthe of tthe most appropriate The Committee is aalso l s o wrestling h e problem of h e most which tto of the sstratigraphic t r a t i g r a p h i c llevels e v e l s aatt which o define the base and tthe h e top of Keweenawan, the assumption that t h a t there there should be some some unifying geotectonic geotectonic Keweenawan, on the many respects respects tthe Disturbance" coherence implied implied by by the t h e name. name. IIn n many h e "Keweenawan Disturbance" could be compared with with tthe of Late T Triassic h e Palisades Disturbance of r i a s s i c time, time, and 8, "Keweenawan" rocks could be defined a as of tthis Keweenawan" rocks s those formed aass a result r e s u l t of his event ofevents eventsiin the area Mid—Continent Gravity High event or o r complex complex of n the a r e a of of tthe h e Mid-Continent High or o r aatt least l e a s t the the Lake Superior Superior District. District. 11 �AN AN UNUSUAL UNUSUAL MANGANESE MANGANESE DEPOSIT IN I NKEWEENAWAN KEWEENAWAN LAVA LAVA COPPER HARBOR, MICHIGAN COPPER HARBOR, MICHIGAN E. Heinrich, Department E. Wm. Wm. Heinrich, Department of o f Geology Geology and and Mineralogy, Mineralogy, U n i v e r s i t y of o fMichigan, Michigan, Ann Ann Arbor, Arbor, Michigan. Michigan. University ABSTRACT ABSTRACT One ooff the t h e rare r a r enon—cupriferous non-cupriferous mineral mineraldeposits depositsin iKeweenawan n Keweenawan lava lava One i s the t h emanganese manganese occurrence occurrence just j u s teast e a sof t oManganese f ManganeseLake Lake and and about about one one is m i l e south south of o fCopper Copper Harbor Harbor in i n sec. 58N,R.R.26W. 26W. Butler sec. 4,4, T.T.58N, mile B u t l e rand andBurbank Burbank (1929, p. p. 59) 59) rrefer e f e r to t o that t h a t deposit d e p o s i t as t h e Manganese Manganese mine" tate as "... the mine" and and sstate that t h a t "... some some ore was was shipped t h e mine." mine. " shipped from from the "... "... The ddeposit e p o s i t is i s aacalcite—rich c a l c i t e - r i c hreplacement replacement lens lensini nananamygdaloid amygdaloid The t h a t is i sstratigraphically s t r a t i g r a p h i c a l lay short a s h odistance r t d i s t a n cbelow e belowthe t h ebase baseofo fthe t h eCopper Copper that Harbor Harbor ("Great") ("Great") Conglomerate. Conglomerate. Old workingsi nindicate Old workings d i c a t e tthat h a t the t h e mineralimineral iz a t i o n extends extends east-west along t h ethe s t strike r i k e oof f tthe h e amygdaloid amygdaloid f ofor r aatt least least zation east—west along a few few hundred hundred ffeet. e e t . The The replacement o n s i s t s ooff material m a t e r i a l grading grading replacementrock rockcconsists from nearly n e a r l y pure pure coarse—grained coarse-grained wwhite h i t e ccalcite a l c i t etot ohigh—grade high-grade black black from manganese oxide ore. The manganese oxide The manganese manganese minerals c l u d e hypogene hypogene brauni te, mineralsi ninclude braunite, o r i e n t i t eand andmanganite manganiteand andsome some supergene supergene ppyrolusite. yrolusite. A orientite A trace t r a c e of o f chalcochalcocite c i t eand and very very minor minor goethite g o e t h i t eare arethe t h eonly o n l other y o t h ehypogene r hypogene species, species, and and l i m o n i t e , chalcedony chalcedony and and opal opal ini nsmall smallamounts m o u n t sare aresupergene. supergene. The The limonite, manganese minerals i n and ace t hthe e ccalcite. alcite. manganese mineralsv evein andrep1 replace T h i s occurrence occurrence of o f orientite, o r i e n t i t ea, hydrous a hydrous calcium-manganese s silicate, ilicate, This calcium—manganese i s believed b e l i e v e d to t obe beonly o n l ythe t h esecond second recorded recorded ffor o r the t h e world. world. (The is (The type type locality l o c a l i t yisi in s i Oriente n O r i e n t Province, e Province,Cuba.) Cuba.) The mineral appears as gglistening The mineral appears as listening copper-red needles forming minute minute rradial exceedingly copper-red need1 es forming a d i a l aggregates aggregates and and exceeding1 y ffineine- grained matted matted lenses. lenses. The amygdaloid,oother than being beingeextensively replaced by by ccalcite, The hhost o s t amygdaloid, t h e r than x t e n s i v e l y replaced alcite, which which aalso l s o f fills i l l s the t h e vesicles v e s i c l e s eentirely n t i r e l y alone, alone, iis s relatively r e l a t i v e l y fresh. f r e s h . Neither Neither native n a t i v e copper copper nor n o r the t h e characteristic c h a r a c t e r i s t i suite c s u i of t e accompanying o f accompanyingsecondary secondary s i l i c a t e sisi present, s present,although althoughnative n a t i v ecopper coppermineralization m i n e r a l i z a t i o nofothe f t hcross— e crosssilicates f i s s u r e type type occurs occurs at a t the t h e Clark Clark mine mine a short s h o r t distance d i s t a n c e to t o the t h e south. south. fissure The ddeposit e p o s i t is i s believed b e l i e v e d to t obe bepenesyngenetic penesyngenetic and rigin. The and volcanogenic volcanogenici nin oorigin. 12 �UPPERMISSISSIPPI MISSISSIPPI VALLEY UPPER VALLEY LEAD—ZINC LEAD-ZINC DISTRICT DISTRICT A. V. V. Heyl, A. Heyl, U.S. U.S. Geological Geological Survey, Survey, Denver, Denver, Colorado Colorado 80225. ABSTRACT ABSTRACT The UpperMississippi MississippiValley Valley ddistrict The Upper i s t r i c thas hasbeen been the the source source of of about about aa billion bi 1 liondollars do1 l a r (present—day s (present-day prices) worth worth of of zinc zincand and lead, lead, and and minor minor amountsofof copper copper and and barite. barite. Ore amounts Ore deposits deposits are are chiefly chiefly ininlimestone limestone and and dolomite of of the Galena, Decorah,and andP lPlatteville dolomite Galena, Decorah, a t t e v i l l e Formations, Formations, aall l l of of Middle Middle Locally, small of lead, Ordovician age. age. Locally, small deposits deposits of lead, zinc, zinc, and and iron iron sulfide s u l f i d ehave have been mined mined from from underlying underlying Lower been Lower Ordovician Ordovi cian dolomite do1 omi t eand andUpper Upper Cambrian Cambrian sandstoneand andover1 overlying UpperOrdovician Ordovicianshale shale and andSiSilurian sandstone yi ng Upper 1uri an dolomite. do1 omi t e . No No post—Precambrian igneous rocks known theregion, region, and andggranitic post-Precambrian igneous rocks areareknown in in the r a n i t i c and and metasedimentaryPrecambrian Precambrian basement rocks unconformably underlie metasedimentary basement rocks unconformably underlie thethed idistrict strict at algal reefs a t depths depths of 1,500 1,500 to t o 2,000 2,000 feet. f e e t . No No algal reefs are are known known in the the Middle Middle Ordovician rocks, rocks, and b u t not not an an unconformity, unconformi t y , separates separates these these Ordovician and a diastem, di astern, but rocks rocks from from Upper Upper Ordovician Ordovician shale. The The sstrata t r a t a are are gently gently flexed and and faulted, probably largely largely the probably the result r e s u l tofofgentle gentlecompressive compressive and and rotational rotational adjustments adjustments in the along the underlying underlying crystalline c r y s t a l l i nbasement, e basement,especially especially alonglineaments lineamentsbetween between basement blocks. blocks. Folds basement Folds of three three orders orders ofofmagnitude magnitude are are recognized, recognized, and and many relatedjoints joints and reverse, sstrike—slip, normalf faults of small many related and reverse, t r i k e - s l i p , and and normal a u l t s of small to to moderate displacements displacements are are present. moderate The zinc—leaddeposits depositsrange rangei ninplan plan from fromllinear The zinc-lead i n e a r through through arcuate arcuate to to Theyare areepigenetic epigeneticand andp opostlithification Most ore eelliptical. l l i p t i c a l . They s t l i t h i f i c a t i o n deposits. deposits. Most and vugs, i n fractures, fractures,breccias, brecci as, and vugsbut , b usome t someimpregnated impregnated openspaces spaces in ffilled i 11edopen and replaced replaced wall wallrock. openspace spacei is along shears, small reverse and rock. The The open s a1 ong shears, reverse and and bedding—plane joints re1 related bedding-pl ane f a ufaults, l t s , joints ated tto o intermediate intermediate tto o small small folds, folds, and and within structures. Sphalerite and galena are are the the principal within solution—slump solution-slump structures. and galena ore minerals, and ore and the the general general sequence sequence of deposition depositionofofmain mainore oreand andgangue gangue minerals was: quartz, iillite, was: quartz, l l i t e dolomite, , dolomite, pyrite, pyrite,marcasite, marcasite, cobaltite(?), cobal t i t e ( ? ) , sphalerite, galena, chalcopyrite,mmillerite, sphalerite, galena, chalcopyrite, i l l e r i t e , barite, b a r i t e , and and calcite. c a l c i t e . Wallrock Wall rock rocks,ssilicification, aalterations l t e r a t i o n s include include solution of the the carbonate carbonate rocks, i l i c i f i c a t i o n dolomiti— , dolomititype of of clay, zation, changes changes i in n type clay, addition additionofoftrace traceelements, elements, and and sanding sanding of dolomite. Country rock between orebodies bodiesiis Country rock between ore s unaltered. Oxygen-isotope, carbon-isotope, lead-isotope, Oxygen-isotope, carbon-isotope, lead-isotope, sulfur—isotope, sulfur-isotope, and and Bubbles in sphalerite—stratigraphy studies studies are or in progress. sphalerite-stratigraphy are completed completed or progress. Bubbles sulfide and mineralsare are ffilled sulfide and gangue gangue minerals i l l e dwith withconcentrated concentratednear—neutral near-neutral chloride brines that lead iinn the brines t h a t have have filling f i l l i n temperatures g temperaturesofof1200 120' tot o40°C. 40°C The The lead the galena iiss notably galena notably radiogenic. radiogenic. Themetals metals and andsulfur sulfur are postulated The postulated to t o be be derived derived from fromheated heated basin basin brines that were later diluted by meteoric waters. magmaticf lfluid brines t h a t were l a t e r diluted by meteoric waters. A A magmatic u i d contribution possible, but b u t iti tisi snot notsupported supported by by present present ffluid l u i d inclusion inclusion data. data. bution is possible, magmatichearth hearthinin the the basin basin areas AA magmatic areas ttoo the the south south and and southwest southwest is i s the themost most possible heat possible heat source. source. AA large lateral l a t e r a component l component of of flow flowthrough throughpermeable permeable Cambriansandstone sandstone updip from basinsi sisprobable, probable, bbut u t available available evidence evidence Cambrian updip from thethebasins 13 �the ddistrict Within the istrict suggests flow through fracture zones. suggests some some flow through basement basement fracture zones. Within the ore from tthe aquifers through ore solutions solutions flowed flowed upward upward from h e aquifers through available fracture fracturesystems systems into i n t oMiddle MiddleOrdovician Ordovician strata s t r a t awhere wherethey theyleached leachedcarbonate carbonate physicalrrestraints properties of of the rocks. rocks. Changes Changes i ninphysical e s t r a i n t s and and chemical chemical properties the ore ore solutions n andnear nearopen openspaces spaces solutions allowed allowed ore ore minerals minerals tot obebedeposited depositedini and derived from from leaching. leaching. derived 14 �THE THE GEOLOGY GEOLOGY OF OF BEECHER BEECHER AND AND PEMBINE PEMBINE TOWNSHIPS TOWNSHIPS MARINETTE MARINETTE COUNTY, COUNTY, WISCONSIN WISCONSIN Robert A. Jenkins Jenkins Robert A. Department of of Geology Geology and and Geophysics Geophysics Department University of of Wisconsin—Madison, Wisconsin-Madison, Madison, Madison, Wisconsin Wisconsin University Four Four metavolcanic metavolcanic formations, formations, separated separated by by major major faults, faults, occur occur in in Beecher Beecher and and Pembine Pembine townships townships in in northeastern northeastern Marinette County, County, Wisconsin. Wisconsin. The formations formations are are the the Quinnesec Quinnesec Marinette Formation, the the Mc Allister Allister Formation, Formation, the the Beecher Beecher Formation, Formation, Formation, the Pemene Pemene Formation. Formation. The relative relative ages ages are are uncertain uncertain and the but but the the order order of of naming naming is is suggested suggested as as the the order order of of decreasing decreasing age. All All the the formations formations have been been folded folded and and regionally regionally metametaage. morphosed morphosed to to greenschist greenschist facies. facies. In In general general the the rocks rocks have have not not been been strongly strongly sheared sheared or or altered, altered, and and primary structures structures volcanics have been been intruded intruded by by are well well preserved. preserved. The The volcanios are granite, granodiorites,quartz quartzdiorites, diorites,and andultrainafics. ultramafics. granite, granodiorites, The The Quinnesec Quinnesec Formation, Formation, over over 10,000 10,000 ft. thick, thick, consists consists predominantly predominantly of of tholeiitic tholeiitio metabasalts metabasalts and and cala-alkaline cala-alkaline metametaandesites. The formation formation is is isoclinally isoclinally folded; folded; axial axial planes planes andesites. of the the folds folds are are vertical vertical and and strike strike east. east. The The andesites andesites are are of of of two two types, types, one one nonporphyritic nonporphyritic and and pillowed, pillowed, having having its its source to the west and the other, other, porphyritic porphyritic and mainly agglomeratic, 100 to to 1,000 1,000 agglomeratic, having having its its source source to to the the east. east. AA 100 ft. thick is interlayered interlayered with with the the thick porphyritic porphyritic rhyolite rhyolite flow flow is andesites. andesites. The Mc Allister Formation, Formation, 1,000 1,000 to to nossibly ~ossibly10,000 10,000 ft ft The thick, consists consists of of metamorphosed metamorphosed tholeiitic tholeiitio basalt basalt agglomeragglomerthick, ate. alps vertically, vertically, and and faces faces ate. The The formation formation strikes strikes east, east, aips south. Fragment Fragment size in in the formation formation increases increases from from west west to to south. east, suggesting suggesting aa vent vent to to the the east. east. east, The Beecher Beecher Formation, Formation, at at least least 10,000 10,000 ft. thick, thick, strikes strikes N50°W, N~O'W, dips dips vertically, vertically, and and faces faces north. north. The The lower lower 9,000 9,000ft. ft. consists mainly mainly of of rhyolite rhyolite and and rhyodacite rhyodacite flows. flows. The The upper upper consists 1,000 ft. of the formation rhyformation is is an an alternation alternation of of bedded bedded rhy— olitic olitic tuffs tuffs and and acidic acidic fragmentals. fragmentals. The lower lower part part of of the the formation formation is is more highly sheared sheared and and altered than than other other formformations ations in in the the area. area. This This may be be due due to to intrusion intrusion of of the the Amberg Amberg granite granite into into the the lower lower part part of of the the formation. formation. Formation consists consists of 7,000 ft. of microspher— The Pemene Formation of microspherulitic ulitic soda soda rich rich rhyolite rhyolite and and rhyodacite rhyodacite flows. flows. The The flows flows are interlayered units and interlayered with a few few thin thin sedimentary sedimentary units and were Individual flows apparently apparently extruded extruded subaqueously. subaqueously. Individual flows are are 500 500 to 1,200 1,200 ft. thick and traceable traceable laterally laterally for for over over four four miles. miles. the The formation formation is is folded folded into into an an east east trending trending asemmetric asemmetric on the north limb limb dip dobly doublyplunging plunging syncline. syncline. The units on 55 SS and and those those on on the the south south limb limb are are vertical. vertical. 55 Thin various rock rock types Thin sections sections of the various types have been been examined examined 15 �ffor o r primary structures s t r u c t u r e s and to t o determine determine metamorphic metamorphic grade. grade. Whole rock major element analyses a n a l y s e s have have been been run r u n using u s i n g the the eelectron l e c t r o n microprobe. microprobe. These analyses a n a l y s e s have been used to to iidentify d e n t i f y rock types o determine h e petrochemical types and and tto determine tthe petrochemical c h a r a c t e r i s t i c s of the t h e voloanios. volcanics. characteristics t r e n d s indicate I n d i c a t e that t h a t the t h e rocks r o c k s of of the the The petrochemical trends aarea r e a may be the t h e products of several s e v e r a l cycles c y c l e s of of volcanism. volcanism. Each formation is i s chemically chemically distinctive. d i s t i n c t i v e . The Qtxinnesec Quinnesec the n north Formation grades from f r o m tholelitic t h o l e l i t i c bbasalts a s a l t s Iin n the o r t h to to ccab-alkaline a l c - a l k a l i n e andesites a n d e s l t e s in i n tne tne south, south, suggesting suggesting that t n a t it It may have formed at a t the t h e edge edge of of an an island i s l a n d arch a r c h enviornment. enviornment. Mc Ablister Preliminary analyses a n a l y s e s indicate i n d i c a t e that t h a t the the M c A l l l s t e r Formation basaLts. It may therefore t h e r e f o r e correlate correlate cconsists o n s i s t s of ttholeittic h o l e l l t i c basalts. Formation oor may rrepresent with part p a r t of of the t h e Quinriesec Quinnesec Formation r Iit t may epresent a sseparate e p a r a t e volcanic v o l c a n i c cycle. c y c l e . The Beecher Formation Formation rhyolites rhyolltes and rrhyodacites are typical cab—alkaline h y o d a c i t e s a r e t y p i c a l c a l c - a l k a l i n e acidic a c i d i c vobcanics. volcanlcs. They may tie be the of the t h e aacidic c i d i c end product of t h e Quinnesec The pemene Pemene Formation rrhyolites volcanism. h y o l i t e s aare r e characterized characterized These These by higher h i g h e r Na20 Na20 and lower lower K20 K20 than t h a n normal normal rhyolites. rhyolites. volcanios are distinctly different from the rocks of the volcanics are d i s t i n c t l y d i f f e r e n t the rocks the Beecher Formation and therefore t h e r e f o r e probably rrepresent e p r e s e n t a separate separate period of volcanism. volcanism. The age of of the not t h e volcanism in i n the t h e area a r e a is is n o t positively positively known b but Rebelbo (1969) U-Pb d date z i r c o n U-Pb ate (1969) rreport e p o r t a zircon u t Banks and Rebello for a rhyolite just to the west of the area of 1905 (+30 for r h y o l i t e just t o the of a r e a of 1905 (+30 to to -10) m.y. This rrhyolite -10) m.y. h y o l i t e probably correlates c o r r e l a t e s with the the Beecher If this correlation is correct then the acidic Formation. cidic Formation. I f t h i s c o r r e l a t i o n i s correct then the a possibly volcanism and p o s s i b l y tthe h e mafic volcanism in In the t h e area a r e a is is upper Middle Precambrian in age. Middle Precanbrian i n age. 16 �PRECAMBRIAN PRECAMBRIAN NORTH-SOUTH NORTH-SOUTH ORIENTED ORIENTED FAULTS FAULTS IN IN THE THE WESTERN WESTERN MARQUETTE MARQUETTE DISTRICT, DISTRICT,NORTHERN NORTHERNMICHIGAN MICHIGAN John S. S. Klasner Klasner John Western Illinois W e s t e r n Illinois University University Macomb, Macomb. Illinois Illinois Thomas Thomas R. R. Turner Turner Michigan Michigan Technological Technological University University Houghton, Michigan Houghton, Michigan ABSTRACT ABSTRACT Recent has R e c e n t mapping mapping in in northern n o r t h e r n Michigan Michigan h a s indicated indicated the the presence p r e s e n c e of of prominent 100W W to t oNN 200 20' E E faults, faults, many many of of which which offset offset east-west east-west prominentNN100 T h e s e faults faults are a r e expressed e x p r e s s e d as a s shear shear trending Keweenawandiabase Keweenawan diabase dikes. dikes. These trending zones zones in in lower lower Precambrian P r e c a m b r i a n granites, g r a n i t e s ,offsets offsetsininthe thecontact contactbetween between middle middle and anddiscontinuities discontinuities and lower lower Precambrian P r e c a m b r i a n rocks, r o c k s , topographic topographic lineaments, l i n e a m e n t s ,and in aeromagnetic a e r o m a g n e t i c trends. trends. in Regionally Regionally tthese h e s e faults f a u l t s are a r e on on trend t r e n d with with major m a j o r lineaments l i n e a m e n t s observed observed ontthe Hinze and and others o t h e r s (1966) (1966) on h e bbasis a s i s of of aaeroeroby by other workers w o r k e r s in in the the area. a r e a . Hinze magnetic studies in eastern Lake Superior show a major north-northeast a m a j o r n o r t h n o r t h e a st magnetic studies i n e a s t e r n Lake S u p e r i o r show trending trending fault fault extending extending nnorth o r t h aacross c r o s s the the lake l a k e just just east e a s tof of the the tip t i pof of the the in nnorth Keweenaw Peninsula. Peninsula. La L a Berge B e r g e (1972) (1972) in o r t h central c e n t r a l Wisconsin Wisconsin has has Keweenaw mapped These mapped major m a j o r northeast n o r t h e a s t trending trending shear s h e a rzones zonesup u pto t oone onemile m i l eininwidth. width. These features f e a t u r e s coupled coupled with with major m a j o r lineations lineations on on psuedo psuedo radar r a d a rphotographs photographs suggest suggest that t h a t aa major m a j o r fault fault zone zone bisects b i s e c t s the the arcuate a r c u a t eshaped shapedarea a r e aoutlined outlinedby by the the midmidcontinent continent gravity gravity high high and and proposed proposedKeweenawan Keweenawan rift. rift. With movement, studies With rregard e g a r d to to the the timing timing of of movement, studies in in the the western w e s t e r n part part of near of the the northern n o r t h e r n complex complex n e a r Herman, Herman, Michigan Michigan suggest s u g g e s t that that at a t least l e a s t some some of the faults may m a y have have been r i o r tto o Penokean e t a m o r p h i s m . For For of been active active pprior Penokeanmmetamorphism. example, north-south fault example, aa body body of of gabbro gabbro occupies occupies aa north-south fault tthat h a t cuts cuts granite granite gneiss, g n e i s s , and and the the gabbro gabbro is i sinterpreted i n t e r p r e t e dtot ohave havebeen beenmetamorphosed m e t a m o r p h o s e d by by Penokean oorr some s o m e earlier e a r l i e r thermal t h e r m a levent. event. Penokean In places dikes aare In many many p l a c e s east-west e a s t - w e s t Keweenawan Keweenawan dikes r e offset offset at a t the the northnorthhas found ffor the dikes No evidence evidence h a s been been found o r sshearing h e a r i n g of of the d i k e s at a t these these south faults. No faults faults and and in in some s o m e instances i n s t a n c e sthe theKeweenawan Keweenawan dikes dikes have have been been found found to t o intrude intrude N e v e r t h e l e s s , the the conclusion conclusion seems s e e m s inescapable inescapable that that along the fault f a u l tzone. zone. Nevertheless, along the numerous occurrence of offset dikes at the north-south faults must denote the n u m e r o u s o c c u r r e n c e of offset dikes a t the north-south faults m u s t denote post-Keweenawan post-Keweenawan fault fault movement. movement. 17 �References Hinze, Wrn. O'Hara, N. W., Trow, Wm. J., O'Hara, N. W., Trow, 3. J. W. W. and and Secor, G. G. B., 1966, 1966, Aeromagnetic Studies Studies ofofEEastern Lake Superior, Superior, in the the EEarth Aeromagnetic a s t e r n Lake arth Beneath the Continents, G. U. U. Geo& Smith, ed. ed. ,, A. G. Beneath the Continents, Steinhart Steinhart & physical physical Monograph Monograph 10, 10, pp. pp. 95-110. 95-110. La Zones in in the the PPreL a Berge, G. G. L., L . , 1972, 1972, Lineaments Lineaments and and Mydonite Mydonite Zones re1: 18th 18th Ann. Ann. Inst. Inst. on on Lake Lake ccambrian a m b r i a n of of northern n o r t h e r nWisconsin Wisconsin [abs. [abs,}: Superior Geology, Michigan, ppaper 27. Superior Geology, Houghton, Houghton, Michigan, a p e r 27. 18 �- GEOCHEMISTRYOF OF THE THE CALCIUM GEOCHEMISTRY CALCIUM - CARBON CARBON DIOXIDE DIOXIDEMETASOMATISM METASOMATISM AT PRESQUE MICHIGAN PKESQUE ISLE, ISLE, MARQUETTE, MICHIGAN M. D. Lewan, Lewan, Department Department of of Geology Geology and and Geological Geological Engineering, Engineering, M. Michigan Michigan Technological Technological University Presently With Shell Presently With Shell Oil Oil Company, Company, New New Orleans, Orleans, Louisiana Louisiana 70160 70160 ABSTRACT ABSTRACT A highly veined rock rock composed of of dolomite dolomite and quartz quartz with with peridotite at minor hematite, hematite, overlies overlies the the Presque Presque Isle Isle serpentinized serpentinized peridotite Marquette, Michigan. Marquette, Michigan. Petrographic Petrographic and field observations observations clearly clearly indicate indicate that that this this rock rock was was originally originally highly highly serpentinized serpentinized peridotite peridotite which has since since been been subjected subjected to to metasomatic metasomatic solutions. solutions. which has The The author author (Lewan, (Lewan, 1972) has interpreted interpreted this this dolomite-quartz dolomite-quartz rock as originally being a peripherial shear zone which which developed during the tectonic tectonic intrusion intrusion of of the the peridotite. peridotite. Either during during or or after after its its emplacement water water from the surrounding country rocks circulated through emplacement this highly fractured fractured peripherial peripherial zone zone causing causing extensive extensive serpentinizaserpentinization tion to the the still still warm warm but but cooling cooling peridotite. peridotite. Following Following the the period of of serpentinization a potash rich granite was was emplaced and and was was apparently serpentinization illitized by late late stage stage magmatic along its its outer outer boundary boundary where where illitized magmatic water water along it contact with with the comes in contact it comes the peridotite. peridotite. Both the the highly highly serpentinized serpentinized peridotite and illitized metasomatic soluperidotite illitized granite were susceptable susceptable to metasomatic soluwhich resulted in the formation of the now now existing existing dolomite-quartz tions which rock. objective of this was to investigate rock. The objective this study was investigate the chemical conditions which may may have induced this period parameters and prevailing conditions of metasomatism. of metasomatism. Comparative analysis of the chemical chemical composition composition of the Comparative the dolomite-quartz rock dolomite-quartz rock with the serpentinized peridotite and illitized granite indicates were introduced into granite indicates that calcium and carbon dioxide were system with with partial removal the system removal of of silica silica and and magnesium. Experimental Experimental work by Gordon with free work Gordon and and Greenwood Greenwood (1970) (1970) and Ellis (1959), (1959), along along with free metasomatism probably never energy calculations calculations suggest suggest that that the metasomatism exceeded 300°C. Luce (1972) has has shown shown that that serpentine serpentine is is most most soluble soluble 300°C Luce exceeded waters which which gradually become become more more basic basic as as the serpentine in acidic waters dissolution continues. dissolution continues. This increase in in pH probably also accompanied metasomatic solutions serpenthe metasomatic solutions during during the the dissolution dissolution of of the the highly highly serpenperipherial zones which which eventually eventually resulted resulted in tinized and illitized peripherial mobilization of silica the mobilization silica released released from from the the serpentine serpentine lattice lattice and and the the precipitation of precipitation of dolomite. dolomite. pre-Jacobsville This period of metasomatism has been dated as pre-Jacobsville peridotite sandstone and post-granite sandstone post-granite illitization. illitization. The occurrence of the peridotite greenstone terrain offers offers an-attractive anattractive hypothesis in greenstone hypothesis that that this this metasomatism may may have been a result somatism result of of the the expulsion expulsion of of fluids fluids from from neighneighboring rocks rocks during during the the regional regional metamorphism metamorphism of of the the area. area. 19 �REFERENCES REFERENCES CITED CITED Ellis, Carbon Dioxide (1959), The The Solubility Solubility of of Calcite Calcite in in Carbon Dioxide Ellis, A. J. (1959), Solutions, Am. 3. Sci., 257, pp 354-365. Solutions, Am. J. 257, pp 354-365. Cordon, M., and and Greenwood, Greenwood, H. H. 3. J. (1970), (1970), The The Reaction: Reaction: Dolomite Dolomite Gordon, T. T. M., + Quartz + Water == Talc +Quartz +Water Talc + Calcite Calcite + Carbon Carbon Dioxide, Dioxide, Am. Am. 3. J. Sc!., Sci., 268, 268, pp 225—242. 225-242. pp + + Lewan, and Weathering Weathering of the Lewan, M. XL D. (1972), (1972), Metasornatism Metasomatism and the Presque Presque Isle Isle Serpentinized Serpentinized Peridotite, Peridotite, Marquette, Marquette, Michigan, Michigan, Michigan Michigan Technological Technological University, University, unpublished unpublished M.S. M.S. Thesis, Thesis, 55 55 pp. pp. Luce, Luce, R. R. Kinetics Kinetics W., Bartlett, W., and Parks, Parks, G. 0. A A. Dissolution W., Bartlett, R. R. W., . (1972), (1972), Dissolution of Magnesium Silicates, Geochim. Cosmochim. Acta, of Magnesium Silicates, Geochim. Cosmochim. Acta, 36, 36,pp pp 35-50. 35-50. 20 �THE BIOGENIC ORIGIN THE ORIGIN OF OFPRIMARY PRIMARY MINERALS MINERALS IN IN LAKE LAKE SUPERIOR SUPERIORPRECAMBRIAN PRECAMBRIAN IRON-FORMATION IRON-FORMATION M. Lougheed and 7. J. Mancuso, Department M. S. S. Lougheed and J. J. Mancuso, Geology, Department of of Geology, Bowling Bowling Green University, University, Bowling Bowling Green, Green, Ohio Ohio 43403 43403 ABSTRACT ABSTRACT Primary Primary minerals minerals in in the the Lake Lake Superior Superior Precambrian Precambrian ironironformations formations are are the the direct direct products products of of the the life life processes processes of of a melange of filamentous filamentous and and unicellular unicellular organisms organisms together together with minerals so with associated associated bacteria. bacteria. Primary Primary minerals so formed formed are are aragonite Pyrite is aragonite and/or calcite, calcite, magnetite, magnetite, and and opal. opal. Pyrite is formed formed during decay decay of of organic organic material material with with attendant attendant sulfate sulfate reducing bacteria and is therefore later in origin than reducing than the the above above three three minerals although although it it too too is is of of biogenic biogenic origin origin and may be Hematite occurs be considered considered primary. primary. Hematite occurs as as an an alteraalteration product of earlier earlier formed minerals and is not considered a primary mineral. a primary mineral. bacteria and is therefore later in Aragonite Aragonite or or calcite calcite crystals crystals are are biogenically deposited deposited structural structural elements elements occurring occurring as as submicron submicron width width prisms prisms oriented normal to an algal mat, mat, and producing in turn a carbonate mat. carbonate mat. A succession succession of of algal algal and carbonate carbonate mats (laminae) occurs occurs in horizontally horizontally banded banded iron-formation; iron-formation; in in domical or columnar domical columnar stromatolites; stromatolites; as as coatings coatings on on granules granules (pellets); or forming forming micro—oncoliths. micro-oncoliths. Micro-oncoliths Micro-oncoliths are are typically 0—50 microns microns in Calcium carbonate typically 220-50 in diameter. diameter. Calcium carbonate can can be dolomitized, dolomitized, sideratized, sideratized, or or silicified. silicified. Magnetite initially occurs subMagnetite occurs as as a a diffuse diffuse cloud cloud of of subwithin the micron sized sized crystals crystals within the protoplasm of unicellular unicellular Too plants. plants. Too high aa concentration concentration of of oxygen oxygen produced produced by by photosynthesis in photosynthesis in these these unicellular unicellular plants can can be lethal lethal to them; they therefore therefore oxidize oxidize iron iron that that is is dissolved dissolved in in the the water to to produce magnetite, thereby attenuating attenuating a a lethal lethal buildup of oxygen. oxygen. During During deposition deposition and and early early diagenesis diagenesis buildup of magnetite may may be be recrystallized to the submicron crystals of magnetite form Diagenesis may subseform coarser coarser octahedra octahedra of of magnetite. magnetite. Diagenesis subsequently produce quently produce megascopic megascopic subhedral subhedral masses masses of of magnetite. magnetite. Some magnetite is produced by oxidation of siderite during the depositional depositional stage, stage, which which subsequently subsequently may may be be recrystalrecrystallized during diagenesis diagenesis in in aa similar similar manner manner to to that that of of primary primary biogenic magnetite. biogenic magnetite. Siliceous Siliceous tests tests of of microorganisms microorganisms yield yield the the hydrous hydrous silica, which during deposition is almost invariably comminuted to an an opaline opaline slurry. slurry. This slurry slurry readily readily dehydrates dehydrates during during diagenesis to diagenesis to chalcedony chalcedony or or more more often often to to chert. chert. From From five five to seven seven types types of siliceous siliceous tests tests of of unicellular unicellular organisms organisms 21 �occur. occur. Usually Usually the t h e cavities c a v i t i e s are a r e filled f i l l e d with w i t h organically organically stained s t a i n e d chalcedony, chalcedony, and and often o f t e n submicron submicron sized s i z e d anhedra anhedra of of carbonate c a r b o n a t e are a r e present. p r e s e n t . The The test t e s t walls w a l l s are a r e not n o t organically organically stained; clear. Occasionally O c c a s i o n a l l y the t h e core c o r e and and s t a i n e d ; they t h e y are a r e water w a t e r clear. test t e s t are a r e recrystallized r e c r y s t a l l i z e d to t o an an optically o p t i c a l l y oriented o r i e n t e d sphere s p h e r e or or ellipsoid e l l i p s o i d of o f quartz. q u a r t z . The The tests t e s t s range range in i n width w i d t h from from 55 to to 25 microns although a l t h o u g h aa few few may may exceed exceed 50 5 0 microns. microns. PreservaPreservation t i o n of o f siliceous s i l i c e o u s tests tests occurs o c c u r s only o n l y when when they t h e y were were deposited deposited in n e v e r when when water w a t e r current c u r r e n t activity a c t i v i t y prevailed. prevailed. i n quiet q u i e t water, w a t e r , never They therefore t h e r e f o r e are a r e not n o t found found in i n association a s s o c i a t i o n with w i t h granules granules or o r stromatoljtes. stromatolites. P y r i t e may be thought t h o u g h t of o f as a s primary in i n the t h e sense s e n s e that that Pyrite it results r e s u l t s from from iron i r o n in i n the t h e water w a t e r reacting r e a c t i n g with w i t h sulphur sulphur produced produced by sulfate s u l f a t e reducing r e d u c i n g bacteria b a c t e r i a during d u r i n g decay decay of of organic o r g a n i c debris. d e b r i s . Pyrite P y r i t e occurs o c c u r s as a s discrete d i s c r e t e octahedrons o c t a h e d r o n s or or octahedrons o c t a h e d r o n s modified m o d i f i e d by aa cube, cube, as a s framboidal f r a m b o i d a l octahedra, o c t a h e d r a , or or as a s framboidal f r a m b o i d a l mats mats or o r spheres. s p h e r e s . Secondary Secondary replacement replacement pyrite pyrite formed during d u r i n g diagenesis d i a g e n e s i s is i s ubiquitous. ubiquitous. 22 �-- THE WOLF RIVER BATHOLITH BATHOLITH -- A L LATE THE WOLF RIVER ATE PRECANBRIA1 PRECAMBRIAN RAPAKIVI MPAKIVI MASSIF I NNORTHEASTERN NORTBBASTERN WISCONSIN WISCONSIN MASSIF IN L. G. G. Medaris, . Nyles, Medaris, Jr., Jr., J. L. L. Anderson, Anderson, and J. J. R B. Myles, Department of Geology Wisconsin, Madison 53706 Geology and Geophysics, Geophysics, University of of Wisconsin, 53706 ABSTRACT AESTRACT Anorogenic, epizonal batholith, epizonal ggranitic r a n i t i c rocks rocks of of the t h eWolf Wolf River River b atholith, covering an aarea of approximately 3600 square miles, miles, represent a major covering r e a of element of the t h e Precambrian Precambrian terrain t e r r a i n in i n northeastern northeastern Wisconsin. Wisconsin. This batholith, 1500 m. m. y. y. iin age, has llithologic, n age, i t h o l o g i c , mineralogic, mineralogic, b a t h o l i t h , 11150 1450 tto o 1500 chemical, and structural respect to that are a r e similar similar in i n every every respect to chemical, s t r u c t u r a l ffeatures e a t u r e s that those those of of the t h e classic c l a s s i c rapakivi rapakivi massifs massifs in i nFinland. Finland. A vvariety been distinguished, distinguished, including including ggranite, A a r i e t y of of rock rock types types have have been ranite, quartz monzonite,r rhyolite, trachyandesite, but quartz monzonite, monzonite, ssyenite, y e n i t e , monzonite, h y o l i t e , and and trachyandesite, but quartz monzonite of tthe monzonite iiss predominant, predominant, accounting accounting for f o r 87% 87% of h e exposed exposed area. A porphyritic porphyriticttexture of aalkali A e x t u r e iis s characteristic, c h a r a c t e r i s t i c , ini nwhich which phenocrysts phenocrysts of lkali feldspar f e l d s p a r and, and, to t o a lesser l e s s e r extent, e x t e n t , plagioclase and quartz quartz are a r e set s e t in i n aa medium— tto mediumo fine—grained fine-grained matrix of quartz, quartz, two feldspars, f e l d s p a r s , and mafic minerals. Rapakivi texture t e x t u r e is i s extensively developed in i n the t h e Waupaca Waupaca quartz monzonite and and occurs occurs in i n minor minor amounts amounts throughout throughout the t h e batholith. batholith. Quartz iis many llithologic units; s euhedral iin n many ithologic u n i t s ; bbiotite i o t i t e and hornblende are Quartz generally anhedral and interstitial i n t e r s t i t i a l to t o feldspars f e l d s p a r s and quartz. quartz. The The granitic g r a n i t i c rocks rocks of of the t h e batholith b a t h o l i t h tend tend to t o be be rich r i c hini nSiO SiO and alkalies, , CaO, and and MgO. TLg batho— andpoor poor in i nAl20 A120 , MgO. ~ bathoe a l k a l i e s , particularly p a r t i c u l a r l yKK0,0,and 11th l i t h has has alkaline a l k a l i n e affiniies, a f f i n i z i e s , although only only eraluminous Jeraluminous and metaluminous metalminous types have been recognized recognized so so far. f a r , Values of of normative Q—Ab—Or Q-Ab-Or for for representative r e p r e s e n t a t i v e specimens specimens plot p l o t close c l o s e to t o a low low pressure thermal trough and and minimum minimum for f o r the t h e experimental experimental "granite" "granite" system, system, with with aa slight s l i g h tdisplacement displacement towards normative Or. Or. towards Perthitic P e r t h i t i c alkali a l k a l ifeldspar feldsparisi the s t hpredominant e predominant mineral mineral in i n the t h e bathoJ.ith, batholith, accompanied quartzand andplagioclase, plagioclase, ranging accompanied bybyquartz ranging in i ncomposition composition from from An An 3 to to )tO, An Iron—richbbiotite 40, with most values falling f a l l i n g between A n 10 1 0 tto o 25. 25. Iron-rich i o t i t e and hornblende are minerals, although olivine, a r e the t h e predominant mafic minerals, o l i v i n e , clino— clinopyroxene, and pyroxene, and orthopyroxene orthopyroxene occur occur in i n monzonite monzonite and and trachyandesite. trachyandesite. Fluorite Fluorite is batholith, i s tthe h e most widespread accessory mineral in i n tthe he b a t h o l i t h , and a halogen— halogenrich biotite i s reflected r e f l e c t e d in i n high Cl C l and F F contents of of b i o t i t e and r i c h environment is hornblende. Wolf River b batholith The Wolf a t h o l i t h may have crystallized c r y s t a l l i z e d from from relatively r e l a t i v e l y dry dry granitic partial off pre-existing pre—existing g r a n i t i c magmas tthat h a t were derived by p a r t i a l melting o crustal materials, basaltic volcanics, v volcaniclastic crustal m a t e r i a l s , consisting c o n s i s t i n g of of b a s a l t i c volcanics olcaniclastic sediments, and quartz dioritic sediments, d i o r i t i c to t o granodioritic g r a n o d i o r i t i c plutonic plutonic rocks. rocks. , 23 �SUMMARY WISCONSIN SUhMkRY OOF F GLACIAL GEOLOGY GEOLOGY OF OFNORTH—CENTRAL NORTH-CENTRAL WISCONSIN D. M. Department of M. Mickelson, Mickelson, Department of Geology Geology and and Geophysics, Geophysics, University University of Wisconsin, Madison, Wisconsin Wisconsin 53706 53706 ABSTRACT ABSTRACT The The Pleistocene glacial g l a c i a lchronology chronology of of central c e n t r a land andnorthern northernWisconWisconnot not well well established. established. Early Early workers workers (Owen, (Owen, l8t7; 1847; Chamberlain, Chamberlain, 1907) outlined o u t l i n e d the t h e distribution d i s t r i b u t i o n of of glacial g l a c i a l deposits deposits and and 1882, Weidman, 1907) recognized aa presumed older o l d e r drift d r i f t outside the t h e terminal moraines of of WisWisconsin consin age. age. Hole Hole (1943) (1943) and and Thwaites (l913) (1943) concluded that t h a t the t h e older older d r i f t (Border order Drift) rift) was of of one one age age and and was deposited deposited in i n the t h e pre—Cary pre-Cary drift (pre—late ( p r e - l a t e Woodfordian) woodfordian) time. time. Radiocarbon Radiocarbon dates d a t e s (Black (Black and and Rubin, Rubin, 1968) beneath beneath the t h e Border Border Drift D r i f t in i n Wood Wood County County are a r e >>i5,O00 45,000 years years B.P. B.P. 1968) In I n southern southern and and western Wisconsin wood wood from from an an old o l d till till possible possible B. P. P. c o r r e l a t i v e with with the t h e Border Border Drift D r i f t is i s dated dated at a t about about 30,000 30,000 years B. correlative and and is i s considered considered Rockian Rockian (late ( l a t e Altonian) Altonian) age. age. The The Border b r d e r Drift D r i f t may may actually a c t u a l l y consist c o n s i s t of of 22 tills t i l l s of of differing d i f f e r i n g age. age. The till was was The lower lower till deposited by by ice i c e moving moving from from the t h e west in i n Marathon County County (LaBerge, (~a~erge, deposited 1972) 1972) and and the t h e upper upper till till by by ice i c e moving moving from from the t h e northwest northwest in i n southern southern Lincoln Lincoln and and Langlade Langlade Counties. Counties. sin s i n is is Three Three ice i c e lobes lobes built b u i l t terminal terminal moraines moraines in i n Lincoln Lincoln and and Langlade Langlade Counties Counties during during late—Woodfordian late-Woodfordian time. time. The The Wisconsin Wisconsin Valley Valley Lobe Lobe advanced advanced from from the t h e northwest northwest depositing depositing aa reddish—brown, reddish-brown, sandy sandy basal basal till. To the t h e east, e a s t , the t h e Langlade Langlade Lobe Lobe deposited deposited aa dark dark reddish—brown reddish-brown till. To basal b a s a l till till as a s ice i c e flowed flowed from from the t h e northeast. northeast. Further Further east, e a s t , the t h e Green Green Bay Bay Lobe, Lobe, advancing advancing from from the t h e east e a s t and and southeast, southeast, deposited deposited aa brown, brom, sandy, sandy, dolomitic dolomitic till. till. No No absolute absolute dates dates are a r e available, a v a i l a b l e , but but stratigraphic s t r a t i g r a p h i c and and geomorphic geomorphic evidence evidence suggests suggests that t h a t the t h e advance advance of of these t h e s e lobes lobes to t o their t h e i r terminal terminal moraines moraines was was not not contemporaneous contemporaneous as a s reported reported by by Thwaites Thwaites (1943). (1943). At At the t h e junction junction of of the t h e Wisconsin Wisconsin Valley Valley Lobe Lobe and and Langlade Langlade Lobe Lobe no no strati— stratigraphic till graphic sections s e c t i o n s showing showing 22 tills t i l l s are a r e available. a v a i l a b l e . Relationships Relationships of of till fabric f a b r i c azimuths, azimuths, moraine moraine alignments alignments and and drainage drainage features f e a t u r e s indicate i n d i c a t e an an early e a r l y advance advance of of the t h e Langlade Langlade Lobe Lobe and and the t h e formation formation of of the t h e Parrish Parrish Moraine. This was was followed followed by by an an advance advance of of the t h e Wisconsin Wisconsin Valley Valley Lobe Lobe Moraine. This and was followed followed shortly shortly and the t h e formation formation of of the t h e Harrison Harrison Moraine Moraine which which was thereafter t h e r e a f t e r by by aa readvance readvance of of the t h e Langlade Langlade Lobe Lobe to t o aa position p o s i t i o n 66 miles miles short and tthe short of of its i t maximum s maximum advance advance and h e formation formation of ofthe t h eSummit SummitLake Lake Moraine. Moraine. Stagnant Stagnant ice i c eofofthe t h Wisconsin e WisconsinValley ValleyLobe Lobemay may have have been been present present during during this t h i sreadvance. readvance. To To the t h e east, e a s t , the t h e Green Green Bay Bay Lobe Lobe advanced advanced to t o its i t s maximum maximum position position and and retreated r e t r e a t e d at a t least l e a s t 20 20 miles miles before beforethe t hmaximum e maximum advance advance of of the the Langlade Bay Lobe till is stratigraphically beneath Langlade Lobe. Lobe. Green that Green Bay Lobe till i s s t r a t i g r a p h i c a l l y beneath that of of the t h eLanglade Langlade Lobe Lobe aat t lleast miles in i~from from the t h e margin margin of the the e a s t 55 miles Langlade Outwash streams h e Langlade Langlade Lobe Lobe iice c e cut c u toutwash outwash streams from from tthe Langlade Lobe. Lobe. Outwash and thet hGreen Bay and till tillofof e Green BayLobe. Lobe. 24 �A PLUTONNEAR NEARELY, ELY, MINNESOTA A LOWER LOWER PRECAMBRIAN PRECAMBRIAN LAMPROPHYRE LAMPROPHYRE PLUTON MINNESOTA M. G. M. Mudrey, ~ r .and and ' A. L. Geldon, Geldon, University U n i v e r s i t yofoMinnesota f Minnesotaand andMinnesota Minnesota G. Mudrey, Jr.1 A. L. Geological Survey. Survey. ABSTRACT ABSTRACT Oneoof bodies ooff lamprophyre One f tthe h e bbetter e t t e r exposed exposed bodies lamprophyre wwithin i t h i n tthe h e Early E a r l y PrePrecambrian Vermilionddistrict cambrian Vermilion i s t r i c t of o fMinnesota Minnesota is i s located l o c a t e d88km km northwest northwest ooff Ely, Ely, on tthe on h e north n o r t h side s i d e of o fBurntside Burntside Lake. Lake. The The ccrudely r u d e l y e elliptical l l i p t i c a l pluton, p l u t o n , about about by0.5 0.5 km, km,i is Lower Precambrian 1 km km by s situated s i t u a t e d in i nthe t h ecore coreofo a f afold f o loutlined d o u t l i n eby d by Lower Precambrian migmatizedb ibiotite amphibolite; howevert hthe migmatized o t i t e sschist c h i s t and and amphibol i t e ; however e p lpluton uton i sisvvitually itual l y 1 unmetamorphosed unmetamorphosed andand i s is d i sdiscordant c o r d a n t t otot hthe e sstructure. tructure. The has aa narrow, narrow, discontinuous discontinuousborder borderzone zoneo fofuuralitized The ppluton l u t o n has ralitized phlogopite-bearing These two two phlogopite-bearing pyroxenite p y r o x e n i t e and and an an inner i n n e r zone zone of o flamprophyre. lamprophyre. These rock types based relations, petrography, f i efield 1 d re1 a t i o n s ,petrography, rock types are a r e considered considered comagmatic comagmati c based on on Both the t h e pyroxenite p y r o x e n i t e and and the t h elamprophyre lamprophyre are are cut c u tbybynumerous, numerous, and and chemistry. Both thin adamell i t i composition, c composition,which whichcontain c o n t a i nxenocrysts xenocrysts t h i n dikes dikes of o fmonzonitic monzoni t i c to t oadamellitic of mafic minerals tthat o f the t h e same same m a f i c minerals h a t occur occur in i nthe t h epyroxenite p y r o x e n i t eand andlarnprophyre. lamprophyre. The The dikes representa al alate dikes are a r e probably probably comagmatic, comagmatic, b ubut t c ocould u l d represent t e ppink i n k lleucocratic eucocratic phaseoof adjacent VVermilion phase f tthe h e adjacent e n n i l i o n ggranite. ranite. The lamprophyre lamprophyrei is Approximately213 2/3 ooff the The s a melanocratic porphyry. porphyry. Approximately the exposed lamprophyrei sisaa bbiotite—bearing hornblendes spessartite; exposed lamprophyre i o t i t e - b e a r i n g hornblende p e s s a r t i t e ; the t h e remainremainThe sspessartite byuuralitized ing 113 is i s augite a u g i t e inokersantite. i n o k e r s a n t i t e . The p e s s a r t i t e iiss dominated dominated by ralitized i n g 1/3 with subordinatec hchloritized ddiopsidic i o p s i d i c aaugite ugite w i t h subordinate l o r i t i z e d bbiotite, i o t i t e , sericitized s e r i c i t i z e dandesine, andesine, andi interstitial and n t e r s t i t i a lpotassium potassium feldspar; feldspar; the t h e relatively re1 a t i v e l yunaltered u n a l t e r e d inokersantite inokersantite is by ddiopsidic i s dominated dominated by i o p s i d i c augite a u g i t e and and biotite b i o t i t ewith w i t hsubordinate subordinateandesine andesineand and interstitial crude subhorizontal subhorizontal llayering i n t e r s t i t i apotassium l potassium feldspar. feldspar. A A crude a y e r i n g within w i t h i n both both types ooff lamprophyre byananupward upward increase types lamprophyre i is s marked marked by increase i ning rgrain a i n ssize i z e oof f the the groundmassand and decrease phenocrysts; an groundmass decrease i n in s i size z e o of f tthe h e phenocrysts; an increase in i n amount amount of of potassiumf efeldspar potassium l d s p a r aatt the t h e expense expense ooff total t o t a l ferromagnesian ferromagnesian minerals; minerals; and and aa change change iinn the t h e compositions compositionsofo the f t hferromagnesian e ferromagnesianminerals——mainly minerals--mainly an an increase increase in i n the t h e iron/magnesium iron/magnesium rratios. atios. Calculated compositions Calculated compositions for f o r the t h erocks rocksbased basedon onmodal modal data data and and microprobe microprobe analyses analyses oof f cconstituent o n s t i t u e n t phases phases i nindicate d i c a t e tthat h a t this t h i s pluton p l u t o nmay may be be related r e l a t e d to to an alkali an an uncommon b a s a lparent, t parent, uncommon petrochemical petrochemical type type ini nLower LowerPrecambrian Precambrian a1 k a l ibasalt an terranes. terranes. The wasemplaced emplaced cooled rrapidly. The ppluton l u t o n was i nina as esemicrystalline m i c r y s t a l l i n e sstate t a t e and and cooled apidly. byeearly IInitially n i t i a l l yhigher h i g h e roxygen oxygen ffugacity, u g a c i t y , as as indicated i n d i c a t e d by a r l y ccrystallization r y s t a l l i z a t i o n of of magnetite andapparently apparently magnetite and h i ghigh h f e ferric/ferrous r r i c / f e r r o u s rratios a t i o s in i n biotite, b i o t i t e decreased , decreased Disequilibrium i s e q u i l i b r i u m ttextures e x t u r e s iindicate n d i c a t e that that somewhat somewhat d uduring r i n g c rcrystallization. ystallization. D crystallization c r y s t a l l i z a t i o nbegan beganata depth t depthand andconcluded concluded at a t shallower, shallower, synvolcanic synvolcanic depths. depths. 1Nowa tatDry DryVValley INOW a l l e y DDrilling r i l l i n g Project, P r o j e c t ,Department Department of o f Geology, Geology, Northern Northern Illinois University, DeKaib, Illinois 60115. I l l i n o i s U n i v e r s i t y , DeKalb, I l l i n o i s 25 �Mineralogical Mineralogical and and Chemical Chemical Studies Studies of Greenstones in i n Wisconsin by G. G. Mursky, G. G. Schriver S c h r i v e r and and A. A. R. R . Venditti Venditti Department of o f Geological Geological Sciences Sciences University U n i v e r s i t y of of Wisconsin—Milwaukee Wisconsin-Milwaukee Milwaukee, Milwaukee, Wisconsin ABSTRACT Central, C e n t r a l , northern n o r t h e r n and and northeastern n o r t h e a s t e r n parts p a r t s of o f Wisconsin contain volcanic—sedimentary c o n t a i n numerous belts b e l t s of of Precambrian volcanic-sedimentary sequences sequences which which are a r e commonly commonly referred r e f e r r e d to t o as a s greenstones. qreenstones. The The units u n i t s appear appear to t o be chiefly c h i e f l y of of middle Precambrian age aye and and they they have been been included included by Stockwell Stockwell (1970) (1970) in i n the t h e Southern Southern Province Province have B e l t which forms forms the t h e southern s o u t h e r n extension e x t e n s i o n of of the the o r Penokean Penokean Fold Fold Belt or 2.5 2.5 to t o 2.7 2.7 b.y. b.y. old o l d Superior Superior Structural S t r u c t u r a l Province Province of of the the Canadian Canadian Shield. S h i e l d . The The volcanic v o l c a n i c rocks in i n Wisconsin have chemical chemical c h a r a c t e r i s t i c s similar s i m i l a r to t o Archean volcanic v o l c a n i c assemblages a s s e h l a q e s of of the the characteristics S u p e r i o r Province Province and and these t h e s e similarities s i m i l a r i t i e s are a r e reflected r e f l e c t e d by the the Superior following following trends: trends: (1) The alkali—lime a l k a l i - l i m e index, index, as a s proposed proposed by by Peacock Peacock (1931), (19311, The f o r Wisconsin's v o l c a n i c rocks has a range from 59 to to for Wisconsin's volcanic 64 and and thus t h u s parallels, p a r a l l e l s , very v e r y closely, c l o s e l y , the t h e alkali—lime alkali-lime index of volcanic v o l c a n i c rocks rocks from from the t h e Superior Superior Province Province index which show show aa range ranqe from from 56 56 to t o 64 6 4 (Wilson (Wilson and and others, others, which 1965). 1965). (2) volcanic Volcanic rocks rocks from from Wisconsin Wisconsin are a r e potassium—poor potassium-poor and and compare to t o Goodwin's (1968) (1968) trend t r e n d of of potassium-poor potassium-poor compare volcanic v o l c a n i c rocks rocks in i n the t h e Superior Superior Province. Province. (3) The The Niggli N i g y l i silica s i l i c a and and total t o t a l alkali a l k a l i values v a l u e s for f o r volvolcanic c a n i c rocks rocks from from Wisconsin, when plotted p l o t t e d in i n relation relation to t o Wilson's Wilson's (1965) (1965) standard s t a n d a r d curve curve drawn drawn for f o r oceanic oceanic alkaline and orogenic calc-alkaline suites, plot alkaline c a l c - a l k a l i n e s u i t e s , p l o t on on t h e orogenic o r o q e n i c calc—alkaline c a l c - a l k a l i n e side s i d e of of the t h e standard s t a n d a r d curve curve the nearly same region r e g i o n as a s the t h e plots p l o t s for f o r the t h e volvoln e a r l y in i n the t h e same canic c a n i c suites s u i t e s from from the t h e Superior S u p e r i o r Province. Province. The greenstones ureenstones have have been been metamorphosed metamomhosed to t o greenschist areenschist facies ~ k o n n a i s s a & z eand and f a c i e s or o r -lower l o w e r amphibolite amphibolite facies. f a c i e s . Reconnaissance detailed s u l p h i d e mineralization mineralization d e t a i l e d work work has has not n o t revealed revealed any any sulphide except e x c e p t for f o r some some disseminated disseminated pyrite. pyrite. 26 �References References Goodwin, Goodwin, A. A. M., M., 1968, 1968, Evolution Evolution of of the t h e Canadian Canadian Shield: Shield: Geol. Assoc. Can. Proc., v. 19, P. -01. Assoc. Can. Proc., v . 1 9 , p. 1—14. 1-14. Peacock, Peacock, M. M. A., A., 1931, 1931, Classification C l a s s i f i c a t i o n of of Igneous Igneous Rocks: Rocks: Geology, V. 39, p. 54—67. Geology, v. 39, p. 54-67. Jour. Jour. Stockwell, Stockwell, C. C. H., H., 1970, 1970, Geology Geoloqy of o f the t h e Canadian Canadian Shield Shield (Introduction), Chapter IV in Geology (Introduction), I V i n Geology and and Economic Economic Minerals Minerals of of Canada, Canada, 5th 5 t h Ed., Ed., Department Department of of Energy, Energy, Mines, and Resources, Ottawa, Canada, p. Mines, and Resources, Ottawa, Canada, p. 44—54. 44-54. Wilson, H. D. D . B., B., Andrews, Andrews, Peter; P e t e r ; Moxham, Moxham, R. R. L., L . , and and Ramlal, Rarnlal, Wilson, H. K., 1965, Archean Volcanism in the Canadian Shield: K., 1965, Archean Volcanism i n t h e Canadian S h i e l d : Can. Can. Jour. J o u r . Earth Earth Sci., S c i . , v. v. 2, 2 , no. no. 3, 3, p. p. 161-175. 161-175. 27 �TEE IRON OREDEPOSITS DESITS AT TIE IMN ORE ATBlACK BUCKRIVER WJER FALlS, WISCONSIN, FALLS, WISCONSIN,GEOlOGY GEOLOGYAND ANDOPERA.TIONS OPEFATIONS John M. Ohison, Inland John M . Ohlson, Inland Steel S t e eCompany, l Compsw, Ishpeniing, Ishpeming, Michigan Michigan h498h9 W9 ATBAC'P Thepresence presenceofofiron iron bearing bearing rocks rocks iin the Black River Falls Falls area The n the Black Mver Attempts ttoo known since since 1839. 1839. Attempts of west-central nest-centralWisconsin Wisconsinhas hasbeen beenknown wereunsuccessful. unsuccessful. u t i l i z ethis t h i sresource resourcebefore beforethe theturn turnofofthe the centumwere utilize century 1nlandts facility, f a c i l i t y ,which whichopened opened iin n 1969, 1.969, u t i u z e s standard standard grinding grinding Inland's utilizes and nagnetic separation and mgnetic s e p m t i o n techniques. techniques. The rocks of of the the area are The rocks are aa sequence sequence of of steeply steeply dipping dipping highly highly metaaorphased sedimentsincluding includingaa thin-banded thin-banded mgnetite-quartz nagnetite-quartz metamorphased sedkmnts iron fornation. iron formtion. The The ssediments e d h e n t s l lie i e on a granite granitegneiss gneissbasement basement and intmded by by both both acid acidand and basic bssicdikes dikes.• The and are intruded %e eentire n t i r ePrecambian Ft-ecambian sequenceiis sequence s overlain w e r l a i n by by flat flatlying lyingC*mbrian Cambrian sandstones. sandstones. Water Water iiss obtained wells iinn aa concealed disobtained from from wells concealed Pleistocene Pleistocene valley valley which which was n s discovered by by geo@ysical geoaysical methods. covered methods. Plant water water circulates circulates in Plant i naaclosed closedsystem. system. Experimental Experimental ttree r e e and and grass Wisconsin gmss planting planting with with the t h ehelp helpofofthe the WisconsinDepartment Ceprixent of Natural Natural Resources, the University of ExtensionService, Service, and and the the SSoil Resources, the of Wisconsin Wisconsin Extension oil conservation Service Servicewwas started on on the the waste waste ddisposal Conservation as started i s p s a l ppiles i l e s within within a year and aa half half of of plant plant startup. %e a year and The plant plant and and waste waste disposal disposal areas were designed designed from from the the outset environmentaleffect. effect. were outset to t ohave havea aminimum minimum environmental 28 �STRUCTURAL EVOLUTION O OF STRUCTUm EVOLUTION F TEE THE DEER DEER LAKE LAKEULTRAMAFIC ULTRAMAFIC COMPLEX, COMPLEX, MINNESOTA MINNESOTA M. Ripley Ripley and Donald N. M. Davidson, Davidson, Jr., J r . , Geology Department, Department, Edward M. Edward University of Minnesota, Minnesota, Duluth, Duluth, Duluth, Duluth, Minnesota Minnesota 55812. 55812. ABSTRACT ABSTRACT Lake Ultramafic Ultramafic Complex Complexisislocated located 6.5 6.5 kilometers The Deer Deer Lake kilometers southsouthThe The magnetic magnetic anomaly anomaly associated a s s o c i a t e d with with this this Effie, E f f i e , Minnesota. Minnesota. The east e a s t of of Archean Complex Complex is is 13 13 kilometers long long and and 33 kilometers wide wide and and trends S. 45W.from the of Deer Lake to just n northeast o r t h e a s t of the the S. 45W.from t h e south tip t i p of t o just town of of Big Big Fork. Fork, The stratigraphic within s t r a t i g r a p h i c succession w i t h i n this t h i s Complex Complex consists c o n s i s t s of two stratiform s t r a t i f o r m differentiated d i f f e r e n t i a t e d gabbroic sills, one nonstratiform gabbroic s t r a t i f o r m sills sills s i l l and and two two locally l o c a l l y discordant discordantultrainafic u l t r a m a f i c lenses. lenses. The stratiform sill (700-1,100 m. m. thick) t h i c k ) are a r e composed composed of: of: basal b a s a l peridotite p e r i d o t i t e (160—330 (160-330 m.), m.), (700—1,100 orthopyroxene m.), gabbro 450—650 m.) 450-650 m.) orthopyroxene clinopyroxenite (less ( l e s s than 160 160 m.) plus medium— to p l u s or o r minus mediumt o fine—grained fine-grained differentiated d i f f e r e n t i a t e d felsic f e l s i c cap cap rock. rock. Zones of plumose texture all t e x t u r e have been observed o b s e ~ e dalong contacts contacts between all zones are a r e interpreted i n t e r p r e t e d as a s spinifex—like s p i n i f e x - l i k e chill c h i l l contacts contacts mafic mafic units. units. These zones r a t h e r than sequential s e q u e n t i a l contact contact metamorphic metamorphic effects. effects. rather , Deformation of the t h e Complex Complex commenced commenced with a period of of folding f o l d i n g which The axial The a x i a l plane plane produced two anticlines with an intervening syncline. two a n t i c l i n e s with an i n t e ~ e n i n gsyncline. trends of of these upright, nonpiunging, isoclinal N. 45 E. E. with upright, nonplunging, i s o c l i n a l folds f o l d s is N. Folding a a wavelength of of 1200 1200 meters meters and and an an amplitude amplitude of of 400 400 meters. meters. Folding was produced in response to the emplacement of the Zeisser's Island i n response t o t h e the Zeisser's Island Pluton located located just j u s t southeast southeast of the t h e central c e n t r a l portion p o r t i o n of the t h e Complex. Complex. Local bending of the Complex to an east—west trend around bending of t h e Complex t o an east-west t r e n d around the t h e north north end of the t h e Pluton also a l s o occurred occurred at a t this t h i s time. time. Conjugate Conjugate shear shear fractures fractures trending N. N. 20 W. W. and N. N. 80 W. W. developed in i n response to t o the t h e same NW—SE NW-SE stress s t r e s s system system which which produced produced folding. folding. The The second second stage s t a g e of deformation deformation resulted r e s u l t e d from from extensional extensional release release The with The ffaults a u l t s trend trend with the t h e development development of of normal normal faults f a u l t s and and joints. joints. W. and have minimum minimum dip dip separations separations on on the t h e order o r d e r of of 400 400 meters. meters. N. 45 W. Faulting produced 800 Longi800 meter—wide meter-wide graben graben and and horst h o r s t structures. s t r u c t u r e s . Longitudinal W.) (N. 45 W. ) release r e l e a s e joints j o i n t s are a r e believed t u d i n a l (N. (N. 45 E.) E.) and traverse t r a v e r s e (N. to t o have developed under the t h e same stress s t r e s s orientation o r i e n t a t i o n as a s the t h e normal faults. faults. Strike N. 45 E. E. trend t r e n d characterizes c h a r a c t e r i z e s the t h e final final S t r i k e slip s l i p faulting f a u l t i n g along a N. U g h t - l a t e r a l strike s t r i k e separation s e p a r a t i o n displacement offset offset s t a g e of of deformation. deformation. Right—lateral stage Renewed movement along this t h i s fault f a u l t preprenormal faults f a u l t s about about 300 300 meters. meters. Renewed sumably produced an additional a d d i t i o n a l 100 100 meters strike s t r i k e separation displacement displacement Precambrian diabase diabase dikes. dikes. of middle Precambrian 29 �THE CHEMISTRY OF THE THE PETROLOGY ETROLOGY AN]) AND CHEMISTRY THE ROUND ROUND [AKE L A E INTRUSION, INTRUSION, NORTHWESTERN NORTIMESTERN WISCONSIN WISCONSIN D. L. Roder Cameron Roder and E. N. Cameron Department of Department of Geology Geology and Geophysics Geophysics University University of of Wisconsin, Wisconsin, Madison, Madison, Wisconsin Wisconsin 53706 53706 ABSTRACT The The Round Round Lake Lake intrusion intrusion is is aa northeast-trending northeast-trending Precambrian Precambrian mafic layered intrusion by subsurface subsurfacedrilling drilling of mafic layered intrusion found found by of an an area area ten ten miles east miles east of Hayward, Hayward, Wisconsin. Wisconsin. The The body may may be as as much much as as eight eight miles long long and two miles magnetitemiles and two miles wide. wide. Portions Portions drilled drilled consist consist of of magnetitetroctolite troctolite with with anorthositic anorthositic gabbro gabbro layers layers that that range range from from threethreefourths fourths inch inch to to more more than than eighty eighty feet feet in in thickness. thickness. Diabase Diabase interintersected sected by the the drill drill holes holes appears appears to to form form later later intrusions. intrusions. Mineral Mineral assemblages assemblages in in the the magnetite-troctolite magnetite-troctolite and and anorthositicanorthositicgabbro gabbro are are the the same, same, the the two two rock rock types types differing differing only only in in mineral mineral proportions. ilmenite, and and proportions. Plagioclase, Plagioclase, olivine, olivine, titanomagnetite, titanomagnetite, ilmenite, apatite apatite are are cumulus cumulus minerals. minerals. Clinopyroxene, Clinopyroxene, biotite, biotite, and and plagioclase plagioclase are minerals. The are intercumu.lus intercumulus minerals. The magnetite-.troctolite magnetite-troctolite averages 28 averages 28 volume volume per per cent cent plagioclase, plagioclase, 36 iron36 per per cent cent olivine, olivine, 33 33 per per cent cent irontitanium oxides, oxides, 33 per per cent cent augite augite and and biotite, biotite, and and aa trace trace of of titanium anorthositic gabbroaverages averages 66 66per per cent cent plagioclase, plagioclase, apatite. The anorthositicgabbro 22 22 per per cent cent olivine, olivine, 88 per per cent cent iron-titanium iron-titaniumoxides, oxides, '-t 4 per percent cent augite, augite, and and less less than than one-half one-half per per cent cent apatite. apatite. Titanomagnetite in in these these rocks rocks is is an an irregular irregular microintergrowth microintergrowth Titanomagnetite of ulv%pinel. of magnetite magnetite and and ulv1spinel. Ilmenite Ilmenite occurs occurs as primary granular granular aggregates, (111) lamellae lamellae in in titanomagnetite, titanomagnetite, and and as as granular granular aggregates, as as (111) aggregates aggregates around around titanomagnetite titanomagnetite grains. grains. Hercynite Hercynite is is found found as as tiny tiny "dots" "dots" in in titanomagnetite. titanomagnetite. Magnetite appears appears to to have have settled settled as as euhedral euhedral crystals. crystals. Anhedral Anhedral aggregates aggregates are are thought thought to to be be due due to to enlargement or partial recrystallization recrystallization of touching crystals after settling. settling. Only Only small-scale small-scale cryptic cryptic layering layering is is displayed displayed by by the the intrusion. intrusion. Plagioclase ranges ranges from from An51 AnS1 to to Anits, An~r,, but chemical Plagioclase but no consistent consistent chemical trend trend is is evident. evident. In X-3, anorthositic•gabbro In core core from from drill drill hole X-3, anorthositic gabbro and and magnetite-troctolite are interlayered; olivine magnetite-troctolite olivine in in anorthositic-gabbro anorthositicgabbro ranges from from P053 FoS3 to to Fo56, FoS6, whereas whereas olivine olivine in in magnetite-troctolite magnetite-troctohte ranges ranges from Fo5, Fo57 to to Fo Fo2. 2 . In In core core from from drill drill hole hole X-2, X-2, anorthositie anorthositic gabbro developed. In gabbro layers layers are are poorly poor y developed. In this this core, core, olivine olivine ranges ranges from from Fo57 of Ca4$lg3,Fel8. CaqMg37Fe18. FoS7 to to Fog1. FoS1. Augite Augite has has an an average average composition of Microprobe analysis analysis of of titanomagnetite titanomagnetite gives gives the the following followmg range range of of Microprobe composition: composition: total total iron iron as as FeO FeO 65 65 to to 7'-!74 weight 20 to to weightper percent, cent, Ti02 Ti02 20 21l per cent, cent, MgO MgO 0.5 0.5 to to 3.8 3.8 per per cent, cent,A1203 A12O3 2.3 2.3 to to 3.9 3.9 per per cent, cent, V203 V03 24 per 1.0 to to ]J3 L.3 per per cent, cent, and and Cr203 Cr203 0.1 0.1 to to 1.2 1.2 per per cent. cent. Primary Primary ilmenate ilmen~te has an an average average composition composition of of Ilmg8Hem2 Ihg8Hem2 and and contains contains up up to to S5 weight weight has per per cent cent MgO. MgO. !? Information Information at at hand indicates indicates the the presence of of sizeable sizeable concentraconcentrations tions of of iron-titanium iron-titanium oxides, oxides, but but further further exploration exploration will will be be necessary necessary to determine determine their their form, form, extent, extent, and and relations relations to to the the Round Round Lake Lake to intrusion intrusion as as aa whole. whole. 30 �UPPER MISSISSIPPI VALLEY EXPERIMENTAL UPPEX MISSISSIPPI VALLEYBASE BASEMETAL MET& DEPOSITS: DEF'OSITS: FXPERIMEIiTAL SOLUTIONS TO PROBLEMS OF ORE ORE GENESIS GENESIS SOLUTIONS TO mOBLEMS OF' B. Romberger, Romberger, Department of of Geology and Geophysics, Geophysics, University of S. B. Wisconsin, Madison, Madison, wisconsin Wisconsin 53706 Wisconsin, 53706 ABSTRACT A BSTRACT Chemical models for of base metals f o r tthe h e ttransport r a n s p o r t and deposition of in Mississippi Valley Type Deposits are studied experimentally using i n Mississippi Valley Type Deposits a r e using object is i s tto o supply evidence tto o a mineral synthesis synthesis approach. approach. The obJect support tthe hypothesis tthat have been been deposited deposited from metalmetal— support h e hypothesis h a t tthese h e s e oores r e s have containing, sulfur—deficient, chloride—rich solutions containing, s u l f u r - d e f i c i e n t , chloride-rich s o l u t i o n s entering a sulfur—containing reducing environment. Copper, iron, sulfur-containing i r o n , lead, l e a d , and and zinc zinc were synthesized together together iin molal sodium chloride chloride ssolutions olutions ssulfides u l f i d e s were n 3 molal between 200 20' and and 200°C 200° under the t h e vapor vapor pressure pressure of of water. water. Copper, iron, iron, lead, barium, and calcium were introduced a ass solid l e a d , zinc, zinc, barium, s o l i d carbonates or or The amount amountofof ssulfur soluble chlorides soluble chlorides along along with with elemental elemental ssulfur. u l f u r . The ulfur The of tthat added a l l metal. metal. The added was iin n excess excess of h a t necessary necessary tto o rreact e a c t with with all products depended dependedonont hthe of tthe products e sstarting t a r t i n g composition composition of h e experiments, experiments, but pyrite, galena, digenite, barite, were generally covellite, covellite, p y r i t e , sphalerite, s p h a l e r i t e , galena, digenite, b arite, Morphology of of some some of tthe he anhydrite, anhydrite, and and aa second second generation generation calcite. c a l c i t e , Morphology composite m metallic e t a l l i c sulfide s u l f i d e grains g r a i n s suggest suggest initial i n i t i a l rreaction e a c t i o n occurred above the indicated by by t h e melting temperature temperature of of sulfur. s u l f u r . Nonequilibrium iiss indicated with of unreacted unreactedssulfur tthe h e presence presence of u l f u r iin n tthe h e cores cores of of grains g r a i n s together with metal concentrations concentrations in i n the t h e co—existing co-existing solutions. solutions. No No metal high metal carbonates remained in i n the t h e run products. products. The sulfides s u l f i d e s showed a regular zonation in in rrelation e l a t i o n to t o the t h e un— unzoningiin terms of reacted ssulfur u l f w and and ccalcite. a l c i t e . Summarizing S m a r i z i n g t hthe e zoning n terms of paragenesis, c o v e l l i t e is i s early, e a r l y , followed followed by by galena galena and and sphalerite. sphalerite. paragenesis, covellite Pyrite F y r i t e forms before galena and s p h a l e r i t e but i t s r e l a t i o n s h i p t o s unclear. Barite B a r i t e and anhydrite form independently of of the the ccovellite o v e l l i t e iis ssulfide u l f i d e zoning, zoning, however the t h e second second generation c a l c i t e i s t h e l a s t phase galena and sphalerite but its relationship to generation calcite is the last phase whichappear appeart otocause causep precipitation, ttoo form. form. The The ffactors a c t o r s which r e c i p i t a t i o n , iin n order order of of activity, sulfur a c t i v i t y , increasing increasing pH pH of of solution, solution, importance, are: a r e : increasing sulfur and decreasing temperature. temperature. To aid a i d in i n determining tthe h e chemical conditions underwhich sulfide sulfide precipitation p r e c i p i t a t i o n took place, p l a c e , tthe h e aqueous solutions s o l u t i o n s were analyzed for f o r copper, zinc, llead, barium, and concentration of of the t h e metals metals zinc, e a d , iron, i r o n , barium, and calcium. calcium. The concentration with decreasing temperature temperature and increasing time; time; and barium decreased with that t h a t of calcium either e i t h e r increased or o r decreased, depending on the t h e starting starting variation i s a ttypical ypical v a r i a t i o n of the t h e molar ratio ratio conditions. The following is Cu:Fe:Pb:Zn iin of l1.0:1.0:1.0:1.0: .O:l.O:l.O:l.O: aatt Cu:Fe:F'b:Zn n solution s o l u t i o n aafter f t e r aa starting s t a r t i n g rratio a t i o of 200°C, 1.0:0.114:1140:360; 120°C, ~1.0:1.0:830:2280; 20O0c, ~ . 0 : 0 . ~ & : ~ 4 0 : 3 6a0at t ; 12O0C, . 0 : ~ . 0 : 8 3 0 : 2 2 8 0 and ;and at a t 25°C, 25OC, 1.0:0.15:3.3:150. The copper concentration ttypically y p i c a l l y dropped from from a few few 1.0:0.15:3.3:150. 200°C, to l000ppm t o less less 100Oppm in i n the t h e starting s t a r t i n g solution s o l u t i o n to t o less l e s s than than 55 ppm aatt 20o0C, v a r i a t i o n s are a r e consistent with the t h e paragenesis than than 11 ppm ppm at a t 25°C. 2F°C These variations not established observed in observed i n the t h e minerals. Because equilibrium was not e s t a b l i s h e d tthe he major significance s i g n i f i c a n c e of of these t h e s e data is i s to t o demonstrate relative r e l a t i v e tendencies ffor o r metal sulfides s u l f i d e s to t o precipitate p r e c i p i t a t e under under the t h e conditions conditions of of the t h e experiment. experiment. 31 �PETROLOGY OF PETROLOGY O F SOME SOME EA1LY EARLY PRECAMBRIM PRECAMBRIAN DIFFERENTIATEDULTRAMAFIC LlLTRAMAFIC BODIES BODIES DIFFERENTIATED IN I NNORTHEASTERN NORTHEASTERN MINNESOTA MINNESOTA Klaus J. Schulz Schulz and and Edward Edward M.H.Ripley, of Minnesota, Minnesota, Duluth, Duluth, Klaus 3. Ripley, University of Duluth, Minnesota Minnesota 55812. 55812. ABSTRACT Mapping iin n the t h e Newton Newton Lake Ely, Minnesota Minnesota and and Mapping LakeFormation Formationnorth north of of Ely, the t h e Deer Lake Lake Area n northern I t a s c aCounty, County, Minnesota Minnesota has l o c a t e d aa Area iin northern Itasca has located number number of of mafic—ultramafic mafic-ultramafic bodies of of Early Early Precambrian age, many many of which which are a r e differentiated. differentiated. Detailed mapping mapping of of these t h e s e bodies bodies has has shown shown Detailed that t h a t they they are a r e conformable conformable to t o the t h e surrounding surrounding country country rocks, rocks, indicating indicating they are either sills or flows. that t h a t they a r e e i t h e r sills o r flows. Country Country rocks both areas a r e a s conconrocks iinn both sist of of medasedimentary medasedimentary and r g e l y pillowed metavolcanic metavolcanic rocks. rocks. No andl alargely No sist evidence evidence for f o r contact contact metamorphism metamorphism has been been observed observed between between the t h e bodies bodies and the country rocks. and t h e country rocks. The bodies o 1,000 e e t in i n thickness thickness and and have have The bodies range range from from400 400t to 1,000ffeet lateral miles. The l a t e r a lextents e x t e n t sfrom from aa mile mile to t o several s e v e r a l miles. The rocks t h eDeer Deer rocks of the Lake Areahave havebeen beenf afaulted andt itightly while those north of Lake Area u l t e d and g h t l y folded folded while of Ely Ely are a r e faulted f a u l t e dand and only only broadly broadly folded. folded. Serpentinization S e r p e n t i n i z a t i o n and t h e r aalterlterand oother isextensive extensiveini nalla lthe l t hbodies e bodies with metamorphism generally generally of the the a t i o n is ation with metamorphism green—schist green-schist facies. facies. I n both areas, areas, bodies composed composed solely s o l e l y of of gabbro gabbro or o r peridotite p e r i d o t i t e exist, exist, In however however most most appear appear to t o be be differentiated. d i f f e r e n t i a t e d . The The typical t y p i c a l sequence sequence in i n the the is peridotite, p e r i d o t i t e , pyroxenite, pyroxenite, d i f f e r e n t i a t e d ones, ones, from from bottom bottom to t o top, top, is differentiated porphyritic p o r p h y r i t i c gabbro, gabbro, gabbro. gabbro. The The peridotite p e r i d o t i t e is i s composed composed of of rounded rounded to to euhedral euhedral olivine o l i v i n e and and rare r a r e chromite chromite surrounded surrounded by o i k i l i t i cpyroxene pyroxene by ppoikilitic and and amphibole. amphibole. At A t least l e a s t some some of of the t h e peridotites p e r i d o t i t e s contain contain both both ortho— orthopyroxene h e r z o l i t e . The The pyroxene and and clinopyroxene clinopyroxene and a s s i f i e d as andwould wouldbebec lclassified as IIherzolite. pyroxenite contains sub— pyroxenite is is in i nsharp sharpcontact contactwith withthe t h eperidotite p e r i d o t i tand e and contains subhedral h e d r a l diopsidic d i o p s i d i c augite a u g i t eand and in i nsome some cases cases also a l s o contains contains bronzite. bronzite. With Plagioclase, Plagioclase, in i nvarying varyingamounts, amounts, forms forms the t h e intercumulate i n t e r c u m d a t e phase. phase. With increasing increasing plagioclase p l a g i o c l a s e content content the t h e pyroxenite pyroxenite grades grades into i n t o porphyritic porphyritic gabbro composed composed ofofaaugite, u g i t e , plagioclase p l a g i o c l a s eand andpyroxene pyroxene phenocrysts, phenocrysts,which which gabbro are gabbro contains contains pplagioclase, a r e now now completely completely aaltered. l t e r e d . The The gabbro l a g i o c l a s e , augite, augite, t e r s t i t a l quartz quartz and and and secondary secondary aactinolite c t i n o l i t e with with varying varying amounts and amountsofofi ninterstital micrographic micrographic intergrowths. intergrowths. Cumulate Cumulate t textures e x t u r e s in i n the t h eperidotite, p e r i d o t i t epyrox— , pyroxandporphyritic p o r p h y r i t i cgabbro gabbro along along with with minor minor layering layering and and size s i z e grading grading e n i t e , and enite, i n d i c a t e that t h a t selective s e l e c t i v e crystallization c r y s t a l l i z a t i o nand and gravity g r a v i t y settling s e t t l i n gofofphases phases indicate were the the main main mechanisms mechanisms ofofddifferentiation. i f f e r e n t i a t i o n . Many Many of t h e bodies bodies examinexaminwere of the ed ed were were also a l s o found found to t ohave have complex complex chilled c h i l l e dmargins. margins. A of sulfide A ddetailed e t a i l e d study study of s u l f i d e mineralization m i n e r a l i z a t i o n in i n the t h e bodies bodies of of the the Deer Areashows showst hthat copper, and and iron i r o n sulfides s u l f i d e s are a r e conconDeer Lake Lake Area a t nnickel, i c k e l , copper, The centrated centrated in i n the t h e chilled c h i l l e d margins, margins, making making up up 22 to t o 3% 3%of of the t h e rock. rock. The 32 �basic b a s i c sulfides s u l f i d e s appear to t o have formed formed from from an immiscible Immiscible sulfide— sulfideof intrusion, oxide lliquid, i q u i d , which aatt the t h e time of i n t r u s i o n , coexisted with the the of ssulfide also silicate s i l i c a t e magma. A general llayering a y e r i n g of u l f i d e phases was a l s o found to t o exist e x i s t through through the t h e bodies bodies with with nickel n i c k e l sulf s u l f iides d e s concentrated concentrated in i n the the peridotite, pyroxenite and p porphritic p e r i d o t i t e , copper sulfides s u l f i d e s in i n the pyroxenite o r p h r i t i c gabbro gabbro u l f i d e s appear to t o have and iron i r o n ssulfides u l f i d e s in i n the t h e upper gabbros. gabbros. These ssulfides magma, p precipitating i l i c a t e magma, r e c i p i t a t i n g aass late l a t e phases been in i n solution s o l u t i o n in i n the ssilicate with the t h e intercumulus intercumulus minerals. chemical analyses of of samples from tthe bodies north north of Chemical analyses samples from h e bodies of Ely Ely show show a a bodies appear appear to The bodies t o be be general withddifferentiation. general iron i r o n enrichment enrichment with i f f e r e n t i a t i o n . The ttholeiitic h o l e i i t i c in i nnature n a t u r e and and very ssimilar i m i l a r to t o differentiated d i f f e r e n t i a t e d ultramafic ultramafic bodies age in i n Canada, Canada, Africa, Africa, and and Australia. Australia. bodies of Early Precambrian age 33 �TECTONIC HISTORY HISTORY OF OFEARLY EARLY PRECAMBRIAN PRECAMBRIAN ROCKS THE TECTONIC ROCKS IN IN THE VERMILION DISTRICT, DISTRICT, NORTHEASTERN NORTHEASTERN MINNESOTA VERMILION MINNESOTA P. P. K. K. Sims, Sims, Minnesota Minnesota Geological Geological Survey, Survey, St. St. Paul, Paul,Minnesota Minnesota55108 55108 ABSTRACT ABSTRACT The Vermilion district, ini nnortheastern The Vermilion northeasternMinnesota, Minnesota, contains contains aa sequence sequence of of complexly complexly bordered on on the the north north by by the the intertonguing volcanic volcanic and and volcaniclastic volcaniclasticrocks rocksthat thatisi sbordered intertonguing Vermilion granite—migmatite granite-migmatite massif massif and Vermilion andon on the the south southby by the the Giants Giants Range Rangebatholith. batholith. The supracrustal rocks adjacent to rocks dominantly dominantlyhave havegreenschist—facies greenschist-facies assemblages; assemblages; adjacent to the intrusive they have amphibolite—facies intrusive granitic graniticrocks rocks(Ca. (ca. 2700 2700m.y. m.y. old) old) they hove amphibolite-focies assemblages. assemblages. The supracrustal rocks rockstrend trendgenerally generally eastward, eastward, are are steeply steeply inclined, and The supracrustal andhave have and faulted. Two Twogenerations generationsofoffolds foldshave havebeen beendistinguished distinguished been complexly folded and in part of of the i n the the western western port the district. The older generation is i s represented represented by to by tight tight to that trend trend northwestward northwestward and axialsurfaces surfaces close folds that and have have planar, planar, steeply steeply inclined inclined axial and axes. The and gently—plunging gently-plunging axes. Theyounger younger generation generationfolds foldsare aresuperposed superposed on on the the older older folds of the district. folds in i n the the extreme extreme western western part of district. These These folds trend eastward eastwardand and folds trend axialsurfaces surfacesand andsteep steep plunges; plunges; they they are are accompanied accompanied by by ao have planar upright upright axial have pervasive steep steep cleavage cleavage and and associated associated lineations lineationsthat thatobscure obscuremost moststructures structures pervasive related relatedto tothe theolder olderdeformation. deformation. Judged Judgedfrom fromthe thedivergent divergenttrends trendsofofstructures structuresand and generally steep steep plunges the rocks rocks in i n the the eastern eastern part of the the district district the generally plungesof of lineations, lineations, the also also were were folded folded during during two two or or more more periods periods of deformation. deformation. Three steep fault fault systems, systems, each each of of which whichhas hasassociated associatedmylonite, mylonite,post—date post-date the the Three folding. folding. The The oldest (2) (?) faults faults have haveaa dominant dominant vertical verticalcomponent componentof ofmovement. movement. The The major major fault faultini nthis thissystem systemoccurs occursat atthe theapproximate approximateboundary boundarybetween betweenthe thelow— lowgrade supracrustal supracrustal rocks and the Vermilion Vermiliongranite—migmatite granite-migmatite massif; massif; another fault fault grade separates separates the eastern part of the the Giants GiantsRange Range batholith batholithand andassociated associatedamphibolite— omphibolitefacies facies rocks rocks from from the the supracrustal supracrustal rocks. rocks. These These faults probably have vertical movements faults probably have vertical movements of 3,000 3,000 to to5,000 5,000 feet, feet,and andappear appeartotohave havedeveloped developedlargely largelyini nresponse response to to isostatic isostatic of adjustments between crustal crustal blocks blocks having having different different rock adjustments between rock densities. densities. The younger (?) represented mainly mainly by straight, steep, (?) system system iiss represented steep, north—northnorth-northThe next younger east trending trending faults that cut cut both both the the granitic graniticrocks rocksand and the the volcanic volcanicrocks rocksand and have have east left—lateral miles. These These faults locallyare areabundant abundant left-lateral displacements displacementsof ofas asmuch much as as 44 miles. faults locally and and closely closelyspaced. spaced. Some Someofofthem themappear appeartotodisplace displacesupracrustal supracrustalrocks rocksmore more than than the the intrusive intrusiverocks, rocks,suggesting suggestingthat thatthey theypre—date pre-dote emplacement emplacementof ofatatleast leastsome some of of the the granitic granitic rocks. rocks. The youngestfaults faultsare aretranscurrent transcurrentfaults faultshaving havinghorizontal horizontalright right lateral displaceThe youngest ments. this system this systemisi sata least t least250 250miles mileslong longand andtransects transectsseveral several ments. The Themajor majorfault faultini n greenstone—granite greenstone-granite complexes. complexes. In I n northwestern northwestern Minnesota Minnesota iti tappears appears to to have have disdisplaced distinctive distinctivegravity gravityanomalies anomalies aa distance distance of about about 35 miles; miles; in i n the the Vermilion Vermilion placed district,where whereit iconsists t consistsofofseveral severalstrands, strands, iti thas hasdisplaced displacedthe the upper upper part part of of the the district, volcanicpile p i l ea adistance distanceofofabout about1212miles, miles,distorting distorting i t from a thick almond-shaped volcanic it from a thick almond—shaped lens lens to toaatenuous tenuouseast—trending east-trending mass. mass. Metamorphism, folding, and andemplacement emplacement of the the granitic graniticrocks rockswere werebroadly broadly Metamorphism, 34 �synchronous, and andoccurred occurredduring during the the Algoman Algomanorogeny. orogeny. The synchronous, The foldng foldingofofthe thesupra— supraresulting from from the the relative relative upwelling crustal rocks is attributed to to compression compression resulting upwelling convergence of of the the flanking batholiths, experiand convergence batholiths, aamechanism mechanism demonstrated demonstrated experimentally by Romberg (1967). The Vermilion massif andat at least least aa part part of of the Giants Ramberg (1967). The Vermilion massif and Giants Range batholith continued continued to rise because becauseofof their their buoyancy buoyancy after after crystallization crystalUzation Range batholith of the the granitic rocks. rocks. The Thetranscurrent transcurrent faulting faultingtook took place placeduring during aa fate latestage stage of of the orogeny, orogeny, after after the the crust crust had had attained attained sufficient sufficient strength strength to to transmit transmit regional regional related to the fracturing can compressive compressive stresses. stresses. Cataclasis Cataclasis related can account account for the the disparity between andmineral mineral ages agesi n in the the Giants Range batholith between whole—rock whole-rock and Range batholith (Prince and Hansen, Hansen, 1972). 1972). 35 �LAYEREDWMAPIC INTRUSION A KEWBENAWAN KEWEENAWAN LAYEmD I C INTRUSION NEAR NZAR FINLAND, FINLAND,LAKE LAKECOUNTY, COUNTY,MINNESOTA XIRXTSOTA R.J. R.J. Stevenson, Department Department of Geologys Geology, University of Stevensons Minnesota-Duluth, Duluth, Ninnesota-Duluth, DuLuth,Minnesota Kinnesota55812 55812 ABSTRACT ABSTRACT and one The NNE The Sonju Sonju Lake h k e Intrusion, Intrusion, four four and one half halfmiles milesNN3 Finland, has an Finland, Minnesota, Minneeota, has an exposed exposed area area of of one one and and one one intrusion isissurrounded miles • The intrusion half two and and one one half half miles. The surrounded half by two granite ,of the granophyric granite,of on three sides on three sidesby by diabase diabase and and granophyric the side is Beaver Beaver Bay Bay Complex, Complex, and and the the western western side isobscured obscured by by lamination, cryptic cryptic layering, glacial. drift. It Itshows shows igneous igneous lamination, layering, and layering, and and rhythmic rhythmic layering, and has has a a stratigraphic stratigraphic thickness thickness of of dip of approximately 3500feet feet based basedon onthe the strike strike and approximately 3500 and dip of the the rock units units comprising the intrusion intrusion igneous igneous lamination. lamination. The The rock comprising the picrite; are, from the base to the are, from the base to the top top respectively: respectively: basal basal picrite; troctolite; a gabbro; an a gabbro; an an apatite-rich ferrogabbro; an a troctolite; olivine-hedenbergite quartz-bearing diorite; diorite; a hedenbergite hedenbergite olivine-hedenbergite quarts-bearing The ferrogabbro granodiorite; granodiorite; and and a a hedenbergite hedenbergite adamellite. adamellite. The ferrogabbro contains 43.50$ SiC2. Si02. contains 19.26% 19.26s FeC FeO and and 43.50% of of glacial drift. The The compositions compositions of the the major major minerals minerals vary vary with with strati— etratigraphic height; height; they have been studied by electron electron microprobe plagioclase varies varies from An33 in and optical optical methods. methods. The plagioclase from An in the the and The piorite to to An An ininthe thehedenbergite hedenbergite adamellite. adame~lite?~ The basal picrite basal picrite to in to Fo12 3'0 in the the divine ?07 in in the basal olivine varies varies from froml#o 12 uppermost uppermost apatite—rich apatite-rich7$errogabbro. The cumulus cumulus clinopyroxene d~nopyroxene hrrogabbro. The ranges ranges from from Ca Ca Mg Ng 6Fe Fe 1 in the lowest gabbro to Ca 0Mg Mg Fe Pe injrmjiatg5ana The int?%ne%!atJ5and ferrogabbro. in the uppermoM upperno@ jatite-rich &ti&rich ferrogabb~o. The in the felsic rocks rocks have hedenbergites hedenbergites clustered felsic clustered around around Ca49Mg03Pe43. Ca49Mg03Fe48* lamination, cryptic layering, The The igneous igneous lamination, layering, and and rhythmic rhythmic P extreme iron—enrichment layering the and the extreme iron-enrichment 3' layering and establish this this intrusion trend all establish intrusion as as a a differentiated, tholeiitic intrusion of the differentiateds Skaergaard type. type. Skaergaard trend all tholeiitic intrusion of the A 36 N �THE THE PITTSVILLE PITTSVILLE (WISCONSIN) THE FORMATION FORMATION OOF F THE (WISCONSIN) MIGMATITE MIGMATITE J. E. Thresher, Department Department ooff Geography Geography and niversity o E. Thresher, andGeology, Geology,UUniversity off Wisconsin—Extension, W i scons i n-Extens ion, Madison, Madison, Wisconsin Wisconsin 53706. ABSTRACT The Pittsvi The P i t t s v ilie l l emigmatite m i g m a t i t ewas was formed formed during d u r i n g the thePrecambrian PrecambrTan by by the the iintrusion n t r u s i o n of o faahydrous hydrous granitic g r a n i t i cmagma magma into i n t o aa series s e r i e s ofo fdiabases diabases and and Duet to the hydrous hydrousnnature spatially extensive extensive b a s a l t s . Due o the a t u r e o of f t the h e ggranite, r a n i t e , spacially basalts. transport of magma into the country rock took place which hasbeen been t r a n s p o r t o f magma i n t o the c o u n t r y rock took p l a c e whichhas recordedbybyppoikiloblasts off quartz potash ffeldspar e l d s p a r wwithin i t h i n the t h e older older recorded oikiloblasts o q u a r t z and and potash rocks, and and the the presence presenceo of the ggranite. rocks, f ooriginal r i g i n a l hydrous hydrous mminerals i n e r a l s wwithin i t h i n the ranite. The observedl ilithologic The observed t h o l o g i c layering l a y e r i n g ini nthe t h emigmatite migmatitehas has formed formed axial axial planar p l a n a r to to a a series s e r i e s of o f subisoclinal s u b i s o c l i n a lnorthwest northwest plunging p l u n g i n g folds. f o l d s . Contemporaneous( (or so) w with was raneous o r nnearly e a r l y so) i t h this t h i sfolding folding wasthe t h edevelopment development of of almandine-amphibolitef afades minerals wwithin almandine-amphibolite c i e s minerals i t h i n the t h e migmatite. migmatite. Later Later more openeast-west east—west were i imprinted on tthis more open t r etrending n d i n g s usubhorizontal b h o r i z o n t a l f ofolds l d s were m p r i n t e d on his ffabric, a b r i c , and and this t h i swas was followed f o l l o w e dby bya agreenschist g r e e n s c h i s tfacies f a c i e smetamorphic metamorphic event, event, apparently a p p a r e n t l y uunrelated n r e l a t e d tto o tthe h e folding. folding. Two episodes wererecorded recorded therocks, rocks,the thef first irst Two episodes o fofj ojointing i n t i n g were w i within t h i n the of o f which which effected e f f e c t e d only o n l ythose thoseofo fPrecambrian Precambrian age. age. The The llater a t e r episode episode also also sandstonesand andi sisthus thus aatt least ffractured r a c t u r e d the the overlying o v e r l y i n gupper upperCambrian Cambrian sandstones least thesej ojoints lower Paleozoic Paleozoic in lower i n age. age. Many Many o fofthese i n t s aare r e f filled i l l e d with w i t h quartz, quartz, granite and/or cchlorite. hlorite. g r a n i t e and/or The rnigmatiteswere werel alater byaaggranitic The migmatites t e r i nintruded t r u d e d by r a n i t i c pluton p l u t o n which which is is considered be rrelated considered tto o be e l a t e d to t o the the greenschist g r e e n s c h i s t facies f a c i e smet met and and possibly possibly Several youngerggranitic Several younger r a n i t i c and and bbasaltic a s a l t i c dikes dikes tthe h e ffilling i l l i n g of o f the t h e joints. joints. crosscut the ccrystalline c r o s s c u t the r y s t a l 1 i n e rocks rocks locally. locally. The eentire The n t i r e sequence sequence is i s unconformably unconformably overlain o v e r l a i nby byupper upperCambrian Cambrian sandstones andconglomerates conglomerates which sandstones and which a r are e e sespecially p e c i a l l y pprevalent r e v a l e n t in i n the the southern the PPittsville area. southern ppart a r t oof f the i t t s v i Il earea. 37 �STRUCTURALAND ANDSTRATIGRAPHICAL STRATIGRAPHICALANALYSIS ANALYSIS OF STRUCTURAL OF THE GECO GECO SULPHIDE DEPOSIT DEPOSIT IN I N MANITOUWADGE, MANITOUWADGE, NORTHWESTERN NORTHWESTERN ONTARIO ONTARIO Jens Geology, U University Jens F. F. Touborg, Touborg, Department Department oof f Geology, n i v e r s i t y of o fOttawa Ottawa and and Departmentoof Geology,UUniversity Department f Geology, n i v e r s i t y of o f Toronto, Toronto, Ontario, Ontario,Canada. Canada. ABSTRACT ABSTRACT In area hhigh rocksc oconsisting I n the t h eManitouwadge Manitouwadge area i g h grade grade metamorphosed metamorphosed rocks n s i s t i n g ooff metavolcanic—and metasedimentary downfoldedi in metavolcanic-and metasedimentary s e rseries i e s l i lie e downfolded n a northeast northeast plunging ssyncline, plunging y n c l i n e , the t h e core core of o f which which is i soccupied occupied by by aa granodiorite g r a n o d i o r i t ebody. body. Regionalssuiphide occurs wwithin Regional u l p h i d e mmineralization i n e r a l i z a t i o n ooff stratabound stratabound nnature a t u r e occurs i t h i n aa quartz-muscovite schist quartz-muscovite s c h i s t horizon h o r i z o nalong alongthe t h econtact c o n t a coft metasedimentary—and o f metasedimentary-and ooverlying v e r l y i n g metavolcanic metavolcanic sseries e r i e s iinn the t h e upper upper part p a r t of o fthe t h esequence. sequence. The GecoCopper-Zinc-Silver Copper-Zinc-Silvers usulphide beingl located The Geco l p h i d e ddeposit e p o s i t being o c a t e d wwithin i t h i n aa synclinal s y n c l i n a l dragfold d r a g f o l d on on the t h e northeast n o r t h e a s t limb l i m b ooff the t h e syncline s y n c l i n e consists c o n s i s t s of o f aa ttabular a b u l a r body body of o f massive massive sulphides sulphides enveloped enveloped by by a a haloe haloe of o f disseminated disseminated pyrite—pyrrhotite—chalcopyrite mineralization. p y r ite-pyrrhoti te-chalcopyri t e m i n e r a l i z a t i o n . A discontinous d i s c o n t i nous zone zone ooff disseminated chalcopyri chalcopyrite—pyrrhotite—sphalerite—gahnite disseminated te-pyrrhotite-sphalerite-gahni t e mmineralization ineralization The occurs along tthe occurs along h e north n o r t h contact c o n t a c t of o fthe t h equartz—muscovite quartz-muscovite sschist c h i s t horizon. horizon. The south ccontact mineralization south o n t a c t ooff this t h i s contains contains disseminated disseminated ssphalerite phalerite m i n e r a l i z a t i o n in i n aa discontinous by magneti magnetite-chert discontinous zone zone ffollowed o l l owed by t e - c h e r t iiron r o n formation. f o r i n a t i on. The massives suiphide bodywhich whichs tstrikes east-west and andddips The massive u l p h i d e body r i k e s east-west i p s ssteeply t e e p l y to to the elongatedlenses lensesbecoming becoming successsuccesst h e north n o r t hisi scomposed composed of o f aastring s t r i n of g o5—6 f 5-6elongated plungeo of thesepparallels iively v e l y smaller s m a l l e r towards towards the t h e east. east. The The plunge f these a r a l l e l s tthe h e aaxis x i s of of the t h e dragfold. dragfold. IIn n detail d e t a i l the t h emassive massive sulphide s u l p h i d e body body cconsists o n s i s t s oof f 33 pprincipal rincipal rock types: coarseggrained rock types: 1) 1) compact compact ore: coarse r a i n e d p pyrite y r i t e rrich i c h sphalerite s p h a l e r i t e ore. ore. coarsegrained grainedppyrrhotite-chalcopyrite-sphalerite-pyriteayered ore: coarse yrrhotite-chal copyrite-sphaleri te-pyri te22)) 1layered Mg schistose ore: 3 ) schistose ore: ffine i n e grained g r a i n e dkneaded kneaded ('durchbewegte") ("durchbewegte") Mg ssilicate i 1i c a t e rich r i c h ore. ore. 3) ore These33 types types ddefine o r e of o f similar s i m i l a rcomposition composition to t o the t h e layered l a y e r e d type. type. These e f i n e aa mineralogical-textural-compositional zoningppattern the m i n e r a l o g i c a l - t e x t u r a l - c o m p o s i t i o n a l zoning a t t e r n wwithin i t h i n tthe h e lenses; lenses ; the compacttype typei siscconfined andt hthickest compact o n f i n e d t otot hthe e ccentral e n t r a l and i c k e s t ppart a r t of o f the t h e lenses, lenses, the the layered l a y e r e d ore o r e is i s arranged arranged along along the t h e north n o r t h contact c o n t a c tand and increases increases in i namount amount with with decreasingwwidth decreasing i d t h ooff the t h e lens; lens; the t h eschistose s c h i s t o s eore oredominates dominates in i nthe t h epinch—out pinch-out areas. W Within i t h i n the t h e compact compact oore r e sphalerite s p h a l e r i t e rich r i c hzones zonesare aredeveloped developed towards towards the t h e south south contact. contact. Textures iindicate Textures n d i c a t e aa metamorphic metamorphic r erecrystallization c r y s t a l l i z a t i o n of o fsulphides sulphides and and Annealingf fabrics Annealing a b r i c s exist e x i s t ini nmonomineralic monomineralic aggregates; aggregates; ppyrite yrite porphyroblasts reveal reveal aacomposite composite aggregate aggregate structure s t r u c t u r eand andare a r ecomposed composed of of 2 2 varieties v a r i e t i e s of o f pyrite; p y r i t e ; microfold m i c r o f o l dstructures s t r u c t u r e s are are characteristic c h a r a c t e r i s t i c of o f the t h e layeredlayeredand sschistose massivetypes types as aswwell and c h i s t o s e massive e l l as as the t h e disseminated disseminated types. types. silicates. silicates. 3 sets s e t s of o fsynkinematic synkinematic dyke dyke intrusions i n t r u s i o n semplaced emplaced as as Dyke chronology: chronology: 3 Dyke q u a r t z ddiorites, i o r i tes, 2) 2 ) amphibolites amphi b o l i t e s and, and, 3) 3) granodiorite g r a n o d i o r i t e and and ffollows, o l l o w s , 1) 1 ) quartz granite showdiscordant discordantr erelationships g r a n i t e pegmatites pegmatites show l a t i o n s h i p s tto o the t h e layered l a y e r e d rocks rocks None ooff these dyke dyke generageneraiincluding n c l u d i n g all a l lthe t h edisseminated disseminatedmineralized m i n e r a l i z e dzones. zones. None Dykes ooff ttions i o n s transect t r a n s e c tthe t h massive e massiveore—quartz—muscovite ore-quartz-muscovite sschist c h i s t contact. Dykes 38 �1) and and 2) 2 ) generations generations occur occur as as highly highly folded foldedboudinaged boudinaged fragments fragments wwithin i t h i n the the Significant metamorphic reaction zones are present present massive sulphide ore types. massive sulphide types. Significant metamorphic reaction zones are in-and as follows: follows: niagnetite-sulphide in-and around around the fragments fragments and and appear appear as magnetite-sulphide impregnated zones thes isilicate rock and andsphalerite sphalerite rich rims impregnated zones in inthe l i c a t e rock rims up up to t o 5" 5" rims, Zinc Within the the sulphide sulphide rims, Zinc rich around the the boudinaged boudinaged fragments. fragments. Within wide around sphalerite nearthe thessilicate sphalerite zones zones are are concentrated concentrated near i l i c a t e contact, contact, Iron Ironrich richsphal— sphale r i t ezones zones away away from his. erite from tthis. In conclusion as as a metamorphosed conclusion the thesulphide sulphidemineralization mineralizationis regarded i s regarded a metamorphosed lithological zoning in in thethe boudin—shaped The lithological zoning boudin-shaped bedded sulphide deposit. bedded sulphide deposit. The massive sulphide massive sulphideore orerepresents representsaaprimary primarystratigraphical stratigraphical configuration, Stratigraphical tops tops have have not not although although accentuated accentuated during the the deformation. deformation. Stratigraphical thedistribution distribution of However the of been determined in been determined in the theManitouwadge Manitouwadge area. area. However relatively r e l a t i v e l ycopper copper rich zones zones tto o the the north, zinc zinc rich richzones zones to t o the the south south followed by by magnetite-chert magnetite-chert iron iron formation formationdefines definesa abroad broadpattern patterncomparable comparable I tisi sproposed proposed to othersynvolcanic synvolcanicsulphide sulphidedeposits. deposits. It t o the the vertical verticalzoning zoningini nother that syncline represents represents the the refolded limbs t h a t the theManitouwadge Manitouwadge syncline limbs of ofan anoverturned overturned nappe structure with w i t hananeast—west east-west axis. axis. nappe structure 39 �THE ATIKOKAN THE ATIKOKAN IRON IRON RANGE RANGE AND AND ITS ITSIRON—COPPER IRON-COPPER MINERALIZATION MINERALIZATION dens. F. F. Touborg, Touborg, Suite S u i t e1006, 1006, 77 77Howard Howard St., St., Toronto TorontoM4X M4X IJD, lJD, Ontario O n t a r i oCanada. Canada. Jens. ABSTRACT The Atikokan Atikokan IIron The r o n Range Range iin n northwestern northwestern Ontario O n t a r i o contains containswidespread widespread magnetite—basemetal suiphide whichi sissspatially magneti te-basemetal sulphide m i mineralization n e r a l i z a t i o n which p a t i a l l y associated associated with w i t h lensoid l e n s o i dbodies bodies ofo ultrabasic—basic f u l t r a b a s i c - b a s i cigneous igneousrocks rockscomposed composed ooff pyroxenites, gabbros, amphibolites and and pperidotites. gabbros, amphibolites eridotites. The lenses, lenses, having The having a strong s t r o n g geophysical geophysical response, response, are are concordantly concordantly enclosed enclosed iinn metavolcanic metavolcanic rocks rocks of o f basaltic—andesitic b a s a l t i c - a n d e s i t i c composition composition and and 16 mmile zoneo of strikes ddefine e f i n e aa 16 i l e llong o n g zone f sstratigraphical t r a t i g r a p h i c a l continuity. c o n t i n u i t y . IItt strikes uniformly andddips The zone zonel lies i e s aa few few u n i f o r m l y eastnortheast eastnortheast and i p s ssteeply t e e p l y tto o the t h e north. n o r t h , The hundredso of whichi in hundreds f f feet e e t nnorth o r t h ooff the t h e Quetico Q u e t i c o Shear Shear S&tructure, t r u c t u r e , which n tthis h i s area area separates Archean Archeanmetavolcanic metavolcanicsseries e r i e s to t o the t h enorth n o r t hfrom fromSeine Seinemetasedimentary metasedimentary separates The impact impact ooff metamorphism area iiss low. metamorphism i nint hthe e area low. sseries e r i e s to t o the t h e south. south. The Concentrations occuri in Concentrations ooff Iron—Copper Iron-Copper m imineralization n e r a l i z a t i o n occur n ttabular a b u l a r deposits deposits up Examples are: The The Atikokan Mines-, Mines-, up ttoo 3000 3000 feet f e e t long l o n gand and50-250 50-250 wide. wide. Examples SapaweLake-, Lake—,Archibald-, Archibald—,Pattison-Roberts Pattison—Roberts and and Mark Mark prospects. Sapawe rospects. IIn n detail detail the disseminated t h e mineralization m i n e r a l i z a t i o n consists c o n s i s t sofo lenses f lensesdominated dominated by by 1) 17 massive—or massive-or disseminated magnetite minor sulphide sulphide vveinlets massive—or disseminated disseminated magnetite wwith i t h minor e i n l e t s and and 2) 2) massive-or ppyrrhotite, y r r h o t i t e , lesser l e s s e amounts r amounts of o f pyrite—chalcopyrite p y r i te-chal c o p y r i t e (.3-.6% (. 3-. 6%Copper) Copper) and and trace trace mineralized amountsoof Nickel—Cobaltbearing bearing sulphides. sulphides. The amounts f Nickel-Cobalt The m i n e r a l i z e d lenses lenses are are characterized by aa banded bandeds tstructure concordanti nintercalations c h a r a c t e r i z e d by r u c t u r e wwith i t h concordant t e r c a l a t i o n s ooff the the zonest the mineralization ultrabasic—basic host rock. u l t r a b a s i c - b a s i c host rock. Within W i t h i n pinch—out pinch-out zones he m i n e r a l i z a t i o n and and interbandedwwith tthe h e host h o s t rocks rocks become become hheavily e a v i l y interbanded i t h tthe h e surrounding surrounding volcanic volcanic rocks. Geometrically Geometrically the t h e ruagnetite-and magneti te-and ssulphide u l p h i d e lenses lenses are arranged arranged in in en—echelon sometimesw with aa complex complex en-echelon s t rstructure, u c t u r e , sometimes i t h t hthe e ssulphide u l p h i d e rich r i c hzones zones confined c o n f i n e d tto o tthe h e ffootwall o o t w a l l side; side; this t h i sfeature f e a t u r emay may be be a a possible possible iindicator ndicator ooff stratigraphical s t r a t i g r a p h i c a l tops. tops. Preliminary P r e l i m i n a r y microscopic microscopic work work reveal reveal the t h epresence presence of primary of primary magmatic magmatic ttextures e x t u r e s in i n both both the t h eoxide-and oxide-and sulphide s u l p h i d ephases. phases. Origin Available t h e mineralization mineralization O r i g i n of o f mineralization: mineralization: A v a i l a b l e data data suggest suggest 1) 1 ) the forms an an i Integrating forms n t e g r a t i n g part p a r t of o f the t h eultrabasic—basic u l t r a b a s i c - b a s i c host h o s t rocks. rocks. 22)) there t h e r e is is no evidencet to no evidence o iindicate ndicate a a possible p o s s i b l e relationship r e l a t i o n s h i p to t othe t h ebedded bedded iron i r o n formations formations Wall rock rock contained within w i t h i nthe t h eSteep SteepRock—and Rock-and Caland Caland deposits nearby. nearby. 3) Wall alteration a l t e r a t i o n isi slacking l a c k i n gapart a p a r from t fromminor minorquartz-carbonate quartz-carbonate vveining e i n i n g ooff the t h e host host There i is 4) There s no no ddirect i r e c t relation r e l a t i o nbetween between the t h e mineralized m i n e r a l i z e d uultrabasicltrabasicrock. 4) synvolcanic i intrusive! A synvolcanic ntrusive/ bbasic a s i c series s e r i e s and and the t h e Quetico Q u e t i c o shear shear sstructure. tructure. A extrusive e x t r u s i v e origin o r i g i n isi sproposed proposed for f o rthe t h estratabound stratabound ultrabasic-basic u l t r a b a s i c - b a s i c series s e r i e s and and iits t s associated associated mineralization. mineralization. 40 �GEOCHRONOLOGY PRECM4BRIANROCKS ROCKSIN IN EASTERN WISCONSIN GEOCHRONOIAGY OFOFPRECAMBRIAN WISCONSIN W. Schxnus,Department DepartmentofofGeology, Geology,University University of . Van Van Schmus, of W. RR. lawrence, Kansas, 66044 Kansas, Lawrence, Kansas,66024k Kansas, geochronological studies studies by the author, in Recent geochronological in Recent conjunction with other published and unpublished data, now conjunction permit the the delineation delineation of of major major chronologic chronologic units units for for Precambrian rocks Precambrian rocks in in eastern eastern Wisconsin. Wisconsin. The The oldest oldest rocks rocks in in the the eastern eastern part part of of the the state state are the metavolcanics, gneisses, gneisses, and intrusive rocks rocks in northeastern corner, the northeastern corner, including including the the Quinnesec Quinnesec Fm., Fm., Dunbar Gneiss, Dunbar Gneiss, Hoskin Hoskin take Lake Granite, Granite, Newingham Newingham Granodiorite, Granodiorite, and AtheLstane Athe-"Sane Quar'z QuaiJ%Monzonite. Monzonite. These These rocks rocks are are about about 1900 m m.y. whole-rock data and 1850 1850 to 1900 .y. old based on Rb-Sr whole-rock published U-Pb U-Pb zircon zircon data. data. Apparently the bulk of of the the state state is is made made up up of of metametavolcanics and volcanics and granitic granitic rocks rocks that that yield yield ages ages of of 1650 1650 to to rocks in Waushara 1700 1700 m.y. m.y. The The author author has has analysed analysed such such rocks in Waushara Co. (granites) (granites) and and to to the the south south (rhyolites), (rhyolites), and and other other workers workers have have reported reported similar similar ages ages from from near near Monico, Monico, Wausau, Wausau, and Baraboo. Baraboo. Intrusive into the 1650—1700 m.y. 1650-1700 m .y. old complex complex is is aa Intrusive large large plutonic plutonic assemblage assemblage that that is isabout about12450 1450 to to 1500 1500 m.y. m.y. old and is is now now referred referred to to as as the the Wolf Wolf River River Batholith. Batholith. It It includes a wide variety of includes of rocks rocks from from Mountain, Mountain, to to Wausau, Wausau, Point, to Waupaca and apparently is to Steven's Steven's Point, is the last major major plutonic plutonic or or metamorphic event event in in the the state, state, except except for for the the Keweenawan Keweenawan rocks rocks in in the the far far northwest. northwest. absolutely dated are Not yet absolutely are gneissic gneissic and and related related rocks in Published rocks in the the Steven's Steven's Point-Wisconsin Point-Wisconsin Rapids Rapids area. area. Published mineral ages from these rocks rocks suggest suggest they may be related mineral ages from to Resolution to the the northeastern northeastern Wisconsin Wisconsin complex, complex, or or older. older. Resolution of this problem, plus extending extending our our knowledge knowledge westward westward and and northwestward, is currently currently in northwestward,is in progress. progress. 41 �"FRMIBOIDAL" WHITEPINE, PINE, MICHIGM "ERAMBOIDAL" CHAJJCOCITE CHALCOCITE FROM FROM WHITE MICHIGAN Thomas A. A. Vogel and and Nancy Nancy Alyanak, Alyanak, Geology Geology Oepartment, Department, Michigan 48823 Michigan State S t a t e University, University,East EastLansing, Lansing,Michigan Michigan48823 ABSTRACT ABSTRACT Chalcocite with nnuclei Chalcocite with u c l e i occurs occurs throughout throughout the t h e mineralized mineralized zone zone aatt White White Pine, Pine, Michigan. Michigan. They They are a r e more more abundant abundant in i n the t h e well—laminated, well-laminated, black, black, fine—grained fine-grained lithologies l i t h o l o g i e s than than in i n the t h e massive massive lithologies. l i t h o l o g i e s . In In polished section nuclei s e c t i o n these n u c l e i are a r e either e i t h e r circular, c i r c u l a r , ellipsoidal e l l i p s o i d a l or o r con— cont o the t h e shape shape of of the t h e grain, g r a i n , with with aa median median circular c i r c u l a r diameter diameter of of four four fform on to microns microns and and aa median median ellipsoidal e l l i p s o i d a l long long axis a x i s of of eight e i g h t microns. microns. Microcrysts Microcrysts at a t least l e a s t as as small small as as 0.2 0.2 microns microns are a r e found found in i n each each nucleus. nucleus. The The nuclei nuclei are pyrite a r e similar s i m i l a r to t o the t h e framboidal texture t e x t u r e commonly observed in in p y r i t e assoassociated c i a t e d with with sediments. sediments. The The chalcocite chalcocite nuclei n u c l e i can can only only be be observed observed after after the t h e polished section s e c t i o n has been etched and stained s t a i n e d with a weak hydrochloric acid acid and and potassium ferrocyanide solution——a s o l u t i o n ~ astain s t a i n very sensitive s e n s i t i v e to t o low concentrations concentrations of of iron. iron. e l e c t r o n microscope shows that The scanning electron t h a t the microcrysts within c i r c u l a r or o r ellipsoidal e l l i p s o i d a l nucleus are a r e densely packed, a well-defined well—defined circular packed, with a few scattered s c a t t e r e d microcrysts in i n the t h e surrounding surrounding grain. grain. However, the t h e micro— microfew crysts c r y s t s are a r e less l e s s densely densely packed packed where where the t h e nucleus nucleus occupies occupies the the entire e n t i r e grain. grain All A l l gradations between between dispersed dispersed and and densely densely packed packed microcrysts a r e found. found. microcrysts are Preliminary microprobe d i c a t e s t hthat a t the u c l e i aare r e higher iron, Preliminary microprobedata datai nindicates the nnuclei higher iinn iron, potassium and carbon carbon than than the the surrounding potassium and surrounding grain. grain. Two Two origins o r i g i n s are a r e possible possible for f o r the t h e framboidal framboidal chalcocite: chalcocite: 1.) 1.) replacement of 2 . ) formation of primary framboidal framboidal chalco— chalcoof framboidal framboidal pyrite p y r i t e and 2.) cite. c i t e . We We are a r e currently c u r r e n t l y evaluating evaluating these these alternative a l t e r n a t i v e genetic models and and their t h e i r implications. implications. 42 �WISCONSIN OF LANDFORMS Na .., ii: Or- tLJ ni story irvey FII rrF F F. Su Unoron I rd Geolo irsi Hanson. Dirnotor and Stoto Genlngiot L'Fur UNIVERSITY ESTENSION, UNIVERSITY OF WISCONSIN 1971 30 Ti __ 0 UCALE OF VILEU EU �A A' lie Cassai Racine boo too 002 455 StiLES IS SCALE iuniuue Fat it] A S imL HOtFrtFTs - id 200 SL Or) _c 10 - 0 - 203 400 25 boo 500 Jr loon, In Leoal cool Sea boo Peat Fr F 'a Fr sri "r ron taboo and Adaoe toFu Eieoatian GriP Gla(n D!der at trio (OrryF (Otto) dssnsnsin V2snirainn ci oi Hordes -. DriP r data) (sisarne Seeks Mntantrri and tgnenes Boors 0rorphie imenLated ii and Graean UndiffererrlLFud h r -tamest iF Marc and Ugeenas irks toeke .1 is miii ndiI UrFjfersrtiarnd and Granite [E a - - BasalE and Gabbrn 'c P r Oornraii000 'chin For tree and Ps' 0mm Graaneitc senptnmerale) 'rotc ncr-rninuodir wirb (sandstones I-crrn',c"s tlnwennerrrn Formutioos Upper a-rd - corns with (sandstones nrA. aed shale) a-ri 5dolomite dotoir snore _55 °oncrr Oncbrinr' air Cumb i_poor Formations Jeo (dolomin) iso "mine dr Pr Ar,a? Chine Group Crrhs none and shale (snrho,crs doreen in usutnF rrsrcrr torrreratr-( ruEd rFFr Parer Fm) '0nr StS (mainly 'usr, Group Aneell Oscs'l F,rtr r--ssils some rune )dclsrnitcoirh shale) oh5 sF and ccc lanresroon with (dolomite Group Sponipea dtu, 'F dolomrtn) srd arrd (ehuls irrein Oct. Forrtiati °rrnurrorr iolrntn Mc,, S'iapaiokr--lu hdcLoortn; (oolomitu( sir Is, Si Formations lurian Furoariors II 1— a a skis' shale) dod O'i (doloroipsin rho Forrrratronn Dovoniuo S LEGEND - -1- I Co L SilLhd GO SCALE 30 1971 1)JF[°lVflLjyj1 WISCONSIN Fj• OF UNIVERSITY )s:H EXTENSION. UNIVERSITY an Geologist State and Director h( F. George 1rr::ni Hanson. 'r :r-:.n. Forli' History 'ir Geological Survey Natural s:•-•j and !YF: F WISCONSIN iF'fl In::) MAP GEOLuGIC fl-il' )l S ,.'f:s d �SHORT GEOLOGIC GEOLOGIC HISTORY HISTORY OF OFWISCONSIN WISCONSIN The bedrock separatedinto intotwo twomajor majordivisions: divisions:(1) (1) older, older, predominantly predominantly crystalline crystalline rocks rocks of of the bedrock of Wisconsin Wisconsin isisseparated Precambrian Precambrian Era; and and (2) ( 2 )younger youngerrelatively relativelyflat-lying flat-lyingsedimentary sedimentaryrocks rocksof of the thePaleozoic Paleozoic Era. Era. The Precambrian Precambrian Era Era lasted lasted from from the the time time the theearth earthcooled, cooled,over over4,000 4,000 million million years years ago, ago, until until the thePaleozoic Paleozoic Era Era which began began about 600 million years ago. ago. During During this vast period which million years period of of 3,400 3,400 million million years yearssediments, sediments, some some of of which which were rich rich in iron iron and and which which now now form formiron ironores, ores,were weredeposited depositedinin ancient ancient oceans; oceans; volcanoes volcanoes spewed spewed forth forth ash and and lava; mountains were built built and and destroyed, destroyed,and and the the rocks rocks of of the upper crust mountains were crust were were intruded intruded by by molten molten rocks rocks of of deepdeepseated origin. Only a fragmentary fragmentary record record of of these these events events remains remains but, but, as as tree treestumps stumpsattest attesttotothe thepresence presenceofofformer former forests, forests, the rocky rocky roots roots tell tell the thegeologist geologist of of the thepresence presenceofofformer formermountains. mountains.Nowhere Nowhere does does any trace trace of of the the original original crust remain, remain, and and the theoldest oldest rocks rocks yet yet found found in inthe thestate stateare areabout about2,000 2,000million millionyears yearsold. old.With Withthe theexception exception of ofthe the Upper Keweenawan formationsthat that outcrop outcrop in in the northwest, northwest, all of of these these rocks rocks have havebeen beenextensively extensively deformed, deformed, Keweenawan formations and in altered that their in many many areas areas they they are are so so highly highly altered their original original nature and and origin origin are are extremely extremely difficult difficult to interinterpret. I n the the north-central north-central part partof of the thestate statesurface surfaceoutcrops outcrops are areso sosparse, sparse, due due to to aa cover cover of of glacial glacial deposits, deposits, that In that details of the bedrock bedrock are are obscured. obscured. In In such such areas areasthe theonly onlyclues clues to t othe theunderlying underlyingrocks rocksare areobtained obtainedindirectly indirectlyby bysuch suchgeogeophysical methods as as airborne physical methods airborne magnetics. magnetics. IIn n the the past past much muchhigh-grade high-grade iron iron ore ore was was produced produced from the Precambrian Precambrian rocks of of northern northern Wisconsin, Wisconsin,and andmuch muchlow-grade low-gradeore ore("taconite") ("taconite") awaits development. work indidevelopment. Recent Recent geologic geologic work cates that that the the area areahas hasa ahigh highpotential potentialfor forfinding findingores oresofofother othermetals metalssuch suchasascopper. copper. At the the close close of of the the Precambrian Precambrian Era Eramost mostofofWisconsin Wisconsinhad hadbeen been eroded eroded to to aa rather ratherflat flatplain plainupon uponwhich which stood stood hills of more resistant rocks as those now exposed in the Baraboo bluffs. There were still outpourings of basaltic exposed in still basaltic lava lava in the the north north and and aatrough troughformed formed in inthe thevicinity vicinity of ofLake LakeSuperior Superiorininwhich whichgreat greatthicknesses thicknesses of of sandstone sandstone were were deposited. deposited. The Paleozoic Era began began with with the the Cambrian Cambrian Period, Period, the rocks Paleozoic Era rocks of which which indicate indicate that that Wisconsin Wisconsin was was twice twice subsubmerged beneath the sea. Rivers draining the land carried sediments which were deposited in the sea to form merged the sea. Rivers draining the land carried sediments which were deposited in the sea to formsandsandstone and plants plants living in the sea stone and shale. shale. Animals Animals and living in sea deposited deposited calcium calcium carbonate carbonate and built built reefs reefs to toform formrocks rocks which are magnesium-rich continued into the dolomit-a magnesium-rich limestone. limestone. These same same processes processes continued the Ordovician Ordovician Period Period are now now dolomite—a during which, was submerged submergedthree three more more times. times. Deposits Depositsbuilt built up up in in the sea which, as indicated indicated by the the rocks, rocks, Wisconsin Wisconsin was sea when when the land land was was submerged submerged were partially or or completely completely eroded eroded at at times times when when they theywere weresubsequently subsequently elevated elevated above sea level. level. During During the the close close ofof the the Ordovician Ordovician Period, Period, and and in the above sea the succeeding succeeding Silurian Silurian and and Devonian Devonian Periods, Periods, Wisconsin is believed Wisconsin is believed to have remained remained submerged. submerged. The youngest youngest rocks rocks outcropping in in Wisconsin Wisconsin are of of Devonian Devonian age age and and are areabout about350 350million million years years old. old. Absence Absence of The of If the thedinosaurs dinosaurs younger rocks makes makes interpretations interpretations of post-Devonian post-Devonian history in Wisconsin Wisconsin aa matter of of conjecture. conjecture. If younger roamed Wisconsin, as well well they they might might have some 200 million million years years ago, no trace Wisconsin, as trace of of their theirpresence presenceremains. remains.AvailAvailevidence from from neighboring neighboring areas, areas, where whereyounger youngerrocks rocksare arepresent, present,indicates indicatesthat thattowards towardsthe theclose closeof of the the PaleoPaleoable evidence some 250 million present. DurDurzoic Era, perhaps some million years years ago, ago, aa period period of of gentle uplift began which which has continued to the present. ing ing this this time time the the land land surface surface was was carved carved by rain, wind wind and and running running water. water. The final final scene scene took took place place during million years when glaciers glaciers invaded invaded Wisconsin Wisconsin from north and and The during the last million years when from the north sculptured thevalleys valleysand andleft leftaadeposit depositof ofdebris debris over over all all exexsculptured the the land land surface. surface.They Theysmoothed smoothed the thehill hilltops, tops,filled filledthe cept the southwest southwest quarter of of the theState Statewhere wherewe wemay maynow nowstill stillsee seethe theland landasasititmight mighthave havelooked lookedaamillion millionyears years ago. ago. �fI;Director si;p 5Hanson,j J•!U]%9#IC State and Geologist :' Survey,, History Natural !4[c au 'FiJOG-> d 'ge !tñJiS% Geological .!IHCOIISIfl i]1.y of University Wisconsin )I.Ii1 PtisIt uqen ds n 'H irf 'tjsoap0 pitted SLft LJSDaiflfl unpitted ne 1t)15.tJ Morn ptrnOJ9 4 or,es .YY;_JOW p'q L r ,• tR: OF dç SCALE MILES 40 p -. iHFI.Jj after 1956 Tliwaites, q Hi 1 'i• _r' n 1] DEPOSITS GLACIAL WISCONSIN F L �I SHORT S HORT HISTORY OF OF THE ICE AGE IN I N WISCONSIN WISCONSIN U 1,000,000 years ago The Pleistocene Epoch or o r "Ice "Ice Age" Age" began about 1,000,000 ago which, which, in f o u r separate separate s h o r t time time ago. ago. There were four i n terms of of geologic geologic time, time, i s a very short g l a c i a l advances advances iin n tthe h e Pleistocene Pleistocene each each followed followed by by an an inter—glacial i n t e r - g l a c i a l period period glacial is whent the The ffourth o u r t h gglacial l a c i a l stage s t a g e is i scalled c a l l e dthe t h Wisconsin e Wisconsin Stage Stage when h e iice c e receded. receded. The because wasi nint hthis that it was first studied detail. because itit was i s SState tate th a t it was first s t u d i e d iin n d etail. The gglaciers snow The l a c i e r s were were formed formed by by the t h e continuous continuous accumulation accumulation of of snow. snow. The snow i n t o ice i c e which reached a maximum maximum thickness of of almost almost two two miles. miles. The The turned into sheet spread spread over over Canada and ppart of it it flowed flowed iin general southerly southerly iice c e sheet a r t of n aa general direction d i r e c t i o n toward Wisconsin and neighboring states. states. f r o n t of the t h e advancing advancing iice c e sheet sheet had had many many tongues or o r "lobes" "lobes" whose whose The front direction wereccontrolled by tthe of tthe d i r e c t i o n and and rate r a t eofofmovement movement were o n t r o l l e d by h e topography topography of h e land land surface over by tthe surface over which which they they flowed flowed and by h e rrates a t e s of of ice i c e accumulation in i n the the different d i f f e r e n t areas from which they were fed. fed. sheet transported transported aa great rockddebris "drift". The ice i c e sheet g r e a t amount amount ofofrock e b r i s ccalled a l l e d "drift". was was "Drumlins" p i l e d up up aatt the t h e margins margins of of the t h e ice i c elobes lobestot oform form"end "end moraines". moraines". piled are of ddrift byt the a r e elongated elongated mounds mounds of r i f t which which were were molded molded by h e iice c e passing passing over over them them and hencei nindicate and hence d i c a t e tthe h e ddirection i r e c t i o n of of ice i c e movement. Some "ground Some ofoft this h i s was was deposited deposited under under the t h e ice i c etot form o form "groundmoraine" moraine"and andsome some pattern of end moraines, moraines, iin red, shows tthe was occupied occupied The p a t t e r n of n red, h e pposition o s i t i o n tthat h a t was advanced down down the t h e basin basin of of Lake Lake Michigan, Michigan, by four f o u r major ice i c e lobes. lobes. One lobe advanced Green Bay, Bay, aa third another another down down Green t h i r ddown down Lake Lake Superior and over the t h e northern peninsula The Michigan and yet a fourth of Michigan fourth entered entered the the state s t a t e from from the t h e northwest northwest corner. corner. The of "Kettle Moraine" well-known "Kettle Moraine" was was formed formed between between the t h eLake LakeMichigan Michigan and andGreen Green Bay Bay well—known lobes. As A s tthe h e ice i c e melted melted the t h e drift d r i f was t wasreworked reworked by by the t h e running running water. water. Large amountsofof sand sand and andgravel gravel were weredeposited deposited tto "outwashplains"; plains"; ppits amounts o form form "outwash i t s were were formed iin whereburied buriedblocks blocks of of ice of these are formed n tthe h e outwash outwash where i c e melted melted and and many many of are now now occupied occupied by by lakes. lakes. The action profoundly modified tthe landscape, smoothing o off a c t i o n of of tthe h e ice i c e profoundly h e landscape, f f tthe he places ititchanged changed I n some some places of hills ccrests r e s t s of h i l l s and ffilling i l l i n g the t h e valleys v a l l e y s with with ddrift. r i f t . In the of tthe Wisconsin t h e course of rivers r i v e r s forcing them to t o cut new channels such aass tthat h a t of h e Wisconsin River at a t tthe h e Dells; Dells; elsewhere it it dammed dammed the t h e valleys v a l l e y s to t o create c r e a t e lakes lakes such such as a s those those of tthe of h e Madison Madison area. area. During rrecent e c e n t years there t h e r e have been intensive i n t e n s i v e studies s t u d i e s made made of of the t h e polar polar caps, and methods have been developed for iice c e caps, f o r dating glacial g l a c i a l events events from from the the of tthe wood, bones, bones, eetc. which aare found iin many of of rradioactivity a d i o a c t i v i t y of h e carbon iin n wood, t c . which r e found n many of these these sstudies previously accepted e s u l t s of t u d i e s aare r e causing many previously tthe h e deposits. deposits. The rresults concepts to t o be changed changed or o r challenged. challenged. We thought tthat were rrather extensive gglacial W e once thought h a t tthere h e r e were a t h e r extensive l a c i a l ddeposits e p o s i t s oolder lder than Wisconsin age age in i n the t h e State, S t a t e , but but age age determinations determinations do do not not support support this. this, It was aalso thought that It l s o thought t h a t the t h e ice i c e left l e f t Wisconsin some some 20,000 20,000 years years ago ago but but aa Countywas wasburied buriedunder under an an advancing advancing iice fforest o r e s t aatt Two Creeks in i n Manitowoc Manitowoc County ce i s accumulating accumulating to t o indicate i n d i c a t e that t h a t ice ice 11,000 years ago. tongue tongue only 11,000 ago. Evidence is may have occupied the Area" of of tthe southwestern p part of t h e so—called so-called "Driftless " D r i f t l e s s Area" h e southwestern a r t of the t h e State S t a t e which hitherto h i t h e r t o has has been been held held to t o be be unglaciated. unglaciated. Most sscientists believe Most c i e n t i s t s now b e l i e v e that t h a t the t h e cause of the t h e Pleistocene "Ice "IceAge" Age" was duet to was due o vvariations a r i a t i o n s in i n the t h e solar s o l a renergy energyreaching reaching the t h eearth, e a r t h ,but buthow howthese thesemay may We haveoccurred occurredisissstill have t i l l aa matter matter of of conjecture. conjecture. W e a are r e sstill t i l l in i nthe t h eIce I c eAge Age and and it anybody's guess whether future millenia it is anybody's future m i l l e n i a will w i l l see s e e the t h e melting melting of of cities, or the regrowth coastal caps and the slow drowning of our t h e slow our c o a s t a l c i t i e s , o r t h e regrowth and and oftthe more tthe more h e inexorable inexorable advance advance of h e gglaciers. laciers. the t h e ice ice once once Prepared by tthe Natural History HistorySurvey, Survey, August August Prepared by h e University University of ofWisconsin Wisconsin Geological Geological £& Natural 19641 1964' �WiSCONSIN OF unIVERSITY A A U II Al IA OAR ._<__,1<., Spruce White Fir, Balsam FOREST BOREAL Cedar Tamarack, Spruce, Black SWAMPS CONIFER —— •—fl.l- Maple, <r— Birch Yellow Hemlock, N FOREST MESIC NORTHERN i:_ t' .', F —. Pine Red Pine, White FOREST PINE Grasses Prairie pine, Jock BARRENS PINE — r 4/ 'C<L<.. Joint, Blue Sedges, Cordgrass MEADOWS SEDGE L___J • r— <Willows, Ash Maple, Soft - HARDWOOD LOWLAND Elm - -c - Stigar Basswood, Maple, FOREST MESIC SOUTHERN Oaks Red ond Block White, FOREST OAK SOUTHERN 1 LI±J 7 t Bluestem Oak, White Oak, Bur I SAVANNA OAK -, -1";,;] Composites Bluestem, -< PRAIRIE a LEGEND 6 I r a / a S C C a L Miles at Scale 80 40 0 1965 Wisconsin of University Director L L:s4 Hanson, G.E. Survey History Natural and Geological Wisconsin 1I\L H j ccc WISCONSIN OF VEGETATION EARLY -. I f pi �INTERPRETATION OF OFTHE THEVEGETATION VEGETATIONOF OFWISCONSIN WISCONSIN about the the middle middle of of the the llast This map map iiss based on the original original land land survey survey conducted conducted about a s t cencenSurveyorswere wererequired requiredtotoplace placeaa stake stake eachhalfmile, tury. Surveyors eachhalfmile, identified identified by by notation notation of of nearby nearby trees, and and to to note note briefly briefly the the general general plant plant cover cover of of each each quarter quarter section. These records records have have been used to been to reconstruct reconstruct the the presettlement presettlement distribution distribution patterns patterns of ofplant plantcommunities communities shown shown on on the map. map. The plant communities recognized,however, however,are arebased basedon on systematic systematic studies studies of presentThe communities recognized, presentday vegetation. vegetation. The day The results results of of these these studies studiesare aresummarized summarized in a recent recent book book (J. T. Curtis, Curtis, The The Vegetation of Wisconsin, University of Wisconsin Press, 1959) in which each community, with Vegetation of Wisconsin, University of Wisconsin Press, 1959) in which each community, its history, history, location, location, and and relationship relationship to toother othercommunities communities and tothe tothe environment, environment, iiss considered considered Since some of the factors determining vegetation vary gradually, the vegetation vegetation itself itself in detail. in Since some of the factors determining vegetation vary gradually, the varies gradually and boundaries on the map are somewhat arbitrary. gradually and boundaries on the map are somewhat arbitrary. The vegetation vegetation of of the the state floristic provinces The s t a t e is is divided divided into into northern northern and southern southern floristic provinces by by aa line that runsinans-curve runs in an S-curvenorthwest northwestfrom fromMilwaukee MilwaukeetotoHudson. Hudson.North Northofofthis this line line the vegetation vegetation Southwest of of the the line, abroadleaf forest containing containing conifers—pines, conifers-pines, hemlock, is abroadleaf hemlock, spruces, spruces, and fir. Southwest conifers are are much much lless andare are replaced replacedby byforests forests with with several several species species of conifers e s s important important and of oaks, and by the the prairies—areas dominatedby bygrasses grasses and and tall herbs. by prairies-areas dominated herbs. Fire has has been been important important in in determining determining almost all of of the the plant plant communities communities and and their their lolothe coming of white white man, man, the the prairies (1) (1) and and the the open open woodlands woodlands burned burned almost almost cation. Before Before the coming of every year. year. Thus every Thus most most of of the the southern southern part part of of the the state s t a t ewas was covered covered with with prairie prairie or or oak oak savanna savanna (2), an orchard-like withaa few few large large bur bur or or white white oaks oaks growing in fields fields of (2). orchard-like community community with growing in of grass. grass. Only in in the the more more protected protectedplaces places did did forests forests survive. (3) but but many many were were Only survive. Some Some of of these these were were oak oak(3) sugar elm forests (4). sugar maple-basswood-slippery maple-basswood-slippery elm (4). The The lowlands lowlands were were occupied occupied by by river river bottom bottom Withsettlement, settlement, the the fires fires were (51, and and sedge sedgemeadow meadow (6). ( 6 ) . With were stopped, and the oak oak savannas savannas forest (5), of the prairies grew up dense white white oak-black oak-black oak oak forests forests found found today. today. Most Most of prairies have have been been grew up to to the dense cultivated, andat and a tpresent, present,with withthe theoak oaksavannas, savannas,are areamong amongthe therarest rarestofofour ourplant plantcommuaities. communities. In part of of the the state, aa combination In the northern northern part combination of fire and and poor poor soil resulted resulted in in the the develdevelopment of pine barrens (7) on the sandy soils, and pine forests (8) on somewhat better soils. In (8) on somewhat better soils. opment of pine barrens (7) on the sandy soils, and pine the the absence absence of of fire, fire, the the white white pine pine forests forestsgradually gradually changed changed to to the thenorthern northern equivalent equivalent of of the the sugar forests, aa community sugar maple-basswood maple-basswood forests, community containing sugar sugar maple, maple, yellow yellow birch birch and and hemlock, hemlock, with beech beech added added in in the the eastern eastern counties counties (9). (9). Also Also present present in in the the north north were were large large tracts tracts of of lowlowwith land, with with tamarack tamarack and andblack black spruce spruce bogs bogs in in the the wetter wetter areas, areas, and white cedar swamps land, swamps in drier, but still still very very moist moist habitats habitats (10). (10). In In the extreme extreme north north are local local occurrences occurrences of of the thenorthern northern but conifer by fir and spruce. conifer forest forest (11) (11) dominated dominated by A comparison comparisonofof this this map map with with maps maps ofof climate, climate, soil, and A and glacial glacial deposits deposits shows shows many many The correspondences, indicating relationships between correspondences, indicating many many relationships between vegetation vegetation and the the environment. environment. The original vegetation vegetation was was thus by the the distribution of both original thus determined determined by distribution of both climatic climatic and and soil soil factors, factors, modified modified by fire. fire. 0. G. Cottam, Cottam, 0. 0. L. L. Loucks Loucks Department of Botany Department The University of of Wisconsin Wisconsin � https://digitalcollections.lakeheadu.ca/files/original/ac9dd9c98d82d2009fc6fa2432059ff8.pdf cc4f1f23c1fae5b8a1976c91c2b31a0d PDF Text Text University of Wisconsin—Extension GEOLOGICAL AND NATURAL HISTORY SURVEY Meredith E. Ostroin, State GeoIogSt and Director GUIDEBOOK TO THE PRECAMBRIAN GEOLOGY OF NORTHEASTERN AND NORTHCENTRAL WISCONSIN 18th Ausnuul Institute on Luke Superior Geology Madison, Wisconsin, 1973 �UNIVERSITY UNIVERSITY OF OF WISCONSIN-EXTENSION WISCONSIN-EXTENSION GEOLOGICAL AND AND NATURAL GEOLOGICAL NATURAL HISTORY SURVEY SURVEY E. Ostrom, Ostrom, State State Geologist Geologist && Director Director Meredith E. GUIDEBOOK TO TO THE PRECAMBRIAN PRECAMBRIAN GEOLOGY OF NORTHEASTERN NORTHEASTERN AND AND NORTHCENTRAL WISCONSIN with Special Papers on Chronology of Precambrian Precambrian Rocks Rocks in in Wisconsin Wisconsin W.R. Van Van Schinus Schmus The Wolf River Batholith——a Batholith--a Late Late Precambrian Precambrian Rapakivi Rapakivi Massif in in Northeastern Wisconsin Wisconsin L.G. L.G. Medaris, Medaris, Jr., Jr., J.L. J.L. Anderson, Anderson, and and J.R. J.R. Myles Myles Precambrian Geology of Marathon County G.L. LaBerge LaBerge and and P.E. PE. Myers G.L. Field Trip Committee Committee C.E. C.E. Dutton, Dutton, U.W. U.W. Geological Survey Survey G.L. LaBerge, LaBerge, UW—Oshkosh; mV-Osh~osh; Wis. Wis. Geol. Geol. && Nat. Nat. Hist. Hist. Sur. Sur. L.G. L.G. Medaris, Medaris, Jr., Jr., UW—Madison UW-Madison G. G. Mursky, Mursky, UW-Milwaukee P.E. P.E. Myers, Myers, UW-Eau mV-Eau Claire; Claire; Wis. Wis. Geol. Geol. && Nat. Nat. Hist. Hist. Sur. Sur. W.R. Van Schmus, W.R. Schmus, University University of Kansas L.W. L.W. Weis, Weis, UW Center System-Fox Valley Valley printed in in limited limited quantities quantities for for the the 19th 19th This guidebook was printed Annual Institute Institute on on Lake Lake Superior Superior Geology. Geology. Madison, Wisconsin Madison, 1973 Available from from the the Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, Wisconsin—Extension, 1815 University University of Wisconsin-Extension, University Avenue, Madison, Madison, Wisconsin Wisconsin 53706. 53706. Price: $5.00. �DEDICAT I DEDICATION This guidebook is is dedicated to to Carl E. E. Dutton Dutton in in appreciation appreciation for for his continual encouragement and and advice advice to to us us all all and and in in recognition recognition of of toward an an understanding of the the Wisconsin Precambrian. his contributions toward I �INTRODUCTION I NTRODUCT ION With the exception of early bulletins of of the the Wisconsin Wisconsin Geological Geological and Natural Natural History Survey produced between about about 1900 1900 and and 1930 1930 little little had been published on the Precambrian geology of of Wisconsin Wisconsin until until the the appearance appearance in in 1970 of of "Lithologic, "Lithologic, Geophysical, Geophysical, and Mineral Commodity Maps of of Precambrian Rocks Rocks in in Wisconsin" by by Carl Carl E. E. Dutton Dutton and and Reta Reta E. E. Bradley, which was the product of aa cooperative effort of Bradley, of the the State State Survey and and the the U.S. U.S. Geological Geological Survey. Survey. That publication is is aa compicompilation which drew together in in concise form at at aa scale scale of of 1:500,000 1:500,000 all all that was generally known about Precambrian geology of of Wisconsin Wisconsin and, and, thus, thus, served to focus focus attention on the the mineral potential of of Wisconsints Wisconsin's Precambrian rocks and and to indicate the inadequacy inadequacy of of available available geological geological and information. As aa direct consequence of the the publication publication and geophysical Information. company exploration activity increased increased markedly and and the the interest interest of of university and and survey survey geologists geologists was was revived. revived. As aa part part of of this this revival revival the the Wisconsin Wisconsin Geological Geological && Natural Natural History History Survey has initiated a program to survey and and map the the Precambrian geology geology of the state in cooperation with geologists on the the faculty faculty of of the the UniverUniversity of Wisconsin System System at at its its various various campuses. campuses. At the the present time time L. LaBerge (UW—Oshkosh), Professors Gene L. (UW-Oshkosh), Paul Myers (UW—Eau (UW-Eau Claire), Claire), and and Joe Mengel (UW-Superior) are supported by the Survey on aa part—time part-time Mengel (UW—Superior) basis during summer months to map Precambrian geology in in Wisconsin. Wisconsin. Other university geologists contributing to the program have obtained support from from various grant programs including the University—Industry University-Industry Program, the Wisconsin Alumni Research Foundation and Research Program, and from Industry. industry. The Survey will soon soon publish aa bouguer bouguer anomaly anomaly gravity gravity map map of of the the state prepared by Professors C. C. Patrick Ervin (formerly state (formerly UW—Madison, UW-Madison, now Northern Illinois (UW—Madison) at at a scale Illinois University) University) and and Sigmund Sigmund Hanuner Hammer (UW-Madison) of 1:500,000, 1:500,000, utilizing over of over 16,000 16,000 stations. stations. In In addition, addition, the Survey has begun aa program under the the leadership leadership of of Prof. Prof. John John Karl (Department (Department of Physics, Physics, UW—Oshkosh) UW-Oshkosh) to to produce an an aeromagnetic aeromagnetic map of of the the northern northern two—thirds of the the state at north—south flight two-thirds at a a north-south flight line spacing of one—half one-half mile. This study was initiated initiated by aa grant from from the the Upper Great Lakes Lakes Regional Regional Commission and has been strongly supported by aa substantial substantial grant from NL Industries Industries and and by aerial aerial photograph prints prints provided provided by by INCO. INCa. This field field guide and accompanying accompanying maps, maps, printed for the the 19th 19th Annual Institute on on Lake Lake Superior Superior Geology, Geology, will will be included in what what is Institute is hoped be aa complete series series of of Precambrian Precambrian field field guides guides and and will eventually be maps for Wisconsin Wiscsin atata ascale maps for scaleofof1:250,000, 1:250,000, published published as as Geological Geological and and Natural History History Survey Survey Information Information Circulars. Circulars. When used in in combination with the the bouguer gravity anomaly anomaly map and and the the aeromagnetic aeromagnetic map map they they will will provide aa basis for identification identification of of areas areas of of above above average average mineral mineral popotential in Wisconsin which can then be made the subject for detailed tential in Wisconsin study. M.E. Ostroin Ostrom & Director State Geologist & �SPECIAL PAPERS Chronology of Pncainbrimn Rocks by W.R. Van Schaus Wolf River Satboiith——a Lst• Precabrian Rspakivi Kant! La Wcrtheasten Wisconsin The by b.C. Medaris, Jr., J.L. Anderson, and J.R, kyle. Ptecnibrtan Geology of Marathon County by G.L. Laflerge and P.E. Myers �Superior Lake Superior u o N ....o --' "" Q Waupaca River Falls Map Symbol Age Im.y.) Chronologic Unit PALEOZOIC Keweenawan COVER 1115 .:20 Wolf River Batholith gr • •rhy• • 1500 .:50 rhy • >1500 Quartzite <1675 1675 .: 50 Central Wisconsin Complex o ~ ~ > 1500 TIgerton Anorthosite < NE Wisconsin Complex ?? o 1875 .:50 Metavolcanics and metasedi ments 1900 .: 50 Archean Complex >2500 Age uncertain or unknown I. Figure 1. Madison Miles 0 0 Kilometers Milwaukee 40 50 • = Primary age determinations Primary age WRVS 2/73 Generalized geochronologic geochronologic map mapofatPrecambrian Precambrianrocks rocksin in Wisconsin Wisconsin and Michigan. Generalized and Upper Upper Michigan. I �11 Chronology of Precambrian Rocks Rocks in in Wisconsin by W.R. Van Schmus* W.R. Geochronologic data for Precambrian rocks rocks in in Wisconsin have have existed existed for for more than aa decade, decade, but until recently the the data were limited limited to to analyses of of separate separate minerals minerals and distributed, so that analyses and were widely distributed, that exact interpretation of primary formational ages ages and and delineation of of chronologic chronologie provinces was not possible. possible. These early data were summarized summarized by by Dutton Dutton and (1970) and will not be be reviewed reviewed in in detail detail here. here. and Bradley Bradley (1970) In terms of of obtaining primary ages In terms ages of Precambrian rocks, rocks, as opposed to metamorphic ages, ages, the geochronologic methods most likely likely to to yield yield reliable results are the Rb-Sr whole-rock isochron isochron method and and U-Pb U-Pb analyses on cogenetic suites suites of of zircons. zircons. Application of these these procedures procedures to Precambrian rocks rocks in Wisconsin has recently been done by P.O. p.O. Banks (Banks (Banks and and Cain, Cain, 1969; 1969; Banks and and Rebello, Rebello, 1969; 1969; and and unpublished unpublished data), data), by Z.E. Z.E. Peterman (unpublished (unpublished data), data), Dott Dott and and Daiziel Dalziel (1972), (1972), and and by by the author Schmus, 1972, the author (Van Schmus, 1972, 1973; 1973; Thurman and and Van Schmus, Schmus, 1973; 1973; and and unpublished data). data). A A summarization summarization of of these these data data is is presented presented in in Table Table 1. 1. unpublished Based on the the available available geologic geologic and and geochronologic geochronologic data, data, aa genergeneralized chronologie alized chronologic map map has has been prepared for Precambrian rocks of Wisconsin and and Upper Upper Michigan Michigan (Figure (Figure 1). 1). A the various various A few comments on the chronologic brief discussion discussion of of their their significance significance is: is chronologie units units and and a a brief presented below, below, but space does not jermit permit detailed detailed description description or or disdiscussion. The "Pb The "Precambrian X", etc. terminology terminology used below below refers refers to to the the Xt, etc. current U.S. U.S. Geological Survey subdivisions of of Precambrian time: time: Precambrian Z, Z, base base of of Cambrian Cambrian to to 800 800 m.y. m.y. ago; ago; Precambrian Precambrian Y, Y, 800 800 to to 1600 m.y. m.y. ago; X, 1600 to ago; Precambrian X, to 2500 2500 m.y. m.y. ago; ago; and and Precambrian Precambrian W, W, oldçr than old~r than 2500 2500 m.y. m.y. Archean Complex (Precambrian (Precambrian W) The oldest rocks rocks in in the the area area are are exposed exposed in in the the northern northern part. part. In In Upper Michigan these have been shown to be 2.5 to to 2.7 2.7 b.y. b.y. old or or older older (Aldrich, 1965; Woolsey, Woolsey, 1971; 1971; Banks Banks and and Van Van Schmus, Schmus, 1971, 1971, (Aldrich, and and others, others, 1965; 1972), 1972), but no dates have been reported reported as as yet yet from from presumed presumed Archean Archean rocks rocks in northwestern Wisconsin. in These latter units unconformably underlie the metasediments metasediments and the and metavolcanics of the Gogebic Range (Aldrich, (Aldrich, 1929) 1929) and there seems little doubt that and that they they are are in in fact fact Archean. Archean. However, the southward extent of these these rocks is is not well known, known, as as outcrops outcrops are are widely scattered throughout the the area area and and lithologic lithologic correlation correlation of of PrePrecambrian crystalline rocks rocks is is risky risky at at best. best. ** Department of University of of Kansas. Kansas. of Geology, Geology, University �2 T&bl.1. 1. 'fable Sury of Primary Gscohronologio S~ of PJ-1aaI7 GeoohronologioData Datafor torPreoeabrisn PNoaabrianRocks Boob in inWisconsin. Vlnouin. Northea.tern Wisconsin Visoonsin COmplezl Compl.xz 1. Northeastern P. (rhyoiit.) Quinnl.. o VIa. (rhyolite) Quinnissc 1906 ~ 25 1805 25 11.7. ..y. Ho skinLake Iske granite granite Hoskin 1880 15 (z) (Z) Banks Banks and Cain, 1969. 1969. Dunbar .iss Dunbar gneiss 1880 2~ 15 1880 15 (Z) Bank8 and Cain, 1969. 1&69. (z) Banks 1860~ 21~l 1880 (2) Banks and Cain, Cain, 1969. (Z) BanD and 1969. 1930 2 o (Z) Aldrioh and and others, 1965. 1965. (z) Aldrich 1810 : 50 (R) Van Sebmus, Unpub.° N.vinghamgranodiorite granodiorit. Newingham "*mb.rg pink "Jllberg p1nk graniti' granit'" (Ath.lstan. quartz (Athel8tane quartsmonzonit.) IIOMOnitlO) }3 ainstte quartz JIuoinett. quartz diorits diorite Atbelatane quartz quarts monsoniti lIOn&onit. Athelotano Hoskin Lake lake granite Hoskin granite } Overall oo.slt. oompo.it..estimate: Ove1"&ll .t1lrate I :t (Z) Banks and RebellO, Rbello, 1909. (z) Bank8 and 1969. 1875 50 1875 ±~ 50 VisooMlnComplex: COmpleZI Central Wisconsin 2. Central Baraboo rWolite Baraboo rI'o1ite 1840 lMO :2 40 m.y. a.,y. (R) Dott and DaIziel, Dalziel, 1972. 1972. So, Wisconsin rbyolit.s So. Wisoonsln rbJo1ites 1665 4D 1666 :2 40 (a) (R) Wausau-Mbnioo voloanios Wausan—bnioe volcanic. 1640 4D 1840 2~ 40 (R) Petel'llllUl,Unpub.° Unpub.* (a) P.t.rman, Co. granites granites Waushapa Co. Waushera ~ 70 70 1846 1646 ± andVan VanSohlllU., Sobmus,19'7a.* 1975. 'l'hurman and (R) Thurman Vausau area Waumau areagranites granite. 1600 :t 85 85 1600 ± CR) (R) Jackson JacksonCo. Co.granit.s granite. 1690 CR) Overall composite OOIlPOsite estimate: e8t1Jla'te I 3. llna.* Thurman and Van Van SobIua, Sobaus, 1975 .'' '!'hU!'lllUl and P.t.rman, Petel'lllU'1,Unpub.* Unpub.* and P-'-run, P.teruan, 1972. 1972. (a) nKismia ..io and 1675 ± 16715 : 50 Volt Wolf River River Batholiths Batholith: Wolf Volt River-Bad River-a.d River quartz quartz monsonites IIODSOnit.s 1450 :± 30 50 lI.y. a.y. 1450 (R) Van Sobmus, Unpub. Belongia Belongia gNnite granite 1~ 1500 :t2 20 (Z) Banks, Banks, Unpzb.' Unpub.** (z) 1480 2 (a) Onpub.** CR)Van VanSohlllU., Sciu5, Unpub.' Wolf River batholith Wolt River batholithoombinad oombined Wolf River River quartz Volt quarts monzonits lIOn&onite a.d River quazo1;s monzonits lIOn&onite Red River quartz Hager complex oomplez B.longla Belongia granite viborgit. granite Vaupaca wiborgite granite Waupeoa Big Palls Big Yells med-gr. m.d-gr. granite Stevens gNnite Stevens Point Point grq gray granite Wausau oomplez Wausaueyenite syenit. complex St.tin iyenit. complex St.tin ~nite oollPlez Hogvty Hogarty hornblende hornblende granite granite Overall Overall oolllpOsit. compositee8tiDate .stimatsI 1500 ± 50 (Z) denote. zircon Zircon U-Pb U-Pb oonoordia age; (R) (R) denotes denote. tho1e-rock whole-rcok (z) denotes oonsordiaintercept intsrc.pt age; Rb-Sr Rb-Sr isochron isoobron a.gs. ~. in preparation. Sohmus, ThtmDan, Thurman, and and Peterman, ** Van Sohmus, 'etel'lDan, 1n preparation. and Banks, *" Van Sohmu., ** Medari., and 1laDU, in in preparation. preparatlon. ScLnu5, Madaris, �3 No Archean rocks rocks are are conclusively present present in in northeastern northeastern Wisconsin. Wisconsin. Although the the Quinnesec metavolcanics metavolcanics have have often often been been referred referred to to as as pospossibly being Archean, Archean, it it now seems seems probable probable that that they they are are much much younger, younger, as mentioned below. below. The lack lack of of Archean rocks rocks in in this this area area is is as will will be mentioned major geologic geologic problem, problem, for for they are exposed just to aa major to the the north in in Michigan (James, (James, and and others, others, 1961). 1961). Recent maps of of the the area area (Dutton, (Dutton, 1971, Dutton and and Bradley, Bradley, 1970) show show the the presence presence of of aa major major east—west east-west 1971, trending Formation trending fault fault system system separating strongly deformed Quinnesec Formation rocks on the south from much less less deformed Badwater Greenstone Greenstone on on the the rocks north; and this fault system may therefore north; therefore coincide coincide with with or or be be part part of of an an old old major tectonic boundary. remaining problems problems are are to to determine determine how how far far Some of the other major remaining south Archean Archean rocks rocks can be be recognized, recognized, to determine their south their ages, ages, and and to to determine the the nature of their their disappearance (burial, (burial, faulting, faulting, orogenic orogenic destruction, etc.). d~~truction, etc.). "Animikie" Metasediments and Metavolcanics (Precambrian (Precambrian X) Metagediments and These rocks represent the the major units of of sedimentary sedimentary and and volcanic volcanic origin in the northern part of of the the area area and and include include the the economically economically vital sedimentary sedimentary iron iron formations. formations. Geochronologic data (Aldrich, (Aldrich, and and others, others, 1965; 1965; Banks and and Van Schmus, Schmus, 1971, 1971, 1972) 1972) indicate indicate that that these these rocks rocks in the the Iron Iron Mountain Mountain area area are are about about 1900 1900 m.y. m.y. old. old. Banks and and Rebello (1969) obtained a 1900 million year age age for zircons from a a Quinnesec (1969) obtained a Formation rhyolite in Wisconsin, and in Wisconsin, and the the author author regards regards these these rocks rocks as as approximately, if if not not exactly, exactly, equivalent equivalent to the units approximately, units in Michigan (for (for example, the example, the Badwater Badwater Greenstone). Greenstone). No direct data exist exist for for similar similar rocks rocks from the northwestern part of the the state, state, namely the the Gogebic Range, Range, but but with the lack of any evidence to to the the contrary, contrary, the the commonly commonly used used correcorrelation with rocks rocks to to the the east east is is accepted accepted here. here. Clearly, Clearly, however, however, direct direct analytical is required. required. analytical confirmation is As with the the Archean rocks, rocks, the the maximum maximum southern southern extent extent of of these these rocks is is unknown. unknown. Northeastern Wisconsin Complex (Precambrian (Precambrian X) are exposed several gneissic gneissic In the northeastern corner of the state are and plutonic units units which are and plutonic are younger than the the Quinnesec Formation, Formation, and and in in places intrude it it (Cain, (Cain, 1964). 1964). U—Pb U-Pb ages on zircons zircons and and Rb-Sr wholerock isochrons (Table (Table 1) 1) show show that that these these rocks rocks are are about about 1875 1875 m.y. m.y. old. old. They can be traced traced southward southward for for more than than 50 50 Km. Km. south south of of the the MichiganMichiganWisconain border, Wisconsin border, but their their maximum southern southern limit limit is is not not known. known. Although these rocks rocks are important in Wisconsin, only small plutons these are important in northeastern Wisconsin, of this age exist in in Michigan (Peavy (Peavy Complex and and scattered scattered dikes dikes and and area; Aldrich, and others, others, 1965; 1965; Banks Banks and and pegmatites in the Felch Trough area; Aldrich, and Again, it Van Schmus, Schmus, 1971, 1971, 1972). 1972). Again, it appears appears that that the the E—W E-W fault fault system system be part part of of aa major major boundary. boundary. may be The westward extent of these these 1875 m.y. m.y. old rocks rocks is is also also not not known, known, but it it is is quite possible possible that that many many of of the the rocks rocks in in the the northern northern part part of of the state (north the (north and and west westof of Rhinelander) Rhinelander)are are similar similar in in age. These and and the older older rocks rocks are truncated on the south by the the the volcanic—plutonic volcanic-plutonic rocks rocks of the Central Wisconsin Wisconsin Complex, but exact the Central Complex, butthethe exactnature natureofofthe the transition transition is also unknown (intrusive, is (intrusive, fault, fault, suture suture zone?). zone?). �4 4 Central Wisconsin Complex (Precambrian (Precambrian Y) Rocks which yield Rb—Sr Rb-Sr whole—rock whole-rock ages ages of of 1650 1650 to to 1700 1700 m.y. m.y. appear appear to make up the the bulk of the the Precambrian basement basement of of Wisconsin, extending extending from Rhinelander in in the the north to to at at least least as as far far south south as as Baraboo Baraboo and and for for at least least 150 Km. Km. in at in an an east—west east-west direction direction (Figure (Figure 1). 1). These rocks rocks are are mainly volcanic, volcanic, volcaniclastic, volcaniclastic, and and associated associated granitic granitic intrusives; intrusives; the the exposures of these rocks in the the Wausau area area are are described in in aa later later section section of this guidebook. guidebook. Other areas areas of these these rocks rocks are are the the Monico area, area, the the granites granites of Waushara County and and the rhyolites to to the the south, south, the the rhyolites rhyolites underlying the quartzite at Baraboo, Baraboo, and and some of of the the rocks rocks in in the the Black Black River Falls area area (Table (Table 1). 1). Although several types types of of rock rock are are represented, represented, outcrop control control is outcrop is presently insufficient for purposes of of major correcorrelations. The full full extent of of these these rocks rocks is is unknown, unknown, particularly particularly to to the the south and west, and represents a major problem in south and west, in Midcontinent Precambrian geology. The geochronologic control on on this this complex complex to to date date is is only only by by Rb—Sr Rb-Sr whole-rock isochrons, isochrons, and and it it is is possible that that the the 1675 1675 m.y. m.y. age age given given here is a time of widespread alteration alteration of of slightly slightly older older rocks. rocks. U-Pb U—Pb zircon ages will for many of these units in the the near future future zircon ages will be be measured measured for in order order to to get get a in a better handle on the true age of these rocks and and to to look for any resolvable age age differences within the the complex. complex. Quartzites (Precambrian (Precambrian Y) Y) Dott and Dalziel (1972) (1972) have recently recently extensively extensively summarized summarized the the Precambrian quartzites in in Wisconsin. Wisconsin. The age of the quartzites is is bounded by by the the underlying underlying 1675 1675 m.y. m.y. old old rhyelite rhy~lite at at Baraboo Baraboo and and 1450 1450 to 1500 m.y. m.y. old intrusive rocks at at Waterloo (pegmatite) (pegmatite) and and at at Wausau Wausau (syenite intruding Rib Mountain Quartzite). (syenite Quartzite). (Precambrian Y) Y) Wolf River Batholith (Precambrian The youngest youngest plutonic plutonic event event in in the the state state was was the the formation formation of of aa large large It complex referred to in this guidebook as as the the Wolf River batholith. batholith. includes includes a a large variety of felsic intrusive intrusive rocks rocks which occur occur from from Mountain to to Wausau to to Stevens Stevens Point Point to to Waupaca Waupaca and and are are all all about about 1500 1500 m.y. old old (Table (Table 1; 1; Figure 1). 1). This complex is is described in in detail in in m.y. later sections of this guidebook and later and will not be elaborated on on here. here. Published mineral mineral ages ages from from several several localities localities (Bass, (Bass, 1959) 1959) indicate that this event event was was the last major thermal event in that this in Wisconsin except except for the Keweenawan activity for activity to to the the north. north. This complex is is relatively relatively well well defined defined as as to to its its areal areal extent, extent, and and it on all all sides sides by by older older units. units. However, However, the the exact exaot shape shape it is is surrounded on still needs to to be better defined, defined, and and more more U—Pb U-Pb ages ages on on zircons zircons will will have to to be determined on on individual individual units units to to fully fully tie tie down down their their absolute absolute age(s). age ( s). �5 Keweenawan Rocks Rocks (Precambrian (Precambrian Y) y) Keweenawan volcanics, volcanics, sediments, sediments, and and intrusive intrusive rocks rocks occur occur in in the but will will not not be discussed here. the northern part part of of the the area, area, but here. The age age of 1115 1115 m.y. m.y. for of for these rocks (Figure (Figure 1) 1) is is primarily based on on the the U-Pb (1963, 1972). 1972). Chaudhuri (1972) (1972) U—Pb zircon data of Silver and Green (1963, and Chaudhuri and Faure (1967, and Chaudhuri (1967, 1968) 1968) have also also reported reported Rb—Sr Rb-Sr ages ages on on similar rocks in Michigan. in Michigan. Miscellaneous The major rocks rocks included included in in this this category category are are the the granites, granites, gneisses, schists, and migmatites in central Wisconsin, gneisses, schists, Wisconsin, extending extending westward from Waupaca to Stevens Point—Wisconsin from Waupaca to Stevens Point-Wisconsin Rapids, Rapids, and and west. west. These rocks have apparently apparently been been intruded intruded by by the the 1675 1675 m.y. m.y. old old complex, and Bass Bass (1959) complex, (1959) has obtained some mineral ages ages as as old old as as Thus, it would appear 1900 m.y. these rocks. rocks. Thus, appear that that these these rocks rocks m.y. from these exact are are at at least 1900 m.y. m.y. old old and and may may even even be be Archean. Archean. Clearly, Clearly, exact determination of of the the primary ages ages of of these these rocks rocks is is important important since since it will will help help define define the minimum southern limit of sialic rocks it rocks younger than 1900 m.y. m.y. in in North North America. America. Regional Significance Significance Several major discrete igneous, Several igneous, metamorphic or sedimentary periods or events can now be recognized in in Wisconsin and and Upper Upper Michigan. Michigan. The 2500 m.y. m.y. and older rocks rocks represent the southern edge of the 2500 and older the Superior m.y. old rocks Province of of the the Canadian Canadian Shield. Shield. The 1850 to 1900 m.y. represent aa major major period period of of sedimentation, represent sedimentation, volcanism, volcanism, and and orogeny and and is considered considered by by the represent the so—called is the author to represent so-called "Penokean Orogeny" in the area Orogeny" area (Van (Van Schmus, Schmus, 1972). 1972). The 1650 to to 1700 1700 m.y. m.y. old rocks can be correlated roughly with rocks rocks of of similar similar age age in in the the Rockies and the Southwest, Rockies Southwest, although although exact correlations will need need to to await further data. In case, it await data. In any any case, it appears appears that rocks with ages ages of 1650 to 1750 m.y. m.y. comprise a a major structural structural belt from from Arizona Arizona to to Wisconsin. The 1500 m.y. m.y. old complex correlates well in in age, age, litholithologic character, to 1500 m.y. m.y. old old logic character, and tectonic setting with 1450 to plutons throughout the Southwest and plutons and volcanic and and plutonic plutonic rocks rocks in in Missouri. These rocks probably are are part of another another structural structural province province of and south of and partially overlapping the 1650 to to 1750 m.y. m.y. old old rocks rocks (Bickford and Van Schmus, Schmus, 1973). 1973). In summary, summary, it it now now appears appears that that the the various various chronologic chronologic units units In recognized in Wisconsin can be related to other rocks throughout recognized throughout North America, America, and and these these correlations may ultimately ultimately provide provide the the framework upon upon which we we can determine the detailed evolution of the framework the continent during during Precambrian Precambrian times. times. �6 Acknowledgements This work has has been largely supported by National Science Science Foundation Foundation The author gratefully acknowledges the Grants GP—1362 GP-1362 and and GA—15951. GA-15951. The cooperation of all all his his colleagues who are are mapping and and carrying carrying out out petro— petrologic studies in the area and logic studies and whose work provides the the base base necessary necessary for for sample collection and and data data interpretation. interpretation. I �7 References Aldrich, Aldrich, H.R., H.R., 1929, 1929, Geology Geology of of the the Gogebic Gogebic iron iron range range of of Wisconsin: Wisconsin: Wisconsin Geol. Geol. and and Nat. Nat. History Survey Survey Bull. Bull. 71, 71, 279 279 p. p. Aldrich, Aldrich, L.T., L.T., Davis, Davis, G.L., G.L., and and James, James, H.L., H.L., 1965, 1965, Ages Ages of of minerals minerals from metamorphic metamorphic and from and igneous igneous rocks near Iron Iron Mountain, Mountain, Michigan: Michigan: Jour. Jour. Petrology, v. v. 6, 6, p. p. 445—472. 445-472. Banks, P.O., P.O., and Cain, J.A., J.A., 1969, 1969, Zircon Zircon ages ages of of Precambrian Precambrian Banks, and Cain, Jour. Geology, granitic rocks, rocks, northeastern northeastern Wisconsin: Wisconsin: Jour. Geology, v. v. 77, 77, p. 208-220. p. 208—220. Banks, P.O., Banks, P.O., and and Rebello, Rebello, D.P., D.P., 1969, 1969, Zircon Zircon ages ages of of aa Precambrian Precambrian Geol. Soc. rhyolite, Soc. Amer. Bull., Bull., rhyolite, northeastern Wisconsin: Geol. v. 80, p. 907—910. v. 80, p. 907-910. Banks, Banks, P.O., P.O., and and Van Van Schmus, Schmus, W.R., W.R., 1971, 1971, Chronology Chronology of of Precambrian Precambrian rocks of Iron and and Dickinson Dickinson Counties, Counties, Michigan Michigan (abs.): (abs.): 17th rocks of Ann. Inst. on Lake Superior Geol., Duluth, Minn., May, p. Ann. Inst. on Lake Superior Geol., Duluth, Minn., May, p. 9-10. 9-10. Banks, P.O., Banks, P.O., and and Van Schmus, Schmus, W.R., W.R., 1972, 1972, Chronology of of Precambrian Precambrian rocks of of Iron and rocks and Dickinson Dickinson Counties, Counties, Michigan. Michigan. Part II II (abs.): (abs.): Ann. Inst. 18th Ann. Inst. on Lake Superior Geology, Geology, Houghton, Houghton, Mich., Mich., May. May. Bass, M.N., M.N., 1959, Bass, 1959, Mineral age age measurements—Wisconsin: measurements-Wisconsin: Inst. of of Washington Year Book Inst. Book 58, 5~, p. p. 246—247. 246-247. Carnegie Bickford, M.E., M.E., and Bickford, and Van Schmus, Schmus, W.R., W.R., 1973, 1973, Possible Middle and and Late Precambrian igneous arcs arcs in in the the Mid—continent Mid-continent region region of of North America America (abs.): (abs.): Program, Program, North-Central North-Central GSA GSA Meeting, Meeting, Columbia, Mo., Columbia, Mo., April. Cain, Cain, J.A., J.A., 1964, 1964, Precambrian Precambrian geology geology of of the the Pembine Pembine area, area, northeastern Wisconsin: Acad. Sd. northeastern Wisconsin: Mich. Mich. Acad. Sci. Arts, Arts, and and Letters, Letters, Papers, v. Papers, v. 49, 49, p. p. 81—103. 81-103. Chaudhuri, Chaudhuri, S., S., 1972, 1972, Radiometric Radiometric ages ages of of Keweenawan Keweenawan intrusions intrusions and extrusions in in Michigan Michigan and and adjacent adjacent areas areas (abs.): (abs.): Geol. Soc. Amer. Amer. Abstracts with Programs, Soc. Programs, v. v. 4, 4, p. p. 470. 470. Chaudhuri, S., Chaudhuri, S., and and Faure, Faure, G., G., 1967, 1967, Geochronology Geochronology of of the the Keweenawan rocks, rocks, White Pine, Pine, Michigan: Michigan: Econ. Geology, Geology, 62, p. v. 62, p. 1011—1033. 1011-1033. Chaudhuri, S., Chaudhuri, S., and and Faure, Faure, G., G., 1968, 1968, Rubidium—strontium Rubidium-strontium age age of of the Mt. Bohemia intrusion, the Mt. intrusion, Michigan: Michigan: Jour. v. 76, 76, Jour. Geology, Geology, v. p. p. 488—490. 488-490. Dott, R.H., Dott, R.H., Jr., Jr., and and Dalziel, Dalziel, I.W.D., I.W.D., 1972, 1972, Age and and correlation correlation of the the Precambrian Precambrian Baraboo Baraboo Quartzite Quartzite of of Wisconsin: Wisconsin: Jour. Geology, v. Geology, v. 80, 80, p. p. 552—568. 552-568. �8 Dutton, C.E., C.E., 1971, 1971, Geology Geology of of the the Florence Florence area, area, Wisconsin Wisconsin and and Dutton, Michigan: U.S. U.S. Geol. Geol. Survey Survey Prof. Prof. Paper Paper 633, 633, 54 54 p. p. Dutton, Bradley, R.E., Dutton, C.E., C.E., and Bradley, R.E., 1970, 1970, Lithologic, Lithologic, geophysical, geophysical, and and mineral commodity maps of of Precambrian Precambrian rocks rocks in in Wisconsin: Wisconsin: U.S. Geol. Survey Map set Geol. set 1—631, 1-631, with with accompanying accompanying pamphlet pamphlet (15 (15 p.). p.). James, H.L., C.L., and and Pettijohn, Pettijohn, F.J., James, H.L., Clark, L.D., L.D., Lanley, Lamey, C.L., F.J., 1961, 1961, U.S. Geol. Geology of of central central Dickinson Dickinson County, County, Michigan: Michigan: U.S. Survey Prof. Prof. Paper Paper 310, 310, 176 176 p. p. Kiemic, H., H., and Klemic, and Peterman, Peterman, Z.E., Z.E., 1972, 1972, in in Geological Survey Survey Research Research 1972. Chapter A: U.S. Geol. Geol. Survey Prof. Paper 1972. Chapter A: U.S. Paper 800—A, 800-A, p. p. 3. 3. Silver, L.T., L.T., and Silver, and Green, Green, J.C., J.C., 1963, 1963, Zircon Zircon ages ages for for middle Keweenawan Keweenawan rocks of the Am. Geophys. Geophys. Union the Lake Lake Superior Superior region region (abs.): (abs.): Am. Union Trans., Trans., v. v. 44, 44, p. p. 107. 107. Silver, L.T., L.T., and Green, Green, J.C., Silver, J.C., 1972, 1972, Time constants for for Keweenawan igneous activity activity (abs.): (abs.): Geol. Geol. Soc. Amer. Abstracts Abstracts with with Programs, Programs, v. 4, v. 4, p. p. 665. 665. Thurman, E.M., Thurman, E.M., and and Van Schmus, Schmus, W.R., W.R., 1973, 1973, Rb-Sr Rb-Sr age age of of Precambrian Precambrian volcanic and and plutonic inliers inliers in in southeastern southeastern Wisconsin Wisconsin (abs.): (abs.): Program, Program, North—Central North-Central GSA Meeting, Meeting, Columbia, Columbia, Mo., Mo., April. Van Schmus, Schmus, W.R., W.R., 1972, 1972, Geochronology of of Precambrian Precambrian rocks rocks in in the the Penokean Fold Belt subprovince subprovince of of the the Canadian ~anadian Shield Shield (abs.): (abs.): Program, Program, 18th Ann. Ann. Inst. 1nst. on on Lake Lake Superior Superior Geology, Geology, Houghton, Houghton, Mich., May. May. Van Schmus, W.R., 1973, Schmus, W.R., 1973, Chronology of of Precambrian Precambrian igneous igneous and and metamorphic metamorphic in eastern Wisconsin and and Upper Upper Michigan (abs.): (abs.): Program, events in 1973 Ann. Ann. Meeting Amer. Amer. Geophys. Geophys. Union, Washington, D.C., April. 1973 Union, Washington, D.C., April. Woolsey, Woolsey, L.L., L.L., 1971, 1971, A A Rb—Sr Rb-Sr geochronologic geochronologic study study of of the the Republic Republic metamorphic node, node, Republic, Republic, Michigan: Michigan: Unpub. Unpub. M.S. M.S. Thesis, Univ. Univ. of Kansas, Kansas, Lawrence. Lawrence. �9 t33:ir JTh f4 i:tc 2LTY y 2j; 2GIC1 1f1:i--= ii-i 4jLj yEa WOLF RIVER BATHOLITH--A LATE PRECMvIBRIAN RAPAKIVI MASSIF IN NORTHEASTERN WISCONS IN -. \2 TIlE by --:, a:: 2L J.L. Anderson*, Jr.*, 2' rf- Medaris, L.G. Myles** and J.R. C- iEE.CJL.JZINTRODUCTION LL-- aLa-aU .-: co tf •- 1L!• Classic rapakivi texture, in which grains of ovoidal alkali feldspar are mantled by plagioclase, has been described from several localities of Precambrian granite in northeastern Wisconsin (Gates, 1953; Elders, 1968), but until the present time, the regional distribution and petrologic significance of these rocks have not been Our investigation, in conjunction with chronologic fully appreciated. studies by W.R. Van Schmus (this guidebook), has established that an extensive rapakivi massif, the Wolf River batholith, underlies an area of at least 3600 square miles and represents a major feature of the This anorogenic, Precambrian terrain in northeastern Wisconsin (Fig. 1). epizonal batholith, 1450 to 1500 million years in age, consists predominantly of reddish, hypersolvus quartz monzonite and granite. In addition to the widespread occurrence of rapakivi texture, the Wolf River batholith has textural, mineralogical, chemical, and structural features that are similar in every respect to those of the classic rapakivi massifs in Finland. L t •-i&;t Li' k:y.a 4121 2 tt flCTh rjp 2!71fl ©1i -rt ras;-- tia #e :2 -it ut a?-. faa, rfl t 2UU r, :ytLr, : C:KCLiliCT.CCCiI i-Li'CfCt.CC. i-; L2tL :1r:yCiia 1j :y;,itL;y:j. r;1iC1i1C t!LtcL -LiC-r--CLi'J.c. ca aqiy-: La€'L -t iiE '5iTh-yrC aU '-U EiC LiiTT eJ' :caCyL& a1€TTICi'-2 y'iñk;I L1ra. lyai;Lt. 2ii,<: 'LirJL Ct C;iag:f, :':C'iTCtC LtC.. ::,J'.tCi'irt:C2.CCIIi, EyLa? 'i:r. flI •'CY-fl:C, 1\ t!f2T7 2T'jir :;MiC:i. C2C ta- I CCC ix rc'L;-c 2€ 1O29Lfl bxü iTnat 'Li]. ntUi C—tt2 nct- I •b - f;aLi CLE -u. -. . - UU- -z-i j•aditiCtL-• t€ CICCitC CtCiitti:LCC! LCI k.CiLC ITCaC tfi- lit 1 fr L5LitiCC.iL., 'iir:ic:a. :11Z"'2t11";f TC ;.;CT : ::rol,: :iZi1 .;yji g:aiUL'ii i:,J ii4cJsiucLi 45{j ?:U-UUL. cJ T7,r,::At :.a'::i:d •U t:: C •: t]TLC'2 : T-Lj .-Ci irCaLi? :,y., ----2 ICoILt'i C€C tttat 1'---, --, C'axiLal. aa. - L.,' LITHLOGY rtCr ±..1i.:1L'::::s€ ih- -— - - 't]'. CCC' General Characteristics liLVtJC 1ACC Cxii •iiy 'k:.C' ECliTcJ. lCJhra; ny;]i Lta'y,Li 7ç1;'T' ;-CCLi A variety of rock types have been recognized in the Wolf River batholith, including granite, quartz monzonite, monzonite, trachyandesite, syenite, and rhyolite. Quartz monzonite and granite are by far the most abundant rock types in the batholith, adcounting for 94% The predominance of alkali of the exposed area (Table 1, Fig. 1). feldspar over plagioclase in the batholith is illustrated by a plot (Fig. 2) of modal quartz, alkali feldspar, and plagioclase for representative specimens, obtained by point counts of both thin sections and stained polished surfaces of hand specimens. 2 1li-li ii-c t-a niii1 iL U a:c--.xli Li €lufrCI CE ix -uCla titi )Ei 1.. r LaU-uUSL lila t:IC.Jliuii U pta U. €L-€L 'yiyfl -. cr.. cE 2B12 1s,i'fT I tCli, - C-CT xAs?IT'r2' 'Liii i1.ii iLiT-ii ' - ] a1kaL- tzau€E Lii- ',j-c 'It,-: ar tL.2iCiiCT ruT-fT x lixvxuia, 'JL'i.- :uc'J-€l :1- iL:s uf lifC-iULihtiii.. ')2vt.1€Th p.. I 1R La TLi1--R,g-IC-9€ tu..-C C.çi-Cr xr).dt •-a :tp€E t P b.u-t:x Li'U LExy Cli ',yc.t'h •.:i -u-TxxuT'tx. CCCL. i'--n.ix 1 ILJC Cxli :xfJ.Jt '-zr:'.LiCibla-ii c-C 3€ -CT.C. itiyii:C iLiH 'r' auuTi-iCL ccxL L€Tituic Rapakivi texture is one of the most characteristic features of being most extensively developed in the Waupaca quartz monzonite, but occurring in minor amount in all of the other granite and quartz monzonite units. Equally characteristic is the development of porphyritic texture in all lithologic units of the batholith. Typically, phenocrysts1 of alkali feldspar, and to a lesser LLi&:•iuiLci 7 JULia.U. Lii" x--.,cy.i-Cl,li-: lyxaiTta ir-vrut .'UCa U: C2itT'-xfJT4T tI-LIt et311C Li-U 11CC- 'C b-a iit rCttlii,i J.CLfl.fTl rxcii,.E CIxe xrit.ciE .1LC?LiiC I I J'IZIl =itlL'L- -L . t:;rtaaa' p-CTiU.j:it:lC iLL .xj.:,f nuuiiaaCC'---ixx--- -.---.j- :€-l'1TF itl -c -i, - h-iiuci-xca.2.t- ,,.I,Cxeyftxi :t-r CE CCJ-f ui''1r 4p.iiii .iHc- :ii-.7tnt_-i irE lkui 1 -i-U; -CILL xxix- Def of Geology & Geophysics, University of Wisconsin—Madison of Geological Sciences, Univ. of California—Santa Barbara A non—genetic descriptive term, such as megacryst, might be more appropriate to describe the large alkali feldspar grains, but since phenocryst is still the term accepted by Finnish geologists, this convention will be followed here. -filL'. WLiifT 'c-a .e:''Lt :CT. 'Ii -_' Li 1 C--- aL.' -c-Sf -C it I- U-fl" fx-x.tC-x, ,LL:xi'a;y C.€-LilgiCtl. CL-Cf ,j 7: Li.. u'xlx .., taL:-Cxx€ trti., IJ'.raul. •:$p2Y vniiui xixi i.-.LL 2:Li.'litf lIC'iLC'i'C CE--x C '-,e-Li --C -a--€ fit lrxiac. Lc--ii-II E1 Ix: 'IcC ttxx Ut-Il .CC-€1Lib-iU If aiaza'n trLC-T,:J.Cs1. -'' cliaUca ** 1 Department Department . :11 :CL ** I * It_i the Wolf River batholith, �P.- 89 - 0 - ':*-- - LjLi - /F: LIMITED EXPOSURE us / - —0 / LIMITED EXPOSURE EXPLA NATION IsLofls5 granite Belongia i LtC1Ctj% 5 Wolf River granite and sd C11oT quartz monzonite 0* Red porphyritic r5CiRiser ru-p0-i:: quartz monzonite it;C- Waupaca J!&Ci wiborgite r7 CEJiUt Stevens Poist grey granite I Hay Creek C!Cifr-C:cI1CC9. quartz monzoriite, T rIi ::rIi F Hsç!s! rfr:c1Cis Hager rhyolite Hager feldspar -]-sQsC -ici5ir porphyry bxsspi'y k{wsr Ci$Clci Hager syenite Peshtigo 1q:-liL nlonzonite CiC and -:sch-'is5Ci trachyandesite i-:i!(I :i-CIIC High Falls51CiCittCi granite 1 H THE WOLF RIVER ?rk•,:BATHOLITH -4—IH1iI1H GEOLOGIC MAP OF Anorthosite :-iIC, rii5PscN], i4C tLG BY G. MEDARIS. JR J L ANDERSON, 01] [j y-y__ ':UJs AP-II Mi_t WA VANVi SCHMUS. AND J,jI:. A. MYLES 10 6 10 Ci 20 22 30 2t MILES Precambrian rocks older than 1450 —- Contact, dashed where C'6C365. 16232 46 approsimaie — Fault Mylonite 1500 M Y �4214 11 Table 1 Proportions of lithologic units in the Wolf River batholith areas only) and key to symbols used in Figures 1—7. I7717'!110 11,1rcp:4rl 21.21:. 20's. 2 :7172 07203111120i '7:'i -fl :10012. 202171:11 22; Areal extent, % .47!',47t1 :212-21:7 o Belongia • Belongia granite, coarse—grained £ Wolf River granite fine-grained 7122 71!-.1'7-'-12-!-"4.; granite, 2 7 '' 1-210,27 2120-2120 '7:2.7020 21-27207 '171 ";fl C'' and quartz monzonite 51.0 2t"'3i.101 -::'a'fl'3 21 72721172102-021,1024: (14.- Red River porphyritic quartz monzonite 20.6 Waupaca quartz monzonite (wiborgite) 10.5 721: 24 (77,1.71' 07-212110 21017; • Hager rhyolite 3.6 57 Hager feldspar porphyry 0.2 - 3-CT': 27212 11204:0177 ,!C14J 221:-i - - Hager syenite 1.9 Hay Creek quartz monzonite 0.1 '6- 21:72021'.';317. C1.-.4? 4:i$-10. •2 • • 0 '17 ";-fl:7-73:..-3 141 0114 4212'. Unit y- :r 74,7o ;lj '4' - Symbol (exposed Peshtigo trachyandesite 2'0c20T'710'2'? 0 4 32424:!370 -'4-, Peshtigo monzonite J -2041002112110 •U-31,1W7, Not Shown Stevens Point grey granite 5.0 Not Shown High Falls granite 4.0 7212 ,' 21 .102121 4: 0140)1 707102-2;- '24i l- 24 ;411'TP 21.27.121 extent plagioclase and quartz, are present in a medium— to fine—grained granitic matrix, consisting of quartz, microcline, plagioclase, and mafic minerals. In all cases, matrix plagioclase is more sodic than plagioclase phenocrysts. Quartz is interstitial to feldspars in some units, but in others, particularly in granite and some varieties of quartz monzonite, quartz displays a distinctive idiomorphic habit and apparently was one of the earliest phases to crystallize. '71100 2 — 7;; I :12:; 272-721 21-724.: 117 3-10 71721.211171 115:21123-; '2021212' TT FL p0'; 102121,1-77:21077 A-trocoao-fw 4,,•;I_1rT; - :c;:-1-:-20.1i;'o-- 212)03 1)1 1'-.r.'327:;720-07 723-0421122 421 '21if;t2152 07712!! 21JL2---L22L SI ;cnr-o$ -n .LjJ720;0 0 ,10207077> s—p ','7c7-Jt- •-0 ,L2 Z:'20J' 7!::214r44:1014 A;10:A-•: 171 10- 2121:22; 277371 274710'7721l 2-4 1112 02 21-42022 72111210('7.A:! 7:107.417 7 24Ti,; -'-,m-. - ',:'''' .',- — .-.• 7 Iron—rich biotite and amphibole are the most common mafic minerals in the batholith, although orthopyroxene, clinopyroxefle, and olivine Biotite and occur in some of the darker rocks, such as monzonite. to subhedral and occur in areas interamphibole are anhedral typically Such an occurrence stitial to feldspar and quartz. suggests that in the biotite and amphibole appeared relatively late crystallization sequence of the granitic rocks. 21 2."-0- 0100 '1:31 .02 ':20'. TI -1021. 21:1120 -:4211-.. 21 - •3o©1coosI:jf 0 --':: 20t-207044.Z0I 2-117:170 C 114q77:.12761. '3 '10 7; 0,FL0lPOl 2-20 2412" TA. 4,' 2-021 2120: 214 2-20-1 1-4 $"7--1 1ir ;7-'71211214201 -1133-11221! '20741271724214:121 34:1 217 21121 21 2021 -ro'31::-'a li 1:;':-2-c;7 1)212124 410 7024-20720 -0:. 202 aCIC-Ip 1021721 21:217717121 21212 -4, -14. 1$ 'ccoo: J, 1422 -174- 37 202101:1223 20:20 12011221! 4:i;::10 P 10111-27 Descriptions of the Lithologic Units IT Twelve lithologic units have been distinguished in the Wolf River batholith, and the following descriptions are intended to summarize only the most salient features of each unit. Actually, some lithologic units are quite heterogeneous with respect to variations in texture and grain size, and the brief descriptions given here are not intended to encompass every conceivable variant that might exist within each of the twelve units. 21321:7 41-221 1t:2a'y-:p.a21;i 202321,2121212; 2I'' 2(12:-I pL1-Lt $4 )C'1 %21';#210' 22-f • -.'- 04: --.; ç0ccJ2;E-- i4J2 IlL 211 -- 14:2 C- -21-rn4:-ap. 7t.'7TL5 421221 21.-I! 4- LIII 21-21,'. -21'tL 221 2 21 flEC 1ç42r11-2 CC -:72)121!. 01CC.L -Ca210 214 1,141 T4 flt21 7212111 2111 flafl ifl;'. ai2a'-21 2•L21 I 114212-2 21.21;t21tCC12fl 17-114-; .72-Li �12 Quartz Fl 2E / 50 50 2,• I!- /• A ----- 10 ;CttT ___ — -— T feldspar eOD[J 10 Plagioclase Figure 2. 2 Wolf Modal analyses of lithologic types from the &q;4 TP°N Xyen? :;bTLflhi. sñ2( CJ rig River batholith. u':t7cCC44q 2°-f i22 (Sbo1s listed in Table 1) -T E bCCjUAA$ ;j'it:.fl1. . This coarse—grained quartz Waupaca quartz monzonite (wiborgite). 21 CCfl resembles z2=:.;:'n rapakivi texture and closely monzonite has abundantly developed I-)ç. Approximately 70 to 80% of the:tCe;1 pink the classic wiborgite in :T Finland. pL(Civtv.I 5U2 ;L: 4i, 21i 5.0 cm in length) are mantled with ovoidal grains (1.5 to ]:i%-r:A;) alkali feldspar .tthCVTC& LCçP-J2 common. 1 to 6 mm thick, and multiple layers are a layer of 4C plagioclase LCfl (rjtC, :2 The thicker a plagioclase mantle•Ci is, the smaller and more rounded is the )LJ texture is characteristic, alkali feldspar the [ 2T- Ci in Cfl core. A porphyritic .s#_1_plagioclase, and idiomorphic quartz with the mantled feldspars, Cfl large [ <•:.LdTs microcline, plagioclase, quartz, set in a medium—grained matrix ::±:t:1 of ;o; 1U Ibiotite, and amphibole. :i C LE 4 LLifl i'an2 :i ;r p cr ]tYL : (k; fIYIii ar 5i:; IL: ro-t r. 'v: iij;•t : .D':t Wolf granite and quartz monzonite. The Wolf River granite and '! River ::.Y12;. quartz monzonite in being coarse— quartz monzonite resembles the Dt Waupaca <crIL: ovoidal alkali feldspars (1 to grained and prophyritic with prominent c :2 texture is much less abundant, 3 cm in length), except that rapakivi L f ';i ;r1TI the alkali feldspar ovoids. plagioclase rims occurring on only 3 to 10% of 2: r:• 2L1J r;zcq - ;dtr :c1 I r;icP :i rr i;fl �.11 -:1 1. 1J a 1:.4Ti1 and groundmass. fine—grained in Yi4':7CC. phenocrysts olivine feldspar — li iii L1 .. a is trachyandesite 4 40% with monzonite, the of equivalent porphyritic ::tIiI?t interstitial of traces and opaques, biotite, amphibole, The quartz. -'E•I:LYL!rC and tL1' r;:T•+:1i: clinopyroxene, orthopyroxene, olivine, amounts TP'::.'1' in subequal feldspar :):j.'jL;::o.c I slightly vp-: L and (IrU alkali and plagioclase 4;yic1 containing porphyritic, mm) (3 ?;TTiio •."° t1.1fl*.1i.] relative 11 medium-grained isT monzonIte 1J[ The minerals. Ic maf of abundance yii Zi11t1.. and quartz, of paucity color, to grey dark brown their by guished 4:. are rocks These trachyandesite. and 1° distinmonzonite Peshtigo I — T I 1 L 11R1.:i4i.Z flt.1l . : Tin.1ar7i1 T.i..T°tfl ..lt:1:t.i i:i.1 c11t 12.1r JT1 41 /-. core. the in that iJ i111:r1z) :1I9944L.trw r °T with continuity optical in is rim granophyric the in feldspar alkali °7Th II cores occur The feldspar. alkali of euhedral around quartz and spar 1j J_L ° L,C1 .4 texture, granophyric presence feld- alkaliE. of intergrowths which in of Ii 1'Lf'L CII grains LC 41 ° 1r the is granite this of feature 1.4L14..' characteristic A matrix. the in 7'ji 7't occurs ':71 r'r' n°U aInriI IC '7CILC .present. IC17rCI IC? ECIçLIIr jr'i as .j of IC clusters mineral only the is and mafic Biotite iICCI2I:LCI:t421cIcJrI:.7CI is texture rapakivi of amount minor a and boundaries, resorbed show U °0iFk-U r .3 — commonly phenocrysts quartz The in cm) 24 matrix. mm) (1 fine—grained a çL;r0 It: ; In £11 •,•0nLI7I :tM50C: IC CI°4 to (0.5 feldspar alkali ovoidal and rum) 5 to (3 quartz idiomorphic of :riLIJ is I.I "nhLn1t .11iC I-i: ii:; :CIrTrmfl of up made phenocrysts granite Inr0r':.P.=t1:I 20%) to (15tI7. fine—grained The C ' I .,1 1 1 irflll'l oi.f rOr'?). T7(,j 'oLi' 11 I't1 .:?i I 47 :° rI'4 &. t ' 1 7 Tt.tl c 4i1 CrIC IlITTI C: 1CIC are texture granophyric present. and '.: rapakivi of amounts Small — 14 IC' 21 a are in set to quartz and feldspar mm). (2 matrix medium—grained 45%) (35 sr c7IC0'CCc7II'.Ii? ICIlilfi. 21 1r0::vr.Cc7 oL1.:.rrJl a CI',ig'ICCI °LIL. alkali of phenocrysts which in texture porphyritic acquires unit zI1:1 IC',:, rT"7T some as biotite I this however, localities, mafic sole the mineral. Jt ' I ,:CI I. 41.'1; U.CIC.t 4 quartz, and feldspar and plagioclase of amounts small with idiomorphic C'AcLI floiIir'1i of [CII U subhedral .:cCc1In mm), :'IC mainly consisting to (3 even—grained alkali 5lIlT, I yi I I l::t rt7r 4.rCt4C4 1W '- U,:' ir :.J].: 7'' itiriCi CIiICt ,T7ii7t pink, i-c'rTCI7.IilThe ilc :::U°t'CVCCJLl: 5r477 €7 predominantlyT1Ct and massive, isal7CTrrrTC'I granite coarse-grained ?LIni. 0iC:iSJInr€2CY1? 07T:Irn [,.IInIC7LCi €ICC'ICLt'Iz'la variety equigranular grained variety. porphyritic fine-grained and lIt ICBelongia JICl"7'oofIn types ffCiiL €74 coarse— a exist: granite Two granite. Belongia liT tI I lIC 7111 CI'liltCJ[°'Ia 114C rock. the to fabric planar imparting ':r'Ti4 [--1iJ !71:njTIrfr'5 C' ,17 l4:2'i Xiiii.I)41 . are aligned, commonly phenocrysts feldspar The slabs. stained in 0' ,i*r_ : 417 to up n' rC.ç.', 1il1I.inCCl on 4 IlL,' the of 15% apparent are phenocrysts feldspar alkali mantles U Yr' not 4C171 €4 plagioclase discontinuous thin, although conspicuous, is texture ' ICCCt: ILU mineral, 01 4. IC '' CIT II 71141 il'27L l7CI5I 111111711 although CI CII T?1 some at Rapakivi localities. present is amphibole mafic sole the as biotite usually and predominant, is plagioclase 40 L1! C' _T "—r'l CI "11 which of feldspars, two quartz, anhedral to idiomorphic of matrix iL'Ino'1iC 1 1i C. m91Tcir: .L,IUTW.C101. 2 with mm) 2 to '14 (1 medium-grained a of consisting 80% remaining the 7jTi: 'sTh'cC ri €17 11' I0 InTL cm 14''1 rock, the of 20% about constitute size) in 2.0 to phenocrysts (0.5 o.loo1oooocrr: feldspar K%cc no L'T1CIT74404J[ ZC2t!7t alkali t411 Typically, IC:l subhedral phenocrysts. feldspar alkali t.Cl1j[CtCii i::,ti Ti .1771 :fl 711104:j::C'Ti'.T° 717 phenocrysts rather angular, and to in ovoidal, ICCITI'l than ,nT.'zo!Uj matrix proportion .'01..t CCI riI00 quartz .r,I,; Wolf and .0C'CIl; River UTL4.CI 411:711 1€174 111 contains nyCv" '1 LI Waupaca fewer unit this monzonites, 'T:i;°7rLo€ quartz porphyritic River Red LC,LiiLLCI1 In the to comparison ThJ monzonite. 0 llTr 'I • 10 Fn', CT7C CT. L I p'4 4ltt4'L 1 '€': ;4.:Tlt CC IttTIC' l. 4 .1 I::-,:.Cc:: 2 nt t'1:. In lT'r i41 r'o ., . .iiTit C: 7:711 predominant 4:11-ri 71717 CI: I 1144 11 C€1CC4 granite II 417.714 type. rock the becomes 0C1CrI.4. 'C01:nx 1c714 IC '1777141. it, 1 t'€ rr" 1411 as appearsI quartz and grains, idioblastic iron, in richer becomes r:ç'T -- TLC .121:? :,rc2€I.rnCI 1141. In 7111171 4:717111 it; .7:, :U amphibole C'1,:°° 141,': -. ;c:T14 :amount, biotite inIcdecrease and plagioclase northeast, the to Yto171I ?.;LI: monzonite, ICC..n:CUJ€Cr: quartz '7,711:2: is ff':0y$-r7114 71111 711111742 granite Belongia the with Xl'TiiiICI contact *11 the towards but 0;: :..Th:nr..LIiIIU: 2r'i'''n plagioclase, iln41C.nIT 4111.the I,14 of CI .i'0U unit River Wolf bulk The amphibole. and LI biotite, .71t.LCC:L;I IC'Ct, :mi,'C:2t °tn: l,7f.:cl:'4LrICC: interstitial 'ircTCI71IC.':I:c:I.40CIiT microcline, quartz,4lIC]71'4rli1 anhedral to subhedral of matrix grained :1 feldspar .1 €JIC7fr'[l and 'To,., Alkali Jr II'C set1111': 1'.ilrCsC 14 plagioclase CI1 a 'IL I 1L11 are phenocrysts mediumin 0 --': 1 r' CCCI 13 �14 :-:cirL:r&10154122:?1'1 222111Lc'-l'ZIIOSLI idiomorphic 0C:.*-2, I'll conspicuous The Illoco:Hager rhyolite t'-L'a-L--rlL:Lt-r contains 'L1''1L,-h2, 131-to Hager rhyolite. 1110L112112112' 51220130772101. IlSoc ;oc.:lI-.ILO-co, :1121(1 less quartz phenocrysts mm) and prominent feldspar phenocrysts -50to to 44 co] :'0311.01 1F'.,Lo :--' 0110 (3 7-tn-:.]rcrcc: :1* quartz, 701911011. feldspar, 11121.0.221.221 f1 11101 ll--15L1.-O-0 matrix (4 to mm) 170 in a '1111-f very ULIOIIfine—grained (0.1 mm) of --14 to-i5 too) '01: -:11-too The pheno— 01111,11.511713. ortcc 11-0 8/00211. con:21 7-: -- and and fL' clusters of li-tc-:. biotite, to ac I] lesser extent, amphibole. ;ooo o:f 120 "1122€: '4201911. :r7ycLito, commonly :2211201-00 0 3322111 crysts, constituting 30 CUL 0' of±2222 the rhyolite, show resorption 37 to 45% 1. :10112.lt,101 t-:-'i4I,-?11t1 of -cd 02101011102 evidence :.o2:22.(112t.80101, without : tO is The 1-105221:: rhyolite cool] homogeneous, 111 massive .1--'-12,11011 and 5-:att 11-:;:; features. :1001: is tS-co:'otto to lot; IrSc-oO:': brecciation or573112-12' pyroclastic 01- thought be intrusive, ir.ot thus 0,122 -It'f.to- and 911180 010 01' :11:1,10 activity, -1'31.1,2iD112S'1-22, rather 1-ftc-ac-c- extrusive. 1201,52112 than 111112211 0711fine— fi'-o ' :1-12.101' 100 03.0.822431 121.1 the "Cr0701111 somewhat In :ccy;f hand op8o?4-1112. specimen the Hager-- rhyolite resembles In 2212 ort c]h-oHager ,1]:cc rhyolite oIlo'o' 0 to has Sac ac much grained Itoh the :'-c±- that to-Il cicpzl-ogranite, : ---.01 ic, except :21 cOol-Il Belongia ,7119 pink, 110221111., 71I-IOF. .C'at.012:' 001be 028 101.12k-I, 4-11-411 to finer grained pii. :ish—grey, rather than 10-: tends 40'2ILILL1O-1. groundmass 3C-912.In.r111123,'211 and jlb:i:-o-':' o 5.'-I,.1-9 ci,rtc::: on a fresh surface. or- 2222220 (11Y1011'l:lIc, f.'-O-.'t I'712'51 is al somewhat The '1:10/ ' feldspar Oolon IC' porphyry '3702 Hager j;111'5.: 5ti1-7-t1ifl50 Hager feldspar porphyry. 22 o..'(' 00, I is ':3111 12210 10511-5021 -p-202t74-' :-o similar to the rhyolite, differing in that the feldspar porphyry t4.tf.:-oI22c€9* :"ft-,-OJIL.:--:, 12:12001110 0-c- 'Lbo feldspar 407 .01,5 t.1'12t110'C221-'-c1111112 001-C, >71'- n:-o o1J11lt;.tlld1 more abu:Ldant darker grey00in color and -woC contains and conspicuous 01cc-Icr .t2211 0011:22.-to LIc :-oc- ol Or is the0cr13' only oo,i-c mafic:01 mineral in 714-1:;: 1 0035' 0?1:1.' phenocrysts to1730000 quartz.- Biotite p54: -01:5122 iL-: compared 71.42-1.0porphyry. :oo.c2 705 the feldspar 11*1:1.1 Scm' SOtO and r11122011.o&, .522'07', foliate, The isOL'-217grey to 12-0 reddish—grey, 111401010 Sw 117.1"dtlt-O 131. syenite Hager syenite. 1971214.011feldspar 7-01 C o: 11:' fCctSl :0 11 Lo:lm-f porphyritic, with aligned phenocrysts (25%) of anhedral alkali >a2L I :00011 pL>cocm c-51.to C2-1"% :td7-15h5--,'v:o1t -In-I tI: SOo000: feldspars, biotite, oil Solic: rco.'c, Jr;11-015:;. -,:. 5'.l.oo=-If.'coi.clrCand 1:25cm-cr minor plagioclase 1111 a fine—grained matrix of t1b077.L11t 0011 in 01101 C-? Granophyric iL103Di'9*7'0t't'011 of '7c1,c-cochdc: . intergrowths wo-r:-:cc- rJ: 81,3121: c,:.L amounts amphibole, small of1111811011quartz. c131:11 702 1.1: and alkali feldspar 0-3102 01010 ±122 12-0111102 a.'1Y22:-38IC to some qua.tz and alkali 1142110,1.110 occur adjacent 01111:0.'- 1 feldspar 5'-,t::r:-.4l01-. 77-s'1307'C"o: 22, phenocrysts. ¶ 11 massive icr-nA :1011111.IL'-iir and This quartz monzonite is 5.100 1112,122 Id lltItC1.7'coStLO ,-1071.1-;:0i -1 Hay 17ClLc Creek quartz monzonite. ]1I1,'L .111111:123,8101': 0 (1 cm) in a 7)2:3:52210 ' 0111 14 5112 -0051212' 11017.:C-.'D 437 ..'fl'11L40 porphyritic, pink alkali feldspar'phenocryStS -1-oOp°-y'2' '21I, containing 70-0121±.--:', 'oS -.lcp.c' cc, biotite, 7711112:' 12, two too feldspars, :-00clcJo'.rtl.t 11'-fl,l medium—grained matrix mm) of anhedral quartz, :12.11101.12121*. -950-4] 401, 801011 (2 1-5111lIlkt amphibole, 01022 sphene. 'l'c-,Lct , and - 2110 1.011-LI unit *1.14- in 71,101.00-37 this have not yet studied -not 5114 '>O '.5001-:c..:' ,572 We granite. -to 5082' :,oL,OILIL1V" actually a grey 31.1:1 -x;t.o-'inorth ocr-IS Ifof ,7002201:.1:o1:,o0 50One Stevens Point is ::-01:711d collected 71.c sample detail. tloc-c.Oi., 11-c.] -21 op to-' alkali feldspar 22 Ltao'n: 17% 122c1h111t122L2-aa porphyritic quartz 10% subhedral ,1,iL:s1:1 '-cttrt about 12210:211(1 022 with 0±11 -110': 12 monzonite o:_r1 iI allotriomorphic 'IL 0 1100101 in a fine—grained pJenocrysts (0.5 to 1 cm in length) I :750 tOot-Otto , This and biotite. 711! ,:c:-±oU 1.11-1.,, 0111L7 '3:011:: c-oitsc:, plagioclase, .-.:-i1 quartz, granular 1111.1&1lCit1c matrix of '-ttc-0o. microcline, 41'20C.'91.5F' 'I,0.72 '41-123 finer grained varieties :1::f5o-o.cc'',0-.11cI 1.12 some 11.0111,of of the rocktois lithologically 2-111.111,11,1 to rook, 11'1411c.1C-J.4 cc 113' similar .'-Io-'111c1:1.t3 flo-7,"lil-T-:OlCci quartz 0,8111 River 1111.02712' porphyritic 110S12'L-S monzonite. of the -1-221 Red 0" '1'.oIt:-1h:11-'a-: 5':81911100 Stevens Point grey 21 ',i 21 ca"c. -151-1.- hetero1151125 granite High 0:1-cool t.: is rather 1-c a :'s;- 5i oil: Falls .:&-c: t-:, The High 42-S'LS,: Falls granite. 5(122: .lJ0;:1.1..771.1222I12':cLllt-I0 oo'-i22 1911, '12013,-I,1-l allotriomorphic geneous mainly ofdt medium—grained OCI'SI 01LT9* 11.01:174 011111 unit, 12227 -1 consisting octorw': oIl-Ill Shear zones 011are extensively 51.12.0 2103.01 9*-L-02011*o.1 wt1oor.. of :7.'911'1712 granular granite and quartz(19-3>1101.0-0, monzonite. 11711 other units 11 the oLir1 11111 -il:':211t 10305-1111 absent developed It'll? 0021,2107:01 outcrops, a1- feature from 12-1510 22222:1.1,0 of 18: '211.1' -1: in some -lb rcr'0" :7110024±22: Eau '-IILOOIci Claire River mylonite :0 '11c-'o,..'.7f 1712,11: :'r50 11:11 of -11.':L'klt the Wolf River exception the 11:::, catrl-:clLlLibI, with 1i',tmr batholith 'i&3,:77oo1, It is ::,.1.o1c150V uncertain 1;, .0 11? this guidebook). 1770-1'. .015 122/11121.1117zone (LaBerge, field trip locality 8, :1' -015 1210: (1 a17c1-cbS-.. 7t-I1'1:,11L11-' It' whether of the 1,12.1 batholith 022000121 I'Ll]: or lIlt" 114r I.½0:C '1-;: truly n"mCft ilL granite 01 II;111l'1.' is whether the 4111911'? High Falls part 122 :.137L&1t1b,1€02011;1 to ItoIn the 1.> '1"°111i12:. 3ii:1"11'32212.2L111-4 terrain. 0' 480- surrounding 71.0 older, it represent :5' the 1211:11 of 11 might mtgkb 0017 .c10IL::, part -: >s tac-]]' assigned to the bath— it. SOS tOlctO: 1 021-10 3:30 oso L,oliac to absence of isotopic dates it has tentatively been ooto-ptc 1,0120110 21201-so cooS tçlOIolti -.150 ol' and is spatially .10:1 1:c-cr:,'-lllm' 01-8 cool-cIlo': ,1T:8.'11L'.tO olith because it intrudes the Macaslin quartzite dli;:1,I'5bl 0-1-30:1012 -'tC-OLCIO. Ito. -oob :101410 monzonite. and Peshtigo ::l -19-12 .1, . -110.: 11c5 Ct29ttl: granite, i'oç'to..*tl- , Belongia 7;: the 1(14 —cr1 : rhyolite, related -o Hager c-tm .al,e-21 to '1 21111 �/t c-'5c-,, at.1; c-y cc;c cc'C:Ic'C'cc6 cCEcIICECcZ /Ld:,LLL -cc:. :c;:ccicc cc ,.C1 ::cc-:cc---5- To illustrate the chemical compositions of the granitic rocks, mesonorms have been calculated after the method suggested by Parslow (1969) (Fig. 4). Such a calculation takes into account the amount of potassium incorporated in biotite, thereby reducing the amount of normative Or and presumably providing a more realistic comparison of normative Q-Ab-Or with experimental data in the "granite" system. SJc-ccCc..,.C: ccL?c:.,lcccp cc,c. ic. c :c-iaccc :1;-: 2cc,:-,cccj 22-c--cU'. /p:p cc: ptc;ccc-T:cccr c::ccccct.c-i cc -'' P :1 cc-C-S -I ci 1•:as I :;:cvccc- 'cy 1c2JIC:cC,'5 cci;: cccfl c-cc::' ILL.Ii;,6;5 Ct fClC:-cC:;f.c.Lc :;c-:cc: cc-i. ,;IC:'1'. 31.;-ccc ccCci C'PL rv,cc.,mc I:; 1CTC6ttc-:e 'CC!. —25:cc:cll c,; 'c2cp.; ..:I3_':L:CC:ci. 'ZLj cc '— I cccc,irc,Li cp'.:cc;cc: L.ttXI6 c-'2J cc' ccc-: :ca'TLt:ccaci; riS4 c; "iccic ! Icc. cc: I!TCiL p,cITC. cc-.;. CttEC PLC:,' Cp; ;C:LC:C: (IN CSLC:LCC:5 l'Lc1, cclcc c['ci A Peacock plot of analyzed specimens (Fig. 3) illustrates the alkalic or aikali—calcic nature of the Wolf River batholith. Despite the alkalic affinities of the batholith, all of the lithologic units so far recognized are peraluminous or metaluminous. However, syenite and associated nepheline syenite in the Wausau area yield isotopic ages of 1450—1500 m.y. (Van Schmus, LaBerge, and Myers, this guidebook) and may represent the peralkaline complement to the peraluminous granitic rocks of the Wolf River batholith proper. PILc.cccc cc cc:' cc-c 'cYs,ccc-rm :':f'c;1C:;';c-C'c-LcccC: c; C.:LI ccc' C C:/L,IIL1'L:ciiP'JL ci ;'--;, ;'.:: 'fltcc CC:C: C:CtcL .Jccc-'C:6L .C-1; iC:177ci1: c:L:JC: clC:;1l..iC::.Ic I 'C:CJ cc:; "IL 6F1'i:C:ciYTl ccc ;c CC.IL'i C:ii,c-,L c',;:CCL.c.=.T'\a,[T PC: Cc-c Lc'ff'Ct5 I'5.c.15 5Cc S':.L °Zji TCC:LC:UtC:915' iC2-CISL" .1c. "ccc :1:'c:ccc1J PLC: cWUCJVL"1: 51 :1:5, a/c-c' ic. Bulk chemical analyses of specimens from the eastern part of the batholith, including Wolf River quartz monzonite, Belongia granite, Peshtigo monzonite, and Hager rhyolite, feldspar porphyry, and syenite have been obtained by electron probe analysis of fused rock samples, following the method described by Gulson and Lovering (1968). From the analyses listed in Table 3, it is evident that these rocks are relatively rich in Si02 and alkalies, particularly K20, and poor in A12O3, CaO, and MgO, features shared by the Finnish rapakivi granites (Sahama, 1945). ccc'.CCP leST .Y'CC'i"CI' cci "5 I-i 'ctc-c, 2C:J'. c-C: : 'CC:CPTIcC T ( C. — I L cccc'c.'.c C H' C:'c-Cc- 'C:'.'; '"1'EIP6/ 'ci cli;'; 'c--Cc sic- LT -I LI c.'-c-Ii:-', cc; IL -.1 ' cc :ccc c.c.cc.:ccpr cc-C c-CRc-c- (c c-ac-.ac-c;cc. pc'pc'c. 2L S r,,c,.Cc-1' ccc5ct'S' :C: çc6"csc-'c 'ccci: c'c' ' ;cI PC ;!.cLT'Ccrc cctccci:' ;cn 'c-cc"; tTc: c--c 5;; 5,5 Thp 'lrI.Tc-c ti i-;":.CC: ccicl.'Lc .'C: cc 'C7"Z' 'Ci-c1'fl p-C:, C:'cTC.i LC.'CC.ilT :6;Ipr'::z'c-; C'IC:PC:']C' Ic c3?SCIC7CCS Ec'PCC:IC.1L :'ctc- : 'cc-; cc 4.rCI 'ccc ic-Cc : '.5': c-cc;.i:c si:cc ROCK CHEMISTRY From published descriptions of rock types in the Finnish rapakivi massifs (Vorma, 1971) and from examination of rapakivi specimens in the petrology collection at the University of Wisconsin, it is apparent that each of the lithologic units in the Wolf River batholith corresponds to one of the distinctive rock types recognized in the Finnish occurrences. A correlation of rock types from the two regions, based on textural, mineralogical, and chemical characteristics, is given in Table 2. The only dubious correlation is that of the Hager rhyolite and feldspar porphyry with granite porphyry and quartz porphyry dike rocks. Texturally, the correlation seems to be valid, and perhaps the only difference is a higher level of emplacement for the Hager rhyolite and feldspar porphyry compared to the rapakivi dike rocks described by Vorma. p'6,:',::: p 'ip ciTc: cc- '2,TC:c-'2c- .,''ccj ','; cci. cccccPC cc "155 "S i. cc'; :,'Irc.cc':'c'.i:c' 1."cr: - C: H; ;,L',,L,'.cm 'IC Cc- ,' C:C:U'C'STC CL2tit S ic c-c. C P':.: CC:c-? (-7 I I cc- PC cc-cc "ccc:'ClCl-ccctc c-Er c': cc " A,c:T-cP,c': cc cc p PTLC:c-Cc:C:cc'c.c"- 't cc- s. :c'i-icC:'c- ccc': pip;' C:T'1cc,-: cc-c cc .,,: :1Cl;C:2cc7- p,'c,;'"c-,l' '2 -c' 'C"l." ;c-r' c-c L'icC 6):PC57 '-;'::':c'c',, 'I'P rIct'L,.6L i'' L"c- C:'pr—c-ici; Lit. 'aciccC:",ccc;c-;XL1 I'C' icc-i I1c..J'15 :'1Cc-C i'L ,,,''.:'c'Tc-cr.,,:te '1 c',. c-.:ctc,ci cc, ',Th -c-c- 'LC,-cTCPP'C:LL' P1 ]'ci',1C I/c cci L.,:m:cp.p' L..(CiPC.: cij; PC c" cc :'c.:;L; cc-cc c':c-cIcP'C ' WE c-Cc-C ci ,?,Lc;/ pc L::6;:c6 cc, ccI-cc- C: P':tJ'ic-'i icc-lIT,' '.,5 'CIT, 'c cc :cc ,,r6Cc ccc-: lcC:c';: :rc-y -'l:: c-Si. cc; ciT ccc, : 'cc-, 1,6:1:! ,;1:CCc .. cc'c'c ic-'J L'JC:c:,:cl: Sc-c-cia ic"cc: c c-Cc' ::_SIP :LlcC:1C:c 1cc'p.r c-i' P 'ccc '.. .,c- rpcp7;:i,;i:r'p':L5c. I :7PIH HH'.i sic's; ccc-.. cci fc;:mlcic-c-c:c- ;c,ii":7:ccx: c LITHOLOGIC CORRELATION OF THE WOLF RIVER BATHOLITH AND FINNISH RAPAKIVI MASSIFS LcI'Si2C:J111L 1::C:::ici Pc-c' :cac''1 pccc.:c-'.Ic-cc :tc;G1E:.ir 5,'c-'p' c'S a Cicc cc C:-i':"lC:c.C.PL :P'i"c-UC:r CfCui 'ic-C:4 Anorthosite. Anorthosite, containing plagioclase of about An 50 composition, occurs within the batholith, where it is intruded by granite (Fig. 1 and Weis, field trip locality 7, this guidebook). Interestingly, anorthosite of similar nature is associated with Finnish rapakivi, where it is also intruded by granite. A genetic relation between anorthosite and rapakivi has been suggested by Kranck (1968), among others, but some Finnish geologists believe that the spatial association is simply fortuitous and that there is no direct genetic connection (Savolahti, 1956). c:';": CC c-cc-pp 6:flC:C:'C':cIlC'C: c-i'll. cc-'PCic c-c- ,_F.cL 1'C:. i;-cc-:ci' P cc-';ccAPc ccc , ia,C PC'cUC"l c-CC:' CT,, c—-c—— " ctwc- C:T'Ic-PH A? :ci, .ccc.:cccc ucic-ciCC; nctp'-ccP I'c- J C " 6',c 'icmL,L..-,,'_Lc_', ''.2'-. 1—c—_c, - Si ClC .1CC:;' 'p c: :cc-c,'CL"P' 4-"':"'c--''4 ,•,—. C-'1'.1 ccccc' .-— 'cc-it-C.' c-nc (..'la SCCC'ST,JC.i Ic-SIC ::.cCc;c..6I ,;12T75:1',r 5:. PJ' Lc-cc'c-/ C 'p, C:.Tc-,,cC:i'iIk. 'f;CC'i'ic''' c-c ?'-'I'CLC:;''i cc-p •" ii's 4. Lj', C: "1 . cic-'c- ' L 6/'— in 15 �16 Table 2 tC.i! Correlation units in the Wolf River with onrc: those 2ar-o:- batholith rrntr O:r'-cLrct Ui -ifof1. lithologic t.n01['J-f .' nyt+ in the i5rr9t Wiborg rapakivi massif in Finland. Et n1ri :irn Er at1i :''!tAL. Wolf River batholith '.ai Wiborg rapakivi massif cr;a•r:te Peshtigo 27&II'C' monzonite Tirilite 1Ckt2C3flI :8 Waupaca quartz monzonite 'i Wiborgite -t Wolfr River izt1'C granite ;c&-t.. and quartz monzonite Pyterlite L1i 1/rL ri: Red quartz monzonite r\ct! River porphyritic Porphyritic granite :: t-•i rrttt L•L.Z'c9 -pL1T_:;r' Belongia crsgL granite, coarse—grained lilt Even—grained granite 3Jis 7 *1Ci: biotite Belongia aririCt granite, fine—grained Porphyry aplite rg aIL1c rrqy1 ( iCrp Dike granite porphyry rr:c2asaa a .e- rocks; and quartz porphyry grL';Q ja( r.rirr' Hager rhyolite and arci feldspar Z&T.t' porphyry ac Na 1: Na20 + K20 -p Ilt 2.- I lU 52 56 - CaO -— 58 6o 2 76 Sc , wt. % Si02 Fl.gur igure 3. 3' ncco1ith River atholith cloif 1ri'nz torn Ure forhpec:iraens specimenc from the Wolf grapb ftc Peaconk Peacock graph �1 17 Table 3 Bulk Chemical Analyses 66.14 0.68 1.13 13.112 51.8 1.145 r 71.14 7, o.6i :i 0.28 iy:'- nC'": '"3: 0.20 'F'"' ".cr's -A-; 0.39 69.6 %9i 'r6.2 714.5 7 6 5 9L2. Tb2 14 5: 69.6 Si02 3 :5'; 2 1 3:-c 12.1)4 1'9°J 99° IJI -r' -Sc 1)4.33 s:. i6.6 14.18 2.53 3_I 2.29 3.72 11.29 6.31 io.8 MnO o.o6 0.03 1—" 0.02 0.02 3 0.02 ;i1F.;. 0.03 ::.-:, 0.12 MgO 0.33 0.13 c_'I'-3 0.08 :5ri3 0.18 51°11 0.37 7".:;' 0.90 1.36 CaO 1.69 0.58 0.58 L 1.111 F[ 2.39 24.07' Na20 L 1.38 3.83 3.13 3.22 11.142 CI 3.3)4 3.611 11.119 1(20 5.83 5.85 5.56 6.02 '"fl-'j ., 6.28 ..-.;3 5.111 T':° .-..i 24.35 100.21 99.09 100.03 100.31 100.9)4 100.5)4 101.0)4 1- F' c-A :4. I —- ii Cc c.w 3% Wolf River ciuartz monzonite 2 ? Belongia granite, coarse, average of four analyses 3 Belongia granite, fine, average of five analyses 14 1T Hager rhyolite 5 Hager feldspar porphyry, average of three analyses ,T'31.33II33. •c;11;'rx 6 Hager syenite, average of three analyses 7 Peshtigo monzonite (c° ci: 1 11 -- Fe as Fe203 ',o. :7 F"" Total IF — * I Total CIT 1)4.3 31 "ii A" Fe203* 11.80 ti: 111.3 991 A1203 3333) .D:3,T? 9-3 73,1: :13 J:33:3 ':.3'i.73 7,33.:F3'3J,?3 tFnL;cToca 1:7 ?32c-' :cc;,cT, CiX313 co7'Fc:i: ?17700:19 5'3ç1':f33ci OX1i9t j3 :9co±935301. •33Y.3 r3v'i,:iO; Jo LI- 3F .9 �18 Q i o--:JorL8!a fC&OAt Belongia granite -5 tatr hcres granite Wolf River granite and quartz c-rr7onlt-e monzonite and 4uartz A feldspar ris cii he • feldspar Hager ffac;-er rhyolite, raritcporphyry, n-or piriTy. and syenite / -- ii- L-— - L2 Or Figure 4. . ilivar compositions of Pull of specimens spec incas from from the ih-c Wolf boll River Bulk c-orapos;tLcns hr. bat-holith in p. Ab, lb. and Or. batholith in t-crzss terms of of mesooornotI-Vi mesonormative Q, 8ourxdarycurve c-ursafor for P11 P1 BounOary = bars shown -shon: for for 1030 hu 1000 2 comnant son. comparison. batals fist-cd (Symbols listedIn inTable Table 11) - I �; TCC -'.-"Yt( 7-it F k-CELl -'C to up determined. been have 1.5% -Ci -'-'-I Cl (CCCI 11.12 7 CC CLCtLCLILI7'fliC( of ,,LIC; '7C'.If a is 7LCiLI'ICC-C- high ITT- (CT.' VCL.C:'L,.T'CkI and to up contents -IC, -Cl) 1.8% of far, So halogens. content ILCI',LCC, River C-Il. L'21fl'C7 CL characteristic ;TCLiI, the "I 7-s77[ of C 'C-CCI.C;-I 11 C!.IITL'.t .7L1112 III '- CI A '-(1 1'-CC.i Wolf batholith from biotite feature 11 - granite. Belongia YC:.7C7.i7.lL'L t(C' .T 5 IT c"CCC-Ci-'-'C YI'LIC"C 1147 IC-' .2C.1LCC-),,'C SIC, - 71121 2(9-112(12Fe+++ 4 -.1! coarse—grained the of biotite in Al octahedral for substituting 5' LkIC'Ct.CI1l of may granite 'C to -LII due iDI1Li,1)';-;'LCL. 7.7 '74t C-Cl) be -CI'4, 7-1(220 11757 CI- 7L2100;.CICY.X1Li1LI711.IL amount larger a of varieties two the from LLL7-.L7.CT'C (CC 2,'C€'2.ii'I1OI- LLI,(ILlCi7IL.CT1Li 71; C-C,C'-I'CC',.,, 4. CC' 11511C-cC"P-&, 'C3C.Tfl,-.CI Belongia biotite of content aluminum in difference The granite. :(.7,, 7,'C2;'7i2ucL11-C-LI? C-CC- T515 C '1 octahedral CLIC.CCT& IC-C CCIII 9-7.r.CCTL'C 21'L,-'0--C fine-grained the from compared when biotite with Al, C'7,IIC 'CC7TCC1C-i "II5CC5CLIL'-CC C?-CCLICCIC I '21201111 C2.(1i1'4 CL? but 'lLCI'.Ci?I[2-? 5.121 particularly aluminum, amounts small relatively of contains ' 7711L'i. LL.TCLCL '-"I' ('7 1:20 71 5,L7:.u.t I(C 2CC-c O' "CL 7'1C-0C 'C.' CC.CCcIzi.. -'CL mineral mafic sole the is which in granite, Belongia biotite grained ,p.7f -coarse— 1111-112111? 1l)C-'C.LC ('11 '1-" '1','C'5.CCCCC - LII CCII. ' River hI'7 216 P 'CCC 'CC the by is rule to exception I TI provided this An granite. Ii '0. the '1(177. 7721.'CC Hager .I-.5.7I'(' the TIC-47 C)JL7ICL.CC IC"?, LI-CCItT:' C CCI? rhyolite, quartz Wolf and monzonite, porphyritic River CC"IC(I 7217':CICCCCCC.'5r7 LIt'IC 7?- -CC' 1.i:I1Ci'2-CJCLCCCLI7,:ICILC7I some as CLI' Red the of members granite, Belongia fine—grained the such C'C5'C-711'C7. 74 211T-1,1.LILI'C.CL- 2177117CC LYfiC 'LI ?1i.I-77'C'C'l' '((PCI! lithologies k-Camphibole—free in occurring biotite aluminous most the .-i4.'7 'C'L7'YC River 'C-C,(CC-.,! I 7(7 12 .1 -CC, followed (It CLCCCCJ C.L5I,c.C-T':t:L is 117,74? ('71 by batholith, Wolf the from biotite pattern 22Tt7 This CIII CI '-21,1? a t'-. 5(C CC'? c:L' 75. "...L'LI. 7'fC"--'- as -W't-C(C 1(1-717 'C'CCIEC C-C.yC.-C21'i, well. amphibole containing rock from biotite than aluminous CCCIII CI more a as 2"CC occurs 1127 97 iCi-"kCs 177 CCC'. CC 1'?'-'? ;C( '"1(121.1 C-711'ICUIL -C' LI-CC be to tends it rock, in mineral L'-""CI-'mafic sole the C-IC?-.(1947), -2.77, 45971.C,CC-k.i 7,Cl7CI37l-iC-'CCL previously .IL2'CC.-C'C"J As 211 biotite where Nockolds C'S, by recognized L 7Cr pis 'C'I11:LkiC,C7 per C11-CCCIC LI 2,,, CI C'CC;SL!CCLI1 CLLI'CI 'CCC' formula CI?'. C-Y"' to unit. atoms 0.5 than less amounting low, '7mT ''.LLcI'©YIICC( ,i1PCC- 7L7'lç..ICCIC-ZCC ,12ITLILZ C' LI' -CTI'7?7 in :(CCIC7,CCLTCVC '11-7 01Cr Ci Al biotite octahedral monzonite, quartz porphyritic River Red and 1-1. ('1111.7? Belongia "41'CTCTLIC(l C171t CL't 3.2 'CI' C' 12192 9CS-CCICC- the "-kkC.C-'CILL .1"CII With '114; .2 - C tI 1 with granite the IL? of exception atoms. Al 3.5 to 1TI-IL'Ci1LI2-t-1Lk2 C-c'9i1C -1.1211117. CLC7CIC cl- fine—grained CSLCIC-TC,, 2CCC'L'II.C-Lbiotite contain 1721717-'. which 7.' of pecimens most granite, Belongia ranges oxygens, 0,IC.LC117 I'IC,C7 2232' 721111 CLI. 2.35 2172117-CC 11 7 -CL to 7.uCL'CI units 1all 'V .1-4,1 1,7 '7 about the 7except from CC'211C2'LCL for 3.10 C an 11 CIII- ;'H-172121 ul uCIlLfiCC,LC The 7-C basis LCICI'C'Cl anhydrous Itl?"CI.- 'LI:.CI4'k 'CCj' on7-1217 "CCLI I?.. of 22 calculated atoms, Al of number -. (CCI (:,7,IC 71-11211 'C'ICC'7 River. ;i,9.? the 41 portion 97--. granitic and '2.1.2011,,'! granite, '12'?'CL"C7 Belongia Wolf 'CCI. of Cl CILI,177213'.LC' L-1'7C -.2:117-I ,(1C1 219-C! consistently 67 -nICIT -CCCLII being CCII-177 than U&LI7C'rLIi 'Cl-CC rhyolite, Hager the (17-51 greater for -:i 90 about -7127-f':: silica—rich '7.20 C.II'CiC'Y' CCLI. ?'7175L_12-217777most 1CC-ILthe (1.7 1i, I'I'4:Y'(1 L4CC-4 'ILITt.'t :1,1 are rocks, in highest ratios Fe—Mg expected, CuI-wC39I(C,'r 11Cit..C,.CC!i'TC7'CI° IL, values 10'.." 01-25221, ..;i'CC(C 2CI,,,)"21.,L, ';"I'II(c( As to 70.1 from ranging be might 98.6. lOOxFe/Fe+Mg of 3iLI"li'"CI with ""'.CT.-LC'CLp.Ci'7. 011.772217 1 The 'TL'I'.u,, in 71121' .77 biotite '517 siderophyllite --'37(11017 tIC -C"7, 1'',I-C,JC'iLL':C and '217 C1 i' eastonite, iron—rich, is 5.7 Fig. C'.CLIT,..10T1LL-'5L 011.731 have C CLfl'LI-iC,-"T-CC'C of 1-1151111 9i-!'f( analyses 73- terms LII ,C'I-"l phlogopite, 'ICC TILCIIIC (Il)'-[ end—member 'CC plotted H -2(1,771 been in annite, ..L(', elements L1 C'4L I'7IC:"T'C'7.I eleven 122111 '97' C1'21C4' I.C means 7"ILC1'UP by 'CC-' 12277? J1f_.LE1T 'k'3,1J. analyzed the and probe, electron the of for 01(117-CC CC -22I'I'c''CC'-?C,2', 1i-.C(1''ILCCL'CCCCC'pC 47 'i'-IC(4 , CCCI! Biotite Biotite. been have specimens representative from CCII'C'C-.7, - 2 11 C.u'CCL!LC.,:p, CC:Ck19C.C-I-3 the accessory minerals. 1!1LC'. :111 and 011772'(C"Y-' 121421177 and 777' widespread 1-CC' C7-1.'I5'-k.:-1 —' most 74??' 'CCC. LIt 'CL pyroxene. 7(7, .LCCI'.i,i Fluorite of characteristic the is 7771)207 iron—rich ''Ilk and 'i..71170u7 1IY''7-C, (CC'!.-'' C'C.C CC.C..fl.,2u74'.Li(I 112.77 biotite olivine locally, and amphibole, plagioclase, (120.1(1CC-CC- smaller .L:-:L-7 :s -:sl fl'"7'-',Q' 77- 42t -11-1.2171-1-C.;: C:'.'L7 73sodic of amounts with quartz, and feldspar alkali perthitic up made are batholith 'CI 1771 (1507 C'" 1'171'T-2111k7-1'2 7r-, 717- 7721.,I1"-L,River C&,"71 .Wolf 11-I' (IT' of predominantly the ,of Rocks , 7. (9C t MINERALOGY CCLI. 219:9771 47,7. 'C17.l C' 1120 -- -1'.7--I (Luth, to respect withj7ILII7JCI21C-: saturated 1969). (12113-1120" could -_.Cc72LEC1 magma aP in -'c;11-I'C'['CC , CIa-7CC C'C..,IC 4LCI-'I72'-i conceivably under— 'CCC7LC"ci equilibria crystal—melt reflect C1"'.7C, -'ic LCL1TIC 7'ICC-CLCnLL' [ -71C77 a '1 41C5'C LCt'7''L-- 'Cs-I- rapakivi 7121>7211.15' IffCt7lLICCCl (('4121 '1;, displacement Such granites. Finnish the by 721.771711 shared -7feature ,-: 13122120 L',,'C,1-"'-C1C'C 71.112 a1 12177.21,21 corner, Or 2194. 11,21217711: -: still 917 from TI .5-C are the toward LL'1I20.'-LL'1CCL minimum C7''I:'I.C;-C granite the displaced (1Y-c' C/-C -7-TI 1 .2,'C Hager IC 7i'Ii,C.'LlC.cLI the Ci313':'c-CC'21-'of 7C calculation '('977114(7(1!,') 310117"'.-! Belongia mesonorms, rhyolite and granite 1,5-C "[(7 CC. 4C':'CIC'(L'LLIO.LLithe 1177. in 0115-77' (''2777: despite C' C feature 7 712110515 'II of C 1174 is 112117-) i3'C IC CCI amount that, by Or normative reduction .C'.77 toward 177191117 \''7'7) IC-It)-?,, 1721CC' 'C1CC' Ab—Or II along extend 'C7'Iti the significant A join. trough thermal the "7)5771 79((15C;the I'll near '017.:-?..: granitic u'C.C,,'11-7LI, -317-k-IC- 711.-'-' '17';. '7-I7- 7.1 and minimum (Cc granite plot rocks the(1-77 for Mesonorms 1121 - , 19 �Al 20 atoms 1002 1OUx 3 90 80 •4 Hager Hay Creek Peshtigo 10 100 90 • A • AAI •A As A 80 o A A Belongia S1 A A Wolf River 10 U K2Fe5A1Si5Al3020(0H) K2Fe6Si6A12020(0H) V 80 vvV V Waupac a Red River 60 40 23 20 gA •OH K2Mg5A1Si53020(0H) (.M-SA1 1:(DH).4 KMg6Si6A10000(0EI) Figure 5. FiRure a of Cumpos'Y cf Comuosition hatholith. tTL frcn from biotite cL:River Fir the Wolf ir LL7L (Symbols listed in Table 1) �21 fr i-i-U li-U)- fli- 15Ui-1 tci ThTZti'-i-iitUp Ut ; Ti-I [-i-U)-'P Si-U -Ui- _..t Ui-ill U4 .U'LJitLU the Biotite from the Wolf River batholith is similar to that Finnish rapakivi granite in displaying high Fe—Mg ratios, relatively low Al contents, especially octahedral Al, and enrichment in halogens (Simonen and Vorma, 1969). i-C Li- i-lU f7' U)lIUi-Ui5Ufl LU U r; •Q:U)i-,i-J 5 r-: -•l i-li-C Ti- U iLiSU)cU3-SlL-U) Lii-U) i--i-2 I?*81 c)iir.a U5U)UUl)'i-U LI k-i-- I i-IHLUTtC U i-i-J-U2 )fl TtitU)i U U U)flj'.L U)I2. Lii- itLUI: t-p ioi-i- ri-i- UI -U-li-f UU)UUU U -i-I 4fl2 Li-a.., Ui-U U -i-T-U U 4€LU2:UU U2t1iUU)L 'i-U Ut i-i-i- 2rim '--rU 1 LU'ti-UL ,-LLJ i-C- S A ubiquitous textural feature exhibited by the Wolf River rocks of biotite and alkali feldspar wherever phases are in contact. Configuration of the contact suggests these two at the expense of alkali feldspar, perhaps rethat biotite has grown of intensive variables during or after crystallization, flecting a change in equilibria among alkali feldspar, biotite, with a resultant change and magnetite, as studied experimentally by Wones and Eugster (1965) and Rutherford (1969). fl 'flU li-I) 5i".'i- UUU .xU:UQ :i-j. i-U)21it\J[3L • L---.1ff5 an intimate intergrowth UU[l-i-2 is i-• I -; 4liUi-U 1U)iI t.1Ul :U): U)li-i_ Cri-IlLi[ i-riI iii- :yi- SUU( i- i-i- LUlL. i-i- -TTLi-1 1Y ir&-; 1-i-) U)Uc i-UUU:flU)U2 i-U LI: 1 U'i-i-ti i-i-i-CLkçU):U)J Ui-U)fl[U iur -U ;-tp-; ;1i.U lit I _U))L2 i-i li-U E -CTU cC-fl flfl- i-U- atcLU.I.t- 14 U)ifl'i- UTU:U€ ''L 11 1 - U)li- ii: p-i-t i-i-i-i- i-.7$v- :c p Amphibole. Electron probe determinations were made for ten elements in amphibole from eleven specimens. According to the classification proposed by Leake (1968), most of the amphibole Is a hasting— sitic hornblende, with values of Ca+Na+K ranging from 2.54 to 2.71, Si from 6.33 to 6.50, and lOOxFe/Fe+Mg+Mn from 77.3 to 93.4, calculated on an anhydrous basis of 23 oxygens. In a few samples Si values around 6.6 were obtained, indicating ferroedenitic hornblende, according to Leake's classification. Like biotite, amphibole contains appreciable amounts of halogens. —r;a L.i-U)L iiC4Ui-i- - Ui-. iI[U.i- •_' U) LCi-U1I :—, rt;: Ifl:-I-:r42 i-U) .S. ii.: •1 U a:r U I. 1. U) U)12Ur •qr[U.Ui): i—U Li- U rii- zY2 - T:L4c acITr y - -U)-1 - -U)Uç ç-- i-LU) lifihili-. :JtU) Si- li-Ui U)U)ui.U)i,U 'U IEi.[U:L: cUll—Ut t' .CflU)1r )CI; Ui-1.:.fU fl UITltl CLJçJ U) iiU -IUYUU ri. TU);UUL U)'UiLU)LU- UUrU) 1jiy2t-4- Lii- i-JU) fl-l:v :i- i-•5'j1- Ui- LU atL1i-: :2.U)ILL LtYL u1it-* U)c:cUiLUU)JU) U4UkOL1 T LcL i3t nr; For comparative purposes the analyses have been plotted in terms of atomic Ca, Fe, and Mg (Fig. 6). Amphibole from the more silica—rich rocks tend to have higher Fe—Mg ratios than that from syenite and mon— zonite. Coexisting amphibole and biotite have similar Fe—Mg ratios, but generally the Fe—Mg ratio in amphibole is slightly higher than that in biotite. :1.: 11 L :_rU -UU)rL I tiIj \_41 — T1- •L;:. 2UCLL1Lt LyU [U( L SL EE U)) i-iIi--: C.U:;Uç. ULU) r; U) 1JQZtU r 21 1tyu2T':u 1i iv- 2 ) 12 çtt:. Ii(:.3U) UT.LUL I [U)UU)IU —e r-.r - cn Ca 20 Fe 80 Mg 0 Ca [U-ti 0 U Composition of amphibole from the Wolf River ct;:- (Symbols listed in Table 1) LU J -[& L {Ct t LY'; k LUT1 u: batholith. 3Tft1: a: PUETt U 6. Ca 20 Fe 50 Mg 30 c I Figure uc Ca 50 Fe 50 Mg flhc �22 41-3'5' The (13] hastingsitic hornblende in Wolf River batholith is closely '57 the 501, ;-,-. 05(17'] i 5751'. similar in chemical composition to ferrohastingsite i'7135145: 7(17:5175 1(3 41.315155555:35. from 55/57 Finnish '4530-5353/ rapakivi 'ç',7./512t*z described :.o'/ Vorma UVL(1."', and 51,551 (1969). 415375513i1 by Simonen 301137 17 'i Olivine, Anhydrous mafic minerals. 1114 '(4-414213 4144 (317(3 clinopyroxene, [0 57(I5'5513.'OU/L I orthopyroxene, 7"/3"55:../'13 /i5775; amphibole, and biotite occur in the Peshtigo 10415117513 sos 7 '5411' (151354- '13(7 .511(1, :4135(07 monzonite 4'55 trachyandesite, 57,03 (I': and 3/15113/3 and where generally surrounded pyroxene amphibole, .3775504 olivine ':7753 51/I is 04', 5(15% .5' .13/ -'13557/415,0 by 3041375 or 35111 (1't5( hiIS 21: Electron probe analyses have only been completed pyroxene, by amphibole. 0 ci:5/43(l'(; : 75/453-[5' 345-51. 3173 13221/ 53:2.3 441310 13553 (15(0' 13'(1.53 Fa for olivine one specimen, yielding an iron—rich composition 5413 L( from 115(11 01/101, 5 T31—5(1' 5 of ,,5( L'•lk'L21• 1321:ss However, it is evident from optical properties that olivine 92.2 toi1, 92.8. 'V '27' -7. 7.30751 (17 4(s-t 'IrlO,37 4101'S/D 130410 57 iron—rich from and pyroxenes as well, will prove to be 3:/3( 'sojs-ss.17: •/k•[ other 354:.': specimens, sssur.. 57trs #n 5:3 3 (1170, '241. 545(5(1.14 when analyzed 114(1' by '5717051 probe. 5 :32 electron 4'7''," ''/51, s C 17(3 '1 '2 3 C Similar olivine from green and gray varieties of Finnish 55157:414, iron—rich 5C4(11--'13t1[l53k :(11[/ 35 (15[ 5041's 1551312155 4(2.4151(1: 41 353544 rapakivi have Simonen 513 -(1553 been 1/5(41 described S1531E (1961). 414155555' by 1 416' :3.4 s The Wolf by Alkali feldspar. 441 4 River 55541. batholith ('55557 is characterized "413 1.5J:5 çsrxs13 41 1::T-1;:4; perthitic hypersolvus S and [:5113 quartz 55 which pink, 5ft/1(A554 granite (:1113 54541 monzonite, (I5,ic3/13.s in 21c:2 3/515 of perthitic alkali feldspar predominant mineral. A variety 41 5L-/k 35 is 47 the s-s :/:4513cc5C513r-1'. js:its13ci .2- LI #;T13L' patch as textures are including sss exhibited, 2147TI41 vein, and 41 tssis:21 perthites, 415 film, qLCS2 433541 i?t1 In general, alkali feldspar in granite well 7113(1 as 41 combinations 31535 51:13 55i 5/I of 13 these. 55557 1755 :/) contains larger amounts of extensively 313125 5'11133 a331431 L4/I(V 5'. perthite and 413 more i:/133 '3515 fl5.(1çi5 developed 5:4.: 553I grid r.'t:.21 twinning does alkali feldspar monzonite. 15134141 5(541135/4 35 quartz 13t41' in /i71i21T/5I than /415.13(14 311r:riy'(AL -5 513- ' ',s5. - - '13 21 i-tI— L from only To date, feldspar ''1-l21 alkali 41 'L5 /113 has 13131 been 54135 examined 41 detail 414335 13, ttXS/ 135531(5 in Hager feldspar four units, including Belongia granite, Hager rhyolite, — 141 " 'F study of porphyry, and River granite :. 45 Wolf V s:s X-ray "2112141/ 11r/' s-41s.41 and quartz 1v-: 141:15 s• sJszC2 monzonite. and Stewart nine specimens, utilizing the method described by Wright J —1 (IL _5 4 1155. 53 feldspar (1968), reveals that the host portion of peithitic alkali 41(1 41- 21 C5oiLL 53 Th7 st;-(:yssC 51415 312fl 5' in 314 these 13241 units 53P1 consists 51551335 of 27 maximum i55(7'15( microcline AYA11321 5c with 4>:• compositions ofr Or 99 22 to that yielded values of Or 95 and (1 100, ... except for (13/ two 5:/k specimens 443 97. 7 (155(215 71!3 t35735 s21 13' T35V3..•; s' — 13 i5/ 1 '1 t 11 I tt5tft5 21 . 2© samples and Perthitic 3•-. 54.55 alkali:- feldspar 12 -S1i; was hand picked L,. 5(3 four 5Tht%t TiAS Tu5 sA:cTs from for K, Na, analyzed by means of atomic absorption spectrophotometer : "55 ;5 The and Ca. -m bulk compositions of s perthite obtained lfl this fashion are -pITASISS in Or 83, 77, 76, and 72 (Fig. 7). 3Vi 0/ 54 :t32'}3 444J ?.:1;4 sits . f4; tt5554 ir . Orthoclase, and feldspar with intermediate /55k Y (:tV alkali 212,713 2T5 A7(5751L2. microcline, rapakivi (Vorma, structural states have been described from Finnish 0' 21 3.1C355/ i12121:'.:: VJUSC::..; from the Wolf River 1971), but has not Vt 1 557 yet ILAA4 1$ 15 i55J orthoclase 55 been V353(A identified However, alkali feldspar from batholith. &_,. only the more silica—rich 1[T JV•% °5JL5 lithologic units has been date, and orthoclase, :35 2154. jtes•. examined .rr((!;:p to (1:1. ic çi5 if present, would probably ::2 occur in C7 units 55 the 51; Waupaca quartz monzonite SCCCL such as 21 (wiborgite) and Peshtigo monzonite (tirilite). (V c1n/k1fl:ri t11 Li 3i.A3 L 21. s /lIAA'( 5T.ZLk Plagioclase in Plagioclase. 57 the •54 batholith 1 is relatively sodic, ,5 .y.T:5-% i:s7fl:21 ranging in composition from sodic andesine to £. albite (Table 4), 4.5 r:iç Li as 215 Within each determined by universal stage measurements. L lithologic Iw1 i1 composition on the order of unit T 4•'r::; is a3 variation tWt.:-J/kc, in plagioclase ;irv' there L2uiytL and phenocrysts are consistently more calcic anorthite, 5 to 15 mol % 2 COAC cicvJr. Act21 Slight normal zoning of phenocrysts than 1/k associated matrix grains. :.2Tzoning has2'Ttcti7 only occurs in allr units, but rL4 oscillatory 21t :L o[1t been observed in the Red River porphyritic quartz monzonite. ;:V"CW1 — I fl ncrla t ci qiz'i I L L Cz lA: irç �' ti iTii11Zi.L7ci zoned iiii ;;:c)jirc1i4 Li -LnLzr4 '[:J4ciiLLN cores. roundedzUriU enclosing overgrowths subhedral o-c to euhedral of 1c1;rtJ 11 'I'7 consisting malacon the is Zircon 1940), others, and (Tyler, variety iiff. cJ.1Ir-çci7iJ2. ' Yi'TTTLiC also I,ccI3 is ix mineral, accessory granites. rapakivi Finnish the in common btWci 'V :VtFTi. J&cj L©Lithe c€ij in Ti tions ubiquitous most the Lqc Fluorite, batholith. River Wolf cr,'-j are I TV'' ILt apatite, rutile, iT combinavarious in present sphene and allanite, i:iiTitT? magnetite, zircon,'t Fluorite, minerals. Accessory ILL I' I I - iriti1-:T TitIt •TV. - cIs'.iii 3n'ri • ilmenite, • ijh .crc:ii ij'f - • - • i' iY'TiC4ii, rapakivi LT 21ii 7..L. texture. of development i:-- LCDi iic L L'i Li may plagioclase flCtt1('7 the in role a •:iic play by feldspar alkali replacement of ti mantles of growth IL" IT pin 1ti1Cli1 c2 TSU.L yi'2 related genetically are ii that and and perthite [i -c&L:ii2-uc ic;Tj. 'i2 rLcI':PL 1 'ir.:Iic:2 that suggests observation patch of formation This plagioclase. •1Ti with continuous rjii i niair:i: tiCi r'1ii2c mantle the to similar compositionally and optically it •2i'q!cLTL 7 •nplagioclase situation this In feldspar. is perthite 1'i1I,l1i parch the in i'1iiJC •"TitTJLi P 'L1TDDL alkali mantled of core the within occurs commonly perthitebT'LIL',i Patch • Ti•c'i ic'iitIii i-i? £L. 4L i-i' "'- --- ct--irp. I :C' iiii i:pci ciit tI'I Lint L'f:CT that Lt—ic specimen. 1.7: 115d1I2iIi in fr-iiL2LL'-I phenocrysts iTiz;i'TL:c plagioclase the of part sodic most the to corresponds 9-iii77 specimen J-'iHT77,tt .97'i'27 any L:' in YM7-composition iPtitiTci' 79a has TiTit7';iri7ii that plagioclase mantle individual 'I17? tT2TT c-cLLT1Ci t2ciiTL i: 17(7 979 ii fliclIiI but Furthermore, quartz Waupaca in 23 An about (wiborgite). monzonite t2777 in ri 7XL17Xf7I -PCi 7'a has .T 9 An TIL( plagioclase ri Ci' Li' Li granite, Belongia the about ofii 1iC7tJ.t7 composition p174.9 exaniple, 'i Lc17?kFor unit. that yn-. ; '1i ULi 7-1bulk :T1 the 7C1LJC. mantle of i-:pt chemistry reflects clase IL:lJ: " ";(? lithologic c;S14c:7 ''7'1799c117 'i2 a Within l7t' IL IcLY'9LL477C the 'i given plagio— mantle of9 composition unit 9'i:L'L79''7iT 217 1717'Y it2iT:. /7 ETi13 774 TCi ' Table in listed (Symbols y-j(;9L 1);c ?1i1 i' p17Li1' C" granite porphyry. feldspar Hager and i17Ot7 WC79 4C)Composition UiTiIi'LiL4C'9 the from nPcDtej feldspar of BelongiaiL', 14 — Or -' • 'c • • •: - Figure 1. ' • Ab 23 �24 Table plagioclase from the Composition Coepoiition otofpi.agiocJ aee .Cooii the 1$ Wolf River Rrvoo batholith • -. iThcC ielc:oi.r P°l°WW i .-—-• = =_ - - - j E.oiIetdt9 3e-J.oo1oI1&. - =--•=-r••••= — — T:T'.l = .LdOt}cJ P•:loer ra,mto 1uoI1. çrot?1 IrDroo.,Io = - jFzt_ttJfl 1j Ij = = I L 0 10 30 20 )ThL rnol % •R•:riT. i±oro ?orpIh..vrLh14 Or:tIThflTO 40 Anorthite or larto graln tetrtt gfl1O Phenocrysts -oiemoero1:e or large grains Matrix grains 4 �:33114 .191' 1. 113113 :1,1c:,tL.:1111 111 131114 773.1-31 31 2.21437, 33J, 'in 1171' 1313;.: 13..$1133.9: cI7111.4, '1471 :141147.313351 155 u7--T17 71 311- 131 c31311414;lc 053.1721173:33'.- -17- 147112.3:14 1111111 14.137- :1133371317-7-353,3 2. A foliated, gradational zone about six inches thick occurs between the Hager rhyolite and feldspar porphyry. The feldspar porphyry is believed to represent a border phase of the rhyolite. 3. Dikes of Red River porphyritic quartz monzonite intrude the Wolf River quartz monzinite at several localities along the Wolf River. 4. The contact between the Wolf River quartz monzonite and Belongia granite is inferred to be gradational, because of the change in lithologic and mineralogic character displayed by the Wolf River quartz monzonite in proximity to the Belongia granite, as summarized previously. :0:3f3 32373 7 4113: tT21 2141.1211111 '11 1T1113-;'l: 31,li%1'JC5 13314 ff: 7-111 14331 1114'. :., 11 2313111 2:ThtrvlIl21l; 111 1 14117- 2111 07 111413-21141113 13 12211-171i1 3111L%;.21141 17','1131113 721 1111137-117227. 3.311112113 121 11::7c3311::6:ar T21-1313 313.1 0111L'0'2 14l,11131113 11 7-121 Ilt.131 l 41 ,L I: 121.31 :1t7 14:1' '131151: 4'15l9 11-31 14 ::14'.13721.: 1314 in 3;. 7-2212-1733 13,cll':i111 .-cin7- 72133111; :1911113313 1:11-7-3111 1117- -Lin- 71 7-' 1T. 31(4 3117 5.3113-1433) 132-143,1131 311-11L'71 111? 2'l '11 17-215313; T143T1: 12111111:1,124 '1: 7-14. 27-' :1:.%331323 cIt 3147-115 1414-l31lj 31 7121114141321 CC 1114 -lt*3(313;147 114:;:;t11. I,11& 247 c-23'7-L .317-371 23-4 1313 :312351 71.11 114.11143715 çç7-1 1:131733: 133 24 11-131:1:17- Peshtigo monzonite and trachyandesite have been intruded by dikes of Belongia granite at High Falls reservoir on the Peshtigo River and on the Oconto River near Mountain. cr;: 17 213:. 17137- -c112.711"1:lI 311; 1-::1:1113:14 :1:17-: Internal contacts of the batholith. Contacts between different lithologic units within the batholith have been found so far in only a few places, with the following relations: 514 1211 3-13371 511 22.21 31 '3111-114:; 113113 4112:-) '111111T747-'1117 .C:i'1V731141 3114, 1-33-13.2131157-211 211133.71131 ii' ,l 31 1 71:4 14:3:7-11: 3)11311 14Ll21:21: 11 7 -1:1451:3 p111c314Ii !114 '7-33l4C-247-- .tl2A1%_1l:1111434,331:r:. The second feature of importance is found at the northeastern end of the batholith, where the Belongia granite, Hager rhyolite, Hager feldspar porphyry, and Peshtigo monzonite are arranged in an arcuate pattern, perhaps reflecting their emplacement in a ring complex. Such an interpretation is supported by the distinctly por— phyritic textures and high—level characteristics of the lithologic units involved. In addition, metasedimentary rocks that occur in the postulated ring complex dip steeply and have strikes that are concordant to the arcuate arrangement of the enclosing igneous rocks. (Ring structures occurring in rocks of similar age occur in the Wausau area, N LaBerge and-Myers, this guidebook.) - _ 1 3311 5 133 2111c 21.7-. 11 1-c.31C0 p213 1147311.3111 1111. 113157-' s. inii 21 7:33 111411. 1141111 2*:2i7-.11r1437 3;3133311.1'311'3 '131111211 141,1233 : 31-7 117;:tl%-:33 43173 :21 2. 33143:' 33114111214-1' 25137.133' 2331 'Cl,clL1: y11c1T1.#c51rb-:1 721- 43-'11'': :7-: 'r :11:1211: .;-2111'13133:1331a1 112-: 11-33112i 1414 3; 11 1:.t1;14%112'J 111:31521 1(7-,.73,1117 C1413% 77- ''11:1113,3131n 1121 73 :11: 33:; L3 ..1'33'&43 7- 6314331' 7-913 21331341311,. 91432142 0-7110 .13:-i31 11:c:7115141131 J1414-7-33 112 1731; ' 3111111117-.: '11 'cii 41'1u1421'cIci1s ' 13,3373.213 1111:321:14 4 S'1:1:31: 7-311 1111-c',3$:13 41'l : r1r1n713:cj2.21z1131o 7'f"'l31r: 13; 7141311 3 73,212113 :3:-' -311111 17124:1114 l 1414113112; 127 1r::11)31,2, .3131') : 13 31; 7321114 173214 411333 114733,1314 1'.71- 17 13C.:'1-11 34 221111.11; 3737-1117213 214 2-1314 41731:12 141 1314.427- 1131131537 7133!.'131 2113111)511 14441111131414 :7-11:1:; 3123', .111723113 433'1J1!L33: 111 31,7 ,C17111'3. '77-4-141 ,141.31413', 121 321'1'137- 54111117111 ':3117-rI-Ic' 11417 137-3111111 1131:'113;1114 1214 7-3133141113317 1:1s:'t 113211 1': 1 14172 .71:13117 7-1151 . '313j% a.T13121' 1'373 212 14111311111 P*1 '$131111414 tIlt II, in 1131,k'117t I 1u211317-133'7-,L3 31"7 4;,311.ff.1'3;L :47- 7; 1131 _12412111 14-14L311 -371i3121 37 :-'lljl 41i3 331347 4131175'7"l37 4." 1111I1,.1 132113 '11413233231 322 33,13 11.11" Although structural studies of the batholith are still in progress, In two major features are readily apparent from the map (Fig. 1). the south—central portion of the batholith, the distribution of the Waupaca, Red River, and Wolf River quartz monzonites defines a major ENE trend that was previously recognized on a more local scale by Borst (1958). The contact between gneiss and Waupaca quartz monzonite probably represents the southern margin of the batholith. 1 .144:15111-53111. 1,c3::. ::( ::' sIll -12 _'&11 14 3-31 14117 14 2311 c—, ,&31 '17 r 113147- '1 1 " '113 1 '77 i11'5L147. 1121lC7-.'1,11-'331"t' 3313,' lf%-:rl,©1r, ; ,' 7-24221-2 .51411 3;':' Many of the granitic rocks in the batholith are Structure. massive, but within some units, in dikes, and near contacts, feldspar phcnocrysts may have a planar or linear orientation, presumably due Shearing is confined to well defined zones along to magmatic flow. Some of this the eastern and western borders of the batholith. emplacement of shearing may be related to the batholith, but some may be later than, and unrelated to, emplacement of the batholith (LaBerge, field trip locality 8, this guidebook). 11t13217-1374137 14;1 312-23:135333 '31,17-3r;37; '437 111'7, 'F;.,;, 314:213313 321: t'%'7-711117- "11 5151113 .14213 1331 73121713 31111-7 'c'- :113tT,) —$ LH11.34 3312 13312 37147314113 15:31 5:721-41411137 13 111 :12375 742 14 -32: . 31143 '.1311111": 11 31:111131*31111 07 5114.11113.lI113111414J21 33111 31r12115 :14:;; 7114 3111343 1.11.1 117,1 .1 r33.1.1t...23 31:; 2.112%:. 133' 12Cr,: 53' 31213,.: 32311 111 141:3191111I:111 11111111 44 11117-1137114 21' 11)51711 7-7137131:11111. 111.323-1 ''i'11 113,:53.3111:'.. 3313 -33-14;: 174311114' 111113 14 7,141:c7, 711'433311 '3' .7. :1:131116 L111'T131411-31 '?l51i'11l1114'3.in1 c.:1c1:, 14113111,231: 3113113 - 11317-17-1 .3:1: '1:1 31141s317'll 7 '1541113 14411 111 STRUCTURE AND CONTACT RELATIONS OF THE BATI-{OLITH 711,71 17, :7-171.1 1113 31747-11111737- ,1741 '077 3J1 l31tTl'7- III1I 111 37: 25 cia �26 ocarI o 070t2 of Lt bab- J! tio m::rL1.i,et: pt of In the northeastern part of External contacts of the batholith. ::.c Lcowl a the Belongia coo ac:0 a±cr•t several well exposed contacts where tioa :ttJ 0 .00 afoot a are the there 0 t batholith tLtkLc. U1t- tLOtOO.OtX0000 metasedimen—OO0 09L2 2'; and 0 LU0Z ptoP 7200 intrude metavolcanic granite and porphyry coo Hager feldspar to 2 1o!flal;1; act ri):-' sharp and discordant, and In all cases the contacts are tary rocks. 000t'0'0000 present in the intrusive rocks. ot oc3anCc1o chilled oar0ta margins are commonly 7t000ff't cotlttO : 0.11 oa iJ : fl :ia fotrof ca rco 010.0 00. the assemblages, much of &c 0 L'0rl0 WOO, basis0± oftEa000Ot textures and mineral 'o1.00o ocoka cat ha intrusion of the granitic rocks can be CO tjo ft rW 'rI 'o tooof bya contact metamorphism induced o-c,tatt totorcoçO :'f too iftiacotacy However, the discovery of 012:01 footca -. facies. fob :01-i hornblende WC coolo ltoot',i: assigned hornfelS to' the f000ti to ;a.bcLOt00 201 1.0=2010001 cto -oct o assemblage, quartz_biOtite_mUsC0vitePota5 .bbo co01t1 the lcTos;'WOtlf apparently stable tOo 0001 ;:ota2Jat410'L;;,0 rock pelitic a; specimen 01 aco'onof of ;a L 0200 metasedimentary feldspar_afldalUsite, in a folIo-pat •cLJ oootC La 0010 01W-. have been the pyroxene hornfels facies may of flo ooo.u;002sO 010it:0' .co-.oo O07 suggestsfathat conditions 0.77010 foot .o.o'01It f.o:a of roT at 07007 r:.;r Ic tO-a •ocoi'Occ 0 in the contact Scapolite to ,:cf: :; 01 is relatively abundant f cro]'L. attained 01. locally. 7114 i-ccbatholith. Ltfocf ttI; 2W the 0:; I.:oo'000,1%010102W:;at:tr-0 of metamorphic rocks,21012W attesting the halogen—rich nature t tCC00, a-ac to 0.0010: On the fiLo Co 1 2 CONCLUS IONS of cotta cot 0 oafaIltat000 been fo to point out1;the existence of toot oat till paper The7';.i purpose of this has Loot 7t ct 00201t0 tic and to describe its Woo: '0.0 zn:1 northeastern :02LI10Lmassif 701 :.:Lincart OFt4 01W- WisconSin , a major rapakivi c ;aojo-r 2W Ot 001711 o01o-7rI o in It seems appropriate, 101 characteristics. crcrcI.o?tZ ;-ofmineralOgic iLt 000ta.0200 petrologic and ffn batho— hypothesis for the origin of this 100 fLo 001 Carl of r2.cifaC-0'± i-- offer -141401NJ 01' conclusion, to o±'tr- aa working :1cn.cl aol ct: frfuture 2Woo studies. c';tai i to, direction of too-loot tO 0712W too tOo lith and to outline the blob Ci I must talCi take 7 r7' t-atLo'I I ;t coot of 0017 the Wolf batholith of 'oi.I River too- scheme 14-iY01W; Oc 0origin cot: Any forIcrthe features: 11170 'cc LC11/ into accounttOo the toOl following !. 1) 1) 2) bulk c.: of 'L 7-Abc constitute the 01,1 granite f 010Ci1 0010 05t:: 1 ocota 11' 1200-00 ,0 and hypersolvUS monzonite oct quartz the batholith, in0027102W nature, 7. c!'ZCP-IL ot 10 epizonal the batholith is io :oo,1vobtti; a'•ooa tOO batholith the tOo ta:Tho) ' oft plot itt-ct near ;!!rto. of oti the granitiC members otOfl7t a,:ft A the compositions of 00000 displaced 01 normative . 4:Q—Ab--Or, =001o1- but tot toO are Ic, terms too: a of granite minimum in t-a;ott•o o!oLo!L!lilr .0,0020 7-c toward Or, :0111 0 t'ob-t7fli feldspar by cI' alkali andratreplacement to 002202 of fcc::- to is -cct0'-011. 25- 012 c;,00c of. there extensive mantling 'P.', oligoclase, aflbote to -clILIfot 000. composition from albite to It ooocol01050I0 plagioclase 017,01200 ranging in respect 02W010t oa_with :2 -7; talc o:t to to be interstitial :ik.ill020 00010)100hydrous tend to co 001010012 mafic 177,t-tc minerals IL! quartz and feldspar, and on fo1tIo0Y 007012003 of Ltz:0 biotite ;' I cthe expense O1717'AP growth noCiCi -A .11 at Oil act.a:0101 apparent late-stage there Ut:---: is to rn-i of alkali OOILO17LIO feldspar. oil. ' 3) 4) -fl ,fl 5) P 6) t'rocoriginated from laothcJ,Of:2 may coo hoc: Wolf?:t River havecooL1oL0-lC1 or '7c'o cOt batholith ±00 oogo.ot that tcti'f the We suggest H20, initially undersaturated with :n çMtc ct0.0 0-C parent jJOi'tct magma, 01101 monzonitiC a 0 pquartz taboO 0 crustal material. .1700,12170 700=-0 i.atcaig 0117-octalpartial melting of00pre_existiflg -70l derived :'AOSd 00 .21t that was by J0L'."I1OLJ. batholith precludes I (87Sr/86Sr)0 in the 01 1002 An average of 0.705 for 0100 value Cii origin 00 000 1 0 i20tat.i 1410 with an crust but is compatible lOt :lcI1tlt 5 01, from focat older r hO 70 lOiittl,C 0' derivation granitiC ott: 50.071012 :':-OcOJOi volcanic and plutonic * atatmood° basic 0701 and intermediate lifor: .Ci,O.t!: (10 0001-0 )77 older from an terrain of 01001 --i't For example, partial Nil' eo0J-c. ±:folotllIfl. northeastern Wisconsin. 110010. 00aa in It ;1.Ot000000717'O material, as09that :oat01. 01 such 1090071 101140 (mean 020-0 granite or :7'10!L0t) Hoskin Lake 2,tLhc,000170Lc co,ast-zmonzonite 0110 -01 10 01 melting of Athelstane quartz trIo IJI cci. LII). years 141110 ,, million rIit a c:oA 10, (87Sr/SGSr)0, 0.7021) after a period of 350 , ,01" 0 Rb/Sr, 2.5; 55, ftC. ratio of 'OtCf.r 001701 of 0.714. strontium 01!.initial tot I 01 0,0-otti .710 isotope :11 07 an would produce aa :7112 rock with nIl 7 pt-cl'017' oh-ct oortaltt an abunMo northeastern 'ocotfcae$°' Wisconsin!, contains c'ao-::aiia in 'to: terrain However, the toto older fb-o'o-000T1, chemically equivalent oI-::amtsooi :01701 17th. intermediate volcanic rocks and dance of -c-I basic La boo tocO.0'lr0k'5.CL000 0100- tcfit material would 01015 tx'IlCta 00-0 'i'col .1 be of :2W,'o Rb/Sr for b-c this crustal 0101values 01200 os: plutonic rocks, 01010 00 and o'tcro f and Ot!0OI0 others, 1970). 01171 ETC.Oc 01C'I I Hart, and 1967; c.'.'21020: 00.11 others, ACt-0 17fl0fl 'jless :C than tOol 2.5t (Peterman, OIL: 77 much irtta2.Hy oa1t1J.'i toat I'll 3 ,i I I - 1702, �27 i the mean value of Rb/Sr were 0.6 or less in such crustal material, partial fusion after a period of 350 million years would yield a rock with an initial strontium isotope ratio like that in the Wolf River j .4c. icc I[ L1 ctr ccl I L-tn ic IL cc1 I N L. I cc' Ii Il') ci I 1111 1 1y '' cccc flycSc r cccc 1 I batholith. c" Lh1 If nYc cc. Future investigation of the Wolf River batholith will include: 'LCcIP.2Fc c1cS1cc ccc O©_LJ1L=iccc cic7IccnLIr -r9 F) Wc1. ccZcc4cc additional mineralogical studies that should enable us to evaluate intensive parameters, such as T, Total' H20 O2 TNcEcicccTcpcc lI -- 1j In cc1 F, and tc.n-iccFcIcL-cc and detailed chemical studies of major, minor, and trace element contents in the batholith that should provide constraints on the mode of origin of this rapakivi massif. ;cci;c;iT1zi yi iic -c *cLcr cccL-- ccjl cYtc icicc cci cIcccc1 ccc i:q,: cc 4iJfliL 1ELI c'7qI' cP4©IF: cj j:-crc2 Lc1cLc 2) Lptccc 1) �28 REFERENCES of Big Falls, ':-pc:c9.c. cC W7 Ccl 2424.1958, 12 The Granites Borst, R.I., !lm/.c,,2 9.7 4Wisconsin, •lcLc Madison. Univ. Wisconsin: 12,2. Thesis, M.S. :) 24. Wisconsin: 21cm granites of from the :2 c14c4w' -cm-22 ".2. ir242c2 Elders, \V.A., 1968, Mantled feldapars 24 .c 11 cmLc:::: 2-i 37—49. 2c2- V.- 76, p. Jour. Geol., -. ,1'.c-citccPtIL'$ of :4 perthite, p. 55—70 in c-:L. :24cc.) 7: significance 12.4. 1953, Petrogenic 2iCi] R.M., Gates, cl plagioclase: c.cm42'cHcrelationships re ccm2L. cc-; of 2c1.cc:i[ ppetrogenic .241-; Selected :r-nLcmcm (ed.) R.C. Emmons 20... ?9'2l 52. dC :ciirr0 Mem. Geol. Soc. Ccc Amer. - "• dL'AElectron .c,2:t.c', 2;; -cd: ij,ctc-: using the ,E-cm-L analysis J.F., iccmcmr.1..cS Qi21968, .24. Rock Gulson, B.L. and Lovering, LJ 2)i27 C2 cm p. 119—122. Geochim. et Cosmochim. Acta, v. 32, >22121:2:" Probe: 2. a volcanic rocks: ccm2cmcmcmcULcrC.'c2Cc:2r 'cct an modern .24'::;4 1970, cl:2- 2:Ancient cm-C. others, Hart, S.R., 52 and Lett., v. 10, p. 17—28. Earti. Plan. Sc trace element model: .:..:j2I:Lt(1y4.'24 .c.:flcwi.!cJ-r >2.7cJ..;1.- c lower I ccc' -2:24 :ccIcm-d AnorthositeS and magmas from the ;'-5. rapakivi, :124. H'C5 Kranck, E.H., 1968, k:'uct2'c72'.9d Rcc..'.:dc:. :244.7 Origin of anorthosite and 7cccmcccc (ed.) '7244 Isachsen crust, p. 93—98 :1:': inY.W. 18. C':--C i24c -l12c Univ. State New York, Mem. 11: cm .fl.,i;; cC :ncy.r:ccd.t: cc:2cc related rocks: and subcalciieroUS ccm:cm 224, .i'cm;:). calciferoUS cc of analyzed cm dcit2I'i cC Leake, B.E.,,lc:2?. 1968, A2. catalog c22;'d, Paper 98. Geol. Soc. Amer., Spec. Ccci, C..c..'t'r-. amphiboles... tR:i - 2. iidc.'\i = Si02 to NaAlSi3O8 — Si02 and KA1S13O8 —.24224 .. 'it> systems Luth, -c,. 1*22). 1969, The ..LniC, W.C., cc betweenc H2O content, p1-120, and Tota1 ' 9 t1' the relationship 20 kb and 267—A, p. 325—341. 12227 ,24'; Amer. Jour. Sci., v. in granitic magmas: '' L ).21-'' .' [ - .-,i-cc'c:cCLcomposition ccm,-:c,24tic'c and ccC >c2cccz chemical relation 241'cL•c:-. between 2-cm Nockolds, S.R., 1947, The Amer. Jour. igneous rocks: !:-244r221 cuiT:1 cI r4dL2lLkiLC2'c :: the biotite micas of '12922 in paragefleSiS c--'. 242,c., 2422, p. 401—420. -. 245, Sci., v. 224 ;u24c, 24':-24,1y Mineral. 12 Mag., cc :2.t7' 'cmiTanalyses: mJ.24cm ccc.crcm'1' c; of granitic rock '2:224 Mesonorms Parsiow, ';y>2-di"- G.R., 1969, 2. 22). 37, p. 262—269. c24-2424 v. . ].'C' >2:19 eugeosynclinal Li some 5::>'>I: -: ratios in ...]:2447', 87Sr/86Sr .2,'2i'9 1967, 2 Peterman, and others, 24±; )i9iy' Z.E., 22::'::magma 24cc dc)". cd bearing on the origin of granitic tac ic Ccc'.: 424 cr24.> and iriS their sedimentary 92CiJ'P3i].2.24 rocks . : 4.21 2; 2, p. 433—439. 2-cm24 Lett., V. '4o ccc' 2-Plan. 24:, Sc 24 rcmicc iCc belts: ':cmtc - Earth in 24. orogenic ., lIlt.". . iron biotite — ,cccmcmc2cmc'7,J1> determination of'>d2 c;2) Rutherford, M.S., 1969, An experimental 2 L, 10, 1:,,.:,. p. 381—408. cccmcmcm.449 Jour. Petrology, V. equilibria: -jC-241feldspar icm±:1;,c'''rhi:lcJ;"' alkali t'r,::24'124 4* 'cr22 its -9L'U'I'.7-1- rapakivi the chemistry of the east Fennoscafldian Cc ±2cc d%2:c!:C'7 24 ?:"'d On Sahama, T.G., 1945, 2424 136, p. 15—67. J1'.2,.'L22d. v. c;c":i Finlande, 24472, comm. ccrcm geol. >; ciC24c: Bull. graniteS 'ill,, .. Savolahti, Icr ci.'::'':l, A., Finlande, , 211'.,L ccl:. 2cm Finland: AhvenistO massif Cc: 24 :c'dtcrd ;ccc 24.' in 1214 The 1956, 114, p. 1—96. v. c 174, from rapakiVi :2cc I'cmc:224;' :7: CL Simonen, A., 1961, Olivine 2-I SN. .26. p. 371—376. v. 196, 2424 Bull. :.c"ir, geol. FcC , comm. ' FcrCHcC22 2411. •c2c,' -. Finlande, Bull. comm. ccc" geol. I �29 I 'J >? c and Vorma, A., 1969, Amphibole and biotite from rapakivi: Bull. comm. geol. Finlande, v. 238, p. 1—28. cL lEE Simorten, A., cL - c C,.71)ClfrTVEE5r 07 11) 1 ¶-c,c5 cwLc3 rTr. 1971, Alkali feldspars of the Wiborg rapakivi massif in southeastern Finland: Bull. comm. geol. Finlande, v. 246, LC::1).çY.I2., LlCC I)2t:) cdwf:L !J5LLLC7 caE: I II 1—72. 1flL '1): l_I ©ICLL p. cC7I7CCEEE L.tC[tcd5IC Vorma, A., Wones, D.R., and Eugster, H.P., 1965, Stability of biotite: Amer. Mineral., v. 50, experiment, theory, and application: 1228—1272. p. I 7)EEI diTcl.AlJ1l CilCt51)cL CLIEC d•dSl1)LCdi C CcC 1i 1Ih' I &tEEEi;IEEIk'EL I L?1) C? 7 3T57d cdi Wright, T.L.,, and Stewart, D.B., 1968, X—ray and optical study of alkali feldspar: Amer. Mineral., v. 53, p. 38—87. 51) LJiCcst rtld:;ditl 713: lJIlTl-l C 77&;J=d c,C, Cc-r.1: .1 . c1 C .cc c• L7CllC;C.1)liJ :cT df 13f0 �This page intentionally left blank �51'4.i?'71 11113132.33 >'1"" >, LI? 3fl 331 24.141111 •1'1c University of WiSCOflsln—Oshkosh University of Wisconsin—Eu Claire 1,,' '•,•i2.:327'7 324.3 of Geology, of Geology, 4121733123 377.12113131 /:. 13>33- '1 131 111)51 .17%:T :3::: Department Department '3' 23 11411201111: * 23411321113 0311 3313111413 ** Some of these problems are included as stops on this field trip. Tentative interpretations of the geology of some of these areas are presented below. However, we emphasize that the interpretations are based almost entirely on field relations, with little petrographic work, and almost no chemical or isotopic studies. Therefore, the interpretations presented here may be subject to change as additional field and laboratory studies are completed. 12143 3.'- .2'12121 4-1241 'C 111>1 133n2 4. 7151> '51,1> "1341S3 '35" :131312L .1313'' 313 (337113 133: 7,21031332733, 1132 1110102,3 14-271 ' 51-13121. 3.3" >11.14 7. (3.1 132.1711:12::: - 31 1 7.1'53 , :-n), ,'l lilt' 7.323; • 0:3:731143 773773231 37 1131 121371.73311' 7>1,2111(13' 7'1T3 '2./Cit1S''?-). 143:: 34' 117 13371233 4.113134.8 79711313 2111174-2 71 rI' 13 37.: 17713171:51 "1' 7:13 73151317135 '-1%. '1212.. 11321273. 7121273372 >' 322' 3-33.212 '3 4-'341'21j11'SL. 1211) '.591'11)732 ' 3174 '21133512121 31317 132fl33"23411 51.;'171h1.'34., 3212 172711o,21) 71217"4L ,s7 '3-13310 111111 327733127 11 42'lll32l3i'1167, .1711 "377. '31.33) '717.21: (.1%413I'711 '4 1711 '..'11,.311% 3131111 117.5 '1512117 3714; (33131'3 ',1414 133732131 41<73:; 31'31,'4313'< '251" i>7.1L71j11 16.11377 7.141 -4-1', 73314 7.721 1130 451:111.1 "11132 41211171 In 1969 the W.G.N.H.S. initiated a program of regional mapping of Approxithe Precambrian in Marathon County at a scale of 1:24,000. mately twelve minute quadrangles (about half of Marathon County) have been mapped to date. Progress reports and data maps of this work have been placed on open file by the Survey (LaBerge 1969, 1971, This field work has provided much new LaBerge and Myers 1972, 1973). data and has identified a number of problems in the area. >3>31323 1)723, 2)23)2.. 1:0 115153 1131371 '(13212273 33273312,1251 310 .33,3113,317323 732cc1J:'.': .51 i351"7',4'3) (1)" "'7.223 7 4-lfl 1'- 3, '<7121334 71,,.33131,:i 5x31%''15557f 711 333f32733<j33'17 E:3211112 :'1., '771)3312 135133175::Y 1121's17'13737(1 3122 1111:17.2, 17351772,,I713 7>7313 ;r 13 11313 77111,) 1113 '1113 33 '33251 m3 '31. ' 4i)027211Yi 1131331 2 7:73 ,i( C'23312 7 ln%2511'12':1'17. ("32. [: 1) (6<3,7 313211)33711712713' 1131 1211)7 The only comprehensive account of the regional geology of north central Wisconsin, including Marathon County was published by Weidman He recognized many of the major aspects of the geology, although (1907). his work was mainly reconnaissance in nature. The geology of the Wausau—Wisconsin Rapids area was examined in 1917 to 1921 as part of a land classification survey of the Wisconsin Geological and Natural History Survey (W.G.N.H.S.). These data are on file in Madison. An unpublished W.G.N.H.S. report by Enunons and Snyder (1944), and geo— physical studies by Vickers (1956), Allingham and Bates (1961) and Henderson, Tyson, and Page (1963) cover parts of Marathon County. Selected aspects of the geology in cntral Wisconsin were presented as the topics for field trips by Emmons (1953), LaBerge and Weis (1968) Theses prepared at the 13W—Madison and and Weis and LaBerge (1969). at 13W—Milwaukee have also dealt with certain aspects of the geology. Recent cooperative work by the U.S.G.S. and the W.G.N.H.S. to compile the geological and geophysical data on the Precambrian of Wisconsin was published by Dutton and Bradley (1970), and Dutton (1971) showed some volcanic—sedimentary belts and sulfide occurrences in Wisconsin. 1', :133211211132 112111517112 113 '.•4.l1[' 32714711' '1 .,acl '2313 13'l 31, 342123271 1P "7111L'311'1:31 "32cl. '.3 172.74 :71321) 1: 2:1"47'±5 117711 7 42t513° :1131 1.2 :' 34113: '1, 51'13'31, 71'3, L .1-141 37712 71')> 21,34',13" 713::, 31331773i '4, C 'o337- 1') i>321 2)21-' 1 74513311127 1y: 13111 >151 51:313 1 13144- ''23173.3.111711.7< 3323,131< '4 42 33123 132318 14,7: '331'3',3113'l1 4151':,1231'43.1113. ''17'4514' 13. 117.11011932 3322313104.33, ,3,,7734j(',7 Los.113.'7 .33:3371;3'3331$2371 321T :i,33,431$ .3. 3. 12:1:'. 7331131 p 1)3)3' 131>713 '33 1-'<' :1333 '213 .1)11' 77: '17.311>1): 3('312327'4 i1T' 3112111125 773 :4183 771'? 111232 233133 171.7 ±1:4 1 '4143231 14.3131 .127L1 '14 .31733'125 '71:7141s1323232 7'42113133rlhc4 23313 '3$(-' 1113231151 £311. 02'' 4.: :4. 32114$: 2.13: "L74r::r:cc'l.slIl,.''t 1.1'111'132 7)47 23113' 132 113 71132 51'1'7';,3315 >74 313332 17' '32132' 31111.7 13I1,.:''",15111123.± :I7s11c'1'E: 4)13, 3>4733 J' .1 6"3321325'4 3213'I'3(3 32'51: '133711 12.2"11 821.534 ,-,3211,11111,J ,31.•3'3314 9.1$: 711 317321313.331 3)5 I332'.13'I3lfl 2'31; 3113:3 1333 '"'1 ,,311LI1 I ';Q'33 32333213' ''1jI1It 332 71(3' 'i';,,'4 113 ';73 11:1513123 ' 13 .32 '.'7:2s37 1)1:3'l7',1$.771: —733 13.3 13'T3'1121,$ • 1$ 13713311171'323g331'l'4611517 311 '1±SLII4LI$21 14 3711.11137:32' .1370133 32:11472132 3'113 11313733. 372 .J32Jc '3312±" 3.32 - 4732313:13 1 S'co':r31i 37332 117 3'.L.127% $31351111 3'43: 41 32i"'., 4.1313711130)1.73 (13 733111111'3'3 '"tI 2'332.'71'.'l'L '%:3'"8 '1.11/' 3:313321131741 1) ,'.',119L'73113'314 117121 '1C".3333 1.1: 13" 11113(1119 33:7 ill 37) £':: 71 -- 4131:3.4-753. <10724. 121, i21231272s'1l :121::7'::c.13. "3 3273113,,7$'37 3241132 321111 '7'>(4 3013311.11 .n-62:o'c:vp' 1331-li The Wisconsin River Valley in central Wisconsin constitutes the southernmost extent of the continuously exposed Canadian Shield. Available radiometric ages indicate that these rocks are mainly of late Middle Precambrian age (Dutton and Bradley, 1970, and Van Schmus, this guidebook), yet the character of these rocks, their relationship to one another and to Precambrian rocks of other parts of the Lake Superior region has been largely unknown. '1J',,'1)7"1:3710: 52611 7:114 337 13'l 717 122(4' 33721111117174)3 311331 '333. '11112 43 14131:13 32i41712u3 72"< 327' 1:'1T4717 )'711',, 1:13111532-3334 :21230232 3111 24 323234 733') 341121- 31(30 3: 1377771.33 3312';'3' 33' 13 .l1121113321247 (1-2'$. 421-st ' :.11:%1s143113111"13 'I 134: '17131' '1331 31711) 11713111232; —>321) 31117343)12(11.2.32 11 1[11'7'; '.'4 .311121 '172321: 71313, 21151"'37I111 '131"" 7'3,<'.':2311)1:1)1323 '1" 4 '14.12/271 - 32307221' 3(33'7'251"% 2'3(32331113131151111 7721'; 4"112Th'7t 311434' 41' 11' 31'1773'34. 134227:7-1331 7>7133':14'44-,c13t113 '11214 137 3 ".7122313 '2'1'11171'211oT1371'1 32'51';5 :713111311:4131 13?:,.:, '74.33 7)1: 311,3 INTRODUCT I ON 513121331.111 Ill' Gene LaBerge* and Paul E. Myers** [7.123 7,324.211311723 751'5 11711' by 341321" PRECAMBRIAN GEOLOGY OF MARATHON COUNTY 131131'.41, M7113.;31i11'.13..'131,1 711 31 �32 General Geology .ici:' dfl!, River ifl Wolf 'fl'Y granite Q the ci;ii 'Cciatflt TLcci The Wausau region in Marathon County west of ciici1 Thi. ci.cc3. and c1 Tbv flcifltThS11%t .;:d kci4 pfl;fl:twccrc batholith is characterized by a.t. northeast—trending patchwork cci of folded hn :•a been flEfla intruded cci: cicii which have flE tc. felsic volcanic block rocks tid (?) maficci. to bjiflcflci faulted Ji ci tI cifltLfl •.c.fl.Ec events. aj:i1 deformational )fii3citfl and :cces]IflTh plutonic and :ccJ1 mylonitized during succeeding 1 iciZflL ci tJh ciciri (1) gabbro— -jC.,::Ycici generalized sequence: :i:flLfl.: The plutonic rocks were intruded in the Tkci p 'o.ci1: Li cy: i t.?'• .iwtc tti•ci i (3) quartz monzonite, flul.LCr .2 anorthosite(?), (2) diorite—quartz diorite, fl 3fl cirtflcj7cilci dia— L- Eci fiLciL by The granite isv cut ENE—trending cci and (5) granite. (4) syenites, 1flflk.3tci CtTL.JH,fl grcinit3 3S ttit; filotci Some granitic intrusions, such as the Granite Heights granite, cic.LIvfl rsTh1 ccie base cijfl.flF dikes. tflL3Lt: OLJLO fci' as indicated JL.t•C3JH•l by the fact that it has .J flfltflflflti ;icttIci b'S evidently predate this1flJ,:flfl-• sequence, t, i'h rcitz ,T-.clcirci.ci:-- plutons werefl t5.s younger :_ cicicicici been in zones along which some of the flflOi. mylonitized rfllLlbi.b .fl-fl1 y'cii- the tcici Granite flOO for O2flb' 0 cicir1i :'u -. Peterman (1970) established a 1600 m.y. age )Ci iflfrrijfl! Pcit•JLLr ficib intruded. Ibiccis TEtiui1'? 91L)3flJf rcitrci Thus, these ages ",cci' i Heights granite, and 1450 m.y. for the Wausau pluton. Ccci mci ci f0nt ton: ci! Some of the plutonic units are citLotorat 0rt , !1acJ ciiat sm are consistent with the field relations. 51'q'ci ::ii: ouiiut' cici.: contaminated and fil C'1.L' i-iltcicij cci cocii-uicibci intru.ve breccias; their contacts tend to be highly ocicot— cifluflt well— 0Th:,alflccontacts, fiCaicitci, abundant, a Strongly discordant cc zcfl:t li-yl: are cic:cic::L:: commonly mylonitized. !i&tfluit..citciflfl d1ci fl' cOcci21 , ta, t 1 ciJL metamorphic aibi- flflici of middle to high grade SflXkCI absence oriented :cEfl ru 1:Jti, and iflThtci' xenoliths, ciplcccii- cucit. icH crlitcc epizonal emplacement. cit 1Cm suggests ci ':ci: cu rafted xenoliths wallrocks except as lower nrccicicixcc: ci LJc e in a broad mylonite NE and ENE—trending shear zones appear to converge !c.flOcii' L'C a! margin to t1'c cci::r.:M ci of the Hogarty hornblende oacacJ i-iL to c:,.i1 parallel zone rc'ar near and the cciatr: western 1i.c.' bci2::JJoib) granite (Wolf River batholith). : ±C 1 'c. a- ciii -ra1- gr:tttc it: ti: !trily C rJC ' 1, flL3. ccc I 7u1] tnni-c'- Rocks L.ciC0 Volcanic i-i-X'1 i'by shear LvCL0.masses, cifliF3 generally separated boiccici2ci rccH4lfl cic cci as large Volcanic rocks occur 03JLi i-ira taaflTciLci ic air iitLl '1 Ti ci. and 'ci accici are basaltic to rhyolitic The rocks Ii-'fl volcanic ' cicici.or fihicirci, 20rci3 and/or zones plutons. nub. ra1c7-iciciLiC. and fragmental ircici- include crc. Ii-ir',pillowed, r:t Iciccic,,massive, ccci TLs The rabta mafic'7Cc: volcanics trachytic. 'ccc. less 1 i-nc. ci' Oi-ILCiLi are 'ticifldii-,. 3fr, volcanics The intermediate ctv.cc cci. iThi-i i-ccitt acicicic 1 i-Oct sediments. unitscat and associated cc ,uI ci'. Ui-i-i-, the "basaltic" varieties. rncty rEutflflTa1t chloritic and cucac more commonly fragmental than fl1 ii'CLbiat ti-cc Lob tuffOs, s, welded cclcioci'.tcifl include :CcLcsC 0 volcanics ;"i-riC cti- 0, felsic The predominantly ,,j, pyroclastic, cici'.J'Ll.fl •iThacc Ttr: nit bbas Eastt of the lJcc':.fl-' tuffs, laharscci,23.cfl'Oitu'fl and associated volcaniclastic sediments. irtilu, 'k,-:rc 3' seg00: ci'fluicilfl the volcanic i-b. cio -atciw ti- contact) in-c western.c batholith 'rC,u nrciu: the Rb."c'ci (nearer Wisconsin - £ciOci'uci 1fi1. River 'r''cflci,fl ciuci-il cdaiciii-cLbycolithologic Li'bt',j ci trends and i-fl '1evidenced chicir,t i-c' ci i-na.. .ti-2 have ments 0 ai-i northeasterly strike as :cMa:cc ''4i Land Ci1,.itOciiacci Classification Maps). Ii. b.- tacit c baciu'FlCtp WL.L1:uC cci on magnetic "lines" township maps (W.G.N.H.S. 1 -? icni:J-i-bc.-:'Ly. No 7i-• 000n'.River northwesterly. 1-4: b1ticO" trend cci'fl'ocJ is more tort: their tI—i- Wisconsin West of the i—cd, bcthe 'to volcanics cC L:i1, Tci'c nabbeen iranrecognized. ;ncntacd, stratigraphic 1Cm base to has yet 1 ci' — - .1' circcitici' a. :1 ''" i' "' '1 'lJrcrS' i-H ofcc1oan:o volcanic rocks 'Ca-ti-r :0the cnscit'tcc:u Hi cict It notycit yettcz:'cic known whether various "blocks" at is a' aoccci-n.ir. once—continuous sequence (a volcanic— :Lci,cccic' cnan.=c0'fl cci-'c. rf are segments of a ic'.adt at i-t represent different 1u000fl.iJciTit&i-Y 'Jr iTciJ to sedimentary "greenstone" belt) or whether they incicluci': occc.md1c'a'ci ni Ccc at work -T,ccic-ttccc"i,5.; c, from ci-'i-ci-' The answer may3-H not',te be forthcoming field i--i-C 0 ci'. "Ce i-fl tt't.ciLc episodes. volcanic ;J'cn'a;rtfi dismembered CLaim.alone. licor.'c: it:, Rocks Plutonic cit plutonic c. (Stop 8) 'P11: The largest mass of •tt-Lcip fl,•' :Hjifluflfl "ti-' flood Li-iCc Cflrcc1.;;ci1 Hogarty Hornblende Granite: i'nCi anCrLitt ciacoorcic acinulaL granite" to which underlies eastern itiaçc: s rccjci'ritiLe:rCc tb.: "Hogarty hornblende rocks cciatn;sci mapped isc the '-cob..': 'r t.o rnir Tigerton u-c•.u ciciZat lucc'ni-mOi-This pluton probably extends eastward to the '21:., a pLat -ci' rCca:.or Marathon Cci;:oty County. 'fltci 'ti-i-cc. to 'Ii'2H.nlcap9 lihologically coLic ccitc.a'' indistinguishable Cc.: act, 'i-r'ci- County, Anorthosite mass in Shawano is cc:a'r ibrc -H :c&at. quartz monzonite (Medaris, M uJ.[b.'mr oiccrba cicrcicin.L:1-r ci ci Wolf River ott the i-i'm ractc.' part oar-b of from the coarser 2 '-cii ticiac:'oj Itti-ccdla. locally intrudes volcanic cub :11001 L:y flTJcLi-0CL14i-? Ortu ci guidebook), and b..' .["fi,, this Anderson, and i-tb Myles, ,.ci Ti-ac :c tati-. 0': cc-l at It is nj,ri-u myionitized along the lc.ni-' Little Eau .mnaafrcErTh o.ircifit In western rocks &Uoucg its margin. cci. along 21L011'c? b.bva: Claire River. icc tn . r' ft cai �icc'!, ci.jcc'cc I', ' [1Li'i "ccc. rc' c LLTh ci' ci, 'i,ccci:.ic.ccC ,iT:' Diorite, quartz diorite, and quartz monzonite intricately intrude volcanic rocks in the region northwest of Marathon City. Alignment of metavolcanic xenoliths is northeasterly. '-cccl , ccc i", ic':' .'4.tccc.'. ccc: cISr,Sii cL,"1"c i,,., L[ccl'cLit 4LL :tLiCR: zcic',i cci' Tccii'ciccccic.;"cci ccc'.iici's'iic 5c1c tic. t,cc c'iccc'cclc Lc L.ir:ccn,cc:,.ci 'rrcicca'.i cc.'c',icc.cc,rcc,.c'cccc.c:ciL'{cc ti5 i;'i2ii c cc''.'c.cicc':ccc iccic,crclcC c2c'ci cA'c'ccccc c''[ccctui s-tic' t!C4 ccco.cc'ccci 'c1'Ei Mafic Intrusive Masses: Several small mafic bodies separated by granitic rocks occur southeast and south of Wausau. The largest mass is a gabbro body which interrupts the Eau Claire River mylonite zone near Callon. Smaller blocks of quartz diorite, gabbro, hornblendite, altered pyroxenite, and anorthosite enclosed mainly in leucogranite extend southwest from the Callon gabbro. Inclusions of pyroxenite and layered gabbro occur in diorite—quartz diorite southwest of Mosinee. It is possible that these mafic rocks are uprafted fragments of an older, subjacent, differentiated gabbro—anorthosite pluton. (Stop 11). ',LL!L cciii. cii 'c'. itc"i't cii ti,'lci'.cic'i :cc 54.c.ci'c:;c ,','T,c",yccc c,.scica 'cci5cciJ,,'cc. c cc':. c"s.q,'tccciC TO' c5'ifci. "Si,, ii". Tic: L'T 'ci:i' ccci ;C,Tccc:cc' ccc" cc'iccscTCtc7c.t UI_ ' '2Tc c.ciI:. [itci' .I'c'":c'.'A'S c .L'c'ccc,ct1t icc:' 'i''i.T_l'ictft ,dc,i'c,C .ji 'c.4't't'C it'. *"; c,:,s'c'.'c V:it's..t" '!n.:',ccct cii'St"ccc cctc'c-ccc iiccc?,_cci: ccccczcct cç..Zt r,crn.cIL"< LII c'.tt,Tc.ci :'i',SL ,c,c:c'c '4 ccc cc.tcc.c cc'. '''ccc' s'' scIc. tic::": 'cii.c'2 ,,.c!LI c4.ccC..cci "ccci "L'uii.'2.S. ic ;'- ccc' c,:5ttc 'ccii'c'i c,T;'rcc— ,,;',cRci i—4cic2cc 'tii'IctL li"l'.'ci [2 'ci'i'',ct Itcccc'briI'[C;ctc'ci .'.,c'Cl'LL ccc ii:'IIL L',,Ii',I''ccL,:'','5 Although elongated northeasterly these two alkalic plutons interrupt several major shear zones, and appear to have been "punched up" through rocks having a pronounced northeast structural grain. They are probably the roots of volcanoes, and their concentric structure must be due in part to caldera collapse. 'yccick"sic''c cc'c .c'c cccrL':,c: c'icI.cccicic..cc.cc.c ciii:': ':c;ci;ccc'.cIci, ,:. 'cc'rc.ccccc.:e'cc ',.ccTh .,c'_ cI.cc"cc ci'ccici-i ic'T' ic"cc'Lc'It' ,cirtcci'c,'icci S.t :c1'Jj(. 'C iifi'Jci tjiic.cc.[ r;',ci" :cicccL cci, i'cccidct ccct' [ccclii's .c',,cc:i?ci .1cc,!,,,, csiiyccy't ctc'I'ccH5t tic ;tccrcc ccc'.sci.'.'.c'cc oc'ci':cO.ci'Lc 1,1cic.i. ''5 'c'c'ccjcc'r'c ,.'cccc: c,.,':: The nearly contiguous, smaller (5 x mile) Stettin pluton (Stop 10) to the northwest is more alkalic and has more pronounced concentric structure. A border zone comprises gneissic nepheline syenite. A more massive intermediate zone of syenite and tabular The coarse amphibole—bearing syenite has swirled flow structures. core margin (1 mile diameter) of nepheline syenite is donut—shaped, rich in magnetite, and encloses a core of massive, gray pyroxene— amphibole syenite. .""[.cc''c [2 l]'tci"i.'CciciSL' c' Cccii c"citccl[c"-cctc:tii ci: ciit ccc''c.'cc',Ci :c ,s"is cc':: 'c,: ::,ccc.c:c :)i, i-cc'st"icc.::.3 ii 'jc •cicrcLL;.,'lcc 'ccci ccl :Pc',ic.'ccccij'c.. 'ii' cc 'cicfct'ccc cc;cCcc c5r',"c]i c'Hc cit'c'.cLl2 C'hciui.:fl.tc'cci'Tctc.,cc:-tcJcc lc:i['.c': 'cc'; ';,'1:"C'5 c..-,c"cicc .,t'-' 1:4]. SiIL. cicr'c.'t'ccc"ccuc, 'c cc =c"cccc'z' ccc ''c,c' tc[tc:'i"c C' 3 c''c4ci'c'.r ccc"' ccc cicc:'cc:cc'::ci ;' ci' c' "'cs'IRcc.ic,ci:'Li ,t'c.c4,.;L'2.cc"r ;ccIc2ci'c'c.ts ccicc,.cc'c: 1c'ci1 ii Jc t' L:,ccc,t :]L:II:L C '' ci; 'cc':: icc's cii ii'. c ' ct.Ii'.c't'i [2 The larger (17 x 8 mile) Alkalic Plutons; Wausau, Stettin: (Stop is elliptical in plan and comprises: (1) a Wausau pluton 9) hornblende-biOtite granite (Ninemile granite), core of younger intermediate zone of quartz syenite containing (2) a semicircular large lensoidal quartzite and schist xenoliths, and (3) a crescentic The southwest north rim of xenolith—rich pyroxene—amphibole—syenite. rim of the pluton is breached by the Ninemile granite which "spills out" to form a nearly circular mass to the southwest. Abundant xenoliths are found in the granite where the "xenolith circle" should Although the Ninemile granite intrudes the syenite, the contact close. In general, where the syenite intrudes between the two is gradational. it is alkalic, and where it intrudes more mafic volcanic rocks it siliceous volcanics and sediments is granitic. cs.: i.c .'-ccc.cs cc..cccc cc': "',. c..cciicc.'H1 .cs.çLcl.,.'lIc.'l iCC, cc.. cii"il:i:. ci' 'c':'c'cc.c 'it,JtLT ccci'. cclj'"cic"Icsc ',' '.' C'5 'ccc's:, ccii cccii '2" ccitT '[2. cc, 1'.'ci'C Pc ciSc" ci2icc;cc"cci': cc. cic'(VLcicCE.T ic]".'Tlt:'.it' c'Pc'.c'cc ccc.': L""i,c"tc [2.": ',c[2 ic.2jcc"ic' 'vcic:c'c.c-Lstci" 'ci ':cilI:L!:"c ciC,ci.tr ttcc'tLc";c: '.'c',i'i:: cci ;.ict, cc4c t':riC;;: tc',cci. :.;':t,,O ciSc', ut '":cc[2, [2 ciccs:i cccc'I.":c'cc'ccci ,c!,L'cii'c cc . .cuiiccc'c,$ cc . ccs.1.ç'cc cciii: ccco ci ALt' Ccci rI"cp'cc1.c'!c.'c.'i[ 'c[ccccic' ""1"'"' f -"S 'ciC,cic,','ccc: ci ,Ic ccu1cc "cc' cc.: ci,.,t'S ccr.;c', 14 .c:cc c.'flc iic';c,L'ici C iI[2Lt"V"c- .c"Itccc'tI Ci-''i[ iici..'l,c'c c-icc ci ccc. 7"c;'cCIci";..l'.Tt ccic'.cc5': 'ccici[ 'r'c,'cccc,cica:'cc' ''ccC',c'icic':.'Cci cc.' ccc; :91 cr'rc'cccc Ii ti, 'ii 'ccIccccccc.tJxc.c ii iccc':c'ci'c ccC'ii.:JY ocr 2.lfc Ac c',c,"cct ccci ccc 'cic',''ric]: Several other felsic plutons have been Other Felsic Plutons: They include the Kalinke quartz intruded into the volcanic complex. monzonite, the Granite Heights granite, which intrude volcanics north A granite and east of Wausau, and are cut by several shear zones. aplite intrusion of, as yet, undetermined size extends southwest from Marathon City. A leucocratic granite, which interrupts the Eau Claire mylonite zone and cuts gneissosity in the Hogarty hornblende River occurs south of Callon. granite, .Te,Tccci.i ccv. S :.LiT'[2cic'c'.c c',,iic cc 'c 0' 'c"' .1cc"cir-'ccccc', ,ccc.c .'Ii;cc;;':cc :'cccc'.ccc.ccrc1c,c ccc'cccc's 'cc' I,cc.,iccii c,ccc:ciic'ciJic ,"c-ci; cc,c'.cc, ':c'c'c'Ccc.,ic;'c ccii .' 4"c-n- rIicicici'Cc':c 1c2 ii4c ccccc 'c'; ''ci'c'.'ciT'c'L:] p;rccc cc. ci ccc.ccc cit 'ccc 'cc"cLt'cc'L c,t',,'.Jliccc.7S:l cA,t,.,c 'cc' ci:'c'c.[cc it'Lci cc",,cc;c:tcc'cici' cc's'cc-c c"ciicc,.,c:c' .ci[ ccccLcc,cc ccccics;cc:'c "cc" '. cicc'c'nc cc,"c:'"ci; a", 'cccc'cl "i ccci cLccii [ccc ccc:ccci,'cci': r"hii,C', ,: l'cc'ccic'ci ccc cc'cf'c'tic Ccci 'ccc'cccci ;c1i.c21'cct c.rrc'ccc''cc,c'cPci)'c cL'ci"'c,,c"C" LIt cc; 'mc,' c' ccc'ic cc:.cciccctc'L .':ccC",',c'C, cc]c1s,c,c cc', A' J,'I[ Ci's:: c'c:'r[.cc cic'cc'sccccc 33 �34 Structural i-->>'*i sn.i - Geology :575y5515c1'j, >>LCIC,naa. fcs.rsra a'. C i,1955'slfi-35-7 ti-::>> dominant Shear are the feature in Marathon County. daawdr'ar" structural 'sa' as ar-a Isls sa::- zones rocks, including 'nani:55 5535-Cit The major zones wide variety of sheared-s-sac> -> s.csan'r aa :1 si-i-is-s comprise lads si-:-ssc :aaa->>,a,s- these Nature displacement i-nt dCa; :>a.aaisaa'Ss across 1:55s3'axa of 'n-'5 can' -i-si-i. n-sal mylonites. gneisses, schists, s-s'SiaXa- and i-i-laX atlh'sa: 5-aC51-ai-i Marathon Several zones extend completely Lssi-si1-u"i-c-CCC C-Cad-a-CS. - across s-s-tiG->>--,-sasiCi shear -5 C-fti--Xzones is, :551kin'ThT's, unknown. —'cs'ss.d-sal: zone liLa. laS'S most555a557511-51a' conspicuous shear 5:55-C-Is' CiCts,>55a' :JC-1n1i-151*Lu:d County and an distancea555735ad-. beyond. The a:-. unknown which >55 155 .171: ':5: Ca' 'Jh.nis-an CLn>sr sari-a' mapped thus far is the N30°S Eau Claire River zone (Stop 8) S LIsa daC 5: 51n>5 -5-" a,t.-c3-3 marginasof ad the tdu -:'- 'Sd the -"a>>-as-- i-tugS ad-n, western is 555155 i-jars'. with, parallels, places is coincident tin plsc->>-a ,a-i-si in 355>>- and inns,>> Other C-'. h_Cr shear >neR : zones l>>55jfRiver 5551-tnPluton). lIla 59.; Hogarty hornblende 'Ksgarty dais:?-: n-Crs'agranite ;raa 55, (Wolf in Marathon -.---ar5 Ca: 55a-tdss west n-.:i-a-sc-",-- farther ;15i ta'nnd a::, present approximately trend are -s this aasnTCn:aci-a i-al.:' parallel pa's-a. -a-I to r55 sc-as: aS La-s ad an the lisa of rock affected to It vCL-::i-:r :;';a,nS County, but none appears to be equal in volume llla.sai-1:a, 5-sn: awn- n-nsa's-as-- to 5: t. Sn-annasS-a ,>>-a-arn,s Thus, intensity of >>a'>>siT">>' shearing seems to diminish C-C a5TLL,a ' 55' 'l'i' Cs ic-nC-, Cl sic--n: River d.s-ar- zone. Eau Claire 55na:l. lbs 5:Cc ' '-s front. i:lC-s batholitic westward away from tic--sri- the ::'aarrarC :;a.ay :- - 1 I - 1. and across n-i-Cc-SC las 5±1:35 Lithology rocks Ii: in s55'nr shear nsasea, zones, —a55C''j. which i-i-n-s varies along s-nC iIlssa51Lss557 of ad :sa.:'C': texture of the original Cast-inn cl tn-s an--i-CL-ass 515: -'3>5S,c 5.'>ra ristrike, is-srss" probably controlled -aiaJiy carat -:'-c-TLsic.s- by mineralogy and C ts-d li-a, is partial pressure of H2O as:: sar-ial saass -s ad 51Ctsr>>si-:'s:'ftassc rock, intensity ci> shearing, sdass--lsnS:, temperature and tntasa-S 55s' of a-s-sd, 5555 Mafic rocks are 5f-i-n ?-ssILa iSCCC_C the rock. :'a-i-i-I:n> c-as-sshiars-ns; C lsCc'i->-iad during shearing, ar.d post—shearing history of .dsrS's'g a'baa::::>> and 155: ->>'i'-sa Granitic 015.555>>' convertedCs toI sad-CL banded as amphibolites oranchioritic phyllonites. cssvsx'::-d SitS n-as: I"Cnalislc'r:tis -51111 From and CL mylonites. icnj',n-a,, Th5'35 gsan.aaan-> ;;-lha.JLcsain-aa as' a-is-a' rocks are converted to augen gneisses, phyllonites, and -ar's CsrrC-rt-n-'3 :>:-slica' I nan--5:r115'sn5553' characterized by interlensing a':,saa arssi an -u-i-rnstarts-ed :; 'n-anti--sn-i, shear zones are map scale to >ck'in: thin section, si-aL-c Cc ti-ni-cjill an-s-s-a'> slip as planes. - c-s'-- example, 5ui5'siQsS shear alIas-a zones. a':sas> For IFS-Si-n intruded Several small plutons i155>>t'uiiS have nn-ni-'-C>>i C;'., In-' Claire River zone i53':r'i- near Callon. 5' -s-S. CCI s-iar i--a' Eau gabbo and leucogranite 5c'51a"->>J-,d 5.51,,5557'alffltainterrupt 275.35 ''CL the sn-33C sass as--cl trend also occur northeast and i_Can a-; srann - -',n-sahythe 515; same 55CC - Ta'S Shear aaitln approximately s->-v n-n- with 151-a' as zones a-r'as'9 ha The'-.iraza-la Granitefls.t:.ls Heights Ida 1,5- granite s>> 'an-cadtS:'.-i"-- pluton. -Isl.s-u-o-:->::ac-s Stettin southwest -alar- discordant -CL the a,-y', -i-la--n-cc of ass-c ca--> sheaied and therefore tibaaT--n-SCaare proascii-h CC_CC-C: 5 i-;have n-2t lan-a',:: and Kalinke quartz monzonite been ulc-,an,'i--sI s-nd dali >sr,'C -55555_Ca ::r—a- lI-sasis.tC-', >a :ra-pre—shearing). 5-n-i-5'5JC5-5CL' bably (or cs.l:'1- pre—kinematic ion's:' repeatedly have been '_C 57 isas-aC 'n-5-n--as19-3lf 15 i-a tin-ass-C SOs- County aaa'Cs in Most of the Precambrian rocks Marathon 31' '5a-s Miss-isoji-;;,cali!'sc'ss: 55-.-? The differing -n-s-all.>>> :is:.iI-san.5 compositions. -s-S widely t—;s'rs"n-ar sheared and magmas of is:5'ar-'s'd -s>.l by an- l intruded a'Ca'ss'nnti ;53LsC:--?tCl'X-> aca'i-2 of 75 3135I the intrusions. 'as some -51- san:: for nibs—i as-s -5>1-s-i- channeiways ::,-.--i-Css,siCIn provided shear au-Si-Si-I evidently alCoa>>: zones -ad of the an"':. many as: asi small 51, 5 plutons 5-n t;as--a::'d and :5.>> s-1Ci-5C55I.S'i?'753'>>-'>>' cn-'355t:'C' The relationship of shearing to intrusion sad all' sn--o5isa s-ui-i(Hogarty hornblende granite) Sd -cICL5s 55 1:5' .i":ttarIs 'asn-t,t) 5,-s-ad-sI 3tti-'-n-s si--I'd the emplacement of a-I the Wolf River batholith i-he si-C 51115'? n--n-s'iPrecambrian geology ICC-a a,iss1a-:si at a>n-all JTof 5" Marathon C am—is s'f Ida -aa,>:'C ;n-rciCl>s-n-C remains one of the major problems in the resun&a.a cat: -- >55._CC u5i, County. i—:-SidLs:; -: Major 55aJa' Problems s-ca In-ma's- sCant anai-s Some the i-an morea important ones are anI 51—c Sara's of '—s-":aaa> ad- can- remain. Many major si-CL a-a problems -rcsn-n--s-Ci-r':.. discussion and sn-sal research. 5 .bsanasa:C-ta: ratIaa':L'Lasas Class :>,:>, sr's. -'>i5ai iS'-s' listed below in the hope that they may stimulate i-it ba-S balsa- S's Li Cataclasis: -i'- Lan-IS: Shear Zones — Cr: - - - 1. 5, and mapped? 'l'ci, -an-lan sacS's sariSclassified -staaaiiiIas- ars: How ass areaa-aa-c71 cataclastic rocks best 2. 5, 1155-1-35" CC dated? Can mylonites be dais: vsssLc:cflin&n-s 3. determined? .>>I5lII aaes:a,s:: c-:ot n-rrrr: 3-55 si--saC- 51 How i-sad amount of displacement 55155 and -3T5- type ia-" are 13 44. Class'? How? -, i-i- -isas-bs:nsa'fl p-': tcdcs':st'ia:dp:- between csdlsnc'n-s What, if any, are and space relationships avisthe j'e time it: nsa. Wl'at, atsiasas; a-n? ,'i-s5:'i9a,aBt'5 shearing magmatic intrusion? cbacvrlsa; and �s? ane err t older subjacent of samples ted upraf they Are variation? fC =— xenoliths Cji, 1t2At4v and orientation (:ICC ofjC Significance lithologic iCZ [ r:• ft$CCEY:1 <%-Y9 C Subvolcanic? — syenite (e.g. 7i;T !ttZ i)r,; When ' ?Ji-•i ci?1j lILCrCYqISC Ccnj intruded? syenites the were f.CtCR how and volcanics Brokaw)? near C CC 5. C 4. trachyte 7 I i—C It— and plutons between Relations comagmatic? are plutons Which iCCCCIV emplacement? of mechanisms and Depth 3. 2. C 1. i:t:C7 Geology: Plutonic 35 I �1! 36 atrSW Bates, •fl0 R.G., fl'. 1961, geophysical data and Allingham, J.W. Xfl '3Ut - "Use 34) of *t.tss%•;o. t'Zflfl ';'r geology i4tç to 4•1 interpret in Precambrian rocks of central Wisconsin": !fliS'V1'13 £.Ptrctl bV $%Y wea 1> U.S.G.S. Prof. Paper rn-cs — D—296. zt •IrJ. .(%',.; 424—D, p. °' D—292 SELECTED REFERENCES 5tF:SS.a'ffi 't1. j , L, ' %.'f Dutton, G.E., 1971, "Volcanic—sedimentary belts and sulfide —rae occur87Ps fl1'r7rC2L StCt C4fl(U U.S.G.S. Prof. Paper 750—B, p. B96—Bl00. rences in Wisconsin": r, r.oswç,s, tr : ;c.a.y rcb.a '—,;çj OtZ tn. • '°q.' •. t"i ';a'tIrtnrxrc;s Dutton, C.E.,. and '..'73SZ Bradley, R.E., 1970, geophysical, and >.E 'char "Lithologic, DLC'4Ln32 mineral commodity maps of the Precambrian of Wisconsin": U.S.G.S. 1c w:42L Arxa•nu ..f,q'g ;ta Misc. Geol. mv. Map •4gfl -15ee •"flf 1—631, :%.I4... 6C sheets. -:rj ;r ru :'wt:.jtn(, pUtfla V $ () r.qe;.p at; Emmons, R.C., Annual Tn—State3 Geological O'eQ 1953, Guidebook for 17th v, :ia( .t$q, flD4tC Field sv,.'-.xarr Conference, 11 yr p.. ,t0Ij rt4'7ii.'9 !rag r' Emmons, and F.G., fl•j Snyder, c'& 1944, y€L "A 'Ii, Structural Study of the cç Cztc.,&a R.C., xq,:iz ta•a Unpublished rept. in the files of the Wisconsin Wausau Area": i1SW% WV ;qa 4 aj; t,Wt47tttft ;'etBr.tV14 ';de.. Geol. 'TU. Survey, 'it&flS 16 p. C 'ba( a:;: t •,'( 'CT, "g'g t:\ttsc. tj) .j •. :, ': i t:b Henderson, J.R., Tyson, N.S., and map P%7I Page, 'at 'o.Qwj J.R., 1963, "Aeromagnetic rr.,:i4'rney U.S.G.S. Geophys. mv. Map GP—40l. of the Wis.": jo :qt Wausau :'sa.rajç, area, SM 49' 'SS't 'ts1 ,. :sfljr "It v' ar LaBerge, G.L.. 1969, report on P.tnnrEsJ. .acSe.t uz' the geology ".ZiGT "Preliminary a5 ma of the northern part of the en Wausau East quadrangle, .nacsfl :tth 'c,2as. Wisconsin Wis. Geol. Nat. Hist. Survey, Open File Rept., 13 p., '2s.C?3 "C map. iee ;* rnas ;ntj i:'t. t.jff f'L •'vc'- LaBerge, on mapping of i1 Precambrian geology :.qh? 1971, s25v.; Report s.r'sg co SZ'LWS$ 'GW4e.q G.L., 'ca1t "Progress Wis. Geol. Nat. in t7flcW Marathon County, Wisconsin": ELf a-a • Survey, :::Tt•sIflr3J4 'tu,c list. Open fli.J File Rept., 27 !Z p., maps. '4rc3 '?3 C.1 'Ai. L0 '.r. 'craet't, vx nrnc4w r taCaaST& tfli: UC'4Ojq n;i 4flc; '1.2? 'flL 5 LaBerge, G,L., sv 1972, "Lineainents and Mylonite Zones in the Precambrian of Wisconsin" (Abstract):t North Central Section Meeting, T2 G.S.A., DeKaib, *e.q.n.z) '•ezoa Ill. U::z*r1 't' •t .trj ts 't.St3 ''O LaBerge, G.L., "1971 %eclSord Progress t•.dej Report on .:,. Mapping t1.3E TL€T,; 4"u'f and Myers, P.E., 1972, Wis. Geol. Nat. Hist. of Precambrian Geology of Marathon County: 1;b C4taPN.Ls: J.$2t->' &.O %'.at1 fl '&.1C1s5 Survey, Open File Rept., 28 p., illus., maps. &j nd'ag bw4, c.çg 'd 4-aç "!na :. 1Ltui VII .vc flo rt LaBerge, G.L., P.E., 1973, "Precambrian Geology of tr)4flflfr( Marathon nrn..*twse. 1an and Myers, Lard sue. Wis. Geol. Nat. Hist. Survey, County; 1972 Progress Report": Sp.4 1.C-) 20.aC 4Z'a.t1 Open fl%C File Rept. (in C;) progress). 'cs.azs.c5 )T "djj 'fly W flr: ;r•i fl.1a3 ?rr, LaBerge, Ci Central ..:.t; and Weis, k"! 1968, "A• Greenstone fltLrj%S'LVaTh Belt in 'I3J4(i. G.L., '.t!Cr4 L.W., Guidebook for 32nd Annual Tn—State Field Wisconsin?": Yt33—(aZ1 ,.4t1.i.CCfliVTk )OtOflt3 aC$ t.LV, Conference, 42 p. .3 4DrdXtat) c'rq ' ''re: 'c;si Vickers, ra part of UJSttCs R.C., 1956, "Airborne .a'q.r:y,, ':t and pfl ground 1WdCUCte.F' of ;n4>s1 reconnaissance U.S.G.S. the syenite 0cm rie.I Wausau, ;utsI'r.JCT c c°u 'p Bull. nit.ts s.a complex near rgnip. Wisconsin": 1042—B, d p. 32—33. xwgna 'tn'ab1 a Weidman, bTId... geology 'Z4ni Central u4TLBt Wisconsin": çu:w.CCCTa. Cktz'ia of North t•::....;#'.•-q S., 1907, '.a.cr "The Geol. Nat. Hist. 697 p. •t$ •V1J! Survey r..t..s Bull. •IrR 0 16, 09 ;I . 'TZ '*1t 'h°1 Wis. '3;j.4 "Central Wisconsin Volcanic Weis, L.W., and Z.1Ct LaBerge, .n)'ja;s G.L., 1969, '44%tJ_ zu:awc,, 4.3VCr.s' Guidebook for 15th Annual Superior Belt": I.?:.2t.p;a3 :'a.it.t Institute rj-4n(fl w on Lake dOfl Geology, Oshkosh, Wisconsin, 30 p. VØ (.j tSo ".atcers ;•1t -— .n; ft 'u;snt: ae a... .. a ..j4uQ �This page does not have a number 1 1:500,000 scale, Wisconsin, northcentral and northeastern in terrain Precambrian the of map geologic and itinerary trip Field 2 1:250,000 scale, Wisconsin, Sheet, Mountain Iron the of map geologic Preliminary 3 1:250,000 scale, Wisconsin, Sheet, Bay Green the of map geologic Preliminary Plate Plate Plate pocket In LaBerge G.L. leucogranite and Masses Gabbroic Locality: Additional Myers P.E breccla intrusive diorite quartz Sheared 11: LocalIty Myers PE. zone pluton—wall syenite Stettin 10: Locality PE Myers Institute Technical syenlte-.Old quartz Wausau volcanics mafic 9 Locality LaBerge G.L. Rivr Wolf between Contact 8B: Park County Dells Claire Eau 8A: Locality and batholith LW Weis anorthosite Tigerton The Scftnus Va.n Schmus Van W•R• and Anderson, J.L. Jr., Medaris, R Schmus Van 7: 6: monzonite quartz porphyritic River Red The and Jr., Medaris, LG Locality LG. 5: W and Anderson, JL. Jr., Medaris, L.G monzonlte quartz River Wolf The WR Locality Locality MM Lahr, area Mountain the 3 Anderson JL. and Mylés, JR. Jr., Medaris, L•G trachyandesite Peshtigo and granite Belongia 4: of geology and porphyry feldspar and rhyolite Hager The Locality Locality JL and Myles, JR. Anderson Lahr, M.M Schmus, Van W.R. Jr.,, Medaris, L•G• monzonite quartz gray Amberg and monzonite quartz pink Athelatane 2: Locality G Hall G.I and Mursky Wisconsin northeastern in volcanics Quinessec 1: Locality Wisconsin Northcentral and Northeastern of Geology Precambrian the to Guide Field �37 L CI'C,':'i 7TCHJ Field Trip Locality 1 TITLE: Quinessec Volcanic.J in Northea;t rn Wisconsin (l'I-7J!,I C C3'CSI CC-XCk? 7 St .7;:; 'T'y CICCC,IYC.,C,:4 LOCATI( MC.: T.37N., RJOE., Marinette County IJ, " "na sec. 1, LI7tC 7',;aa.;:7t7r; Centr, AUTHORS: t,c;:'?L± .CCi. 7':,';ai,r, i"C[ 'a fI:r.17; ,;:a,1 ,'r• C"Ca. ''Ii; I,7C,C"7M: L,uZ77 Gregory Mursky, Department of Geological Sciences, UW—Milwaukee George I. Hall, Hudson Bay Mining & Smelting Ltd., Calgary '7CC, I ;:a CC KtI• ":H':aaf"7 1yT7', DATE: February 1, 1973 't 2C7'C'i1S SUMMARY OF FEATURL$: part oi Marintte County in northeastern Wisconsin Northeastern is underlain by Quinessec volcanics which consist of pillowed and •;:;: :;r,:CZJC '7., '77CC "CThCC "TC'taCQ C'C7 Cc "IC,:': :7';: CC 'CJ . ,C13C S$LCNCI, aT'tC [ YI' iC1P'4"t 1CC 'C7CL i'" •,7C [':'C '!tC '1 t 'Y'CJ' )':ICIL3E1 aC"<tIitC'T,C,C' rLiC'Ci7C I1C'CQ1C,4 S.'.ICCC' C4 vi"CC",LC1CC1a a . fragmental basalt, massiv basalts, amygdaloidal basalts, myrmekitic basalts and a very small percentage of tuffs and rhyolites (Fig. 1). The volcanics display shearing as a dominant structural feature with two distinct trends at N60°E and S6O°E and signs of regional metamorphism which varies from quartz—albite—epidote—chlorite subfacies, away from the granitic intrusions to quartz—albite—epidote—almandine subfacies near the Hoskin Lake granite (Hall, 1971). C' r 1Ia '.';:aa. •a/;!.:zc•Z. wa474t1ir2-. I'C.':z1I,:, 7C CI C': [::;:"L'1 C,7;,;,LC ., ;3,'IC'T'zJi. CICLC VT7CTCLC 'a : :;;:;: 'a C'C1 'E1?C:,,Cd Titt7 'CC'' il;: 1ia 'C CCt's''a: J7117 7 C';: C" L1• cs• '1' C'C1C tCi CcC'7XtY ;:''aI ;:,C:,;:. c_.;:01©.'11 ;,1:a::C ''' ':' a. •aicaa ttp17 'CCC17::. '.C'Ck",a,I] CLt I'i7-ç m',7 'C=; lP' 'flC1ICC "ai 7T4COLL '-'T'1 C12 jrcr'; The Quinessec volcanics have chemical characteristics comparable t:7Y'J1 ICCICfC :3CLC4C a:'7'q 'C 7u7CCvI-'. y{I• CY',TY' tI;, •'•'• C JU .CCL v'ç 'flit; CCC. :? Ct7 CC a a Y' f:a'j,,Cu;:;:CtI C4 7C7t'T'17 IaaR12T71 C'5. C' . CT'7I to the Archean volcanic assemblages from the Superior Province o the Precambrian Shield in Manitoba, Ontario, and Quebec, and thus show the WCZJ '- 'St L silica: alkali values from Quinessec volcanics, when plotted in refernce oceanic alkaline and orogenic calc— alkaline curve of Wilson (1965), plot in the same orogenic calc—al :aline wield as suites from the Superior Province (Fig. 2). iwa;: o —pa ';:'y'a '17a7 'n ©;:: I : CLL± •;:rL •.':q °9.jj7 C'CIiC_C"z.ç[ •:s-C'CCL' CT1C cY'1; i'.'C•4-'1.C cCC:iicti' ,;:,Cat ''JC7 JC iC''LC ""CiCVI,''y C'Cj, JC j :i t;1r7.C'Ja The c tion equivalent percnt of An—Ab—Or for Quinessec volcanics is quite similar to Goodwin's (1968) Archean assemblages from th Superior Province (Fig. 3). t/I'i,L7LCC 'Ci ;:tir:;r:'a IJiI;77ji C c:e Y"1 JC I II,7":i CY'R1; ?i'C;fl :,Li a;: ,c-:7t'r a CCjj (2) t'C Nili ii "c.'qa CTçi ;;t (1) 4't following similarities: : A plot o.. oxide ratios relative to stratigraphic thickness (Fig. 4) does not show any pronounced chemical trends although there appear to be three separate zone within the pillowed and fragmental basalts. c: Ca:ttc1:; :T7hCTYI,flL ::4 L: :CCC; apCC:C :::,1aCa ac.r.i. :: aiqC 7CL7 '.. L•;'..Lta, ;- .,'.CC 3C'''i' •C.:C:. :,Th:,c.'.:ia, a'p.aac. 'nz .'i'c•,.:; pc:',:C.::;:'.,ri ira tu'çc .-;r ''i C' �ii 38 -Ii 8800 7'07 - --., -- Nocra 1 177 \ 1_ £ rriC:,,, T' / — 2 — — — ,.'NtMrnet C'HIIT C ,STUDr' 'N / -) * / A 7 L_ y—1'-,, a 7\ t, toN 'N 4.*4*47* AA A A'\\,7'.-.it'- — 7-' '1H'c221J.t'C —-;,,--._ .AAT3N II 4—"ii 'Ni cons N H-— 27 - A -- - 7 7- CL 1 - ',,,_ a—-—-- - 'N—- -, -- - _1-L--7--.- Jfl=cn - - *-'7 —- -- - 10 ,L_-r-- —I — ' N' - - ;- - - 27 1— -. P.. 7-1 ;0'''7-°"--- -Nt--H, 7—- rrmI n (1 r '.j.-[\ C fl7-_° 77-- 7, 21 '- 1 i-n Li e 't,,oCit'li,'. - - 'N — -- - (7a / - -*4 2_ — 7 -"N t'Nt.,q —-_a,t Y.-:---. / 7 -t ,-i.;, lot (/ 'N N,' 27 0 '/ — 'N I - 1''N';*,/ 0 of -b • oN 17 a.- 1 N oCt— ' .-!'NL ,fi -'27-7—-- N 0.1t&_,t " A -A : s,,b —'t,-"S — A a r - r >, c I '. ( 07 'S 7- I / 'N'" 7-pLOt - - /1 17 . 'S — -- Ca-21 AREA — / 77 I là CA L4 a- 45•45- - * —---- 7--''S 'N /21. - -.7*7--f - ' 'Nk. i-'7-%_ - a VI 7-N. I LEGEND 1- Precambrian mt rusive —' L rocks 70, - - '7-.-'o 21 7-— 1i .1Fraqmenta1 7-4 I 'I volcanics 1Arnygdaloidal /LjJ basalt ara:J 6-I!77If 721/'CJIN I 0 7,-;.J-1 p o— '' "N I Myekitic C • - H —- I a -''S-— - - •.. '1d basalt -L * - - - Chr-'Nt 1-731---c' rk.,0i'Nu:.,elco Acidic volcanics 7- 0 7. 7 LCCAON MAP CE o_jbasalt U) . (1 r1 - - 0 -o Luny >, - i/f,-,ç Wi •-ns',-- — 12 -' -- Mo r,,.?te -* ---- k,om.er - - �'r\ LI I. 3',j 'C[' ''Th' C.C' Hall, 1971) 3' (After 7—U- Canadian 3 '1 the of Province Superior the in Shield. 13'22IOft J37;1-C-l,-" assemhlaes7 volcanic Archean 3'23'2L;c. three ;.122;, for trend 'uT1-2/3'33'T-C curve ri:Cj3'crr Dashed Wisconsin. (1968) Goodwin's is 333'1'.3' 3':.,-'''7 acidic County, Marinette NE in rocks volcanic -= '— 2:1523 Cation :.3'7.-( in 23' .2:1 13'-3'--23'[2percent 11,12.322 equivalent Ic 3' basic and ith—An-Or C , I 22; /\ \ \ ' I: 3. Figure \ 0 3 /C II Number Sample ,z C An /-,1'V"Ci T., G. '3'3'1;121i :1:3''121 caic—alkalifle rocks. p33'.A1 'ri13:_: (Mter Hall, :: 1971) rocks3' alkaline oceanic separating orogenic from _l 3' with made is curve standard (1965) Wilson's County, Marinette NF c WiscOnSin. — r' '1 I cI' I_ : C--— comparison 1721/ :!C " C— -'' aniilyzed and basic )'C acidic ci volcanic rocks in 3'/ ofci Plot 3'003, I3'.3' ':• I13'Gr;2. Niqqli :17 :511123:' values silica-alkali of - - - - , — —C VLj c 400 500 12' 2. 5172.3' Figure CO 4gI Sit 300 00 200 7 l0 I 7/ 4 / / /7 / / // / 20 12 > 0 / 12 CALCALKALNE ," OROGENIC 12 7-V 39 0: - 30OCEANIC ALKALINE 40- �40 40 V Si/I.E N,crn.H .: i 54- . Cl — / -. 25 0.23. 50 .5, — 75 H\ 'N'1;\l .7' 01 - I -. — N,1 - ------! 1/ : 0.3 ,0',, C .04 A' 10. / ..' H — -1 xA — C .4. /1/ /,/ A ,.' .Jo1 - - /A H / // r Ceo 0332 L.tSiUI I . 20 (I; t P. nu5' i I it .- t II -— -1 7. fly 04-." 7 --- / 00 —- 0 I '4- I c '4- 0 :: ((S 3 C. :; 5-—.,. I. •1 -o 1A C - ' I-.. C 0 // •1 0 -c /7 /7 'I 10- 7 7 —.. — 1 a.'-C'-. -' '. " • .'0.' I: -- 5 -- .7' T 1 / JL.' 0 H -- - ,±J1 Bottom Bc -1-L_ Ir tr'Sit' dItIIn 5. 5, .:''H''sv,-,I,''12 ('IL.' — - l(C7 Figure 4. ' 0)01 /I'fl( t'kr' - —- -. Tt1 0.5 0.3 V sc. Bottom '3's A55 (ion l..I ", I -t FeC) ) J '3 A 1515504: Plot of chemical 5555c/:t c- with stratigraphic d0457nS,2.C .sjI. variation 4 04552044335533555504/04 04"r:5e33335 in Ni Marinette :;1;t-5-.t Cocsit.y.. thickness 7555 hasalts NIE County, bsc/c.5T.tS ins.c '55 shows: Wisconsin. ,55..'(-5,33j/5r5 5550 JL07 zhz': 001 Generalized qeoloqv r->. Si 550455355.555 sc1s' scs's d5Ct??04*5 3 qrain size -4555.5.04 75.5,55; increase; grain size decLse; -.-- hcsc4 (i55 7 i r (EnrpBc'cT L.':3 basalts; isis Bc 55' Ct /4 shearing; porphyritic (.4 2"?'10455.a"''(S 55: basalts; CtjiL55557L 045575.A 55555 q fragmental modal StC'. iLL auartz. 55-75, 'JcS"I' (AfterssBcI, Hall, '.'s. G. I., Bc, 1971) .5 c. " Wi, I, ,_,-_., 5_ A'.' Si �41 DESCRIPTION: U l/ce n:cYk t,jc 14i.V a'oci' ri' 'u :a:aL :xn vi 'UU Massive basalts crop out to the north of myrmekitic (1) Massive basalts: basalt and comprise one unit within which there are three quartz—rich zones containing up to 10 percent of quartz grains measuring 0.15 mm in Massive basalts contain varying proportions of albite, epidote, diameter. Most of these minerals clinopyroxene, chlorite, actinolite and leucoxene. average 0.2 mm in size. Clinopyroxene is commonly altered to actinolite and plagioclase to epidote. Pyrite constitutes up to 1 percent of the rock but may occur in greater quantities in the quartz—basalt zones. :1L c : tecc1 tsa I I cLa: cc Ui tr ci c21i Ct F3eELcL1 S. - Xccii p I 'U cc. rJ c cccc/. a1: cctt'cUL UJ"c/RLtc cU eca Pitci tititre L±i-UILI. 'U a i Mctcc c'tkcc.tQ L& :crc k nc - c. :rr a-cc-i e•:c:'c cay cc.YCLC:ic ftS 134L1 irL 'U aft aagc .fctc0 cc cr .ccJLaSe i caL act iic.: c-c cUr r--eUicd cii 2eachae g cc - chsaccic sL'trect ii: cU-fl.. ratrcc tibia calLer icaci lice cc fl iL fS;.-iIi-Lf.IL-- 5rtt ataice c cc Ltii a cc U 'Ucr I rca -cc cc lUC cciiai a cc -L c'c:•H ate Ifcar UI U Ucac'U cc a a ';Lcc-c ccii at. - calU iniic-U; a'cc.ab cc;: ticac cc aa.lian cii a -racial Ha t UcccU ccc ti T1LL JUic -.leTh tS±L ace C/c. CccThL' :- cmi- icc ccc a-ta - cc-rat a t'U 1tJR -ar: t'a. 1Li ccc as::.: ;c'Ua ic: ii i;ufl9L cc :c:a cc- cit cL:-r 1: - -cc ccc cccc p1 cc-I- crit.trL cccci--: ccc- c' a iii:;' i-c U Urit ii:, hit-cc Ui 'U ccl cc-i :cycLnta_ iliac-. LL ci (2) Pillowed and fragmental basalt: Rocks to the north of massive basalts are fragmental and pillowed with well developed shearing and flow structures. The fragments are mostly angular, at times elongated, The pillows, where present, are and measure up to 5 inches in length. deformed. These rocks are made up of plagioclase phenocrysts and a groundmass consisting of epidote, actinolite, some chlorite and dm0pyroxene and occasional grains of quartz. ,- ccii :;1ccctth i-cc-cpa-c H rath -ira pUL:c-i1 aiU ci ecai'vccc ccc ar-ella (Y:i/Lc'IL_ 'IL ccalc.c ccciii ic-eU ccci i-rca i: ci cci 'U ccl -ci CC.' La.. SLLC !CtiC atiLcag --crc a cci ytmic-cacctr ccc ;PL-rgtcU -f cc Lie c cciL -cciiti :ci:ci hiU ccc L UIL 1ccckSct. t'ca-a tTI 11 LltJc -a iia'hccc iitt& I C --j.c-ac dcci :i.ILc 'Up-aL ILLC7 Ce 'U IL tm3i TLC (cjCC.?:ILtS - r:-i - cccl a1 2/c Ui iT iciacla ti-al arc etacitcaca kcic'cL La -cica lea icaraIra criiaJ. Tic (3) Amygdaloidal basalts: These rocks in hand specimen are uniformly fine grained, massive, gray in color, and contain up to 20 percent of disseminated dark green chlorite grains which measure up to mm in size. In thin sections the chlorite grains form amygdules which are Plagioclase in the form of surrounded by a fine mosaic of quartz. laths averaging 1—2 mm in length forms about 30 percent of the rock. The groundmass is composed of a fine mass of chlorite and epidote. cc Ii. cc ccc ccc ccc- icc icc ••- aac - 'c -ii- cc-. aca)r.ci/L'c aca7 yr LC-H-H c-c-ct teucia elite culcrt-cc cha acce cci cc Ian uccancre greca -U ilaccc the hr.: -ccc taLc-Ui cc Iii- claciccicita- :L.r.caJ'U'U ctcbc-clai i 1 1ccttc- nnr:ccc icuc a cacic -rtcc a CI :-ecci can a- a I Ic ccU aJjuJ:jIcc u-Y 1 - cia -ci eccacat era cicica it-c n,air,ec-LaI.. yrea:Urc nrccniti-ci-i cci La ac-a ca:cLcca-lla ecnii 'Li'; inacicica] 'U :cuut.cuThflil'l ycceacca n-cc 'U ccc arc-scec.a ::acc-L.i.-z cci c-ac- aUcta1 iat'U j:Iapa-.:cIea-e cc.tc1 ci: -ccci ace c-c-ai-acl --aria tiatacig a .lcrr.nti ear ccc "C•Cti'U a: ci i-cf cc-ecU a: 'I-c. Ua-i iac ccc rn'-: car -:r'ar a ccci c•ihc rljtflfl'Ulitcarccc cc J lr -ii (4) Myrmekitic basalts: To the north of amygdaloidal basalts the volcanics become slightly coarser grained and do not show the abundant chlorite amygdules. Under the microscope the rocks are composed of myrmekitic intergrowths of plagioclase and quartz, plagioclase laths, quartz, chlorite, epidote, and actinolite. Clinopyroxene may be present occasionally and some carbonate minerals are to be found as interstitial groundmass material. The southern contact of the myrmekitic basalts with the amygdaloidal basalts is gradational. c t cc ccc 'rica ct:ia 'C c1/.'tj c)'J1CU tU SU 'U tLcr:O Massive basalts contain isolated patches of welded ash flow tuffs and rhyolites which indicate acidic variety of volcanism in this region. The The thickness of tuffs and rhyolites is estimated at 400 feet. tend clastic with rounded quartz tuffaceous rocks to show appearance grains up to inch in diameter and cherty fragments up to 1 inch in size embedded in fine grained chloritic matrix with distinct shards which have devitrified to quartz and feldspar. The rhyolites are dark gray to black and very fine grained and contain quartz, orthoclase, cherty material and plagioclase. icc -a J ala c-cia 1 arcifc;r. bIl -b-c :r 11cr cc a -ccccL.r-ci ccc ic-acita lU i aia;yca,1c:a2.-c!L Air ccciii. tcc TcaU ccc ccci:: cii; �42 42 SELECTED BIBLIOGRAPHY 8'Liv:.t Goodwin, A.M., A0M., 1968, J!S% Evolution 'o1t'.ionof*2the •b Canadian .AU1 W4Shield: Oucihilti. 7 19, P. Canada Proc., v. Cer.&Ss .L; . 1—14. T"r.; Ct.C. Geol. Assoc. t9fl. G.I., A Study of the 'r.z?Precambrian fl3x,brtt1 Greenstones in Northeastern 6xsy a2 0,1, a 1971, J. Unpublished£.t? M.S. Thesis, tr:i.r, 'fl:t,g.Jv, Univ. Marinette County, Wisconsin: V:.nctctt; I':'jjj.b* flrcgotce Wisconsin—Milwaukee, ¶Mt' watuxMt, Wise., 'n4, ac. 80 p. kaecariu-kUvriks. Milwaukee, Hall, '*3.3, l:.tt MacDonald, Gtsj of Hawaiian rbra'.w T•cvn; Lavas: tact Origin Cct.a.ceit:.cct and Jor.z'.Id G.A., 2.JL. 1968, Composition II. In ic C1A.. Studies in R.R., Hay, R.L., Anderson, C.A., Li L., and im3 PZ'13't1D, .ntR; E.3.., 13 Volcanology, Coats, Geol. Amer. Memoir 116, ..1. p. !Lrtc.t' ed.: p. 477—522. 41''.-.t. C... . Soc. Ln td..,. 5c. A ?i3 tflTlti Wilson, H.D.B., and Archean Volcanism in the Canadian s'td others, 3*h1b. 1965, £racar. 4ssct, '1fl,fl., TIC?,3, & p. 161—175. Can..c."r Jour. Earth ttr1tt Science, ¼c1tfl?G, v. 7- 2, no. Shield: (!a isiC ', �'111101-32072quarries. rinP0Ni'L-lI: are monzonite 11:0,' (CLI 11110 0 - n:ioAmberg ,12375' of o'coon .049 0-23 areasS.1--401001-,C exposed:420 quartz extensive east, the 70. 1 7'LTU -4- About 17>77:010dates. _.t (1- isotopic 07 40701' by' indicated LJ'>--'7 70-4 UZ'LOLIO 2370: these -040;.1of. age to mile types rock 107 OLE,1101L7 I 101009 grey 4,04 i[0--0 901: 2oii::.o>oo,o:'- ,0Ci 1o .17 2,177011027175 22 relative the confirming thus monzonite, quartz Amberg of dikes 217 intruded po°i:coi:ii 0> "i÷11:,CL2i.E0TiJ C"C703177 07110. At to by is monzonite quartz 1'1tJLI pink 1tTht.7'100'[:7 Athelstane .02110017:. locality this -o%io in 't'I m.y. age. ill CLY 2o':o-p ':,[1723100LL 1670 to 0070:1 1640 being possibly ICY 04 01,1.11711711, 0:01,0-1 .$1t,:$1 younger grey 10.01117 1t10 Jon 'to0 23o' '0 .0':.is quartz monzonite Amberg the that suggest data isotopic '7700 .r7010E0 .21 10170. 2 m.y. 770' with 141-704.171 1110 0, o;17 the )SCm: 023C and Preliminary Cain Banks by given 2. ->24fl 18604-C of age (1969). 70: 171>41101 I Co7j,i407'01- (111110' 9:. 17'7 232 0 agreement 1 9IL2 good in monzonite, quartz pink Athelstane the for C 2017101>2" obtained sJtI}fr (Rb-Sr, 'UJCY'l[LO'ILOlL '1--Il-,: 7001-'> has - " '707 -1210 An m.y. 3011 isochron) CI' 0.17 age 70-0, >. been rock whole 50 ± 1810 "[2 of - '1 - ' op grey tro7artL monzonite. quartz :,co2 Amberg the ((10077017 be L14401-r2Zt1i!quartz Y.O&ol5 ¶'7"J J.04236y '7070' grey31the .iool0o?' '1. and (7-71- monzonite 92( variety, pink71170 the called Athelstane oN 0" 20'. 701-LI 971. 0.0144 -oo''rNj2 c-c L1277017'J'L177 1-4 ICLO';71'1 2>[ CoO 0211. propose we variety pink the that two the lithologies, of distribution [013 1 (Plates 79 -°Oi'0170[j 0-0107010345.1 9'; 0" 0t'7'([71]'1area geographic the of Because '2). '17 and Atheistane -7 the in in :-',-ntI being 4"-0, variety ,Costot:, pink '.distribution, 11 141171.' 101711 501>O '0 has t!C72J'1112-I 4111 U 9'. 231 of 11101 abundant ,7'.:ctc particularly wide a the 411 J'1 1042' I 04, and 1173 plutons, "OIJ O'ji'14,; 02,-2,O'n300 -'>4702711:1 7.110. 17° 0.1 -230.01: 2 270 that distinct four in occurring Amberg, of vicinity the in 4LITOTJ'011,10"-ilCo c'9 110 the oioo01mm grey 0o:o 05o11104:NL 99 040 %"4(",,'IIIL(U 10,> predominant €0is variety that established has mapping L7[0"4,;1 Field 7 were I(grey?) 0'. 1-14 ,n'c'L711012 2-0074LL'y 11047.2) 417(1 -distinguished. c'71II1I":0071194[: .0o-1 granodiorite Amberg S703L117110 separate atO 1770 and (pink) ite 10 granuI,,11.o 4L1 map a 'm:'fl'170:1,c4 .jo,74 which 0017 granite 23 170,% 27:3 t04' 711017I 1023 2Amberg on IJ.'00, presented and pink >0 of sample Amberg 't'rp 0427±701: 011:0, 4,0 103 2347--i';o (U—Pb, a ,00:: m.y. an pc'ooccoo :237:1:: Cain for zircon) 15 ± CCCI 1860 of age reported (1969) 4173 Banks .f0704" Beckman tLJ01"JG'?1110.01 ;7102,.$([4'141.1.''4114j,itN .lOfOO(1 "200112779 ((140 ,211 recognized were subsequently and (1964). and '1400 Cain by i.17'33by '- .21."OJ.2 ,:OILO.1t 710':. opo0 and (1963), so: '(Efn.C. .24227 grey '7-vo:7.1-707- Cain name the granite2oop1: varieties and pink Amberg 13,0 $:c04w-'0'7290'. originally 0d200in 70 1727fl..j LI'I'J17'>[-°' 13777> area rocks Granitic given:5 were Athelstane—Amberg1 the ' L41 DESCRIPTION: '$'L41.E-'-i-'2-2ltt 0.071372 quartz771.701 pink monzonite. 170131.1' 14 17704>023 40.7 0170.4. Atheistane into intrusive C: '7307414 41 11040,701.1 quartz are 0.'.II7 1%' grey -J1,0070'0'1'1' of 970.' monzonite Amberg Dikes 217>274-, '0 23 >7,47077(27,0 FEATURES: OF SUMMARY 1'00 1973 4,4:41 24 1972 700>07070 to March, '>C001111'25 Summer, DATE: 04 707 '1LIIO..:I5''o0 J.L. 011,207(2117,1Santa '0,1144 11(10:11270(1 -1771 Anderson, UW—Madison and Barbara; '"12077Cotter 722,73 0,70'j ''4>01 ,174'12°0Jy Corp., Lahr, M.M. 111>1" California- of 'opcq Univ. "o"7707; Myles, J.R. Colorado; 0.7 Medaris, 4"1VtC1(. 74 Van €L7.O 0007123 7-2 ':l7C'94[17'o4i o.fl Jr., - 41-123471 -"oLIlO L.G. '417 :1> UW—Madison; Kansas; of Univ. Schmus, W.R. 0 ' - AUTHORS: ., 1230 '720 sec. SW, 72 '7019,1171, R.20E., T.35N., ''741 C'T 10, County Marinette C *lUi: NW-&, LOCATION: °-: nol 01070 11111000 I 1.1110.,:Coo3ik.4 17-CO 012101-c quartz 9' :7041171: quartz 2310 2 >-fofl grey Amberg pink Athelstane monzonite and OIL monzonite TITLE: 17 2 i7'7"J7-[14137'7 Trip 171 Field Locality 43 so �44 to cra'n-g: tnc8, The Atheistane •' ?ti.rtar.squartz qta rmonzonite mennritehasana amedium— .tdtt- to coarse—grained, allotriomorphic granular contains tnC1 both biotite hornblende, grnttiisc texture, cazte, aotlafla blit.t: n:and !ctDbJSilfl4, and laSt has a a distir4ctivs distinctiveappearanze appearancedts due the;?4aGtLcS presence of pink perthitic toto VSe tH from five specimens tve pasine .i microcline and white plagioclase :L%4iC41dZiP(An fLu23—28). 2ti- 2E. Biotite ttog yielded values of lOOxFe/Fe+Mg from 71 to 78, but two other samples gave free '1 tc 10:. but ti., gavu y.eideC 'mpiUte aisSrhastingsitic iaorsgatzt'hornblende hrLh 'nieorr magnesian values of 85 said and 91. of 3? SI. Amphibole "aluts Foliation is common in this as are 'atit. as an hastingsitic hornblende. .yaattcr So acts's 4, tbta unit, recrystallization textures, such as aggregates of quartz grains aoryista.IUnt lea tn'.'a.'t, eush as s.srnstt'v e. 'vact endnmwith 'nts Saussuritizationof of;1.gtoe1.wsc plagioclase is is widespread, ''S'ep,d and a..J mosaic outlines. wunic c.t :.taa a*ssaLtrezcc epidote is usually bpdct9 43'S Jy associated with biotite and hornblende. tat flontc*rrp.nc n4.trocive •n 'stit. -/aluc. o 1cCflefZkt ot $.ct tbi sai;In hntsti: iorcts&e. ii aErcJx!? ittib bloti.u rx1 'bunfl.su's. The greyntet' quartz monzonite has a medium— kcdL'r'totc'fine—grained, fuav.znaad, ?ns Amberg 3btng rns nnvzcut.e PSLS Although hornblende few J) tto4L bovir twtdt occurs catynj in ft c.a ...fl hypidiomorphic hypi5 cnrfl to granular :'saaigir texture. tO Values of sinisrsl. Vctun samples, L1o;ite biotite is the most a4teant waCts mafic mineral. 'c. by 'ayfar tn t)as sol abundant martin. tn lOOxFe/Fe+Mg of 67 69 have been obtained C?and rn E3 Jte.ve t#sn ctcwkfor i'vrbiotite ?Co:ictfrom trri two i3 the ji, ..tflstit ;uac vcctv'.ib", toLiecSn Atheistane quartz monzonite, foliationsad and specimens. As saetnon. 4.c: in recrystallization textures common in the Amberg. Plagioclase tat nbov,. P\'aioo3 we ita.tt ! tmcn@'. tezttns b.ry,are CC!14vfl n' IJ, slip nd (An fl 22—39) is sxartrc extensively saussuritized, bsat.tt biotite is Li partially altered 39) iu y gna:c:ttzcci, to chlorite, and epidote plagioclase and with is, iS 0p2.*t* 14iis1 present t'bSift.t in :r p134.CtSta* satassociated 6rcctttsti R±1. tO CLLtZi biotite. blDt ito - I �,V 45 REFERENCES CJ[.idul! .CC r! y:' Banks, P.O., and Cain, J.A., 1969, Zircon ages of Precambrian granitic Jour. Geol., v. 77, p. 208—220. rocks, northeastern Wisconsin: T-'C ça&; - a a 3ZaC iRi1&t VVvrVy-:: :•L1.fC citA:C -: .J: - 7—14. J.A., and Beckman, W.A., 1964, Preliminary report on the Precambrian geology of the Athelstane area, northeastern Ohio Jour. Sci., v. 64, p. 57—60. Wisconsin: c:V. wViyr2;i:J t3-.r) aw V a L7V-7VVC p. #cl;lJ'C, r p.ct 3cn1V:.Cavr 1 or :.fc.TraC3Cr7 CICC C.. VVCC Cain, C C- 1963, Some problems of the Precambrian geology of a review: Ohio Jour. Sd., v. 63, northeastern Wisconsin: Cain, J.A., a �This page intentionally left blank �I 47 Field Trip Locality :771177 3 7 4Ci . 7217. . TITLE: .1:177,7.1 Belongia granite and Peshtigo trachyandesite : [7777717777177 77 774777' 77 1 777]7 '- 's771:p 774 1" LOCATION: T.32N., R.18E., Marinette County, west end of '.713? 77i:L'3.1": 77' 5r.: ,fl]7: 1, .777777, sec. 77" NW, .774 High Falls Dam 17,7] :1 t 1777 AUTHORS: Medaris, Jr., UW—Madison; J.R. Myles, Univ. of California— Santa Barbara; and J.L. Anderson, UW—Madison 77177771 °1f 7,7 .1"":77',.7] 11771"[7t7,! L.G. "7'77.I7i7.7]] 1' 7 5777777t3 DATE: 1971 and 1972 Summers, SUMMARY OF FEATURES: fl.:"" Peshtigo trachyandesite has been intruded by Belongia granite. A syenitic border phase of the Belongia occurs at contacts between granite and trachyandesite and as veinlets in the trachyandesite. .77'773 1777,7 .4,7 1"177177711.11 : '7711 77. 074(7!!I'777'7777L :7711 _•.••.1"7'[71.i77i7:7P77 2rc "l' 13:77 777 IL )7S,77:11. .72 77:77 .1777:11777.771 ''1"" 1 2777' 77 777777137717721377 7:77 '1771, .11'37i777 DESCRIPTION: Belongia granite and Peshtigo trachyandesite are in contact at but we were initially puzzled by the rather ambiguous However, after examination of thin sections, relations displayed here. chemical analysis of rock and mineral specimens, and discovery of more explicit Belongia—PeshtigO outcrops near Mountain, we believe that the Belongia granite has intruded the Peshtigo trachyandesite and that the syenitic rocks occurring here are a border phase of the Belongia. I 1'! '771.74 7771715'r.:]1i711 -'7 ''1"' .7 .1::.:. 7:7 1" L:771477727117 :714 777: .7 1:7117]. 77'I )hif' %7'.:''7r 1:) 72277 --"i"-j-L77.77 fl 71 717717717777: 17r1':ln ..7277i777...171,'7717.cL7:7'C€ .1:177.7 7)1 .7777777 57,777:7 '7'":'7c 7.777 1' 3.277]. 41 7'r.7] 71.7717 , 77 7777 577's 7772'71117771:1C1 7772 :7;7. this locality, 4"" tO.€ :r71"j0 7777." 13771 771" 7Y77 17'1]Z1.i7 7771 7717': 7 In thin section the Belongia granite is typical in appearance, consisting of euhedral to subhedral phenocrysts of alkali feldspar and quartz in a fine-grained matrix of biotite, quartz, and feldspar. Granophyric texture, a characteristic feature of the fine—grained Belongia granite, is present at the margins of alkali feldspar pheno— crysts. In contrast, the Peshtigo trachyandesite clearly shows evidence of recrystallization. Relict feldspar phenocrysts are set in a fine—grained granoblastic matrix, and the phenocrysts are surrounded by a well—defined rim that is intergrown with minerals of the matrix. In addition, anhedral poikiloblastic hornblende and biotite are scattered throughout the matrix. Thus, thin section study suggests that the Peshtigo has been recrystallized, presumably due to intrusion by the Belongia. Th7.T177': 1171:17. "775fl[ 7717 77 71773177112 7777:1777 L77 :fl 777".5.7 7["'777 .1]]; " )74fl14177 "i::7flfl 72.7.177 77 7 7771[:7 7 "L"' 7:7717 .77177'777j' 77777 13 21 27712772 7:.] 71" " 773.i77771771: :7L 71777.7777* L :777. 71.7:1fl7> . [77 :7 .777 1.7777 7: 1]: L,7]17711111717; 7 11277777 1 W.%' 77:'7.1 1]7:'77 7:2 71752 .17 •'1 771: J3.:'777 771". 777 1-:j7..;71.)7 ]77.t. c..11-:1tse.J Cc::"777]i T.7771":1 :7 ::71, .7"7L)777TI"".177#' 47 77111 :7,Ltl '77 1)7771277 17 2 :7777 5)771 •70777a'!l 777 77.7: 7. 7271] 7!1$ILTZJT'73 .771 7]12777]LItflLl7. 777 L"p: 7j7 77127.21477 c'77 711'1 771r!717"1:771.I. "1,7 57177C71321.'717T.77T7]77]1.:17:7777t 7771 777777 177,772' 2 7777 7157: 1:.7 177": 77.] 77,)*" -ij 777] 71 71717247 ,:7117'71$.C7]1 7717 751 1T\77.1.777 :7c.477t? 13 .717 ]717 7i:17"77'.121*" 7.17777.771 :]771]7ifliJ7,77, '• I LI 1177)77771 7.127 F*"V 247711€ 1.! 777 1<"L 777 7,1' LI £2 �48 If sooolttc con'ca'o to Do Lweaothe th: tctcocgla The occurrence syeniteatat contacts between Belongia ot'oi. and 5l,o(1''3'i1Ct of 33,0 1130 ?'aootlg'c. o:gc,rthat tool the Ito Peshtigo and as Peshtigo, suggest :'sii,I 543 :ijcutting ','to'nc the at- veinlets PSOJt ig'IcLc" 31 soil ai coct'iaco; t%o Fir 'Loll :a Chemical syenite phase cS of the Belongia. analyses-'o,,,:-cio'a":'o±o demonstrate 'a border to,'1oo ;l,ooo to' a 371 33 Ic is t'Ic,t of i,'30j nie4!,r::e between teI-'co-a' that ,:3 granite tYct I to La that composition ofI syenite is intermediate to'a ocopcoTttitoia tin— '1 the laic na!c'ci: , 3 Lilt Tot I -oo 0 of E' biotite t1"aI amphibole I:' 433,'a' and and trachyandesite analyses -L a tO 1), but ai'aca'noD'aioitirJ 1,9 (Table to-,':- mafic t',3333c 3:01375330 (Table reveal that To Fe—Mg St :aL:Lco ratios acoare 'Li (1.':(1,ir higher for minerals from coal 'toao 1,3 jilT:- 2) iD 101 cAlthough i,'Oli oc'aOI::'a1013o I .; granite and syenite for those from trachyandesite. 300 tiJti" .3 to than Inca :Fctr'.ooov't 010'tlL71liOtaiOili o'aY3been toot due coo ppartly cool4 to contamination development ofaDo thest-coin syenite could have cçco'at 33 :c' COOLO. 40::3 in the it': '000lL-:icof granite by in':' reaction i"ac",3or 'ttL with i33--oij5i,'o'ac't1:atotrachyandesite, perhaps reflected 00 47-0233 :' oco (1969) have occi '['.4': '-orb. a 'ta'o;tatvc :3"a:c(J,o 1: Ti02 content of the syenite (Table 1), Luth and Tuttle TaL 3Iii"L/i'ji_ :looo, in a granite DLI 'a 7 cici'S flO: shown experimentally that a syenitic border phase may form 3,1:3233 3:0303 tool: 333t4- tl"at a rot' tiC bcc'do:'t margin of '1, t'ova, 'lino cov'c,'a1iotto 5'ai'içO, 04 113(133 taicc,:'o :3 m:at,a33al, due to '.0 vapor transport of material between the crystallized 'cot' olcJLly a:-' -, to. still partially molten. 3 1-111 33:3. '30 Theinterior attot' ci.' portion, an intrusive body and the otto- oat:": 1:33: ., 113Th : fl331 53123'i'34 other o':'oi"c, Belongia iIOiL'Cv' 'a 1 coal 1,':i:t where :441301 localities Syenite hasU'o'co been observed 'ja'aor'co:I at 3-' several St-a'otts tao 03713231(1 to-i 0? 'Di':,t3o alliLlOl' 4001111 40' 1PC'(1'0'flL 'to, granite40has intruded either Peshtigo monzonite or Waupee volcanics. 030'L3' 30: 'Il,tflhiilo',I Doctirltig'; lco'30 monDi,: _.a Peshtigo on.:4L4' intrusive oa o'ic'CLT?t into For example, a clearly 1T33J'cI1.2 'a granite 03:7(1(10 to is JILt:' co:'o'pl c'. Belongia t:'at-ooc:t 33310, tiT 3 037'L':to' ''at ((1311 0307' 1:130:175 - (at the boundary between sees. zonite Mountain 133. a a arailroad aOL -i,-.ti cut near '':'tc'c.t'o in o"o.II:',,. over -ova:: -33-toogranite 7aznt to grades ::co)a::: :113,T.31N., 3 2a - R.l6E., toar'lc County), 14 and 23, 5, 1411, -' Oconto where 44 an'S " 14 sharp that lb-ta :':."icoo several inches into aa ot-a':.ita syenite zone 11 inches thick that has a "-'23,0' 18 L,n too :co,,c orCosi. contact against monzonite. 00(1,3107 0-33--o- Peshtigo Foahtig'o acoacasi,'ne . - - - :1 os:: 32' 23 7110 Jtra--O IT, Electron probe analyses of331 Belongia granite, -o'ot'o-ta 37:130and Poolct:t 1(1:03 •o:ctoco-to Belongia border phase, and Peshtigo trachyandesite 117230 Do: cog La 3-o'--do" Table 1'fc:lo 1. : - 1 31133 Si02 Ti02 1144 153' Al203 76.8 2 65.2 3 .68.3 4 57.8 0.21 0.70 0.64 '3-14 1.45 11.62 13311 15.31 141,43 14.28 16.60 Fe203* 3.20 :- . 6.67 4.48 10.80 MnO 0.03 0.02 0.05 0.12 MgO C, 13 0.10 0.57 0.63 1.36 CaO 0.75 1.52 1.74 4.07 Na20 3.16 3.66 11,13 3.76 41,434.49 K20 TO 5.15 6.69 5.73 4.35 101.02 130, 4 100.40 99.61 101.04 331,331 Total * 1 1 2 :j 3 Iii l-i' as Fe203 Total FtFe151 Total Belongia TM' 2C 7-si cng1s granite, g"iaou' <.0', tb TM 2B ,': ar in iic Po,3c'' <ki<:.Y-i,?3-.,.,0a113 Syenitic veinlet Peshtigo trachyandesite, 'TI 44-',ji,-' 'at LcOAi±,.Yc,'0 localities Ji'0335 at In-oi"co: border o':'tii,-' phase Average two coca:yooo.. analyses, Belongia '3 433 7.7 '23135 of iLt'i - 33 and 331-3 M2 near cr4 69 '1va:c. 507'L, 171.2G :0: Mountain, -S 4 33-4 Po:t'cSoci Peshtigo traco'H'ctd-oo'' trachyandesite, to, PP3 �r ;ratictf. rnn.tt: 513—548. 115, 144S. Mem. Amer. 513-tk4 p.p 113, magmas: ra4xnc granite and cqut Soc. Geol. 'wti granite with -v..tl' equilibrium in phase 't p)tas vapor hydrous Thc The 1969, o.',, 0.F., Tuttle, sa and W.C., Luth, 'c4., u.ctb, b.1. 'rico: hynct Lr br RENCE FE RE Tfl PP1 ittu. trachyandesite, Peshtigo hyeztlc tr Psuitico 2B ai e •nvhth: frar from Amphibole iii 33 from toltts Biotite i?n 44 TM nttD)et, veinlet, syenitic nctatti o's from1 Amphibole te.ptf'ace trachyandesite, Peshtigo psgi; t.1'v&&Sp' 'r ytr2.sj, PP1 13.07 3$' 8.81 33.18 32.07 32.eV 28.91 0.95 t\t LT4 0.74 ..Jt 1.06 3.85.r —— . 9.76 :.. 10.00 .0 —— l.fl 1.75 1.76 •,fl 1.33 1.45 98.18 98.51 94.5 80.8 95.1 •—-. - z ''.3 Mg + Fe Fe x 100 t caE Total a; Fe LeO as FeO • 1.59 8.37 t • 22 2B TM CL veinlet, syenitic M\I&).tfrkl from trON Biotite g:aat, granite, 85.2 93-4 96.4 0.92 3.72 3.tt 2.81 2.3' 1.92 40.97 41.40 96.22 93.54 43.4 95.72 9.12 .aC CaO MgO 0.74 —- MnO 34.96 541S6 34.4 34.98 '* Total Na20 -— —— 1.02 ipr ItS 3.23 K20 8.59 8.61 —— —— t —— —— 14.26 13.22 2 3 1•,• 5 1 Belongia Biotite lainsgLt from fr3u' igtite 2C TM 2 ts.' '5.i 34.07 34 34.17 .fl.fl 37.81 4 5 FeO* A1203 Ti02 TiG Si02 FtC2 .1 1 Peshtigo svt granite, Belongia Bc1cv.hs trachyandesite kcsht.7. tp.cl';'w&lsssatu and tw.e, phase, border :cndc: Belongia $,1tvtga gns:.ts.. amphibole and btuu.tr, Electron ¾, 2. Table Yc,tle 'ca from açb±ao.s biotite of a! PaL:flS analyses ;tct* probe :O4v,n 49 �This page intentionally left blank �ICnI CCiT 4. 201CC C of rocks. older CI:o--otcCoo:: CC. contact CC diorite quartz Hines the of Emplacement T CCC 505 and metamorphism 5. p1Cc gneiss, Macauley quartzite. and I51!C q11CC. Waupee 50CC coo and CI:;:cLt-o of i 'n5-5 CjC C-C clasts contains metasediments, metavolcanics which conglomerate, Baldwin the of deposition subsequent and Erosion Ill I 1 ::LncF -C v. s> iir.y contemporaneous). IC5Ci 2:CIT been have may 1. -;:Yr;o os:TzCCpL C5=-C4 5505 rocks. sedimentary quartz—feldspar "Cp;C1Ci:tCnCoiC:. pooo CC53I5.0CCC !4TN pzoo agglomerates and volcaniclastic, and 3P5:17 "0C0CJbCfi0C I?C'IP"Ss the t? 1531 001;. of Deposition formation, Waupee 2. rCLiCTCCCIFICrC CCCIILYIC 1:*.CCJI-:;J:L1. metamorphism. contact attendant with TC7CC5 CC0CC quartz to 5CJr2;0C2C2(C gneiss ;;CLCtCVC Macauley t5]5 the of Emplacement monzonite) (granodiorite 55050: 3. CC.OUI101111C55.C cCCCCJ Ccn ECO metamorphism andpC1 Deformation (Events 3 CCC and IF 2 T CI?C-lC;1CUC •Pco "OCCOCCOSS tuffaceous, and calcareous, s-si: , o::coopJ.. o500CCC flows volcanicC — of consisting i: CCC;: CCss5 CIIICn-5-I 1o youngest: to oldest from events, following the including "00CC 5105 CQ:CC5 515. 05 [CCC C C area, 03. preserved CC SCC0s Pis s'; history CC T :oo 0C3[inCCcC. Mountain the in Precambrian complex A AREA MOUNTAIN THE OF GEOLOGY DESCRIPTION: 5Th CC C yocovos:siffare 0CCarea 5525 Mountain 5055 •5fljp 55 theC10 of history geologic presented. j%05 " iTs I? p5±5:05-C: C 5CC are 001. 0iIL map iIT:iiT55 outlineIbCC sketch A this at illustrated the C ofr:rT1[1s,t and iCtC locality. T20,.tC.ssclfeldspar .5005 ç;- Hager and rhyolite, C5'5C.C..:C 5503 Baldwin 1: l:10flp --F po Hager iCStsy:3 conglomerate, Th; porphyry 115100551 c CCC0?2Ci CC 0111 the soI1C.1CC.54:L ;cs member upper :51 Waupee Cs:. between formation, the of Relations 5-: C .JX5. :1 Th FEATURES: OF SUMMARY 0±1:31 C3 C53, "CCSummers, 515 0151 1972 and 1971 DATE: Kansas; of Univ. ChlC" I"C"1 Lahr, "1.soo; Cotter C CT and M.M. Colorado -Corp., ''I iS0CICi5iC1I._L33L ":— Medaris, 1To_ -"_y; L.G. Schmus, Van W.R. UW—Madison; Jr., AUTHORS: .05:550 R.l6E., T.31N., 505 Oconto P110:3 County 1,- "51511 sec. OilS SE, NE-, LOCATION: 5525 15Mountain area C51CCC1 5I5 rooTs and 5i-i'5j: The 55 of geology :'o:c: P5511550:3 CS and ". 1:50.10. Hager rhyolite the porphyry 3"Ci1±5:5 feldspar TITLE: ;-iIs 55±:13[ 4 Locality •P-sp Trip P1 Field 51 �52 ". 6. H7495707)f,aJ:Ci .7,5', o'ios.t batholith OItco.asIs"Th (1450—1500 cf"1sc of the4aosf Wolf River m.y.), including H, .5nc1s0J, 7.57l5y7$),L5, 1's-Is'S Igo ,)ç71(33t Ott Hager 51'051'," syenite, Oju'tlfS. feldspar the Peshtigo monzonite, and :t'IJ .137 '.7" porphyry, 9,00 )159551:17ç0755:7,351 of xa0 Ool 0777.0 granite, son's tO with rhyolite, Belongia '2, and 75. lOs contact 1c)ltol, S metamorphism .1:)' older ..dcicr ,&557'J.Kt9'77:,51'5 Emplacement 11 : rocks. r"77''3'1 1' and 11153. steeply 2713 Waupee 0'1157'55',t.'sOi dips The 'l1710'cs formation '.111 strikes N55E. M15)507•O' about '55ss011't Ot.o':, 7-oH sot Relict llTGaO cross-stratification -3)77)3'- 555333711 '1' 370- :1' 3111W '1.7 cccfs.Loss.g ¶959 155a55'3 that graded bedding and consistently indicate 'I,7ll'075'1,0'I'L' 17'a'lst tops llTs 0: of1150053:9 beds are to to tilt the.5-cotio; north; there 1't$9. is no evidence repetition "16 01531. )1a955' for ''01 '25197:5 Hc:is of of. beds 3159 '90101199 15. 0571115 the within Waupee formation. C'r'flt CI'S, 5 15 /Ot. 51531191 has 11751 Waupee l'a'ITJSOOI formation ,sLo-a9 units ooc'ossI,s.tLrs'. The fIlLS. been i35,t")5757'5 divided offosSinto fo'•:a three (Fig. 1): 1)5 1195107 ot.55:1i3. of SI'S' metavolcanic a basal member consisting 17I1''ois aIl91a1:f'9$ £9.;-5.."OsLC-2.111.5: and llat'95. volcaniclastic 10 0jIt,L3'jLI4111-'1O meta— 1s-tS5-' 0 and sedimentary 1701 rocks, .s. .i:r: .L 515517 .9075 '91317 :o'o 1115719 1:71)517' 2'3t1J510'LsttiO'7 3,' a :nmiddle metasedimentary member, IsIS. an Ii's upper 505,105 577, the 1•''hP'S'a9omo 97i5'31-,9'.1. 995'"a,Y'T member. Within 7155711] tuffaceous metasedimeutary 0)19 'bas,sT. basal member, .111-:'5JLY-157 basalt 7r)t),51.f"7'1i75777,7 7:7357, but 71j'95j577l977.90al5 type is tHe the predominant of volcanic rock, andesite39 and so 553,'5.7171,55,9, 95,7 rhyolite 7'575:.7J 17553 LL77of 3-"'11M 53'H. occur toward the IsIt top the unit. '0091a5)5L. ll,rt5719 505 Chemical analyses of 18 specimens fo:..caa,r1c 7'''-L1' belong )1 calc—alkaline 'S's a 'IL's.volcanic 'loScolt: rocks demonstrate that :la57', the 5505)7259, to :::li053&1OI,5L.i1S sequence 61'.7617101100 )1.Ja-5 7"t9.?aO 'lOs 7,15:7 setting 7 15571,5 '1717 (Lahr, '7755 and 55557:J could have originated in an Ifs island si 1010 arc 0511:57:7 - 1972). 15 ., flC."')071,079 in formation have not been '50aup:c' .ls:-as 1395 11513'I '.1 the 'LOso Waupee IICIiU.tO 75377' evaluated 091.955077: 73 L 55S .e.1700 of completely yet because 0.1 complexities '3 lo.ç'I357._ '0.5555 introduced 5517 1710'7953050 by over11' 9523.' lapping ro),.esn0:s'caJI',:ot.'oaotlll metamorphic events. 02551 Most ,ss.jsocoLccoI specimens cOOT) display 2157710 :)0'9t7'107 9' assemblages 119515 :.os05bs.s5-os.., but characteristic of amphibolite 775555a'l 1a1'OT :3 facies '9) 57's metamorphism, ffl'.,'I:,'esso 5253 505 s :05 S:,'I garnet, 99251r17:IL, idocrase, 951-7','s occur 5j05'51,']0i05 :7'): of .a5.,7.2:0i1rs)Ls7o origin 07 contact 1:50795' .15371757 in scapolite, and 917551 andalusite 1c5715515535 metamorphic 151. rocks 11052.957rhyolite 05120112:07 a-'.1'.'.':112 ' S LOs, .11,93,1 51'-55 1591.Ca1s7'lOsSI Hager i05"15'7i 719 and of15i.lr-a7-si:5:''so.as appropriate composition near the Belongia 11 granite '2 91507 191519315's porphyry. poJ1o1'-a-r7. and feldspar 54.5tss,j/:1''701H1s Metamorphic assemblages sC71i07.,L1,a-535I' - I .Yo' 0505137'rIrtf FIELD TRIP LOCALITY Oi' '12 57t11&5.' W are 9552 tuffaceous In the woods south ofofCounty :17025 outcrops '3'S '15' '5152 of oco51 S'a.a53'j, Ccor Highway Jo. 255-1 3'S:. the upper :sLseWaupee 'Ozcspeo formation. I scoaost)'oRl , Cot On .sp,o"— member co-s 5500of c2 the :),',5 r,"i1a'J5711 a 7H50'1a9 15i517'N3,.,9 rr 351L75o1Tll 015 232 the north side 95) of the highway ", are outcrops of Baldwin conglomerate. 155' 571111 '5550 1,i,a 1 :1195'i.99 t'LaI of isiS Hager 7:55:95 consists 7150151105:112 00,'I1t1:. in .,5sli05751' 10959, prominent The highest, most outcrop area 1I.osOOr feldspar 071 this 51513.51517':53'9 porphyry, and between porphyry s7157 Baldwin iOssl7,'sr 305. '9 S l91:1tt fa57']feldspar 2T1515 10071950.) fl:. and -170-a an 501 intrusive contact l'07a55211 ,.$j)07JL base 7J115 5 '),995':' Ca.JI1L/ii0'7 On conglomerate is 9-97,1,35,7 exposed along of the '571.9 outcrop. f37,5 the 7,75'55 5' IsO a95to'10 the 1.150 southern 3a-1,-,j,,'7, :55 7'7';:177:711'5'.7551 S a,'505a5751117 97 55515s5.t 3117.11 1':571,Wf90 15157,955 north side istot)' '5577,1 of the 171 prominent outcrop a gradational contact between Hager 513:571555775115 is exposed. 512,25,'s'4'955, rhyolite feldspar porphyry Cf 'Ccilooosao' "Jr fl I SLISO and 55) 1sot1.rl.aio'rocks "3/3171]inr, metasedimentary .579 55'- : REFERENCE 77:111715.153'? of a greenstone a:o Oconto 7:173,j1595'S.'1 a lbol.. in Lahr, M.M., belt i0'1k, Precambrian .51]39s95.5'5 95, geology .1,19.: 1972, '.i1,57'.715'çj'iT eoa;c-- ''3L7;5J115O. 93'0)'i95!'s'11,17',: of County, Wisconsin and isiS the 117,15 Waupee volcanics: on'I geochemistry -50155117; ')'b"cO' Univ. i'a'yl 797j'sis,, 505555 M.S. Thesis, Wisconsin, '55'H.s')'1n7 LI, Madison. 'a I �P4/ // -. . ' 1? / P. / Jp \j r4 ( "/ /7/ \4 . A /i '-I ( - ILI 1 i-i;-' 7 ILk .1'<• - '4/ ) LL L.G.MedarJr&MJviLahr Baldwin conglomerate bc Macauley gneiss WI wm wu mgn Hines quartz diorite hqd JUM ['?IL¼ 4 LI bg Peshtigo morizonite pm 1 metasedimentary rocks metavolcanic and metasedimentary rocks ::;. tuffaceous metasedimentary rocks Waupee formation ' fl4LA!1.. ../ 4..I/;1'. i :-.-'I bg Hager feldspar porphyry Hager syenite hs hfp /)7I:4.75 Ii5r! L_ '/.fl/II/1,lp J4I., T"L4//J A/. H a..' 7 1//—/-. ://j// Mountain Hager rhyolite hr 4/'.'' J11 [7 tiar'I•t I [7 d I4/iiA] /1// 1/4 —117 hr Belongia granite bg EXPLANATION ±iL j *¼-; C,T R / 7 \/ 7:; /1/4/ I mile iL ¼ijI(4// ri 4/ 17/ If•; Tij 1 A S J. I//v hs I'.. j(( / -. / L A" j ,; ;.f/.:/,H LdhiJI.% 'I 1kv\/ D.cH (T. ¼' GEOLOGIC MAP OF THE MOUNTAIN AREA 1• j I i �This page intentionally left blank �55 Field Trip Locality 5 [17 TITLE: The Wolf River quartz monzonite t1ILL_JJT C:tCHH[1 I_• L LOCATION: Menominee County, on the 11° IL — -t IT VT — Z,? — H:. _— SE*, L sec. 22, T.28N., R.15E., of the Wolf River west bank NEQ, V IZ"'I]°( AUTHORS: L.G. Medaris, Jr., UW-Madison; W.R. Van Schmus, Univ. of Kansas; J.L. Anderson, mv—Madison; and J.R. Myles, Univ. of California- •1Ii C! H HHF4 <Jj 'C ° HL1 I ° c-HTrI - — I I — Santa Barbara l1J&flL H >(j(! j DATE: and 1972 1971 1LIIC [L 4IT°'I HHTI Summers, FHHU1H SUMMARY OF FEATURES: 1;2 (FFjj!i' Exposure of typical Wolf River quartz monzonite. rT4I ;i HLT DESCRIPTION: VJHCcYi The Wolf River quartz monzonite is the most extensive lithologic unit in the Wolf River batholith, accounting for 51% of the exposed area (see Fig. 1, page 10, this guidebook). :cc çT :I I TI .T1FIHTJH H i :• L — The quartz monzinite consists of large, pink, ovoidal alkali feldspar grains (1 to 3 cm) with a medium—grained interstitial matrix of quartz, two feldspars, biotite, and hornblende. The quartz mon— zonite is massive to slightly foliated and is cut by aplite dikes, some of which contain scattered, subhedral alkali feldspar phenocrysts. 'yHT-H[iE i1 H=1I3 C)CCI JTflT1 ''HH TcH Z:tC cq 4T'L©H t= 2Hi)II He;C5 c(qI HHItJ:HI .CCI HIP 'IHI L.V :H !F L H4 I C L ;4Q p' tJ L — II F' :H -( At several localities along the Wolf River the quartz monzonite has been intruded by dikes that resemble the Red River porphyritic quartz monzonite. Two such occurrences are well exposed at Beartrap Falls on the West Branch of the Wolf River (sec. 4, T.28N., R.l5E.) arid at Ducknest Falls on the Wolf River (sec. 27, T.30N., R.l5E.). F 1PE I (C ° ( °]i 1 IF Cc 4j1 — t7• :.:Z '1J :__L: 1 I Tj )14V C CvI&L i:;: 1 IH T1? �This page intentionally left blank �57 l.it:c Field Trip Locality T: TITLE: 6 The Red River porphyritic quartz monzonite LV' VeEV' n!I41.V'iSLVt eL'ç LOCATION: :;l :.*T1Ti °fl R.14E., Shawano County, T.27N., 2, V sec. on the Red River )çy) LV' 3IV'C Lyi; SE-, aL •IpLVI:. SW-, 37 AUTHORS: UW—Madison; W.R. Van Schmus, Univ. rV)Vi IV' L.G. Medaris, Jr., and J.L. Anderson, of Kansas; 13W—Madison 3: 3 -3rL-t uTmfl )JV DATES: Summer, 1972 LLZ1 SUMMARY OF FEATURES: V'J Exposure of typical Red River porphyritic quartz monzonite IL c:V'VLVV'I ty r)1[ V'L TT. fl.d:c r DESCRIPTION: IV' The Red River porphyritic quartz monzonite constitutes 20.6% of the exposed area of the Wolf River bgtholith and is located in an ENE-trending belt between the Wolf River quartz monzonite and the Waupaca quartz monzonite (see Fig. 1, page 10, this guidebook). ')t ç •iV' i ThLV' t)L7- V':tJ V11:rL LVV' 1V'V tT LV'4'Fli i ir — - Fl I1 —ft VD& :: j VS Cif1V2 'LIL7 4•II.E '11 1> tcCL7 At this locality the quartz monzonite consists of 10 to 20% subhedral alkali feldspar phenocrysts (0.5 to 2.0 cm in length) in a medium-grained matrix (1 to 2 mm) of idiomorphic to subhedral quartz, two feldspars, and biotite. The quartz monzonite displays a prominent foliation due to alignment of feldspar phenocrysts. çJ t. ;"zV':i' 2QVSLLtIL tLY- zci rzc1; LV') ° C)51 I i i —n nj:tccri cj ' LI I $3 'I TTi3i. LTfl- LJ H7Q7f 1'4.T 7Lta1V'fiIflC LC TL6I;=LY c 11 I €4 i)v&: �This page intentionally left blank �Dissertation. i iv .pcc...Lc I cli7Vl LiC/, 447, 4I - 1965, The Origin of the Tigerton Anorthosite. IITIL W., Cl-1c41J, L. C-.Il-: unpubi. Ph.D U. ci ycv Weis, Wis., fill-a,.- (IL.fl Reference -ccr-aiI avccc-vcc E NY. y'cc 1s14.; The most common twin is the Aibite twin. Pericline and Carlsbad twins are common, the latter has reentrant angles. External optical scatter occurs. Grain size reflects cataciastic deformation, with some outcrops, e.g. SW-, Sec.11, T27N, R11E, appearing almost layered. - --21 a- 1,1:1cc1 ILsCflacc C-nt-C-I c Ct d-yC- 411'tL)CC-Ll IltILl I Ill-till :?fii.a-fl ILl cca(a II4Cfi\C vral3cc c mc,ff'lvaw.;. cc-vt tc-;fl,; cat- rcrt-ntc'c c-cc- crr.a-: ma- t'r d-a 'cacc:ca1 - - 1fl'- l-714kC)ll 111 -q. [I 'C - 1t11-:cO1'ILLclnCI :ccw cn4 ccc a, La-trcitczcc JlaC(.)© 1-ILl The composition of the plagioclase by outcrops has a median value of An53, with only one outcrop having an average over An56 (An60). The larger common inclusions in the plagiociase are hematite, hornblende, biotite, ilmenite and magnetite. Very fine rods of these plus rutile also occur commonly in the 010 plane. C -1:15 ;fi-- 11117 CCflV II c-4;4c-a]aiI fill 9hiT .. -----Cr r'CCccc-accrC I41( 1,ji .11-I-1141".LT flC.'-iiftL)tCCll.iCCrIlr 1.-I Ti Ic'.: fl1-cr ar-;a 511:5-Il pa 71 ccv caaltC- cat iall: tilcIlla SILL l4t1c cccync city CLLLCa-l .- I aCvcc'-.'L-rcr-- a-y1 a-ILL - - 72-rn C--m:ig c- Lid pita- fill-cl cia: 111:,ILlfl t 14 a-fl TIc c-c 4p1fi.1471: 4 Tdll The Tigerton anorthosite outcrops always include granitic material. The anorthosite exposures generally are small with the largest continuous The contact with the Wolf masses exposed only about 35 meters long. River batholith is sharp, both megascopically and microscopically. C- l.-L1IL C 4llIIlLlli s-1 Cr1: 1ILfitilT1 4-c- -fit-IL? .111 pat.-: mc --fl icy c--cc -r-;nt 7ia-a-- ccc Sr Lccr;-:c-5- CCr.L!-C,IC.S, I4cc)I1IJtLcI LCt -? ll1-rcill cLttcc ducc-ca:-c cc macc-Cr ,Lt c- -I-Li- cU I cct—aa;caac 1111 'i'jj .clcCnrczv 4( ififi 'wIIc C_i.4jL :c'ca [IICLS The Tigerton anorthosite may cover 125 sq. ml. in western Shawano Most exposures are anorthosite, hornblende anorthosite, biotite anorthosite, or gabbroic anorthosite; a few are anorthositic gabbro. The plagioclase ranges from An32 to An64, with most of it An4 to An56. Grain size of the plagioclase is riab1e; 5 cm. grains are common and There is local foliation. grains up to 20 cm. occur in porphyritic parts. Biotite is second. Hornblende is the most conspicuous mafic mineral. At some localities pyroxene occurs as cores within hornblende, occaIlmenite/magnetite are common, with ilmenite sionally it is discreet. Locally, as in the SW-, NE-, Sec. 33, far more abundant than magnetite. T.28N RilE, these affect the compass. - 1'C--Pfi-dP 'lftT -cCL C 0147 C '- cc-a-c1::' c:n-::--c4crn 1r1k1 a1.c71rcL-c CflC:rT fit c-fl ?cuvfi 1tcc flalcILa -mir cc -s- CL3r1:c-; ca-c-i 71 I .rrjrcLflcC, 1 fl1 imLad I.- 71 --••c•'.1,T-fi ;ICL :1111-ca- II .11 40 lIla 47 v-IL-v1- I;LIc 711LC:L. It l- 'ta- - fl Tha-LLa-..Lr.plc :2 -: IL11 v; 1OCT11 iv 'my H ;1:;l1caifl: cc-co'rcicaa'Crl a.CflILc-1 cc Cfl l.t iltrI.II. IL? 1-IL -ca-; 1i-filc.1iCi ct-cl pcc---J- C'IfiL di -cPU Cm II- iIL-0I- ILL/v a-; l'1fi-c-LJlJtC..,-lc- It -ILlIC d-ll-t.' 11: C., I CCCII Ii CJyII13 tt:tdt.IL-'c9 ca--n vcc: -Il 210 c-ala-crap wcc-. alIt .1 : ma-arc :ra-171IL-.:l? --cc 7. c-t7 v5rycrcrcc -c-laIr 1:1: lift —flIc fl -I-fl 7a- F I?P 1a--A5.IIL am cap-ct s. 3111ilyfitLcilfl SI-Il iccr:ILC Or? Ca-a-la- I71ui cmiv Cq ILI-i'.-p Co. acILCLICL4 DE SCR I PT ION: '-c-c cLLcaI-zccrcrcc r-;r-c-c3y, - p :l.l?lIlfll- Lt--[ a-c Contact relationship of the Tigerton anorthosite. - ?S'7cfl,,:cc £4 SUMMARY OF FEATURES: -,,- 1, 7.S4aJJOIS Summers, 1962, 1963, 1972. DATES: ::cy-=crv-aw-14- ::.r,,-1l- . dd?IC/ -c a W. ;a--Il1. L. UW Center System—Fox Valley Weis, AUTHOR: pcc-c a::.:ip-[ cva-vc.xct1ta5 7'IlL.I-J 1C Art 50i1, SW--, sec. 23, T.27N., R.l2E., Shawano Co., Middle Branch Embarrass River & Co. Road J. CrC -cT m4fl Cr1a' Cram m.-ra-1rv iafi 4c NW, SW, LOCATION: 0711104 211?' iti J(?lirtj, a-kr. The Tigerton Anorthosite TITLE: Lcc-mca- -rfl;a- p407,1 Field Trip Locality 7 59 1 �This page intentionally left blank �61. 61 ;' r:iLca ctr:L,o '1 Field Trip Locality 8A TITLE: Ec1. :9.e 1 au b Eau Claire Dells County Park LOCATION: CR sec. T.29N., 7, R.1OE., Marathon County c SW-, AUTHOR: LFLtirg; UW-Oshkosh ]1 Gene L. LaBerge, DATE: i61TL iTa\ 31.1b721 Summers 1970, 1971, 1972 k ''..J1i1S J.5l AH1A: A SUMMARY OF FEATURES: i2]7s; bt izA1I ti2 D:1L :Laite Ia •iL9.:g;, Eau Claire Dells is on the western margin of the Wolf River batholith, consisting of a large expanse of relatively homogeneous "granite". This is in marked contrast to the volcanic rocks with a myriad of small plutons and large scale shearing which characterizes the geology of Marathon County mapped by LaBerge and Myers. ti;i 2' Ai Ian©b Ja ct eTk aag 1xaa a; g$gj ;a-& iLt:.ny riA by i2t :-J tztiL L(C) :tLCJ .CCRH ;cauaacti.c th;. I bt]huA ijc1i ThISCZ ra' IaL'Ltari±n C,oaarA •f gaagy a.:atEcat a3tcrc tXT CBC a arIact A major shear zone which strike approximately N30°E occurs at or near the western edge of the Wolf River batholith (informally called This shear zone is the Hogarty hornblende granite by LaBerge, 1971). particularly well exposed at Eau Claire Dells, where it is more than However, the zone has a mile wide and consists mainly of mylonite. been mapped for about 30 miles along strike, and reconnaissance to the southwest indicates that it probably continues for at least another A number of other shear zones parallel to this trend have 10 miles. The magnitude and been recognized farther west in Marathon County. number of these shear zones thus constitute a major aspect of the Precambrian geology of central Wisconsin. Cl AIaL9©11 V .t 72i icr: race Ltaa :cccta it b isad ArAc: c'c. c:'.rc;r CL raiUj La icl.IrcI•de LjC I Ac blacaIb-ci Ia; -cc-el; arAbic: I ciA re:ecIgi7i.: beea icrccc Are-i .-; cc! 1ircbac *. Ire.- at IA air. LId cIt asp-c-cl c-rIce a :c11 C I-rrAL.i-cc 1Iae at cc;iele I - 11 cr jCHCcTiHcUJ7 Eta ci; S.t$yO€;Sdl wthta- yc tcrabI3Tc2e c.cCcty tIAa : Able lad 9 ]a:JLCcga Ia ccntc 1JL -c ;cA . LTz I Ia7 il; —r bare Tb CR ciA acre Lcccc c ride-Al tbviic Re-s aç•9 ccii elI tic ceec 1 cc! JPU.c:aci-lLeIaa -cieiLcyy cC; DESCRIPTION: maccc-rely •rGii ttccccidy iii; IlIad cartacci, dcc ci:;; Li ;icii 'rr-4 Al irL Ac ?LaIcI At Eau Claire Dells county park the exposed rocks are moderately to well banded. The banding dips vertically and strikes approximately N30°E. At the Dells proper (just downstream from the highway bridge) the rocks are relatively fine grained, felsic, and homogeneous, and CL-fluid —U c1.LCRc ip Idri iCc 1 cc A It d cc bT1 f-c ,CRiLHC Icac D y-ç -j Cj91[ — AIcr; be c-:acum i:Incd ccrccc Ac ;clc-;w]c LCRLL. l 1 Irpli A caR 1-I___ cccl; Ac do not display conspicuous banding. However, further downstream (near the foot bridge) the rocks are more mafic and are more banded. Upstream from the highway bridge the rock is well banded with alternating mafic and felsic lenses and well developed quartz lenses (boudinage structures) evident near the dam. Small garnets are abundant in several zones immediately below the dam on the north side of the river. East of the swimming and picnic area are outcrops of banded amphibolite. Thus, cicpriic 1R-cCCIVelrhtdLii U cci i lb izerc;i-cl elcuic bccrAiw4igc 'ii L 11411 c Ic clIcL eCu; 4 I LLi tK2 :iJi'Gii'CClCR :i jiij lrcc-c-c-: i51C_it re tic 4 44i Lw ci cc—' C I rcuurc; la-c'c-:--iiia!,, c ICc_ 1 cc airi Ii 4uiliLc2,H - -r — I 1 — IcceciLl IcLL _c U-1i 'ci 11 TiItdV 1' i1 l111l eccA L I Ll1' -_-' it II �62 EXPLANATION FOR MAPS OF EAU CLAIRE DELLS AREA, MARATHON CO. II Scale 1:24,000 — L cd Cary drift; terminal moraine. m 2 Mylonite- and related cataclastic rocks. kqm Kalinke quartz monzonite. '1± LI'J hhg [ dJ mvJ k',j?'J,j,'2, granite. JJt,.:L' hornblende Hogarty Diabasic intrusions. 1.25 '''1 1' :":1., '±:2 and Maf Ic volcanics (locally metagabbro amphibolite). Outcrops, or outcrop areas Geological 0i'jc2'; contacts Rockpiles ' Quarries I �— 2J N6 I. — — 1 F r i ¶1 _________ I /--" , U - - 5-' - ,_" - :- LU - / 4' —— ——— —— I -' ,k7e 4':—... F ' I' I US 5' U,: U —F' ' -:; —' - II -U - 1 : I, - It/I // -s -- - - 4 - t114q -':4 ':1], Il • 44-- IC t—-_ I: - 4si - •1 • / I z 2\J - C' -I - - - �64 J1 Figure 1. j-• l3 and lens-structures in Eau Claire Delic Ba ding LÀ • - upstream fjAL. ±'om the t1t Licge brdg on CTH—Y Light gray iense% al Larker gray banded materifl 1± i rt prcb1 v boudin. quartz, i babl areqatz :;mjH Park •fic rich. :: Ltthth mafth is rrelatively structures a- aoth the banding and the lens t P fJ- tearing. thrmed as a result of sh thg hct are believ 1 to ihave L D Figure 2. Ba1d. CnJin!.g mc' ltns structures in fe]sic mylonite ±L_tJ. just downstrE?arr from dir bridge on CTH-Y. Where the rock is i more homogt --meous, the I L. banding and lens structures are less obvious, hut they are still a common featureS ktl - - I - �Lcturestru flow groundrass. ndirr - f surrou the tH of and feldspars the of most fof shape lens the :- the grained Not matrix. Felc 4. Figure fine a in "eyes" flJrkspar L .1 - ce p fracturec the that Y1 sir'± irrdu ua rt'1air pc overall or Cl De S L'ie from 'tevct' au&rtz formed lens-shaped taller grain, z River LC2 ç the f nt. JJTh t7±. Eau 'e lens . - - 30 X31 X fragments. also note and i. zone. shear Figure - - Jhe iote Nc u 3. 65 �66 tti the n-Itt IT: 'IL'aaicittlct' on the composition range from cc,'lr,'S 4ILy of nIL' the cir'n mylonitic L ciaci i'arocks :'4m- :"a4ILa ttam "basaltic" east nan C 4" the LitmCenter 'L'a'vI:';'Dells tam Inarea tans taIL Itt ti"basaltic" mta,t a a to "granitic" in and'ILant back to 'ct 'gamin ,, - j ci,r::;:m ttS':L2 Compositional acmIncn i'll' 'nau4nci ' I' downstream alongrhthis cross—section of tin the ci,caama" shear zone. ILcirn,a: tt"na'n: attiama LaS tat a'of I-isa 4' a.; 'r;:r,lmn. Inca? are variations inca. common both andacitacts across talUs thea strike the shear cltit:i:iCLL 1,t tact,": anal ". maalong , 'r,' appearance alt: character 'tint aa,ncnic' 'tr:ar"aan-m'.c':a'a and with the LIt':: result variation in I' the :a'Tata' 1 of zone nIL aa -'a:'ttti.'nLr' zcanni,LL cof the 1:'am zone. Variations aa'ci,aaadepending ILanami - na 'W4t'? upon cU whether Ct,Rt> t hydrous act-n :Yr C, 7am a an lcra also tItan' arise a ant' , eat' anhydrous ;acrla',L,:c:,m minerals Lan'aILt during i'iaairL4: ', t,,p'aJ,,, (feldspars) yam tna'tra'ti formed minerals (micas, etc.) or cn:i',r,'tatILai'a:i,tac1 'tamIli an,tIL'an, recrystallization. alt. taIL 5t 5çc laSt along it, and aititaL::the tic: Most of the Dells elsewhere act Eau tat CIClaire :- a' Cal cl,:, Itbanding itt; c-IL? ac'aaIta tIg at acatactal and 'actc atic'a,it,S' of aiRvariously -'nainacs" ILflattened Eau Claire River actually Fain, :lcIrt F. ''a' zone ?a';ta;tlIa? ,s consists IL: length IT ttgn aILS ni'::range cnsct in ft nit, material elongated ::tt,:t of na .-hrla which caL mafic tInt" canand IL' felsic at at;:rzm'a:d lenses Snnclr. Figures ansi 22 Fi':na'te 1IL and mci a ':-rtc:',c:Th'aof cL aim from more than a fraction an inch. f;ncc accca tacta amile Lit' to Microscopically cataclastic mnymlJiaja lenses. lcanams ott the ant smaller illustrate some 'l'l';raenco; - aaiLLI' oanaTLca,atI,n a: of Thus, "tb-as: maIL4 4are art tcnaa'-features, such inifS Figures 4:t'i'5t 31 and common. at SU:as asillustrated i,, tt.ttitdI La IL anti a cia ?'ni;Tc:5[ tectonically. ,,:,itt :tr}n,:c tt,i 1 i, a have 'tarn formed 'a'n Ut! t-a'agt to the rocks in this zone believed ,,cy'c are 'itt rc,nlUaL::ltmt' a-n 9::crnags: Shearing ttai7 may ;'acmctt:t produce the banding (as well as ar, cataclasis) ta:cacilaaai R't'ji from an tI't 4anILiLf aa 'antI a:c'ac zone stint ap;;:ci,aILan a: crosses 'actitac aa shear initially L,'n',o'gaa':a't''as homogeneous rock, maIL' when approaches or t,it:,mLam,,l.:: "cot-, and raIL, a cattaIL 4at,c'nc:'i '$.":nai '5 'n "L:tl,t:j:aaia,, Inca at's Lam contact between:tacontrasting lithologiesLas thetam banding may be r:na'i'nna pronounced. -Its ILLs rocks r';tim ILn'tk'c'n'n*'c This situation is ta 14::, II represented ac.,cr-'caicadT by 4; the between the ti-n evidently '"a "a latter !a'nls " ittaiat;':Ta tim-n hut tin''' road bridge damLa; upstream. anaL the titan 'IL: ''caaa and - I - �67 Field Trip Locality 8B :811 1IC'I"7j 1)1011. )ITS1I TITLE: Contact between Wolf River batholith and mafic volcanics !Y1II CtI 111 it IFi11i,1I CIlUlCIf 1C'070U 'C 11111 OCII-0L.fCtCTI k1ao': II LOCATION: I P1) IL -'r T.29N., R.1OE., Marathon County 18, sec. oqLCC1I:Ip Ct0-flUC$UII't I ej C;-. 5j3 I I N, N4, NE, AUTHOR: Gene L. LaBerge, UW-Oshkosh DATE: Summers 1971, 1972 s OF FEATURES: SUIVUVIARY The locality is typical of the contact between the Wolf River batholith (Hogarty hornblende granite) and mafic volcanics. Near the granitic rocks the greenstone has been converted to an amphi— bolite and, as at this locality, when shearing occurs the amphibolite may be well banded. Although lack of outcrops prevents determining the width of the contact metamorphic effects with certainty, it is recognizable in the field in a zone 'about one half mile wide. J.LU'0.i — CU-CI =-p•P;:: —I _ : - 8flU RC{i 1111 : ItO —' , r,_ . t"— T L-CI41 OCIl 1- I 1 St CICIL ' 4 jV •lfl :8 1 zIr;I1C'jr,J:CCplTII 1U111LIT18t- ICC -: 11C U' E C P:ICi,CIU'C 'I.lU' 8C'U-iIiCU p3 U L '—'- CII ,-CCCOfl 0€- CU' j :11 I1tI;_.CI TIll ILIfUtCI -CIp (1 71:1:111 Ci €17412 :-: TiI.11I L IC tq CCII-C I --c iwIr 1r.;iPT-173*V 1I) L1 Although the contact between the "granite" and greenstcne is poorly exposed, it was mapped on the basis of lithology of rockpiles. Rockpiles along what is believed to be the contact consist of a mixture of amphibolite (meta—greenstone), granite (commonly pegmatitic), vein quartz and in places metagabbro. Small dikes and veins of granite vein the amphibolite blocks were observed at a and quartz cutting east of the "contact zone" consisted number of places. Rockpiles granitic rocks, whereas west of the almost entirely of porphyritic "contact zone" the rockpiles and small float in fields consisted almost This change in rock entirely of slabby amphibolite and greenstone. 40 type was generally restricted to a acre (-- mile) width or less, and at least locally the change in lithology takes place on opposite sides of a creek bed. Thus even without outcrops one can locate bedrock contacts quite closely in many (but not all) areas on the basis of the lithology of rockpiles and/or float. Trenches dug for burying telephone cables were especially useful in providing information on underlying bedrock. ,I7'C7 CIIIZ CIT - I j - - TUU'"U' s- U':Ux,7UJ r' - (U' UU-L— t8IL LU U 11 ::81t 8)U't r& '1118. OCL. -y - I' - U EU1I-i UICICIU 1 tJL"I:I?cA 1 5U'1 - 1_t •3f1 — 1t tL 8 t I 7cU1:.:j: U-J1ETh:::U±DIT1t I L CI T I $Illt. —T :1i c li ;Lcn Cc::t 811711 Vfi :155I8 T &[ -Cit ;xirU tJ.E7 UI -f 'YI)i c3;ILz 1ifLt; -. 5t I r•:r i3 - 1tL ¼'LrL1CtJJI ,CU' ' 8IU7 I- 93T;dItcC-- I .CyC.! rF71I2!t2 — C' ¶1-I C i'31:c7U:15i;U214-IIi Ui Y:oU:CUvU L - L-C ;CIiLi4 1fr:c 118 8I1Ut t:1:I t5';icIv:i-:I :I7rrI 11 6Ut r- C ::: t:LX ct: rzt L;:: it if I Tr;Lez: i1ir:i:i89 :-: r a:rq z �68 '<if•'i FOR MAPS c) EXPLANATION ?.c0 :L,:J 'q AREA, fJA'SJEu1 ILP<J<2.L DELLS OF EAU CLAIRE MARATHON CO. <2<J ,i-•;<2 LIi Scale 1:24,000 5:.< <21?L7h SL moraine. Cary drift; terminal cd 1 m <2T<2 Mylonite and related cataclastic rocks. 'UT<2 kqm Kalinke quartz monzonite. hhg Hogarty hornblende granite. :i:Y•y i'l'c,v±c.. dj JD* L.1L"1<2: my .:&J=.l1 and • L i.<2.'L;< Mafic:i't2z1; volcanics (locally metagabbro amphibolite). 1 L Diabasic H intrusions. <j:c1HH ''<2<2 <22' outcrop Outcrops, or areas ,-'..- <2 Geological ':•1 c" 2' XL<2<22contacts Rockpiles ' Quarries I �1' R.IOE. I - - I0 M / hhg - my k , 19 .. V - I •1 - , I — d / — - — — C. / I / 1. d - / / '•-•-- r •,' ,' my hhg / / 29 I / m I- /1 C. — : / I. hg h i• I. ,Tr r It. 1 / , 'I I I. I 'I , i,i , , I .1. • / I,. Ir / A m / / m, — —I m '.4 / / A / A A' A 0 / A my, .-— - C- // .1••' my / / ,mv / / 1L) m m / 4- A l, (iI -- 'p — / C / / qm / A 'A , - —— / ,/ I I rtitt• .tii—z. C I PV -4 K Th 4 / f I ,1 'I K —— /' / I -I • .— C. C .• 'K : III I / •_—\ Q tr Cc 4 C I i.)C •--:-. ,;; N. R.9E. -J i1es F' / / C. •, — C -- C, N - -T-J .-- Cj CtJ I. cd ¼ It •• K S -.—- '-.4 JJ 1' "'C •\C / a::H ,$/ - A , / N. / kqm / A 1 '1 N-- - 7—. "C �70 DESCRIPTION: 5cL iLSS' au f!/ @5the Sbc contact .lLc.rttc- @rs cc ccl are coarse Outcrops of "granite" within 100 feet of St.: :1. cc cc-lcc712 ctc:c "granite" for several miles to the east. Sc N•ciT-S of the cc.c grained tcU ccitt and typical 4111 ir icc to "granite" throughout much Indeed the rock is strikingly similar T'ti fltLtt lt.TSiT-tc c::Jcc and Menominee counties to the east. 1ftIllJ .ctt. lIt cc. - valley in Shawano ck.c 55.? River of the Wolf @5 of : -. l - ' ii L- ' lcici -I con@t:,i is itiL1l1SC'f', but ? IN cit tcc' The contact hasc,:ct notb3i,fl beenLCICI@ found inci outcrop, I'!lcift cc,'i-c/ itself c:.c?r ccl itc:LI191 Y Along this valley one can -.j:citcac swamp. c'ccif.t•r under •rcrciLiLl; or Sift. a ri. valley veniently in :;c&ct icc,ccc: ::;cinc'sIlc -'c-IfS granite with abundant mafic inclusions. .iIij:Cc1.lc 11@cY¾ find blocks @5 of the tcccciiccit1 :L—i-: numerous Vi:LIV narrow liTil rsrc'cc zone evidently frccr form a very 5c"-•ct@, cy1.i±-itijJ 5 :.:- Ctc-,, however, 'ctiii ¶-5,cJ1 blocks, • -c5. The inclusion—rich -'ciii Ic-cd S t-c rcnSc@ tI,cc tcic' @'Iit. 'I and the granitic rocks on 55cr west cc the between Sc '.-iittr.ithe 55 amphibolitic ' iic.Ttiti IS : rocks on - .- r1,•c *311 5 the east. :'c'c-ticmapped ccpcJ1 all r15 rocks '?-cc'iplutonic cIt5cc. :ct± the '5t ct•cs t if also : C$flLT'J This stop is typical&cin that itt7 -,-,c5.cr.r:i'-i',r oiLcttcc-' Sr.,c :-45.:- the intrude older volcanic sequence. I 121-il is the ;L itT' iccgeneral dLfl''da area Ic this cccI dccl ci: cit. '.c,ia in 5 important ,i9cTcft1 and An interesting problem Sc-•:jt •c@;3 uc&jnrci: of :5 cS@ the Il-SLI Wolf River :1* [i; the cSc@z SI'.a shearing relationship to emplacement cr5 c± crlI.. of the 5?LciccLJ,c-cr1 cccc crc cii:' cc 'clcflcc:IS of here one can demonc:? localities ccc': S 5cc At a number of southwest ;tt, 5wi5kircJt'S?' batholith. cd'rclu21ti-I 55cdiL5lI hcti rdrcT'lT'-ji hornblende granite) has :.'i'r-.r- batholith Sn:ccS ± :1: (Hogarty -cc:t ttct 55cca' River strate that theWcI Wolf clLc:: Sc nc-c: 1cim:crgneiss, -:'.Ccc - mylonite and granite, i.ct.-i5cc gcrcc5. 51, augen ;-L.cccC ar1. gneissic -Ic produce been c,;i-ccic'cC! sheared to 'c-cic. c@iL-cill. will :-: if -R This Iproblem 123511cataclastic c-cd---?,ocd:,r-j.c i:cScon cc a¾ rather 1 -aIccI large scale. other rocks c.cclclcifL and512cc-nINatural 1:--the t@ Wisconsin :crcrcc GeologicalticS -ccc tc.c by ea mapping --:--c- as be @zclitrcl@ examined further Lnt pr.'c ccci:-:, The presence tibitI cd southwest along zone. LL:-LtLS-± this dc-ic 101 -cc History Survey continues to the c: c.'rcc' c.-.'c-tb7 1515' crocks r dcc may ct c 15115 of the batholithiC icc S'rcrii.: c±L:c.cof major s;cc-,.cT'rL.t shear zone along the front @5? @2 a ¾ cii c-tc-cticd c-c Cit-I batho— the c-cc emplacement 5la3ftLlt-tL-t of the ccJ ncc.2 cc ccinftncirc,gT'T'I indicate that cISc', the shearing is related to ccilT' crits cc-icr, cf-ic-cf which i-SlitS Lt1TT,CnCI@ along 1,-.,r,U1L L.J ±'l-ck- as iii a buttress behaved ,l' 5-ltIitlfltL 51 lith, or perhaps itc&t that 'Tcd the batholith Ni:- t@•1¾L.SL. the shearing occurred. - 1 -". �71 Field Trip Locality i±CC 9 J, iji TITLE: L-'UI Wausau quartz syenite — Old Technical Institute c- 'U-2:'CTioC.:'ojt. :iTcC0C,c',1Lc-itCIt' :i-r -'=r LOCATION: Marathon County T.29N., R.7E., 'U'U- 'U 35, 'U sec. !:fl_' NE*, 'U AUTHOR: UW—Eau Claire 0—C1T:2: Ltc-Uc- : Paul E. Myers, "I'U,:OOUiYO 'U DATE: 2:-fl February, 1973 .TTt7tJEt€.C SUMMARY OF FEATURES: c;crIIU 7n'q(U! An early, medium—grained pyroxene—amphibole quartz syenite containing NW-oriented quartzite, schist, and volcanic xenoliths is cut by coarser-grained, flow-lineated quartz syenite of similar composition (Figure 1). Average xenolith orientation here is structurally continuous with the concentric lamination of the Wausau syenite pluton whose granite core is in Ninemile Swamp 5 miles southwest of here. "Rootless", lenticular pegmatite with walls of coarse K—feldspar and cores of quartz were probably differentiated from the nearly crystallized syenite at places of greatest quartzite assimilation. Thin screens of biotite schist and quartzite were raf ted up(?) and brecciated in the viscous syenite magma (Figure 2). —"CCC IlçU4'UU.c-I CCCC1C TC05TCthC.=c-QCCCCfC CC'C'çCC2:-=TO'C'0Ci Tj ijC C i'C,C T flTh TOC2: CC t ri ' r ; tiiI ki 3'4 CCC CC CiCi:2t" tk' i J(il =ur 0 TiQi :4Io2:T i::'TCC LL 'Ito r:;mitt. i'Itt1ci ,i,'l; &\trli UC,0CCii 2:1L7 WT(1' CC - CX4TX'v22'0'L ,2: 000 ii:•::c-rc 104.T1!iX U' Lc — fl'IL''tT00ii c:iz,o.Lni0t o:2 2:0 CT:7 r,4,,)itiic-l t ''•rC',C 7CC C''Ct Ut c- I I 4 i20U,k Ci O,c-c-i[ YT'0tiit± F.T.04 'Ti C tian DESCRIPTION: 4iTP TI' fi ' 1T'1r cf iLi 4"1[I According to Weidman (1907, p. 203—208) the "Wausau-type" quartz syenite is composed of alkali feldspars (orthoclase, microcline, albite, and microperthite), barkevikite, hedenbergite, fayalite, biotite, and quartz. Accessories include fluorite, apatite, magnetite, zircon, and allanite(?). L'.tlc-.[ '--r T ti Ir ]0Iic--0act ::ti2L 0 S' c-i viJI3p;4: 0 r I iT - <) 1JT : tcCL :1 - I i(iflT0t1flT ;Y:B 4i;$ Structures and cross—cutting relations of the syenite phases exposed here typify those seen throughout the crescentic northern rim of the Wausau syenite pluton. They are listed and described below in order of decreasing age. [)1L4 0c-Ti. ..1-c- 00 ?f0T.an:1- c-c-OfI. 0.:ThflI!Jc-;t&:4= uii-ic--•o ThJDL ji4c :4: :j. r2Ii7. o-rot (LLtt -iT-i OLIL fC• c-i i0C TJ.1 i1i �72 -: II .4 I- — 1 5- 4 5 I — -5- — — ,_zl., -A" A L,:;-' --r • 1 j V ' -A I *I•-••_ • - - '-21 - — ' - I At — ' - 4- ---S -• - - C— - •'-" '1— 4A -- _••__IA - • -" - — _•', 1' -1' — - - - _•1, I -' -- -- - , / •• - - 5- : -' ' -' ': -II, -- - I - •• —- ,'4' ':4 - - ': ''4/' - '.-: ' 1, - 5-:' I-I- - --5-_k -, 15s'I -A •,, s,'I 'hi . 45-', , , — A A — I '•,5A-42-'_ - / — -, -- ' — -''2- • - I' 1 • '/4 2- -— - _;A -- - -_ - -h //5_ - - A • • 5-5- A - '—S 5- - - ' — - l.'\',', 41' • I 5- ,, '-'5- 5,5 • - - L - -• '5. • . I"1 -lw',' 4'',5-:5-5' — ' - çt5 5-ç I - I, • - I . • - 4- - '4 - • -- '-,-T:_ • -l - - ::4' : - — I — '• 7 5- I - ,::-'- • II5I 5- • ft J,_ -• •• I — -• I - 1" - -: ,-• - ' -•,•,' ••- ,. ' - I: • k ,. I T I' --. - H- -5- A_I' '.1 I,,2121'IA_ A '- :2_' ' • 9' A I 5 ''-'''-" C- - • 1 A -A5-5-' --'- P 'I 2- I 55- - -----—I A - •21:--- ---2s. .1 ' - •, '_&••*, - fl5-:4s": seams 5-2-slt4.,::LElj:l,L:5-.2-2-1I with swirled lineation and thin Amphibolite (a) xenolith •:lc:.JA,._i'1421L1b1,A,42Figure 1 Lenticular veins with - ;- A.534'P2-'5Thf"ftL-1'2- 1 1'' '11 of syenite is 'El cut by coarse pyroxene syenite (psy). c:'1,-.1tatQ ; ,,— t1LZ4-1L'-1L1_'i EHsIJA mutually crossq-:2-r- (q) show walls of K—feldspar-: (Kf) and cores of quartz 2(ICI_ Joint f'!VLt'rhI:2-Ifl',s1 intervening offset a small fault. 111 W _'-2-_ along cutting relations an1Th,C2-'VL1'2*1'th'1 15-21? '-'15- with 24 115-Al I' -1,11 amphibole. 1_s. A"' i'i- 5-s' coatings are of coarse, sodic Ah- 'f2-- 5' 4Ui - I 151,5- •, - 1. 1. 21---1H41:;2 syenite. They in2-12-il i-La xenoliths in 2-21 the :c: X'lh,!IA1'L".2i5 The oldest 15.5- cAt :'::5cIftt,: rocks :1:4::': here are '.'2 ILC21 *1 2-4,IC I meta— -:-c1,t1t-21151 amphibolitiC 1-2-21.112 4121 -: -lr,-J, schistose, clude recrystallized, 212FA!41214442 :121.1.4 thoroughly L*2-1AV' ±2,15*12-S tuff(?). unaltered felsic 5-1-2-211:5'-.L,fll22-2t45-2l 4*1*1 volcanics(?), quartzite, 'I222-2-5-A/flH' and virtually 2CsJ.A!1_i:,2-LI4)IC-I parallel to xenoliths tend 2-14: to - be .r2I1-•1*1ltl -T5-± aer,:: 5.2-2-2 of Note that long dimensions it1'2 ::i4 disparity, despite lithologic 211-152-45441 21% tIal15471.4%:, lamination and/or foliation and that, *1124121 i-Cl :*14:.6j4)Ic,1I-: -s 1:4211%' :5"a.L "grain" to distinct structural a ã.2-tlLCC ,—:ar i: -Lka±r c:52-tkP: 1117:5:2their mutual alignment imparts a 21.? :::s21.21j2, considerable 2-21 of tCi- be factor believed 14211-2112- to fa:'.tc:2, tlLc 1:2- — a the21'rJCL*1%21 enclosinghIyE21LI syenite *1l1it21L5 4' this 11545-LI pluton. rnechanisma 55-2--2122- 1:2154 :15 for '5,2-,1a-iI-211412t 42-151221 45I:215--ICç I significance in working out emplacement 2-I 2-' l-- 14 5-4 rai , 2-'- 22. ilyllIl-ib I 4.1? .-: 2-: syenite flow—laminated -1-2-C :; 21.-I quartz - -E'It1i5.5424' lensoidal 41:csm15rair.L?2- - '152-121 An early, fine—grained, .-IrC phase. —. chilled -.m15!lal 2155-2242-. may represent Ta-'--Y,C 45-Al/-C_I a I - �'3I,3L'1$ 'UI'? 377$i'35(7'3'7573 Segmented metadiabase(?) screen in flow—banded, quartz syenite. 117' 4- L4"712337—11A7-"[ 36 - 'y77'.e33-: '' 357-:cI'316P'75-17 r7nam,, rr-,---', -' — - — — 2 Of,4f • 7": Figure 7/ - — "4- 8 N - ,84 8. N • A A- — A-I — 1 t ' I '4-4 - - 8 j '4-- 4-"4-54 — a_A-' 24- -- :4 8 : -I,; :44 '448- A- —4 - 4-4 -4 x 2 -. eA— 'I :4 ' A A 41 — 2 - '4 A- A — — A — , 1 - Ar - — 31 A -- A- - 4-' 71 H : - '"'8'.I7'LJC, 33,%1. 'L31[t :7823_H'TA':A531.:Y-c':y.'':-:',':PTS- -=A-A-A--" Coarse, sodic amphibole crystallized along joint surfaces. '7/'31!, 7'7': 7'31:':L:18(:73 '' 5. 2323331':? 3. 4-5- Coarse—grained, flow—lineated pyroxene—amphibole quartz syenite cuts the fine—grained phase with sharp discordance. This unit contains irregular, lensoidal and tabular inclusions of amphi— bolite, schist, and quartzite most of which show little assimilation. Although most of these inclusions show northwesterly elongation, the enclosing quartz syenite displays highly discordant flow—lineation with swirls and eddies suggesting considerable turbulence and viscosity in the quartz syenite magma. After gaining access to the xenolith along its banding or schistosity, the magma pulled loose segments from its surface. With increasing magma/xenolith ratio the xenoliths became plastic and were strongly deformed in the flowing magma. Quartzite xenoliths appear to have been more readily plastiA screen of cized presumably because of lower melting point. schistose metadiabase(?) crosses the south end of the outcrop. Its thin western end shows plastic deformation and "pull—outs", whereas its more brittle eastern end is segmented into many angular fragments (Figure 2). '74 Late—stage, lenticular granite pegmatite veins with quartz cores probably represent residual liquid segregations along incipient contraction fractures in the already crystallized syenite. They appear to be "rootless" and of local derivation perhaps from zones of abnormally high quartzite assimilation. — — 77t11'3 8(8771-31A ,(,7'%:7 P-331'Efl': (4485 71773 "718 L'S.7'3'L811-1':': ('(In-I ç4-7171.,( '- 75 T1'871 73317 - 7'-; 3.8(17 'L571 717'445 : 357 87'71':33115 31— 33-75-1':-' :Th-i:ï. 37337' 5(4-8 -73'',':—:' 73,7131(1-5-3 .1- Th'r,l - 4-127-V-lI''1Ctt- 3:iAL3T7 37733" '174Y 'V/,J 5,877) 3T75'1Yi"L-7J ':':4d5731--114' J- L137'43 '5',:[',-'1(3 753371. 7;'PL-3': fl7, .771717 ,237331- '5 4-7'.318j8'72 -:4 :-77': 11-'73'4': '753715 1231 (81'i',1s'4'3.53 — [3-13773 53371 -3313SF ':': 7)8(t-U7 3-, 2377 75 375'7": 3'1331;3 (173 -1'& 71,7(3:44 423,.33.-3S,[717 Y'3 ':'78:-4713-37;- 1': 37" 7'3": i 37 75 -1 $771 473 -:I,3.3-$11:1M 513.1-34 3.3 33%'77'472333€': '35 3471-"':(4-' 4717 -J'U'':' --751172343 4. '3133''. 3's-s-cs,: 77:11 —:-3":x, 23823373: ,:-123721814-,': 23 4(173'A5LL 337573(757 5-34 '8718, 3-7,'!,,A-3348788 '(1'j('3-771':-_-1t7'':237'5- 5-3177 1575-Tr''33'3371'(,$ 7711":2 1323341331 731'4'C7513 (5157' '5,33 5:" °i':-:H'.: ;1-L3--'2'•':-(33.'; ,575%[771,'14- "171'%:131- ,77' C'5. 3(7-AC,- •ThtT$71'.8.33"1"4 ':711,7 23-731-'. ;38771:37(;::; 175, t,334-',7 '337733 1571', 1311-1 Sx':3 7'7'7-4'7'-131,3':'5(35 --C: ':"-k7"1":-x71- 3'l 3'317':41,?,'23 ii1i175—2 -1311 -7,31,it 73 'i771315'( 3—':-'fl 731313333:4 'I73 51 4771171' 3,7354373' 7::."iICi)'I A-r,A17'3-5 731'3271 1'i15$ 51i1J1 - C."I1375477 :':'-' 3,33, 1172171 :377758-73 48733 ;t-:-- ':':-: 175433-77'17'75 '735233-: 317(13-? --31373-5? (-Y''7' 714 ,'731-::': 71,[)-':Aç; ''5 :7'.733': ;5337735718'7'7. 4'7''5P -3: 1:15' '315 734T?j2. '73443135- :337317 ''13"73.5-53':':5 77 3313734 pa;3-7'4 a': 2317 373(3 - '7 - I - ".314-ICY 3153.73 731 L1513- — 731,11':17.'7317'I3 t,:7,'' 34 '74137 8 7'813f5 473.5 A'7'71'-'3-)'3iAA 7773 (5''337Y, 'c7L'ç83D - 5551_-1-3 7517583 73 �74 a ih* the syttitea syenites eM and It is '.s suggested that many of the structures in itt San1v. Sntfr L,.&zbr3cn .Liin1' indicate forceful, subvolcanic stS3L*a •( t? ii Ytuasu. quartz syenites of the Wausau pluton 4trIN,tULa1 aftt."'tlS .! Careful structural analysis may '22e-ILL o trz w5.uclrJs avafltt V3$tVjection of dry, viscous syenite magma. of magma flow and xenolith mixin rithi:. 1i themchanism5 ;wasntnt in time time s'ts'WRl reveal the twc instance, traLtrce, nC ?t&t' t fn.çcmwrcs fnt 1.a Do the xenoliths, for represent fragments from the magma. thvtM'vJ g :salttr& eM ta;;;. aatl J aflr during caldera collapse and later invaded fault breccia formed initially a:rLt -asvnn? by ticw,fllflA upwelling syenite magmas? t,q cvg..;tz;'rl :tat nr 2! the 3tflfl4rfl the marjn D the ntc] t;o. f wit brte3. i £:sst atE anz f;nv efl r: ,t; tt':tg *itt'D 2rrY tJJ! RE FERENCE a*rth of north iTLoraw, g..tcsL, w,The fl' nalts: Weidman, Sanluel, 1907, geology cS 'Faaa3L3Lr: central Wisconsin: £'C. Bulletin c7taat and ax! Natural Fsti..nl' History £4tctcfl Survey, !wtey1 BCLsttft XVI. Geological tV::cscs.':D Wisconsin I �uiclrYrkJ,, south. the to tc FuNiclgJNtcuru volcanics 1 ru t j Ncontiguous from derivation suggest iN mafic syenite nepheline the in auruiuui ui lenses and INuruNuisur; bands ft'NYI7 tAtut1] Mafic vr'I;rur, pluton. the of ciLL ucuuru)7113U1cuucuruizt emplacement urvt duringi-il itization itttRrNutiNiN mylon— by segmented and lenticulated locally were crystals feldspar -5 ' 2. ICL'I C contorted: strongly is syenite nepheline the in banding positional 54) ui,:iUuiLuii))YN) and clinochlore(?) iC lirY'lui JUNNNNN1L 1117 cancrinite, c-r-irNrr::Nrr tJtcu7cuuiu-I'Nb5'u Comallanite(?). thorogummite, uruyIu. (red) (N WL N apatite, r' here), cu5 fluorite, abundant (unusually I_ Yui_t zircon include Accessories Jj (lepidomelane). 1— mica brown, and (arfvedsonite) amphibole sodic ±± sodalite at::riuiuia nepheline, uiNil rc:rjoNtir1 vNINiii composed aegirine, Ltak:r±LNuj1il1r-i microperthite, anorthoclase, of mainly &NCYçJ.YiP1Nr1 is :t4a nepheline o'7N:di7-Nug here syenite k-iNN 7i2iiil Dvrrriel the N17N 235—264) T'7'7N) p. (1907, Weidman '7aaz1 '7 to According I 4 't[ 5Ni ±' c' UYTY I I t,fl .i - L ,_ 1 NI U [ '- _i2 t: l'7I :r NY location. this at N tI across east—northeasterly strikes property mine N:1a zircon tN17 abandoned the syenite N$IriN77N trtLN,JT: tabular and syenite N'7GiJZr nepheline brirrNarr contact r1ccN1tazu The !Tjr,_ LiliN ttrryrl banded J1iFilri. b between 7UN It:'ly DESCRIPTION: i:r, rI5Ier7 : (Nt$Z; ivN1:1i2lI NJJNN, near zone wall the :crrr ibe 1J. ILJ stop in is t.zNyr This pluton. the INI of edge south the 1 pyroxene s Ii (psy). syenite anorthoclase—rich of core a and 235—245) p. tite—rich 1907, (Weidman, syenite nepheline—hedenbergite—fayalite 1L magne1 Nil, -:r: caa 1:: in of rim a comprising diameter 7:i, atIl2 mile a zone core circular a (3) ' > pyroxene and amphibole vu t and lineation, flow swirled with syenite —RH — I' an (2) (lsy), syenite LjCL' pegmatitic to aplitic of zone intermediate aplitic lensoidal, La and (tsy) syenite tabular (nsy), syenite nepheline banded comprising zone wall a (1) mapping: field in distinguished were zones yr major Three zoned. concentrically a2d and northeasterly, 1L!• is J! elongate ]1LL)t. in oval pluton 'JLi.7c syenite ;7v(J!c1f Stettin S.tit7tz, The JL2tcL L:a1, 1) (Figure plan, 1,TJ 1 r lIV 1rl_ i :iaKair Ii c at 1 I i7 L ' 1b JL — 7_I' N17i=/Jcrv FEATURES: OF SUTvIMARY February, 1973 DATE: \ib,Lf1 UW—Eau Myers, E. Paul Claire AUTHOR: t>/ County Marathon XCaJtJrYs R.6E., T.29N., 22, sec. SE--, corner, NW C.T.H. '7 & Rd. Stettin7 0: LOCATION: zone 'wall tr'ita, tt!t; Stettin It• — pluton :L':N syenite TITLE: j-1!IJ Trip -H 1: I' Locality 10 jc7,r'7 Field 75 �Figure FF'/ .7/ I 76 '4-' 4-"" - ,: /7 " SYv 4--" my "4- .7/' 4-——. 'F'- tsy 1 F•" F / 7r / - / 1,7-Ft -'7 4/ 7.7.- '>' '',7 C4--- 7- -".- -' 1 1 --i-i-" 4- / / , '1/ ' 44- 1_F '/ 7-", -: 1/4- 1,, '4- 4---' i, , - , '' 4-4 2 ''j''i ,-'_f / - -. - /_ F'-. F ' F/$&f, .,. 4-''" - 4-' F" /./ ' F- -F 'FFF4- '4 / '-"F 4-7 4-' ,_e/4' /7/ '4 4/ -- 4-4- -4-' / 4/ 'F' - .4/ 4./' j ' \ /L 4-' 4-- F,4/4-f -"'"- — 4-'--F4--V4--F- ->ç4-74- - -- - -. —9 4/ "-' /4- 1 ''fl- .- -I 1.1 7' '-4- - y':- .—--",-,--.4- - 4- ' 4-—" - F' F, "7' '27"- - - - -S_,4__-,,_., '4-'F'7'4-I 7- '-74-' .# 4-1 7' 4- /4- 1/4' ,t,,,, 4. '"-F -4- cii - - - '1 —-F 4-4-,4/ -, my — '-"iFt7-,- /4-1 IF-_>,, 74- 5TTTIN L'-17'TT"7'' 7-7 4- / C 4-> 4- 77/7/ - .4-4 '"l c '.4-'..->- ,•_,,,.. - 1 ' "'-,. F .'F'47 .1 r•f$F - 1-' -' ,".77'i .; '-4-'/',.'/I - Ii ' 4-V -- —/4- 1 fv ,.' 4,,. I -' IL / /ts / -— / I C F 4- ——-—4- : 1 4 • - , :. / / 4, / 71 - - F I 7/v 7' I / ._ 4-F7. I: 4' /' ' , I - 1, >4- F.4 / 'C ,,, - ''v-1"'" /.- / F,-..: I ' F I ilL ri N / t Ii STETTIN H LIT I PWTON 4-'- " 1 I - 4/' F . 1" OF THE 4- / - ,,,,, F c7- my F H 4-/F 4-p).' MAP '.! • ,, — 'F /7 "•'-"• "S - /fr/LE - - '44/ ,,0 F I.- 4- 4-' ',, ,,/ by PE.Myers '1 ,_ Geology F'—. '4/174/4 p:'!,1,1 111:1 IF/-F) Nil '. Survey Wisconsin Geol. & Nat. Hist. 4-i I I I I 4- 973 >Hi-.ft1 Li,yI4711C EX7>PLAN ATION Qal ; LL'II r Lii tsy 1f L/4-V!U-•) A]]uvum :: (U C L I) i-fl Qgt n sy TM] p UNCONFORM TY C gr • F •I Syenitized vo]canics :'."ti,itispyroxene syenite - —7 rsyap ic/Fr /74/ .j,4, 5- 5/fl Lensoida] syenite V Granite Amphibole syenite Svenite 5'2i'- 4-/i ap]ite t-> - - 3/4/i/i Nepheline syenite 7sy - :4--n' Tabular syenite r mvb --'--F-,--. ,,F_1 is -' -½ '-,' , vo]canics Brecciated mafic 4-, F4-F., fv Felsic vo]canics'I mv I Mafic F,,• • - • volcanics a �77 2 . L.... Figure 2B Figure 2A Porphyroblastic(?) tabular syenite with mafic lenses (Fig. 2A) in a matrix of alkali feldspar and interstitial sodic pyroxene and amphibole. With increase in mafic content, the tabular syenite becomes poikil— itic (Fig. 2B) H.. -.-' ;4= 'H :•.. IJ_, ='H H' 'H' 'H 'H H'. H•'-- -'H H—•-=-'' ==; 'H -;-=. H: Ci . _;'H 'H 'H 'H E 'H H.- ii 'H "H — 'H 'H 'H- 'l 'H 'H 'H Li: 'H-: Figure 3 —— Tabuar syenite with abundant mafic lenses. Note para alignment of feldspars in maf Ic lenses and serrated margins. (3/14 x) L (A 1/ H-- 'H 'H H) - .;-..' I 'H 'H 'H 'H 21 'H Ci; amphi bole. 'Hr. 'H 1.4 'H 'H 'H -'H C') 'H 'H I,L 14 H-. H. 'H Figure —— Detail of mafic tabular syenite from NE Sec. 22, T.29N.,R 6 E, Porphyroblasts(?) of microperthite (white) Black crystals are sodic �78 ii cr Zircons ''C CL'ICCCC and I'C% some IRiCS thorogummite (C'C,C L3ltrIC II, may C collected 'CtCC :13(113 from hit: be hiitCC. pegmatitic tC).ClCIZliL'C phases of the nepheline syenite along the pit wall and west of the •C' C.. Ict-I :CC.C:LC Ctfli just iCac' (LII C.CC Please mill headframe, where a jig table was set up to separate zircons. YC(". 7ZIL.ICC,.I:j iiC'i-iizz e iiCCCIj,C iCr C-C'; it CLSAC 'ikit Cc ci r:3Ii'CC'3 'g3C(3 stay out of the building as it is very dilapitated. CCC CC. .L?.dlt:.. Lila (CC '3:3 ].:CIC C.:: ,L3 aq: liiTC':I.1 s: s ': 1 ;3 The tabular syenite itniCt a: at i.E this location (Weidman, ILIC p. 255—264) auCrLL: 1907, is pale orange with long, slender porphyroblasts (?) of zi1tCi C$cCtL: (Lilt r14 .Y&Ci'HLiC HEICYLICC(C5 ii4 C.-" HI gray micro— Smaller perthite and 2A). Ct mafic r.itti ii lenses C:31C5: (Figure :1iiCLhii1 felcspar t,:,( aadii:' laths 'C'ykLC are a,ra CLCLCiT:,I The feldspar crystals show considerable size variation pinkish. Th ii,'i- SCCC 2t1 Cm: 1a3 CcaitlI'cCtCC CC in 'Lr this All are in planar array so that the rock is banded but not Why? i1Vi.,i Cit CII, ,J5Ii71C •CiXC,CL 3:3 ThIEC.. II1[1 CacC rock. .Ctt•Ci LI' 2t31iC Some of the microperthite porphyroblasts(?) conspicuously lineated. °?CCLCdCYI (CIII'', 5C' CCIC.L (TiTiiCCi.CflCC:,l 14 iCCLLtLiCiCtC, (L1HE-i contain zoned mafic have rims. Concordant (C :3 licCi inclusions ICC. C tt[' CCC ' and tiuC'ii. some ICC C4LTCCII mafic CCC mafic lenses (altered mafic volcanic xenoliths) ciCaTiicc 131:1 are ,za composed ;c sodic atçiCa çC'CCtCE-C't: of amphibole, brown mica, and and contain perthite porphyro— i,Lt CILC't hit (-tiC green pyroxene Pfl 'CCC IlL CTC::iC.. ci-)XCL.C1 C blasts(?) of to CC similar 1LPI C'' size, L 'lE-C shape, CC and 3IC orientation CLC'IC Ci those iiCC.i4 in u:.1 the C1CC. enclosing 2ciiCtp:::C suggesting pink syenite — aii feature strongly t33CCCrL HE5r origin of ;C the Cfl7 iS r;2CCLC Ct metasomatic Tabular syenite l-mile east of here consists dominantly microperthite. C HIJ ii JargC. CiCC!CC &ii:a2c At another of crJCi'1 poikilitic and Pt33 , pyroxene 4.j c-:l sodic ;YI'C amphibole C.nj:: ti,cLnrs çoaj - (Figure 'C'tc; €1 2B). riCiJ d location 0.8 north—northwest contains C)L.LCC a°c mile i-IP CCC ::CCCCCLC of here C-C.L the LCH tabular FCCYF-C syenite C.c rCC_: Some C much more 'HEflCi C,ii( abundant: maf Ic lenses (Figure ELLcL 3). 3CCC boulders at CC this Cli. ii same location irT are composed entirely this mafic rock (Figure -i Cc 4). •2LCiC C $CCi- taL1 CCC iCLCtCC of '' - C,. L a' , e-ic 1f:"14C CC !c'-t iatty C rii Itt L j-Iir3C3ij ii rica 'CCtiC C C cfa It CC is suggested shearing C3.,th5eiFL that CViC iiUIS mylonitization J[C:C i. TC3tLZ accompanied -.rTli3..C333 CCL and Fragments forceful injection of pluton. TaTZi.tiJ subvolcanic aCCflC .:CaC ;.- the j.L Stettin XstsJ,-, syenite c:tuiitE-E iC of ?3if; mafic volcanic loose C,t7TL rocks 33CC broken rct.2C SiiCCtI from )EC2![ the €CC walls were EJ3- rafted up ZiL along £(art These fragments locally acted as them in the magma. 3C viscous C37C 'it syenite cii1t,j c4!Taa; c.rCaLii cia-iit nuclei L-4 crystallization SL1 ICc of 1:3 the C./1C syenite, itLCC to CC. have IIL2iICutt for C&itii r-. although thqy appear Considerable metasomatic alteration been resistant to assimilation. LJC%QJ T CL znC ufl54 C fl1C of the early wall zone complex Cti at ni emplacement Lii followed 1i...:.Ir7 its ri original J.: çrc;:;: as evidenced by the coarse, euhedral microperthite porphyroblasts(?). ')Cfld: 1'.th: ::1c€ Textures in poikilitic phases of the tabular syenite suggest nearly Cç7$ TC.L izCc CC.LI7 ;tc.J simultaneous crystallization of feldspars and CC2iS'LLiC 52EZC ..Ei C5TTT C Y(fl mafic minerals, :ir- although T1 the amphibole is 2L:ruDi. younger than the pyroxene. xyj. 7 iC F24. •CC !'- t :•:j ittn;9Ji a >Ij : j 1? I. :c Your ideas are solicited! These CLJL tentative SricFGC conclusions [CLCC ?7 are CC presented to stimulate discussion and debate. C. CcCt TX RE FE HENCE S L' X'S ST Emmons, R.C., V Wausau ':1: and Snyder, F.C., 1944, A structural study of the Wisconsin Geological & Natural History Survey, unpub. report. area: iC icc;1rL rj$)CrCr igxt'Q .C1t J. EZ dci :qtu Geisse, Elaine, 1951, The petrography L AF!T of the syenites, nepheline C1 sye— M.A. Thesis, nites and related rocks west of Wausau, Wisconsin: 'T t&r:u piTc; iiE7CSJ L4CC;L CC•k ICt i'&.'P Smith 4LL( College. :JC;. rr ;. C' i Turner, D.S., 1948, minerals tt- Heavy accessory t'T radioactive CQC3 511CifL and LE1PCTP13T studies of Ph.D. Dissertation, Univ. the igneous Croi rocks in the Wausau area: of IC Wisconsin. t':i* ''J1 u Weidman, Samuel, 1907, The of North Central Wisconsin: JIL geology tC1 1.ZC Geological and Natural aj, jttJi1I History j(.. EStJjI1 Survey Bulletin XVI. TLkityD .•&![• Wisconsin i ii- 2tcr;iz �l fl -.344 4747) ,4i217L 247-417.' low 2112 Ii '444 bridge -"=" 77 water. at only of times C1 . west the from it 117, 210 location this 1 the of end reached be may Note: gabbro. t1:21I17r214i.21212 :1421,17:171 ;141:7,T[4?1! 'I11'11117147 1242 4171: 171113'111I12121171L11$11 the of consolidation complete before stratification of disturbances 17 " 1717 the 11 inI layers I t121 clase r212LI in represent probably 2) Figure detail (see gabbro ij4 114'' 211 1 '44 I Di plagio- ¶ strong I 21 in crenulations discordance. with gabbro "Stair—step" $42134 2 7 1 —The c211JL IL the in banding the into cuts diorite quartz NE. strike planes 311212 3717174214 -14'2'117. 1-211) axes '21: 41274 quartz 211211? fold - 1'-1-7'44 2444444 7112)1' The are axial their and vertical, nearly diorite. 1r_ 4411714 14T77442. 2 271 11?,.i 3 was xene '247 the in incorporated then and open—folded xenolith gabbro 21214417 a in pyro— large 221274121141 At 111-1 :1: 211.prLln banding compositional I,: 3':' tl-L#. '47 1) 2-411311412: (Figure #1, Location 1 I I L14 i 1 I 'Ii1 I I 4 - 1 I 101 — 1 1-1 37.4?.' r' magma. 47 24414114412 quartz diorite 14242 —1Pj vertical AL 1414 '1 the in 4447' xenoliths of transport considerable suggests This east. 1447'(1711111 71:1:15 -441241114.7172 212I['71I14 1 4441144 411 74412 171112217 12, -- 1111444.it[2. 2412117 northat least at :7 miles 2 least and here from southwest miles 4 extends 4711112237 '11 4711171. 2711-1114 hIlt 17111:1121: 11741'5%' 121:42121714 447.1212,14 1t2444'± 371. probably which body, diorite quartz the around place in found is them of J4i44274337 4444:14.. :,L7iIt1LIrw:p 7i47'3- I none 174217 2: -.14-Tc11:l5.14 as 2141 .2412 '311 .4423115 and are 121-12±1 121442. 17242 yet xenoliths, here found types rock dominant the quartz 3-1 774T_42 17 schist, chlorite—epidote metapyroxenite, banding, showing depositional(?) 7112 in- 22 some gabbro, PyroxeneC $122 - 421 2 outcrops here. of east mile exposed 2126 are 141211440 :1141'047ItI11'444 '147424-2.2. 114441117411 21111i117 2242271721-41117 117114' 1 i-'211''2'which rocks, volcanic and diorite quartz hornblende taminated $1224471211014 2371437. 14'14.:71j1 con- 11212212224 11241211422I10 excellent between1713144211124 contact 412112122'22 sheared 1477747 the near is outcrop This 'ccl5Il 11 111L12i2H[— rir1 'It?"" 17 j'' [47117 [1717 7J.r1411A72127J[1' DESCRIPTION: 5 .17411:41714414 of .1r 2lt[11:4.147-71t:17712 stress. shearing conditions '[1714,7 different 7444±11 1l$44771i12177114 :1.1110:c41:7-1 rare 12a 1410-f.111i-liltl.±1 [1212..'.171. i-;17[2'24121t_d!C 4424 1l-7s'['L['.[i[714 compare under types rock specific of behavior to opportunity a 1 142/'7[3' branching, 1i17 zone, shear ENE.-trending :1 ' T''H ii affording thus along mylonitized 1.17-44 .[4773fl%1_ '4751741114471 :11t1 'ii:424n '42.4122112 771121: 3724 was quartz 37 747242-2 pyroxenite, gabbro, banded and schist xenoliths angular of 514,-,fl4-:44:14 221 7i=121 21114111424421344 127.174421114 quartz :3117142:i,47:71 44514'$1-41417' '14237,4 abundant, containing diorite hornblende Flow—lineated 'i,1 ' TA A 1 2717±U.L 14172 OF SUMMARY 174151444474417174 FEATURES: ;i7417i '1%:-nj--t;tFebruary, 1717-1717 1973 DATE: 4111.115 -47422s171s:ir Myers, E. Paul 211113151 Claire 1)[274'-'[4417 UW—Eau AUTHOR: R.7E. :47.4411)7 771,4 '4:444 '07sec. T.27N., 29, SE--, [1 4:110 u&14111'31 ®211'$172 at Mosinee: River 7412411'1"-111171) Wisconsin LOCATION: 7442.1(111124147 [31,fl57'711' Sheared 51t,111'112 quartz 2114127 intrusive 425-. '1.214:144.111171 breccia diorite 74 22 41 TITLE: 5i1J[. Field 37M7 Locality Trip 11 79 �1 -- LOcat°' �/ , / Ill , diorite. quartz ' / / / 1 \ " ' / in / / '' 1 i, / / I I' / _ I I '- / i / / ' NI / / , I / I v / / f \ / /1 / 'S / - / I — / 3 " / 1" / / Figure /\ I' / — I t /__.: — — / / •- :- / 'I t/ /\ / (Detail.) crenulated locally Banding quartz in gabbro pyroxene Folded — — it': U• / — r / / /, 1 / ' / diorite. Figure 2 • U_U :, •. U: 4 S / S — t I ' --- - —=-- ir— / 1; I / , , / \ maic :/ / T— i '•I 44 I U - 44 54' US — '5 '\ 4, ',,.'lI 5, .5 'S. I •• / o I / — - I A Epidote—chiorite /'L_____________—J /5incs ' — — __ U -:,-eQ / // xenolith schist I '/ I ' -—-=-- -: — ' •/,i 'A -A A I, ' 5-.-44(5-.; I 5 ) • •-•:• U, U -.c,-'4 :h-.?-H',' I I " UI s1I / U,, • •' U, 5/ A 'U •. • —4 A U ç Ii I.! I •, —,., ..A . H '.: SI U: c.,,.4' rI H '-S • - 4,, U -. •<, .tA/",,' 44- '4,2171, '4•1A -1 U- 1 U U - U •;•_•i :1 54 5- —U' 54' --U AT 45 .5-A •'"•'' • 'I . 5, U,'4 4 1* '.:- H H .. -. A - • ,U S -I A U •• • • 2 •- —I / 5, / '1 V 44. * 544'— / US. • 1': / —I 12'' 5, — I -1- 5,.,.. 4', .±... / -' U — •' I I — AlE_ TA/1 LE L 81 �82 7 H :;' L i'ittntditw Pitcc'cisa brecciatsi'tct withq!ciartc:; quartz 3tctctht intrusive Figure 4 —— Sheared alL ILLquartz wnaztc cars 'c-at I with tic-. contact lenses (cross—ruled) (crcna= ratia:2 I along aJLc'ic: the Criasas tc'wcJt 2 "Pt a, tHr!c:;te acm ccc ±;tti-,cggabbroic gt5. 'ci' it xenoliths. diorite containing ac±lPa,t criica—ra-a i.ir:li;.$ schist xenolith cc' of rtial chiorite—epidote LttItLt4@W #2(Figure 'FCUris 1) L: a dttLL'tmt-itt\ AtIt Location #2, vxlittct,:; are i:c: truncated rUt I rt,acattt4 tc; pl.a.cnttzt which is segmented ;.C.(+t cciii by shear planes by the :r.tntrJLttttgi; a2iria'r ii;:; interlensing Ia! awl ath.t'ari.nrlP (and It clear tinalP that shearing ,;,It therefore tt.ttriiftrtt claw':; 5-t. is UlLitic'r 3). 2) ±t!±Ks:ritii (Figure quartz 3;anr-ta- diorite tr,rst episodes .tmt±cn&taIt 2caw two th'crcncri - Thus, wcvl Lttintrusion. çrttittttittctquartz qiticir diorite metamorphism?) preceded 3a2r'nrcrp1i2aaU) ccc the tle snibiat cawtsainp crn..cc:;cw. development of schist contemporaneous S i t '25Iw'!LC;!ISL,i:;t:; ni:;:svalidated, rat I C atarI, Was Its.iddtcLt3 are cii shearing of r,n iLl the cit ii in The a absence -"°- cc of syenite xenoliths riP the gabbro? Ciii with folding of nii: two 'Wti 'Its 'c"t" units :Tw'Ltiiti'tage aa of the ticS PwUsy quartz diorite only cncdcc.,:;.scti indicationsciF of relative its the Lc'rJcc-c3 is qinartc satin:; it:; ctiatiStt seen in contact. nit twit snLca'nncLcs n' yt 'Pccan been since they have not yet n arc £ it'itsltw Lrwcni,i.a tact itria;t :; the intrusive breccia has been rcaran'titlP converted :.gccra 1) i 21w Lcccttcnr #3, #3, (i Figure ci Location At itt:; 'w c _ig tnt by shearing to a lensoial gneiss showing differential lenticulation 1. xenoliths with resultant length/width ratios largely litha with racai't-aicnt m:LIq'cIh!cticta ccaicicsc acacacit cclP cci cai.crvcc,ca'cjw' and segmentation of lr.awtcta, Several tt1tt crc-alLintermediate :1wcr,a.c:; St ' texture. ccc ir ic c!iofrcenctL ittI tflt.tLttdd.i Ll" and xenolith mineralogy a function Lilt a mLacc;ati,©h, Cit ctsac"acd at erc1H'Incs!. car:; stages cf of tracali xenolith Ut attenuation can be observed at this location. There stct-;ac Liatcancri. intrusive thtcctiaiLvc:3aLlitcLa!Kti between as is throughout titia thisragiani regiona ac'urizci'tc curious association It tJcct!CJlfTtitt?Jt' gmindtt 4. miia See Figure 4. aTc.Lat..i' l,tLic I -nUt tcstititi'ci' (rich (a-Icc in Ic ac-cal contacts xenoliths) and shear zones. ij'itwt 1c l' itit. bci4 mma;:'a.racl gabbro naL±tzc body ani-iccitic a ni'-fcjitcttat'it CUrl the subjacent layered cp:ca'ctz diorite .2±ctr:'te intrude lists quartz Did r' L:;1 4 j !LIt,i is this body related Li. If so, Ce H ii cvii,, and raft the xenoliths up to this level? atj,crtttosttc' :;li-'st:;.-srtcicc ± the to Tigerton anorthosite? F F - �83 Additional Locality iC L ttctYT'L'T'iiu'21 119-C TITLE: Gabbroic masses and leucogranite iiL.ILIttU .11'L7?11'T:'C '- IITTI LOCATION: sec. 31, T.28N., R.9E., Marathon County. Low and CTH J southeast of Callon. outcrops float along TLLYL. 'c:.cctL11LLCtcE'.'TI 'ZPL,IL ,: it W-, W-, '-ccc 1, L '.iLYii Cf'' C H-TC 1:-c mc 'i'i•• cTc: c'i',w AUTHOR: :: UW—Oshkosh LaBerge, L. $ DATE: Summers 1970, cr Gene 1972 SUMMARY OF FEATURES: T:T These exposures will not be visited on this trip but constitute an interesting part of the overall geology along the trend of the Eau Claire River shear zone. .3Ct:j9y I' CC T-:-'IL'H Ct ;c i'9-c LLi-.',?C1Ct2 In -Tc:-- :ttL22 "c:Ln;c 1111 iLçu,.qcT:.j- ;!:L - 1-i '3'u- IL 'iY T-:11C,: fl The Eau Claire River mylonite zone is interrupted in the vicinity of Callon by a gabbroic mass, at lest some of which appears metamorphosed (mg). Although the gabbro mass lies athwart the shear zone, it is substantially unsheared, and it contains inclusions of banded Thus amphibolite (sheared meta—greenstone?) and other sheared rocks. this mass seems to be younger than the major shearing in this area. Tc1 "11;Cti .111117111 ..L';Lm; 3CrL. :c'ti'111'tt 1-UEC CUEIa 11c.li.E ccci; , 11.i:tlc -cc TLTC1TL,TJ1LL3 3r' 1Ic'cc C-9T :±-cT, -r. -ccyç ii uLLcc: tt:LcuJ.I,L p-nL: Lr,L.c, t-Ec-:c:E U11t' 11 !TE'.c' u-.E :'•I', Ct " :;:T) '1H• T:ICI TTTIY5L I -L1 iT1'9c: ' IL:&ct_c:'J 61 611cc-cc .-Ur:uT TT1i t.t11'-.LLi.&7LLf .t'c:Ic:C EL:. ic. ,,.t- .,-rIc:tt cc tiL •'C'C CCt:4t''iYE .';,7)uC:q.:cI11CCX :-- LL! :—c ": cut': 1132. -nq u97' '1' I Southwest of the Callon area are numerous blocks of mafic rock The surrounded and intimately intruded by leucocratic granite (lg). maf Ic rocks have a range in composition, including hornblendite, gabbro, cliorite, quartz diorite; the leucogranite contains much pegmatite and graphic granite. A small altered pyroxenite (now talc-serpentine— actinolite, etc.) (ts) which outcrops near the N* corner, sec. 10, T.27N., R.8E. and a number of probably indigenous blocks of anorthosite near the SE corner sec. 8, T.27N., R.8E. may also be related to the gabbroic masses. And inclusions of pyroxenite and what appears to be layered gabbro are present in the dioritic rock in the Wisconsin River Valley at Mosinee (NW, SE-, sec. 29, T.27N., R.7E.). If all these rocks are related, it would indicate the presence of a well— differentiated mafic intrusion which was subsequently segmented and intruded by granitic rocks, mainly the leucogranite. An additional piece of this maf Ic jigsaw puzzle may be the large roadcut of grano— phyre just north of the intersection of U.S. 51 and WIs. 153 at Mosinee (near the center of SW*, sec. 28, T.27N., R.7E.). :19111 iiLi2I 'L :1:,'1'C '1'' L .''•'" flL E- ,',,bCT ,-T; 'CT T1CL. L;;ci:'.c.l1. fiI:L,i,L>n c;c c<1 )c9i:"Lm - cu -Ic: T9,IiLLT' .Lr t-L:Tii9 .JL2 C:,sL1cT :Izm i-TcUETE'.n ',.c.,m:uc .':,'€iLi'LLC:,iILI ;—cc:cct- :c; -;n Eu' ttt .n-c ;CLCIityQ T.:c:: . L9L"?LL' cTc.;cuc:. E: c-,.9c.J pc)Cc' L(T'CLL L.t' EL L'-L'.\''Li 1cLLt cci. CL pcnLc :.'1 .,nL icn C:T. i-; jCC.Li C :-Y7--L C,:Ls TUE C.'L 2tEL iTT JI i'4 -c:::Etrt, :Yi 'c-nc-cc :c-;cZ - ;i;-ci 2[P Cj- :tcI. CLt :1(J TT :Cr ju ct.' cT c<-. 'C:Iitc tTyTht. 'LLY ;TrULLt.tTLCL cu- Ti titl1-T. -1t• : )i LT tIt9tCiL- rIcv-:J ii 1 ccc:- u-nc 71,. tl'mL ': E.tCtT'V'tEL?[LtCLcCCtLr Tm f' iLH 'I .TT • uin ccLclJIYT -1I)auI uu pcLcuLtC... L .L9tO kz- I L2,itL c4LL. Li9 ?LV ; ct:cc .QYj:T tLCL. L [ccacr i99- Cc LLL H:,'41:y,, r •9u c; Ii :t �84 ,y EiE EXPLANATION JLk*17 i.711 AREA MAP FOR ict1l CALLON gal Quaternary alluvium ss Lower iLc;: PaleozoiC sandstone ig LeucocratiC granite mg 117 gabbroMetagabbro and related(?) ±7j1t• 7:Hr: diorite rocks ts Talc-Serpefltiflite m 1tL.(I :1h:iH Mylonite and:1related sheared rocks g Small granitiC bodies hhg :fl[:i.X.1 granite HogartyF, hornblende qd Quartz diorite - fv Felsic volcanics and associated volcano-genic sediments my Mafic volcanicS and associated volcano•?I& sediments jd:J-iir±b? genic 1 • granodiorite tH masses 7:.-r 'fli1 ii9: j:jTi Geologic contact Shear zone �'f"%. 31 Th! qal P - - T.28N. F IS ft 2'- 1 -, I I -. -"ml I - if! ft P ((ft "2 2 ' / I 121 / -P qI qal mg - Jl /7 - :7i[ — 2 I 2 — - 2 I 2 - "2 3 i1! -'. 7 Ig / qal( — I. itilIt -ft - 12 - t - '— ( /1 1._I 2 — 2 '1 '1k — -L / —-. "2 —. -P K- C J I ---I — . J I £ -( ig — L A -__..__m_ I / 1 - I c-s -- — - I 7 - — - I? - 2 -L'1" ç 'I 1$, - Miles — . Ig C 2 ft / / / 1. hhg 1 / I 7.. .1 I "-- LI — 11/71 SS (2( -'- : _.—-c' PU2TILI" d 1') qal -'/H 1/2TPJ -- --- T.28N. - IC mg hhg 2 - --;:. _' Jv ICI I). --='---71'---'---"=', -._i_--' -1 .1 qd / '( _4-P.1tL;._t 1 -'1-71 - —-- i7't L ,/' rng —— ILi:'& '1.41 ;Yi-..'-' a4:- 2-P ft ,/, m 7 h- . ,1-1 _D-P 'A' ¶2H ..- " ' ] - •'• 1 12 C k—I i'L .)hh94 -? (),-' ,/ '(2 p--'/' I-P - —1 ±A,;i _.71-S.LJ Ig 731 /5Ii"2 l9 :-———— —— ' — -1 lID m' ,1 '/211 1' P2 .1 / hhg '(U l\ I[o / I — —__=—tC41E —— AT Ig 1/fl -J 'U.'1 . Ig \ '9 J mg /1' 7o7'17' mg\ .' .—'----''-- '1.: 1 [ mg J 2 ft :11.11 qal — m r. — mg 2 4icti)Ec. '-.4, ,t;t+_.I_I.+4.+4* - — / '3 I -. — 11 7 A 11• 1/' ní2 ...7(2 ? my ' / /?/ ____ ___ ____ ____ ___ ____ _______ _____ E. R. C_i1Iory_\ - -— ' -' mg, .k%.:.L—II ', '11 \ 1- - Sç. - 26 25 2 - L cI9-L\ .1_i - -' qc nI \Ig) '1'tJx(/ - Alt2 / - H — ii , -- 4"—1 jH qal ,7') - — ft1 ft' 1-; " 33—-' H. - "21---'' / 15 —jI jr ft/I •.pft;q77 t1/1 -:' ' ft V - — -' — i-P'—i ii , I 1. (1 28??,/ -. 21 —--- - — —ç-—--.- T4 \m4 '- - - / A IL I'I,L I . _,Ig / 1_—- — / 11 TT — Ig I (x) 29 J-.------ ... — I" 'r - , J uit— ,LJL. /fi L' _1- ' fv —— L' 17 Li T I — " c/iT1V/ L • al 1 'N tL__—,Ia 1 / r - - ____ ________ �'c:c;y&at the -t'ii- cLL-cin. ac-c-u-scccs ccm-rcc-tc 'Ii tk F Field Ld ccc] relations a-c',ILc• suggest following sequenceccof events in the cc-: Hogarty -)d the ccc; a,;:•r1 of cc ;t-c .cc. 1) clb-c'ic'' on iY emplacement area shown theacccy;-iccc:5CLcr accompanying map: cc-cc. )iLr-cc 31 T3'ccJ-m.y. ,c-c;into the mafic volcanic hornblende granite l5OO ago vcJtcaccLc sequence; cccc-ca;cccii :C'JrJLILF uii3.@:;i9jd,.i -s: ltc-a- mylonite a-tc]cc vi: zone scc-:c 'L:c 3L:irZ 2) c;Fc•ca::L shearing 33 to t;cctcu.cFcproduce the Eau Claire River (the shearing LlFricict,acrcc:c:-i. ilL iL::F ficil:-:: rcJ ct-cd c d'-dcif't3' may be at least in part related to the emplacement of the Hogarty 3ist-L-ldd.' L c-c:• cci ,:c-cii;.5 t:.cct5 of :tc '.-i ' ,c Lac4 -c hi--c gabbroic hornblende 3) intrusion (and differentiation?) the c-iccclls granite); ccc'ca-c'ci-: d-c.r:,cb is:iLc? 'CI'') 3 iccis;s: ;"rv-:Isc:--3 ci' Fr3ii-5ThI3F5 :1, ct -u:cc mass; 4) intrustion of the leucogranite with segmentation of the &'St sr- a_ri :5,,, subsequent to emplacement I) has L -icc place Minor shearing taken gabbroic ,,3 mass. ti-s ac :gxzt.t.c ic—c the tici youngest Thus seems -Ic to be "hac the leucogranite -cccc -- cr-c cyvtcvic,ii of c the leucogranite. 3; iF tC'33 igneous rockmapped Yc2c-iic.F-t. in this FFTiL area. • iii Li? ijcc c "3 '- I P ' P : DESCRIPTION: Iiic,u-3 c-ct maf .c ,scStrvtc-3 and Low -cr' outcrops cc:,'ir-'rp aid and3iLFFs-t float of Ci leucogranite ic -'cc--S rocks c-c-icc occur Icrfor :ti,.iIic -;.c.;c ;'-J,;rc the ciclll tIc-: fields and woods along approximately a mile along c :1. in the c 1iL-cac-csCTH t3 J and xc:-c-:ic of JEt IdE5. ftJ_iLaii'cttc- zones Alternating -:31 maf c ciIc rocks -EL, T.28N., -:7. tic-iLL -;j:3zc; edge of sicsec. iiiis 31, western R.9E. iii the tci. Leucogranite is cr'.ccB&ciialong cio•ccthe lix ccroad. -cidi- iL-xsr5u;-i-c-'tx-c present and leucogranite are W1 :33ofit granite predominant rock type 2:3cvc:c1c-it-3-'t cic ii-',,'-i: in the cccc, area, cad and veins and dikes '-Zi s'cc cutting the mafic rocks were seencc atcccra1 several;Ic-ccaplaces. Lack of outcrops tIc tI--c---: :1FLi3 :tar— cc F idF- and precludes shape of the mafic zLstc-cr :3 sii the size '3lC ;Iii4, accurately 2c c—ic:-'. IF-Li.- determining I -is leucogranite. ciLa;-. 32 I3j-J.I)SU by the No clear c-c5c-c-ccc:'t a] seem to be surrounded masses, but Il-ct all tccscia. 15 ]clFcit Is ic-c--c -t.;;--'.-s-i iii.-: cc cc-Itt33 the occurrences of maf Ic rocks cutting granite were ccc-c seen. cd the c-tt - ;'i - ,Lcca il u': :/ci scr'c' c-lIt: the icc-c Ii ccccQL—ICat t-'c EL with -F--cc,:,:AIL.L- have ii :rcr-g-c The ccxc mafic rocks evidently range in composition, 1ccicc a '-cc :cccccic 5-r ;5r33r Biotite differences reflected Fr in the ferromagnesian minerals present. FtDcdWiLt, and lbLcci—lIcLtcbdIs is '3- abundant, cct -3i--Fr--! Is 7--t,-clt:1?ar-t predominant in ccc:c samples, others hornblende 3-cii iF5. in ii some iccctc iiiscc-icc5 commonly present Iiinc-Iothers Lac-ci :--t r--c'cvsca accl icc:-cfl-c-c-c1c both pyroxene and hornblende c-cc'uic occur. Quartz -"tc:Li.L,,'tCI it-c cccxc: cccLUt;usEL c'c;cc. variation Lit-c The c:-:5ctcccc extent to which cc; the compositional 'tctctcc:.,c itt-icc--c It; In the phases. 'ic-b-S blotitic fxc_'ic S.F 11cc to 1-c- partial it-aft cclc original -r-i1.c:ill cCtccFc t-i:-- ej in vii: the cc, maflc rocks reflects compositions orIs-; is due F,-s ax-sic cc-i: known. No it2cc'c;c-ac±ic petrographic work $itlc Fcc has yet c:ca-v. tV "digestion" by the Ilta ic;cxf'..-s granite is it not L77"'2cJ1c Cii -. c-cplagioclase rc;t :';,t cc: cccccsb I dcxc are arc Lcc' been done on these so compositions largely unknown. c2i,i,cc rocks, c--cctcc 'FLisi 'ccc I - i_3 3 ���� https://digitalcollections.lakeheadu.ca/files/original/e490e5cc4d21cd046bce02006cfdf9de.pdf dce4b4bbbee755b78cfd691154fc6c7f PDF Text Text University of Wizcensir,—Extsnsien GEOLOGICAL AND NATURAL HISTORY SURVEY Meredith E.Ostrom, State Geologist and Director GUIDEBOOK TO THE GEOLOGY AND MINERAL DEPOSITS OF THE CENTRAL PART OF JACKSON COUNTY AND PART OF CLARK COUNTY, WISCONSIN Prepared in cooperation with the U.S. Geological Survey and the Inland Steet Company tor the 19th Annual Institute on Lake Supetior G.otogy Madison, WisconsIn, 1973 �UNIVERSITY OF WISCONSIN-EXTENSIa1 GEOLOGICAL Afl NATURAL HISTORY SUit flY Meredith E. Ostrcn, State Geologist & Director GUIDEBOOK TO THE (ZOLOGY AND MINERAL DEPOSITS OF TH CENTRAL PART OF JACKSON COUNTY AND PART OF CURE COUNTY, WISCC*ISIN by Harry Alemic, U.S. Geological Survey, Washington, D.C. 20244 John M. Ohisan, Chief Geologist, Inland Steel Co., Ishpeming, Michigan This guidebook was printed in limited quantities for the 19th Annual Institute on Lake Superior Geology. Madison, Wisconsin Publication authorized by the Director, U.S. Geological Survey. Available from the Wisconsin Geological and Natural History Surveys University of Wisconsin—Extension, 1815 University Avenue, Madison, Wisconsin 53706. price $1.50. �GUIDEBOOK THE GUIDEBOOK TO TO THE AND MINERAL MINERALDEPOSITS DEPOSITS OF PART OF GEOLOGY AND OF THE THE CENTRAL PART OF JACKSON COUNTY COUNTYAND ANDPART PARTOF OF CLARK CLARKCOUNTY, COUNTY,WISCONS WISCONSINJJ JACKSON INlI by Harry and John Harry Klemioa" Klemi~/ and John M. M. Oh1son/ Ohlso~ IINTRODUCT NTRODUCT ION This field field trip is designed to provide an introduction to the general central part of of Jackson general geology and the economic geology of the central It includes includes aa visit visit to the Jackson County and part of Clark County. It magnetic taconite mine and County Iron Company's modern magnetic taconite mine and agglomeration plant, examination of plant, of outcropping Precambrian features, features, Upper Upper Cambrian strata, strata, and various local local physiographic physiographic features. features. will include Stops 1 through 9 (Figure 1), if if The trip will include visits visits to Stops (Figure 1), time permits. Additional places of interest interest are are shown as as localities 10 through 27 on the the maps and and are are described described briefly briefly in in the the text. text. general geology of of the northern part part of of this this area and of the The general the northern and of the the north has been been described described by by Wiedman Wiedman (1907). (1907). adjoining area to the Ostrom, Davis, Davis, and and Cline Cline (1970) have made made excellent excellent Ostrom (1966) (1966) and and Ostrom, (1970) have descriptions and correlations descriptions and correlations of of the the Upper Upper Cambrian Cambrian strata that that cover cover much of west—central west-central Wisconsin and and extend into into Jackson Jackson and and Clark (1961) discussed the clastic sedimentation Counties. Potter and Pryor (1961) of the the Paleozoic rocks of this general area of area and and noted noted the the presence presence of of phosphatic material in in the the Cambrian Cambrian rocks. rocks. The modern mining and and beneficiation facilities the Jackson facilities of of the County Iron Iron Company have have been been described described by by Skillings Skillings (1970). (1970). An occurrence of wavellite in Jackson County was described rence described by by Klemic Klemic and and Mrose Mrose (1972). The senior author is indebted to the Jackson County Iron Company for information information concerning concerning the the iron iron deposits. deposits. The cooperation and access access to their their property of many others in providing information and is gratefully acknowledged. is acknowledged. Much unpublished information information concerning the local local geology was was also also obtained from the the Wisconsin Geological Geological and and Natural History History Survey. Survey. Most of Jackson Jackson County and and parts of Clark County are in the "drift— "driftless area', but thin thin gravel gravel deposits deposits interpreted interpreted to to be be glacial glacial drift drift less area", but or outwash from glacial glacial deposits are present in many places east of the Black River. River. 11 Publication Publication authorized authorized by by the the Director, Director, U.S. U.S. Geological Geological Survey. Survey. ~/ U.S. U.S. Geological Survey, Survey, Washington, Washington, D.C. D.C. 20244. 1/ Chief Geologist, Inland Inland Steel Steel Co., Co., Ishpeming, Ishpeming, Michigan. Michigan. �2 9O0Os I1r d N (P I r 2 it S ho rtv ill e /J1c(T _ 141 rrc 1 \ atfi 1 6- eth7 2Q__. KSON / I c'°cT'r1 if 0 -18 41oj 'lL 1 23 IT Figure 1. 1. Figure S4 I I887 7 IJI (77) N Ti I i -o \ milee _44°15t=4 Field trip etops end other localities of geologic interest stops and in Jackson Jackson and end Clark C1rk Counties, in Counties, Wisconsin,. Wisconsin .. Base by U.S. Claire, 1964. 196)i. Eau Geological Survey, 1:250,000, Claire, l:2S0,000, Geological Survey, �r r 3 Exposures of Precambrian rocks in Jackson County and in the southern part part of of Clark Clark County County are are largely largely limited limited to to the the valley valley of of the the southern Black River and and its its tributaries. tributaries. A A few few mounds of Precambrian iron— ironformation and and associated associated schists schists and and some some quartzite quartzite knobs knobs occur occur as as windows in the Upper Cambrian sedimentary strata which form the the bedrock over most of of the the area. area. The exposed Precambrian rocks rocks consists consists mainly mainly of of paragneisses, paragneisses, schists, schists, phyllites, phyllites, quartzites, and, and, locally, locally, iron—formation. iron-formation. Granite and associated rhyolite and and aplitic aplitic dikes, dikes, and and gabbroic, gabbroic, dioritic, dioritic, and and doleritic dikes are are exposed in in many places. places. gneisses are are mostly mostly of of granitic granitic to to granodioritic granodioritic composition, composition, The gneisses and volcanic volcanic rocks. rocks. Thin chloritic and are metamorphosed sedimentary and layers of greenstone in in the the gneisses gneisses may may be be sills sills or or volcanic volcanic rocks. rocks. The foliation of the gneisses generally dips steeply and in some places In most most places the the gneisses are highly contorted migmatites. In the the weathered zone zone at at the the top top of of the the Precambrian Precambrian rocks rocks is is relatively relatively shallow, shallow, and or no no saprolitic saprolitic zone zone at at the the top top and it appears that there was little or of the the Precambrian Precambrian at at the the time time of of deposition deposition of of the the basal basal Upper Upper Cambrian Cambrian of sediments. age, totaling more Sandstone strata of Late Cambrian age, more than than 400 fe~t feet in thickness thickness in in places places in in Jackson Jackson and and Clark Clark Counties, Counties, rest rest unconformably unconformably in on the Precambrian Precambrian rocks. rocks. In most of the area area east of of the the Black Black River, River, however, however, the the sandstone cover cover is is less less than than 200 200 feet feet thick. thick. In In ascending order, the formations include include the Mount Simon and and Eau Eau Claire Claire order, the Cambrian formations the Mount Sandstones and and the Wonewoc and and Lone Lone Rock Rock Formations Formations of of Ostrom Ostrom (1966). (1966). units are are described described in in Figure Figure 2. 2. These units The Cambrian formations formations dip dip very very gently gently (less (less than than 10) 1°) southwest. southwest. or minor minor features features related related to to the the sedimentary processes involved Except ffor involved gradual transgression and in gradual and regression regression of of seas seas in in aa marine—shelf marine-shelf sediment zone, zone, these formations are are conformable conformable with with each each other. other. Most of the rocks cemented, very porous porous rocks are quartz arenites arenites which are weakly cemented, and permeable, permeable, and which have been intensively and intensively leached. leached. Loose sand accumulated by the disintegration of the accumulated the sandstone sandstone mantles mantles large large areas areas and conceals conceals formational formational contacts in and in most places. Deposits of river gravel derived largely from glacial deposits of the few tens of feet feet thick thick on some some terraces terraces along along north of the area are are a a few tens of the Black Black River. River. STOPS OF GEOLOGIC INTEREST STOPS STOP 1: STOP 1: Upper part of Mount Simon Sandstone. Sandstone. Location: quadrangle. West side of U.S. Black River Falls quadrangle. U.S. Rte. Rte. 12 about 500 feet north of Interstate about Interstate Rte. Rte. 94 94 (Figure (Figure 3). 3). The roadcut exposes flat—lying, medium—bedded, cross— flat-lying, thick— thick- to medium-bedded, crosslaminated, poorly poorly cemented, cemented, pale-gray pale—gray to to buff, buff, mediummedium- to to fine-grained fine—graiñed laminated, quartz sandstone with a few thin, white, clayey partings partings and thin, white, and minor �4 Upper Cambrian Cambrian formations Lone Rock Rock Formation 1966). Sandstone Sandstone Formation (Ostrom, (Ostrom, 1966). buff to to greenish-grey; greenish-gray; sandstone, sandstone, and shale, shale, huff and thinto medium-bedded, thinly crossbedded, thin- to medium-bedded, thinly crossbedded, some layers ripple ripple marked, medium- to to finesome layers marked, mediumgrained, glauconitic end grained, and micaceous, micaceous, fossiliferous; shale, buff to gray, mostly in very to gray, mostly in very thin thin erous; shale, exposed in borrow borrow pits on on layers. Unit is is well well esoosed ridgetops FEET FEET ~·~·;.:i:;;:{f~~t~:~~.ji~:~·i·;·:::: 200 ·,;':":::::;"'W.,,\(.l!II.!t~·.?\;.::> ·..·.·...::"i' .. ~·zone .:.,::.."...... Wonewoc Formation (Ostrom, 1966). Wonewoc 1966). Sandstone, white, pale-yellow to light-yellowish-brown, white, light-yellowish-brown, thick- to thicktomedium-bedded, medium-bedded,crossbedded, crossbedded, some some thin layers layers and and shalay shaley partings. partings. PredomiPredomiranges from coarse nantly medium grained, grained, but but ranges grained silty; weakly weakly cemented cemented escept except for grained to silty; thin zonesthat thatare arecemented cemented by by brown brown thin irregular irregularzones Unit forms forms bluffs iron osides. oxides. Unit Eau Eau Claire Claire Sandstone. Sandstone. Sandstone and and shale; shale; sandstone, pale-yellow-brown pale-yellow-brown to to buff, mediumsandstone, to thin-bedded, croasbedded, medium- to very ~wtjA2)i~~lJ/jJ~I\1~:lil;~~~~{~::~~:~~!~~~~~~~~i~:J,~;~~~~ fine grained, some thin coquinoid layers of ·:,::•.···..,;·;,;,··:·..... :·c>::"... :.:· small brachiopods, weakly cemented, friable, except for thin irregular megular zones zones that are are locally escept cemented by iron osides; shale, light-greenish- ~~ltl'~ §ig~i~·Y:5.:;~~~:r:i:~l~.:.;: gray to buff, generally in thin partings, but locally more than 1 foot thick. Unit generally poorly esposed o C • • • • ••• .. '~ " Mount Simon Simon Sandstone. Sandstone. Sandstone and shale; shale; sandstone, pale-yellow-brown pale-yellow-brown to to white. white, thickthicksandstone, to thin-bedded, thin-bedded, crossbedded, crossbedded, mainly mainly mediummediumgrained, but ranging from grained, from pebble pebble conglomerate conglomerate in basal layer layer to to very very fine fine grained grained and and in thin basal silty, weakly weakly cemented, cemented, friable; friable; shale, shale, lightlightgray, greenish-gray, locally locally red, red, mostly mostly gray, buff, greenish-gray, foot thin partings, partings, but but locally locally more more than than 11foot in thin bluffs along along streams. streams. Unthick. Unit forms bluffs conformity at base at base -:!.f":: ;'-':~/~"~~~\to ',' ,'. ',',:: \ ; I_'~ ,-, " < ", -I: ~ A • ;, _', \,' ~ ~, ., " ,', ,,-;. ~,- ~"... , -, - < '" < v Precambrian metamorphic and igneous igneous rocks Figure 2.—Generalized stratigraphic section aection of Paleozoic 2.-Generalized stratigraphic Paleozoic aedisnentary sedimentary rocks near near Black Black River River Falls, Falls, Jackson Jackson County, CoWlty, Wia., Wis., showing showing the approximate position position of of the the wavellite wavellite occurrence. occurrence. Data from Klemic DRtA 1972. Kiemic end and Mroa8, l4roee, 1972. �5 Figure 3. Blsck Rivsr Fall. area: Stop. 1, 2, 4, 6, and localities 11, and 25. Base by U.S. Geological Survey, Black River Falls nuadrangle, 1968, 1:62,500. 10, �6 partings stained by iron oxide. The Cross—beds dip southeast. No fossils noted here. this outcrop is typical of exposures of the upper part of the Mount Simon Sandstone west of the river. These beds are about 100 the Black to 120 feet above the base of the formation as exposed near River to the northeast and to the south. The lower part of the formation in most areas has thicker bedding and in average grain size. is slightly coarser The forested mound 3. mile to the east is Tilden Mound or section u Mound. It is a motadnock of Precaubflan iron-formation, schist, and phyllite. The relief on the Precambrian surface between the top of the mound sad the surface of the Precambrian rocks on the west side of Black River is 170 feet in a horizontal distance of about 400 feet. Unfoliated Precambrian granite crops out in the river valley locally between Tilden Mound and Interstate Rte. 94. Castle Mound, $ miles to the south—southeast is Upper Cambrian sandstone. STOP 2t Precambrian monadnock of iron—formation. Location: Black River Pails quadrangle in the NE sec. 12, T. 21 N., R. 4 W. near the junction of Levis Creek Road and West Bottom Road (Figure 3). Precambrian iron-formation flanked and partially capped by remnants of the Upper Cambrian Mount Simon Sandstone extends 50 feet above the surrotmding plain that is underlain by the Mount Simon Sandstone. The surf icial part of the iron—formation contains both itagnetite and martite. The strong magnetic anomaly associated with the mound of iron—formation extends both northwest and southeast of the mound. The extent to which the magnetic anomaly at the crest of the mound has been altered by lightning strikes is an interesting question. STOP 3: Jackson County Iron Company magnetic taconite mine and agglomeration plant. Location: Hatfield SW 71—minute quadrangle, SE fr, sec. 15, P. 21 74., R. 3 W. (Figure 4). The open pit mine is at the site of iron Mound, a nonadnock of Precambrian iron—formation that fornierty extended about 150 feet above the surrounding plain. Eron Mound was flanked and partly capped by the Mount Simon Sandstone. The uppermost part of the mound was approtiraately at the altitude at which the Lau Claire Sandstone (which overlies the Mount Simon Sandstone) formerly occurred. Iron—formation here dips about iV SW and is in an interval as much as 350 feet thick. This thickness may represent an isoclinally folded unit or it may be a faulted segment of a thick formation. It extends to below 650 feet above sea level. Quartz—chlorite schists border the iron— formation. Magnetite is the predominant iron-rich mineral, but some thin layers contain abundant specular hematite. The iron—formation has Mat Sc dikes, granitic been metamorphosed to garnet—actinolite grade. or aplitic dikes, and quartz veins cut the iron—formation. A zone of tRic schist parallela the layering of the iron—formation near the center of the pit. �7 '-I I' S �S The ore averages 20 to 23 percent in recoverable iron. About 3 of crude ore are required to produce 1 ton of pellets containing 63.5 percent iron and 1 percent silica. The nagnetite and gangue minerals are so finely interlocked that in order to obtain suitable iron ore concentrates, a final grind is made to a size at which 93.5 percent of the ore will pass through a 325—mesh screen. The Tnagnetite t€ separated from the gangue minerals by magnetic separators. Twenty pounds of hen— tonite clay is added per ton of concentrate in a mixer. The nixture is fed to a balling mill in which the powdered concentrates are converted to pellets, about 85 percent of which are 3/8 to 5/8 inch in diameter, The pellets are dried and preheated and then are heated to 2500 degrees F. In this process, the nagnetite is converted to hematite, and the finished pellets become hardened enough to withstand a compression of 800 lbs. tons Pellet shipments in 1972 were 887,000 long tons. More details concerning the iron deposit and the mining, beneficiaticrn, and pelletizing of the ores, tailings disposal, water supply, and environmental factors will be discussed at stop 3. ST4W 4: Eau Claire Sandstone and Wonawoc Formation of Ostron (1966). Black River Falls quadrangle, SW fr, sec. 24, T. 21 N., Location: R. 4W. Esst end of Castle Mound, 500 feet west of U.S. Rte. 12 on Castle Mound Road (Figure 3). Castle Mound is an elongate ridge capped by the lower part of The upper part of the Mount Siron Sandstone forms the basal part of the ridge from about 880 to Wonewoc Formation of Late Cambrian age. 995 feet above sea level, and, except at the eastern end of the ridge, it is largely concealed by talus and soil derived from the overlying rocks. The Eau Claire Sandstone, which includes fossiliferous tedium— to fine—grained sgndstone, forms the strata at altitudes of 995 to 1025 feet above sea level. The fossils in the Ea Cl.tre Sandstone are snail white phosphatic brachiopod shells composed of fluorapatite. These distinctive white shells are chars.cteflstic of the Lao Claire Sandstone In the area west of the Black River. East of the river the formation has been intensively leached, and although the fossiliferous zones are present, the fossil shell remnants are generally stained by iron oxides. Commonly the shells have been coaipletely removed and are represented by empty molds in the sandstone. A noticeable anount Of glauconite is generally present in the formation. Close exaninstion Of specimens of the coquina of phosphatic brachiopod shells reveals that quartz grains in contact with the shell mates-ia]. have been partially dissolved, leaving flat surfaces that conform to the adjoining smooth shell surfaces. Empty molds of fossils also show this modification of the innermost layer of quartz grains. Remnants of the Esu Claire Sandstone capping low hills in the area to the ecist are generally stained and cemented by brown iron oxide and weather out as small platy fragments that contrast with the pale—colored and weakly cemented and nonfossilt— lerous rock of the underlying Mount Simon Sandstone. The Mount Simon sad the Wonewoc, however, also contain iron oxide—cenented layers, but these are generally inedium—grained s andstane s. �9 STOP 5: STOP 5: Lone Rock Formation of of Ostrom Ostrom (1966). (1966). 1 Black River Falls quadrangle, NW NW 4' , sec. 10, 10, T. Location: River Falls quadrangle, T. 21 21 N., N., Borrow pit on south side of Pine Creek Road Road near R. W. (Figure (Figure 5). 5). pit of R. 5 W. crest of of hill. hill. The Lone Lone Rock Formation of of Late Late Cambrian age extends from from near near the The age extends the 1120 foot foot contour to to the the crest crest of of the the hill. hill. The formation formation consists consists mainly of light brownish—gray, brownish-gray, medium— medium- to to thin—bedded, thin-bedded, medium fine— fine- to fine—grained cross—laminated fine-grained cross-laminated sandstone sandstone and and thin thin layers layers of of shale. shale. The sandstone is argillaceous and and glauconitic. glauconitic. Some beds are are abundantly abundantly fossiliferous, and trails, ripple ripple marks, marks, and and mud mud cracks cracks are are well well fossiliferous, and worm trails, in thin thin sandstone sandstone layers. layers. The rock exposed here here is is typical typical preserved in of the rock in the of the the Lone Lone Rock Rock Formation at at other "shale "shale pits" pits" near near the the crests of ridges in both the the Black Black River River Falls Falls and and adjoining adjoining quadrangles. quadrangles. The environment of deposition of the Lone Rock Formation was similar It was was one in which shallow seas to that of the the Eau Eau Claire Claire Sandstone. Sandstone. It seas transgressed over over lagoonal lagoonal areas areas and and in in which which marine marine life life flourished flourished in in transgressed Local concentrations of brachiopod the littoral and the and neritic neritic zones. zones. Local shells in coquinalike layers resulted from from the the winnowing winnowing of of sediments sediments containing abundant abundant shells shells and and shell shell fragments. fragments. chitinous The rocks have been extensively leached of calcareous and and chitinous material, leaving fossil molds. Phosphatic brachiopod shells, material, shells, however, however, have been more more resistant leaching, as white resistant to leaching, as indicated by the the remaining white brachiopod shells. shells. The sandstone and and shale of the the Lone Rock Formation are extensively used for for surfacing dirt dirt roads and for for fill fill at bridges and and culverts culverts in used roads and at bridges Jackson County because they are to erosion because they are more more cohesive cohesive and and resistant resistant to the readily than is is most most of of the readily available available rock rock of of the the underlying underlying Cambrian Cambrian sandstones in in this this general general area. area. Soil developed on on the the Lone Lone Rock Rock ForFormation is rich in potash because of the presence of glauconite and clay and is and is rich in phosphorus from marine organisms. organisms. In In comparison, comparison, poor soils occur occur on the the Wonewoc Wonewoc and and the the Mount Mount Simon, Simon, which which consist consist largely largely soils of quartz quartz sand. sand. STOP 6: STOP 6: Wonewoc Formation Formation of of °strom Ostrom (1966). (1966). Location: Black River River Falls Falls quadrangle, quadrangle, SE SE sec. 31, T. 22 22 N., N., 31, T. W. (Figure R. 5 W. (Figure 3). 3). On south side of Wisconsin Rte. Rte. 27, 27, at at roadside roadside rest area and dirt road leading leading up up hill hill to to shale shale pit. pit. t, The Wonewoc Formation is well well exposed in large roadcuts on the Rte. 27 and south side of Rte. and on the the north side side of of Interstate Interstate Rte. Rte. 94. 94. More than 100 100 feet feet of of beds beds of of the the Wonewoc Wonewoc Formation Formation are are visible visible in in the the face face than of the the large large roadcut roadcut to to the the north. north. The top top of the the formation formation is near altitude altitude 1210 1210 feet feet and and is is approximately approximately at at the the top top of of the the exposed exposed rock rock formation is is below road face. The base of the formation road level level and and is is probably near altitude 1040, 1040, at at the the base base of of the the steep steep slope slope of of the the ridge. ridge. �1.0 Figure . Creek Rod ere!* Stop . Base by U.S. Geological Survey, Black River Falls cuadrangle, 1968, 1:62,500. Pine �11 white, pale yellow to The sandstone of the Wonewoc Formation is white, to thick thick bedded, bedded, cross-laminated, cross—laminated, and and predominantly predominantly light light brown, brown, medium to coarse— to very fine—grained medium grained, grained, but includes coarsefine-grained sand and and minor amounts of of clay. clay. Some thin zones are are cemented cemented by by brown brown iron iron oxides. oxides. A large large chamiel channel in in the the sandstone sandstone is is exposed in in the the lower part of the the A The rock here here is of that Wonewoc Formation The is typical typical of that in the the Wonewoc roadcut. In some some places, places, iron—oxide throughout this general general area. area. In iron-oxide cement is is more fossils were were found found at outcrop, but but in some some places places abundant. No fossils at this this outcrop, vertical tubular markings may represent represent burrows burrows made made by by marine marine creatures. creatures. At Wildcat quadrangle, and quadrangle, and and cemented cemented by by and has been called has Humbird, in in the the southern part of Fairchild Mound east of Humbird, at several other localities, localities, variegated variegated sandstone sandstone colored colored at several iron oxide oxide is is very very distinctive distinctive in in appearance appearance and and locally locally iron "Zebra rock" rock" because because of of the the pattern pattern of of its its markings. markings. Although the the Wonewoc Formation forms bluffs and and cliffs, cliffs, the rock is is generally only weakly cemented, and and bedrock bedrock on on the the lower lower slopes slopes of of ridges hills underlain underlain by by this formation is is commonly commonly concealed concealed by by ridges and and hills this formation loose sand and and rubble from flom overlying overlying beds. beds. STOP 7: 7: Eau Claire Sandstone Sandstone and and Wonewoc Wonewoc Formation Formation of of Ostrom Ostrom (1966). (1966). STOP 35, T. Black River Falls quadrangle, SW -, sec. Falls quadrangle, SW~, 35, T. 23 23 N., N., Location: R. 55 W. (Figure (Figure 6). 6). At Silver Mound and in the field field on the southwest R. of Silver Mound. of Fossiliferous and glauconitic sandstone beds of the Eau stone stone are are well well exposed exposed in in aa small small excavation excavation on on aa prominence prominence field Mound, and loose fossiliferous fossiliferous Eau field southwest of of Silver Mound, stone occurs occurs at at an an altitude altitude of of 1025 1025 feet feet on on the the south south tip tip of of stone near the the highway. highway. Claire in in the the Claire Silver Silver SandSandMound Mound Silver Mound is is an an important important archeological archeological locality. locality. The mound is is capped by the the Wonewoc Wonewoc Formation. Formation. The lower lower part part of of the the formation formation is is largely concealed. concealed. The uppermost 100 feet or so of beds, beds, however, however, is thoroughly cemented by silica, silica, and and the the rock rock is is aa brittle brittle quartzite. quartzite. This rock was was extensively extensively used used by by prehistoric prehistoric Indians for the manufacThis Indians for the manufacture of tools tools and and weapons. weapons. Artifacts are numerous in the fields fields surrounding the part of of Silver Mound, Mound, and artifacts and and whitish whitish rounding the southern part and artifacts flakes of quartzite from this flakes this locality locality are are widespread widespread in in Jackson Jackson County. County. Similar quartzite occurs in lesser amounts miles amounts on a ridge several miles northwest of of Silver Silver Mound. Mound. The source of the the silica that that cemented the sandstone sandstone and and the the conditions conditions under under which which it it was was deposited deposited in in the the formation formation of the quartzite in this this almost isolated occurrence require require an explanation. Upper Cambrian strata of this There is no lack of silica in the the Upper this general but most most of of it form of of quartz quartz general area, area, but it is is in the the relatively inert inert form sand. Therefore, Therefore, some some local chemical environment that that differed from the the general conditions must have made silica general silica available available in in solution. solution. Perhaps the chemical the the chemical environment environment of of the the fossiliferous fossiliferous beds, beds, particularly of of the coquina layers, layers, may have been the the source source of of the the silica. silica. As previously described, the the quartz sand grains in contact with the phosphatic brachiopod described, shells have have been been partially partially dissolved dissolved into into hemispherical hemispherical forms forms having having their their shells �·OO$'G9:! '996! 'a!~ue~penu r'uadrangle, s!!ed Falls 1:62,OO. 1968, l:iw~:20!OalJ U.S. fleological ·S"n Aq by aseg Base "L 7. dOlS Stop ~ooH Rock ~oe!g Black 'AaAInS Survey, :a~.Ia pree: punai'{ Silver Mound .leAHS "9 Figure 6. e.:nj,:.!I (';1 12 �13 flat against the the shell shell surfaces. surfaces. The chemical environment environment that that flat surfaces against produced this result in the Eau Claire Claire and the Lone Lone Rock, Rock, both both of of which which produced this result the Eau and the are are fossiliferous and and contain phosphatic phosphatic brachiopods, brachiopods, would would have have made made available large quantities of of silica silica in in solution. solution. Such silica—bearing silica-bearing waters percolating from the fossiliferous fossiliferous Lone Rock Formation may have the silica silica cement cement in in the the Wonewoc Wonewoc Formation Formation at at Silver Silver Mound. Mound. deposited the Small zones of silicified sandstone a few inches thick, thick, in the Mount Simon Sandstone near its contact with the Eau Claire Sandstone have been noted in in several several places places in in Jackson Jackson County. County. STOP 8: 8: STOP Exposure showing complexities complexities of of Precambrian Precambrian rocks. rocks. This stop also provides an opportunity to also to examine examine some some economic economic uses uses of of local local geologic features problems and possibilities arising features and some of of the problems and possibilities from the pressures of demands demands for for their their use. use. Hatfield 7-i-—minute quadrangle, SE -, Location: Hatfield 7!-minute quadrangle, ~, sec. 3, 3, T. T. 22 22 N., N., R. W. At Black River, River, north of County Rte. Rte. K K and and south south of dam at at R. 33 W. Lake Arbutus (Figure (Figure 7). 7). Because of of load load limitations limitations at at the the bridge bridge over over the the canal canal at at Hatfield, Hatfield, it will be necessary to to walk about about 11 mile mile to to the the large large exposure exposure of of PrePrecambrian metamorphic immediately below the at the metamorphic rocks rocks immediately the unconformity at the the Upper Upper Cambrian Cambrian sandstone. sandstone. base of the Lake Arbutus is an an artificial artificial lake impounded behind a dam built bedrock in in the the valley valley of of the the Black Black River. River. Water level upon Precambrian bedrock in the the dam dam is is maintained maintained at at or or near near the the level level of of the the unconformity unconformity at at the top of the the the Precambrian. A A canal canal aa little little more than than 22! miles long long has been cut in the Upper Cambrian sandstone to carry water to the penpen— stocks of aa small small electrical electrical power power plant. plant. The hydraulic hydraulic head at the power plant is is nearly 100 100 feet. feet. This power plant is is an an important important local local nonpolluting source source of electric energy. energy. Lake Lake Arbutus Arbutus has has a a surface area of of slightly more more than two square miles and and is is aa popular recreation center, center, having two two county parks and and aa State campsite on its shores. on its shores. Hatfield, Hatfield, aa small resort community on the the west west side side of of the the lake, lake, is is in an an area in in which which only only about about 10 10 to to 30 30 feet of of beds beds of of Upper Upper Cambrian Cambrian Mount Mount Simon Simon Sandstone Sandstone overlies overlies the the metametafeet morphic and and igneous igneous Precambrian Precambrian basement basement rocks. rocks. The community obtains obtains its water supply largely from wells in its in the the sandstone. sandstone. A A few wells extend into into the the Precambrian Precambrian basement basement rocks. rocks. disposed into the surficial mantle of Sewage from the the community is is disposed surficial mantle of sand and in the the upper layers layers of of the the sandstone sandstone strata. strata. Thus the the possipossibility exists for pollution of of the the water water supply. supply. Should the local local substantially, both the the amount amount of waste redemand for water increase substantially, quiring disposal and and the the possibility possibility of of pollution pollution of of the the local localgrc*ind ground waters would would also also increase. increase. Alternative sources sources of of water water and and improved improved facilities eventually be be needed. needed. facilities for sewage disposal will eventually - �14 'U . JAO CO 21 T. 22 N. 25' C" C" 0 ; 19 i- J9 \)./.;iç;// y 4O- -, HatfI) eld O7 / fl9• I /l-o ( Backw \'\ C' ) JiVt\ jJJ/ (fl I'? 1Y U(1 ¼) 18 II OA 0 OLD 897 LA V 93 ,/ 0 I 895 0 11 I Loca],i'- 200000 FEET HIGH BANK 1jii 889112$ i7,ei Pits 16 440 Locality 25 - 22'30" 900 45' Pigure Figure mile 7. 680 1810000 FEET I c.1ty 17 ° 4.2 MI. To WIS. 54 '23J 42' 30" localities 17, 17, 24, 24, and and 25. 2. Stop 8 and and localities Hatfe].d quadrangle, 1970, Base from U.S. Geological Survey, Hatfield 1970, ].: 214,000. 1:24,000. Lake Arbutu8 area: area: Lake Arbutue �15 1 The contact between the Mount Simon Sandstone and the underlying west end of the bridge where Precambrian rocks rocks is at road level level at the west mile southwest County Rte. southwest of of the the dam dam at at Rte. K K crosses the Black River Lake Arbutus. A A thick thick bed of of coarse—grained coarse-grained cross—laminated cross-laminated sandstone sandstone is is exposed exposed on on the the west west side side of of the the road, road, and and Precambrian Precambrian granitic granitic gneiss gneiss the east side side of of the the road. road. The channel of the the Black River crops out on the has been cut about about 50 50 feet feet into into the the Precambrian Precambrian rocks rocks at at the the bridge. bridge. t -' Rte. K, K, then go northeast northeast on Clay School School Proceed east on County Rte. Road about 0.2 mile to to aa dirt dirt lane lane on on the the west west side side of of the the road. road. Follow woods and dirt lane to clearing in woods and turn north on path leading down into valley. Proceed northeast northeast toward toward the the foot foot of of the the dam. dam. the river valley. This large large exposure of bedrock shows shows some some of the the complexity of the the basement rocks. rocks. Granitic and and chloritic chloritic gneisses, gneisses, schists, schists, Precambrian basement A large and greenstones trend trend northwest and and dip dip steeply steeply northeast. northeast. A northeast—trending metagabbro dike dike at east end end of of the the dam cuts cuts the the northeast-trending at the the east gneisses. Another large dike on the west side of the east channel of the river is more dioritic in in composition. composition. The intervening granite the gneisses and chloritic sills sills are are contorted contorted in in sinuous sinuous forms forms on on which which gneisses and chloritic there is is well-developed well—developed quartz quartz rodding rodding or or slickensides slickensides that that dip dip to to the the there A feet southwest of the dam a prominent siliceous east. A few hundred feet metarhyolite(?) and the adjoining gneiss are cut by a contorted mass of metarhyolite(?) dipping mafic dike or or sill. sill. An east—trending east-trending swarm of narrow steeply dipping' unfoliated siliceous siliceous and and chloritic chloritic dikes dikes cut cut all all the the other other rock rock types. types. Minor quartz—filled quartz-filled fractures fractures cut the younger dikes and the other rock units. At one place on the west side of the river a quartz vein is more than three three feet feet thick. thick. Minor amounts amounts of of pyrite pyrite are are evident in in the the rocks, and fine—grained pyrite is abundant in the youngest dike. rocks, and fine-grained pyrite is abundant in the youngest dike. STOP 9: STOP 9: Wavellite occurrence occurrence in in the the Eau Eau Claire Claire Sandstone. Sandstone. quadrangle, SW Location: Black River Falls Falls quadrangle, SW -, sec. 23, 23, T. T. 22 22 N., N., R. (Figure 8), 8), roadcut roadcut on on East East Snow Snow Creek Creek Road. Road. R. 4 W. W. (Figure t, Wavellite (Al3(P04)2(OH)35H20) (A13(P04)2(OH)3'5H20) occurs occurs as as thin thin botryoidal botryoidal crusts, erusts, small masses, and cement in the the sandstone sandstone at outcrop small spherical spherical masses, and as as cement at this this outcrop and at several other places where where this this stratigraphic stratigraphic unit unit is is exposed exposed in this general general area. area. The source of the phosphorus is believed to have been phosphatic phosphatic fossil fossil material material such such as the phosphatic phosphatic brachiopod brachiopod shells shells as the in the Eau Claire Sandstone. Sandstone. The Wonewoc Formation which crops out on the west side of the road is weakly cemented, is cemented, very porous and and permeable permeable sandstone. sandstone. It It is is coarser in grain size than the underlying rock in grain rock and and is is thoroughly thoroughly leached. leached. The Wonewoc-Eau Claire contact zone zone is is favorable favorable for the the development of aa Wonewoc—Eau perched water table in places is abundant abundant in in the the places where where shale or clay is Claire. Eau Claire. in many places in Wisconsin where the Eau Wavellite probably occurs in Claire Sandstone is is present and where conditions for movement of ground water were comparable comparable to to those those in in this this area. area. In addition, similar conIn addition, ditions for occurrences of wavellite in association with the Lone Rock Formation may exist. Wavellite, however, may may be be readily readily overlooked, overlooked, Wavellite, however, particularly icial stains of particularly in in cases cases where where it it contains contains surf surficial of iron iron oxides. oxides. �16 -I ZLji *_—:•1: - °• -.-i---- 19• 25 F IF LocalY 24 Locality 23. I 23N Ei 928 1 ' cc; 25 O1I 96 III\ EVERG EEN :T -3 'p23 \ ,** - o T.22N — M 48 13 889 f OF - POWERHO LOcZty 16 17 GreI I 21 Fj \1],'?'Locality iave1 15 .x-= Figure 8. 8. localities 12, Merrillan ares: area: Stop Stop 99 and localities 12, 15, 1', 19, 19, 20, 20, 21, 21, 22, 22, and and 27. 27. Base Base by by U.S. U.S. Geological Survey, Geological Black cuadrangle, 1968, 1968, 1:62,500. l:62,O0. Black River Falls Falls quadrangle, �17 ADDITIONAL LOCALITIES OF GEOLOGIC INTEREST INTEREST of Precambrian Precambrian rocks. rocks. Exposures of Falls 15-minute 15—minute quadrangle, quadrangle, SE SE ~, , sec. 15, Locality 10: Black River Falls Locality 10: T. 21 21 N., N., R. R. 44 W. W. (Figure (Figure 3). 3). North of U.S. U.S. Rte. Rte. 12 at Black River T. Falls. Accessible from from east east end end of of bridge bridge crossing crossing Black Black River. River. Unfoliated jointed granite granite at at the Falls below the the dam dam appears appears Unfoliated the Falls fresh, but much of the fresh, the hornblende is is altered altered to to chlorite. chlorite. Similar granite cuts cuts iron-formation iron—formation and rocks adjoining adjoining the the iron-formation iron—formation in granite and rocks Z.E. Peterman Peterman of of the the U.S. U.S. Geological Geological Survey Survey has has deterdeterthe subsurface. Z.E. mined that that the the rubidium—strontium rubidium-strontium ratios in these granites indicate an age of years (U.S. (U.S. Geol. Geol. Survey, Survey, 1972). 1972). age of about 1,690 million years Locality 11: 11: Black River Falls Falls 15—minute 15-minute quadrangle, quadrangle, NE NE -, ~, sec. 22, the valley of Black River at T. 21 21 N., N., R. R. 44 W. W. (Figure (Figure 3). 3). In the at the the base base T. On south side of river. of river. of bluff of Mount Simon Sandstone. On Granitic gneiss and gray chloritic gneiss are cut by dolerite In In contrast to the deep channel cut cut by by the the Black Black River River in in the the Precambrian rocks Arbutus, the-channel rocks below the dam at Lake Arbutus, the· channel here here is only about only about 10 feet feet down into into the the Precambrian Precambrian rocks. rocks. The outcrops here may be concealed if if water water level level is is high. high. dikes. 15—minute quadrangle, quadrangle, NE NE ~, , sec. 30, Locality 12: Black River Falls Falls 15-minute Locality 12: T. N., R. R. 33 W. W. (Figure (Figure 8). 8). West side side of Black River near junction junction T. 22 N., Creek and and river. river. Readily accessible by road road to to canoe canoe landing. landing. of Hall's Creek bluffs leads leads to exposures exposures of of phyllite phyllite and gneiss Path to south along bluffs and gneiss beneath unconformity at at base base of of Mount Mount Simon Simon Sandstone. Sandstone. Weathered schist and and phyllite at at the the base of cliffs of Mount Simon Sandstone are are exposed a short exposed a short distance distance upstream from from the the mouth of of Hall's Hall's Creek; Creek; chloritic chloritic mafic mafic intrusive intrusive rocks rocks also also occur occur in in the the creek creek valley. valley. t, Locality Falls 15-minute 15—minute quadrangle, quadrangle, SE SE , sec. 17, Locality 13: 13: Black River Falls T. W. (Figure (Figure 8). 8). West side side of of Black River River about about 0.4 0.4 mile T. 22 22 N., N., R. R. 33 W. quarry near near river. river. southwest of power plant. plant. Abandoned quarry Strikingly contorted dark gray and and white hornblende gneiss of and a fine—grained fine-grained intrusive rock granitic to granodioritic composition and of gabbroic composition are present are exposed in the the quarry face face and and are are present in loose blocks. blocks. The composition of of feldspar feldspar augen augen in the the gneiss gneiss has has not been determined. Locality -, sec. 25, 25, T. Locality 14: 14: Hatfield 15—minute 15-minute quadrangle, quadrangle, NW NW~, T. 23 23 N., N., R. R. 33 W. W. (Figure (Figure 9). 9). West side side of of Black Black River River near near French French Island. Island. Pink granite typical of that in several several localities along along the Black River north of of Lake Lake Arbutus is is well well exposed exposed along along the the river. river. The basal beds of the the Mount Simon Simon Sandstone Sandstone crop crop out out on on the the west west side side of of the the road. road. Similar granite crops crops out out at the abutment of the abandoned bridge on the east side of of the Black River 0.2 mile mile south of Wisconsin Rte. Rte. 95 95 in the NW , in the NW~, sec. 19, 19, T. T. 23 23 N., N., R. R. 22 W. W. �18 15 17 Levis Mound I Sch . ·r l own Hall ~ 2~ ,, . ·., .~ I "Locality .. 14 ~.:~:;.' "-29 \ /. / "-/ 34 I( (, If /I If figure Figure 9. '-< .. -< L I II•• v· t.ke Arbutus Arbutu area: L.ke ( .l'Gravel Pit - ( I Localittea 14 and 15. 1. Base Locelities 14 and Baseby by U.S. U.S. Geological Geo1op,ica1 Survey, Hatfield Hatfield planimetric l98, l:1L8,000. Survey, planimetric map, map, 1958, 1:48,000. �19 Locality Locality 15: 15: Hatfield 15—minute 15-minute quadrangle, quadrangle, R. 2 W. (Figure 9). North side of of East Fork R. W. (Figure 9). east of of the the bridge. bridge. t, NW 4, T. T. 22 NW -, sec. 4, 22 N., N., of Black River River 250 feet of 250 feet Large outcrop of of granitic granitic and and migmatitic migmatitic gneiss gneiss cut cut by by maf mafic and ic and aplitic dikes. During periods of normal or low water level this outcrop is is well exposed. exposed. Quartz rodding or slickensides on minor folds folds in the the gneiss gneiss is in is similar to that in the the outcrop near near the the dam dam at at Lake Lake (Stop 8), 8), but but the the rodding rodding here here plunges plunges east east at at aa low low angle. angle. Arbutus (Stop of the mafic and aplitic dikes dikes at at this this locality locality have have The relative relative ages ages of the mafic and aplitic not been determined. Pink granite and and small aplitic dikes crop out at several several other places along along the the East Fork Fork of of the the Black Black River. River. t, 20, T. T. 23 Locality 16: 16: Hatfield 15—minute 15-minute quadrangle, quadrangle, SW SW -, sec. 20, 23 N., N., R. 1 W. (Figure (Figure 10). 10). Brushy Ridge Road. Road. R. Quartzite, a small Quartzite, probably of Precambrian age, age, is exposed in ina small roadcut tributary of of Rock Rock Creek. Creek. Quartzite roadcut on the south side of aa tributary zones in in the the Mount Mount Simon Simon Sandstone Sandstone occur occur in in aa small small knob knob on on the north zones the north side of the east-trending east—trending road 0.8 mile north side north of of this this roadcut. roadcut. t, Hatfield 15-minute 15—minute quadrangle, quadrangle, NE NE , sec. 22, Locality Locality 17: 17: Hatfield 22, T. T. 22 22 N., N., R. R. 3 W. W. (Figure (Figure 7). 7). Morrison Creek at at County Rte. Rte. K. K. Granite gneiss cut by mafic dikes is is exposed beneath the the bridge during periods of of low low or or normal normal water water level. level. Bluffs of of the the basal basal beds beds of the Mount Simon Sandstone and metamorphic and outcrops outcrops of of the the Precambrian metamorphic rocks and mafic maf Ic and and granitic granitic intrusive intrusive rocks rocks are are exposed exposed along Morrison rocks Creek to the the east of of this this locality. locality. 15—minute quadrangle, quadrangle, NW NW t, , sec. 9, 9, T. T. 21 Locality 18: Hatfield 15-minute 21 N., N., Locality 18: R. W. (Figure (Figure 11). 11). On north side of Battle Point Road. Road. R. 2 W. Precambrian quartzite is is exposed exposed in in aa small small quarry. quarry. The quartzite is is brecciated and recemented by by silica. silica. Basal sandstone of the Mount fragments of of the the quartzite quartzite at the unconformity unconformity includes fragments at the Simon Sandstone includes between the Precambrian and and the the Cambrian Cambrian rocks. rocks. Exposures of of Cambrian Cambrian rocks. rocks. t, Locality Black River -h-, sec. 19, Locality 19: 19: Black River Falls Falls 15—minute 15-minutequadrangle, quadrangle,SE SE 19, T. T. 22 22 N., N., R. R. 33 W. W. (Figure (Figure 8). 8). At bridge on on County Rte. Rte. E E crossing crossing Hall's Creek. Creek. Basal beds of Mount Simon Sandstone Sandstone are are exposed exposed near near stream stream level. level. bedded, cross-laminated, cross—laminated, medium to very coarse coarse The sandstone is is thick bedded, grained, and has at the the base the grained, has a thin pebbly layer at base in places places along the creek. �20 NEILLSVILLE 1S.4 MI. MI. TO WIS. 91S ~.~ r-ri-''l. ) / _.~~l~le Sch . "I / _. -'"- . " .1/-;... ~ _. "":' l..~ '. \, @. . 73 ........... R1W rf'o '' 44°30' 1 660000 FEET 6 5 0. BM 1005 ShortviIle 9 'v" 16 13 1--....·. '- 24 9 ",:-~,;";"",,,.lL'·~~ I •• I "--,. ":-,------.--- .. Figure 10. 10. Figure } -:- .. ,,'- mile ---.. by U.S. 3bortville Shortville area: area: Locality Locality 16. 16. Base by U.S. plazimetric map, Geologieal map, Survey, Hatfield Hatfield planimetrie Geological Survey, 1958, 1:48,000. l98, l:1.i8,000. �21 , F'1inmak r ',Flowage 36 ,.r:..-;-" ~~\~:.:. , ,-- / J f!t>:3,) .......\ \1 L I: Ii II II ft II II II II 1/ II .. ~ ~~~~~:.:_;~ f~~( "' )' vp , " /1 (~~/ / ,, >dk'2 . --' /.-9~. /; /' r, /I. ::~ l \'./ / - - :;', , ~ .... ..... _ _ :', /" ... ~ ';' 1\, \\~ 1 ~~~ {3 . t \{} ....... , ,\\.'-..,'~'.~,\ \" \.\; { \\. I.' {~ ~- ....."'\.,-:-. "- {\. '" ....... t. '.:= ~"~~~ .. .' <~ ~-, \~:-..\ /'" ;.'): . -" . 1/ /'~}/. ~ I~;~:~~~-'') :. ......._- ,\("~ ~')~~2,~ "- 5 v . I' .... ' Figure 11. 11. • Town Line Flovege area: Locality F1owge area: 18. Base by U.S. Geological Locality 18. 1958,l:Ii8,000. 1:48,000. Survey, Hatfield Hatfield planimetric planimetric map, map, 19S8, �22 Locality 20: ?, sec. 26, Locality 20: Black River Falls Falls 15—minute l5-minute quadrangle, quadrangle, NW NW~, 26, T. T. 23 23 N., N., R. R. 44 W. W. (Figure (Figure 8). 8). At park on west side of U.S. U.S. Rte. Rte. 12 at at south edge of Merrillan. Thick-bedded sandstone of the Mount Simon Sandstone is well well exposed at on Hall's Hall's Creek Creek where where there is aa scenic at the darn dam on scenic waterfall. waterfall. Locality 21: Locality 21: Black River Falls 15—minute 15-minute quadrangle, quadrangle, sec. sec. 30, 30, T. T. 23 23 N., N., R. R. 3 W. W. (Figure (Figure 8). 8). At Bruce Mound, in in Clark Clark County. County. Prominent cliffs of the Wonewoc Wonewoc Formation are are strikingly exposed exposed along the southwestern side side of of the the mound. mound. The Lone Rock Rock Formation Formation caps caps the mound at at the the lookout lookout tower. tower. The Eau Claire and and Mount Simon Sandstones stones are largely concealed on the the lower lower slopes slopes of of the the mound mound but but are are partly exposed exposed near near the the ski ski resort resort facilities facilities on on the the east east side side of of the the mound. Locality River Falls Locality 22: 22: Black .River Falls 15—minute 15-minute quadrangle, quadrangle, sec. sec. 22, 22, T. T. 22 22 N., N., R. R. 4 W. W. (Figure (Figure 8). 8). Along road following the top of ridge leading from West Snow Creek Road Road toward toward radio radio tower. tower. Shale pits in Lone Rock Formation have have excellent exposures exposures of of the the fossiliferous glauconite sandstone sandstone and and shaly shaly strata. strata. Locality 23: 15—minute quadrangle, quadrangle, NW~, NW , sec. 29, Locality 23: Black River Falls Falls 15-minute 29, T. N., R. R. 44 W. W. (Figure (Figure 3). 3). Roadcut on east side of Moss Hill Hill Road. Road. T. 21 N., Exposures of upper part of Mount Simon Sandstone are are capped at at an an altitude of 940 feet by the the Eau Eau Claire Claire Sandstone Sandstone which which has has thin thin layers layers of brachiopod shells. shells. A of coquina consisting of white brachiopod A similar occurrence is miles to the west. is at an altitufe altitufe of of 940 940 feet feet along along Wold Wold Road Road l-- miles Note the concentration of brachiopod shells along some of the cross It laminae. 14, T. T. 22 Locality Hatfield 15-minute 15—minute quadrangle, quadrangle, SW~, SW , sec. 14, Locality 24: 24: Hatfield 22 N., N., On northwest northwest side side of of Mollies Mollies Creek, Creek, at at sharp sharp bend bend R. R. 33 W. W. (Figure (Figure 7). 7). On about about 1000 feet feet northeast northeast of of junction of of Mollies Mollies Creek Creek and and Morrison Morrison Creek. Thin basal beds of the Mount Simon Sandstone have a thin basal basal layer of acts. The underlying Preof quartz quartz pebbles pebbles that that resemble resembleventif ventifacts. cambrian gneiss and schist is is deeply weathered to greenish—gray greenish-gray clay at the the unconformity unconformity between between the the Precambrian Precambrian rocks rocks and and the the Cambrian Cambrian at sandstone. Locality Locality 22, T. T. 22 N., Hatfield 15-minute 15—minute quadrangle, quadrangle, NE NE ~, , sec. 22, Hatfield N., On south bank of Morrison Creek about 1600 feet R. (Figure 7). 7). of feet R. 3 W. W. (Figure mouth of of Hay Hay Creek. Creek. southwest of mouth 25: 25: the Mount Simon Sandstone is is cemented Basal quartz conglomerate of the by pyrite in small about 6 inches inches thick a few feet small lenticular zones zones about feet above normal water water level. level. The streambank is is slightly overhanging in in places, places, and and careful search may be required to to find the the pyritic conglomerate. conglomerate. 1 �23 Locality 15—minute quadrangle, quadrangle, NE NE ~, , sec. 33, Locality 26: 26: Hatfield Hatfield 15-minute 33, T. T. 22 22 N., N., R. 1 W. (Figure 12). 12). Saddle Mound, Mound, north north of of Wisconsin Wisconsin Rte. Rte. 54. 54. R. W. (Figure The crest of the mound at at the lookout tower is capped by about 60 feet feet of the Lone Rock Formation. Glauconitic sandstone 60 sandstone is is well well exposed in a small small abandoned quarry near the foot foot of the tower, tower, and Ostrom's Ostrom's (1966) (1966) Birkmose Birkmose Member Member of of the the Lone Lone Rock Rock Formation Formation is is exposed exposed near the the guard rail rail several several hundred hundred feet feet east east of of the the tower. tower. steep southern slopes slopes The Wonewoc Formation is well well exposed on the steep the mound. mound. Minor amounts of weathered fossiliferous fossiliferous sandstone, sandstone, of the probably of the Eau Claire Sandstone, Sandstone, can be found found on the the spur on the northwestern side side of the the mound near near an an altitude altitude of of 1100 1100 to to 1130 1130 feet. feet. Most of of the the Eau Claire Sandstone, Sandstone, however, however, is is concealed by debris from the overlying formations, formations, and of the loose fossiliferous fossiliferous rock on and some some of the loose the lower slopes is is talus talus from from the the Lone Lone Rock Rock Formation. Formation. Holocene river river gravels. gravels. Locality 27: Falls 15-minute 15—minute quadrangle, quadrangle, SE SE ~, , sec. 20, Locality 27: Black River Falls T. T. 22 22 N., N., R. R. 33 W. (Figure (Figure 8). 8). Gravel pit on on west west side side of of Black Black River. River. gravel deposits deposits at this locality are are on aa wide wide terrace terrace Sand and and gravel at this about 20 feet feet above above river river level level and and cover an area of of more more than than one one square square about mile. The gravels include aa wide variety of siliceous igneous and rock types types and and minor minor amounts amounts of of sedimentary sedimentary rock. rock. Most of metamorphic rock the gravel gravel is is outwash from from glacial glacial deposits deposits that that are are abundant abundant to to the the the north. gravel deposits occur on the west side of the Black Similar gravel River in Clark County north of Wisconsin Rte. Rte. 95, 95, and in Jackson County as indicated on on both sides of the river south of Black River Falls, Falls, as the of these these areas. areas. the topographic maps of During construction of these deposits of Interstate Rte. Rte. 94, 94, these deposits were were important sources of sand and gravel, important gravel, and and they they currently currently supply supply local local needs. �r 24 ~(~4 Figure 12. .\ Saddle Mound: Locality 26. Base by U.S. Geological Survey, Hatfield SE quadrangle, 1970, 1:62,500. I �25 25 REFERENCES Klemic, Harry, Harry, and Mrose, Mrose, M.E., M.E., 1972, 1972, Geologic relations and X-ray X—ray Klemic, crystallography of of wavellite wavellite from from Jackson Jackson County, County, Wisconsin, Wisconsin, U.S. Geol. Geol. Survey and implications: U.S. Survey Prof. Prof. and their geologic implications: Paper 800—C, BOO-C, p. p. C53—C62. C53-C62. Ostrom, M.E., 1966, Ostrom, M.E., 1966, Cambrian stratigraphy stratigraphy in in western western Wisconsin: Wisconsin: Wisconsin Wisconsin Geol. Geol. and and Nat. Nat. History History Survey Survey Inf. Inf. Circ. Circ. 7, 7, 79 79 p. p. Ostrom, M.E., M.E., Davis, Davis, R.A., R.A., Jr., Jr., and Cline, L.M., L.M., 1970, 1970, Field Field trip trip Ostrom, and Cline, guidebook for Cambrian-Ordovician Cambrian—Ordovician geology geology of of western western Wisconsin: Wisconsin: Wisconsin Geol. Geol. and and Nat. Nat. History History Survey Survey Inf. Inf. Circ. Circ. 11, 11, 131 131 p. p. Potter, P.E., P.E., and Pryor, W.A., W.A., 1961, 1961, Dispersal Dispersal centers centers of of Paleozoic Paleozoic Potter, and Pryor, and and later clastics of the the Upper Upper Mississippi Mississippi Valley Valley and and adjacent adjacent areas: Geol. Geol. Soc. Soc. America America Bull., Bull., v. v. 72, 72, no. no. 8, B, p. p. 1195—1250. 1195-1250. Skillings, DN., Jr., Skillings, D.N., Jr., 1970, 1970, Jackson Jackson County County Iron Iron Co.: Co.: Mining Rev., Rev., v. v. 59, 59, no. no. 24, 24, p. p. 1, 1, 10—14. 10-14. Skillings U.S. U.S. Geological Survey, 1972, 1972, Iron—formation Iron-formation in in Jackson Jackson County, County, Geol. Survey Prof. Wisconsin: U.S. U.S. Geol. Prof. Paper Paper 800—A, BOO-A, p. p. A3. A3. Weidman, Samuel, 1907, 1907, The The geology geology of of north north central central Wisconsin: Wisconsin: Weidman, Samuel, Wisconsin Geol. Geol. and and Nat. Nat. History History Survey Survey Bull. Bull. 16, 16, Sci. Sci. ser. ser. 4, 4, 697 p. p. 697 — � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1973 Description An account of the resource Institute on Lake Superior Geology. University of Wisconsin, Madison, Wisconsin. May 3-6, 1973. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1973 Contributor An entity responsible for making contributions to the resource J.L. Anderson C.R. Bentley Richard Berger Emmy Booy Brenton M. Hamil Ruth J. Sobanski W.F. Cannon Roger W. Cooper G.H. Dury John. C. Green E. Wm. Heinrich A.V. Heyl Robert A. Jenkins John S. Klasner Thomas R. Turner M.D. Lewan M.S. Lougheed J.J. Mancuso L.G. Megaris Jr J.L. Anderson J.R. Myles D.M. Mickelson M.G. Mudrey Jr A.L. Geldon G. Mursky G. Schriver A.R. Venditti John M. Ohlson Edward M. Ripley Donald M. Davidson D.L. Roder E.N. Cameron S.B. Romberger Klaus J. Schulz Edward M. Ripley P.K. Sims R.J. Stevenson J.E. Thresher Jens F. Touborg Thomas A. Vogel Nancy Alyanak Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/eddbd61b970180849763678b02b3769c.pdf 1ac2e8ab662d00b13fc5c7262915a1e8 PDF Text Text ������������������������������������������������������������������������������������������������������������������������������������������������������������������������ Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1974 Description An account of the resource Institute on Lake Superior Geology. Sault College of Applied Arts and Technology, Sault Ste. Marie, Ontario. May 1-5, 1974. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1974 Contributor An entity responsible for making contributions to the resource L.L. Babcock Ronald F. Bacon R.L. Bauer Emmy Booy Theodore J. Bornhorst W.F. Cannon B.A. Carlson W.J. Hinze Jeffery L. Clarke A.R. Coyner K.J. Freeman T.A. Vogel Gene L. LaBerge John C. Green H.C. Halls J.B. Heslop W.M. Tupper D.G. Innes J. Kalliokoski William H. Listerud M.S. Lougheed J.J. Mancuso P.R. Mainwaring A.J. Naldrett S.C. Nordeng David I. Norman R.V. Oja Richard W. Ojakangas James M. Robertson A.P. Ruotsala C.A. Salotti D. Weirauch R.W. Sersor P.C. Thurston N.F. Trowell M.A. Vos P.I. Wallace J.W. Cosgrove P.M. Clifford David H. Watkinson Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/e35ceec1dbed2f5f4680805765eddaaa.pdf dd07255052a20bd1b07f793d1b8cec30 PDF Text Text ����������������This page intentionally left blank ����������������������������������This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ������This page intentionally left blank ��This page intentionally left blank ����This page intentionally left blank �����This page intentionally left blank ���This page intentionally left blank ��This page intentionally left blank ����This page intentionally left blank ����This page intentionally left blank ��This page intentionally left blank ����This page intentionally left blank ����This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ������This page intentionally left blank ��This page intentionally left blank ������This page intentionally left blank ��This page intentionally left blank ������This page intentionally left blank ����This page intentionally left blank ��������This page intentionally left blank ������This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ����This page intentionally left blank ����This page intentionally left blank ����This page intentionally left blank ��This page intentionally left blank ����This page intentionally left blank ��This page intentionally left blank ����This page intentionally left blank ����This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ����This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ����This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ���������������������������This page intentionally left blank ��������������This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ����������This page intentionally left blank �������������� Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1975 Description An account of the resource Institute on Lake Superior Geology. Northern Michigan University, Marquette, Michigan. April 30-May 4, 1975. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1975 Contributor An entity responsible for making contributions to the resource D. Jay Johnson J.R. Mangham M.L. Cummings J. Wood Norris W. Jones Eugene I. Smith P.K. Sims Zell E. Peterman Frank W. Holcomb S.C. Nordeng B.M. Hamil A.M. Johnson Milton A. Gere Jr E. Wm. Heinrich David G. Meineke K.B. Rundman J.J. Mancuso M.S. Lougheed R. Seavoy R. Shaw Erich Dimroth Ronald F. Bacon G.E. Frantti Lloyal O. Bacon John H. Karl S. Chaudhuri D.T.A Symons L.J. Pesonen C. Patrick Ervin M.G. Mudrey Jr Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/82858b8f595b98020f0953e1a612ab90.pdf b1079fef31aa6fb4274a211f38225596 PDF Text Text �PROCEEDINGS TWENTY - SECOND SECOND ANNUAL ANNUAL INSTITUTE ON INSTITUTE ON LAKE LAKE SUPERIOR SUPER lOR GEOLOGY held at held RADISSON ST. ST. PAUL 11 East Kellogg Boulevard 11 St. Paul, Minnesota 55101 55101 Paul, Minnesota May May 3-7, 1976 1976 under the sponsorship sponsorship of Minnesota Geological Survey Survey IS11 l5jl University University of Minnesota Minnesota 1633 Eustis Eustis Street Street 1633 St. Paul, Paul, Minnesota Minnesota 55108 55108 G.B. and R.F. R.F. Beltrame G.B. Morey '\:\orey and Be1trame General Editors Editors p �SALES Please order from: Publications Geological Survey, Survey, 1633 Eustis St., Please Publications Sales, Minnesota Minnesota Geological 1633 Eustis St. Paul, Minnesota sales tax tax where where applicable. Minnesota 55108. 55108. Price Price$5.00 $5.00 (U.S.), (U.S.), plus 496 496 sales Make Make checks payable to Minnesota Minnesota Geological Geological Survey. Survey. Printed at: Printed University of Minnesota Minnesota Minneapolis, Minnesota 55455 Minneapolis, 55455 �TABLE OF TABLE OF CONTENTS CONTENTS v GENERAL INFORMATION V INSTITUTE INSTITUTE BOARD BOARD OF DIRECTORS v V LOCAL COMMITTEE COMMITTEE Vi vi SESSIONS CHAIRMEN SESSIONS Vi vi ANNUAL BANQUET SPEAKER ANNUAL SPEAKER Vii vii ACKNOWLEDGEM ENTS ACKNOWLEDGEMENTS VII vii CALENDAR OF EVENTS EVENTS AND PROGRAM PROGRAM VIII viii ABSTRACTS 3 FIELD TRIPS TRIPS 71 A. MINNESOTA MINNESOTA RIVER RIVER VALLEY VALLEY FIELD CONFERENCE CONFERENCE 73 B. B. ENGINEERING ENGINEERING AND AND PLEISTOCENE PLEISTOCENE GEOLOGY GEOLOGY IN IN THE THE TWIN TWIN CITIES AREA 75 111 iii �GENERAL INFORMATION GENERAL INFORMATION 22nd Annual INSTITUTE ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY Radisson Radisson St. Paul Paul St. Paul, Paul, Minnesota Minnesota 55101 5510 1 May 3-7, 1976 May 1976 by Sponsored by Minnesota Geological Survey Survey University of Minnesota Minnesota 1633 Eustis 1633 St. Paul, Paul, Minnesota Minnesota 55108 55108 INSTITUTE INSTITUTE BOARD OF DIRECTORS DIRECTORS RE. Giblin, of Mines, Mines, Ministry Ministryofof Natural Natural Resources, Resources, Sault Sault Ste. Division of P.E. Giblin, Ontario Division Marie, Ontario 1D. Hughes, J.D. Hughes, Department of of Geography, Geography, Earth Science and Conservation, Northern Michigan University, Marquette, Michigan Marquette, Michigan Michigan M.E. Geological and and Natural History Wisconsin Geological History Survey, Survey, Madison, Madison, Wisconsin Wisconsin M.E. Ostrom, Wisconsin *R.C. Reed (Secretary-Treasurer), (Secretary-Treasurer), Geological Geological Survey Survey Division, Division, Department of Natural Resources, Resources, Lansing, Lansing, Michigan Michigan M.S. Walton, Minnesota MinnesotaGeological GeologicalSurvey, Survey,University Universityof of Minnesota, Minnesota, St. St. Paul, M.S. Walton, Minnesota *Permanent *Permanent Member Member vv �;; LOCAL COMMITTEE COMMITTEE Conference Chairman Chairman Matt Walton, Minnesota Geological Survey, University of of Minnesota, Minnesota, 1633 1633 Eustis St., St. Paul, Paul, Minnesota Minnesota 55108 55108 Eustis Technical Program G.B. Minnesota Geological Geological Survey, Survey, University University of Minnesota, 1633 G.B. Morey, Morey, Minnesota 1633 Eustis St., St. Paul, Paul, Minnesota Minnesota 55108 55108 Eustis P.W. Weiblen, Weiblen, Department Department of Geology P.W. Geology and and Geophysics, Geophysics, University of Minnesota, Minnesota, Minneapolis, Minnesota 55455 Minneapolis, 55455 Field Trips Trips Stanley E. E. Chernicoff, Department Stanley Department of of Geology Geology and and Geophysics, Geophysics, University of Minnesota, Minneapolis, of Minneapolis, Minnesota Minnesota 55455 55455 S.S. Goldich, Goldich, Department Department of Geology, S.S. Geology, Northern Illinois Illinois University, DeKaib, DeKalb, illinois Illinois 60115 G.B. Morey, Morey, Minnesota MinnesotaGeological GeologicalSurvey, Survey,University Universityof of Minnesota, Minnesota, St. St. Paul, Paul, G.B. Minnesota 55108 55108 V.R. Murthy, Murthy, Department Department of Geology University of Minnesota, Y.R. Geology and and Geophysics, Geophysics, University Minneapolis, Minnesota 55455 55455 C.R. Nelson, C.R. Nelson, Department of of Civil Civil and and Mineral Mineral Engineering, Engineering, University of Minnesota, Minneapolis, Minnesota 55455 Minnesota, Minneapolis, Minnesota 55455 D.H. Yardley, Yardley, Department of Civil D.H. Civil and Mineral Mineral Engineering, Engineering, University of Minnesota, Minneapolis, of Minneapolis, Minnesota Minnesota 55455 55455 Physical Arrangements Physical i\rrangements Gordon J. 3. Amundson, Arnundson,Department Departmentofof Conferences, Conferences, Nolte Nolte Center for Continuing Gordon Continuing Education, University of Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota Minnesota 55455 55455 SESSION SESSION CHAIRMEN D.M. Davidson, Davidson,Jr., 3r., Department Department of Geology, University of Minnesota, D.M. Minnesota, Duluth, Duluth, Duluth, Minnesota Minnesota 55802 55802 S.S. Goldich, Goldich, Department Department of Geology, Geology, University of Northern Northern Illinois, Illinois, DeKaib, DeKalb, S.S. Illinois 60115 Department, 3M, Clare Goldsmith, Geology Geology Department, 3M, Bldg. Bldg. 526-2, St. Paul, Paul, Minnesota. Minnesota. Alan M. Goodwin, Goodwin,Department Department of of Geology, Geology, University University of of Toronto, Toronto, Toronto, Alan M. Ontario, Ontar io, Canada. vi �1C. Green, J.C. Green, Department Departmentof of Geology, Geology, University University of of Minnesota, Minnesota, Duluth, Duluth, Duluth, Duluth, Minnesota 55802 55802 R.W. Marsden, Marsden, Department Department of Geology, University of Minnesota, R.W. Minnesota, Duluth, Duluth, Duluth, Minnesota 55802 55802 Z.E. Peterman, Peterman, U.S. Z.E. U.S. Geological Geological Survey, Survey, Denver, Denver, Colorado Colorado 80225 80225 F.i Sawkins, F.J. Sawkins, Department DepartmentofofGeology Geologyand and Geophysics, Geophysics, University University of of Minnesota, Minnesota, Minneapolis, Minnesota 55455 55455 Weiblen, Department Department of Geology Geology and Geophysics, Geophysics, University of Minnesota, Minnesota, P.W. Weiblen, Minneapolis, Minnesota 55455 55455 of Civil Civil and and Mineral Mineral Engineering, Engineering, University University D.M. Yardley, Department of of Minnesota, Minneapolis, of Minneapolis, Minnesota Minnesota 55455 55455 BANQUET GUEST GUEST SPEAKER ANNUAL BANQUET Prof. Eugene Shoemaker, Geology GeologyDepartment, Department, California California Institute of Eugene M. M. Shoemaker, of Technology, Pasadena, California. Technology, Pasadena, ACKNOWLEDGEMENTS The organizing committee committee of the The organizing the 1976 1976 Institute Institute on on Lake Lake Superior Superior Geology Geology gratefully acknowledge in typing typing the the final manuscript acknowledge the work work of 3o Jo Behm Behm in manuscript for for the Proceedings. Proceedings. Richard Richard Darling Darling prepared the cover cover illustration. illustration. vii �CALENDER OF OF EVENTS CALENDER EVENTS AND PROGRAM MONDAY, May 5, 1976 3:30 p.m. 3:30 Pre-Institute field Pre-Institute field trip tripA, A,1976 1976Minnesota Minnesota River River Valley Valley Field Field Trip and and Conference Conference departs from the Radisson Trip Radisson St. Paul Paul for for Donovan's Motel, Motel, Redwood Donovan's Redwood Falls, Minnesota. Minnesota. TUESDAY, May May 6,1976 6, 1976 TUESDAY, 8:00 a.m. 8:00 Minnesota River Valley Field Trip Trip departs from Redwood Minnesota River Valley Field Redwood Falls to Granite Falls Falls and and Montevideo. Montevideo. 5:00 p.m. Minnesota River Valley Field Trip Trip returns returns to Redwood Minnesota River Valley Field Redwood Falls. 8:00 8:00 p.m.10:00 p.m. 10:00 Discussion session, Minnesota Minnesota River River Valley Valley Conference, Conference, Z.E. Discussion session, Z.E. Peterman, Chairman. G.B. Morey Morey Introduction L'1troduction R.L. Bauer Bauer OF PRESTRUCTURAL STUDIES STUDIES OF CAMBRIAN ROCKS ROCKS IN IN THE MINNECAMBRIAN SOTA SOT A RIVER VALLEY VALLEY C.E. Hedge Hedge & & S.S. Goldich S.S. Rb-Sr GEOCHRONOLOGY GEOCHRONOLOGY OF THE THE MONTEVIDEO GNEISS, GNEISS, MINNESOTA MONTEVIDEO RIVER VALLEY VALLEY W. Wilson & w. & GEOCHRONOLOGY AND GEOGEOCHEMISTRY OF OF GRANULITE FACIES CHEMISTRY ROCKS NEAR NEAR GRANITE GRANITE FALLS FALLS IN THE MINNESOTA RIVER VALLEY IN VALLEY V.R. Murthy Murthy B.R. Doe B.R. Doe & & M.H. M.H. Delevaux LEAD ISOTOPE INVESTIGATIONS LEAD INVESTIGATIONS IN THE MINNESOTA IN MINNESOT A RIVER VALLEY VALLEY S.S. Goldich, J.L. Wooden, Wooden, PRECAMBRIAN HISTORY PRECAMBRIAN HISTORY OF THE THE MORTON-NEW ULM ULM REACH REACH OF MORTON-NEW THE MINNESOTA RIVER VALLEY VALLEY G.A. ]r. Ankenbauer, Jr. G.A. Ankenbauer, TM. T.M. Levy Levy & & R.U. Suda Suda P.W. Weiblen Weiblen,, P.W. K.3. K.J. Schulz Schulz & & B.V. B. V. Nielsen COMPOSITIONAL VARIATIONS VARIATIONS OF MINNESOTA MINNESOTA RIVER RIVER VALLEY VALLEY AMPHIBOLITE S.S. Goldich S.S. Summary viii 4 �F WEDNESDAY, May 5,1975 WEDNESDAY, May 8:00 a.m. 8:00 Minnesota River Valley Field Trip departs Redwood Minnesota River Valley Field Redwood Falls for for Morton and New New Ulm. Ulm. 8:00 a.m. 8:00 Field Trip on Engineering and Pleistocene Geology Trip B on Engineering and Geology in the Twin Cities area departs Twin Cities departs Radisson Radisson St. St. Paul. Paul. 5:00 p.m. 5:00 Field Trip on and Pleistocene Geology returns to on Engineering Engineering and Geology returns to Radisson Radisson St. Paul. Paul. 6:00 p.m.6:00 9:00 p.m. 9:00 Paul. Early registration, Minnesota Early Minnesota East, East, lower lower level, level, Radisson Radisson St. St. 8:00 p.m. 8:00 Conferences Smoker Smoker (cash bar) Capitol Ballroom, Ballroom, lower level Radisson St. Paul. Radisson 8:00 p.m. 8:00 Minnesota River River Valley Valleyfield field trip trip returns, returns, Radisson Minnesota Radisson St. Paul. THURSDAY, THURSDAY, May May 8, 1976 1976 7:30 7:30 a.m.9:30 9:30 a.m. Registration, outside outside Minnesota Minnesota East, Radisson Radisson St. Paul. Paul. 8:00 - General Chairman, 1976 Welcome, Matt \Valton, Walton, General 1976 Institute on on Lake Superior Super ior Geology. 8:10 8:10 SESSION I - SYMPOSIUM ON GEOLOGY AND SESSION AND GEOCHEMISTRY GEOCHEMISTRY PRECAMBRIAN ROCKS, ROCKS, 5.5. S.S. Go1dich Goldich and A.M. OF EARLIEST EARLIEST PRECAMBRIAN A.M. Goodwin, Co-Chairmen. Goodwin, 8:10 G.P. Beakhouse Beakhouse A REAPPRAISAL OF OF THE THE WESTERN WESTERN PORTION OF THE THE ENGLISH ENGLISH RIVER RIVER SUBPROVINCE, NORTHWESTERN SUBPROVINCE, ONTARIO AND SOUTHEASTERN ONTARIO MANITOBA 8:30 C.F. Gower Gower THE GEOLOGY GNEISSIC ROCKS THE GEOLOGY OF GNEISSIC IN THE IN THE KENORA DISTRICT, ENGLISH ENGLISH RIVER GNEISS RIVER G NEISS BELT BEL T 8:50 A.M. Goodwin LITHIC ELEMENT LITHIC AND MAJOR ELEMENT COMPOSITION IN IN THE THE SUPERIOR COMPOSITION GEOTRA VERSE, 0ONTARIO G EOTRA VERSE, NT ARlO 9:10 C.-L. Chou, Chou, N.B.W. & N.B.W. Harris, & ABUNDANCES OF RARE EARTH ABUNDANCES OF EARTH AND OTHER ELEMENTS. IN ARCHEAN ELEMENTS- IN GRANITIC AND GNEISSIC GRANITIC GNEISSIC ROCKS FROM THE THE ENGLISH ENGLISH RIVER RIVER GNEISS GNEISS BELT, ONTARIO A.M. Goodwin 9:30 G.N. Hanson Hanson & & S.S. Goldich 5.5. RARE EARTH EARTH ELEMENT ELEMENT STUDIES STUDIES OF THE THE ARCHEAN ARCHEAN GNEISSES GNEISSES OF THE MINNESOTA MINNESOT A RIVER VALLEY VALLEY ix �9:50 Welsh J.L. Welsh J.L. PETROLOGY PETROLOGY OF OF THE THE ARCHEAN ARCHEAN GNEISSES GNEISSES AT AT THE THE NORTHWEST CORNER CORNER OF THE SACRED HEART PLUTON; PLUTON; MINNESOTA RIVER VALLEY, VALLEY, MINNESOTA 10:10 10:10 W.R. Van &. W.R. Van Schmus & J.L. J. L. Anderson GNEISS GNEISS AND AND MIGMATITE MIGMATITE OF OF ARCHEAN AGE BASEMENT AGE IN IN THE THE PRECAMBRIAN BASEMENT OF CENTRAL WISCONSIN, WISCONSIN, U.S.A. 10:30 Z.E. Peterman, Z.E. R.E. Zartman, & R.E. &. P.K. Sims OLD W GNEISSES GNEISSES OLD PRECAMBRIAN W IN MICHIGAN IN NORTHERN MICHIGAN 10:50 M.M. Kehlenbeck M.M. NATURE THE QUETICO-WABIGOON QUETICO-WABIGOON NATURE OF THE BOUNDARY BOUNDARY IN IN THE THE de de COURCEYSMILEY SMILEY LAKES LAKES AREA, AREA, NORTHWESTERN WESTERN ONTARIO 11:10 D. Birk ELEMENTS IN THE ARCHEAN TRACE ELEMENTS IN THE GRANITOID GRANITOID DIAPIRS PIERCING WABIGOON GREENSTONE THE WABIGOON BELT 11:30 I.E. Smith, T.E. Smith, A. Turek, Turek, & &. C. Riddle THE THE GEOCHEMISTRY GEOCHEMISTRY OF THE GAMITAGAMA LAKE COMPLEX, GAMITAGAMA WAWA, ONTARIO WAWA, 11:50 E.C. E.C. Perry, 3r. Jr. SN. Ahmad S.N. Ahmad IN METAMORPHOSED METAMORPHOSED CARBON IN ISUA, WEST WEST SEDIMENTS FROM ISUA, GREENLAND THURSDAY, THURSDAY, May May 8, 1976 1976 8:10 8: 10 am SESSION SESSION IIII-- ENGINEERING ENGINEERING AND AND ENVIRONMENTAL ENVIRONMENTAL GEOLOGY, D.M. Yardley and and C. C. Goldsmith, D.M. Yardley Goldsmith, Co-chairmen. 8:10 H.O. Pfannkuch Pfannkuch SYSTEMS APPROACH TO TO ENVIRONENVIRONA SYSTEMS MENTAL GEOLOGY 8:30 8:30 D. Pollack Pollack & &. H.O. Pfannkuch IMPLICATIONS ENVIRONMENTAL IMPLICATIONS GROUNDW ATER-LAKE INTEROF GROUNDWATER-LAKE WITH LAND USE APPLICATION ACTION WITH 8:50 8:50 W. W. Rohrer & &. H.O. Pfannkuch Pfannkuch GROUNDW ATER SPREADING OF GROUNDWATER HYDROCARBON SPILLS SPILLS WITH WITH HYDROCARBON EMPHASIS ON MONITOR MONITOR SPECIAL EMPHASIS SYSTEM DESIGN DESIGN IN DRIFT SYSTEM IN GLACIAL DRIFT 9:10 9: 10 D.I. D.I. Siegel Siegel OF DISSOLVED OISSOL VED SOLIDS SOLIDS SOURCES OF IN GROUNDWATER GROUNDW ATER FROM SUPERIOR SUPERIOR IN AND RAINY RAINY LOBE LOBE TILL TILL AND xx �ji 9:30 S.!. S.I. Jacobsen THE TRACE ELEMENT THE ELEMENT GEOCHEMISTRY GEOCHEMISTRY OF PEAT PEAT BOGS BOGS OVER OVER DIFFERENT BEDROCK TYPES, TYPES, SOUTHERN BEDROCK HOUGHTON COUNTY, MICHIGAN MICHIGAN Coffee 9:50 10:10 10: 10 M.G. Mudrey, Jr. M.G. Mudrey, B.C. B.C. Parker, K. K. Cartwright Cartwright & &. L.D. McGinnis L. D. McGinnis DIAMOND DIAMOND DRILLING DRILLING IN ENVIRONENVIRONMENTALLY SENSITIVE SENSITIVE AREAS - ENVIRONMENTAL IMPACT: MONITORING MONITORING AND AND ASSESSMENT ASSESSMENT 10:30 E. Booy Booy & &. STRATIGRAPHIC STRA TIGRAPHIC VARIATION VARIATION IN IN MINERALOGY AND ENGINEERING MINERALOGY ENGINEERING CHARACTERISTICS OF ONTONAGON ONTONAGON CLAY NEAR A CLAY A MAJOR SLOPE SLOPE FAILURE, ONTONAGON ONTONAGON COUNTY, COUNTY, MICHIGAN S.). Dyl, S.J. Dyl, II II 10:50 A.M. A.M. Johnson Johnson & & H.O. Sorenson Sorenson ENGADINE DOLOSTONE OF OF MICHIGAN'S MICHIGAN'S EASTERN UPPER PENINSULA: PENINSULA: GEOLOGY AND RESOURCE EVALUATION GEOLOGY EVALUATION 11:10 E. Booy Booy & &. R.D. Harris SECONDARY MINERAL GROWTH SECONDARY OF THE THE WHITE WHITE PINE SHALE SHALE COMPARED WITH WITH CLASSIC "HEAVING" SHALES SHALES C.R. Nelson Nelson & &. D.H. Yardley D.H. MODIFICATION OF ENGINEERING MODIFICATION ENGINEERING PROPERTIES OF ST. ST. PETER PETER SANDSTONE SANDSTONE 11:30 12:10 12: 10 p.m.— p.m.1:30 p.m. 1:30 12:10 12: 10 p.m.1:30 1:30 p.m. 1:30 Lunch Informal meeting of of geologists geologists interested in Informal meeting in Precambrian Precambrian of of Wisconsin. Mudrey,Jr., Jr., convenor. convenor. All Wisconsin. M.G. M.G. Mudrey, All interested interested geologists geologists bulletin board board for for notice of location). are welcome. welcome. (See (See bulletin locaticn). SESSION III III - GENERAL GENERAL GEOLOGY, D.L. Southwick and R.W. SESSION GEOLOGY, D.L. R.W. Marsden, Co-Chairmen 1:30 R.W. R.W. Ojakangas ANATOMY OF OF A WELL-COVERED ANATOMY WELL-COVERED GREENSTONE BELT, NORTHWESTERN NORTHWESTERN MINNESOTA 1:45 D.L. Southwick D.L. HIGH-GRADE HIGH-GRADE METAMORPHISM METAMORPHISM ASSOCIATED WITH THE VERMILION ASSOCIA TED VERMILION BATHOLITH, MINNESOTA-ONTARIO BATHOLITH, 2:00 R.S. Maass Maass & &. L.C. Medaris, L.C. Medaris, Jr. PENOKEAN STRUCTURES AND PENOKEAN AND PLUTONIC ROCKS ROCKS IN PLUTONIC IN PORTAGE AND WOOD AND WOOD COUNTIES, WISCONSIN WISCONSIN xi �—— 2:15 G.L. LaBerge LaBerge & &. P.E. Myers Myers THE CENTRAL CENTRAL WISCONSIN WISCONSIN BATHOLITH BATHOLITH 2:30 P.E. Myers Myers THE WAUSAU SYENITE OF OF CENTRAL THE WAUSAU SYENITE WISCONSIN 2:45 E.J. Smith GEOLOGY AND AND GEOCHEMISTRY GEOCHEMISTRY OF THE PRECAMBRIAN PRECAMBRIAN MARCELLON RHYOLITE, COLUMBIA COLUMBIA COUNTY, WISCONSIN Coffee 3:00 3:15 P.K. Sims Sims MIDDLE PRECAMBRIAN PRECAMBRIAN AGE AGE OF MIDDLE VOLCANOGENIC MASSIVE MASSIVE SULFIDE DEPOSITS IN IN NORTHERN NORTHERN WISCONSIN WISCONSIN 3:30 W.C. W.C. Prinz CORRELATIVE CORRELA nVE IRON-FORMATIONS IRON-FORMAnONS AND VOLCANIC ROCKS OF OF PREAND VOLCANIC ROCKS CAMBRIAN X X AGE, AGE, NORTHERN CAMBRIAN NORTHERN MICHIGAN 3:45 M.S. Lougheed & &. 3.1. J. J. Mancuso ORIGIN OF LAMINAE ORIGIN LAMINAE IN IN PRECAMBRIAN IRON-FORMAION 4:00 T.-M. Han GEOCHEMICAL PROCESSES FOR GEOCHEMICAL THE FORMATION OF MAGNETITE MAGNETITE IN LOW-GRADE METAMORPHIC IN METAMORPHIC PRECAMBRIAN IRON-FORMATIONS IRON-FORMATIONS 4:15 W.F. W.F. Cannon & &. L.J. Drew Drew RESOURCES OF RECOVERABLE RECOVERABLE IRON ON THE THE MARQUETTE MARQUETTE RANGE, RANGE, MICHIGAN BY A MICHIGAN — - ESTIMATES BY MONTE CARLO SIMULATION SIMULATION MONTE CARLO METHOD 4:30 D.W. Snider D.W. A GROUND INVESTIGATION INVESTIGATION OF AN AEROMAGNETIC AEROMAGNETIC ANOMALY, ANOMALY, DICKINSON COUNTY, MICHIGAN MICHIGAN DICKINSON 5:30 p.m.5:30 6:30 6:30 p.m. SOCIAL HOUR HOUR(cash (cashbar) bar)CapitAL CapitAL Ballroom, Ballroom, Radisson Radisson St. St. Paul SOCIAL 6:30 6:30 p.m. ANNUAL BANQUET,Capital Capital Ballroom, Ballroom, Radisson Radisson St. St. Paul, ANNUAL BANQUET, Eugene M. Shoemaker, Shoemaker, Guest Guest Speaker. Eugene M. FRIDAY, FRIDAY, May May 9, 1976 1976 8:00 a.m. 8:00 SESSION IV GEOLOGY. P.W. P.W. Weib1en Weiblenand and J.C. J.C. IV - GENERAL GEOLOGY. Green, Co-Chairmen 8:10 8: 10 F.3. F.J. Sawkins Sawkins ORE DEPOSITS DEPOSITS IN RELATION TO TO HOTSPOT-GENERATED HOTSPOT-G ENERA TED INTRACONTINENTAL RIFTING RIFTING xii ~ �8:30 8:30 1M. Robertson J.M. GEOLOGY AND MINERALOGY GEOLOGY MINERALOGY OF SOME SOME COPPER SULFIDE SULFIDE DEPOSITS DEPOSITS NEAR MOUNT BOHEMIA, KEWEENAW MOUNT BOHEMIA, KEWEENAW COUNTY, MICHIGAN MICHIGAN 8:50 W.A. Bartlett, Bartlett, W.A. M.S. Lougheed, M.S. U.J.Mancuso J. Mancuso & & L.3. Walters L.J. DISTRIBUTION IN DISTRIBUTION OF OF SULFUR IN THE WEST KIERNAN THE WEST KIERNAN SILL, SILL, IRON COUNTY, MICHIGAN MICHIGAN 9:10 B. Bonnichsen & B. & R.I. Botto R.I. THE BEHAVIOR OR PRECIOUS BEHAVIOR OR METALS METALS AND AND OTHER OTHER TRACE ELEMENTS DURING ELEMENTS DURING THE FRACTIONAL CRYSTALLIZATION OF DULUTH CRYSTALLIZATION COMPLEX SULFIDES SULFIDES 9:30 LA. Vogel, T.A. Vogel, M.B. McBride & M.B. & R. Ehrlich Ehrlich SYNGENETIC MODEL FOR THE THE SYNGENETIC MODEL ORIGIN WHITE PINE ORIGIN OF THE WHITE PINE COPPER DEPOSIT 9:50 N. Scofield CHEMISTRY OF PRIMARY AND CHEMISTRY AND SECONDARY MINERALS OF SOME SOME SECONDARY MINERALS PORTAGE LAKE LAKE LAVAS, LAVAS, KEWEENAW KEWEENAW PENINSULA: PENINSULA: DEVELOPMENT OF MODELS OF MODELS OF DIFFERENTIATION AND LOW-RANK METAMORPHISM METAMORPHISM Coffee 10:10 10:30 1G. Grimes J.G. Grimes APPLICATION OF A A FLOW FLOW DIRECTION DIRECTION PORTAGE TECHNIQUE TO THE PORTAGE VOLCANICS, MICHIGAN MICHIGAN LAKE VOLCANICS, 10:50 C. Brumleve Brumleve FRACTURE PETROLOGY AND FRACTURE THE KINGSTON KINGSTON CHARACTERISTICS OF THE CONGLOMERATE,KEWEENAW CONGLOMERATE, KEWEENAW COUNTY, MICHIGAN MICHIGAN 11:10 B.E. B. E. Aaquist AN INTERPRETATION OF THE THE AN KINGSTON CONGLOMERATE AS AS KINGSTON IN THE THE PORTAGE PORTAGE A A RHYOLITE RHYOLITE TUFF lUFF IN LAKE LAVA LAVA SERIES, SERIES, KEWEENAW KEWEENAW PENINSULA, MICHIGAN MICHIGAN 11:30 3.M. J.M. DeGraff STRUCTURAL AND AND AGE AGE RELATIONRELATIONSHIPS AT THE LAC LAC LA LA BELLE BELLE SHIPS ANOMALY, KEWEENAW KEWEENAW MAGNETIC ANOMALY, COUNTY, MICHIGAN MICHIGAN 11:50 L.L. L. L. Babcock Babcock CONTACT RELATIONSHIPS RELATIONSHIPS BETWEEN BETWEEN CONTACT THE IACOBSVILLE SANDSTONE JACOBSVILLE SANDSTONE AND THE THE PORTAGE LAKE LAKE LAVA LAVA AND A PROGRESS PROGRESS REPORT GROUP: A xiii xiii ji �;;; 12:15 12:15 p.m.1:15 1: 15 p.m. Lunch 12:15 p.m.12:15 1:15 1: 15 p.m. Annual Business BusinessMeeting, Meeting,Institute Institute Board Board of of Directors. Annual 1:30 p.m. 1:30 SESSION V - GENERAL GEOLOGY, GEOLOGY, F.J. Sawkins Sawkins and and D.M. D.M. Davidson, Jr., Jr., Co-Chairmen. Davidson, 1:30 F.M. Swain, F.M. 1. Baysinger & J. & 3.M. J.M. Bratt HYDROCARBONS OBTAINED OBTAINED BY BY PYROLYSIS PYROLYSIS OF SOME SOME PRECAMBRIAN PRECAMBRIAN ROCKS OF MINNESOTA MINNESOTA 1:50 S.W. Stuhr & & S.W. E.N. Cameron E.N. GEOLOGY OF THE ROUND LAKE GEOLOGY INTRUSION, SAWYER INTRUSION, SAWYER COUNTY, WISCONSIN 2:10 R.M. Tyson Tyson & & B. B. Bonnichsen HORNFELSED BASALTS BASALTS IN THE THE DULUTH COMPLEX 2:30 1R. J.R. Burnell, Burnell, 3r. Jr. THE PETROLOGY AND AND STRUCTURAL STRUCTURAL RELATIONS OF THE THE LATER RELATIONS OF LATER PREPRECAMBRIAN BRULE LAKE LAKE INTRUSIONS, INTRUSIONS, COOK MINNESOTA COOK COUNTY, MINNESOTA 2:50 D.M. Davidson, Jr., D.M. Davidson, H. Halls & & 3.R. J.R. Burnell, 3r. Jr. PALEOMAGNETISM OF OF THE THE LATE PALEOMAGNETISM PRECAMBRIAN BRULE LAKE LAKE INTRUSION, INTRUSION, COOK COOK COUNTY, COUNTY, MINNESOTA Coffee. 3:10 3: 10 3:30 N.M. Pope N.M. PETROLOGY AND STRUCTURE STRUCTURE OF THE THE LATE LATE PRECAMBRIAN PRECAMBRIAN SILVER CREEK CLIFF AND SILVER CREEK AND LAFAYETTE LAFAYETTE BLUFF MAFIC INTRUSIONS, INTRUSIONS, LAKE COUNTY, MINNESOTA MINNESOTA 3:50 R.P. Meyer, Meyer, GEOPHYSICAL PROSPECTING OFF THE THE KEWEENAW KE.WEENAW PENINSULA 3.R. Moore, J.R. E.L. Nebrija Nebrija & & C.T. C. T. Young Young 4:10 H.C. Halls Halls THE SLATE THE CENTRAL THE SLATE ISLANDS: ISLANDS: THE UPLIFT OF OF A A METEORITE METEORITE IMPACT IMPACT CRATER? xiv �U) —1 C) -1 U) w ABSTRACTS • �I AN AN INTERPRETATION INTERPRETATION OF OFTHE THEKINGSTON KINGSTON CONGLOMERATE CONGLOMERATEAS ASAA RHYOLITE INTHE THEPORTAGE PORTAGELAKE LAKELAVA LAVASERIES, SERIES, RHYOLITE lUFF TUFFIN KEWEENAW KEWEENAW PENINSULA, MICHIGAN MICHIGAN B.E. Department of of Geology, Geology, University University of of Western Western Ontario, Ontario,London, London, B.E. Aaquist, Aaquist, Department Ontar io N6A N6A 5B7 5B 7 Ontario ABSTRACT The The rock rock type included included under under the the formation formation name nameof ofKingston Kingston Conglomerate Conglomerate within quadrangleisis interpreted interpreted as as having formed by by the fracturing within the Ahmeek Ahmeek quadrangle having formed fracturing and reworkingof of aa rhyolite rhyolite tuff. tuff. The and minor minor reworking The average average thickness thickness of of the the formation formation isis 10 layers, which which commonly commonlyare are lenticular lenticular in IO meters and individual individual layers, in shape and and cross cross bedded, range thickness from from 1I mm mm to to 65 65 cm. cm. Fragments Fragments consist consist entirely of of bedded, range in thickness rhyolite rhyolite having having quartz and and plagioclase plagioclase phenocrysts phenocrysts in a cryptocrystalline cryptocrystalline groundgroundmass. deep embayments embayments characteristic characteristic mass. The The phenocrysts phenocrysts have have vague vague boundaries boundaries and and deep parts of of the formation volcanic origin. origin. Sandy Sandy parts formation consist consist of angular angular quartz quartz and and of a volcanic feldspar feldspar crystals, feldspar feldspar laths, fine fine angular angular grains grains of cryptocrystalline cryptocrystalline material, and grainsofofhematite. hematite. Some and rounded rounded grains Some of the the poorly poorly sorted, sorted, coarse-grained coarse-grained layers layers have a texture indicative indicative of of in in situ situ fracturing fracturing of of fragments fragments with with separation separation the theonly only Also, sand around fragments in these layers appears movement of the fragments. Also, sand around fragments in these appears movement of fragments. to have have formed by by the breakdown breakdown of fragments. of adjacent fragments. The distribution of of the Kingston rhyolite plus plus similar similar rhyolitic rhyolitic facies facies in The distribution Kingston rhyolite in three other interflow interflow horizons horizons in the overlying overlying basaltic basaltic sequence sequence suggests suggests the source source of of the rhyolite rhyolite was was to to the the southeast, southeast, and and indeed, indeed, rhyolite rhyolite domes domes outcrop outcrop within within the lower part of from the the area lower part of the the Portage Portage Lake Lake Lava Lava Series Series from area of of the theAhmeek Ahmeek quadrangle to east end end of ofthe theKeweenaw KeweenawPeninsula. Peninsula. Native copper has has been been quadrangle to the east mined from from the the rhyolite facies of mined rhyolite facies of all all four four interflow interflow horizons horizons in in the the Ahmeek Ahmeek quadrangle quadrangle map map area. 3 �CONTACT RELATIONSHIPS RELATIONSHIPS BETWEEN BETWEEN THE JACOBSVILLE JACOBSVILLE SANDSTONE SANDSTONE AND THE THE PORTAGE LAVA GROUP: AND PORTAGE LAKE LAKE LAVA A PROGRESS PROGRESS REPORT Larry L. of Mineral Mineral Research, Research, Michigan Michigan Technological Technological UniverUniverLarry L. Babcock, Babcock, Institute of sity, Houghton, Houghton, Michigan Michigan 49931 49931 ABSTRACT Logs of of all theLaurium Laurium quadrangle quadrangle which which collar collar Logs all diamond diamond drill drill holes holes in in the between the Scales between Scales Creek Creek Flow Flow (PSc) (PSc) and and the the Jacobsville Jacobsville Sandstone Sandstone (JS) (JS) - Portage Lake contact were were officially Lake Lava Lava Group Group (PLLG) (PLLG) contact officially obtained obtained from from Universal Universal Oil Oil logs comprise 105 holes holes and Products. These These logs comprise 105 and represent represent 25,000 25,000 m m of of drilling. drilling. Stratigraphic correlation correlation between Stratigraphic between the southernmost southernmost four four field field sections sections along along the contact trace contact trace and and adjacent adjacent drill drill holes holes has hasbeen beencompleted. completed. These These sections sections are Gooseneck, Quincy, Oneco (ON), (ON), New New Gooseneck, Quincy, Dover, Dover, and and Dover Dover (north) (north) Creeks Creeks and and the Oneco (NB), and A) drill Baltic (NB), and New New Arcadian Arcadian (N (NA) drill holes, holes, respectively. respectively. The stratigraphic stratigraphic succession four The succession across across the the JS-PLLG JS-PLLGcontact contact zone zone in in the four field consists of of the the following following units, from from oldest oldest to to youngest: youngest: (1) (1) "typical" "typical" field sections consists (3) "contact" "contact" conglomerate, conglomerate, and and PLLG PLLG flat-lying JS, JS, (2) (2) basal basal PLLG PLLG melaphyre, melaphyre, (3) flat-lying lavas. However, However, an is present present between between (1) (1) and and (2) (2) in in the theQuincy Quincy an additional additional unit unit is Creek gravel quartzite Creek section: 35 35 to to 48 48 m m of of steeply steeply dipping dipping JS beach sand-beach sand-beach gravel conglomerate. The contact zone The JS-PLLG JS-PLLG contact zone on on Quincy Quincy Creek Creek was was mapped mapped in in detail. detail. An asymmetrical this asymmetricalbuttress buttresszone zoneextends extends250 250toto300 300mmacross acrossthe the contact contact at at this south%ast from PLL$ lavas, dip ste8pen in location. Proceeding Proceeding southeast from PLLG lavas, theth dip steepen3 in three three successivestages stagesfrom from15~290+ l5-29 + NW to 22-55 successive 22-55 0++ NW to 30 30 0++ NW÷-90 NW+-90 0—50 -50 ++ SE. The latter in the la tter stage stageisisan anantieinal anticlinalflexure flexureconsisting, consisting,-in thecrushed crushed axial axial portion, portion, of of large large quartzite blocks blocks (NW (NW limb) limb) and and sandstone sandstone blocks blocksand andslabs slabs(SE (SElimb). limb). Typical Typical flatflatlying JS JS is is encountered encountered immediately immediately southeast of this buckle. buckle. Results of field and diamond drill section correlations are are outlined outlined below: below: Results diamond drill (1) Interbedding between between the JS JS and and PLLG PLLG is is noted noted in in four four of ofsix sixNA NAholes holes Interbedding near Gooseneck Gooseneck Creek. Creek. Isopach maps constructed on on two two Isopach maps were were constructed successive, successive, essentially essentially flat-lying undisturbed undisturbed stratigraphic intervals interVals in in these four four holes: holes: volcanics volcanics (3-14 (3-14 m) m) and and sediments sediments (4-18 (4-18 m) m) which which these underlie underlie these these volcanics. volcanics. Two transport transport direction direction solutions solutions were were Two 0 computed0for each interval: computed for each interval: volcanics, volcanics, S27°E S27 E and and S45°E; S450E; sediments, sediments, both N15 E. The N150E. The latter direction direction is is identical identical to to those those measured measured on on "typical" JS JS exposed in the bed Creek and and represents represents the bed of of Gooseneck Gooseneck Creek "typical" exposed in "normal" JS JS transport transport direction direction in the "normaF' the Laurium Laurium quadrangle. quadrangle. Sediments Sediments exposed in the the bed bed of the the creek creek directly directly overlie overlie the theabove above mentioned mentioned exposed in volcanic interval. (2) The contact conglomerate conglomerate is is exposed exposed in all four four field field sections sections and and was was The intersected by by five five adjacent adjacent drill drill holes. holes. In In three of of these these holes, holes, 12 12 to 120 120 m m of lava lava separate separate this thisconglomerate conglomerate from from the theunderlying underlying Baltic Baltic No. conglomerate, i.e. i.e. the contact 4. No.33 conglomerate, contact conglomerate conglomerate is is No. No.4. (3) Between Creek section section and and the the nearest nearest dr!Hdrl holes Between the Dover Dover Creel< holes(0N9), (ON9),Nos. Nos. 3 and conglomerates exhibit exhibit identical identical dips, dips, 6.2 6.2 NW, NW, and and identical identical and 44conglomerates 4 �stratigraphic separation stratigraphic separation intervals, intervals, 120+ 120+44m. m. These These values values are are constant constant over aa horizontal horizontal distance distance of 2.3 km. over km. (4) (4) The uppermost The uppermost JS conglomerate conglomerate in Section isis in the the Dover Dover Creek Creek Section correlative with with the the Baltic correlative Baltic No. No. 33 of PLLG: the lowermost of the PLLG: the lowermost conglomerate, No. 2. conglomerate, No.2. (5) (5) A regionwide regionwideunconformity unconformityininthe theJS JSoccurs occursatatthe the top top of of the the uppermost A uppermost JS conglomerate conglomerate on JS on Dover Dover Creek Creek (Babcock, (Babcock, 1975). 1975). This This unconformity unconformity represents aa definitive at represents definitive rock-and rock-and time-stratigraphic time-stratigraphic break break (timeline) (timeline) at the top top of the Baltic 3 conglomerate which is present present in in both both the the Baltic No. No.3 which is JS the and PLLG. and the JS JS exposed exposed on These These correlations correlationsrequire requirethat that virtually virtually all all of of the on the Keweenaw Peninsula Peninsulaisistime time equivalent equivalent to to lowermost lowermost portions portions of of the PLLG. Keweenaw PLLG. REFERENCE Babcock, L.L., L.L., 1975 Babcock, 1975 The The Jacobsville Jacobsville Sandstone: Sandstone: Evidence Evidence for a Lower-Middle Lower-Middle Keweenawan Age: Age: Field Field Trip Trip 3, 3, Proc., Proc., 21st Inst. on Keweenawan 21st Ann. Ann. Inst. on Lake Lake Superior Superior Geol., Geol., pp. 87—123. 87-123. 55 �DISTRIBUTION DISTRIBUTION OF SULFUR SULFUR IN IN THE THE WEST WEST KIERNAN KIERNAN SILL, SILL, IRON IRON COUNTY, COUNTY, MICHIGAN MICHIGAN W.A. Bartlett*, M.S. iJ. Mancuso, W.A. Bartlett*, M.S. Lougheed, Lougheed, J.J. Mancuso, and and L.J. L.J. Walters, Walters, Department Department of of Geology, Green University, University, Bowling Green, Ohio Ohio 43403 43403 *Current address: Bowling Green, address: Geology, Bowling Bowling Green Lindgren Lindgren Exploration Co., Wayzata, Wayzata,Mn. Mn.55391 55391 ABSTRACT The West West Kiernan Kiernan Sill, located located in in eastern eastern Iron IronCounty, County,Michigan, Michigan, is is a The differentiated body body of of mafic mafic igneous igneous rock rock ranging ranging in in composition composition from from peridotite in age, and through gabbro gabbro to to granophyre. granophyre. It It is is Middle Middle Precambrian Precambrian in and has has been been through metamorphosed to greenschist facies. The The sill was intruded into the the Hemlock Hemlock metamorphosed to the the greenschist formation, and occupies an an outcrop outcrop area of and now now occupies of approximately 26 26 square square miles. miles. The The sulfur sulfur content content of of the the West West Kiernan Kiernan Sill Sill varies varies with rock rock type, type, but but in in general averages for for similar similar rocks. rocks. The general is low low as compared compared to published published averages The peridotitic rocks of sill average average 55 micromoles/gram sulfur, the gabbroic gabbroic rocks rocks average average 40 40 rocks of the sill micromoles/gram sulfur and micromoles/gram sulfur and the the granophyric granophyric rocks rocks average average 11 11 micromoles/gram micromoles/gram on statistical analyses sulfur. Based Based on analyses and and graphical graphical techniques techniques the the distribution distribution of of of sulfur. copper and copper and nickel nickel in in the the sill sill isis shown showntoto correlate correlate with with the distribution of Because copper and and nickel nickel ore deposits in Because copper in mafic mafic igneous igneous rocks are made made up up of concentrations of sulfide sulfide minerals, minerals,the the distribution distributionofof sulfur sulfur can can be be used concentrations of used as as aa in mafic prospecting tool to to indicate the prospecting tool the relative relative abundance abundance of of sulfide sulfide minerals minerals mafic igneous bodies. 66 �I STRUCTURAL STUDIES STUDIES OF PRECAMBRIAN PRECAMBRIAN ROCKS ROCKS IN THE THE MINNESOTA MINNESOT A RIVER RIVER VALLEY VALLEY Robert L. L. Bauer, Bauer, Department Department of of Geology Geology and and Geophysics, Geophysics, University University of of Minnesota, Minnesota, Minneapolis, Minnesota Minnesota 55455 55455 ABSTRACT ABSTRACT The The gneisses in the the Minnesota Minnesota River River Valley Valley between between Montevideo Montevideo and and Morton, Morton, Minnesota have been folded into a series of shallow, eastward-plunging Minnesota have been folded into a of shallow, eastward-plunging antiforms antiforms and synforms, (F2), (F2)' with wavelengths on on the order of of several kilometers major structures structures are are pre-dated (Himmelberg, 1968; 1968; Grant, 1972). 1972). These These major pre-dated in in the the (Himmelberg, Granite Falls Falls area area by, by, rare rare isoclinal, isoclinal, intrafolial intrafolia1folds, folds, (F1), (F 1)' which which are are coaxial coaxial with, with, but deformed deformed by by the F2 structures. structures. A third (F),), not third period period of folding, folding, (F notevident evidentfrom from aathe themapping mapping of of the themajor major structures, from aa det'ailed of the minor structures, is is deduced deduced from deiailed analysis analysis of minor folds folds and and mineral mineral Heart area area this third lineations lineations in the the gneisses. gneisses. In In the Morton-Sacred Morton-Sacred Heart third period period of of 0 folding yields minor minor folds trending trending about about N53°E, N53 0 E,plunging plunging 200 20 (Grant, (Grant, 1972). 1972). In the Granite area the orientations Granite Falls Falls area orientations of the the minor minor folds folds vary vary with with their their location location on on the Granite ). On the north of the antiform Granite Falls Falls antiform antiform (FJ). north limb of antiform the the folds folds have have an average average orientation orientation of of N6°E, N60 0 E, plunging plunging 30°. 30 0 • The The axial axial planes planes of of these these folds folds is very very close close to the generally with aa moderate moderate to steep generally trend NE-SW NE-SW with steep SE SE dip. dip. This This is the orientation ofof the the south orientation south limb limb of of the the Granite Granite Falls Falls antiform antiform and and the the foliation foliation near coincidence results in aa orientation orientation in the the outcrops outcrops near nearMontevideo. Montevideo. This This near coincidence results large variation in the F. to variation in F 3 fold fold axis axis orientations orientations in in these these areas, areas, ranging ranging from from NE NE to axial plane foliation defined by flattened quartz lenses is SE to SW-plunging. An SE SW -plunging. An 53 plane foliation defined by quartz lenses is locally well well developed developedon onthe the south southlimb limbofofthe theGranite GraniteFalls Fallsantiform. antiform. L. locally L 3 quartz quartz lineations defined by by the the intersection lineations defined intersection of of SS(compositional <Compositional banding) banding) and ana S3 S3 are are common in this this area, and show the the same same rangg range in in orientation orientation as as the F3 common in and show F 3 fold axes. A fourth generation A fourth generation of of minor minor folds, folds, (F4) (F4) is is common common only only in in the outcrops outcrops near near Montevideo. F, Montevideo. F 4..axial axialplanes planesgenerally generallytrend trendNW-SE NW -SE and and are are moderately moderatelyinclined0to inclined to 0 the northeast. northeast. The 1 heF4 F 4fold fold axes axes in in this this area areahave havean anaverage averageorientation orientation of of S80 S80 E, E, 4Q0 and generally occur as open warps of the gneissic banding with amplitudes 40° and generally occur open warps of the gneissic banding with amplitudes ranging from from 20-50 20-50cm. cm. A folds on onthe the north north limb limb of of the Granite ranging A few few NW-trending NW-trending folds Granite Falls antiform antiform have have orientations orientations which whichare are consistent consistent with with that that expected Falls expected of of F4 F 4folds superimposed superimposedon onthis this limb. limb. Unlike area, these folds Unlike the F4 F lJ. folds in in the the Montevideo Montevideo area, folds folds are concentric, concentric, parallel parallel folds folds with with wavelengths wavelengths ranging ranging from from 1-5 1-5 meters. meters. Both FF4 fold types types occur occur in in granitic granitic gneiss suggesting aa distinct distinct difference in the Both 4. fold gneiss suggesting the mechanical properties properties of of the the gneiss at the time of mechan'lcal gneiss at of folding. folding. A similar difference properties of of the A similar difference in in mechanical mechanical properties the gneiss gneiss is is suggested suggested by by the difference the difference in in the the character characterofofnarrow narrowNW NW and andNE-trending NE-trending shear shear zones zones which which The shear occur in both occur both the the Granite Granite Falls Fallsand andMontevideo Montevideo areas. areas. The shear zones zones near near Similarly oriented Granite Granite Falls Falls are mylanitic mylanitic and and have have aa cataclastic cataclastic microfabric. microfabric. Similarly zones in the the Montevideo area are are generally diktyonitic structures structures rather than zones in Montevideo area generally diktyonitic than shear shear zones, commonly commonlycontaining containingremobilized remobilizedgranitic graniticmaterial materialwithout without aa cataclastic zones, microfabric. REFERENCES REFERENC ES CITED CITED Grant, J.A., Grant, J.A., 1972, 1972, Minnesota Minnesota River River Valley, Valley, southwestern southwestern Minnesota, Minnesota, in Sims, Sims, P.K. P.K. and Morey, and Morey, G.B., G.B., eds., Geology Geology of Minnesota: A centennial volume; volume; Minnesota Minnesota Geol. Survey, Survey, p. 177-196. Geo!. 177-196. F-Iirnmelberg,G.R., G.R.,1968, 1968,Geology GeologyofofPrecambrian Precambrian rocks, rocks, Granite Granite Falls-Montevideo Himmelberg, Falls-Montevideo area, southwestern southwestern Minnesota; Minnesota; Minnesota Minnesota Geol. Geo!. Survey Survey Spec. Spec. Pub. Pub. Ser. 5, 33 33 p. 7 �I A A REAPPRAISAL REAPPRAISAL OF OF THE THE WESTERN WESTERN PORTION PORTION OF OF THE THE ENGLISH ENGLISH RIVER SUBPROVINCE, SUBPROVINCE, NORTHWESTERN NORTHWESTERN ONTARIO ONTARIO AND SOUTHEASTERN SOUTHEASTERN MANITOBA MANITOBA Department of Beakhouse, Centre Centre for Precambrian Precambrian Studies, Studies, Department of Earth Earth Sciences, Sciences, G.P. Beakhouse, University of of Manitoba, Manitoba, Winnipeg, Winnipeg, Manitoba, Canada. ABSTRACT ABSTRACT The River subprovince has been been considered consideredtoto be be a high The English English River subprovince has high grade, grade, Archean metasedimentary basin flanked by typical greenstone-granite terranes. Archean metasedimentary basin flanked by typical greenstone-granite Recent investigations, suggest that this investigations, however, however, suggest this is is an an oversimplification oversimplification and and that divisible into two units; a northern, the English English River River subprovince subprovince is is divisible into two units; a northern, largely largely sedimentary, gneiss belt) belt) and sedimentary, unit unit (Ear (Ear Falls-Manigotagan Falls-Manigotagan gneiss and aa southern, southern, mainly mainly plutonic unit River batholithic batholithic belt). unit (Winnipeg (Winnipeg River The gneiss belt belt comprises The Ear Ear Falls-Manigotagan Falls-Manigotagan gneiss comprises aa high high grade grade metagraymetagrayThe wacke-metasiltstone sequence intruded wacke-metasiltstone sequence intruded by by subordinate subordinate felsic plutons. distribution primary sedimentary sedimentary structures imply distribution of lithologies and and recognizable recognizable primary imply a major sedimentary basin basin with with sediment sediment deposited below wave wave base base from major sedimentary deposited below from turbidity turbidity sedimentationis, is, at at least least in part, flows. This This sedimentation part, aa distal distal facies facies of of volcanism volcanism in in the the Red subprovince to to the north. Red Lake Lake subprovince In contrast, the River batholithic batholithic belt belt is In the Winnipeg Winnipeg River is largely largely aa felsic felsic plutonic plutonic terrane comprising two major major suites; suites; an an earlier, massive comprising two massive to weakly weakly gneissic, gneissic, prepreand syn-tectonic trondhjemite-granodiorite-quartz diorite suite and a later, massive, post-tectonic granodiorite-quartz A complex massive, post-tectonic granodiorite-quartz monzonite-granite monzonite-granite suite. A complex assemblage of well assemblage of well layered, layered, felsic felsic orthogneisses orthogneisses with with subordinate subordinate interlayered interlayered remnants of recognizable metavolcanic and and metasedimentary metasedimentary rocks remnants of recognizable metavolcanic rocks occurs occurs on the the The southern southern flank flank of of this plutonic plutonic terrane. terrane. The origin origin of of the theWinnipeg Winnipeg River River are currently batholithic belt belt is problematic, problematic, and and several several possibilities are currently being being batholithic evaluated, includingthe the possibility possibilitythat thatthe the belt belt could evaluated, including could represent represent aa reactivated reactivated ancient crustal remnant. Regional geophysicalanomalies anomaliessupport support the the two-fold of the Regional geophysical two-fold subdivision subdivision of the gneissbelt belthas has aa thicker English subprovince. The The Ear Falls—Manigotagan Falls-Manigotagan gneiss thicker English River River subprovince. granitic crust, than the granitic crust, thinner thinner total curst, curst, and and higher higher Bouguer Bouguer gravity gravity values values than Aerornagnetic patterns also also are Winnipeg River batholitic Winnipeg River batholitic belt. Aeromagnetic patterns are disintincly disintincly different in In the two belts. 8 I �I TRACE AEAN GRANITOID TRACE ELEMENTS ELEMENTS IN IN THE THE ARCH ARCHAEAN GRANITOID DIAPIRS DIAPIRS PIERCING PIERCING THE THE WABIGOON WABIGOON GREENSTONE BELT BELT Dieter Dieter Birk, Birk, Department DepartmentofofGeology, Geology,McMaster McMaster University, University, Hamilton, Hamilton, Ontario OntarioL8S L8S 4Ml 4M1 ABSTRACT ABSTRACT Major and trace element element analyses analyses are are reported reported for for twelve twelve synkinematic synkinematic to to Major and late-kinematic granitoid granitoid diapirs diapirs intruding intruding Keewatin Keewatin greenstones greenstones of of the theWabigoon Wabigoon are included Greenstone Belt Belt of of northwestern northwestern Ontario. Ontario. Analyses Analyses are included of of associated associated Greenstone enclaves and aplitic dikes to evaluate the role of endomorphism and late diking. aplltic dikes to evaluate the role of endomorphism and late diking. Despite Despite a common common tectonic setting, setting, these thesediapirs diapirsrange rangefrom fromhomogeneous homogeneous granodiorites to concentrically zoned granodiorites to zoned plutons plutons or or complexes complexes of of granite-monzodiogranite-monzodiorite. The Therange rangeofofelement elementconcentraitons concentraitons(4.3>Na/K>O.9) (4.3>Na/K>O.9) is not compatible with a "late K K granite" granite" classification classification as required required by by current Archaean Archaean models models of secular secular of trace granitoid chemistry. chemistry. Each Each pluton pluton carries carries a distinctive distinctive "fingerprint" "fingerprint" of trace granitoid element abundances, but as a group abundances, but group these granitoids granitoids carry carry high high Sr Sr and and Ba, Ba, and and low low Th, and and U. U. Rb/Sr, Th, The The lensoid lensoid mafic mafic enclaves, enclaves, ubiquitous ubiquitous in these these plutons, plutons, have have undergone undergone basification and/or alkali alkali rnetasomatism, resulting in in trace element basification and/or metasomatism, resulting element abundances abundances markedly different different from from either their markedly their granitoid granitoid hosts hosts or orsuggested suggested metavolcanic metavolcanic sources. Strong Strong enrichment enrichment in in Rb, Rb, Ce and and Th Th can be be demonstrated, demonstrated, whereas whereas Sr Sr and and Although aa reciprocal reciprocal reaction process Ba values more erratic. Although process is is envisioned envisioned Ba values are are more between enclave enclaveand andhost, host,there there isis little little evidence of large scale between evidence of scale contamination contamination of Homogeneousgranodiorite granodioriteplutons plutons(such (suchasas the the Burditt the host plutons. plutons. Homogeneous Burditt Lake Lake the host Stock, Scattergood Stock) show heterogeneous heterogeneous enclave enclave distribution distribution without without noticeStock, Scattergood Stock) show able modal mineral or chemical effect. able modal mineral or chemical effect. Aplitic patches and and dikes show trace trace element of late Aplltic patches dikes show element contents contents typical typical of late core-to-rim zoning. differentiates complicated complicated by by strong strong core-to-rim zoning. Aplite Aplite apophyses apophyses cutting metavolcanic rocks rocks differ differ little little from metavolcanic from the intraplutonic aplites. 99 �THE BEHAVIOR BEHAVIOROF OF PRECIOUS PRECIOUS METALS METALS AND AND OTHER OTHER TRACE TRACE ELEMENTS THE ELEMENTS DURING THE THE FRACTIONAL FRACTIONAL CRYSTALLIZATION CRYSTALLIZATION OF OF DULUTH COMPLEX SULFIDES DURING Bill Bonnichsen, Bonnichsen,Department Department of of Geol. Bill Geo!. Sciences, Sciences, Cornell Cornell Univ., Univ., Ithaca, N.Y. N.Y. 14853 14853 and Robert I. and 1. Botto, Botto, Exxon Exxon Corp., Corp., Box Box 4255, Baytown, Texas 77520 77520 ABSTRACT In the Duluth the sulfide can be be described Duluth Complex, Complex, the sulfide mineral assemblages assemblages can described in In terms of the terms the high high temperature temperature phases phases that that crystallized crystallized from from sulfide sulfide melts. melts. The (1)(1)MSS three principal principal phases phases that thatformed formedfrom fromsuch suchmelts meltsare are MSS(monosulfide (monosulfide solid solid solution) which which cooled cooled to to pyrrhotite solution) pyrrhotite with with exsolved exsolved chalcopyrite-cubanite chalcopyrite-cubanite and and pentlandite, (2) ISS ISS (intermediate solid solution) solution) which pentlandite, (2) (intermediate solid which cooled cooled to to chalcopyrite chalcopyrite and cubanite (commonly in exsolution cubanite (commonly in exsolution intergrowths), intergrowths), and and (3) (3) BSS BSS (bornite-chalcocite (bornite-chalcocite solid solution), solution), which whichcooled cooledtotobornite-chalcopyrite bornite-chalcopyrite intergrowths. solid For normal For normal Fe-rich sulfide melts, melts, the the early early crystallization crystallizationofofMSS MSS leads to Cu Cu field enrichment in the the liquid. liquid. On Onthe theCu-Fe-S Cu-Fe-Ssystem systemliquidus liquidus surface surfacethe theMSS-ISS MSS-ISS field boundary not aa cotectic, but boundary isis not but isis aareaction reactionboundary, boundary, with with the the ISS ISS field on on the low temperature side. temperature side. Thus, continued crystallization crystallization of MSS MSS will will enrich enrich the the Thus, the the continued residual melt melt in Cu residual Cu until until its its composition composition migrates migrates into into the the ISS ISS field, field, causing causing the cessation of MSS andstart start of of ISS crystallization. The has aa lower lower CufFe Cu/Fe ratio ratio cessation MSS and ISS crystallization. The ISS ISS has than the melt melt so so that thatits itsremoval removalwill willcause causefurther furtherCu Cuenrichment, enrichment,which which can can lead lead to liquid compositions compositions reaching reaching the theISS-BSS ISS-BSS field boundary. boundary. In In the the Duluth Duluth Complex, Complex, the thesulfide—rich sulfide-rich basal segregations segregations crystallized crystallized as MSS, whereas MSS-ISS mixtures. MSS, whereas the the disseminated disseminated sulfides suifides crystallized crystallized as MSS-ISS mixtures. The Curich epigenetic sulfides which which percolated percolated into the footwall footwall and and inclusions, crystallized mainly and BSS. BSS. Fractional crystallization of mainly as ISS ISS and of sulfide sulfide liquids, liquids, as outlined above, is is one that may outlined above, one of several mechanisms mechanisms that may account for the the wide wide range range that characterize of compositions compositions that characterize the theDuluth Duluth Complex Complex sulfides. sulfides. Such Such a process process seems particularly applicable seems applicable to the Cu-enriched Cu-enriched epigenetic occurrences. Six samples, chosen chosen to to encompass the observed Six Duluth Duluth Complex Complex samples, encompass the observed range range of Cu/Fe CufFe ratios, were were analyzed analyzed by by neutron neutron activation, activation, spark-source spark-source mass mass spectrospectrometry, to further metry, and and atomic atomic absorption absorption to further examine examine the the fractional fractional crystallization crystallization process. The for fractional The results resultsare areininvery verygood good agreement agreement with with our predictions for crystallization During crystalliza tion trends. During sulfide sulfide crystallization, crystallization, Ni, Ni, Co, Co, and and Mo Mo were were incorporated into MSS MSS along whereas Ag, Ag, Au, Rh, Ir, Ir, selectively incorporated along with with Fe, Fe, whereas Au, Pd, Pd, Pt, Rh, Zn, Zn, Cd, Pb, TI, Se, Te, Te, Sb, Sb, Bi, Bi, W, W, and Sn were enriched enriched in in the theliquid liquid along along with with Cu, CU, to eventually in the eventually become become incorporated incorporated in the Cu Cu minerals. minerals. Our investigation investigation of of Our element indicates preferences preferences for for octahedral lattice element behavior behavior indicates lattice sites sitesininMSS, MSS, verses tetrahedral tetrahedral sites sitesininISS, ISS, which which largely largely governs governs element elementdistributions distributionsduring during sulfide sulfide liquid crystallization. crystallization. 10 10 �STRATIGRAPHIC VARIATION IN MINERALOGY MINERALOGY AND AND ENGINEERING ENGINEERING CHARACTERISTICS CHARACTERISTICS STRATIGRAPHIC VARIATION IN CLAY NEAR OF ONTONAGON ONTONAGON CLAY NEAR A MAJOR SLOPE FAILURE, FAILURE, ONTONAGON ONTONAGON COUNTY, COUNTY, MICHIGAN MICHIGAN Emmy Booy Booy and and Stanley Stanley J. Dyl, II, Department Geology and and Geological Geological Emmy Department of Geology Engineering, Michigan Engineering, Michigan Technological University, Houghton, Houghton, Michigan Michigan 49931 49931 ABSTRACT 45 for for approximately one mile mile north north and and south south of of the East U.S. 45 approximately one East Branch Branch of the OntonagonRiver River on on the Keweenaw Keweenaw Peninsula Peninsula of Michigan Michigan is is plagued plagued by by slope slope Ontonagon failures of of varying types and and sizes sizes along the road road cuts. cuts. The particular failures varying types along the The area area of particular interest for this the largest largest slide whichlies lies to to the the north interest this discussion discussion isis the slide which north of the East East Branchalmost almostatat the the crest crest of the Branch the hill. hill. The is one one in in which which the river river has has The area area is incised a valley about 200 feet feet deep deep into into aaflat flatglacio-lacustrine glacio-lacustrinedeposit depositofofthinly— thinlyincised about 200 layered red clays and silts. The particular is approximately The particUlar slide slide under under discussion discussion is approximately 700 700 feet long long and and 400 400 feet high. high. ItItisisimmediately immediatelyadjacent adjacenttotoHighway Highway 45 45 and and causes causes annual annual disruption disruption of the drainage the drainage on on the west west side side of of the theroadway. roadway. Both Bothmud mudflows flows and and block block gliding gliding contribute at various and in in different different areas to the slope various times and slope recession. recession. contribute Material of of the the slope was studied studiedatat 11 meter meter vertical intervals in the the as-yet intervals in Material slope was unfailed zones zones north north and and south south of of the the failed failed area area in in order order to to ascertain variability of unfailed the clay-silts of the clay—size fraction, Atterberg Atterberg Limits, the clay-silts in situ. situ. Mineralogy Mineralogy of clay-size fraction, Limits, shear strengths were determined. particle-size distribution, and vane vane shear The material, previously studied regional scale, scale, ranges ranges The material, like that previously studied on on a regional throughout the clay throughout clay and and clay-silt clay-siltregions regionsof ofthe theCorps CorpsofofEngineers Engineersand andU.S. U.S. Bureau Bureau of Soils Soils classifications. In In general, sand content isis less less than than5% 5%although although in in some some layers this is not true. The the layers, layers, in of the The mineralogy mineralogy ofof the in agreement agreement with with the the variability variability of the particle sizes, layer to layer. particle sizes, varies varies from from layer layer. However, However, itit may may be be accurate accurate to to state that the rock flour includes quartz and the rock flour includes considerable considerable quartz and feldspar feldspar in in the the clay-size clay-size fractions as as well fractions well as the the clay clay minerals minerals kaolinite, kaolinite, iiite, illite, and and mixed-layer mixed-layer material material which appears appears to to be be dominantly dominantly smectite. smectite. which Plastic limits limits vary vary in in the the general general range range of of24-30 24-30 and and liquid liquid limits limits vary vary from from 35 to 70 in particle size and clay mineral mineral content. content. The 35 to 70 reflecting variation variation in and clay The natural moisture content content of the moisture the material material generally generally approach approach the the plastic plastic limits limitsalthough although in in certain cases it is is higher higher than the plastic plastic limit. limit. This This moisture moisture content content increases increases in general the base general towards towards the base of the the hill, hill, but but not not atataauniform uniform rate. rate.Anomalously Anomalouslyhigh high values occur occur part way up higher clay content. values up the hill in zones of higher Shear strengths strengths are are extremely extremely variable, variable, generally generally in in the the4—25 4-25 tons/sq. tons/sq. ft. Shear region. This variability occurs occurs not only on up the the slope, slope, but region. This not only on aa scale scale of of tens tens of feet up within hole at vertical distances of of inches. inches. The vertical and and horizontal horizontal distances The variation variation within aa single single hole within hole may may be be as as much much as as 10 10 tons/sq. tons/sq. ft. ft. within a hole 11 11 U �SECONDARY MINERAL GROWTH OF OF THE WHITE SECONDARY MINERAL GROWTH WHITE PINE SHALE COMPARED COMP ARED WITH WITH CLASSIC "HEAVING" "HEAVING" SHALES SHALES Emmy Booy, Booy, Department Geology and Emmy Department of of Geology and Geological Geological Engineering, Michigan Technological Co., Technological University, University, Houghton, Houghton, MI, MI, 49931 49931and andRobert Robert D. D. Harris, Harris, Gillette Co., South Boston, MA. MA. ABSTRACT Workersinin the the eastern United Workers United States States and and Canada Canada have have observed observed secondary secondary mineral growth, particularly particularly gypsum gypsumand andaa variety variety of iron mineral growth, iron sulfates sulfates which which have have caused "heaving" of shales caused "heaving" of shales under under buildings. buildings. Because Because of of conditions conditions of similarities of (i.e. high oxygen (i.e. high oxygen contents contents and and presence presence of of moisture) moisture) between betweenshales shalesat at the the surface of the of the earth earth and and along along the the surfaces surfacesofofmine mineopenings, openings, the the possibility possibility that similar similar phenomena might might be the White phenomena be taking place in the White Pine Pine Mine, Mine, Michigan Michigan was was investigated. shales near In occurrences in shales near Ottawa, Ottawa, Ontario, Cleveland, Ohio, and Pittsburgh, substantial (up Pittsburgh, Pennsylvania, Pennsylvania, substantial (up to several several inches) inches) vertical verticalexpansion expansion has has taken place taken place in shales shales which which contain contain some some pyrite pyrite and and calcite. calcite. It has been been It has hypothesizedthat that the the reactions take place place in in the the shales hypothesized reactions which which take shales are catalyzed catalyzed by by oxidizing bacteria. oxidizing These would include include Thiobacillus Thiobacillus ferroxidans ferroxidans and and These bacteria would Ferrobacillus ferrooxidans. Repeated Repeated efforts to to grow grow such such bacteria in in cultures cultures of of Ferrobacillus ferrooxidans. proven unsuccessful. unsuccessful. Therefore, Therefore, a bacterial the White White Pine Pine Shale Shale have have proven bacterial mechanism mechanism growth on on White White Pine Pine shales shales has has been ruled out. for gypsum gypsum growth Samples ranging in in time of exposure exposure to the the mine mine atmosphere atmosphere from from 11 day day to to 10 10 Samples ranging years were years were collected collected from from the the mine mine roof roof — - most samples were from the the Brown Brown samples were Massive but several several were Massive but were from from the the Dark DarkGray GrayMassive. Massive. These contain These strata contain scattered nodules source for for Ca Ca in in the expected nodules of calcite calcite which which provide provide a logical logical source reactions. Microscopic 0.2 and and 0.4 0.4 Microscopicexamination examinationsuggests suggeststhe the presence presence of of between 0.2 percent pyrite coincideswith withdata data for for sulfur of the material. percent pyrite which which coincides sulfur analyses analyses of material. Therefore, the basic for the generation of gypsum are present. Therefore, basic chemicals needed needed for gypsum are Soluble sulfates in in the samples Soluble sulfates samples were were on the order order of of magnitude magnitude of of 10 10 ppm ppm or less. However, careful examination examination of of samples samples exposed exposed to to the mine However, careful mine atmosphere atmosphere showed some gypsum on surfaces of the the samples. samples. However, showed some growth growth of of gypsum on the the surfaces distribution throughoutthe the samples samplesstudied. studied. The The absence absence of of aa linear distribution was was random random throughout relationship between between time time of of exposure to the relationship exposure to the mine mine atmosphere atmosphere and and quantity quantity of of gypsum present isis attributed attributed to the gypsum present the anisotropic anisotropic distribution distribution of parent materials materials in in the mine. mine. Subsequently, Subsequently, similar similar gypsum gypsumgrowth growth was was observed observedon on the the surfaces of polished thin sections sections made made of of the the interior of the rock. polished thin rock. It has of the strata has been been concluded concluded that that possible possible weakening weakening of strataby byprogressive progressive growth does not not present present aa major growth of secondary secondary gypsum gypsum does major hazard at at the theWhite White Pine Pine Mine. However, some such such growth growthisis possible possibleand andisis concentrated concentrated at at the However, some the rock rock surfaces. Further, halite halite may may also also be be growing growing on on the the surfaces surfaces of of the theWhite White Pine Pine Shale. Shale. The The relatively relatively low low rate rateof ofgypsum gypsum growth growth in this this atmosphere atmosphere may may be due due to relatively high high pH pH (about (about 8) mine which which inhibits the relatively 8) in in the mine inhibits growth growth of of the the bacteria which elsewhere are are reported which elsewhere reported to catalyze catalyze the thechemical chemical reactions reactionsresponsible responsible for for shale deterioration. 12 12 �PETROLOGY AND AND FRACTURE FRACTURE CHARACTERISTICS OF THE PETROLOGY CHARACTERISTICS OF KINGSTON CONGLOMERATE, CONGLOMERATE, KEWEENAW KINGSTON KEWEENAW COUNTY, MICHIGAN MICHIGAN Charles Brumleve, of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan Charles Brumleve, Department of Technological University, Houghton, Technological Houghton, Michigan Michigan 49931 49931 ABSTRACT The Kingston Kingston conglomerate conglomerate is is composed of subangular subangular to to subrounded subrounded clasts clasts of The composed of quartzy feldspar porphry. 60 quartzy porphry. These rhyolite gravels gravels make make up up approximately approximately 60 These red rhyolite percent of of the percent the total total rock. rock. The matrix is predominantly predominantly sand the same same The matrix sand of of the compositionasas the the clasts, of copper, composition clasts, with with secondary secondary mineralization mineralization of copper, hematite, hematite, calcite, and calcite, and chlorite, chlorite, in in order order of ofincreasing increasing abundance. abundance. The whole is is The unit unit as aa whole unsorted but is made up of bands bands or or lenses lenses of of poor poor to to well well sorted sorted clasts. up of unsorted The intensity intensity of of mineralization mineralization isis related related to the amount The amount of matrix matrix present present and and is an indication indication of the original original permeability permeability of the the rock. rock. The Thehanging hanging wall wall zone zone has has is the most the most matrix matrix and and received received the themost mostsecondary secondary mineralization mineralization whereas whereas the the has the the least matrix intermediate zone zone has matrix and the least mineralization. mineralization. Permeability tests tests using air demonstrated demonstrated the the tight cementation Permeability using compressed compressed air cementation of the rock. Conductivitytests tests were were used usedtoto determine determinethe the nature nature of of the the native of rock. Conductivity copper framework framework in elongate lenses parallel to copper to bedding. bedding. The The fracture characteristics characteristics of of the theconglomerate conglomerate are are controlled controlled by by the the degree degree of cementation cementation and and type type of of matrix matrix mineralization. mineralization. Silica cement produces produces a of Silica cement competent, nonfriable rock which tends to fracture competent, nonfriable rock which tends fracture transgranularly transgranularly across across clasts. clasts. Chlorite and in the matrix Chlorite and copper copper mineralization mineralization in matrix produces produces weak weak clast bonds. bonds. This This results results in failure failure by by intergranular intergranular fracturing fracturing of of matrix, matrix, clasts clasts and and native native copper copper masses. 13 13 �THE PETROLOGY AND STRUCTURAL RELATIONS RELATIONS OF THE LATER LATER PRECAMBRIAN PRECAMBRIAN BRULE LAKE INTRUSIONS, COOK COOK COUNTY, COUNTY, MINNESOTA MINNESOTA James R. R. Burnell, Burnell, Jr., Jr.,Department DepartmentofofGeology, Geology, University University of ofMinnesota, Minnesota, Duluth, Duluth, Duluth, Minnesota 55801 Minnesota 55801 ABSTRACT The splits into two tonguesatat its its eastern east-trending tongues eastern The Duluth Duluth Complex Complex splits two east—trending extent extent to to form form aanorthern northern and and a asouthern southernprong, prong, exposing exposing a strip strip of of older older Brule Keweenawan volcanic rocks rocks between between them. them. Brule Lake Lake is is located at the Keweenawan volcanic westernmost extent of of the strip westernmost extent strip of of volcanic volcanic rocks rocks just east east of of the the point point where where the the gabbro prongscoalesce. coalesce. The rocks are are intruded by aa series of large sillgabbro prongs The volcanic volcanic rocks intruded by like terminate against like bodies bodies which which terminate against rocks rocks of the the nearby nearby Duluth Duluth Complex. Complex. Thus, Thus, these intrusions, known informally as as the Brule Lake sills, sills, were were formed formed between the Brule Lake known informally time of of the theeruption eruptionofofthe thelocal localKeweenawan Keweenawanvolcanic volcanic rocks rocks and and the thesubsequent subsequent gabbroic intrusions. The the Brule Brule Lake Lake area, area, which which occur occur as as both both dikes dikes and and The intrusive intrusive rocks rocks of the non-porphyritic intrusions. intrusions. The sills, consist of porphyritic intrusions and subsidiary sUbsidiary non-porphyritic The porphyritic intrusionsform form the the most features at Brule most striking striking geologic geologic features Brule Lake. Lake. porphyritic intrusions These diabase porphyries are are approximately approximately 80 80 to to 300 300 meters meters thick and and extend for 22 diabase porphyries kilometers along along strike. strike. Most Most contain contain 50-60% 50-60% plagioclase plagioclase phenocrysts. phenocrysts. to 88 kilometers Mineralogy simple, consisting consisting of of plagioclase, plagioclase, augite, opaque opaque oxides oxides (magnetite Mineralogy isis simple, A typical mode and and ilmenite) ilmenite) with with minor minor quartz and and potash potash feldspar. feldspar. A mode includes includes plagioclase plagioclase 68%, 68%, augite augite (—uralite) (-uralite) 17%, 17%, opaque oxides oxides 9%, 9%, quartz quartz2%, 2%,K—feldspar K-feldspar chlorite-groundmass-epidote 3%. 1 %, chlorite-ground 1%, mass-epidote 3%. The units are are tabular tabular in in form The porphyry porphyry units form and and are tilted tilted totoform formsteep steepnorth-northfacing and more gradual south south slopes. slopes. Several sills are concordant facing slopes slopes and more gradual concordant with with the the trnd trendofofthe theintruded intrudedflows flows whereas whereas others others transect transect this this trend trend at at angles angles of of up up to to 0 30 • is dominated The texture texture of of the theporphyry porphyry units uni ts is dominated by by abundant abundant plagioclase plagioclase The Fine—grained groundmass groundmass phenocrysts textures poorly poorly developed. developed. Fine-grained phenocrysts with with subophitic subophitic textures occurs in the interstices of of the the plagioclase plagioclase laths, commonly commonly including including vermicular occurs in intergrowths of quarzt-plagioclase or quartz-potash feldspar. Small bodies bodies of of non-porphyritic diabase intrude intrude both both the volcanic Small non-porphyritic diabase volcanic rocks and the diabase intruded into into one diabase porphyries. porphyries. When When intruded one of the porphyritic porphyritic bodies, bodies, they are typically irregular in form thetrends trends of of the the larger larger intrusions. typically form and and cross—cut cross-cut the intrusions. When When intruded into into volcanic volcanic units, units, they they form form small small tabular tabular sills, sills, several several meters meters in intruded The mineralogy mineralogyofof these these smaller smaller intrusions intrusionsisis identical identical to to that that of the the thickness. The porphyries although, although, modally, modally, the the proportions porphyries proportions of plagioclase plagioclase are are less less (45-52%) (45-52%) and and of augite, more more (19-25%). (19-25%). Chemically the the Brule intrusions represent represent aa tholeiitic magma Chemically Brule Lake Lake intrusions magma saturated MgO is They are are characterized by with to silica. silica. They by values values of Si02 Si0 == 50%. MgO with respect respect to the2 non-porphyritic low, ranging ranging from from 2-3% 2-3% in in the low, the porphyry porphyry units, units, 5-6% 5-6% in in the non-porphyritic intrusions. Na20 NaZO isis particularly particularlyhigh high (>4% (> 4%in inthe theporphyries) porphyries) as as isis Ti02 TiO Z(2.25%). (2.25%). intrusions. Consideringthe the abundance abundance of of plagioclase phenocrysts inin the Brule Considering plagioclase phenocrysts Brule Lake Lake intrusions the bulk chemistry of of the intrusive intrusive melt melt closely closely approximates approximates the intrusions the bulk chemistry chemistry of several several Keweenawan Keweenawan basalts of of the the North NorthShore Shore Volcanic Volcanic Group. Group. 14 l~ �RESOURCES OF OF RECOVERABLE IRON ON THE MARQUETTE RESOURCES RECOVERABLE IRON MARQUETTE RANGE, MICHIGAN— MICHIGANESTIMATES BY BY A A MONTE MONTE CARLO SIMULATION MODEL ESTIMATES W.F. Cannon Cannonand andL.J. LJ. Drew, U.S. Geological Survey, Survey, National National Center, 12201 W.F. U.S. Geological 12201 Sunrise Sunrise Valley Drive, Drive, Reston, Virginia Valley Virginia 22092 22092 ABSTRACT The Negaunee Iron-formation, MarThe Negaunee Iron-formation,the the principal principal iron-bearing iron-bearingunit unitinin the the Marlong tons tons of material averaging quette Iron Range, contains about 205 205 billion billion long averaging about about 32 percent iron. About 49 49 billion billion tons tons are are within within 1,000 1,000 feet feet of the surface, 32 iron. About surface, which which we consider consider aa reasonable reasonable average depth for some present present we for open-pit open-pit mining, mining, although although some mines will probably be be deeper. mines will probably Three classes Three classes of iron-formation iron-formation are now now being being beneficiated beneficiated on on the the range. range. These are: These coarse-grained hematitic hematitic and 1) coarse-grained and magnetic magnetic iron-formation iron-formation beneficiated by by froth flotation, 2) magnetic iron-formation iron-formation beneficiated magnetically, and magnetic 3) fine-grained (less (less than than 0.05 0.05 mm) mm) nonmagnetic nonmagnetic iron-formation beneficifine-grained ated by selective flocculation and and flotation. We have have divided dividedthe the range range into into 1/4 square-mile We square-mile areas and and computed computed the the tonnage tonnage and characterized in each characterized the iron-formation iron-formation in each according according to its suitability for for and its suitability beneficiation by one one of these beneficiation by these processes, processes, using using a detailed detailed computerized computerized data bank bank developed by the the senior senior author. author. By By using using available available metallurgical data data and and by by means means developed by of by the the junior junior author, author, we we have have of aa Monte Monte Carlo Carlo simulation simulation model model designed designed by estimated the the total total amount amount of of metallic metallic iron iron recoverable recoverable from from the the Marquette Marquette range range by surface mining miningtoto 1,000 1,000feet. feet. The by each process, process, assuming assuming surface The model model considers considers the quality of concentrate, quality standards standards of of Fe Fe >60 percent quality of concentrate, using using quality percent and and Si09 SiO <10 < 10 percent; itit estimates estimatesthe theamount amountof ofiron-formation iron-formation that thatwill willmake makeconcentra4tes concentrates of this quality. empirical distribution distribution of of recoverable recoverable iron iron derived derived from from quality. From From the empirical many metallurgical tests, tests, the the total recoverable recoverable iron iron is is then then estimated. estimated. Figure 11 many metallurgical indicates that that ifif recoverable recoverable grades grades of of about about 20 20 percent percent Fe Fe are areeconomically economically indicates feasible, short tons 11 billion billion short tons of metallic metallic iron iron can can be be recovered recovered from from feasible, then then about about 11 iron-formation iron-formation that responds responds satisfactorily to to beneficiation beneficiation by by an an existing existing process. process. Most 7.2 billion billion tons-is tons—isininfine-grained fine-grained nonmagnetic nonmagnetic iron-formation. iron-formation. -about 7.2 Most of this this —about About tons is is in magnetic in About 3 billion billion tons magnetic iron-formation, iron-formation, and about 0.7 0.7 billion billion tons is in coarse-grained hematiticiron—formation. iron-formation. coarse-grained hematitic These These figures figures indicate indicate the the geologic geologic availability availability of of iron ironand andplace placemaximum maximum limits on on iron iron reserves reserves on on the the range range in in terms terms of ofcurrent currentmining mining and and beneficiating beneficiating technology. percentage of of this this iron iron that thatisisnow, now,or orever everwill willbe, be,economically economically technology. The The percentage available cannot cannot be estimated estimated without without much much more more detailed study. study. 15 15 �a "c0 30 ... ~0 7 S <II 6 C C ......~ 5 a 3 ::: 4 ~ a "a ".~S ~ 0 o 2 1 flocacion "0 <lJ '" 20 20 25 25 30 35 35 40 45 45 50 50 Recoverable (%) Recoverable Fe e (Z) Figure 1. — between estimated estimated tonnage - Relationship between tonnage of recoverable recoverable iron iron and and percentage of recoverable iron for three three beneficiating beneficiating processes. processes. 16 16 �ABUNDANCES OF RARE EARTH AND ABUNDANCES OF AND OTHER ELEMENTS ELEMENTS IN IN ARCHEAN GRANITIC AND AND GNEISSIC GNEISSIC ROCKS FROM FROM THE THE ENGLISH ENGLISH RIVER RIVER GNEISS GNEISS BELT, BELT, ONTARIO ONTARIO C.-L. Chou, Goodwin, Department Department of Chou, N.B.W. N.B.W. Harris, arid and A.M. A.M. Goodwin, of Geology Geology and and Erindale Erindale College, University of Toronto, Toronto, Canada Canada M5S M5S IAI. 1Al. ABSTRACT ABSTRACT The rocks in in the eastern The early early Precambrian Precambrian rocks eastern Lac Lac Seul Seul region region of of the the English English River River gneiss gneiss belt consist mainly mainly of tonalitic and and trondhjemitic trondhjemitic gneisses gneisses overlain overlain by by tonalitic migmatized migmatized metasedimentary rocks. rocks. Both Both are are intruded intruded by by granitic granitic plutons plutons and sills and and pegmatite pegmatite veins. veins. Smaller and sills Smaller bodies bodies of amphibolitic amphibolitic gneiss gneiss also are are found. found. Using neutron activation activation techniques techniques we have analyzed analyzed an amphibolitic amphibolitic gneiss, gneiss, two Using neutron tonalitic gneisses, gneisses, two granites, and and two pegmatites for for 24 24 elements elements (Na, (Na, K, K, Sc, Sc, Cr, Cr, Mn, Mn, Fe, Co, Ni, Ni, Zn, Zn, Rb, Rb, Zr, Zr, Sb, Sb, Ba, Ba, La, La, Ce, Ce,Nd, Nd, Sm, Sm, Eu, Eu, Tb, Tb, Yb, Vb, Lu, Lu, Hf, Hf, Ta Ta and and Th). Th). Scandium, Mn,and andCo Coare are positively positivelycorrelated correlatedwith with Fe, Fe, as as they they generally generally are are Scandium, Mn, concentrated in mafic minerals. The K/Rb ratios of three granitic rocks concentrated minerals. The K/Rb ratios of three granitic rocksare are290-. 290Slight variation Zr/Hf ratios ratios in in granitic granitic and and tonalitic tonalitic rocks rocks(32-28) (32-28) variation of of Zr/Hf 440. Slight contrasts contrasts with large variation variation of Hf Hi by by a factor of of 3. 3. AAfine-grained fine-grained amphibolitic amphibolitic gneiss has aa flat REE gneiss has REE pattern and and a total total REE REE content content of of 12X 12X chondritic chondritic abundance. abundance. It resembles basalts, suggesitng suggesitngthat that its its parent resembles Archean Archean basalts, parent is is basaltic, basaltic, formed formed by by partial melting old gray gray tonalitic gneiss melting of upper upper mantle mantle material. material.AA3.04—Gyr 3.04-Gyr old gneiss (74(74115) has aa smooth smooth and and steep-sloped steep-sloped REE REE pattern with with remarkable remarkable enrichment enrichment of of 115) has light REE REE and and depletion depletion of of heavy heavy REE REE (LaN (LaN == 71, and YbN Yb == 6.4). It has has a total total N REE and aa CeN/YbN REE content of about 2X 2X and CeN/Yb ratio ratio of of 0.5X 0.5X those those of of Saganaga Saganaga tonalites analyzed by Arth Arth and and Hanson Hanson(1975)'. (1975) ItIt i~isNlikely likely that that this tonalite analyzed by tonalite may may have have formed formed from from a granitic granitic melt melt which which has has been been significantly significantly contaminated by by mafic material. material. A secondtonalitic tonalitic gneiss gneiss (74-222B) (74-222B)has hasa atotal total REE REEcontent content 2X 2Xhigher higherthan than that that of A second 74-115 and and aa significant suggesting that that a plagioclase-rich 74-115 significant negative negative Eu Eu anomaly, anomaly, suggesting plagioclase-rich component was removed removedfrom fromthe themagna. magna. The REE patterns patterns of two component was The REE two granites granites have have very steep ratios are 160 steep slopes, slopes, their theirCeN/Yb..,J CeN/Yb N ratios 160 and and 85, 85, respectively, significantly higher than that of higher than of granitic granitic roèks roCks from from the the Vermilion Vermilion distirct. distirct. These These granites might have formed by by crustal crustal anatexis of might have formed of earlier earlier Archean Archean metasedimentary metasedimentary rocks. rocks. Two pegmatites show a strong positive Eu anomaly, but differ in total REE Two pegmatites show a strong positive Eu anomaly, but differ in REE and and other trace element contents reflecting that they are derived from different source element that they are derived from source materials. 17 �PALEOMAGNETISM PALEOMAGNETISM OF THE LATE LATE PRECAMBRIAN PRECAMBRIAN BRULE BRULE LAKE LAKE INTRUSIONS, INTRUSIONS, COOK COOK COUNTY COUNTY MINNESOTA MINNESOTA Donald M. Davidson, Davidson,Jr., Jr., Henry Henry Halls*, Halls*, and and James James R. R. Burnell, Jr., Department Donald M. Burnell, Jr., Department of of Geology, Geology, University University of Minnesota, Minnesota, Duluth, Duluth, *Department *Department of of Geophysics, Geophysics, University University of Toronto Toronto of ABSTRACT ABSTRACT Paleomagnetic involving ac ac demagnetization demagnetization up up to to 40 Paleomagnetic analysis, analysis, involving 40 oe, has has been been carried carried out out on onone onerhyolite rhyoliteflow flow(Keweenawan) (Keweenawan) and and two two porphyritic porphyritic intrusions intrusions which which flows in in the the Brule Brule Lake Lake area. area. These These flows flows and and intrusions intrusions are truncated truncated by by cut flows the Duluth Duluth Complex. Complex. of the various units of The The Brule Brule Lake Lake intrusive units units give indications of of primary reverse magnetizamagnetization which which has has been been altered by by normal normal intrusive intrusive activity, activity, probably probably associated associated with emplacement of of the theDuluth DuluthComplex. Complex. The Thenorthern northernintrusion intrusion(Fishbox (FishboxIsland) Island) shows shows a hard is closer closer to a reversed primary component component which which is reversed than than normal normal direction. The The hard primary southern intrusion (Jock (Jock Mock Mock Point) Point) exhibits exhibitsstable stable end end points points but but with with aa two southern intrusion two component responsewhich whichininatatleast least one one sample sampleindicates indicatesaa soft, soft, reversed reversed state. state. component response The rhyolite The rhyolite flow flow exhibits exhibits aa mixed mixed magnetic magnetic response response with with aa harder harder normal normal reversed components. components. and soft reversed Mean site determinations and paleo paleo pole pole positions positionsfor for these these sites sites are given Mean site determinations and given below: Paleo Pole Position Mean Mean Site 0 Intrusive- u No. No. Intrusive-u Intrusive-c No. No. Intrusive-c 139° 139 0 120 120° So. Intrusive-u Intrusive-c So. Intrusive-c So. 316 0 317 317° Rhyoli te Flow-u Rhyolite Rhyoli te Flow-c Rhyolite N N K <95 0<95 12 0 22° 22 3 3 3 35 35 35 4800 3 3 31 31 II D D 00 0 307.5 307.5°c 0 299 Lat. Long. 21 31 34.04N 145.41E 23 23 45.70N 173.35E 173.35E _66 -66°0 _75 -75°0 0 48 55 uu - uncorrected cc - corrected structurally Thus itit appears appears that that the southern Thus southern most most intrusion intrusion and adjacent flow flow unit more more Although the the clearly show show the the effects of clearly of remagnetization remagnetization than than the the northern northern sill. sill. Although results are consistent results consistent with with available available data data on on both both normal normal and and reversely reversely magnetized magnetized rocks of age, positive positive correlation between rocks of Keweenawan Keweenawan age, between the the Brule Brule Lake Lake intrusions intrusions and Logan sills and the the Logan sills does does not not appear appear feasible. feasible. 18 18 �STRUCTURAL AND AGE RELATIONSHIPS AT THE THE LAC LAC LA BELLE STRUCTURAL AND AGE RELATIONSHIPS AT MAGNETIC ANOMALY, COUNTY, MICHIGAN KEWEENAW COUNTY, MICHIGAN MAGNETIC ANOMALY, KEWEENAW James M. M. DeGraff, Department DepartmentofofGeology Geologyand andGeophysics, Geophysics, Michigan Michigan Technological Technological University, Houghton, Houghton, Michigan Michigan 49931 49931 ABSTRACT Along the Keweenaw Peninsulaof of Michigan Michiganthe thecontact contact between between the the Portage Keweenaw Peninsula Lake Lake Lava Lava Series and the Jacobsville Jacobsville Sandstone Sandstone has generally been considered considered to be thrust fault. fault.This ThisKeweenaw KeweenawFault Faultdescribes describesaasite sitealong alongwhich which the theMiddle Middle a great thrust KeweenawanPLLS PLLSononthe the north north has has been been thrust thrust southward southward over over the the Lower Lower Keweenawan Cambrian(?) Jacobsville Sandstone, Sandstone,with withaa possible possible vertical vertical throw throw of 10,000 10,000 feet feet Cambrian(?) Jacobsville (Bacon, 1966). 1966). Aeromagnetic maps (Bacon, maps for this this region region compiled compiled by by Baisley Balsley et et al al in in 1963 1963 delineate this regional well. However, However, an an earlier earlier map map comiTed compiled from from delineate regional contact quite well. the same data by shows that that a prominent magnetic anomaly exists along by L.O. L.O. Bacon Bacon shows this contact This anomaly anomalytakes takes the the form form of of a contact near near the site site of of Lac Lac La La Belle. Belle. This this magnetic "high" which which projects projects southward southwardfrom from the the nearly nearly east-west magnetic magnetic magnetic "high" lineations of of the PLLS by lineations PLLS into into aa region region of oflow lowmagnetic magnetic gradients gradients underlain underlain by Jacobsville Sandstone. Sandstone. Diamond has shown shown that that this Lac Jacobsville Diamond drilling and and field mapping mapping has Lac associated with with aa lobe La lava flows flows La Belle Belle magnetic magnetic anomaly anomaly is is associated lobe of of basaltic basaltic lava southward from from the PLLS into the Jacobsville Sandstone. PLLS into extending southward this project The purpose project was was to to investigate investigate the the structural structural and and age age The purpose of of this relationships of of the the PLLS, Jacobsville Sandstone Sandstoneand andbasalts basaltswithin withinthe thearea area of of the relationships PLLS, Jacobsville In order Lac Lac La La Belle Belle magnetic magnetic anomaly. anomaly. In order to accomplish accomplish this, the the following following four four field methods methods were were used: used: (1) ground magnetic magnetic work over the Lac La Belle magnetic anomaly, ground work over anomaly, (2) palaeomagnetic palaeomagnetic studies of basalts basalts in in the theanomalous anomalous zone zone in incomparison comparison with basalts of the PLLS immediately to to the north, PLLS immediately (3) geologic mapping mapping and and diamond diamonddrill drill hole hole correlations, correlations, and geologic (4) two regional PLLS—Jacobsville regional gravity gravity traverses traversesacross acrossthethe PLLS-Jacobsville Sandstone Sandstone contact, one contact, one on on either either side side of of the the Lac Lac La La Belle Belle magnetic magnetic anomaly. anomaly. Some conclusions conclusionswhich whichcan canbebedrawn drawnatatthe thepresent present time time are that: Some that: 1) 1) the flows rotated up up to to 45 flows within within the the anomalous anomalous zone zone have have b0een been rotated 45 degrees 0 counter-clockwise with with respect respect to to the N.70 N.70 E. E. strike of of the the PLLS PLLS to the counter-clockwise north, (2) faulting on both east and and west west sides sides of of the theanomaly anomaly has has been been very very faulting on both the east important in controlling the emplacement and rotation of of the the anomalous anomalous lavas, (3) the basalts associated associated with with the the anomaly are the the eastern eastern the exposed exposed basalts anomaly are extension of a larger larger block block of oflavas lavaswhich whichhas hasbeen beendowndropped downdropped on on the the west and and covered by Jacobsville Sandstone, (4) lavas in the lavas the lower lower section section of of the thePLLS PLLS and and within within the the anomalous anomalous zone zone 19 I �are not not reversely reversely magnetized, magnetized, and and therefore correlate correlate with with the theMiddle Middle Keweenawan rocks of of the Lake Keweenawan rocks Lake Superior Superior basin, basin, and and (5) in in this this area area the theevidence evidencepoints points totothe theJacobsville JacobsvilleSandstone Sandstone being being younger than the PLLS. PLLS. younger REFERENCES CITED CITED Bacon, L.O., 1966, 1966, Geologic Geologicstructure structure east and Bacon, L.O., and south of the the Keweenaw Keweenaw fault on on the basis of geophysical basis geophysical evidence, in The The Earth Beneath the Continents-A Continents-A Volume Volume of Geophysical Studies in in Honor A. Tuve: Tuve: Am. Am. Geophys. Geophys. Union of Geophysical Studies Honor of Merle Merle A. Geophys. Mono. 10, p. 42-55. Geophys. Mono. 10, 20 �LEAD ISOTOPE ISOTOPE INVESTIGATIONS INVESTIGATIONS IN IN THE MINNESOTA MINNESOT A RIVER RIVER VALLEY VALLEY B.R. and M.H. Delevaux, U.S. Geological Survey, Survey, Denver, Colorado 80225 B.R. Doe, Doe, and M.H. Delevaux, U.S. Geological ABSTRACT The isotopic systems systems have have been been investigated investigated for for whole-rock whole-rock and and The U-Th-Pb U- Th-Pb isotopic feldspar of the foliated feldspar samples samples of foliated and and also also more more massive massive phases phases of of the theMontevideo Montevideo Gneiss of Lund (1956),the the Sacred Sacred Heart Heart Granite, Granite, and Gneiss of Lund (1956), and the adamellite adamellite of of Section Section 28 28 near near Granite Granite Falls. Falls. We We have have not been been able able to to resolve resolve events events which which affected affected the the that time Montevideo Gneissprior prior to to 3.0 Montevideo Gneiss 3.0 b.y. ago. ago. At approximately approximately that time a thermal thermal event event reset reset the the U-Th-Pb U-Th-Pb system system in the the older, older, dark-colored dark-colored foliated foliated phase. phase. This event may by or or resulted resulted from from the introduciton of granitic may have been been accompanied accompanied by magma which formed the massive phase of of the gneiss. which formed gneiss. The age of Scared Heart Granite Granite has has aamicrolirie-whole-rock microline-whole-rock isochron isochron age of 2590 2590 The Scared m.y. The age is is in The feldspar feldspar isochron isochron model-lead model-lead age in excellent agreement at at 2560 2560 m.y., m.y., whereas the Pb-208/Pb204 age is is somewhat m.y. The Pb-208/Pb204 model model age somewhat younger younger at 2300 2300 m.y. The cause cause for this variation is not not understood understood at present. The adamellite of Section The epizonal epizonal adamellite Section 28 28 has has aa feldspar-whole-rock feldspar-whole-rock isochron isochron of of approximately 1850m.y., m.y.,determined determined by byan anacid-leach acid-leach method. method. The approximately 1850 The modellead modellead age is 2200 age is 2200 m.y., m.y., but the the Pb-208/Pb-204 Pb-208/Pb-204 model model age is in excellent agreement with with the the acid-leach, isochronatat 1850 1850m.y. m.y. The acid-leach, feldspar-whole-rock feldspar-whole-rock isochron The anomaly anomaly of about about 350 350 m.y. m.y. in the the model model ages ages isis similar similar to tothat thatfound foundininrejuvenated rejuvenatedcratons cratonswhere where Mesozoic and and Cenozoic Cenozoicigneous igneousrocks rockshave havepenetrated penetrated an 1800 Mesozoic 1800 m.y.-old basement. The m.y.-old adamellite adamellite of of Section Section 28 has penetrated penetrated an Archean The 1850 1850 m.y.-old 28 has Archean basement of 3800 m.y. m.y. in rocks ranging from 2600 rocks ranging from 2600 to 3800 in age. It is one one of the the few few Precambrian Precambrian examples displayingderivation derivationofof lead lead from from aa cratonzied examples displaying cratonzied continent and the the only only example as old old as as 1850 1850 m.y. 'V All rocks appear to have have lost about about half half of of their their uranium uranium fairly recently, recently, All the rocks but thorium thorium has hasbeen beenaffected affectedtoto aa lesser lesser degree. degree. These appear to be but These relationships relationships appear common in near-surface near-surface crystalline rocks and may may reflect reflect dilatancy. common in rocks and dilatancy. 21 �PRECAMBRIAN PRECAMBRIAN HISTORY HISTORY OF THE MORTON-NEW MORTON-NEW ULM ULM REACH OF THE MINNESOTA RIVER VALLEY THE MINNESOTA RIVER VALLEY S.S. Goldich, S.S. Goldich, 3.L. J.L. Wooden, Wooden, G.A. G.A. Arikenbauer, Ankenbauer, 3r., Jr., T.M. T.M. Levy, Levy, and and R.U. R.U. Suda, Suda, Northern Illinois illinois University, University, DeKaib, DeKalb, Illinois Illinois 60115 60115 ABSTRACT On the basis On the basis of current current research research on on the thePrecambrian Precambrian rocks rocks in inthe theMinnesota Minnesota River of events area is River Valley Valley aa tentative chronology chronology of events in the the Morton-New Morton-New Ulm Ulm area proposed. Time - M.Y. Time-M.Y. Event (?) Folding 1800 - 1200 (?) of the Sioux Deposition of Deposition Sioux Formation. Uplift and and erosion. 1900 - 1800 Emplacement of of diabasic diabasic dikes dikes and and small small granitic granitic plutons. Emplacement Thermal strong enough enough to to reset mineral Thermal metamorphism metamorphism strong mineral ages. ages. rv2600 rv 2600 Late tectonic emplacement emplacement of of aplitic aplitic and and pegmatitic pegmatitic dikes. dikes. Late tectonic or Late or syntectonic syntectonic emplacement emplacement of Sacred Sacred Heart and related adamellites. and (?) 2700 - 2550 2800 3000 ++ 150 3050 Deformation and and low-grade low-grade metamorphism. Deformation Emplacement of of granodiorite granodiorite and and adamellite. adamellite. Emplacement Deformation and and metamorphism metamorphism of of high-potash high-potashgranite, granite, basaltic basaltic Deformation rocks, and and gray gray tonalitic gneiss. rocks, gneiss. Possible Possible formation of of speckled speckled gneiss in shear zones. gneiss Emplacement of of high-potash high-potash granite granite and and pegmatite. Emplacement high- and and low-alumina low-alumina basaltic dikes Emplacement (?) (?) of highor sills. Deformation and metamorphism. 3550+ 125 - Extrusion and and intrusion intrusion of of trondhjemitic, trondhjemitic, tonalitic, and Extrusion and granodioritic Possiblybasaltic basaltic magma magmaalso alsoatat this this time. time. magma. Possibly 22 �LITHIC LITHIC AND MAJOR ELEMENT ELEMENT COMPOSITION COMPOSITION IN THE THE SUPERIOR GEOTRA VERSE, ONTARIO GEOTRAVERSE, A.M. Goodwin, Goodwin,Department Department of of Geology, Geology, University University of of Toronto, Toronto, Toronto, Toronto, Canada. Canada. A.M. ABSTRACT 2 The Geotraverse constitutes0 a a recta~ular rectanular area The Superior Superior Geotraverse constitutes area of of 24,610 24,610 mi2 mi 0 0 bounded by 90 90° and and 92°W longitudeand and 49 49° and and 52 52 N N latitude 92 W longitude latitude in in the the western western bounded by Superior Province Provinceofofthe the Canadian CanadianShield. Shield. The The area area crosses crosses or or includes Superior includes parts of six six major east-trending or belts belts which major east-trending subprovinces subprovinces or which in alternating alternating succession succession from from south to north south north are: are: Wawa WawaVolcanic, Volcanic, Quetico QueticoGneiss, Gneiss,Wabigoon Wabigoon Volcanic, Volcanic, English River Gneiss, Uchi and Berens Berens Plutonic Belt. River Uchi Volcanic, Volcanic, and Lithic proportions proportions (percent) in the Geotraverse Geotraverse are are as asfollows: follows: Granitic Granitic rocks rocks Metasedimentary rocks rocks - 5.3; Volcanic - 69.2; Migmatite - 10.5; Metasedimentary Volcanic rocks - 14.0; Mafic to ultramafic ultramafic intrusions intrusions - 0.5; and Syenite - 0.4. Granitic rocks rocks are are equally equally divided divided rocks comprise comprise mafic between gneissic (34.8) (34.8) and massive (34.6) (34.6) phases. Volcanic Volcanic rocks mafic and massive (12.8) and felsic (1.2) phases. The ratio of mafic to felsic volcanic rocks is 91.5 (12.8) and felsic (1.2) phases. The to felsic volcanic rocks is 91.5 to to 8.5. Lithic proportions in the the two gneiss Lithic proportions in gneiss belts differ significantly significantly with with the the English English River equally high high proportions proportions of of migmatite River Belt Belt containing containing equally migmatite (49.7) (49.7) and and granitic granitic gneiss (46.1) and negligible metasedimentary material, material, whereas gneiss (46.1) and negligible metasedimentary whereas the Quetico Quetico Belt Belt has has predominant predominant migmatite migmatite (64.8) (64.8) and and metasedimentary metasedimentary material material (29.0). (29.0). This contrast reflects reflects aa higher higher degree degree of of metamorphism metamorphism together together with with greater greater exposure exposure of older basement gneiss gneissdated datedto to be be at least of older basement least 3040 3040 m.y. m.y. old old in in the the English English River River Belt to to the north. Belt The three The three volcanic volcanic belts belts are are essentially essentially similar similar in in lithic lithiccompositon. compositon. A A salient feature feature is the of granitic in the two salient the high high proportions proportions of granitic rocks rocks especially especially in two northern Wabigoon - 77.1) equally northern belts belts (Uchi (Uchi - 65.0; Wabigoon equally divided divided between between numerous numerous latter appears massive plutons plutons and massive and adjoining adjoining gneissic gneissic rocks. rocks. The The latter appears to to represent represent foliated plutonic foliated plutonic rocks rocks intrusive intrusive into into nearby nearby volcanic volcanic rocks rocks which which would would imply imply aa post-volcanic age dated at 2750-2850 m.y. at 2750-2350 The weighted mean major major element element composition of the the Geotraverse is as The weighted mean composition of Geotraverse is as follows in in weight weight percent: percent: Si0 SiO,2 _-- 65.64, AL,O FeO (total) follows A1 2 0 3 -- 15.96, FeO (total) - 4.98, MgO MgO 2.32, CaO - 4.20, Na2O CO2 H20 - .88, CO Na 20 - 3.85,1C,O 3.85'£<.2° - 2.32, TiY2 Ti0 2 - .45, MnO MnO - .09, H....O 2 This compares c'losely with that of the Red compares closely with that Red Lake-Lansdown Lake-L~nsdownregion regIOn .09, P,O5 P 20 - .07. This 5 of northwestern Ontario (Shaw, (Shaw,et. et. a1.) a!.) as as well well as as both of northwestern Ontario both of of the theCanadian Canadian Shield Shield (Fahrig and Eade) and the the Ukrainian shield (Ronov, (Ronov,et. et. al.), (Fahrig and Eade) and Ukrainian shield al.), the the only only significant significant K20 and higher higher CaO CaO contents contents in in the Geotraverse. difference being being low low K Geotraverse. 0 and 2 tectonic development Although Although the the tectonic development of the Geotraverse Geotraverse crust remains uncertain, available available data data indicate of (1) uncertain, indicate some some blend blend of (1) spreading spreading of older older gneissic gneissic crust (older (older than than 3.0 3.0 b.y.) b.y.) with with (2) (2) accretionary accretionary growth growth of of ensimatic ensimatic volcanic volcanic belts belts (2750 -2900m.y.) m.y.)ininresulting resultingtroughs troughsand andbasins basinsrelative relativetotoaa metastable metastable craton to (2750 -2900 to the north. north. 23 �I THE GEOLOGY GEOLOGY OF GNEISSIC GNEISSIC ROCKS IN IN THE KENORA DISTRICT, DISTRICT, ENGLISH RIVER GNEISS RIVER GNEISS BELT. BELT. C.F. Gower, Gower, Department Department of of Geology, Geology, McMaster McMaster University, Hamilton, Hamilton, Ontario Ontario ABSTRACT ABSTRACT After After an an initial initial reconnaissance reconnaissance geological geological investigation investigation of of 2400 2400 sq. sq. km. in the southwest part part of of the the English English River River Gneiss Gneiss Belt, an area of of 100 100 sq. km. near near Kenora Kenora detailed study. study. was selected for detailed Most of the area range from from granitic granitic to Most of area is is underlain underlain by by gneissic gneissic rocks rocks which which range are best withthe the aid aid of of aa trianguiar untramaiic composition. composition. They They are best described described with "triangular untramafic diagram diagram" having having granitic granitic pegmatoid pegmatoid gneiss, gneiss, biotite biotite tonalite tonalite gneiss, gneiss, and and amphibolite amphibolite end members. members. as end BIOTITE BIOTITE TONALITE TONALITE GNEISS GNEISS 1 Mixed biotite tonalite —granitic pe~matoid gneiss, gneiss, granitic pegmatoid minor amphibolite minor arnphibolite . .. . Tonalite/leucotonalite gneiss, gneiss, minor minor amphiholite amphibolite and granitic gneiss Hornblende—biotite Hornblende-biotite tonalite tonalite gneiss, gneiss, common amphibolite enclaves enclaves . Amphibolite—leucotonalite gneissic Amphibolite-leucotonalite association, minor hornblende— association, hornblendebiotite tonalite gneiss Amphibolite, medium Amphibolite, medium grained, grained, network leucotonalite leucotonalite veins veins Granitic pep,matoid Granitic pegratoid gneiss Amphibolite, fine grained, Amphibolite, concordant leucotonalite, leucotonalite, uartz—epidote pods quartz-epidote pods GRANITIC PEGHATOID GNEISS GRANITIC PEGMATOID AMPHIBOLITE AHPHIBCLITE (1) much muchofof the the granitic Field studies suggest suggest that, (i) granitic material material represents represents Field studies pegmatite, (ii), represents both both mafic intensely Oi), the amphibolite amphibolite represents intensely deformed deformed intrusive pegmatite, (iii) do do not not assist assist in in determining protolith for for the the lavas and mafic mafic dikes, dikes, but but (iii) determining aa protolith lavas and biotite gneiss. biotite tonalite gneiss. isodilnal folds folds have have been The tectonic tectonic history The history is is complex. complex. FF isoclinal been refolded by by been used to define major F2 folds. iLve tight to open F2 folds. The minor F, folds open folds. The minor F?_ folds ~ave been used to F2 These major major structures have have been been re'folded rerolded by by an an F3 F fold which which appears to be a rim rim These 3 synformassociated associatedwith withthe the margin marginofofaalarge largetonalIte/granodiorite tonalite/granodiorite batholith. Two synform batholith. Two later (F4, also are are recognized. recognized. Mafic ter periods periods of of open open folding folding (F 4' FF5) 5) also Mafic dikes dikes which which have la with of the area which, been intruded throughout together with throughout the history of been intruded superimposed fold fold relationships superimposed relationships assist in in distinguishing distinguishing individual individual deforrnational deformational phases. 24 24 �APPLICATION OF A FLOW APPLICATION FLOW DIRECTION TECHNIQUE TO THE PORTAGE LAKE TO LAKE VOLCANICS, VOLCANICS, MICHIGAN MICHIGAN James G. James G. Grimes, Grimes, Department Department ofofGeology Geologyand andGeological GeologicalEngineering, Engineering, Michigan Michigan Technological University, Houghton, Houghton, Michigan Michigan 49931 49931 ABSTRACT A study study was was made made to to test ifif the theflow flow direction directiontechnique techniquedeveloped developed by by Elston Elston A and Smith Smith (1970) (1970)could couldbe be applied appliedto to the the Portage Lake in Michigan. Lake Volcanics Volcanics in Michigan. The The and technique, as as modified for basalts, basalts, presumes presumes that technique, modified by by Smith Smith and and Rhodes Rhodes (1972) (1972) for elongated will statistically align themself elongated fragments fragments (i.e. (i.e. crystals) crystals) will statistically align themseif in in the direction of flow. Samples were were collected collected from from various various locations locations within within the the series. series. The Samples majority of of samples were collected collected within majority samples were within the City City of of Houghton Houghton and and represent a rough stratigraphic section section through The remaining through the series. series. The remaining samples samples were were rough stratigraphic collected between South Range and Keweenaw Point. between South Range and Keweenaw The orientation orientation of of plagioclase crystals having havingaa length/breath length/breath ratio ratio greater plagioclase crystals The than three was in oriented oriented thin thin sections. sections. The than was measured measured in The results results were were then then submitted submitted for statistical statistical analysis. to a computer program program for analysis. Lineation values values all all had aa chi—square valueabove abovethe the90 90percentile percentile for for two two Lineation chi-square value degrees of of freedom. effect degrees freedom. Aximuth Aximuth was was determined determined by by imbrication imbrication and blocking blocking effect criteria. Two samples samples were were collected collected within withinfour four feet feet of each other Two other within within the the same same flow to to check the repeatability of the flow check the the method. method. In In addition addition to these these two two samples, samples, another thin section The difference another section was was measured measured twice. twice. The difference between between the two two flow flow directions were were 10.3 and 11.2 11.2 in in each each case, case, respectively. respectively. This This difference could could be directions 10.3 and mostly accountedfor for by bythe the ten ten degree degree intervals intervals that that the data data is is divided divided into for for mostly accounted analyses. The of the Scales Scales Creek Creek Flow Flow also also was was The upper, upper, middle, middle, and and lower lower portions portions of sampled to test the application of the method to some of the thicker flows in the application of the method to some of the thicker flows in the the sampled to sequence. Flow S35.OE,and andSO.6E S0.6Erespectively. respectively. The upper Flowaximuths aximuthswere wereS16.GW, S16.6W, S35.0E, and lower lower samples generally conform conform to to the aximuth aximuth directions directions of of samples samples above above and samples generally (S2.8W)and and below below (S9.DE) (S9.OE)the theScales Scales Creek Creek Flow. (S2.8W) Taken together, the results Taken together, results indicate indicate aa general general flow flow direction direction from from the the north. north. Within City of of Houghotn, Houghotn, the theflow flowazimuth azimuthwas wasS9.OE S9.0E for for the thelower lowerpart, part,S2.OW S2.0W Within the City for the for the the upper upper part part of the series. the middle middle part, part, and and S28.OW S28.0W for series. Individual Individual sample sample directions for the directions are areS17.OE S17.0E and and SLOE SLOE for the the lower lower part, part,S7.2W, S7.2W,S4.OE, S4.0E, and S4.5W S4.5W for middle and S33.7W S33.7Wfor forthe the upper upper part. part. middle part, and and S23.4W S23.4W and Further application application of the the technique technique could could demonstrate demonstrate regional regional patterns for for directions of of lava lava flow flow movements, movements, and and multiple multiple sampling sampling of long long strike lengths of of certain certain flows flows might might allow allow triangulation triangUlation of the source source area. area. 25 25 �REFERENCES REFERENCES Elston, W.E., flow direction of rhyolitic rhyolitic Elston, W.E., and Smith, 1970, Determination Smith, E.1., E.I., 1970, Determination of of flow ash-flow tuffs tuffs from ash-flow from fluidal fluidal textures: textures: Geol. Geol. Soc. Soc. America America Bull., Bull., v. v. 81, 81, pp. pp. 3393—3406. 3393-3406. Smith, E.1., E.I., and and Rhodes, R.C., 1972, Flow direction direction determination determination of lava Smith, Rhodes, R.C., 1972, Flow lava flows: flows: Geol. Soc. Soc. America Bull., v. 83, Geol. 83, pp. 1869-1874. 1869-1874. 26 26 �I I THE THE SLATE SLATE ISLANDS: ISLANDS: THE CENTRAL UPLIFT UPLIFT OF OF A A METEORITE METEORITE IMPACT IMPACT CRATER? Department of of Geology, Halls, Department Geology, Erindale Erindale College, College, University University of of Toronto, Toronto, H.C. I-Jails, Mississauga, Ontario L5L 1C6 IC6 and Grieve, Earth Earth Physics Physics Branch, Branch, DepartDepartMississauga, Ontario L5L and R.A.F. R.A.F. Grieve, of Energy Energy Mines 'Mines and Ontario ment of and Resources, Resources, Ottawa, Ontario ABSTRACT ABSTRACT Shock metamorphic effects in in samples samples from from the the Slate SlateIslands, Islands,Lake Lake Superior Superior Shock metamorphic 0 (48°40'N, 87°OOW) suggest thatthetheislands islandsare arepart part of of aa meteorite (48 0 40'N, 87 00'W) suggest that meteorite impact impact structure. The The islands islands form form the the central central uplift upliftof ofaacomplex complex crater craterand andare areringed ringed by aa submerged trough and and annular annular ridge ridge with a dimater dimater of of 30 30 km. km. Precambrian Precambrian submerged trough bedrock units are are locally breccia dikes. bedrock units locally brecciated and and cut by by aliochthonous allochthonous breccia dikes. These These clasts of identifiable country country rock rock and and also also fragments fragments of of a dikes contain clasts sedimentary unit, in age, age, which is no longer present in unit, possibly possibly Upper Upper Keweenawan Keweenawan in which is no longer in of shatter The orientations orientations of shatter cones cones present present in in the the breccia breccia host host rocks rocks outcrop. The indicate indicate the interior interior of of the the islands islands as as the the approximate approximate shock shock centre. Microscopic Microscopic planar features, equivalent planar features, equivalent to those those described described from from other other impact impact sites, occur occur in in quartz and and piagiociase plagioclase and and the level level of of shock shock deformation deformation increases increases towards towards the the interior of of the the islands. islands. The The shock shock event postdates postdates Keweenawan Keweenawan igneous igneous activity interior (about 1.1. b.y. old) old) and on the basis basis of of the the erosion erosion level, level, may may be be early early Paleozoic Paleozoic in in (about and on age. 27 27 �GEOCHEMICAL PROCESSES PROCESSES FOR THE GEOCHEMICAL THE FORMATION FORMATION OF OF MAGNETITE MAGNETITE IN IN LOW-GRADE LOW-GRADE METAMORPHIC PRECAMBRIAN IRON FORMATIONS METAMORPHIC FORMATIONS Tsu-Ming Han, Han, The The Cleveland-Cliffs Cleveland-Cliffs Iron Iron Company, Company, Ishpeming, Ishpeming, Michigan Michigan 49849 49849 Tsu-Ming ABSTRACT A substantial substantial number number of of magnetite ores, magnetite-containing magnetite-containing specimens specimens and A collected from their oxidized equivalents collected from the low-grade low-grade metamorphic metamorphic iron iron formations in the Mesabi, Gogebic, and Marquette districts of the Lake Superior formations in Mesabi, Gogebic, and Marquette districts the Lake Superior region, and and the Lake region, Lake Albanel Albanel District of of the the Quebec Quebec Province, Province, Canada Canada have have been been study reveals reveals that the microscopically investigated. The microscopically The study the magnetite magnetite in in these these iron iron crystallinity, external formations not only varies formations not only varies in in grain grain size, size, crystallinity, external morphology, morphology, inclusion composition, composition,distribution, distribution,and and genetic genetic relationships inclusion relationships to its coexisting minerals but also also significantly significantlydiffers differsinininternal internalmicrostructures. microstructures. The minerals but The last variable was found to to be was found be the the most most useful useful key key to to the theinterpretation interpretation of of the thegeochemical geochemical processes of of the the magnetite formation. processes formation. These These internal internal microstructures microstructures are are normally normally not microscopically visible unless unless aa laboratory-induced oxidtion precedure not microscopically visible laboratory-induced oxidation precedure is employed. The sections were were heated heated at at about about 300 3000 C for three to employed. The well-polished well-polished sections to four four days and then then cooled days under under weakly weakly to moderately moderately oxidizing oxidizing conditions conditions and cooled to room room temperature for for reexamination. reexamination. The The most most important important internal microstructures microstructures in in by the the artificially produced this study, as outlined by produced hematite are are listed listedas asfollows: follows: 1. Lath-like, Lath-like, bladed, bladed, wedge-shaped, wedge-shaped, rhombhedral, rhombhedral, and and hexagonal hexagonal crystals crystals arranged or subparallel, arranged randomly, randomly, or subparallel, or in in such such forms forms resembling resembling druses druses and and inner inner linings of geodes crystals, clusters, geodes within within individual individual crystals, clusters, granules, granules, and and laminae laminae of of linings of magnetite. Irregular bodies Irregular bodies resembling resembling spheroids spheroids uniformly uniformly scattered throughout throughout granules, of magnetite. granules, clusters, and laminae laminae of 2. 3. Botryoidal Botryoidal structures structures in in clusters, clusters, laminae, laminae, and and granules granules of magnetite. magnetite. Zonal and and core-and-shell concentric structures structures in 4. Zonal core-and-shell concentric in individual individual magnetite crystals with of the the preexisting preexisting lath-like crystals. with or or without without inclusions inclusions of All of of the ore mentioned All the af afore mentioned internal microstructures microstructures have have been been found found in the the magnetite (b) hematite hematite and and chert, chert, (c) (c) carbonates carbonates and and magnetite coexisting coexisting with: with: (a) (a) chert, chert, (b) chert, chert, (d) (d) silicates and chert, and and (e) carbonates, silicates, and and chert. chert. The outlines of crystals, irregular bodies, and botryoidal masses masses are are apparently of of restored apparently restored preexisting preexisting hematite hematite which which was was probably probably deposited deposited as Fe(OH)3 gel. The Fe(OH)3 gel. The later later magnetite magnetitewas wasdeveloped developedby: by:(a) (a) nucleation nucleation followed followed by by one or several stages replacement of of hematite or stages of of enlargement, enlargement, and and (b) (b) pseudomorphic pseudomorphic replacement supplemented by by extensive overgrowth. overgrowth. Based onthe the ratio ratio of: of: (a) (a)the the size sizeofofthe the existing existingmagnetite magnetite crystals crystals to to that of Based on their initial nuclei, and and (b) (b) the the amount amountofof magnetite magnetitetoto that that of of the their initial magnetite magnetite nuclei, restored preexisting preexisting hematite, hematite, the thefollowing following conclusion conclusion is is drawn: drawn: The The migration migration of of in conjunction with the the redepositoin of iron iron as conjunction with redepositoin of as magnetite magnetite on on nuclei nuclei of of iron in magnetite or or preexisting magnetite preexisting hematite is is aa much much more more important important magnetite magnetite forming forming process than the simple process than simple reduction reduction of of hematite or or the the metamorphic metamorphic oxidation oxidation of the primary ferrous ferrous minerals like siderite and minerals like and greenalite. The The presence presence of of preexisting preexisting hematite hematite in in the the magnetite magnetite laminae, laminae, clusters, and and 28 �granules of the silicate granules of silicate and and carbonate carbonate iron iron formations formations indicates indicates that that some some iron iron formations normallyreferred referred to to as "silicate", fades formations normally "silicate", "carbonate", "carbonate", and and "mixed" "mixed" facies might fades prior might have have been been oxide oxide facies prior to topost-depositional post-depositional alterations alterations - silication, matter isis believed magnetitization, magnetitization, carbonatization, carbonatization, etc. Carbonaceous Carbonaceous matter believed to be be responsible for the facies change. responsible for change. On On the basis basis of the the results results of of these theseiron ironformation formationstudies, studies,one onecould could conclude conclude that the the magnetite magnetiteininthe thelow-grade low-grademetamorphic metamorphic Precambrian Precambrian iron iron formations formations of of the Lake elsewhere may may well well have have the the same same ancestry. Lake Superior Superior type found found elsewhere 29 �RARE RARE EARTH EARTHELEMENT ELEMENT STUDIES STUDIES OF OF THE THE ARCHEAN ARCHEANGNEISSES GNEISSES OF OFTHE THEMINNESOTA MINNESOTARIVER RIVERVALLEY VALLEY G.N. G.N. Hanson, Hanson, Department Department of of Earth Earth and and Space Space Sciences, Sciences, State State University University of ofNew New York, York and and 5.5. S.S. Goldich, Goldich, Department Department of Geology, Geology, Northern Northern York, Stoney Stoney Brook, Brook, New New York Illinois University, University, DeKaib, DeKalb, Illinois. Illinois. illinois ABSTRACT ABSTRACT Rare earth earth elements elements (REE) (REE) have have been been analyzed analyzed on on tonalitic tonalitic to to granodioritic granodioritic units units of of the the up up toto3800 3800m.y. m.y.old oldMorton Mortonand andMontevideo Montevideo gneisses, gneisses, mafic mafic and and ultramafic units units within within the the gneisses, gneisses, and and later later granitic granitic intrusions. intrusions. The Thesubparallel subparallel REE patterns along with similarities similarities inin other other geochemical geochemicaldata data suggest suggest that that the REE patterns along with upper upper amphibolite amphibolite to granulite granulite grade grade gneisses gneisses and and later granitic granitic intrusions intrusions have have aa similar origin resulting resulting from from partial partial melting of maf Ic quartz quartz diorite similar origin melting of mafic diorite or diorite diorite crust. sources, perhaps in the crust. Significantly Significantly different REE REE patterns for for K-rich K-rich pegmatoidal pegmatoidal veins veins and and zones zones containing hornblende within within the nebulitic containing porphyroblastic porphyroblastic hornblende nebulitic Morton Morton Gneiss Gneiss suggest suggest that tha t under under conditions conditions of recrystallization recrystallization and and major major element element mobilization, mobilization, the the REE REE mobilized on may have been mobilized on dimensions dimensions of of many many centimeters. centimeters. A relatively flat REE A relatively REE pattern for for aa tholeiitic tholeiiticamphibolite amphibolite is is similar, similar, although although slightly more more enriched enriched in in REE, REE, to to the 2700 m.y. old old Archean Archean basalts basalts in in aa greenstone slightly 2700 m.y. Hornblende belt in northeastern northeastern Minnesota Minnesota (Arth (Arth and and Hanson, Hanson, 1975). 1975). Hornblende rich, rich, komatiitic amphibolites have havepatterns patterns with with about about 30 30 times times chondrites komatiitic amphibolites chondrites for for Ce Ce and and about 8 times chondrites for Yb. This would suggest that if the REE have not been chondrites for Yb. This would suggest that if the REE have not been affected by the source (the mantle?) for this this rock affected by recrystallization, recrystallization, the source (the mantle?) for rock type type also also is is REE enriched. light REE 30 30 I �w Rb-Sr GEOCHRONOLOGY OF OF THE THEMONTEVIDEO MONTEVIDEO GNEISS, GNEISS, MINNESOTA MINNESOTA RIVER RIVER VALLEY VALLEY C.E. Denver, Colorado Colorado 80225 80225 and and S.S. 5.5. Goldich, Goldich, C.E. Hedge, Hedge, U.S. U.S. Geological Geological Survey, Survey, Denver, Northern illinois Illinois University, University, DeKaIb, DeKalb, illinois Illinois 60115 60 115 ABSTRACT Gneiss of of Lund Lund (1956) (1956)isis aa hybrid hybrid rock rock consisting consisting of biotitebiotiteMontevideo Gneiss The Montevideo quartz-feldspar gneissic, and granitic granitic phases phases of of different ages. gneissic, amphibolitic, amphibolitic, and ages. The biotite gneiss, gneiss, the the oldest oldest major majorphase, phase,was wasprobably probably derived derived from from volcanic volcanic material material of andesitic andesitic to to rhyodacitic rhyodacitic compositon compositon and and is is 3700 3700 ++ 100 100 m.y. m.y. old. old. Amphibolite Amphibolite clasts in represent basaltic basaltic lavas lavas or or dikes diks that in the gneiss gneiss may may represent thatwere were broken broken up. up. At approximately 3000 m.y. m.y. ago, ago, granitic granitic magma was intruded intruded in in the form of approximately 3000 magma was small irregular masses, masses, sheets, sheets, and and lit-par-lit lit-par-lit injections. small irregular injections. The The Rb-Sr Rb-Sr systematics systematics in in the at this the older older gneiss gneiss were were disturbed disturbed at this time. time. Failure Failure to recognized recognized the age age difference between the older foliated gneiss and the younger more massive difference between the older foliated gneiss and the younger more massive leucogranitic of the leucogranitic phase phase invalidates invalidates the earlier earlier geochronologic geochronologic investigations investigations of the Montevideo Gneiss. to lower metamorphism (upper (upper amphibolite amphibolite to lower granulite granulite facies) facies) High-grade metamorphism High-grade affected phase as as well well as as the the older but we we are are not certain affected the massive massive phase older gneiss, gneiss, but certain whether this occurred occurred shortly shortlyafter after emplacement emplacementofofthe theleucogranite leucogranite(N( 3000 m.y. whether this ago) or during the interval from ago) or during the from 3000 3000 to 2600 2600 m.y. ago. A 2600-m.y. 2600-m.y. event event isis represented represented in in the the emplacement of large granitic masses masses exposed inin the the Minnesota Minnesota River River Valley Valleysoutheast southeast and and northwest northwest of of the Montevideoexposed Montevideointensive cataclasis cataclasis affected the Granite Falls Granite Falls area. Locally Locally intensive therocks rocks approximately approximately These events events also also affected affected the the Rb-Sr in the older 2400 m.y. ago. These Rb-Sr systematics systematics in older 2400 m.y. ago. rocks. Small masses of of adamellite adamellite and numerous diabasic dikes dikes were were intruded intruded in in the Small masses numerous diabasic Montevideo Gneiss1850 1850m.y. m.y.ago, ago,and andlocally locallythese these intrusions intrusions affected affected the Montevideo Gneiss the Rb-Sr Rb-Sr system in the older older rocks. rocks. 31 31 I �I THE TRACE TRACE ELEMENT ELEMENT GEOCHEMISTRY GEOCHEMISTRY OF PEAT PEAT BOGS BOGS OVER OVER DIFFERENT BEDROCK BEDROCK TYPES, TYPES, SOUTHERN SOUTHERN HOUGHTON HOUGHTON COUNTY, COUNTY, MICHIGAN MICHIGAN Department of Jacobsen, Department of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan Sue I.I. :Jacobsen, Sue Technological University, University, Houghton, Houghton, Michigan Michigan 49931 49931 ABSTRACT A investigation of of the feasibility preliminary investigation feasibility of of using using peat peat iningeochemical geochemical A preliminary prospecting was carried carried out using prospecting in in the Upper Upper Peninsula Peninsula of Michigan Michigan was using twelve peat peat to determine bogs bogs in in southern southern Houghton Houghton County. County. The The bogs bogs were were sampled sampled to determine if if difference type isis reflected in difference in in bedrock bedrock type in the the trace trace element element geochemistry geochemistry of the the peat layers layers above above them. them. The The bogs bogs were were selected selected to to provide provide as asmany many bedrock bedrock varieties varieties as as possible: possible: Portage Portage Lake Lake Lava Lava Series, Series, Copper Copper Harbor Harbor Conglomerate, Conglomerate, Nonesuch Shale, Freda Sandstone, and Nonesuch Shale, and 3acobsville Jacobsville Sandstone. Sandstone. Samples were weretaken taken at at sites 100 Samples 100 ft. apart along along at least least one one line line run run through through both the Davis each bog. bog. As As both Davis and and the Hiller Hiller peat peat samplers samplers proved proved inadequate, inadequate, a simple sampler was simple aluminum aluminum piston—type piston-type sampler was used. used. Peat samples samples 15 15 inches inches long long at depth intervals of depth intervals of 3 3 feet feet were were taken, taken,asaswell wellasassamples samplesofofthe theliving livingSphagnum Sphagnum moss mat and mineral material material where where possible. possible. Peat and the underlying underlying mineral Peat was was identified identified moss mat in the field field as as to to type type and and degree degree of of humification. humification. Maximum Maximum peat peat depth depth differed differed from to bog bog and and ranged rangedfrom from33feet feet to to 30 from bog bog to 30 feet. The pH was was0determined thelaboratory laboratoryand andranged ranged om 3.1 3.1toto 6.0. 6.0. After The pH determined ininthe from oven dryingatat 85 850 CC for ashedat at 500 5000 C oven drying for 24 24 hours, hours, the peat was was ashed C for for 22 hours. hours. Trace Trace the Atomic element concentrations are being being determined determined using using the Atomic Absorption Absorption Spectrometer. As peat profiles profiles are are not As element element distributions distributions inin peat not uniform, uniform, a study study of the the vertical distribution of trace elements vertical distribution of elements is is being being made. made. Spatial Spatial distributions distributions of of elemental concentrations concentrations and and pH pH are also also being being investigated. investigated. 32 I �ENGADINE ENGADINE DOLOSTONE OF MICHIGAN'S MICHIGAN'S EASTERN UPPER UPPER PENINSULA: PENINSULA: GEOLOGY GEOLOGY AND AND RESOURCE RESOURCEEVALUATION EVALUATION Allan M. M. 3ohnson,Institute Johnson,Institute of of Mineral MineralResearch, Research, Michigan Michigan Technological Technological University, University, Allan Houghton, and Harry Houghton, Michigan Michigan 49931 49931 and Harry 0.O.Sorenson, Sorenson,Michigan Michigan Geological Geological Survey Survey Division, Division, Department of of Natural NaturalResources, Resources,Stevens StevensT.T.Mason MasonBuilding, Building,Lansing, Lansing, Michigan 48926 48926 Michigan ABSTRACT ABSTRACT Results Results of of geologic geologic mapping mapping and and core-drilling core-drilling of of the theMiddle MiddleSilurian SilurianEngadine Engadine The work is part of a continuing cooperative project dolostone are reported. The work is part of a continuing cooperative project dolostone reported. between Geological Survey Surveyand andthe the Institute Institute of Mineral between the the Michigan Michigan Geological Mineral Research Research to evaluate limestone resources resourcesofof the the State. evalua te high-purity high-purity limestone State. Preliminary Preliminary results results of of similar work on the Fiborn limestone were reported last year at this similar work on the Fiborn limestone were reported last year this Institute Institute (Johnson and and Sorensen, Sorensen, 1975). 1975). (Johnson The Engadinedolostone dolostoneisisexposed exposedasasaa resistant resistant cuesta for massive Engadine for more more The massive 100 miles along along the northern northern margin margin of of the theMichigan Michigan Basin Basin from Manistique Manistique to to than 100 Drummond Island. Despite Drummond Island. Despite a thickness of only 200 200 feet the the shallow shallow regional regional dip dip of of 50 50 feet/mile south south allows allows the unit unit to to form form aa belt beltfrom from 55to to10 10 miles miles wide wide along along the the northern shores shores of of Lakes Lakes Michigan Michigan and and Huron. Huron. northern Three Three steel steel companies companies quarry quarry grade stone stone from from the the Engadine. Engadine. metallurgical grade Previously unpublished field work by by G.M. G.M. Ehlers, University of Michigan, Michigan, and and unpublished field establishe the following for the H.O. Sorenson, Sorenson, M.G.S., M.G.S., establishe following stratigraphic subdivisions subdivisions for H.O. Engadine dolostone: Engadine Name Descriotion Description . Thickness Bush Bush Bay Bay dolostone -massive, It. gray with cream -massive, mottling, med. med. to coarsely mottling, crystalline, porous porous 50' Swede Swede Road Road dolostone -massive (weathers (weathers thin), buff-massive brown, brown, finedly finedly crystalline crystalline 33' Prentiss Prentiss Creek dolostone -thinly bedded, bedded, gray to brown, brown, chert layers, med. crystalline chert 26' 26' Rapson Rapson Creek Creek dolostone dolostone -massive, It. It. gray-buff gray-buff with with -massive, lighter mottling, med-coarsely lighter crystalline, porous crystalline, porous 60' 60' Rockview Rockview dolostone dolostone -massive, gray, gray, med-coarsely med-coarsely -massive, crystalline, stromatolitic stromatolitic crystalline, at at base base TOTAL TOTAL 44' 44' 2flT 2TY 33 33 - ---~------------------- �These were established established from from field field mapping in the eastern These divisions divisions were mapping in eastern portion portion of of the Engadine. Examination of 16 cores drilled during 1975 spanning 100 miles of the the Engadine. Examination of 16 cores drilled during 1975 spanning Engadine, support these these stratigraphic subdivisions in the eastern Engadine, support subdivisions in eastern portion. portion. Cores Cores However, if the the western westernportion portionshow show some some inconsistencies. inconsistencies. However, the Engadine Engadine is is from the interpreted interpreted to to have have formed formed as as aareef reefororcarbonate carbonatebank bankalong alongaashelf shelfmargin marginwhere where minor minor onlap-offlap onlap-offlap fluctuations fluctuations occurred, occurred, these these inconsistencies inconsistencies can can be be resolved. resolved. Features Features of of the the Engadine Engadine dolostone dolostone supporting supporting this this origin origin include include its its massive, massive, porous porous structure, complete complete dolomitization, dolomitization, fossil fossil assemblage, assemblage, and and its position position in in relation to to other other shelf shelf formations formations and and to tothe theMichigan Michigan Basin. Basin. Core logs be employed employed to to evaluate evaluate the potential logs and and chemical analyses will will be potential of of Engadine as aa high high purity purity dolostone. dolostone. Results Results are are scheduled scheduled for for publication publication by by the Engadine the Michigan Survey inin 1977. Michigan Geological Geological Survey 1977. This This year year similar similar work work will will begin begin on on Traverse group in the the northern part of group limestones limestones (Devonian) (Devonian) in of the theLower LowerPeninsula Peninsula Michigan. of Michigan. REFERENCES Ehlers, and Kesling, R.V. Silurian rocks rocks of of the the Northern Kesling, R. V. 1957, 1957, Silurian Northern Peninsula Peninsula of Ehlers, G.M., G.M., and Michigan, Mich. Basin Basin Geol. Geol. Soc., 63 p. Michigan, Guidebook Guidebook Mich. Ehiers, G.M., 1973, 1973, Stratigraphy Stratigraphy of of the the Niagaran Niagaran Series Series of the the Northern Northern Peninsula Peninsula Ehlers, G.M., of Michigan, Univ. of Mich. Papers on Paleontology, no. 3, 200 Michigan, Univ. of Mich. Papers on 200 p. 3ohnson, A.M., and and Sorensen, Sorensen, H.O., H.O., 1975, 1975, Michigan Michigan Upper Peninsula Peninsula Middle Middle Silurian Johnson, A.M., Limestones: Geology Geologyand and Resource Resource Potential, Potential, (abs.), Limestones: (abs.), 21st 21st Annual Annual Inst. Lake Superior Geology, 16-17. Lake Superior Geology, p. 16-17. 34 34 on I �• NATURE NATURE OF OF THE THEQUETICO-WABIGOON QUETICO-W ABIGOON BOUNDARY BOUNDARY IN IN THE THE dE dE COURCEY-SMILEY COURCEY-SMILEY LAKES LAKES AREA, AREA, NORTHWESTERN NORTHWESTERN ONTARIO ONTARIO M. Kehienbeck, Kehlenbeck, Department Department of of Geology, Geology, Lakehead Lakehead University, University, Thunder Thunder Manfred Manf red M. Ontario Bay, Ontario Bay, ABSTRACT ABSTRACT In area, the boundary In the de de Courcy-Smiley Courcy-Smiley Lakes Lakes area, boundary between between the Quetico Quetico and and \Vabigoon Beltsisisexpressed expressedbybya asequence sequenceofof pelitic pelitic to semi-pelitic Wabigoon Belts semi-pelitic schists schists and and gneisses. At At the the present present level level of oferosion, erosion, these these metasedimentary metasedimentary rocks rocks are are in in gneisses. contact contact with with granodioritic granodioriticgneisses, gneisses, granites, granites,and and pegmatites, pegmatites,which which are areexposed exposed to to the south. south. the To To the north of of this this area, area,regional regional metamorphism metamorphism of of volcanic volcanic and and sedimentary sedimentary rocks rocks has has resulted resulted in in greenschist greenschist facies facies assemblages assemblages which which characterized characterized the Wabigoon Belt In the boundary boundary zone the metamorphic metamorphic grade grade increases increases Wabigoon Belt in in general. In de Courcey Courcey and and Smiley Smiley Lakes. Lakes. southward toward de Formation of of three distinct Formation distinct foliation foliation surfaces surfaces was was accompanied accompanied by by synsyntectonic as well well asaspost-tectonic post-tectonicrecrystallization recrystallizationproducing producingpolymetamorphic polymetamorphic tectonic as schists. In the boundary In boundary zone, zone, mineral assemblages comprising comprising andalusite, sillimanite, cordierite, garnet, biotite, biotite, and form aa facies fades series cordierite, garnet, and muscovite muscovite form series of of the theAbukumaAbukumatype. The boundary between Quetico Quetico and and Wabigoon WabigoonBelts Beltsinin this this area area is a complex The boundary between complex zone belts have have been been reconstituted reconstituted by bymultiple-phase multiple-phase zone in in which which rocks rocks of of both both belts metamorphism and melting. metamorphism and partial melting. 35 35 �J THE THE CENTRAL CENTRALWISCONSIN WISCONSIN BATHOLITH BATHOLITH Gene L. L. LaBerge, LaBerge, Geology Geology Department, Department,University UniversityofofWisconsin-Oshkosh, Wisconsin-Oshkosh, Oshkosh, Oshkosh, Wisconsin 54901 54901 and and Paul Paul E. E. Myers, Myers, Geology Geology Department,Washington Department,Washington State State Wisconsin University, Pullman, Pullman,Washington Washington University, ABSTRACT ABSTRACT 1500 square miles miles in in Marathon Marathon County, County,Wisconsin, Wisconsin, Geological mapping of over 1500 Geological has has revealed revealed an an extensive extensive complex complex of of volcanic volcanic and and possible possible co-genetic co-genetic intrusive intrusive The volcanic volcanic rocks, as as pendants pendants and and xenoliths, xenoliths, are aresurrounded surrounded by by granitic granitic rocks. The intrusions showing an inward inwarddecrease decrease inin the the volume volume of of contaminant contaminant material. material. The showing an The volcanic "pendants" generally generally decrease decrease in in size and volcanic "pendants" and relative relativeabundance abundance westward westward across County, thus thus suggesting suggestingexposure exposureofofthe the eastern eastern portion portion of of a across Marathon Marathon County, convex batholith roof with its apex extending approximately along the west edge convex roof with its apex extending approximately along the west edge of of county. The The batholith batholith comprises comprises at least least twenty twenty separate separatestock-like stock-likeplutons, plutons, the county. which has has its own own contaminated contaminated margin. Mafic quartz diorites and and quartz each of which margin. Mafic monzonites grade inward inward to to a more monzonites grade more granitic core. core. The The younger younger plutons plutons are more more felsic. Gravity and Gravity and aeromagnetic aeromagnetic maps maps and and geological geological reconnaissance reconnaissance suggests suggests that Marathon County and and most most of of central are underlain Marathon County central Wisconsin Wisconsin are underlain by by granitic granitic rocks rocks containing scattered volcanic containing scattered volcanic roof roof pendants. We We suggest that that this this plutonic plutonic complex complex the "Central "Central Wisconsin Wisconsin batholith." be called the Aeromagnetic and geologic geologic mapping mappingshow showthat thatseveral several major majorstructural structural trends Aeromagnetic and intersect within within Marathon Marathon County. County. These These structural structural trends trends coincide coincide with with zones zones of intense cataclasis which intense which occurred before, before, during during and and after batholith batholith emplacement. emplacement. Most of of the six to date terminate Most six northeast-trending northeast-trending cataclastic cataclastic zones zones mapped mapped to terminate against or merge merge with with aa major major northwest-trending northwest-trending zone zone which which crosses crosses the the the cataclastic cataclastic zones locally acted acted as southwestern county. Although Although the zones locally as southwestern part part of of the county. conduits for for magmas, conduits magmas, most most of the the plutons plutons show show features features of of pervasive pervasive shearing, shearing, suggesting Available isotopic suggesting aa long long period period of of intrusion intrusionalternating alternating with withcataclasis. cataclasis. Available ages indicate the the batholith batholith was was formed formed during duringMiddle Middle Precambrian (Penokean?) (Penokean?) ages indicate time. 36 U �ORIGIN ORIGIN OF OF LAMINAE LAMINAE IN IN PRECAMBRIAN PRECAMBRIAN IRON-FORMATION IRON-FORMATION M.S. Lougheed Lougheed and and 3.1 J.J. Mancuso, Mancuso, Department Department of of Geology, Geology, Bowling Bowling Green Green M.S. University, Green, Ohio Ohio 43403 43403 University, Bowling Bowling Green, ABSTRACT ABSTRACT The original original particulate particulate constituents constituents of of Precambrian Precambrian iron-formation iron-formation are are The biogenic-carbonate minerals, opaline opalinesilica silica tests tests and biogenic-carbonate minerals, and organic organic material. material. These These constituents control control Eh Eh and and pH pH of of contiguous contiguous water water which which is is replenished replenished from an an open open sea source. source. Important Importantsecondary secondaryminerals, minerals, which which include include ferroan ferroan carbonates, carbonates, iron oxides, oxides, iron silicates, chalcedony-quartz, chalcedony-quartz, and and pyrite, pyrite, are are produced produced in in response response to environmental environmental factors factors affecting affectingthe theoriginal originalconstituents, constituents,and andwe wehave havediscussed discussed genesis over over the past past several several years years at at these these meetings. meetings. Typically, in in banded banded their genesis iron-formation, the thickness and lateral lateral extent of iron-formation, the thickness and of the the bands bands or or laminations laminations are are determined by the the presence determined by presence of of opaline opaline slurry slurry or gel. gel. An An exception occurs occurs when when grains of secondary carbonate constitute the bedload grains of secondary carbonate bedload during during current transport and and then deposited deposited as as thin thin laminae laminae of of nearly nearly pure pure carbonate, carbonate, (ex. (ex.Empire Empire mine, mine, are then however, laminae laminae are deposited Negaunee-siderite facies.). Most Most commonly, commonly, however, deposited from from Negaunee-siderite a bedload composed primarily of biogenic opaline gel or slurry which functions bedload composed primarily of biogenic opaline gel which functions as a medium iron-formation. medium of of support support for for any any combination combination of of the the other other constituents of iron-formation. Siliceous laminae, which whichmay maybe be more more than than one Siliceous laminae, one centimeter thick, thick, often often contain contain components such components such as flakes flakes and and shreds shreds of of algal algalhash, hash,which which commonly commonly show show evidence of having by laminar of having been been transported transported by laminar or or turbulent turbulent current current flow. flow. Commonly undulating bedded algal algal mats mats are inundated undulating bedded inundated by by an opaline opaline slurry mix mix to produce produce an an anoxic conducive to to the anoxic environment environment conducive the production production of of pre-greenalite pre-greenalite(greenaloid) (greenaloid) which the precursor precursor of of greenalite. greenalite. Beds Beds of of this this nature, nature, as as well well as as beds beds principally principally which isis the composed of greenalite granules, composed of granules, upon upon dewatering dewatering and and concomitant concomitant compression, compression, produce thin undulating laminae, notably notably in in "slaty" "slaty" facies, but produce thin undulating laminae, but when when oxidized oxidized they commonlyoccurs occurs in in chert produce iron-oxide iron-oxide chert laminae. laminae. Graded Graded bedding bedding commonly produce laminae containing particulate particulate material such laminae containing such as as granules. granules. The Thesuspended suspended load load was was apparently coming to to rest, rest, apparently transported in aa tenuous tenuous silica slurry slurry or gel, gel, which which upon upon coming is at at least allowed the load load to to gravitationally allowed the gravitationally settle into aa graded graded profile. profile. There There is least one case in one in which which chalcedonic chalcedonic laminae laminae were formed formed by by gravity gravity accumulation accumulation of siliceous tests tests of planktonic planktonic organisms. organisms. Normally Normally the tests tests would would be be comminuted comminuted siliceous to a slurry during bedloadtransport transport by bywater water currents. currents. These during bedload These few few genetic genetic examples examples of laminae in iron-formation, emphasize the complexities involved when we use the of iron-formation, emphasize the complexities involved when "banded iron-formation." term "banded 37 37 �• PENOKEAN PENOKEAN STRUCTURES AND AND PLUTONIC PLUTONIC ROCKS ROCKS IN IN PORTAGE PORT AGE AND AND WOOD WOOD COUNTIES, COUNTIES,WISCONSIN WISCONSIN Jr., Department R.S. Maass Maass and and L.G. L.G. Medaris, Medaris, Jr., Department of of Geology Geology and and Geophysics, Geophysics, R.S. University University of of Wisconsin, Wisconsin, Madison, Madison, 53706 53706 and W.R. W.R. Van Van Schmus, Schmus, Department Department of of Geology, University of Kansas, Kansas, Lawrence, Lawrence, 66044 66044 Geology, ABSTRACT ABSTRACT Three Three exposures exposures of Precambrian Precambrian rocks rocks along along the theWisconsin Wisconsin River River (Stevens (Stevens Point, Point, Conants Conants Rapids, Rapids, and and Biron Biron Dam) Dam) have been investigated in in order order to to establish establish the relative units and and to to characterize the relative and and absolute absolute ages ages of lithologic lithologic units the geometry geometry and age of folding. and age of folding. Relative Rela tive ages ages of of the the lithologic lithologic units units from from oldest oldest totoyoungest youngest are: are:banded banded quartzo-feldspathic quartzo-feldspathic gneiss gneiss and and amphibolite amphibolite (the (the Basal Basal Group Group of ofWeidman, Weidman, 1907); 1907); medium-grained tonalite; aa series series of fine-grained medium-grained tonalite; fine-grained tonalite dikes, dikes, less mafic mafic with with decreasing age of of intrusion; intrusion; maIic mafic dikes; dikes; and and diabase. diabase. All All these rock rock types types except except diabase have have been been recrystallized recrystallized under under middle middle grades grades of ofmetamorphism. metamorphism. for diabase Quartzo-feldspathic gneiss and and tonalites Quartzo-feldspathic gneiss tonalites contain contain quartz, quartz, microcline, microcline, plagioclase plagioclase (oligoclase to andesine), biotite, hornblende, epidote, sphene, sphene, and and opaques; opaques; amphibolite amphibolite and mafic mafic dikes dikes contain contain hornblende, hornblende, plagioclase plagioclase (andesirie (andesine to labradolabradoite and rite), and and sphene sphene +=blot biotite and epidote. rite), An early An early deformation deformation produced produced isoclinal isoclinal folds, folds, F1 F 1 ,' and a a penetrative penetrative foliation, SS,l' inin the is parallel to to compositoinal foliation, thebanded banded gneiss. gneiss. S S1 is parallel compositoinalbanding, banding, S0, SO' except in fold fold hinges, where So S0isistransected transected by by St' S1. A later deformation except hinges, where deformation produced producea broad open folds, folds, F2' F2, in the at aa high broad open the gneiss, gneiss, with with axial axial surTaces surfaces at high angle angle to to Sl' The gneiss contains a pronounced mineral lineation, L1, parallel to F1 and F2 fold F1 foW axes. gneiss contains pronounced mineral lineation, L l' The Ic dikes, dikes, although although intrusive intrusive mto into the gneiss The tonalites and and maf mafic gneiss and and discordant, at at least in least in part, part, to tostructures structuresininthe thegneiss, gneiss,contain containmineral mineral lineations lineations which which are parallel steeply to the parallel to the the linear linear elements elements in in the thegneiss, gneiss, plunging plunging steeply the southeast. southeast. In addition, S1 is medium-grained tonalite. is present in the medium-grained A A U-Pb U-Pb age of of 1900 1900 m.y. m.y. from from zircons zircons in in the themedium-grained medium-grained torialite tonalite (Van (Van Schmus, et et al, al, 1975) indicates that intrusion 1975) indicates intrusion and and deformation deformation occurred during during the Schmus, Penokean Orogeny. Orogeny. Although the banded gneiss may may be be Archean Archean inin age, age, itit was Penokean Although the banded gneiss was reworked during duringthe the Penokean PenokeanOrogeny, Orogeny,and andthe the predominant predominantstructures structures inin itit were worked produced produced during duringthat that event. REFERENCES REFERENCES Weidman, S., S., 1907, 1907, The The geology geologyofofnorth north central central Wisconsin, Bull. No. No. 16, 16, Wis. Wis. Geol. Geol. Weidman, Wisconsin, Bull. Na tural History Survey. Survey. Natural 1975, Geology Geology and and Rb-Sr Van Schmus, W.R., W.R., et Rb-Sr chronology chronology of Middle et al., aL., 1975, Van Schmus, Precambrian rocks Precambrian rocks in eastern eastern and and central centralWisconsin: Wisconsin: Geol. Geol. Soc. Soc. Am. Am. Bull. Bull. 86, 86, 1255-1265. 1255- 1265. 38 38 �GEOPHYSICAL PROSPECTING PROSPECTING OFF OFFKEWEENAW KEWEENAW PENINSULA PENINSULA Robert Robert P. P. Meyer, Meyer, 3. J. Robert Robert Moore, Moore, Edgardo Edgardo L. L. Nebrija Nebrija and and Charles Charles T. T.Young, Young, Department and Polar Department of of Geology Geology & &. Geophysics, Geophysics, Geophysical Geophysical and Polar Research Research Center, Center, University of of Wisconsin, Wisconsin, Madison Madison 53706 53706 University ABSTRACT With SeaGrant Grant sponsorship, sponsorship, we we have With NOAA-Wisconsin NOAA-Wisconsin Sea have been been conducting conducting experiments using using towed resistivity resistivity and andactive-source active-sourceaudiomagnetotelluric audiomagnetotelluric(AMT) (AMT) measurements measurements and and magnetic magnetic and and high-resolution high-resolution seismic seismic profiling profiling to explore explore for for copper copper deposits deposits offshore offshore of Keweenaw Keweenaw Peninsula. Peninsula. Among Among the areas areas studied studied were were Copper Copper Harbor Harbor and and Silver Silver Island Island where where there there are areknown known underwater underwater copper copper veins, veins, Great Sand Sand Bay Bay where where offshore offshore extensions extensions of of onshore onshore copper-bearing copper-bearing fissures fissures may may exist, Five-Mile Points where where we we searched searched for for a chalcocite deposit Five-Mile and and Seven-Mile Seven-Mile Points deposit within and Bete Bete Grise where aa potential placer Nonesuch Shale, Shale, and Grise Bay Bay where placer deposit deposit within the Nonesuch may exist. may Surface- and bottom-towed bottom-towed arrays arrays were were both both used used in in resistivity resistivityprofiling. profiling. In In 1975, AM AMT tests were were started started using 1975, T tests using a 150 150 m diameter circular circular loop loop of of wire wire laid laid on on the lake lake bottom bottom and and excited excited by by aa 400 400 Hz Hz AC AC generator generator as source. source. With With the the ship's ship's position regulated by by electronic electronic navigation, concentric arcs arcs were traversed about position regulated navigation, concentric about the loop the loop to to measure measure the the vertical vertical magnetic magnetic field, field, radial radial magnetic magnetic field, field, and and Both methods yielded distinct and reproducible anomalies field. Both methods yielded and reproducible anomalies tangential electric field. in apparent apparent resistivity resistivity and and E/H E/H ratios ratiosover overknown known copper copper veins veins at at Copper Copper Harbor Harbor A zone and anomalies over over expected expected lithologic lithologic contacts. zone of heavyheavyand correlatable anomalies mineral concentrations inside with towed towed resistivity mineral inside Great Great Sand Sand Bay Bay was was discovered discovered with The apparent and verified verified with with AMT. AMT. The apparent resistivity resistivity correlates inversely inversely with with the the and A heavy-mineral of the sands. sands. A probably probably underwater underwater vein vein was was also also heavy-mineral content content of At discovered in in this area. At Five-Mile Five-Mile and and Seven-Mile Seven-Mile Points, Points, the the offshore offshore discovered extensions of of the Nonesuch Shale were were mapped mapped and and structures structures favorable favorable to copper extensions Nonesuch Shale copper Both methods methods are are strongly delineated. Both strongly affected affected by by topography. topography. deposition deposition were were delineated. For For resistivity profiling, profiling, aa first-order first-order correction correctionfor fortopography topography has has been been developed developed and applied. High-resolution seismic seismic and and magnetic magnetic profiling profiling at at Bete Grise Bay Bay delineated a High-resolution basin off the Montreal Montreal River River characterized characterized from from grab grabsamples samples by byanomalous anomalous basin off the concentrations of of trace trace metals that decrease concentrations decrease outward outward from from the center of of the filled filled Within this this area area we also delineated offshore manifestation manifestation of of the basin. Within we also delineated aa logical logical offshore Keweenaw Fault. Fault. Whether Keweenaw Whether the anomalies anomalies represent the lake lake bottom bottom expression expression of a deeper hydrothermal deposit, a placer deeper placer deposit deposit formed formed during during lower lake levels from results from materials delivered by the Montreal Montreal River, or results from more more current current by the enrichment of of surficial sediments enrichment sediments is is not not presently presently known, known, and and this this question question awaits awaits the opportunity for physical sampling at at depth. depth. the opportunity for physical sampling 39 39 �DIAMOND DRILLING IN ENVIRONMENTALLY DIAMOND ENVIRONMENTALLY SENSITIVE SENSITIVE AREAS AREAS — ENVIRONMENTAL IMPACT: MONITORING MONITORING AND AND ASSESSMENT ASSESSMENT M.G. Mudrey, Jr., Wisconsin Geological and Natural Geological and Natural History Survey, 1815 University Avenue, Avenue, Madison, Madison, Wisconsin Wisconsin53706, 53706,Bruce BruceC.C. Parker, Parker, Department of University of Biology, Virginia Virginia Polytechnic Polytechnic Institute Institute and State Biology, State University, University, Blacksburg, Blacksburg, Virginia Virginia 24601, Keros State Geological Cartwright, Illinois Illinois State Geological Survey, Survey, Natural Natural Resources Resources 24601, Keros Cartwright, Building, Urbana, Urbana, Illinois Illinois 61801, 61801, and and Lyle Lyle D. Building, D. McGinnis, McGinnis, Department of of Geology, Geology, Northern illinois Illinois University, DeKaib, DeKalb, illinois Illinois 60115 60115 ABSTRACT A drilling program program can can be sophisticated exploratory exploratory diamond diamond drilling be mounted mounted to to A sophisticated moderate modera te depths, depths, and and environmental environmental disturbance disturbance minimized minimized in aa conscientious conscientious program involving impact impact assessment, assessment, training, training, and and real-time feedback program involving feedback among among all parties. Although not normally Although not normally the case case with with exploratory exploratory drilling, drilling, environmental environmental disturbance can occur occur in in sensitive sensitive areas areassuch suchas aswilderness wilderness areas, areas,public public park park lands, lands, and delicate, delicate, unique regions,such suchasasthe the polar polar regions. regions. One One factor, factor, of course, and unique regions, course, is the public public fear fear that thatthe theproposed proposedexploratory exploratorydrilling drilling program program might might irreversibly irreversibly disturb environmental conditions in areas noted for their recreational and disturb environmental conditions in areas noted for their recreational and scientific value. AA secondary value. secondary fear fear isis that thatexploitable exploitable natural natural resources resources will will be be found, found, and and that that they they will will be be developed developed causing major major impact to the the local local environment. environment. It is is important important to to recognize recognize that that the theconcept concept of of no no impact impact is is an an unrealizeable unrealizeable The objective objective of of all human goal. The human all impact impact statements statements is is to to minimize minimize or or reduce reduce potential adverse adverse impacts impacts to to the theenvironment, environment, whenever whenever and and as as far far as aspossible possible and and practical. We propose to to address address only only the the design design and and implementation implementation of of an an environmentWe propose ally exploratory drilling drilling program programinin aa sensitive sensitive area, area, the ally responsible responsible exploratory the dry dry valley valley From lanuary region of of Antarctica. region Antarctica. From January 1973 1973 until until December December 1975, 1975, aa comprehensive comprehensive diamond drilling drilling program program inin antarctic antarctic permafrost diamond permafrost and and under under severe severe environmental environmental Dry Valley Drilling Project restraints — restraints - the Dry Project— - was carred on. on. A A total total of of 13 13 months months of resulted inin the the recovery of over meters of of core of drilling drilling resulted recovery of over 2100 2100 meters core at 15 15 sites. sites. Although scientific scientific in in objectives, the Although the international, international, multidisciplinary multidisciplinary program, program, and and analysis are are applicable applicable to resource-oriented drilling its techniques techniques of of environmental environmental analysis drilling programs in other other areas programs in areas of of environmental environmental and and public public concern, concern, such such as as the the scenic scenic vistas of the Lake Lake Superior Superior region. The evaluation, after after identification of of the target of environmental environmental evaluation, target The first stage of sites, was was the the preparation preparation of of an anenvironmental environmental assessment, assessment, in in which which the theproposed proposed engineering operations plans, environmental impacts impacts were engineering operations plans, and and possible possible environmental were identified. These were were addressed addressed by by an an impact impact matrix which These which identified identified all projected projected actions extent, and Probability, areal extent, environment. and and all characteristics of the environment. significance were were assessed assessed atat this significance this time time by by an an impact impact committee committee consisting consisting of of environmentalists, project engineers, environmentalists, engineers, and and other other knowlegeable knowlegeable scientists. Potential environmental impacts impacts were were identified, identified, and environmental and revision revision of proposed proposed operations operations were made without without undue hardshiptoto the the environment environment or or to to the the drilling drilling contractor, contractor, in as made undue hardship much as no no operations operations had had yet yet started. started. much as Subsequently,appropriate appropriate documents documentswere weresubmitted submittedfor for review review to to governSubsequently, governQuestions raised raised were were addressed mental bodies. bodies. Questions addressed by by the environmental environmental committee. Pertinent documents Pertinent documents directly directly addressed addressed the proposed proposed program, program, and and the the language language Technical details details were were appended. appended. An was directed directed to the the general general public. public. Technical An effort was was made to to make make the the main was made main text of of the the document document readable readable and and concise. 40 �I In In the case case of of DVDP, DVDP, the antarctic antarctic soil soil and and lake lake ecosystems ecosystems are are particularly particularly delicate, and and consequently consequently vulnerable vulnerable to any any human human activity. activity. An An environmental environmental of each scientist scientist on on the the drill site, and and prior prior environmental environmental discussion discussion of each site by by scientists scientists and and drill drill team teampersonnel personnel comprised comprised the thebasis basis for forthe theDVDP DVDP environmental environmental An protection program. program. An operations operations procedure procedure and and monitoring monitoring scheme scheme was was implemented to detect implemented to detect and and control control environmental environmental impact. impact. Monitoring Monitoring before, before, during, during, and after after the thedrilling drillingoperations operationsidentified identifiedenvironmental environmentalchanges changescaused causedby by the activities at all all sites, sites, and and those those results results were were reported reported to to enhance enhance the accuracy accuracy of the the predictive predictive model, model, the Environmental Environmental Impact Impact Appraisal. Appraisal. One One objective was was to to prevent prevent or reduce reduce impacts impacts by by DVDP, DVDP, and and thus thus assist assist planning planning for any any future future projects in Antarctica. projects in Antarctica. For DVDP, critical environmental DVDP, critical environmental limitations included included no no surface transport, transport, minimal crew size, size, few few drilling options with with respect to minimal crew drilling options to equipment equipment and and circulating circulating fluids, fluids, an absolute absolute requirement requirement that that all all waste waste and and equipment equipment be be removed removed from from the be in site areas, areas, and and that that an aninteractive interactiveenvironmental environmental monitoring monitoring program program be in operation. constant operation. 41 �SYENITE OF CENTRAL THE WAUSAU WAUSAU SYENITE CENTRAL WISCONSIN WISCONSIN Myers, Paul Department of ofGeology, Geology, Washington Washington State State University, University, Pullman, Pullman, Myers, Paul E., E., Department Washington 99163 99163 ABSTRACT The Wausau syenite-quartzsyenite syenite pluton pluton inin two two segments and the more The Wausau syenite-quartz segments and more alkalic Stettin Stettin syenite syenite pluton pluton are areexposed exposed west westof ofthe theWisconsin Wisconsin River River near near Wausau Wausau in central These Middle plutons are in central Wisconsin. Wisconsin. These Middle Precambrian Precambrian (1650 (1650 ÷ + 50 50 m.y.) plutons concentrically zoned zoned and and show concentrically show a distinct distinct north-northeasterly north-northeasterly elongation. elongation. Each pluton has has a contact pluton contact metamorphic metamorphic zone zone of of fenitized fenitized wall wall rocks, rocks, an an alkalic, alkalic, laminated, xenolith-rich laminated, xenolith-rich wall wall zone, zone, an an intermediate intermediate zone, zone, and and a core. core. Silica content increases increases inward inward in each pluton. pluton. The southern southern segment segment of of the Wausau pluton isis circular circular in plan with a diameter Wausau pluton diameter The of eight miles. half of of this this caldera-like caldera-like structure were of miles. Although Although the core core and and south half were intruded the Ninemile preserved as as a intruded by by granite granite of the Ninemile pluton, pluton, its structure is preserved discontinuousring ringofoflarge largexenoliths xenolithsfive fivemiles milesinindiameter. diameter. The discontinuous The largest of of these these over two miles in the xenoliths xenoliths -- the Rib Mountain Mountain quartzite quartzite — - is over miles long. long. Bedding Bedding in The top top of xenolith dips very very steeply toward the the granite xenolith dips steeply southward southward toward granite core. core. The of the the xenolith has has been eroded xenolith eroded leaving leaving aa keel-shaped keel-shaped mass, mass, slightly slightly convex convex northward, northward, and surrounded at depth depth by by quartz quartz syenite and surrounded at syenite of the the crescentic crescentic intermediate intermediate zone. zone. Quartzite xenoliths xenoliths near near intrusive intrusive contacts contacts are aretypically typicallyveined veinedand and impregnated impregnated by by Pyroxene and amphibole syenite commonly containing volcanic K-feldspar. Pyroxene and amphibole syenite commonly containing volcanic xenoliths, form form a discontinuous outer rim rim (wall zone) of of the southern segment. discontinuous outer (wall zone) xenoliths, The northern northern segment segment of of the Wausau is semicircular The Wausau pluton pluton is semicircular in in plan plan with with its truncated southern southern edge edge along along the Rib Rib River. River. The TheStettin Stettinpluton plutonisiscontiguous contiguous with with it on internal structure are similar on the northwest. northwest. Although Although its size and and internal similar to that that of of the southern southern segment, segment, its intermediate intermediate zone zone consists consists of coarse coarse gray gray syenite, syenite, and and volcanic xenoliths xenoliths predominate. predominate. The probably represents represents aa The older older northern segment segment probably volcanic caldera caldera structure, structure, which which was was partially partially destroyed destroyed by by intrusion intrusion of of the the southern southern segment. The Stettin pluton The pluton is is oval oval in in plan plan with with dimensions dimensions of of 5.0 5.0 x 3.5 miles. Three major in mapping were: (1) major zones zones distinguished distinguished in mapping were: (1) a wall wall zone zone comprising comprising aplitic aplitic biotite syenite, an intermediate syenite, nepheline nepheline syenite syenite gneiss, gneiss, and "tabular syenite", (2) (2) an zone, zone, aplitic aplitic to to pegmatitic pegmatitic amphibole amphibole and and pyroxene pyroxene syenite syenite with with swirled swirled flow flow lineation, and and (3) (3) a circular circular core zone zone one one mile mile in in diameter diameter comprising comprising aa rim rim of of magnetite-rich nepheline-hedenbergite-fayalite nepheline-hedenbergite-fayaiite syenite,andandananinner inner core core of magnetite-rich syenite, pyroxene syenite. Both Both the Wausau Wausau and and Stettin Stettin plutons plutons possess possess strongly strongly metasomatized, metasomatized, but but Concentric cataclastic unassimilated xenolith-rich xenolith-rich wall unassimilated wall zones. zones. Concentric catac1astic lamination lamination was was developed by displacements accompanying accompanying the the forceful emplacement of developed by high-angle high-angle displacements of these plutons. plutons. Subsequently, Subsequently, more more passive passive intrusion intrusion of of the the Ninemile Ninemile granite granite caused caused a partial partial foundering foundering of the the southern southern part part of of the theWausau Wausau pluton. pluton. 42 �MODIFICATION MODIFICATION OF ENGINEERING ENGINEERING PROPERTIES OF ST. ST. PETER PETER SANDSTONE SANDSTONE C.R. C.R. Nelson Nelson and and D.H. D.H. Yardley, Yardley, Department Department of of Civil Civil and andMineral MineralEngineering, Engineering, University University of of Minnesota, Minnesota,Minneapolis, Minneapolis, Minnesota Minnesota55455 55455 ABSTRACT ABSTRACT The Peter sandstone sandstone is is aa formation formation of of major major geotechnical geotechnical importance importance in in The St. Peter the Twin Twin City Metropolitan Metropolitan area area as as well well as as elsewhere elsewherein inMinnesota Minnesota and and some some nearby nearby states. Nearly Nearly 200 200 miles miles of of tunnels tunnels and and other other openings openings have have already already been been constructed in it in in the the Metro Metro area. The The St. Peter Peter is is aa rather rathermassive, massive,weakly weakly cemented, cemented, very very pure pure sandstone sandstone of of 98.5% 98.5% - 99% 99% SiO2. Si0 2 • The compressive strength strength varies varies between between 670 670 and and 2800 2800 psi psi in in The compressive harder zones, zones, but but in In softer softer zones zones ititcommonly commonly varies varies from from less less than than100 100to to300 300psi, psi, hence some openings openings inin itit will hence while while some will support support themselves themselves most most need need some some type of of support. Because Because most most of of its strength strength is is aa result result of of compaction compaction and and grain grain is water-sensitive to the the degree that if water interlocking, interlocking, it is water-sensitive to degree that water agitates agitates the the grains grains St. Peter has much of the sandstone will deteriorate deteriorate r':!Jidly. raidly. The much of sandstone will The St. has aa porosity porosity of of per second. about 28% 28% and and a permeability permeability of 3.5 3.5 xx 10 10 cm cm per second. The The grains grains are quite quite about rounded, have aa frosted frosted surface and rounded, have and a diameter diameter of of 0.1 0.1 mm mm to to 0.5 0.5 mm. mm. A spray-grouting technique has has been been developed by the senior author, spray-grouting technique developed by author, using using a silicate-based liquid liquid that that can permeate for a few silicate-based permeate into into exposed exposed sandstone sandstone for few inches. inches. This forms aa hardened of sandstone with aa compressive strength on on the order This forms hardened shell shell of sandstone with compressive strength of 1500 psi in in the the soft zones. Test of 1500 psi Test patches patchesin inplace placefor for 33years yearsshow show no no evidence evidence of deterioration. This system of artificially for rehabilitaThis system artificially stengthening stengthening sandstone sandstone is being used used for It is also being used as the main excavation support tion tunnels. is also being used the main excavation support on on aa 10 10 tion of utility tunnels. foot tunnel where itit has the use at a foot tunnel where has replaced replaced the use of of steel steel rings rings and and oak oak lagging lagging at substantial cost reduction. substantial reduction. Elimination Eliminationof ofsteel steeland andwood wood support support makes makes itit possible possible to pour so that when to pour aa final final concrete concrete lining lining directly directly against against the sandstone sandstone so when the tunnel is is pressurized the resistance tunnel pressurized the resistance of of the the coupled coupled sandstone sandstone wall wall will will so so greatly decrease lining lining deformation deformation that that steel reinforcing decrease reinforcing is is not not required. required. Spray-hardening Spray-hardening also makes makesitit possible possiblefor forthe the first first time to the also time to apply apply shotcrete shotcrete to the St. St. Peter Peter sandstone in in this this area. sandstone It has has been estimated that that the thecost costsavings savings on on one one large large tunnel, tunnel, and and for for one one utility utility tunnel tunnel repair project, project, both both in in progress, progress, will will be be about about 1.3 1.3 million million dollars. dollars. Support funds funds of of less than from the NSF, program have have led led to the Support than $100,000 $100,000 from NSF, RANN RANN program the development. 43 �ANATOMY ANATOMY OF A WELL-COVERED WELL-COVERED GREENSTONE BELT, BELT, NORTHWESTERN MINNESOTA MINNESOTA Richard W. W. Ojakangas, University of Minnesota, Minnesota, Duluth, Duluth, Duluth, Duluth, Minnesota Minnesota55812 55812 ABSTRACT The rocks of of the Birchdale-Indus Birchdale-Indus area are part part of of aapoorly-exposed poorly-exposed volcanicvolcanicThe rocks sedimentary sequence sedimentary sequence within within the the Wabigoon Wabigoon Volcanic Volcanic Belt. Belt. The bedrock is Early Early The bedrock Precambrian in in age, age, and includes mafic mafic to intermediate Precambrian and includes intermediate flows flows and and intrusives; felsic dikes, dikes, agglomerates, agglomerates, tuffs and and volcaniclastic volcaniclastic rocks; rocks; iron-formation iron-formation and and associated associated metasediments; and granitic granitic rocks of Algoman age. All of these lithologies are cut metasediments; and rocks of Algoman age. All of lithologies are by by northwest-trending Middle Middle Precambrian mafic mafic dikes. dikes. The The area is is well-covered well-covered by by Pleistocene deposits. deposits. The volcanic-sedimentary sequence has has been been isoclinally folded; northeastThe volcanic-sedimentary sequence isoclinally folded; trending beddingand and foliations foliations are are generally generally steep steep to to vertical. trending bedding vertical. One One doublydoubly- plunging anticline and and one one syncline syncline have have been been mapped mappedwithin withinthe thearea. area. AA second plunging anticline second folding with with more folding more northerly-trending northerly-trending fold fold axes is is indicated indicated by by some some general general and and detailed relationships. sets of faults relationships. Three Three sets faults and and fractrures fractrures are aredocumented; documented; the the first set set trends trends east-west, east-west, the the second second northwest, northwest, and and the third third northeast. northeast. All of the Lower Lower Precambrian rocks rocks have have been been metamorphosed metamorphosed to amphibolite amphibolite grade. grade. Synthesis ofof the the geology of the Birchdale-Indus area with with that that of the Synthesis geology of Birchdale-Indus area the Emo Emo area in allows an an interpretation of in adjacent adjacent Ontario Ontario (Fletcher (Fletcher arid and Irvine, Irvine, 1954) 1954) allows of the the Mafic and and intermediate volcanic development of the volcanic development of volcanic accumulation. accumulation. Mafic volcanic and and intrusive rocks apparently apparently constitute constitute the lowest intrusive rocks lowest stratigraphic stratigraphic unit. unit. An An explosive felsic volcanic volcanic center, center, marked marked by by abundant abundant agglomerates, developed developed upon upon the mafic platform and Emo. Emo. Felsic tuffs, volcaniclastics, platform in the the vicinity vicinity of of Birchdale, Birchdale, Indus Indus and volcaniclastics, and iron-formation iron-formation were were deposited deposited outward outward from from this this center. center. and The Birchdale-Indus Birchdale-Indusarea, area, and and areas areas to to the west and The and south, have been actively explored for for base base metal for the past explored metal sulfide sulfide deposits deposits for past decade. decade. Thick Thick zones zones of of massive, sub-massive, sub-massive, and and dissemianted dissemianted pyrite and/or pyrrhotite have have been been penetrated at at several several localities, localities,but butcopper copperand andzinc zincminerals minerals have have not not been been found found Several of the drilled iron-sulfide bodies are associated in economic economic quantities. quantities. Several of drilled iron-sulfide bodies associated in with oxide iron-formation. REFERENCES CITED CITED Fletcher, Fletcher, G.L., G.L., and and Irvine, Irvine, T.N., T.N., 1954, 1954, Geology Geology of the Emo Emo area: area: Ontario OntarioDivision Division of of Mines 63rd annual annual report, report, V. V. LXIII, LXIII, part part5,5,3636p.p.plus plusmap mapNo. No.1954—2, 1954-2, scale scale 11 Mines 63rd inch to 11 mile. inch 44 �CARBON IN METAMORPHOSED SEDIMENTS CARBON SEDIMENTS FROM ISUA, ISUA, WEST GREENLAND WEST GREENLAND FROM Eugene C. C. Perry, Perry, 3r. Jr. and and Syed Syed Neaz Neaz Ahmad, Ahmad, Department Department of of Geology, Geology, Northern Northern Eugene illinois University, DeKaib, Illinois DeKalb, illinois Illinois 60115 60115 ABSTRACT ABSTRACT 0/00 ~. aphitic carbon carbon (S13 (6'3C vs. PDB) About 2.5% §aphitic C == -16.1 0100 PDB)occurs occurs in in aa specimen from the the 3.7 10 year year old at Isua, Greenland. The from 3.7 x 10 old supracrustal supracrustal sequence sequence at Isua, West West Greenland. The specimen, which whichcontains containsquartz, quartz,amphibole, amphibole,and andminor minormagnetite magnetiteand and pyrite, pyrite, is specimen, is associated with with a thick associated thick succession succession of of metamorphosed metamorphosed chert and and magnetite-bearing magnetite-bearing iron-formationand andwithin within2.4 2.4km kmacross acrossstrike strikeofof aa thick thick quartz-magnetite iron-formation quartz-magnetite unit unit containing sufficient sufficient iron iron to to be commercial significance. significance. Rocks in the the containing be of possible possible commercial Rocks in area have been metamorphosed to amphibolite facies and area metamorphosed to amphibolite facies and are sufficiently sufficiently sheared sheared so that that primary textures are are obliterated. so primary textures Carbonaceous organic organic matter matter is a common Carbonaceous common constituent of of iron-formation, iron-formation, and and it has has been suggested that the iron oxide of iron-formation been suggested that the iron oxide of iron-formation is aa biogeneic biogeneic facies ironprecipitate. Thus, Thus, the theassociation association of of carbonaceous carbonaceous material material with with oxide oxide facies for mationatat Isua Isua isis consistent with an gganic formation consistent with larganicorigin origin for1 for; this ancient ancient carbon. carbon. However, the the Isua Isua carbon carbon is However, is enriched enriched in in jc about 15 15 0/00 0 00 compared compared to C by about to later Precambrain material material of of known knownbiogneic biogneicorigin. origin. Since Since metamo~phism metamophism accompanied Precambrain accompanied /oo carbon reactions could by isotope-fractionating reactions could produce carbon isotope isotope produce a 15 0/00 fractionation, the stratigraphic fractionation, stratigraphic association association of of this this carbon carbon with with iron-formation iron-formation may may to its origin than is its present be a more reliable guide guide to present isotopic isotopic composition. composition. 45 45 I t �OLD PRECAMBRIAN W GNEISSES GNEISSES IN IN NORTHERN MICHIGAN OLD Zell E. ZeU E. Peterman, Peterman, Robert Robert E. E. Zartman, Zartman, and andP.K. P.K.Sims, Sims,U.S. U.S.Geolgoical Geolgoical Survey, Survey, Denver, Colorado Colorado 80225 80225 ABSTRACT dating of of gneisses in the western Radiometric dating gneisses in western part part of of northern northern Michigan Michigan has confirmedthe the presence presenceofof an an ancient ancient sialic sialic terrane terrane that formed confirmed formed more more than than 3400 3400 m.y. ago. An antiformal antiformal structure structure in in the the Watersmeet area contains contains aa core core of m.y. ago. An Watersmeet area of tonalitic to to granitic surrounded by by folded tonalitic granitic gneiss gneiss that that is surrounded folded and and metamorphsed metamorphsed Precambrian X graywackes. graywackes. The is cataclasitcal!y cataclasitcally deformed and recrystalPrecambrian X The gneiss gneiss is deformed and lized, and and geochronologic geochronologicdata datareflect reflectthe the effects effects of of severe tectonic and lized, and thermal thermal events. Whole-rock Whole-rock Rb-Sr Rb-Sr systems systems are are highly highly disturbed, disturbed, but but data datafor forsamples samplesfrom from two localities localitiesdefine definesecondary secondary isochrons of aut 00 m.y. two isochrons of 19ut m.y. AAsubstantially substantially older older age of the Sr/ Sr age the gneiss gneiss is is indicated indicated by by high high initial Sri 0.773 to 0.717 0.717 for Sr ratios of 0.773 These high high i~7ial int7ial ratios ratios resulted resulted from from local the two two isochrons. isochrons. These local redistribution redistribution of previously generated radiogenic Sr during the major previously radiogenic Sr during the major period period of of cataclasis cataclasis and and Metamorphismofof adjacent adjacent Precambrian X rocks recrystallization. Metamorphism Precambrian X rocks occurred occurred synchronouslywith withthe the reactivation and mobilization of the gneiss synchronously mobilization of gneiss as suggested suggested by 1810 m.y. m.y. isochron obtained on on four an 1810 isochron obtained four whole-rock whole-rock samples samples of graywacke of graywacke immediately adjacent adjacent to to the gneiss along the the northern northern contact. contact. immediately gneiss along U-Pb data obtained on zircon from the gneisses also reflect reflect the U-Pb data obtained on zircon separated separated from gneisses also complexgeology geologyhistory historybut butclearly clearlyplace placethe the time time of of primary crystallization at complex primary crystallization 90 rn~~b agoago or more. Three size fractions ofofzircon ~890 or more. Three size fractions zirconfrom froma atonalititc tonalititcgneiss gneiss have have Pb ages ages ranging ranging from from 3310 to 3370 m.y. and Pb/ Pb 3310 to 3370 m.y. and a primary primary age age of of about about 3500 3500 m.y. is is suggested. suggested. Zircon Zircon from from aa compositionally compositionally similar ~~t mU<i~&;10r20tj;or~ly m.y. defogpd aj recrystallized phase Pb! Pb! U, U, def02~d ~ recrystallized phaseofofthe thegneiss gneissyields yields Ph/ Pb/ Pb ages that are Pb/ Pb ages are concordant concordant at at 1760 1760 m.y. This This lower lower age age agrees agrees with with and Pb! Rb-Srages ages and andapparently apparently indicates indicates total total resetting or the whole-rock whole-rock Rb-Sr or perhaps perhaps even even crystallization of the zircon during this metamorphic episode. Data for two zircon crystallization of zircon during this metamorphic episode. Data two fractions from aa leucocratic phase of of the the gneiss gneiss plot plot on on aa chord fractions from leucocratic phase chord that intersects intersects concordia at about data may indicate the the presence concordia about 2600 2600 m.y. m.y. These These data may indicate presence of granitic granitic intrusions that were intrusions that were emplaced emplaced in in the the older oldergneisses gneisses during during the theAlgoman Algoman orogeny. orogeny. About 2710 m.y.—old About 20 20 km km northwest northwest of of the thegneiss gneissatatWatersmeet, Watersmeet,thethe 2710 m.y.-old Puritan Puritan Quartz Monzonite and Precambrian Quartz Monzonite and Precambrian W W metavolcanic metavolcanic and and metasedimentary metasedimentary rocks rocks form aa greenstone-granite form greenstone-granite terrane that that evolved evolved in an ensimatic ensimatic environment. environment. The The presence of Algoman granitic rocks rocksininthe the older older gneiss gneiss terrane terrane may presence of Algoman granitic may indicate indicate that that both blocks blocks were in juxtaposition juxtaposition at at 2600 2600 to to 2700 2700 m.y. m.y. ago ago and and subsequently formed a continuous continuous and and coherent coherent sialic sialic basement basement to the the Precambrian Precambrian XX sedimentary sedimentary basins. tgOO 46 U �APPROACH TO A SYSTEMS SYSTEMS APPROACH TO ENVIRONMENTAL ENVIRONMENTAL GEOLOGY H.O. of Geology Geology and and Geophysics, Geophysics, University University of of Minnesota, Minnesota, H.O. Pfannkuch, Pfannkuch, Department of Minneapolis, Minnesota 55455 55455 ABSTRACT term "environmental geology" has has been been loosely loosely applied applied to to situations The term "environmental geology" situations ranging from pure problems to to those ranging from pure engineering engineering problems those of of traditional traditional general general geology. geology. The concept concept needs needs clarification clarification and and definition in order order to to provide the reference The definition in provide the reference space in in which solutionsfor for the the most most pressing pressing problems problemscan canbebeattempted. attempted. This space which solutions This is attempted attempted by by aa systems systems approach approach where where the the three three interacting interactingprincipal principalcomponents components are human on aa global human ecology, ecology, geology geology on global scale, and and clutural clutural anthroplogy anthroplogy from from aa socio-economic point of view. socio-economic The based on approach is based on an an The approach analogy argument, argument, that is that human analogy human ecosystems behave inin a similar ecosystems behave similar way way as as other otherecosystems. ecosystems. This This means means that ecosystem concepts concepts such ecosystem such as structure, structure, process process dynamics dynamics and and evolutionary evolutionary trends trends from to mature, from young young and and unstable unstable but highly highly productive productive to mature, complex complex and and stable stable systems can can be used systems used as parallels. The Theinterface interfacewith withgeology geologyisisprovided provided by by global global material cycles and energy flow processes. processes. The impact of material energy flow The impact of interaction is is measured measured in a first order simple mass mass change changeto to total total mass, in order approximation approximation by by simple mass, and and rate change change It has to geologic geologic rate relationships. relationships. It has to be refined to include include effects of of additivity additivity and accumulation, and those those of of stability and accumulation, and stability of of feedback feedback relations. relations. In In the the latter latter category fall the the triggering triggering effects effectsofofpossibly possiblysmall small temperature temperaturechanges changeson on world world Limitations of geological nature can be climatic changes. be expressed expressed by consumption or or use use rates, such as in resources where rate of consumption of formation formation is is compared compared to rate to rate of of consumption consumption or or with with the the carrying carrying capacity capacity of of the the earth earthwhere where loading loading or regeneration rates. rates are are compared compared to dissipation dissipation or In In the socio-economic socio-economic context, environmental environmental geology geology has two two contributions contributions to make. help make environmentally to make. On On a short short term term basis basis itithas hasto to help make environmentallysound sound compromisesthat that can can be be achieved achieved within within the the present present structure of time time and and space space compromises references in in the the decision decision making making process. process. This, This, however, however, is only only a temporary temporary and and transitional solution, solution, in in the end will have have to to provide transitional end environmental environmental geology geology will provide the the basis on on which new and and consistent consistent time time and basis which new and space scales will will have to be be developed developed for environmentally environmentally acceptable acceptable decision decision making making processes. processes. 47 I �ENVIRONMENTAL IMPLICATIONS IMPLICATIONS OF OF GROUNDW GROUNDWATER-LAKE ENVIRONMENTAL ATER-LAKE LAND USE USE APPLICATION INTERACTION WITH WITH LAND Dave Pollack Dave Pollack and and H.O. H.O. Pfannkuch, Pfannkuch, Department Department of ofGeology Geology and andGeophysics, Geophysics, University of Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota Minnesota 55455 55455 ABSTRACT Many lakes, if not Many the majority, majority, have have to be viewed viewed as of and and an an not the to be as part part of expression of of local local and and regional groundwater flow flow systems. systems. Lake expression regional groundwater Lake level level variations variations are therefore are therefore strongly strongly related related to to watertable watertable fluctuations, fluctuations, especially especially in in lakes lakes Current methods without surface water inlets or outlets. Current methods of of establishing general lake lake water groundwater contribution to the general water balance balance only only give give net net contributions which whichare are insufficient insufficient to to calculate contributions calculate residence residence times of of chemical chemical or or biological inputs. An An areal areal flow biological flow net net method method is is discussed discussed to to calculate calculate absolute absolute amounts of of groundwater inflow and and outflow outflow and and its its spatial amounts groundwater inflow spatial relationships relationships with the the lake. Analysis of aa cross cross section section through through aa lake lake and and its its aquifer shows Analysis of shows that even with a fully lake bed of streamlines streamlines near fully permeable permeable and and uniform uniform lake bed there will will be crowding crowding of the shore, the shore, which which means means relatively relatively higher higher flow flow velocities velocities of of groundwater groundwater and and enhanced transport transport activity in enhanced in this this region. region. Analog Analogand and dimensional dimensional analysis analysis of some some very simple simple cases cases are carried very carried out out to to demonstrate demonstrate the thedependence dependence on on lake-aquifer lake-aquifer geometry and and toto define define the the critical critical parameters. geometry parameters. These These are are thickness thickness of of the the lakelakeaquifer, degree of depth penetration of the lake, and ratio of the aquifer flow aquifer, degree of depth penetration of the lake, and ratio of the aquifer flow section is given given by bythe the lake lake diameter. diameter. Further section to the the lake-aquifer lake-aquifer interface which which is Further increase of of flux large portions of the lake increase flux near near shore shore occurs occurs when when large portions of lake bottom bottom are are sealed by by impermeable sediments. sediments. The The direct environmental environmental implications implications are two two fold: fold: First First it is is necessary necessary to have a clear picture outflow ininorder ordertoto relate relate it to picture of of true true groundwater groundwater inflow inflow and and outflow the into the the total total lake lake budget, budget, this this provides provides insight insight into the relative relative importance importance of of groundwater groundwater carried pollution. pollution. Localization Localization and with high high and identification identification of areas with groundwater flow activity in groundwater flow in the thenear-shore near-shoreregion regionhave haveobvious obvious application application to to land land use planning and regulation regulation such such as as the the implacement of domestic sewage disposal planning and disposal or treatment facilities. The severity treatment facilities. The severity of impact impact depends depends on on length length of of flowpaths, flowpaths, residence time time of of pollutants, or regeneration capacity of of the residence pollutants, and and adsorption adsorption or regeneration capacity hydrogeologic Guidelines are are given given to to classify hydrogeologic unit. unit. Guidelines classify lakes lakes on on a semi-quantitative semi-quantitative basis to the expected basis according according to expected volume volume contribution of the the active activeflow flow region region near near shore. 48 �PETROLOGY AND AND STRUCTURE STRUCTURE OF THE LATE PETROLOGY LATE PRECAMBRIAN PRECAMBRIAN SILVER CREEK CREEK CLIFF AND LAFAYETTE BLUFF BLUFF MAFIC MAFIC SILVER INTRUSIONS, LAKE LAKE COUNTY, MINNESOTA INTRUSIONS, MINNESOTA Neil M. M. Pope, Pope, Department Department of of Geology, Geology, University University of of Minnesota, Minnesota, Duluth, Duluth, Duluth, Duluth, Neil Minnesota, 55801 55801 ABSTRACT Approximately4-1/2 4-1/2 Miles Miles northeast northeast of Two Approximately Two Harbors, Harbors, Minnesota, Minnesota, the North North Shore Volcanic VolcanicGroup Groupisisintruded intrudedby bythe the Silver Silver Creek Creek Cliff Cliff sill sill which which trends trends northnorthShore northeast from Cliff for for 66 miles. northeast from Silver Silver Cliff miles. The The Lafayette Lafayette Bluff Bluff sill, sill, approximately approximately 61/2 miles northeast of 1/2 of Two Two Harbors, Harbors, intrudes intrudes the theNorth NorthShore ShoreVolcanic VolcanicGroup Group and and trends north toward the Silver Silver Creek Cliff sill. sill. The Silver Silver Creek Creek Cliff sill The sill is is dominantly dominantly olivine olivine diabase diabase with thin layers layers and and lenses of of olivine-free diabase. lenses diabase. Commonly Commonly aa plagioclase plagioclase - augite pegmatitic pegmatitic facies borders the lenses lenses or or an an entire entire lens be pegmatitic. pegmatitic. The borders the lens may may be The Silver Silver Creek Creek Cliff Cliff sill sill is is approximately approximately 200 200 feet thick thick and and is is conformable conformable with with the the lava lava flows flows throughout throughout most of of its its extent. In In the Encampment Riverarea area the the contact contact of of the sill is steep most Encampment River and crosscuts the flows. This area may represent the feeder zone and crosscuts the flows. This zone for the the sill. sill. The The Lafayette Bluff Bluff sill sill isis an anamygdaloidal amygdaloidal porphyritic porphyritic olivine olivine diabase diabase with with plagioclase phenocrysts which which average average 22 cm plagioclase phenocrysts cm in in length. length. The The sill is is approximately approximately 600 600 feet thick thick and and isisdeformed deformedinto intoa south-plunging a south-plunging syncline syncline and and anticline. anticline. Subsidence of the the underlying flows into into the magma Subsidence of underlying flows magma chamber chamber is is proposed proposed for the the origin of of this deformation. The mineral mineral compositions compositionsof of the the sills sills are similar. The The The olivine olivine diabase diabase of each sill sill normally normally consists consists of an an average average of of66% 66% plagioclase, plagioclase, 12% 12% olivine, olivine, 16% 16% augite, 2% Ca-poor pyroxenes, pyroxenes, 2% 2% altered altered interstitial interstitial material, 2% Ca-poor material,2% 2%opaques opaques (ilmenite (ilmenite and and magnetite), magnetite), and and trace amounts amounts of apatite and and aa interstitial interstitialgranophyric granophyric intergrowth of quartz and alkali feldspar. Field evidence does does not not support support any any definite definite structural relation Field evidence relation between between the the sills. The The Lafayette LafayetteBluff Bluff sill sill isis poorly poorly exposed exposed where it appraches appraches the the Silver Silver Creek Creek Cliff contact between them. AA Cliff sill, and and there there are are no no outcrops outcrops which which show show any any contact between them. whole rock analysis analysis (by (by 5.5. S.S. Goldich, Goldich, 1939) 1939)ofofthe the diabase diabase from from the the Lafayette Lafayette Bluff Bluff whole rock 4.7% MgO. MgO. An An average of of sill shows 46.9%Si0 SiO2, 21.0%A1Al2O, 8.8%total total Fe, and 4.7% sill shows 46.9% , 21.0% 0 , 8.8% 2 2 3 three new new whole whole rock rock analyses analyses of' of the the Silver Silver Creek CreekCliff Cliffolivine olivinediabase diabase shows shows 47.8% Si02, AL,03, 11.2% total Fe, and 6.5% MgO. The Fe/Mg is 1.73 for 0 , 11.2% total Fe, and 6.5% MgO. The FelMg 1.73 47.8% Si0 , 17.5% 17.5% A1 2 3 2 the Silver Silver Creek Creek Clift Clift sill SIll olivine olivine diabase diabase and and 1.86 1.86 for for the the Lafayette Lafayette Bluff Bluit sill sill olivine diabase. Both Both sills sills contain contain normative normative hypersthene. hypersthene. The The olivine diabase diabase olivine diabase. from the Silver indicating the diabase is Silver Creek Creek Cliff Cliff sill sill has has 7.1% 7.1 % normative normative olivine indicating an olivine of the Lafayette olivine tholeiite. tholeiite. The The diabase diabase of Lafayette Bluff Bluff sill sill has has 0.2% 0.2% normative normative quartz the diabase diabase isis on on the border or of quartz suggesting suggesting the border of of oversaturation oversaturation or of being being a quartz tholeitte, tholeitte, despite despite the themodal modal olivine. olivine. 49 �CORRELATIVE IRON-FORMATIONS IRON-FORMATIONS AND AND VOLCANIC VOLCANIC ROCKS ROCKS CORRELATIVE OF PRECAMBRIAN X AGE, AGE, NORTHERN NORTHERN MICHIGAN MICHIGANj J OF PRECAMBRIAN X C. Prinz, William C. Prinz, U.S. U.S. Geological Geological Survey, Survey, National National Center Center -— Stop Stop 954, Reston, Virginia 22092 ABSTRACT The Ironwood, Ironwood, Vulcan, Vulcan,and and Neguanee NeguaneeIron-formations Iron-formations have have long long been been accepted accepted The as correlative. They, along slate and as correlative. They, along with with immediately immediately underlying underlying slate and quartzite quartzite (Palms, Felch, Feich, Siamo, and Ajibik), are sandwiched sandwiched between between shallow-water shallow-water quartzite quartzite (Palms, Siamo, and Ajibik), are and dolomite and dolomite below, below, except where where locally locally absent absent because because of of erosion erosionor ornondeposinondeposition, and tion, and eugeosynclinal eugeosynclinal graywacke graywacke and and slate slate above above (Michigamme, (Michigamme, Copps, Copps, and and Volcanicrocks rocksofof the the Hemlock Formation in in Iron Tyler). Volcanic Hemlock Formation Iron County, County, the Emperor Emperor Volcanic Complex Complexofofthe the eastern eastern Gogebic Gogebic range, range, and and possibly possibly the the volcanic volcanic rocks rocks at Volcanic Blair Lake near Watersmeet also occupy this stratigraphic interval. Except for the the Blair Lake near Watersmeet also occupy this stratigraphic interval. Except for eastern end eastern end of the the Gogebic Gogebic range, the distribution distribution of the the iron-formations iron-formations and and the the volcanic units units is mutually volcanic mutually exclusive. exclusive. Volcanic Iron Volcanicunits unitsare are centrally centrally situated situated in Iron and eastern eastern Gogebic Gogebic Counties, Counties,whereas whereasthe theiron-formations iron-formationsare aretoto the the east east in the the and Marquette and and Menominee Menomineedistricts districts and andtoto the the northwest northwest in in the the Gogebic Gogebic range. range. The Marquette The ironformationsare are relativley relativley thin compared ironformations compared with with the the highly highly variable variable and and locally locally great thicknesses of the volcanic volcanic units. Volcanic rocks of of the Volcanic rocks the Emperor Emperor Volcanic Volcanic Complex Complex are interbedded interbedded with with and and overlie the upper in the the eastern Gogebic upper part part of of the theIronwood Ironwood Iron-formation Iron-formation in Gogebic range, and tuff tuff beds and beds are present in in the the lower lower part part of of the theIronwood Ironwood in the main main part of of the the and the Ironwood range. Thus, Thus, the Emperor Emperor Volcanic Volcanic Complex Complex and Ironwood Iron-formation are, are, at least at least in in part, part,equivalent equivalent in in time. time.Hemlock Hemlockvolcanics, volcanics, on on the the other other hand, hand, have have been been thought thought to be be younger younger than than the the iron-formations. iron-formations. This This isis based based on on correlation correlation of ferruginous conglomerate conglomerate beneath Hemlock with Goodrich Quartzite, Quartzite, of ferruginous beneath the the Hemlock with the Goodrich which suggest here here that that this conglomerate which overlies the Negaunee Negaunee Iron-formation. Iron-formation. I suggest conglomerate is not Goodrich, and that Hemlock rocks correlate correlate with the Emperor, is Goodrich, and Hemlock volcanic volcanic rocks Emperor, and and thus, at at least leastininpart, part,with withthe theIronwood, Ironwood,Vulcan, Vulcan, and and Nagaunee Nagaunee Iron-formations. Iron-formations. I postulate postulate that the the iron-formations iron-formations were were deposited deposited in relatively relatively stable and and slowly subsiding areas areas bordering bordering aa tectonically unstable slowly subsiding unstable and and rapidly rapidly subsiding subsiding basin basin series of troughs in in which or series of basins basins or or troughs which large large volumes volumes of volcanic volcanic material material accumulated. near the eastern accumula ted. The The northwestern northwestern margin margin of the volcanic volcanic basin basin was was near end of the the Gogebic Gogebic range, range, probably probably striking striking west-southwest west-southwestinto intoWisconsin Wisconsin south south of of the main main iron iron range. range. The Theeastern easternmargin margin of of the thebasin basin lay lay approximately approximately along along the boundary between Dickinson and Iron IronCounties. Counties. The may have have extended extended south boundary between Dickinson and The basin basin may and to include and the and southwest southwest to include the the volcanic volcanic units units in in north-central north-central Wisconsin Wisconsin and volcanogenic base-metal The extension extension of of the the basin basin to to volcanogenic base-metal deposits depositsthat that they they contain. contain. The the north north is is uncertain. /Work the Geological /Work done done in cooperation witfE with the Geological Survey Survey Division, Division, Michigan Michigan Department of of Natural Natural Resources. Resources. 50 50 �GEOLOGY AND MINERALOGY GEOLOGY MINERALOGY OF SOME SOME COPPER SULFIDE DEPOSITS NEAR NEAR MOUNT MOUNT BOHEMIA, BOHEMIA, KEWEENAW KEWEENAW COUNTY, MICHIGAN MICHIGAN James M. M. Robertson, Robertson, New New Mexico Mexico Bureau Bureau of of Mines Mines & & Mineral Mineral Resources, Resources, Socorro, Socorro, New Mexico 87801. 87801. ABSTRACT Copper sulfides, in in interesting amounts, have been recently discovered Copper sulfides, discovered in in the the Keweenaw Peninsula Peninsula of of northern northern Michigan, Michigan,aa district district long long famous famous for for its deposits Keweenaw deposits of of The sulfides occur extensively native copper. copper. The sulfides occur extensively in the the vicinity vicinity of ofMount Mount Bohemia, Bohemia, chiefly flow tops, chiefly as open-space open-space fillings fillings and and replacements replacements in in amygdaloidal amygdaloidal flow tops, aa of occurrence of native copper in the the region. traditional mode mode of copper in region. An An andesite dike dike (or (or dikes), almost almost invariably associated with with the mineralized invariably associated mineralized flow flow tops, tops, typically typically dikes), carries at least trace traceamounts amounts of of sulfides. sulfides. The The present present study study indicates indicates that that both both copper copper and and sulfur sulfur have have been been added added to to dikes and flow tops in the dikes and flow the Mount Mount Bohemia Bohemia area, area, probably probably by by hydrothermal hydrothermal solutions solutions moving upward along along zones zones of of structural structural weakness, moving upward weakness, and and outward outward along along relatively permeable flow flow tops tops and and broken broken dike dike margins. margins. The permeable The sulfur sulfur and and most most of the the copper copper are most most likely likely of of direct direct magmatic magmatic origin, origin, although although some some copper copper may may have have been been derived der ived at depth from pre-existing pre-existing flows. flows. Microscopic studies, studies, supplemented supplemented by by X-ray Microscopic X-ray fluorescence fluorescence analyses, analyses, have have defined aa zonal defined zonal pattern pattern of of total totalcopper, copper,sulfur, sulfur,and andsulfide sulfideminerals mineralsdeveloped developed about the Bohemia Fault, a northwest-trending break on on the the northeast about Bohemia Fault, northwest-trending break northeast flank flank of of Mount Chalcocite predominates predominatesnearest nearest the the fault, with bornite, Mount Bohemia. Bohemia. Chalcocite fault, with bornite, chalcopyrite, and chalcopyrite, and finally finally pyrite pyrite becoming becoming increasingly increasingly abundant abundant with with increasing increasing distance from from the break. break. The sequence developed developedinin the the Mount area is: The chronologic chronologie sequence Mount Bohemia Bohemia area is: dike dike emplacement and and alteration, faulting and fissuring, and sulfide sulfide mineralization. mineralization. At emplacement fissuring, and At least some least some of the the faulting faulting isis related relatedtotoregional regionaldeformation deformation thought thought to to have have occurred in in later Upper time. Regionally, is occurred Upper Keweertawan Keweenawan time. Regionally, native native copper copper deposition deposition is also believed to have followed this period of deformation and preceded copper have followed this period of deformation and preceded copper also believed sulfide mineralization. sulfide Mineralization in in the Mount several chemical trends Mineralization Mount Bohemia Bohemia area followed followed several trends during the the period with each each point point in in a mineralized during period of of sulfide sulfide deposition, deposition, with mineralized dike dike or flow top top undergoing at least part flow undergoing at part of ofa ageneralized generalizedsequence sequencewhich whichincluded: included: (1) (1) solutions whose whose initial initial Cu/S Cu/S ratios introduction of solutions ratios were were relatively relatively low; low; (2) progressiveincrease increaseinin the the Cu/S progressive Cu/S ratios ratios of of the theore-forming ore-forming solutions; solutions; and and (3) (3) 022 of the progressive increase in the ff0 the solutions. solutions. 51 �GROUNDWATER SPREADING OF HYDROCARBON GROUNDW ATER SPREADING HYDROCARBON SPILLS SPILLS WITH WITH SYSTEM DESIGN DESIGN IN IN GLACIAL GLACIAL DRIFT SPECIAL EMPHASIS EMPHASIS ON MONITOR MONITOR SYSTEM W. Rohrer Rohrer and and H.O. H.O. Pfannkuch, Pfannkuch, Department of W. of Geology Geology and and Geophysics, Geophysics, University of Minnesota, Minneapolis, Minneapolis, Minneosta Minneosta 55455 55455 ABSTRACT The introduction introduction of immiscible immiscible hydrocarbons hydrocarbons into the the hydrogeologic hydrogeologic environThe ment by accidental spills ment spills or or subsurface subsurface pipeline pipeline breaks breaks presents aa class class of of problems problems that is is different different from from miscible miscible leachate leachateor or soluble soluble contamination contamination propagation. propagation. The mechanisms of subsurface spreading comprise comprise three three distinct The mechanisms of subsurface spreading distinct stages; stages; downwardmovement movementofof the the free hydrocarbon downward hydrocarbon phase phase through through the unsaturated unsaturated zone, zone, spreading on on the the groundwater table and spreading groundwater table and through through the capillary capillary fringe, fringe, and and finally finally transport of transport of the the dissolved dissolved hydrocarbon hydrocarbon phase phase vertically with infiltrating recharge recharge water and horizontally in the groundwater flow field. Each one of these processes water and horizontally in the groundwater flow field. Each one of processes is characterized by is by different material material constants. constants. For Forthe thedownward downward movement movement it it is is the retention capacity capacity of of the the unsaturated unsaturated zone zone that determines determines the total amount amount of hydrocarbonphase phase reaching reachinggroundwater, groundwater,the the capillary capillary characteristics characteristics of of the hydrocarbon capillary fringe fringe system system defines defines the the extent capillary extent of of spreading spreading on on the watertable, watertable, and and hydrodynamic dispersion the dissolved dissolved hydrodynamic dispersioncoefficients coefficients delimit delimit the the shape shape and and extent extent of the phase spreading. about these these material phase spreading. Very Very little is is known known about material constants constants in in drift drift material, since material, since most most reported research research has has dealt with with alluvial alluvial deposits. deposits. This This work work presents results for for retention capacity presents experimental experimental results capacity of of glacial glacial drift drift and and hydrocarhydrocarbon depth depth in in the capillary bon capillary zone zone of of spreading. spreading. The The retention capacity capacity depends depends on on grain size size distribution, distribution,initial initialwater watersaturation, saturation,and andsurface surfacecharacteristiss characteristis of the grain the liquids invol~ed. invol'ed. The liquids The values values for for outwash outwash sands sands are on on the the order order of of 20 20 1/rn 11m and for tills 80 80 1/rn 11m.. Furthermore some some preliminary preliminary values values of hydrocarbon hydrocarbon thickness in in is given givenfor for the the same same material. the capillary fringe of equilibrium equilibrium is The design design of of aa monitoring system deals deals with with the the recognition of the the spatial The monitoring system recognition of distribution of of the free phase ininthe the subsurface subsurfaceafter after the distribution free and and dissolved dissolved hydrocarbon hydrocarbon phase spill, spill, the reconstruction reconstruction of inflitration inflitration site site and and infiltration infiltration mechanism mechanism (intergranOntergranular or or preferred path), the determination determination of of general general flow pattern and and emplacement emplacement of interceptor wells, and the establishment of background noise, well interceptor wells, and the establishment of background noise, well sampling sampling and analytical methods. techniques and methods. 52 �ORE DEPOSITS DEPOSITS IN IN RELATION RELATION TO TO HOTSPOT-GENERATED ORE INTRACONTINENTAL RIFTING INTRACONTINENTAL 3. Sawkins, Sawkins, Department Department of of Geology Frederick J. Geology and and Geophysics, Geophysics, University University of Minnesota, Minneapolis, Minnesota, Minneapolis, Minnesota 55455 ABSTRACT ABSTRACT It can be demonstrated It demonstrated that the the tectonic, tectonic,igneous, igneous, and and sedimentary sedimentary processes processes associated with associated with subcontinental subcontinental hotspot hotspot activity activity provide provide favorable favorable environments environments within which whichore-generating ore-generating systems systems can can operate. operate. within In particular particular certain certain tin deposits In deposits are associated associated with the products products of crustal melting during during the the early early stages stages of hotspot melting hotspot activity. Copper Copper mineralization mineralization is is in some cases cases closely some closely associated with with hotspot hotspot controlled controlled geologic geologic regimes, regimes, and and both both hydrothermal and and stratiform stratiform copper hydrothermal copper deposits deposits can results. results. Copper-nickel Copper-nickel mineralization in some rocks isis also to be be aa product zation some layered layered mafic igneous igneous rocks also considered considered to product of hotspot-associated basaltic basaltic magmatism. magmatism. Other Other metal metal deposit deposit types types that, that, at least in hotspot-associated some instances, instances, appear appear to to bear bear a relationship to hotspot stratiform some relationship to hotspot activity include include stratiform in shales shales and and lead-zinc lead-zinc replacement replacement deposits deposits in in carbonate carbonate rocks. rocks. lead-zinc deposits deposits in Two major continental fragmentation Two major continental fragmentation events events related to subcontinental subcontinental hotspot activity, activity, have in the geologic hotspot have occurred occurred in geologic past and and aa number number of of important important metal deposits deposits can can be be correlated with metal with each. each. This age This approach, approach,that that relates relates the age and geologic environment of intracontinental ore deposition to hotspot activity, and geologic environment of intracontinental ore deposition to hotspot holds holds significant promise for exploration geologists. geologists. 53 53 �KOMATIITES AND AND THEIR CHEMICAL KOMATIITES CHEMICAL VARIATIONS VARIATIONS K.3. K.J. Schulz, University of of Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota Minnesota 55455 55455 ABSTRACT komatiites from from South South Africa, Canada, Australia and Examination of komatlites Minnesota (Vermiliondistrict) district)shows showsthat that distinct distinct chemcial Minnesota (Vermilion chemcial suites can can be be defined defined which, while showing showingaageneral generalsimilarity similarity also also have have notable notable differences differences (Fig. which, while (Fig. 1). 1). A A striking difference difference isis the the CaO/Al203 ratio of the striking CaO/ Al 0 ratio the South South African African ( :> 1, Fig. 1a) > 1, Fig. la) 2 3 versus the the Australian Australian and and Canadian Canadian (generalIy1, (generally $1, Fig. Fig. ib, 1b, c) c) komatiites. komatlites. Vermilion Vermilion versus samples are relatively high Fe, Fe, Ti (Thisisis also also true true of of the samples are relatively high Tl and and PP (Fig. (Fig. 1d). the id). (This Minnesota River Valley low Al Al2O. amphibolites, see Weiblen and others, this Minnesota River Valley low amphibolites, see Weiblen and others, this 0 2 meeting). Work Workinin progress progresssuggesis suggest'sthat thatononaa global globalscale scaleat at least least two two distinct distinct Archean komatiite suites may Archean komatlite may exist, exist, distinguished distinguished not not only only by by CaO/A1203 CaO/ Al 0 ratio but 2 3 In Minnesota, appears that the also by FeO/MgO and AL,03/TiO.,. also by A1203 Al 0 vs vs FeO/MgO and Al 03/TiO. In Minnesota, itit appears that 2 3 unique occurrence occurrenceofof komattites komattites witi witi norrnar tholeiites isis repeated repeated in unique normJ tholeiites in time in in the the Lower and Upper Upper Archean Archean and and the Keweenawan. Lower and Keweenawan • .;:1° 10 .1\ .4+ ~ .J t .3 t '. • ,-,' i ? TI ._ .2+ 1 • L : .6 .5 SOUTH ~F~ICRN qFHICRN KOMATIITES SOUTH KOMRTIITES .2 ·1 I T t .0 .1 •1 .2 .3 • .33T~ .5 .5 •.1<1 .5 .6 l T I 1 .6++ .6 .55 1 C .; t . ~~ ,,' t ~\\ .6- ORNROIRN ITES CRNRDIRN KOMRTI KOMRTIITE5 .:J A .1 I .0 .11 t! d • t + / + / .1 + .2 + .2 .3! .3 1 + t .1 I L .00 + l j VErMILION VERMiLIC~ KOMRTIITES <OMRTIITES i .2 t .1 .;.i. .2 i '3 + '" T • .J r .t .2 PUSTRRLIRN I TES RUSTRRLIRN OMRTI KOMRTIITES .3 \ .0 .1j_ .1 T .21 .2 ~ 4. b .<1 '. .._,. / // \\ 'I I " X t .1 .J + .5 .6 .5 .0 .;. MS RL SI MG FE FE MN MN OR CR AL 51 TI iI P NR NR ' cCi " T t MGFE FEMN MN~RCRRLL St MG Sf II TI K K .11 40 + 23 P NR NR F 38 27 ~ 1. Log Fig. 1. Log plots plots of komatilte komatilte compositional compositional normalized normalized to Hawaiian Hawaiian tholeiite (as (as oxides, right to left: left: 8.1, 8.1, 10.04, 10.04, .17, .17, 10.9, 10.9, 13.4, 13.4, 50.4, 50.4, 2.7, 2.7, .28, .28, 2.3, 2.3, .53). .53). Numbers oxides, right below 0 have have negative negative values. values. Data Data from from various various sources. sources. below a 54 �CHEMISTRY OF OF PRIMARY PRIMARY AND AND SECONDARY SECONDARY MINERALS OF SOME CHEMISTRY MINERALS OF SOME PORTAGE LAKE LAKE LAVAS, KEWEENAWPENINSULA: PENINSULA: DEVELOPMENT OF PORTAGE LAVAS, KEWEENAW MODELS OF OF DIFFERENTIATION AND MODELS AND LOW-RANK LOW-RANK METAMORPHISM METAMORPHISM Nancy Scofield, Scofield, Department Department of of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan Nancy Technological University, Houghton, Technological Houghton, Michigan Michigan 49931 49931 ABSTRACT Minerals from from the the Scales Scales Creek Creek flow flow (SCF) (SCF) and and two thinner thinner (40', (40', 55') 55') basalt Minerals flows above above SCF SCFwere were analyzed analyzedby byelectron electron microprobe. microprobe. The interior of flows The interior of the the SCF SCF shows some some igneous igneous differentiation differentiation as shows as evidenced evidenced by by increases increasesofofFe/Fe-s.Mg Fe/Fe+Mg (9%) and Fe/Fe+Ca Fe/Fe+Ca (14%) an increase of and (14%) in augite and and an of Na/Na+Ca Na/Na+Ca (6%) (6%) in in plagioclase. plagioclase. plag (ZAn) (%An) (40—702modal) aodal) (40-70% Drill—hole Drill-hole depth depth cpx (20—402 da1) cpx (20-40: modal) Wo En Pa \00 la Fsl0* Fe203* MgO HgO CaO <:40 Na20 K20 Je20 10.3 10.5 11.1 11.1 2.06 7.83 18.8 18.8 6.9 6.9 0.07 0.07 4.30 0.02 0.02 0.07 0.07 85 85 180 180 (3) (3) 12.0 12.0 (J) (3) 11.7 11.1 (2) (2) (2) (2) 12.2 12.2 12.3 12.3 12.3 5,b4 5.04 7.75 7.75 7.43 7.45 7.80 3.90 5.90 8.2 8.2 9.9 9.7 9.1 10.4 10.4 8.4 3.90 3.90 2.26 2.26 2.15 2.15 2.32 2.90 0.30 0.27 0.30 0.31 2.10 2.10 455 455 130 130 110 110 150 130 420 420 puap 081-1832 081—1832 pWllp ab 081—1839 081-1839 055—1185 055-1185 5C 1233 SCF 1233 1285 1285 200' 1320 1370 1310 2—3 2-3 (6) (6) 42— 4239 39 42 38 62— 1616— 4239 22 38 20 44 44 18 34 44 22 14 44 16 40 44 42— 43— 15— 4243- 1538 39 23 2—3 (5) (5) 2-3 48—80(11) (U) 48-80 50—82 (8) (8) 50-82 65—80 (5) 65-80 (5) 43—30 (3) 43-30 (5) CII (p"lII) Cu (pptu) (5) (5) (8) (8) a. Mumthr analyses in in parenthessu. "uaber ofotanalyae. parentheae•• Pump pupsL1yits•••tadolll&1n astadosaln Pump —• p~.llyit *Total iron *Total iron am 1e203, 1e203' albitized ba.aalt ab basalt ab —• albit1zed C4EMICAL TRENOS IN SC..LES CREEK FLOW 0.4 0.5 Fe/Mg F'/M9 0.& *— .mi.$ry • -llulIl .....' " OJ 0.4 0.5 0.6 BOTiOY 0—.9ts; peq .dçsa I 2 3 .. NoICo FuCo D—cflnft. Q-c/lIOIit.; pIaqcoss plaqc:or.. A—oiyi 0.05 Q.l 0.15 0..$ Ci X/Ne K/Nn C'!·;:J-4lt...... The basalts basalts are are altered by by low-rank low-rank metamorphism metamorphism of the prehnite-. prehnitepumpeilyite of secondary pumpellyite facies. facies. The The proportion proportion of secondary minerals, minerals, as alteration alteration products products and in and in veins veins and and amygdules, amygdules, increases increases toward toward flow flow tops. Augite Augite is replaced replaced by by chlorite chlorite and and plagiodase plagiodase is is albitized. The Ca thus thus released released is is available available for for The Ca pumpellyitization pumpellyitization of plagioclase, plagioclase, which which occurs occurs concurrently concurrently and and subsequently subsequently to to a.Ibitization, releasing albitization, releasing Na. Na. However, aa closed-sytem closed-sytem model model demands demands overall overall However, participation of the participation of the relatively relatively unaltered unaltered flow flow interiors interiors by by a depletion depletion of of aa few few percent of the the Na Na present, present, but but this this isis not notobservable observable petrographically. petrographically. Pyroxene in in pumpellyite metadomains isis altered altered to pumpellyite pumpellyite metadomains pumpellyite and/or and/or epidote. epidote. The Mg Mg thus thus mobilized augments the the Mg content of chlorite mobilized augments Mg content chlorite and and results results in in higher Mg Mg values in in chlorite chlorite than than in in augite augite from from which which chlorite chlorite isis derived. derived. Both Both pumpellyitized pumpellyitized and and albitized are depleted in K K relative relative to less albitized zones zones are depleted in less altered altered parts of of flows, flows, and and K K is is concentrated concentrated in in the the base base of of the SCF, SCF, where where sericitization sericitization of of plagioclase plagioclase isis extensive. extensive. . 55 55 �SOURCES OF DISSOLVED GROUNDWATER DISSOL VED SOLIDS SOLIDS IN IN GROUNDW ATER FROM SUPERIOR AND RAINY FROM RAINY LOBE TILL Siegel, Department of Donald I. Siegel, of Geology Geology and and Geophysics, Geophysics, University of Minnesota, Minnesota, Minneapolis, Minnesota 55455 ABSTRACT Preliminary study study of of recent analyses Preliminary analyses of water water quality quality shows shows that groundwater groundwater within surficial aquifers aquifers related related to Superior within surficial Superior and and Rainy Rainy lobe lobe deposits deposits contains contains significantly less less sodium than is found significantly sodium than found in bedrock bedrock aquifers aquifers within within igneous igneous rocks rocks of central and northeastern Minnesota. Minnesota. Inasmuch Inasmuch as as Superior Superior and Rainy Rainy lobe lobe deposits consist mainly of materials consist mainly of materials derived derived from from these these and and similar similar igneous igneous rocks, rocks, the the observeddifference difference in in sodium sodium content content between between groundwaters groundwaters within within the the surficial observed surficial and bedrock and bedrock aquifers aquifers may may be be considered considered anomalous anomalous assuming assuming that that groundwater groundwater most influenced Possible mechanisms chemistry is most influenced by by aquifer mineralogy. explaining the the differing sodium values and and gross gross water water chemistry chemistry are suggested, explaining sodium values suggested, in particular, by theoretical reconstructions of surficial particular, by using using theoretical reconstructions of surficial and and bedrock bedrock waters. waters. Initial results results highlight Initial highlight the importance importance of of compositional compositional differences within aquifers in local local and and small, small, intermediate intermediate flow flow systems systems as as the the dominant in dominant control of both both gross gross groundwater chemistry chemistryand and ultimately ultimately the the gradual gradual evolution evolutionofof water water types groundwater types as as deduced by by Chebotarev and deduced and others. 56 56 �MIDDLE MIDDLE PRECAMBRIAN AGE OF VOLCANOGENIC VOLCANOGENIC MASSIVE MASSIVE SULFIDE DEPOSITS IN NORTHERN NORTHERN WISCONSIN WISCONSIN P.K. Sims, U.S. Denver, Colorado Colorado 80225 80225 U.S. Geological Survey, Denver, ABSTRACT The copper-zinc at the copper-zinc massive massive sulfide sulfide deposits at the Flambeau Flambeau mine, mine, near near The Ladysmith and at Pelican River, east of Rhinelander, Wisconsin, have model lead Ladysmith and Pelican River, east of Rhinelander, Wisconsin, have model ages of 1,830+150 m.y. (J.S. (iS. Stacey, ages 1,830+150 m.y. Stacey, B.R. B.R. Doe, Doe, and and L.T. L. T. Silver, Silver, written written commun., commun., Inasmuchas as the the deposits 1976). Inasmuch deposits are considered considered as as being being of of submarine submarine volcanic volcanic exhalative also are interpreted exhala tive origin, or igin, the associated volcanic rocks rocks also interpreted as as being being middle middle Precambrian (Precambrian X) X) in age. The analytical analytical data on The on the leads leads from from the the two two ores, ores, provided provided by by Stacey, Stacey, Doe, Doe, and Silver, Silver, are tabulated tabulated below. below. 206 Pb 204 Pb 207Pb 204 Pb 204 208Pb 204 Pb Model Model age in m.y. Flambeau 15.323 15.167 35.016 1,820 Pelican River 15.688 15.359 35.202 1,835 Deposit The isotopic composition compositionofof the the leads leads is is similar to the the least least radiogenic radiogenic leads leads from from The isotopic The model model lead lead ages the massive massive sulfide sulfide deposits deposits at Flin Flin Flon, Flon, Manitoba. Manitoba. The ages are and granitic grartitic rocks rocks consistent with with zircon zircon U-Pb U-Pb ages ages of of 1,800-1,900 1,800-1,900 m.y. on volcanic volcanic and in and adjacent Michigan, in northeastern northeastern Wisconsin Wisconsin and Michigan, determined determined by byW.R. W.R. Van Van Schmus Schmus and his and his associates in in 1975. 1975. The volcanic volcanic rocks rocks in in the the Ladysmith-Rhinelander Ladysmith-Rhinelanderbelt belt are are interpreted interpreted as The as being being approximately correlative correlative with with the the dominantly submarine volcanic volcanic rocks rocks that that are approximately dominantly submarine are interbedded with with turbidite-like the upper of the interbedded turbidite-like sedimentary sedimentary rocks rocks in the upper part of the Marquette northern Michigan. Apparently these these rocks Marquette Range Range Supergroup Supergroup in in northern Michigan. Apparently rocks accumulated in in a eugeosynclinal environmentininthe the southern southern part part of the accumulated eugeosynclinal environment the middle middle Precambrian basin basin in the the Lake Lake Superior Superior region. region. 57 �GEOLOGY AND GEOCHEMISTRY GEOCHEMISTRY OF THE THE PRECAMBRIAN PRECAMBRIAN MARCELLON MARCELLON RHYOLITE, RHYOLITE, COLUMBIA COUNTY, WISCONSIN COLUMBIA WISCONSIN Smith, Divsion Divsion of Science, Science, University University of ofWisconsin-Parkside, Wisconsin-Parkside, Kenosha, Kenosha, Eugene I. Smith, Wisconsin 53140 531ltO ABSTRACT The inlier isis formed formed by by four four mineralogically mineralogically and and chemically chemically distinct distinct The Marcellon Marcellon inlier rhyolite tuffs which rhyolite flows flows and and ash-flow ash-flow tuffs which are folded folded into into aa northeast-striking, northeast-striking, asymmetric arjifom. Rhyolite asymmetric antiform. Rhyoliteononthe thewestern westernlimb limbofofthe theantiform antiformstrikes strikesN.N..50 50 0 0 E. and E. and dips dips 50 50 -85 _85 to the the northwest. northwest. The The units units on on the the eastern eastern limb limb also also strike strike N. N. 0 50 50 E., E., but dip dip steeply (80° (80 to vertical) vertical) to to the the southeast. southeast.Two Twochemically chemicallydissimilar dissimilar greenstone dikes intrude the rhyolite flows. dikes rhyolite flows. The The core of the the antiform antiform isisformed formedby bya aquartz quartz(2%), (2%),plagioclase plagioclase(15%), 05%), and and alkali (2%)rhyolite rhyolite with with well well preserved preserved shard shard outlines outlines in in the matrix alkali feldspar feldspar (2%) matrix (unit (unit unit probably is an Structurally above It). This unit probably is an ash-flow ash-flow tuff. Structurally above unit 4It is: is: (a) (a) well well 4). This banded, plagioclase-bearing Olt-18%) (14-18%)rhyolite rhyolite with with local local spherulitic spherulitic lenses (unit banded, plagioclase-bearing (unit 3); 3); (6%), alkali feldspar feldspar (4%), (It%), plagioclase (1%) 0 %) rhyolite (unit 2); (b) flow (b) flow banded, banded, quartz (6%), and (c) (c) quartz quartz (296), (296),alkali alkalifeldspar feldspar (2%), (2%),plagioclase plagioclase0(1%) rhyolitecharacterized characterized by %) rhyolite and spherulites up up to 15 15 cm in diameter diameter (unit (unit 1). 1). The rhyoliteisis one one of of ten major The Marcellon Marcellon rhyolite major rhyolite rhyolite and and granite granite inliers inliers in in south-central Wisconsin. Chemicallymost mostofof the the rocks form the inliers Wisconsin. Chemically rocks which which form inliers can can be divided divided into into three threegroups: groups:(1) 0)high high CaO CaO(1.48-1.68%), (1.48-1.68%), high high TiO, Ti0 2(0.30-0.42%), (0.30-0.42%), and and low rhyolitesand andgranites granites(Observatory (ObservatoryHill HillRhyolite hyolite dikes dikes and and low Rb/Sr Rb/Sr (0.37-0.79) (0.37-0.79) rhyolites the Baxter Baxter Hollow Hollow Granite); Granite); (2) (2) intermediate intermediateCaO CaO(1.28#O.32%) (1.28+0.32%) and and Rb/Sr Rb/Sr (1.09+ 0.09+ 0.29) rhyolite rhyolite (unit (unit 33 at Marcellon 0.29) Marcellon and and the the Marquette Marquette Rhyolite); Rhyolite); and and (3) (3) low low CaO Cad Rb/Sr (159) (0.37+0.14%), (0.37 +0.14%), high Rb/Sr 05~) rhyolites rhyolites and and granites granites (Observatory (Observatory Hill, Hill, Berlin, Berlin, Utley, and rhyolites, and and granophyric granophyricgranites granites at at Moritello Utley, and Endeavor Endeavor rhyolites, Montello and and Red Red Althoughunit unit 33 at Marcellon falls into chemical 2, the other Granite). Although Marcellon falls chemical group group 2, other Marcellonunits, units,along alongwith with rhyolites rhyolitesinin the the Baraboo area, are transitional Marcellon Baraboo area, transitional in chemistry chemistry between between groups groups 2 and and 3. 3. For For example, example, units units 1 and 22 are are more more closely closely related to to group group 33 in in terms termsof oflow lowCaO CaO(0.29-0.36%), (0.29-0.3696), but but differ differ by by having having lower lower Rb/Sr (2.27+0.57). Unit 44 isis similar similar to group 2 because of intermediate Rb/Sr (2.27+0.57). Unit intermediateCaO CaO(0.94%) (0.9lt96) and but it isis higher and Rb/Sr (1.32), 0.32), but higher in in K2O/Na20 K 0/Na 0 and and lower lower in in Ba Ba than than typical typical group group 22 2 2 rocks. Rocks of the three with the the transitional Rocks of three chemical chemical groups, groups, along along with transitional types, types, fall along aa trend along trend typical typical of of aarock rockseries seriesshowing showing strong strong caic-alkaline calc-alkaline affinities. affinities. Rhyolites are are cornagmatic, and the granophyric Rhyolites comagmatic, and granophyric granites granites are apparently apparently the the subvolcanicequivalents. equivalents. These chemical data along subvolcanic These chemical along with with available available U/Pb dates (1.8 (1.8 b.y.) confirm that that these rhyolites the last stages of rhyolites and and granites formed formed during during the of the the b.y.) confirm Penokean Orogeny. 58 �THE GEOCHEMISTRY GEOCHEMISTRY OF THE THE GAMITAGAMA GAMITAGAMA LAKE COMPLEX, COMPLEX, WAWA, WAWA, NORTHERN ONTARIO I.E. Smith, T.E. Smith, A. A. Turek, Turek, and and C. C.Riddle, Riddle, Department Department of ofGeology, Geology, University University of of Windsor, Windsor, Windsor, Ontario, Canada Canada ABSTRACT The The Gamitagama Gamitagama Lake Lake Complex Complex is is aa calc-alkaline calc-alkaline stock stock (Ayres, (Ayres, 1969), exposedwithin within the the Abitibi volcano-plutonic exposed volcano-plutonic belt in in the the Superior Superior Province Province of of Canada, south Canada, south of of Wawa Wawa in in Ontario. It penetrates penetrates a a series series of regionally metamorphosed felsic and and mafic mafic volcanic volcanic rocks metamorphosed felsic rocks interbedded interbedded with metasedimentary metasedimentary rocks with aa variety variety of of other plutons. rocks and and iron-formation, iron-formation, and and is associated associated with plutons. The The metamorphic gradevaries variesfrom from greenschist greenschisttoto amphibolite amphibolite facies facies within within the metamorphic grade the area area and is overprinted by contact metamorphic aureoles adjacent adjacentto to the the plutons. plutons. The and is overprinted by metamorphic aureoles The plutonic rocks plutonic rocks include include cataclastic cataclastic and and gneissose gneissose trondjhemites, trondjhemites, gabbros, gabbros, norites, diorites, dior ites, syenites, syenites, and and granites. Major Major and and trace elemental elemental contents contents of the the volcanic volcanic and and plutonic plutonic rocks rocks are are usedtoto identify identify the igneousrock rocksuites suitesofofthe the area, area, to to follow used the various various igneous follow their their evolution and Comparisonswith with recent evolution and to determine determine which which are are co-magmatic. co-magmatic. Comparisons recent igneousrock rock suites suitesare areused usedtotoreconstruct reconstructthe the development developmentof of the the Archean Archean crust crust in in igneous this this area area and and to to identify identifythe thetectonic tectonicenvironments environments ininwhich whichthe themagmas magmas were were generated. 59 �A A GROUND GROUND INVESTIGATION INVESTIGATION OF AN AN AEROMAGNETIC AEROMAGNETIC ANOMALY, ANOMALY, DICKINSON DICKINSON COUNTY, COUNTY, MICHIGAN MICHIGAN David Snider, Geology and Minerals David W. W. Snider, Geology and Minerals Research Unit, Unit, Geological Geological Survey Survey Division, Division, Michigan Department of Natural Natural Resources, Resources,Lansing, Lansing, Michigan Michigan 48926 48926 Michigan Department ABSTRACT ABSTRACT During the the latter latter part of of September, September, 1975, 1975, the the Geology Geology and and Minerals Minerals During Research Research Unit Unit of the the Michigan Michigan Geological Geological Survey Survey conducted conducted a ground ground reconnaisreconnais- sance of aa small, sance investigation investigation of small, closed closed aeromagnetic aeromagnetic anomaly anomaly in in north-central north-central Dickinson County. The The purposes purposes of of the the study were two-fold: (a) Dickinson County. study were (a) to determine determine what what geologic feature caused geologic feature caused the the aeromagnetic aeromagnetic anomaly anomaly and, and, (b) (b) to to investigate investigate any any mineral resource potential associated with the area in and around the anomaly. mineral resource potential associated with the area in and around the anomaly. Nearly Nearly all of of the the closed closed anomaly anomaly lies lies within within an an east-west east-west trending trendingswamp swamp covering covering an area of of nearly nearly three three square square miles. miles. The of investigation consisted of sampling The methods methods of sampling outcrops for petrographic and chemical chemical analyses, analyses, ground ground magnetic magnetic surveys, surveys, and andaaVLF-EM VLF-EM survey. The results of of the the study indicate that The combined combined results that the theclosed, closed, airborne airborne anomaly anomaly peridotite that was caused caused by by the the near-surface near-surface occurrence occurrence of of serpentinized serpentinized peridotite that was contains appreciable of magnetite. This appreciable amounts amounts of This ultrarnafic ultramaficbody body underlies underlies most most of of the northern northern portion portion of of the the swamp swamp area, area, strikes strikesN75°-80°W N750 -800 W and and dips dips to the the south. south. The relative position positionofof the the body body with with respect respect to to metasedimentary rocks to to the The relative metasedimentary rocks south and and southwest southwest suggest suggest that that this this ultramafic unit south unit was was emplaced as a sill. The results of the The the chemical chemical analyses analyses show show no no anomalous anomalous Ni-Cu-Co values. surveyshow showthe the presence presence of of two The results of the the VLF-EM VLF-EM survey two separate separate The results first is anamalous zones within withinthe the project project aera. The anamalous zones The first is caused caused by by the the relatively relatively magnetic, serpentinized peridotite peridotite that crops magnetic, serpentinized crops out within within the the swamp. swamp. This This area produced aa high high ground ground magnetic magnetic response response as as well well as as aa VLF-EM response. However, produced VLF-EM response. However, the combined geophysical, geological, and chemical evidence indicate that the the combined geophysical, geological, and chemical evidence indicate that the surface exposures of the the magnetic, surface exposures of magnetic, serpentinized serpentinized peridotite has has limited limited ecomonic ecomonic potential. The feature responsible The responsible for for the thesecond secondVLF-EM VLF-EM anomalous anomalous zone zone does does not not express itself itself at at the express the surface, surface, nor nor does does ititcorrespoind correspoind with with any any ground ground magnetic magnetic anomalies. All of of the anomaliesgenerated generatedinin the the project All the major major VLF-EM VLF-EM anomalies project area were were correlated with with the the serpentinized correlated serpentinized peridotite peridotite and and showed showed aa reverse reverse cross-over cross-over to anomaly was determined determined that that the theVLF-EM VLF-EM instrument instrument was was responding responding to anomaly form. It was It was the magnetic permeabilityofof the the rock the magnetic permeability rock rather rather than than its itsconductivity. conductivity. It was survey yielded yielded no no reliable therefore concluded concluded that the the VLF-EM VLF-EM survey reliable data concerning concerning the the conductivity conductivity of of the the serpentinized serpentinized ultramafic. ultramafic. The VLF-EM VLF-EMinstrument instrumentused usedininthis thisstudy studyisisa arather rather restrictive, restrictive, reconnaisThe reconnaissance tool, tool, and and as as such be used sance such cannot cannot be used for for detailed detailed interpretation interpretation of of buried buried conductive bodies, bodies, especially especially when when those those bodies bodies possess possess high high magnetic magnetic permeabilpermeabilconductive this occurrence of ultramafic therefore suggested ity. suggested that this occurrence of ultramafic rock rock be be ity. ItIt is therefore investigated in in more investigated more detail by by those those using using a more more discriminating discriminating EM EM method method which which wouldbetter better determine determine its economic economic potential. would 60 60 �HIGH-GRADE HIGH-GRADE METAMORPHISM METAMORPHISM ASSOCIATED ASSOCIATED WITH WITH THE THE VERMILION VERMILION BATHOLITH, MINNESOTA-ONTARIO MINNESOTA-ONTARIO David L. L. Southwick, Southwick, Department Department of of Geology, Geology, Macalaster Macalaster College, College, St. Paul, David Minnesota. ABSTRACT Aluminous, magnesianschists schistsalong alongthe the north north contact Aluminous, magnesian contact of of the theVermilion Vermilion batholith contain various combinations combinationsofofsillimanite, sillimanite,cordierite, cordierite, staurolite, staurolite, garnet, contain various is rarely and and sapphirine sapphirine along along with with biotite, biotite, oligoclase, oligoclase, and and quartz. quartz. Muscovite Muscovite is rarely So far as present; tourmaline is a common and sometimes abundant accessory. present; tourmaline is a common and sometimes abundant accessory. So as known, this is the first reported occurrence of sapphirine in Minnesota or western known, this is the reported occurrence of sapphir ine in Minnesota or western Ontario. Ontario. Staurolite-bearing assemblagesappear appeartoto represent represent the the highest Staurolite-bearing assemblages highest metamorphic metamorphic grade. grade. There There is is excellent excellent textural textural evidence evidence that the the reaction reaction garnet garnet ++ staurolite + taken place. Experimental quartz-cordiertie has has taken Experimental work work indicates that this this reaction reaction quartz—cordiertie is with lower lower pressure pressure favoring favoringthe the formation formation of of cordierite. is pressure-controlled, pressure-controlled, with cordierite. Sapphirine occurs together together with with staurolite staurolite in some Sapphirine occurs some rocks, rocks, indicating indicating formation formation at the highest metamorphicgrade. grade. There is no no clear-cut evidence as to the reactions highest metamorphic There is evidence as reactions governing sapphirine formation. governing sapphirine Field relations indicate that the Field relations the high-grade high-grade schists are the the product product of of thermal thermal assemblages inin the the schists metamorphism by adjacent batholith. batholith. Observed Observed assemblages schists metamorphism bythe the adjacent 0 suggest maximum suggest maximum temperature and and pressure pressure in in the theneighborhood neighborhood of of 600-700°C 600-700 C and and This environment environmentisiscompatable compatablewith withthe the inferred inferred temperature temperature and pressure 3-5 kb. This at crystallization crystallization of of the the major major part partof ofthe theVermilion Vermilion batholith. batholith. Detailed investigations investigations of of the phase chemistry currently are are underway. underway. 61 �GEOLOGY OF THE ROUND GEOLOGY ROUND LAKE LAKE INTRUSION, INTRUSION, SAWYER COUNTY, WISCONSIN SAWYER WISCONSIN S.W. Stuhr and and E.N. S.W. Stuhr E.N. Cameron, Department Department of of Geology Geology and and Geophysics, Geophysics, University University of Wisconsin, Wisconsin, Madison, Madison, Wisconsin Wisconsin 53706 53706 ABSTRACT enclosed in in Archean rocks aa short The Round Round Lake Lake intrusion intrusion is enclosed Archean rocks short distance distance southeast of the edge southeast edge of of the theLake LakeSuperior SuperiorSyncline SynclineininSawyer SawyerCounty, County,Wisconsin. Wisconsin. Geophysicaldata dataindicates indicatesthat that the the intrusion intrusion isis at at least five Geophysical five miles miles long long but but less less The intrusion intrusion may maybe be aa derivative than than one one mile mile wide. wide. The derivative of aa gabbroic gabbroic magma. magma. Diabasic gabbro gabbro occurs occurs as as inclusions inclusions inin the the outer outer portions Diabasic portions of of the oxide-rich oxide-rich core. core. Magnetite-troctolite, and mafic pegmatite Magnetite-troctolite, magnetite, anorthositic anorthositic olivine olivine gabbro gabbro and form the troughshaped form troughshaped core of the intrusion. intrusion. The dominant dominant minerals minerals are olivine, and titanomagnetite titanomagnetite in The olivine, plagioclase and in various various In the core of the intrusion, olivine and plagioclase crystallized early proportions. In the intrusion, olivine and plagioclase and the iron-titanium oxides crystallized crystallizedlate. late. At and the iron-titanium oxides At the the base base of of the thenarrow narrowintrusion intrusion of magnetite magnetite troctolite was aa thick zone zone of was formed. formed. The The iron-titanium iron-titanium oxides oxides became became enriched in the the residual liquid and andaalarge largezone zoneofofmagnetitite magnetitite formed formed in in the the central central enriched in residual liquid part of the intrusion. intrusion. As As differentiation differentiation proceeded, proceeded, additional additional magnetite-troctolite magnetite-troctolite clusters accumulated formed toward the the top formed toward top of of the the intrusion. intrusion. Plagioclase Plagioclase clusters accumulated into lenses of anorthositic olivine gabbro gabbro inin the the lower of the lenses of anorthositic olivine lower and and middle middle portions portions of the intrusion. Finally, Finally, mafic mafic pegmatites, pegmatites, consisting consisting of of plagioclase, plagioclase, perthite, augite, augite, iron-titanium oxides and apatite apatite as major oxides and major minerals, minerals, developed developed in the upper upper portions portions of the intrusion. intrusion. Chemical variation variation of of specific Chemical specific minerals minerals is is a function function of both both the the oxide/silioxide/silicate ratio cate ratio and and cryptic cryptic changes changes related related to to position position in the the intrusion. intrusion. Olivine, plagioclase plagioclase and and iron-titanium oxides oxides show show slight but consistant consistant chemical chemical changes. changes. Cryptic variations variationsare are most most pronounced pronouncedininthe the portion portionofof the the intrusion Cryptic intrusion that crystallized last. The oxides were were concentrated concentrated in in the The iron-titanium iron-titanium oxides the residual residual liquid liquid under under the intrusion the product conditions of low conditions of low oxygen oxygen fugacity. fugacity. If the intrusion is the product of of iron enrichment of basaltic magma, it must have migrated migrated from from the site of differentiation. After After the the iron-rich iron-rich magma magma was was intruded, intruded, itit followed followed aa "normal" "normal" path of differentiation in in place. place. 62 U �HYDROCARBONS HYDROCARBONS OBTAINED OBTAINED BY BY PYROLYSIS PYROLYSIS OF OF SOME SOME PRECAMBRIAN ROCKS OF MINNESOTA* PRECAMBRIAN ROCKS OF MINNESOTA* F.M. :i. Baysinger, and 1M. F.M. Swain, Swain, J. Baysinger, and J.M. Bratt, Bratt,Department DepartmentofofGeology Geologyand andGeophysics, Geophysics, of Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota Minnesota 55455 55455 University of ABSTRACT ABSTRACT Drill Drill core samples samples of of 42 42 Precambrian Precambrian sedimentary, sedimentary, igneous, igneous, and and metamorphic metamorphic rocks partial vacuum rocks were were analyzed analyzed by by heating heating under under partial vacuum at 100°C 1000C and and at 400°C 400 0 C to to release hydrocarbons and other volatile products. hydrocarbons and products. The yielded methane methane inin amounts amounts ranging rangingfrom from traces traces to to 33 The core core samples samples yielded way of comparison, but averaged averaged much much less. less. By By way comparison, samples of microliters per gram, but Middle Marcellusblack black shale, shale, from Middle Devonian Devonian Marcellus from Pennsylvania, Pennsylvania, yielded yielded methane methane in in am ounts up to 77 ul/g. ul/g. amounts Other up to to C11 were Other straight straight chain chain hydrocarbons hydrocarbons up C were found found in the the volatile volatile ll o products, especiall' especiallj: those those obtained obtained atat400°C; 400 C;benzene benzenealso also was was aacommon common product, product, mainly in the the 400 mainly in 400 C C experiments. experiments. Carbon Carbon dioxide dioxide and and nitrogen nitrogen appear appear to form form aa large part of of the the non-hydrocarbon non-hydrocarbon volatiles in at least least some some of of the the samples. samples. Spectral data data indicate of the Spectral indicate that the the straight straight chain chain pyrolysis pyrolysis products products of Precambrian rocks are mainly alkenes, whereas those of the Devonian rocks, Precambr ian rocks are mainly alkenes, whereas those of the Devonian rocks, to above, above, are are aamixture mixture of ofalkanes alkanes and and alkenes. alkenes. Alkanes Alkanes were however, however, referred to Available obtained from from several several algae-bearing algae-bearing Middle Middle Precambrian Precambrian argillites. argillites. obtained evidence indicates, indicates, although not conclusively, conclusively, that that the alkenes evidence although not alkenes were were contained contained in the rock rock rather ratherthan thanbeing beingproduced produced from from alkanes alkanesduring during pyrolysis. pyrolysis. The writers believe believe that surface contamination The writers contamination in most most of the drill drill cores cores was was minimal owingtotothe the low lowpermeability permeabilityofofthe the rocks rocks studied, studied, and and that that contamination minimal owing by drilling was also minimal. by not formed that the There is aa reasonable reasonable possibility possibility that the volatiles, volatiles, if not formed from from There is kerogeri residues residues by bythe the pyrolysis pyrolysisexperiments, experiments, are are in in part juvenile kerogen juvenile igneous igneous gases gases or or are substances substances that that were were distilled distilled out out of of the thedeeper-lying deeper-lying rocks rocks during during intervals intervals of of folding and and metamorphism, metamorphism, and and subsequently subsequently accumulated accumulated at at higher higher levels. folding *The paper paper isis scheduled scheduled for for publication publication in in July 1976 "Origins of of Life." Life." *The 1976 "Origins 63 63 �—- HORNFELSED BASALTS BASALTS IN THE THE DULUTH DULUTH COMPLEX COMPLEX Department of of Geological R.M. B. Bonnichsen, Bonnichsen, Department Geological Sciences, Sciences, Cornell Cornell R.M. Tyson Tyson and and B. Ithaca,New NewYork York14853 14853 University, Ithaca, ABSTRACT ABSTRACT Two typesofof hornfelsed basalt (see (see figure) figure) occur occur in compositional types hornfelsed basalt in the the Two compositional Babbitt-Hoyt of the Duluth Babbitt-Hoyt Lakes Lakes region region of Duluth Complex. Complex. The The Erie Erie Hornfels Hornfels (Sec. (Sec. 18, 18, T.59N., Dunka Railroad Railroad Hornfels T.59N., R.13W.), R.13W.), Dunka Hornfels (Sec. 33, 33, T.60N., T.60N., R. R. 12W.) 12W.) and and Reserve Reserve Hornfels (Sec. 32, (Type1)I) are are olivine Hornfels (Sec. 32, T.60N., T.60N., R.12W.), R.12W.), (Type olivine tholeiites tholeiites consisting consisting of of plagioclase augite (16-45%), olivine (0-2196), (0-21%),and and inverted inverted pigeonite plagioclase (40-62%), (40-6296), augite 06-45%), olivine pigeonite (018%). 1896).- The The Reserve Reserve body body has less than than 1% 1% opaque opaque oxides and more than than 10% 10% olivine, whereas whereas the others others have have 1-3% 1-396 opaque opaque oxides oxides and and generally generally less less than than 10% 10% olivine. olivine. The range from from granoblastic granoblastic in in the theDunka Dunka Railroad Railroad and and Reserve Reserve bodies, bodies, The textures range which are surrounded surroundedby byintrusive intrusiverocks, rocks,totoaabetter-preserved better-preserved basaltic fabric in which are in the This type contains plagioclase-two Erie Hornfels at the base of the complex. Erie Hornfels at base of the complex. This contains plagioclase-two pyroxene and plagioclase pyroxene metamorphosed metamorphosed amygdules amygdules and plagioclase phenocrysts. phenocrysts. The The Colvin Colvin Creek Hornfels and T.59N. T.59N. R.13W.) R.13W.)isisan an example example of of Type Hornfels (T.58N. (T.58N. and Type H, II, and contains contains (28-34%), equant plagioclase (52-56%), irregular to locally poikilitic augite (28-3496), hypersthene mantling augite, and hypersthene (1-6%) 0-6%) mantling and magnetite magnetite(10-20%). (10-2096). It represents represents an an type has oxidized basalt which which has has been been metamorphosed. metamorphosed. This This type has aa granoblastic granoblastic oxidized basalt texture texture and and contains contains zoned zoned plagioclase plagioclase phenocrysts phenocrysts and and metamorphosed metamorphosed amygdules amygdules . composed composed of of augite enclosing plagioclase. \Ve believe believe these these hornfels hornfels bodies bodies were were originally originallyflows flowsthat that were were part of the We the Their metamorphism to the pyroxene North Shore Volcanic Volcanic Group. Group. Their metamorphism to the pyroxene hornfels hornfels or North Shore sanidinite facies was thermal in sanidinite facies was predominantly predominantly thermal in nature. Devolatilization Devolatilization was one one major major effect as as shown shown by by the the anhydrous anhydrous minerals minerals now now constituting the the amygdules amygdules and the the scarcity scarcityofofhydrous hydrousminerals mineralscommon common in inunmetamorphosed unmetamorphosed North North Shore Shore and Volcanicrocks. rocks. Partial Partial melting locally occurred occurred with with the the formation melting locally formation of syenite and Volcanic Such dikes, dikes, composed composedofof Na-plagioclase, Na-plagioclase,quartz, quartz, chlorite chlorite and local dikes. Such granite dikes. biotite and occur in in the Dunka and tremolite, tremolite, conspicuously conspicuously occur Dunka Railroad Railroad- Horniels Hornfels and and have have been observed many other been observed at at many other localities. The volcanic volcanic horfelses horfelsesatat the the base base of of the lie above only aa few The the complex complex lie above only few hundred feet of of Virginia VirginiaFormation. Formation.This Thisisismuch muchthinner thinnerthan thanfarther farther to to the the west. hundred feet suggests the the Virginia was eroded eroded prior prior to extrusion Virginia was extrusion of of the the volcanic volcanic rocks. rocks. It suggests Perhaps this this accompanied preceeding the Keweenawan Perhaps accompanied regional regional doming doming preceeding Keweenawan episode episode of continental continental rifting rifting.• .... L 01 + . /I pi px 40 so 64 64 60 70 �I SYNGENETIC SYNGENETIC MODEL MODEL FOR THE THE ORIGIN OF OF THE THE WHITE WHITE PINE COPPER COPPER DEPOSIT DEPOSIT Thomas Geology Department, Department, Michigan Thomas A. A. Vogel, Vogel, Geology Michigan State University, University, East East Lansing, Lansing, Michigan 48824; M.B. M.B. McBride, McBride, Department Department of Agronomy, Michigan 48824; Agronomy, Cornell Cornell University, University, Ithaca, New New York York 14853; 14853; and Robert Robert Ehrlich, Ehrlich, Geology Geology Department, Department, University University of of South Carolina, Carolina, Columbia, Columbia, South South Carolina Carolina29208. 29208. South ABSTRACT ABSTRACT The syngenetic model model for the the mineralization mineralization of of the thelower lowerNonesuch Nonesuch Shale Shale at at The syngenetic White Pine, Michigan depends upon copper entering the basin complexed White Michigan depends upon copper entering the basin complexed to clay clay In order order for this this model model to to be be viable viable for for the the White White Pine Pine deposit, deposit, it it isis minerals. In necessary to demonstrate necessary to demonstrate that significant significant copper copper can can be be complexed complexed to clay clay minerals and that that these in the source minerals and these minerals minerals can be be produced produced in source terrane for for the the lower Shale. Furthermore, if copper lower Nonesuch Nonesuch Shale. copper entered entered the the basin basin complexed complexed to clay minerals, the clay clay mineral mineral fraction fraction present presentininthe thelower lowerNonesuch Nonesuch Shale Shale may may record occurrence. its occurrence. Basalts and andesites are extensively exposed inin the the rocks Basalts and andesites are extensively exposed rocks of of the theMiddle Middle Keweenawan and all all workers workers agree agree that that the sediments Keweenawan and sediments of of the the Nonesuch Nonesuch Shale Shale are derived from weathering of these rocks. derived predominantly predominantly from rocks. In In most environments, the first clay clay mineral mineral to to form form from from weathering weathering of of basalt basalt isismontmorillonite. montmorillonite. The dominant clay mineral mineral assemblages assemblagesthat that exist exist in Shale are are aa dominant clay in the the lower lower Nonesuch Nonesuch Shale complex intergrowth of of chlorite chlorite and and illite. illite. AA probable for these intergrowths complex intergrowth probable origin for dlagenetic alteration of of montmorillonite. montmorillonite. Many Many workers workers have is due to a diagenetic have traced the change from from montmorillonite montmorillonite to chiorite-illite chlorite-illite intergrowths intergrowths in in the thegeologic geologiccolumn column and the alteration to chlorite-illite and experimentally, experimentally, the alteration of of montmorillonite montmorillonite to chlorite-illite is is well well known. It It is is reasonable reasonable that that the thechlorite-illite chlorite-illiteintergrowths intergrowthsininthe thelower lowerNonesuch Nonesuch known. Shale been diagenetically Shale represents represents montmorillonite montmorillonite that that has been diagenetically altered. their ability One of of the One the characteristic characteristic features features ofofmontmorillonite montmorillonite is is their ability to to adsorb cations, and and considerable considerableresearch researchhas hasbeen been devoted devotedtoto the the study adsorb cations, study of the the adsorption and exchange exchange properties properties of of copper adsorption and copper and and clays. clays. Heydemann Heydemann (1959) (1959) 1959, 1959, was the first firstworkers workers totoshow showexperimentally experimentally that that copper copper could could be be was one one of of the In addition, selectively adsorbed from copper selectively adsorbed on on montmorillonite montmorillonite from copper ions ions in in solution. solution. In well-knownthat that organic-clay organic-clay complexes complexeswill will adsorb adsorb copper copper from from dilute it is well-known dilute Steger has suggested aqueous solutions solutions (Kaufherr, (Kaufherr, et. et. al., 1971; aqueous 1971; Steger, 1973). 1973). Steger suggested that organic-clay complexes complexes could could be be used used to to remove remove trace amounts organic-clay amounts of of copper, copper, zinc zinc and and Many workers workershave have shown shownthat that copper copper is is bound lead from from water. water. Many bound preferentially lead over on organic-clay complexes. over other divalent cations on A study study of of the clay A clay fraction fraction of of samples samples from from aa copper-rich, copper-rich, black black shale shale was was undertaken determine if some some of the the copper copper was was structurally structurally bonded bonded in undertaken in in order order to determine the clay lattice and state of the the clay mineral mineral lattice and also also to determine determine the oxidation oxidation state the iron iron in in order to to better of formation of these these minerals. minerals. The order better understand understand the the environment environment of formation of The original samples samplescontained contained4.75% 4.75%copper copperand andthethe <<22 micron micron (clay) (clay) fraction fraction original micron fraction After leaching leachingthe the << 2 micron fraction with contained 0.96% copper. copper. After with sodium sodium contained 0.96% no Cu Cu II was removed, chloride (NaTPB NaC1), no tetraphenyl boron - sodium (NaTPB - NaCl), II was removed, thus tetraphenyl boron sodium chloride A indicating that that the copper indicating copper is is not not present present as as interlayer interlayer Cu Cu IIII or or soluble soluble Cu Cu II. II. A detailed electron microscopeand and microprobe microprobestudy studyofofthe the <<22 micron detailed electron scanning scanning microscope micron fraction failed failed to show the presence presence of of any any free free native native copper copper or or chalcocite grains. fraction show the grains. Electron Spin Resonance studies studies of of these samples Electron Spin Resonance samples show show Fe Fe III III (G (G about 4.0) 4.0) in octahedral sites sites in in the the clay of Fe III is octahedral clay minerals. minerals. Abundance Abundance of III in in the clay day minerals minerals is 65 65 �probably about 2-3% probably about 2-3% (determined (determined by by comparing comparing the spectrum spectrum with with known known clays). clays). The presence of of Fe Fe III HIininthe the octahedral octahedral sites sites must result The presence result from from the themontmorillonite montmorillonite having formed in an an oxidizing oxidizing environment. environment. These These data are are consistent consistent with withaamodel modelininwhich which montmorillonite montmorillonite formed formed in in the weathering and copper probably as as a copperweathering environment environment and copper was was complexed, complexed, probably coppercopperinin the the <<22 micron organic complex. complex. The The insoluble insoluble copper micron fraction fraction indicates indicates that that when broke down, some of of the copper when the copper-organic-montmorillonite complex complex broke down, some copper was was forced forced into into the octahedral octahedral sites sites of of the theresulting resulting chiorite-illite chlorite-illite intergrowth. intergrowth. However, most of of the the copper copper was was released released and and provided provided the the source source of of copper However, most copper for for the mineralized mineralized zone. zone. REFERENCES CITED CITED Heydemann, A., 1959, Heydemann, A., 1959, Adsorption Adsorption ans sehr sehr verdUnnten verdUnnten Kupferlösungen Kupferlosungen an reinen reinen Tonmineralen; Geochim. Geochim. Cosmochim. Cosmochim. Acta. v. 15, 15, p. p. 305-329. 305-329. Kaufherr, N., N., Yariv, Yariv, S., S., and and Heller, Heller, L., L., 1971, 1971, The The effect effectof ofexchangeable exchangeable cations cationson on the sorption by montmorillonite; montmorillonite; Clays Clays and and clay clay minerals, v. sorption of chiorophyllin chlorophyllin by 19, p. 193-200. 193-200. Steger, H.F., the mechanism of adsorption adsorption of of trace copper Steger, H.F., 1973, 1973, On On the mechanism of copper by bentonite; Clays and clay minerals, minerals, v. v. 21, 21, p. p. 429-436. 429-436. 66 �GNEISS AND AND MIGMATITE MIGMATITEOF OF ARCHEAN ARCHEAN AGE AGE IN IN THE THE PRECAMBRIAN GNEISS BASEMENTOF OF CENTRAL CENTRAL WISCONSIN, BASEMENT WISCONSIN, U.S.A. W.R. Van Van Schmus, Schmus, Department of Geology, University University of of Kansas, Kansas, Lawrence, Lawrence, W.R. of Geology, Kansas, 66045, 66045,and and J.L. 1L. Anderson, Department of of Geological Kansas, Anderson, Department Geological Sciences, Sciences, University University of Southern Angeles, California California 90007 of Southern California, Los Los Angeles, 90007 ABSTRACT Many of of the the southernmost of the the Precambrian in central southernmost exposures exposures of Precambrian shield shield in central Many Wisconsinconsist consistofofgneiss, gneiss,migmatite, migmatite, and/or amphibolite with associated younger Wisconsin younger intrusive rocks rocks ranging ranging in in compositon compositonfrom from tonalite tonalite to granite. Rb-Sr intrusive Rb-Sr whole-rock whole-rock analyses and U-Pb zircon analyses show that analyses and U-Pb zircon analyses show that the migmatitemigmatite- and and gneiss-forming gneiss-forming events occurred events occurred about about 2.8 b.y. b.y. ago. ago. Ages Ageson onminerals minerals and and younger younger plutonic plutonic rocks rocks indicate that older indicate older gneiss gneiss and and migmatite migmatite were were intruded intruded and and locally locally metamorphosed metamorphosed during major major events events 1.5 during 1.5 to 1.9 b.y. ago. Rb-Sr isochrons for for the the migmatite have Rb-Sr isochrons have elevated initial initial Sr87/Sr86 Sr 87 /Sr 86 ratios (ca. 0.710), suggesting suggestingthat that the the migmatites migmatites formed formed from from crustal rocks 0.710), rocks of intermediate intermediate to granitic were themselves themselves formed formed more more than than 3.0 b.y. ago. granitic composition composition arid and which which were 3.0 b.y. ago. If this If this is true, true, then then the thegneissic gneissic and and migmatitic migmatitic rocks rocks inincentral centralWisconsin Wisconsin may may represent an an eastward extension of of the the ancient represent eastward extension ancient ( >> 3.3 3.3 b.y. b.y. old) old) Minneosta Minneosta River River Valley Valley Terrane. 67 �COMPOSITIONAL VARIATIONS VARIAnONS OF MINNESOTA RIVER VALLEY VALLEY AMPHIBOLITES AMPHIBOLITES P.W. K.3. Schulz, Schulz, and and B.V. B. V. Nielsen, Nielsen, Minnesota Minnesota Geological Geological Survey, Survey, St. P.W. Weiblen, Weiblen, K.J. Paul, Minnesota Minnesota 55108 55108 ABSTRACT Studies of Archean at Morton, reveal that hornStudies of Archean amphibolites amphibolites at Morton, Minnesota Minnesota reveal horn- blende-plagioclase enclaves(two (twometers meters inin size) size) contain contain only blende-plagioclase enclaves only rare rare clinopyroxene, clinopyroxene, whereas larger enclaves Both types types are whereas larger enclaves (20 (20 meters long) long) contain contain up up to to 30%. 30%. Both rimmed by biotite. biotite. Except rimmed by Except for for K, K,compositional compositional variations variations within within and between between the two types types reflect reflectigneous igneous processes processes and and resemble resemble northern northern Minnesota Minnesota greenstones greenstones (Figs. la & & b). Some Some amphibolites amphibolites from from near near Delhi Delhi and and Montevideo Montevideo contain contain -<< 10 10 wt, % Al2O.. wt. Al 20 j • Their Their compositions compositions mimic mimic komatilte-like komatlite-like greenstones greenstones (Figs. (Figs. Ic lc & & d). d). The data that magmas data 'uggest suggest that magmas of of igneous igneous precursors precursors of of certain southwest southwest The Minnesota amphibolites and and northern northern Minnesota greenstones were were generated generated from Minnesota amphibolites Minnesota greenstones similar source rocks in comparable tectonic regimes. regimes. .6 .5 to ta 1• .4 .4 .33 MINN l'lINN ' .6 .EttI .5 + b T\iC;::l RVEP VRLlEY TH TH MPHI60LITES • '. L. \ RLLEY RMPHI80LITES ; i ! .4 ! .3 t r .1 T 1.2 .2 .1 .2 .2 .1 :L t t .0 + .1 • i .0 EN—S 9N-S SN—7 5N-7 ... .4 .il c. .5 (!) CD .:J t ;9 m 19 17 • : T '!' CD <:> c. ! .b .~ i I .5Ir iCJ .6+ d , .6 .5 Td .6'- PVE9 \IPLLEY MI~·j~. Fl:VER W,U_EY HEL HBlPMPHISOL1TES RMPHI80LITES .34- cC MINr\ .4 .3 .3 17 15 IS 1d 13 12 x 12 ÷3 + 32 :~.4 ~ 8N-3 3N-2 EN—i 8N-I 36 'A 32 20 y 20 t 1.3 .6 1 VERMILION KOMRTIITES VERMiLION KOMRTI ITES I I .~ T .2 :~ ~ .11- i .0 .0+ . ~ .2 .2 <:> CD .3 .3 + . 1 TiI EN—S '" 8N-6 SN-S 3N-5 8N-4 xx SN—4 I .2 + t O-F,EENSTONE VERMILION GREENSTONE __ '" t .1 •.2 2 ~I' .3 ~b-I~1 j .; K56-75 ' x 56-756 i- 56-754 to 56-665 .• J T (!) 56-66:J i .5 cD 1- .3 + . -1- T .5. .o- ~ I' -i. W MO FE .I1N MN CR OP Rl PL SI MS FE SirIII PNR P NR T (!) CD 39 35 38 37 I .,. i K K j 40 6. t 1 <:> xX CD MG FE MN OP RL TI MG MN CR Rl SI 5 I TI PNP P NR K i< Log plots plots of of compositions compositions normalized normalized to Hawaiian tholeilte (as Fig. 1. 1. Log Hawaiian tholeiite (as oxides, oxides, right right to left: 8.1, 8.1, 10.04, 10.04-, .17, 10.9, 10.9, 13.4, 13.4-, 50.4, 50.4-, 2.7, 2.7, .28, .28, 2.3, 2.3, .53). .53). Numbers Numbers below below 00 have negative values. negative values. (Data (Data from Nielsen, Nielsen, in in prep., prep., Sims, Sims, P.K., P.K., 1972, 1972, and and Green Green and and Schulz, in prep). REFERENC ES REFERENCES Sims, P.K., 1972, Metavolcanic and associated Metavolcanic and associated synvolcanic synvolcanic rocks rocks in in Vermilion Vermilion Sims, P.K., 1972, district, in district, in Sims, Sims, P.K. P.K. and and Morey, Morey, G.B., G.B., eds., eds., Geology Geology of of Minnesota: Minnesota: A A Centennial Volume, Volume, Minnesota Geological Survey, p. 632. 68 �Rb-Sr GEOCHRONOLOGY AND TRACE ELEMENT ELEMENT GEOCHEMISTRY GEOCHEMISTRY OF GRANULITE FACIES ROCKS NEAR FACIES NEAR GRANITE GRANITE FALLS, FALLS, IN IN THE THEMINNESOTA MINNESOTA RIVER RIVER VALLEY VALLEY Wendell E. E. Wilson Wilson and and V. V. Rama Rama Murthy, Murthy, Department of of Geology Geology and andGeophysics, Geophysics, Wendell University of Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota Minnesota 55455 55455 ABSTRACT Sr- isotopic isotopic composition compositionand and the the trace-element trace-element abundances abundances of K, Rb, Rb, Sr, Sr, The Srand Ba Ba have have been been determined determined in in several several whole and mineral and whole rocks rocks and mineral separates from from four lithologic four lithologic units units in the the Minnesota Minnesota River River Valley, Valley, near Granite Granite Falls, Falls, Minnesota. Minnesota. The sampled units units are are the inner The sampled inner and and outer units units of of hornblende-pyroxene hornblende-pyroxene gneiss, gneiss, the biotite-garnet gneiss, gneiss, and and the the metagabbro metagabbro originally originally included included in in the the"hornblende"hornblendepyroxene gneiss" of Himmelberg Himmelberg (1968). (1968). Rb-Sr data give The The whole whole rock rock isochron isochronages ages (T) (T) obtained obtainedfrom from the the Rb-Sr data are give below; ages ages obtained obtainedfor for metamorphic metamorphic events, events, as as determi~ed determiied by below; by mineral mineral isochrons isochrons are given giveni21;ra8~ets. ibraets. All All ages areare in inunits yrs); all all errors errorsare are 20-. 2-. are ages unitsofofaeons aeons (10 (10 yrs); The initial Sr/ Sr ratios ratios (I) refer to the Sri Sr (I) refer the whole whole rock rock isochrons. isochrons. The Garnet-.Biotite gneiss Garnet-Biotite 0.14 (1.81); (1.81); I == 0.7008 +÷0.0009. 0.0009. T == 3.54 ~÷0.14 I-Iornblende-Pyroxene Gneiss Gneiss (outer (outer unit) Hornblende-Pyroxene T == 3.31 ~÷0.26 0.26 (1.78); (1.78); I == 0.7011 :-÷0.0012. 0.0012. Gneiss (inner Unit) Unit) Hornblende-Pyroxene Gneiss Data Data scatter precludes precludes attempts at dating. dating. Meta-gabbro of of Himmelberg Himmelberg (1968) (1968) T ==2.68 :+ 0.20 (l.80); (1.80); I == 0.7037 :-÷ 0.0001. Interpretations of the the above Interpretations of above data data are are subject subject to to the theusual usualambiguities ambiguities in in discussions ofgeochronological geochronologicalproblems problemsofofearly earlyArchean Archeanterranes. terranes. The discussions of The simplest simplest explanation seems to be that the combined section of hornblende-garnet-pyroxene explanation seems be that the combined section of hornblende-garnet-pyroxene granuLitefacies faciesrocks rocksatat Granite age of granulite Granite Falls Falls has has aa minurnum minumum age of 3.55 3.55 AE AE with with a pronounced metamorphism at at 1.8 1.8 AE. AE. The element patterns patternsofofthe thehornblende-pyroxene hornblende-pyroxene gneisses gneisses and and garnetgarnetThe trace element biotite gneisses graywackesofof island-are-alkali island-arc-alkalibasalt basalt affinities affinities and gneisses resemble resemble graywackes and the metagabbros resembles aa low-K metagabbros resembles low-K tholeiite. tholeiite. The rocks at Granite Granite Falls Falls The granitic rocks therefore represents aa very very old old layered sequence of of basaltic therefore probably probably represents layered sequence basaltic rocks rocks and and graywackes intruded by by the the Montevideo Montevideo Gneiss. Gneiss. 69 69 t �I PETROLOGY OF THE NORTHWEST CORNER OF PETROLOGY OF THE ARCHAEAN ARCHAEAN GNEISSES GNEISSES OF NORTHWEST CORNER THE SACRED HEART THE HEART PLUTON; PLUTON; MINNESOTA MINNESOTA RIVER RIVER VALLEY, VALLEY, MINNEOSTA MINNEOSTA lames L. Welsh, James Welsh, Department of of Geology Geology and and Geophysics, Geophysics, University Universityof ofWisconsinWisconsinMadison, Wisconsin ABSTRACT Approximately 66 miles miles south south of of Sacred Sacred Heart, Minnesota, Approximately Minnesota, along along the Minnesota Minnesota River Valley, the Sacred Sacred Heart Heart quartz monzonite River Valley, the monzonite is intrusive intrusive into into an an older older gneissic gneissic complex. Detailed in the the gneisses along the the northwestern Detailed mapping mapping in gneisses along northwestern portion portion of the the outcrop outcrop belt reveals reveals four four structurally structurally concordant concordant lithologies, lithologies, which which are are described described below from from south south to to north. below The southern part part of of the the area consists of the Sacred The southern consists of Sacred Heart Heart pluton. pluton. To To the the north, the pluton is in in gradational, gradational, but but apparently apparently intrusive intrusive contact contact with a salmonnorth, pluton is salmonpink clinopyroxene clinopyroxene syenite, syenite, which which contains contains abundant, nebulitic, mafic pink abundant, commonly commonly nebulitic, Manyofof the the larger inclusions inclusions. Many inclusions are zoned, zoned, consisting consisting of of pyroxene-rich pyroxene-rich rinds and rinds and hornblende-rich hornblende-rich cores. Separated Separated from from the syenite syenite by by aa sill-like sill-like body body of of quartz monzonite is aa sequence of interlayered tonalitic monzonite is sequence of tonalitic gneisses gneisses and and amphibolites, amphibolites, which are are in in turn which turn separated separated by by another another sill sill of quartz quartz monzonite, monzonite, from from a layered layered gneiss consisting consisting of of alternating alternating pink leucogranitic gneiss pink microcline-rich microcline-rich bands bands and and yellow yellow plagioclase-rich bands. bands. Numerous inclusionsofof tonalitic tonalitic gneiss gneiss are are contained contained in in the the plagioclase-rich Numerous inclusions quartz monzonite quartz monzonite monzonitelies lies toto the the north, monzonite sills. sills. More More quartz north, with with tonalitic tonalitic gneisses again again cropping cropping out out across across the the river. gneisses The represent the oldest The interlayered interlayered tonalitic tonalitic gneisses gneisses and and amphibolites amphibolites represent oldest Isoclinal folding foldingand andshearing shearingwithin withinthe the unit unit indicate rocks exposed exposed in in the the area. Isoclinal rocks deformation and probable probable metamorphism metamorphismprior priortoto the the intrusion intrusion of of the quartz deformation and quartz monzonite. Field monzonite. Field relations relations and and modal modal data suggest suggest that that the theplagioclase-rich plagioclase-rich bands bands of are part of the the layered layered leucogranitic leucogranitic gneiss gneiss are part of of the thetonalitic tonaliticgneiss gneisscomplex. complex. Mineral textures and Mineral textures and modal modal data also also suggest suggest aa possible possible relationship relationship between between the microdine-rich microcline-rich bands bands of of the the layered layered leucogranitic leucogranitic gneiss gneiss and and the thepyroxene pyroxene syenite. syenite. Although the the microcline-rich microcline-rich bands bands of of the layered leucocratic Although leucocratic gneiss gneiss are are somewhat somewhat the syenite more more quartz-rich quartz-rich it is thought thought that desilication desilication of of the syenite occurred occurred by by conversion of of aa former former amphibolite conversion amphibolite to aa pyroxene-rich pyroxene-rich rock, rock, during during the intrusion intrusion of a potassium-rich potassium-rich magma. This This reaction reactionisisevidenced evidenced by by the the zoning zoning of of the the inclusions inclusions within the the syenite. within The following sequence sequence of of events events is is thought to have The following have occurred: (1) (1) deformation and metamorphism and metamorphism of a volcanic pile forming forming the the tonalititc gneisses and amphibolites; (2) dilatation dilatation of of the gneiss followed by by infiltration infiltration of of a amphibolites; (2) gneiss sequence sequence followed potassium-rich magma magma into into the the rupture zones, forming potassium-rich forming the pyroxene pyroxene syenite and the layered leucogranitic gneiss; intrusion of of the the quartz monzonite. gneiss; (3) (3) intrusion 70 �FIELD TRIPS �I FIELD TRIP A FIELD MINNESOTA RIVER VALLEY MINNE50TA VALLEY FIELD TRIP AND FIELD AND CONFERENCE No formal formal guidebook for the the Minnesota No guidebook for Minnesota River River Valley Valley Field Field Trip Trip has has been prepared prepared at the been the specific specific request request of ofS.S. 5.5. Goldich, Goldich, convenor. convenor. Abstracts of talks talks given given at at the theTuesday Tuesday evening evening discussion discussion at RedwoodFalls Fallsare areincluded includedasasa apart partofof these these Proceedings. Proceedings. A Redwood A collection collection of of reprints pertaining reprints pertaining to the the geology geology of of the theMinnesota Minnesota River River Valley Valley and and an an informal set set of stop informal stop descriptions descriptions will will be be provided provided to the the participants. participants. However,inasmuch inasmuchasasthe thelatter latter are not However, not quotable quotable for for publication publication they are not included included here. 73 73 I �• FIELD TRIP BB ENGINEERING GEOLOGY, PLEISTOCENE GEOLOGY AND ENGINEERING GEOLOGY, GEOMORPHOLOGY IN THE THE TWIN TWIN CITIES AREA AREA INTRODUCTION INTRODUCTION 8:00 May 5th 5th St. Paul 8:00 a.m. Wednesday, Wednesday, May Paul Radisson Radisson Hotel, Hotel, St. St. Paul. cost parking parkingisis available available just just across across the the river river from Paul. Low Low cost from the the hotel, hotel, immediately west of the immediately west the first firstexit exitfrom fromthe theWabasha WabashaAvenue Avenue bridge. bridge. Field Field clothes are recommended for underground construction inspection. inspection. Bring recommended for underground construction Bring aa hard by bus bus to to the hard hat if if you you have have one. one. Transportation Transportation by the University University of of Assemble: Assemble: Minnesota pus. Minnesota cam campus. a.m.,back of Pillsbury Optional Optional Assembly Assembly Point: Point: 8:30 8:30 a.m.,back Pillsbury Hall, Hall, University University of of Minneosta campus. Near-by opportunities are are limited. Those who Minneosta campus. Near-by parking parking opportunities who find it convenient may join join the the field field trip trip at this point rather than find convenient to do do so so may than going Paul. going to to St. Paul. MORNING ITINERARY MORNING The will divide divide into into two two equal at the The excursion excursion will equal groups groups at the University University of of Minnesota campus. One One group groupwill willbebetransported transportedtoto site site A A by by bus bus for for the Minnesota campus. on foot foot to site B. first half half of of the the morning. morning. The The second second group group will will proceed proceed on B. In mid-morning mid-morningthe the two two groups groups will willexchange exchangesites sites via via bus bustransportation. transportation. In Site A; Site A; Como Como Avenue Avenue Storm Storm Sewer Sewer Tunnel. Tunnel r City City of ofMinneapolis: Minneapolis: Ralph Rabus and Ray Ray Sterling; Sterling; guides) guides) The The portal portal of of the the tunnel tunnel isis located located at the Rabus and the foot of the River on on the the northeast bank foot the bluffs bluffs along along the the Mississippi Mississippi River bank about The site site affords view of of the half a mile half mile below below St. St. Anthony Anthony Falls. The affords aa good good view incised gorge gorge of of the Mississippi, carved since since the the end incised Mississippi, carved end of of the the Pleistocene Pleistocene glaciationasas St. St. Anthony AnthonyFalls Fallsretreated retreatedfrom fromits its original originalsite site at at the glaciation confluence of of the Minnesota and Mississippi Riverstotoits its present present site, confluence Minnesota and Mississippi Rivers about 88 miles miles upstream. upstream. The about The falls falls is is now now stabilized stabilized by a lock lock and and dam dam as facilities for control and well as water control and diversion facilities for the experimental experimental operations of of the St. operations St. Anthony Anthony Falls Falls Hydraulic Hydraulic Laboratory of the University University of Minnesota. Abovethe the falls falls the the river river flows flows on on aa pavement pavement of of hard, hard, slabby slabby Above Platteville Limestone. Limestone. The Platteville Platteville Limestone is underlain by two two to The Limestone is underlain by 75 �three feet feetofofsoft softshale, shale,known knownasasthe theGlenwood Glenwood Formation, Formation, beneath beneathwhich which is the St. St. Peter PeterSandstone, Sandstone, aa light light yellow yellow to to almost almost white, white, medium-grained medium-grained to fine-grained, fine-grained, friable friable sandstone sandstone composed composed almost entirely entirely of of well well rounded rounded but of quartz sand or two but frosted grains grains of sand with with one one or two percent of of clay clay binder. binder. The is very The sandstone sandstone is very massive, massive, and and in in many many exposures exposures appears appears to to have have almost no no bedding. bedding. It is is about about 150 150 feet thick thick in in the theTwin Twin Cities Cities basin. basin. These formations are are well exposed inin the the river These formations well exposed river bluffs bluffs visible visible from from the the portal site. A storm sewer A storm sewer tunnel, tunnel, 10 10 feet in in diameter, diameter, is is being being excavated excavated in in the St. Peter Sandstone by hydraulic hydraulicmining miningmethods. methods. AA jet jet of of water directed Sandstone by directed at the the St. St.Peter PeterSandstone Sandstoneloosens loosensthe theclay claybinder binderand andthe therock rockdecomposes decomposes into a slurry into slurry of of incoherent incoherent sand. sand. The The properties properties of the the sandstone sandstone which which allow it to allow it to be be mined mined by by this this method method also also allow allow the the rock rock to to ravel ravel upon upon exposure, especially especially where where skin skin stresses exposure, stresses are are developed developed ininunderground underground at the The Department Department of of Civil Civil and and Mineral Mineral Engineering Engineering at the openings. The University of Minnesota has developed University of Minnesota has developed aa sodium sodium silicate based based chemical chemical grout which grout which penetrates porous porous rocks rocks and and hardens hardens to consolidate consolidate the rock rock into aa strong, strong, durable durable material. material. The is sprayed sprayed on on the the surface surface of of the into The liquid liquid is tunnel to form tunnel form aa strong strong skin, skin, which which supplies supplies all of the the support support needed needed where where has not not been the St. Peter Peter Sandstone Sandstone has been adversely adversely affected by by fracturing and and In weaker weaker zones decomposition. In zones shotcrete and and epoxy-cemented epoxy-cemented rock rock bolts bolts are used used for additional support. Research Research by by Walter Walter Parham Parham of of the theMinnesota Minnesota Geological Geological Survey Survey has has shownthat that the the primary primary clay clay minerals minerals inin the the St. St. Peter Sandstone are illite shown Sandstone are and montmorillite, montmorillite, which which form form an an effective effective binder, and binder, even where present in in where these clays very small quantities. In very small In zones zones where clays have have been been converted converted by by diagenesis toto kaolinite, kaolinite, the the kaolinite diagenesis kaolinite tends tends to occupy occupy interstices between between sand grains, grains, rather rather than than coating sand coating the grains, grains, and and much much of the intergrariular intergranular slight change cohesion This slight change in in mineralogy mineralogy greatly weakens weakens the St. cohesion isis lost. This Peter Sandstone and has has strongly strongly affected underground Sandstone and underground construction locally locally This phenomenon phenomenondoes doesnot not appear appear to to have in the Twin in Twin Cities Cities area. This have been been encountered encountered in in the the present tunnel. Experimental Tunnel Tunnel and and Test Site B; Test Chamber: Chamber: (Donald (Donald Yardley Yardley and and 13; Experimental Charles Nelson, guides). The Charles Nelson, guides). The Department Department of of Civil Civil and and Mineral Mineral Engineering Engineering at the at the University University of of Minneosta, Minneosta, aided aided by by aa grant grantfrom from NSF-Rann, NSF-Rann, is is construting an an experimental experimental tunnel tunnel and and large underground chamber beneath construting underground chamber 76 �I the University University of Minnesota Minnesota campus campus to develop develop construction construction methods methods and and structural parameters spaces. One parameters for the the design design of of large large underground underground spaces. One of of the primary is to take advantage primary purposes purposes is advantage of of the the very very large largeenergy energy savings savings that may may be be achieved achieved through through the the better better use useofofunderground underground space. space. Underground space also also provides provides opportunities opportunities for for relieving relieving urban urban congesconges- tion tion and and mitigating mitigating the the environmental environmental impacts impacts of many many transportation, transportation, industrial and and utility facilities. The will be The experimental experimental excavation excavation will be entered entered through through an an existing existing steam tunnel tunnel of the the University University heating heating system system (The (The temperature temperature is is high. high. steam Be to shed prepared to shed your your jacket). jacket). At At one one point point in in the the passage passage through through the Be prepared concrete-lined steam tunnel there is is an an intersection intersection with with an an unlined unlined tunnel. tunnel. This tunnel, excavated excavated in in the the St. This tunnel, St. Peter Peter Sandstone, Sandstone, exhibits exhibits a persistent, persistent, vertical crack or fissure in its crown which makes makesitit appear appear that that the crown which the tunnel tunnel follows aa vertical joint joint zone. zone. In In fact, the the fissure fissure has has developed developed as as the the follows result of the tensional characteristically develops tensional stress which which characteristically develops in in the crown crown of a circular circular arch archininan anunderground underground structure structure when when the the overlying overlying load load is is of shifted from the the rock that was to the the rock on either either side side of of the shifted from rock that was removed removed to rock on tunnel in arch. tunnel in the the abutments to the arch. The stratigraphic stratigraphic succession successionatat the the site consists The consists of: Glacial Glacial drift, 45 45 St. Peter Platteville limestone, 30 ft.; ft.; Glenwood shale, 44 ft. ft. to 55 ft.; ft.; Platteville limestone, 30 Glenwood shale, ft.; St. Peter sandstone, penetrated penetrated 99 ft. ft. to 10 ft. at sandstone, 10 ft. at invert invert elevations. elevations. The experimental tunnel and and chamber chamber isis partly partly excavated The experimental tunnel excavated in weak weak shale of the Glenwood Formationand andpartly partly in in St. St. Peter shale of Glenwood Formation Peter Sandstone. Sandstone. The roof the chamber chamber is is formed formed by by hard, hard, slabby slabby limestone roof of the limestone of of the Platteville 100feet feet of of unlined access tunnel tunnel isis traversed Formation. About About 100 unlined access traversed in the the GlenwoodFormation, Formation,a ashale shaleunit, unit,two twototo three three feet thick, Glenwood thick, characterized characterized by aa persistent by persistent soft mud mud seam seam about about one one inch inch thick thick containing containing pyrite pyrite The shale severe deterioration and air crystals. The shale shows shows severe deterioration and air slaking slaking due due to to exposure. About 70 70 feet feet of excavated in in St. St. Peter About of the access access tunnel tunnel have have been been excavated Sandstonewhich whichhas hasbeen been grouted grouted by by spraying spraying with with the the sodium Sandstone sodium silicate compound A. compounddescribed described under under Site Site A. Another 70 70feet feet of of the the tunnel Another tunnel in in St. Peter Sandstone Sandstone has has been beenleft left untreated as a control. The test test chamber is in of excavation. excavation. A The chamber is in the process process of A drift drift has has been been driven the the full full length lengthofof 100 100feet, feet, and and aa cross cross drift has been driven been driven driven the full width of of 50 50 feet. feet. The in one one section section to to 20 20 feet. feet. width The long long drift drift has has been been widened widened in Thecompleted completedchamber chamberwill willbebe100 100byby5050feet, feet,8 8feet feethigh. high. The The Platteville Platteville The 77 77 I �Limestone will form form the the roof roof of of the the chamber. Limestone will chamber. The The invert invert will will be be in in the the St. St. Peter Sandstone. from the the roof will cut cut about Sandstone. The The walls walls from roof down down will about 4 feet of of Glenwood shale and andabout about 44feet feet of of St. Peter Glenwood shale Peter Sandstone. Sandstone. Excavation of the the access tunnels Excavation of tunnels and and chamber chamber has has been been entirely entirely by by hand using pneumatic pneumatic drills drills and and spades hand operations, operations, using spades and and hydraulic hydraulic rock rock splitters. This This has has been been necessitated necessitated by by the small small size of the access access tunnels both the the St. Peter (4 (4 feet wide wide by by 6.5 feet feet high). high). However However both Peter Sandstone Sandstone and and the Glenwood shale are are readily readily excavated excavated in in this Glenwood shale this way. way. The The hydraulic hydraulic rock rock splitters have very useful useful in in spalling spallingoff off the the shale splitters have proved proved very shale to the the bedding bedding surface in the surface the overlying overlying Platteville Platteville Limestone Limestone which which has has been been chosen chosen to to form form the roof. As As construction construction proceeds, proceeds, the the underground underground chamber is being being thoroughly instrumentedtoto determine determine rock rock deflections, deflections, stresses, stresses, and thoroughly instrumented and the influence of an an overlying overlying perched perched water water table on structure. influence of on the underground underground structure. Instrumentation includes six-point extensometers, extenso meters, two-point extensometers, and the roof meters, and inverted inverted piezometers piezometers installed installed from from below below through through the roof into the perched into perched water water table table above above the the Platteville PlattevilleLimestone. Limestone. A boresupport for for the roof scope is being used to to examine drill being used dr ill holes. Principal Pr incipal support roof is is provided by epoxy-grouted rock bolts provided by epoxy-grouted rock bolts which which consolidate consolidate the the overlying overlying Platteville Limestone Limestone into a rigid rigid plate. Noon: Box lunch picnic. Noon: Box AFTERNOON ITINERARY ITINERARY Stanley Chernicoff, Field Leader Stanley Leader the Twin The surficial geology geology of of the Twin Cities Cities Metropolitan Metropolitan Area Area is is The surficial dominatedby bythe the effects effects of of the late dominated late Pleistocene Pleistocene glaciation glaciation of of Minnesota. Minnesota. The glacial glacial events events that modified are reconstructed The modified the regional regional landscape landscape are by interpreting the deposits of glacial by interpreting the deposits of glacial materials materials and and their their associated associated landforms. landf or ms. In the Metro In Metro area, area, glacial glacial deposits deposits from from two two points points of of origin origm have have been identified. identified. Approximately years ago, ago, an an ice lobe accumulating been Approximately 20,000 20,000 years basin advanced in the Lake Superior basin advanced along along aa bedrock bedrock conduit conduit (the MinneapolisLowland) Lowland)totoaa terminal Minneapolis terminal position position topographically topographically expressed expressed locally as as the St. Croix locally Croix moraine. moraine. This This land land form, characterized by by hills hills and and is composed of poorly depressions ice-block lakes, lakes, is composed of poorly sorted sorted depressions dotted dotted with with ice-block traversed eastern mineral constituents constituents entrained entrained by by the the glacier mineral glacier as as it traversed eastern 78 �Minnesota. The quantities of red The bedrock bedrock supplied supplied quantities red sandstone, sandstone, basalt, basalt, and and red that impart impart the the characteristic red granophyre granophyre that characteristic red red hue hue to to Superior Superior lobe lobe drift. drift. Approximately 16,000 years years ago, Approximately 16,000 ago, ice ice originating originating in in southeastern southeastern Manitoba and northwestern northwestern Minnesota Minnesota advanced advanced along along the the Red River Manitoba and River valley valley toward a terminal terminal position position near near Des Des Moines, Moines, Iowa. Iowa. A A short-lived short-lived extension extension of the the Des Des Moines Moines lobe lobe (the (the Grantsburg Grantsburg sublobe) sublobe) entered entered the the Minnesota Minnesota lowland from the the southwest across the northwest lowland from southwest and and proceeded proceeded across northwest corner of the metropolitan the recently metropolitan area overriding overriding the recently deposited deposited red red glacial glacial drift. The of the Grantsburg are markedly different from The deposits deposits of Grantsburg sublobe sublobe are markedly different from the Superiorlobe lobematerials. materials. A long its its route route of of advance, advance, the the ice ice traversed Superior A long traversed a sedimentary sedimentary terrane terrane incorporating incorporating fragments fragments of of Paleozoic Paleozoic limestone, limestone, The and the dolomite, dolomite, and and siliceous siliceous shale. The carbonate carbonate composition composition and the diagnostic grey grey color color (yellow (yellow or tan tan in in oxidized oxidized exposures) exposures) easily easily distinguish distinguish sublobe drift from Grantsburg sublobe from the thereddish—colored reddish-colored Superior lobe sediments. A field review review of the the geology geology of of an an urban urban center centershould should describe describe the the geologic character character of of the area and, geologic and, wherever wherever possible, possible, relate the the observed observed physical conditions conditionstoto their their land-use land-use potential. potential. The The object object of of this part of physical of the excursion to introduce the salient features excursion isis to introduce the features of of the thelocal localgeology geology and and promote discussion regarding responsible responsible urban urban development development within within the promote discussion regarding geologic framework. ace: Stop Grey Till Till - Red Till Till Interf Interface: Stop C; C; Grey New New Brighton Brighton Quadrangle Quadrangle - N. The stratigraphic relationship and Matterhorn Matterhorn Drive. Drive. Danube Road Road and Danube till and between the the red between red Superior Superior lobe lobe till and the theoverlying overlying grey grey Grantsburg Grantsburg of red red till have sublobetill till isis demonstrated demonstrated at at this sublobe this locality. Masses Masses of have been been incorportated into into the the grey till creating the thin incorportated grey till thin interlaminations. interlaminations. Stop D; Anoka Anoka Sandplain: Sandplain: Stop ID; New Brighton Quadrangle-County Road Road I and New Brighton Quadrangle-County and Lexington Ave. Ave. Sand-charged Sand-chargedmeltwaters meltwatersassociated associated with with the the wastage Lexington wastage of of the Grantsburg sublobe constructed constructed this this extensive extensive sandplain. sandplain. The the Grantsburg sublobe The plain is characterized by characterized by ice-block ice-block depressions depressions and sand sand dunes. dunes. The high The high water of the relatively table is a consequence consequence of relatively low low transmissivity transmissivity of of the the underlying underlying glacial till. glacial River; Abandoned Valley Valley of the Mississippi Stop Ej Mississippi Riverj E; Abandoned Quadrangle—WheelockParkway Parkwayand and Nebraska Nebraska Ave. Quadrangle-Wheelock Ave. 79 Paul East St. Paul East Alongthe the route Along route of of �travel travel from from the theAnoka Anoka Sandplain Sandplain to this locality, the the alignment alignment of of ice-block ice-block lohanna, Josephine, Josephine, McCarron) McCarron) represents represents a lakes (Round, (Round, Valentine, Johanna, lakes former course course of of the theMississippi Mississippi River. River. The The bedrock bedrock valley valley is buried buried by by deep deposits of glacial drift. drift. Stop Park: St. Paul Stop F; Fi Indian Indian Mounds Mounds Park: Paul East East Quadrangle Quadrangle -- Warner Road. This This site affords affords aa view view of of the theMississippi Mississippi River River floodplain. floodplain. The The geological and and environmental elements of environmental elements of the floodplain floodplain management management issue issue (ie. the construction of dikes dikes at at the Holman construction of Holman Field Field airport airport and and the Pig's Pig's Eye Eye coal coal terminal) are visible. visible. Stop Stop G; G; Perched Lake Lake Plains Plains within within the the St. St.Croix CroixMoraine:White Moraine:White Bear Bear Lake Lake This This level level plain plain represents reversalofofaa glaciated glaciatedterrain. terrain. At represents aa characteristic topographic topographic reversal At one byice ice that that fed one time, time, the plain plain was was surrounded surrounded by fed meitwater meltwater into into an an East Quadrangle East Quadrangle - County Highway Highway 99 and and 115 115 St. St. The subsequent subsequent wastage wastage of of the surrounding enclosed basin. basin. The surrounding ice resulted in in the perching perching of basin basin sediments sediments above above the surface surface previously previously covered covered by by ice. Stop Hi H; Land-Use Land-Use Planning PlanningininaaGlaciated Glaciated Terrain: Terrain: Marine Stop Marine on on the St. Croix This This site was was one of of several proposed County Sanitary Sanitary Landfill. Landfill. The proposed for the the Washington Washington County The glacial glacial drift of the drift the locality locality includes includes a mantle mantle of of bess loess(windblown (windblown silt) and and dense dense red till. The red The suitability suitability of of this this site sitefor foraalandfill landfillwill will be be discussed. discussed. 81 (May Ave.) and and 155 Quadrangle - County Road 81 Quadrangle (May Ave.) 155 St. 80 �1 tr ?fkt? \ N '\\\ III 1ri4 I —- . I - L i FL 'Lii NJI\. ------—------ .... -- :- 1111 - • 1-94 to 1m -... -~ 0 sr . F - - / IF F-r-irt r7—1 rr-i / .5 .s- IL. .. \.Jr =-T: — ... S 0 ___ :: Pa -- LJiiEijF IJ JUf r1Jc?tLTi1JA1)o 1 —.-.i[ '- ii . N CAMPUS ..- z.4 I - ,/ 4.. J _ J i V. __ I r:: .... � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1976 Description An account of the resource Institute on Lake Superior Geology. St. Paul, Minnesota. May 3-7, 1976. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1976 Contributor An entity responsible for making contributions to the resource B.E. Aaquist J.L. Anderson G.A. Ankenbauer Larry L. Babcock W.A. Bartlett Robert L. Bauer J. Baysinger G.P. Beakhouse Dieter Birk Bill Bonnichsen Emmy Booy J.M. Bratt Charles Brumleve James R. Burnell, Jr. Keros Cartwright E.N. Cameron W.F. Cannon C.L. Chou Donald M. Davidson, Jr. James M. DeGraff B.R. Doe M.H. Delevaux L.J. Drew Stanley J. Dyl Robert Ehrlich S.S. Goldich A.M. Goodwin C.F. Gower James G. Grimes N.B.W. Harris Henry Halls Tsu-Ming Han G.N. Hanson C.E. Hedge Sue I. Jacobsen Allan M. Johnson Manfred M. Kehlenbeck Gene L. LaBerge T.M. Levy M.S. Lougheed R.S. Maass J.J. Mancuso M.B. McBride Lyle D. McGinnis L.G. Medaris, Jr. Robert P. Meyer, Jr. Robert Moore M.G. Mudrey, Jr. Paul E. Myers Syed Neaz Ahmad Edward L. Nebrija C.R. Nelson B.V. Nielsen Richard W. Ojakangas Bruce C. Parker Eugene C. Perry, Jr. Zell E. Peterman H.O. Pfannkuch Dave Pollack Neil M. Pope William C. Prinz V. Rama Murthy C. Riddle James M. Robertson W. Rohrer Frederick J. Sawkins K.J. Schulz Nancy Scofield Donald I Siegel P.K. Sims Eugene I. Smith T.E. Smith Harry O. Sorenson David W. Snider David L. Southwick S.W. Stuhr F.M. Swain R.U. Suda R.M. Tyson A. Turek W.R. Van Schmus Thomas A. Vogel L.J. Walters P.W. Weiblen James L. Welsh Wendell E. Wilson J.L. Wooden D.H. Yardley Charles T. Young Robert E. Zartman Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/4d5f21876dae8187655f5bdd3788714d.pdf 68bc6e24596e10eeea5abbcd8bbaf56f PDF Text Text I INNESOTA i' ;i �I I 1 2 1 3 I I I I 1 I. 1. THREE SYMONS SYMONS55 1/2' 1/2' SHORT-HEAD, THREE SHORT-HEAD JAND ANDTWO TWOSYMONS SYMONS I 1/14' STANDARD 4 1/4' STANDARD CONE CONE CRUSHERS CRUSHERS OPERATING OPERATING AT /4 BLYVOORUITZICHT GOLD MINE MINE, BLYVOORUITZICHT GOLD CARLETONVILLEJ J CARLETONVILLE, TRANSVAAL, REPUBLIC AFRICA, TRANSVAALJ REPUBLIC OF OF SOUTH SOUTH AFRICA. 2, 2. P & H MINING ~ MINING SHOVELS, SHOVELS J BUILT BUILT ININMILWAUKEE MILWAUKEE BY BY HARNISCHFEGER., HARNISCHFEGER J HAVE HAVE BEEN BEENWORKING WORKINGYEAR—ROUND YEAR-ROUND REMOVING OVERBURDENAND ANDMINING MINING IRON REMOVING OVERBURDEN IRON ORE ORE AT AT I I 1 DOFASCO'S ONTARIO J DOFASCO'S ADAMS ADAMSMINE MINEAT AT KIRKLAND KIRKLAND LAKE LAKE, J ONTARIO, CANADA SINCE IT IT BEGAN IN 1964k CANADA SINCE BEGAN OPERATIONS OPERATIONS IN 1964. 3. 3, ROTARY KILN KILN COMPLETES INDURATION OF OF IRON ROTARY COMPLETES INDURATION IRON ORE ORE PELLETS AT AT 2400°F 2'400°F IN PELLETS INTHIS THISGRATE—KILN ~ PELLETIZING PELLETIZING PLANT IN PLANT IN MINNESOTA. MINNESOTA. I �PROCEEDINGS Twenty Fourth Twenty Fourth Annual Annual Meeting Meeting INSTITUTE ON LAKE INSTITUTE LAKE SUPERIOR SUPERIOR GEOLOGY HELD AT HELD AT THE THE PFISTER HOTEL PFISTER HOTEL MILWAUKEE r~IlH,~UKEE WISCONS IN WISCONSm MAY9-14 9-1I4 1978 MAY 1978 J SPONSORED BY BY THE SPONSORED THE DEPARTMENTOF OF GEOLOGiCAL GEOLOGICAL SCIENCES DEPARTMENT SCIENCES UNIVERSITY OF UNIVERSITY OF WISCONSIN-MILWAUKEE WISCONSIN-MILWAUKEE 53201 MIlWP\UKEE WISCONSIN \JI SCo;~S IN 53201 MILWAUKEE, G, MURSKY C,A, SAlOTTI AND ANDW1H. W,H,SCHRAMM SCHRAMM G1 MURSKY) C.A1 SALOTTIJ GEiJERAl IT Ji"{S GENERAL ED EDITJRS J J J I �1 I I I I I 1 I I I I I SALES I Department of Geological Sciences, Please order from: from: Department Sciences, Univer— University of of Wisconsin-Milwaukee, Wisconsin—Milwaukee, Milwaukee, Milwaukee, Wisconsin, Wisconsin, 53201. sity 53201. Price Make checks checks payable payable to to Institute on Lake Lake Superior Superior $5.00 (U.S.A.). Make Institute on $5.00 (U.S.A.). Geology, Wisconsin. Geology, Milwaukee, Wisconsin. I I I I I �TABLE OF OF CONTENTS CONTENTS GENERAL INFORMATION GENERAL INFORMATION . . . . . . . . . . . . . . vv INSTITUTE BOARD OF DIRECTORS . INSTITUTE . . . . . . . . . . . . v . LOCAL COMMITTEE . . . . . . . FIELD TRIP COMMITTEE COMMITTEE . SESSIONS CHAIRMEN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. vi vii vii ANNUAL BANQUET KEYNOTE SPEAKER . . . . . . . . . . . ix ACKNOWLEDGEMENTS . . . . ix . . . . . . . . . . CALENDAR OF EVENTS AND PROGRAM . . . . . . . . . . . . . . POSTER SESSION . . .. xv ABSTRACTS OF OF PAPERS PAPERS . . . . . . . . . . . . . . . . . . . 1 1 FIELD TRIPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INDEX OF OF AUTHORS AUTHORS . . . . . . . . . . . . . . . . . . x . . .. 43 49 �GENERAL INFORMATION INFORMATION 24 TH 214TH ANNUAL ANNUAL INSTITUTE ON INSTITUTE ON LAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY PFISTER HOTEL PFISTER HOTEL MILWAUKEE, MILWAUKEE) WISCflNSIN WIsrn~SIN MAY 9-1 9-14LL 1978 ~1AY SPONSORED BY BY THE SPONSORED THE DEPARTMENT OF OF GEOLOGICAL DEPARTMENT GEOLOGICAL SCIENCES SCIENCES UNIVERSITY OF UNIVERSITY OF WISCONSIN-MILWAUKEE WISCONSIN-MILWAUKEE MILWAUKEE, MILWAUKEE) WISCONSIN WISCO:~SIN INSTITUTE BOARD OF DIRECTORS Giblin, Ontario Division of Mines, P.E. Giblin, Mines, Ministry of of Natural Natural Resources, Ontario. Resources, Sault Ste. Marie, Ontario. J.D. J.D. Hughes, Hughes, Department of Geography, Geography, Earth Science and Conservation, Northern Michigan University, Conservation, University, Marquette, Michigan. Marquette, M.M. Kehienbeck, Department Department of of Geology, Geology, Lakohead Lakhead UniverM.M. Kehlenbeck, University, Thunder sify, Thunder Bay,. Bay" Ontario. G. Mursky, Mursky, Department Department of of Geological Geological Sciences, Sciences, University University G. of'Wisconsin-Milwaukee, Milwaukee, Wisconsin. Wisconsin. of Wisconsin—Milwaukee, Milwaukee, R.C. Reed (Secretary-Treasurer), R.C. (Secretary-Treasurer), Geological Survey Survey Division, Division, Department of Natural Natural Resources, Resources, Lansing, Lansing, Michigan. Michigan. M.S. M.S. Walton, Walton, Minnesota Geological Survey, Survey, University of Minnesota, Minneapolis, Minnesota, Minneapolis, Minnesota. Minnesota. v b �LOCAL COMMITTEE Conference Chairman Gregory Mursky, Mursky, Department Department of of Geological Geological Sciences, Sciences, University University of Wisconsin—Milwaukee, Wisconsin-Milwaukee, Milwaukee, Milwaukee, Wisconsin. Wisconsin. Organizing Committee Committee Richard Bains, Corporation, Milwaukee, Milwaukee, Wisconsin. Bains, Rexnord. Rexnord Corporation, Frank J. Qf Geological Geological Sciences, J. Charnon, Charnon, Department Of Sciences, University of Wisconsin—Milwaukee, Wisconsin-Milwaukee, Milwaukee, Milwaukee, Wisconsin. Wisconsin. John Erb, Milwaukee, Wisconsin Erb, Allis-Chalmers Corporation, Co~po+ation, Milwaukee, Robert E. E. Gernant, Gernant, Department of Geological Sciences, Sciences, University of Wisconsin-Milwaukee, Milwaukee, Milwaukee, Wisconsin. Wisconsin. Donna McElroy, McElroy, Department of of Geological Geological Sciences, Sciences, University University of Wisconsin-Milwaukee, Wisconsin—Milwaukee, Mill·'aukee, Milaukee, Wisconsin. of Wisconsin. Katherine G. G. Nelson, Nelson, Department of Geological Geological Sciences, Sciences, Milwaukee, Wisconsin. Wisconsin. University of of Wisconsin, Wisconin, Milwaukee, Mervin Nelson, Nelson, Mervin Nelson Nelson and and Associates, Associates, Milwaukee, Milwaukee, Wisconsin. Wisconsin. A. Paull, Richard A. Paull, Department of Geological Sciences, Sciences, University University Wisconsin-Milwaukee, Milwaukee, Wisconsin. of Wisconsin-Milwaukee, Wisconsin. Gordon R. R. Pirie, Pine, Department Gordon Department of of Geological Geological Sciences, Sciences, University University Qf Wisconsin-Milwauk~e, Wisconsin-Milwaukee, Milwaukee, of Mi~waukee, Wisconsin. Wisconsin. Charlene Ryder, Ryder, Harnisch~eger Harnischeger Corporation, Charlene Corporation, Milwaukee, Milwaukee, Wisconsin. Wisconsin. Charles A. A. Salotti, Salotti, Department Department of of Geological Geological Sciences, Sciences, University University Charles Wisconsin—Milwaukee, Milwaukee, Wisconsin. of Wisconsin-Milwaukee, Wisconsin. Department of of Geological Sciences, University University William B. Schramm, Department Geological Sciences, William }. of Wisconsin-Milwaukee, Milwaukee, Wisconsin. of Wisconsin—Milwaukee, Milwaukee, Wisconsin. Robert W. W. Taylor, Taylor, Department Department of of Geological Geological Sciences, Sciences, University Robert Wisconsin'. of ~visconsin-Milwaukee, Wisconsin—Milwaukee, Milwaukee, Wisconsin. Carol Taylor, Cedarburg, Cedarburg, Wisconsin. David E. E. Willis, Willis, Department Department of of Geological Geological Sciences, Sciences, University of Wisconsin—Milwaukee, Wisconsin-Milwaukee, Milwaukee, Wisconsin. Wisconsin. vi �FIELD TRIPS Chairman, R.A. Chairman, R.A. Paull, Paull, Department of of Geological Geological Sciences, Sciences, UniverUniverof Wisconsin-Milwaukee, Wisconsin-Milwaukee, Milwaukee, sity of I1ilwaukee, Wisconsin. Trip II -- Southwestern Southwestern Wisconsin Zinc Zinc — - Lead District W.A. Broughton, W.A. Broughton, University of Wisconsin-Platteville, Platteville, Platteville, Wisconsin. A.V. A.V. Heyl, Heyl, U.S. U.S. Geological Geological Survey, Survey, Reston, Reston, Virginia. Virginia. M.G. M.G. Mudrey, Mudrey, Jr., Jr., Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, Madison, Wisconsin. Madison, Wisconsin. W.S. West, West, U.S. W.S. U.S. Geological Survey, Platteville, Platteville, Wisconsin. Wisconsin. Trip II Mineral Extraction and Processing II -- Mineral Equipment Manufacturers in the Greater Equipment Milwaukee Area C.A. Salotti, C.A. Salotti, Department of Geological Sciences, Sciences, University University of of Wisconsin—Milwaukee, Milwaukee Wisconsin. Wisconsin-Milwaukee, Trip III -- Precambrian Rhyolite and and Granite Granite Inliers in South—Central Inliers South-Central Wisconsin. E.I. Smith, Wisconsin—Parkside, E.I. Smith, Division rf nf Science, University of Wisconsin-Parkside, Kenosha, Kenosha, Wisconsin. SESSIONS CHAIRMEN A.T. A.T. Broderick, Broderick, Manager, I1anager, Mineral Mineral Development, Development, Inland Inland Steel Steel Company, Company, Ishpeming, Michigan. Ishpeming, J.D. Hughes, J.D. Hughes, Chairman, Chairman, Department of ~f Geography, Earth Earth Science Science and Conservation, Conservation, Northern Michigan University, University, Marquette, Marquette, Michigan. J.O. Kalliokoski, Kalliokoski, Chairman, Chairman, Department Department of of Geology, Geology, Michigan Michigan J.O. Technological University, Houghton, Houghton, Michigan. Michigan. vii �M.M. M.M. Kehienbeck, Kehlenbeck, Chairman, Chairman, Department of Geology, Geology, Lakehead University, Thunder Thunder Bay, Bay, Ontario. Ontario. E.R. May, Senior Geologist, E.R. May, Geologist, Exxon Exxon Company U.S.A., U.S.A., Rhinelander, Rhinelander, Wisconsin. Rachel Rachel K. K. Paull, Panll, Department of Geology of Wisconsin-Madison, Madison, Madison, and and Geophysics, Geophysics, University University Wisconsin. Wisconsin. P.K. P.K. Sims, Sims, U.S. U.S. Geological Survey, Denver, Denver, Colorado. Colorado. M.S. M.S. Walton, Walton, Director, ~irector, Minnesota Minnesota Geological Geological Survey, Survey, Minneapolis, Minneapolis, Minnesota. viii �ANNUAL BANQUET BANQUET KEYNOTE KEYNOTE SPEAKER SPEAKER Congressman James James Santini, Santini, House House of of Representatives, Representatives, Washington, Washington, Member, D.C. Member, Committee Committee on on Interior Interior and and Insular Insular D.C. Affairs; Affairs; Subcommittee Subcommittee on on Oversight Oversight of of Public Public Lands Mines Mines and and Mining. Mining. ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS The organizing committee for for the the 24th 24th Annual Annual Meeting Meeting on on Lake Lake Superior Geology gratefully gratefully acknowledges acknowledges the the support support of of the the followfollowing corporations in in the the Milwaukee Milwaukee area: area: Allis-Chalmers Corporation Corporation Harnischfeger Corporation Rexnord Corporation Ix ix �CALENDER OF EVENTS CALENDER AND PROGRAM Tuesday Tuesday 9, 9, 1978 1978 May ~lay Pre—Institute Field Trip I Pre-Institute I — - Southwestern Wisconsin Zinc-Lead District, departs Zinc-Lead departs from Madison, Wisconsin to Platteville, from Madison, to Platteville, Wisconsin at 12:30 12:30 P.M., P.M., and and return return to to Milwaukee, Wednesday May 10, 1978 Milwaukee, 10, 1978 about about 6:00 P.M. P.M. Wednesday May 10, 10, 1978 1978 Pre—Institute Mineral Pre-Institute Field Trip Trip II II —- Mineral Extraction and Processing Equipment Processing Equipment Manufacturers in the facturers the Greater Milwaukee Milwaukee Area, Area, departs from from the the Pfister Pfister Hotel Hotel about about 8:30 A.M., and return 8:30 A.M., return about about 4.30 4:30 P.M. P.M. 1:00 -- 3:30 3:30 P.M. and 6:00 —9:00 -9:00 P.M. P.M. Early Registration, Registration, near the the Imperial Imperial Ballroom, Pfister Hotel Ballroom, Hotel 7:30 -- 10:00 P.M. Conference 'Smoker", "Smoker", Henry Henry && Louis Louis Room, Room, Pfister Hotel. Hotel. Thursday May Hay 11, 1978 1978 7:00 —- 8:00 A.M. 7:00 Early Registration near near the the Imperial Imperial Ballroom, Ballroom, Pfister Pfister Hotel. Hotel. 8:00—11:55 8:00-11:55 A.M. A.M. Morning Session, Session, Imperial Imperial Ballroom, Ballroom, Pfister Hotel. Hotel. 9:00 A.M. A.M. -- 4:50 P.M. Poster Session, Session, Henry and Louis Room, Room, Pfister Hotel 1:30 —- 4:50 P.M. Afternoon Session, Session, Imperial Imperial Ballroom, Ballroom, Pfister Hotel. 6:00 P.M. P.M. Cocktail Hour Hour (cash (cash bar), bar), Henry Henry and and Louis Louis Room, Room, Pfister Pfister Hotel. Hotel. 7:00 P.M. P.M. Annual Banquet, Banquet, Imperial Imperial Ballroom, Ballroom, Pfister Pfister Hotel. Keynote speaker: Congressman James speaker: Congressman James Santini. Santini. xx �Friday Friday 12, 1978 1978 May 12, 8:10 A.M. A.H. —- 12:10 12:10 P.M. P.M. Morning Morning Session, Session, Imperial Imperial Ballroom, Ballroom, 8:10 Pfister Pfister Hotel. Hotel. 4:10 P.M. P.r-!. 1:30 —- 4:10 Afternoon Afternoon Session, Session, Imperial Imperial Ballroom, Ballroom, Pfister Pfister Hotel. Hotel. 6:30 P.M. P.M. 6:30 Post—Institute Post-Institute field field trip trip III III —Precambrian Precambrian Rhyolite Rhyolite and and Granite Granite Inliers Inliers in in South-Central Wisconsin departs from from the Pfister Hotel, Hotel, for for Oshkosh, Oshkosh, Wisconsin. Wisconsin. This field field trip trip will will return return to to Milwaukee, Milwaukee, Saturday, May 13, 13, 1978 1978 about about 6:30 6:30 P.M. P.M. xi xi �TECHNICAL PROGRAMS A.M. 8:00 —- 11:55 11:55 A.M. Thursday, May 11, 11, 1978 1978 Morning Session Session -- Co-Chairmen: Rachel Rachel K. K. Paull Paull and and Paul Paul K. K. Sims Sims 8:00 8:00 Opening Remarks Remarks 8:15 8:15 Smith, E.I. E.I. A A New Precambrian Surface Contour Map for for South-Central South-Central Wisconsin. Wisconsin. 8:35 Zietz, I. I. A A New Detailed Detailed Aeromagnetic Map Covering Most of of the the Precambrian Precambrian Shield Shield in in Wisconsin. Wisconsin. 8:55 Sims, P.K. P.K. Peterman, Z.E. Z.E. Precambrian Geologic Framework of Northern Wisconsin. Wisconsin. 9:15 Cannon, W.F. W.F. A A Middle Middle and and Late Late Precambrian Precambrian Fault System System in Northern Wisconsin and Northern Michigan. 9:35 Jones, D.G. D.G. Geology of the Iron Formation and Associated Rocks of the the Jackson Jackson County County Iron Iron Mine, Mine, Jackson Jackson County, Wisconsin. Wisconsin. 9:55 -- 10:15 COFFEE BREAK 10:15 Van Schnius, Schmus, W.R. Woronick, R.E. R.E. Egger, N.L. N.L. Geochronologic Relationships Relationships in in the the Carney Geochronologic Lake Gneiss Gneiss and other Basement Gneisses Gneisses in in Dickinson County, County, Upper Michigan. 10:35 DuBois, J.F. J.F. Van Schxnus, Schmus, W.R. Petrology and Geochronology of Archean Gneiss in the Lake Arbutus Area, Area, West-Central West-Central Wisconsin. 10:55 R.D. Hammond, R.D. Van Schmus, W.R. W.R. Geochronology of Archean Rocks Rocks in Marquette County, County, Upper Michigan. Michigan. 11:15 Peltonen, D.R. D.R. Salotti, C.A. Salotti, Taylor, R.W. Taylor, R.W. Relations Between Soil Geo9hemistry Geochemistry and Bedrock Geology, Iron Iron County, County, Wisconsin. Wisconsin. 11:35 11:35 Cummings, M.L. M.L. Myers, P.E. P.E. Petrology and Geochemistry of Amphibolites, River, Eau Claire County, Wisconsin. Eau Claire River, Wisconsin. 11:55 — - 1:30 LUNCH xii �1:30 1:30 —- 4:50 4:50 P.M. P.M. Thursday, Thursday, May May 11, 11, 1978 1978 Afternoon Session Session -- Co-Chairmen: Co-Chairmen: A.T. A.T. Broderick Broderick and and J. J. Kalliokoski Kalliokoski 1:30 1:30 Ojakangas, R.W. R.W. Criteria Criteria for for Alligator Alligator River River Type Type Uranium Uranium Deposits Deposits in in the the United United States. States. 1:50 1:50 Kalliokoski, J. J. Kalliokoski, The Unconformity-Type Unconformity-Type Proterozoic Proterozoic Pitchblende Ore Body Model and and Its Its Application to to Northern Northern Michigan. Michigan. 2:10 2:10 Peterman, Z.E. Z.E. Peterman, P.K. Sims, P.K. Baseline Uranium and Thorium in Archean and Lower Lower Proterozoic Proterozoic Rocks Rocks of of the the Marenisco—Watersmeet Marenisco-Watersmeet Area, Area, Michigan. Michigan. 2:30 2:30 D.G. Meineke, D.G. M.K. Vadis, M.K. Klaysmat, A.W. A.W. Pilot Exploration Geochemical Survey of Uranium Uranium in in Organic-Rich Organic-Rich Lake Lake Sediments, Sediments, Northeastern Northeastern Minnesota. Minnesota. 2:50 J. Trow, J. Possibilities possibilities for for Uranium-Gold Uranium-Gold QuartzQuartzPebble Ores in the the Lake Superior Region in the Light of a New Model for for Elliot Elliot Lake—Witwatersrand Lake-Witwatersrand Genesis. Genesis. 3:10"3:l0 - 3:30 COFFEE BREAK 3:30 W.S. Meddaugh, W.S. Salotti, C.A. Mursky, G. G. The Distribution of Uranium and Thorium in the Wolf Wolf River River Batholith, Batholith, Northeastern the Wisconsin. 3:50 Heinrich, E.W. E.W. Industrial Sand and Sandstone Resources of of Michigan. 4:10 Nebrija, E.L. Welkie, Welkie, C,J. CJ. Meyer, Meyer, R.P. Gere, Jr. Gere, M.A. Jr. Offshore Sand and and Gravel Gravel Exploration Exploration Offshore in Western Lake Michigan. 4:30 4:30 Economic Mineral Mineral Production in in Michigan Michigan Economic Past and Present. Present. xiii xiii �8:10 8:10 —- 12:10 12:10 A.M. A.M. Friday, Friday, May May 12, 12, 1978 1978 Morning Morning Session Session -- Co-Chairmen: Co-Chairmen: M.M. M.M. Kehienbeck Kehlenbeck and M.S. M.S. Walton 8:10 Molling, MoIling, P.A. P.A. Tyson, Tyson, R.M. R.M. Chang, I..L.Y. L.L.Y. Chang, A iA Petrographic Petrographic Guide Guide for for Unit Unit Identif Identification River Troctolite, cation of of the the Partridge River Duluth Duluth Complex, Complex, Minnesota. Minnesota. 8:30 8:30 Foose, M.P. M.P. Cooper, R.W. R. W. Faulting in in Part Part of of the the Duluth Duluth Complex, Complex, Northeastern Northeastern Minnesota. Minnesota. 8:50 8:50 Bauer, Bauer, R.L. R.L. Polyphase Deformation Deformation in in Archean Archean Schists Schists of the the Western Lake Lake Vermilion Vermilion Area, Area, Minnesota. Minnesota. 9:10 9:10 Cambray, Cambray, F.W. F.W. Plate Tectonics Tectonics as as aa Model Model for for the the EnviEnvironment of of Sedimentation Sedimentation the the Marquette Marquette Super group and the Subsequent Supergroup Subsequent Deformation Deformation and Metamorphism Metamorphism Associated Associated with with the the Penokean Orogeny. Orogeny. 9:30 Larue, D.K. D.K. Problems in in Paleogeographic Paleogeographic ReconstrucReconstruction of the Chocolay and and Lower Lower Menominee Menominee Group Sedimentation, Marquette Range Range Supergroup , Lake Superior Region. Supergroup, Region. 9:50 -- 10:10 COFFEE BREAK 10:10 Massey, N.W.D. N.W.D. The Geochemistry of Keweenawan Keweenawan Lavas Lavas of of the Mamainse Point Formation, Formation, Ontario. Ontario. 10:30 Jirsa, M.A. M.A. The Petrology and Tectonic Tectonic Significance Significance of the Interf low Sediments Sediments in in the KeweeInterflow nawan North Shore Volcanic Group of Northeastern Northeastern Minnesota. Minnesota. 10:50 10:50 West john, D. D. Westjohn, Cambray, F.W. Cambray, F.W. Finite Strain in the Precambrian Kona Formation Formation of of the the Marquette Marquette Synclinoriuxn. Synclinorium. 11:10 11:10 Strakele, A.E. A.E. The Geology and and Petrology Petrology of of the the Wine wine Lake Intrusion, Lake Intrusion, Cook County, County, Minnesota. 11:30 11:30 Cambray, F.W. The Origin and Timing of Cleavage FormaThe Formathe Siamo Siamo Slate Slate of of Precambrian Precambrian tion in the X X Age, Marquette County, County, Michigan. Michigan. 11:50 11:50 Hughes, J.D. Hughes, J.D. A A Post Two Creeks Buried Forest in in Michigan's Northern Peninsula. 12:10 — - 1:30 LUNCH xiv �1:30 —- 4:10 P.M. Friday, May 12, Friday, 12, 1978 Afternoon Session Session -- Co-Chairmen: J.D. J.D. Hughes and E.R. E.R. May May 1:30 Banaszak, K.J. K.J. The pH of Ore Ore Fluids of of Mississippi Mississippi Valley Type Deposits. Type Deposits. 1:50 Cummings, M.L. M.L. Stratigraphy and Mineralization, Mineralization, Quinnesec Formation, Northeastern Northeastern Wisconsin. 2:10 Aaquist, B.E. B.E. Hodder, R.w. R.W. Microstylolites—An Microstylolites-An Indicator Indicator for an Early Stage of Native Copper Deposition in a Phyolite Tuff, a Rhyolite Tuff, Keweenaw Peninsula, Peninsula, Michigan. Michigan. 2:30 Scofield, N. N. Native Copper Deposits Derived from from Keweenawan Basalt by by Combined Nearby Keweenawan Igneous, Igneous, Deuteric, Deuteric, and Metamorphic Processes. 3:10 2:50 -- 3:10 COFFEE BREAK 3:10 Johnson, A. A. Scofield, N. N. Doane, V. V. Geology and Mineralogy of Northern Michigan Phosphorites. Phosphorites. 3:30 Shanabrook, D. D. Precambrian X X Paleopoles from the Upper Peninsula and a a New Method for Remanent Vector Determination. Determination. 3:50 Luther, F.R. F.R. The Geology of of the the Gore Gore Mountain Mountain Garnet The Deposit, Southeastern Adirondacks, Deposit, Warren County, County, New New York. York. END OF TECHNICAL SESSIONS SESSIONS POSTER SESSION Thursday, May ii, Thursday, 11, 1978 4:50 P.M. 8:00 A.M. A.M. -- 4:50 M.G. Mudrey, M.G. Aereomagnetic Map Map of of Northern Northern Wisconsin. Wisconsin. Sims, P.K. Sims, Cannon, W.F. W.F. Mudrey, M.G. M.G. Preliminary Geologic Map of Northern Wisconsin Wisconsin. Shaffer, N. N. Possibility of Mississippi Valley-Type Ore Deposits in in Indiana. Indiana. xv �h I �MICROSTYLOLITES-AN MICROSTYLOLITES-AN INDICATOR INDICATOR FOR FOR AN EARLY STAGE STAGE OF NATIVE NATIVE COPPER COPPER DEPOSITION DEPOSITION IN IN AA RHYOLITE RHYOLITE TUFF, TUFF, KEWEENAW KEWEENAW PENINSULA, PENINSULA, MICHIGAN MICHIGAN B.E. B.E. Aaquist, Aaquist, American American Copper Copper && Nickel Nickel Co., Co., Milwaukee, Milwaukee, Wi, Wi, 53226 53226 and and R.W. R.W. Hodder, Hodder, University University of of Western Western Ontario9 Ontario p London, London, Ont. Onto N6A N6A 5B7 5B7 ABSTRACT Microstylolites Microstylolites are are contact contact surfaces surfaces between between clasts clasts in in aa rhyolite rhyolite tuff tuff hosting hosting native native copper copper in in the the Kingston Kingston mine. mine. The microstylolites conform conform to to Pettijohn's Pettijohn's (1949) (1949) definition: definition: "a stylolite seam seam is is aa surface surface of of contact contact marked marked by by interlockinterlockor mutual mutual interpenetration interpenetrationof' of the two sides. sides. The teethteething or like projections projections of of one one side side fit fit into into the the sockets sockets of of like like on the the other." other." The microstylolites are are mostly mostly dimensions on chlorite grains grains with with their their long long axis axis parallel parallel to to the the contact contact surface. Some fine fine grained grained hematite hematite is is also also present3 present. Quartz and feldspar phenocrysts terminated terminated by by aa microstylolite microstylolite are are Fluid inclusions in neither neither fractured, fractured p nor nor stressed. stressed. in pheno— phenocrysts are similarly similarly terminated terminated by by microstylolites. microstylolites. Depth of burial is the the single single most important factor factor in microstylolite development. development. In sandstones, sandstones p microstylolites microstylolite have been been recorded recorded at at depths depths of' of burial burial of of 1250 1250 to to 1650 1650 meters meters (Trurnit 1968). Tuft Tuff in the Kingston mine is overlain overlain by by (Trurnit,p 1968). about 1700 1700 meters of of lavas lavas and and sedimentary sedimentary rocks rocks of of the the Portage Portage Lake Lava Series, Series, sufficient sufficient weight to induce induce formation of microstylolites. micro stylolites. native copper copper is common in white white rims rims on In the the tuff, tuff p native These rims are white where potash rhyolite clasts. clasts. These reddish rhyolite feldspar grains in clasts clasts are are clear clear and and lack lack disseminated disseminated hematite of of reddish reddish grain grain interiors. interiors. Microstylolites terminate terminate This suggests deposition of the white, white p copper-bearing copper-bearing rims. rims. This the native copper and whiting of the rims of clasts clasts prior prior to to native the rims microstylolite formation and, and, hence, hence, before before lithification of microstylolite the tuff'. tuff. the References Pettijohn, F.J. (1949); (1949); Sedimentary Sedimentary rocks: rocks: Pettijohn, F.J. Brothers,p New and Brothers New York, York, 526 526 p. p. Publ. by Harber Publ. (1968); Pressure Pressure solution phenomena phenomena in detrital Trurnit, P. p. (1968); Sed, Geol., Geol., vol. rocks: vol. 2, 2, p. p. 89—114. 89-114. rocks Sed. —3— -3- �The pH of Ore Fluids of Mississippi Valley Valley Type Type Deposits Deposits by Konrad J. J. Banaszak Department of Geology Indiana/Purdue University at at Indianapolis Indianapolis 925 W. Michigan Michigan,t Indianapolis, 925 w. Indianapo1is t Indiana Indiana 46202 of the solutions responsible responsible for for Mississippi Mississippi Valley The pH of the ore solutions type deposits is critical chemical chemical variable variable in the the discussion type ore deposits is aa critical musthave havebeen been acid, acid, based based of the origin of of these these deposits. deposits. This p1-I pH must curves,t equilibrium relations relations with with silicate on zinc zinc dispersion curves minerals of "modern "modern ore fluids", fluids", and the absence of magnesium silicates in the paragenetic sequences sequences of of the the deposits. deposits. Zinc and dispersion curves were recreated recreated in the the laboratory by Lavery and Barnes (1971) buffered to to aa pH of of 6 at at (1971) with model ore solutions solutions buffered 0 basic did did not not reproduce 100 C. C. The model ore solutions that that were basic the curves. have both aa low partial curves. Modern "ore fluids" fluids" appear to to have acidic pH, pH, and are probably in pressure of carbon dioxide and an acidic equilibrium equilibrium with with silicate silicate rocks. rocks. The composition of fluid fluid inclusions inclusions in an assumed equilibrium with K-spar, K—spar, albite, albite, quartz, quartz, muscovite, muscovite, and 0 montmorillinite indicates of 5 for at 150 150° montmori11inite indicates an approximate pH of for brines at to 200°C. minerals in the 200 0 C. Other evidence is is the the absence of silicate minerals the paragenetic sequence sequence (See (See Drever, Drever, 1974.). 1974.). In Mississippi Valley type deposits, deposits, the the absence of sepiolite, sepio1ite t an easily crystallized others,t 1973)t 1973), especially restricts restricts the phase (Christ (Christ and others the pH of the ore solution to acidic values. In the presence of a silica silica phase, phase t quartz or opa11ine opalline silica, and at at the the magnesium activities either quartz si1ica t and of the ore fluid must have been indicated by fluid fluid inclusions, inc1usions t the the pH of the ore fluid must no greater greater than than 66 at at 100°C 1000 C and and 55 at at 150°C. 1500 C. Christ, C. C. L. L.,t Hostet1er Hostetler,t P. P. B. B.,t and and Siebert Siebert,t R. R. M. M.,t 1973 1973,t Studies Christ, Studies in the system MgO —- Si02 -— C02 -— H20 (III): The activity product of sepiolite: sepiolite: Amer. Amer. Jour. Jour. Sci., Sci. t v. v. 273, 273 t p. p. 65—83. 65-83. Drever,t J. J. I., 1974,t Geochemical Geochemical model model for of Precambrian Drever I., 1974 for the origin of Bull. Geol. banded iron iron formations: formations: Bull. Geo1. Soc. Soc. Amer., Amer. t v. v. 85, 85 t p. p. 1099—1106. 1099-1106. Lavery, N. N. G., G., and and Barnes, Barnes, H. H. L' L., 1971, Zinc Zinc dispersion'in dispersionin the LaverYt the t 1971, Econ. Geol., Wisconsin zinc—lead zinc-lead district: district: Econ. Geo1., v. v. 66, 66 t p. p. 226—242. 226-242. Wisconsin —4— -4- �POLYPHASE DEFORMATION IN POLYPHASE IN ARCHEAN SCHISTS SCHISTS OF THE THE WESTERN WESTERN LAKE VERMILION VERMILION AREA, MINNESOTA* MINNESOTA * Bauer, Department Robert L. Robert L. Bauer, Department of of Geology Geology and and Geophysics, Geophysics, University University of of Minneapolis, Minnesota Minnesota, Minneapolis, Minnesota 55455, 55455, and Department of Geology, Macalester College, College, St. St.Paul, Paul,Minnesota Minnesota55105 55105 ABSTRACT A and structural structural study study has has been been initiated detailed petrologic petrologic and initiated in in the the A detailed Norwegian Bayquadrangle quadrangleand andparts partsof of adjacent adjacent quadrangles quadrangles in in the western Norwegian Bay western Lake The rock Lake Vermilion Vermilion area. The rock exposures exposures consist consist of of Archean Archean schists schists and and lamprophyres metamorphosed metamorphosedto to the the middle middle amphibolite amphibolite facies facies and and intruded by lamprophyres quartz monzonite monzonite stock stock(Wakemup (Wakemup Bay Bay stock). stock). The The stock and and adjacent adjacent aa quartz schists are bounded on the the north north by by the the Vermilion fault, on on the southeast schists are bounded on Vermilion fault, southeast by by the Frazer the Frazer Bay Bay fault, fault, and and on on the the south south by by the the Haley Haley fault. fault. The The structural studies reported on on here studies reported here indicate the the schists schists have have undergone undergone four periods periods of deformation The most evident evident structural structural feature in The most in the the area areaisisaaprominent prominent foliation foliation which wraps around around the the Wakemup WakemupBay Baystock. stock. This This foliation foliation (S (si) which wraps 1) is axial planar planar parallel to to bedding to rare rare isoclinal isoclinal F1 F 1 folds folds and and is is parallel bedding (S(Sj r in in the the schist. schist. Numerous thin Numerous thin lamprophyre and granitic veins cutting 0 the schist are boudinaged or folded folded by by the the flattening flattening normal boudinaged or normal to S 5l' F2 F 2 folds folds are are the the most mostcommon common minor minor structures structures preserved preserved and and are are commonly accompanied accompaniedbybyaa weak weak to to strong commonly strong axial axial plane plane foliation foliation (S,). (S). The distribution of of minor distribution minor F2 F 2 folds folds indicates indicates the thepresence presenceofofa amajor majorsou'Thwestsou1hwestaxes of plunging FF,2 antiform south of of the plunging antiform partially partially exposed exposed south the stock. stock. The The axes of the the minor F, 'Tolds show aa systematic variation inin orientation orientation to to the minor F lolds show systematic variation the west, west, northwest and olding (F.) northwes~ and north of the the intrusion intrusion as as aa result result of ofref refolding (F 3) of of the the major major F, structure stoc1. Despite F2 structure around around the the western western end end of of the theWakemup Wakemup Bay Bay stOCK. Despite the la1ge-sca1e F3folding foldingaround aroundthe thestock, stock,minor minorF'3 F folds large-scale F3 folds are are rare rare and and occur occur only only Th'se folds along the western margin of the along the margin of the intrusion. intrusion. The-se folds are are open, open, westwardwestwardplunging warpsof ofthe the foliation foliation with with near near vertical axial plunging warps axial planes. planes. The shallow shallowdips dipsofofthe the schist schist near near the the contacts contacts of of the stock The stock and and the presence of a flat-lying roof pendant of of schist and lamprophyrenear near the the center center and lamprophyre of the stock's stock's exposure, exposure, suggest suggest the surface surface exposures exposures are very very near the the top top of of the stock. stock. Evidence for for an an Fh is restricted to Evidence F 11. deformation deformation is to kink kink bands, bands, up up to 55 cm cm wide, which whichdeform deformthe theS2 2 foliation. wide, A similar similar sequence sequence of of structural structural events has been recognized north of of the A recognized north Vermilion fault. Further study lead to the Vermilion fault. study of the the area area isis in in progress progress which which may may lead of major correlation of major structural features across across the the fault. fault. *Research supported by by the the Minnesota Minnesota Geological Geological Survey Survey -5- —5— �PLATE TECTONICS PLATE TECTONICS AS AS AAMODEL MODEL FOR FOR THE THE ENVIRONMENT ENVIRONMENT OF OF SEDIMENTATION SEDIMENTATION THE AND THE SUBSEQUENT THE MARQUETTE MARQUETTE SUPERGROUP SUPERGROUP AND SUBSEQUENT DEFORMATION DEFORMATION AND AND METAMORPHISMASSOCIATED ASSOCIATED WITH THE METAMORPHISM THEPENOKEAN PENOKEANOROGENY OROGENY CAMBRAY, William,Department Departmentofof Geology, Geology, Michigan Michigan State CAMBRAY, F. F. William, University, East University, East Lansing, Lansing, Michigan Michigan 48824 The Marquette Supergroup Supergroupof of Precambrian Xage agehas hasbeen beendivided divided into into The Marquette Precambrian X three groups. This sequence can be be compared comparedtoto the the one one which which forms forms on on groups. This sequence can plate margin suchasasthe theAtlantic. Atlantic. The aa passive passive plate margin such The Chocolay Chocolay Group Group represents anepicontinental epicontinentalshallow shallowsea seafollowed followedbybythetheinitiation initiation of represents an rifting thethe beginning of of Menominee riftingatat beginning Menominee times. times. The The doming doming associated with rifting would thethe unconformity rifting wouldaccount accountforfor unconformitybetween between the thetwo twogroups groups and the the separate separate basins basins in in which the banded iron formations formations and andturbidites turbidites and which the banded iron were depositedformed formedasasa aresult resultof of rifting rifting producing were deposited producing local localdepressions depressions such as the the Marquette, Republic and andIron Iron River/Crystal River/Crystal Falls such as Marquette, Republic FallsTroughs. Troughs. This extensional wasaccompanied accompanied intrusionofoftholeiite tholeiite dykes This extensional phase phase was by by intrusion dykes parallel to Troughand and intrusion sills into parallel to the the Marquette Marquette Trough by by thethe intrusion ofofsills the sediments within the Subsequently the area the sediments within the troughs. troughs. Subsequently area underwent underwent subsidence and accumulated accumulatedthe the large large thickness subsidence and thickness ofofBaraga BaragaGroup Group sediments sediments which compare comparefavourably favourablywith withthe the turbidites turbidites which which which formed formed on on the the subsubshelf edge edge of ofthe themodern modern Atlantic AtlanticOcean. Ocean. siding shelf In this interpretation proposed In interpretation ititis is proposed that thatthe theIron IronRiver/Crystal River/Crystal which includes includes the the Riverton Riverton Iron Formation, Falls area area succession, succession, which Formation, is contemporaneous with the the Menominee Groupofof the the Marquette and that contemporaneous with Menominee Group Marquette Range Range and Greenstonesrepresent representsubmarine submarine extrusionsrelated related to to the the Badwater Badwater Greenstones extrusions the of the the troughs troughs referred referred to rifting which at this time. rifting which isisproposed proposed at time. Each Each of are which are are found found today today on on constructive plate plate margins. margins. are likened likened to to those those which Subsequent to deposition was Subsequent to depositionthe thearea area wascompressed compressedand andmetamorphosed metamorphosed It isisproposed Orogeny(1.85 (1.85- - 1.9 1.9 Ga B.P.). It in the the Penokean Penokean Orogeny Ga B.P.). proposed that that during during this episode Archean this episode deformation deformation ofofthe theunderlying underlying ArcheanBasement Basement occurred occurred by by particularly the ductile shears shears along along pre-existing weaknesses, weaknesses, particularly the mafic mafic dykesreferred referred to to above, producingeast-west east-westfolding folding in in the dykes above, producing the overlying overlying Marquette Supergroup. During this phase Marquette Supergroup. During phase troughs troughs are thought thought to to have have beenthe the locii locii ofofgreater andand that weaknesses been greaterstrain strain that weaknessesdeveloped developed during during the were utilised to narrow them andandproduce the earlier earlierrifting rifting were utilised to narrow them producea amore more intense folding. The seeminglyanomalous anomalous orientationsofoffolds folds in the intense The seemingly orientations the troughs as the the Republic are thought thought to have controlled troughs such such as Republic Trough Trough are have been been controlled by the stress stress distribution distribution across troughswith withvariable initial orientaby the across troughs variable initial orientations. history of the The deformation deformation was The was accompanied accompanied by by metamorphism. metamorphism. The The history the region has manyfeatures featuresinin commonwithaplate commonwithaplatetectonic tectonic cycle cycle involving region has many followed byby subsidence aa continental continental rift rift followed subsidenceatatthe themargin marginof,ofananexpanding expanding ocean followed followed by movement, ocean by reversal reversal ofofplate plate movement, subduction, subduction,compression compression and metamorphism. Thefact fact that that all the cited is situated and metamorphism. The the evidence evidence cited situated on on crust does older Archean Archean crust does not negate negate the hypothesis. hypothesis. All the themore more recent recent examplessuch suchasas the the Appalachian Appalachian and andAlpine Alpine Orogeny are underlain underlain by examples Orogeny are by continental crust. All this thethe supposed continental thismeans means isisthat that supposedocean oceanwas was comcompletely andcontinental continentalcollision collision resulted. The suture zone pletely subducted subducted and resulted. The zone associated with with this weare are left left totodebate associated this event event has has not not been been located located and and we debate whether whether itit is is present present but but cryptic cryptic ororthat thatProterozoic Proterozoictectonics tectonicswas was similar in in all allother otherrespects respects to to plate plate tectonics. tectonics. —6— -6- �THE IN THE THE ORIGIN ORIGIN AND AND TIMING TIMINGOF OFCLEAVAGE CLEAVAGE FORMATION FORMATION IN THE SIAMO SIAMO SLATE SLATE OF OF PRECAMBRIAN X AGE, MARQUETTE PRECAMBRIAN X MARQUETTE COUNTY, COUNTY, MICHIGAN MICHIGAN CAMBRAY, William, Department Departmentof of Geology, Geology, Michigan CAMBRAY, F. F.William, Michigan State State University, University,East EastLansing, Lansing,Michigan Michigan 48824 48824 In the the previous previous work work (Powell, (Powell, C. C. McA; McA; 1969, 1969, Bull. Bull.Geol. Geol.Soc. Soc.America) America) itithas cleavage formed hasbeen beensuggested suggested that thatthethe cleavage formedpenecontemporaneously penecontemporaneously with the of sandstone sandstonedikes dikes and andthe the origin origin of theemplacement emplacement of ofboth bothwas was ascribed ascribed to to dewatering dewatering during during late latediagenesis diagenesisororlow lowgrade grademetamormetamorphism. In the the outcrop outcrop referred referredtotobybyPowell Powellthe thedikes dikescan canbebeshown shown to tohave have been emplacedbefore beforedeformation deformation and and to to have undergonerotation rotation as been emplaced have undergone as rigid rigid bodies bodies prior priortotothe theformation formationofofthe thecleavage. cleavage. The The cleavage cleavage cuts cuts acros thedikes dikesand andthe thehost hostsediment, sediment,and anditit is across the theboundary boundary between between the not deformed folds in in the bedding whichare arerelated related to to the the rotation deformed bybyfolds bedding which The sense of this rotation is consistent with of the the dikes. dikes. The sense of this rotation is consistent with the the shear shear magnitude however couple on the the limbs limbs of of the couple on the major major fold. The The magnitude however is greater than one than that thatpredicted predictedif if oneassumes assumes the the dikes dikes originated originatednormal normal to bedding and were deformed by flexural slip or flexural flow folding. bedding and were deformed by flexural slip or flexural flow This can can be introducing aa flattening This beexplained explainedbyby"additional "additionalstrain" strain" introducing flattening can across as the across the bedding bedding as the fold fold develops. develops. The The flattening canbebedemondemonstrated strated by by the the variation ininbed bed thickness thickness as as a function function of of distance distance from the rigid from the rigidsandstone sandstone dikes. dikes. The cleavageisisdefined definedbybythin thin laminae laminaeofofoptically optically irresolvable The cleavage material areascontaining containing quartz, quartz, chlorite, material separated separated by by broader broader areas chlorite,muscomuscoquartz, chlorite vite and and aa carbonate. carbonate. The The quartz, chloriteand andmuscovite muscovite show show features features vite which suggestthe thecleavage cleavageoriginated originatedbybyrecrystallisation, recrystallisation, possibly which suggest possibly in conjunction conjunction with with pressure pressure solution. solution. All the theevidence evidence points points totocleavage cleavage forming forming late late inina asequence sequence of of deformation and metamorphism which involvedrotation rotation of the deformation and metamorphism which involved thesandstone sandstone dikes, flattening and and rec~ystallisation. dikes, recrystallisation. —7— -7- �middle and and late late Precambrian fault system A middle Precambrian fault system and northern Michigan in northern Wisconsin Wisconsin and by W. F. Cannon W. U. S. Geological Survey Survey Reston, Virginia 22092 Reston, 22092 Interpretation Interpretationofofaeromagnetic aeromagneticand and gravity gravitymaps mapsof ofnorthern northernWisconsin Wisconsin and and northern Michigan that major regional faults Michigan suggests suggests that faults are are much much more more abundant abundant than previously previously believed. believed. The newly identified identified faults abrupt linear than The newly faults appear appear as as abrupt scale aeroaerotruncations of aeromagnetic aeromagnetic patterns patterns on on aa newly newly compiled compiled 1:250 1:250 000 000 scale (U.S.G.S.map mapMF MF888). 888). Some Somefaults faults also also coincide coincide with with steep magnetic map map (U.S.G.S. gravity gravity gradients. gradients. Many Manyfaults faultsproduce producelateral lateraloffset offset(some (someasasmuch muchas as 20 20 km) km) of magnetic magnetic anomalies anomalies caused caused by by middle middle Precambrian Precambriansupracrustal supracrustaland andPenokean Penokean indicates that that large-scale large-scale lateral adjustment intrusive rocks; rocks; this evidence evidence indicates adjustment took took place orogeny(-1,800 (-1,800m.y. m.y.ago). ago). Other Other faults, faults, place in the area area after the the Penokean Penokean orogeny especially in northern Michigan, hadlarge large vertical vertical displaceMichigan, are known known to have have had ments during during the the Penokean Penokeanorogeny. orogeny.Some Somefaults faultscut cutrocks rocksofofthe the Wolf Wolf River River ments batholith intrusive and and flow flow rocks (-1,100 ('1,100 batholith 4-1,500 ~1,500 m.y. m.y. old) old) and and Keweenawan Keweenawan intrusive m.y. old). old). Some m.y. Some east-trending faults and and fractures fractures contain contain lower lower Keweenawan Keweenawan diabase diabase dikes. Although the the age age at at which which it it began is unknown, unknown,the the faulting faulting is at least Although began is least as as old as orogeny,and anditit continued continued until until at least as the Penokean Penokean orogeny, least 1,100 1,100 m m y. y. ago, ago, probably probably episodically. Some, most, lateral Some, and and perhaps perhaps most, lateral movement movement isis of ofKeweenawan Keweenawan age. age. Much of of the the map map pattern pattern in in northern northern Wlsconsin Wisconsinreflects reflectsmajor majorlateral lateral fault fault moveMuch movements; ments; it may may be be aa reflection of of intraplate intraplatetectonics tectonicsduring duringthe theopening opening of of the the Keweenawan rift, as Keweenawan rift, as the the older older Precambrian Precambrian rocks rocks ininMichigan Michiganand and Wisconsin Wisconsin were caught between the somewhat opposed opposedopening openingdirections directions of of the midconwere tinent arms of of the the rift rift system. tinent and and mid-Michigan mid-Michigan arms system. AApre-Keweenawan pre-Keweenawan fault fault and and fracture fracture system system probably probably controlled the the location location and and orientation orientation of of the the KeweenKeweellawan rift and of pre-existing awan rift and associated associated transform faults, faults, so so that that some some segments segments of faults behaved as transform transform faults during rifting, behaved as rifting,whereas whereas other other segments segments shifted so as to to alter the the Wisconsin-Michigan Wisconsin-Michigan plate plate as as it it moved so as the shape shape Of of the moved generally southward. Regardless of its its origin origin and and history, history, the the fault system Regardless of system is important important geologically geologically because its control control on on the the regional regional map mappattern. pattern. Additional faults because ofofits faults having having displacements displacements too small to resolve resolve by by means means of existing existing aeromagnetic aeromagnetic data data probably probably are also also abundant abundantand andwill willbe beimportant important in in interpreting interpreting the map map pattern on a a larger scale. scale. —8— -8- �I Petrology and and Geochemistry of Amphibolites, Amphibolites, Eau Petrology Eau Claire Claire River, River, Eau Claire Claire County, County, Wisconsin Wisconsin Eau M. L. L. Cummings, Cummings, Dept. M. Dept. of of Geology Geology and and Geophysics, Geophysics, LJW UW -- Madison P. E. Myers, Myers, Dept. Dept. of of Geology, Geology, UW Claire - Eau Claire P. E. Precambrian amphibolites, amphibolites, mica schists, Precambrian schists, and intrusives intrusives crop crop out out for for 12 km km along along the the Eau Eau Claire Claire River River in north—central Eau Claire 12 in north-central Claire County. County. Massive Massive and and banded. banded. mafic mafic amphibolites, amphibolites, with with more more than than 40 40 percent percent hornblende local mineral mineral assemblages: hornblende-garnet--plagiohornblende, have local hornblende-garnet-plagioclase-quartz, and and hornblende-cummingtonite-garnet-plagioclase-quartz clase-quartz, hornblende-cummingtonite-garnet-plagioclase-quartz with accessory apatite, and opaques opaques as as sulfides and with apatite, sphene, sphene, biotite, biotite, and sulfides and oxides. amphibolites, oxides. Feldspathic amphibol ites, with 10 10 to to 25 25 percent percent hornblende, hornblende, are are characterized by dominant plagioclase. characterized plagioclase. Accessory epidote, quartz, quartz, sphene, and and garnet garnet show show variable variable abundance. abundance. Banding Banding and and hornblende hornblende 1inunsphene, eation are Hornblende analyses analyses from from amphibolites amphibolites show show eation are indistinct. indistinct. Hornblende Al203 15.7 weight weight percent with in 1.05 1.05 to to 1.81 between 9.8 Al 203 between 9.8 and 15.7 with Al Al in 1.81 tetrahedral sites. 100 Mg/(Mg Mg/(Mg + Fe) vary from hedral sites. 100 from 20 20 to 70 70 with values below with values 50 dominant. 50 dominant. , Mica schists schists with assemblages: assemblages: biotite-hornblende—epidote-plagioclasebiotite-hornblende-epidote-plagioclasequartz, and subordinquartz, and muscovite-biotite-epidote—plagioclase-quartz muscovite-biotite-epidote-plagioclase-quartz and subordinate amphibolite layers layers composed composed of hornblende, hornblende, biotite, biotite, plagioclase and quartz underlie the 100 Mg/(Mg + Fe) of quartz the eastern half half of of the the area. area. 100 of hornhornthese amphibolites amphibolites ranges ranges from from 47 47 to to 52. 52. Epidote in blende in. in. these in both both assemblages contains contains 11.5 11.5 to to 13.0 13.0 weight weight percent percent Fe203. Fe203' An intrusion intrusion breccia 0.75 km south of Big Falls Falls contains amphibolite xenoliths in in strongly foliated foliated granodiorite(?) granodiorite(?) composed of biotite, biotite, muscovite, epidote, epidote, plagioclase, plagioclase, and and quartz. quartz. AA second intrusion intrusion breccia breccia at at county highway highway KK 1.5 1.5 km km east of Big Big Falls Falls contains mafic amphibolite xenoliths corase—grained, flow-laminated flow-laminated tonalite(?) tonalite(?) matrix. matrix. The xenol iths in in a, a corase-grained, The rocks rocks described above are cut cut by by granite granite pegmatite pegmatite and and diabase diabase dikes. dikes. The following, following, tentative tentative chronology chronology is is based based on on petrochemistry, petrochemistry, structure, structure, and and regional regional geology. geology. The oldest rocks rocks -- mica schists schists and and amphibolites amphibolites -- representing volcanic sediments sediments and mafic flows(?) flows(?) were intruded by aa gabbro which differentiated into intruded by into mafic mafic and and anorthositic anorthositic layers. layers. Metamorphism of these these rocks rocks to to garnet amphibolite amphibolite grade grade accomaccompanied intrusion intrusion of tonalite, tonalite, trondhjemite trondhjemite and adamellite north north of the the panied area. area. AA second second metamorphism produced produced coarse coarse hornblende hornblende and and plagioclase plagioclase in in the the amphibolites amp~ibolites , while while compositional compositional layering layering was ~as transposed transposed by by strong strong compressional compressional stresses. stresses. Synkinematic Synkinematic intrusion intrusion of tonalite tonalite (1850 (1850 ++ 50 m.y.) produced produced the the breccias breccias east east and and west west of of Big Big Falls, Falls, and and was was 50 m.y.) followed by by postkinematic postkinematic intrusion intrusion of of granite granite pegmatite pegmatite dikes. dikes. ShearShearing ing with contemporaneous contemporaneous formation formation of of epidote epidote and and chlorite chlorite was was followed followed by by prolonged prolonged erosion erosion after after which east—northeast-trending east-northeast-trending olivine 01 ivine diabase diabase dikes dikes were intruded intruded (1100-900 (1100-900 m.y.). m.y.). Weathering and and erosion erosion continued continued until until marine marine deposition deposition of of Upper Upper Cambrian Cambrian sandstones. sandstones. , This chronology chronology implies implies an an Archean Archean age age for for the the mica mica schists schists and and This layered layered gabbro gabbro sequence. sequence. —9— -9- �Stratigraphy Stratigraphy and and Mineralization, Mineralization, Quinnesec Formation, Formation, Northeastern Wisconsin Wis cons in M. M. L. L. Cummings, Cummings, Dept. Dept. of of Geology Geology and and Geophysics, Geophysics, 13W UW —- Madison Madison Volcanogenic semi—massive semi-massive to to massive sulfide zones zones occur at several stratigraphic stratigraphic levels levels in in the the Quinnesec Quinnesec Formation Formation in in Narinette Marinette County, County, Northeastern Northeastern Wisconsin. Wisconsin. The Quinnesec Quinnesec Formation Formation includes includes basic basic to to felsic felsic flows, flows, tuffs, tuffs, iron iron formation formation and and clastic clastic sediments, sediments, that that were were intruded intruded by by quartz diorite to to quartz quartz monzonite monzonite at at about about 1850—1900 1850-1900 m.y. m.y. Two Two types types of of conformable conformable massive sulfide sulfide deposits occur occur in in the the Quinnesec Formation. Formation. 1) 1) 2 to 10 cm cm beds with up up to to 70% 70% sulfide sulfide in in iron iron Quinnesec formation, formation, and and 2) 2) 33 to to 20 20 meter meter sulfide sulfide zones zones characterized characterized by by subangular subangular quartz clasts clasts and and rounded rounded graphitic graphitic muscovite—chlorite muscovite-chlorite clasts clasts supported supported in aa sulfide sulfide matrix. matrix. Two Two main zones zones have been defined at at stratigraphic stratigraphic in levels levels separated by approximately approximately 300 300 meters meters of of basalt basalt flow, flow, tuffs tuffs and and iron formation. formation. The lower deposit overlies overlies graphitic, graphitic, sulfide—bearing sulfide-bearing felsic felsic tuff and is overlain by garnetiferous garnetiferous iron iron formation formation and and biotite— biotiteThe upper deposit overlies a 30 to 60 meter amphibole metasediments. overlies a 30 to 60 meter iron formation and is capped capped by thinly thinly laminated, laminated, graphitic, graphitic, siliceous siliceous sediments that grade upward into into fine fine grained, grained, well—bedded well-bedded siltstones. siltstones. Both main sulfide sulfide deposits deposits overlie overlie and and are are interbedded interbedded at at the the base base with with tremolite and anthophyllite—bearing assemblages, possibly representing anthophyllite-bearing assemblages, possibly representing alteration zones. zones. The sulfide mineralogy of of the the massive massive sulfide sulfide deposits deposits alteration Sphalerite and is simple, simple, with monoclinic pyrrhotite pyrrhotite predominant. predominant. is chalcopyrite occur throughout throughout the the deposits deposits with with sphalerite sphalerite forming forming loloPyrite is generally secondary, associated with fracthin beds. beds. is generally secondary, associated with fraccalized thin tures, however, however, some pyrite may be part of the tures, the metamorphic metamorphic sulfide sulfide Highest Zn and and Cu concentrations concentrations are are 1.0% 1.0% and and 0.1% 0.1% respecrespecHighest assemblage. tively. Iron formation formation is is represented by the assemblage Iron assemblage grunerite—quartz, grunerite-quartz, grunerite—ferro—actinolite—quartz, grunerite—ferro—hornblende—ferro— grunerite-ferro-actinolite-quartz, grunerite-ferro-hornblende-ferroactinolite—quartz, and gruneritegrunerite— actinolite-quartz, grunerite—ferro—hornblende—garnet—quartz grunerite-ferro-hornblende-garnet-quartz and Grunerite— All assemblages can contain calcite. stilpnomelane-quartz. contain calcite. Gruneritestilpnomelane—quartz. ferro—actinolite—garnet—quartz occurs in ferro-actinolite-garnet-quartz in high Mn bulk bulk compositions. compositions. phase with with magnetite magnetite and and ilmenite locally Pyrrhotite is is the main opaque phase locally Sphalerite occurs either or pyrrhotite, abundant. Sphalerite occurs with magnetite or pyrrhotite, abundant. chalcopyrite tends tends to be restricted to to pyrrhotite—bearing pyrrhotite-bearing samples. samples. The formation that that underlies the upper main massive sulfide iron formation sulfide zone zone is is divided into into upper upper and and lower lower units units separated separated by by aa sulfide sulfide rich rich zone zone divided unit is containing 0.5% Cu and and 0.5% 0.5% Zn. Zn. The lower unit is characterized by The upper unit numerous sulfide-rich beds. beds. upper unit is is characterized by numerous thin sulfide—rich Base metal ions garnetiferous beds, beds, some of which are garnetiferous are highly graphitic. graphitic. Base were available periodically during iron formation deposition with precipitation controlled controlled by by local local Eh-pH Eh—pH conditions conditions and and intensity intensity of of hydrothermal hydrothermal pitation activity. Metamorphic conditions conditions were were in in the the epidote epidote amphibolite amphibolite facies facies of of Metamorphic Primary textures are well preserved with penetrative amphibolite facies. Primary textures are well preserved with penetrative amphibolite facies. deformational features features weakly weakly developed. deformational developed. —10--10- �PETROLOGY AND GEOCHRONOLOGY OF OF ARCHEAN ARCHEAN GNEISS GNEISS IN THE LAKE ARBUTUS AREA, AREA, WEST-CENTRAL WEST—CENTRAL WISCONSIN THE James F. F. DuBois DuBois and W. W. R. James R. Van Schmus Department of Geology University of Kansas Lawrence, Kansas 66045 Lawrence, 66045 The gneiss of of central out along the Black central Wisconsin crops out The basal gneiss River in in Clark Clark and and Jackson Jackson counties counties and and is is particularly particularly amenable amenable to to River detailed study at at a detailed a series of exposures below below Arbutus Arbutus Dam Dam near near Hatfield, Hatfield, gneiss has has aa heterogeneous heterogeneous composition, composition, ranging from Wisconsin. The gneiss granite to granite to tonalite, tonalite, and contains interlayered inter layered amphibolite amphibolite units. units. There is considerable considerable scatter scatter of of the the Rb—Sr Rb-Sr geochronologic geochronologic data, data, but an upper age limit limit can can be be defined defined by by aa 2.8 2.8 b.y. b.y. isochron. isochron. This age presumably dates the time of upper amphibolite to granulite facies metamorphism. Later open system conditions are probably due either to Rb metasomatism or to loss of to Rb of radiogenic radiogenic Sr. Sr. The former former may be be explained as an an effect effect from from intrustion intrustion of of Penokean Penokean granite granite (1830 (1830 m.y. m.y. old) old) 33 k.m. k.m. north of of the the study study area. area. Two models are proposed for the structural relationships between between the the gneiss gneiss and and granite. granite. The granite may be a small body intruding continuous and extensive gneissic terrane, terrane, or the gneiss may be present as a a roof pendant within a large Penokean batholithic batholithic complex. complex. Due to limited exposure it may be difficult to prove either either model. model. U—Pb U-Pb data on zircon from the the gneiss yield a concordia intercept intercept corresponding to The lower concordia to an an age age of of 2.9 2.9 b.y. b.y. concordia intercept intercept of 1.0 b.y. b.y. is too high to be interpreted by a simple diffusion model. model. It may, may, however, however, be explained by U U and Pb diffusion affected by a second second metamorphic metamorphic event event about about 1.8 1.8 b.y. b.y. ago. ago. —11— -11- �FAULTING IN PART OF OF THE THE DULUTH DULUTH COMPLEX, COMPLEX, NORTHEASTERN NORTHEASTERN MINNESOTA MINNESOTA FAULTING IN PART FOOSE, Michael S. Geological Geological Survey, Survey, Reston, FOOSE, Michael P., P., U. U. S. Reston, Va. Va. 22092, and and COOPER, Roger W., W., Minnesota Geological COOPER, Geological Survey, Survey, University University of of Minnesota, Minnesota, St. St. Paul, Paul, Minn. Minn. 55108 55108 faulting and and fracturing Intense faulting fracturing in in part part of the the Duluth Duluth Complex, Complex, northnortheastern Minnesota, Minnesota, has eastern has been documented by by detailed detailed field field mapping. mapping. Faulting is Faulting is recognized principally by by the the displacement displacement of of mappable, mappable, mineral graded layers mineral layers that that were were probably probably formed formed in in aa manner manner analagous analagous to that to that of of sedimentary sedimentary turbidites. turbidites. Recognition of the the faulting, faulting, fracturing, and depositional fracturing, depositional environment establishes establishes aa basic basic geologic geologic style that that may have significant regional regional implications. implications. The area mapped in Lake Lake County, County, approximately approximately 23 23 km southeast mapped is is in of Ely, Ely, Minn., Minn., near near the the basal basal part part of of the the Duluth Duluth Complex. Complex. It It is is between Birch Lake, between Lake, the the Tomahawk Road, Road, and and Minnesota Minnesota Highway Highway 1. 1. Two distinct rock sequences were identified. distinct identified. The lower lower sequence is is prepremedium—grained troctolites 10 percent dominantly medium-grained troctolites that that contain contain 33 to 10 intercumulus pyroxenes and/or oxides; oxides; the intercumulus pyroxenes the upper sequence sequence is is mediummediumto to fine-grained fine-grained troctolites troctolites that that contain contain little little or or no no intercumulus intercumulus pyroxenes or or oxides. oxides. Well-defined and mappable layering layering is is best best developed in in these these upper upper troctolites. troctolites. Most common are layers layers that that have have abundant cumulus cumulus olivine olivine at at the the base base and and decreasing decreasing amounts amounts of of olivine olivine abundant upward. Contacts of layers layers are sharp, sharp, but but inclusions inclusions of of olivine-poor olivine-poor clasts clasts occur within the the olivine-rich basal basal part part of of overlying overlying layers. layers. The olivine-poor top of one layer is approximately 10 m thick top layer is approximately 10 m thick and and provides a distinctive marker horizon provides horizon that that can can be be traced traced through through much much of the the study study area. area. Layers Layers appear to to have been been formed formed by by density density currents currents carrying olivine and and plagioclase plagioclase grains. grains. Faults and fractures are the Faults fractures the most abundant abundant and and important important strucstructures recognized in the area. They are identified principally tures in the area. identified principally by by the the off—setting off-setting of mappable layers, layers, but also by variations in in the the orientation mineral laminations, occurrence of of gouge, gouge, and and the tation of mineral laminations, the the occurrence the presence of marked topographic the study area are three topographic lineaments. lineaments. In In the three major major directions of faulting. direction trends trends N30-40E, N3O—OE, and faulting. The principal principal direction and less prominent faults less prominent faults are usually oriented N-S N-S and and N35W. N35W. However, However, virtually any direction of of faulting faulting may may be be observed observed locally. locally. Rarely, minor folds folds are are observed observed in in association association with with some some major major faults. faults. Previously, Previously, only a few few faults faults have have been been identified identified by by groundgroundcontrolled mapping, largely owing to great difficulty difficulty of of detailed detailed controlled mapping, largely owing to the great field field mapping in in the the Duluth Duluth Complex. Complex. However, However, the the intense intense faulting faulting documented area defines defines aa structural structural style that may be documented in in this this small small area that may common to to much of of the the region. region. Certainly, Certainly, the the possibility possibility of of intense intense faulting and fracturing fracturing must must be be considered considered in in any any further further work work and and interpretation of the the Duluth Duluth Complex. Complex. —12— -12- �ECONOMIC MINERAL PRODUCTION ECONOMIC MINERAL PRODUCTION IN MICHIGAN MICHIGAN PAST PAST AND AND PRESENT PRESENT Milton Milton A. A. Gere, Gere, Jr. Geological Geological Survey Survey Division Michigan Michigan Department Department of Natural Natural Resources Resources Box 30028, Lansing, Michigan Box 30028, Michigan 48909 48909 ABSTRACT ABSTRACT Michigan's mineral production production statistics statistics have compiledeither either in Michigan's mineral have been been compiled whole or in part whole or part from from 1845 1845 to the the present. present. In 1877 1877 Act Act 99was was passed passed which created the the position of MineralStatistics. Statistics. The which created of Commissioner Commissioner ofofMineral The duty of wastoto give give the of the theCommissioner Commissioner was the governor governor an an annual annual report report about the yearly mineral about the mineral production production statistics statisticsand andthe thedevelopment development of of the smelting industries. industries. Part the mining mining and and smelting Part of Act Act 99 required required all all mining mining companies submittheir their production companies toto submit production figures figurestotothe theCommissioner. Commissioner. In 1911 the duties duties of weretransferred transferred to to the 1911 the of the theCommissioner Commissioner were the Geological Geological Survey, Survey, now now aa Division of ofthe theMichigan MichiganDepartment Department of of Natural Natural Resources. Resources. Presently, receives most mostof of the the yearly mineral mineral Presently, the the Geological Geological Survey Survey receives production statistics, exclusive production statistics, exclusiveofofpetroleum petroleum and and natural natural gas, gas, through through understandingwith withthe the U.S. U.S. Bureau a memorandum memorandum of ofunderstanding Bureau of Mines. Mines. Company data submittedto to the the U.S.B.M. sent on on to to the data submitted U.S.B.M. isis sent the State. State. Oil and and gas gas silver production is collected by directly. Copper, production is by the the State State Survey Survey directly. Copper, silver and iron iron ore ore figures figures are for taxation and are also also received received separately separately for taxation as as well well as through the the U.S.B.M. U.S.B.M. as through Tabulationsof of the the value value of of nonmetallic, Tabulations nonmetallic, metallic, metallic, and and fuel fuel minerals minerals from 1910toto present present show showthat thatuntil until 1977, from 1910 1977, the the fuel fuel minerals mineralswere were always the the smallest smallest group group with with the metallics always metallics and and nonmetallics nonmetallics switching switching leading leading places places several several times. times. In 1977 1977 the the fuels fuels formed formed the the middle middle group group for the first time. the first time. Michigan's 1977 mineral production production value, value, according 1977 mineral according to the the U.S.B.M. U.S.B.M. Michigan's 1976total total value annual, preliminary preliminary report, report, was $1.51billion. billion. The annual, was $1.51 The 1976 value it was million. record at $1,543.5 $1,543.5 million. 1910 it was $80.5 $80.5 million~ set a record million. In 1910 Everyone the8383counties countiesininthe theState Statecontribute contribute to to the the total mineral Everyone ofofthe mineral However,all all of the value. However, the metallic metallicminerals minerals and and aa large large amount amount of the the high value high value for nonmetallic nonmetallic minerals minerals isisproduced produced ininthe theUpper Upper Peninsula. Peninsula. The balance balanceofofthe the nonmetallics nonmetallicsand andall all of of the The the fuel fuel minerals minerals are are derived derived from the the Lower Lower Peninsula. Peninsula. from —13— -13- �GEOCHRONOLOGY GEOCHRONOLOGYOFOFARCHEAN ARCHEANROCKS ROCKSIN IN MARQUETTE COUNTY, COUNTY, UPPER MICHIGAN MICHIGAN Roger D. D. Hammond Hammond and and W. W. R. R. Van Schmus Roger Department of Geology University of Kansas Lawrence, 66045 Lawrence, Kansas 66045 According to Morey and and Sims Sims (1976) the Archean Archean basement basement of of the Lake According to Morey (1976) the the Lake is composed of two two different different terranes, gneiss terrane Superior region is composed of terranes, aa gneiss terrane dnd aa granite-greenstone granite—greenstone terrane, terrane, which which differ differ in age, and type, strucstrucage, rock type, tural style, and metamorphic grade. tural style, and metamorphic grade. They extend the boundary between these two two terranes these terranes through the central part of of Marquette Marquette County, County, Michigan, Michigan, beneath the middle Precambrian rocks of the Marquette Range rocks of the Marquette Range Supergroup. Supergroup. Locally, the north of the boundary, which which are are part part of the Locally, the Archean rocks rocks north the boundary, the granite—greenstone terrane, are known as as the and those granite-greenstone terrane, are the Northern Complex and those south boundary, which which are are part of the gneiss terrane, are known south of the boundary, part of the gneiss terrane, are as as the Southern Southern Complex. Complex. If Morey and Sims' Sims' model is is correct, correct, rocks rocks m.y. should be present in the gneiss older than 3,000 m.y. gneiss terrane, terrane, and the rocks of of the the granite-greenstone granite—greenstone terrane terrane should should not not be be older older than than about about rocks 2,800 A geochronologic study was was done 2,800 m.y. m.y. A done on the the rocks of of the Northern and on on aa granite granite body body of of the the Southern Southern Complex Complex which which had had yielded yielded Complex and anomalous Rb—Sr Rb-Sr age age systematics systematics with with one one sample sample giving giving aa 3,200 3,200 m.y. m.y. Woolsey, 1975), 1975), to model age (Van (Van Schmus and Woolsey, to verify or revise Morey and Sims' Sims' model. The Northern Complex Complex consists consists of of granitic granitic to to tonalitic tona1itic gneisses, gneisses, with lesser lesser amounts amounts of of granites, granites, amphibolites, amphibo1ites, and and volcanics, volcanics, that that extend extend approximately 80 80 kilometers kilometers east—west east-west and and 40 40 kilometers kilometers north—south. north-south. The eastern part part of of the the Complex Complex includes includes aa greenstone greenstone belt. belt. U—Pb U-Pb isotope isotope studies on zircons from samples of the gneisses and volcanics do not indicate an age any greater than 2,750 m.y. m.y. for rocks of the Northern Complex. Complex. The rocks of the Southern Complex are primarily granitic gneisses with lesser lesser amounts amounts of granites, granites, mafic gneisses, gneisses, and and amphibolites, amphibo1ites, which extend approximately 75 75 kilometers east—west east-west and 50 kilometers north— northsouth. body, 1.5 by 4 kilometers in size, south. One granite body, size, was mapped about 8 kilometers south south of of Ishpeming. Ishpeming. It is a medium-grained medium—grained granite which appears gray gray in in outcrop outcrop in in the the western half half and and red red in in the the eastern eastern half. half. Parts of of the the granite granite body are are quite quite porphyritic porphyritic with with aligned aligned feldspar feldspar phenocrysts. phenocrysts. Although Although no no direct direct contacts contacts were observed, observed, the the presence presence of gneissic inclusions suggest that the granite was intruded intruded into into the the surrounding surrounding gneiss. gneiss. Rb—Sr Rb-Sr isotope isotope data data on on wholerock wholerock samples samples from from the the granite define a 2,400 m.y. m.y. isochron with a Sr87/Sr86 Sr 87 /Sr 86 intercept intercept of 0.7200. U—Pb V-Pb isotope studies on zircon Zircon from from the the granite do do not indicate indicate an an age age any any greater greater than than 2,600—2,700 2,600-2,700 m.y. m.y. The The granite granite is is possibly possibly remobil— remobilized crustal crustal material material as as indicated indicat~d by by the the high high initial initial Sr87/Sr86 Sr 87 /Sr 86 ratio. ratio. Ages Ages of of the the rocks rocks studied studied from from both both these these complexes complexes conform conform with with Morey Morey and 5j? Sims'model, model,even eventhough thoughprimary primaryages agesininexcess excessofof2,800 2,800 m.y. m.y. have have yet yet to to be be found found from from the the Southern Southern Complex. Complex. —14— -14- �INDUSTRIAL INDUSTRIAL SAND SAND AND AND SANI)STONE SANDSTONE RESOURCES RESOURCES OF OF MICHIGAN MICHIGAN E. E. Wm. Heinrich Heinrich Dept. Dept. Geology and Mineralogy The The University University of of Michigan Michigan Ann Arbor, MI 48109 MI 48109 Michigan's silica, silica, sand sand and and sandstone sandstone deposits, deposits, which range range in in age from Middle Precambrian to to Quaternary, Quaternary, embrace a considerable diversity of geological types types and have a remarkable diversity of technological applications. applications. Historically, Historically, Michigan sandstones were famous for for two two pur- poses: poses: 1) 1) the the Jacobsville sandstone (Cambrian) (Cambrian) used as a colorful dimension stone in the construction of of larger larger buildings buildings (churches, (churches, courthouses, courthouses, breweries), breweries), mainly in in the the Upper Peninsula and 2) 2) the the Marshall sandstone (Devonian), (Devonian), utilized in the last half of the the 19th 19th century century for for abrasive abrasive (Grind Stone Stone City, City, Huron Huron Co.). Co.). wheels (Grind The spectrum of deposits and and poten— poten- tial deposits, deposits, by formation, tial formation, age and application, includes: includes: 1. 1. Sunday, Sturgeon, Middle Precambrian quartzites: quartzites: Sunday, Mesnard, Ajibik, Ajibik, and Goodrich Mesnard, Goodrich quartzites: quartzites: aggregate; the Ajibik Ajibik may be of potential value for the for ferrosilicon. ferrosilicon. 2. 2. Munising sandstone (Late (Late Cambrian): Cambrian): 3. 3. Sylvania sandstone (Lower (Lower Devonian): presently exploited glass—sands of the near Rockwood as one of the premier glass-sands United States; States; also also abrasive abrasive sand sand and and silica silica flour. flour. 4. 4. Napoleon sandstone (uppermost Napoleon (uppermost Devonian): quarried near Jackson for for flagging, flagging, riprap riprap and and sandstone-bituminous sandstone—bituminous Jackson hot hot mix for pavement. 5. 5. Pleistocene till, till, glaciofluvial deposits, deposits, and and lakebeds: lakebeds: fill fill sands sands and aggregate. 6. 6. Dune sands in southwestern Michigan Michigan (Quaternary): (Quaternary): active mining for for molding molding sands sands (considered mining (considered the industry industry standard for such such sands); sands); also also evaluated as glass—sand. for glass-sand. —15— -15- glass—sand potential. glass-sand potential. �A POST POST TWO TWO CREEKS CREEKS BURIED FOREST A IN MICHIGAN'S MICHIGAN'S NORTHERN PENINSULA IN John D. D. Hughes, Hughes, Department Department of of Geography, Geography, Earth Earth Science Science and and John Conservation, Northern Northern Michigan University, Conservation, University, Marquette, MI MI 49855 9855 ABSTRACT In 1976-77, 1976—77, spruce spruce and and tamarack tamarack trees trees in in growth growth position position In were exposed exposed between six and eleven meters below the were eleven meters the surface surface during construction construction of the tailings basin for during the Gribben Gribben tailings for the the Cleveland—Cliffs Iron Cleveland-Cliffs Iron Company. Company. The The site, site, located sixteen kilometers southwest southwest of Marquette, Marquette, Michigan, Michigan, lies kilometers lies within the the outwash apron of the outer Marquette Marquette moraine. moraine. Throughout the excavation, excavation, there there is no evidence that glacial glacial override the is ~o evidence that override occurred following following the the period of growth such as presence occurred as the the presence of distorted strata, strata, sheared sheared trees, trees, or or intercalated intercalated till. till. + 1he outer parts parts of two trees yere dated at + 14he treesl~ere at 9780 . —250 C.y.a., C.y.a., W3904 W3901 and and 98509850± 300 300]C.y.a., -250 C.y.a., W3866 W3866 (N. (M. Rubin). Rubln). Spruce needles needles from the Spruce the upper pars part of the the buried A0 Ao soil horizon were dated dated at at 10,230±3001 10,230~3001 C.y.a., C.y.a., W3896 W3896 (M. (M. Rubin). Rubin). The largest tree collected has a diameter of sixty centimeters largest has sixty centimeters and 150 growth rings. and rings. Most trees trees suffered a severely severely reretarded growth growth rate rate during their final tarded final thirty thirty or forty forty years years of growth, growth, a a condition that is is attributed to climatic climatic deterideterioration accompanying accompanying the the glacier's glacier's return. return. Evidence in in the Gribben Gribben tailings tailings basin indicated indicated aa minimum period of of plant plant growth growth of of 150 150 years years following following recession of the Valders (Great (Great Lakean) Lakean) Stadial. Stadial. Tree growth in the the basin was terminated by local local ice-marginal ice-marginal ponding caused by glacial glacial readvance readvance into into the the area. area. Deposition of lacustrine sediment capped capped by outwash gravel gravel and and sand occurred during building of the Marquette-Munising moraine Similar dates have moraine system. system. have been obtained from from detrital detrital spruce and hemlock found found in red till and and red red clay clay till in Michigan's westernmost westernmost county county and and near near Ashland, Ashland, Wisconsin at elevations elevations 400 00 to Wisconsin at to 600 600 feet feet above above present present Lake Lake Superior. Superior. It It appears that a a glacial glacial advance advance climaxed climaxed slightly slightly less less than 10,000 years years ago, ago, and and at at that that time, time, almost almost all, all, if not not all, all, of the Lake Superior Superior basin was occupied occupied by by glacial It glacial ice. ice. It is is proposed that the name Marquette Stadial Stadial be adopted adopted for for the the period period of of glacial glacial advance advance and and Gribben Gribben Interstadial for for the the preceding preceding time time of of retreat. retreat. —16— -16- �THE THE PETROLOGY PETROLOGY AND AND TECTONIC TECTONIC SIGNIFICANCE SIGNIFICANCE OF OF THE THE INTERFLOW INTERFLOW SEDIMENTS SEDIMENTS IN IN THE THE KEWEENAWAN KEWEENAWAN NORTH NORTH SHORE SHORE VOLCANIC VOLCANIC GROUP GROUP OF OF NORTHEASTERN NORTHEASTERN MINNESOTA MINNESOTA Mark Mark A. A. Jirsa Jirsa University University of of Minnesota—Duluth Minnesota-Duluth Duluth, Duluth, Minnesota Minnesota 55812 55812 Interfiow Interflow sediments sediments occur occur as as lenticular lenticular bodies bodies between between and. and crevice cre~ce fillings, fillings, within, lavas lavas of of the the North North Shore Shore Volcanic Volcanic Group. Group. Their Their structure, structure, texture, texture, and composition composition offer evidence of the the depositional/erosional relrelationships ationships between between the the volcanic volcanic and and sedimentary sedimentary accumulations accumulations and and the the borderland during during Keweenawan Keweenawan rifting. rifting. surrounding borderland The The majority majority of of the the 380 380 (total) (total) of of interflow interflow sediments sediments occur occur as as bedded bedded interflow interflow sandstones, sandstones, conglomerates, conglomerates, and and minor minor shaly shaly sediments. sediments. Tabular Tabular and and trough trough cross—bedding, cross-bedding, planar bedding and lamination, lamination, and ripple marks are the the most most prevalent prevalent primary primary structures. structures. Other deposits include include sediment—filled sediment-filled flow—top flow-top breccias, clastic clastic dikes, dikes, and and sedimentary/volcanic sedimentary/volcanic breccias. breccias. Nearly Nearly Most clastic all interflow interflow beds beds lie lie on on uneroded uneroded flow flow tops. tops. Most clastic dikes dikes are are the the result result of sediment filling filling fractures in upper lava surfaces; surfaces; however, however, some were were filled filled by by sediment sediment injected injected into into lava lava fractures fractures from from underlying underlying clastic. clastic. Mud cracks, slump structures, and convolute laminations occur in cracks, structures, in deposits. most types types of of deposits. deposits. most These volcanogenic arkosic sediments are reddish—brown reddish-brown to to buff, buff, and consist of predominantly fine—to well—sorted grains fine-to medium—grained, medium-grained, subrounded, subrounded, well-sorted of plagioclase, clinopyroxene, clinopyroxene, magnetite, magnetite, and and various various rock rock fragments. fragments. The The dominant rock fragments fragments are volcanic; volcanic; however, however, agate, agate, chert, chert, shale, shale, and glass Minor constituents shards also occur. occur. Actual tuff tuff beds beds are are rare. rare. Minor constituents are are potpotGrains are fresh assium feldspar, quartz, and accessory heavy minerals. feldspar, quartz, and accessory heavy minerals. Grains are fresh to to altered, and in many cases, altered, cases, replaced replaced by by various various zeolites, zeolites, chlorite, chlorite, calcite, calcite, and potassium feldspar. In In addition to silica and hematite, these these minerals minerals potassium feldspar. form the major chemical chemical cements. cements. Paleocurrent indicators show predominant current flow sourhward and southeastward towards the the present Lake Lake Superior Superior Basin. Basin. These data imply imply a a fluvial environment of deposition, and sedimentary structures support this fluvial environment of deposition, and sedimentary structures support this Several deposits deposits may may reflect reflect influences influences of of fluvio-lacustrine fluvio—lacustrine implication. Several and eolian environments. The response response of of the the Keweenawan Keweenawan terrain terrain to to rifting rifting and and basinal basinal developdevelopThe and ment is interpreted from a combination of sedimentological, sedimentological, petrographic, petrographic, and In general, sediment bodies are thicker clastic dike orientation orientation analyses. analyses. In general, sediment bodies are thicker and more more variable variable in in lithology lithology in the the area area from from Tofte Tofte to to Grand Grand Portage Portage than than and This may suggest more ponding and/or longer in the area from Duluth Duluth to to Tofte. Tofte. This may suggest more ponding and/or longer periods of of volcanic volcanic quiescence quiescence in in the the northeasternly northeasternly portions portions of of the the basin. basin. periods Petrology indicates indicates predominantly predominantly local local (Keweenawan) sources for for sediments; sediments; Petrology (Keweenawan) sources however, several several deposits deposits had had variable variable sources sources which which may may include include some some prepre— however, The presence of agate fragments some Keweenawan sediments and intrusions. intrusions. The presence of agate fragments in some deposits implies implies mineralization mineralization of of lava lava prior prior to to erosion, erosion, and and thus earlier deposits thus an earlier Data obtained obtained from from cycle of of volcanism, volcanism, burial, and uplift cycle uplift in in the the source source area. area. Data clastic dike dike orientations orientations is is significant significant because because sediment sediment filling filling (by whatclastic (by whatdating the the stress stress ever process) process) occured occured near near the the time time of of lava lava deposition, deposition, thus thus dating ever Although many of these orientations are scattered and patterns at that time. Although many of these orientations are scattered and patterns at time. reflect cooling cooling fractures fractures filled filled with with sediment, sediment, some some conjugate conjugate orientations orientations reflect occur stresses. occur which which may may reflect reflect regional stresses. This study study was was partially funded This funded by the Minnesota Geological Geological Survey. Survey. —17— -17- �Geology and and Mineralogy Mineralogy of of Northern Geology Northern Michigan Michigan Phosphorites Phosphorites Scofield and Allan Johnson, Johnson, Nancy Nancy Scofield and Virginia VirginiaDoane Doane Institute ofofMineral Institute MineralResearch Research Michigan Technological Technological University University Michigan Houghton, Michigan 49931 Houghton, Widespreadoccurrences occurrencesofof Middle Middle Precambrian Precambrianphosphate-bearing phosphate-bearingstrata strata in Widespread in the werefirst first reported the central part partofofthe theUpper Upper Peninsula Peninsula of Michigan Michigan were reported by by Cannonand andKlasner Klasner (1976). Surface Surface exposures Cannon exposures of the the bedded bedded phosphorites phosphorites were were found of several basins near near the the contact contact with with older found at margins margins of several sedimentary sedimentary basins older Archean crystalline rocks. The thickest thickest known phosphorite section section (100 Archean crystalline rocks. The known phosphorite (100 m) m) is the eastern eastern margin margin of of the in Section Section 15, 15,T49N T49N R28W, R28W, ononthe the Dead Dead River River Basin Basin 17 17 miles northwest The rocks rocks here here strike strike NS miles northwest of of Ishperning, Ishpeming, Michigan. Michigan. The NS and and dip steeply to the Early in 1977, wascollected collected for steeply the west. west. Early 1977, aa bulk bulk surface surface sample sample was mineralogical study studyand andpreliminary preliminarybeneficiation beneficiationtests testsbybythe theInstitute Institute of mineralogical Mineral Research During the the summer 1977,the theupper, upper,richest richest section Research (IMR). (IMR). During summer ofof1977, was diamonddrilled drilled by in cooperation was diamond by IMR IMR in cooperation with the theMichigan Michigan and and U.S. U.S. Geological Geological Surveys. Results the apatite to thiswork work showed showed the to be be present present as as pebbles, pebbles, oöids ooids Results of this andasasfine finecrystallites crystallites in aa quartzitic the apatite apatite is is in and quartzitic matrix. matrix. Most Most ofof the in length. Aphanitic apatite dark, elongate elongate pebbles pebbles 1-30 1-30 mm mm in apatitecomprises comprises75-80% 75-80% Submicrongraphite, graphite, pyrite pyrite euhedra, of the the pebbles. pebbles. Submicron euhedra, quartz quartz and and stilpnomelane stilpnomelane are also present. This apatite has identified by francolite, the are present. This has been been identified by XRD XRD asasfrancolite, the carbonatefluorapatite. fluorapatite. carbonate Someofofthe the rich surface P205,but but the the bulk Some surfacebeds beds contained contained as as much much as as 15% 15% P205, However, the drill drill core However, ininthe coreapatite apatitedecreased decreased zones with depth, depth, although although intermittent intermittentricher richer zoneswere wereencountered. encountered. Calcite Calcite was was observed with depth replaced some apatite. observed to be be more more abundant abundant with depth and and may may have have replaced some apatite. Several pyrite-rich pyrite-rich zones Several zoneswere were encountered, encountered, but but surface surface weathering weathering had had oxidized The conglomerate conglomeratecontaining containing the the apatite muchofof the the pyrite pyrite in much inthe theupper upper 55meters. meters. The pebbles appears appearsto to have shale-pebble origin origin and pebbles have aa shale-pebble and the theoccurrence occurrencemay may be be aa channel channel deposit. surface 6.95% P205. P205. surface sample sample averaged averaged 6.95% The bestresults resultsofof initial initial beneficiation fatty acid The best beneficiationtests testsusing using aa standard standard fatty acid float produced float produced aa27% 27% grade grade P205 P205 at 60% 60% recovery. Reference F. and Kiasner, J. J. S. ApatiteCannon, W. W. F. and Klasner, S. (1976), (1976), Phosphorite Phosphorite and and Other Other ApatiteBearing Rocksinin the Precambrian of Northern Bearing Sedimentary Sedimentary Rocks Precambrian of Northern Michigan, Michigan, U.S.G.S. U.S.G.S. Circular 746, 746, 66 p. p. —18— -18- �GEOLOGY OF OF THE THE IRON IRON FORHATION FORMATION AND ASSOCIATED ROCKS GEOLOGY OF THE THE JACKSON JACKSON COUNTY COUNTY IRON IRON MINE, MINE, JACKSON COUNTY, OF COUNTY, WISCONSIN WISCONSIN David G. C. Jones, Jones, Department Department of of Geology Geology and Geophysics, David Geophysics, University University of Wisconsin, Madison, Madison, Wisconsin Wisconsin 53706 53706 Wisconsin, AB STRACT ABSTRACT Precambrian Precambrian magnetite magnetite iron iron formation formation crops crops out out as as low low hills hills in in Jackson County, Jackson County, Wisconsin. Wisconsin. The pit The Jackson Jackson County Iron Company's open pit taconite mine mine was was opened opened in in the taconite the largest of the the hills. hills. The The ore ore body body mined mined strikes northwest northwest and and dips dips 70—80 degrees southwest. strikes 70-80 degrees southwest. The The ore ore body body is is aa lens 915 915 meters meters in length and 150 meters in lens in width. It It averages averages about about 35% magnetite. magnetite. Dominant the iron iron formation formation are: Dominant mineral mineral assemblages within the are: 1. magnetite-quartz-grunerite-ferroactinolite magnetite—quartz—grunerite—ferroactjnolite 1. 2. magnetite-quartz-cummingtonite-biotite magnetite—quartz—cummingtonjte_bjotite 2. 3. magnetite-quartz-garnet-Ca-rich magnetite—quartz-.garnet—Ca—rich hornblende-ferroactinolite-grunerite hornblende—ferroactinolite—gruneritc 3. Amphiboles commonly contain visible exsoiution Amphiboles exsolution features. features. Ca-rich Ca—rich hornblende (hastingsite) replaces garnet. (hastingsite) garnet. Southwest of Southwest of the the iron formation formation is is aa highly highly weathered weathered siliceous siliceous schist schist as the of quartz, and mapped as the hangingwall hangingwall schist. schist. It It is composed of quartz, biotite, biotite, and sericite. Weathering decreases sericite. decreases with depth. depth. The schist, northeast The footwall footwall schist, of the ore body, of the ore body, is is identical identical to to the the unweathered unweathered hangingwall hangingwall schist. schist. Both are composed mainly of three are three assemblages: assemblages: 1. quartz-chlorite-muscovite-andalusite quartz—chlorite—muscovite—andalusje 1. 2. quartz—biotite—chlorite_stauroljte_garnet_andalusjtemuscovite 2. quartz-biotite-chlorite-staurolite-garnet-andalusite-muscovite 3. quartz-biotite-oligoclase-muscovite quartz—biotite--oligoclase—muscovite 3. Phase relations relations suggest suggest that rocks attained attained chemical chemical equilibrium at at Phase that the the rocks staurolite—grade metamorphism. staurolite-grade metamorphism. Texturally the the footwall footwall schist ranges from from a a highly foliated foliated coarse—grained coarse-grained schist schist to to aa nearly nearly granular granular schist. schist. Interlayered with the pelitic schist schist are are zones of grunerite-garnet-quartz grunerite—garnet—quartz Interlayered with the pelitic zones of iron iron formation and poorly foliated, foliated, dark dark green green amphibolite. amphibolite. A A lenticular zone zone of talc talc schist about 350 meters long and 40 meters wide is is situated within the the iron iron formation formation in in the the eastern portion of the the mine. mine. The assemblages taic-garnet—andalusite, talc-garnet-andalusite, talc—biotite, talc-biotite, and talc—cummingtonite talc-cummingtonite are locally locally present. present. the Compositional banding of quartz and magnetite is prominant within the iron iron formation formation and and provides provides the the contrast contrast necessary necessary for for viewing viewing minor minor structure. structure. The rocks rocks have been isoclinally isoclinally folded folded around nearly vertical axes and and sheared sheared into into boudins. boudins. Features Features observed observed include: include: 1) 1) small small boudins boudins and and isolated isolated and and rotated rotated fold fold hinges hinges of of minor minor isoclinal isoclinal folds, folds, 2)transposed, 2)transposed, bedding, 3) 3) prominent prominent lineation lineation of of amphiboles amphiboles developed in in the the plane plane parallel bedding, of compositional compositional banding, banding, and and 4) 4) distinct thickening thickening and and thinning thinning of of iron iron formation formation along along strike. strike. Upper Upper Cambrian Cambrian Mount Mount Simon Simon Sandstone Sandstone unconformably unconformably overlies overlies the the PrePrecambrian cambrian terrane. terrane. Within Within the the Mount Mount Simon Simon aa basal basal conglomerate conglomerate containing containing clasts clasts of of angular angular hematitic hematitic iron iron formation formation is is well well developed. developed. The The congloconglomerate merate grades grades rapidly rapidly upward upward into into well well sorted, sorted, poorly poorly indurated indurated sandstone. sandstone. The The deposit deposit has has not not been been dated, dated, but but structural structural and and metamorphic metamorphic style style indicate indicate that that it it may may be be Archean. Archean. —19— -19- �U The The Unconformity-Type Unconformity-Type Proterozoic Proterozoic Pitchblende Pitchblende Ore Ore Body Body Model Model And And Its Its Application Application to to Northern Northern Michigan Michigan J. J. Kalliokoski Kalliokoski Michigan Michigan Technological Technological University University Houghton, Houghton, Michigan Michigan 49931 49931 Previous Previous studies studies establish establish that that this this class class of ofore orebodies bodieshasP has aa characcharacteristic setting: setting: aa short short distance distance below below an an unconformity, unconformity, in in almost almost any any teristic kind kind of of host host rocks rocks that that have developed developed permeability through either physical or chemical chemical ground ground preparation preparation (or (or both). both). This This chemical chemical ground ground preparapreparaor tion tion is is represented represented in in the the viscinity viscinity of the the ore ore body also also by various types of of low low temperature temperature alteration, alteration, none of which need to to be a a direct direct effect or the deposition deposition of of the the pitebblende. pitchblende. The The quantity quantity and and intensity intensity cause of the of of alteration alteration cannot cannot be related related to to the the size size of of the the pitchblende deposits. deposits. In In a similar similar coincidental coincidental fashion, fashion, pitcbblende pitchblende ore ore bodies bodies can can adjoin adjoin also economic concentrations concentrations of of nickel—cobalt nickel-cobalt arsenides arsenides and and gold. gold. By By contrast, graphite graphite and and pyrite pyrite are are interpreted interpreted to to be be related related more more directly directly the ore ore body body and and to to the the mineralization mineralization process. process. to the An evaluation of the geochemical system indicates indicates there to be be adequate adequate major outstanding sources and and uranium uranium transport transport mechanisms. mechanisms. The The major outstanding uranium sources problem concerns the locus locus and manner in which uranium is deposited deposited as as pitchblende. There is some indirect geological evidence to suggest that uraniferous fluids the precipitation results results from the mixing mixing of of oxidized oxidized uraniferous the from the fluids methane and with those containing containing large quantities of such reducants as methane and within are capable capable of precipitating precipitating pitchblende pitchblende within H2S, These substances substances are H2S. remaining of of their low little evidence remaining their low temperature systems, systems, with very little previous existence. existence. thick the model model to to northern northern Michigan Michigan one one can note note that that aa very very thick Applying the sandstone body of young Precambrian continental rests continental redbed redbed Jacobsville Jacobsville sandstone rests Thus, unconformably on a a floor floor of middle and and lower lower Precambrian Precambrian rocks. rocks. Thus, oxidized system the first first requirement requirement of of the the model model is is met, met, that that of of an an oxidized the system The basement is cut by aa series series of of situated a more reduced reduced one. one. The basement is cut by situated above a These provide the easterly faults and diabase dikes. dikes. These provide the easterly trending trending major faults The second requirement, requirement, that of secondary permeability second permeability in in the the basement. basement. The Jacobsville grade metasedimentary metasedimentary rocks rocks below the the Jacobsville middle Precambrian low grade It is is proposed proposed that because of their are are quite quite carbonaceous and pyritic. It the gaseous gaseous hydrohydrolow low metamorphic metamorphic grade grade these these rocks rocks could could have have provided provided the precipitate carbons carbons or or possibly possibly HH2S that are are required required by by the the model model to to precipitate 2 S that pitchblende zones of of mixing. mixing. pitchblende in and along the permeable zones —20— -20- �Problems in in Paleogeographic Reconstruction of the the Chocolay and lower lower Menominee Group Sedimentation, Sedimentation, Marquette Range Supergroup, Supergroup, Lake Superior region Larue, D. D. Knight, Knight, Northwestern University, University, Evanston, Evanston, Il. Larue, II. 60201 60201 Due to structural complications and few outcrops, outcrops, little is to structural complications and is known about the regional sedimentary facies and source areas of the Chocolay about facies and areas of and Menominee Groups and their Groups of the Marquette Range Supergroup and their Animikian equivalents. In structurally deformed areas isopachous areas isopachous and and paleocurrent data are equivocal (Ramsay, 1961, 1966), 1966), but have have been used used (Ramsay, 1961, Trends in in previous previous reconstructions (Taylor, in (Taylor, 1972, Sims, Sims, 1976). 1976). regional mineralogy are are employed employed by by others others (Morey, (Morey, 1973, 1973, Gair, Gair, 1975). 1975). Data bearing on paleogeographic reconstructions reconstructions of the the Chocolay 1) an increase in feldspar and grain size Group include: include: 1) size in in basal basal quartzites toward toward the the Lake Lake Mary Mary Quadrangle Quadrangle (Bayley, 1959, Gair Gair and and quartzites (Bayley, 1959, to weakly weakly unimodal NE — Weir, 1956); Weir, 1956); 2) 2) strongly unimodal NW — - SE to - SW orientations of of symmetric—ripple symmetric-ripple mark crests crests in in quartzites; quartzites; 3) 3) regional regional decrease in basal quartzite thickness toward the west (excluding (excluding the poorly understood understood Trout Trout Lake Lake Formation) Formation) (Sims, (Sims, 1976); 4) 4) local local westerly westerly thinning of quartzite quartzite in the the Gogebic Gogebic Range; Range; 5) 5) restriction restriction of of large large thinning of domal stromatolites stromatolites to Kona Dolomite Dolomite (Marquette area); 6) 6) greater greater domal to the the Kona (Marquette area); volume of intercalated clastic silica in the the Kona Dolomite than than strati— stratigraphic equivalents; equivalents; 7) 7) presence presence of of subrounded subrounded quartzite quartzite and and chert chert graphic Symmetric— pebbles in channel deposits of of the the Randville Randville Dolomite. Dolomite. Symmetricripple spacing in quartzite indicates indicates short short period period waves. waves. Evaporite casts (Taylor, 1972) with mud mud cracks cracks in dolomitic dolomitic units units indicate indicate mineral casts (Taylor, 1972) aa semi—arid semi-arid to to arid environment with with periods periods of of subaerial subaerial exposure. exposure. facies transition in North — - south facies in the the lower lower Menominee Menominee Group Group continues into Iron Iron Formation Formation sedimentation sedimentation (Gair, (Gair, 1975). 1975). Available of the paleocurrent data suggest flow parallel to to the the trend trend of the transition (E -— W). (E data, though obviously scant, scant, support the interThese available data, pretation of aa shallow basin deepening gently to to the south, south, with aa major detrital source source to to the the north, north, and a local source for feldspar feldspar and subrounded pebbles pebbles near near the the Lake Lake Mary Mary Quadrangle. Quadrangle. Shorelines possibly extended NW NW —- SE during deposition of Chocolay Chocolay sediments. sediments. Water depth varied from intertidal (possibly (possibly supratidal) supratidal) to to shallow subtidal for for the entire area, area, thus thus the significance of the term "shoreline" for for the dolomitic units is is questionable. questionable. The Wewe Slate may represent aa still deeper—water deeper-water phase of sedimentation (Puffett, (Puffett, 1974, Gair and Thaden, 1968). 1974, 1968). Lower Menominee Group Group sedimentation was similarly influenced influenced by by aa northern northern source source (Morey, 1973) and and by by mean mean similarly (Morey, 1973) water depths increasing southward, southward, but the contribution of local faulted uplifts is indicated faulted indicated (Gair, (Gair, 1975, 1975, James, James, 1954). 1954). —21— -21- �THE GEOLOGY OF THE GARNETDEPOSIT, DEPOSIT, THE GEOLOGY OF THE GORE GORE MOUNTAIN MOUNTAIN GARNET SOUTHEASTERNADIRONDACKS, ADIRONDACKS, WARREN WARREN COUNTY, COUNT!, NEW SOUTHEASTERN NF.W YORK YORK Frank R. Luther, Department of Geological Sciences, Sciences, Lehigh University, Frank R. Luther, of Geological Lehigh University, Bethlehem, Pa. Pa. (now University of Bethlehem, (now at Department Department of Geography-Geology, Geography-Geology, University Wisconsin -- Whitewater, Whitewater, Wis.) Wisconsin deposit, aa garnet amphibolite, amphibolite, is The garnet deposit, is located on the north slope of Gore Mountain Mountain in slope in the the southeastern southeastern Adirondack Adirondack Highlands. Highlands. The 1) rocks rocks of of charnockitic affinity, 2) major rocks rocks of of the the area area are: are: 1) 2) ananorthosite, gabbro; all of these rocks are orthosite, and 3)corona-bearing olivine gabbro; metamorphosed to the the upper amphibolite or hornblende granulite facies. facies. The garnet amphibolite contains euhedral to anhedral garnet porphyroblasts which which are are commonly commonly 10-20 10-20 cm in in diameter diameter (some range up up to to 30 30 roblasts (some range cm). These garnets are surrounded oy a surrounded by 1-2 mm ~u rim of plagioclase (an52) (an52) em). and biotite, biotite, a thick (up (up to to 10 cm) em) shell of hornblende, hornblende, and often a pressure shadow of plagioclase (an40) and orthopyroxene sure (an 40 ) and orthopyroxene (en67). (en67). Electron microprobe analyses show the composition of microprooe of the garnets to be remarkably uniform for for garnets of this this size. size. To the north, north, the garnet amphibolite grades through a 2 m m transition transition zone into aa layered layered gabbro containing igneous olivine, olivine, pyroxenes, pyroxenes, and and plagioclase plagioclase and and corona corona structures structures of of igneous metamorphic pyroxenes, pyroxenes, garnet, garnet, and and plagioclase. plagioclase. This contact is is charcharacterized by major changes in mineral proportions and texture texture while the the 3 /Fe+ Z change Fe+3/Fe+2 Change in bulk chemistry is small (an (an increase in H2O HZO and Fe+ toward toward the the garnet amphibolite). amphibolite). Electron microprobe analyses show that that compositional compOSitional variations between minerals occurring in the the garnet ampnibolite and gabbro are very small; small; compositions are: are: plagioclase (p1)-an39, (pl)-an39, garnet -ai47py40gr1sp1, orttiopyroxene garnet (g) (g)-a147PY40grl2sPl, orthopyroxene (opx)-en68, (opx)-en b8' norublende hornlJlende (h)(h)paragasite, clinopyroxene clinopyroxene (cpx)—augite, (cpx)-augite, and and magnetite magnetite (mt). (mt). These two two rocks are surrounded surrounded by by anorthosite anorthosite on on the the west, west, north, north, and and east. east. Tne gabbro contains contains xenoliths xenolithS of of deformed deformed anorthosite. anorthosite. To the the south, south, there there is with syenitic granulite granulite (mangerite); patches of ananis aa sharp contact with (mangerite); patches orthosite up up to to 55 mm thick thick occur occur along along this this contact. contact. The following A hot dry gabbrolc follOWing geologic geologic history history is is proposed. proposed. A gabbroic magma was intruded intruded along the the contact of already deformed mangerite and anorthoanorthosite. The magma crystallized slowly slowly without tectonic tectonic disturbance to to proproduce the was absorbed absorbed by the layered layered gabbro. gabbro. Water from from an external source was by the of the the margin of the gabbro during subsolidus subsolidus cooling causing aa transformation from gabbro to trom to garnet garnet arnphibolite amphibolite following tollowing tne the reaction: reaction: 19 p1++ S8 cpx+ opx+4 mt+ - 66 h+ 19 pi cpx +1.0 10 0px + 4 oi+ 01 + I. l rot + 66H20 HZO ~ h + 9Y p1+4 pi -:- 4 g+ g +1 1opx. opx. A A petrogenetic petrogenetic grid grid suggests suggests that that aa temperature temperature of of about about 800°C BOUoC and and aa load load pressure of of large large garof 77-~kb kb isisconsistent consistent with with this this reaction. reaction. Growth Growth of nets consumed piagioclase yielding aa hornblende shell around around each garnet. consumed plagioclase garnet. Later detormation produced pressure shadows garnets and shadows around the the.garnets and aa weak weak toliation foliation through through the the garnet garnet amphibolite. amphibQlite. Reference Luther, Frank R., 1976, 1976, The petrological evolution evolution of ot tue the garnet garnet deposit deposit at at Gore Mountain, Warren Warren County, County, New New York; unpublished unpublished dissertation, dissertation, Lehigh Lehigh University. University. —22— -22- �THE GEOCHEMISTRY GEOCHEMISTRY OF KEWEENAWAN LAVAS LAVAS OF OF THE THE MAMAINSE MAMAINSE POINT POINT THE FORMATION, ONTARIO FORMATION, N.W.D. N.W.D. Massey, Massey, Dept. Dept. Geology, Geology, McMaster McMaster Univ., Univ., Hamilton, Hamilton, Ont. Onto The Mamainse Point Formation Formation outcrops outcrops at at Mamainse Mamainse Point, Point, about 80 about 80 km north of Sault Ste. Ste. Marie, Ontario. Ontario. It consists of tholeiitic flood flood basalts with rhyolites rhyolites and conglomeratic sediments, and and spans spans the the palaeomagnetic palaeomagnetic reversal reversal normally normally sediments, regarded as the boundary between Lower Lower and and Middle Middle Keweenawan. Keweenawan. The The flows flows consist of olivine-phyric melaphyres melaphyres at at the the base base which pass up up into into feldspar-phyric feldspar-phyric melaphyres melaphyres and and ophites. ophites. The Alona Bay Bay sequence is is also also olivine-phyric olivine-phyric and The thin Alona with the basal section of the Mamainse probably correlative with the basal the Mamainse Point sequence. sequence. Low—grade, burial burial metamorphism has has caused zeolite—grade Low-grade, zeolite-grade secondary minerals minerals to develop, both both within within the to develop, the rock rock and in veins and vesicles. vesicles. Although laumontite occurs throughout, throughout, a a crude metamorphic zoning zoning is is developed developed with with epidote epidote occuroccurring mainly mainly in in the the basal basal section section and and stilbite stilbite in in the the upper upper ring Heterogeneity, with the development of parts. Heterogeneity, of epidote-, epidote-, chlorite— chlorite- and albite—rich—metadomains, albite-rich-metadomains, is is restricted restricted to to feldspar-phyric melaphyres in lower feldspar-phyric lower parts of of the the section. section. The metamorphism was was accompanied by increases in The in Na, Na, K, K, Rb, Rb, Li, Li, Ba, Ba, Fea/Fe2, Fe3/Fe2, H2O+ H20+ and and C02, C02, and and increases increases or or decreases decreases in Ca, Ca, Sr and in and Cu. Cu. Al, AI, EFe, ~Fe, Ti, Ti, P, P, Y, Y, Zr, Zr, Nb, Nb, ?FeOT/MgO ?FeOT/MgO and ?MgO appear to be immobile or little and little affected affected by by the the The immobile trace elements confirm the tholeialteration. The confirm the tholeiitic nature of the itic the lavas and suggest an an ocean—floor ocean-floor to to within-plate character. within-plate character. The occurrence of a suite of of flows flows of of distinctive distinctive chemchemical type beneath the "Great Conglomerate", but ical type the "Great but not not repeatrepeated above, above, would suggest the triple triple reversal reversal in the the palaeo1 magnetic stratigraphy of Mamainse Point' is real and not Point due to strike strike fault fault repetition. repetition. (1970) Paleomagnetism Paleomagnetism and and correlation correlation of of some Ipalmer, H.C. (1970) 'Palmer, H.C. Can. Jour. Middle Keweenawan rocks, rocks, Lake Lake Superior. Superior. Can. Jour. Earth Sci., 7, I, 1410—1436. 1410-1436. —23— -23- �THE DISTRIBUTION DISTRIBUTION OF OF URANIUM URANIUM AND THORIUM IN THE THE WOLF WOLF RIVER RIVER BATHOLITH, IN BATHOLITH, NORTHEASTERN WISCONSIN Meddaugh, t-leddaugh, W. \.J. S.; S.; Salotti, Salotti, C. A.; and and Mursky, Mursky, G. G. Department of Geological Geological Sciences Sciences University of Wisconsin —- Milwaukee Milwaukee, Milwaukee, Wisconsin 53201 53201 Measurements of outcrop radioactivity radioactivity at at over over 175 175 locations locations and and wholewholerock and thorium analyses rock uranium and analyses by gamma spectroscopy have have revealed revealed significant differences differences in in the the radioactive radioactive character character and and radloelement radioelement distribution of several several of the the lithologic lithologic units units that that comprise comprise the the Wolf Wolf River Batholith. is aa large Batholith. The batholith, batholith, dated about about 1500 1500 m.y., is large epizonal anorogenic composite pluton consisting epizonal consisting mainly of of quartz quartz mon— monzonite and and granite granite with much lesser lesser amounts amounts of of monzonite, monzonite, syenite, syenite, and and rhyolite. For the the purposes purposes of of this For this study the the batholith has has been been arbiarbitrarily divided trarily divided into into a southern section and and aa northern northern Section. section. In the the southern southern section, section, the the Red monzonite, the In Red River quartz monzonite, the most radioradioactive unit of the entire batholith, active unit of batholith, is is considerably considerably more more radioactive radioactive than than either the Wolf River quartz monzonite or or the the Waupaca Waupaca quartz quartz mon— monzonite. Two somewhat some~"hat anomalous anomalous areas, areas, one one east east of of Tigerton Tigerton and and the the other near near Big Big Falls, Falls, have have been been located located within within the the more more radioactive radioactive interior region of the monzonite. Preliminary analyses interior region of the Red Red River quartz monzonite. analyses of typical yield average values of oF typical samples samples of Red River quartz quartz monzonite yield average values 37 and 10 10 ppm ppm UU (Tb/U (Th/U == 3.7) 3.7) while while samples of mafic—rich mafic-rich material material 37 ppm Th and yield individual individual values values as as high high as as 150 150 ppm ppm Tb Th and and 190 190 ppm ppm U. U. Peripheral areas of the areas the Wolf River quartz monzonite, particularly particularly near near its its contact contact with the the Tigerton anorthosite, anorthosite, are are more more radioactive radioactive than than central central areas. areas. The \1aupaca Waupaca quartz monzonite and The and the the Wolf River River quartz quartz monzonite monzonite have have similar average outcrop radioactivities. radioactivities. The Belongia Wolf River Belongia granite, granite, slightly more radioactive radioactive than the Wolf is the the most most radioactive quartz monzonite, is radioactive unit unit in in the northern section of the the batholith. batholith. Marginal l-larginal regions regions of of the the granite granite tend tend to to be be more more radioactive than inner inner areas. areas. Typical Typical samples of Belongia Belongia granite granite yield yield preliminary average values of 27 27 ppm ppm Th Th and and 6.3 6.3 ppm UU (Th/U (Th/U == 4.3). Average outcrop radioactivity radioactivity of of the the Hager Hager rhyolite rhyolite is is slightly slightly less less than than that of the the Belongia Belongia granite. granite. Samples of the the Peshtigo Peshtigo monzonite, monzonite, the least least radioactive radioactive unit unit of the the entire entire batholith, batholith, yield yield preliminary preliminary the 5.14). ftverage 114ppm ppm Th Tb and and 2.6 2.6 ppm ppm U U (Th/U /verage outcrop radio— values of of 14 (Th/U == 5.4). radioactivities activities of of the Hager feldspar feldspar porphyry porphyry and and the the Hager Hager syenite syenite are are intermediate between that that of the the Belongia Belongia granite granite and and Peshtigo Peshtigo monzonite. monzonite. intermediate —24— -24- �PILOT EXPLORATION GEOCHEMICAL SURVEY OF URANIUM IN ORGANIC—RICH ORGANIC-RICH LAKE SEDIMENTS, NORTHEASTERN MINNESOTA D.G. Meineke, M.K. M.K. Vadis and A.W. A.W. K1aysmat, Klaysmat, Minnesota Department of D.G. Meineke, of Natural Resources, Minerals, Hibbing, Hibbing, Minnesota 55746 Resources, Division of Minerals, ABSTRACT As part of the National Uranium Resource Evaluation Program (NURE (NURE Program) Carbide—Nuclear Program) of the the U. U. S. S. Department of Energy (DOE), (DOE), Union Carbide-Nuclear Division, Division, the DOE contractor responsible for for geochemical exploration surveys, decided to surveys, to investigate investigate the the use use of of organic—rich organic-rich lake lake sediments sediments for for the NURE Program Program in in Minnesota. Minnesota. This study was done in conjunction NDNR with the the Minnesota Minnesota Department Department of of Natural Natural Resources Resources (MDNR). (MDNR). The MDNR had previously applied organic—rich sediment to various areas of organic-rich lake 1ake'sediment northern Minnesota for for the the evaluation evaluation of of base base metal metal potential. potential. The observations and and conclusions conclusions described described here here are are those those of of the the MDNR MDNR and and observations do not necessarily represent those those of of Union Union Carbide—Nuclear Carbide-Nuclear Division. Division. Organic—rich lake sediment samples samples were were selected selected to to represent represent five five Organic-rich lake sediment major geologic geologic formations formations from from previous sediment surveys conducted by the MDNR in the the Western Vermilion Vermilion District District of of northeastern northeastern Minnesota. Minnesota. The objectives of of this this study study were: 1) 1) to determine whether or not uranium in the various various rocks is reflected reflected in the sediment, and and 2) 2) to to rocks is the sediment, determine if of the raw data was was necessary in order order to to if any treatment treatment of use this information for for evaluation evaluation of of uranium uranium potential. potential. of the bedrock is Results indicate that the uranium content content of is reflected in in the the sediment. sediment. The uranium concentrations in in sediments sediments over the Vermilion Massif Massif are about twice those over over other rocks; rocks; which compares with with the the difference difference in in relative relative radioactivity radioactivity levels levels of of the the compares same rocks rocks as reported by Ojakangas (1976). (1976). Examination of the data suggests that uranium may be concentrated in the inorganic fraction of the the sediment. sediment. Although the reflection of the uranium content content of of the the bedrock is is discernible discernible by by basing basing the the uranium the unignited unignited (total) sample weight, weight, the the distribution distribution concentration on the (total) sample of uranium based on on the the ignited ignited sample sample weight weight (inorganic fraction) more more of (inorganic fraction) reflects the bedrock bedrock geology geology because because of of loss-on-ignition loss—on—ignition varivariclearly reflects ation between samples. samples. No significant relationships were observed for for or manganese, manganese, which which would would suggest suggest that that uranium is is not not uranium and iron or preferentially preferentially adsorbed adsorbed by by iron—manganese iron-manganese hydroxides hydroxides and, and, therefore, therefore, does not create elevated uranium uranium values values unrelated unrelated to to the the bedrock bedrock geology. geology. REFERENCE Potential ininPrecambrian 1976, Uranium Potential Ojakangas, R.W., R.W., 1976, Precambrian Rocks Rocks of of Report to U. Minnesota: Report U. S. S. Energy Research and Development Administration, Contract ContractAT(O5—l)—1652, AT(05-1)-1652, 259 259 pages. —25— -25- �A PETROGRAPHIC PETROGRAPHIC GUIDE GUIDE FOR UNIT UNIT IDENTIFICATION OF THE THE PARTRIA IDENTIFICATION OF DGE RIVER TROCTOLITE, TROCTOLITE, DULUTH COMPLEX, COMPLEX, MINNESOTA MINNESOTA DGE Molling, Philip Philip A., A., Tyson, Tyson, R. R. Michael, Michael, and and Chang, Chang, Luke Luke Molling, L. Y., Y., Department of Geology, Geology, Miami University, L. University, Oxford, Ohio 45056 Oxford, The partridge Partridge River River Troctolite Troctolite (PRT) has aa lithology lithology simisimiThe (PRT) has lar to to that that exhibited exhibited by by the the south South Kawishiwi Kawishiwi Intrusion Intrusion lar However, the the units units recognized recognized in the SKI SKI do do not not (SKI). However, in the extend into extend into the PRT (Bonnichsen (Bonnichsen and Tyson, Tyson, 1975). 1975). The The PRT does exhibit exhibit aa cryptic-like cryptic—like layering layering as as it it becomes becomes more more does However, there is no distinct distinct variabimafic with depth. depth. However, is no lity in the mafic mineral species which thus thus provides provides aid in the definition of correlatable units. little aid units. This study of one drill core has concentrated on on the the silicate silicate and oxide mineralogy and their their relationships relationships with with depth. depth. Five specific petrographic relationships relationships used in conjunction have been determined as indicators indicators of units: units: (1) (1) Some This epitaxial bio— biotite grows epitaxially epitaxially to to augite. augite. This biotite is is characteristic of the lower lower portion of of the the drill drill (2) Inclusions Inclusions of of biotite biotite aligned aligned in core studied. (2) in paralin the the upper upper half half of lel arrays arrays within within augite augite are arecommon cornmon in of is believed believed to to be aa rethe drill core. This This occurrence occurrence is (3) Oxide Oxide inclusions, inclusions, reddish—brown placement texture. texture. (3) reddish-brown rutile and and opaque opaque ilmenite, appearing in in augit augit as as minute minute rutile ilmenite, appearing blebs and rods are arranged in rows, rows, locally throughout the drill core and may represent gradational contact contact zones. zones. (4) The texture texture and and amount amount of of exsolved exsolved oxide inclusions in (4) The in the plagioclase crystals varies consistently with depth and is believed believed to to be be the the most most diagnostic diagnostic feature of differenis feature of tiation. (5) wormy, symplectitic symplectitic intergrowth Gf of plagio(5) AA wormy, clase and orthopyroxene similar to Taylor's (1964) (1964) mymer— mymerkite is is evident. evident. This This fine fine grained grained symplectite symplectite appears appears to to have set up have set up its itsown own plagioclase plagioclasedomain domain wherein wherein the the opx opx blebs blebs exist. Another symplectite, symplectite, coarser coarser in in grain grain size, size, appears as an earlier phase relative to the fine grained symplectite and does does not not exhibit exhibit aa separate separate domain. domain. Of the the petrographic relationships relationships used, used, only two two appear to be representative representative of of the the primary primary conditions conditions of of the the magma; magma; the oxide inclusions inclusions in in augite augite and and in in plagioclase. plagioclase. The The others appear appear to to be due due to to later later stages stages of of crystallization crystallization or deuteric deuteric alteration. alteration. The use of these these relationships relationships will allow allow for for the the definition definition of of crystallization crystallization units units which heretofore heretofore have have not not been described described for for the the Partridge Partridge River River Troctolite. Troctolite. the drill core. —26— -26- �AEROMAGNETIC MAP MAP OF OF NORTHERN NORTHERN WISCONSIN WISCONSIN AEROMAGNETIC (Poster Session) Session) (Poster M. G. G. Mudrey, Mudrey, Jr., Jr., Geological Geological and and Natural Natural History History Survey, Survey, University University of M. of Wisconsin—Extension, 1815 University Avenue, Madison, Wisconsin Wisconsin-Extension, 1815 University Avenue, Madison, Wisconsin 53706, 53706, and J. J, H, H, Karl, Karl, Department Department of of Physics, Physics, University of Wisconsin—Oshkosh, and Wisconsin-Oshkosh, Oshkosh, Wisconsin 54901 Oshkosh, Wisconsin 54901 ABSTRACT In 1973, In 1973, the the Geological Geological and and Natural Natural History History Survey Survey and and the the Department of Physics, University of Wisconsjn—Oshkosh, initiated aa detailed of Physics, University of Wisconsin-Oshkosh, initiated detailed aeroaero— magnetic survey survey of of northern northern Wisconsin Wisconsin with with primary primary funding funding from from the the Upper Upper magnetic Great Lakes Lakes Regional Great Regional Commission. Commission. The is a a color compilaThe map map on display is tion at at 1:250,000 1:250,000 by Zeitz, Zeitz, Karl tion Karl and and Ostrom (1977) (1977) published published as U, S. as U, Geological Survey Survey Open-file Open—file Report Report 77-598, 77—598, and and is is available available in in black black and Geological white as white as U. U. S. S. Geological Survey Miscellaneous Miscellaneous Field Field Study Study MF—888. MF-888. The map is derived by photographic The reduction of 86 aeromagnetic aeromagnetic survey survey maps published at a scale of 1:62,500 maps 1:62,500 by the Geological and and Natural Natural History History Survey with a a standard line line spacing spacing of of 0,8 kilometers flown flown north—south north-south at at an an elevation of 150 meters (48,000 (48,000 square square kilometers of of coverage), coverage). The process of construction of the the maps maps consisted consisted of removing the the regional regional magnetic magnetic varivariation of the the earth's total total magnetic magnetic field field as determined by by Fabiano Fabiano and and Peddie (1969), (1969), and and contouring contouring the the reresidual at at 20 20 gammas. gammas. If the regional regional variation is is not not removed, removed, aa severe severe banding banding effect, effect, which which •is .is not related related to the geology, geology, subdues subdues the the magnetic magnetic pattern caused by by the the geology, geology. An additional 3,400 square square kilometers kilometers were were flown flown in in 1977. 1977. An obvious obvious correlation correlation when the the map map is is compared compared to to a a geological map map (Sims, (Sims, Cannon and Mudrey, Mudrey, 1978, and and presented presented at at this this Institute Institute on on Lake Lake Superior Superior Geology Geology meeting) meeting) in in addition addition to to the the parallelism parallelism of of magnetic magnetic and and geological geological trends trends is is that that the the broad broad magnetic magnetic "low" "low" areas areas coincide coincide very very well well with with regions regions of of predominantly predominantly metasedimentary metasedimentary and and metavolcanic metavolcanic rocks, rocks, and and their their gneissic gneissic equivalents. equivalents. The The magnetically magnetically "high" "high" areas, areas, on on the the other other hand, hand, correlate correlate well well with with more more extensively extensively granitized granitized terranes, terranes. The The Gogebic Gogebic Iron Iron Range, Range, other other iron iron formations, formations, and and Middle Middle and and Late Late PrePrecambrian cambrian gabbroic gabbroic plugs plugs are are readily readily discerned discerned as as magnetic magnetic highs highs of of over over 7,000 7,000 gammas. gammas. —27— -27- �OFFSHORE IN SAND AND GRAVEL EXPLORATION EXPLORATION WESTERN LAKE MICHIGAN Edgardo L. L. Nebrija, Nebrija, Carol Carol J. J. Welkie, Welkie, and and Robert Robert P. P. Meyer Meyer Geophysical and Polar Research Research Center Center Lewis Weeks Weeks Hall, Hall, University University of of Wisconsin Lewis 1215 W. W. Dayton Dayton St., St., Madison, Madison, Wisconsin Wisconsin 53706 53706 Offshore sand and gravel deposits are are potentially potentially important resourgravel deposits important resources, near high-use high—use urban centers centers which which usually usually lack nearby nearby ces, especially near land sources and, of this low—cost, high-bulk high—bulk and, thus, thus, require transport transport of this low-cost, commodity from aa distance. Conventional acoustic acoustic profiling and and coring coring distance. Conventional of these deposits however, because because the high acoustic acoustic imdeposits is is difficult, difficult, however, the high impedance of sands and and gravels and because because concongravels inhibits inhibits sound penetration and ventional coring is is generally generally inapplicable. inapplicable. off Kewaunee, At three three test test areas in in Western Western Lake Lake Michigan Michigan —- off Kewaunee, Mani— Manitowoc, and Rawley Point towoc, Point —- experiments experiments to to determine the lateral extent extent and thicknesses of sands and gravels were conducted conducted using using combined combined sands and gravels were acoustic and Schlumberger resistivity profiling, profiling,resistivity Schlumberger resistivity resistivity sounding from the the water water surface, surface, and selective surficial surficial sediment sediment sampling. sampling. PrePrevious detailed sediment sampling by other workers workers showed showed temporally temporally changing sediment patterns off Kewaunee, Kewaunee, and and laterally laterally uniform, uniform, well— wellsorted, fine sorted, fine sands off Rawley Point. Point. Knowledge of of the the apparent apparent resisti— resistivities obtained over these sediments was used used to offshore exsediments was to determine offshore extensions of of known onshore gravels at Manitowoc. tensions Initial testing of of this this integrated integrated geological-geophysical geological—geophysical approach approach Initial testing shows that: that: (1) Where Where surficial surficial sediments sediments are thin, (1) thin, there is is low low correlation correlation between the and the sediment type inferred the observed apparent apparent resistivity and inferred from acoustic profiles or physical samples. samples. Instead, Instead, the the contours contours of of apparent resistivity resistivity reflect reflect the the trends trends in in the the till till and and glaciolacustrine glaciolacustrine apparent clays beneath beneath the the thin thin sediments sediments and and point point to to prospective prospective areas, areas, such such as as clays probable buried channels channels or or ancient ancient shorelines. shorelines. (2) In In areas areas where where acoustic acoustic profiles show thick the ob(2) thick sediments, .the observed apparent resistivity is correlatable served correIa table with with the the type type and and distribudistribution of of the tion the sediment. sediment. The lateral uniformity of of the the acoustically—impenetacoustically-impenetrable sands sands off off Rawley Rawley Point, Point, for for example, example, is is reflected reflected in in the the relativerelativerable ly constant apparent resistivity over most of ly of the the area. area. (3) Given Given the the water water depth depth from acoustic profiles, (3) profiles, the the water resisresistivity from independent independent specific-conductance specific—conductance measurements, measurements, and and the the tivity from resistivity ranges ranges of the sands sands and underlying till till from resistivity profiling elsewhere, yields aa resistivity— elsewhere, then, then, resistivity sounding yields resistivitydepth structure structure which which is is helpful helpful in in estimating estimating thicknesses. thicknesses. The The electrielectridepth cal pseudo-section pseudo—section also also aids aids in in interpreting interpreting the the lateral lateral changes changes in in sand sand cal thickness. (4) gravel deposits deposits (4) The The offshore offshore extensions extensions of of the thick thick onshore gravel are mappable mappable on on the the basis basis of of their their relatively relatively high high resistivity resistivity and and potenpotenare tial tial subsurface deposits undetectable from from surficial surficial samples samples are are inferinferred from the resistivity red resistivity data. data. —28— -28- �CRITERIA CRITERIA FOR FOR ALLIGATOR ALLIGATOR RIVER RIVER TYPE TYPE URANIUM URANIUM DEPOSITS DEPOSITS IN IN THE THE UNITED UNITED STATES STATES Richard Richard W. W. Ojakangas Ojakangas Department Department of of Geology, Geology, University University of of Minnesota, Duluth, Minnesota 55812 55812 Three Three geologically geologically similar similar uranium uranium subprovinces—-Rum subprovinces--Rum Jungle, Jungle, South South AlliAlligator River Valley, Valley, and Alligator Rivers——are Rivers--are present in the top end of the Northern Territory Territory of of Australia. Australia. Pitchblende Pitchblende deposits, deposits, with with minor minor secondary minerals, minerals, are found in a specific, specific, generally carbonaceous carbonaceous and chloritic horizon of of Lower Lower Proterozoic Proterozoic metasedimentary metasedimentary rocks. rocks. This This horihorizon consists of the presumably equivalent Golden Dyke, Dyke, Koolpin, Koolpin, and Cahill Formations Formations in in the the three three respective respective subprovinces. subprovinces. In the Rum Jungle and Alligator Rivers Rivers subprovinces, subprovinces, Archean Archean basement basement rocks rocks are are also also exposed. exposed. The The ore ore bodies generally generally occur occur at relatively relatively shallow shallow depths, depths, and most intersect the the eroded Lower Lower Proterozoic Proterozoic surface. surface. The grade grade of of ore ore genergenerally ally ranges ranges from from 0.25 0.25 to to 0.40 0.40 percent U308, with short short lengths lengths of of core core as 72 72 percent. percent. Structural preparation of of the host rocks rocks is is evias rich as dent dent in in each each deposit. deposit. Remnants of of aa hematite—quartz hematite-quartz breccia are associassociated with many ore ore deposits, deposits, and and may may represent represent aa Proterozoic Proterozoic regolith. regolith. Throughout the eastern part of of the region, region, the Middle Proterozoic (1500 (1500 m.y.?) Kombolgie Formation Formation of conglomerates, conglomerates, quartzose quartzose sandstones sandstones and and volcanics, overlies overlies the the Lower proterozoic metasedimentary rocks rocks with Rivers subpro— unconformity. All ore bodies in the Alligator Rivers subproangular unconformity. vince occur near this this unconformity. unconformity. In the South Alligator River River Valley Valley subprovince, Volcanics and the overlying Kombolgie Formasubprovince, the Edith River Volcanics deposits occur tion overlie the the Lower Proterozoic rocks, rocks, and all ore ore deposits In the the Rum Jungle Jungle subprovince, subprovince, the the Depot Depot Creek near this this unconformity. unconformity. In m.y.) may may have had essentially Sandstone of Upper Proterozoic Proterozoic age age (<1400 ~1400 m.y.) the same same relationship relationship to to the the Lower Lower Proterozoic Proterozoic and and to to the the ore ore deposits deposits the as do the Kombolgie and and Edith Edith River River Volcanics Volcanics in in the the other other subprovinces. subprovinces. Evidence can be amassed for for both both syngenetic syngenetic and and supergene supergene origins. origins. Most workers seem to prefer a Australian workers a syngenetic origin with initial deposition of uranium in Lower Proterozoic geosynclinal rocks rocks during sedimentation. Additional enrichment is is attributed to anatexis and metamorphism, with later morphism, later local local supergene supergene enrichment. enrichment. The original sources sources of the uranium are generally generally thought thought to to be be the the Archean Archean complexes. complexes. Some River Volcanics Volcanics as as the source rock in the workers suggest the Edith River Alternatively, a South Alligator subprovince. Alternatively, a strong case can be made for aa dominant dominant supergene supergene origin, origin, with with oxidizing oxidizing waters waters having having carried carried for eroded Lower Proterozoic surface either before, before, during uranium along the eroded or after after deposition of the overlying rock or rock units. units. What is the What the applicability of these criteria to exploration in the United Regardless of of the hypothesis hypothesis of of origin, origin, the major field States? Regardless field criteria The presence presence of of aa major major unconformity unconformity is is of of remain essentially the the same. same. The primary importance, importance, as as is is the the reducing nature of the structurally preThe significance significance of of the the relative relative ages ages of of the the rock rock units units pared rocks. The pared host rocks. beneath and above the the unconformity unconformity is is not not clear. clear. —29— -29- �Relations Between Between Soil Soil Geochemistry and Bedrock Geology, Relations Geology, Iron County, County, Wisconsin Iron Peltonen, D.R., D.R., Salotti, Peltonen, Salotti, C.A., C.A., and and Taylor, Taylor, R.W. R.W. Department of Geological Sciences Wisconsin—Milwaukee University of Wisconsin-Milwaukee Milwaukee, Milwaukee, Wisconsin 53201 heavy metal metal geochemical geochemical soil soil (B horizon) and and biogeochemical biogeochemical (aspen A heavy (B horizon) (aspen twigs) survey survey was was completed completed over over approximately approximately 100 100 square square miles miles directly directly twigs) south of the the Gogebic Gogebic Range Range in in aa granite-greenstone granite—greenstone terrain terrain in in Iron Iron south County, Wisconsin. County, Soil samples samples were were dry dry sieved, sieved, the the -80 —80 mesh mesh fraction fraction Soil and taken taken into into solution solution using aa lithium metaborate metaborate fusion fusion collected and technique. The twigs The twigs were ashed and dissolved in in 2M 2M HC1. HCl. 3000 Nearly 3000 elemental analyses were made using using atomic atomic absorption absorption spectrophotometry. spectrophotometry. These results were processed by by computer computer and statisttcal statistjcal parameters parameters These results were assigned to to all anomalous anomalous values. values. indicates there there is is communication between the the B Geochemical data indicates soil horizon in in the the glacial glacial till till and and the the underlying underlying bedrock. bedrock. Nickel and and copper are distinctly lower lower in in soils soils overlying overlying "granites" "granites" than than in in soils soils the underlying rock rock types be disdisoverlying greenstones, greenstones, and allow the types to be tinguished with greater than than aa 97.5% 97.5% confidence confidence level. level. In two areas where Zn Zn concentrations are known to be greater than 0.1% in parts of the bedrock, bedrock, anomalous values values of of Zn Zn in in the the overlying overlying soil soil samples samples occur. occur. —30— -30- �BASELINE URANIUM URANIUM AND AND THORIUM THORIUM ININARCHEAN ARCHEANAND ANDLOWER LOWER PROTEROZOIC PROTEROZOIC ROCKS OF OF THE AREA, MICHIGAN ROCKS THE MARENISCO-WATERSMEET MARENISCO-WATERSMEET AREA, MICHIGAN E. Peterman K. Sims Z. E. Peterman and and P. P. K. Sims U.S. Geological U.S. Geological Survey, Survey, Denver, Denver, Colorado Colorado 80225 80225 Radiometric dating in area, northern Radiometric inthe theMarenisco-Watersmeet Marenisco-Watersmeet area, Michigan, has Michigan, has delineated delineated aalower lowerArchean Archean (Precambrian (Precambrian W) W) gneiss gneiss terrane at least terrane least 3,400 3,400 m.y. m.y. old old adjacent adjacent to to and and south south of aa greengreenstone-granite terrane terrane (2,600 to 2,700 m.y. old). old). Both stone-granite (2,600 to 2,700 m.y. Both terranes formed the basement basementfor for the the lower formed the lower Proterozoic Proterozoic (Precambrian (Precambrian X) X) sedsedimentary Marquette imentary and and volcanic volcanic rocks rocks ofofthe the MarquetteRange RangeSupergroup. Supergroup. The gneisses were were involved involved in folding during the The gneisses foldingand andmetamorphism metamorphism during Periokeanorogeny orogeny (1,750 m.y.ininthis this area). Analyses Analyses of UU Penokean (1,750 ++ 5050 m.y. and Th Thin in samples samplescollected collectedfor for radiometric and radiometric dating dating provide provide basebaseline data line data for forevaluating evaluatingradioelement radioelement mobility, mobility, and and possibly possibly enenrichment, during richment, during reactivation reactivation ofofthe theancient ancientbasement basement rocks. rocks. The lower Archean gneiss at Watersmeet contains 1.4 to lower Archean gneiss Watersmeet contains to1414ppm ppm UUand and 99 The available available data to 35 35 ppm ppm Th. Th. The data suggest suggest UUand and Th Th enrichment enrichment in in more highly cataclasized cataclasizedfacies fades of the more highly the gneiss. gneiss. A leucogranite dike in the dike the gneiss, gneiss, provisionally provisionally related related totothe thelate lateArchean Archean event, contains and6868ppm ppm fieldscintillometer scintillometer event, contains 18 18 ppm ppm UUand Th,Th, andand field measurements suggestthat that these these high high values in the measurements suggest values are are common common in granite near nearThayer ThayerofofFritts Fritts (1969), dikes. The The granite (1969), also thought thought to be reactivated Archean gneiss, has has U Uand andThThcontents contentssimilar similar to be Archean gneiss, those of the leucocratic phase of this those the gneiss gneiss atatWatersmeet. Watersmeet. A leucocratic phase of The Puritan Puritan Quartz rock contains contains2121ppm ppm UUand and 29 29 ppm ppm Th. Th. The Quartz MonzoMonzonite, aalate nite, lateArchean Archean intrusion intrusion ininthe thegreenstone-granite greenstone-granite terrane, terrane, is higher Th/U ratio. ratio. Uranium higher than than average average in Th Th content content and and Th/U ranges from from 2.5 to ranges to 88ppm ppm and and Th Th from from 17 17 to to 62 62ppm. ppm. In In all the the crystalline rocks, crystalline rocks,K Kand and UUvary vary independently, independently, aa feature feature suggestsuggestof the ing post-crystallization movement post-crystallization movement of of U. U. Metagraywackes Metagraywackes of Marquette Range RangeSupergroup Supergroup consistentlylow low in in both Marquette areare consistently both UU and and Th, Th, These values values are are simiwith averages averages of of2.6 2.6ppm ppmUUand and 6.6 6.6ppm ppm Th. Th. These with lar mayreflect reflect a lar totothose thoseofofother othergraywackes graywackes and and may a high high volcanic volcanic componentininthe thedetritus. detritus. component —31— -31- �NATIVE COPPER COPPER DEPOSITS DEPOSITS DERIVED DERIVEDFROM FROM NEARBY NEARBY KEWEENAWANBASALT BASALTBY BY COMBINED COMBINED IGNEOUS, KEWEENAWAN DEUTERIC, DEUTERIC, AND ANDMETAMORPHIC METAMORPHICPROCESSES PROCESSES NancyScofield, Scofield, Institute Mineral Research Nancy Instituteof of Mineral Researchand andDepartment Department ofofGeology Geology and and Geological Engineering, Technological University, University, Houghton, Geological Engineering, Michigan Michigan Technological Houghton, Michigan, Michigan, 49931 ABSTRACT flow) from A thick (60 (60 m) m) basalt basalt flow flow (Scales (Scales Creek Creek flow) from the the middle middle of the the Portage LakeVolcanics Volcanicswas wasintensively intensivelystudied studiedpetrographically petrographically and and its its conPortage Lake conIn the stituent minerals stituent mineralsanalyzed analyzed by by electron electronmicroprobe microprobe techniques. techniques. In the interior chemically: 1) 1) whole rock CuCuabundance of the the flow, flow,which whichisisnearly nearlyunaltered unaltered chemically: whole rock abundance is 110-150 ppm;2)2) microscopically-visible microscopically-visible native 110-150 ppm; native Cu Cu isispresent presentwithin withinpseudopseudomorphsafter after olivine; olivine; and morphs and 3) 3) Cu Cu concentrations concentrations in oxidized oxidized titanomagnetite titanomagnetite (2-3 modal modal %) %) are are2000-2500 2000-2500ppm. ppm. With With increasing degree degree of deuteric deutericand and metametamorphic alteration, alteration, Cu morphic Cu was was released released from from primary primary minerals, minerals, disseminated, disseminated, and and mechanismsofof Cu Cuconcentration concentration incorporated into incorporated into secondary secondary minerals. Dominant Dominant mechanisms 1) igneous differentiation by transfer within after extrusion extrusion are: are: 1) igneous differentiation by gaseous gaseous transfer the flow, 2) the 2) release release of ofnative nativeCu Cu during during deuteric deuteric oxidation oxidation of ofFe-Ti Fe-Ti oxides oxides and Fe-Mg Fe-Mg silicates, and and3)3)mobilization mobilization and andredistribution redistribution by and silicates, by later latermetametamorphic fluids. morphic fluids. Extrusion of the Extrusion the flow flowonto ontoaawet wetsurface surfaceproduced produced aa basal basal zone zone of high high oxygenand andvolatile volatile activity, accompanied oxygen activity, accompaniedbybygaseous gaseous transfer transferdownward downward of of Cu, Cu, This zone, Cu by by this this gaseous transfer, was Fe, and and Ti. This zone, enriched enriched to to 420 420 ppm ppm Cu gaseous transfer, was Fe, immediately abovethe thevesicular vesiculartop top of of the immediately above the underlying underlying flow, flow, and and provided provided aa source of Cu Cufor for later later circulating source of circulatingmetamorphic metamorphic fluids which which followed followed the the perperIf this within meable flow-top flow-top channeiways. meable channe1ways. If thisprocess processwas was repeated repeated elsewhere elsewhere within the volcanic pile, belowthe the basal basal zones zonesofof thick thick flows the pile,channelways channe1ways below flows may, may, in some cases, have haveunusually unusually high high Cu some cases, Cu concentrations. —32— -32- �POSSIBILITY OF OF MISSISSIPPI MISSISSIPPI VALLEY-TYPE VALLEY-TYPE ORE ORE DEPOSITS DEPOSITS IN IN INDIANA INDIANA POSSIBILITY Shaffer, Nelson Nelson R., R., Indiana Indiana Geological Geological Survey, Survey, Bloomington, Bloomington, Indiana Indiana Shaffer, The midwestern midwestern United United States States is is recognized recognized as as aa lead-zinc lead—zinc metallmetall— The ogenic province due to the occurrence there of low—temperature ogenic province due to the occurrence there of low-temperature ore deposits deposits of the the Mississippi Valley-type. ore Valley-type. Such Such deposits deposits commonly rocks on on the the flanks flanks commonly occur within within Paleozoic dolomite host rocks of structurally high areas of areas far from from regions regions of of igneous igneous activity. activity. They are are characterized by simple mineral suites, They suites, usually usually sphalerite, sphalerite, fluorite, galena, galena, or or barite, barite, that that are are believed believed to to have have formed formed fluorite, at moderate moderate temperatures temperatures from strong brines. at brines. One One explanation of the origin and characteristics characteristics of of Mississippi Mississippi Valley-type Valley—type of the origin and deposits suggests that they formed as a natural consequence of deposits suggests they formed as a natural consequence of when sedimentary sedimentary connate connate waters, waters, the the metalmetalbasin development when brines, migrated migrated updip from the basin basin and precipitated bearing brines, from the ore minerals upon encountering encountering sources sources of of reduced reduced sulfur. sulfur. Indiana lies lies near near this Indiana this general province and and contains contains many many geologic geologic features that appear suitable for the development of Mississippi features development of Mississippi Valley-type deposits. A structurally high high region collectively deposits. known as the Cincinnati and Kankakee Arches, crosses Indiana and as the Kankakee Arches, crosses separates the Michigan and Illinois Basins. separates the Paleozoic carbonates occur in the Knox Dolomite (Cambrian Ordovician); Black River (Cambrian and Ordovician); and Trenton Limestones Limestones (Ordovician); Salamonie, Louisville, Louisville, and (Ordovician); Salamonie, Wabash Formation (Silurian); Muscatatuck Group (Devonian); (Silurian); (Devonian); and Salem, St. Louis, and Ste. Genevieve Limestones Salem, St. and Ste. Genevieve Limestones (Mississippian). (Mississippian). Unconformities Knox, Trenton, Trenton, and Wabash Unconformities exist at the the tops tops of Knox, Formations. Numerous occurrences of of sphalerite, sphalerite, fluorite, fluorite, barite, barite, and galena galena have have been been noted noted in in Indiana Indiana in in the the past, past, and and more more than than and 60 new but generally minor occurrences have been found found during this recent recent study, study, many many in in the the Black Black River—Trenton River-Trenton section, section, especially in northern Indiana where extensive dolomitization has occurred. occurred. The dolomitized reef facies facies of the Wabash Formation had many mineral occurrences in northern Indiana as did the overlying lying Devonian Devonian limestones. limestones. Limestones of the the Salem Salem and and Ste. Ste. Genevieve also had occurrences of sphalerite and fluorite fluorite in southern southern and and southwestern southwestern Indiana. Indiana. Limited information information from from fluid fluid inclusions inclusions in in sphalerite, sphalerite, barite, barite, and fluorite fluorite indicates indicates that that some some samples samples have have formed formed from from brines brines in the range of temperatures reported from Mississippi Valleytype deposits. deposits. Minor elements in 80 sphalerite specimens from Indiana Indiana included included cadmium cadmium (.03 (.03 to to 6.9 6.9 percent), percent), iron iron (.01 (.01 to to .61 .61 percent), percent), and lesser amounts of gallium, gallium, germanium, germanium, copper, copper, and manganese. Silver was not not detected detected in in sphalerite sphalerite samples. samples. Due to favorable favorable geology, geology, occurrence of minor amounts of ore minerals, arid tentative evidence that that fluids fluids of the ore—forming and tentative evidence ore-forming type passed through suitable host rocks, rocks, a real possibility exists exists that that undiscovered undiscovered Mississippi Mississippi Valley-type Valley-type ore ore deposits deposits may occur in Indiana. occur in Indiana. —33— -33- �PRECAMBRIAN X PALEOPOLES THE UPPER PRECAMBRIAN X PALEOPOLES FROM FROM THE UPPER PENINSULA PENINSULA AND AND AANEW NEWMETHOD METHOD FOR REMANENT VECTOR DETERMINATION FOR REMANENT VECTOR DETERMINATION SHANABROOK, David, Department Geology,Michigan Michigan State State SHANABROOK, David, Department ofofGeology, University, University, East EastLansing, Lansing, Michigan Michigan 48824 A method methodwill will be which makes makesitit possible possible to use be described described which use the the three-dimensional modelingprogram programofofWhitehill Whitehill modified three-dimensional magnetic magnetic modeling modified so so as magneticvector vectorinto intoaccount account thatitit is as to take take the the remanent remanent magnetic soso that possible the declination declination and inclination of possible to determine determine the and inclination ofaabody's body's remanentvector vector directly directly from remanent fromobserved observed magnetic magnetic data. This This is is done done by SHALOCI writtenbybyWilliam William Ciolek, Ciolek, by using using aacomputer computer program program named named SHALOCI written Mark Locher,and andthe theauthor authortotocalculate calculate the the induced field due Mark Locher, induced field due to to This induced field isisthen the body. body. This induced field thensubtracted subtractedfrom fromthe theobserved observed data data to yield yieldthe themagnetic magnetic field fielddue due totothe thebody's body'sremanent remanent vector. vector. SHALOCI thenused used againtotocalculate calculate the the magnetic magneticfields fields due SHALOCI is isthen again due to to various vectors various vectors in inorder ordertotomatch matchthe theobserved observed anomalie. anomalie. This method method is accurate of the the vector's vector's true accurate to within within 10 10 degrees degrees of true declination declination and44degrees degreesofofits its inclination. inclination. Because this, the the results results of and Because ofofthis, are often often useful this method method are useful in in determining determining the the age age of aa body body which which is very very helpful ininPrecambrian Precambrian shield areas areas like likethe theUpper Upper Peninsula Peninsula of of Michiganwhere wherethere thereare aremagnetic magneticbodies bodiesofofdifferent different ages. Michigan ages. At Present, this computer-oriented approachisislimited limited to bodies present, computer-oriented approach bodies with fairly strong fairly strongremanent remanentmagnetic magnetic vectors vectorsand and which which have have not not been been metamorphosed very severely,but butfuture futurework workmay maybebeable abletotoalleviate alleviate metamorphosed very severely, these problems. problems. Paleomagnetic work done done on on samples samplesfrom from aa metadiabase metadiabase dyke dyke of of Paleomagnetic work PrecambrianXXage ageinin connection connection with the of supposed supposed Precambrian themagnetic-modeling magnetic-modeling described hasyielded yieldedsome some interestingresults. results. Thermal described above above has interesting Thermal dedemagnetization hasestablished establishedaapaleopole paleopolethat that falls falls on magnetization has on the the apparent apparent polar wandering curvefor for North Americaeither either at 2.04 wandering curve North America 2.04 bybp bybp or 1.84 1.84 bybp depending dependingononwhether whetheritit is is normal bybp normal or reversed. reversed. Further work work is being undertaken clarifythe thesituation, situation,but butitit is is clear being undertaken to to clarify clear that the the long long held held idea idea that thatthe themany many positive positivemagnetic magnetic anomalies anomalies in the the Upper Peninsula of of Michigan were due due to to "normally" Upper Peninsula Michigan were "normally" magnetized magnetized PrePrecambrian metadiabases have revised lightofof the the fact cambrian XXmetadiabases willwill have to to be be revised in in light that they Southern they yield yieldnorth-seeking north-seekingpaleopoles paleopolesininthethe SouthernHemisphere. Hemisphere. —34— -34- �Precambrian geologic geologic framework framework of northern Wisconsin by P. K. Sims Sims and and Z. Z. E. E. Peterman U.S. u.S. Geological Geological Survey, Survey, Denver, Colorado Colorado 80225 80225 Northern Wisconsin contains rocks belonging to each of the three major major subdivisions subdivisions of of the the Precambrian. Precambrian. Lower Precambrian Precambrian (Archean (Archean or or Precambrian W) rocks rocks constitute constitute the the basement. basement. Except for the the Gogebic Gogebic Range and vicinity, vicinity, which is underlain by 2,700—m.y.—old 2,700-m.y.-old greenstone— greenstonegranite complexes, complexes, the the basement rocks are dominantly gneisses and amphibolite. m.y. have amphibolite. Minimum ages for the the gneisses of 2,800—3,000 2,800-3,000 m.y. been obtained at a few localities in central Wisconsin (by W. R. (by W. R. Van Schmus) Schmus) and near Morse, south south of of Nellen. Mellen. Middle Precambrian Precambrian (Precambrian (Precambrian x) X) supracrustal rocks occur on the the Gogebic Range, Range, in in a 75—km—wide belt across across northern Wisconsin, Wisconsin, and and in 75-km-wide east—trending east-trending belt Marathon Marathon County County and and vicinity vicinity in in central central Wisconsin. Wisconsin. The proportion proportion of volcanic rocks rocks Increases that of of sedimentary increases southward relative to to that rocks; rocks; these volcanic rocks contain the valuable massive sulfide deposits known at at Crandon, Crandon, Ladysmith, Ladysmith, and and Pelican Pelican River, River. near near Monico. Monico. Abundant granitic m.y. old) granitic rocks (1,800—1,850 (1,800-1,850 m.y. old) intrude intrude the the volcanic rocks. As known previously, the the youngest rocks are local platform quartzite deposits m.y. old, l,500—m.y.— deposits more than 1,500 m.y. old, the large 1,500-m.y.old Wolf River batholith and associated syenite, syenite, and the approximately l,l00—m.y.—old 1,100-m.y.-old (Keweenawan) (Keweenawan) volcanic volcanic and and sedimentary sedimentary rocks rocks related related to to the midcontinent rift the rift system. system. The middle Precambrian rocks that overlie Archean gneisses, gneisses, together basement, were folded m.y. ago, with the basement, folded and metamorphosed about 1,800 m.y. ago, and were cataclastically cataclastically deformed deformed locally locally about about 1,600 1,600 m.y. m.y. ago. ago. In In contrast, strata overlying overlying the the greenstone-granite greenstone—granite basement basement on the the Gogebic Gogebic contrast, Range were not deformed deformed during during this this interval. interval. At least three three major high—angle high-angle fault fault sets sets have have been been recognized. recognized. The youngest, related related to to the the midcontinent midcontinent rift rift system, system, consists consists of of N. N. 50—55 E. E. faults faults that that were were formed formed in in late late Keweenawan Keweenawan time; time; they they probably probably 50-55 produced most of of the the northward northward tilting tilting of of strata strata on on the the Gogebic Gogebic Range. Range. North—northeast—trending North-northeast-trending faults faults that had repeated movements and that that typically have wide wide zones zones of of mylonite mylonite bound bound the the middle middle Precambrian rocks rocks in the Marathon County area, as as described described earlier earlier by by G. G. L. L. LaBerge. LaBerge. Probably the the oldest set consists of long, long, northwest—trending northwest-trending faults that reactivated and and have have apparent apparent right-lateral right—lateral movemovethat were repeatedly reactivated f— ments; the the major fault, fault, the the Mineral Mineral Lake Lake fault, fault, is is interpreted interpreted to to of offset Archean rocks about 160 160 km km and and middle middle Precambrian Precambrian rocks, rocks, 10—15 10-15 km. km. —35— -35- �A NEW PRECAMBRIAN PRECMIBRIAN SURFACE SURFACE CONTOUR CONTOUR MAP MAP FOR SOUTH-CENTRAL WISCONSIN, Eugene I. I. Smith, Smith, Division Division of of Science, Science, Univ. Univ. of of Eugene Wisconsin-Parkside, Kenosha, Wisconsin-Parkside, Kenosha, WI 53141 A new surface su~face contour map for for the the buried Precambrian Precambrian basement of south-central Wisconsin was constructed constructed using using data from from 200 200 deep water water and oil test wells, wells, geophysical data studies, and and previously published Precambrian surface studies, contour maps of of Wisconsin. The new map shows that that (1) (1) the the Precambrian surface Precambrian surface slopes slopes gently to the the east, east, southeast southeast and south off the and the Wisconsin arch. arch. Standing above this this surface are are numerous numerous ridges ridges and knobs of resistant rhyolite, surface granite and quartzite, quartzite, many of which protrude through granite through the the Paleozoic and Pleistocene cover as inliers (e.g., (e.g., at Waterloo, in in the loo, the Fox River Valley, and and at at Baraboo). Baraboo). Buried knobs of Precambrian rock occur occur at at Ripon Ripon (granite), (granite), BrotherBrothertown (quartzite), Waupun (quartzite), town (quartzite), Waupun (quartzite), Whitewater (quartz(quartzite) ite) and Rosendale (rock (rock type type unknown) unknown) . Both the the exposed knobs rise abruptly from and buried knobs from the the peneplained peneplained PrePrecambrian surface; surface; for for example, example, the the rhyolite knob at at Berlin stands stands over 600 feet feet above this this surface, surface, and that that at at Marcellon, 470 470 feet. feet. The change in in elevation elevation in in both both cases cases occurs occurs over a a lateral lateral distance of less less than than 11 mile. Other knobs have The eastward plunging have similar similar relief. relief. (2) (2) The Waterloo syncline syncline is is revealed revealed by by an an arcuate arcuate ridge ridge that that in in places stands 700 700 feet feet above the the level level of of the the surrounding surrounding Precambrian surface. surface. This ridge ridge is is only only exposed exposed in in the the area to the east of Waterloo, near Portland. to the east of Waterloo, near Portland. The nose of of the Waterloo Waterloo fold is the is in in the the Portland Portland area. area. The north limb limb extends as a ridge from from Portland Portland to to near Hartford Hartford in in WashWashington County, aa distance distance of of 30 30 miles. miles. The south south limb limb extends as aa continuous continuous (?) (?) ridge as far as Fort Atkinson and then then continues as a series series of of quartzite quartzite knobs knobs into into central Walworth County, aa distance distance of of 45 45 miles miles (( a buried quartzite knob is is located located at at Whitewater, and and quartzite quartzite is is found Delavan). (3) found beneath Delavan). (3) The subsurface subsurface data data is is supsupportive portive of a northeast trending trending fault fault extending extending from from near near Sheboygan to to central central Walworth Walworth County County (( as shown shown on onmaps mapsby by Thwaites, and Dutton and and Bradley), but but the the presence presence of of other other faults faults in in the the Precambrian Precambrian basement basement of of south-central south-central Wisconsin Wisconsin is is uncertain. uncertain. . —36— -36- �THE GEOLOGY AND PETROLOGY OF OF THE THE WINE WINE LAKE LAKE INTRUSION, INTRUSION, COOK COOK COUNTY, COUNTY, MINNESOTA by Andrew E. E. Strakele, Strakele, Jr. Jr. University of Minnesota, Duluth Duluth, Duluth, MN 55812 Exposures of of granophyric granite and associated associated felsic felsic intrusive rocks Exposures granophyric granite intrusive rocks of the eastern part part of the Duluth Complex form form an east-west east—west trending belt of the eastern the Duluth trending belt which parallels the the northern or basal contact of the North Shore Volcanic Group in Cook County, County, Minnesota. Minnesota. Along the western limit limit of of this this belt, belt, where it begins to to trend trend southwestward near the county line, line, there there exist several bodies of medium—grained medium-grained diorite diorite and and quartz quartz diorite. diorite. The largest body of these bodies, together with these dioritic rocks and some smaller satellite bodies, an adjacent adjacent unit unit of recrystallized recrystallized rhyolite rhyolite and and granite granite have have been been informally informally an designated as as the Wine Lake Intrusion Intrusion by Grout, Grout, Sharp, Sharp, and and Schwartz Schwartz in in 1959. 1959. Coarse—grained gabbroic gabbroic anorthosite anorthosite underlies underlies this this general general area to to the Coarse-grained the north and west, west, being locally overlain by a fine medium—grained gabbro. fine to medium-grained gabbro. dioritic rocks rocks also also occur above above the the gabbroic gabbroic anorthosite anorthosite as as bodies bodies of of 1 The dioritic to to 5 km2 km 2 in in area. area. Both gradational and intrusive contacts appear to exist between these these three three rock rock units. units. The rhyolite and granite unit of the Wine Lake Intrusion has an outcrop pattern pattern suggestive suggestive of of aa subhorizontal subhorizontal sheet. sheet. locally contains contains both both irregular cuspate cuspate and and sometimes sometimes angular The granite granite locally inclusions inclusions of fine—grained fine-grained quartz quartz diorite diorite near near the the granite—diorite granite-diorite contact. contact. Large xenoliths xenoliths of amygdaloidal amygdaloidal basalt basalt and and some some late-stage late—stage basaltic basaltic dikes dikes Large have also also been observed observed in in the the Wine Wine Lake Lake area. area. Field relationships, relationships, petrography, petrography, chemistry, chemistry, and modelling of chemical trends by by aa least least squares squares approximation approximation program for for crystal crystal fractionation fractionation trends and magma mixing support the derivation of gabbro by fractionation of and support the derivation gabbro by fractionation of plagioclase from gabbroic anorthosite. The gabbro was apparently altered from gabbroic anorthosite. The altered by the addition of the components of albite, albite, quartz, quartz, orthoclase, orthoclase, and H2O H20 to produce the diorite and quartz to quartz diorite diorite phases. phases. The evidence also suggests that the components were were derived derived from the the remelting of of that the granitic granitic mineral components xenoliths of of rhyolite rhyolite composition. composition. This model is in conflict with the the model of Weiblen and Morey (1975) (1975) which states that the the felsic felsic series rocks rocks were the differentiation differentiation of of gabbroic gabbroic anorthosite. anorthosite. produced by the —37— -37- �POSSIBILITIES POSSIBILITIESFOR FORURANIUM-GOLD URANIUM-GOLD QUARTZ-PEBBLE QUARTZ-PEBBLE ORES ORES IN IN THE THE LAKE LAKE SUPERIOR SUPERIOR REGION IN IN THE REGION THE LIGHT OF AANEW NEW MODEL ~lODEL FOR ELLIOT IAKE-WITWATERSRAND lAKE-WITWATERSRAND GENESIS James Trow, Thow, Department of Geology, Michigan Michigan State State University, University, East Lansing,Michigan Michigan 48824 L882 East Lansing, Gibbs free-energy calculations support support a new model for the the formation of quartz-pebble tion quartz-pebble oresg oresl 1) 1) a typically granitic, granitic, alkaline, alkaline, or metamorphic source area was exposed to to 2) 2) oxygenated atmospheres during mamorphic jar C02—impoverished episodes jor glacial C02-impoverished episodes since zince the the Early Early Precambrian. Precambrian. Lower PC02 P002 and related higher pH pH of rain rain and and runoff runoff inhibited the the dissolvdissolvirig oxidizeduranium uraniumasasU020~, UO20},U0 UO2CO°, UO2(CO3)2(H2O) to ing ofofoxidized C0 0, and U02(C01)2(H20)2 to propro2 3 duce some some clastic clastic hydrated hydrated uranyl uranyl oxide oxide pseudomorphs seudomorphs arter duce after uraninite, uraninite, some water-soluble U02(HP04)i u02(HP0) complex some water-soluble complexions, ions, and and possibly possibly (if (if not not exposed exposed too long) long) some uraninite clasts 3) 3) which were transported by streams along with with magnetite magnetite and and hematite hematite clasts, clasts, ferric ferric hydroxide hrdroxide hydrosols, hydrosols, nuggets, and and ilmenite ilmenite clasts, clasts, among among others. others. 4) ) These materials were gold nuggets, where hydrated uranyl uranyl oxide oxide clasts clasts were were carried to aa steep Eh gradient where re-reduced to to uraninite uraninite pseudomorphs, pseudomorphs, where whereU02(HP04)Z UO2(HPO) complex complex ions ions were were reduced to interstitial uraninite, uraninite, where where magnetite and hematite hematite clasts were reduced to pyrite "clasts", "Clasts", where where ferric ferric hydroxide hydrosols were were reduced to interstitial pyrite, lost their their clastk clastc pyrite, and where gold nuggets lost Au5 (to precipitate much much later as as non-clas~ non-clastt character by dissolving as AuS(to precipitate gold), gold), all by reactions paradoxically requiring 02 as well as anticiHS, the pated H2S or HS-, the latter latter two two from from interbedded interbedded and and underlying underlying sulfidic sulfi~ from the the reaction of botanic botanic sugars sugars upon upon S04. SOC. Quartz quartz pebbles pebbles basalts or from indicate the the sedimentary environment and and imply the the availavailindicate the vigor of the ability elastic ilmenite resulted in ability of of reactant reactant air. air. Sulfurization of clastic iron sulfide sulfide (later to to become become pyrrhotite) pyrrhotite) and and Ti021 T102; the the latter latter then then endure as ore, joined U02 to form brannerite. 5) To endure ore, the reduced system from renewed renewed oxidation under under post-glacial highhighwas sealed and preserved from A 55,000-miles er PC02 climates, climates. A 55,OOO-miles Jeep reconnaissance reconnaissance in the Basin and Range, Mountains, and the Range, the Rocky Mountains, the Appalachians has discovered five five of further Late Precambrian targets worthy worthy of further study, study,ofof Late Precambrianand andEocambrian Eocambrian ages. ages. Additional glacially-related glacially—related terranes terranes to be Additional be reconnoitered reconnoitered include include Late Late and Pliocene-Pleistocene. Pliocene-Fleistocene. Ordovician-Early Silurian, Permocarboniferous, and Late Precambrian possibilities in the Lake Superior region inviting examination include i) Mt. McCaslin NcCaslin (Wis1) the parent ledge ledge from which the Nt. (Wisconsin) consin) pyritic-quartz-pebble conglomerate boulder was wrenched during the Pleistocene, Pleistocene, 2) 2) conglomerates conglomerates at at the the base base of of the the Keweenawan, Keweenawan, ininthe cluding the the Bessemer Bessemer Conglomerate Conglomerate (Wisconsin), (Wisconsin),Nopeming Nopemingand andPuckwunge Puckwunge Conglomerates (Minnesota),and andcorrelatives correlativesalong alongthe the northern northern and and easteastConglomerates (Minnesota), ern shores of of Lake Superior Superior (Ontario), (Ontario), and and 3) 3) the southwestward continuation of the pyritic quartz-pebble conglomerate conglomerate at at the the base base of of the the Fond du Lac Lac Formation (Minnesota) (Minnesota) particularly where it overlies the St. Cloud Granite, Granite, and the St. the correlative top of the the Copper Harbor Conglomerate (Michigan). (Michigan). AA Pleistocene possibility possibility beneath beneath lake—bottom lake-bottom U ppb Ste. Marie (Michigan), (l'iichigan), suggested by 37 37 U in in well well clays near Sault Ste. source as Elliot Lake ores. water, may have been derived from the same source as Elliot Lake ores. water, may have been derived from the same —38— -38- �GEOCHRONOLOGIC RELATIONSHIPS RELATIONSHIPS IN GEOCHRONOLOGIC THE IN THE CARMEYLAKE LAJCEGNEISS GNEISS AND AND OTHER CARNEY OTHER BASEMENT BASEMENT GNEISSES GNEISSES IN DICKINSON DICKINSON COUNTY, COUNTY, UPPER MICHIGAN IN W. R. R. Van Van Schmus, Schmus, R. R. E. E. Woronick, Woronick, and N. W. N. L. L. Egger Egger Department of Geology Department of of Kansas University of Lawrence, Kansas Kansas 66045 66045 Lawrence, The Carney Carney Lake Lake Gneiss Gneiss and and other other granitic granitic gneisses gneisses exposed exposed in The in the the Feich trough trough region, region, Dickinson Dickinson County, County, have have generally generally been been assumed Felch to assumed to be Archean Archean (Lower be (Lower Precambrian) Precambrian) in in age. age. According According to to the the model model of of Morey Morey and Sims Sims (1976), gneisses belong belong to to aa terrane and (1976), these these gneisses terrane that is in in part older than older than 3.0 3.0 b.y. b.y. We are carrying out total—rock total-rock Rb—Sr Rb-Sr and zircon U—Pb analyses analyses from from these rocks in in order order to to determine determine their primary age U-Pb these rocks their primary age and to to evaluate effects of post—Archean and post-Archean metamorphic metamorphic events. events. for the Carney Lake Lake Gneiss Gneiss indicate indicate that that this unit has has aa Data for the Carney this unit of about about 2.8 2.8 b.y. b.y. and and has has undergone undergone extensive extensive redistribution primary age of of Rb Rb and Sr of Sr during during aa metamorphic metamorphic event event about about 1.8 1.8 b.y. b.y. ago. This event event was probably regional metamorphism associated with emplacement of the the during the the Penokean Orogeny northeastern Wisconsin plutonic complex during about Orogeny about 1.83 b.y. 1.83 b.y. ago. ago. Feich Trough region continue to reflect the Data from the the Felch to reflect the complex geochronologic relationships relationships reported on previously by Banks and Van Schmus (1971, Schmus (1971, 1972). 1972). There is is clear clear evidence for for a major event 2.1 2.1 b.y. ago that that caused caused extensive Rb—Sr Rb-Sr re—equilibration re-equilibration in in the the basement gneisses. gneisses. Our preferred interpretation interpretation is is that that the the event was high—grade high-grade metamorphism, perhaps with minor anatexis, affecting 2.8 2.8 b.y. b.y. old old gneisses. gneisses. Alternatively, Alternatively, it it is is possible that that much of the the gneiss has has primary primary ages of about about 2.l 2.1 b.y., b.y., but have have incorporated incorporated substantial substantial amounts amounts of of older older radiogenic radiogenic Sr87. Sr 87 • Finally, Finally, even even though though the the age age systematics systematics are quite quite complex, complex, there there is is no clear clear evidence evidence that that any any of of the the units units studied studied to to date date are are older older than than 2.8 2.8 b.y. b.y. —39— -39- �FINITE THETHE PRECAMBRIAN FINITESTRAIN STRAININ IN PRECAMBRIANKONA KONAFORMATION FORMATIONOFOFTHE THEMARQUETTE MARQUETTE SYNCLI SYNCLINORIUM NORIUM WESTJOHN, Davidand andCAMBRAY, CAMBRAY, William,Department Department of of Geology, WESTJOHN, David F. F. William, Geology, Michigan State University, Michigan State University, East EastLansing, Lansing, Michigan Michigan 48824 Slates ininthe thePrecambrian Precambrian Kona Kona Formation Formation of the the Marquette Marquette SuperSupergroup contain ellipsoidal reduction spots and deformed group contain ellipsoidal reduction spots and deformed veins. veins. Each Each feature has independently in other has been been used used independently other areas areas as as aameans means of measuring finite strain measuring finite straininduced induced in in rocks rocks during during tectonic tectonicdeformation. deformation. However, the strain values obtained from either However, the strain values obtained from either of these these indicators are open open to questions questions because because the the following followingassumptions assumptionsmust mustbebemade; made; the werepredeformational predeformationaland and initially spherical, the reduction reduction spots spots were initially spherical, and the veins veins were were predeformational predeformationaland andinitially initially had and the had aa wide wide range range of presenceofof these these features features in planar planar orientations. orientations. The The presence in the thesame same lithology provided an opportunity opportunitytoto test test the the validity validity ofofsuch provided an such assumptions. Both Both indicators occur occur ininthe thesame same strain straindomain, domain, and and should show showthe thesame same strainstate stateif if the are valid. valid. should strain the assumptions assumptions are In this and thisstudy, study,reduction reductionspots spots anddeformed deformedveins veinsfrom fromthe thesame same strain domain are used to determine the orientation strain domain are used to determine the orientation and and dimensions dimensions of the minimum finitestrain strain ellipsoid. ellipsoid. the minimum finite In using the two methods it is possible test is valid to In using the two methods it is possible to to test if ifitit is to use them independently as a measure of finite strain. use them independently as a measure of finite strain. Preliminary suggests that that there are differences which Preliminary work work suggests are some some differences which indicate that the veins may have developed after some increment strain that the veins may have developed after some increment ofof strain and that they record only part of the strain history and that the and that they record only part of the strain and that the rereduction spots provide a more complete record. spots provide a more complete If this may If thisisisthe thecase caseit it maybe be possible possible to to plot plotpart partofofthe theincremental incremental strain history of the region and to record both magnitude and history of the region and to record both magnitude and orientation orientation of strain thethe Penokean strainatatseparate separatetimes timesduring during PenokeanOrogeny. Orogeny. The reduction spots indicate a minimum finite strain ininwhich The reduction spots indicate a minimum finite which Orientations Orientations of Principle Axial Ratios Ratios k value value Extensions Principle Axes Axes V Z (a-i/b—i) V X Z X : YY :: ZZ (a -1/ b-l) XX Y Z XX Y Z Reduction +58% +7% -43% 82°/O93° 8°/273° 10/0030 1.5:1.1:0.6 0.50 Spots : —40— -40- �— AA new new detailed detailed aeromagnetic aeromagnetic map map covering covering most most of of the the Precambrian Precambrian shield shield in in Wisconsin Wisconsin by by Isidore Isidore Zietz Zietz U.S. U.S. Geological Geological Survey, Survey, National National Center, Center, Reston, Reston, Virginia 22092 22092 ABSTRACT ABSTRACT A A detailed aeromagnetic survey, survey, having a flight flight separation of ½ ~ flight altitude of 500 feet, feet, has been made over most of mile and a flight the Precambrian shield shield in in Wisconsin. Wisconsin. The survey survey was under under the the direction ofofJohn direction John1-1. H. Karl Karl of the University of of Wisconsin Wisconsin at at Oshkosh. Oshkosh. An aeromagnetic aeromagnetic map, map, published published by by the the U.S. U.S. Geological Geological Survey Survey in in 1977, 1977, was prepared at was at a scale of 1:250,000 by photographically reducing and compiling 86 maps that that cover cover areas areas shown on standard 86 aeronlagnetic aeromagnetic maps standard U.S. U.S. Geological Survey 15' IS' quadrangles. quadrangles. In addition, addition, a colored colored aeromagnetic aeromagnetic and at the same has been map of the the same area and at the same scale (1:250,000) (1:250,000) has prepared and placed on on open-file open-file by by the the U.S. U.S. Geological Geological Survey. Survey. By using using these these two two aeromagnetic aeromagnetic maps, maps, together together with with the the existing existing By regional gravity data, regional data, available available outcrops, outcrops, and and existing existing isolated, isolated, sparse geologic geologic mapping, mapping, Paul Paul Sims Sims and and William William Cannon Cannon have have prepared prepared sparse aa regional regional geologic map. In the the main, main, the In the uncolored aeromagnetic map was was used used for for structural analysis, analysis, whereas whereas the the colored colored version version of of the the map map on on which which structural the differences differences of magnetic magnetic intensity intensity are are conspicuous conspicuous was was used used for for the inferring inferring lithologic variations. —41— -41- �— — — — —; ——— I- m -Fl — �FIELD FIELD TRIP TRIP II SOUTHWESTERN SOUTHWESTERN WISCONSIN WISCONSIN ZINC-LEAD ZINC-LEAD DISTRICT DISTRICT LEADERS: LEADERS: M.G. M.G. Mudrey, Mudrey, Jr., Wisconsin Geological and and Natural Natural History Survey, Survey, W.A. W.A. Broughton, Broughton, University University of of Wisconsin-Platteville, Wisconsin-Platteville, Walter Walter S. S. West, West, U.S. U.S. Geological Geological Survey, Survey, and and Allen Allen V. V. Heyl, Heyl, U.S. U.S. Geological Geological Survey. Survey. DATE: DATE: 1978. May 99 —- 10, 1978. This trip will visit the Wisconsin part of the historic Upper Mississippi Mississippi Valley Valley Zinc-Lead Zinc-Lead District. District. Stops Stops at at quarries and and roadcuts roadcuts will provide a a background on the ore—bearing ore-bearing Paleozoic rocks before going underground at a historic mining site, site, and and aa producing producing zinc-lead zinc-lead mine. mine. 1. 1. Assemble in in Madison, Wisconsin, Wisconsin, at at 12:30 12:30 p.m. p.m. on on Tuesday, Tuesday, May May 9, 9, 1978, and proceed to to Platteville, Platteville, Wisconsin Wisconsin for for overnight overnight lodging. lodging. Tour southwest southwest Wisconsin, and and journey journey to to Milwaukee Milwaukee on on Wednesday, Wednesday, May 10, 10, for for the the evening evening festivities. festivities. 2. 2. The cost is is $40.00 $40.00 and and includes: includes: a) a) b) b) c) c) d) d) Overnight accommodations accommodations (double (double occupancy) occupancy) at at Platteville. Platteville. Bus transportation from Madison to Platteville with a a return trip trip to to Milwaukee. Milwaukee. An evening banquet in Platteville on Tuesday, Tuesday, May 9, 9, and lunch on Wednesday, May May 10. 10. Guidebook. 3. 3. participants. Limited to a a maximum of of 36 participants. 4. 4. The guide materials designed for for this this field field trip trip are: are: a) a) b) b) c) c) d) d) Geology of Upper Mississippi Valley Zinc-Lead Zinc-Lead District, District, Information Circular Number 16, 16, 1970. 1970. ($3.00) Upper Mississippi Mississippi Valley Valley Base Base Metal Metal District, District, Field Trip Trip Upper Guidebook Number Number 1. 1. ($4.00) If purchased purchased together, together, the cost is $6.00. If $6.00. Available from: from: Natural History Survey Wisconsin Geological and Natural 1815 University University Avenue Avenue 1815 Madison, Madison, Wisconsin 53706 608-262-1705 608—262—1705 —45— -45- �FIELD TRIP II II FIELD TRIP MINERAL MINERAL EXTRACTION EXTRACTION AND AND PROCESSING PROCESSING EQUIPMENT EQUIPMENT MANUFACTURERS MANUFACTURERS IN THE GREATER GREATER MILWAUKEE MILWAUKEE AREA AREA LEADER: LEADER: Charles Charles DATE: DATE: May 10, 10, 1978 1978 A. A. Salotti, Salotti, University University of of Wisconsin-Milwaukee. Wisconsin-Milwaukee. This tour will visit a number of major manufacturing plants where mineral and and solid solid fuel fuel extraction and processing equipment is fabrifabricated. Milwaukee is is a world center center for for this activity, activity, and much of the equipment used in the the Lake Superior Region originated in southeastern Increased coal utilization, utilization, coupled with rapidly changing Wisconsin. Wisconsin. technologies processing, are are reflected in technologies in mineral and solid fuel fuel processing, the dynamic character character of this this industry. industry. 1. 1. Depart from the the Pfister Hotel, Hotel, downtown downtown Milwaukee, Milwaukee, on Wednesday morning about about 9:00 9:00 a.m., a.m., May May 10, 10, 1978. 1978. Return to the Pfister Hotel Hotel about about 4:00 4:00 p.m. p.m. 2. 2. There is no guidebook for for this this trip. trip. —46— -46- �FIELD FIELD TRIP TRIP III III I PRECAMBRIAN PRECAMBRIAN RHYOLITh, RHYOLITE, GRANITE, GRANITE, AND QUARTZITE INLIERS INLIERS IN IN SOUTH-CENTRAL IN SOUTH-CENTRAL WISCONS WISCONSIN LEADER: LEADER: Eugene Eugene I. I. Smith, Smith, University University of of Wisconsin—Parkside. Wisconsin-Parkside. DATE: DATE: May May 12 12 -- 13, 13, 1978 1978 This field trip will visit rhyolite ash—flow ash-flow tuff and granite of Middle Precambrian age age (1765 (1765 + ~ 20 20 m.y.), which are are inliers inliers on the the southern southern margin of of the the Precambrian Precambrian shield. shield. These rocks are younger than than granite granite margin and rhyolite in the Wausau area of central Wisconsin (1900 m.y.), and (1900 m.y.), older than the Wolf River River batholith batholith of of northeastern northeastern Wisconsin Wisconsin (1500 (1500 m.y.). m.yJ. the Wolf Stops are are designed designed to to illustrate illustrate stratigraphic stratigraphic and and structural structural relations relations interesting province. province. in this interesting 1. 1. Depart Milwaukee on Friday evening, evening, May 12, 12, 1978, 1978, at at 6:30 6:30 p.m., p.m., and proceed to Oshkosh, and Oshkosh, Wisconsin for for overnight overnight lodging. lodging. Tour south—central south-central Wisconsin on Saturday, May May 13, 13, and and return return to to Milwaukee Milwaukee about about 6:30 6:30 p.m. p.m. 2. 2. The cost is $35.00 $35.00 and includes: includes: a) a) b) b) c) c) d) Overnight accommodations accommodations (double occupancy) at at The The Pioneer Pioneer Overnight (double occupancy) in Oshkosh, Oshkosh, Wisconsin. Bus transportation from Milwaukee to to Oshkosh Oshkosh and and return return Bus from Milwaukee to Milwaukee. Lunch on May May 13. 13. Guidebook. 3. 3. No limit on number of participants. No 4. 4. The guide materials designed for for this this trip trip are: are: a) a) b) b) c) c) d) d) Introduction, Introduction, Geochronology, and and Engineering Engineering Geology Geology of of Precambrian Rocks Rocks in South-Central South-Central Wisconsin, Wisconsin, Geosciences Geosciences Precambrian Wisconsin Number 2. 2. ($4.00). ($4.00). Wisconsin Number Wisconsin, Field Precambrian Inliers Inliers of South-Central Wisconsin, Trip Guidebook Guidebook Number Number 2. 2. ($5.00). ($5.00). If purchased purchased together, together, the cost is If is $8.00. $8.00. Available from: from: Natural History Survey Wisconsin Geological and Natural 1815 1815 University Avenue Madison, Madison, Wisconsin Wisconsin 53706 608-262-1705 608—262—1705 —47— -47- �U INDEX OF AUTHORS AUTHOR PAGE • • • • 3 Aaquist, B. B. E. E. Banaszak, K. K. J. J. · 44 • • • • • • • • • 55 Bauer, R. R. L. L. 6, 6, 7, 40 40 Caxnbray, F. F. W. Carnbray, . Cannon, W. Cannon, W. F. F. . 8 26 • 26 Chang, L. L. L. L. Y. Y. Cooper, R. R. W. W. . . . 12 Cummings, M. M. L. L. . . 9, 10 . 9, Doane, v. V. 18 DuBois, DuBois, J. J. F. Egger, . . . . 11 11 L. 39 Foose, N. Foose, M. P. P. 12 · 12 Gere, N. 13 M. A., Jr. M. Jr. Hammond, R. R. D. D. . . . • . 14 Heinrich, E. E. W. W. . . . . . 15 15 3 Hodder, R. R. W. W. . Hughes, J. J. D. D. . . . . . . . . . 16 17 · 17 Jirsa, M. Jirsa, M. A. A. Jonnson, A. A. 18 Jones, D. D. G. G. 19 19 • • • . 20 J. Kalliokoski, J. Klaysmat, Klaysrnat, 25 A. W. W. A. 21 Larue, D. K. D. K. • R. F. R. Luther, F. W. D. D. N. W. Massey, N. W. S. S. Meddaugh, W. e. • • • • • • • • • • • • • 22 · 23 23 • • • • • • • • • • • • • • • • 24 -49-49- �AUTHOR PAGE Meineke, D. D. G. G. 25 · 25 Meyer, R. R. P. P. 28 Molling, MoIling, P. P. A. A. . . . . . . . . . . . . . 26 Mudrey, Mudrey, M. M. G., G., Jr Jr. 27 • 27 Mursky, G. G. 24 Myers, P. P. E. E. 9 Nebrija, E. E. L. L. 28 Ojakangas, R. R. W. W. 29 Peltonen, D. D. R. R. 30 Peterman, Z. Z. E. E. 31, 31, 35 35 Salotti, C. C. A. A. 24, 24, 30 30 Scofield, N. N. 18, 32 32 Shaffer, N. N. 33 Shariabrook, D. Shanabrook, D. 34 Sims, P. Sims, P. K. K. · 31, 31, 35 35 Smith, E. E. I. I. • . Strakele, A. A. S., Strakele, E., Jr Jr. . . . . • • . . . • 36 37 • 37 Taylor, R. R. W. W. 30 Trow, J. J. 38 • 38 Tyson, R. R. M. M. 26 Vadis, M. M. K. K. 25 Van Van Schmus, Schmus, W. R. W. R. 14, 39 11, 14, 39 Welkie, C. C. J. J. 28 Westjohn, West john, D. D. • • 40 Woronick, R. R. E. E. 39 · 39 Zietz, I. I. 41 —50— -50- �TWENTY—SEVENFIRMS FIRMS IN IN THE TWENTY-SEVEN THE GREATER GREATER MILWAUKEE MILWAUKEE AREA AREA EITHER EITHERMANUFACTURE MANUFACTURE OR SUPPLY FOR MINERAL OR SUPPLY COMPONENTS COMPONENTS FOR EXTRACTION EXTRACTION AND AND PROCESSING PROCESSING MACHINERYI MACHINERY, THEIR SALES IN IN 1977 THEIR AGGREGATE AGGREGATE SALES 1977WAS WAS 9.5 BILLION 9,5 BILLIONDOLLARS. DOLLARS, �2,51O,000'E §+ OZAUKEE CO. OZAUKEE CO. '7 LEGEND 2,590,00~E 2.5+00' +§ R·21-E Port~ c.m.nL-----J U.S... STATE ~ Bitum. J.. Concret. COUNTy Bilumilo<ls a u « ::J: Vl """_".._ 6'0"1 =--==-_ Eo""- =====> ·T~n R~ ========= Fire Lont ========== W '" « :::> 3' Multilane Oivided ==:=1== Freeway ;::;;;;;::;;;;:=;::;;;;= Intorchol\9' """"~'*'~== H~hwoy S.porotion T-B·N ==='t'~T~== Int.rstat. Hi9t!woy Nq. - - - - - - - - Gj3 U.S Hipoy No. @ Stott Highway NO. Counly Hwy. L,tter- - - IAl Roilrood ~~~ Dom .. ¢2_ _~~~~-"" •• _ •• _ Co""ty Boundory ._._._._ _ mm.@U%G15 Corporol. Limits "0 Not. T·)·N ..... ...... ~ o o a Stot. Forests G1't:U:i Airport ~ Fi5h Hatchery .... ~ Game Form ..... CO Counly SeOL @ UnincOfp. VilloQl O Schools- • Public Hl.Ilt.or Fi$h.Grds. ~. Hospilol + RO"9"Stotioft _ Public Camp 8 Picnic Grdl. State Pork + Without COmPllt•• .~ Without Focilltle Woyside A With Compllt., County Pork __W1th Focllitl.. T·6·N __ Stole Bwndory C;,il Town Boundory --' (]) C€§) • 0 With FOcllltl.. A Without Fociliti.' 6 -Surface types on town roods not shown. T·5-N a u « Bi w '" « :::> MILWAUKEE CO. 3' -1 Town of Raymond 2,510,DOO'E RACINE CO. ~ 2,550,000' ~~ PopulalrorL Co. Seat ~_ 239 SQ. MI. 1,046.268 . . Ililwaukee ~+ Town of Caledonia R·22-E R·21-E Land Area + § 2,590,000'E RACINE CO. 254 83 2278 0 Grid based on Wisconsin coordinate system, south zone TOTAL FOR COUNTY DEPARTMENT OF TRANSPORTATION ') DIVISION OF HIGHWAYS STATE OFFICE BUILDING Madison, Wisconsin o I , SCALE ~:::::::J MILES MILES OF HIGHWAY asofJan.I,1975 STATE COUNTY.. . LOCAL ROADS OTHER ROADs.. r .... 2615 COflected for ¢41 JAN. 1976 ~ Compiled frcrn U.S.G.S. Quad/angles Based on Aerial Photographs MILWAUKEE 40·9 � https://digitalcollections.lakeheadu.ca/files/original/cdb7e5f2759e322eb662e91633befa43.pdf 8b8cb45be09f5be9ace0f0580c35e58a PDF Text Text UNIVERSITY OF WISCONSIN-EXTENSION GEOLOGICAL AND NATURAL HISTORY SURVEY Meredith E. Ostrom, State Geologist and Director UPPER MISSISSIPPI VALLEY BASE-METAL DISTRICT Prepared for: TWENTY-FOURTH ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY UNIVERSITY OF WISCONSIN-MILWAUKEE MILWAUKEE, WISCONSIN MAY 9—14, 1978 FIELD TRIP GUIDE BOOK NUMBER 1 1978 �Field Trip Guide Book Book Number Number 11 University University of of Wisconsin—Extension Wisconsin-Extension GEOLOGICAL GEOLOGICAL AND NATURAL HISTORY SURVEY Meredith Meredith E. Ostrom, Ostrom, State Geologist and and Director UPPER MISSISSIPPI MISSISSIPPI VALLEY BASE-METAL DISTRICT DISTRICT (companion volume to Information volume to Information Circular CircularNumber Number 16) 16) With contributions contributions by With by W. A. A. Broughton, A. A. V. V. Heyl, Heyl~ M. M. G. G. Mudrey, Mudrey, Jr., Jr., M. M. E. E. Ostrom, Ostrom, Rachel K. A. Paull, W. S. K. Paull, paull, Richard A. Paull, and W. S. West Edited by M. M. G. G. Mudrey, Mudrey, Jr. Jr. Natural History Survey Geological and Natural Prepared for Annual Meeting Twenty-Fourth Annual INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIORGEOLOGY GEOLOGY University University of ofWisconsin, Wisconsin,Milwaukee Milwaukee Milwaukee, Milwaukee, Wisconsin May 9-14, 9-14, 1978 Richard A. A. Paull, Chairman, Field Trip Committee PaUll, Chairman, University of Wisconsin-Milwaukee Available from the the Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, of Wisconsin-Extension, Wisconsin—Extension, 1815 University of 1815 University University Avenue, Avenue, Madison, Madison, Wisconsin 53706 53706 1978 �CONTENTS OONTENTS Page INTRODUCTION INTRODUCTION by by M. G. G. Mudrey, Mudrey, Jr Jr. • • • • • • • . • • • • • • . • • • • • 1 TUESDAY, MAY MAY 9, 9, 1978 1978 TUESDAY, Geologic Road Road Log Log for for U. U. S. S. 151 151 from from Madison, Madison, Wisconsin Wisconsin (U. (U. S. S. 12 12 and and 14 junction) junction) to to Platteville, Platteville, Wisconsin Wisconsin (Wisconsin (Wisconsin 80 80 and and 81 81 junction) junction) by by Richard Richard A. Paull Paull and and Rachel Rachel K. K. Paull Paull • • • • • 77 • Geologic Road Road Log Log for for Grant Grant County County by by M. M. G. G. Mudrey, Mudrey, Jr., Jr., W. W. A. A. 14 Broughton, Broughton, A. V. V. Heyl, Heyl, and and W. W. S. S. West West • • • • • • • • WEDNESDAY, MAY MAY 10, 10, 1978 1978 WEDNESDAY, Geologic Road Road Log Log for for Lafayette Lafayette County County by by M. M. G. G. Mudrey, Mudrey, Jr., Jr., W. W. A. A. Broughton, Broughton, A. V. V. Heyl, Heyl, and and W. W. S. S. West West . • • • • • • • • • • • • • • 16 16 Geologic Road Log for for Madison Beltline, Beltline, 1—90, 1-90, and and 1—94 1-94 from from Madison, Madison, Wisconsin Wisconsin (U. (U. S. S. 12 12 and and 14 14 junction junction with with U. U. S. S. 18 18 and and 151) 151) to to Milwaukee, Milwaukee, Wisconsin Wisconsin (1—94 (1-94 junction junction with with 1—43 1-43 and and 1-794) 1-794) by by Rachel Rachel K. K. Paull and and Richard Richard A. Paull Paull • • • . • • • . • • • • • • • • 17 17 SlOP DESCRIPTIONS GFXHl>GICAL S1UP DESCRIPTIONS GEX)LOGICAL Stop 11 Stop Stop Stop Stop Stop 22 33 44 55 — ——-—- ...3228 M. E. Hoadley Hill by M. E. Ostrom • • • • • Section 22 Quarry by M. Section M. G. G. Mudrey, Mudrey, Jr Jr .• Hill by M. M. E. E. Ostrom Ostrom. • . • • • Potosi Hill St. John Mine by M. St. M. G. G. Mudrey, Mudrey, Jr Jr . • • Industries Shullsburg Mine by Shullsburg by Staff, Staff, Eagle—Picher Eagle-Picher Industries (not (not attached to road road log) log) . . . 28 32 33 37 37 ILLUSTRATIONS Figure 1. 1. Figure 2. 2. Figure 3. 3. 4. Figure 4. Map of main part of Upper Mississippi Valley Valley zinc—lead zinc-lead district district. . . . . . . . . . . . . . . . . . . . . Highway map showing route route of of field field trip trip • • . • • • • • Detailed stratigraphic column column of of Platteville, Platteville, Decorah, Decorah, and and Galena formations in in zinc—lead zinc-lead district district • . • • • • • • • • • Simplified stratigraphic column column showing showing relative relative quantitative quantitative . stratigraphic distribution of zinc and lead in Wisconsin. stratigraphic Stalactites in Cave Cave of the the Mounds Mounds near near Blue Blue Mounds Mounds. • Cross section through Blue Mounds Cross Mounds from west to east • • Blue Mound viewed viewed from from west • • • • • • • • • • . • • • • • • . . •. of glacial glacial deposits Photograph of deposits of southeast Wisconsin polished Precambrian Waterloo Quartzite . • Glacially polished • Intensively farmed Intensively farmed drumlin near Sullivan • • . • . • • • • • • Scenic overview of the southern Kettle Interlobate Scenic Interlobate Moraine. Moraine • • . Figure Figure Figure Figure Figure Figure Figure Figure 5. 5. 6. 6. 7. 7. 8. 8. 9. 9. 10. 10. 11. . . i :i. 22 3 4 5 9 10 11 18 20 22 23 �I NTRODUCT ION INTRODUCTION M. G. G. Mudrey, Jr.' M. Jr.1 The zinc zinc and and lead mines of of southwestern Wisconsin Wisconsin are are part part of of the the oldest oldest The lead mines producing zinc-lead zinc-lead mining district district in the the United United States, States, the continuously producing The largest and most most productive parts Upper Mississippi Valley District. The largest and parts of of this district district extend extend across across five five Wisconsin Wisconsin counties counties and and into into small small areas areas in in this Illinois and and Iowa (Fig. Over 1.2 1.2 million million tons tons of of zinc zinc and and nearly 100,000 Illinois (Fig. 1). 1). Over tons of of lead lead have have been been recovered recovered from from the Wisconsin portion of tons of the the Upper Upper MissMississippi Valley Valley district district from 1910 to issippi to 1974, 1974, with with aa combined combined value value in in excess excess of of Heyl and and others others (1959) suggest that an an additional additional 250,000 tons $267 million. Heyl (1959) suggest tons of zinc zinc and and 350,000 to 400,000 tons of lead were produced produced in the Wisconsin part of tons of lead were the Wisconsin of of the district in in the the period period following following 1800. 1800. The text that accompanies this this field trip (Heyl and others, others, 1970) 1970) covers covers the of the region, and field (Heyl and the early history of the region, the the geologic controls on ore ore mineralization. mineralization. In (1976) In addition, addition, West West and Weeks (1976) provide additional information information on on the the district district and and its its production. production. The field field trip commences commences in Madison, Madison, proceeds The proceeds to Platteville for for an overnight stop, examines the formations directly related related to the horizons, and night stop, examines the formations the ore horizons, visits an historic lead Mine) and and an operating zinc-lead mine visits lead mine (St. (St. John Mine) near Shullsburg Shullsburg (Fig. (Fig. 2). 2). The returns to Madison where private The field field trip returns vehicles can be picked up, up, and vehicles and terminates terminates in downtown Milwaukee prior to the 25th Annual Institute Institute on on Lake Lake Superior Superior Geology. Geology. Potosi and Shullsburg 7.5Geologic stops will be in in the the Dickeyville, Potosi In addition, addition, the the route leads through minute topographic quadrangles. In through the the Platteville, Platteville, Cuba City, and and New New Diggings Diggings 7.5-minute 7.5-minute topographic topographic quadrangles. quadrangles. Geologic (1963); Dickeyville, Geologic quadrangle references references are Cuba City, City, Agnew (1963); Dickeyville, Whitlow and West (l966a); Diggings, Mullens Mullens (1964); Potosi, Whitlow and West (l966b); (1966a); New Diggings, (1964); Potosi, (1966b); Shullsburg, Mullens (1964). and Shullsburg, (1964). cuts and a The trip starts with two road cuts a quarry that include units of the the The first Sinnipee Group (Figs. (Figs. 33 and and 4). 4). The first day ends ends with a a visit to an early lead mine (St. (St. John Mine), Mine), that that may well have been the the first operating mine in in Wisconsin. The second day the the Shullsburg Mine Mine of of Eagle Eagle Picher Picher Industries, Industries, Inc. Inc. will be be visited. visited. After a lunch lunch stop stop in in Shullsburg, Shullsburg, the the route leads leads back to to cultural tour along back roads, roads, and and then returns Platteville via aa cultural returns to Madison and Milwaukee. This year marks the the 125th l25th anniversary anniversary of the the first Wisconsin geological survey. Under an act of of the Legislature approved March 25, 25, 1853, 1853, a a State Geological Survey was created, created, with an annual annual appropriation appropriation of of $2,500 per per year year for four years. years. Edward Daniels was appointed appointed State Geologist by Governor Leonard J. J. Farwell. Daniels' Daniels' instructions instructions were to to "complete his his survey survey of of that that of the state known as mines' before commencing the survey of portion of as the 'lead 'lead mines' the remainder of of the the state." state." We welcome you you to to the the Zinc-Lead Zinc-Lead District, and and hope that that you you find find the the geology, geology, companionship, and and tour tour rewarding! rewarding! 1 Wisconsin Wisconsin Geological Geological and and Natural History Survey, Survey, Madison Madison 1 1 �Pb \ "'" "ALLAMAKEE Cu ) RICHLAND * Pb* CRAWFORD / * COLUMBIA SAUK Pb* Cu ( River Pb* I' Pb Madison * * DANE Zn *Pb o Pb Zn * 0 Pb CLAYTON -- Belmont • ·Calamine .Darlington Platteville _ IOW4 "\ LAFAYETTE ~ Dubuque • Shullsburg ~ Pb --~bO--- "ol'ol' . '-"ol'ol'/ DELAWARE ~O WISCONSIN -ILLINOiS - - .,~-.- - ~.o.... DUBUQUE • Galena STEPHENSON Cu Zn PbOAu Freepo·rt -Opb ~...t.. -..!?....-...-.- JONES --I-_=-----,:---------j JACKSON Pb A. CARROLL o Pb 0o 10 I I I I Pb Lead Zn Zinc Cu Copper Au Silver Silver 0o Miles 20 Miles I I I EXPLANATION OGLE I I I io 10 20 Kilometres * * Mine or or prospect prospect inin dolomite dolomite of Mine Silurian age age o Mine or prospect Mine·or prospect in in Galena, Galena, DecoDecorah, and and Platteville Platt~ville formations formations A prospect in in Prairie Prairie du du Mine or prospect Chien group Boundaryof of main main part part of of district Boundary Figure 1. 1. Figure Map of main part of the the Upper Upper Mississippi Valley Valley zinc—lead zinc-lead district, district. 2 �Route from Madison t. Platteville and return via U.S. Hwy 151 (69 miles) iH?E HHHr \ P iiNL - 'I lmH fl0 1HRRI - i-t )JTF F- -I \ (ELMON LAIi _=i__ , S -4=4 --S ' I /11/ \V F TN ' : )Jf — r (Ii 1 k 1ff S—f— -7L ij I• Figure 2. 2. hul Isburg 1k WHITEII F- RI-N STATE OF STATE OF ILLINOIS ILUNOIS ---- j / )SHUL/UR j MON R-2•W ........ I k-2 O( Jj 7L oi - ENONç L — — T'1JL/ ,/ I '- ELKVE 1- - / - /L J 17 '— t R.2E Tuesday May May 99 Route Route Tuesday Wednesday May Route Wednesday May 10 10 Route Scheduled Stops Scheduled Stops Highway map map showing showing route route of of field field excursion. excursion. 3 3 Of TRANSPORTATION TRANSPORTATIClH DEPARTMENT OF D1VI~0t4 . SCALE? SCALE O' MIG"",AYS , .1Lf:S MILES �System System Series Group Upper Unner Devonian Devonian Member Kenwood Kenwood (55') (55' \ Milwaukee (80') (80') Thiensville Thiensville (65') (65') Lake Lake Church Church (35') (35' ) Middle Cayugan Silurian Formation Waubakee (30') (30') Racine Racine (100') (100' ) Manistique Manistique (150') (l50' ) I1endricks Hendricks) (110')) (1l0' Byron Bvron Mayville (175') (175' ) Niagaran Alexandrian Alexandrian Cincinnatian Sinnipee Sinnipee Champlainiao Champlainian Ordovician Neda (55') (55') Maquoketa (240') (240' ) Galena 230' Galena (230') (25') Decorah Decorah (25') Platteville (100') (lOO' ) St. St. Peter Glenwood (13') (13' ) Tonti ) Tonti 332')) (332' Readst own Readstown Shakopee Canadian Prairie du Chien Chien Willow Willow River River (50') (50' ) New Richmond Richmond (25') (25') Oneota (200') (200' ) Jordan Trempealeau Trempealeau Cambrian St. Lawrence St. (50 )) (50' St. Croixan St. . Tunnel City City (200' (200')) Lone Rock Lone Mazomanie Maz~ Wonewoc (100') (100' ) Sunset Point Point Van Oser Oser) Norwalk j (60') .Black Black Loch Lodi < -. Earth Earth < Reno Tomah Birkmose Ironton (40') Ironton (40') Galesville Bonneterre (20') (20') ~onneterre Elk Mound (250')Eau Claire (250') Mt. Mt. Simon (500') (500') Figure 3. Detailed stratigraphic column of Platteville, Detailed Platteville, Decorah, Decorah, and and Galena formations Galena formations in the Upper Mississippi Valley Valley zinc—lead zinc-lead district. 4 �I Known]ECIl relative Quantities -1:<;0 • • I ~ t;, Q) _-'-';~- i~I' ~ ' G roup or formation In Dolomite, buH, cherty; Ptllt4mtru, at lop, ~~; I ~ ~~~ 0( ~ Average thickness. Description 90 fLjP-=A--o-o,-om-,-..-.-"-11-.-oh-'-ff'-;-'-"-i1-,,-,,-o,-,-n-.-,,-,-,-,.---t-- -jO 200 II DolomIte. yellowlsh·buff. thln·bedded, snaly_ I Dolomite. yellowlsh.buff, thiCk. bedded :.Rt. f!ptucullt1!S In middle 225 105 Dolomite. drab to butt: cherty; Rrclpta.cutiU. near base limestone and doIOI'T"te. brown and grayish: green, sandy shale and phosphatic nO(lules at base DISCONFORMITY 40 80 Galena dolomite St. Peter sandstone I I 108=l Shale, blue. dolomitiC: phosphatic depauperate fauna <1t base Maquoketa shale I feet_I 55 75 40 ~ Sandstone. quartz, coarse. rounded . , f - - - - - - - D1SCONF'ORMITV------f---I 280- -f". Dolomite, Iight·buff, cherty; sandy near base and Prairie du ChIen group ~:~ .~:, ~:".~".~.~.' lundifferentlated) Trempealeau formation FranconIa sandstone Sandstone and Siltstone. glaucoroitlc Dresbach sandstone Sandstone f.------l';;:±8-----------Eau Clai,e sandstone Siltstone and sandstone 0- I 320 I ---~ 110· 140 ~o l 70 330 1050 I 700 I I Mount Simon sandstone Figure Figure 4. 4. Sandstone 440 780 I __J Simplified stratigraphic stratigraphic column column shOWing showing relative relative quantitative quantitative Simplified stratigraphic distribution distribution of of zinc zinc and and lead lead in in the the Wisconsin Wisconsin stratigraphic district. district. 55 �References Cited Agnew, Agnew, A.F., 1963, 1963, Geology Geology of of the the Platteville Platteville quadrangle quadrangle Wisconsin: Wisconsin: U.S. U.S. Geol. Geol. Survey Bull. l123—E, 1123-E, p. p. 245—277. 245-277. Heyl, A.V., Jr., Heyl, A.V., Jr., Agnew, Agnew, A.F., Lyons, Lyons, E.J., E.J., and and Behre, Behre, C.H., C.H., Jr., Jr., 1959, 1959, The Geology of the the Upper Upper Mississippi Valley valley Zinc—Lead Zinc-Lead District: District: U.S. U.S. Geol. Geol. Survey Prof. Paper 309, 309, 310 310 p. p. Heyl, A.V., Ay., Jr., Heyl, Jr., Broughton, Broughton, W.A., W.A., and andWest, West, W.S.,, W.S., 1970, 1970, Guidebook Guidebook to to the the Upper Mississippi Valley Geol. and valley base base metal metal district: district: Wisconsin Geol. Nat. Nat. History Survey Inf. Inf. Circ. No. No. 16, 16, 49 49 p. p. Mullens, T.E., City, New New Diggings, Diggings, and and Shullsburg Shullsburg Mullens, T.E., 1964, 1964, Geology of of the Cuba City, quadrangles, Wisconsin U.S. Geol. Geol. Survey Wisconsin and and Illinois: Illinois: U.S. Survey Bull. 1123-H, 1123-H, p. 437-531. p. 437—531. West, W.S. West, W.S. and and Weeks, R.A., R.A., 1976, 1976, Zinc Zinc and and Lead Lead in in C.E. C.E. Dutton, Dutton, ed., ed., Report prepared by the Mineral and and Water Resources Resources of of Wisconsin: Wisconsin: Report U.S. Geol. Geol. Survey in U.S. in collaboration with the the Wisconsin Wisconsin Geol. Geol. and and Nat. Nat. History Survey for the Committee on Interior Interior and and Insular Insular Affairs, Affairs, United States Senate, p. p. 132—145. 132-145. Whitlow, J.W., West, W.S., W.S., l966a, Geologic map of of the Dickeyville Whitlow, J.W., and West, 1966a, Geologic the Dickeyville quadrangle, Grant County, quadrangle, County, Wisconsin: Wisconsin: U.S. U.S. Geol. Geol. Survey Survey Map Map GQ-488. GQ-488. Whitlow, Whitlow, J.W., J.W., and and West, W.S., W.S., 1966b, 1966b, Geology Geology of of the the Potosi Potosi quadrangle, quadrangle, County, Wisconsin, Wisconsin, and Dubuque County, Iowa: U.S. Geol. Geol. Survey Grant County, Iowa: U.S. 1123-1, p. p. 533—571. 533-571. I Bull. 1123—I, 6 �Tuesday, Tuesday, May 9, 9, 1978 1978 for U.S. U.S. 151 151 from from Madison, Madison, Wisconsin Wisconsin (U.S. (U.S. 12 12 and an 14 Geologic Road Road Log for Geologic 14 junction) junction) to Platteville, Wisconsin (Wisconsin to platteville, (Wisconsin 80 80 and and 81 81 junction) jUnction)* A. Paull Richard A. 11 and Rachel K. K. Paull and 2 2 U.S. U.S. 151 from Madison to to Verona traverses traverses aa recently recently glaciated glaciated (Woodfordian) (Woodfordian) part of the Eastern Ridges and and Lowlands Lowlands physical physical province. province. Since the the drift in in this area was was deposited deposited near near the the ice margin, it it is and the the this ice margin, is generally thin, thin, and exerts considerable considerable influence on the the character of of the landunderlying bedrock exerts influence on the landFrom the scape. the western edge of the the Wisconsinan (Woodfordian) (Woodfordian) terminal moraine just west west of of Vernoa to the River, the route crosses crosses aa thin sliver of of older the Sugar River, the route (Illinoian) drift. drift. The remainder of the route lies within the the classic Driftless Area of of the the Western Western Uplands Uplands physical physical province. province. and Mt. Mt. Horeb, Horeb, rock exposures exposures along along the Between Madison and the highway are mainly dolomite assigned to to the the Lower Ordovician Ordovician Prairie Prairie du du Chien Chien Group. Group. However, The bedrock from Mt. some younger rocks are are also also present. present. The Mt. Horeb to to Platteville Plattevil1e is predominantly Middle Ordovician limestone is limestone and and dolomite dolomite of of the the Platteville, Platteville, Decorah, and Galena formations, formations, although the the Middle Middle Ordovician St. St. Peter Sandstone Decorah, is also exposed along along the the highway highway in in aa few few places. places. Several isolated mounds (outliers) of Upper Upper Ordovician Ordovician Maquoketa Maquoketa Shale Shale capped capped by by resistant, resistant, Silurian Silurian (outliers) of dolomite are present near U.S. of Blue Mounds Mounds and Platteville. U.S. 151 in the vicinity of and Platteville. Mileages 0 o (69) U.S. 12 and 14 on the southwest Junction U.S. U.S. 151 and 18 with U.S. The road road log edge of Madison, Madison, Wisconsin. Note: The log from from Madison Madison to Milwaukee Milwaukee provided provided for for Wednesday Wednesday May May 10, 10, 1978 1978 also also begins begins to at this this intersection. intersection. 1.5 (67.5) Gravel pits pits to the southeast southeast are in glacial outwash that fills fills aa preglacial bedrock bedrock valley. valley. 2.5 (66.5) Rock exposures exposures along the valley sides sides are red and yellow St. Peter Sandstone capped by Middle Ordovician weathering St. Platteville-Galena dolomite. 8 (61) Verona, Wisconsin and Verona, and junction junction with with Wisconsin Wisconsin 69. 69. The thin thin drift cover here was deposited near the margin of Wood— of the Woodfordian ice. ice. 9 (60) Moraine, the terminal moraine of Wisconsinan Cross the Johnstown Moraine, (Woodfordian) glaciation in (Woodfordian) in this this area. area. *This road road log is is published pUblished with permission permission of of Kendall/Hunt Kendall/Hunt Publishing Publishing Co., Co., Dubuque, Iowa and it should not not be be duplicated duplicated by by any means means without without written Dubuque, permission. 11 The University of WisconsIn—Milwaukee Wisconsin-Milwaukee Alverno College, 22 The The University University of of Wisconsin-Madison and Alverno College, Milwaukee Milwaukee Wisconsin-Madison and 7 �Mileages Mileages 10 10 (59) (59) Cross the the Sugar River. River. The of the Sugar River, The upper upper course of which flows flows south and which and southeast to to join the the Rock River, developed along along the developed the western margin of the the Woodfordian glacier. glacier. This broad, broad, terraced terraced valley once carried great quantities This quantities of of meltwater and outwash southward southward from from the the wasting wasting ice ice front, front, which lay immediately east of of here. The Sugar River defines the the edge of of the the Driftiess Driftless Area Area here. here. The outer edge edge of of the the Woodfordian Woodfordian terminal terminal moraine moraine forms forms the the The partially wooded wooded ridge ridge on the east side of the partially the valley. The deposits between the Sugar River River and and the the terminal terminal moraine moraine deposits the Sugar probably include include aa thin strip of Illinolan probably Illinoian glacial deposits. deposits. River, the the route route gradually gradually ascends ascends toward toward aa From the the Sugar River, ridge crest which marks marks the the edge edge of of the the Middle Middle Ordovician Ordovician ridge crest Platteville-Galena upland Platteville-Galena upland surface. surface. 15 (54) Junction County County P. P. Friable St. St. Peter Sandstone is is quarried quarried just north of of here here at at Kievenville. Klevenville. A thin layer of overlying Middle Middle Ordovician Platteville Platteville Dolomite Dolomite is is stripped stripped away, away, and and the poorly poorly consolidated consolidated quartz sandstone below is the is mined for for foundry and and refractory refractory sand. sand. 18 (51) Mt. Mt. Horeb, Wisconsin Wisconsin occupies occupies aa ridge ridge top. top. Originally settled settled Swiss farmers, farmers, its its heritage heritage is recalled by by by Norwegian and and Swiss is recalled commercial establishments along along the the route. route. 20.5 (48.5) (48.5) Junction with with County County JG. JG. This steep, steep, wooded road road descends descends one one mile north to to Little Norway, Norway, a a restored Norwegian pioneer homestead. The side ttV?i side road road follows follows a anarrow, narrow,deeply—cut, deeply-cut, "V"shaped valley that is is typical typical of of the the upper upper reaches reaches of of drainages drainages in the Driftless Area. The Tyrol Ski Basin, 22 miles miles north north of of Little Norway, Norway, takes takes advantage advantage of of these these steep steep valley valley walls. walls. 20.8 (48.2) Entrance to to Cave Cave of of the the Mounds Mounds is is north north of of the the highway, highway, off off County County F. F. This cave is developed in the the Middle Ordovician Galena had no no natural entrance, Galena Dolomite. Dolomite. It It had entrance, and was accidently accidently discovered by by quarry quarry blasting blasting in in 1939. 1939. The cave, cave, which which features features aa variety variety of of intricate intricate dripstone dripstone deposits, deposits, is is open open for for tours tours during the the summer summer months months (Fig. (Fig. 5). 5). Brigham Brigham County County Park, Park, on on East Blue Mound, is is aa short short distance distance beyond beyond the the cave cave on on County County F. F. 21 21 (48) (48) The wayside park park north north of of the the highway highway is is developed developed in in an an old old quarry quarry in in the the Galena Galena Formation. Formation. 88 �Figure 5. 5. Dripping Dripping stalactites stalactites hang hang from from the the ceiling ceiling of of this this narrow passageway in in Cave of the the Mounds near near Blue Blue Mounds, Wisconsin. Photo courtesy of Cave of of the the Mounds. Mileages 22.7 (46.3) village of Mounds, nestled beneath Village of Blue Mounds, beneath the the west west and and east east summits of of the Blue Mounds (Fig. summits (Fig. 6). 6). The summits summits of East and West Blue Mounds are The are about about 1.6 1.6 miles miles apart (Fig. (Fig. 6). 6). The East Mound, Mound, site of Brigham Brigham County County Park, Park, has aa broad flat has flat top top developed on the the Upper Upper Ordovician Ordovician led Silurian Silurian Maquoketa Shale. However a a few blocks blocks of of silicif silicified 9 �Mileages dolomite are are found found on the crest and flanks. dolomite flanks. The The elevation of the West West Mound Mound is the is 1716 feet, feet, some 230 feet higher higher than than its its neighbor to the east. This mound has a the This a smaller, smaller, more rounded rounded led Silurian Silurian summit area, area, and it it is is capped capped by by 85 85 feet feet of of silicif silicified dolomite. Thus, Thus, West Mound is is an outlier of of the the Silurian escarpment, which has has retreated about 50 miles to escarpment, to the the southwest southwest as aa result of downdip as downdip erosion. erosion. Iowa Co. Dane Co. EAST WEST W MOUND Silurian dolomite O~I--------il o 1.6 Mil. Km E. MOUND U. Ord. Maquoketa Shale M. Ord. Plalteville-Goleno dolomites Figure Figure 6. 6. section through through Blue Blue Mounds Mounds from from west west to to east. east. Cross section Elevation in in feet is indicated along the the right margin. After Black, 1970. 1970. Blue Mounds State Park, Park, on West Blue Mound, Mound, is is reached by a well—marked well-marked road road that that goes goes north north through through the the village. village. At the the mound top, top, observation towers towers are located located at both the the east and and west ends ends of of an an old old racetrack. racetrack. The towers towers provide an opporthe Driftless tunity to view the Driftless Area Area to to the the west, west, the the glaciated Madison, and and the the Precambrian Baraboo Baraboo Range Range countryside toward toward Madison, to the north. Indians reportedly used used the mound top as as an an north. Indians reportedly the mound led cap rock into observation post, post, and and fashioned fashioned the the silicif silicified projectile points. points. They attributed the blue haze, haze, which often veils these wooded mounds when viewed from below, below, to the the pipe smoke of Wakanda, the the Earth—maker. Earth-maker. The Upper Ordovician Maquoketa Shale, Shale, which makes up East Mound the Silurian on West Mound, forms the the upper part and underlies the Mound, forms of the the gently sloping sloping sides sides of of these these wooded wooded mounds mounds (Fig. (Fig. 6). 6). The Platteville—Galena Platteville-Galena formations formations are the basal foundation for both mounds, mounds, which are perched perched on the edge of the the Middle Ordoviclan Ordovician cuesta cuesta called called Military Military Ridge. Ridge. To the north, north, steep drainages flow toward toward the the Wisconsin River valley, valley, about 11.5 away. The headwaters of one of these north-flowing miles away. streams forms the separation separation between between the the two two mounds. mounds. 22.9 22.9 (46.1) (46.1) Dane/Iowa County County line. line. Enter Iowa Iowa County in in an an area where Dane/Iowa roadcuts expose thin—bedded, thin-bedded, nodular nodular Middle Middle Orcovician Orcovician dolomite. dolomite. Several small quarries quarries along the highway between here and Barneveld also also provide provide exposures of of the the Middle Ordovician Platteville—Galena Platteville-Galena formations. formations. 10 10 �Mileages 26 (43) Barneveld, Wisconsin. Wisconsin. The Blue Mounds, the the most northeasterly northeasterly of of the Silurian outliers, outliers, are are visible visible to to the the east east (Fig. (Fig. 7). 7). Figure 7. Figure 7. A A view east east to to the the gently—sloped, gently-sloped, wooded wooded Blue Blue Mound, Mound, from a a quarry developed in in the the Middle Ordovician Ordovician Galena Dolomite. The route westward from Barneveld to to Ridgeway Ridgeway passes passes numerous numerous roadcuts in the Middle Ordovician Ordovician Platteville-Galena Platteville-Galena formations formations as as it traverses Military Military Ridge. Ridge. 31 31 (38) Ridgeway, named for the Town of Ridgeway, the Middle Ordovician Ordovician cuesta cuesta of of Military Ridge, Ridge, upon upon which which it it is is perched. perched. 35 35 (34) Wayside to for to north of the the highway has a a historical marker for Military Road". Road". This road was completed in 1835 to link "Old Military Fort Howard Howard at at Green Green Bay Bay to to Fort Fort Crawford Crawford at at Prairie Prairie du du Chien. Chien. In this this area, area, the the route route followed followed the well-defined, well-defined, broad, In treeless ridge crest at the the northern edge edge of of the the Middle Middle Ordovician Ordovician Platteville-Galena cuesta. Platteville-Galena cuesta. Since this this ridge forms the the drainage divide between the the Wisconsin River to to the the north north and and the the Platte, Platte, Galena, and Pecatonica rivers Galena, rivers to to the the south, south, it it is is not not dissected dissected by streams. This aided aided road road construction construction by by eliminating eliminating the the need for bridges. bridges. Besides army traffic, thousands of of pioneers pioneers passed passed this this way way to to Besides traffic, thousands the booming booming lead lead mining area, the area, the early territorial territorial capitol of of Wisconsin, and and the the thriving thriving port port cities cities on on the the Mississippi Mississippi River. River. This same route was utilized utilized later later by by the the Chicago Chicago and and NorthNorthwestern Railroad. 11 �Mileages Mileages 39 39 (30) (30) Junction with with U.S. U.S. 18 18 and and State State 23. 23. U.S. Junction U.S. 18, 18, west west from from here, here, continues continues along along the the route route of of the the historic historic army army road road along along Military Ridge. Ridge. Military Governor Park, located 3 miles north north of of this this Governor Dodge Dodge State Park, intersection intersection along along Wisconsin Wisconsin 23, 23, embraces embraces two two lakes lakes formed formed by by impounding Mill Mill Creek, Creek, aa tributary to impounding to the the Wisconsin River. Bedrock exposures exposures in in the the park park include include roadcuts roadcuts through through the the Bedrock Platteville-Galena Platteville—Galena upland upland surface, surface, and and scenic, scenic, natural natural outcropoutcrop— pings pings of of the the underlying underlying Middle Middle Ordovician Ordovician St. St. Peter Peter Sandstone Sandstone along the floor of the the valleys. valleys. Turn south on U.S. U.S. 151 into Dodgeville, Wisconsin. U.S. Turn U.s. 151, from here here to Platteville, Platteville, generally follows an from an historic historic cutoff cutoff from the the Military Military Road to the lead mines, from mines, and and the the river river ports ports along the Mississippi. 395 39.5 (29.5) (29.5) Dodgeville, Wisconsin. The The city was was named named for for Henry Dodge, Dodge, an early lead miner and Indian Indian fighter fighter in in this this district. district. Since avid supporter of of President Andrew he was well-liked and an avid Jackson, he he was was appointed appointed as as the the first first territorial territorial governor governor Jackson, of Wisconsin in in 1836. 1836. 43 43 (26) (26) Silurian outliers of Belmont outliers of Belmont Mound Mound and and Platte Platte Mound are are visible to the the southwest, southwest, as as the the highway highway crosses crosses the the rolling, rolling, partiallypartiallyto dissected, Middle Ordovician dissected, Ordovician upland upland surface. surface. Roadcuts provide of Middle Ordovician dolomites this part of of the exposures of dolomites along this route. 47 47 (22) (22) of the commemorates the The historical marker north of the highway commemorates early days of of Mineral Mineral Point. Point. 48 48 (21) (21) Mineral Point, Point, Wisconsin. This part of the the zinc—lead zinc-lead district was settled settled in in the the l820t5 1820's and 1830's by miners from other mining regions in the U.S., U.S., and and by by Cornish Cornish immigrants. immigrants. A A short short side side trip into this historic town, town, with with its its narrow, narrow, steep steep streets, streets, is interesting. Here, Here, on Shake Shake Rag Rag Street, Street, the the Cornish Cornish miners miners their small small homes from local local dolomite along the side side of of built their aa narrow narrow valley valley across across from from the the mines. mines. The street street received received its name because the the miners' miners' wives waved waved dish dish rags rags to to call call the the menfolk menfolk home home when when dinner dinner was was ready. ready. As aa carry—over carry-over from from these these days, local local restaurants and bakeries still make pasties pas ties (meat (meat days, pies), pies), the the traditional, traditional, hearty hearty lunch lunch of of the the Cornish Cornish miner. miner. Part of Shake Rag Street contains a a complex of of restored Cornish Cornish cottages cottages from from the the 1830's 1830's and and 1840's, 1840's, that that includes includes Pendarvis Pendarvis House. House. This This site site is is operated operated by by the the Wisconsin Wisconsin Historical Historical Society Society for for the the public. public. The The Mineral Mineral Point Point Historical Historical Society Society has has aa museum at at Pine Pine and and Davis streets that contains excellent mineral mineral samples samples from from local local mines. mines. 49 49 (20) (20) The The highway highway south south of of Mineral Mineral Point Point follows follows aa narrow narrow ridge ridge that that forms forms aa drainage drainage divide divide overlooking overlooking numerous, numerous, small, small, steep—sided steep-sided valleys valleys on on either either side. side. 12 12 �Mileages Mileages 52 52 (17) (17) The The wayside wayside park park north north of of the the road road provides provides another another view view of of Platte and and Belmont Mounds, as as the the route route traverses traverses the the dissected dissected Middle Middle Ordovician Ordovician highland highland surface. surface. 54 54 (15) (15) Iowa/Lafayette Iowa/Lafayette county county line. line. Enter Enter Lafayette Lafayette County. County. Within Within one mile mile the the highway has has crossed crossed Mineral Point Point Branch Branch and and the the upper upper reaches reaches of of the the Pecatonica Pecatonica River. River. The valleys valleys formed formed by by these these drainages drainages cut cut through through the the Middle Middle Ordovician Ordovician PlattevillePlattevilleGalena formations into into the the underlying underlying Middle Middle Ordovician Ordovician St. St. Peter Peter Sandstone. The contact between between these these formations formations is is exposed exposed west west Sandstone. of the the highway highway near near the the county county line. line. 61 61 (8) (8) Belmont, Wisconsin. Wisconsin. Enter Belmont, dolomite. 61.5 (7.5) Junction Junction with with County County GG in in Belmont. Belmont. A A short short side side trip trip along along this this highway highway provides provides access access to to two two interesting interesting state state parks. parks. Three Three miles northwest northwest on on County County GG (and (and B) B) is is First First Capitol Capitol State State Park, Park, the restored site of the the first Wisconsin Territorial Territorial Capitol Capitol in in This apparently remote 1836. remote location location was was in in the the booming booming lead lead 1836. mining district, district, and and consequently consequently at at the the population population center center of of this this territory when Governor Henry Dodge called called the the Territorial Territorial Legislature to to order. order. They met here for 46 46 days in in 1836 1836 to to Madison, then essentially develop aa constitution. Eventually Madison, uninhabited and undeveloped, undeveloped, was selected selected as as the the permanent permanent capitol. Roadcuts Roadcuts expose expose Middle Middle Ordovician Ordovician Less than aa mile mile east east of of First First Capitol Capitol State State Park Park on on County County G G Less Here, a scenic parking area is is Belmont Mound State State Park. Park. Here, a parking area is is This is another Silurian located on the the south south side side of of the the mound. mound. This outlier, as evidenced by abandoned outlier, abandoned quarry quarry exposures exposures of of thin— thinbedded Lower Silurian Silurian dolomite. dolomite. An observation observation tower tower affords affords a a panoramic view that includes includes numerous numerous mounds, and and the the distant distant edge of of the Silurian escarpment to to the the south south and and southwest. southwest. Both the mounds and the the escarpment are are capped capped with with resistant resistant dolomite, and and once once were were part part of of aa continuous continuous bedrock bedrock Silurian dolomite, surface that that sloped sloped gently to the southwest. surface southwest. There are several old lead and zinc mines in old in this this area. area. U.S. 151 turns west here. U.S. here. 62 (7) Junction of Wisconsin 126 126 in in Belmont. Belmont. 66 (3) Platte Mound, Mound, north of of the highway, rises to an elevation Platte the highway, elevation of of Locally, this 1430 feet. feet. Locally, this wooded hill is is called "M" "M" Mound, because because of the the letter letter formed formed of of white white painted stones that is of is maintained annually by by mining mining engineering students from the University annually University of of This feature, feature, and Little Platte Mound to Wisconsin-Platteville. to Wisconsin—Platteville. This the east, east, are are capped capped by resistant, the resistant, cherty Lower Silurian Silurian dolomite. dolomite. The nonresistant nonresistant Upper Ordovician Maquoketa Shale underlies The underlies the the Silurian (cap rock), rock), and forms forms the gradual slopes that Silurian that rise rise These isolated isolated upward upward from from the the Middle Middle Ordovician Galena surface. These hills are are remnants remnants (outliers) (outliers) of of an an extensive extensive Silurian upland hills The edge of of this surface, which which eroded downdip to surface, to the the southwest. southwest. The highland is is low low located located in in northwestern northwestern Illinois highland Illinois and east—central east-central Iowa. Iowa. 13 13 �Mileages 67 (2) (2) Lafayette/Grant county line. line. 69 69 (0) Enter Platteville and pass a a large quarry developed in in the the Middle Ordovician Galena Galena Dolomite Dolomite to to the the north of of the highway. Middle the highway. Wisconsin 80 Junction U.S. U.S. 151 with Wisconsin 80 and and 81. 81. Enter Grant County. The University University of of Wisconsin-Platteville, Wisconsin—Platteville, with its The its long history of training engineers and and geologists, geologists, is located in this of training mining engineers is located this The Mining Mining Museum, Museum, on on Main Main Street Street in in Platteville, Platteville, provides city. The provides an opportunity for for tourists tourists to to tour tour uiilerground underground in the historic Bevan lead mine, mine, and to to view relics from the the early days of the the lead rush. rush. MADISON—PLATTEVILLE LOG END OF U.S. U.S. 151 MADISON-PLATTEVILLE Geologic Road Log for Grant County 3 l , W.A. W.A. Broughton1'2, M.G. Mudrey, Broughton l ,2, A.V. A.V. Heyl3, Hey13, W.S. W.S. West3 west M.G. Mudrey, Jr. Jr., Continuation of Tuesday, May May 99 Continuation This leg of of the visits four four localities localities that Middle This the trip visits that illustrate the the Middle Ordovician succession of southwestern Wisconsin, Wisconsin, and a a tour of a vintage 1830 lead mine now operated as as aa tourist tourist attraction. attraction. After the the visit visit to to the the mine, mine, we will return return to to Platteville Platteville for for the the evening. evening. Lodging and dinner this this evening follow the the Individual stop descriptions follow are covered by by the the field field trip trip fee. fee. road logs. logs. Mileages 1 2 33 0.0 Governor Governor Dodge Dodge Motel. Motel. on U.S. U.S. 151 and proceed proceed right right (southwest) (southwest) Leave motel and 6.1 Stop Stop 11 —- Hoadley Hill. Hill. Excellent exposure exposure of of St. St. Peter, Peter, Platteville, and Decorah formations. Continue west on Platteville, on U.S. U.S. 151. 151. 7.4 Right turn turn onto onto Church Church Road Road (gravel). (gravel). 7.8 Bear left, left, at at YY in in road. road. 8.1 2 quarry in upper part part of of Platteville Formation Stop 2 -- Section 2 stop and Decorah Formation. Quimbys Quimbys Mill Mill Member of of Decorah Decorah Formation is especially especially well well exposed. exposed. Middle Ordovician Ordovician fossil fossil locality. locality. Turn around around at at top top of of hill, hill, and and return return to to U.S. U.S. 151. 151. Continue Continue west on on U.S. U.S. 151. 151. Wisconsin Wisconsin Geological and and Natural Natural History History Survey Dept. of Geology, IJW—Platteville Dept. of Geology, UW-Platteville U.S. U.S. Geological Survey Survey 14 14 �Mileages 11.7 11. 7 Enter Dickeyville. Enter 12.0 12.0 Right turn (north) Right (north) onto U.S. U.S. 61 and State 35. 35. 15.9 15.9 Cross Platte River. Cross River. 16.1 16.1 Base of of Potosi Potosi Hill Hill roadcut. roadcut. 16.6 Stop 3 Potosi Hill. Excellent exposure of upper part stop - Potosi part of of Platteville Formation, Shale,an.d lower part part of of the the Formation, Decorah Shale, axd lower Galena Formation. Continue north on U.S. U.S. 61 and and State 35. 35. 18.5 Enter Tennyson. 19.1 Turn left left (west) (west) on on County County 0. O. 19.7 Enter Potosi. Potosi. 20.3 sign. Proceed straight ahead (south) Stop sign. (south) on State 133. 133. 20.5 Stop 4 -- St. St. John's Mine. Mine. Old lead lead mine from the the 1830's. 1830's. Retrace route to to intersection intersection State State 133 133 and and County County 0. O. 21.9 Intersection with U.S. U.S. 61 61 and and State State 35. 35. County County 0. O. 27.6 Enter Cornelia. 31.5 Junction with with U.S. U.S. 151. 151. 34.7 Governor Dodge Dodge Motel. Motel. Turn left left (north) (north) toward toward Platteville. Platteville. END OF LOG 15 15 Continue east on �Wednesday May 10, 1978 1978 Geologic Road Road Log Log for for Lafayette County Hey13, W.S. 1 , W•• A Broug h ton 1,2 , A.V. Broughton1'2, d rey, Jr. M.G. Mu Mudrey, Jr.', LA. M.G. A.V. Heyl3, W.S. West3 West 3 of the trip visits the Shullsburg Mine of of Eagle-Picher Industries, This leg of Industries, the only only operating operating zinc-lead zinc—lead mine mine complex complex in in the the Upper Upper Mississippi Mississippi Valley Valley base base the metal district. Participants are are reminded reminded to to wear wear appropriate appropriate safety safety equipment; equipment; including hard hat, hat, light, light, self—rescuer, self-rescuer, safety safety boots boots and and glasses. glasses. In the afternoon afternoon we we will will return return to to Platteville, Platteville, Madison Madison (where private In the (where private automobiles can be be picked picked up), up), and and Milwaukee. Milwaukee. Historical and cultural cultural stops stops may be made en en route. route. We plan plan to to arrive arrive in in Milwaukee Milwaukee about about 6:00 6:00 P.M. P.M. Morning, Morning, May 10 10 Mileages 11 2 3 0.0 Leave Governor Dodge Motel and and proceed proceed left left (east) (east) on on U.S. U.S. 151. 151. 0.2 Turn right (south) (south) on on State State 80 80 and and State State 81. 81. 6.8 Buildings and tailings pond of of abandoned New Jersey Zinc Company's Elmo Mine can can be be seen seen in in left left distance. distance. 9.4 Enter Cuba Cuba City. City. 9.7 Turn left on County County H (best route). left (east) (eas~on 10.9 Junction with County County J. J. Turn right, right, proceed proceed south south on on County County J. J. 11.9 Vinegar Hill Acid Plant, Plant, closed in 1948, 1948, was located south of road. 13.6 Enter Benton. 14.0 14.0 Join State 11. 11. Turn left left (east). (east). are along this this road. road. 21.8 Shullsburg. Enter Shullsburg. 23.1 Right turn (south) (south) on County 0. o. 24.7 Tailings area of of Eagle-Picher Industries, Mine Tailings Industries, Inc. Inc. Shullsburg Mine on left. left. 25.1 Left turn turn (east) (east) on on County County W. W. Numerous abnadoned abnadoned mines mines Wisconsin Geological and Natural History Survey Dept. of of Geology, Geology, TJW—Platteville UW-Platteville U.S. Geological Survey U.S. 16 �Mileages Mileages 25.8 Left Left Stop Stop hat, hat, mine mine 29.8 About noon; noon; return to to Shullsburg Shullsburg for for box box lunch. lunch. turn (north). (north). Entry to Eagle-Picher property. property. Shullsburg Mine. You 55 -— Shullsburg You are are reminded reminded to to have have on hard light, self-rescuer, self—rescuer, safety boots, light, boots, and and glasses. Tour complex with company geologists. geologists. Afternoon, Afternoon, May May 10 Scenic return to Scenic to Platteville. Historical sights en route via via W, include County W, include towns towns of of New New Diggings, and and Hazel Hazel Green. Green. Right turn (north) turn (north) on State 80 and 11 to to Cuba City and and Platteville. Platteville. 57.1 Enter Platteville. Return to Madison. Stop to pick up private Bus will will continue continue to Milwaukee, arriving arriving about about automobiles. Bus to Milwaukee, 6:00 P.M. Geologic Road Road Log for Geologic for Madison Madison Beitline, Beltline, 1—90, 1-90, and and 1-94 1-94 from from Madison, Madison, Wisconsin Wisconsin (Junction (Junction U.S. U.S. 12 12 and and 14 14 with with U.S. U.S. 18 18 and and 151) 151) to to Milwaukee, Milwaukee, Wisconsin (Junction (Junction 1—94 1-94 with 1—43 1-43 and and I_794)*. 1-794)*. 2 Rachel K. K. Paull' paull l and and Richard A. Paull2 paul1 Milwaukee is within the Eastern This route from Madison to Milwaukee is entirely within the Eastern Ridges and at right right angles angles to to the the Ridges and Lowlands physical province, province, and and it it trends trends at general strike of the the Paleozoic Paleozoic formations. formations. Consequently, Consequently, the the bedrock along the route, route, although largely obscured by Woodfordian the Woodfordian glacial glacial deposits, deposits, ranges ranges from Upper Upper Cambrian Cambrian formations formations on on the the west west to to Silurian Silurian dolomite dolomite on on the the east. east. The glacial geology encountered encountered along along 1—94 1-94 is is spectacular. spectacular. As shown shown in in Figure 8, 8, the the interstate interstate cuts most of these these glacial features features essentially at right angles. angles. From From west to to east, east, these these include include well-developed well-developed drumlin drumlin fields, fields, outwash plains, plains, the the Kettle Kettle Interlobate Interlobate Moraine with numerous scenic lakes, lakes, and recessional moraines of of the the Lake Lake Border Border morainic morainic system. system. Other significant significant attractions along this this route route include: include: the Lapham Peak Peak overlook overlook high high in in the the Kettle Moraine and the the subcontinental subcontinental divide divide that that separates separates drainage drainage destined destined for the the North North Atlantic Atlantic via via the the St. St. Lawrence Lawrence from from that that which which reaches reaches the the Gulf Gulf of Mexico Mexico via via the the Mississippi. Mississippi. *This *This road road log log is is published pUblished with with permission permission of of Kendall/Hunt Kendall/Hunt Publishing Publishing Company, Company, Dubuque, Iowa, means without written Iowa, and and it it should should not be duplicated by any means permission. permission. 1 1 University University of of Wisconsin—Madison Wisconsin-Madison && Alverno Alverno College, College, Milwaukee Milwaukee 22 University of Wisconsin-Milwaukee University of Wisconsin-Milwaukee 17 17 �1/ f 1\ .........- I /I ; ' l c•• 3m.1 I "I I II I II ,I II 'pm. ~ GLACIAL LAKE DEPOSITS I ,\ \ ~----<16km ~ ~VALDERAN DRIFT I i-T7@;--.---\fij.+:.w 1._...... I I I II" UE££E1!..S~ Whit_atr- G> ~ I WALWORTH I I I I R.cine r - -++·~4)H+.:f>{ I i--- ..... I I (WOODFORDIAN) IT] RECESSIONAL MORAINE 'i ~ L..nG_..... Figure 8. Figure 8. ::...... ;:. I I I 1·...:·.. :·:1 LAKE BORDER MORAINE rn D TERMINAL MORAINE WOODFORDIAN DRIFT [l] INTER LOBATE MORAINE [Z[] DRUMLIN TRENDS • AL TONIAN DRIFT KENOSHA Glacial deposits deposits of Wisconsin, including of southeast Wisconsin, glacial lake lake deposits, the the Kettle Kettle Interlobate Interlobate Moraine, Moraine, drumlin patterns, patterns, and and the the Lake Lake Border Border morainic morainic system. system. The Altonian drift shown shown in in Rock Rock and and Walworth Walworth counties, counties, Wisconsin Wisconsin also also includes includes drift that that is is older than than Interstates 94, 43, and 90 are also Wisconsinan. Interstates 94, 43, also indicated. Generalized from numerous numerous sources, sources, including Thwaites, 1956. 1956. Mileages Mileages o 0 (83) Intersection of U.S. U.S. 12 and 14 14 with U.S. U.S. 18 18 and and 151 151 on on the the southeast edge of of Madison, Wisconsin. Wisconsin. Turn east on the Madison Beltline (U.S. (U.S. 12, 12, 14, 14, 18, 18, and and 151). 151). Note: This was the the starting point point for for the the U.S. U.S. 151 151 Madison Madison to to Platteville Platteville roadguide roadguide starting provided for Tuesday May 9, 9, 1978. 1978. 11 (82) The wooded tracts on both sides of the highway are parts of the 1,240 acre University of Wisconsin Arboretum. Although primarily aa research and study area, area, hikers are are permitted permitted on on 24 24 miles miles of of extends north from here to foot trails. trails. This nature preserve extends the south shore of of Lake Lake Wingra. Wingra. 3 3 (80) Intersection of of U.S. U.s. 12 and and 18 with U.S. Intersection U.S. 14 and and 151. 151. east on U.S. U.S. 12 12 and and 18. 18. 4.5 (78.5) Monona, north of the Lake Monona, the highway, highway, is is the the second second largest largest of of Madison's four four lakes. lakes. These lakes are the result of Pleistocene erosion and deposition along the the Yahara Yahara River River drainage. drainage. 5.5 (77.5) wooded, irregular ridge visible visible to the the south over over the the flat flat The wooded, irregular ridge part of of the Woodfordian Johnstown-Milton outwash surface surface is is part the Woodfordian terminal moraine system. terminal 6.2 (76.8) Cross the the Yahara River, River, which which connects connects Madison's Madison's four four lakes. lakes. flows southeasterly to to join the the Rock River north The Yahara flows The relatively flat flat land surface of Janesville, Janesville, Wisconsin. The of south of of the the highway highway is is probably probably an an outwash outwash deposit deposit (valley south (valley train) formed formed during the complex Pleistocene history train) history of of the the Yahara River. 18 18 Continue �— Mileages 7.5 (75.5) of U.S. Junction of U.S. 12, 12, 18, 18, and U.S. U.S. 51. 12 and 18. 18. east on on U.S. U.S. Continue east 9.2 (73.8) and 18 with 1—90. Junction of of U.s. U.S. 12 and 1-90. Turn north (left) (left) on on 1—90. 1-90. 12. 12. (71) Interstate 90 90 traverses traverses rolling, rolling, morainal countryside. Interstate 13.7 (69.3) Junction of 1—90 1-90 with with 1—94. 1-94. Turn east on 1—94 1-94 to to Milwaukee. Southeast of of this this intersection, intersection, crushed crushed stone stone is is produced produced from from theMiddle Ordovician Platteville Formation. The underlying St. Peter Sandstone is also exposed in St. in this this quarry. quarry. 18 (65) (65) Exit County NN to to Sun Sun Prairie Prairie and and Cottage Cottage Grove. Grove. Well-developed drumlins, trending southwesterly, rise drumlins, rise above above rolling rolling ground ground moraine, moraine, and and are are cut by by the the interstate. interstate. The irregular, irregular, hilly ridge on the skyline to the the south is is the the Woodfordian Woodfordian MiltonMiltonJohnstown terminal moraine system of the the Green Bay Bay lobe. lobe. 21 (62) Area of poorly poorly drained, drained, peaty peaty soil soil in in an an interdrumlin interdrumlin area. area. A commercial sod sod and mint farm is is north of the the highway. highway. This region is drained by Koshkonong Creek, which crosses This crosses This stream flows into beneath the interstate at Baxter Road. This into Lake Koshkonong to the south, Lake south, after draining aa vast, vast, marshy marshy area. area. 24 (59) Exit Wisconsin 73 Southwest—trending 73 to to Marshall and and Deerfield. Deerfield. Southwest-trending drumlins form islands between swamps within the drumlins the rolling rolling countryside. countryside. Just east of this junction, junction, a a large large number number of of glacial glacial erratics erratics are present. These are part of of the the boulder boulder train train derived derived from from exposures of exposures of the Precambrian Waterloo Quartzite northeast northeast of of here. here. 27 (56) Goose Lake Lake and the swamp to the Goose the south south are are remnants remnants of of aa much much larger shallow lake that once existed between between drumlins drumlins in in this this area. Much of the the land land here here has has been been ditched ditched for for drainage, drainage, but but drumlins still rise as wooded islands some drumlins islands surrounded surrounded by by swamps. swamps. Fossil remains of of aa mastodon mastodon and and aa giant giant beaver beaver dated dated at at 9,000 9,000 to 10,000 years years B.P. B.P. were found in to in shallow peat peat deposits deposits nearby. nearby. 28 (55) Dane/Jefferson county county line. line. Enter Jefferson Jefferson County, and and aa specspectacular array of drumlins. An excellent swarm swarm occurs occurs where where County 0 crosses crosses the the interstate. interstate. The extensively tiered tiered roadcut roadcut at the at the county line provides a a transverse section section through through aa drumlin. Erratic boulders are common in in the the drift drift in in this this area. area. 33 (50) Exit Wisconsin 89 to to Lake Lake Mills and and Waterloo. The rough country immediately west of of here consists of pitted pitted outwash outwash between between patches of of the Lake Mills recessional moraine system. patches system. Rock Lake, Lake, .25 mile mile to to the the southwest, southwest, occupies occupies aa very large kettle. .25 kettle. There are also many small ice stagnation features in are in this this area. area. Most of these are are sandy deposits, of deposits, some of which lap lap onto onto the the margins margins of drumlins. of 19 �Mileages Exposures of Precambrian quartzite exist north and east of Waterloo, where they form low hills waterloo, hills and ledges which protrude through thin thin glacial glacial drift drift (Fig. (Fig. 9). 9). Most of these these outcrops outcrops are polished and striated by glaciation. are Figure 9. 9. Exposures of glacially polished, polished, gently eastwarddipping, Precambrian Waterloo Waterloo Quartzite Quartzite near near dipping, Hubbleton, Wisconsin. Milwaukee Public Museum Hubbleton, Museum photo. photo. This quartzite quartzite is similar to to that exposed in the the BarabooBarabooThis is similar that exposed Devil's Lake Lake area. area. A basal conglomerate is is present between the quartzite quartzite and and the the the overlying Paleozoic sandstone. sandstone. Small Small potholes are scoured scoured on on some some quartzite quartzite surfaces, surfaces, and and bedding bedding potholes are planes are occasionally ripple marked. planes The main outcroppings of of Waterloo Quartzite are about a a mile east of Portland, of Waterloo Creek and Portland, and at the junction of the Crawfish Crawfish River. River. These exposures occur occur on on the the borders borders of of connect4d series series of of marshes, marshes, which which mark mark aa preglacial preglacial valley valley aa connect4d that was was a that a tributary to to the the Rock Rock River. River. 35 (48) Eastbound rest area in in an an area area of of rolling rolling ground ground moraine. moraine. 37 (46) 1-94 crosses crosses the 1-94 the Crawfish River, River, a tributary tributary to to the the Rock. Rock. miles south on the west bank of of this Aztalan State Park is is 1.5 1.5 miles the west this river. In Late Woodland Indian In addition to Late Indian effigy mounds, mounds, this park park contains contains aa two-tiered two-tiered pyramidal pyramidal mound, mound, and and aa partly partly this restored stockaded led with with the the Middle Middle Mississippi stockaded village village identif identified culture. When the the site was first described in in 1837, 1837, it it was named Aztalan in the hope hope that the cultural cultural remains remains preserved here were were those here those of of the Mexican Aztecs. Aztecs. To reach the the park, park, use use the Lake Lake Mills Mills exit and then turn the turn east on on County County B. B. 38 (45) Westbound rest area, area, in in an area of ground moraine and low—lying low-lying drumlinoid hills. hills. 20 �Mileages Mileages 39 39 (44) (44) 1-94 crosses crosses the the Rock Rock River. River. The The Rock Rock marks marks aa general general 1-94 vegetation vegetation divide divide between between native native hardwood hardwood forests forests to to the the east, east, and and oak oak savannas savannas and and prairies prairies to to the the west. west. Some Some think think the the river river formed formed a a barrier to to prairie prairie fires, fires, thus thus preserving preserving the the on the the east. east. forests on Jefferson, Jefferson, 6.5 6.5 miles to to the the south at the the junction junction of of the the Crawfish Crawfish and and Rock Rock rivers, rivers, experienced experienced aa short—lived, short-lived, geology-related, geology-related, land boom boom about about 1840. 1840. A A federally-assisted federally-assisted project project was was planned planned land to to construct a a canal from Lake Michigan at Milwaukee to to the the Rock River River near near Jefferson. Jefferson. Some Some construction construction was was actually actually Rock accomplished accomplished before before the the million—dollar million-dollar project project was was abandoned. abandoned. Meanwhile, Meanwhile, land land values values had had sky—rocketed sky-rocketed in in Jefferson Jefferson as as the the prospect prospect of of a a connection between the the Mississippi River and and Lakes seemed seemed imminent. imminent. Land promoters promoters arrived, arrived, and and the Great Lakes a a steamboat made it it up up the the Rock Rock River River from from St. St. Louis. Louis. Tracts Tracts of of swampland swampland were bought bought by local local residents residents and and newcomers newcomers at at inflated prices, prices, in the hope that great profits would result when· the the canal canal was was completed. completed. The land land promoters promoters left left town town when with well—laden well-laden carpetbags, carpetbags, before before news news of of the the abandonment abandonment of of reached southern southern Wisconsin. Wisconsin. the canal plans reached 40 40 (43) (43) Exit Wisconsin 26 26 to to Watertown, watertown, Johnson Johnson Creek, and and Jefferson, Jefferson, within the the Jefferson Jefferson County County drumlin drumlin field. field. Where the the interstate interstate within drumlin, the roadcuts cuts through a a drumlin, roadcuts have been carefully sodded over to conceal the internal character of the sandy and clayey till. However, However, at the the northwest northwest corner corner of of this this intersection, intersection, behind the service station and restaurant, restaurant, an excavated drumlin is exposeq. is exposed. 46 46 (37) Irregular ground ground moraine moraine assumes assumes symmetry symmetry and and order order as as the Irregular the highway traverses traverses aa classical classical drumlin drumlin field, field, produced produced by by the the highway Green Bay lobe lobe of the the Woodfordian Woodfordian ice ice advance advance (Fig. (Fig. 10). 10). These drumlins trend essentially north-south north—south in in this area, but but nearer nearer drumlins trend essentially this area, to Madison Madison the orientation was southwesterly. to southwesterly. Poorly drained drained areas areas and and tamarack tamarack swamps swamps flank flank many many of of the Poorly the drumlins this area. area. drumlins in this 50 50 (33) (33) Wisconsin 135 exit. 52 52 (31) (31) Enter Waukesha Waukesha County. County. The Jefferson/Waukesha county line. Jefferson/Waukesha line. Enter drainage in this rolling countryside is poor, and farm fields fields drainage in this rolling countryside is poor, and farm Numerous tamarack swamps with red osier must must be ditched. ditched. Numerous tamarack swamps with red osier dogwood are are lingering lingering evidence evidence of of the the boreal boreal climate climate of of the the dogwood Pleistocene. Pleistocene. 21 21 �Figure 10. 10. An intensively—farmed, intensively-farmed, north—south north-south trending drumlin Sullivan, in Jefferson County, Wisconsin. In near Sullivan, this this area, area, these streamlined hills hills are are so so numerous numerous that they are termed a a drumlin swarm swarm or or field. field. Milwaukee Public Public Museum Museum photo. photo. Mileages 55 (28) (28) Wisconsin Wisconsin 67 67 exit exit to to Oconomowoc Oconomowoc and and Dousman. Dousman. The interstate interstate now traverses outwash and proglacial lake lake sediments sediments in in an an area area once occupied by the the Green Bay lobe during the the Woodfordian Woodfordian ice ice advance. To the the east, east, the the view view of of the the Interlobate Interlobate Moraine Moraine looming above the flat outwash surface surface is is impressive. impressive. A A few overgrown kettles are adjacent to to the the highway on on the the south south side. side. To the the north, north, rising rising above above the the flat flat outwash outwash plain, plain, is is an an inconincongruous gruous landform that that resembles the the classic moulin moulin kames kames of of the the northern northern Kettle Kettle Moraine. Moraine. This is is an an artificially—created artificially-created ski ski hill near Oconomowoc. 59 (24) (24) provides a a side trip to to view the the Kettle An exit on County CC provides Kettle Interlobate Moraine from the the observation observation tower tower on on Lapham Lapham Peak Peak (Fig. This tower (Fig. 11). 11). tower provides provides an an excellent excellent overview overview from from the the highest vantage vantage point point in in the the southern southern Kettle Kettle Interlobate Interlobate Moraine. Moraine. To the the west west is i~ Genesee Genesee Flat. Flat. To the the east is is the the glacial spill— spillway described described at at Mile Mile 61. 61. Several scenic scenic glacial glacial lakes lakes are are also visible. visible. 22 22 �Figure 11. 11. Kettle Interlobate A scenic overview of of the southern Kettle Interlobate Moraine from the the observation tower tower on on Lapham Lapham Peak. Peak. Photo by Professor R.F. Black, University of University of Connecticut. To reach Lapham Peak, To Peak, go south on County CC (Kettle (Kettle Moraine Moraine Scenic Drive) Drive) about 1.8 miles to a crossroad. Scenic crossroad. Turn left (east) (east) onto Government Hill Hill Road. Road. Continue about 0.7 mile to to a a small small The tower park that that includes includes the the Lapham Peak observation tower. park tower. The A marker at 1233 for state station WHAD is also located for located here. A feet of of elevation, elevation, on a feet a glacial erratic boulder boulder in in the the park, park, is is dedicated to one of Wisconsin's earliest geologists dedicated geologists and and "Increase A. A. Lapham, Lapham, Eminent scientist and naturalists: and useful naturalists: "Increase citizen". citizentt. The route ahead crosses a a region of pitted pitted (kettled) (kettled) outwash outwash Nagawicka deposits, and and many many kettle kettle lakes dot the deposits, lakes dot the landscape. landscape. Nagawicka Other Lake, immediately immediately north of of the highway, is such a Lake, the highway, a lake. lake. Other examples are are Upper Upper and and Lower Nemahbin lakes, examples lakes, which sandwich the the 23 23 �Mileages interstate about 1 mile west west of of here. here. The The ice ice blocks blocks which formed these lake basins basins were were derived derived from from the formed these lake the Green Bay lobe lobe along the the western western edge of of the Interlobate Moraine. along 60 (23) The interstate approaches the The the crest crest of of the the Interlobate Interlobate Moraine. Moraine. A small ski area south of the highway utilizes part of this this slope. From the crest of this this ridge, ridge, the radio tower tower and observation tower on Lapham Peak Peak are are visible visible south south of of the the highway. highway. The Kettle Kettle Interlobate Moraine, whi.ch which trends trends northeasterly northeasterly across across The Interlobate Moraine, miles, from Walworth to Wisconsin for about 130 miles, to Kewaunee counties is the premier glacial feature in is in Wisconsin. It It is is probable that the the resistant Silurian that the position Silurian dolomite dolomite influenced influenced the of the deposits in in this area, by by retarding retarding the of the interlobate interlobate deposits this area, the spread of the the Green Green Bay Bay lobe. lobe. Within this this morainal complex, complex, the country is rolling and rugged, rugged, with abundant abundant knobs knobs and and kettles. kettles. This feature formed during the the Woodfordian glacial advance by a a juxtapositioning of the the terminal terminal moraines of of the the Green Green Bay Bay and and Lake Lake Michigan Michigan lobes. lobes. Between these icy walls, walls, complex complex drainageways drainageways developed, developed, and and meltwaters meitwaters these icy reworked some of the morainal materials. The resultant resultant deposits deposits are a a mixture of of sand, sand, gravel, gravel, boulders, boulders, and and clayey clayey till. till. Much of the coarser material was derived from of from the the Silurian Silurian dolomite, dolomite, but igneous and metamorphic metamorphic rock rock types from far far to to the the north but igneous and types from are also present. present. 61 (22) Wisconsin 83 Wisconsin 83 exit. exit. This'highway This/highway follows follows low ground along an agandoned drainage drainage channel channel which which carried carried the the last last meltwater meltwater agandoned that drained southward southward through through this this part part of of the the Kettle Kettle Inter— that drained Interlobate Moraine. Water drained drained down down this this .25 .25 mile mile wide wide valley valley until it reached Wales, Wales, about about 33 miles miles to to the the south, south, where where it until it reached cut through the Interlobate Interlobate Moraine to to flow flow west. west. Gravel flank this this drainage, drainage, and and aa remnant remnant of of aa high outwash terraces terraces flank terrace is is visible on the the east side side of of this this valley. valley. 62 62 (21) Pewaukee Lake Lake lies lies to to the the north. north. The church at Holy Hill, Hill, a kame high on on the the Interlobate Interlobate Moraine, Moraine, is is also also visible visible kame perched perched high to the north on aa clear clear day. day. Pewaukee Lake occupies a a pre— preglacial river valley which was scoured into the Upper Ordovician Maquoketa Shale. Shale. This ancient valley was Maquoketa was blocked by morainal debris deposited along its eastern margins by the the Lake Michigan lobe during the Woodfordian ice ice advance. advance. 63 63 (20) Ground moraine deposits deposits in in this this area area are are thin. thin. North of the the highway on the west edge edge of of the golf course, course, there the west the Tumblebrook golf there is is a a small quarry quarry in in Silurian Silurian dolomite. dolomite. Glacial striae striae on on bedbedrock in this area indicate indicate that that ice ice movement movement was was west—southwest. west-southwest. South of the the Valley), and and character of road, names of of aa subdivision (Pebble road, the the names a farm (Stoney (Stoney Hill), Hill), bear testimony testimony to to the the the morainal material. the 24 �Mileages 65 (18) Exit County GG to to Pewaukee. Pewaukee. A A drumlin field lies lies south of the the highway for the the next next several several miles. miles. These east-west trending trending drumlins abundant drumlins are composed of of sandy clay till till that that contains contains abundant boulders. 68 (15) Exit County County F. F. West of of this this intersection, intersection, the the route route crossed the Pewaukee River, River, which is the is tributary tributary to to the the Fox. This valley valley is paralleled by outwash terraces, is terraces, which are are commercial commercial sources sources of sand sand and and gravel gravel in in this this area. area. 69 (14) Exit Wisconsin 164 164 to to Sussex Sussex and and Waukesha. Waukesha. East—west East-west trending trending drumlins are north and and south south of of the the highway. highway. Dunbar, while visiting Waukesha in 1869, Colonel Dunbar, 1869, drank from from some of of the springs which issue some issue from the the glacial glacial drift drift in in this this area with high amounts of dissolved calcium area calcium magnesium magnesium bicarbonate. bicarbonate. Upon deciding that the local Upon local mineral waters had had eliminated eliminated his his !tincurable ailments", ailments", he he began began to to advertise advertise his his cure cure nationwide, nationwide, "incurable and Waukesha Waukesha soon became a and a fashionable health health spa. spa. Although this fad waned after about 30 this fad 30 years, years, bottled bottled spring spring water water is is still a Waukesha product. product. Waukesha is is located located on on the the Fox Fox River. River. Outwash terraces terraces along along this this river are important commercial sources sources for for sand sand and and gravel. gravel. Since the glacial drift drift is quite thin in this this region, region, Silurian dolomite is extensively quarried along the the valley oC of the the Fox from the from the Waukesha area northward to to Sussex, Sussex, Lannon, Lannon, and and Menomonee Falls. Falls. 71 (12) Road) to Waukesha and Wisconsin State Exit U.S. U.S. 18 (Blue (Blue Mound Road) Patrol headquarters. headquarters. 74 (9) Moorland Road. Road. The flat terrain here is is poorly poorly drained, drained, Exit Moorland clay—rich ground moraine. Ditching and clay-rich and channelization channelization were required for for the extensive development of required of the the land land north north of of the highway. The golf course to to the the south south represents represents aa more more intelligent land land use. use. A A few few isolated isolated patches patches of of moraine, moraine, and and east—west trending drumlins rise several east-west rise above above the the generally generally swampy ground. The route ahead ahead descends descends aa prominent prominent ridge, ridge, which which is is part part of of the Woodfordian Woodfordian Lake Border recessional the recessional moraine system. system. Sunny Slope Road traverses this forms the drainage drainage divide divide this crest, crest, which forms between Lake Michigan Michigan and and the the drainage drainage basin basin of of the the Fox Fox River. River. The Fox flows southward southward parallel parallel to to the the Woodfordian Woodfordian moraines moraines to to reach the Illinois River, River, and and ultimately ultimately the the Gulf Gulf of of Mexico Mexico via the Mississippi. 76 (7) Milwaukee/Waukesha county county line. line. 78 (5) Exit 1—894 45 north to 1-894 (U.S. (U.S. 45) 45) south to Chicago and and U.S. U.S. 45 du Lac. Lac. The Milwaukee County Zoo Zoo is is northwest northwest of of this this Fond du intersection. 25 Enter Milwaukee County. County. �Mileages 79 79 (4) (4) Wisconsin State Exit Exit Wisconsin Wisconsin 181 181 (84th (84th Street). Street). The Wisconsin State Fair Fair Park grounds and an Olympic-size Olympic—size outdoor outdoor ice are southeast grounds and ice rink are of of this this junction. junction. The interstate traverses traverses Wisconsinan (Woodfordian) ground moraine and recessional moraines of (Woodfordian) ground of the the Border system. system. The highway here is essentially parallel Lake Border to the east—west direction of of ice movement, and and consequently the east-west ice movement, the inorainic ridges trend north-south. About 100 morainic ridges 100 feet feet of of glacial glacial deposits, deposits, primarily primarily a boulder clay till, till, overlie Silurian dolomite in in this this area. area. 81 (2) U.S. u.S. 41 exit (north (north and and south). south). Milwaukee Milwaukee County County Stadium, Stadium, home home of the the Milwaukee Brewers and also the the site of the the Milwaukee games of the the Green Bay Packers, Packers, is is just just west west of of this this junction. junction. The large large hill southwest of the the stadium is a Silurian dolomite of the Veterans Administration exposure on the the grounds grounds of the U.S. U.S. Veterans Hospital. 82 (1) Route parallels parallels the the industrial industrial complex complex along the the east—west east-west Menomonee River River valley. valley. Three large, large, glass glass domes in in trending Menomonee Mitchell Park Park are are visible visible to to the the south. south. One contains aa display of vegetation native to a desert environment, environment, another features features a desert tropical houses local flora and is often tropical plants, plants, and the last houses local flora used for special special flower flower shows. shows. 83 (0) Junction 1—94 1-94 with with 1—43 1-43 (U.S. (U.S. 141) 141) and and 1—794. 1-794. The Milwaukee Harbor is is to to the the woutheast, toward toward the the high—rise high-rise Harbor Freeway bridge along along the the lakeshore. lakeshore. Three rivers rivers merge at the Milwaukee Harbor, Harbor, the Menomonee west, the Milwaukee River comes River flows flows from the the north and west, from the the north, north, and the Kinnickinnic Kinnickinnic River originates to the west and and south. south. Milwaukee grew from three settlements that were originally separated by these these rivers. rivers. Walker's Point, Point, east east of of the the Kinnickinnic River, River, is now dominated by the towering towering clock of the Allen Bradley Company. Company. The Milwaukee River flowed between Kilbourntown on the west and Juneautown Juneautown to to the the east. east. The high smokestack to the the east is part of of the Jones Island Island Here, sewage sludge is dried and Sewage Plant. Plant. Here, and Metropolitan Sewage Milorganite, aa commercial converted to Milorganite, commercial fertilizer. fertilizer. Jones Island, Jones Island, an artificially breached breached peninsula, peninsula, also also contains contains aa tanker pier, pier, cargo terminals terminals and and aa heavylift heavylift wharf, wharf, and and is is headquarters for the the Port of of Milwaukee. Milwaukee's inner harbor was was developed developed by by an enlargement enlargement of of the lower Kinnickinnic Kinnickinnic the lower River, and it serves serves as as the and wintering wintering area for for part River, the service service and part of U.S. U.S. Steel's Steel's iron ore carrier fleet. of fleet. END OF LOG through downtown Milwaukee to the Pfister Proceed through Pfister Hotel; Hotel; headheadquarters for for the the 24th 24th annual annual meeting meeting of of the the Institute Institute on on Lake Lake quarters Superior Geology. We hope you enjoy enjoy your your stay stay in in Milwaukee! Milwaukee! 26 �— GX)LOGICAL GIDLOGICAL STOP SIDP DESCRIPTIONS DESCRIPTIONS Page Stop Stop 1I —- Hoadley Hill Hill Hoadley 28 28 Upper Upper part part of of the the St. St. Peter Peter Sandstone, Sandstone, the the Glenwood Glenwood Formation, Formation, aa complete complete section section of of the the Platteville Platteville Formation, Formation, and the the lower lower part part of the the Decorah Formation Stop 22 —- Section Section 22 Quarry Quarry Stop 32 32 QUimby's Mill Mill (upper (upper part part of of the the Platteville Platteville Quimby's Formation) Formation) Stop 33 —- Potosi. Potosi Hill Hill Stop 33 33 Upper part of the Platteville Formation, Formation, the Decorah Formation, Formation, and the lower part of the Galena Galena Formation (Snake Cave) Cave) Stop 44 —- St. John Mine (Snake Dunleith Member (cherty (cherty (non-cherty upper (non—cherty upper unit) unit) 37 37 lower unit) and and Wise Lake Lake lower of the Galena Formation Formation 27 27 �Title: Title: Hoadley Hill Hill Hoadley Location: Exposure Exposure in in roadcut roadcut at at north north side side of of U. U. S. S. Highway Highway 151 151 about about 6.5 6.5 miles southwest of of Platteville Platteville in in the the NW!, NW, NWI, Sec. Sec. 12, 12, T.2N., T.2N., R.2W., R.2W., Grant Grant County (Dlckeyville (Dickeyville 7.5—minute 7.5-minute topographic topographic quadrangle, quadrangle, 1972), 1972). Author: NWt, M. M. E. E. Ostrom (modified (modified from Agnew et. al., al., 1956) 1956) section for for the the Platteville Platteville Formation. Formation. Description: This is the reference section exposed qere lere are are the the upper upper part part of of the the St. St. Peter Peter Sandstone, Sandstone, the the The strata4 strat~exposed Formation, a Formation, and the Glenwood Formation, a complete section of of the Platteville Formation, the lower et. al,, al., (1956) (1956) lower part part of of the Decorah Formation. Description from Agnew et. is: ORDOVICIAN SYSTEM Decorah Formation Spechts Ferry Shale Member Member (+1.0 (+1.0 feet) feet) 62.9' - 63.4' 62,9' — 0.5'+ Shale, bluish—green. Shale, bluish-green. 62.7' — 62.7' - 62.9' 0.2' Bentonite, white; Bentonite, white; weathers weathers orange orange brown. brown. 62.7' 62.5' — 62.5' - 62.7' 0.2' Shale, yellowish-green yellowish—green above above to bluish-green below. below. Shale, 28 �62.4' —- 62.5' 62.5' 62.4' 0.1' 001' Shale, Shale, brown brown and and olive, olive, soft. soft. Platteville Platteville Formation Formation (54.3 (54.3 feet) feet) Quimbys Quimbys Mill Mill Member Member (0.3 (0.3 —- 0.5 0.5 feet) feet) 62.0' —- 62.4' 62.4' 62.0' 0.4'+ 0.4'± Limestone, Limestone, conchoidal conchoidal dark—brown dark-brown parting parting at at dark dark purple, purple, fine—crystalline, fine-crystalline, dense, dense, fracture; fracture; very very wavy wavy upper upper surface; surface; thin, thin, to to black, black, fossiliferous fossiliferous platy platy shale shale base. base. McGregor McGregor Limestone Limestone Member Member (30.9 (30.9 feet) feet) 61.1' —- 62.0' 62.0' 0.9' 0.9' Limestone, Limestone, light—gray, light-gray, very fine fine crystalline, crystalline, very very dense, dense, conchoidal fracture like like "glass rock" rock" above, above, fairly massive, massive, very very fossiliferous; fossiliferous; wavy upper upper surface. surface. 60.4' —- 61.1' 61. l' 60,4' 0.7' 0.7' Limestone as next above above but less less dense, medium— mediumbedded above to to thinthin- bedded below, fossiliferous; fossiliferous; wavy upper surface. surface. 58.8' —- 60.4' 1.6' Dolomite, light Dolomite, light olive drab, drab, fine fine crystalline, crystalline, "sugary", argillaceous, argillaceous, very very thin—bedded; thin-bedded; molular, molular. 55.8' —- 58.8' 3.0' Dolomite as above above but thick—bedded; thick-bedded; calcite calcite near near middle. 55.2' —- 55.8' 55.2' 2.6' Limestone, thin—bedded Limestone, thin-bedded yet stands massively as one unit; light greenish unit; greenish gray gray brown; brown; weathers weathers brown, brown, with a a few argillaceous streaks; streaks; sparingly fossiliferous, ferous, but with fossils fossils and and fucoids fucoids on on top top surface. surface. 51.8' — - 55.2' 55.2' 51.8' 3.4' Limestone, Limestone, thin—bedded thin-bedded as above but the the beds are a~e distinct; modular beds and shaly partings; distinct; partings; argillaceous is is upper 0.3 feet, ceous feet, which which is is very very fossiliferous, fossiliferous. 48.2' - 51.8' 51.8' 48,2' — 3.6' 3,6' Limestone, light buff ish gray, gray, in in medium medium to to thick Limestone, buffish beds; in places beds; places gradational gradational into into above above unit, unit. 44.3' - 48.2' 48.2' 44,3' — 3.9' 3,9' Limestone, light light greenish to to bluish gray, gray, in massive Limestone, beds but but composed composed of of thin thin beds beds which are are not sepabeds rated; ample ample shaly shaly material material in in wavy wavy bands; bands; fairly fairly rated; fossiliferous, argillaceous; argillaceous; aa peculiar mottled fossiliferous, light gray gray and and darker darker gray 0,1-foot light O.l-foot zone, zone, 11 foot foot below top, top. 40.3' 44,3' 40.3' -— 44.3' 4.0' 4,0' Limestone, light light gray, gray, very very fine fine crystalline, crystalline, very very Limestone, dense, sublithographic, sublithographic, in. in extremely extremely thin thin and and modumodudense, lar beds beds with with thin thin calcareous calcareous shaly shaly partings partings which which lar become thinner thinner below; below; the the shale shale beds beds are are light light become grayish blue,mottled, blue,mottled, very very fossiliferous; fossiliferous; weathers weathers grayish slightly recessed. recessed, slightly 29 29 �36.7' —- 40.3' 40.3' 36.7' 3.6' 3.6' Limestone, Limestone, as as above, above, but but beds beds are are not not quite quite as as thin; thin; fossiliferous; fossiliferous; poor poor gastropod gastropod zone zone 1.7 1.7 feet feet above above base; base; shaly shaly zone zone at at base, base. 33.1' —- 36.7' 36.7' 33.1' 3.6' 3.6' Limestone, Limestone~ dolomite, dolomite, light—gray, light-gray, fine fine crystalline, crystalline, very very slightly slightly argillaceous, argillaceous, very very fossiliferous, fossiliferous, medium—bedded; medium-bedded; Indistinct indistinct argillaceous argillaceous partings, partings, not not wavy; wavy; calcite calcite and and limonite, limonite, especially especially In in basal basal 0.6 0.6 feet. feet. Pecatonica Pecatonica Dolomite Dolomite Member Member (21.5 (21.5 feet) feet) 28.3' —- 33.1' 33.1' 28.3' 4.8' 4.8' Dolomite, Dolomite, light light grayish grayish brown, brown, very very coarse coarse crystalcrystalline and vuggy, vuggy, upper 2 feet a mixture of of lithology lithology and a somewhat argillaceous fine crystalline "sugary" "sugary" laminated dolomite; dolomite; a 1-foot I-foot bed of very very vuggy vuggy dolomite dolomite from from 1.8 1.8 to to 2.8 2.8 feet feet above above base; base; shaly shaly in lower part; part; stylolitic partings 1 foot above above base. base. 21.4' —- 28.3' 21.4' 6.9' DolomIte, gray, laminated, laminated, somewhat argil— Dolomite, mediuin medium-gray, argillaceous, laceous, fine—crystalline fine-crystalline "sugary", "sugary", fossiliferous, fossiliferous, especially in lower 0.9 feet; feet; medium— medium- to to thick— thickbedded; shaly at top; bedded; top; weathers brownish in in lower lower 2.5 feet. 17.8' —- 21.4' 3.6' Dolomite, medium medium gray, gray, laminated, laminated, argillaceous; argillaceous; very fossiliferous partings. partings. 16.4' 17.8' 16.4' —- 17.8' 1.4' 1.4' Dolomite, light light grayish grayish brown, brown, very very coarse coarse crystalcrystalline and and vuggy; vuggy; thin thin brownish gritty dolomitic line and platy shaly parting at top. and top. 13.6' 16.4' 13.6' -— 16.4' 2.8' 2.8' Dolomite, medium gray, Dolomite, gray, laminated, laminated, somewhat argillaceous, fine crystalline. laceous, H.6' 13.6' 11,6' -— 13.6' 2.0' 2.0' Dolomite, medium gray, Dolomite, gray, laminated, laminated, argillaceous, argillaceous, silty and and sandy sandy with with fine fine to to coarse coarse quartz quartz grains grains silty similar to to those those of of the the St. St. Peter Peter Sandstone, Sandstone, phossimilar phate nodules nodules abundant (especially phate (especially in in two two zones, zones, one at at base, base, the the other 1 foot above one above base). base). Glenwood Formation (1.5 (1.5 feet) feet) 11.2' 11.6' 11.2' -— 11.6' 0.4' 0.4' Shale, sandy with rounded quartz grains, Shale, grains, khaki to to drab, soft; drab, soft; phosphate nodules. H.O' 11.2' 11.0' -— 11.2' 0.2' 0.2' Shale, sandy, sandy, olive olive to to grayish grayish brown; brown; mottled mottled Shale, yellowish brown, brown, friable. friable. yellowish 10.4' 11,0' 10.4' -— H.O' 0.6' 0.6' blocky, Shale, sandy, sandy, mediummedium— to dark—gray, Shale, dark-gray, olive, olive, blocky, very hard, very hard. 30 30 �10.1' — 10.1' - 10.4' 0.3' Shale, medium-gray, medium-gray, blocky; blocky, hard, Shale, hard, sandy; sandy; streak of carbonaceous material at at top. top. St. Peter Sandstone Formation St. Formation (÷10,2 (+10.2 feet) feet) 10.0' — 10.1' 10.0' - 0.1' Sandstone, red and white; white; rounded; Sandstone, rounded; frosted, frosted, coarse to medium-grained. medium—grained. 9,8' 9.8' —- 10.0' 0.2' Sandstone, gray, Sandstone, gray, pinkish, pinkish, very very friable. friable. 9.7' 9.7' —- 9.8' 0,1' 0.1' Sandstone, brown, Sandstone, brown, iron—stained, iron-stained, hard. hard. 8.4' — 8.4' 9.7' 9.7' 1.3' 1. 3' Sandstone, yellow to gray, Sandstone, gray, very friable, friable, with irreirregular lower lower surface. surface. 8.3' — 8.3' - 8.4' 8.4' 0,1' 0.1' Sandstone, light—gray, Sandstone, light-gray, very very friable. friable. 8,1' — 8.1' - 8,3' 8.3' 0.2' Sandstone, yellow to Sandstone, to dark—brown, dark-brown, laminated, laminated, hard, hard. 7.0' 7.0' —- 8.1' 8.1' 1.1' 1.1 ' Sandstone, gray and yellow; Sandstone, yellow; hard irregular lower lower surface. - 7,0' 7.0' 7.0'+ Sandstone as above, above, but but medium— medium- to to fine-grained; fine-grained; spoils. 0.0' 0.0' — EXPOSURE BASE OF EXPOS URE Significance: This is the reference section section for for the the Platteville Platteville Formation. Formation. The contact relationships and lithologies of the St. St. Peter, Peter, Glenwood, Glenwood, Platte— Platteville, and Decorah Formations can be examined. yule, and Note the lithology, mineralogy, and structure of the St. Formation, lithology, mineralogy, St. Peter Formation. What direction did it it come from? Does it contain evidence of life? How do for its mineral homegeniety? What was the you account for the environment environment of of deposideposiit change toward toward the the top? top? What is is the the significance significance of of no no change? change? tion? Does it of of change? What is is the the relationship of of the the St. Peter Peter to to the the Glenwood? Glenwood? Note the various beds beds of of the the Glenwood, Glenwood. What is is their their significance? significance? If If they could for long distances distances of of several hundred miles, miles, what would be the signibe traced for ficance? What is is the the nature and and significance significance of of the the Glenwood/Platteville conconlithology, i.e. i.e. phosphate nodule beds, beds, tact? Note the variable Platteville lithology, fossil etc. What is is their their significance? significance? What would be be the the fossil beds, beds, sandy beds, etc. significance if if they could be be traced several.hundred several. hundred miles? References: Dapples, Dapples, 1955; 1955; Agnew et. et. al., al., 1956; 1956; Templeton Templeton and and Willman, 1963; 1963; Ostrom, 1964 and Ostrom, and 1970. 1970. 31 �Title: Title: Section 2 Quarry Section Location: Abandoned Abandoned quarry on west side of gravel road Location: road about about 0.7 0.7 miles miles north north of U. S. Highway 151 about 0.3 miles west of Piddington Cementary in the the SW!, SW, of U. S. Highway 151 about 0.3 miles west of Piddington Cementary in SW, SE, Sec. 2, T. 2 N., R. 2 W., Grant County (Dickeyville 7.5—minute SW!, SE!, Sec. 2, T. 2 N., R. 2 W., Grant County (Dickeyville 7.S-minute topographic quadrangle, quadrangle, 1972). Map location location on Hoadley Hill Hill description. topographic description. See Hoadley Hill Hill description. description. QUimby's Quimby's Mill Mill Member of Decorah Description: See ,Formation is is well well exposed. Excellent Excellent Middle Middle Ordovician Ordovician fossil fossil locality. "Formation locality. 32 32 �Title: Title: Potosi Hill Hill Potosi at east east side side of of U. U. S. S. Highway Highway 61 61 in inthe theSW!, SW, NW!, NW, Sec. Location: Location: Roadcut Roadcut at Sec. 7, 7, R.2W., Grant Grant County. County. (Potosi (Potosi 7.5-minute topographic topographic quadrangle, quadrangle, 1972), 1972). T.2N., R.2W,, Author: M. E. E. Ostrom Ostrom (modified from Cline dine et M. (modified from et al, aI, 1956, 1956, Kruse, Kruse, 1970). 1970). in Description: The lower part of the section exposed here can be examined in The major major emphasis emphasis here here is is focused focused closer detail at the the Hoadley Hill Hill Stop. Stop. The uppör part wh~ch which includes Ferry, Guttenberg, Guttenberg, and Ion on the the upper includes the Spechts Ferry, Ion Members of of the bers the Decorah Shale Formation and and the the lower part of the Galena Dolomite The Quimbys Quimbys Mill Mill Member consists consists of purplish gray-brown, Formation. The gray-brown, sublitho— sublithographic, thick-bedded, thick—bedded, conchoidally fractured fractured limestone graphic, lilnestone with uneven upper surIt is is called called the the "Glass "Glass Rock" Rock" locally locally because because face base. It face and and shale at its base. when broken, broken, and and when broken pieces pieces are are shaken together, when together, it sounds like broken glass. The Quimbys Quimbys Mill Mill is is overlain overlain by by the the Spechts Spechts Ferry Ferry Member Member which which consists consists The of fossiliferous, fossiliferous, gray-brown gray—brown limestone limestone with with green green shale shale interbeds. interbeds. At this of this Metabentonite exposure two thin beds of "metabentonite" occur near its its base, base. Metabentonite The metametais of volcanic volcanic ash ash dust. dust. The is believed believed to to be be the product of alteration of bentonites are are orange orange to to light light reddish brown and about 2 inches thick. bentonites thick. The The Spechts Spechts Ferry Ferry is is overlain overlain by by the the Guttenberg Guttenberg Limestone Limestone Member Member which which 33 �consists of of hard, hard, finely consists fossiliferous, light light brown, brown, finely crystalline, crystalline, thin-bedded, thin—bedded, fossiliferous, limestone with with brown brown carbonaceous shale interbeds, limestone interbeds. The The presence presence of of these these interbeds has has led led to to the the member member being being referred referred to to as as the the "Oil "Oil Rock" Rock" in in the interbeds the southwest Wisconsin Wisconsin zinc-lead zinc—lead mineral district, southwest district. The Ion Dolomite Dolomite Member overlies the The the Guttenberg. Guttenberg. It It is is aa gray gray to to blue dolomite, medium-crystalline, medium—crystalline, and and medium-to medium—to thick-bedded thick—bedded with with green dolomite, green shale shale interbeds, It It is is locally called interbeds. called the the "Bluet'. "Blue". The Galena Dolomite Formation overlies the The the Ion, Ion. It It is is aa light light buff buff to drab, cherty, cherty, thick-bedded, thick—bedded, vuggy vuggy dolomite dolomite with with medium medium to drab, grains. to coarse coarse sugary grains, The basal basal contact is gradational. gradational. A zone of of Prasopora insular The is Ulrich marks insularis marks the top top of of the Ion Member in some areas. the areas. It It is is absent here. here, Good fossil hunting in in the the Spechts Spechts Ferry Ferry and and Guttenberg Guttenberg Members. Members. Near the north end of of the roadcut there is is a a quarry in which can be seen seen an example of is the main site of of zinc and of "pitch-and-flat" "pitch—and—flat" structure which is lead mineralization mineralization in the district, lead district. Here Here there there is is no mineralization. mineralization, Description of outcrop follows: follows: ORDOVICIAN SYSTEM Galena Dolomite Formation Cherty Unit 45.8' — 45.8' - 65.8' 65.8' 20.0' Dolomite, yellowish-buff, yellowish-buff, medium—to medium-to coarse—grained, coarse-grained, Dolomite, vuggy, chert in in upper upper 10', 10'. vuggy, abundant white chert Decorah Decorah Formation Formation (43,8 (43.8 feet) feet) Ion Dolomite Member Member (19,5 (19.5 feet) feet) (Gray unit) 38 3' —- 45 8' 38.3' 45.8' 7,0' 7.0' buff, thick-to thick-to massive—bedded, massive-bedded, vuggy, vuggy, Dolomite, buff, green shale shale partings throughout, throughout, sparry sparry calcite calcite present. present. 33,8' 33.8' —- 38.3' 38.3' 5.0' 5.0' Covered Covered interval, interval. 32,8' 32.8' —- 33.8' 33.8' 1.5' Dolomite, buff, buff, medium—grained, medium-grained, medium—bedded, medium-bedded, with with green green shale shale partings, partings. (Blue unit) unit) 27.2' 27.2' —- 32.3' 32.3' 5.1' 5.1' Dolomite, purplish purplish gray, gray, medium—grained, medium-grained, slightly slightly Dolomite, fossiliferous. fossiliferous. Green Green shale shale present present as as partings, partings, and as as a 05' 0.5' bed bed 0.8' 0.8' below below the the top top of of the the interinterand val, val, calcite calcite present. present. 26.3' 26.3' —- 27,2' 27.2' 0,9' 0.9' Shale, green. green. Shale, of of interval, interval. 0.3 green green dolomitic dolomitic shale shale in in middle middle 0.3 Guttenberg Guttenberg Limestone Limestone Member Member (15.3' (15.3' feet) feet) 34 34 �21.7' 21.7' —- 26.3' 4.6' Limestone, Limestone, purplish brown, brown, fine-grained to to sublithosublithographic, graphic, fossiliferous, fossiliferous, upper 1' l' fine—to fine-to medium— mediumgrained, grained, brown shale shale present as as partings, partings, calcite calcite and limonite after iron iron sulfide sulfide present present in in small small amounts. 21.6' —- 21.7' 21.6' 0.1' Metabentonite, brownish brownish orange, orange, crumbly, crumbly, sticky sticky when when wet. wet. 12.0' -- 21.6' 9.6' 9.6' Limestone, Limestone, purplish brown, brown, sublithographic, sUblithographic, thinthinwavey—bedded, wavey-bedded, fossiliferous, fossiliferous, brown brown carbonaceous carbonaceous shale present as thin thin beds and partings, partings, calcite calcite and limonite limonite present. present. 11.0' - 12.0' 12.0' 11.0' — 1.0' 1.0' Limestone, Limestone, brown—gray, brown-gray, Line—grained, fine-grained, thick-bedded. thick-bedded. Spechts Ferry Shale Shale Member Member (9.0 (9.0 feet) feet) 11.0' 10.2' —- 11.0' 0.8' Shale, Shale, orange—gray, orange-gray, calcareous, calcareous, and and limestone, limestone, tan— tangray, gray; fine—grained, fine-grained, limestone limestone 0.4' 0.4' to to 0.7' 0.7' from from base of of unit. unit. 9.6' —- 10.2' 9.6' 0.6' Limestone, gray, gray, fine—grained, fine-grained, thin-bedded. thin-bedded. 6.4' 6.4' —- 9.6' 9.6' 3.2' 3.2' Shale, Shale, gray, gray, green, green, brown, brown, fissle, fissle, some some beds beds fossi— fossiliferous, limestone limestone present as thin lenses near liferous, middle of of the the interval. interval. 5.6' 5.6' —- 6.4' 08' 0.8' Limestone, Limestone, tan, tan, with iron iron oxide mottlings, finefinegrained, thin—bedded. thin-bedded. 3.9' 3.9' —- 5.6' 5.6' 1.7' Shale, gray-green—brown. gray-green-brown. Fissle, with with thin thin lenses lenses Shale, of gray fine-grained fine—grained limestone. of limestone. 3.2' 3.2' —- 3.9' 0.7' Limestone, Limestone, dark to light gray, gray, thin-bedded, thin-bedded, fossilfossilif erous. iferous. 2.7' —- 3.2' 2.7' 3.2' 0.5' Shale, Shale, brown—green-orange—gray, brown-green-orange-gray, brown carbonaceous carbonaceous shale parting at top, top, metabentonite metabentonite near near middle. middle. 2.2' —- 2.7' 2.2' 2.7' 0.5' Limestone, Limestone, purplish-brown, purplish-brown, fine-grained, fine-grained, thin— thinbedded, bedded, very fossiliferous, fossiliferous, fucoids at at base. 2.2' 2.0' —- 2.2' 2.0' 0.2' Metabentonite, orange, Metabentonite, orange, sticky when wet, wet, with with brown brown shale partings. Platteville Formation Quimbys Mill Member Member (1.2 (1.2 feet) feet) 2.0' 0.8' — 0.8' - 2.0' 1.2' Limestone, purplish gray-brown, gray-brown, sublithographic, Limestone, sUblithographic, thick—bedded, conchoidal fracture, fracture, irregular upper thick-bedded, surface, shale at surface, at base. base. 35 �McGregor Limestone Limestone Member Member (0.8 (O8 feet) feet) 0.' -- 0.8' 0.8' 0.' 0.8' O8' Limestone, purplish gray-brown, medium— Limestone, gray-brown, fine—to fine-to mediumgrained, thick-bedded. grained, thick-bedded. Spechts Ferry and Metabentonite beds beds are Significance: The Spechts are not present everywhere. In addition, addition, in in the the district district mineralization mineralization it it quite quite often often occurs occurs In where the the Spechts Spechts Ferry Ferry is is thickest0 thickest. could one one account account for for the the local absence of of the How could local absence the Spechts Ferry Member? one account for for the the thickening of of the The metabentonite beds? How could one Spechts Ferry Shale coincident coincident with mineralization? for Spechts for the location and mineralization minerali'zation of "pitch—and—flat" "pi tch-and-flat" structures? References: Cline et al,, Wiliman, 1963; al., 1956; 1956; Templeton and Willman, 1963; Kruse, Kruse, 1970. 1970. 36 �Title: Title: St. John John Mine Mine (Snake (Snake Cave) Cave) St. Location: Opening Opening is is in in valley valley wall wall on on the the north north side side of of State State Highway Highway 133 133 Location: about about 0.2 0.2 miles miles south south of of intersection intersection of of County County Highway Highway "0" "0" and and State State Highway in Potosi Potosi in in the the swi, SW, NW, SW, Highway 133 133 in swi,Sec. Sec.34, 34,T.T.3 3N., N., R.R. 2 2 E,, E., Grant County County (Potosi (Potosi 7.5—minute 7.S-minute topographic topographic quadrangle, quadrangle, 1972), 1972). Grant NW!, M. G. G. Mudrey, Mudrey, Jr., Jr., (Modified St. John Mine brochure, Author: M. (Modified from St. brochure, L.C. L.C. Ihm, Ibm, owner, 1966). owner, and and Whitlow Whitlow and West, West, 1966). This mine mine is is aa natural natural cave cave that that was was extensively exploited for Description: Description: This By 1843, 1843, it it had had yielded yielded 2S0,000 250,000 pounds of lead, lead 1870. By lead. The lead prior to 1870, Potosi sub-district sub—district produced produced 21,300 21,300 tons tons of of 80 percent lead from 1862 to Potosi to 1876, 1876. The vein strikes Galena joints. The Galena occurs occurs in in gash gash veins veins and and openings openings along minor joints, N. its length and N. 6So 65° W., W., and and is is noted noted for for its and continuity. continuity. Host rock rock is is Ordovician Ordovician Galena Dolomite, Dolomite, with Maquoketa Shale on the Host the ridge ridge to the west. 37 37 �The floor floor of of the the cave cave is is in the Dunleith Member (cherty The (cherty lower iower unit) unit) of of the Galena Dolomite. In most most outcrops, outcrops, it it is is aa pale-yellowish-brown pale—yellowish-brown to the Galena In light-olive—gray and and grayish-orange finefine- to medium~grained medium—grained vuggy light-olive-gray vuggy fossiliferous fossiliferous dolomite containing abundant chert as nodules or or as as nearly nearly continuous continuous layers. layers. Chert in the Dunleith Member is nodular and and distributed parallel parallel to to the the bedding. bedding. Near mineralized mineralized zones zones chert is Near is selectively mineralized and contains microscopic microscopic grains of of disseminated disseminated iron iron sulfide sulfide that that color color it it bluish bluish gray gray and and locally locally very very grains dark gray. gray. The top of the cherty unit is is marked by by two two discontinuous discontinuous layers layers of of chert chert odulea separated from the main cherty section by 6—9 feet of non—cherty odulesnseparated section by 6-9 feet of non-cherty dolomite., dolomite. The roof of the cave is in in the Wise Lake Member (non—cherty (non-cherty upper upper unit) unit) of the Galena Dolomite. The strata of the non-cherty unit are pale—yellowish— of The of pale-yellowishbrown to yellowish— yellowish- and grayish-orange fine—grained fine-grained porous porous fossiliferous fossiliferous dolomite. The minerals minerals of of the zinc and and lead lead deposits deposits in in the the Potosi Potosi quadrangle quadrangle are are the zinc mostly simple suif ides, carbonates, and sulfates, simple sulfides, carbonates, sulfates. The primary sulfide sulfide minerals are sphalerite, sphalerite, galena, galena, pyrite, pyrite, marcasite, marcasite, chalcopyrite, chalcopyrite, and and digenite. digenite. Galena is fairly fairly stable and persists the others others are are commonly is persists above above the the water water table.; table.; the altered. These include smithsonite, smithsonite, cerussite, limonite, limonite, melanterite, melanterite, malachite, malachite, azurite, azurite, and erythrite, erythrite. Mine, originally a natural cave, History: St. St. John Mine, cave, was first first named named LaSalle LaSalle Cave, de La Salle, Salle, an an early early French French explorer explorer in in Cave, after Robert Cavelier Sieur de North America, America, who traveled with his company on on an an expedition expedition through through the the upper upper Mississippi River Valley Valley in in 1679 1679 and and again again in in 1687 1687 after after King King Louis Louis XIV XIV names names him Viceroy of North North America. LaSalle is is the man who claimed and and named named" Louisiana Province Province for for the the French French king. king. St. John Min~ Mine was worked by the St. the Indians Indians many years years before before white white pioneers pioneers arrived in the the 1827 1827 "lead "lead rush". rush". Drifts of of the the old old mine follow follow the the natural natural crevices filled with with stalactites. stalactites. The foxes who used used it it for for dens dens are are said said to to have have uncovered uncovered the the rich rich lead lead deposits near near the the entrance entrance by by digging digging and and running running in in and and out out the the natural natural cave cave crevice. The Indians mined galena for barter but but it it was left left to to the the white white men to to extensively develop develop these these diggings, diggings. The first white man John Mine man known known to to have have worked worked St. St. ·John Mine and and who who gave gave it it the the name it still bears was Willis St. St. John, John, who made aa small small fortune fortune from from this this mine between between 1828 1828 and and 1870. 1870. In the Upper Mississippi Valley, valley, lead lead seems seems to to have have been been discovered discovered about about noted in in 1700 1700 by by LeSueur, LeSueur, who who 1692 by Nicholas Nicholas Perrott. Perrott. This metal was als,o als.o noted took lead out of a place which we believe from the the description description must must have have been been Snake Hollow, Hollow, now now Potosi, Potosi, Wisconsin, Wisconsin. In 1766 John Carver brought to to St. Louis Louis aa 500 pound hunk of lead lead he had received from barter barter with with the the Indians Indians who who mined mined a a cave on the eastern Mississippi bank somewhere somewhere between between the the mouth mouth of of the the Grant Grant and Platte Platte Rivers. Rivers. This 500 pound pound piece of lead lead may have have been been taken taken from from St. St. John Mine, Mine, which which points points to to the the importance importance St. St. John John Mine Mine played played in in bringing bringing settlers to to the the lead lead region. region. 38 38 �With With the the arrival arrival of of permanent permanent settlers settlers in in 1825, 1825, the the Winnebago Peace Treaty and and "lead "lead rush rush of of 1827", 1827", the the convening convening of of the the first first Wisconsin Wisconsin Territorial Territorial Legislature in in 1836, 1836, Potosi Potosi and and its its suburbs suburbs (La (La Fayette, Fayette, Van Van Buren, Buren, Dutch Dutch Hollow, Hollow, British Hollow, Hollow, Buena Buena Vista, Vista, and and Rockville) Rockville) flourished. flourished. Potosi Potosi in in 1838 1838 was was British hoping hoping to to become become the the capital capital of of Wisconsin; first first state state capitol capitol was was Belmont, Belmont, but Madison Madison won won out. out. The The Mexican Mexican War War of of 1847; 1847; the the Gold Gold Rush Rush of of '49 '49 and and the the but cholera cholera epidemic epidemic in in 1854 1854 depleted depleted its its citizens citizens for for aa few few years; years; but but by by 1859 1859 when the the Civil War broke broke out, out, production production of of lead, lead, and and with with it it the the growth growth of of the the village of of Potosi, Potosi, was was on on an an upswing. upswing. village Well Well over over two—thirds two-thirds of of all all lead lead for the the North was supplied during the . Civil War by by the the Galena, Galena, Benton, Benton, New New Diggings, Diggings, Shullsburg, Shullsburg, Mineral Mineral Point Point and and mines. The The remainder remainder was was furnished furnished by by mining mining towns towns called called Platteville, Platteville, Potosi mines. Hardscrabble, Hardscrabble, Yuba, Yuba, and and Meeker's Grove, Grove, all all in in the the southwestern southwes~ern Wisconsin Wisconsin zinc-lead region. region. zinc—lead W. S., References: Whitlow, Whitlow, J. J. W., W., and and West, west, W. S., 1966, 1966, Geology of the Potosi References: quadrangle, Grant Wisconsin, and Dubuque County, Grant County, Count~ Wisconsin, County, Iowa: Iowa: U.S. Geol. Geo!. Bull. 1123—I, 1123-1, p. p. 533—571. 533-571. Survey Bull, Heyl, Heyl, A. A. V., V., Jr., Jr., Agnew, Agnew, A. A. F., Lyons, Lyons, E. E. J., J., and and Behre, Behre, C. C. H., H., Jr., Jr., 1959, Zinc-Lead District: U.S. 1959, The The Geology of of the Upper Mississippi Valley Zinc—Lead Geol. Survey Survey Prof. Prof. Paper P~per 309, 309, 310 310 p. p. Geol. Ibm, L. undated, St. Brochure, Potosi, Wisconsin. Ihm, L. C., C., undated, St. John Mine Brochure, It N I Flowstone ST. MINE MAP ST. JOHN JOHN MINE Grant County, County, WI. WI. March, March, 1967 By By Norm Norm Frater, Frater, Mike Mike Wopat, Dome to Surface and Priscilla Wilson Wilson and Priscilla Length, Length, 1050 1050 ft. ft. o0 , 25 I 50 50 I 39 39 500-3J8T026-78 500-3J8T026-78 � https://digitalcollections.lakeheadu.ca/files/original/84e51458c8021c67351733b42c3176a9.pdf 9836a92afb4f6a9e8da7322e3a3cdf9c PDF Text Text LU~ UN IVERSITY OF UNIVERSITY OFWWISCONSIN-EXTENSION IS CO NS IN -E XT EN SI ON GE OL OG IC AL AN D NA GEOLOGICAL AND NATURAL HISTORY SURVEY TU RA L HI ST OR Y SU RV EY M er ed ith E. Os tro m I St Meredith E. Ostrom, State and Director at e Geologist Ge ol og ist an d Di re ct or PRECAMBRIAN INLIERS PRECAMBRIAN INliERS IN IN SOUTH-CENTRAL W SOUTH—CENTRAL WISCONSIN ISCONSIN Prepared Pr ep ar ed for: fo r: TW EN TY -F OU RT ANNUAL MEETING TWENTY-FOURTH H AN NU AL ME ET IN G IN ST IT UT E ON ON LAKE INSTITUTE LA KE SUPERIOR SU PE RI OR GEOLOGY GE OL OG Y UN IV ER SI TY OF UNIVERSITY OF WISCONSIN-MILWAUKEE W IS CO NS IN -M IL W AU KE E MI LW AU KE E, WISCONSIN MILWAUKEE, W iS CO NS IN M AY9—14, MAY 1978 9_ 14 ,1 97 8 FI ELD TR IP FIELD TRIP GU ID E BO OK GUIDE BOOK NU M BE R 22 NUMBER 19 78 1978 �Field Trip Trip Guide Guide Book Book Number Number 22 University of Wisconsin-Extension Wisconsin—Extension GEOLOGICAL GEOLOGICAL AND AND NATURAL NATURAL HISTORY HISTORY SURVEY SURVEY Meredith E. Ostrom, Ostrom, State Geologist Geologist and and Director Director PRECAMBRIAN PRECAMBRIAN INLIERS INLIERS IN IN SOUTH-CENTRAL SOUTH-CENTRAL WISCONSIN WISCONSIN (companion volume volume to Geoscience Wisconsin Wisconsin Volume Volume 2) 2) With With contributions contributions by by Rachel K. A. Paull, K. Paull, Paull, Richard A. Paull, and Eugene I. I. Smith Edited by by Eugene I. I. Smith, Smith, University of Wisconsin-Parkside of of Wisconsin-Milwaukee A. Paull, Paull,University University Wisconsin-Milwaukee Richard A. G. Mudrey, Mudrey, Jr., Jr., Geological and Natural History Survey M. G. for Prepared for Twenty—Fourth Twenty-Fourth Annual Meeting INSTITUTE ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY University of Wisconsin, Milwaukee Milwaukee Milwaukee, Milwaukee, Wisconsin May 9—14, 9-14:, 1978 A. Paull, Paull, Chairman, Chairman, Field Trip Committee Richard A. University of Wisconsin—Milwaukee Wisconsin-Milwaukee Available from the Wisconsin Geological and Natural History Survey, Survey, of Wisconsin—Extension, 1815 University University Avenue, University of Wisconsin-Extension, 1815 Avenue, Madison, Madison, Wisconsin 53706 1978 �CONTE NrS CONTENTS Page Page INTRODUCTION by Eugene I. I. Smith Smith. • • • • • • • • • • • • • • • • • • • • • 11 FRIDAY, FRIDAY, MAY MAY 12, 12, 1978 1978 Geologic Geologic Road Road Log Log for for U.S. U.S. 41 41 from from the the Intersection Intersection of of Wisconsin Wisconsin 74 74 Menomonee Menomonee Falls Falls at at the the North North Edge Edge of of Waukesha Waukesha County County to to Oshkosh, Oshkosh, Wisconsin Wisconsin (junction (junction Wisconsin Wisconsin 21) 21) by by Richard Richard A. A. Paull Paull and and Rachel Rachel K. Paull Paull K • . . . . . . . . • • • . . • • . . • . . . . . 5 . SATURDAY, MAY 13, 13, 1978 1978 SATURDAY, to Precambrian Rhyolite and and Geologic Road Log for aa Field Excursion to Granite Inliers Inliers of South—Central South-Central Wisconsin by Rachel K. K. Paull Paull A. Paull • • • • • • • • • • • • • and Richard A. 11 11 GEOLOGICAL STOP STOP DESCRIPTIONS by Eugene I. I. Smith Stop 11 —- Granite Granite at Flynn's Quarry Quarry County Park. Park • • • Stop Stop 2 —- Rhyolite Rhyolite at Observatory Hill Stop 33 —- Rhyolite at Marcellon Marcellon.• • • • • Stop 4 -- Rhyolite at Marquette • • • • • . . • . • • • . •• Supplemental Stop —- Rhyolite • Rhyolite at Ingall's Knob • Stop 5 —- Quartzite Portland. Quartzite at Portland . • . 33 49 49 57 68 76 83 88 REFERENCES REFERENCESCITED. CITED. • •• . . ILLUSTRATIONS Figure 1. 1. Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure 2. 2. 3. 3. 4. 4. 5. 5. 6. 6. 7. 7. 8. 8. 9. 9. 10. 10. 11. 11. 12. 12. 13. 13. 14. 14. 15. 15. Figure Figure Figure Figure Figure Figure Figure Figure 16. 16. 17. 17. 18. 18. 19. for the Lake Superior Institute field Route for field trip to the south— southcentral Wisconsin Precambrian rhyolite and granite inliers •. • Flynn's Quarry County Park • • compass map of of Flynn's Pace and compass Contact between granite porphyry dike and granite • • • Metabasalt dike cutting cutting granite. granite. • • • • • • • • • Route map from Redgranite to to Montello. Montello. ~ • •. •. • . . • • . Elemental concentrations for for rhyolite rhyolite groupings groupings • • • Geologic map of Observatory Observatory Hill Hill • •. • • • • • • • • sandstone outcrops on Observatory Hill. Cambrian sandstone Hill. • . . . • • in Cambrian Cambrian sandstone Conglomerate in sandstone • • • • • • • • • • . . . Contact between rhyolite dike and rhyolite • of contact of Close-up of rhyolite dike and and rhyolite. rhyolite. Close—up of • Route map for for traverses on the Marcellon exposures • • • • • Geologic map map of of the the Marcellon Marcellon inlier inlier • • • • • • • Geologic Photomicrograph of of Marcellon Marcellon rhyolite rhyolite ash-flow ash—flow tuff tuff • • • • • • • Photomicrograph Stratigraphic variation in in elemental elemental concentrations concentrations for for Stratigraphic the Marcellon Marcellon rhyolite rhyolite • • • • • • • • • • • • • • • • • • the • • . •. •• . .. Weathered spherulites in the Marcellon rhyolite. rhyolite • • of spherulitic spherulitic texture texture in Marcellon Marcellon rhyolite Photomicrograph of of spheroid spheroid with with concentric concentric bands bands • • • • • Photomicrograph of Photomicrograph of of spheroid spheroid with with aa core core of of coarse coarse quartz quartz Photomicrograph and epidote. and • . . . . . . • • . • . . • . • . . . • . . . epidote. • •. • . • . . • • i1 22 32 32 33 35 35 36 37 48 49 49 50 50 53 53 56 56 58 58 59 59 59 59 60 62 62 62 63 63 �Page Figure 20. 20. Pumice Pumice and and shard shard fragments fragments in Marcellon Marcellon rhyolite rhyolite • • Figure Figure 21. 21. Lineation formed formed by by stretched stretched pumice pumice in in the the Tertiary A. A. L. L. Figure Tuff, San San Mateo Mateo Mountains, Mountains, New New Mexico Mexico • • . • . • Peak Tuff, . ••••••• Figure 22. 22. Folds in the Marcellon rhyolite rhyolite. • • • • • • • • • • • ••• Figure 23. 23. Sketches Sketches of of folds folds in the the Marcellon Marcellon rhyolite rhyolite• • • • • • . • . •. • Figure Figure 24. 24. Route Route map map for for traverses traverses at at the the Marquette Marquette exposures exposures • •. •. •. • Figure Figure 25. 25. Geologic map of the Marquette inlier • • • • • • • • Figure 26. 26. Rb/Sr-Na Rb/Sr—Na20/K20 plot for for Marquette Marquette rhyolite rhyolite • • • . • . . • Figure 0/K 0 plot 2 2 Figure 27. 27. Photomicrograph Photomicrograph of of shards shards in in Marquette Marquette rhyolite rhyolite • • Figure . Figure 28. 28. Photomicrograph of shards in Marquette rhyolite. rhyolite • • • • • • • Figure 29. 29. Sketch map of breccia on Ingall's Ingall's Knob • • . . ••• Figure 30. 30. Detailed map of of the Portland quartzite quarries. quarries • • . . . . . . . Figure 31. 31. Photomicrograph of of the Waterloo Quartzite • • • • • Figure 32. 32. Detailed route map through the Waterloo Quartzite area area. Figure 33. 33. View of phyllite layer in quartzite quartzite. • • • • • ••• Close—up of foliated Figure 34. 34. Close-up foliated Waterloo Quartzite • • • • • • • •. . . . . 65 65 66 67 68 6969 70 76 77 79 82 84 85 87 87 TABLES TABLES Table 1. Table 1. for Central Wisconsin inliers and igneous Chemical analyses analyses for rocks in in the the Baraboo area area. • • • • • • • • • • • • • • • • • 39 �INTRODUCT ION INTRODUCTION Eugene I. Smith1l Eugene I. Smith v years very little attention has has been paid to the For the the past seventy years At the well known igneous rock in in the the Fox Fox River River Valley. Valley. At the turn of the the century well geologists Chamberlin, Weidman. Weidman. Leith and Hobbs described geologists such as as Irving, Irving, Chamberlin, and Hobbs these isolated these isolated exposures of Precambrian rock. rock. Between 1907 and 1972 few The last geological studies studies were were initiated. initiated. The last major field field trip to visit these was conducted by A. A. Leith in 1935 for Precambrian rocks rocks was for the the Kansas Kansas Geological While the will be be shown to you on this Society. While the geology that that will this Lake Superior Institute field trip is based for Institute field for the the most part part on on geological geological studies studies comcom1972, descriptions descriptions of the Hill rhyolite pleted since 1972, the Observatory Hill rhyolite and and the Waterloo This field trip Waterloo Quartzite Quartzite rely rely considerably considerably on on the the earlier earlier work. work. This trip is intended intended to to introduce introduce you you to to the the rock rock types types and and the the rock rock fabric fabric formed formed is post—Penokean igneous event (1765 m.y. ago) ago) and during a a major post-Penokean igneous event (1765 m.y. and to demonstrate the structural structural style of a post—Penokian The the post-Penokian deformation deformation (1650 (1650 m.y. m.y. ago?). ago?). field trip stops oldest to youngest field stops are are arranged arranged in stratigraphic stratigraphic order from from oldest youngest (fig. 1). 1). Since the the exposures are are on on the the flank flank of of the the Wisconsin Wisconsin Arch, Arch, (fig. travelling to the travelling the southeast off the the crest of of the the arch arch conveniently conveniently exposes exposes younger units. units. Here fine—grained The first first stop is is at at the the Flynn's Granite Granite Quarry. Quarry. Here fine-grained granophyric granite is is cut cut by by granite granite porphyry porphyry and and metabasalt metabasalt dikes. dikes. The granite probably is the equivalent of of the rhyolites to be the subvolcanic subvolcanic equivalent the rhyolites 3, and viewed at at stops stops 2, 2, 3, and 4. 4. Hill (stop by a sequence of of steeply dipping Observatory Hill (stop 2) 2) is is formed formed by a sequence porphyritic rhyolite which erupted erupted from from source source chambers chambers now porphyritic rhyolite ash—flow ash-flow tuffs tuffs which represented by granite cropping out to represented to the the northwest northwest (Flynn's (Flynn's Quarry, Quarry, The rhyolite rhyolite is cut by by finefine— and coarse—grained Montello and and Redgranite). Redgranite). The is cut and coarse-grained rhyolite dikes and and is is surrounded surrounded by by exposures exposures of of Cambrian Cambrian sandstone. sandstone. Stops 33 and Marcellon and and Marquette Marquette rhyolites) rhyolites) display the fabric Stops and 44 (The (The Marcellon the fabric and and mineralogy of the the texturally texturally variable variable rhyolites. rhyolites. In In the the volcanic volcanic section sparsely-porphyritic sparsely—porphyritic plagioclase-bearing plagioclase—bearing rhyolite rhyolite commonly alternates alternates with with quartz, plagioclase, porphyritic quartz, plagioclase, alkali alkali feldspar feldspar rhyolite. rhyolite. The rocks rocks show show fabrics common common to ash-flow ash—flow tuffs have undergone undergone compaction, compaction, welding welding and and fabrics tuffs that that have late—stage primary laminar flowage (eutaxitic and spheruloidal spheruloidal textures late-stage laminar flowage (eutaxitic and textures and and large flow folds). folds). The Waterloo Quartzite Quartzite (stop 5), the youngest exposed exposed Precambrian Precambrian rock The (stop 5), the youngest in south-central south—central Wisconsin, Wisconsin, is is folded folded into into a broad eastward eastward plunging synsyn— a broad dine. The The nose nose of of the structure lies lies in the Portland Portland area area near near the quarry cline. the structure in the the quarry visited during Stop stop 5. 5. 1'Division Division of of Science, Science, University University of of Wisconsin—Parkside, Wisconsin-Parkside, Kenosha, Kenosha, Wisconsin Wisconsin 53141 53141 1 1 �Red granite Redgranite S TO p'1)!e!.---.oE::-----I CD Flynn's Quarry County Park STOP Du Lac @) Marquette Rhyolife Rhyolite Hill Marcellon R hy o life / z C, Waterloo Quart zite I \ '::')"""----~+--~I Mllwaukee\ o o 0 10 20 30 30 C-) w uJ ~ <t -J ...J 40 MIles 40 Miles SCALE Figure 1. 1. Route for the Lake Lake Superior Superior Institute the south— Route for the Institute field field trip to to the southcentral Wisconsin Precambrian rhyolite and granite inliers. central rhyolite and granite inliers. 2 �I thank Pattie Pattie Fields-Troha Fields—Troha for for typing typing draft draft copies copies of I thank of these these stop descriptions and Jill Ann Hartnell for for drafting drafting the the figures. figures. Diane Pyper made many useful editorial corrections corrections that that helped helped smooth smooth out out the rough spots. many useful editorial spots. also thank thank Frank Frank Luthur Luthur (University (University of of Wisconsin-Whitewater) Wisconsin—Whitewater) for for an an II also informative discussion on on the the metamorphic metamorphic rocks rocks from from Waterloo. Waterloo. Participants on this trip will traverse Participants trip will traverse the the scenic, scenic, glaciated countryside side of southeastern and and south—central south-central Wisconsin to study isolated exposures of Precambrian granite, granite, rhyolite, quartzite that rhyolite, and and quartzite that project through a cover of Paleozoic rocks of rocks and Pleistocene drift (Fig. (Fig. 1). 1). Board bus at 6:30 P.M. P.M. sharp on Friday May 12, 12, 1978 in in the front of the the Pfister Hotel (Headquarters (Headquarters for for the the 24th 24th Annual Annual Lake Lake Superior Superior Institute). Institute). of travel will follow U.S. Our route route of travel will U.S. 41 41 to to Oshkosh, Oshkosh, Wisconsin. Wisconsin. A A geological roadguide for for this this part part of of the the trip trip is is provided. provided. Overnight accommodations accommodations will will be at at the Pioneer Inn, Inn, on the west shore of Lake Winnebago in in Oshkosh 8:00 trip This 6:30 On Saturday Saturday May May 13, 13, 1978, 1978, board board the the bus bus in front of of the the Pioneer Pioneer at at On in front A.M. A.M. sharp. sharp. The guidebook includes includes a a geologic roadguide for the field field route, route, as well as as detailed information information on on each each of of the the geologic geologic stops. stops. field field excursion will terminate at the Pfister Hotel in in Milwaukee about about P.M. P.M. A companion volume to this Geoscience Wisconsin Volume 2, 2, contains papers papers by Smith (1978c), Van Schmus (1978) (1978c), Van (1978) and Haimson (1978) (1978) on the the geology, geology, ages, ages, and and engineering properties of of the the granites, granites, rhyolites rhyolites and and quartzites. quartzites. 3 �Friday, Friday, May May 12, 12, 1978 1978 Geologic Geologic Road Road Log Log for for U. S. S. 41 41 from from the the Intersection Intersection of of Wisconsin Wisconsin 74 74 Menomonee Menomonee Falls Falls at at the the North North Edge Edge of of Waukesha Waukesha County County to to Oshkosh, Oshkosh, Wisconsin Wisconsin (junction (junction Wisconsin Wisconsin 21) 21) 1 2 Richard Richard A. A. Paull1 Paull and and Rachel Rachel K. K. Paull2 Paull U. U. S. S. 41 41 trends trends north—northwesterly north-northwesterly through through the the glaciated glaciated Eastern Eastern Ridges Ridges and Lowlands Lowlands Province Province of of Wisconsin. Wisconsin. The The orientation of this this route route is is such such and that that it it cuts cuts obliquely obliquely across across the the strike strike of of the the Paleozoic Paleozoic formations. formations. From From south—southeast south-southeast to to the the north—northwest, north-northwest, these these units units include include Silurian Silurian dolomite, dolomite, Tipper Ordovician Maquoketa Maquoketa Shale, Shale, and and the Middle Ordovician Upper Ordovician Ordovician Platteville— PlattevilleGalena formations. formations. However, However, the the bedrock bedrock along along the the highway highway is is largely largely obobGalena scured scured by by Wisconsinan (Woodfordian (Woodfordian and and the the younger younger Valderan) Valderan) glacial glacial deposits. deposits. exception exists exists along along the the crest crest of of the the prominent prominent Niagaran Niagaran (Silurian) (Silurian) An exception escarpment, where where glacial glacial deposits deposits are are thin. thin. escarpment, Included Woodfordian glacial glacial features features are are well—displayed well-displayed along along U. U. S. S. 41. 41. Included are a a recessional moraine related to retreat of the Lake Michigan lobe, lobe, kames kames and kettles kettles associated with the spectacular Kettle Interlobate Interlobate Moraine, Moraine, and and well—formed well-formed drumlins drumlins within the area occupied by the the Green Bay lobe. lobe. Deposits Deposits that accumulated accumulated in in Glacial Glacial Lake Lake Oshkosh Oshkosh when when retreat retreat of of the that the last last Wisconsinan (Valderan) ice ice tongue tongue blocked northeastward drainage (Valderan) drainage into into Green Green Bay Bay are are also also traversed. Details on the the geology geology encountered encountered along along U. U. S. S. 41 are provided provided in the Details 41 are the geologic road log that that follows. follows. We hope this this will help to make your your enjoyable. Mileages in in the the road road log log are are cumulative, cumulative, with journey more enjoyable. mileage increments between each each entry entry included included in in brackets. brackets. Mileages o 0 (2.0) (2.0) Con— 74 exit exit from U. U. S. S. 41 Wisconsin 74 41 to to downtown Menomonee Falls. Falls. Continue northwest on U. U. S. S. 41 Oshkosh, the tinue northwest 41 and and 45 toward toward Oshkosh, the location of tt our "watering our watering hole" hole " for for this this evening. evening. Lime Kiln Village Village Park is mile west west in the Lime is about about one mile the heart heart of Here, the the business business district district of Menomonee Falls. the Falls. Here, the Silurian Dolomite dolomite forms a small falls on the dolomite forms a small falls the Menomonee River. River. was quarried here for lime production as early as the 1850's, was quarried for lime as as the 1850's, and Glacial three historic historic kilns three kilns are preserved within the the park. park. striae on on the the Silurian bedrock in striae in the the vicinity vicinity of of the the kilns kilns establish an an east-west east—west flow flow direction direction for for advance advance of of the the Lake Lake establish Michigan glacial glacial lobe during the Michigan the Woodfordian. 2.0 2.0 (5.0) (5.0) Enter Washington Washington county county in an Waukesha/Washington county line. Waukesha/Washington line. Enter area of of foIling folling countryside, countryside, on on the the northwestern northwestern edge edge of of the the intensely intensely area lThe 1The University University of of Wisconsin-Milwaukee, Wisconsin—Milwaukee, Milwaukee, Milwaukee, Wisconsin Wisconsin University of of Wisconsin-Madison, Wisconsin—Madison, Madison, 22The The University Madison, Wisconsin; Wisconsin; and and Alverno Alverno College, College, Milwaukee, Milwaukee, Wisconsin Wisconsin 55 �Mileages Mileages urbanized, greater greater Milwaukee Milwaukee area. area. This urbanized, This region region was was last last glaciated glaciated during the the Woodfordian Woodfordian by by the the advance advance of of the the Lake during Michigan Lake Michigan lobe. lobe. The outermost outermost (oldest) (oldest) of of a a series series of of three, three, major major ridgeridge— The forming recessional recessional moraines moraines (Lake Border Moraines), Moraines), which forming (Lake Border which parallel parallel the shore of Lake Michigan in the Milwaukee the shore of Lake Michigan in the Milwaukee area, area, trends trends through through this area. area. this To the the west, west, one one catches catches glimpses glimpses of of the the irregular irregular hills To hills of of the the Woodfordian interlobate moraine that developed Woodfordian interlobate moraine that developed between between the the Lake Lake Michigan lobe lobe on on the the east east and and the the Green Green Bay Michigan Bay lobe lobe on the west. This This is the Kettle Interlobate Moraine, which trends is the Kettle Interlobate Moraine, which trends north-northeast from Walworth Walworth County County to to Kewaunee Kewaunee County County to from to form form the the glacial glacial backbone of eastern Wisconsin. bone of eastern Wisconsin. Northwest-trending Northwest—trending u.s. U.s. 41 41 is is on on aa collision course course with with this this prominent prominent topographic topographic feature. collision feature. 7.0 7.0 (1.0) (1. 0) 8.0 8.0 Wisconsin 167 167 (Holy Hill Road) Road) exit; exit; continue continue on Wisconsin (Holy Hill and 45. 45. on u.s. U.S. 41 41 and Holy Hill, aprominentkame topped by Holy Hill, a prominent kame by aa picturesque picturesque church, church, is located about about 77 miles miles west west of of here here within within the the heart of the Kettle located Interlobate Moraine. U.S. u.s. 45 exit exit to to West West Bend; Bend; continue continue north north on U.S. 45 u.s. 41. 41. (4.0) (4.0) 12.0 12.0 (1.0) (1. 0) 13.0 13.0 (lO) (1. 0) 14.0 14.0 (0.4) (0.4) 14.4 14.4 (0.9) (0.9) The highway highway ascends ascends the the eastern eastern edge edge of the the Kettle The Kettle Interlobate Moraine, and leaves the lowland occupied by the Lake Michigan lobe Moraine, during the Woodfordian advance. advance. This This country is is higher and more more irregular,with with kettles kettles and and abundant abundant locally locally derived derived erratics irregular, of erratics of light—colored Silurian light-colored Silurian dolomite. dolomite. Wisconsin 60 exit to Slinger and Hartford within the Kettle Inter— Interlobate Moraine. Moraine .. The Hilltop Restaurant on the west side of the highway is is well well named, named, for for it it occupies occupies the the crest crest of of the the Kettle Kettle Interlobate Interlobate Moraine. Moraine. The The scenic scenic kettle kettle and and kame kame topography topography that that characterizes characterizes this this region region formed formed when the Green Bay and Lake Michigan glacial lobes lobes stagnated stagnated along along their their junction junction during during the the Woodfordian. Woodfordian. As As the the ice ice at at the the melting edges edges of of these these juxtaposed juxtaposed lobes lobes began began to to thin, thin, sedimentsedimentladen meltwater meltwater •flowed flowed down in the the ice ice to to provide provide laden down cracks cracks and holes in aa source source for for subglacial subglacial streams. streams. Meltwater Meltwater also also cascaded cascaded over over the the ice ice surface surface into into the the widening abyss abyss between the the tongues. tongues. Here, Here, large large chunks chunks of of ice ice were buried in in the the outwash outwash sands sands and and gravels. gravels. The The resulting resulting maze maze of of crevasse crevasse fills, fills, moulin moulin kames, kames, eskers, eskers, outwash outwash fans, fans, and and kettles kettles is is superimposed superimposed on on aa dual dual complex complex of of ridges ridges which which had had previously previously formed formed as as lateral lateral moraines. moraines. Little Switzerland Switzerland Ski Ski Hill, Hill, to to the the west west of of the the highway highway at at the the edge edge Little of of Slinger, Slinger, utilizes utilizes aa prominent prominent moulin moulin kame. kame. The The internal internal makeup makeup of of aa similar similar kame kame is is revealed revealed in in an an abandoned abandoned sand sand and and gravel gravel operation operation about about 0.1 0.1 mile mile north north of of the the ski ski hill. hill. The The gravel gravel in in this this kame kame is is well—stratified, well-stratified, and and it it includes includes an an abundance abundance of of lightlightcolored Silurian Silurian dolomite dolomite cobbles cobbles and and aa few few large large boulders. boulders. Other Other colored well-formed well-formed kames kames are are present present east east of of the the highway. highway. 66 �Mileages Mileages 15.3 15.3 Junction Junction U.S. u.s. 41 41 and and Wisconsin Wisconsin 144. 144. Continue Continue north north on on U.S. u.s. 41. 41. (1.7) (1.7) 17.0 17.0 (0.8) (0.8) 17.8 17.8 (3.5) (3.5) Junction Junction U.S. u.s. 41 41 and and County County K. K. The The highway highway descends descends from from the the Interlobate Interlobate Moraine toward toward the the lowland lowland area area occupied occupied by by the the Green Green Bay lobe lobe during during the the Woodfordian Woodfordian ice ice advance. advance. Bay The sand sand and and gravel gravel pit pit west of of the the highway highway is is on on the the northnorthwestern western edge edge of of the the Kettle Kettle Interlobate Interlobate Moraine. Moraine. This This is is one one of of many many such such operations operations that that exploit exploit the the abundant abundant resource resource of of waterwaterwashed washed sand sand and and gravel gravel within within this this unique unique morainal morainal complex. complex. The route poorly—drained ground route ahead ahead traverses traverses gently gently rolling,, rolling, poorly-drained moraine. Tamaracks Tamaracks flourish flourish in in some some of of the the wetter wetter areas. areas. moraine. 21.3 21.3 (1.7) (1.7) 23.0 23.0 Junction Junction U.S. u.s. 41 41 and and Wisconsin 33; 33; continue continue north north on on U.S. u.s. 41. 41. The The route route crosses crosses aa recessional recessional moraine that that formed formed as as the the Woodfordian Woodfordian Green Bay Bay lobe lobe paused paused during during its its retreat. retreat. Green Wayside east east of of the the highway is is in in an an area area of of swampy, swampy, rolling rolling ground ground (4.0) (4.0) moraine. moraine. 27.0 27.0 (2.5) (2.5) This high area provides an excellent overview of scenic, scenic, irregular irregular abundance of of erratics erratics in in the the till till here here is is documented documented countryside. An abundance by by stone stone fences fences that that line line some some fields, fields, and and by by rock rock piles piles in in others. others. 29.5 (0.6) (0.6) u.s. 41 41 and and Wisconsin Wisconsin 28. 28. Junction U.S. 30.1 (1.9) (1.9) county line. line. Enter Dodge County in in an an area area dominated dominated Dodge/Washington county large, well—formed well-formed druinlins. drumlins. Erratics in in fence fence rows rows and and farmyards farmyards by large, the stony stony nature nature of of this this till. till. testify to the 32.0 (0.4) (0.4) Wayside east of of the the highway. highway. 32.4 (1.6) (1.6) Wayside west of of the the highway. highway. 34.0 34.0 (2.4) (2.4) The Junction 67. Continue north on U.S. u.s. 41. 41. The Junction u.s. U.S. 41 and Wisconsin 67. route ahead ahead gradually gradually climbs climbs the the gentle gentle (2°-5°), route (2°-5°), easterly dipslope However, the the bedrock in this of resistant Silurian Silurian dolomite. dolomite. However, of the theresistant region is is covered covered by by aa swarm of broad, broad, low drumlins drumlins that create region aa gently gently rolling landscape. 36.4 36.4 (1.0) (1.0) Junction 49. Junction u.s. U.S. 41 41 and and Wisconsin 49. 37.4 37.4 (1.4) (1.4) Fond line. Fond du du Lac/Dodge Lac/Dodge county line. 38.8 38.8 (0.5) (0.5) highway utilize utilize a Sand and and gravel gravel operations operations on on both both sides sides of of the the highway Sand a local local area area of outwash deposits. 39.3 39.3 (2.7) (2.7) Roadcut on on the the west west side side of of the the highway highway exposes exposes Silurian Silurian dolomite dolomite Roadcut The proximity proximity of of bedrock bedrock to to the the where thin. The where glacial glacial deposits deposits are thin. 77 Continue north north on on U.S. u.s. 41. 41. Continue north north on on U.S. Continue u.s. 41. 41. Enter Fond du du Lac County. Enter County. �Mileages Mileages surface has has facilitated facilitated the the development development of of numerous numerous dolomite quarries surface in this this general area. This rock rock is is an excellent dimension in area. This dimension stone, stone, but most most of it it is is crushed for but for agricultural lime and road building. building. However, some some is is kilned to produce chemical However, chemical lime. lime. This high high point point provides provides aa good good view view of of the the north-northeasterly This trending Kettle Kettle Interlobate Interlobate Moraine Moraine along along the the skyline skyline to to the the east. east. trending A lowland region, nonresistant Middle Middle region, developed on relatively nonresistant and Upper Upper Ordovician rocks, and rocks, lies lies to to the the west. west. 42.0 42.0 (0.6) 42.6 42.6 (2.0) Large Large quarries quarries in in Silurian dolomite are located east and west of U.s. 41. U.S. 41. This is is the the edge of the the Silurian (Niagaran) This (Niagaran) escarpment, escarpment, and it provides a fine view of the Ordovician lowland ahead. provides a fine the ahead. This excarpment (or ment (or cuesta) cuesta) is the the most significant bedrock feature in eastern Wisconsin. It It emerges emerges from from aa thick thick cover cover of of glacial glacial deposits deposits aa few miles miles northeast northeast of of Milwaukee, Milwaukee, and and trends trends north-northeast north—northeast as few as aa prominent cliff along the the east side of Horicon Marsh and Lake Winnebago. From here, here, the the escarpment persists northeastward to form the the rocky rocky spine of the Door Peninsula. It continues across form Lake Michigan as as a Lake a string of bedrock islands before it rises rises as the the rugged Garden Peninsula of of Upper Upper Michigan. Michigan. The route descends toward the Ordovician lowland through route ahead descends through an an area of gently rolling ground moraine. rolling ground moraine. 44.6 44.6 (0.6) The highway in this vicinity crosses the ill—defined The ill-defined terminal terminal moraine of the latest Wisconsinan (Valderan) (Valderan) ice advance of the the Green Bay Bay lobe. The wooded edge of the Silurian escarpment is is visible visible along along the the skyskyline to to the the east. east. 45.2 (1.8) Junction U.S. U.S. 41 and Wisconsin 175 to Fond du Lac, Lac, at at the the south south end end of Lake Winnebago. Winnebago. Continue northwest northwest on on U.S. U.S. 41. 41. Lake Winnebago, Winnebago, with a surface area of 215 215 square square miles and and aa maximum maximum depth depth of of 21 21 feet, feet, is is the the largest largest inland inland lake lake in in Wisconsin. Wisconsin. It sprawls for for 28 28 miles along the west edge of the the Silurian Silurian escarpment, escarpment, and is situated in an area underlain by relatively relatively nonresistant Middle Middle and and Upper Upper Ordovician Ordovician rocks. rocks. This lowland lowland extends extends from from Green Bay southwestward through through Lake Winnebago, Horicon Horicon Marsh, Marsh, and over a a low low drainage divide into into the the broad valley valley now now occupied occupied by by the the Rock Rock River. River. During the the Pleistocene, the the Green Green Bay Bay lobe lobe advanced and and retreated retreated along along this this route route numerous numerous times. times. The ice, ice, in part confined by the the resistant resistant Silurian Silurian escarpment, escarpment, scoured scoured the the Ordovician bedrock and deposited aa variety variety of of glacial glacial landforms. landforms. During northeastward regressions regressions of of the the Woodfordian Woodfordian and and Valderan Valderan glaciers, glaciers, drainage along along the the lowland lowland into into Green Green Bay Bay was temporarily temporarily blocked blocked by by the the retreating retreating wall wall of of ice. ice. A A vast vast lake, lake, termed termed Glacial Glacial Lake Lake Oshkosh, formed impounded behind behind the the youngest youngest formed from from the the meltwaters meltwatersimpounded (Valderan) (Valderan) of of these these icy icy dams. dams. At At this this time, time, the the site site of of Fond Fond du du Lac Lac was was under under 40 40 to to 60 60 feet feet of of water. water. Eventually Eventually Green Green Bay Bay became became ice ice free, free, and Glacial Lake Oshkosh drained into Lake Michigan via via the the 88 �Mileages Mileages Winnebago remnantofofthis this feature, feature, surviving Fox River. River. Lake Lake Winnebago is isa aremnant surviving Fox in a shallow irregularity on the floor floor of of this this ancient ancient water water body. body. in a shallow irregularity on the Cross Cross east east branch branch of of Fond Fond du du Lac Lac River. River. 47.0 47.0 (1.8) (1.8) 48.8 48.8 (4.2) (4.2) Junction Junction U.S. U.S. 41 41 and and U_S. U.S. 151. 151. Continue Continue north north on on U.S. U.S. 41. 41. The The route route ahead ahead traverses traverses aa relatively relatively subdued subdued area area underlain underlain by by sediments sediments deposited deposited in in Glacial Glacial Lake Lake Oshkosh. Oshkosh. Junction U.S. U.S. 41 41 and and Wisconsin Wisconsin 23. 23. Junction Continue Continue northwest northwest on on U.S. U.S. 41. 41. The The wooded wooded Silurian Silurian escarpment escarpment continues continues to to dominate dominate the the horizon horizon to to the east. east. the 53.0 53.0 Wayside Wayside west west of of the the highway, highway, as as U.S. U.S. 41 41 curves curves northward. northward. (4.0) (4.0) 57.0 (1.7) (1.7) 58.7 58.7 (3.2) (3.2) ascends to to reddish, reddish, rolling rolling Valderan Valderan ground ground moraine moraine at at Highway ascends the western western edge edge of of Glacial Glacial Lake Lake Oshkosh. Oshkosh. the Winnebago County Fond du du Lac/Winnebago Lac/Winnebago county county line. line. Enter Enter Winnebago County in in an an area area Fond rolling ground ground moraine. moraine. There is a good view to to the the east east of of the the of rolling Silurian escarpment escarpment along along the the far far shore shore of of Lake Lake Winnebago. Winnebago. The The sediments deposited deposited route from here to Oshkosh traverses reddish sediments Lake Oshkosh. Oshkosh. in Glacial Lake 61.9 61.9 (0.7) (0.7) of the the highway. highway. Wayside east of 62.6 62.6 (2.7) (2.7) U.S. 41 Junction U.S. U.S. 41 and Wisconsin Wisconsin 26. 26. Continue north on U.S. through aa subdued subdued area underlain by flat-lying glacial lake through deposits. 65.3 65.3 (2.9) (2.9) Continue north north Junction U.S. U.S. 41 and Wisconsin 26 26 and and 44 44 to to Oshkosh. Oshkosh. Continue Oshkosh, on on the west shore Winnebago, is on U.S. U.S. 41. 41. Oshkosh, shore of Lake Winnebago, developed on the ancient floor floor of of Glacial Glacial Lake Lake Oshkosh. Oshkosh. 68.2 68.2 The geologic geologic roadguide roadguide for Junction U.S. U.S. 41 and Wisconsin 21. 21. The for intersection, the Precambrian Precambrian inliers inliers field field trip trip begins begins at at this this intersection, the and 21. and continues continues westward on State 21. A PLEASANT PLEASANT EVENING: EVENING HAVE A END - HAVE END OF OF LOG - 99 �__________ __________ Saturday, Saturday, May May 13, 13, 1978 1978 Geologic Geologic Road Road Log Log for for aa Field Field Excursion Excursion to to Precambrian Precambrian Rhyolite Rhyolite and and Granite Granite Inliers Inliers of of South—Central South-Central Wisconsin Wisconsin l 2 Rachel Rachel K. K. Paull' Paull and and Richard Richard A. A. Paull2 Paul1 This This road road log log starts starts at at the the intersection intersection of U. U. S. S. 41 41 and and Wisconsin 21 21 on on the the northwestern northwestern edge edge of of Oshkosh, Oshkosh, Wisconsin, Wisconsin, and and terminates terminates in in Milwaukee, Milwaukee, 'Wisconsin "Wisconsin at at the the junction junction of 1—94 1-94 with 1—43 1-43 (U. (U. S. 141) and and 1—794 1-794 (see (see Fig. i). 1). Fig. The The route route of travel travel on this this trip trip is is due due west from from Oshkosh for for 26 26 miles miles to Redgranite, Redgranite, and then then south—southwest south-southwest nearly nearly to to Portage Portage (Marcellon (Marcellon inlier). inlier). to Since Since we detour to to look look at at two two Precambrian Precambrian inliers, inliers, this this leg leg involves involves about about 50 50 we proceed northeast miles of of travel. travel. From here, here, we northeast to to a a rhyolite inlier near miles Marquette; aa distance distance of of 20 20 miles miles by by road. road. After After aa 5 mile segment segment to to the the east, east, Marquette; our route route trends trends south south for for 40 40 miles. miles. From immediately immediately north north of of Waterloo, Waterloo, our we travel travel eastward eastward for for 7 7 miles miles to to the the Waterloo Waterloo Quartzite, Quartzite, and and then then south south for for we to reach reach Interstate Interstate 94 94 at at Lake Lake Mills. Mills. After aa fast fast 50—mile 50-mile run run to to 8 miles to In all, all, we we will will cover 206 east, we are are back back in in Milwaukee. Milwaukee. 206 miles, miles, make make the east, 5 geologic stops, and even stop stop for for lunch lunch (Fig. (Fig. 1). 1). It will be be aa busy busy day day: 5 geologic stops, This odyssey through east—central east-central Wisconsin traverses traverses parts of two two of However, the four four major physical provinces provinces recognized recognized in in Wisconsin. Wisconsin. However, in in the the the provinces are area the features are area covered covered by by this this field field excursion, excursion, the features of of both both provinces The Eastern Ridges and by young young glacial glacial deposits. deposits. The and Lowlands Lowlands parallels parallels masked by This province province contains contains aa sequence sequence of of generally generally north—south north-south Lake Michigan. This striking, Ordovician Ordovician through through Devonian formations, formations, with with the older rocks striking, the older rocks to to the the Differences in in resistance resistance of of these units result west. Differences these units result in broad, broad, subdued subdued ridges alternating with lower lower areas. areas. The Central Plain is is aa lowland lowland region, region, ridges developed on Upper Upper Cambrian sandstones, sandstones, that west of of the developed that lies lies to to the the west the Eastern Ridges and Lowlands. Lowlands~ Ridges Within the the general region of the the Central Central Plain covered by this this trip, trip, there are are ten localities localities where where Precambrian granite granite and and rhyolite there rhyolite project project through through aa cover cover of of Lower Lower Paleozoic Paleozoic rocks rocks and and unconsolidated unconsolidated Pleistocene Pleistocene The igneous igneous rocks rocks in these inliers deposits. The inliers are dated dated at at 1765 1765 m.y. m.y. old, old, and they they probably probably formed and formed during the waning stages stages of of the the Penokean Penokean orogeny. orogeny. Although Granite inliers inliers lie lie northwest Granite northwest of the the area area where rhyolite rhyolite is is exposed. exposed. Although the field field relations relations are are not not established established at at present, present, the the rhyolite rhyolite and and granite granite the If so, so, the the granite granite is are comagmatic. If is a a subvolcanic are generally generally believed believed to be comagmatic. equivalent of the extrusive rhyolite. equivalent of the rhyolite. After accumulation of of the sequence of of Precambrian quartz After the rhyolite, rhyolite, a a thick sequence After deposition, these sandstone deposited. After deposition, sandstone and and other other sedimentary rocks was deposited. rocks and and the the underlying underlying rhyolite rhyolite were were subjected subjected to to an an intensive intensive episode episode of of rocks Detailed information information on on the the Precambrian Precambrian folding, m.y. ago. ago. Detailed folding, possibly possibly 1650 m.y. history of of this this region region is is provided provided by by Eugene Eugene I. I. Smith Smith in in the the next next section section of of history this this guidebook. guidebook. The five five stops stops on on this this field field excursion excursion provide provide an an opportunity opportunity to to examine examine The However, rhyolite rhyolite each types described above. above. However, each of of the the major major Precambrian rock types receives the the most most emphasis, emphasis, with with three three stops stops devoted devoted to to an an examination examination of of this this receives diverse diverse rock rock type. type. 11 11 1 1University of Wisconsin—Madison, Madison, Madison, Wisconsin; and Alverno College, University of Wisconsin-Madison, Wisconsin; and Alverno College, Milwaukee, Wisconsin Milwaukee, Wisconsin 2University of of Wisconsin-Milwaukee, Wisconsin—Milwaukee, Milwaukee, Milwaukee, Wisconsin Wisconsin 2University �The glacial glacial geology geology of of east-central east—central Wisconsin Wiscctisin is is also also spectacular, spectacular, and and The quite varied. The trip trip begins begins in in an an area area occupied occupied by by the the youngest youngest Wisconsinan Wisconsinan quite varied. The (Vanderan) ice ice advance, advance, and and by by lakes lakes which which formed formed during during the the retreat retreat of of this this (Vanderan) ice. However, However, most most of of the the route route traversed traversed is within the ice. is within the region covered by an older older Wisconsinan Wisconsinan (Woodfordian) an (Woodfordian) advance of of the the Green Green Bay Bay lobe. lobe. Deposits Deposits formed by by this this icy icy tongue tongue include large expanses of formed of glacial glacial lake lake sediments, sediments, recessional moraines moraines related related to to the the retreat retreat of of this this lobe, lobe, outwash outwash sands sands and and recessional gravels, scenic scenic kettle kettle lakes, lakes, and and some some of of the the best best drumlin drumlin swarms swarms in in the the gravels, world. All All of of these these features features combine combine to make make this this region region a glacial showworld. a glacial case, and a most pleasant place to case, a most pleasant,place to spend spend aa field field day. day. We hope hope the the geologic geologic roadguide roadguide that that follows follows makes makes your trip more We enjoyable. Mileages Mileages are are cumulative, cumulative, with with mileage mileage increments enjoyable. increments between each entry provided in in brackets. brackets. Detailed for each stop is Detailed geologic geologic information for provided by Eugene I. provided I. Smith in in the the next next section section of of this this guidebook. guidebook. It It would would be beneficial beneficial if if you you would would read read the the detailed detailed descriptions descriptions of be of each area area before we stop. we stop. Mileages Mileages o0 (2.2) (2.2) Start of of Geologic Geologic Road Road Log Log at at intersection intersection of of V.. S. 41 Start 41 and Wisconsin 21 at the the northwestern edge of of Oshkosh, Oshkosh, Wisconsin. Wisconsin. west on State Highway Proceed west Highway 21. 21. is located located on on the west shore shore of of Lake Lake Winnebago, Winnebago, the largest Oshkosh is the west inland lake in in Wisconsin. This shallow lake lake is is aa remnant remnant of of Glacial Glacial Lake Lake Oshkosh, Oshkosh, a much larger larger Pleistocene water body formed formed when the the retreating retreating Valderan ice blocked northeastward northeastward drainage drainage along Valderan ice blocked along the the Green Bay lowland into into Lake Lake Michigan. Michigan. The route ahead traverses lacustrine lacustrine sediments that that accumulated in in Glacial Glacial Lake Lake Oshkosh. Oshkosh. 2.2 2.2 (2.6) Enter an an area area of of higher, higher, gently gently rolling rolling countryside. countryside. This is ground moraine moraine and is a a Valderan ground and outwash complex that that once stood stood as as an an island island in in Glacial Glacial Lake Lake Oshkosh. Oshkosh. 4.8 4.8 (2.2) (2.2) the flat floor of of Descend from the morainal "island" onto the Glacial Glacial Lake Lake Oshkosh. Oshkosh. Here, Here, the the lake lake sediments sediments are are well-drained to to be be intensively intensively farmed. farmed. sufficiently well—drained 7.0 7.0 (0.7) (0.7) This This subdued subdued ridge ridge is is the the western western edge edge of of the the gentle, gentle, east—dipping, east-dipping, Middle Ordovician Ordovician (Platteville—Galena (Platteville-Galena formations) formations) cuesta. cuesta. The route route ahead ahead descends descends through through the the Ordovician St. St. Peter Peter Sandstone Sandstone onto onto aa relatively relatively Middle Ordovician flat surface surface developed developed on on dolomites dolomites of of the the Lower Lower Ordovician Ordovician flat Prairie Prairie du du Chien Chien Group. Group. However, However, the the bedrock bedrock in in this this area area is is obscured obscured by by glacial glacial deposits. deposits. 7.7 (0.3) Enter Enter Omro Omro on on the the Fox Fox River. River. The The Fox Fox flows flows northeasterly northeasterly to to join the the southeasterly southeasterly flowing flowing Wolf River River drainage drainage in in Lake Lake join Butte Butte des des Morts. Morts. This This shallow shallow lake lake is is another another remnant remnant of of Glacial Glacial Lake Lake Oshkosh, Oshkosh, and and it it drains drains into into Lake Lake Winnebago Winnebago at at Oshkosh. Oshkosh. 12 12 �Mileages Mileages The The Middle Middle Ordovician Ordovician St. St. Peter Peter Sandstone Sandstone is is quarried quarried for for foundry foundry This sand sand a few miles south of here near Waukau. sand a few miles south of here near Waukau. This sand is is trucked trucked to to Berlin Berlin for for processing, processing, but but from from 1870-1878, 1870-1878, the the St. St. Peter Peter in in this this area supplied aa glass factory in Omro. glass factory in Ornro. 8.0 8.0 (0.5) (0.5) The The park park on on the the south south bank bank of of the the Fox Fox River River represents represents Unfortunately, use use of of the the flood flood plain. plain. Unfortunately, such such foresight foresight exercised exercised when when downtown downtown Omro Omro was was developed. developed. intelligent intelligent was was not not 8.5 8.5 (2.5) (2.5) Junction Junction Wisconsin 21 21 and and 116 116 at at the the west west edge edge of of Omro. Ornro. Continue Continue on on State State 21, 21, and and cross cross the the Fox Fox River. River. The route ahead ahead parallels the north side of the swampy Fox River valley for for the the next next few few miles. miles. 11.0 11.0 (2.8) (2.8) Another Another area area of of rolling rolling Valderan Valderan moraine moraine that that once once stood stood as as an an island island in Glacial Glacial Lake Lake Oshkosh. Oshkosh. 13.8 13.8 (2.0) (2.0) Intersection Wisconsin Wisconsin 21 21 and and County County K. K. The gentle gentle ridge ridge just just east east of this intersection is the easterly—dipping, western edge of the easterly-dipping, edge of the Lower Ordovician Ordovician Prairie Prairie du du Chien Chien escarpment. escarpment. As such, such, it it serves serves to define the boundary between the Eastern Ridges Ridges and and Lowlands Lowlands and and Central Plain. Plain. the Central The bedrock underlying the the Central Plain is is predominantly predominantly sandstone sandstone Late Cambrian Cambrian age. age. However, the the bedrock in in this this vicinity vicinity is is of Late covered by glacial lake lake sediments. sediments. A A quarry developed developed in in the the Prairie Prairie du du Chien Chien dolomite dolomite is is immediately immediately intersection. The glacial deposits here are are thin thin southeast of this intersection. edge of of the the cuesta. cuesta. along the edge 15.8 15.8 Waushara/Winnebago WausharajWinnebago county county line. line. Enter Waushara Waushara County. County. (1.3) (1.3) 17.1 (2.0) (2.0) 19.1 (1.8) (1.8) bogs, like the one north of the highway, Tamarack bogs, highway, are common common in in poorly— poorlydrained localities throughout throughout this this region. region. The truck-farming area south of the road was a former The former tamarack tamarack bog. When drained by ditching, ditching, the peaty bog soils are highly productive. A remnant of the former habitat still exists along the west edge edge of of the tilled tilled land. land. The prominent line of northeasterly trending ridges about about 33 miles here is northwest of here is part part of of the the Woodfordian Woodfordian morainal morainal complex. complex. These ridges, ridges, which which mark mark the the western western edge edge of Glacial Lake Oshkosh, These Oshkosh, are older older than than the the patches patches of Valderan Valderan till previously traversed. are traversed. Continue west west on on 21. 21. 20.9 (0.3) (0.3) Junction of Wisconsin 21 21 with 49. 49. 21.2 21.2 (5.2) (5.2) Good view view to to the the northwest of the hilly Woodfordian Good Woodfordian drift. drift. The soils adjacent adjacent to the road are lacustrine sediments pinkish to red soils Poor drainage drainage and that accumulated in Glacial Lake Oshkosh. that Oshkosh. Poor numerous tamarack tamarack swamps swamps are are characteristic characteristic of of this this lowland area. numerous area. 13 13 �Mileages Mileages 26.4 26.4 (1.3) (1. 3) Enter Redgranite Redgranite and and Junction Junction with with County N. N. Enter County NN toward toward Lohrville. Lohrville. County Proceed Proceed west west on on Redgranite was was once once the the site site of of aa thriving thriving quarry quarry operation operation and and Redgranite pickle factory. factory. The aa pickle The pickle pickle factory factory might might prosper prosper again, again, but but the quarry quarry is is permanently permanently abandoned. abandoned. Now the Now flooded, flooded, it it is is the the focus focus of aa city city park. park. of This This quarry, quarry, adjacent adjacent to to Wisconsin Wisconsin 21 21 aa few few blocks blocks northwest northwest of of here, employed employed about about 260 260 workers workers in in 1909 1909 to to produce produce hand-trimmed here, granite paving paving blocks blocks for for aa few cents apiece. granite apiece. With With the the average average trimmer producing producing up up to to 300 300 blocks blocks per per day, day, four four trains trains were trimmer were required required to to haul haul the the daily daily output output southward southward to to the the booming booming towns towns of of Milwaukee, Chicago, Chicago, and St. Milwaukee, St. Louis. Quarrying Quarrying declined declined rapidly rapidly after 1915, 1915, when when concrete concrete became became the the preferred road building after material. However, material. a more modest However, other other uses uses of granite granite allowed a operation to continue until the the pit pit was was closed closed in in 1931. 1931. By this time, the the quarry quarry occupied occupied 77 acres acres and extended downward to aa depth time, depth of 200 of 200 feet. feet. As the name of the town indicates, indicates, the rock rock exposed here is a reddish granite. reddish granite. It is and granophyric granophyric in in texture, texture, is fine-grained and and leucocratic leucocratic in in composition, composition, with quartz quartz and alkali feldspar and feldspar comprising 90% to 98% of the the rock. rock. Subordinate minerals include biotite (altered (altered to to chlorite), chlorite), sphene, muscovite, and sphene, hornblende, hornblende, muscovite, zircon. zircon. This granite, granite, like others exposed in in this this general general area, area, is is dated dated at at 1765 1765 m.y. m.y. old. old. A A well-exposed, well-exposed, greenish-black, vertical vertical dike of fine—grained fine-grained metabasalt trends trends northeasterly across across the the lake. lake. This dike is about 5 feet feet wide, wide, and it it has sharp sharp contacts contacts with with the the granite. granite. The Precani1rian bedrock at at this locality Precambrian bedrock locality was polished polished and and striated striated by by westerly westerly moving moving Woodfordian Woodfordian ice. ice. 27.7 27.7 (0.3) (0.3) 28.0 28.0 (0.1) (0.1) 28.1 28.1 (0.1) (0.1) 28.2 28.2 (0.1) (0.1) 28.3 28.3 Enter Enter the the village village limits limits of of Lohrville, Lohrville, once aa thriving thriving center center for for granite granite quarrying. quarrying. County NN turns turns south. south. County County NN turns turns west. west. An An abandoned, abandoned, small small quarry quarry north north of of the the road road exposes exposes aa medium—to medium-to coarse—grained, coarse-grained, reddish reddish granite. granite. The The Lohrville Lohrville Stone Stone Company Company north north of of the the highway highway occupies occupies aa building building constructed constructed from from local local granite. granite. The The piles piles of of glacial glacial erratics erratics gathered gathered together together by by this this firm firm suggest suggest that that these these are are aa more more important important commodity commodity today today than than the the local local bedrock. bedrock. County County NN turns turns south. south. The The large, large, glacially-smoothed glacially-smoothed knob knob of of granite granite north of the highway establishes that Pleistocene deposits north of the highway establishes that Pleistocene deposits are are thin thin in in this this area. area. Depart Depart Lohrville Lohrville as as County County NNturns turns westward. westward. (0.8) (0.8) 14 14 �Mileages Mileages 29.1 29.1 (0.6) (0.6) STOP STOP 11 at at Flynn's Flynn's Quarry Quarry County County Park Park south south of of the the highway. highway. This This park, park, like like the the one one at at Redgranite, Redgranite, is is developed developed around around aa flooded flooded granite quarry. quarry. The The park park road road is is an an old old quarry quarry road, road, which which loops loops granite around around the the lake lake before before returning returning to to County County Highway Highway N. N. Details Details on on the the geology geology at this stop are described by Eugene Smith Smith in in the the next next section section of of this this guidebook. guidebook. Unfortunately, Unfortunately, only only 30 30 minutes is is available available to to examine examine this this interesting interesting locality: locality~ After After stopping, stopping, continue continue westward westward on on County County N. N. The The route route ahead ahead passes passes through through aa low low area area occupied occupied by by tamarack tamarack bogs bogs before before ascending ascending to to higher, better-drained, better-drained, Woodfordian Woodfordian ground ground moraine. moraine. 29.7 29.7 (0.5) (0.5) County County N N turns turns southward southward along along an an irregular, irregular, rolling rolling morainal morainal ridge. ridge. The The till till is is studded studded with large, large, locally—derived locally-derived granitic granitic erratics. erratics. 30.2 30.2 (0.2) (0.2) Enter community community of of Spring Spring Lake. Lake. Enter 30.4 30.4 (0.3) (0.3) Junction County County NNand in Spring Spring Lake. Lake. Junction and FF in 30.7 30.7 (4.1) (4.1) County NN turns turns west. west. Turn northward northward on on N. N. County NNand Z. Turn southwesterly on N N and and leave leave Spring Spring Junction County and Z. Lake, Lake, through an area of rolling sandy till till within the the Woodfordian complex. Large glacial erratics of of local local derivation derivation are are morainal complex. common in the fields fields adjacent to the highway, highway, and and several several kettle kettle lakes general area. area. lakes are present in this general The attractive countryside between here and and Neshkoro is is part of of As such, Green Lake Lake recessional recessional moraine. moraine. As such, it it has the Woodfordian Green little value value for agriculture, but but it is little for agriculture, is highly prized as recreational land for city dwellers who want to be land for city dwellers who want to be weekend "tree farmers." farmers." The The pine plantations that enhance this landscape are the are the result result of of their their endeavors. 34.8 (0.5) (0.5) Pine Bluff Bluff Enter Marquette County. Pine Waushara/Marquette county county line. line. This prominent landmark is located about 33 miles west of is of here. here. landmark is is a glacially-smoothed, elliptical knob of coarse-grained, a glacially-smoothed, elliptical knob coarse-grained, gray to pinkish granite granite that that rises rises more more than than 100 feet above the swampy pinkish feet above The granite of this lowlands River. The this inlier is lithlowlands along the White River. related to the granites exposed in in the the ologically and genetically genetically related to the granites exposed Redgranite-Lohrville and Montello areas. Redgranite-Lohrville areas. Glacial striations striations on on the the bedrock bedrock at at this this locality locality trend trend about about Glacial N65°W. 35.3 35.3 (0.7) (0.7) in an an area area Turn west west on on County County Nand N and E in Junction Nand E. Turn Junction County N and E. where sand sand dunes dunes formed where formed on top of the the sandy Woodfordian drift. drift. 36.0 36.0 (0.5) (0.5) Junction County County Nand N and E with Wisconsin 73. Junction 73. and E. and County County E. 36.5 36.5 (0.7) (0.7) Cemeteries on on both both sides sides of of the the highway highway provide provide ample ample evidence evidence of Cemeteries the monument-quality monument-quality of central Wisconsin granites. the granites. 15 15 Turn south south on on State State 73 73 Turn �Mileages Mileages 37.2 37.2 Cross White White River in downtown Neshkoro. Cross (0.4) (0.4) 37.6 37.6 (1.3) (1. 3) 38.9 38.9 Junction Wisconsin 73, Junction 73, and County E E and and N. N. Turn west on EE and and N. N. The route route ahead ahead leaves leaves the the lowland lowland occupied occupied by by the the White White River and The traverses aa scenic, scenic, rolling rolling upland upland within within the the Woodfordian Woodfordian morainal traverses complex. complex. and E. Junction County County NNand E. Continue west on E. Continue E. (1.6) (1. 6) 40.5 40.5 (2.6) There are are several kettle lakes There lakes of various sizes developed nearby in in sandy, glacial outwash. This This is is another another region region with with low agriculagriculsandy, tural potential, potential, which which is is rapidly rapidly being being converted to to recreational tural recreational !Ifarms "farms." 43.1 43.1 (0.4) Junction County E and and Wisconsin Wisconsin 22. 22. 43.5 43.5 (0.6) Wisconsin granite granite headstones headstones dominate the cemetery east of Central Wisconsin the highway. 44.1 44.1 (0.3) Junction County E and Wisconsin Wisconsin 22. Continue south south on on 22. 22. The route ahead ahead traverses traverses sandy, sandy, rolling, route rolling, Woodfordian ground moraine. moraine. 44.4 44.4 (4.0) (4. 0) 48.4 (2.9) (2.9) 51.33 51. (1.6) (1. 6) 52.9 52.9 Turn 22. Turn south on E and 22. Cross Mecan River, River, one of many fine fine trout trout streams streams in in central central Wisconsin. Peat swamps along the highway were drained and and developed developed as as muck muck farms. The route traverses a The route ahead traverses a stony till formed into broad, broad, low drumlins with aa general general east—west east-west orientation. orientation. This better— betterdrained land supports aa growth of pine and land supports and cedar. cedar. The sand and gravel pit east of the the road road is is developed developed in in Woodfordian Woodfordian outwash. outwash. Kettles are are also also present present in in this this area. area. Enter the the city city of of Montello. Montello. (0.5) (0.5) 53.4 53.4 (0.3) (0.3) 53.7 53.7 (0.1) (0 .1) Junction of of Wisconsin Wisconsin 22 22 with with 23 23 in in Montello. Montello. 22 22 and and 23. 23. Turn west on Wisconsin Quarries north of the the highway exploited aa ridge ridge of of finefine- to to mediummediumgrained, red to grayish—red granite to produce monument stone, grained, red to grayish-red granite to produce monument stone, paving paving blocks, blocks, building building stone, stone, and and crushed crushed rock. rock. When When this this granite granite was was selected selected for for the the tomb tomb of of U.S. u.s. Grant Grant in in New New York York City, City, business business boomed. activity peaked, peaked, with with some some 200 workers employed. boomed. By 1910, 1910, activity employed. In In later later years, years, business declined until the the last last quarry quarry closed closed in in 1976, 1976, after nearly nearly 100 100 years years of of operation. operation. The The longevity longevity of of operations operations at at this locality locality was facilitated facilitated by well—developed well-developed vertical vertical joints joints that that allowed the the rock rock to to be be removed removed in in large large "precut" "precut" blocks. blocks. The granite of this this inlier is granophyric and leucocratic like area and and at at Pine Pine Bluff. Bluff. It It those those exposed in in the the Redgranite-Lohrville Redgranite-Lohrville area is is also also of of the the same same age age (1765 (1765 m.y. m.y. old). old). Several Several near-vertical near-vertical dikes dikes 16 16 �Mileaqe of of greenish-black, greenish-black, fine-grained fine-grained metabasalt metabasalt up up to to 55 feet feet thick thick cut cut the the granite, granite, and and are are well well exposed exposed in in the the quarries. quarries. Well monadnock Well drilling drilling adjacent adjacent to to the the granite granite ridge ridge discloses discloses that that this thismonadnock stood stood more more than than 200 200 feet feet above above the the general general level level of of the the Precambrian Precambrian surface surface prior prior to to transgression transgression of of the the Late Late Cambrian Cambrian sea sea (see (see article article by by Eugene Eugene I. I. Smith Smith in in this this guidebook). guidebook). Glacial Glacial striae striae on on the the bedrock bedrock surface surface indicate indicate ice moved westerly westerly across across this this area. area. ice 53.8 53.8 (0.5) (0.5) 54.3 54.3 (0.4) (0.4) Junction Wisconsin Wisconsin 22 22 and and 23. 23. Junction that that the the Woodfordian Woodfordian Turn Turn south south on on State State 22. 22. Cross the the Fox Fox River River once once Cross again. again. The The Fox flows flows northeasterly northeasterly to to reach reach Lake Winnebago, Winnebago, and and ultimately Lake Lake Michigan at at Green Green Bay. Bay. We We first first crossed it it about about 46 46 miles miles ago, ago, at at Omro. Omro. The Fox was part of the historic canoe canoe highway highway across across Wisconsin. Wisconsin. Although used used by by Indians Indians for for centuries, centuries, it it was was "popularized" "popularize& by Marquette and and Joliet on their their historic journey journey from from Lake Lake Michigan Michigan A flood of explorers, missionaries, trappers, Mississippi. A flood trappers, to the Mississippi. The Fox is dammed just and traders traders soon soon paddled paddled after after them. them. just upstream and and enlarge enlarge Buffalo Buffalo Lake. Lake. Thelocks The locks visible from from here to deepen and the highway were part of of a a navigation scheme scheme originally originally designed designed to link the the North Atlantic (via the Great Lakes) with the Gulf of (via Lakes) Shifting Mexico (via the Wisconsin River and the Mississippi). (via the Wisconsin River and the Mississippi). Shifting sandsandbars along the shallow Wisconsin River ruled against this the River ruled against this plan plan from from the beginning. 1.5 A canal at Portage, Wisconsin was started in 1838 to eliminate the at Portage, the 1.5 mile land bridge between the headwaters of the Fox and the Wisconsin mile This project was finally completed in 1876, River. 1876, but the cost of maintaining a a channel in the Wisconsin River proved prohibitive, prohibitive, and and soon abandoned. abandoned. the project was soon 54.7 (1. 8) (1.8) 56.5 (1. 7) (1.7) 58.2 58.2 (1. 5) (1.5) into an an Leave Montello and Leave and the the lowland lowland along along the the Fox Fox River, River, and proceed proceed into area ground moraine. moraine. area of rolling, rolling, Woodfordian ground The prominent, prominent, wooded wooded hill hill about about 44 miles miles to to the the southwest southwest is is The Observatory Hill, Hill, the highest point in with an an Observatory in Marquette Marquette County, County, with This will will be the locale of our elevation feet. This our second second stop. stop. elevation of 1080 feet. deposited in The in aa The truck truck farms farms in in this this flat flat area area utilize utilize fertile fertile soils soils deposited glacial lake, lake, which which formed formed when when northeasterly northeasterly drainage drainage was was blocked glacial by ice. by the the retreating Woodfordian ice. 59.7 59.7 (0.2) (0.2) We will will return return to this Junction B. We this interJunction Wisconsin 22 and County B. loop. section in in aa few few hours, hours, and and go go east east on on BB after after making making aa large large loop. section outwash. Continue south south on on State State 22 22 in in an an area area of of pitted pitted sandy sandy outwash. Continue purity of of Gravel Gravel pits pits in in this this area area are are testimony testimony to to the the water-washed water-washed purity these these deposits. deposits. 59.9 59.9 (0.9) (0.9) Our Turn east on Gem Road. Junction 22. Turn Road. Our Junction Gem Gem Road Road and Wisconsin 22. southwest immediate destination destination is is Observatory Observatory Hill, Hill, about about 22 miles miles southwest immediate 17 17 �Mileages Mileages of here. here. To To of and approach and approach reach our our objective, objective, we we must must circle circle this this promontory, promontory, reach from the the west. west. A small small kettle is located northwest northwest of of the the highway. highway. 60.8 60.8 (1.4) (1.4) Large glacial glacial erratics erratics of of local local derivation derivation litter the field north of Large the road. the road. 62.2 62.2 (0.2) Junction 14th Road and Gem Road. Junction Road. 62.4 62.4 (1.0) Junction 14th Road and 13th Road. Turn Junction (left) on 13th Road Turn south (left) in an an area of rolling ground moraine. At long last, in last, we are closing in on Observatory Observatory Hill! in Hill~ 63.4 63.4 (0.5) An irrigation well west of the road encountered Precambrian Precambrian porphyritic rhyolite, rhyolite, lithologically identical to to exposures exposures on on Observatory Hill, Hill, at a a depth of of 300 300 feet. feet. 63.9 63.9 (0.4) (0.4) 64.3 64.3 (1.1) (1.1) Turn (left) on 14th Road. Road. Turn west west (left) - Junction 13th Road and Gillette Ave. Ave. Proceed southeasterly (straight (straight ahead) on on Gillette Gillette Ave. Ave. and ascend the ahead) the flank flank of Observatory Hill. Hill. STOP 22 for for Observatory Observatory Hill rhyolite. STOP rhyolite. This bedrock hill, hill, which rises rises about 250 above the level of the surrounding landscape, about 250 feet feet above the level landscape, has aa core of resistant core resistant rhyolite rhyolite flanked by medium—to medium-to coarse—grained, coarse-grained, friable, friable, iron-stained Upper Upper Cambrian Cambrian sandstone. sandstone. Locally, Locally, this sandgrades into a stone grades a conglomerate that contains clasts derived from from the Precambrian bedrock. the bedrock. Glacial striae on the rhyolite vary from N45W to N74W, Glacial N74W, and record record the movement of ice over and around this resistant knob. the knob. A A detailed description of the the rocks rocks at at this this locality locality is is provided provided by by Eugene Smith Smith in in the the next next section section of of this this guidebook. guidebook. Since only 60 60 minutes is is allocated for for this this stop, stop, we should should proceed proceed with with enthusiasm: enthusiasm~ NOTE: Since this road dead ends ends about about 0.4 mile ahead, backtrack northwesterly to to the the intersection intersection of of Gillette Gillette Road Road and and 13th 13th Road. Road. The logged mileage that follows follows' assumes a turn—around turn-around at the the dead end end of Gillette Gillette Road Road after after this this stop. stop. a 65.4 65.4 (0.7) (0.7) 66.1 66.1 (0.2) (0.2) 66.3 66.3 (0.4) (0.4) 66.7 66.7 (1.5) (1.5) Intersection of Gillette Road Road and and 13th 13th Road. Road. The bedrock bedrock of of the the high, high, wooded hill west of of this this intersection intersection is is Upper Cambrian Cambrian sandstone sandstone with no no rhyolite rhyolite exposed. exposed. Turn south south on on 13th 13th Road. Road. 13th 13th Road Road turns turns sharply sharply to to the the west west in in an an area area of of rolling rolling countryside countryside formed by aa Woodfordian Woodfordian recessional recessional moraine. moraine Pine plantations, cedars, cedars, and oaks accentuate accentuate the the beauty beauty of of this this glacial glacial landscape. landscape. Junction Junction 13th 13th Road Road and and Gillette Gillette Drive. Drive. Continue Continue west west on on Gillette. Gillette. NOTE: NOTE: It It seems seems that that the the Gillettes Gillettes are are important important in in this this country! country~ AA low low bedrock bedrock ridge ridge north north of of the the road road is is the the Taylor Taylor Farm Farm rhyolite rhyolite locality. porphyritic rhyolite exposed here locality. The The well-jointed, well-jointed, porphyritic here is is 18 18 �Mileages Mileages similar similar to to that that found found on on Observatory ObservatoryHill. Hill. However, However, the the high high bedbedrock rock hill hill of of sandstone sandstone northeast northeast of of here here separates separates these these two two localities. Glacial Glacial striae striae on on this this rhyolite rhyolite document document aa general general localities. N70W N70W direction direction of of ice ice flow flow for for the the Green Green Bay Bay lobe lobe of of Woodfordian Woodfordian ice at at this this locality. locality. ice Turn Turn south south on on County County F. F. 68.2 68.2 (0.2) (0.2) Junction Junction Gillette Gillette Drive Drive and and County County F. F. " 68.4 68.4 LUNCH STOP STOP at at John John Muir Muir County County Park Park on on Ennis Ennis Lake. Lake. LUNCH (1. 4) (1.4) John John Muir, Muir, aa distinguished distinguished naturalist naturalist and and aa prime prime mover mover in in the the establishment establishment of of our our national national park park system system in in 1890, 1890, was was born born in in His family came to Wisconsin to farm the land Scotland in 1838. His family came to Wisconsin to farm the land Scotland in 1838. he was only a boy of across the lake from this memorial park when he was only a boy of across the lake from this memorial park when Fountain Lake 11. He grew up on this beautiful kettle lake (called Fountain Lake He grew up on this beautiful kettle lake (called 11. ingredient in the in those days), and it proved to be a significant ingredient in the in those days), and it proved to be a significant development of his love of nature. development of his love of nature. The The importance importance of of this this lake lake to to Muir Muir is is well well documented documented on on page page 96 96 Youth" (University of his autobiography, autobiography, "The "The Story of My Boyhood Boyhood and and Youth" (University Press, 1965). 1965). of Wisconsin Press, "Our beautiful beautiful lake, lake, named Fountain Lake by father, father, but Muir's Muir's Lake Lake lakes by the neighbors, neighbors, is one of the many small small glacier glacier lakes that that adorn adorn It is Wisconsin landscapes. landscapes. is fed by twenty or thirty meadow the Wisconsin surrounded by by springs, is is about about half a mile long, wide, and surrounded springs, a mile long, half as wide, meadows low finely-modeled hills dotted with oak and hickory, and finely-modeled hills hickory, meadows and ferns. full of grasses ferns. full grasses and and sedges sedges and many beautiful orchids and First there a zone rushes, and just just beyond beyond the the there is is a zone of green, green, shining rushes, fifty or or sixty rushes sixty feet feet rushes aa zone zone of of white white and orange orange water-lilies fifty On bright days, forming aa magnificent magnificent border. border. days, when the lake wide forming sun—spangles danced together together breeze, the lilies lilies and and sun-spangles danced was rippled by a breeze, between in radiant radiant beauty, beauty, and and it it became became difficult difficult to to discriminate discriminate between in them. them. and Bible-lessons, Bible—lessons, On chores and sermons and On Sundays, Sundays, after or before before chores especially in lily time, we the lake lake for for hours, hours, especially in lily time, we drifted about on the ducks, getting finest finest lessons lessons and and sermons sermons from from the the water water and flowers, getting flowers, ducks, In particular particular we we took took Christ's Christ's advice advice and and fishes, fishes, and and muskrats. muskrats. In they grow grow up up in in beauty beauty out out how they devoutly devoutly "considered the lilies" -- how ideglOri0USlY among the breezy sun-spangles." of of gray gray lime lime mud, mud, and and ride gloriously among the breezy sun-spangles." of rolling, rolling, After lunch, lunch, continue continue south south on on County County FF through through an an area of After Immediately to to the the west, west, the the north-flowing north-flowing Fox Fox River River sandy sandy drift. drift. Immediately parallels parallels the the highway. highway. 69.8 69.8 (1. 7) (1.7) The rolling, rolling, sandy, sandy, Turn east east on on County 0. Junction O. Turn o. The Junction County County F and 0. Differences ground moraine moraine contains contains large large erratics erratics scattered about. ground about. Differences with tamaracks tamaracks in in drainage drainage are are clearly clearly reflected reflected in in the vegetation, vegetation, with the higher, well— in in swampy swampyplaces, places,and andoaks oaksand andplantation plantation pines pines on on the higher, welldrained drained soils. soils. 19 19 �Mileages Mileages 71.5 71. 5 (1.4) (1. 4) 72.9 72.9 Junction County County 00 and and 13th 13th Road. Road. Junction Turn Road. Turn south south on on 13th Road. Knights Lake, Lake, on on the the east east side side of of the the road, road, occupies occupies aa small Knights small kettle. kettle. (0.7) (0.7) 73.6 73.6 (0.4) (0.4) Junction 13th Road and 14th Road. Junction Road. Turn (right) on 14th Road. Road. Turn south south (right) This road road curves curves eastward immediately ahead. This ahead. 74.0 74.0 (0.9) (0.9) Junction 14th 14th Road Road and and Dalton Dalton Road Junction Road at at the the Marquette/Columbia Marquette/Columbia county line. Turn south south (right) on Dalton Dalton Road Road and and enter enter Columbia County, County, line. Turn (right) on through rolling rolling country country with with some some land land suitable suitable for agriculture. through for agriculture. 74.9 74.9 (0.2) (0.2) Junction Dalton County CM. CM. Junction Dalton Road Road arid and County Turn (right) Turn southwesterly (right) County CM CM in in an an area with abundant erratics. County erratics. We will backtrack We will this intersection after Stop 3. this 3. 75.1 75.1 (0.4) (0.4) well on on the the A. A. Uchtung farm on the right side of the road reached A well Precambrian rhyolite at at aa depth depth of of 390 390 feet. feet. Drilling continued 170 feet into the rhyolite. feet into the rhyolite. 75.5 75.5 (0.6) (0.6) 76.1 76.1 (0.1) (0.1) 76.2 76.2 (0.7) (0.7) Junction County CM and and Monthey Monthey Road. Road. Road. Road. on to Turn south (left) (left) on Monthey Exposure road. Exposure of Middle Middle Precambrian Marcellon rhyolite east of the road. This is is one one of four This four isolated exposures of rhyolite in this immediate immediate area. area. STOP 33 at Marcellon rhyolite locality. STOP locality. This scenic exposure is is aa 70 feet feet above above glacially rounded and polished knob that rises nearly 70 the surrounding surrounding countryside. countryside. Glacial striae indicate aa westerly direction for for Woodfordian Woodfordian ice ice flow flow at at this this locality. locality. A A detailed description of of the geology geology to to be be observed observed here is is supplied supplied by Eugene Smith Smith in in the the next next section section of of this this guidebook. guidebook. only 45 45 minutes for for an an examination examination of of this this Unfortunately, we have only interesting interesting exposure. exposure. After studying studying the the rock rock here, turn turn around around and and backtrack backtrack northward northward along along Monthey Monthey Road. Road. 76.9 76.9 Junction Junction Monthey Monthey Road Road and and County County CM. CM. Turn northeast northeast (right) (right) on on CM. CM. Turn (0.6) (0.6) 77.5 77.5 (2.7) (2. 7) 80.2 80.2 (0.6) (0.6) 80.8 80.8 (0.2) (0.2) Junction Junction CM CM and and Dalton Dalton Road. Road. Continue Continue northeastward northeastward on on CM CM through through rolling, rolling, glacial glacial countryside. countryside. Junction Junction County County CM CM and and Wisconsin Wisconsin 22. 22. Turn .=T:.. :u:.::r:..:.n=-.north . :n.:.:o::..:r=.t.=.h:..:. . .(left) --'(.=1:.. :e:.. :f::..:t"-'):.. .-o::.on .:n:..:. . . =State S:.. :t:..:.a::..:t::..:e::.. . .22 . :2::..:2=. and and cross cross Columbia/Marquette Columbia/Marquette county county line. line. Enter Enter Marquette Marquette County County once once again. again. State State Historical Historical Marker Marker on on the the east east side side of of the the highway highway is is entitled entitled "John "John Muir Muir Country," Country," and and it it describes describes his his sojourn sojourn in in this this area. area. It It also also includes includes this this meaningful meaningful quote quote of of Muir's: Muir's: 20 20 �Mileages Mileages "Everybody needs beauty as well as as bread; bread; places to play in and places to pray to in and to pray in, in, where nature may heal heal and and cheer, cheer, and and give give strength to body and and soul soul alike." alike." 81.0 (1. 2) (1.2) The house house west of the fieldstone, the trade 82.2 (3.6) Wisconsin 22 22 climbs climbs onto a a highland littered littered with with glacial glacial erratics. erratics. 85.8 (3.5) road name is a a showplace for samples of Wisconsin for for glacial glacial erratics. erratics. Junction Wisconsin Wisconsin 22 22 and and County County B. B. Turn east on County B, in in a a region of sandy outwash outwash occupied occupied by by gravel gravel pits. pits. The route ahead is is numerous swamps, characterized by numerous swamps, some of which are drained for muck farming. Higher areas support support pine pine plantations. plantations. 89.3 (0.7) Marquette/Green Marquette/Green Lake Lake county county line. line. Enter Green Lake Lake County. County. 90.0 (3.1) (3.1) The poorly drained lowland lowland north of of the the road road is is part part of of the the extenextensive Grand River Wildlife Area. Area. When the retreating Woodfordian ice dammed the the northeastward flowing flowing drainage drainage of of the the Fox Fox and and Grand Grand rivers, rivers, In time, time, it filled with meltaa glacial lake formed formed in in this this area. area. In water, westward into water, and overflowed westward into the the Wisconsin River. River. However, continued retreat of the Green Bay lobe lobe of the Woodfordian ice redrainage, and this lake was emptied. However, Lake stored northeasterly drainage, emptied. However, Puckaway and and Buffalo Lake Lake exist exist as as remnants remnants of of this this ancient ancient water water body. body. 93.1 Junction County and H.. Junction County BBand H. Continue northeasterly (left) (left) on on BBand H. and H. (0.3) 93.4 (2.4) 95.8 (0.5) (0.5) 96.3 (0.3) and H. Junction County B Band H. Turn north north on on County County H. H. The high, high, wooded hill to the northeast of this this intersection intersection is is Bartholomew Bartholomew Bluff. Bluff. It It is a is a bedrock feature feature composed of Upper Cambrian formations formations capped by resistant Lower Ordovician dolomite dolomite of of the the Prairie Prairie du du Chien Chien Group. Group. The route ahead traverses the the east east edge edge of of an area of of poorly—drained, poorly-drained, glacial lake deposits now occupied by the Grand River Marsh. glacial lake deposits Marsh. The bedrock hill immediately northwest of the the road road is is one of several isolated rhyolite exposures, exposures, which trend northwestward from from here for for about one mile. about one mile. In In all, all, there there are are seven rhyolite knobs knobs in this general area. area. These features features stood several hundred feet feet above above the the general general Precambrian erosional level as monadnocks,prior to transgression of of the the Upper Cambrian sea (see (see article by Eugene I. I. Smith in this guidebook). guidebook). STOP 4 STOP 4 at an exposure of the the Marquette Marquette rhyolite. rhyolite. The cedar-covered, cedar-covered, glacially-smoothed, bedrock bedrock knob west of the highway rises about glacially-smoothed, 100 feet above poorly-drained tamarack swamps to the north. 100 feet above north. A A similar exposure lies immediately east east of of the the road. road. Glacial striations and chatter marks on the bedrock indicate indicate that that the the Woodfordian ice generally moved westward at this locality. locality. However, measurements vary vary from from N57W N57W to to N86W. N86W. analysis of of the the rhyolite rhyolite at at this this stop stop is is provided provided by by Eugene Eugene Smith An analysis in the next section section of of this this guidebook. guidebook. About 60 60 minutes are available to study the the exposures exposures at at this this locality. locality. 21 �Mileages After examining the rhyolite, rhyolite, continue northeasterly on County H. H. 96.6 (1.0) (1. 0) 97.6 (3.8) KK. Turn Turn east (right) and KK. Junction County H H and and KK. (right) on H Hand KK. The route ahead traverses traverses rolling rolling ground ground moraine moraine studded with with numerous numerous erratics. erratics. ahead The shape of the east—west east-west trending drumlin south of the road road estab— establishes that ice movement in this area lishes area was was to to the the west. west. Junction County H, Continue straight ahead (east) H, KK, KK, and and B. B. Continue (east) on County H. The route ahead traverses scenic, County scenic, glacial countryside countryside with some agricultural potential. some potential. Lake Lake Puckaway, Puckaway, an an enlargement of the Fox River, River, is occasionally occasionally visible visible to to the the north. north. 101.4 (2.1) Junction County HH and Wisconsin 73. Turn south (right) and Wisconsin (right) on State State 73. 73. The route ahead traverses traverses rolling rolling agricultural agricultural land. land. 103.5 (0.3) Junction Wisconsin 73 73 and and 44. 44. 103.8 (0.6) Enter Manchester, Manchester, a a hilltop community astride the the Green Lake Lake recessional recessional moraine. This prominent glacial feature, feature, which trends trends north-northwestnorth-northwestward and south—southeastward south-southeastward from from here, here, formed formed as as the the Green Bay Bay lobe lobe of the Woodfordian ice paused paused during during retreat. retreat. 104.4 104.4 (0.4) Leave Manchester in an an easterly easterly direction. direction. The boundary between two major physical provinces trends trends northeast—southwest northeast-southwest through through this this area. area. The Central Plain, Plain, to the northwest, is a The the northwest, a subdued region characterized by Upper Upper Canibrian Cambrian bedrock. The Eastern Ridges and Lowlands, Lowlands, with younger bedrock, occupies the the region region to to the the east east and and southeast. southeast. However, this However, this division is ill—defined ill-defined here because of the thick cover cover of young glacial glacial deposits. deposits. 104.8 (0.4) (0.4) Junction Wisconsin 73 73 and and 44. 44. rolling agricultural agricultural land. land. 105.2 105.2 Cross Grand River. River. Continue south on 73 73 and and 44. 44. Turn south on State 73 in an area area of (1.6) (1. 6) 106.8 106.8 (0.7) (0.7) The highway intersects intersects aa drumlin drumlin that that trends trends east-west. east-west. The blunter, east—facing east-facing nose of this drumlin indicates westerly ice ice movement in in this area. area. 107.5 107.5 Lake Maria, Maria, east of the highway, highway, lies lies along the trend of the the Green Lake recessional moraine. moraine. (1.8) (1. 8) 109.3 (0.6) (0.6) Green Lake/Columbia Lake/Columbia county county line. line. Enter Columbia County in in an an area area where intensively farmed farmed drumlins stand stand above above flat, flat, low low areas areas that that are poorly poorly drained. drained. When drained, drained, these lowlands lowlands are are productive muck farms. farms. 109.9 109.9 (2.9) (2.9) Several roadcuts the next 0.5 mile expose thin-to medium-bedded roadcuts in the Lower Ordovician Ordovician dolomite dolomite of of the the Prairiedu Prairie du Chien Chien Group. Group. Some of of these bedrock exposures form form the the cores cores of of drumlins. drumlins. 112.8 112.8 (2.0) (2.0) The high-voltage power lines crossing the highway come come from from aa large, large, coal-fired power plant plant at at Portage. Portage. This facility facility utilizes Wisconsin River water water as as aa coolant. coolant. 22 22 �Mileages Mileages 114.8 114.8 (0.5) (0.5) Junction Junction Wisconsin Wisconsin 73 73 and and 33. 33. 115.3 115.3 (1.0) (1.0) Enter Randolph. Randolph. Enter 116.3 116.3 (0.2) (0.2) Leave Leave Randolph. Randolph. '116.5 ll6.5 (13.0) (13.0) Continue Continue south south on on 73. 73. Cross Cross Columbia/Dodge Columbia/Dodge county county line, line, as as Wisconsin Wisconsin 73 73 turns turns east, east, and and then south. south. Enter Enter Dodge Dodge County. County. The route route ahead ahead traverses traverses rich rich agricultural land land developed on a swarm swarm of broad, well—formed, well-formed, southsouthwesterly-trending drumlins. drumlins. westerly-trending 129.5 129.5 (1.3) (1.3) Junction Wisconsin 73 73 and and U.S. u.s. 151. 151. 130.8 130.8 (0.9) (0.9) Dodge/Columbia Dodge/Columbia county county line. line. Enter Columbia County and and the the city city of of Cross southeasterly flowing Crayfish River. Columbus. southeasterly flowing Crayfish River. Columbus. 131.7 131.7 (0.6) (0.6) Junction Wisconsin Wisconsin 73 73 and and 89 89 in in Columbus. Columbus. Wisconsin 89. Wisconsin 89. 132.3 132.3 (3.0) (3.0) Leave Columbus. Columbus. The route route ahead ahead traverses traverses intensively intensively farmed, farmed, rolling, rolling, glacial countryside. countryside. 135.3 135.3 (4.8) (4.8) Columbia/Dane county county line. line. Enter Dane County. County. drumlins here trend trend southwesterly. southwesterly. 140.1 (1.4) (1.4) Dane/Dodge county county line. line. drumlins. 141.5 (0.7) (0.7) Stop sign at junction junction of of Wisconsin Wisconsin 89 89 and and County County T. T. (east) on on Dalman Dalman Road. Road. ahead (east) 142.2 (1.0) (1.0) Junction Dalman Road Road and and County County I. I. 143.2 (1.0) (1.0) village of Portland and junction with Wisconsin 19. Village 19. 19, and and leave leave Portland. Portland. on State 19, 144.2 (0.3) (0.3) Cross Maunesha Maunesha River. River. 144.5 (0.1) (0.1) Knobs of of glacially-smoothed, glacially-smoothed, Middle Middle Precambrian Precambrian Waterloo Quartzite Knobs These exposures exposures are are two of lie lie north north and south of the highway. These about aa dozen dozen quartzite quartzite knobs knobs that that protrude protrude through the the glacial drift about All of the the exposures exposures are are smoothed by glacial in area. All in this general area. action, and and some some have have small potholes developed action, developed on on the the upper upper surfaces. surfaces. This quartzite quartzite is is quite quite This Baraboo syncline, syncline, about Quartzite, ripple ripple marks marks Quartzite, also present present within within the also Continue south south on on State State 73. 73. Turn south south (left) (left) on on Broad, Broad, well-shaped Enter Dodge County in an area with occasional Proceed straight Turn south (right) (right) on County County I. I. Turn northeast to that that exposed in the well-known similar to Like the the Baraboo 35 35 miles to to the the northwest. northwest. Like cross bedding, and conglomeratic beds are cross bedding, thick quartzite sequence sequence in in this this area. area. 23 23 �Mileages The structure here is an easterly plunging The plunging syncline. syncline. as at at Baraboo, Baraboo, may have occurred 1650 as 1650 m.y. m.y. ago. ago. This folding, folding, Measurements of glacial striae indicate that the ice flowed Measurements flowed about S2OW at at this locality. S20W locality. 144.6 (0.3) STOP 5 at at the the abandoned abandoned John John O'Laughlin O'Laughlin quarries quarries in in the the Waterloo Waterloo STOP Quartzite. The quartzite quartzite at this stop is described by Eugene Smith in the next The at this minutes Is section of this this guidebook. guidebook. About 30 30 minutes is allotted to assimilate the geology at at this this locale. locale. 144.9 144.9 (1.7) Junction Wisconsin 99 99 and and Hubbleton Hubbleton Road. Road. 19. Proceed east on Wisconsin About 1 mile north along along Hubbleton Road, Road, in in the the ditch ditch along along the the eastern edge edge of the the road, eastern road, an isolated exposure of Paleozoic conglomThis conglomerate, erate is is present. present. This conglomerate, which contains rounded Waterloo Quartzite boulders boulders up to 66 feet across, is probably a Quartzite feet across, a local facies facies of the Middle Ordovician St. St. Peter Peter Sandstone. Sandstone. It is is also one of the few Paleozoic exposures in in this this general general area. area. About 0.5 0.5 mile mile straight north of the St. About St. Peter conglomerate locality, locality, at the at the junction of Maunesha Creek and the Crawfish River, River, is is Stony Stony Island. This is This is another glacially rounded mass of Waterloo Quartzite. Here, several pegmatite dikes dikes up to 3.2 feet thick intruded the Here, quartzite after after folding. folding. These dikes were dated by L.T. L.T. Aldrich and and others in 1959 as as 1444 1444 m.y. old. old. The route more drumlin county, The route ahead traverses traverses more county, although the agricultural potential is not as good as it was is as good as it was east east of of Portland. Portland. 146.4 146.4 (0.4) Easterly dipping Middle Precambrian Waterloo Quartzite adds dipping ledge ledge of Middle adds interest to Interto the lawn of the the farmhouse farmhouse south of the highway. highway. mittent exposures indicate indicate that that this this ledge ledge persists persists southward southward along along strike for almost a mile. for almost a mile. 147.0 (0.3) (0.3) Another exposure of Waterloo Quartzite is is visible visible about about 100 100 yards yards north north of the highway. the highway. 147.3 (0.5) (0.5) Junction Wisconsin Wisconsin 19 19 and and County County GG (north). (north). Continue east east on on 19. 19. Exposures of brecciated Waterloo Quartzite cemented cemented by by milky milky quartz quartz are located about 0.75 0.75 mile to to the the north. north. Additional exposures of quartzite are present in in the the vicinity vicinity of of Mud Mud Lake, Lake, about about 55 miles miles north—northeast north-northeast of of here here along along County County G. G. 147.8 147.8 (0.5) Dodge/Jefferson Dodge/Jefferson county county line. line. Enter Jefferson County. County. 148.3 148.3 (2.4) Hubbleton Hubbleton and and junction junction Wisconsin Wisconsin 19 19 and and County County G. G. Turn south south (right) (right) on GG in a a broad area of flat, flat, poorly-drained muck soils soils located located between between intensively intensively farmed drumlins. drumlins. Where ~ihere ditched, ditched, the muck soils soils are also also cultivated. cultivated. 24 24 �Mileages Mileages 150.7 150.7 (2.1) (2.1) County county GG continues continues southward southward through through drumlin drumlin country. country. 152.8 152.8 (1.4) (1.4) The The low low ridge ridge of of Waterloo Quartzite Quartzite in in the the field field about about 150 150 yards yards east of the highway is sometimes referred to as the Lake east of the is sometimes referred to as the Lake Mills Mills here is is light light blue blue to gray in exposure. exposure. The The quartzi-te quartzite here in color, color, and and it is composed almost entirely of coarse, interlocking quartz it is composed almost entirely of coarse, interlocking quartz grains grains with with rare rare mica. mica. Primary Primary foliation foliation (bedding) (bedding) strikes strikes N. 500 W. and dips 70° northeast on the south N. 50° W. and dips 70° northeast on the south limb limb of of the the Waterloo syncline. syncline. Waterloo 154.2 154.2 (2.0) (2.0) Junction Junction County County GG and and Wisconsin Wisconsin 89. 89. through good good drumlin drumlin country. country. through 156.2 156.2 (1.8) (1.8) Junction Junction Wisconsin Wisconsin 89 89 and and Interstate Interstate 94. 94. Milwaukee. 1 Milwaukee.1 Turn south on Wisconsin 89 89 Turn east on 1-94 I-94 toward toward The 1-94 I-94 route from from the Lake Mills-Waterloo interchange interchange to to Milwaukee is entirely within the Eastern Ridges and and Lowlands physical province, and the highway trends at right angles to the the general general strike strike of of the the Paleozoic Paleozoic formations. formations. Consequently, Consequently, the bedrock along along the the route route ranges from from Middle Ordovician formations formations on the the west to to Silurian Silurian on the the east. east. However, However, these rocks rocks are are largely largely obscured obscured dolomite on glacial deposits. deposits. by Woodfordian glacial The glacial geology encountered along along 1-94 I-94 between here and and Milwaukee Milwaukee spectacular. The orientation of the the route route is is such such that that the the interinteris spectacular. state cuts cuts most glacial glacial features state features essentially at right angles. angles. From west to east, east, these include well—developed well-developed drumlin drumlin fields, fields, outwash outwash plains, plains, the Kettle Interlobate Interlobate Moraine with numerous scenic scenic lakes, lakes, and recessional recessional moraines moraines of the the Lake Lake Border morainic system. and system. Other significant attractions along along this this route route include: include: the Lapham Peak overlook high in the Kettle Moraine, Moraine, and and the subcontinental subcontinental divide, divide, which separates drainage destined for for the North Atlantic via via the the St. Lawrence Lawrence from that that which flows to the St. flows to the Gulf of Mexico via the Mississippi. 158.0 (2.0) (2.0) Eastbound rest area in in an area area of rolling rolling ground ground moraine. moraine. 160.0 (1.0) (1.0) 1-94 crosses the Crawfish River, I-94 River, aa tributary tributary to to the the Rock. Rock. Aztalan In State Park is is 1.5 miles miles south on the west bank of this river. State river. In addition to to Late Late Woodland Woodland Indian Indian effigy effigy mounds, mounds, this this park park contains contains addition two—tiered pyramidal mound, mound, and a aa two-tiered a partly restored stockaded village identified with the the Middle Middle Mississippi Mississippi culture. culture. When the site was was first first described described in in 1837, 1837, it it was was named named Aztalan Aztalan in the the hope hope site that the the cultural cultural remains remainspreserved here were were those those of Mexican Mexican Aztecs. Aztecs. that preserved here To reach reach the the park, park, use use the the Lake Lake Mills Mills exit exit and and then then turn turn east on To County B. County B. 161.0 161.0 (1.0) Westhound rest rest area, area, in in an an area area of ground ground moraine moraine and low—lying Westbound low-lying drumlinoid drumlinoid hills. this geologic guide published with with permission ofofKendall/ 1ndof The remainder of this road geologic roadis guide is published permission Kendall/ be duplicated duplicated by by any any means means Hunt Publishing Company, Company, Dubuque, Dubuque, Iowa, Iowa, and and it should not not be Hunt without 25 without written permission. permission. 25 �Mileages Mileages 162.0 162.0 (1.0) (1.0) 1—94 crosses the Rock The Rock Rock marks marks aa general general vegetation I-94 Rock River. River. The divide between between native native hardwood hardwood forests forests to to the the east, east, and and oak oak divide savannas and prairies to the west. Some think think the the river river formed savannas west. Some formed barrier to to prairie prairie fires, fires, thus thus preserving preserving the the forests forests to to the the aa barrier east. east. Jefferson, 6.5 miles miles to Jefferson, to the south at the junction of the Crawfish and Rock Rock rivers, rivers, experienced experienced aa short-lived, short—lived, geology-related, geology—related, land and boom about about 1840. 1840. A federally—assisted federally-assisted project was planned to to construct aa canal canal from from Lake Lake Michigan Michigan at at Milwaukee Milwaukee to to the the Rock River construct Some construction construction was was actually actually accomplished before near Jefferson. Jefferson. Some the million-dollar million—dollar project was was abandoned. abandoned. Meanwhile, Meanwhile, land land values had sky—rocketed sky-rocketed in Jefferson as as the prospect of a connection the Mississippi Mississippi River River and and the the Great Great Lakes Lakes seemed seemed imminent. iminent. between the Land promoters arrived, arrived, and a a steamboat made it up the Rock River River from St. St. Louis. Tracts of swampland were bought by local residents residents and newcomers newcomers at at inflated inflated prices, prices, in in the the hope hope that that great profits profits and would result when the the canal canal was was completed. completed. The The land promoters left town town with with well-laden well—laden carpetbags carpetbags before before news news of the the abandonabandonleft ment of the canal plans plans reached reached southern southern Wisconsin. Wisconsin. 163.0 (6.0) Watertown, Johnson Creek, Exit Wisconsin 26 to Watertown, Creek, and Jefferson, Jefferson, within the Jefferson County County drumlin drumlin field. field. Where the interstate interstate cuts through a a drumlin, drumlin, the roadcuts have been carefully sodded sodded over to conceal the internal character of the sandy and and clayey clayey till. till. However, However, at the northwest corner of this intersection, behind the the service station and restaurant, restaurant, an excavated drumlin is is exposed. exposed. 169.0 (4.0) moraine assumes assumes symmetry and order as Irregular ground moraine as the highway traverses a classic drumlin field, field, produced by the the Green Green Bay Bay lobe lobe drumlins trend essentially of the Woodfordian ice ice advance. advance. These drumlins north—south, north-south, but nearer to Madison the the orientation is southwesterly. Poorly drained areas and tamarack tamarack swamps swamps flank flank many of of the the drumlins. drumlins. 173.0 (2.0) Wisconsin Wisconsin 135 135 exit. exit. 175.0 (3.0) Jefferson/Waukesha Jefferson/Waukesha county county line. line. Enter Enter Waukesha Waukesha County. County. The The drainage in this rolling rolling countryside countryside is is poor, and and farm farm fields fields must must be ditched. ditched. Numerous tamarack tamarack swamps swamps with red red osier osier dogwood dogwood are are lingering evidence of the the boreal boreal climate climate of of the the Pleistocene. Pleistocene. 178.0 (4.0) Wisconsin 67 67 exit exit to to Oconomowoc Oconomowoc and and Dousman. Dousman. The interstate now traverses traverses outwash and proglacial lake sediments in an area once occupied by the the Green Bay Bay lobe lobe during the the Woodfordian Woodfordian ice ice advance. advance. To To the the east, the the view of the the Interlobate Interlobate Moraine Moraine looming looming above above the the flat flat outwash surface surface is is impressive. impressive. A A few few overgrown kettles are are adjacent to to the the highway highway on on the the south south side. side. To the north, north, rising rising above the flat flat outwash plain, plain, an incongruous landform landform resembles resembles the classic moulin kames kames of of the the northern northern Kettle Kettle Moraine. Moraine. This is is the artifically—created artifically-created ski ski hill hill near near Oconomowoc. Oconomowoc. 182.0 182.0 (1.0) (1.0) An An exit exit on on County County CC CC provides provides aa side side trip trip to to view view the the Kettle Kettle 26 26 �Mileages Mileages Interlobate Moraine Moraine from from the the observation observation tower tower on on Lapham Lapham Peak. Peak. This This tower tower provides provides an an excellent excellent overview overview from from the the highest highest vantage vantage point point in in the the southern southern Kettle Kettle Interlobate Interlobate Moraine. Moraine. To To the the west west is is Genesee Genesee Flat. Flat. To the east is is the the glacial glacial spillway spillway described described at at mile mile 184. 184. Several scenic, scenic, glacial glacial lakes lakes are are also also visible. visible. To reach Lapham Peak, Peak, go south south on County CC (Kettle (Kettle Moraine Scenic Scenic Turn left (east) onto Drive) about 1.8 miles to a crossroad. Drive) about 1.8 miles to a crossroad. left (east) onto Government Government Hill Hill Road. Road. Continue about 0.7 0.7 mile to to aa small small park that includes includes the the Lapham Lapham Peak Peak observation observation tower. tower. The The tower tower for for state station station WHAD WHAD is is also also located located here. here. A A marker at at 1233 1233 feet feet of elevation, elevation, on a a glacial erratic boulder in in the the park, park, is is dedicated dedicated to one of of Wisconsin's earliest earliest geologists geologists and and naturalists: naturalists: "Increase A. A. Lapham, Lapham, Eminent scientist scientist and and useful useful citizen." citizen." The route route ahead ahead crosses crosses a a region region of of pitted (kettled) (kettled) outwash outwash deposits, and and many many kettle kettle lakes lakes dot dot the the landscape. landscape. Nagawicka Nagawicka Lake, Lake, immediately immediately north north of of the the highway, highway, is is such such aa lake. lake. Other examples examples are are Upper and Lower Nemahbin lakes, lakes, which sandwich the interstate west of of here. here. The ice blocks which formed formed these lake lake about 1 mile west basins were derived from from the the Green Green Bay Bay lobe lobe along along the the western western edge edge of the Interlobate Interlobate Moraine. Moraine. 183.0 183.0 (1. 0) (1.0) The interstate approaches the crest of the Interlobate Interlobate Moraine. Moraine. A small ski area south of the highway utilizes A small ski area south of the highway utilizes part part of of this this slope. slope. From the crest of this ridge, ridge, the radio tower and and observation tower tower on Lapham Lapham Peak are are visible visible south south of of the the highway. highway. The Kettle Interlobate Moraine, Moraine, which trends northeasterly across across Wisconsin for for about 130 miles, miles, from from Walworth to to Kewaunee Kewaunee counties, counties, It is is probable that the is the the premier glacial feature is feature in in Wisconsin. Wisconsin. It resistant Silurian Silurian dolomite dolomite influenced the the position of the inter— resistant interlobate deposits deposits in in this this area, area, by retarding the spread of the Green lobate Bay lobe. lobe. Within this morainal complex, complex, the country country is is rolling rolling and and rugged, rugged, This feature formed with abundant knobs knobs and and kettles. kettles. formed during the Woodfordian glacial advance by a a juxtapositioning juxtapositioning of of the the terminal terminal inoraines of the the Green Green Bay Bay and and Lake Lake Michigan Michigan lobes. Between these moraines of walls, complex drainageways drainageways developed, developed, and meltwaters reworked icy walls, some a some of the morainal materials. The resultant deposits are a Much of the mixture of sand, mixture sand, gravel, boulders, and and clayey clayey till. till. material was was derived from the Silurian dolomite, coarser material dolomite, but igneous and and metamorphic metamorphic rock rock types types from from far far to to the the north north are are also also igneous present. 184.0 184.0 (1. 0) (1.0) This highway highway follows an Wisconsin 83 83 exit. exit. This follows low ground along an abandoned drainage drainage channel channel which which carried the the last meltwater that abandoned drained southward southward through through this this part part of the the Kettle Kettle Interlobate drained Water drained drained down down this this .25 mile wide wide valley valley until until it Moraine. .25 mile Moraine. Water reached Wales, Wales, about about 33 miles miles to to the the south, south, where where it it cut cut through through the the reached Gravel outwash outwash terraces terraces flank flank Interlobate Interlobate Moraine Moraine to to flow west. west. Gravel this drainage, drainage, and and aa remnant remnant of aa high terrace terrace is this is visible on the east east side side of this valley. 27 27 �Mileages 185.0 (1.0) (1. 0) Pewaukee Lake Lake lies lies to to the the north. north. The church at at Holy Holy Hill, Hill, on on aa kame kame perched high on the Interlobate Moraine, is also visible to the north Interlobate is also visible to the north on aa clear clear day. day. Pewaukee Lake occupies aa preglacial river river valley valley which which was scoured into the Upper Ordovician Maquoketa Shale. This Shale. This ancient valley was blocked by morainal debris deposited along along its its eastern eastern margins by the Lake Michigan lobe during the Woodfordian ice lobe the ice advance. advance. 186.0 (2.0) Ground moraine deposits in in this this area area are are thin. thin. North of the highway on the west edge of the Tumblebrook golf golf course, course, there there is is aa small small quarry in Silurian dolomite. Glacial striae on bedrock in this in Silurian dolomite. area indicate that ice ice movement was was west—southwest. west-southwest. the road, road, the the names names of a South of the a subdivision (Pebble (Pebble Valley), Valley), and Hill), bear testimony to the character of the aa farm (Stoney (Stoney Hill), the morainal material. material. 188.0 (3.0) Exit County GG to the highway to Pewaukee. Pewaukee. A drumlin field lies south of the for the next several several miles. miles. These east—west east-west trending drumlins are composed of sandy clay till till that contains abundant boulders. boulders. 191.0 (1. 0) (1.0) Exit County County F. F. West of this intersection, intersection, the the route route crossed crossed the the Pewaukee River, River, which which is is tributary tributary to to the the Fox. Fox. This valley is is paralleled by outwash terraces, terraces, which are commercial commercial sources sources of of sand sand and gravel gravel in in this this area. area. 192.0 (2.0) Exit Wisconsin 164 164 to to Sussex Sussex and and Waukesha. Waukesha. lins are ,north north and and south south of of the the highway. highway. East-west trending drum- Colonel Dunbar, Dunbar, while visiting Waukesha in 1869, drank drank from from some some of of the springs the springs which issue from the glacial drift, drift, with high amounts amounts of of dissolved calcium calcium magnesium magnesium bicarbonate. bicarbonate. Upon deciding that the local local mineral waters had eliminated his "incurable "incurable ailments," ailments," he he began to to advertise advertise his cure cure nationwide, nationwide, and and Waukesha Waukesha soon soon became became aa fashionable health spa. fashionable spa. Although this fad fad waned after about about 30 30 years, years, bottled spring water is still a Waukesha product. spring is still a Waukesha product. Waukesha Waukesha is is located located on on the the Fox Fox River. River. Outwash terraces along along this this river are important commercial sources for for sand and and gravel. gravel. Since the glacial drift is quite thin in this region, the region, Silurian dolomite is is extensively quarried along the valley of the Fox from from the the Waukesha area area northward to to Sussex, Sussex, Lannon Lannon and and Menomonee Menomonee Falls. Falls. 194.0 (3.0) U.S. 18 (Blue Exit U.S. (Blue Mound Road) Road) to Waukesha and WiscOnsin Wisconsin State Patrol Headquarters. 197.0 (2.0) Exit Moorland Moorland Road. Road. The flat terrain here is is poorly drained, clayclayground moraine. moraine. Ditching and channelization were required required for for rich ground the extensive development development of of the the land land north north of of the the highway. highway. The golf course to the south represents a more intelligent intelligent land land use. use. A few few isolated patches of moraine, moraine, and several east—west east-west trending trending drumlins rise rise above above the the generally generally swampy swampy ground. ground. The route route ahead descends aa prominent ridge, The ahead descends ridge, which is part of the 28 �Mileages Mileages Woodfordian Woodfordian Lake Lake Border Border recessional recessional moraine moraine system. system. Sunny Sunny Slope Slope Road Road traverses traverses this this ridge ridge crest, crest, which which forms forms the the drainage drainage divide divide between between Lake Lake Michigan Michigan and and the the drainage drainage basin basin of of the the Fox Fox River. River. The The Fox Fox flows flows southward southward parallel parallel to to the the Woodfordian Woodfordian moraines moraines to to reach reach the the Illinois Illinois River, River, and and ultimately ultimately the the Gulf Gulf of of Mexico Mexico via via the Mississippi. Mississippi. the 199.0 199.0 (2.0) (2.0) Milwaukee/Waukesha Milwaukee/Waukesha county county line. line. Enter Milwaukee Milwaukee County. County. Exit Exit 1-894 1-894 (U.S. 45) south south to Chicago and U.S. (U.S. 45) U.S. 45 45 north north to to Fond Fond du du Lac. Lac. The The Milwaukee Milwaukee County County Zoo Zoo is is northwest northwest of of this this intersection. intersection. 202.0 202.0 (2.0) (2.0) Exit Wisconsin Wisconsin 181 181 (84th (84th Street). Street). The The Wisconsin State State Fair Fair Park Park Exit grounds and an Olympic-size outdoor ice ice rink rink are are southeast southeast of of this this Wisconsinan (Woodfordian) junction. junction. The interstate traverses traverses Wisconsinan (Woodfordian) ground moraine moraine and and recessional recessional moraines moraines of of the the Lake Lake Border Border system. system. The The highway highway here here is is essentially essentially parallel parallel to to the the east-west east-west direction direction of ice ice movement, movement, and and consequently consequently the the morainic ridges ridges trend trend north— northsouth. About 100 100 feet feet of glacial glacial deposits, deposits, primarily primarily aa boulder boulder south. clay clay till, till, overlie overlie Silurian Silurian dolomite dolomite in in this this area. area. 204.0 (1.0) (1.0) U.S. U.S. 41 41 exit exit (north (north and and south). south). Milwaukee County County Stadium, Stadium, home home of of the Milwaukee Brewers and also the site of the Milwaukee games and also the site of the Milwaukee games of of the Green Green Bay Bay Packers, Packers, is is just just west west of of this this junction. junction. The large large hill southwest of the stadium is a Silurian dolomite stadium is a Silurian dolomite exposure exposure on on the grounds of the the the U.S. U.S. Veterans Veterans Administration Administration Hospital. Hospital. 205.0 (1.0) (1.0) Route parallels the the industrial industrial complex complex along along the the east-west east-west trending trending Three large, glass domes in Mitchell Park River valley. valley. large, Menomonee River are to the the south. south. One contains a a display of vegetation are visible to native to a desert environment, another features environment, another features tropical tropical plants, plants, and the the last houses houses local flora and is used for special flower shows. shows. 206.0 Junction 1—94 1-94 with with 1-43 1-43 (U.S. (U.S. 141) 141) and and 1—794. 1-794. The Milwaukee Harbor is to the southeast, toward the highrise Harbor Freeway bridge along is to the southeast, the the lakeshore. Three rivers merge at at the the Milwaukee Milwaukee Harbor. Harbor. flows from from the the north north and and west, west, the the Milwaukee Milwaukee flows north, and the north, the Kinnickinnic River originates The Menomonee Menomonee River The River comes comes from the the to the west and south. south. Milwaukee grew from three settlements that were originally separated Walker's Point, by these rivers. rivers. Walker's Point, east of the Kinnickinnic River, River, is now now dominated dominated by by the the towering towering clock clock of of the the Allen Allen Bradley Company. Company. is The Milwaukee River flowed between Kilbourntown on the west and The Juneautown to to the the east. east. The high high smokestack smokestack to to the the east east is is part part of the the Jones Jones Island The Here, sewage sewage sludge sludge is is dried and Metropolitan Sewage Plant. Metropolitan Plant. Here, converted to Milorganite, Milorganite, aa commercial converted commercial fertilizer. fertilizer. Jones Island, Island, an an artificially artificially breached breached peninsula, peninsula, also contains Jones contains tanker pier, pier, cargo cargo terminals terminals and and aa heavylift heavylift wharf, wharf, and is aa tanker is Milwaukee's inner harbor headquarters for the Port of Milwaukee. Milwaukee's headquarters 29 �was developed by an enlargement of the lower Kinnickinnic River, was River, and it it serves serves as as the the service service and and wintering area for and for part of U.S. Steel's iron ore carrier fleet. u.s. fleet. END OF OF LOG END Proceed through downtown Milwaukee to Proceed to the the Pfister Pfister Hotel. Hotel. 30 30 �,/ * N I o0 NE NE QUARRY QUARRY A A ,,- \\ \I / '\ '\ rn 1! 200 FEET FEET Flynn's SW QUARRY QUAR RY QUARRY -- — \ / , , / -:.- \I I " \ "'/ ,"- '\, [J I " -V,-. \ \ / .::: N ~ A' \ \ ./ E X P L A N AT I 0 N EXPLANATION METABASALT METABASALT DIKE DIKE STRUCTURE RELATED RELATED TO TO I• STRUCTURE QUARRY OPERATION OPERATION QUARRY J o DEBRIS DEBRIS PILE PILE D [Tj GRANITE PORPHYRY r,o "0) GRANITE PORPHYRY DIKE DIKE l'v I GRANITE GRANITE AT AT REDGRANITE REDGRANITE Figure Figure 2. 2. ! y' 1' QUARRY WALL OR STEEP STEEP QUARRY WALL OR SLOPE SLOPE Pace Pace and and compass compass map map of of Flynn's Flynn's Quarry Quarry County County Park, Park, Waushara Waushara County. County. 32 32 �Geologic Geologic Stop Stop Descriptions Descriptions . 11 Eugene Eugene I. I. Smith Smlth STOP 11 -- GRANITE GRANITE AND AND RELATED RELATED INTRUSIONS INTRUSIONS AT AT FLYNN'S FLYNN'S QUARRY QUARRY COUNTY COUNTY PARK PARK STOP Location: All All exposures exposures at at this this stop stop are are reached reached by by an an easy easy walk walk from from the the ParkParkLocation: ing area area (Fig. (Fig. 2). 2). ing Description: Description: Granite Granite Fine—to Fine-to medium—grained medium-grained red red (granophyric) (granophyric) granite with micropegmatitic micropegmatitic and and myrmeketic texture texture is is exposed in in three three quarries within the the boundaries boundaries of of Flynn's Flynn's County Park Park (Fig. (Fig. 2). 2). Quartz and and alkali alkali feldspar feldspar compose compose 90 90 to to 98 98 perperQuarry County cent cent of of the the rock, rock, with biotite biotite (partially (partially or or wholly altered altered to to chlorite), chlorite), sphene, sphene, muscovite and and zircon zircon as as subordinate subordinate minerals. minerals. The granite for for the the hornblende, muscovite most part part is is texturally texturally homogeneous. homogeneous. Locally Locally however, however, grain grain alignments alignments and and fine— fineThe mineralogy and texture of the granite grained bands (dikes?) (dikes?) are are observed. observed. (especially the intergrowths intergrowths of of quartz quartz and and alkali alkali feldspar) feldspar) suggest suggest that that it (especially the it is is a a shallow intrusion. shallow intrusion. Granite Porphyry Dike Dike In northeast quarry, quarry, the the granite granite is is cut cut by by aa 200 200 m wide wide east east trending In the the northeast granite porphyry dike dike (strike (strike east—west, east-west, dip dip 75° 75° to to the the south). south). The dike rock rock is characterized by by large large (5 mm) alkali alkali feldspar feldspar phenocrysts phenocrysts set set in in aa fine— is characterized (5 mm) fineof quartz, quartz, biotite biotite and and chlorite. chlorite. The finely disseminated chlorite grained matrix of gives the matrix of the the dike rock a a green color, color, thus thus making it easily distinguishable from from the the red red granite. granite. The contact between granite and dike rock is is clearly visible visible on on aa ledge ledge on on the the north north wall wall of of the the northeast northeast quarry quarry (Fig. (Fig. 3). 3). In detail, the the contact contact bends bends in in and and out, out, suggesting suggesting some some assimilation assimilation of granite In detail, of granite during intrusion. intrusion. Fragments (xenoliths) (xenoliths) of of granite are found found within the the dike near the the contact; contact; also also feldspar feldspar phenocrysts phenocrysts are are concentrated concentrated and and weakly weakly aligned aligned near in the granite mornhvrv porphyry dike at at the the contact. contact. in the Figure 3. Figure View of of the the contact contact between between the the granite granite porphyry porphyry dike dike and and granite granite View Note in Flynn's Flynn's Quarry Quarry County County Park (dashed in (dashed line traces traces contact). contact). that the the feldspar feldspar phenocrysts phenocrysts are are concentrated concentrated and and weakly weakly aligned aligned that in the the dike dike rock near the in the contact. contact. of Science, Science, University University of of Wisconsin-Parks Wisconsin—Parkside, lDivision ide , Kenosha, Kenosha, Wisconsin Wisconsin 53141. 53141. Division of 33 33 �Chemically, the the dike dike is is aa less less differentiated differentiated phase phase of of the granite. It It is Chemically, the granite. lower in SiO , and K K20 and higher higher in in Al A1203, Fe20 and CaO when when compared to lower 0 and 0 , FeO + Fe 0 and 2 3 uarry granite 1, an~lyses analyses 18 18 and and 31). 3). In terms terms of trace the Flynn's auarry g~anite (Table (Table 1, In elements the the dike dike is is higher higher in in Ba, Ba, and and has has aa lower lower Rb/Sr Rb/Sr ratio than the granite. elements the granite. , Metabasalt Dike Dike On the the north north wall wall of of the the main main quarry, quarry, the the granite granite is cut by a m wide) wide) On is cut a thin (2 (2 m 0 metabasalt dike striking striking N. N. 80 80 E. E. and and dipping dipping 700 70 to to the south (Fig. (Fig. 2). 2). The dike rock is is fine fine grained grained and and has has aa distinctive distinctive green color color on both weathered and fresh ~ock fresh surfaces. In thin section, the metabasalt displays intergranular texture with In thin section, the metabasalt displays intcrgranular texture with laths of of plagioclase enclosing mats of laths of epidote, epidote, clinozoisite clinozoisite and and iron iron oxide. oxide. The contact between the metabasalt and granite is clearly observed on a contact between the metabasalt and granite is observed a ledge just above Here lenses lenses of of granite granite are above water level level (Fig. (Fig. 4). 4). Here are completely enclosed by stringers of metabasalt. Except for these lenses, no granite fragments lenses, fragments were noticed within dike rock. These contact relationships suggest that rock. that the the meta— metabasalt intruded primarily by the dilation of country rock. intruded primarily by the dilation of country rock. Comparison of of Flynn's Flynn's Quarry Quarry Granite Granite to to Granite Granite in in Nearby Nearby Areas: Areas: Redgranite to to Pine Bluff— Bluff- Granites and Dikes Granites similar in Granites in mineralogy and and texture texture to that that at at Flynn's Flynn's Quarry are exposed in discontinuous discontinuous outcrops Redgranite to Pine Bluff exposed outcrops from from the the city of of Redgranite (Fig. (Fig. 5). 5). Dikes of of metabasalt trending east—west east-west and and approximately approximately N. N. 45E. 45E. cut cut the One of the most easily visited of the granite in in many many localities. localities. One the most of these dikes forms distinct ridge ridge jutting into the forms aa distinct the quarry lake lake north of S.T.H. S.T.H. 22 in downtown Redgranite Redgranite (just (just north north of of Griffs' Griffs' Cafe). Cafe). A A coarse—grained coarse-grained diorite dike cuts granite in in a small small quarry in in the the N N 1/2, 1/2, Sec. Sec. 27, 27, T.18 N. N. R. R. 11 11 E. E. (Fig. 5). The The dike dike is about 5 m (Fig. 5). m thick thick and and trends trends N. N. 40 40 E. E. (dip vertical). In thin section, section, flow—aligned flow-aligned plagioclase plagioclase laths laths surround surround clots clots of of chlorite chlorite and and epidote. epidote. Montello Granite Granite Another granite similar in in lithology to to that that at at Flynn's Quarry and and at at Red Red Granite is located in the city of Montello (Buckley, 1898). in the city of Montello (Buckley, 1898). There is is also also an an exposure to the the east of Montello in in the the SE SE 1/4, 1/4, Sec. Sec. 9, 9, T. T. 15 15 N., N., R. R. 10 10 E. E. This granite granite was was extensively extensively quarried quarried from from 1880 1880 to to 1976. 1976. President Grant's sarcophagus in in New York City is is carved carved from from Montello Montello Granite. Granite. The rock in in the the Montello quarry is is a a red granite composed of of intergrown intergrown quartz and and alkali alkali feldfeldspar crystals (myrmeketic (myrmeketic and and micropegmatitic textures textures are common) common) with chlorite, chlorite, biotite, biotite, and and euhedral euhedral zircon zircon as as accessory accessory minerals. minerals. Attempts to to date this this rock rock by the the fission—track fission-track technique technique failed because an an insufficient insufficient number of of zircon zircon grains were separated separated and and most most of of the the separated separated zircons zircons were were metamict. metamict. The Montello granite is is cut by thin thin metabasalt dikes (plagioclase (plagioclase and and sausserite sausserite as as dominant minerals) Quarry minerals) which which trend trend northeast, northeast, north—south north-south and and northwest. northwest. faces faces at Montello are are commonly commonly bounded bounded by by these these dikes. dikes. The metabasalt metabasalt dikes dikes are closely sheared at at their their margins; margins; several several dikes dikes are are sheared sheared throughout. throughout. The granite commonly shows shows aa dark red red bake zone zone extending 22 to to 5 5 cm em inward inward from from the the intrusive contacts, contacts, also small more common in granite near small grains grains of of pyrite are more metabasalt metabasalt than than farther farther away away from from the the granite—dike granite-dike contacts. contacts. 34 34 �Figure Figure 4A. 4A. View of a a thin metabasalt metabasalt dike that that The dike in this view County Park. County Park. in this view dips about southern southern contact contact (left) (left) dips about Granite (G) to the north of line). (G) in the dike rock rock (D). (D). Figure 4B. Figure 4B. Close—up of the contact between the Close-up the metabasalt dike dike and and granite. granite. Basalt intruded granite along Basalt along closely closely spaced spaced joints. joints. 35 cuts cuts granite in Flynn's Quarry is is 22 meters mete~s thick. thick. The 10° to the north north (dashed the dike appears appears as as a window �Lohrville Lohrville Quarries Redg ranj.t(f~~---/' .c-"~edgranite Quarry —2'FIynns Spring Lake, Lake"", /_Jf\. Flynn's Quarry (STOP (STOP I) I) Spring Quarri es Quarries I" WAUSHARA COUNT COUNTY WAUSHARA -MARQUETTE COUI COU .YY ;,.' - Quarry Quarry with with Diorite Dike Dike — T;-- GREEN GREEN LAKE LAKE COUNTY COUNTY 00 Berlin Gran ite Berlin Pine Pine Bluff Granite I I I o I I "--1 ~ Granite Montello Granite Buffalo Lake Figure 5. 5. 3:iiii~ 2 3 4 5 Miles 0 .Oiii32• 3iE! Mil es SCALE SCALE I I Princeton EXPLANATION ... C.J Granite Exposures ~ Quarry 00 City Field Trip Trip ~ Field Route Route Detailed route route map map from from Redgranite Redgranite to to Montello Montello showing showing granite granite Detailed exposures and and locations locations of important quarries. exposures quarries. 36 36 �_____________ _________ Chemical Comparisons: The granite at at Redgranite (and (and presumably Flynn's Quarry) Quarry) is is similar in in chemistry, mineralogy and age to that chemistry, that at Montello, Montello, except for noticably higher higher amounts of of Cu and Cr in amounts in the the Montello Montello Granite, Granite, (Table (Table 1, 1, analyses analyses 14 14 and and 18). 18). These similarities indicate that the granites are comagmatic and and that that they they formed during the same intrusive formed intrusive event. event. Studies of cuttings from from deep deep wells wells show that that granite lithologically similar to to that that exposed at at Redgranite and and Montello occurs in the basement over a a large area of south—central south-central Wisconsin. Wisconsin. These rocks rocks probably probably form form aa large large late—Penokean late-Penokean or or post—Penokean post-Penokean (1765 (1765 m.y. m.y. old) old) composite batholith which is exposed only in in the the Redgranite area area and and at at Montello (Smith, 1978c). (Smith, The similarity of the the granites at Montello and and Redgranite was noted noted long long ago by Weidman (1904) who labelled these rocks the Waushara Granite. (1904) labelled these rocks the Waushara Granite. Emmons (1940) also also suggested the presence of aa large (1940) large batholith batholith in in central central Wisconsin. Wisconsin. However, he did not distinguish between the older Penokean aged granites However, the aged granites in in central Wisconsin (Wausau area) area) and and the younger granites granites in south—central central the younger south-central Wisconsin. - 44 -- 3 -- - -- - -- - - 2 -- - 0. Co :::J 0 (I o I I I I I I o0200500400500600 200 300 400 500 600 0 10 Zr 20 - - - • ~I I I 3040 30 40 50 50 I 0 50 I I 10015020 100 150 20 3040 30 40 Cu Cr I --I 0) 50 Pb I I 100150200250 100 150 200 25 o Zn Zn 4— 4 3 -3 2 0. Co :::J 0 o1 ~I I 0 o 000 1000 500 Ba Ba ao 2.0 I I 50 50 00 100 I I 150 150 00 200 Sr La tOO 150 50 200 100 200 Rb 10 10 30 50 I I I 70 70 90 90 ItO 110 V Y (ppm) Figure 6 6. chemical groups groups (from Some elemental concentrations for for the four four chemical (from elemental concentrations for Smith, l978a). 1978a). Bars indicate indicate the the range range of of values values for each each chemical chemi~al Smith, group. Dot indicates that data point is is based based on on one one analysis. analysls. that the the data Dot group. 37 �Relationship of Granites to to Rhyolite: Rhyolite: The Redgranite Redgranite and and Montello Montello Granites Granites are are similar similar in in major major 8nd cnd mino~ minor element element The chemistry and and age age to to the the rhyolites rhyolites exposed exposed to to the the south south (stop for example) example) chemistry (stop 22 for (see table analyses 4-29; 4—29; and and Fig. Fig. 6; 6; and Smith, (see table 11 , analyses Smith, 1978c by Van Van Schmus, Schmus, 1978. 1978. These similarities similarities strongly strongly suggest suggest that that the the granites granites and and rhyolites rhyolites are are comagThese comag— matic. In other other words, words, the the granites granites may may represent represent the the magma magma chambers chambers from from matico In which the which the rhyolite ash—flow ash-flow tuffs tuffs were erupted. erupted. Later, its Later, granite intruded its own volcanic volcanic cover engulfing much of 9wn of the the rhyolite. rhyolite. Surviving Surviving rhyolite exists as roof roof pendants within as within the the granite. granite. , 38 38 �Table 1. 1. NEW CHEMICAL ANALYSES FOR CENTRAL WISCONSIN INLIERS AND IGNEOUS ROCKS ROCKS IN THE BARABOO BARA~OO AREA AREA 11 2 2 3 3 4 4 5 5 6 6 w CA, °t.O BB Ba Ba Co Co Cr Cr Cu La La Mo Ni Ni V Y Y Zr Pb Pb Rb Sr Zn Zn Sc Sc 20 20 1300 1300 33 32 32 30 30 49 10 10 12 12 77 32 32 320 28 165 165 210 210 55 70.61 0.37 14.29 0.92 2.03 0.34 1.61 4.45 3.78 0.92 0.04 0.08 99.55 70.26 0.30 14.10 0.86 2.66 0.10 1.02 1.48 4.29 3.69 1.32 1. 32 0.04 0.17 100.29 71.79 71. 79 0.28 14.46 1.40 0.86 0.07 0.30 1.34 3.48 4.63 1.25 1. 25 0.09 0.08 100.03 24 1350 33 15 20 55 10 10 10 33 38 440 22 22 154 212 190 55 25 1200 33 25 50 31 31 10 10 66 15 15 320 22 22 120 324 110 55 28 690 33 55 120 35 10 10 66 30 200 40 40 152 105 130 0.11 O.ll 8 8 99 10 GROUP 22 GROUP 11 69.28 Si02 0.42 Ti02 TiO2 A1203 13.90 Fe203 1.37 2.89 FeO 0.14 MnO 0.90 MgO CaO 1.68 Na20 4.17 K20 4.33 H20+ 0.92 0.07 H20H20— 0.18 P205 P205 TOTAL 100.25 7 7 71.81 71. 81 0.26 14.29 1.57 1. 57 0.90 0.06 0.20 1.15 4.14 4.54 1.09 0.05 0.09 100.15 33 650 33 10 55 40 10 10 88 22 230 30 125 97 70 72.95 0.25 13.77 13.77 1.69 0.72 0.06 0.26 0.91 3.88 4.46 0.73 0.04 0.04 99.76 71.11 71.11 0.28 14.68 1.67 0.84 0.06 0.26 1.11 4.00 4.35 1.21 1. 21 0.06 0.09 99.72 20 590 33 11 60 35 10 10 99 28 210 45 137 97 145 20 650 33 10 45 45 10 10 10 30 240 30 134 137 105 73.07 0.28 14.65 1.60 0.69 0.06 0.06 0.13 0.94 3.78 4.21 0.78 0.06 0.05 100.30 28 690 33 11 II 55 47 10 10 6 30 210 40 138 95 105 72.85 72.85 0.27 0.27 13.88 1.13 1.09 1. 09 0.05 0.05 0.27 0.27 1.09 1.09 3.58 3.58 4.53 0.96 0.05 0.05 0.10 99.85 71.85 71. 85 0.29 14.32 14.32 0.68 0.68 1.82 1. 82 0.09 0.09 0.26 0.26 1.25 1. 25 3.68 3.68 4.52 4.52 0.78 0.78 0.08 0.08 99.70 99.70 22 630 33 10 55 40 10 10 88 22 230 35 35 130 130 130 130 70 70 20 20 720 33 12 12 45 42 10 10 10 10 55 30 200 200 45 116 116 150 150 115 115 �Table 1. 1. (Continued) (Continued) 11 11 12 12 13 13 14 14 15 15 16 16 17 17 GROUP 22 Continued) GROUP (Continued) Si02 Si02 Ti02 A1203 A12O3 Fe203 FeO MnO MgO CaO GaO Na20 K20 H20+ H20P205 71.22 0.24 0.24 14.15 14.15 1.53 0.70 0.12 0.12 0.15 0.15 2.03 2.03 3.14 4.66 1.94 0.05 0.07 TOTAL 100.00 71.64 71.64 0.28 14.36 14.36 1.84 1.84 0.65 0.07 0.28 1.37 1. 37 4.07 3.74 1.50 0.09 0.10 99.99 18 18 19 19 20 20 GROUP 33 72.27 72 .27 0.30 13.83 13.83 1.51 1. 51 1.08 1.08 0.08 0.24 1.61 1. 61 3.87 3.72 1.51 1. 51 0.07 0.09 72.33 72 .33 0.28 13.62 1.94 1.94 0.68 0.07 0.29 1.27 4.70 3.73 1.16 0.05 0.10 75.83 0.21 11.92 11. 92 1.08 0.98 0.07 0.06 0.53 3.43 5.45 0.54 0.01 0.01 75.09 0.21 12.33 12.33 1.08 1.12 0.08 0.04 0.39 3.76 5.58 0.49 0.00 0.01 100.18 100.22 100.12 100.18 25 25 20 73.73 0.29 12.09 12.09 1.83 1.83 1.34 0.11 0.04 0.36 3.50 6.03 0.36 0.01 0.01 0.00 99.69 76.14 0.24 11.79 11. 79 1.10 1.10 0.88 0.02 0.09 0.45 3.16 5.65 0.58 0.01 0.01 0.01 0.01 100.12 75.30 0.19 0.19 12.04 12.04 1.04 1.04 1.04 1. 04 0.06 0.06 0.04 0.04 0.33 0.33 4.65 4.65 4.63 4.63 0.33 0.33 0.03 0.03 0.00 0.00 99.68 99.68 75.60 75.60 0.17 0.17 12.59 12.59 0.99 0.99 0.71 0.71 0.03 0.03 0.04 0.04 0.13 0.13 4.46 4.46 4.95 4.95 0.47 0.47 0.02 0.02 0.00 0.00 100.16 100.16 A o B B Ba Co Co Cr Cu La La Mo Ni Ni V yy Zr Pb Pb Rb Rb Sr Zn Zn Sc Sc 29 29 730 33 11 11 55 55 45 10 10 10 10 77 27 27 190 50 50 155 155 126 120 26 26 26 26 20 20 630 3 3 9 9 55 55 35 35 10 10 10 12 12 28 200 40 116 126 126 115 750 33 88 72 37 37 10 10 10 10 12 12 22 22 210 40 102 102 135 135 85 - - - 650 3 3 77 50 37 37 10 10 10 10 10 27 270 35 75 106 106 120 120 - 440 3 3 38 23 78 10 10 10 10 5 5 70 420 22 190 190 25 55 55 33 410 3 3 23 22 90 10 10 10 5 5 71 590 23 152 152 31 125 125 33 20 20 390 33 27 26 120 10 10 55 85 550 22 152 11 115 33 20 20 390 33 88 9 95 10 10 10 55 65 590 28 202 21 65 3 22 22 22 22 115 115 545 545 3 13 13 22 22 72 10 10 10 10 55 49 450 19 19 117 117 55 105 105 33 33 16 16 25 25 65 10 10 10 10 55 49 480 480 28 120 120 28 28 95 95 33 �Table Table 1. 1. (Continued) (Continued) 21 21 22 22 23 25 25 24 24 26 26 27 27 28 28 MARCELLON Si02 Si02 Ti02 Ti02 A1203 A1203 Fe203 Fe203 FeO FeO MnO MnO MgO MgO CaO CaO Na20 Na20 K20 K20 H20+ H20+ H20H20P205 P205 TOTAL TOTAL B B oJ:>. Ba ,.... Co Cr Cr Cu Cu La La Mo Mo Ni Ni Co V V Y Y Zr Zr Pb Pb Rb Rb Sr Sr Zn Zn Sc Sc 75.68 75.68 0.12 0.12 12.46 12.46 0.68 0.68 1.09 1.09 0.13 0.13 0.12 0.12 0.36 0.36 3.66 3.66 5.00 5.00 0.57 0.57 0.04 0.04 0.07 0.07 99.98 99.98 78.25 78.25 0.11 0.11 11.05 11.05 0.95 0.95 0.84 0.84 0.07 0.07 0.16 0.16 0.29 0.29 3.66 3.66 3.72 3.72 0.70 0.70 0.09 0.09 0.09 99.98 75.55 75.55 0.14 0.14 12.21 12.21 0.42 0.42 1.71 1.71 0.17 0.17 0.29 0.29 0.45 0.45 2.82 2.82 5.16 0.85 0.04 0.06 99.87 76.63 0.12 11.38 11.38 0.97 0.97 1.13 0.12 0.12 0.13 0.62 3.16 4.66 0.59 0.01 0.06 99.58 40 40 240 240 33 54 54 95 95 47 47 10 10 55 55 50 50 200 200 22 22 131 131 72 72 100 100 55 25 25 160 160 33 44 44 115 115 35 35 10 10 11 11 55 42 42 180 180 19 19 108 108 61 61 130 130 55 20 20 180 33 62 62 160 160 50 50 10 10 55 55 52 52 200 180 180 165 165 61 61 105 105 55 35 35 240 33 41 80 45 45 10 10 55 55 50 50 190 190 14 14 130 130 46 110 55 , 29 29 BARABOO BARABOO 71.99 71. 99 0.26 0.26 13.57 1.93 1. 93 0.88 0.11 0.37 1.10 4.34 4.91 1.20 1. 20 0.08 0.03 100.77 . 30 970 5 5 15 15 40 90 10 10 55 88 60 150 22 102 95 95 102 102 77 71.80 0.32 13.74 1.30 1.72 0.11 0.58 0.85 4.43 4.49 0.60 0.04 0.13 100.11 100.11 20 1050 3 3 58 105 52 10 55 55 35 220 18 110 176 135 135 77 73.77 0.14 0.14 12.35 1.01 1.81 1. 81 0.13 0.13 0.39 0.94 3.26 4.92 1.25 0.04 0.07 100.08 100.08 22 22 410 3 3 58 58 110 42 10 55 55 38 160 19 108 82 82 110 55 73.83 73.83 0.16 0.16 13.33 13.33 0.96 0.96 1.21 1. 21 0.07 0.07 0.31 0.31 0.43 0.43 2.51 2.51 5.28 5.28 1.43 1.43 0.05 0.05 0.08 0.08 99.65 99.65 27 1100 1100 3 3 25 25 42 42 49 49 10 10 10 33 31 240 55 205 110 110 35 35 55 72.76 72.76 0.22 0.22 13.34 13.34 1.77 1.77 0.72 0.72 0.12 0.12 0.18 0.18 0.45 0.45 4.39 4.39 5.25 5.25 0.77 0.77 0.08 0.08 0.01 0.01 100.06 100.06 35 35 950 950 5 5 22 22 45 45 80 80 10 10 55 55 33 33 140 140 25 25 115 115 62 62 115 115 77 I �Table 1. 1. (Continued) Table (Continued) 30 31 32 33 34 35 35 36 36 37 37 DIKES Si02 Ti02 A1203 Fe203 FeO MnO MgO CaO CaO Na20 1(20 K20 H20÷ H20+ H20— H20P205 P205 TOTAL >l:> t'V B B Ba Ba Co Co Cr Cr Cu La La Mo Mo Ni Ni V V Y Zr Zr Pb Pb Rb Sr Zn Sc 63.92 0.94 0.94 15.65 15.65 1.92 1. 92 4.38 0.20 1.40 1.40 1.58 1.58 4.71 4.71 3.34 3.34 1.51 0.11 0.11 0.31 0.31 99.97 99.97 72.10 0.30 12.74 1.06 2.21 0.12 0.09 1.08 3.12 6.12 0.73 0.03 0.04 99.74 20 20 20 1050 1050 1170 3 3 3 3 12 12 65 65 26 16 16 88 88 10 10 10 10 5 5 63 590 19 180 56 110 33 40 10 10 10 10 15 15 25 25 200 30 30 113 218 218 75 75 - 60.59 0.93 16.47 1.61 1.61 4.50 0.18 1.77 3.86 4.27 3.27 1.50 0.11 0.48 99.54 50 1200 4 4 16 70 68 10 10 6 6 92 28 28 220 25 25 105 514 180 20 48.94 0.99 17.84 2.21 6.56 0.19 6.57 9.59 3.25 1.11 2.97 0.12 0.31 100.29 25 660 24 42 50 10 10 10 24 24 240 11 11 75 75 28 28 38 642 180 27 49.47 0.94 14.77 1.46 7.42 0.19 7.05 6.54 4.59 1.09 5.57 0.18 0.36 99.63 52.02 1.27 15.84 2.66 7.72 0.21 4.78 7.87 3.23 1.66 1.96 0.10 0.34 99.66 15 680 20 155 77 21 10 19 240 14 86 15 15 55 55 270 170 25 25 33 950 20 27 27 75 75 29 10 10 270 31 31 180 180 20 20 154 154 419 190 24 24 60.72 0.99 15.72 1.13 5.86 0.19· 0.19 1.89 1. 89 3,94 3.94 3.90 3.31 1.43 0.10 0.46 99.64 56.21 1.33 1.33 13.20 13.20 1.95 1. 95 6.66 6.66 0.14 0.14 5.10 6.01 3.09 2.56 2.34 0.14 0.98 99.71 22 22 1250 77 20 32 32 33 33 10 16 55 55 32 32 240 22 22 155 155 420 220 16 16 70 70 1100 37 150 80 95 95 10 10 51 51 260 260 45 620 21 21 75 75 625 160 160 23 23 I �Table 1. 1. (Continued) (Continued) Si02 Si02 Ti02 Ti02 A1203 A1203 Fe203 Fe203 FeO FeO MnO MnO MgO MgO CaO Na20 Na20 K20 K20 H20+ H20+ H20H20P205 P205 TOTAL TOTAL ..,. w B B Ba Ba Co Co Cr Cr Cu Cu La La Mo Mo Ni Ni V V yY Zr Zr Pb Pb Rb Rb Sr Sr Zn Zn Sc Sc 38 38 39 39 40 40 69.76 69.76 0.37 0.37 13.77 13.77 0.76 0.76 2.25 2.25 68.44 68.44 0.50 0.50 14.20 14.20 1.46 1.46 2.99 2.99 0.17 0.17 0.62 0.62 2.02 4.78 4.78 3.06 1.11 1.11 0.04 0.13 99.52 70.22 70.22 0.35 14.26 14.26 0.94 2.47 2.47 0.19 0.34 0.34 1.30 4.48 3.76 1.07 0.06 0.09 99.53 17 17 990 990 33 28 28 135 135 40 40 20 20 10 10 55 22 22 280 280 25 25 105 105 205 205 97 97 20 20 1250 1250 55 15 15 110 110 29 29 20 20 55 22 22 29 29 260 260 20 20 1400 55 25 25 90 40 20 55 55 30 270 ----- ----- --- 10 55 0.13 0.43 0.43 2.30 2.30 . 3.95 3.95 3.55 3.55 2.12 2.12 0.03 0.03 0.11 0.11 99.53 99.53 ----- ----- 72 72 420 84 84 275 275 41 41 42 43 43 71.20 71.20 0.47 0.47 14.90 1.72 1.60 67.60 67.60 0.44 0.44 15.10 1.75 1. 75 2.24 2.24 76.17 76.17 0.17 0.17 12.05 0.96 0.96 1.00 0.03 0.11 0.26 3.76 4.27 0.63 0.07 0.06 99.53 ----- --- 0.72 0.71 0.71 1.70 1. 70 5.98 0.70 0.40 1.10 2.10 1.95 1.95 4.95 1.60 0.90 100.38 100.62 ----- 18 550 33 45 410 33 20 10 10 40 20 220 220 10 190 190 26 110 66 --- 25 25 450 25 17 370 35 20 17 35 20 220 40 40 180 79 205 66 16 16 165 165 33 45 45 155 55 20 10 17 26 340 16 95 26 120 55 �Table 1. 1. Number Sample Number Explanation Description. Description 1. 1. 179 Coarse-grained rhyolite dike on Observatory Hill. 2. 2. 180 Contact zone of coarse-grained rhyolite dike on Observatory Hill. on Hill. 3. 3. 183 Baxter Hollow Hollow Granite. Granite. 4. 89 5. 5. 102 Marquette rhyolite rhyolite (unit (unit G). G). 6. 6. 106 Marquette rhyolite rhyolite (unit (unit G). G). 7. 7. 101 Marquette rhyolite rhyolite (unit (unit F). F). 8. 8. 100 Marquette rhyolite rhyolite (unit (unit E). E). 9. 9. 103 Marquette rhyolite rhyolite (unit (unit D). D). 10. 104 Marquette rhyolite rhyolite (unit (unit D, D, massive massive phase). phase). 11. 91 Marquette rhyolite rhyolite (unit (unit C). C). 12. 92 Marquette rhyolite rhyolite (unit (unit B). B). 13. 98 Marquette rhyolite rhyolite (unit (unit B). B). 14. 99 99 Marquette rhyolite rhyolite (unit (unit B). B). 15. 15. 107 Montello Granite. Granite. 16. 16. 108 Observatory Hill Hill rhyolite. rhyolite. 17. 17. 109 Endeavor rhyolite. rhyolite. 18. 110 Granite at Redgranite collected collected in in Flynn's Flynn's Quarry. 19. 19. 112 Berlin rhyolite. rhyolite. Marquette rhyolite (unit (unit C) G) from from Noble's Quarry. Samples 4-14 are are keyed keyed to to figure figure 45. 45. 44 �Table Table 1. 1. Explanation Explanation (Continued) (Continued) 20. 20. 114 114 Utley Utley rhyolite. rhyolite. 21. 21. 173 173 Marcellon Marcellon rhyolite rhyolite (unit (unit A). A). Sample Sample numbers 21-27 are keyed to figure numbers 21-27 are keyed to figure 33. 33. 22. 22. 176 176 Marcellon Marcellon rhyolite rhyolite (unit (unit A). A). 23. 23. 174 174 Marcellon Marcellon rhyolite rhyolite (unit (unit B). B). 24. 24. 161 161 Marcellon rhyolite rhyolite (unit (unit B). B). 25. 25. 145 Marcellon rhyolite rhyolite (unit (unit C). C). 26. 26. 175 175 Marcellon Marcellon rhyolite rhyolite (unit (unit C). C). 27. 27. 178 178 Marcellon rhyolite rhyolite (unit (unit D). D). 28. 28. 182 182 Caledonia Church rhyolite rhyolite (south (south limb limb of the the Baraboo Syncline). Syncline). 29. 29. 147 Baraboo rhyolite from the the NE NE ~, , sec. 23, rhyolite from T. 12 T. 12 N., N., R. R. 7 E. 30. 30. 105 Marquette andesite andesite dike dike (figure (figure 45). 45). 31. 31. 111 111 Granite porphyry dike from from Flynn's Quarry County Park. Park. 32. 32. 148 Marcellon andesite andesite dike dike (figure (figure 33). 33). 33. 33. 177 Marcellon basalt dike dike (figure (figure 33). 33). 34. 34. 153 Netabasalt dike Metabasalt dike at Montello (collected (collected from from 23). quarry just north north of of S.H. S.H. 23). 35. 35. 154 154 Metabasalt dike at Redgranite (from (from quarry city of Redgranite). 36. 36. 155 dike from granite quarry near Diorite dike from granite 11 E.). E.). 27, T. T. 18 N., R. Spring Green Green (NE (NE ~,, sec. 27, Spring R. 11 37. 37. 184 Denzer diorite 45 45 �Pable 1. 1. Table Explanation (Continued) (Continued) Explanation 38. 38. 192 192 Dacite dike dike at at Marquette Marquette (figure Dacite (figure 45). 45) . 39. 39. 190 190 Dacite dike dike at at Marquette Marquette (figure Dacite (figure 45). 45) . 40. 40. 191 191 Dacite Dacite dike dike at at Marquette Marquette (figure (figure 45). 45) . 41. 41. 210 210 Dacite Dacite dike dike in in the the Utley Quarry. Quarry. 42. 42. 211 211 Andesite Andesite dike dike in in the the Utley Quarry. Quarry. 43. 43. 193 193 Taylor Farm rhyolite. Taylor rhyolite. major element element analyses analyses on on Table Table 6 (except All major #41 and (except 'ft4l and 42) 42) were made made using conventional wet-chemical methods were methods (K. (K. Aoki, Aoki, analyst). Major element analyses 41 and 42 were analyst). were done done by 0. Joensuu. Joensuu. Trace element analyses (Rb, O. (Rb, Sr, Sr, Pb Pb and and Zn) Zn) by atomic absorption spectrometry (0. (0. Joensuu, analyst). analyst). All other trace trace elements by optical emission spectrography spectrography (0. Joerisuu, analyst). (0. Joensuu, analyst). The for Zr Zr are are accurate accurate to to The result~ result for ± 107g. Sr and Rb are accurate to ± 10%. Sr and Rb are to -- 5% the amount present present 5% of of the xcept for ~xcept for low low Sr Sr (less (less than than 20 20 ppm) ppm) which which is is accurate accurate to to 1070 of -- 10% of the the amount amount present. present. 46 46 �') ( .5 MILES 0 zz <{ a:: CD EXPLANATION rn :E <{ containing rounded Friable quartz sandstone, locally containing rounded rhyolite fragments C) u zz <{ a:: CD :E <{ C) u Ui lLI a:: LII E3 t"(\/] 0 ~ I Fine-grained Fine - grained rhyolite dike Coarse-grained rhyolite dike Coarse-grained rhyolite rhyolite Hill rhyolite Observatory Hill Q. a- Location of Location -+- Figure 7. Figure 7. field fi eld trip stops Quarry Vertical banding Geologic Hill adapted adapted from from Hobbs Hobbs and and Leith Leith (1907). (1907). Geologic map of Observatory Hill Approximate locations of field field trip Stops stops are superimposed. Contour interval 20 20 feet feet between between 800 800 and and 960 960 feet; feet; above above 960 960 feet feet the the interinterinterval val is val is 10 feet. feet. Contour Contour lines lines between between 900 900 and and 960 960 feet feet are are approxapproximately located. located. 48 �STOP 22 -- RHYOLITE RHYOLITE AT AT OBSERVATORY OBSERVATORY HILL HILL STOP Location: Location: Observatory Observatory Hill Hill (Hobbs (Hobbs and and Leith, Leith, 1907) 1907) is is one one of of five five porphyritic porphyritic rhyolite inliers inliers in in south—central south-central Wisconsin Wisconsin (others (others are are at at Endeavor, Endeavor, Taylor Taylor rhyolite Farm, Utley Utley and and Berlin). Berlin). The The hill hill is is formed formed by by steeply steeply dipping dipping flows flows of of Farm, quartz—and quartz-and alkali alkali feldspar—bearing feldspar-bearing rhyolite rhyolite tuffs, tuffs, cut cut by by coarse—grained coarse-grained and and fine-grained rhyolite rhyolite dikes. dikes. Observatory Observatory Hill Hill is is surrounded surrounded by by outcrops outcrops of of fine—grained Upper Cambrian Cambrian sandstone sandstone and and conglomerate conglomerate (Fig. (Fig. 7). 7). Upper The traverse traverse to to the the summit summit of of Observatory Observatory Hill Hill will will follow follow an an easy easy but but The It is Please stay together during the climb. sometimes indistinct trail. Please stay together during the climb. It is sometimes indistinct trail. Observatory Hill. quite easy to become lost on the slopes surrounding Observatory Hill. quite easy to become lost on the slopes surrounding Description: Description: Stop 2A 2A Stop The climb climb to to the the summit summit of of Observatory Observatory Hill Hill begins begins at at exposures exposures of of Cambrian Cambrian The sandstone just just to to the the east east of of the the bend bend in in Gillette Gillette Road Road (north (north side side of of road) road) sandstone of rhyolite The outcrop at this stop is about 300 m to the south (Fig. 7). outcrop at this stop is about m to the south of rhyolite (Fig. 7). outcrops on Observatory Hill and and is is composed composed of aa friable friable reddish—brown reddish-brown quartz quartz No fragments of rhyolite are found here; they are quite common, sandstone. fragments of rhyolite are found here; they are quite common, sandstone. however, in in sandstone sandstone exposures exposures closer closer to to the the rhyolite ledges. ledges. however, Stop 2B 2B Stop Walk from from stop stop 2A 2A to to the the northwest over over the the low low rise rise to to the the first first northnorththe outcrops of sandstone and east trending valley (Fig. 7). Note the outcrops Cambrian east valley (Fig. 7). A conglomerate conglomerate on the southeast side side of of the the valley valley (Fig. 8). 8). A conglomerate thick and and contains contains rhyolite bed in this exposure is approximately 40 cm thick cropping m to fragments to rhyolite rhyolite cropping out out 200 200 m to the the north. north. fragments lithologically similar to rounded and reach 10 cm in size The fragments within the conglomerate are rounded and reach 10 cm in size The fragments are pebbles in Occasionally, quartzite quartzite is is found found as as small small rounded rounded pebbles (Fig. 9). OCcasionally, in the the (Fig. 9). of quartz— The source of these clasts may be in the large area conglomerate. The source of these clasts may be in the large area of quartzconglomerate. (Smith, 1978c) 1978c) or or from from vein vein quartz quartz ite ite to to the the northeast northeast of of Observatory Hill (Smith, within the rhyolite. Figure Figure 8. 8. View of of Cambrian Cambrian sandstone sandstone outcrops outcrops at at stop stop 2B 2B on on the the south south flank flank View of 49 of Observatory Observatory Hill. HIll. �Figure 9A. Figure 9A. Figure Figure 9B. 9B. Close—up of of aa conglomerate conglomerate layer layer interbedded interbedded with with Cambrian sandClose-up stone at stop stop 2B. 2B. In fragments are angular (compare (compare In these these bands, bands, fragments with Fig. with Fig. 9B). 9B). Most Most of the fragments fragments are are porphyritic porphyritic rhyolites rhyolites similar to to those cropping out on Observatory Observatory Hill. Hill. View View of of large large rhyolite rhyolite fragments fragments (up (up to to 10 10 cm cm in in size) size) in in aa conconglomerate glomerate layer layer at at stop stop 2B. 2B. In In this this band, band, fragments fragments are are rounded rounded (compare (compare with with Fig. Fig. 9A). 9A). 50 50 �o On On Observatory Observatory Hill Hill exposures exposures of of conglomerate conglomerate containing containing rhyolite rhyolite pebbles pebbles are are usually usually restricted restricted in in occurrence occurrence to to aa zone zone 55 to to 20 20 mm wide wide about about the the rhyolite rhyolite ledges. The The conglomerate conglomerate layer layer at at Stop Stop 2B 2B is is located located an an unusually unusually large large distance distance ledges. from from rhyolite rhyolite exposures exposures (200 (200 m), m), and and its its deposition deposition probably probably reflects reflects aa relatively relatively short lived lived and and highly highly energetic energetic event. event. In In the the Baraboo Baraboo region region Dott Dott and and Dalziel Dalziel short (1970) (1970) reported large large boulders of of Baraboo Quartzite entrapped within Cambrian sandstone. They They envisaged envisaged transport transport of of cobbles cobbles and and boulders boulders by by waves waves and and strong strong sandstone. currents currents generated generated by by violent violent tropical tropical storms storms that that pounded pounded the the Baraboo Baraboo islands islands during Cambrian Cambrian time. time. Observatory Observatory Hill Hill probably probably existed existed as as aa small small island island in in during Strong late Cambrian time and was probably also hit by violent tropical storms. late Cambrian time and was probably also hit by violent tropical storms. Strong currents currents generated generated during during these these storms storms are are probably probably responsible respon$ible for for the the transtransport port of of rhyolite rhyolite fragments fragments away away from from the the Observatory Observatory Hill Hill island, island, thus thus forming forming the conglomerate band observed at Stop 2B. the conglomerate band observed at Stop 2B. Stop 2C 2C Stop From Stop Stop 2B 2B climb climb the the ridge ridge above above the the sandstone sandstone exposure exposure and and join join aa trail trail Follow this trail to where it running along along the the crest crest of of the the ridge. ridge. Follow this trail to where it joins joins the the running main main trail trail and and then then continue continue up up the the hill on on the the main trail trail (Fig. (Fig. 7). 7). Note the the first first outcrops outcrops of of rhyolite rhyolite to to your your left left and and straight straight ahead. ahead. There There vicinity is at least 500 feet feet of relief on the Precambrian surface in in the the vicinity of of is Observatory Hill. Hill. Just ahead rhyolite exposures are are at an elevation of of 1080 1080 Observatory northwest of of Observatory Observatory Hill, Hill, rhyolite rhyolite was was enfeet. About About 1200 1200inm to the the northwest feet. countered in in an irrigation irrigation well at a depth of 300 feet feet (480 (480 feet above above sea sea level). level). Cross into into the the rhyolite exposures and and continue to to the the trail trail junction. junction. the trail trail to to the the right right (south). (south). The fork to the the left left (north) (north) goes goes to to Follow the 1920's the summit summit where where aa lookout tower was was once once located located in the the lookout tower the early 1920's The ruins ruins of of the the tower can still still be be observed observed along along the (Fig. 7). The tower can the inscriptions (Fig. 7). carved into the rhyolite by by several several of of the the workers workers who manned manned the carved the rhyolite the tower. tower. Follow the trail (south) to aa large large area area of of bare bare rock rock which forms Follow the trail (south) to forms the bluff). sharp the south bluff). sharp southern southern edge edge of of Observatory Hill Hill (hereafter called called the rhyolite exposures exposures (20 From the south bluff bluff the the Marcelloii Marcellon rhyolite (20 km to to the the south) clear and the the Baraboo Baraboo Hills Hills (30 (30 km km to to the the southwest) southwest) can can be be easily easily seen seen on on aa clear and At this stop, we we will will examine examine the Hill rhyolite rhyolite and a day. At this stop, the Observatory Hill a day. coarse-grained dike. coarse—grained rhyolite dike. Observatory Observatory Hill Hill Rhyolite Rhyolite rhyolites exposed exposed The Observatory Observatory Hill Hill rhyolite rhyolite is is typical typical of of porphritic porphritic rhyolites The It contains contains phenocrysts phenocrysts of of quartz quartz (< 1 mm in in (~l in size size in south-central south—central Wisconsin. Wisconsin. It in size) size) set set in and in a a and rounded) rounded) and and pink pink to to white white alkali alkali feldspar feldspar (1 (1 to to 55 mm mm in On close close examination, examination, the the matrix matrix of of the the rhyolite rhyolite dark dark gray to black matrix. On and pumice pumice fragments. fragments. shows shows faint faint flow flow structure structure formed formed by flattened shards and o 50°E. The rhyolite rhyolite is In E. The is an an In general, general, these these bands bands dip dip steeply steeply and and strike strike N. N. 50 the entire entire hill. ash-flow hill. ash—flow tuff tuff and and is is remarkably remarkably texturally texturally homogenous homogenous over over the pheno—crysts Petrographic studies studies indicate indicate that that the the rhyolite rhyolite is is composed composed of of pheno-crysts Petrographic The devitrified ground-mass. ground—mass. The of of quartz quartz and and alkali alkali feldspar feldspar set set in in aa coarsely coarsely devitrified 51 51 �quartz is is anhedral anhedral and quartz and is is usually usually strained strained (7%). (7%). Some Some of of the the quartz quartz is is deeply deeply embayed. Alkali Alkali feldspar feldspar (23%) (23%) is is probably probably orthoclase orthoclase and and may may display display carlscarlsembayed. bad twinning. twinning. Accessory Accessory minerals minerals are are chlorite, chlorite, biotite biotite (?), bad epidote, iron (?), epidote, iron oxide and and zircon. The matrix matrix commonly commonly contains contains aligned aligned and and flattened flattened Y Y shaped shaped oxide zircon. The and cuspate cuspate shards. and shards. o In terms terms of of major major and and minor minor element element chemistry, chemistry, the the rhyolite rhyolite belongs belongs to to In chemical group group 33 (Table 1, analysis analysis 16; 16; Fig. Fig. 6), 6), of of Smith Smith (1978a) and is chemical (Table 1, (1978a) and is therefore similar similar in in chemistry chemistry to to granophyric granophyric granites granites and and porphyritic porphyritic rhyorhyo— therefore lites in the Fox River Valley. The group group 33 rhyolites rhyolites and and granites granites are are lites Valley. The distinguished , distinguished from from other other south-central south—central Wisconsin Wisconsin igneous igneous rocks rocks by by high high Si0 Si02, 2 K20/Na20, La, Zr, Y and Rb/Sr; and low CaO, A1203 and Ba (Table 1). K 0/Na 0, La, Zr, Y Rb/Sr; and low CaO, A1 0 and Ba (Table 1). 2 2 3 2 Coarse—Grained Rhyolite Coarse-Grained Rhyolite Dike coarse—grained rhyolite dike strikes north south across Observatory A coarse-grained rhyolite dike (Fig. 7). The dike is about m wide wide at (Fig. 7). The about 70 m at the south bluff but pinches out to to the north. m thick) dike of similar coarse—grained the north. A thin (15 (15 m thick) dike coarse-grained rhyolite strikes N. N. 50 E. E. across the strikes the southeast southeast slopes slopes of of Observatory Observatory Hill. Hill. These dikes were were originally identified by Hobbs and Leith (1907) dikes (1907) who referred referred to to them as as granite dikes. them The contact between the the dike and the Observatory Hill rhyolite is well displayed on the east edge the edge of of the the south south bluff. bluff. The contact shows complex interfingering of of dike dike rock rock into into Observatory Observatory Hill Hill rhyolite rhyolite (Fig. 10) and and in interfingering (Fig. 10) in locality a a rhyolite zenolith is is found found in in dike dike rock rock close close to to the the contact. contact. Locally the Hill rhyolite is intensely fractured near the the Observatory Hill the contact contact (Fig. 11). Also, quartz veins are concentrated on either side of the (Fig. 11). Also, the contact. contact. Extending 55 to to 10 10 m m into into the the dike from from the the intrusive intrusive contact contact is is aa fine— finegrained contact zone (chill zone?). grained contact zone zone?). The rock in this zone is is gray—green gray-green in in color and and contains large large plagioclase plagioclase phenocrysts. phenocrysts. Petrographic Petrographic studies studies of of the the dike rock rock of of the the contact zone zone reveal reveal sub— subhedral hedrHl zoned zoned plagioclase phenocrysts (30%) (30%) with cores altered to to sausserite sausserite and unaltered unaltered rims, rims, subhedral alkali feldspar feldspar (5%), (5%), fractured and broken quartz (3%) (3%) and and small small subhedral subhedral feather—like feather-like grains grains of of biotite (1%). (1%). The matrix is a microbreccia containing fragments of fine—grained is a fragments of fine-grained rhyolite, rhyolite, basalt and and eutaxitic eutaxitic rhyolite. rhyolite. At this this locality locality also also notice notice the the glacial glacial polish polish and and grooving. grooving. glacial striations trend N. 70° W. glacial striations trend N. 70° W. Here Here Walk Walk to to the the east east of of the the south south bluff bluff to to the the first first major major outcrop. outcrop. Here Here rhyolite in the central part of the dike is well exposed. rhyolite in the central part of the dike is well exposed. This This rhylite rhylite is is similar similar in in mineralogy to to that that of of the the contact zone, zone, but differs by by having having aa coarser—grained coarser-grained matrix matrix than than the the contact—zone contact-zone rock. rock. Also, Also, it it is is pink pink to to red red in in color color in in outcrop, outcrop, not not green green in in color color like like the the contact—zone contact-zone rock. rock. Petro— Petrographic graphic examination examination indicates indicates that that plagioclase is is the the dominant phenocryst phenocryst (46%). (46%). Alkali Alkali feldspar feldspar is is present present in in micropegmatitic micropegmatitic intergrowths intergrowths with with quartz quartz (21%). (21%). Quartz, Quartz, in in addition addition to to its its occurrence occurrence in in alkali alkali feldspar—quartz feldspar-quartz 52 52 �Figure 10. 10. Figure View of the contact between the coarse—grained coarse-grained rhyolite dike (below), (below), Hill rhyolite rhyolite (above). (above). Note Note the the fingers fingers of of and the Observatory Hill coarse—grained rhyolite rhyolite extending extending into into the the Observatory Observatory Hill coarse-grained Hill rhyolite rhyolite Also noteworthy are the numerous veins of quartz (dashed line). line). veins that the contact. contact. that roughly parallel the Figure Figure 11. 11. Close—up view view of of the the shattering shattering of of the the Observatory Observatory Hill Hill rhyolite rhyolite Close-up at dike. at the the contact contact with with the the coarse-grained coarse—grained rhyolite dike. 53 53 �intergrowths, intergrowths, (10%) include include (10%) oxide. These oxide. These is present present as as small small anhedral anhedral phenocrysts is phenocrysts (2%). (2%). Accessory Accessory minerals minerals chlorite in in irregular irregular clots, clots, epidote, epidote, clinozoisite, clinozoisite, and chlorite and iron iron minerals are set led groundmass groundmass (21%). set in in aa finely finely devitrif devitrified (21%). This dike dike and and aa fine-grained fine—grained granite at This at Baxter Hollow Hollow (Gates, (Gates, 1942) 1942) are are similar in chemistry, and form chemical group 1 of Smith (1978a) similar in chemistry, group 1 of Smith (1978a) (Table (Table 1, 1, analyses 11 and The rocks rocks are are distinguished distinguished from from the the other other analyses and 2; 2; and and Fig. Fig. 6). 6). The granites and rhyolites in the the Fox Fox River River Valley Valley and and Baraboo Baraboo area area by by higher higher granites and rhyolites in Ti02,, CaO, CaO, Ba, Ti0 Ba, V V and Sr Sr and and by by lower lower Si02 Si0 and and Rb.Sr Rb.Sr ratio. ratio. Both Both the the ObserObser— 2 2 vatory Hill Fox ovatory Hill rhyolite rhyolite and and the the Baxter Baxter Hollow Hollow Granite are younger than the the Fox River Valley Valley and and Baraboo Baraboo rhyolites. Baxter Hollow Hollow Granite Granite intrudes rhyolite River rhyolites. Baxter intrudes rhyolite (Gates, 1942) 1942) but but its its relationship relationship to the overlying Baraboo (Gates, Baraboo Quartzite Quartzite is is unclear (Dott Daiziel, 1972). unclear (Dott and and Dalziel, 1972). This This stratigraphic stratigraphic and and chemical chemical evidence evidence suggests that that the the intrusion intrusion of of the the Baxter Baxter Hollow Hollow Granite Granite and and the the Observatory Observatory suggests Hill rhyolite rhyolite was was a discrete igneous event that occurred after the emplacement Hill a discrete igneous event that occurred the emplacement and folding folding of of the the widespread rhyolite ash—flow and ash-flow sheets. sheets. The for aa short short time time at at the turn The coarse-grained coarse—grained rhyolite rhyolite dike dike was was quarried quarried for of the the century. century. This This opera~ion operation is evidenced by by aa large of is evidenced large area area of broken dike rock located just just below and and to to the the east east of of the the south south bluff. bluff. Labradorite Porphyry Dike Dike Hobbs and east—trending "labradorite porphyry" Hobbs and Leith (1907) (1907) reported reported an east-trending porphyry" dike just to to the the north north of of the the south south bluff. bluff. A for this this dike dike A careful search for revealed an east-trending east—trending fine—grained quartz—feldspar rhyolite dike about fine-grained quartz-feldspar 5 5 m m in in width. width. This This dike is is truncated by the north—trending north-trending coarse—grained coarse-grained rhyolite rhyolite dike as as is the "labradorite porphyry" porphyry" dike described by Hobbs and Leith. In terms terms of of location, location, orientation orientation and and stratigraphy, stratigraphy, it almost Leith. In it is is almost certainly the the same same dike dike mapped mapped by by them. them. In In thin thin section, section, this rock contains rounded rounded and embayed quartz phenocrysts phenocrysts (2%) (2%) and alkali feldspar with perthitic texture (altered (altered to to sericite sericite and and dusted dusted with with iron iron oxide) oxide) (3%). (3%). These minerals occupy a a fine—grained fine-grained matrix (devitrified) (devitrified) with iron oxide accentuating a a crude evidence of crude banding banding (95%). (95%). The only evidence of metabasalt on Observatory Hill is found found on on the the south south bluff. bluff. Here aa green metabasalt that that occurs occurs in in an an outcrop outcrop only 3 m m long long and and 0.3 0.3 mm wide wide may may intrude intrude rhyolite. rhyolite. Other Other Exposures Exposures of of Porphyritic Porphyritic Rhyolite: Rhyolite: Other Other exposures of of porphyritic porphyritic rhyolite rhyolite (Endeavor, (Endeavor, Utley, Utley, Berlin, Berlin, and and Taylor Farm) Farm) are are mineralogically, mineralogically, texturally, texturally, and and chemically similar similar to to the the rhyolite rhyolite at at Observatory Observatory Hill. Hill. However, However, common common in in the the Utley rhyolite rhyolite are are zones zones of of spherulites spherulites and and lithophysae, lithophysae, also also disk—shaped disk-shaped coarse—grained coarse-grained inclusions inclusions may may represent represent recrystallized recrystallized collapsed collapsed pumice. pumice. Rhyolite is is locally locally sheared sheared at at Berlin (Weidman, (Weidman, 1898) 1898) and and slickensided slickensided surfaces surfaces are are found found at at Utley Utley (Gram, (Gram, 1947). 1947). Rhyolite at at Utley Utley is is intruded intruded by by rhyolite, rhyolite, dacite dacite and and metabasalt metabasalt dikes. dikes. 54 54 �1/ / o / CC ~_ ~ I ~~v'1'\:Y N t4 /' .>.. ~ t J ~ ( --- -/ ) / (A/ (AI J ~< ~4 ~ /' EXPOSURES EXPOSURES /OF WELL BANDED WELL BANDED ?/ UNIT C ---- "---.,,, ~ -- ~ UW DEEP HOLE HOLE ) WAYNE / BUSH FARM BUSH FARM SPHEROIDS) I / f ~/u,,~ / (~~~~ ---- ,..- L BOX - PARK HERE WELL BANDED UNIT B QUARTZ VEINS EXPLANATION --- -o O .. 200 200 400 400FEET FEET I 4 4- CONTACT STRIKE AND AND DIP DIP OF OF STRIKE FLOW BANDING BANDING FLOW PLUNGING ANTICLINE ANTICLINE PLUNGING PLUNGING SYNCLINE SYNCLINE PLUNGING FIELD TRIP TRIP ROUTE ROUTE ,,~;~ FIELD I'' -+-+-+- FENCE FENCE Figure Figure 12, 12. Route Route map map for for traverses traverses at at the the Marcellon Marcellon rhyolite rhyolite exposures, exposures. Letters Letters A, A, B, B, CC refer refer to to Marcellon Marcellon rhyolite rhyolite unit unit numbers numbers (see (see text text and and Fig, Fig. 13). 13). 56 56 �STOP 33 -- THE THE MARCELLON MARCELLON RHYOLITE-SPHEROIDAL RHYOLITE-SPHEROIDAL TEXTURES TEXTURES STOP Location: Location: To To reach reach the the outcrops outcrops of of spheroidal spheroidal rhyolite rhyolite we we will will walk walk into into the the woods woods at at the the mail mail box box located located across across Monthey Monthey Road Road from from the the Wayne Wayne Bush Bush Farm. Farm. This This traverse traverse requires requires aa bit bit of of climbing climbing on on bare bare rock rock that that becomes becomes quite quite slippery during during wet wet weather. weather. Wear Wear proper proper field field boots boots and and take take considerable considerable slippery care while while on on this this traverse. traverse. care (west) (west) This This stop stop will will illustrate illustrate several several of of the the textural textural types types of of rhyolite rhyolite in in the the Marcellon inlier. inlier. See Figure Figure 12 12 for for the the traverse traverse route. route. The The rhyolite rhyolite exposures exposures Marcellon to to the the east of of Monthey Monthey Road Road are are described described in in aa supplemental supplemental stop. stop. Introduction to the the Marcellon Rhyolite: Rhyolite: The The Marcellon Marcellon inlier inlier (Hobbs (Hobbs and and Leith, Leith, 1907; 1907; Smith, Smith, 1978a) 1978a) is is composed of texturally texturally variable rhyolites rhyolites similar similar in in chemistry and and lithology lithology to to rhyolites at the the Marquette exposure (Stop (Stop 4), 4), and and in the Baraboo Baraboo area. area. The Marcellon inlier inlier is is formed by four four mineralogically and and chemically distinct ash—flow ash-flow tuffs tuffs folded into into aa northeast striking striking asymmetric asymmetric (and possibly overturned) overturned) antiform antiform (Fig. (Fig. 13). 13). The western limb limb of of the the antiform antiform (and N. 500 50° E. E. and and dips dips 50—85° 50-85° to to the the northwest. northwest. The eastern limb limb also also strikes N. strikes strikes N. N. 50° 50° E. E. but dips dips steeply steeply (80° (80° to to vertical) vertical) to to the the southeast. southeast. The The rhyolite are cut cut by a northeast trending andesite dike and by an east rhyolite flows flows are a northeast (Table 1, 1, analyses analyses 32 32 and and 33). 33). The andesite andesite dike dike cuts cuts trending basalt dike (Table and is is therefore therefore younger. younger. the basalt dike and The structurally highest A) at Marcellon Marcêllon is a The highest unit unit (unit (unit A) a sparsely porphy— porphyritic ritic plagioclase (1%), (1%), quartz (2%), (2%), alkali feldspar feldspar (2%) (2%) rhyolite characterized diameter) composed of radiating by abundant abundant large spherulites spherulites (up (up to 15 cm in diameter) On the fibers of alkali feldspar and quartz. On the eastern flank of the the fold, fold, fibers alkali feldspar and quartz. spherulites are are less less distinct and and smaller, smaller, but but still still conspicuous. conspicuous. Structurally below unit unit A is is a a rhyolite (unit (unit B) (6%), alkali B) which contains sparse quartz (6%), feldspar (4%) feldspar (4%) and plagioclase (1%) (1%) phenocrysts in a a banded matrix with Several samples samples show show perlitic perlitic cracks cracks in occasional occasional faint faint spherulitic growths. Several characteristically well banded and contains plagioclase the Unit Unit C is the matrix. Bnnding in unit as (14-18%). B~nding unit C is is continuous and as the the dominant phenocryst (14—18%). 0 relatively consistent in orientation (N. 50°E.) but locally broad westward westward relatively consistent in orient~tion (N. 50 E.) but locally broad Several lenses of spherulitic rhyolite plunging exposed. Several lenses of spherulitic rhyolite lie lie plunging flow folds folds are exposed. Unit C parallel sharp contacts contacts with with nonspherulitic nonspherulitic rock. rock. C parallel to banding and have sharp mineralogy to rock on on the on the on the the eastern eastern flank flank of of the the fold fold is is similar similar in in mineralogy The core core of the antiform is western flank, flank, but it it lacks lacks conspicuous conspicuous banding. banding. The is (2%), formed (unit D) formed by by aa rhyolite rhyolite (unit D) which which contains contains phenocrysts phenocrysts of of quartz quartz (2%), plagioclase (15%) and alkali alkali feldspar feldspar (2%) in aa fine-grained fine—grained devitrified devitrified plagioclase (15%) and (2%) in groundmass with numerous shards, flattened pumice and perlitic fractures groundmass with numerous shards, flattened pumice and perlitic fractures All units at are interpreted as ash—flow tuffs. (Fig. 14). All Marcellon ash-flow tuffs. (Fig. 14). Marcellon includes: Evidence at Marcel10n includes: Evidence for for the the northeast northeast striking striking antiform at (b) geologic map (Fig. (a) (Fig. 13); 13); (b) (a) the the symmetric symmetric pattern pattern of of lithologies on the geologic map rhyolite) which indicates structural (orientation of structural data data (orientation of banding banding within within the the rhyolite) which indicates 50° E. E. and and dips dips to to the the that N. 50° that the the western western part part of of the the structure strikes N. but dips steeply to the the northwest; the eastern part also also strikes northeast, northeast, but dips steeply to northwest; the rhyolite The chemical chemical correlation correlation of of lithologically lithologically similar similar rhyolite southeast. (c) The (c) southeast. Similarities in structure. Similarities from the eastern flank of of the the structure. in from the the western western flank flank to the 57 57 �o0 250 500 1000 250 500 750 750 1000 2000 FEET 250 250 o0 500 METERS N 1 :j ':·1 ~ l:{:. Basalt DIke Baaalt Dike 'f",$#!) Quartz Plagloclase Alkali Feldspar Quartz·- Plavlacla .. -- Alkali Feldapar Rhyolite Rhyolite .' I, .......,/ :j176 YII76 ::.::::rr-——, ....~';T ,.::. :':.:::.) )•_• ,,, ....~:.y EXPLANATION ':6~ '/ Andesite grained And..lte Andesite Dike And..lte Dike Dike,• Coarse Caar.. -—vralned Dike I, '- Unit Unit D D Plagloclase Plav1acla.. RhyolIte Rhyolite banded and flaw flow folded banded and folded Unit Unit C C Quartz— Plagloclese Alkali Feldlper Feldiper Rhyollte Quartz - Plavlacla .. • -Alkali Rhyolite Unit Unit B 8 Spheruiitlc Spherulllic Rhyellte Rhyeille U,dt Utit AA 45 Strike Strike and and Dip Dip .f efBanding Bandlnv ~+- Vertical Vertical Banding BandlllV -_ .. +- ~+- Contect, whereInferred, lnf.rred, dotted Contact, dashed daahed where dotted where where I4 burled burled Flow Flow Foldln Faldln, Trace of of axIal axial Diane ,lane of orrow indicates Indlcat .. Trace of anticline, enticllne, arrow direction direction of ofplunge plunve Trece of axialplane plane of of syncline, Iyncllne, arrow arrow indicates Indlcat.. Trace of xlal direction direction of of plunge plunve Sample Location Location Sample Antlcllne, trace of Anticline, showing Ihowlnv trace of azlal axial plane plane Figure Figure 13. 13. Geologic Geologic map map of of the the Marcellon Marcellon inhier inlier (adapted (adapted from from Smith, Smith, 1978a). 1978a). 58 58 �Figure 14. 14. Figure Photomicrograph Photomicrograph of cuspate and Y—shaped Y-shaped shards shards in in the the Marcellon rhyolite ash—flow ash-flow tuff tuff (unit (unit D). D). Bar scale scale is is 11 mm mm long. long. rhyolite the ratios of of lithologically lithologically similar similar units units (Table (Table 1, 1, analyses analyses 21—27) 21-27) the Rb-Sr Rb—Sr ratios For example, both spheru— s.tratigraphically suggest that they are &tratigraphically equivalent. For example, both spherusuggest that they are Similar groupexposures (unit (unit A) A) show similar Rb/Sr Rb/Sr values. values. Similar grouplitic rhyolite exposures Unit D D (Quartz_plagioclaSe—alkali ings for units units B Band (Quartz-plagioclase-alkali feldfeldings are apparent for and C. Unit quartz—bearing rhyolites by a spar) can be distinguished from from the the other other quartz-bearing rhyolites by a lower lower spar) (2.82% as as compared compared with with a Fe20 Rb/Sr and higher 0 (2.82% a Rb/Sr ratio and higher Ba, Ba, CaO, CaO, and and FeO ++ Fe 2 he other rhyolites by having a 1.77-2.13 %). Also, C from ~he other rhyolites by having a unit is different from 1.77—2.13 %). higher Ba content content (Fig. (Fig. 15). 15). higher Ba Bt- DtD- • • • S • • • S • CtC Bha. B o0 Cf> A CD :> I 100 100 ~oo 500 Ba Ba Figure Figure 15. 15. 1000 30 40 50 ~o 60708090 60 70 80 90 00 0003040 La La I ~o 50 100 00 50 I~O Sr Sr HI 00 100 ISO I~O Rb Rb 2000 1.00 2.0 2.0 Rb/Sr Rb/Sr 0) 0.5 O.~ 1.0 1.0 CoO CaO .20 I.~O 0.5 Stratigraphic variation variation in in elemental elemental concentrations concentrations for for the the MarMar— Stratigraphic Ba, La, La, Sr Sr and and Rb Rb are are in in ppm; ppm; CaO CaO and and MgO MgO are are cellon cellon rhyolite. rhyolite. Ba, For comparison, elemental concentrations for in in weight weight percent. percent. For comparison, elemental concentrations for (from Smith, 1978a). the Baraboo rhyolites (B) are also plotted the Baraboo rhyolites (B) are also plotted (from Smith, 1978a). 59 59 O.~ MO MgO �Marcellon Traverse: Walk into into the the woods woods to the the west west Marcellon Traverse: Walk Monthey Road from the Wayne Bush Farm. See Figure 12 Monthey Road from the Wayne Bush Farm. See Figure 12 at the the mailbox located at located across across for the traverse traverse route. for the route. Unit B B Unit Note the the well-banded well—banded unit unit BB rhyolite rhyolite to to your your right right in in the exposure just Note the exposure just to the west of Monthey Road (Fig. 12). The bands bands are are discontinuous discontinuous and to the west of Monthey Road (Fig. 12). The and are are formed by by collapsed pumice fragments and formed and shards. shards. At At this this exposure, exposure, bands bands strike N. N. 50° 500 E. E. and and dip dip to to the the northwest northwest at at 50° 50° to to 70°; 70°; thus thus indicating indicating the the strike orientation of orientation of the the west limb of the the Marcellon Marcellon antiform. antiform. Band is Band orientation orientation is remarkably consistent consistent in in this this area, area, but but several several broad broad folds folds interrupt this remarkably interrupt this pattern. In several several places unit B is pattern. In is spherulitic. spherulitic. Walk to the southwest along along the the margin margin of of the the bluff. bluff. Cross Cross the barbedbarbed— wire fence and wire and climb to to the the crest crest of of the the bluff bluff (Fig. (Fig. 12). 12). As ascend, As you ascend, note the grooves in differentially weathered unit B rhyolite note the lichen lichen growing in grooves (the grooves grooves are are parallel parallel to (the to the the banding described desc~ibed above). above). At the crest of At the the bluff bluff notice notice the the glacially glacially polished polished and and striated striated surface surface (striations the (striations trend trend N. 70° of milky quartz on the N. 70° W.). W.). Also noteworthy are are the the large large veins veins of south flank of of the the bluff. bluff. One is 20 cm wide and and over over 66 mm long. long. One quartz quartz vein is Cross the the summit the hill hill and descend descend to its base (you Cross summit of of the (you should now be on the the west west side on side of the hill and almost at at its its end) end) (Fig. (Fig. 12). 12). Notice that that as hill is east to west west the as the the hill is traversed traversed from east the banding so common in in unit B disappears and and that the rock becomes becomes highly charged charged with spheroids (characterdisappears that the (characteristic istic of of unit unit A). A). This the contact between between unit unit BB and and unit unit A. A. This change marks the Spheroidal Spheroidal Texture Texture Unit A is a a poorly—banded poorly-banded ash—flow ash-flow tuff with a a spheroidal texture texture (Figure (Figure 16). 16). Banding trends trends N. N. 20°E. 20 0 E. to to N. N. 30° 30° W. W. and and may may swirl swirl about about spheroids or may be truncated truncated by by them. them. Three important types of spheroids are are present present in in this this exposure. exposure. Figure Figure 16. 16. View Vi~w of of weathered weathered spherulites spherulites in in the the Marcellon Marcellon rhyolite rhyolite (unit (unit C). C). These These spheruljtes spherulites are are identical identical to to those those observed observed in in unit unit A. A. 60 60 �Spherulites Spherulites composed composed of of radiating radiating fibers fibers of of quartz quartz and and alkali alkali feldspar feldspar A small alkali feldspar crystal may be present in the (Fig. 17). A small alkali feldspar crystal may be present in the core core of of the the (Fig. 17). Spherulites In outcrop they appear massive and may be broken. spheroid. In outcrop they appear massive and may be broken. Spherulites spheroid. commonly commonly form form by by the the devitrification devitrification of of volcanic volcanic glass, glass, and and commonly commonly occur occur in in the densely welded vitric basal zone of an ash—flow cooling unit. the densely welded vitric basal zone of an ash-flow cooling unit. (1) (1) Spherulites Spherulites are are also also quite quite common common in in felsic felsic lava lava flows. flows. Spheroids with with concentric concentric bands. bands. In thin section they they are are composed composed of of Spheroids alternating led glass alternating concentric concentric bands bands of of coarsely coarselyand and finely finelydevitrif devitrified glass (Fig.l8). (Fig.18). "Thesespheroids spheroids may may be be concretionary concretionary lapilli lapilli (??). (??). These (2) (2) (3) Lithophysae Lithophysae with with hollow hollow cores cores and and in in many many cases cases with with drusy drusy quartz quartz lining lining (3) In thin the cavity cavity wall. wall. These These spheroids spheroids may may not not have have aa central central cavity. cavity. thin the section many of of them them have aa core core of of epidote, epidote, and/or and/or quartz quartz (Fig. (Fig. 19). 19). The The spheroids spheroids have have cross sections sections that that are are nearly nearly circular circular (average (average ratio ratio ± 0.11). of minor to to major major axis axis == 0.71 0.71 ~ 0.11). The cross sections of of these these of length of spheroids may be regarded as strain ellipses, ellipses, and their their nearly circular suggests that that these these rhyolites rhyolites were were not not strongly strongly deformed. deformed. Also Also supportsupportshape suggests ing this this suggestion is is the the overall freshness of the the rhyolites rhyolites (there (there is is little little evidence for medium— medium- or high—grade high-grade metamorphism, metamorphism, and and original textures textures are are in the the matrix). matrix). Also considering considering their their age, age, these these rocks rocks are are preserved in remarkably fresh fresh in in terms terms of of their their chemistry chemistry (Smith, (Smith, l978a). 1978a). Deep Well: Well: Return Return to to Monthey Monthey Road. Road. Walk from from the the Bush Farm Farm to to the the tree tree Deep covered hill just to to the the north north of of the the farm farm (Fig. (Fig. 12). 12). The outcrop of well— wellbanded unit at the base of of the hill was was the banded unit C at the base the hill the site of a a deep hole drilled by B. Haimson and students students from the the University of of Wisconsin—Madison. Wisconsin-Madison. Two B. ninety—seven feet of core core was was recovered hundred and ninety-seven feet of recovered before drilling had to hundred and The 1978). be stopped because of of the the extreme extreme hardness hardness of of the the rock rock (Haimson, (Haimson, 1978). The hole penetrated banded banded unit C. and hole unit C. and then then entered a a poorly banded rhyolite C. This This poorly banded banded rock is most probably mineralogically identical identical to unit unit C. separate ash-flow ash—flow cooling aa textural textural variant variant of of unit unit C. C. and and may may represent represent aa separate Also, a 1 m thick dike trending trending N. N. 26°E. 26°E. was was intersected intersected unit. Also, aIm thick inetabasalt metabasalt dike unit. at feet in in the the hole. hole. at aa depth of 132 feet 61 61 �Figure 17. Figure 17. Figure Figure 18. 18. Photomicrograph of spherulitic texture in the Marcellon rhyolite unit These spherulites spheruljtes are are composed composed of of radiating radiating fibers fibers of of unit A. A. These quartz and and alkali alkali feldspar. feldspar. Bar scale in in 11 mm mm long. long. Photomicrograph Photomicrograph of of aa spheroid spheroid with with concentric concentric bands. bands. Core Core is is composed composed of of coarse—grained coarse-grained quartz and and alkali alkali feldspar; feldspar; rim rim is is formed formed by by fine—grained fine-grained quartz quartz and and alkali alkali feldspar. feldspar. Several Several spheroids spheroids show show alternating alternating bands bands of of coarse— coarse- and and fine—grained fine-grained material. material. Bar Bar scale scale is is 11 mm mm long. long. 62 62 �Figure Figure 19. 19. and Photomicrograph of of aa spheroid spheroid with with aa core core of of coarse coarse quartz quartz and Photomicrograph Quartz grains grains are are interlocking interlocking and and probably probably grew grew in in aa epidote. epidote. Quartz surrounded The core core is is off-center off—center within within the the spheroid spheroid and and is surrounded cavity. cavity. The Many of the the by aa band band of of fine-grained fine—grained quartz quartz and and alkali alkali feldspar. by feldspar. Many of fine— and spheroids are are more more intricate intricate and and have have alternating alternating bands bands of of fine- and spheroids These coarse—grained alkali alkali feldspar feldspar and and quartz quartz about about the core. These coarse-grained Bar scale scale is is 11 mm mm long. long. structures structures may may be be lithophysae. lithophysae. Bar 63 63 �Supplemental Stop Stop -— Flow Flow Structures Structures in in the the Marcellon Marcellon Rhyolite: Rhyolite: Supplemental This stop stop illustrates illustrates structures structures and and textures textures in in unit unit C. This From C. From the the Bush Bush Farm walk walk to to the the north north on on Monthey Monthey Road Road to to the the tree tree covered covered knob Farm (Fig. knob (Fig. 12). 12). Turn right right (east) on the dirt road road (just Turn (east) on the dirt (just south south of of the the hill). hill). Walk the Walk~st st the drilling site site (described (described in in Stop Stop 3) 3) and and continue continue walking walking for for about drilling 70 m about 70 m (Figure 12). 12). Turn Turn left left (north) (north) into into the the trees trees and and follow follow the the "canyon" "canyon" to (Figure to the the bare steep steep exposure exposure on on the the right right (a (a distance distance of of about about 50 50 m, bare on the way, m, on the way, you you should pass pass aa large large red red granite granite erratic). erratic). The should The textures textures described described below below are are located on on this this exposure. exposure. located Unit CC is is aa well-banded well—banded rhyolite rhyolite containing containing plagioclase plagioclase (15-25 (15—25 %) Unit as the the %) as dominant phenocryst. The unit unit strikes strikes N. N. 30° E. and dips steeply dominant phenocryst. The 30° E. steeply 500 50° to to 80° 80° to the the northwest northwest (this exposure is to (this exposure is on the west limb limb of of the the Marcellon antiform). Marcellon antiform). Bands are discontinuous and are in general lighter—colored Bands are discontinuous and are in general lighter-colored than than the the matrix matrix (Fig. 20). 20). Many Many bands bands have have aa dark dark medial medial line, line, and and in in places places they they are (Fig. are observed to bend bend about about phenocrysts. phenocrysts. The to The bands bands were were formed formed during during primary primary flowage flowage and and compaction of an ash-flow ash—flow tuff tuff by by shearing shearing and and compaction compaction of compaction of an shards. of pumice and shards. Banded ash-flow ash—flow tuffs tuffs similar similar to to those those observed observed here here are Banded in are quite quite common in outflow deposits about Tertiary volcanic centers (Schmincke outflow deposits about Tertiary volcanic centers (Schmincke and Swanson, 1967; Deal Deal and 1967; and Rhodes, Rhodes, 1976). 1976). When viewed perpendicular to the foliation plane, these Tertiary ash—flow tuffs tuffs display display strong strong lineation formed plane, these Tertiary ash-flow formed by flattened pumice (Fig. 21). flattened pumice (Fig. 21). The be 20 20 to to 11 on the The axial axial ratio of pumice may be on the flow plane, plane, and flow and as as high high as as 200 200 to to 1 1 on to the the flow flow surface surface on the the plane normal to and parallel parallel to and to the the direction direction of of flow. flow. Where pumice shows a a high degree of stretching and flattening the rock and the rock may may resemble resemble aa flow-banded lava, but the the flow—banded lava, presence of glass shards shards and the discontinuous nature of the bands suggests suggests instead that that the the rock rock is highly foliated foliated ash-flow ash—flow tuff instead is aa highly (Smith, 1978b). 1978b). tuff (Smith, The banding at this locality is is folded folded into aa series anticlines series of broad anticlines and synclines that plunge steeply (50° that plunge steeply (50° to to 80°) 80°) to the the west. west. Fold amplitudes amplitudes are as great as as 30 30 mm and and wavelengths wavelengths vary vary up up to to 10 10 m. m. In most most cases where aa fold nose is observed, the plunge of the fold fold is observed, the plunge of the fold axis parallels the the dip dip of of unit unit C C as as aa whole. whole. Fold Fold limbs limbs are are themselves themselves folded folded into antiforms and synforms synforms that plunge steeply steeply to to the the west west (Fig. (Fig. 22). 22). These minor minor folds folds have amplitudes amplitudes of up to 10 m and wavelengths that of up to 10 m and wavelengths that vary vary from from several several centimeters centimeters to to several several meters. meters. Flow Flow bands bands on on fold fold limbs limbs may may truncate truncate each each other, other, also fold crests may may not not completely completely close, close, forming forming fanning fanning patterns patterns (Fig. (Fig. 23). 23). The ae interpreted The folds folds:re interpreted as as ramp ramp structures structures formed formed during during the the flowage flowage of of an an ash—flow tuff. ash-flow tuff. In In detail detail they they are are formed formed by by compressional compressional buckling buckling and and thrustthrusting ing of of the the upper upper part part of of an an ash—flow ash-flow cooling cooling unit unit over over aa more more fluidal fluidal interior interior (Smith, 1978b). In Tertiary ash—flow (Smith, 1978b). In Tertiary ash-flow tuffs tuffs ramp ramp structures structures are are broad broad warps warps in in the the flow flow foliation foliation that that resemble resemble large large folds folds in in felsic felsic lavas. lavas. Amplitudes Amplitudes are are up up to to 50 50 mm and and wavelengths wavelengths vary vary from from several several meters meters to to tens tens of of meters. meters. Many Many are asymmetric with gentle limbs dipping 10° to 30° sourceward, are asymmetric with gentle limbs dipping 10° to 30° sourceward, and and are are convex convex upward upward (Schminke (Schminke and and Swanson,l967). Swanson,1967). 64 f14 �20. Figure 20. Highly flattened and sheared sheared pumice pumice and and shard shard fragments flattened and fragments forming forming a a pronounced lineation lineation in in the the Marcellon Marcellon rhyolite rhyolite (unit (unit C). C). The The bands bands colored than are discontinuous and and are are in in general general lighter lighter colored than the the matrix. matrix. Note that that several bands bands trend trend to to form form about about cavities cavities and and phenocrysts. phenocrysts. Figure Figure 21. 21. Close—up of of lineation lineation formed formed by by highly highly flattened flattened and and stretched stretched Close-up pumice in in the the Tertiary Tertiary A. A. L. L. Peak Peak Tuff, Puff, San San Mateo Mateo Mountains, Mountains, New New pumice The strong lineation formed during the late—stage laminar Mexico. The strong lineation formed during the late-stage laminar Mexico. Also note note the the numerous numerous rotated inclusions. flowage flow. Also inclusions. flowage of of the the ash flow. 65 65 �Figure Figure 22A. 22A. A large steeply plunging flow fold fold in the Marcellon rhyolite The fold fold axis axis strikes strikes N. N. 50° 5Ø0 W. W• and and plunges plunges 8So 85° to to (unit C). C). The The plunge of the fold axis the west. The axis parallels parallels the the dip dip of of unit unit as aa whole. Dashed line traces C as Dashed traces the limbs limbs of of the the fold. fold. Figure Figure 22B. 22B. AA small small fold fold in in the the Marcellon Marcellon rhyolite rhyolite (unit (unit C). C). This This structure structure probably probably formed formed during during primary primary flowage flowage of of the the ash—flow ash-flow tuff. tuff. Its Its axis axis strikes strikes east—west east-west and and plunges plunges 60° 60° to to the the west. west. 66 66 �I 23A. Figure 23A. I foot Sketch of a fold fold in in the Marcellon rhyolite unit C C where does not completely close producing a fanning pattern. not completely close producing a fanning pattern. truncation of of banding. banding. fold fold Also Also crest crest note note O.5m 0.5 m Figure 23B. Figure 23B. Sketch of of aa large large fold Sketch fold in Marcellon rhyolite rhyolite unit unit C. C. steeply (left). steeply to to the the west west (left). 67 67 Fold plunges Fold plunges �STOP 44 -- THE THE MARQUETTE MARQUETTE RHYOLITE RHYOLITE(NORTH (NORTh OF OF COUNTY COUNTY HIGHWAY STOP HIGHWAYH) H) Location: The The stratigraphy stratigraphy and and fabric fabric of of the the Marquette Marquette rhyolite rhyolite to Location: to the the north north of of County Highway H will be examined at this stop. County Highway H will be examined at this stop. AA supplemental supplemental stop stop views views banding, pumice pumice lenses lenses and and aa block-flow block—flow breccia breccia in in exposures banding, exposures to to the the south south of of County HH on on Ingall's Ingall's knob. knob. See See Figure Figure 24 24 for for traverse traverse routes. routes. County EE -- r N t4 STOP 400 FEET 400 FEET = /) I z- UNIT B —, ' — FIAMME BR EC CIA EXPLANATION CEJ GEOLOGIC GEOLOGIC UNIT UNIT .--- CONTACT CONTACT _——-- ~ Figure Figure 24. 24. -+--t-+- see see text text for for xpI an at ion '3xplanation PLUNGING PLUNGING ANTICLINE ANTICLINE —-----. ' - GATE GATE ~ TRAIL TRAIL --:yo PLUNGING PLUNGING SYNCLINE SYNCLINE FENCE FENCE FIELD TRIP FIELD TRIP ROUTE ROUTE Route Route map map for for traverses traverses at at the the Marquette Marquette rhyolite rhyolite exposure. exposure. Introduction Introduction to to the the Geology Geology of of the the Marquette Marquette Exposure: Exposure: The The rhyolite rhyolite at at Marquette Marquette (Pretts, (Pretts, 1895; 1895; Hobbs Hobbs and and Leith, Leith, 1907; 1907; Smith Smith and and Hartlaub, Hartlaub, 1974; 1974; Smith Smith l978a) 1978a) occupies occupies seven seven small small hills hills surrounded surrounded by by PleisPleistocene tocene sediments sediments and and Paleozoic Paleozoic sedimentary sedimentary rocks rocks (Fig. (Fig. 25). 25). The The extensive extensive cover cover prevents prevents reliable reliable field field correlation correlation of of units units from from hill hill to to hill, hill, and and since most contacts are obscured, relative since most contacts are obscured, relative age age of of the the Marquette Marquette units units can can only only be be inferred inferred by by noting noting their their stratigraphic stratigraphic position position within within major major folds. folds. CorreCorrelations lations depicted depicted on on the the geologic geologic map map (Fig. (Fig. 25) 25) are are based based primarily primarily on on chemical chemical 68 68 �"'J fool· I-'. (J'q — 'i CD CD ~ l!..:I U1 . ~ .... C'l CD El 2 ll> "0 'i .c t: ffi CD CD C"t C"t CD CD 1-4 H ::s .... I-S fool· i-a. CD CD '"i Plagioclose Rhyollte Plagioclase Rhyolite Volts EE and Units and C C V.~~;ij Breccia Breccia ILI'/- E$KtFJ C. Strike and dip of of contact Strike and dip contact Normal fault, fault, dashed Normal' dashed where where ,~ approximately located, approximately located, UUD .... ""U upthrown upthrown side, side, D-downthrown D-downthrawn ,,"" Antlcllne, trace of Anticline, showing showing trace of axIal plane directIon axial plane and and direction )'7 ,,"" Syncline, trace of Syncline, showing showing trace of axial dIrection axial plane plane and and direction of plunge of plunge Overturned Anticline, Overturned Anticline,showing showing trace trace of of axial axial plane plane and and direction of direction of plunge plunge c' Overturned ","" Overturned Syncline, Syncline, l' showingtrace trace of of axial showing axial plane and and direction direction of plane of plunge plu n g e ) I I I I I — Sample SampleLocation Location I I I I Quarry ,. 1 .1. .1 I I. ,2 4'KK)" / ~, , ,, .•I. \ ll> c-lC"t CD CD y ""y ~..., Andeslte C?) Andesite (f) Dikes Dikes Fine- Gralned Rhyolite Rhyollte Dike Fine-Grained Dike 8 ':• • ll> "" C. "0 Vertical Vertlcol banding bonding of plunge of plunge Very fine-grained rhyolite. coarsely porphyritic rhyolite H> ~ StrIke and Strike and dip dip of of banding bonding s side side [2] L Very fine—gralned rhyollte, rn coarsely porphyritic rhyollte 0 CD CD Quartz Quar t z- Plagloclase P 10 g I ocla se - AlkalI AI ka II Feldspar Feldspar Rhyollte Rhyolite ,'/ ' 1/oils B,O,F 8,O,F and Units and A A (J'q o.q fool· i-S. C"t Porphyritic Quartz-Alkali Porphyritic Quartz-Alkali FeldFeldspar Rhyollte with spar Rhyolite with interbedded Interbedded flne-gralned rhyollte flow fine-grained rhyolite flow (Jolt 6 Unit G D 0 0 I-. 0 ::r Contact, dashed where where InInContact. dashed (erred, ferred, dotted dolled where where burled burled -. ~' EXPLANATION t: I N N , \ t ..CLUPPER1S CLUPPER1"S HILL H, H> 'i 0 0 2 El '60 C/) El 2 I-a. fool· HC"t .... 0 ....I-I 1.0 0 . ::r ....:t —1 00 a, OJ '-' ~O 250 !SOO 500 7'0 750 10'00 000 2000 20'00 FEET FE ET • INGALLS KNOB 2.!50 250 xoo METERS !SOO METERS i �________________ and petrographic petrographic similarities. and similarities. The inlier inlier is is formed formed by by seven seven mineralogically mineralogically and and chemically chemically distinct distinct The volcanic flows, ash—flow tuffs, and breccias. volcanic flows, ash-flow tuffs, The The units units lettered lettered A A to to G from from southeast to to northwest northwest are are broadly broadly folded folded into into aa series series of of normal normal and and oversoutheast overturned anticlines anticlines and and synclines synclines with with an an average average wavelength wavelength of of 300 300 m. turned The m. The fold axes axes strike strike N. N. 200 N. 400 fold 20° to N. 40° E. E. and plunge plunge to to the the northeast. northeast. These These folded rhyolite rhyolite units units are are cut cut by by aa 100 100 m m thick thick andesite andesite dike dike (Table 1, analysis analysis folded (Table 1, 30) which was intruded along a northeast trending normal fault. 30) which was intruded a trending normal fault. The The fault fault is downthrown downthrown to to the the north, north, and and the the displacement, displacement, calculated calculated by by estimating estimating the is the amount of of structural structural shortening, shortening, probably probably does does not not exceed exceed 600 600 m. amount The m. The structures structures to the the north north of of the the fault fault have have aa one one to to one one correspondence correspondence to to those those to to the the to south, except except that south, that they are displaced to to the the southwest. southwest. While the the map shows map shows simpler structural structural patterns patterns to to the the north north of of the the fault fault then then to to the the south, south, this this simpler difference is probably due due to poor poor structural structural control control to difference is probably to the the north of the fault. fault. The youngest youngest rock in northeast trending fine—grained The in the the inlier inlier is is aa northeast fine-grained massive dacite dacite dike, dike, 35 35 m m thick, which cuts cuts the fault and dike massive thick, which the fault and the the andesite andesite dike (Table 1, 1, analyses 39 The dike dike is unit C in lithology (Table 39 and and 40). 40). The is similar to unit (fine—grained with with plagioclase plagioclase as as the dominant phenocryst), (fine-grained phenocryst), but but it it is is disdistinguished from unit unit C C on on chemical chemical grounds grounds (Fig. (Fig. 26). 26). 89 "ioo G—.-•\ \106\ 'I98 !1194 —II 10 10 i'92.—B I / ' 9 Rb! Rbi /Sr I Sr 97 'I — jP5 !e'P5 191 (i ', , 191 (....... Rhyolite Rhyolite dike dike , \ \ "Andesite" \ \ dOk ..... .... \ \ \dike I e ~ \ 190' \ \ ..... I9O \, \ , ~.J 189 189 0 0 l.a 1.8 Na20/K20 Figure Figure 26. 26. ° Rb/Sr—Na20/K Rb/Sr-Na 2 0/K 0 plot plot for for Marquette Marquette inlier inlier samples. samples. This This plot plot de~ de monstrates monstrates tat t5at mineralogically mineralogically similar similar rhyolites rhyolites can can be be distindistinguished guished on on the the basis basis of of Rb/Sr Rb/Sr and and Na20/K20 Na O/K ratios. Also Also note note the the ratios. cyclic cyclic change change in in Rb/Sr Rb/Sr ratio. ratio. Plagioclase_bearing Plagi~cla~e-bearingrhyolites rhyolites (unit (unit CC and and E) E) have have Rb/Sr Rb/Sr greater greater than than 1, 1, whereas whereas quartz—plagioclase_ quartz-plagioclasealkali alkali feldspar feldspar rhyolites rhyolites (units (units B, B, D, D, and and F) F) have have Rb/Sr Rb/Sr less less than than 1. 1. Unit Unit GG is is the the quartz—alkali quartz-alkali feldspar—plagioclase feldspar-plagioclase rhyolite rhyolite (from (from Smith, Smith, l978a). 1978a). ° 70 70 �unit GG is is aa thick thick (1000 (1000 m) m) quartz quartz (10 (10 %), %), alkali alkali feldspar feldspar (commonly (commonly perth— perthUnit Except for minor porphyry. rhyolite thitic) (16 %) and plagioclase (7 %) rhyolite porphyry. Except for minor plagioclase (7 %) and thitic) (16 %) variations variations in in phenocryst phenocryst abundance abundance and and faint faint banding, banding, the the unit unit is is texturally texturally Shard—like forms were observed in the matrix of unit G, homogeneous. Shard-like forms were observed in the matrix of unit G, indicating indicating homogeneous. it is is an an ash—flow ash-flow tuff. tuff. AA fine—grained fine-grained rhyolite rhyolite is is interbedded interbedded with with that it unit unit G, G, and and crops crops out out near near the the south south end end of of the the unit unit GGexposure. exposure. The The 66 units units lying lying to to the the southeast southeast of of unit unit GG are are texturally texturally variable, variable, with with banded, banded, fine—grained fine-grained and and porphyritic porphyritic varieties varieties common. common. Most of of the the units units show show evidence ~vidence of of brecciation brecciation and and micro—brecciation. micro-brecciation. Coarse Coarse breccia breccia is is found found on on the the southeast southeast margin of Ingall's Ingall's Knob where clasts of of porphyritic porphyritic and and fine—grained fine-grained red to to black black rhyolite rhyolite exceed exceed 10 10 mm in in size. size. Unit D D on on Cluppert's Hill is is also also Eutaxitic texture is well displayed in several of extensively brecciated. brecciated. texture is displayed in several of the the extensively units. units. Each unit unit in in the the Marquette inlier inlier has distinguishing chemical chemical and and mineralogical characteristics which are used to correlate units between are used to correlate units between (Fig. 46, 46, Table Table 1, 1, analyses analyses 4—14). 4-14). Units Units A, A, B, B, D, D, and and FF are are porphy— porphyexposures (Fig. ritic ritic plagioclase (18 (18 to to 27%), 27%), quartz (2 (2 to to 8%), 8%), and and alkali alkali feldspar feldspar (1 (1 %) %) 20 to to 36 36 % % total total phenocrysts. phenocrysts. Unit B is is distinguished from from rhyolites with 20 the other quartz bearing rhyolites by Na Na20/K20 0/K 0 greater than 1.0 and and low low Rb/Sr 2 2 0.92). Unit D D and Unit F P are similar in in both major and and minor element (0.64 —- 0.92). however, contains in its upper part aa 100 m D, however, m thick thick massive chemistry. Unit D, phase; similar massive masive rock phase; aa similar rock is is not not associated associated with with unit unit F. F. To date, date, no Units C and E are I ine--grained been made made on on unit unit A. A. Units C and E are fine-grained chemical studies have been (10 to 15 15 %% phenocrysts) with plagioclase plagioclase as as the the dominant dominant phenocryst. phenocryst. Unit E (10 is C by lower lower CaO. CaO. is distinguished distinguished from unit C Noteworthy is the cyclic change from phenocryst—poor phenocryst-poor plagioclase rhyolite (units E) to phenocryst—rich (units C and E) phenocryst-rich three—mineral three-mineral rhyolite (units (units B, B, D, and F). F). This cyclic variation in mineralogy is is also reflected in in trace trace D, and element chemistry (Table (Table 1, 1, analyses 4—14); 4-14); for example, example, Rb/Sr ratios ratios vary vary from 1.45 1.45 to to 1.23 1.23 for for units units EE and and C and and from from 0.71 0.71 to 1.0 for from for units units F, F, D, D, and B (Fig. (Fig. 26). 26). Chemical and flow direction data (Smith, (Smith, 1978a) 1978a) show that that all all of of the the Marquette units are comagmatic and that all flows flows erupted from from aa source source to to This evidence evidence suggests the outcrops. This suggests that that cyclic the northwest of the present outcrops. variation in chemistry, mineralogy, mineralogy, and texture reflect reflect eruption from a variation in chemistry, and texture a differentiating source. source. Fine—grained Fine-grained units probably represent eruption eruption from from On the the other other hand, hand, more more highly porphyritic fractionated crystal-poor magma. On fractionated crystal—poor varieties may may represent represent eruption from from zones zones of of crystal crystal accumulation within varieties The lower lower Rb/Sr Rb/Sr ratios ratios in phenocryst phenocryst and the source chamber. chamber. The and feldspar rich units (F, and B) B) may may be be explained explained by aa model model where where Sr is units (F, D and is concentrated into As a the crystallizing feldspar and the and Rb Rb is is enriched enriched in in the the liquid liquid phase. phase. As a consequence phenocryst phenocryst and rich units would have have lower Rb/Sr than the consequence and feldspar feldspar rich units would the fine—grained, feldspar-poor feldspar—poor varieties varieties (units (units C C and and E) E) which which formed formed from from fine-grained, fractionated, crystal- and and feldspar—poor feldspar-poor magma. magma. fractionated, crystal— Alternately, fine—grained Alternately, fine-grained and and phenocryst—rich phenocryst-rich pairs pairs may represent compositionally zoned zoned ash-flow ash—flow sheets sheets with with the the phenocryst-rich phenocryst—rich unit unit at at the compositionally the Zoned ash-flow ash-flow tuffs tuffs commonly commonly top at the the base. base. Zoned top and and the the fine-grained unit at show an an upward upward increase increase in in MgO, MgO, CaO, CaO, A1 Al203, TiO2 and and Sr/Rb Sr/Rb and and may may vary vary in 0 , Ti0 show 2 3 2 71 71 �from quartz quartz latite latite at at the top to rhyolite rhyolite at composition from the top at the the base (for (for example see Smith, Smith, 1960; 1960; Ratte Ratte and and Steven, Steven, 1964; 1964; Smith Smith and and Bailey, Bailey, 1966; 1966; Noble Noble and and see Hedge, 1969; 1969; and Phenocryst abundance, abundance, and and xenolith xenolith abundance abundance Hedge, and Rhodes, Rhodes, 1976). 1976). Phenocryst and size size usually usually increase increase upward, upward, with with pumice pumice commonly commonly showing showing reverse reverse zonation zonation and (Sparks, 1976). ash—flow sheet sheet the (Sparks, 1976). Within one one ash-flow the transition from phenocryst—poor phenocryst-poor to phenocryst-rich phenocryst—rich tuff tuff can can be be abrupt abrupt (Noble, 1970). Marquette Marquette units units FF and and EE to (Noble, 1970). may together represent a single compositionally zoned ash—flow sheet with unit may together represent a single compositionally zoned ash-flow sheet with unit B the differentiated fine—grained base and unit F the less differentiated pheno— E the differentiated fine-grained base and unit the less phenocryst-rich top. Grouping of of units units D D and and C C is is doubtful doubtful since since they they are are separated separated cryst-rich top. Grouping . by a a fault fault and by an an andesite andesite dike. dike. More More detailed detailed field field and and chemical chemical data must be obtained before this be this model model can can be be properly properly evaluated. evaluated. The Marquette Rhyolite Traverse: The Stop 4A — Unit CC Stop - Unit Walk due then turn to to then turn north from the the locked locked gate on the woods (east) the woods (east) to the the first first the the north side side of County Highway H, H, exposure (see exposure (see Fig. Fig. 24 24 for for the the route). route). This exposure exposure is formed by by a plagioclase—bearing rhyolite rhyolite ash—flow This is formed a plagioclase-bearing ash-flow tuff tuff (unit C). It contains contains small small (up to 55 mm mm in in size) size) anhedral anhedral to to subhedral subhedral plagioplagio— C). It (up to clase laths set in a fine—grained matrix matrix that brown. clase laths set a black fine-grained that is is streaked reddish brown. Unit C is well banded, banded, and and may may also also display spherulitic and Unit is commonly well and brecciated texture. texture. At this this locality, locality, bands stand out prominently due to to differential erosion. The bands form the erosion. the reddish—brown reddish-brown streaks, streaks, and and under under careful scrutiny scrutiny they are observed observed to be be composed composed of discontinuous lenses lenses of collapsed pumice they are o£ discontinuous and shard fragments. fragments. The banding trends trends N. N. 60 E. E. and dips 85° south south or or is is vertical. Since this exposure is on the flank of of a northeast plunging vertical. Since this exposure is on the south flank a northeast syncline, syncline, aadip dip to to the the north north is is expected. expected. This is probably due This deviation is due to flow folding folding in the ash—flow tuff supplemental stop at flow the ash-flow tuff (see (see the the supplemental at the Marcellon rhyolite for for further further discussion discussion of of flow flow folding). folding). Stop 4B 4B —- Unit Unit B B This stop is is just to to the the west of an old stone fence (Fig. (Fig. 24) 24) constructed about 1900 as about as part of of the the old old Driblow Driblow farm. farm. Unit B is is a a porphyritic quartz, quartz, plagioclase, plagioclase, alkali feldspar—bearing feldspar-bearing rhyo— rhyolite with aa reddish—brown reddish-brown to to black black matrix. matrix. Quartz is is rounded and and clear and and may may be be up up to to 33 mm mm in in size. size. Plagioclase is is pink to to white in in color and and occurs in in laths up up to to 66 mm mm in in size; size; some some grains grains show show prominent prominent albite albite twinning. twinning. Alkali Alkali is is difficult difficult to to identify identify in in hand hand specimen. specimen. On weathered surfaces surfaces faint faint banding banding and and minor minor brecciation brecciation are are observed. observed. This quartz—bearing quartz-bearing rock is is distinguished from other quartz—bearing quartz-bearing rhyolites in in the the Marquette inlier inlier by its its higher ratio. higher Na20/K20 Na 0/K ratio. Unit B is is the the only sodic rhyolite in in the the inlier inlier 2 (Fig. (Fig. 26). 26). Unit ufiit B changes in in lithology lithology laterally. laterally. On Ingalls Ingalls Knob Knob (south (south of of Highway Highway H) H) quartz quartz is is small small and and rarely rarely observed observed in in outcrop outcrop whereas quartz quartz is is large and and easily identified identified in in unit unit BB exposures exposures to to the the north north of of HighwayH. HighwayH. ° The The contact contact between between unit unit BB and and unit unit C C trends trends No. No. 10° 10° W. and and passes passes to to the the south south and and east east of of this this stop. stop. Many Many of of the the large large blocks blocks observed observed just just to to the the south of our present position are breccias with an assortment of fragment fragment types. types. It It is is doubtful, doubtful, however, however, whether whether these these blocks blocks are are in in place. place. 72 72 �Stop 4C 4C —- Small Small Andesite Dike Intruding Intruding Unit C C Rhyolite Stop Traverse due north north from from Stop Stop 4B to to the the low low outcrops outcrops across across the the field field in in the trees (just (just to to the the north north of of ihe the Bee Bee Hives) Hives) (Fig. (Fig. 24). 24). At this this stop stop aa fine—grained unit C is fine-grained variety of unit is cut by a a thin andesite dike (an (an off—shoot off-shoot trending dike). dike). The andesite andesite and and rhyolite rhyolite are are at at first first of the main northeast trending difficult The following difficult to to distinguish distinguish from from one one another another in in the the field. field. following characteristics will aid aid in in their their identification. identification. Unit C C rhyolite rhyolite breaks breaks irregularly irregularly with with aa splintery splintery surface. surface. Sparse small plagioclase laths laths are are the the dominant phenocryst. ,dominant phenocryst. Jointing produces straight breaks and angular angular corners rock. The andesite contains small plagioclase laths (1/2 (1/2 mm) mm) set in in a a in the rock. fine—grained fine-grained matrix with with aa characteristic characteristic greenish greenish hue. hue. Jointing Jointing produces produces irregular breaks and and rounded corners corners in in the the dike dike rock. rock. A A fresh fresh surface surface of of the rhyolite reflects when reflects light light from from numerous numerous planes, planes, and and thus thus "twinkles't "twinkles" when rotated in in direct direct sunlight. sunlight. Partially Partially separated separated splinters splinters of of rock rock are are lighter lighter in color than unbroken rock rock and and form form grooves grooves on on the the broken broken surface. surface. In concontrast, trast, the andesite has aa smooth smooth and and dull dull freshly freshly exposed exposed surface. surface. In several several places, places, aa very fine fine banding is observed in the is observed the andesite and (N. 450 45° E.) obliquely to to the the strike strike of of the the dike. dike. These bands may may be be trends (N. flow bands sheared into into this this orientation orientation after after dike dike emplacement. emplacement. Alternately they may reflect aa rock rock cleavage cleavage formed formed during during the the folding folding of of these these rocks. rocks. Stop 4D (Optional) (Optional) — - The Contact Between the the Andesite Dike and and Unit Unit C C Rhyol ite Rhyolite Since the exposure is small, it will not not be be visited on the the size of this this exposure is small, it will It is is of of considerable considerable interest, interest, however, however, because because it it displays displays one one field trip. trip. It of the few exposed contacts contaots in in the the inlier. inlier. east across From Stop 2C walk to the east across the the field field to the the gap in the north— northThe exposure exposure (piled trending fence fence (Fig. (Fig. 24). 24). The (piled with rock) rock) encountered on the way is composed of of unit unit C C rhyolite rhyolite cut cut by by numerous numerous quartz quartz veins. veins. After passpassing through through the ing the gap in the fence proceed through through the the forest forest (bearing (bearing N. N. 10 10 E.) E.) The contact contact between rhyolite rhyolite and to the the first first rock rock ledge. ledge. The and andesite is is exposed on top of has toppled exposof this this ledge where a a juniper tree tree with shallow roots roots has ing aa fresh fresh rock roák surface surface (the tree was was uprooted uprooted during during aa major major ice ice storm storm in in ing (the tree April, 1976). 1976). The intrusive contact trends trends N. N. 87° 87° E. E. and and dips dips 60° 60° to to the the north. north. This dip dip probably reflects reflects the northeast—trending normal This the inclination of of a a northeast-trending normal fault fault (later (later intruded intruded by the the dike) dike) (Fig. (Fig. 25). 25). The difference between rock rock types types is subtle (see (see discussion discussion under under Stop Stop 4C). 4C). The contact is is sharp; sharp; no no are found dike and and no contact contact effects effects are xenoliths of of rhyolite rhyolite are found within the the dike in the the rhyolite. rhyolite. This dike is is fine—grained fine-grained and and shows shows little little change observed in In thin thin section, section, the in grain size from ôontact in contact to to center. center. In the texture of the the dike rock is intergranular to ophitic of sausseritized plagio— dike ophitic with aa framework framework of plagioclase laths clots set in aa patchy matrix of epidote—clino— clase laths and clots of iron oxide oxide and and epidote-clinozoisite. Both andesite and and rhyolite rhyolite are are jointed jointed with with N. N. 60° 60° E. E. and and N. N. 40° 40° W. W. as as important directions. displays the contact contact between the dike and Another exposure that displays the andesite dike unit C rhyolite can be reached by walking through the the trees trees from Stop 4C (bearing N. N. 10° 10° W.) W.) to to an an exposure piled with rock (Fig. (bearing (Fig. 24). 24). The contact here trends N. N. 80 E. and and dips dips 65° 65° to to the the north. north. Piled on top of the the exposure exposure 73 ..., �are rocks rocks moved moved to to this this location location from from the the cleared cleared field field to to the the north. north. Most Most of of the are the blocks are massive unit D rhyolite. This rock is similar in outward appearance blocks unit D rhyolite. This to unit unit C, C, but but it it can can be be distinguished distinguished quickly in the field from the other fine— to the field finegrained units grained units by the bell-like sound sound emitted emitted when when hit hit by by aa hammer. hammer. Also the rock breaks with aa distinctive "breaking "breaking glass" glass" sound. sound. Stop 4E — Massive Unit Unit D, D, and Unit E - Massive See Figure 24 for directions from See from Stop Stop 4D 4D to to this this locality. locality. at point 4E* 4E* (see Fig. 24) For orientation stand at (see Fig. 24) and and look to the northwest; northwest; the contact contact between between unit unit D D and and unit unit EE trends trends N. N. 30° 300 E. E. through through the the grassgrass— the Unit E lies on the covered depression before you. you. Unit the rock rock ledge ledge to to the the northwest. northwest. Massive unit rhyolite is fine grained near near its Massive unit D rhyolite is very fine its contact with unit E, E, but becomes noticeably coarser in in grain size to to the the south. south. Plagioclase altered to sausserite sausserite occurs occurs in glomeroporphyritic glomeroporphyritic clots and altered and is the the dominant dominant Phenocrysts are set in a devitrified matrix that phenocryst. Phenocrysts are set a devitrified that contains coarser— coarsergrained pod—shaped pod-shaped areas areas (pumice (pumice fragments?). fragments?). Broken spherulites are also Unit D locally displays displays fine fine striations that observed in in the the matrix. matrix. Unit that are similar to those in in the the andesite andesite dike dike (see (see description description of of Stop Stop 4D). 4D). These 0 striations strike (N. 30°E.) contact between units D striations (N. 30 E.) parallel parallel to the the contact D and E but dip obliquely to it striations as dip it (80° (80° south for for the the striations as compared to 60° 60° north for the the contact). Unit D at at this Unit this location is is similar in lithology to the the fine—grained fine-grained variety of of unit unit C observed at Stop 4C; 4C; it however, splinters like glass glass.when at Stop it however, .. when This fine-grained broken and commonly rings rings like like aa bell bell when when hit hit by by aa hammer. hammer. has chemical chemical characteristics characteristics that rock has that distinguish it it from other fine—grained fine-grained Marquette rhyolites (Fig. (Fig. 26). 26). Walk across across the the grass covered depression to to the the low low rock rock ledge ledge of of banded banded unit E rhyolite. rhyolite. The contact between unit unit D D and unit unit E trends trends northeast northeast through this this depression. depression. Banding in in unit unit E is is formed formed by discontinuous white to pink streaks pumice fragments fragments and streaks that that represent represent pumice and shards sheared and compressed during late—stage late-stage primary flowage and and during post—depositional post-depositional compaction compaction and welding. Bands may be up to to 50 cm long, long, but are are usually usually less less than than 55 mm mm in in width. Commonly they they bend bend about about phenocrysts. phenocrysts. Bands strike N. N. 53°E. 53°E. and and dip 47° to to the the west. west. On the southwest corner of of the near the On the southwest the outcrop near the base of the the unit, unit, unit E grades into into aa spherulitic spherulitic rhyolite. rhyolite. Spheruites Spherulites are are as as large large as as 33 cm cm in in diameter. diameter. To the the west, west, the the outcrops are are covered by aa drumlin elongated in in an an east— eastwest direction. direction. This orientation reflects the the movement of the the Green Bay Bay Lobe Lobe (Woodfordian) (Woodfordian) from east east to to west west in in this this area. area. Stop 4F 4F (Optional) (Optional) —- Porphyritic Porphyritic Unit DD From From Stop 4E walk north north to to the the east—trending east-trending fence, fence, then then follow follow the the fence fence eastward (300 (300 m) m) to to the the north—south north-south fence fence (Fig. (Fig. 24). 24). Outcrops encountered to to the east—trending fence fence are are of of unit the north north of the the east-trending unit E rhyolite, rhyolite, blocks in the field field 74 74 �to to the the south south are are fine—grained fine-grained unit unit DD rhyolite. rhyolite. Continue Continue walking walking Note the angular blocks fence to to the the first first exposure. exposure. Note the angular blocks of of rock rock to to fence of the the fence. fence. Here aa wide wide assortment assortment of of rhyolite rhyolite lithologies lithologies is is of blocks blocks were were probably probably transported transported by by ice ice aa short short distance. distance. along along the the the the north north found. found. These These Unit Unit DD is is gray gray on on weathered weathered surfaces surfaces but but pink pink on on freshly freshly broken broken fractures. fractures. In In hand specimen abundant abundant phenocrysts of rounded quartz up up to to 3 3 mm in in size size and and subhedral feldspar (plagioclase and alkali feldspar) up to 5 mm in length (plagioclase feldspar) up to in length are are -easily identified. identified. In In thin section the rock contains large large rounded rounded and and embayembayeasi1y ed quartz (10%), (10%), subhedral grains of sausseritized plagioclase (8%), (8%), and and ortho— orthoperthitic texture texture (14%). (14%). Banding in in unit D D at at this this locality locality is is clase with perthitic faint; faint; band trends trends vary vary from from N. N. 7° 7° E., E., 70° 70° east east to to N. N. 500 50° E, E, 85° 85° southeast southeast (deviation due to to flow flow folding?). folding?). (deviation Unit D D is is easily distinquished from unit B, B, particularly by differences in Na20/K20 ratio (the greater than 11 for for unit (the ratio is is greater unit B and and less less than 1 for unit D). D). Also, Also, unit D D contains a 100 m m thick thick massive phase (stop (stop 4E); 4E); aa unit similar similar massive phase phase is is not not associated associated with with unit unit BB (or (or in in fact fact with with unit unit F, F, the other quartz, plagioclase, alkali alkali feldspar—bearing feldspar-bearing rhyolite rhyolite unit). unit). the quartz, plagioclase, 75 75 �SUPPLEMENTAL STOP STOP -- MARQUETTE MARQUETTE RHYOLITE RHYOLITE ON ON INGALL'S KNOB SUPPLEMENTAL INGALL'S KNOB Highlights of of this this stop stop include include the the well-banded well—banded unit unit C, C, and and pumice pumice Highlights lenses and and breccia in lenses in unit unit A. A. Unit C — Banding: Park Park at at the the entrance entrance to to the the Ingall's Knob gravel gravel pit pit (see Unit - Banding: Ingall's Knob (see Fig. 24). Walk along along the the dirt dirt road road toward toward the the gravel gravel pit pit and and then then bear bear right right Fig. 24). Walk (south) to to the the outcrops outcrops of of dark rhyolite clearly visible (south) visible on on the the flanks flanks of of Ingall's Knob. These These outcrops outcrops are are composed composed of of well well banded banded unit unit C C rhyolite rhyolite Ingall's (Fig. 27) • (Fig. Figure Figure 27. 27. Photomicrograph of highly highly flattened flattened and and crenulated crenulated shards shards in in the. the. Marquette rhyolite rhyolite (unit (unit C). C). Flattening probably occurred during during primary movement of the Folding may have occurred during the ash ash flow. flow. during flowage or during during later later deformation. deformation. Bar scale scale is is 11 mm mm long. long. The bands are discontinuous and are formed by sheared and collapsed pumice fragments. Banding strikes strikes N. N. 50°E. 50 0 E. and dips 700 70° to to 800 80° to the the south; south; bands are locally folded. The rock in this locality also contains lenses of breccia locally folded. in this and spherulitic spherulitic rhyolite. rhyolite. Unit AA —- Fiamme Fiamme (Pumice Lenses): Lenses): Walk Walk to to the the end end of of Ingall's Ingall's Knob Knob (see (see Fig. Fig. 24) 24) and and climb directly directly up up the the rock rock face. face. The The rock rock forming forming the the bluff bluff on on the the southeast end of Ingall's Knob is a porphyritic quartz, orthoclase, plagio— Ingall's is quartz, orthoclase, plagioclase—bearing ash—flow tuff tuff showing showing nicely nicely developed developed fiamme fiamme (the black clase-bearing rhyolite rhyolite ash-flow (the black lens—like features in the rock). The fiamme are collapsed pumice fragments lens-like features in the rock). The fiamme are collapsed pumice fragments and and are are elongated elongated parallel parallel to to the the strike strike of of unit unit AA (N. (N. 50°E.). 50 0 E.). They They have have an an average average axial axial ratio ratio of of 12 12 ++ 8/1 8/1 (based (based on on the the measurement measurement of of 50 50 fiamme). fiamme). In thin section, section, unit A A rhyolite rhyolite contains contains rounded rounded and and embayed embayed quartz quartz (10%), alkali feldspar with perthitic (10%), feldspar perthitic texture texture (8%), (8%), partially partially sausseritized sausseritized 76 76 �plagioclase and iron plagioclase (5%), (5%)"and iron oxide oxide (tr). (tr). The The matrix matrix is is finely finely devitrified devitrified but but contains bands bands that that are are more more coarsely coarsely recrystallized. recrystallized. Flow Flow texture texture is is common common contains with with shard—like shard-like forms forms aligned aligned and and locally locally bent bent about about phenocrysts phenocrysts of of quartz quartz Ic xenolith xenolith was was identified in and feldspar feldspar (Fig. (Fig. 28). 28). One One small small maf mafic in thin thin and sections. sections. Figure 28. 28. Figure flattened shards shards in the Marquette rhyolite Photomicrograph of flattened rhyolite ash-flow tuff tuff (unit (unit A). A). Shards are are aligned and locally ash—flow locally bent bent about about quartz and and feldspar. feldspar. Bar scale is phenocrysts of quartz is 11 mm mm long. long. The change in slope above the rock face face marks the contact Unit A A —- Breccia: The between the top of unit unit A ash—flow ash-flow tuff tuff (below) (below) and and the base of unit A A breccia o contact varies in orientation between N. 40°E. and N. 30°W., (above). This in orientation between N. 40 E. and N. 30 o W., (above). o The wavy nature of this trends N. N. 50°E. 50 E. The this contact suggests that that but in general trends it is an unconformity. it is It is Unit is poorly sorted and and is is approximately approximately 50 50 mm thick. thick. It is Unit A breccia is o 50°E. banded with large clasts and crudely banded and matrix matrix fragments fragments elongated elongated in in aa N. N. 50 E. Along the the route of this direction (parallel to the the strike of of unit unit A). A). Along this traverse, traverse, direction (parallel concentrated toward toward the aa crude is observed with large fragments concentrated the crude size size sorting sorting is This size size sorting, sorting, however, however, is is not not characteristic characteristic of of upper part of the the unit. unit. This In other locations, large of rhyolite are the unit as a whole. In other locations, large fragments rhyolite are the unit On our our route, route, breccia breccia near near the the base base of of the the unit unit found the unit. unit. On found throughout the contains (less than contains small small (less than 30 30 cm cm in in size) size) dark-colored dark—colored porphyritic porphyritic rhyolite rhyolite Toward fragments. are quartz—bearing quartz-bearing rhyolites. rhyolites. Toward Only aa few few of of the the fragments fragments are fragments. Only the top top of of the the unit unit the the fragments fragments become become huge; huge; one one block block is is 33 33 m m long long in in aa the o Most of of the the larger larger fragments fragments are E. direction and is is 12 m m wide. Most are similar N. N. 50 50°E. However, three in lithology to the quartz-bearing unit A ash-flow tuff. However, three other in lithology to the quartz—bearing unit ash—flow tuff. rock types types are are present;l)banded present;.l)banded rhyolite rhyolite with with small small white white feldspar, feldspar, 2) 2) banded banded rock rhyolite with with large large (5mm) (5mm) white white feldspar, feldspar, and and 3) 3) massive massive rhyolite rhyolite with with small small rhyolite The matrix matrix of of the the breccia breccia is is gray gray in in quartz phenocrysts. The quartz and and alkali alkali feldspar feldspar phenocrysts. 77 77 ------------------------------------------..., �color on on weathered weathered color with crystal, rock with crystal, rock surfaces. In thin thin section section the the matrix matrix is is microbrecciated microbreccjated surfaces. In o and angular angular shard shard fragments fragments aligned aligned in in the the N. and E. direction. N. 50 50°E. direction. Breccia Exposure Exposure at at the the Summit Summit of of Ingall's Knob: Details Breccia Ingall's Knob: Details of of the the relationship relationship between fragments and matrix are revealed in an exposure between fragments and matrix are revealed in an exposure at at the the summit summit of of Ingall's Knob Knob (Fig. The largest largest fragment fragment at at this this location location is is aa porphyporphy— Ingall's (Fig. 29). 29). The ritic (black (black in in color) color) rhyolite rhyolite composed composed of of quartz quartz and and alkali alkali feldspar feldspar phenoritic pheno— o crysts. It is 5 in wide and over over 10 10 m m long long in in the the N. N. 50 50°E. direction. Contacts crysts. It is 5 m wide and E. direction. Contacts between it it and and the the breccia matrix (gray between (gray in in color) are are sharp. sharp. Note Note the the smaller fragments of of black black rhyolite rhyolite in in the the matrix matrix on on both both sides sides of of the the larger fragments larger blackblack— colored rhyolite rhyolite fragment. colored fragment. These These fragments fragments probably probably are are pieces pieces of of rhyolite rhyolite that broke broke off off the the larger larger fragment fragment during during transport. that transport. Just Just to to the the north north there is a large red fragment impregnated is a large red fragment impregnated with quartz veins. veins. The fragThe size size of of this this fragment is is difficult difficult to estimate because of extensive cover. ment cover. Notice Notice the the smaller smaller red—colored fragments fragments in in the the matrix matrix just just to to the the south south of of the the red red-colored red clast. clast. The The red fragment fragment is is aa porphyritic porphyritic rhyolite rhyolite similar similar in in mineralogy mineralogy to red to the the black black fragments. Both Both fragment fragment types are similar similar in mineralogy to to the unit A ashfragments. types are the unit ash— flow tuff. flow tuff. Origin of Origin of the the Breccia: Breccia: In this breccia in in the the In order order to to explain explain the origin of this following observations observations must be accounted for: following for: 1. The matrix matrix of of the the breccia breccia may may show a crude layering that 1. The a crude that resembles resembles a flowage a flowage texture. texture. Smaller and shards aligned in the the Smaller fragments, fragments, crystals crystals and shards are are aligned N. 50°E. N. 50 o E. direction. direction. Many of of the the larger clasts have unequal dimensions in in section and have have section and their long axes oriented in in the the N. N. 50°E. 50 o E. direction. direction. 2. 2. There are are aa wide variety variety of of clast clast types. types. Many of the the larger larger fragfragments are are similar in in lithology to to the unit A A ash—flow ash-flow tuff. tuff. 3. 3. 4. 4. There is is only a a slight suggestion of size sorting in in the the deposit. deposit. 5. 5. Many of of the the fragments fragments are are very very large large (up (up to to 33 33 mm long). long). The unit unit is is similar similar in in overall overall fabric fabric to to mud—flow mud-flow breccias or or lahars lahars commonly tuffs and lavas in commonly interbedded interbedded with with ash—fLow ash-flow tuffs in Tertiary Tertiary and and Holocene Holocene volcanic volcanic piles, piles, in in terms terms of of poor poor sorting sorting and and fragment fragment size size (Parsons, (Parsons, 1968; 1968; Smith, Smith, 197Gb). 1976b). However, However, mud—flow mud-flow breccias breccias usually usually do do not not contain contain elongated elongated or or oriented oriented fragments, fragments, and and the the matrix does not show show flow flow structure. structure. The The unit unit may may instead instead represent represent aa pyroclastic—flow pyroclastic-flow breccia breccia (that (that is, is, aa block block avalavalanche anche or or block—flow block-flow deposit). deposit). Modern Modern examples examples of of this this type type of of deposit deposit are are described described by by Aramaki Aramaki (1963) (1963) and and Parsons Parsons (1968) (1968) from from Asama Asama Volcano Volcano in in Japan. Japan. Modern Modern block—flow block-flow deposits deposits may may erupt erupt initially initially as as ash ash flows flows and and then then during during emplacement emplacement may may pick pick up up large large fragments fragments from from the the surface surface over over which which they they travel. travel. Also, Also, fragments fragments from from the the walls walls of of the the vent vent and and cognate cognate pumice pumice are are often often incorporated. incorporated. The The matrix matrix of of the the Holocene Holocene block—flow block-flow deposits deposits around around Asama Asama Volcano Volcano may may be be crudely crudely banded banded and and is is commonly commonly composed composed of of fine fine ash ash and and dust. dust. These These breccia breccia units units extend extend as as far far as as 18 18 km km from from Asama Asama Volcano Volcano and and vary vary in in thickness thickness from from 40 40 cm cm to to 10 10 mm (Parsons, (Parsons, 1968). 1968). There There are are many many similarities similarities between between the the Holocene Holocene pyroclastic—flow pyroclastic-flow breccias breccias about about Asama Asama Volcano Volcano and and the the unit unit AA breccia; breccia; consequently, consequently, II suggest suggest that that the the 78 78 �Matrix Matrix NN 0 : o \/ I— Ii Cover Cover quartz veins veins quartz k~~v~:'~>:"? _ ~~ ~ \N? . /" '. . ~/ . .,; 0 — o() oO 00 o "" \ " - 0 0 - / "", ?... '" ......."" ",......... ---/ 00 —7-Matrix oo~ ~ 7 7- --~/ Matrix \ " I - / \ ' ./ ./,r-. -~/~. /. -=- /. ......... -::: . : \ - / .r -. ? • ~ ?:;:~/- \ ~ °/....-- / ...... • ?/ / C/. ct:1/.· . 7/ ' / 110 T Tree Tree feet _I 00 0 00 00 . ?"- - ? /1' / .. • _ . Tree ?"2? ree 7' .. Matrix Matrix Stump EXPLANATION fH Black r::I Red Red rhyolite rhyolite rhyolite Small of rrhyolite Sma II ffragments rag men t s of hy 0 lit e in matr ix in matrix o11 Figure Figure 29. 29. Matrix, microbreccia Matrix, microbreccia Sketch map map of of an an exposure exposure of of unit unit A breccia Sketch breccia on Ingall's Ingall's Knob. Knob. 79 79 �unit A A breccia breccia is is aa pyroclasticpyroclastic— or or block-flow block—flow breccia breccia and and not not aa mud-flow mud—flow unit deposit. deposit. Unit A-Unit A—Unit B Contact Unit The contact contact between between unit unit A A and and unit unit B B on on Ingall's Ingall's Knob Knob is is gradational. gradational. The The basal basal part part of of unit unit B B contains contains numerous numerous beds beds and and lenses lenses of of breccia breccia that that The grade into unit A Just to to the the northwest northwest of of the the outcrop outcrop of of unit unit A grade A breccia. Just detail above) good exposure exposure of brecciated unit breccia (described (described in detail above) is is a a good This lens of breccia is separated from from massive massive unit B by a B (Fig. (Fig. 24). 24). This lens of is separated a thin (2 m m wide) wide) sheared zone. Unit B breccia at (2 zone. Unit at this this exposure is is monomictic. monomictic. This is contrast to other other unit lenses, and This is in contrast unit B breccia lenses, and the the unit A breccias that are are polymictic. that 80 80 �N WATE RTOWN WATERTOWN t+ IUNCTION TO WATERLOO STOP 5 - POLISHED EXPOSURE NORTH QUARRY SOUTH QUARRY SOUTH QUARRY UW DRILLIN DRILLING SITE .5 MILES 0 CONTOUR INTERVAL CONTOUR INTERVAL 10 FEET 10 FEET EXPLANATION — ====ROAD ROAD • BUILDING BUILDING QUARRYWALL WALL JVQUARRY Figure Figure 30. 30. Detailed map of the Portland Portland Quarries. Quarries. Field trip Stop 55 is is in in the the north quarry. quarry. South quarry should should be be entered entered from from the the east. east. 82 82 �QUARTZ ITE NEAR NEAR PORTLAND PORTLAND STOP 5 -- WATERLOO QUARTZITE This stop illustrates quartzite, the This illustrates the the lithology of the the Waterloo quartzite, the youngest major Precambrian rock est rock unit unit in in south—central south-central Wisconsin. Wisconsin. These outcrops are at at the the extreme extreme southeastern southeastern edge edge of of the the exposed exposed Precambrian Precambrian shield shield in in are Wisconsin. gate on the 19, walk south Location: From the the locked gate the south side side of of S.T.H. S.T.H. 19, toward ~oward the the John John O'Laughlin O'Laughlin Quarries Quarries (this (this area areaisis-a -a Department Department of of Natural Natural Resources hunting hunting preserve). preserve). At the the road road junction junction take take the the left left fork. fork. The right of the Wisconsin's two deep drill drill right fork leads leads to the the site site of the University of Wisconsin's holes, about 900 feet of holes, of core core was was obtained obtained from from one one of of them. them. Drilling was terminated before intersecting the base of quartzite (see Haimson, guide terminated before the base of the the quartzite (see Haimson, Walk past the large corrugated iron building and then turn 1978). the large iron and then turn west (right) (right) 1978). and walk walk about about 70 m m through the and the trees trees to to the the quarry quarry (see (see Fig. Fig. 30 30 for for route). route). The Waterloo Quartzite is Introduction: The is probably stratigraphically equivalent to the the Baraboo Baraboo and and Barron Barron Quartzites Quartzites in in Wisconsin Wisconsin and and to to the the Sioux Sioux Quartzite Quartzite to In south—central in Minnesota Minnesota and South Dakota (Dott in (Dott and and Dalziel, Dalziel, 1972). 1972). In south-central Wisconsin the quartzite quartzite sheet lies lies stratigraphically above late—Penokean late-Penokean aged rhyolites rhyolites and and granites granites and and is is mainly mainly preserved preserved as as infolds infolds into the aged the igneigneThe absolute age ous basement. basement. The age of the quartzite can only be determined by indirect means. At Baraboo Baraboo the the quartzite overlies overlies rhyolites rhyolites that that are are similar similar in chemistry to those rocks in the Fox River Valley dated at 1765 m.y. in in the Fox River Valley dated at 1765 m.y. old. old. This date is This is the the maximum maximum age age of of the the quartzite. quartzite. Both the rhyolite and overlying quartzite quartzite were were deformed deformed during an event suggested by Smith (1978a) (1978a) to to Rb—Sr apparent age of the have occurred 1650 1650 m.y. ago. ago. This date is the Rb-Sr the Fox River Valley igneous igneous rocks rocks (Van (Van Schmus Schmus and and others, others, 1975). 1975). These data suggest suggest that Baraboo—Waterloo Quartzite was was deposited on an eroded rhyolite—granite that the the Baraboo-Waterloo rhyolite-granite basement between 1765 1765 and and 1650 1650 m.y. m.y. ago. ago. A pegmatite dike with with coarse coarse quartz, quartz, feldspar and muscovite crystals crystals that feldspar and muscovite that cuts the Waterloo Quartzite (on (on Rocky T. 9N., R. l3E.) has been dated at 1440 m.y. Island —- NW Sec. 27, 27, T. 9N., R. l3E.) has m.y. old by the Rb—Sr method (Aldrich Also, muscovite from a phyllite the Rb-Sr (Aldrich and and others, others, 1959). 1959). Also, bed in the Quartzite has has been dated dated at m.y. old by the K—Ar bed the Waterloo Quartzite at 1410 m.y. K-Ar technique (Goldich dates place a (Goldich and and others, others, 1966). 1966). These dates a minimum age on the the deposition of of the the quartzite. quartzite. , t, At Waterloo, Waterloo, the the dominant rock rock is a a red to to gray vitreous vitreous quartzite comcomposed of 75 to 98% Si02. Quartz is present as interlocking posed to 98% Si02' is interlocking and and strained strained sand—sized grains (Fig. sand-sized (Fig. 31). 31). Muscovite in in the the matrix of the the quartzite commoncommonly displays displays lepidoblastic lepidoblastic texture, with increasing amounts ly texture, and and with amounts of mica the Occasionally, thin phyllite layers rock may grade into aa foliated foliated quartzite. quartzite. Occasionally, are found found interbedded with the Bands of are the quartzite. quartzite. Bands of andalusite andalusite schist were identified in core core recovered recovered from from the the deep deep well well drilled drilled just to the identified in the east of the quarries quarries (Haiinson, (Haimson, 1978). The andalusite is is partially partially altered altered to to sericite. sericite. The assemblage andalusite—muscovite—quartz andalusite-muscovite-quartz suggests that that the the quartzite was locally, if not regionally, regionally, metamorphosed metamorphosed to the part of the locally, if not the upper upper part the greenschist facies. An amphibolite dike was also encountered in in the the well (Haimson, (Haimson, 1978). 1978). In the the Waterloo Waterloo area area the the quartzite quartzite forms forms aa broad broad east-plunging east—plunging syncline syncline In (Buell, 1892, 1892, Warner, Warner, 1904, 1904, Sumner, Sumner, 1956) 1956) which which is is almost almost entirely entirely buried buried (Buell, by Ordovician and and Cambrian sedimentary sedimentary rocks rocks (Fig. (Fig. 32). 32). Outcrops to to the the north of -h-, Sec. 25, T. 8N., 8N., R. R. l3E.) define the north of Lake LakeMills Mills(NE(NE 25, T. l3E.) define the south limb of the structure. structure. Here bedding dips dips to to the the north north at at 500. 50°. The apparent nose t, 83 �of the of the fold fold is in the Portland area area (the (the area area of of Stop Stop 5). 5). Here the strike o of bedding changes from N. 30°W. (in the the south) south) to N. N. 30°E. of bedding from N. 30 W. (in 30 o E. (in (in the the north) north) defining a a broad concave eastward arc; arc; the the nose nose of of the the syncline. syncline. Strike and dip dip measurements measurements are are a bit erratic erratic in this area suggesting that and a bit this area that the the structure in the nose of the syncline is complex. The north limb of of the syncline is complex. The of the the syn— syndine is cline is exposed exposed near near Mud Mud Lake Lake where where quartzite quartzite strikes strikes N. N. 80°E. 80 o E. and and dips dips The north north limb limb may may extend extend as as far far to the east as steeply to the the south. south. The the east as Hartford in Washington County (Sumner, ford (Sumner, 1956). 1956). Figure Figure 31. 31. Photomicrograph of of the the Waterloo Waterloo Quartzite Quartzite from from the Photomicrograph the Portland Quarry. Quarry. Interlocking and strained quartz grains grains are are interrupted interrupted by aligned laths of laths of muscovite. muscovite. With increasing increasing amounts of muscovite the the rock rock grades into into aa foliated foliated quartzite quartzite and and finally finally aa phyllite or schist. grades Bar scale scale is is 11 mm mm long. long. The quartzite at at Waterloo is well jointed jointed with N. N. 40°E. 40 o E. and N. N. 80°E. 80 o E. o directions common (also (also N. N. 70°W. 70 W. as as aa minor minor direction). direction). However no no detailed studies of of the rock fabric in studies in the the Waterloo Waterloo area area have have been been undertaken. undertaken. Thick Thick layers of of phyllite, layers phyllite, so common in in the the upper upper part part of of the the Baraboo Baraboo Quartzite, Quartzite, are lacking in the Waterloo Quartzite. Phyllite beds at Waterloo are thin are thin (rarely thicker thicker than than 25 25 cm) cm) and and commonly commonly pinch pinch out out over over aa lateral lateral distance distance (rarely of 10 to to 20 20 m. m. Primary structures such as bedding planes, planes, cross bedding and and conglomerate beds are common, common, and ripple marks are occasionally observed. observed. The unravelling of the structural history of the Waterloo Quartzite is is crucial to the understanding understanding of of the the 1650 1650 m.y. m.y. old old event. event. The Waterloo Waterloo Quartzite Quartzite is is overlain overlain by by Cambrian Cambrian sandstones sandstones that that locally locally contain large large rounded rounded boulders boulders of of quartzite. quartzite. About 3 km north north of of Stop Stop 55 (Fig. (Fig. 32), 32), blocks of quartzite 1 meter in size are embedded in Cambrian sandstone sandstone close to the quartzite exposures; exposures; the size of the the clasts decreases rapidly until just 700 m m from the the sandstone—quartzite sandstone-quartzite contact the the Cambrian sandstone is fine grained and friable and is fine and contains contains no no quartzite quartzite fragments fragments (Buell, (Buell, 1892). 1892). 84 84 �PORTLA D SHIELDS 19} - . . - - - - - - l 1 WATERTOWN o 2 MILES WATERLOO N MILFORD t EXPLANATION E X P L A N AT I ON o0 QUARTZITE QUARTZITE EXPOSURE EXPOSURE DIP OF OF BEDDING AND DIP BEDDING STRIKE STRIKE AND -®—i--— f -.-...;:)~ H.R. H.R. ROAD ROAD RAILROAD TRACK RAILROAD TRACK FIELD ROUTE TRIP ROUTE FIELD TRIP HUBBLE TON HUBBLETON ROAD ROAD Stop 55 Figure Detailed route route map map through through the the Waterloo Waterloo Quartzite Quartzite area. area. Stop Figure 32. 32. Detailed Map adapted adapted from from Buell Buell (1892). (1892). is is at at the the Portland Portland Quarries. Quarries. Map 85 85 �If the the Paleozoic Paleozoic sedimentary sedimentary rocks rocks and and the the Pleistocene Pleistocene sediments If sediments were were stripped from the Waterloo area, the quartzite would stripped from the Waterloo area, the quartzite would stand stand as as an an arcuate arcuate ridge (concave (concave to to the the east) east) 500 500 to to 900 900 feet feet above above the ridge the surrounding surrounding Precambrian Precambrian surface. For example, to the north of the city of Waterloo, Waterloo, quartzite surface. For example, to the north of the quartzite is is intersected in in deep deep wells wells at at 135 135 feet feet above above sea intersected sea level. level. Just Just 22 miles miles to to the the east, quartzite quartzite is is exposed exposed at at the the Portland Portland quarries quarries at east, at an an elevation elevation of of 860 860 feet (see (see Smith, Smith, 1978c). l978c). feet Only one one deep deep well well has has penetrated penetrated quartzite. quartzite. This Only This well well located located near near Reesville in western Dodge County penetrated 500 feet feet of of quartzite Reesville in western Dodge County penetrated 500 quartzite before before entering aa mica-rich mica—rich rock described by Thwaites (1940) entering (1940) as as aa gneiss gneiss or or aa schistose quartzite. schistose quartzite. Studies of of well well cuttings cuttings show show that that the the Waterloo Waterloo Quartzite Quartzite is Studies is part part of of aa large area of quartzite extending from Waterloo to Milwaukee large area of quartzite extending from Waterloo to Milwaukee and and north north to to Fond du du Lac Lac (Smith, Fond (Smith, l978c). 1978c). Thwaites Thwaites (1940) (1940) reported reported iron-bearing iron—bearing shale shale interbedded with this large quartzite sheet. interbedded with this sheet. Stop Description: Description: After Stop its steep south wall. After entering entering the the quarry, quarry, walk to its south wall. The rock this quarry quarry is typical of of Waterloo Waterloo Quartzite Quartzite in The rock in in this is typical area. in the the Portland area. It is is coarsely coarsely recrystallized and is It is rich in in muscovite. muscovite. Bands Bands of conglomerate are common and and contain quartzite quartzite fragments fragments up up to to 33 cm in are in size. size. Conglomerate Conglomerate bands strike N. 35°E. and dip 42° to the south. bands N. 35°E. and 42° to the south. On the western part of of the the quarry wall a 25 cm thick thick phyllite phyllite lens lens is is exposed exposed (Fig. (Fig. 33). 33). The phyllite The phyllite thins thins to to 3 3 cm cm and and eventually eventually pinches pinches out out to to the the west. Color banding that that represents primary bedding parallels conglomerate represents parallels conglomerate layers. layers. Cross is Cross bedding bedding is observed just above the the phyllite lens lens (Fig. (Fig. 33). 33). Dott and Dalziel (1972) (1972) report report a a mean current direction of of 165 165 degrees degrees (S. (S. l5°E.) 15°E.) for for the Waterloo Quartzite based on measurements of 38 Quartzite based on measurements of 38 cross sets. sets. This compares with aa direction of 171 degrees measured for the Baraboo Quartzite Quartzite (Dott (Dott and and Dalziel, Dalziel, 1972). 1972). Common current directions for these two quartzites strongly strongly suggest suggest that that the the Baraboo Baraboo and and Waterloo Waterloo Quartzites Quartzites are correlative. correlative. In In outcrops just to the the south south of of the the quarry, quarry, foliated foliated quartzite quartzite is is highly polished and grooved (due to highly polished and grooved (due to glaciation). glaciation). Grooves Grooves trend trend N. N. 20°E. 20 o E. Foliation Foliation and and cross cross bedding bedding (?) (?) impart impart aa swirl—like swirl-like pattern pattern to to the the outcrop. outcrop. In places the foliatedquartzite In places the foliated quartzite has has weathered weathered out in in aa series series of of low low ridges ridges each each about about 11 cm cm high high (Fig. (Fig. 34). 34). 86 86 �Figure 33. 33. Figure View of aa thin thin phyllite phyllite layer layer (between (between arrows) arrows) interbedded interbedded with with quartzite at at the the Portland Portland Quarry Quarry (Stop (Stop 5). 5). Note Note the the crossbedding crossbedding in the quartzite just just above above the the phyllite phyllite bed. bed. Figure Figure 34. 34. located just just to to the the Close-up Close—up view view of of foliated foliated Waterloo Waterloo Quartzite Quartzite located Foliation planes planes are are south south of of the the quarry quarry visited visited at at Stop Stop 5. 5. Foliation each about about 11 cm cm high. high. weathering out out here here into into aa series series of of low low steps steps each weathering 87 87 �References Cited Cited References Aldrich, LL, T., Wetherill, Wetherill, G. G. W., W., Bass, Bass, M. Aldrich, o T., M. No, N,, Compston, Compston, W., W., Davis, Davis, G. G. 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Hobbs, Hobbs, W, W. H., H., and and Leith, Leith, C. C. K,, K o , 1907, 1907, The The Precambrian Precambrian volcanic volcanic and and intrusive intrusive rocks of the Fox River Valley, Wisconsin: rocks of the Fox River Valley, Wisconsin: Univ. Univ. Wise, Wisc oBull. Bull. 158, 158, Sci. Sd. Series, Series, v. v. 3, 3, no. no. 6, 6, p. p. 247-277. 247-277. Noble, Noble, D. D. C, C, 1970, 1970, Loss Loss of of sodium sodium from from crystallized crystallized comendite comendite welded welded tuffs tuffs of the Miocene Grouse Canyon Member of the Miocene Grouse Canyon Member of of the the Belted Belted Range Range Tuff, Tuff, Nevada: Nevada: Geol. Geol. Soc. Soc. America America Bull., Bull., v. v. 81, 81, p. p. 2677—2687. 2677-2687. Noble, Noble, D. D. C,, Co, ash—flow ash-flow 86 87 and C. E., E., 1969, 1969, Sr Sr8/Sr86 and Hedge, Hedge, C. /Sr variations within within individual individual variations sheets: sheets: U. U. 5, So Geol. Geol. 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Sd, Thwaites, Arts and Letters Letters Trans., Trans., v, v. 32, 32, p. p. 233—242. 233-242. Van Schmus, Sbhmus, W. W• R., R., 1978, 1978, Geochronology Geochronology of of the the southern Wisconsin Wisconsin rhyolites rhyolites and granites: granites: Wisc. Wisc. Geol. Geol. and and Nat. Nat. History History Surv. Surv. Geoscience Geoscience Wisconsin and Vol. Vol. 2, 2, p. p. 19—24. 19-24. Van Schmus, Schmus, W. W, R., R,, Thurman, Thurman, E. M., and and Peterman, Peterman, Z. Z, E., E,, 1975, 1975, Geology Geology and E. M., and Rb—Sr of Middle Middle Precambrian rocks rocks in central Rb-Sr chronology of in eastern and and central Wisconsin: Geol. Wisconsin: Geol. Soc. Soc. America Bull., Bull., v. v. 86, 86, p. p. 1255—1265. 1255-1265. Warner, J. Warner, J. H., H., 1904, 1904, The The Waterloo Quartzite Quartzite area area of of Wisconsin: Wisconsin: Madison, Madison, Univ. Wisconsin, B, Univ. Wisconsin, B. A. A. thesis, thesis. Weidman, S., Weidman, S., 1898, 1898, Precambrian Precambrian igneous igneous rocks rocks of of the the Fox Fox River River Valley, Valley, Wisconsin: Wjsc. Wisconsin: Wisc. Geol. Geol. and and Nat. Nat. History History Surv. Surv. Bull. Bull. 3, 3, 63 63 p. p. Weidman, S., district of Wisconsin: Wisconsin: Wisc. Wise, Weidman, S., 1904, 1904, The Baraboo iron—bearing iron-bearing district Geol, and and Nat. Geol. Nat. History Surv. Surv. Bull. Bull. 13, 190 190 p. p. 89 1 000-3K8T007-78 1000-3K8T007 -78 �OMISSIONS OMISSIONS South-Central Wisconsin Wisconsin Precambrian Inliers Field Field Trip Trip Guide Guide Book Book Number Number 22 -- Precambrian Inliers in in South-Central off the bar scales In preparation publication, the the bar scales were were inadvertently inadvertently left left off the In preparation for for publication, following figures. figures. Figure 14 14 (p. (p. 59) 59) Photomicrograph Marcellon rhyolite Photomicrograph of of Marcel10n ash-flow tuff. tuff. Marcellon rhyolite ash-flow Horizontal dimension, 3.3 mm. Horizontal dimension, 3.3 rom. Figure 17 17 (p. (p. 62) 62) Photomicrograph of Marcellon rhyolite Photomicrograph of Marce1lon rhyolite spherulitic spherulitic texture0 Marcellon texture. Horizontal dimension, 6.4 mm. Horizontal dimension, 6.4 rom. 62) Figure 18 18 (p. (p. 62) bands. Photoinicrograph of of aa spheroid spheroid with with concentric concentric bands. Photomicrograph Horizontal dimension, Horizontal dimension, 6.4 6.4 mm. rom. Figure 19 19 (p. 63) (po 63) (p. and Photornicrograph of of aa spheroid spheroid with with aa core core of of quartz Photomicrograph quartz and Vertical dimension, 11.2 mm. epidote. Vertical dimension, 11.2 rom. epidote. Figure 27 27 (p. 76) (p. 76) in the Photomicrograph crenulated shards Photomicrograph of of flattened flattened and and crenulated crenu1ated shards in the Marquette rhyolite. dimension, 6.6 Marquette rhyolite. Horizontal Horizontal dimension, 6.6 mm. rom. Figure 28 77) 28 (p. (p. 77) Photomicrograph of of flattened Marquette in the Photomicrograph flattened shards shards in the Marquette Horizontal dimension, rhyolite ash-flow rhyolite ash-flow tuff. tuff. Horizontal dimension, 6.6 6.6nun0 rom. (p. 84) Figure 31 31 (p. 84) Photomicrograph Quartzite. Photomicrograph of of the the Waterloo Waterloo Quartzite. Horizontal dimension, 6.6 Horizontal dimension, 6.6nun. rom. Figure 33 33 (p. (p. 87) 87) View em thick. View of of thin thin phyllite phyllite layer, layer, about about 40 40 cm cm thick. in middle middle of in of layer. layer. Pen lies Pen lies � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1978 Description An account of the resource Institute on Lake Superior Geology. Milwaukee, Wisconsin. May 9-14, 1978. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1978 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English Contributor An entity responsible for making contributions to the resource Aaquist, B. E. Banaszak, K. J. Bauer, R. L. Carnbray, F. W. Cannon, W. F. Chang, L. L. Y. Cooper, R. W. Cummings, M. L. Doane, v. DuBois, J. F. Egger, N. L. Foose, M. P. Gere, M. A., Jr. Hammond, R. D. Heinrich, E. W. Hodder, R. W. Hughes, J. D. Jirsa, M. A. Jonnson, A. Jones, D. G. Kalliokoski, J. Klaysrnat, A. W. Larue, D. K. Luther, F. R. Massey, N. W. D. Meddaugh, W. S. Meineke, D. G. Meyer, R. P. MoIling, P. A. Mudrey, M. G., Jr. Mursky, G. Myers, P. E. Nebrija, E. L. Ojakangas, R. W. Peltonen, D. R. Peterman, Z. E. Salotti, C. A. Scofield, N. Shaffer, N. Shanabrook, D. Sims, P. K. Smith, E. I. Strakele, A. E., Jr. Taylor, R. W. Trow, J. Tyson, R. M. Vadis, M. K. Van Schmus, W. R. Welkie, C. J. Westjohn, D. Woronick, R. E. Zietz, I. https://digitalcollections.lakeheadu.ca/files/original/0b9bd71e6ea5d2bd92035b333128d0ca.pdf de6d723232fadd49a8389d502051a921 PDF Text Text DULUTH, MINNESOTA INNESOTA MAY 8-13,1979 MAY 8-13, 1979 •e 25th ANNUAL ANNUAL INSTITUTE ON ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY ___;_• ,. �TECHNICAL SESSIONS and ABSTRACTS for the the 25th ANNUAL 25 th AJ.\lNUAL INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIORGEOLOGY GEOLOGY Sponsored by Sponsored UNIVERSITY OF OF MINNESOTA, MINNESOTA, DULUTH DULUTH held at DULUTH, MINNESOTA Joint Session with the in Joint the North Central Central Section Section Geological Society of America May 8 —- 12, 1979 Donald M. M. Davidson, Davidson, Jr., Jr., Program Chairman Chairman David G. G. Darby, Darby, Field Trip Chairman Moss, Technical Editor Carol Moss, Editor �TABLE OF CONTENTS Page Page No. No. INSTITUTE DIRECTORS AND LOCAL COMMITTEE 1 1 PROGRAM 22 ABSTRACTS OF OF TECHNICAL TECHNICAL SESSIONS SESSIONS 8 8 ** COVER DRAWING: large anticline. anticline. View from the the east east bank of of the the The large St. bridge, St. Louis Louis River, River, just south of the highway bridge, looking west. Thomson Dam Area, near near Thomson, Thomson, Minnesota. Minnesota. W. Wilson, Wilson, May 30, W. 30, 1968 �-1—1— 25th Annual INSTITUTE ON LAKE SUPERIOR GEOLOGY Sponsored by University of of Minnesota, Duluth Duluth at at Duluth, Minnesota Duluth, May 8 —- 12, 1979 1979 INSTITUTE BOARD OF DIRECTORS DIRECTORS Donald M. M. Davidson, Davidson, Jr., Jr., Department of of Geology, Geology, University University of of Minnesota, Minnesota, Duluth, Duluth, Duluth, Duluth, Minnesota* Minnesota* J. J. D. D. Hughes, Hughes, Department of of Geography, Geography, Earth Earth Science Science and and Conservation, Conservation, Northern Michigan, Michigan, Marquette, Marquette, Michigan M. F. M. F. Kehlenbeck, Keh1enbeck, Department of of Geology, Geology, Lakehead Lakehead University, University, Thunder Thunder Bay, Bay, Ontario G. G. Mursky, Mursky, Department of Geological Sciences, Sciences, University of of Wisconsin, Wisconsin, Milwaukee, Milwaukee, Milwaukee, Wisconsin Wisconsin R. C. C. Reed, Reed, Geological Geological Survey Division, Division, Department of R. of Natural Resources, Resources, Lansing, Lansing, Michigan M. Walton, M. Walton, Minnesota Geological Survey, University of of Minnesota, Minneanolis, Minneapolis, Minnesota *Present address: address: Department of Geological Sciences, Sciences, University of of Texas, Texas, El Paso, Paso, El Paso, Paso, Texas Texas �—2— -2- PROGRAM Tuesday, May 8, 8, 1979 8 a.m. Field Trip 1 leaves Hotel Radisson Duluth Duluth Wednesday, May 9, Wednesday, 9, 1979 8 a.m. a.m. Field Trip 2 leaves Hotel Radisson Radisson Duluth Duluth 12 noon opens, Superior Superior Foyer, Foyer, Hotel Hotel Registration opens, Radisson Duluth p.m. 5 p.m. return Hotel Radisson Radisson Duluth Duluth Field Trips 1 and 22 return 7-10 p.m. 7—10 p.m. Smoker poolside, poolside, Hotel Radisson Duluth Duluth Thursday, May 10, Thursday, 10, 1979 7:30 —12 a.m. Registration, Registration, Superior Foyer, Hotel Hotel Radisson Radisson Duluth �—3— SESSION 1 Morning Thursday, May 10, 1979 Early Precambrian Co—chairmen; Manf red Kehienbeck, Paul Meyers 8:45 D. H. Davidson, Jr. Opening Remarks 9:00 John Klasner and Paul Sims Geologic Interpretation of Gravity Data in the Marinesco, Thayer and Watersmeet Quadrangles, Michigan 9:20 K. Howard Poulsen Polyphase Deformation of Archean Rocks at Rainy Lake, Ontario 9:40 Elizabeth Palmer and Donald Davidson Paleostrain Analysis - Across a Shear Zone, Northwestern Marathon County, Wisconsin 10:00 Stephanie Wurdinger Structural Geology of Amphiboliric Gneisses, Northeast Chippewa County, Wisconsin 10:20 Coffee Break 10:40 Hanfred Kehienbeck Structural Interpretations in the }Iazelwood Lake Area, Thunder Bay, Ontario 11:00 Paul Sims and David Southwick New evidence on the stratigraphy and structure of the Soudan area, Western Vermilion district, Minnesota 11:20 Bruce Brown Deformational History of Arehean Creenstone Terrane, Eastern Lake of the Woods, Ontario 11:40 Thomas Waggoner and Thomas Mroz Palmer Gneiss Update 12:00 Noon. Adjourn for Lunch Luncheon Meeting of Board of Directors — location to be announced. �—4— SE S SI ON 2 Afternoon Thursday, May 10, 1979 Middle Precambrian Co—chairmi: Ralph W. Marsden, Glen Morey 2:00 David Larue and F. William Cambray Cross folding in the eastern part of the Marquette Trough, Michigan 2:20 Roy Shegelskl. Stratigraphy of the Cunflint Formation, Kakabeka Falls Area, Ontario 2:40 Karen Kimball Coexisting Ainphiboles in the metamorphic iron formation, Jackson County, Iron Mine, Wisconsin 3:00 Mike Cutmnings Phase relations of oxide—free iron formation in the Amphibolite Facie 3:20 Coffee Break 3:40 Mark Kirstein Contact Metamorphism of iihe Virginia Fonna— tion in the Minnamax Deposit, St. Louis County, Minnesota 4:00 Jesse Dann Comparative najor element variations within the Emperor Igneous Complex, and the Hemlock and Badwater Volcanic Formations, northern Michigan 4:20 C. Bennett and 0. C. Innes Stratigraphy and Petrochernistry of Huronian Volcanies, North Shore of Lake Huron, Ontario 4:40 Discussion Session 5:00 Adjourn **** ****** *** Even ln& 7:30 Banquet with North Central Section GSA — Speaker: Dr. Vincent McK'lvey For"ie r Di e I: t United States Geological Survey Hot1 Normandy �—5— -5- SE ON 33 S E S SSI ION Morning Friday, May Friday, ~fuy 11, 1979 Late Precambrian Late Co—chairmen: Co-chairmen: Foos Stan Watowich, Mike Foos 9:00 William Matlack Geology of of the Duluth Complex-Virginia Complex—Virginia FormaFormaGeology the Duluth tion Contact, Contact, Minnamax Deposit, Minnesota tion 9:20 George Lehman and and Donald Davidson Petrology Aspects of the the Troctolite—Olivine Troctolite-Olivine Gabbro Series, Series, Duluth Duluth Gabbro Gabbro Complex (Late Gabbro (Late Precambrian), Northeast Cramer Cramer Quadrangle, Quadrangle, Minnesota 9:40 James Hahnenberg James Petrology and a~d Geochemistry of Keweenawan Diabase Dikes in Michigan's Western Upper Peninsula 10:00 Coffee Break Coffee 10:20 John Green Green Bedrock Geology of the Milepost 7 Area, Area, Silver Bay, Bay, Minnesota 10:40 Stephen Cuggenheim, Guggenheim, Peter Wilkes and S. hT. W. Bailey S. The Nature of Greenalite Greenalite 11 :00 11:00 Discussion Session 11:20 Adjourn for Lunch �—F.— SESSION 4 Afternoon Friday, Nay 11, 1979 Ceneral Session Co—chairmen: Cedric Iverson, Mike Mudrey 1:40 Business Meeting of the Institute 2:00 William Cannon and Dennis Kostick Ronchi Filtering — an easy, inexpensive tech— nique for linear enhancement of many kinds of Geologic Data 2:20 Elizabeth King and William Cannon Results of a Truck Magnetometer Survey of the Southwestern Quarter of the Iron River 20 sheet 2:40 Jim Trow DOE-Bendix—Michigan Geological Survey Diamond— Drilling for and Geologic Information in Marquette Iron Counties 3:00 Coffee Break 3:20 Maurice Brock, Jo Kalliokoski and Richard Ojakangas Status of USGS Uranium Studies in Michigan's Upper Peninrula 3:40 Tom Evsns State Legislation Affecting Mineral Development in Wisconsin 4:00 End of Technical Session Saturday, May 12, 1979 Field Trips 3, 4, 5, 7, 8 Depart Leave 0800 Normandy Inn �—7— -7- POSTER PAPERS Morning Friday, Friday, May 11, 1979 1979 9:00 to to 12:00* 12:00* Room, Radisson Duluth Duluth Hotel Hotel Explorer Room, Glenn R. R. Bruck Glenn A for the Origin of the Horse A new Proposal for Creek Channel, Channel, in in Polk Polk && St. St. Croix Croix Counties, Counties, Wisconsin Jeff Greenberg and Bruce Brown Preliminary Geologic Geologic Interpretation lnterpretation of the the Northeastern Wisconsin 1:250,000 Geologic Geologic Map Frank Karner and and John T. T. Ray The Precambrian Basement Basement of of North Dakota M. P. M. P. McKenna and L. L. W. W. Gladen and and Mineral Potential of Cook Mineral Survey and County, Minnesota County, Nancy Scofield and David B. B. Jorgenson Pink and Green Albite Phenocrysts from the the and Green Mohawk Mine, Mine, Michigan--Indicators Michigan——Indicators of Changes in Hydrothermal Fluids D. tv. N. Snider D. and B. B. K. K. Parker copper—sulfide potential of several igneous The copper-sulfide plugs in Michigan's Keweenaw Peninsula G. G. Bennett and D. D. G. G. Innes Innes Huronian Volcanic Volcanic Rocks, Rocks, North Shore of Lake Huron, Ontario Huron, *Authors to 12:00 *Authors will will be be present present 11:00 to �—8--8- HURONIAI'TVOLCANIC VOLCANIC ROCKS, NORTH SHORE HURONIAN SHORE OF OF LAKE HURON, ONTARIO HURON, ONTARIO G. Bennett G. Innes Bennett andand D. G.D. Innes Ontario Ministry of Natural Ontario Ministry ofResources Natural Resources ABSTRACT distribution, petrochemical and The distribution, and stratigraphic stratigraphic relationships relationships of volcanic and and clastic clastic formations formations at at or or near near the the base base of of the the Huronian Huronian of Supergroup of the the Southern Structural Structural Province Province of of Ontario Ontario permits permits the the following following reconstruction of of Middle Precambrian Precambrian events events in in terms terms of of rift tectonics. tectonics. 1. 1. Sands Sands and gravels of the the Livingstone Creek Creek Formation Formation are deposited on on Archean Archean basement. basement. 2. 2. Thermotectonic uplift centered east east of of the the present present Elliot Elliot Lake area (probably (probably in the the Sudbury Sudbury area) area) causes causes an an easteastward erosional erosional beveling beveling of of the the Livingstone Livingstone Creek Creek Formation. Formation. 3. 3. The andesitic member of the The the Thessalon Formation Formation erupts erupts from central vents and fissures in in aa subsiding subsiding basin basin or or graben. The study of of 110 110 chemical chemical analyses analyses indicates indicates that that in spite of local spilitization, these these oldest oldest vol— volcanics included (tholeiitic) canics (tholeiitic) basaltic andesite, andesite, icelandite, icelandite, rhyolite; rhyolite; and (mildly (mildly alkalic) alkalic) hawaiite, mugearite mugearite and and ankaramitic flows. flows. 4. 4. The of compositionally uniform uniform tholeiitic tholeiitic flood flood The eruption of basalt forms the upper (basaltic) member of the Thessalon forms the (basaltic) Formation. 5. 5. Reoccurrence of of uplift in in the the Sudbury Sudbury area area results results in in of the upper member of the erosion of the Thessalon Thessalon Formation Formation east of of Thessalon and its complete removal east removal east east of of the the Elliot Lake area. area. 6. 6. In the Sudbury area the the thick thick accumulations accumulations of of tholeiitic tholeiitic In the basalt (Elsie erupt from (Elsie Mountain and Stobie Formations) Formations) erupt fissures basin or or graben. graben. Increasing subsubfissures in a subsiding basin sidence and/or waning volcanism causes causes much intercalated intercalated Formation; while in wacke and conglomerate in the Stobie Formation; the Massey area (80 the Massey (80 km to the the west), west), basalt to to rhyolite rhyolite of of the the Salmay Lake Formation is is erupted on on aa surface surface in in part part of exhumed, exhumed, layered gabbro—anorthosite of gabbro-anorthosite which was probably probably emplaced during the Thessalon volcanic event. event. Coarse Coarse sands sands and and uraniferous gravels of the the Matinenda Matinenda Formation are on the the eroded surface of of the are laid laid down down on eroded surface the Thessalon Formationinin the the Elliot Thessalon Formation ElliotLake Lake area areaand andwestward; westward; but in the but are are intercalated intercalated with with the the younger younger volcanics volcanics in the Massey and Sudbury areas areas to to the the east. east. 7. 7. The eruption of the the predominantly predominantly rhyolitic rhyolitic Copper Copper Cliff Cliff the Sudbury area marks the final Formation of of the marks the final Huronian Huronian volcanic episode. episode. 8. 8. Cessation of volcanism in in the the Sudbury—Massey Sudbury-Massey area area is is folfoland the deposition of the lowed the lowed by by prolonged subsidence and thick thick turbidite turbidite sequence of the the McKim Formation. �-9—9— STATUS OF USGS URANIUM STUDIES IN MICHIGAN'S UPPER PENINSULA U.S. Geological Geological Survey, Survey, Denver, Denver, Colorado Colorado 80225, 80225, Richard Richard Maurice Brock, U.S. W. Ojakangas, Ojakangas, University of Minnesota, Duluth, Duluth, Duluth, Duluth, Minnesota Minnesota 55812 55812 W. and Survey, and J. J. Kalliokoski, Michigan ~1ichigan Technological Technological and U.S. U.S. Geological Survey, University, Houghtor, Houghton, Michigan 49931 49931 and and U.S. U.S. Geological Geological Survey Survey University, ABSTRACT The U. U. S. S. Geological Survey is is conducting work work related related to to uranium uranium Lower, Middle, Middle, and Upper Precambrian Precambrian rock rock units. units. Randomly potential of Lower, selected samples from all units are being being analyzed analyzed for for uranium uranium content. content. In knowledge is is In general, general, base-level base—level data data are being generated where such knowledge lacking. Possible enrichment enrichment of shear zones zones is is one focus focus of of the the study. study. Mylonitic shear zones containing radioactive biotite biotite and and chlorite chlorite pods pods cut granitic rocks; rocks; some Some of these these porphyritic or or porphyroblastic porphyroblastic rocks rocks A number of primary are 3—5 3-5 times times more radioactive than than other granites. granites. A radioactive occurrences are present in in the the granitic granitic terrane terrane (see (see Kallio— Kalliokoski, 1976). koski, 1976). All the the major Middle and and Upper Precambrian Precambrian sedimentary sedimentary units units of of the the Cogebic Range in Michigan and Wisconsin, and other units Cogebic and Wisconsin, units to to the the east, east, are are in the the process of being being studied. studied. Paleocurrent patterns have been been determined determined (largely on cross--bedding) cross—bedding) for for the the Sunday Sunday Quartzite (72 (largely on (72 readings——bimodal readings--bimodal WNW I~l and ESE), ESE), the the Palms Formation Formation (102 (102 readings——bimodal ceadings--bimodal W~ and and E), E), the the Bessemer ENE and and W), W), and and the the Jacobsville Jacobsville Bessemer Sandstone Sandstone (105 (105 readings—--biniodal readings--bimodal ENE Formation (150 (150 readings——local readings--local variability). variability~ Field data are of primary importance, but but drill drill core core samples importance, samples of the the Jacobsville are also being studied. studied. Paleogeographic—depositional Paleogeographic-depositional models are are being being constructed; constructed; these these should should be be of value in determining sources and and transport transport directions directions of of radioactive radioactive However, to date abnormal radioactivity mineral grains grains and/or and/or solutions. solutions. However, radioactivity has only been found has found in detrital monazite of of the the Goodrich Goodrich Quartzite Quartzite (Vickers, (Vickers, 1956) in phosphatic zones zones of of the the Michigaimni Michigammi Formation (Cannon and 1956) and in Formation (Cannon Kiasner, 1976). Klasner, 1976). There are a number of minor radioactive radioactive occurrences occurrences which which may be related to the sub—Jacobsville sub-Jacobsville unconformity unconformity (Kalliokoski, (Kalliokoski, Langford Langford and Ojakangas, 1978). 1978). References Cannon, W. W. F. Klasner, J. Cannon, F. and Klasner, J. S., S., 1976, Phosphorite and and other other apatite— apatitebearing sedimentary rocks rocks in in the the Precambrian Precambrian of of Northern Northern Michigan: Michigan: U.S. Geological Geological Survey Survey Circular Circular 746, 746, 66 p. p. U.S. Kalliokoski, Kalliokoski, J., J., (with (with C. C. Johnson), 1976, 1976, Uranium Uranium and and thorium thorium occurrences occurrences in Precambrian rocks, rocks, Upper Upper Peninsula of Michigan and northern in Wisconsin, with thoughts Wisconsin, thoughts on other possible possible settings: settings: U.S. ERDA, ERDA, Grand Junction, BJX—48(76), BJX-48(76), 294 294 p. �-10- Kalliokoski, J., J., Langford, F. F. F., F., and and Ojakangas, Ojakangas, R. R. W., W., 1978, 1978, Critera Critera Kalliokoski, guides to to for uranium cccurrences occurrences in Saskatchewan and Australia as for as guides favorability for for similar deposits deposits in the United States: fsvorability States: U.S. D.O.E., D.O.E., Grand Junction, Junction, CJBX—1l4(78), Grand CJBX-114(78), 480 480 p. p. Vickers, 1956, 1956, Geology and monazite content content of of the the Goodrich Goodrich Quartzite, Quartzite, Vickers, Palmer area, area, Marquette County, County, Michigan in in Contributions Contributions to to the the U.S. Geological Survey Bulletin geology of uranium, 1955: 1955: U.S. Bulletin 1030, 1030, p. p. 171-185. �-11-· —11.-DEFORMATIONAL HISTORY OF AN ARCHEAN ARCHEAN GREENSTONE GREENSTONE TERRANE: TERRANE: EASTERN LAKE OF THE WOODS, WOODS, ONTARIO ONTARIO A. Brown* Bruce A. Department of Earth Sciences University of of Manitoba, Winnipeg Winnipeg ABSTRACT ABSTRACT A A structural and stratigraphic study study has has been been completed completed in in the the east— eastcentral part of the the Lake Lake of of the the Woods Woods region. region. The rocks of this this area area conconstitute aa typical greenstone assemblage of volcanic and stitute and sedimentary sedimentary litho— lithologies. The greenstones occupy an east—to—west east-to-west trending trending belt belt bounded bounded on on the the north, north, south, south, and east by granitic batholiths in in the the study study area. area. The results this study indicate that that the the greenstones have have undergone undergone aa comcomresults of of this can be be related related to to the the diapiric diapiric emplacement emplacement plex deformational history which can of the large bordering plutons of the large plutons and several smaller stocks stocks within the the belt. belt. features of of the the area area are are aa series series of of major major The earliest structural features east-west trending isoclinal folds folds (F1) (F I ) with horizontal to to shallow shallow plunging plunging east—west trending axes. F1 folds FI folds have an associated axial axial planar planar foliation foliation and and are are well well defined by top defined top reversals reversals within the the volcanic—sedimentary volcanic-sedimentary section. section. These folds are are aa regional folds regional feature feature and can be traced traced beyond the the area area of of study. study. facies distribution distribution as as well well as as structure structure supports supports Evidence from sedimentary facies their early early origin. origin. Deformation which accompanied emplacement emplacement of of the the granitic granitic plutons plutons produced folds folds (F2) (F 2 ) and aa complex complex pattern pattern of of faults faults and and shear shear zones. zones. Axial planar cleavages, cleavages, penetrative mineral lineation, lineation, and and aa complex complex set set of of F2 folds and related fabrics crenulations are associated associated with with the the F2 F2 folds. folds. F folds fabrics 2 show a consistent style throughout throughout the the area, area, but but their their orientation orientation and and degree of development is is variable depending depending on on their their location location relative relative to to the deformational deformational and and metamorphic regime surrounding the the the plutons. plutons. Where pluton contacts parallel the the structural structural grain grain of of the the greenstones, greenstones, F1 FI folds folds were tightened tightened and and flattened, flattened, and and shear shear zones zones developed developed along along litho— lithologic boundaries. Vertical displacement occurred occurred along along these these zones, zones, causing causing repetition of section and development development of of cataclastic cataclastic textures. textures. Where the the structural grain met a pluton contact contact at at aa high high angle, angle, shear shear zones zones acted acted as as detachment faults faults to to accommodate flexural flexural folding folding of of bedding bedding and and F1 F I axial axial planes around steeply steeply plunging plunging F2 F 2 axes. axes. In In the late stages of deformation, deformation, a set set of of northwest— northwest- and and northeast— northeasttrending kink kink bands bands was was overprinted on rocks trending rocks with strong planar fabrics. fabrics. Kinks grade into crenulation cleavage Kinks cleavage in in fine fine grained grained pelitic pelitic rocks rocks and and fine fine grained cataclastic cataclastic rocks. rocks. The latest latest structures are a series of northwest—trending northwest-trending faults faults into into diabase dikes dikes were intruded intruded in in Late Late Proterozoic Proterozoic time. time. which diabase *Present address: address: Wisconsin Geological and Natural History Survey, Survey, Madison, WI 53706 Madison, �—12— -12- A PROPOSED SOUTHERN SOUTHERN SPILLWAY SPILLWAY FOR FOR GLACIAL GLACIAL LAKE LAKE GRANTSBURG GRANTSBURG A Glenn R. R. Bruck and Earth Earth Science Science Department of Plant and The University of Wisconsin—River Wisconsin-River Falls Falls 54022 River Falls, WI 54022 ABSTRACT In 1935 W. W. S. S. Cooper described Glacial Lake Grantsburg Grantsburg which which was was formed when the Mississippi and St. St. Croix Croix Rivers Rivers were dammed dammed by by the the glacial advance of of the the Grantsburg Grantsburg Sublobe. Sublobe. Lacustrine sediments sediments indiindicate that the lake occupied an area of of approximately approximately 11,500 11,500 km2 km 2 mi 2 ). The estimated geographic center center of of this this body body of of water water (4,500 mi2). lies within Burnett County, County, Wisconsin. Wisconsin. Lacustrine sediments also indiindicate that the lake maintained a level level between 305 305 mm (1002 (1002 ft) ft) and and 325 325 mm (1070 ft) a possible maximum maximum at at 335 335 mm (1100 (1100 ft). ft). (1070 ft) with with a Cooper's the lake includes includes aa southern southern limb limb of of water water Cooper's description of the This limb was extending to the vicinity of St. St. Croix Croix Falls, Falls, Wisconsin. This confined on the west by the the Grantsburg Sublobe Sublobe and and on on the the east east by by the the St. Croix Moraine, Moraine, which was deposited about St. about 1,300 1,300 years years earlier earlier by by the the Superior Lobe. Lobe. The present investigation investigation suggests suggests that that the the lake's lake's southern extension terminated near St. St. Croix Croix Falls Falls and and Dresser, Dresser, Wisconsin; Wisconsin; this this location being determined by evidence evidence indicating indicating that that the the Grantsburg Grantsburg was pinned against the Sublobe was the St. St. Croix Moraine in in this this area. area. Although Cooper's most detailed of the the Cooper's study is is the most detailed investigation investigation of lake to date, date, he was unable to to find aa drainage drainage spiliway spillway associated associated with with its highest highest level. level. As a result, result, he hypothesized that that the the lake, lake, at at its its highest stand, stand, might have drained over over the the Grantsburg Grantsburg Sublobe. Sublobe. A A topographic topographic examination examination of of the the St. St. Croix Croix Moraine Moraine near near Dresser, Dresser, Wisconsin, reveals reveals a gap that lies lies at at the 304 304 m (1,000 ft) level, fully Wisconsin, m (1,000 ft) level, fully (180 ft) ft) below the the morainal ridge ridge it it divides. divides. During the the glaciation, 55 m m (180 this gap gap was was low enough enough so so that this that it was penetrated by outwash outwash from from the the marks the beginning of of a 42 km nearby Grantsburg Sublobe. Sublobe. The gap also also marks the beginning a 42 (26 mi) is clearly defined by the the 304 304 m m (1,000 (1,000 ft) ft) contour. contour. (26 mi) channel channel which which is The channel trends trends southward and and merges with the the Apple Apple River River near near HuntingHuntington, Wisconsin. From here it follows ton, follows the Apple River to to a a point point 6.5 6.5 km (4 it finally the St. St. Croix (4 mi) mi) WNW WNW of of Sommerset, Sommerset, Wisconsin, Wisconsin, where where it finally joins the River. This route describes a course which bypasses aa 26 This 26 km km (16 (16 mi) mi) stretch of the the St. St. Croix Croix River. River. The present study suggests suggests that that this this bybypass represents a southern spillway spillway for for Glacial Glacial Lake Lake Grantsburg Grantsburg which which facilitated the the lake's lake's drainage drainage during during the the maximum maximum advance advance of of the theGrants-' Grants~ burg Sublobe. Sublobe. Evidence in support of this this hypothesis consists consists of of two two major major observaobservations: First, the altitude altitude of of the the channel channel First, the close correlation between the and the level of of Glacial Lake Grantsburg; and the level Grantsburg; and and secondly, secondly, the the outwash outwash from from the the gap gap at at Dresser Dresser indicates indicates that that the Grantsburg Grantsburg Sublobe found east of the from the the ice ice flowed flowed through through the the gap. gap. drainage from �—13— -13- RONCHI FILTERING--A FILTERING——A RAPID INEXPENSIVE TECHNIQUE TO AID IN THE DETECTION OF LINEATIONS LINEATIONS IN PHOTOGRAPHS, PHOTOGRAPHS, MAPS, MAPS, ROCKS, ROCKS, AND THIN SECTIONS F. Cannon and Dennis Kostick William F. U.S. Geological Survey U.S. Survey Reston, Virginia 22092 Reston, 22092 ABSTRACT Ronchi filtering filtering is is a simple visual technique that that can aid in identifying linear trends trends in in Landsat Landsat images, images, aerial aerial photographs, photographs, geologic geologic identifying linear maps, aeromagnetic and gravity maps, maps, and topographic maps; maps; it can also be maps, It may used to to detect subtle subtle linear linear features features in in rocks rocks and and thin thin sections. sections. It sometimes be be an an adequate adequate substitute for for more more expensive expensive and and time—consuming sometimes time-consuming computer enhancement enhancement of of data. data. A A Ronchi parallel thin thin width of each parent area. area. filter is a type type of linear diffraction opaque stripes stripes are are arranged arranged on on aa clear opaque opaque stripe is equal to to the the width of The filter used in our work contains contains 88 grating in in which so that plastic so that the the the adjacent adjacent transtransstripes stripes per per millimeter. millimeter. filter is held about about 10-30 10—30 cm in front front of of the eye, The filter is held eye, and the object to be studied, studied, for for example, aa Landsat Landsat image, image, is is viewed viewed through through the the filter. filter. when viewed viewed in this way is Any small object when this way is seen as as multiple images images aligned to the the direction direction of of stripes stripes on on the the filter. filter. For example, example, aa perpendicular to dot dot appears as a line line of of several several individual individual but but closely closely spaced spaced dots. dots. This property can be used to to enhance enhance subtle subtle linear linear trends. trends. For example, example, by viewing aa Landsat image image through through the the filter filter and and slowly slowly rotating rotating the the filter filter 0 , a through 180 1800, a user user performs performs aa rapid rapid linear linear enhancement enhancement in in all all possible possible through directions. Subtle linear trends, not easily visible to the untrends, commonly not aided eye, eye, may become readily visible through the filter when it is is stripes on the grating is is perpendicular oriented so that the direction of of stripes to the to the trend on the the image image or or object. object. This technique has has been useful in regional tectonic studies in the the Lake Superior region by helping us us to identify linear trends trends in Landsat images, maps. images, aeromagnetic, aeromagnetic, and gravity maps. �—14— -14FOR~ATION IN THE AMPHIBOLITE FACIES FACIES PHASE RELATIONS OF OXIDE-FREE IRON FORMATION M. L. M. L. Cummings Department of Geology University of of Wisconsin Eau Claire, Claire, Wisconsin 54701 54701 ABSTRACT Iron Iron formation formation units, units, up up to to 50 50 m m thick, thick, occur occur in in the the Precambrian Precambrian Quinnesec Formation, Formation, west central central Marinette Marinette County, County, Wisconsin. Wisconsin. The iron formations metasediments and formations are associated with basalt flows, flows, graphitic metasediments and sub-economic sub—economic massive sulfide. sulfide. The iron formation well—bedded gray quartz and iron silicate formation contains contains well-bedded Locally, are Locally, quartz beds beds are fractured fractured and in some cases cases fragments fragments are separated by thin septa of iron silicates. Some sections are charactercharacterized by by rounded, ized rounded, 1 to to 2 cm, em, quartz nodules. nodules. Oxides and/or sulfides are are disseminated in iron silicate beds with beds or occur as as thin layers layers interbedded interbedded with iron silicates. Ilmenite is the oxide phase, phase, but magnetite is is locally locally Ilmenite is abundant. Monoclinic pyrrhotite is is the the main main opaque opaque phase. phase. Sphalerite grains interstitial to to iron silicates or associated associated with occurs as isolated grains with pyrrhotite. only in in pyrrhotite—bearing pyrrhotite-bearing beds. beds. Chalcopyrite occurs only beds. sequences can be determined by the the The metamorphic grade of of volcanic sequences iron silicate assemblages in oxide—free iron oxide-free iron iron formation. formation. Iron silicate assemblages in oxide—free oxide-free samples samples from from the Quinnesec Formation include include grunerite/quartz, grunerite/stilpnomelane/quartz, grunerite/stilpnomelane/quartz, grunerite/ferro—hornblende/ grunerite/ferro-hornblende/ stilpnomelane/quartz, grunerite/garnet/ferro—hornblende/quartz, grunerite/garnet/ferro-hornblende/quartz, grunerite/ grunerite/ ferro—actinolite ferro-actinolite ± ± ferro—hornblende/quartz. ferro-hornblende/quartz. Calcite is a common accessory accessory mineral. Stilpnomelane, Stilpnomelane, restricted restricted to to grunerite grunerite and and grunerite/ferro— grunerite/ferrohornblende assemblages, assemblages, is is more more iron—rich iron-rich than than associated associated amphiboles. amphiboles. grunerite in garnet-free garnet—free Manganese is preferentially partitioned into grunerite samples. samples. Magnesium is is preferentially partitioned into into ferro—actinolite ferro-actinolite in in Ferro—hornblende is grunerite/ferro—actinolite grunerite/ferro-actinolite assemblages. assemblages. Ferro-hornblende is the the silicate phase containing containing the the highest highest concentration concentration of of titanium. titanium. The iron silicates can be represented in the simplified system FeOFeO— A1203—CaO—Si02—H20. Na2O in stilpnomelane, MgO, MnO MnO and and Ti0 TiO2 A1203-CaO-Si02-H20. K2O K20 and Na20 stilpnomelane, MgO, in 2 in amphiboles remove remove the the system system from from the the ideal ideal simplified simplified system. system. Iron silicate assemblages assemblages in the Quinnesec Formation indicate that that the the assemblage assemblage hornblende/grunerite/quartz is approxiis stable under metamorphic conditions, conditions, approximated from associated associated metasediments, metasediments, at at 5200 520 0 CC and and 1.5 1.5 to to 3.5 3.5 kb. kb. Actinolite/ high—manganese bulk garnet/quartz is is stable at at higher temperatures temperatures or in in high-manganese compositions. �—15— -15- MAJOR-ELEMENT VARIATION WITHIN THE EMPEROR IGNEOUS COMPLEX AND THE HEMLOCK AND BADWATER BADWATER VOLCANIC FORMATIONS FORMATIONS Jesse C. C. Dann Department of Geology && Geological Engineering Engineering Michigan Technological University Houghton, Houghton, Michigan Michigan 49931 49931 ABSTRACT Major—element variations variations within the Emperor Igneous Major-element Igneous Complex, Complex, and the the Hemlock and Badwater volcanic formations formations of of the the Lower Lower Proterozoic Proterozoic of northern Michigan were studied studied to to determine determine the the magma magma series series type. type. Fifty-two Fifty—two new new analyses analyses indicate indicate that that continental continental tholeiite tholeiite dominates dominates and that most of of the the less less abundant abundant calcalkaline calcalkaline rocks rocks are are not not really really and that most distinguishable from from those those associated associated with with aa Lower Lower Proterozoic Proterozoic Cu-Zn Cu—Zn distinguishable massive sulfide deposit in in Wisconsin. The Emperor Emperor Igneous Igneous Complex Complex in in the the East East Gogebic Gogebic Range Range consists consists of of The two two distinct suites: suites: calcalkaline volcanic rocks and and tholeiitic tholeiitic sills. sills. The the Ironwood The volcanic volcanic rocks, rocks, interbedded interbedded with with the Ironwood Iron-formation, Iron—formation, consist consist mostly of andesite breccia with minor lava flows; flows; they they are interpreted to to S1O2 increases upward from represent a subaqueous volcanic apron. apron. Si0 increases upward from 2 54 to to 62 62 percent with FeO remaining remaining at at 99 to to 11 11 percent. percent. The sill comcomintruded the iron—formation in in three stages which which show aa FeO FeO increase increase plex intruded the iron-formation three stages from 12 to to 19 19 percent. percent. Formation north north of of Crystal Falls Falls displays displays tremendous The Hemlock Formation tremendous Rhyolite lava lithologic and geochemical variety. variety. Rhyolite lava and/or volcaniclastic deposits occur at three horizons the formation formation which is dominated deposits at three horizons within within the which is and volcaniclastic sediments sediments (pillow breccia, flow by basaltic lavas lavas and (pillow breccia, breccia, hyaloclastite, and and turbidites). turbidites). The lowermost basalts, deposited deposited breccia, hyaloclastite, about b.y. ago, ago, are are poorly poorly differentiated oceanic basalts, basalts, perhaps about 2 b.y. perhaps in aa fault—bound fault-bound basin; ironerupted in basin; these are are overlain by slate and iron— formation. continental tholeiite The succeeding lavas, lavas, composed composed of. of. continental basalt, subcycles of of FeO FeO and and Ti02 Ti0 2 enrichment. enrichment. The upperbasalt, display several subcycles high-iron basalt (up (up to to 25 25 percent percent FeO) FeO) is is most unit of extraordinarily high—iron immediately overlain by by iron—formation. iron-formation. The rhyolites do do not not occur occur at at the top the top of volcanic cycles. cycles. The Badwater Greenstone outcropping along the north margin of the Iron Iron River-Crystal River—Crystal Falls Falls basin basin consists consists of of several several different different sequences sequences of of dominantly tholeiitic tholeiitic volcanic volcanic rocks. rocks. Exposures on the south limb of the basin exhibit a close relationship between high iron tholeiite basalts and iron-rich iron—rich sediments; sediments; these these rocks rocks are are interpreted interpreted to to belong belong to to the the Hemlock Hemlock Formation. It is is clear clear that that lavas lavas associated associated with with the the Ironwood Ironwood Iron-formation Iron—formation It are not not enriched in are in iron. iron. However, is some evidence which leads one However, there is to suspect to suspect aa relationship relationship between between iron-rich iron—rich lavas lavas of of the the Hemlock Hemlock Formation Formation and the and the overlying Amasa Iron—formation. Iron-formation. �—16— -16- STATE LEGISLATION AFFECTING AFFECTING MINERAL MINERAL DEVELOPMENT IN IN WISCONSIN WISCONSIN Thomas J. J. Evans Evans Geological and Natural History Survey Survey University of of Wisconsin Wisconsin —- Extension 1815 University University Avenue 1815 Madison, Wisconsin Wisconsin 53706 53706 ABSTRACT development in Wisconsin has has stimulated stimulated Proposed metallic mineral development wide—ranging wide-ranging legislative legislative activity activity by by the the State State of of Wisconsin. Wisconsin. The new legislation, 1977 and and 1978, 1978, also also has has impact existlegislation, passed in 1977 impact on the the two two existing metal mines in Wisconsin. ing metal in to Metal mining operations are subject to new laws concerning concerning (1) (1) taxation taxation of of mineral mineral revenues revenues (Chapters (Chapters 31, 31, 185, and (2) controls controls on on operating operating procedures procedures and environmental 185, and 423), 423), (2) impacts from from the exploration (drilling) impacts (drilling) phase phase through through actual actual mine mine propro(Chapters 377, 377, 420, 420, and and 421), 421), (3) (3) controls controls on on metallic metallic mineral mineral duction (Chapters exploration lease terms procedures (Chapter and terms and and recording recording procedures (Chapter 253), 253), and (4) submittal submittal of of metallic metallic mineral mineral exploration information of (4) of geologic geologic interest to the the State State (Chapter (Chapter 422). 422). Some of will be be of the background leading to to the the recent recent legislation will reviewed with with aa brief discussion of the reviewed the current current status status of of each each law, law, its its impact the mining industry, industry, and subsequent regulatory regulatory activity. activity. impact on the Potential modifications of of the the laws laws will will also also be be noted. noted. Proposed legislation in the the 1979 long1979 legislative sessions sessions concerns concerns long— term of mining companies and and registration registration of of severed severed mineral mineral term liability of interests. Prospects for and ramifications ramifications of this additional Prospects for of this additional legislative legislative addition, the activity will will be be examined. examined. In addition, the work of of the the Legislative Legislative Council Council Mining Committee's Committee's Subcommittee Subcommittee on on Reclamation of Nonmetallic Mining will be reviewed. �—17— -17- BEDROCK GEOLOGY AREA, SILVER BAY, BAY, MINNESOTA GEOLOGY OF OF THE MILEPOST 7 AREA, C. Green Green John C. Geology Department University of Minnesota Duluth, Duluth, Minnesota 55812 55812 ABSTRACT tailings disposal disposal area area lies lies in in the the Reserve Mining Company's new tailings broad valley of the the Thirty—nine Thirty-nine Creek Creek tributary tributary to to the the West 'vast Branch Branch of of the Beaver River about five the five miles miles west west of of Silver Silver Bay. Bay. The basin basin is is underlain by lavas of the the North Shore Shore Volcanic Group Group whereas whereas the the high high the southeast side is is held up up by by diabase diabase of of the the Beaver Beaver Bay Bay ridge along the complex. The the northwest flank flank is is also also underunderThe more more gradual slope on the by mafic mafic intrusive intrusive rocks. rocks. All of of the the bedrock bedrock is is of of lain predominantly by Keweenawan (Late (Late Precambrian) Precambrian) age. age. During the summer of 1978 the the bedrock geology of the the area was studied by field field mapping and and examination examination of of drill cores obtained obtained for for dam dam foundation foundation testing. testing. The lavas The lavas in the basin and along strike to to the the south south can can be assigned assigned to of Green Green (1942). (1942). They dip gently (about (about to the the Gooseberry River basalts of 90) 9 0 ) to to the southeast, southeast, and consist of roughly roughly 700 700 feet feet of of intergranular intergranu1ar andesites andesites and basaltic andesites overlain by about about 850 850 feet feet of of ophitic ophitic olivine basalts. basalts. The later tend tend to to hold up low low hills within the the southsoutheast part of of the the basin. basin. The high ridge along the the east east side side is is made predominantly predominantly of of ophitic ophitic olivine diabase, diabase, but but a olivine a few anorthosite xenoliths and and thick thick screens screens and and blocks of basaltic hornfels are are also also present present as as well well as as minor minor interflow interflow volcanic sandstone sandstone and and breccia. breccia. The main diabase intrusion intrusion appears appears to to have been localized localized along along aa major NNE—trending NNE-trendin8 fault fault which which also also divides divides the lava succession into two the lava two separate structural and stratigraphic blocks; blocks; the flows east east of of the ridge the flows ridge strike WNW and dip south whereas those those to to the the west strike NE NE and and dip dip SE. SE. Some also occurred occurred since since intrusion, intrusion, Some faulting faulting has also producing breccias and topographic topographic cross—valleys cross-valleys and and juxtaposing juxtaposing unmeta— unmetamorphosed sediments sediments next next to to diabase. diabase. morphosed The intrusive rocks rocks of the the western flank flank are are more diverse diverse and and are are probably interdigitated with lavas lavas but exposures exposures are are too too poor poor to to show show contact relations. relations. The uppermost unit is is aa ridge—forming, ridge-forming, fine—grained, fine-grained, iron—rich trachybasalt iron-rich trachybasa1t sill, sill, probably probably with with two two branches. branches. The other major units the west side of the the area are are mostly ophitic ophitic olivine olivine diabase diabase units along the and gabbro of various types; types; some have highly zeolitized zeo1itized roof roof zones. zones. This the Minnesota Geological Survey Survey with This project was was supported by the the cooperation cooperation of of Reserve Reserve Mining Mining Company and Klohn Leonoff Consultants, the Consultants, Ltd. �—18— -18- INITIAL PROGRESS AND INTERPRETATION OF GEOLOGICAL MAPPING IN IN NORTHEASTERN NORTHEASTERN WISCONSIN WISCONSIN J.K. J.K. Greenberg and B.A. B.A. Brown Brown and Natural Natural History History Survey Survey Wisconsin Geological and Madison, Wisconsin Madison, ABSTRACT Initial results Initial results from reconnaissance—scale reconnaissance-scale bedrock geological geological mapping mapping in (an area bound by 45°N, 45 0 N, 90°W 90 0 W and the the state state border) border) in northeastern northeastern Wisconsin Wisconsin (an suggest the presence of four distinct tectonic tectonic regions regions separated separated by by three three structures which which are are best best defined defined by by their their geophysical geophysical signasignamajor boundary structures tures. Available age data data indicate indicate that that most, most, if if not not all, all, of of the the observed observed rock units are Middle Precambrian. Precambrian. The three The three boundaries extend approximately east east to to west across across the the map map area. The northern one is is nearly parallel with and and just just north north of of the the of Vilas County and just just south south of of the the Wisconsin—Michigan Wisconsin-Michigan southern border of border in Forest and Florence Counties. Counties. The central boundary extends from from the northern border of Lincoln County County in in the the west, west, across across central central Forest Forest The southern boundary County, and through Amberg in in eastern Marinette County. County. The County, continues from northern Marathon County County east—northeast east-northeast through through Merrill Merrill and and across southern Forest County before swinging across swinging to to the the south south along along the the eastern eastern border of Oconto County. County. The northernmost tectonic tectonic region region consists consists of of Michigamme Michigamme and and equivalent equivalent sedimentary rocks including iron iron formation formation and and small small volumes volumes of of volcanic volcanic rocks, rocks, all of of aa wide range range in in metamorphic metamorphic grade. grade. The next region to to the the is separated from from these these rocks rocks by by the the northern northern boundary, boundary, aa complex complex south is series of of fault fault zones. zones. This region is is characterized characterized by by isolated isolated areas areas of of migmatitic gneisses gneisses associated associated with with foliated foliated granitic granitic intrusions. intrusions. These areas areas of of felsic felsic rocks are surrounded on on the the north north and and east east by by predominantly predominantly mafic volcanic volcanic rocks, including the the Quinnesec Quinnesec Formation, Formation, and and are are apparently apparently mafic rocks, including However, late truncated on on the truncated the south by the central geologic boundary. boundary. However, late to to post—kinematic post-kinematic plutons, plutons, ranging ranging in in composition composition from from gabbro gabbro to to granite, granite, the regions to to the the north north and and south south of of the the boundary. boundary. Much of of intrude both the the immediately to to the the south south is is typical typical ofofa at!greenstonelt "greenstone" terrane the region immediately terrane composed of metavolcanic and and metasedimentary rocks rocks which which are are the the hosts hosts for for major major massive sulfide sulfide mineralization. mineralization. The southern boundary between between the the greenstone greenstone terrane and and rocks rocks including the McCaslin Mountain Quartzite terrane Quartzite and and Wolf Wolf River River intrusives to to the the south south is is expressed, expressed, at at least least in in part, part, as as aa major major Batholith intrusives shear zone. zone. All of of the tectonic tectonic features in in the the map area area will will be be better better understood as future future work extends extends mapping mapping coverage coverage to to the the west west and and south. south. �—19— -19- THE NATURE OF OF GREENALITE GREENALITE Stephen Guggenheim, Guggenheim~ Department of Geology, Geo1ogy~ University of of Illinois Illinois at at Peter Wilkes, Wi1kes~ Department of of Metallurgical Metallurgical and and Mineral Mineral Engineering, University of Wisconsin—Madison, Engineering~ Wisconsin-Madison~ and and S. S. W. w. Bailey, Bai1ey~ DepartDepartment of Geology Geology and and Geophysics, Geophysics~ University University of of Wisconsin—Madison, Wisconsin-Madison~Madison, Madison~ Wisconsin Chicago, Illinois, Chicago~ I11inois~ ABSTRACT Pure samples of greenalite, greena1ite~ including including aa single single crystal, crysta1~ have have made m&de detailed structural structural characterization characterization than than before. before. All possible a more detailed samples studied consist of an intimate lntergrowth samples intergrowth of of aa predominant predominant trigonal trigonal phase and and a a minor monoclinic phase, phase~ even even down down to to the the smallest smallest in the the electron electron microscope. microscope. Specific polytypes cannot cannot particles visible in 3n reflections, be assigned because of absence absence of of the the diagnostic diagnostic kl I 3~ ref1ections~ but the mode of layer layer stacking stacking differs differs in in the the two two phases. phases. The single crystal allows allows the crystal the sense of the axes to to be established and and leads leads to to the the conclusion that that the monoclinic phase is is in in a fixed fixed orientation orientation relative relative to the trigonal trigonal host~ layers. Tetrahedral inversion inversion to the host, but but with inverted layers. is for relief of the the lateral misfit anticipated anticipated due due is aa known known mechanism for 2+-rich octahedral to Si—rich tetrahedral tetrahedral sheet sheet and and aa Fe Fe2—rich to aa Si-ric~' octahedral sheet. sheet. As in in antigorite, antigorite~ it it causes elimination elimination of of octahedral octahedral cations cations and and surface surface OH OH groups at at the groups the inversion loci, loci~ thus thus simulating an excess excess of of Si Si upon upon con— conventional allocation of chemical chemical analyses analyses assuming assuming aa full full complement complement of of anions. Hexagonal arrays of satellite spots spots around around sharp sharp kl I 3n 3~ spectra on hkO hkO electron diffraction nets are interpreted spectra interpreted as as due due to to multiple diffraction caused by the the coherent coherent intergrowth intergrowth of of the the mono— monoclinic phase scattered as islands islands throughout throughout the the matrix matrix of of the the trigonal trigonal 2+-rich and Mn2+_rich host. and its its abundance abundance increases The is Mn Thc monoclinic phase is with fromgreenalite greenalitethrough through the the species species tosalite tosalite to to caryc— carycwith Mn2+ Mn2+ cont conttntfrom pilite, pilite~ the the Mn ~ill or-analogue grecnalite~ where the the monoclinic phase phase is is —analogue of of greenalite, predominant and the the trigonal trigonal phase phase is is minor. minor. predominant 2 �—20— -20- PETROLOGY AND GEOCHEMISTRY OF KEWEENAWAN DIABASE DIKES ONTONAGON, ONTONAGON, GOGEBIC, GOGEBIC, IRON AND DICKINSON COUNTIES, COUNTIES, MICHIGAN James J. J. Hahnenberg Hahnenberg Department of of Geology Geology Western Michigan University Kalamazoo, Kalamazoo, Michigan 49008 Keweenawan diabase dikes in Michigan's Upper Peninsula Peninsula are are being being trace element element (Rb, (Rb, Sr, Sr, Ba) Ba) concenconcenanalyzed for major and selected trace trations compositions. Specifically, techniques techniques trations and bulk mineral compositions. microscope, x—ray using the the petrographic microscope, x-ray fluorescence, fluorescence, atomic atomic absorption absorption spectrographic analysis analysis and and the spectrographic the magnetometer are being used to to accurately define mineralogical and and chemical chemical trends trends and and magnetic magnetic Sample distribution is character of the the dikes. dikes. Sample is spaced as uniformly as possible on a trend trend roughly perpendicular to to the the Keweenawan Keweenawan "rift "rift trend". The dikes dikes will be compared to to other Keweenawan igneous igneous units, units, in the the region region (the (the Powdermill Powdermill specifically lower Keweenawan flows in Group, formerly the Group, the South South Trap Trap Range). Range). Correlation with chemical trends in more recent trends recent rift rift systems systems will will be be attempted. attempted. The larger dikes are composed of subophitic subophitic plagioclase plagioclase and and pyroxene (augite (augite and and pigeonite). pigeonite). Opaque minerals are a minor, minor, but minerals are orthoclase and ubiquitous, constituent. constituent. Interstitial minerals quartz which occur locally locally as micropegmatitic intergrowths intergrowths associated associated with needles of of apatite. apatite. Some altered, being Some dikes dikes are only slightly altered, uralitized and chioritized, chloritized, while others others consist consist of of 15—25% 15-25% secondary secondary minerals. In In small small dikes, dikes, mineral grains are microcrystalline to to cryptocrystalline. The dike~ have narrow chilled margins The larger dikes abruptly changing to to phaneritic texture texture toward toward their their centers. centers. �—21— -21- INTERPRETATIONS IN THE HAZELWOOD STRUCTURAL INTERPRETATIONS AREA, THUNDER THUNDER BAY, ONTARIO ONTARIO LAKE AREA, M.M. Keh1enbeck Kehienbeck M.M. Department Department of Geology Geology Lakehead University University Lakehead Bay, Ontario Ontario P7B P7B SB1 5l Thunder Bay, ABSTRACT The Hazelwood is underlain by Hazeiwood Lake area is by Archean stratified sedimentary rocks rocks and and fragmental fragmental volcanic volcanic rocks. rocks. Primary structures, structures, particularly graded bedding, bedding, are well in most most outcrops. outcrops. Pillow lava lava flows flows occur occur sporadisporadipreserved in cally interlayered inter1ayered with agglomerates and and tuffaceous tuffaceous units. units. All rocks possess a well developed cleavage which appears parallel to axial surface surface of of observed observed minor minor folds folds in parallel to the the axial in the the sedimentary sequence. sequence. Applying the the technique technique of structural facing to to the the rocks rocks gives the sense of of younging younging of of the folded stratigraphic stratigraphic gives the sense the folded succession. Results from from Hazelwood Hazelwood Lake Lake indicate Results indicate that that a a significant the stratigraphic sequence down prior to to portion of of the sequence was was upside upside down the last last folding event the event in in the the area. area. �—22— -22- COEXISTING AMPHIBOLES ANPHIBOLES AT AT BLACK RIVER FALLS, FALLS, WISCONSIN WISCONSIN Karen Kimball Department of Geology and and Geophysics University of Wisconsin Madison, Wisconsin Madison, Wisconsin 53706 S3706 ABSTRACT Extensive outcrops outcrops of of iron iron formation formation are are present present seven seven miles miles west west of of Extensive Black River Falls, Falls, Wisconsin. Wisconsin. The dominant mineral assemblages in The in the the iron iron formation are: are: 1) 1) magnetite—quartz-.grunerite—ferroactinolite magnetite-quartz-grunerite-ferroactinolite 2) magnetite—quartz—cummingtonite—biotite magnetite-quartz-cummingtonite-biotite 3) 3) magnetite—quartz—garnet—hornblende—ferroactinolite—grunerite magnetite-quartz-garnet-hornblende-ferroactinolite-grunerite The amphiboles amphiboles in in the iron formation formation are are products products of of aa metamorphic metamorphic event event The the iron which reached reached lower lower amphibolite amphibolite facies. facies. Coexisting amphiboles amphiboles occur occur as as disdis- grains in in contact contact with with each each other, other, as as coarse coarse intergrowths, intergrowths, or or occaoccacrete grains sionally as as 20—25 20-2S micron blebs of of one one amphibole amphibole in in another. another. are not are not altered and and not not exsolved. exsolved. The amphiboles Individual amphibole grains are are homogeneous. homogeneous. Multiple electron microprobe analyses show that that compositional variations are less than than two two percent. percent. The amphibole assemblage hornblende—ferroactinolite—grunerite hornblende-ferroactinolite-grunerite is is the only three amphibole assemblage found found in in the the iron iron formation. formation. three quartz this assemblage quartz assemblage is is invariant. invariant. In the In the presence of of The chemical formulas formulas for for these these amphi— amphi- boles are (Na,K) 2Ca9(Mg,Fe,Al)5Si75023 for 9Mg1 4Fe4 boles are (Na,K) .2Ca.g(Mg,Fe,Al)SSi7.S023 for the the hornblende, hornblende, Ca1 Cal.9Xgl.4Fe4 Si7 . 8023 for the ferroactinolite and 7Si7 7023 for Si and (Mg,Fe)6 (Mg,Fe)6.7Si7.7023 for the the grunerite. grunerite. 7 8 0 23 for are abundant abundant and and include: include: Amphibole pairs are (Na,K)1Ca19Mg3Fe11Al29Si5023 grunerite—hornblende Mg14Fe57Si77023 —- (Na,K)lCal.gMg3Fel.lAlZ.gSiSOZ3 grunerite-hornblende Mgl.4FeS.7Si7.7023 grunerite—ferroactinolite Mg18Fe57Si79023 —- Ca19Mg14Fe39Si78023 grunerite-ferroactinolite Mgl.8FeS.7Si7.9023 Cal.gMgl.4Fe3.9Si7.8023 cummingtonite—gedriteMg4.SFe2.lSi7.SAl.4023 Mg48Fe21S178A14023 —- Mg12Fe47A12Si56A115023 cummingtonite-gedrite Mgl.2Fe4.7A12SiS.6All.S023 cummingtonite—actinoliteMg3.7Fe3.8Si7.9023 Mg37Fe38Si79023 — cummingtonite-actinolite - Ca19Mg32Fe15Si8O23 Cal.gMg3.2Fel.SSiS023 �—23— -23- Ferroactinolite coexisting with with grunerite grunerite has has higher higher Mg/Mg+Fe Ng/Mg+Fe and and Ferroactinolite Ca/Mg+Fe ratios than ferroactinolite coexisting with with grunerite grunerite and and hornhorn— Ca/Mg+Fe ratios than ferroactinolite blende. Grunerite Gruncrite in the two two phase assemblage assemblage has has lower lower MgIMg+Fe Mg/Mg+Fe ratios ratios and higher Ca/Mg±Fe Ca!Mg+Fe ratios than than in in the the three three phase phase assemblage. assemblage. Cumming— Cumming- tonite with gedrite gedrite has has higher higher Mg!Mg+Fe Mg/Mg±Fe and and lower lower Ca/Mg+Fe tcnite coexisting coexisting with ratios ratios than cummingtonite cucrmingtonite coexisting coexisting with with actinolite. actinolite. The the chemistry the The composition composition of of the the amphiboles amphiboics is is related related to to the chemistry of of the rocks. The in magnetite sections of the The Fe-rich Fe—rich amphiboles amphiboles occur occur in magnetite deficient deficient sections of the iron formation. formation. The magnetite. The Fe-poor Fe—poor amphiboles occur with magnetite. The !1g-rich Mg—rich The amphiboics occur in a transition amphiboles transition zone zone surrounding surrounding aa talc talc schist. schist. �—24— -24- PRELIMINARY RESULTS OF A A TRUCK-MOUNTED MAGNETOMETER SURVEY OF THE THE SURVEY OF THE SOUTHWEST QUARTER OF IRON QUADRANGLE, MICHIGAN AND AND WISCONSIN WISCONSIN IRON RIVER 10x2° l°x2° QUADRANGLE, R. King and and William William F. F. Cannon Cannon Elizabeth R. U.S. Geological Survey U.S. Survey Reston, Virginia 22092 22092 Reston, ABSTRACT In August August of of 1978, 1978, the U.S. U.S. Geological Survey In Survey made made aa survey survey of of the the southwest quarter of the southwest the Iron River l°x2° 10x2° quadrangle, quadrangle, Mich.—Wis., Mich.-Wis., using using a truck—mounted This work, work, which is part truck-mounted magnetometer. magnetometer. This part of of aa mapping resource-evaluation program in in the the Iron Iron River and resource—evaluation River quadrangle, quadrangle, was was done done over poorly exposed Proterozojc Proterozoic and and Archean Archean terrane, terrane, which which is is covered covered by a thick thick layer layer of glacial alluvium. alluvium. The survey consisted of 470 miles traverses generally of nearly 470 miles of of traverses generally The traverses in aa north—south north-south direction. direction. The traverses were done over over oriented in selected unpaved forest forest roads roads to to minimize minimize the the effects effects of of heavy heavy traffic traffic and of steel in in the the roadbed. roadbed. The system used a fluxgate fluxgate magnetometer magnetometer on aa boom on the the top top of the the truck, truck, and the the variations in the the mounted on total field were recorded in in both analog analog and and digital digital form. form. total magnetic magnetic field The purpose of the the survey survey was to to augment augment existing existing aeromagnetic aeromagnetic coverage, which which was was flown coverage, flown at a 1/2—mile 1/2-mile line line spacing spacing and and at at an an elevation elevation of 500 ft. above the surface, with with ground-level ground—level magnetic magnetic data data to aid in in of ft. above the surface, to aid detailed geologic geologic interpretations. interpretations. A A number of domal domal uplifts uplifts have have been been both mapped and inferred inferred from from sharp sharp linear linear magnetic magnetic anomalies anomalies that that outoutline them. them. The Archean Precambrian gneisses in in the the cores cores of of these these domes domes have relatively low magnetic relief, relief, as as do do the the metasedimentary metasedimentary rocks rocks of of the overlying overlying Michigamme Michigamme Formation, the Formation, and are not readily readily distinguishable distinguishable on the aeromagnetic aeromagnetic map. map. However, However, there there are subtle differences differences in the magnetic signatures between the Michi— the almost magnetically featureless featureless Michigamme rocks. These differences gainme slates slates and and the the more more variable variable gneissic rocks. can be observed on the the detailed detailed ground ground magnetic magnetic profiles profiles and and permit permit more more accurate interpretation of the the aeromagnetic aeromagnetic map. map. complex system system of of faults faults having having predominant predominant The The area has has been cut by a complex northwest and northeast trends, trends, some some with considerable horizontal horizontal and and vertical displacements, of displacements, which are apparent from the magnetic pattern of the the contoured contoured aeromagnetic data and the the ground profiles. profiles. The magnetic profiles also also detect detect relatively relatively low amplitude, amplitude, sharp sharp negative negative magnetic magnetic profiles anomalies anomalies associated with a series series of of reversely reversely magnetized magnetized Keweenawan Keweenawan diabase dikes djabase dikes striking approximately east. east. �~25- FORMATION CONTACT METAMORPHISM OF THE VIRGINIA FORMATION MINNAMAX DEPOSIT, ST. ST. LOUIS LOUIS CO., CO., MINNESOTA Mark Kirstein Department of Geclogy Geology University of Minnesota—Duluth Minnesota-Duluth Duluth, Minnesota 55812 Duluth, 55812 ABSTRACT Calc-silicate Calc—silicate bodies occur in the Virginia Formation Formation and and as ns xenoliths xenoliths in metadiabase dikes near the contact with the the base of of the the Duluth Duluth Complex Complex in the Minnamax Deposit, Deposit, St. St. Louis County, County, Minnesota. The rocks of of the the footwall footwall have been matamorphosed to to the the pyroxene pyroxene hornfels hornfels facies. facies. Later sulfide mineralization is present in in all metamorphic rocks. rocks. The calc—silicate calc-silicate bodies are are ellipsoidal ellipsoidal to to spherical spherical and and range range in in length from 4 inches to to 44 feet. feet. They are generally generally light light gray gray and and are are fine to fine to medium grained grained granofels. granofels. There are are three three types types of of bodies: bodies: (a) (a) homogenous, (b) (b) layered, layered, with alternating alternating layers layers of of leucoxene leucoxene or or diopside, diopside, homogenous, and (c) concentric' two distinct mineral layers. layers. The most and Cc) concentric showing at at least two common mineral assemblages are diopside and wallastonite with either common mineral assemblages either grossularite or or anorthite. anorthite. Accessory minerals include include ilmenite, ilmenite, sphene, sphene, and leucoxene. Later sulfide replacement occurs with chalcopyrite, and chalcopyrite, exsolved exsolvcd cubanite, and Associated with cubanite, a~d minor magnetite. with the the sulfide sulfide mineralization mineralization is the the development development of of poikiloblastic quartz, is quartz, calcite, and and apophyllite apophyllite with minor anhydrite, and laumontite. laumontite. minor anhydrite, fluorite, fluorite, humite, humte, and The Virginia Formation, Formation, a pelitic hornfels, hornfels, and and later later metadiabase metadiabase dikes look almost identical in in hand sample. sample. They are fine fine grained, grained, massive, massive, and dark dark gray. gray. Relict bedding, bedding, when seen seen in in the the hornfels, hornfels, is is highly highly concontorted and discontinuous. The hornfels consists dominatly torted dominntly of of equigranular equigranular plagioclase, cordierite, and hypersthcne hypersthene with with minor minor quartz, quartz, untwinned plagioclase, apatite, and and graphite. graphite. Biotite and orthoclase orthoclase occur occur locally. locally. Black "reacticn" "reaction" rims rims exist for for 3 inches into into the the hornfels when in in contact contact with with calc—silicate bodies. calc-silicate bodies. The rima rims consist of plagioclase, plagioclase, hypersthene, and and poikiloblastic augite. augite. The metadiabase dikes dikes consist consist primarily primarily of of lathy lathy interstitial hypersthene hypersthene and and augite. augite. Ilmenite, quartz, quartz, labradorite with interstitial and apatite occur as accessory accessory minerals. minerals. Sulfides in the the hornfels consist consist of pyrrhotite with exsolved pentlandite, pentlandite, chalcopyrite, chalcopyrite, and and minor minor magnetite magnetite and ilmenite. ilmenite. Sulfides Sulfides in the metadiabase are restricted restricted to to fractures fractures and and are dominatly composed of are of pyrrhotite. pyrrhotite. The calc—silicate calc-silicate bodies show metasomatic effects effects with aa gain gain of of aluminum and and aa loss loss of of calcium. calcium. This is responsible for for the the formation formation of of the "reaction" rims. the rims. Some the bodies may bc the top top of the the Some of of the be from the that were brought up up by by the the intrusion intrusion of of the the Duluth Duluth Biwabik Iron Formation that Complex. The to have originated as concretions in in the the The majority appear to Virginia Formation. Formation. The sulfides and associated silicates silicates are are related related to to a a later retrograde retrograde metamorphic metamorphic event. event. �—26— -26- GEOLOGIC INTERPRETATION OF GRAVITY DATA DATA IN IN THE THE MARENISCO-WATERSMEET AREA, AREA, NORTHERN MIGHIGAN J. S. Kiasner, Klasner, U. U. S. University, J. S. S. Geological Geological Survey Survey and and Western Illinois University, S. Geological Survey, Macomb, Illinois Illinois 61455, 61455, P. P. K. K. Sims, Sims, U. U. S. Survey, Denver, Denver, Macomb, Colorado, Colorado, 80225, 80225, and S. S. A. A. Jankowski, Jankowski, Department of of Geology, Geology, Western Western Illinois 61455 Illinois University, University, Macomb, Macomb, Illinois Illinois 61455 ABSTRACT Geophysical studies have been conducted in in the the western part part of of northern Michigan to aid in determining the the geology geology of of the the tectonic tectonic zone zone marking the the boundary between between two two Archean Archean terranes terranes recognized recognized in in the the Lake Lake Superior region;.a region;. a greenstone—granite greenstone-granite terrane terrane on on the the north north and and aa gneiss gneiss terrane on the the south. south. A the area having aa 22 milligal milligal contour contour A gravity map of the interval stations. The map interval was was prepared prepared using using data data from approximately 310 stations. includes gravity readings obtained includes obtained along along 33 profiles profiles with with 300 300 in m station station spacing to to aid in in interpretation interpretation of of the the data. data. The gravity anomalies generally are in The in good agreement agreement with the the mapped mapped geology. Pronounced lows coincide coincide with the the large large pluton pluton of of Archean Archean Puritan Quartz Monzonite west of Lake Gogebic and and the the Archean Archean gneiss gneiss dome dome Small positive anomalies anomalies coincide with synclinal basins near Watersmeet. Small of the lower Proterozoic Formations and and with magnetic of Proterozoic Copps Copps and and Michiganmie Michigamme Formations anomalies interpreted as being caused anomalies caused by lean lean iron—formation iron-formation and and associated associated rocks. Amphibolitic layers layers in in both the the quartz quartz monzonite monzonite and and the the gneiss gneiss also have positive gravity gravity anomalies. anomalies. A A relatively steep steep (approximately (approximately 5 milligals per km) km) north—sloping north-sloping gradient coincides coincides with the the inferred inferred position of of the the boundary zone zone between the the Archean greenstone greenstone and and gneiss gneiss terranes. A two—dimensional A two-dimensional gravity model consistent consistent with mapped geologic geologic units units and measured rock densities suggests that that the the synclinal synclinal basin basin within within the the greenstone terrane which involves involves the the Copps Copps Formation Formation is is about about 2.0 2.0 km km deep, deep, whereas the gneiss terrane which includes Michigamme the basin within the gneiss terrane which includes the the Michigamme Formation may be approximately 33 km deep. deep. A north-sloping north—sloping regional gravity gradient extrapolated A extrapolated from from data data outoutside the study area corresponds with the the boundary zone zone between between the the two two basement terranes and reflects an increase increase in in density density from from north north to to south south rocks of the the upper crust and perhaps also also in in the the lower lower crust crust and/or and/or in rocks upper mantle. �—27— -27- CROSS FOLDING IN THE PRECAMBRIAN CROSS PRECAMBRIAN X STRATA STRATA OF OF THE THE EASTERN EASTERN MARQUETTE MARQUETTE TROUGH, TROUGH, MICHIGAN MICHIGAN D. D. K. K. Larue Larue F. F. W. W. Cambray Cambray Michigan State University Michigan State Northwestern University Evanston, Illinois 60201 East Lansing, Lansing, Michigan 48824 ABSTRACT X Chocolay and Menominee Group strata The Precambrian X strata in in the the eastern Marquette trough trough of Michigan show evidence evidence of of two two episodes episodes of of deformation. The first and major nlajor deformation deformation CD1) (Dl) folded folded the the strata strata E-W slaty slaty cleavage cleavage (S1). (Sl). The second, second, less less intense intense and formed vertical E—W deformation (D2) (D2) locally formed cross cross folds of of bedding bedding and and folded folded cleavage. The major synclinal fold fold in the the trough, trough, termed termed the the Marquette syn— synclinorium, was Dl deformation. Macroscopic D1 Dl folds folds are are clinoriuni, was formed formed by by the D1 confined to the the hinge region of this this synclinorium (e.g., (~.£., Harvey Harvey Quarry, Quarry, Marquette). Minor Dl fold axes plunge gently gently to to the the EE or or WW in in vertical vertical E—W E-W axial planes. planes. At localities, the Enchantment Lake Formation along along U.S. U.S. 41 41 in in At two localities, Negaunee and the Kona Formation in Sec. Sec. 32, T48N, T48N, R26W, R26W, Negaunee, Negaunee, the the quartzose beds beds exhibit minor folds folds with steeply plunging plunging axes, axes, F2, F2, and and aa vertical NW—SE NW-SE axial axial plane, plane, S2. S2. These minor folds folds have an an S—shaped S-shaped profile profile and can be shown to to deform deform Sl. Sl. Similar features features of minor folds folds can be (northeast shore of of Teal Lake), Lake), in in the Mesnard observed in the Siamo Slate (northeast Marquette), and in Quartzite (shore (shore of Lake Superior, Superior, Marquette), in the the Negaunee Negaunee Iron Iron Formation (New (New Richmond Mine, Palmer, and on Jasper Knob, Knob, Negaunee). Negaunee). These Mine, Palmer, lithologies rarely develop cleavage so it it is is not possible to to determine determine the the sequence of folding directly. directly. However, However, minor folds folds showing showing steeply steeply plunging plunging fold axes fold axes are thought to have been superimposed on the the already already steeply steeply dipdipping limbs of In addition, addition, small intrafolial of the the Marquette Marquette synclinorium. synclinorium. In folds in bedding with an E—W folds E-W axial surface and steep plunge can can be seen seen on on an island in Teal Lake and are attributed to to the the D2 episode. episode. folds in the Marquette synclinorium exhibit aa somewhat The major folds variable fold—axis fold-axis orientation orientation from from south south of of west west to to north north of of west, west, as as exhibited by the Goose Lake syncline and the the folds folds associated with the the Isabella syncline in in the the Palmer Palmer area. area. These major folds folds may be either refolded D1 Dl folds or or both both D1 Dl and and D2 D2 folds. folds. Absence of a pervasive slaty cleavage makes assignment assignment difficult. difficult. The sequence of events is is consistent consistent with aa north—south north-south compression compression to to D1 structures, structures, followed by a NE—SW produce Dl NE-SW compression to to form form the the D2 D2 structures. The NE—SW NE-SW compression could could be induced induced by aa left—lateral left-lateral strike— strikeslip movement on the Marquette trough in the the late late stages of of D1 Dl compression. compression. Such displacement shortening displacement would would be expected if the regional directions of shortening during Dl D1 were were not not precisely orthogonal to during to the the trough. trough. It is interesting interesting to note that It is to note that the the regional regional shortening represented by D2 has a similar orientation to to that that represented represented by the the folds folds in in the the Republic trough. trough. �—28--28- PETROLOGY OF THE TROCTOLITE—OLIVINE TROCTOLITE-OLIVINE GABBRO SERIES, SERIES, DULUTH DULUTH GABBRO GABBRO COMPLEX COMPLEX (LATE (LATE PRECAMBRIAN) NORTHEASTERN NORTHEASTERN CRAMER CRAMER QUADRANGLE, LAKE AND AND COOK COOK COUNTIES, QUADRANGLE, LAKE COUNTIES, MINNESOTA MINNESOTA George Lehman Dames and Moore Co. Co. Lakewood, Colorado Colorado 80401 and Donald M. Davidson, Davidson, Jr. Jr. Donald ~. Dept. Dept. Geological Sciences Sciences University of Texas, Texas, El Paso El Paso, Paso, Texas Texas 79968 in the the northeast quarter quarter of of the the Cramer Cramer quadrangle, quadrangle, MinneMinneAs observed in sota, textures, the orientation of igneous igneous laminations, laminations, systematic systematic sota, rock textures, in modal abundances abundances of of minerals as as well well as as the the chemical chemical comcomvariations in of major minerals Indicate position of indicate that that the the troctolite—olivine troctolite-olivine gabbro gabbro series series in the Duluth Gabbro Complex (Keweenawan) differentiated differentiated in situ situ as Complex (Keweenawan) as a a result of crystal crystal settling. settling. Here, Here, the the troctolite—olivine troctolite-olivine gabbro gabbro series series is is exposed as as a southwest—northeast trending band of outcrops approximately exposed a southwest-northeast approximately two two km in in width which lies lies between two two distinct distinct terrains. terrains. The area to to the the northwest is is dominated by rocks rocks of of the the anorthosite anorthosite and and felsic felsic series series while while the area to southeast contains flow units of the the area to the the southeast the North North Shore Shore Volcanic Volcanic Group. The general orientation of igneous igneous laminations laminations (N6OE, (N60E, 15SE) lSSE) within within the the troctolite—olivine gabbro gabbro series troctolite-olivine series is interpreted to to be be the the result result of of gravity gravity settling, suggesting that that the the unit has has tilted tilted approximately approximately 15 IS degrees degrees toward toward settling, the southeast since solidification. The general strike of the of the the troctolite troctolite unit is parallel to to a well defined defined lineament lineament which which occurs occurs along along the the northnorthwestern contact contact of of the the unit. unit. Textures Textures of of the troctolitic troctolitic and and gabbroic gabbroic rocks rocks indicate indicate that, that, in in general, general, plagioclase and olivine are are cummulate, cummulate, while pyroxenes pyroxenes and and oxides oxides are are interinterstitial. stitial. Modal analyses show that rocks rocks of troctolitic troctolitic affinity affinity (P1 (PI -— 70%; Cpyx —- 10%; 01 — - 16%) are the northwest boundary (base?) (base?) are abundant abundant along the is the the most abundant while olivine gabbro (P1 (PI —- 68%; Cpyx —- 22%; 01 —- 8%) is lithology along along the the southeastern southeastern contact contact (top?). (top?). Interstitial ilmenite is is the major major oxide oxide component and occurs as 1—1.5% the 1-1.5% of the the rock rock unit. unit. Electron microscope analyses of of plagioclase, plagioclase, olivine, olivine, and and pyroxene pyroxene mineral grains from rocks of the troctolite series vary vary nearly continuously and systematically in in composition composition upward upward through through the the column. column. These compositional variations are: are: An77 to to An58 AnS8 (plag), (plaf,), Fo70 Fo 70 to to Fo50 FoSO (01), (01), and and Wo41 En45 Fs14 to Wo38 En36 Fs26 (Cpyx). W0 4l En4S FS 1 4 to W038 En36 FS 26 (Cpyx). the troctolite—olivine troctolite-olivine gabbro gabbro series series as as calculated calculated The bulk composition of the from modal abundance data data and and individual individual mineral mineral compositions compositions suggests suggests that that the could have been derived from aa magma with aa composition composition identical identical the series series could to that of the chilled margin of the the Pigeon Point Point sill. sill. The results of of this this to that of the investigajion support the investigation the model proposed by Weiblen which indicates indicates that that units units the Duluth Complex Complex (other (other than than the the anorthosite anorthosite and and felsic felsic series) series) have have of the been derived from from aa late late stage, stage, high—Al high-Al magma, magma, the the composition composition of of which which is is compatable with the the Pigeon Pigeon Point Point sill. sill. �—29— -Z9- GEOLOGY OF THE DULUTH COMPLEX-VIRGINIA FORMATION CONTACT MINNAMAX DEPOSIT, MINNAN.AX DEPOSIT, MINNESOTA MINNESOTA William Matlack Department of Geology University of Minnesota-Duluth Minnesota—Duluth Duluth, Minnesota 55812 Duluth, 5581Z Deposit, near Babbitt, Babbitt, Minnesota, is is aa large, large, low— lowThe Minnarnax Minnamax Deposit, sulfides at at the of the grade deposit deposit of of iron—copper—nickel iron-capper-nickel sulfides the contact contact of the and the the Virginia Formation. Formation. Mineralization is is primarily Duluth Complex and disseminated disseminated in in troctolitic troctolitic rocks rocks of of the the Duluth Duluth Complex, Complex, and and is is locally locally massive at the the contact and in the immediately adjacent Virginia Formation. tion. ° In In the the Minnamax test shaft area, area, the the contact contact dips dips 0 to to 35 35 degrees degrees is highly irregular. irregular. Apophyses Apophyses of the the Duluth Complex intrude SE and is the Formation and and xenoliths xenoliths of of the the Virginia Virginia Forrna— Formathe underlying Virginia Formation tion, feet in dimension, dimension, occur occur in in the the complex. complex. tion, ranging ranging upwards upwards of of 150 feet primarily of of argillic argillic hornfels hornfels with with The Virginia Formation consists consists primarily calc-silicate concretions. concretions. Minor lithologies include include graphite abundant calc—silicate Bedding, schist, schist, and calcareous argillic argillic hornfels. hornfels. Bedding, schist, biotite schist, where visible, for a a few feet feet and is locally locally conconvisible, can only be traced for and is torted; concretions appear randomly oriented. oriented. Metadiabase dikes dikes and and torted; concretions sills, metamorphosed metamorphosed by by the the Duluth Duluth Complex, Complex, occur occur in in the the Virginia Virginia sills, Formation. The Duluth Complex consists primarily of a mineralized phase which is characteristically troctolitic. troctolitic. Near the the contact contact it it is is commonly noritic. Here it contains cumulus cumulus plagioclase and intercumulus hypersthene, olivine, olivine, and and augite, augite, and and is is highly highly variable variable in in composition, composition, hypersthene, texture, Sulfides are primarily interstitial texture, and sulfide sulfirle content. content. Sulfides interstitial to to Xenoliths of of an an unmineralized unmineralized phase, phase, ranging ranging upwards upwards of of 100 100 silicates. Xenoliths feet in dimension, dimension, occur in in the the mineralized mineralized phase. phase. These xenoliths feet range from olivine olivine gabbro gabbro to feldspathic peridotite, peridotite, and and range in composition composition from to feldspathic Fractures and cumulus olivine olivine and and plagioclase. plagioclase. are characterized by cumulus breccia zones, zones, both in in the the Virginia Virginia Formation Formation and and the the Duluth Duluth Complex, Complex, commonly contain ides and and granitic granitic veins veins and veinlets. contain massive massive sulf sulfides Sulf ides locally locally replace replace hornfels, hornfels, particularly particularly at at the Duluth Complex Sulfides Complex contact. Field relationships and and petrography petrograhy indicate Field relationships indicate that that the the Virginia Virginia and metamorphosed to pyroxene hornfels Formation was was highly highly deformed deformed and metamorphosed to hornfels facies facies by the the Duluth Duluth Complex. Complex. The common cornmon pelitic mineral assemblage assemblage of of plagioclase—hypersthene—cordierite plagioclase-hypersthene-cordierite suggests suggests substantial substantial loss loss of of Si02, SiOZ, Na20, from the the Virginia Virginia Formation Formation (Bonnichsen, NaZO, K20, KZO, and and 1120 HZO from (Bonnichsen, 1971). 1971). These constituents constituents contaminated contaminated the the base base of of the the mineralized mineralized phase phase of of the the comcomplex. formed from a residual fluid of Granitic vein material may have formed the the mineralized mineralized phase, phase, or or by by direct direct partial partial melting melting of of the the Virginia Virginia Formation. of unmineralized metadiabase dikes and sills in Recognition of the Virginia Formation explains many complexities complexities in in the the petrology, petrology, the structure, of the the contact contact zone. zone. Massive sulfides sulfides structure, and mineralization of appear to to have formed formed by: by: 1) 1) migration of a sulfide—rich sulfide-rich fluid into into and along fractures, and fractures, and and 2) Z) local the Virginia Formation. Formation. local replacement of the �-30MINERAL SURVEY MINERAL SURVEY AND MINERAL POTENTIAL OF COOK COUNTY, COUNTY, MINNESOTA M.P. and D.G. M.P. McKenna, McKenna, L.W. L.W. Gladen, Gladen, M.K. M.K. Vadis, Vadis, and D.G. Meineke Resources, Division Division of of Minerals Minerals Department of Natural Resources, P.O. 567 P.O. Box 567 Hibbing, 55746 Hibbing, Minnesota 55746 ABSTRACT ABSTRACT This This study was was conducted to to obtain and compile information on on the the mineral potential potential of of Cook Cook County, County, Minnesota. Minnesota. This This information will be used to the Minnesota Department of Natural Resources Resources (MDNR) (MDNR) in in making making to assist assist the decisions in in relation to to mineral lands it land management management decisions mineral lands it administers administers and and to to provide provide information which may lead to to further further leasing leasing and and exploration exploration of of MDNR administered administered lands. lands. The study included included various various informatfon information gathering gathering activities. activities. Initially, aa literature survey was conducted to to determine determine the the existence existence and and location location of of reported economic mineral occurrences. This was followed by reported by aa field field examinexamination, during during which which outcrop outcrop samples samples were were collected collected for for assay assay and and microscopic microscopic ation, study study in in order order to to determine determine the the nature nature and and extent extent of of mineralization mineralization and and the the host rock rock geology. geology. A A compendium was prepared on past mineral exploration activity in in Cook Cook County; County; it it includes includes available available drill drill logs logs and and assays, assays, geologic, geologic, geophysical, and geochemical In some some cases, cases, where drill logs and assays geophysical, geochemical data. data. In were not available, the the cores cores were were logged logged and and assayed. assayed. An organic'-rich organic--rich lake sediment e~~loration exploration geochemical reconnaissance sediment reconnaissance survey survey was was conducted conducted concurconcurthe field field examination examination of of mineral mineral occurrences. occurrences. rently with the A report will contain all derived A report is is in preparation which will all information derived from this study. study. It It also describes the the various models models which which were were used used in in models are are based based on the mineral potential potential of of the the area. area. These models determining the economic mineral occurrences occurrences found Minnesota and and in similar environ— economic mineral found in Minnesota similar geologic geologic environments in other parts of ments of the the world. Results Results of of this this study indicate indicate that that significant significant vanadium concentrations concentrations exist in titaniferous magnetlte magnetite deposits deposits occurring occurring within within the the Duluth Duluth Complex. Complex. Disseminated low grade grade Cu-Ni in the the more Cu—Ni mineralization also also occurs occurs in more mafic mafic units of the the Duluth Duluth Complex. Complex. Ag—Cu—Zn Ag-Cu-Zn fissure—vein fissure-vein mineralization occurs in the Rove Formation where the the Rove Rove is is intruded intruded by by Logan Logan sills. sills. The lake lake sedisedithe ment geochemical geochemical survey survey indicates indicates anomalous values in in certain areas which have potential for for economic economic mineralization. mineralization. survey did did not not include include the the Boundary Boundary Waters Waters Canoe Canoe Area Area (BWCA); (BWCA); This survey however, however, some some of the the highest mineral potential areas in Cook County were added added to to the BWCA after the the field field surveys surveys were were completed. completed. �—31— -31- PALEOSTRAIN ANALYSIS ACROSS AA "SHEAR "SHEAR ZONE", ZONE", NORTHWESTERN MARATHON COUNTY, COUNTY, WISCONSIN Elizabeth Palmer Department of Geology University of Minnesota Duluth, Minnesota Duluth~ and N. Davidson, Jr. Donald M. Jr. Department of of Geological Geological Sciences Sciences University of of Texas Texas El Paso, Paso, Texas Texas ABS TRACT ABSTRACT The boundary between two major trending Precambrian terranes between two major northeast northeast trending Precambrian terranes (superbelts?) is is structurally structurally concordant concordant with geological units which (superbelts?) which trend trend approximately 750 approximately 75 0 through Athens, Athens, Wisconsin vTisconsin in in northwestern northwestern Marathon Marathon County. County. This 0.75 to width, generally, generally, though not This belt or "shear" "shear" zone, zone, 0.75 to 4 km in width, though not uniquely, gneissic amphibolites amphibolites of of the uniquely, separates separates gneissic the Chippewa Amphibolite ComCom(Archean?) to to the north from volcano-plutonic (greenstone-granite plex (Archean?) north from volcano—plutonic (greenstone—granite units (PG (P8 x?) on on the the south. south. Foliations within the host host rock strike 50_700 50-70 0 and dip dip 50—75° 50-75 0 N N while 0 0 lineations trend trend 230_2500, 230-250 , and and plunge plunge 65—75°. 65-75 . The zone itself has gradational gradational boundaries and is is composed of of cataclasized equivalent greenstone and amphibo— amphibolite units showing showing mortar mortar texture, texture, feldspathic feldspathic porphyroclasts, porphyroclasts, comminution comminution lite units and structure, and varying degrees degrees of of recrystallization. recrystallization. Discrete and fluxion fluxion structure, fault fault planes have also been recognized recognized within within the the zone. zone. Paleostrain Paleostrain analysis analysis was was carried carried out out on on samples samples from from each each host host unit unit at at distances up up to km from from the the shear shear zone zone as as well well as as on on samples samples located located distances to 99 km within the the zone zone itself. itself. At least 50 strain indicators, indicators, usually deformed fragments, were measured from 3 sets of orthogonal mineral grains or volcanic fragments, faces cut on to the the principal faces cut on each each sample sample as as well well as as the the angle angle relative relative to principal directions directions (foliation, (foliation, lineation lineation and and right right angles angles to to both) both) in in the the rock parallel to to which cuts cuts were were made. made. Strain was the methods of of was analyzed using the Ramsay (Rf/Q), Ramsay (Rf/8), Elliott's polar polar plot plot and and the the Hsu Hsu plot. plot. A fit strain A best best fit for each each sample sample using using the the Pase Pase 55 program program of of Siddans. Siddans. ellipsoid was was calculated for Error the best Error limits limits on on the the dimension dimension and and orientation orientation of of the best fit fit strain ellipsoid and its its orientation orientation were were calculated calculated at at less less than percent for for each each soid and than 2 percent sample. Results indicate that that both the gneiss Results indicate both the gneiss and and volcano-plutonic volcano—plutonic regimes regimes are characterized by fabric (V=+O.16, (V=+0.16, 0.19, characterized by aa flattened flattened fabric 0.19, 0.3; 0.3; K=0.4) K=O.4) with with generally low strain values (G5=O.75, (8 s =0.75, 1.29, 1.29, 0.5). 0.5). As the the shear shear zone zone is is approached, (V=-0.5; K=2.4) is approached, aa strong strong linear linear fabric fabric (V=—O.5; K=2.4) is is developed developed which is generally one order of magnitude greater greater in in €s value than than is is flattening flattening in in the host host rocks. the rocks. This This linear linear fabric fabric cannot cannot have have developed developed from simple shear alone. alorre. The lineation appears to have as aa result The lineation appears to have developed developed as result of of ductile deformation along the the deformation which, which, though though regional regional in in scope, scope, appears appears localized localized along zone. zone. A consistent with the strain A strong strong vertical vertical stress stress component component appears appears consistent pattern. �—32— -32- POLYPHASE DEFORMATION DEFORMATION OF OF ARCHEAN ARCHEAN ROCKS ROCKS POLYPHASE AT AT RAINY RAINY LAKE, LAKE, ONTARIO ONTARIO K. K. Howard Howard Poulsen Department of Geology Geology Lakehead University Thunder Bay, Bay, Ontario ABSTRACT The Archean geology geology of of the the Rainy Rainy Lake Lake area area has has been been the the subject subject of of considerable study study for considerable for nearly a a century. century. A.C. A.C. Lawson Lawson mapped mapped the the region region (1888, 1913) 1913) and and interpreted the (1888, the stratigraphy. stratigraphy. He placed aa sequence sequence of of metasedimentary metasedimentary biotite schists schists (the (the Coutchiching Group) Group) beneath beneath aa sequence sequence He further of metavolcanic schists schists (the (the Keewatin Keewatin Group). Group). He further recognized a second sequence of metasedimentary rocks (the of largely largely congloineratic conglomeratic metasedimentary (the Seine Seine Group) which he placed unconformably above Group) above the the Keewatin. Keewatin. Various workers re-studied the the area applying the the techniques techniques of a a number of geological have re—studied subdisciplines. Some of the the Coutchiching Coutchiching Group Group Some have have disputed the existence of and have placed it above the and the Keewatin as as aa lateral lateral equivalant equivalant of of the the Seine Seine Group. Others have have upheld upheld Lawson's Lawson's original original interpretation interpretation and and the the conconOthers flicting points the Seine-·Coutchiching flicting points of of view view have have become become referred referred to to as as the Seine-Coutchiching problem. proble~. present study re—examines re-examines the the significance of the Keewatin— KeewatinThe present boundary in in light light of of detailed detailed structural structural investigation investigation of of two two Coutchiching boundary type localities. At Rice Bay, and geometric analysis of of fabric At Bay, lithological mapping and geometric analysis fabric reveals the the presence presence of of aa major major antiform antiform with with moderate moderate plunge. plunge. elements reveals Observed younging information (graded (graded bedding and and pillow shapes) shapes) does does not not to this this simple simple interpretation interpretation and and part part of of the the sequence sequence is is recognized recognized conform to as having a downward structural structural facing facing with with respect respect to to the the major major fold fold closure. closu~e. This implies that that the the sequence sequence was was overturned overturned by by an an episode episode of of folding folding (F1) (F l ) predated the the development development of of the the major major closure closure (F2). (F 2 ). which predated At Bear Passage, Passage, structural structural elements elements similar similar to at Rice Rice Bay Bay are are At to those those at Fold axes axes (F2) axial surfaces surfaces (S2) no longer have systematic systematic exposed. (F2) and and axial (S2) no longer have orientations, however, however, and and appear appear to be complexly due to orientations, to be complexly redistributed redistributed due to the the intrusion of a quartz monzonite pluton. The crest of this pluton conforms pluton. The conforms to to a a broadly antiformal antiformal structure structure (F3). (F 3 ). The rocks rocks of of the the Bear Bear Passage Passage area area are are transected by by aa penetrative crenulation cleavage S4 transected S4 which which is is axial axial planar planar to to minor folds folds (F4). (F4). While simple stratigraphic interpretations interpretations are precluded precluded by this this polyphase deformation, deformation, a a key exposure at at the the Keewatin—Coutchiching Keewatin-Coutchiching contact reveals the contact the presence of of structurally structurally overturned overturned strata. strata. These strata appear to appear to have a a downward structural structural facing facing with with respect respect to to each each of of the the observed fold observed fold phases and hence overturning overturning is is assigned assigned to to F1. Fl. The documentation of polyphase deformation The deformation in in the the Rainy Rainy Lake Lake area area makes makes clear the clear the reason for for previous conflicting conflicting stratigraphic stratigraphic interpretations. interpretations. The of structurally overturned strata recognition of strata favours favours the the stratigraphic stratigraphic supersuper" Fold nappes (F1) position of the the Coutchiching Coutchiching upon upon the the Keewatin. Keewatin. (FI) may have responsible for for inverting inverting part part of of the the sequence. sequence. It It is not clear clear whether whether been responsible this and subsequent deformations were unique this and unique events events or or merely merely progressive progressive episodes in in a a continuous continuous sequence sequence of of deformation. deformation. �—33 -33- THE PRECAMBRIAN PRECf~BRIAN BASEMENT OF NORTH DAKOTA John T. T. Ray Ray and John and Frank R. R. Karner North Dakota Geological Geological Survey Survey and and University of North Dakota Grand Grand Forks, Forks, North Dakota Dakota 58202 58202 ABSTRACT Information on on the Information the Precambrian basement of of North North Dakota Dakota is is based based on on cores and and cuttings cuttings from 132 drilling tests cores tests (Lidiak, (Lidiak, unpublished; unpublished; Muehiberger Muehlberger and others, 1967; Moore, unpublished), unpublished), 11 age age determinations determinations (Peterman and and ethers, 1967; Moore, (Peterman and Hedge, data and and correlation correlation with with surrounding areas areas of of Hedge, 1964), 1964), geophysical geophysical data exposure. The North North Dakota Dakota Precambrian Precambrian consists consists of of several several types of Archean Archean The types of Superior Province Province and and possibly younger terranes Superior terranes in in the the east, east, often often with with deep deep profiles, and and much much less less well well known known terranes in the west, including weathering profiles, terranes in the west, younger rocks, rocks, possibly aa southern southern extension extension of of the the Churchill Churchill Province. Province. The Williston basin, basin, centered centered in northwestern ~orth North Dakota, Dakota, is is the dominant strucstrucWilliston in northwestern the dominant tural that determines the depth to to the the Precambrian. Precambrian. From aa depth of tural feature feature that determines the approximately 200 m the Precambrian approximately 200 m in in eastern eastern North North Dakota, Dakota, the Precambrian surface surface slopes slopes The distribution of 3 rn/kin m/km totoa adepth of radiometric radiometric age age S depthof of 5100 5100 m m in in the west. dates and dates and a pronounced break in in the the trend trend of of geophysical geophysical features features suggests suggests that the the Superior/Churchill Superior/Churchill Provincial boundary transects that transects central central North North Dakota. The Precambrian Precambrian basement basement of of east2rn eastern North North Dakota Dakota has has been been divided divided into into The five terranes terranes based based on on predominant predominant petrographic character five character and and r2gional regional gravity gravity features (Lidiak, unpublished). Amphibole Amphibole schist schist terrane is characterized by features (Lidiak, belts of belts of low and medium grade grade metamorphic rocks rocks with with associated associated gravity gravity highs. highs. The predominant predominant rock rock types types are arc actinolite actinolite and and hornblende hornblende schists schists with with occuroccurThe rences rences of of retrogressive quartz—biotite—feldspar quartz-biotitc-feldspar gneiss, gneiss, serpentinite, serpentinite, stretched stretched lithic lapilli tuff, lithic tuff, massive and porphyritic porphyritic basalt basalt and and banded banded iron iron iron iron formaformaThe Ramsey Ramsey gneiss tion. The gneiss tërrane terrane consists of of silicic silicic to to intermediate intermediate rocks rocks with aa persistent The characteristic lithology persistent gneissic gneissic fabric. fabric. The lithology is is layered layered gneiss metamorphosed metamorphosed to amphibolite facies gneiss facies and and fine— fine- to to medium—grained medium-grained gneiss gneiss with subordinate foliated foliated plutonic plutonic rocks. rocks. The three terranes terranes are are The remaining three characterized by silicic silicic to to intermediate intermediate massive massive plutonic plutonic rocks rocks with with associated associated gravity gradient and are are distinguished by by location. location. The Grand Grand gravity lows lOWS of of gentle gradient terrane (east—central), (east-central), McIntosh ~1cIntosh granite granite terranc terrane (southeast), (southeast), Forks plutonic terrane and Towner terrane (north—central) (north~central) all and Towner granite granite terrane all contain contain occurrences occurrences of of amphiamphi— bolite facies faci2s gneiss. gneiss. The generalized pattern of large l3rgc plutonic plutonic areas ureas within gneissic terranes terranes and intervening intervening greenstone greenstone belts belts is is consistent consistent with with the the gneissic exposed 2XpOSeG Archean rocks rocks to to the the northeast. northeost. ~ew information infor~ation on the Precambrian of eastern North Dakota Dakota was New was added added by the Red River River Valley Valley drilling drilling program program of of 1977 1977 (Moore, (Moore, unpublished) unpublished) which which propro the Red vided 26 26 cores. ceres. Preliminary petrographic results results suggest suggest that that the the concept concept of the amphibole schist schist terrane terrane be be ret&ined retained and and the the distinction distinction of of the the remainremainof the amphibole ing tcrranes on the ing terranes on the basis of rock fabric fabric ha b2 abandoned. abandoned. Amphibole schist schist tcrrane terrane is is characterized charactGrized by ty low low to to medium mediu~ grade grade metasedimentary ~et3sedimentaryand and tnetavolcanic metavolcanic rocks sever. cores which included included the the following following rock rock types; types; rocks and and was was penetrated penetrated by seven pillowed basalt, basalt, porphyritic porphyritic basalt, basalt, stretched stretched lithic lithic lapilli l&pilli tuff, tuff, mica mica schist, schist, talc-chlorite schist, (with graded graded beds), beds), and and meta—graywacke. meta-graywacke. The talc—chlorite schist, phyllite (with remaining cores cores pen2trated penetrated fine— re~aining fine- to to coarse—grained coarse-grained igneous igneous rocks, rcck8, gneiss, gneiss, and and �—34— -34- banded gneiss. gneiss. The intcrpretation interpretation of the the dominant igneous igneous character of banded the Grand Grand Forks Forks plutonic plutonic terrane terrane is is revised revised by the occurrence of of rocks the the occurrence rocks with aa gneissic-migmatitic gneissic-migmatitic fabric fabric in in six six of of seven seven cores. cores. Accordingly, the distinction of the the remaining terranes terranes by predominant fabric fabric may be misleading and will be be eliminated. eliminated. Subdivision of these these gneissic gneissic and and the basis of rock rock chemistry and plutonic terranes is being attempted on the petrographic character. character. Lidiak, E. G., G., Buried Precambrian Rocks of North Dakota: Dakota: unpublished Lidiak, E. manuscript. Moore, W. W. L., 1978, AA Preliminary Preliminary Report Report on on the the Geology Geology of of the the Red Red River River Valley Drilling Project, Project, Eastern North Dakota and Northwestern Minnesota: unpublished manuscript. manuscript. Muehlbergcr, Muehlberger, W. W. R., R., R. R. E. E. Denison, Denison, E. E. G. G. Lidiak, Lidiak, 1967, 1967, Basement Rocks in in Interior of of United United States: States: AAPG Bull. v. 51, 51, no. no. 12, 12, Continental Interior p. 2351-2380. p. 2351—2380. Peterman, Z. Peterman, Z. E., E., and and C. C. E. E. Hedge, Hedge, 1964, 1964, Age of Basement Rocks from the the Basin of of North North Dakota Dakota and and Adjacent Adjacent Areas: Areas: USGS Prof. Prof. Williston Basin Paper, 475—D, Paper, 475-D, p. p. Dl00—D104. DlOO-Dl04. �—. -I — -35- PINK AND GREEN ALBITE PHENOCRYSTS FROM THE MOHAWK MINE, - INDICATORS OF CHANGES IN IN HYDROTHERMAL HYDROTHERMAL FLUIDS FLUIDS MINE, MICHIGAN - Nancy Scofield Institute of Institute of Mineral Research and and Department of Geology and and Geological Engineering Michigan Technological University Houghton, Houghton, Michigan 49931 49931 B. Jorgenson David B. Department of of Geology Geology Central Michigan University Mount Pleasant, Pleasant, Michigan 48859 ABSTRACT Albite phenocrysts phenocrysts with with green green rims and pink interiors Albite rims and interiors are are present in samples of altered altered basalt basalt taken from the and known to be presamples of taken from the Mohawk mine and In the #3 and and #4 #4 mines. mines. In the collected samples, samples, phenocrysts are sent in Ahmeek #3 5-20 rom long and and 1—10 1-10 mm mm wide. wide. Some the smaller phenocrysts are green 5—20 mm long Some of of the only. Microscopically, the green portion consists Microscopically, the green consists primarily of of pumpellyite with some white to to light light green green remnant remnant albite. albite. Some of the the pumpellyite pumpellyite extends into into the the pink pink interiors interiors which which are are predominantly predominantly albite albite with with an an extends abundance of of sericite as an alteration product. abundance product. Under high power, power, small amounts of of red red iron iron oxide oxide are are apparent apparent in in the the phenocryst phenocryst interior, interior, appearappearamounts ing as as clouds clouds or clots of dust—like ing dust-like particles. particles. Albite twin lamellae lamellae are are continuous through through the the green green and and pink pink portions portions of of the the phenocrysts phenocrysts although continuous masked by alteration in in the the pink pink portion. portion. Flat stage extinction angle measurements on albite albite twins twins suggest suggest a composition of about An5. AnS. X—ray X-ray diffraction analysis analysis of the phenocrysts verifies the the mixture of of albite and and pumpellyite pumpellyite in in the the green green rims, rims, with with albite albite showing showing up up as as the only albite Structural differences differences between between the pink and phase of of the the pink pink interiors. interiors. Structural green albite were not not detected. detected. Electron microprobe microprobe analyses analyses show pumpellyite compositions Electron compositions in green and pink portions portions to to be identical identical with total total iron, iron, calculated calculated as as FeO, FeO, about about 5%. 5%. in major element element compocompoAlbite compositions are near AnO with no difference in sition between the exception of of a range of K K between pink pink and and green green albite albite with with the (0—3% in pink albite. (0-3% 1(20) K20) in albite. The suggests its its presence in The distribution distribution of of K K suggests alternation products. products. Measurement of minor Mg and Fe concentrations concentrations in in albite revealed that that incipient incipient pumpellyitization pumpe11yitization is is common. common. But only pink pink albite showed showed minor minor Fe Fe (up 0.7% Fe203) Fe203) unaccompanied by Mg, Mg, consistent albite (up to to 0.7% with the the red red iron oxide microscopically observed as as aa possible possible source source of of the the pink coloring. coloring. Because cross-cuts albite, to be Because pumpellyite pumpellyite cross—cuts albite, pumpellyite is assumed to paragenetically paragenetica11y later later than than albite. albite. The of sericite suggests The distribution of control by the original calcic calcic interior interior of of plagioclase. plagioclase. But whether sericitization preceded preceded or contemporaneous with albitization is is unclear. unclear. sericitization or was was contemporaneous At least two two stages fluids of of different comAt least stages of of alteration alteration by by hydrothermal hydrothermal fluids comare inferred. inferred. position and/or conditions are �—36— -36- AREA, ONTARIO STRATIGRAPHY OF THE GUNFLINT FORMATION, FORMATION, KAKABEKA FALLS AREA, J. Shegeiski R. J. Shegelski Lakehead University Thunder Bay, Bay, Ontario ABSTRACT total of ten stratigraphic stratigraphic sections sections of the Gunflint For.mation A total of ten of the Gunflint Formation have been measured measured over a distance of a lateral distance of 3.6 3.6 kilometers kilometers in the the From the m Kaministikwia River River gorge. gorge. the study, study, a a composite section 57 57 m Kaministikwia thick was was found found to to contain six distinct distinct lithostratigraphic lithostratigraphic members. members. These members members are, These are, in ascending order: order: 1. (3 meters) 1. basal basal member (3 composed of of conglomerate, composed conglomerate, quartzite, quartzite, stromatolites, stromatolites, taconite taconite or or pyritic, pyritic, black chert—carbonate; meters) composed of chert-carbonate; 2. 2. lower shale member (7 (7 meters) of fissile carbonaceous shale; fissile shale; 3. 3. lapilli lapilli member member (4 (4 meters) meters) composed composed of of felsic quartz—feldspar felsic quartz-feldspar lapilli—tuffs; lapilli-tuffs; 4. 4. middle middle shale shale member member (22 (22 meters) meters) composed of of fissile fissile carbonaceous carbonaceous shale; shale; 5. 5. chert-carbonate chert—carbonate member member (11 composed (11 meters) meters) composed composed of of alternating alternating layers layers and and lenses lenses of of chert chert and and siderite; siderite; 6. (at least least 10 10 meters; top top not not exposed) exposed) composed composed of of 6. upper shale member (at fissile carbonaceous shale. shale. The composite section section therefore therefore contains contains 70% fissile 70% fissile carbonaceous shale, 20% 20% chert—carbonate, chert-carbonate, 7% 7% lapilli—tuff lapilli-tuff and 3% diverse lithologies of of the the basal basal member. member. and 3% Primary in the the various Primary sedimentary sedimentary structures structures are are well well preserved preserved in various strata. Well rounded, rounded, well sorted sorted sand sand grains grains in in the the basal basal quartzites, quartzites, in association with taconites taconites and and stromatolite stromatolite mounds mounds suggest suggest aa shallow, shallow, littoral environment. environment. The presence presence of of accretionary accretionary mudball mudball lapilli, lapilli, graded ash-fall ash—fall tuffs and large large scale scale crossbedding crossbedding in in the lapilli—tuffs graded tuffs and the lapilli-tuffs indicate subaerial derivation and and shallow shallow water water reworking reworking and and deposition. deposition. Dessication Dessication features features and and soft soft sediment sediment slumpage slumpage and and brecciation brecciation occur occur within chert chert carbonate carbonate layers layers and and lenses. lenses. The The lenticular geometry of of chert chert carbonate beds as well as as their their intimate intimate interlayered interlayered relationrelationships with with ripple-marked, ripple—marked, and and mud-cracked mud—cracked carbonaceous carbonaceous shales shales suggest suggest aa ships The entire strati— shallow water origin for for both both of of these these lithologies. lithologies. The stratigraphic is therefore therefore considered to have in aa graphic section section is considered to have been been deposited deposited in shallow water environment environment at at the the margin margin of of aa large large restricted restricted basin. basin. �—37.-37- NEW EVIDENCE ON THE STRATICRA2HY STRATIGRAPHY AND AND STRUCTURE STRUCTURE OF OF THE SOUDAN AREA, AREA, WESTERN VERMILION MINNESOTA VEmlILION DISTRICT, DISTRICT, MI~mESOTA P. P. K. K. Sims Sims U.S. Geological Survey U.S. Survey Denver, Colorado 80225 80225 Denver, and D. D. L. L. Southwick Minnesota Geological Survey Survey St. St. Paul, Paul, Minnesota ~innesota 55108 55108 ABSTRACT southeast of of Soudan, Soudan, Minnesota at scale Recent geologic mapping southeast 1:24,000 has has further further clarified clarified the the stratigraphy stratigraphy and and structure structure of of the 1:24,000 the western Vermilion Vermilion district. district. Numerous top—indicators top-indicators confirm the the major structure the area to be structure of of the area to be aa broad, broad, steep-limbed, steep—limbed, southward-overturned southward—overturned anticlinorium, the axial trace trace of of which trends trends about about N.70° N.70 o W. W. The core core anticlinorium, the of the anticlinorium is is metabasalt metabasalt belonging belonging to of the of the anticlinorium to the the lower member of the Ely Greenstone. On the the upright north limb of the fold, fold, the the stratigraphic succession succession above above the the lower lower member member is is as as follows: follows: Soudan Soudan Iron—formation Iron-formation Member of Ely Greenstone, Greenstone, upper member of Ely Greenstone, Greenstone, and and Lake Vermilion Formation. Although the the Soudan Member is is characterized characterized by the the presence of of cherty iron—formation, stratigraphy is iron-formation, its its internal. internal stratigraphy is complex and and more more than than half of it is composed half composed of of volcanic and and volcaniclastic volcaniclastic rocks. rocks. Felsic volcanic and and volcanogenic rocks of of the the Lake rest volcanogenic sedimentary sedimentary rocks Lake Vermilion Formation rest directly Soudan Member in the directly on the the Soudan the Soudan quadrangle, quadrangle, but pinch out out toward the east beneath a tongue toward the east tongue of pillow pillow breccia, breccia, mafic mafic aquagene aquagene tuff, tuff, iron—formation, and and pillowed pillowed metabasalt metabasalt belonging belonging to to the the upper upper member member of of the the iron-formation, Ely Greenstone. The iron—formation iron-formation at at Jasper Peak is a lenticular body member; it within the the lower Ely member; it is is stratigraphically beneath the Soudan Iron—formation Member. Iron-formation The stratigraphy of of the overturned south limb of the the anticlinorium is as as follows: follows: lower lower member member of of Ely Ely Greenstone, Greenstone, member member of of Ely Ely Greenstone Greenstone near near Two Rivers, Rivers, upper member of of Ely Ely Greenstone, Greenstone, and and Lake Lake Vermilion Vermilion Formation. Formation. The member near Two Two Rivers Rivers is is aa heterogeneous heterogeneous sequence sequence of of pillowed pillowed basalt, basalt, tuff, felsic felsic porphyry, porphyry, felsic tuff, tuff, and cherty iron—formation iron-formation that that basalt tuff, appears to be slightly slightly below the stratigraphic position position of of the appears to be the stratigraphic the Soudan Iron— Ironformation connect with with it. it. formation Member and does not connect lower and upper members of the the Ely Greenstone are distinct in in terms terms The lower of of primary structures, structures, textures, textures, and and bulk bulk chemical chemical compositions compositions (Schulz, (Schulz, 1977). The lower member the form The lower member consists consists chiefly chiefly of of calc-alkaline caic—alkaline basalt basalt in the of massive massive and and pillowed pillowed flows; flows; the pillows typically of the pillows typically are irregular irregular in size and shape and are highly highly amygdaloida1, amygdaloidal, indicating and shape and are indicating deposition in shallow water. The tholeiitic basalt the form of of pillowed The upper upper member member is is chiefly chiefly tholeiitic basalt in the flows. The The pillows pillows are are regular regular in in size size and and shape and and are generally non— nonamygdaloida1, indicating deposition deposition in in deep deep water. water. amygdaloidal, indicating The stratigraphic record clearly clearly indicates indicates a a highly mobile vo1canostratigraphic record volcano— tectonic environment that may a smaller scale to to the tectonic environment that may have been been analogous analogous on a modern volcanic arc arc and and back—arc back-arc basin. basin. REFERENCE Schulz, K.J., K.J., 1977, Schulz, 1977, The petrology petrology and and geochemistry geochemistry of of Archean Archean volcanics, volcanics, district, northeastern Minnesota: Minnesota: Unpublished Ph.D. Ph.D. western Vermilion district, Dissertation, p. Dissertation, University University of of Minnesota, Minnesota, 349 p. �-38—38— GEOCHEMICAL AND GEOPHYSICAL ANOMALIES ASSOCIATED WITH THE BEAR LAKE INTRUSIVE, INTRUSIVE, SECTIONS 24 24 AND AND 25, 25, T56N, T56N, R34W, R34W, HOUGHTON COUNTY, SECTIONS COUNTY, MIGHIGAN D. D. W. W. Snider and and B. B. K. K. Parker Michigan Geological Survey Survey Geology and Minerals Research Research Unit Unit Lansing, Lansing, Michigan Michigan ABSTRACT The Bear Lake Intrusive Intrusive is is aa nearly circular circular felsic felsic igneous igneous body body which appears to to have intruded intruded the the Freda Freda Sandstone. SQndstone. The The body is roughly 1.3 km km in diameter and is 1.3 is located about 11.2 km (7 (7 miles) miles) north north of of the the city of of Hancock, Michigan. Michigan. The work at the the Bear Lake body was part part of of aa larger larger investigation investigation that was designed to that was to test test a a model based upon the the copper copper sulfide sulfide mineralimineralization at at Mt. Mt. Bohemia (Section zation (Section 29, 29, T58N, T58N, R29W, R29W, Keweenaw Co., Co., Michigan). Michigan). Basically, Basically, the the model model suggests suggests that that several, several, isolated isolated intrusive/extrusive intrusive/extrusive bodies of Keweenawan age distributed throughout throughout the the Keweenaw Keweenaw Peninsula Peninsula may represent exploration targets targets for for copper copper sulfide sulfide mineralization. mineralization. Both the soil geochemistry and the soil and the ground geophysics tend tend to to support support this this idea idea at the Bear Lake body. at body. The results of the the field mapping, mapping, geochemistry geochemistry and and geophysics geophysics indiindicate the following: following: 1. 1. The predominantly felsic body displays displays an an easily easily recognizable recognizable magnetic signature. signature. 2. 2. There are two two relatively strong conductors conductors (VFL—EM) (VFL-EM) associated associated with the the body. body. 3. The body has has potassic rock rock chemistry, chemistry, averaging averaging 6.43% 6.43% K20, K20, with with a high K20 Na20 0 ratio averaging 3.4. K2 0 : Na 3.4. 2 Trace element analyses indicate indicate that that the the copper copper values values for for the the felsic felsic body average 190 ppm ppm which is is anomalous anomalous when when compared compared to for that that rock type type (15—3Oppm). (15-30ppm). to the the published published averages averages for : 4. 4. 5. 5. The results results of a soil geochemistry survey survey indicate indicate aa pattern pattern of of anomalous copper values that that appears appears to to be be associated associated with with the the anomalous location of of the VLF—EM VLF-EM conductors. conductors. development of of aa model model or or "type" "type" deposit deposit based based upon upon the the Although the the development Mt. Bohdmia sulfide mineralization mineralization is is still still in in its its early early stages, stages, we we Mt. Bohemia copper sulfide hope that chemistry studies studies as as well well as as geophysical geophysical and and case case that further further rock rock chemistry history studies studies from history from several several other other known known areas areas of of similar similar copper copper sulfide sulfide the idea that Michigan's Copper mineralization will confirm or refute the Country may may have have another type Country type of of mineralization for for which to to explore explore in in addition to addition to the the native copper and White Pine—type Pine-type copper copper settings. settings. �—39--39- DOE-BENDIX-MICHIGAN GEOLOGICAL SURVEY DIAMOND-DRILLING DIAMOND-DRILLING DOE-BENDIX-MI CHIGAN GEOLOG ICAL SURVEY INFORMATION IN MARQUETTE AND IRON COUNTIES, FOR GEOLOGIC FOR GEOLOGIC INFORMATION COUNTIES, MICHIGAN James Trow Department of Geology Michigan State University East Lansing, Lansing, Michigan Michigan 48824 East ABSTRACT Many Precambrian XX argillites argillites and and slates slates are are carbonaceous carbonaceous and and pyritic, and some contain pyrrhotite, chalcopyrite, pyritic, chalcopyrite, sphalerite, sphalerite, and and galena. PrecambrianW metabasalt Precambrian.W metabasalt (1059—1148') (1059-1148') at at DL—5 DL-5 contains contains strata—bound ides with with 130-2010 130—2010 ppm Cu and 20—50 strata-bound suif sulfides 20-50 ppb ppb Au. Au. Maximum uranium content in holes occurs in a 2"—thick conglomerate in a 2"-thick conglomerate at at 3011' 3011' at DL—4, with 130 ppm U U (nitric/perchloric) at DL-4, (nitric/perchloric) or or 260 260 ppm ppm UU (hydro— (hydroW metarhyolite fluoric/nitric/perchloric acid acid digestion). digestion). Precambrian W fluoric/nitric/perchioric at DL-S (997-1059') with 72—76 72-76 ppm U U is is aa possible possible source source rock rock for for at DL—5 (997—1059') uranium in in Precambrian Precambrian XX strata. strata. In Marquette County, County, age Y dikes and minor gravity gravity faults faults In Y diabase dikes appear in E-.W, vertical, vertical, and and 2) 2) parallel parallel to in two two orientations: orientations: 1) 1) E-W, to SW— SWE—W vertical faults Precambrian XX slaty slaty cleavage. cleavage. Such E-W faults at at DL—1 DL-l dipping Precambrian and DL—7 have downthrown north sides; and DL-7 sides; SW—dipping SW-dipping faults faults at at DL—3, DL-3, DL—5, DL-5, and DL-4 DL—4 have downthrown SW sides, and sides, suggesting the the possibility possibility of of age age YY horst and graben structure in horst in the the region, region, in in harmony with Cannon's Cannon's north—south tension enunciated at 1978 Institute north-south Institute on on Lake Superior Superior Geology. Epigenetic X rocks Epigenetic sulfide remobilization in Precambrian X appears to be structurally related to to the the post—Penokean post-Penokean faulting, faulting, which appears to drags drags slaty cleavage cleavage as as well well as as bedding. bedding. Lower dip of Penokean slaty cleavage at DL—5 is at DL-5 is thought thought to to reflect post—Penokean post-Penokean rotation rotation of of Clark Clark Creek block. block. �I DL—l: DL-l: DL—3: DL-3: DL—7: DL-7 : DL—5: DL-5: DL—4: DL-4: DL—6: DL-6: NWk-4, NW¼, SW~, Sw¼, NW~, NW¼, NW~, NW¼, SW!t;, NE~, SW¼, NE¼, NW~, SE~, NW¼, SE¼, NWk-4, NE¼, NE~, NW¼, 28W, Section 5, 5, TT 50N, 50N, RR 28W, 29W, 14, TT 50N, Section 14, 50N, RR 29\01, Section 4, T SON, 50N, RR 28W, 4, T 27W, Section 16, 16, TT 49N, 49N, RR 27\01, 2, TT 48W, 48N, RR 28W, Section 2, 30, TT 46N, 46N, RR 33W, NE~, NE~, Section 30, NE¼, NE¼, Hole number -- DL—l DL-l 2148' Terminal depthdepth. ............ Terminal 2148' Maximum deviation deviation 56~0 from vertical ............ 56½0 Overburden ................ 0—71' 0-71' Age Y Y diabase diabase ............. --X strata Age X Dip of bedding ........... 30°SE— 30 0 SE3 0 m'1 Dip of cleavage cleavage .......... 37°—65°SW 37 0 -65 0 SW (Argillite, (Argillite, slate slate, ...... 71—2148' 71-2148 ' (turbidite, marble, marble, (algal stromatolite (algal Cherty carbonate,...) carbonate, ... ) --)) clastics, algal clastics, )) stromatolite, stromatolite, )) "iron—formation" "iron-formation" (Argillite (Argillite and ....... --(g r aywacke (graywacke Quartzite ............... --Age W W basement ............ --- O I 0 --r I Shallowest phosphate ...... --- I I East Baraga Basin, Marquette County East Baraga Basin, Marquette County East Baraga Basin, Marquette County Clark Creek Basin, Marquette County Dead River Basin, Marquette County NW of of P.masa Amasa Oval, Iron County DL-3 DL—7 DL-7 DL—5 DL-5 DL—4 DL-4 DL-6 1634' 697' 697' 1148' 3176' 1093' 1 4½0 l41P 0—243' 0-243' 0 330 0-320' 0—3 20' 523—602' 523-602' 12° 0-76' 0—76' 2286—2358' 2286-2358' 2825-2827' 2825—2827' 41.,,,0 4½0 2 0-236' 0—2 36' 0 SW1 55°—70° -70 0 S1' 0 l5 -45 0 S\-7 l5°—45°SW O -40 0 NE 55°—40°NE 55° S— 55 S- 0 -65 0 SW 37°—65°SW 37 243—569' 243-569' 20°—40°SW 20 0 -40 0 sw 320-523' 320—523' 0 -6S o SW 3 5°—6.5°SW 35 76—2966' 76-2966' 569—659' 569-659' 660—714' 660-714' 2966-3019' 2966—3019' 440 44 0 0—163' 0-163' 1545—15 51' 1545-1551' 20 0°NE— NE0 SW 0.T. 60°SW 60 O.T. 40 0-55 0 SW 40°—55°SW 163—1634' 163-1634' --- --- 0 vertical 0 65 65 °NN ? --- --- 714-884' 714—884' ----- --- 884—997' 884-997' 997—1059' 997-1059' metarhyolite 1059—1148' 1059-1148' metameta— basalt 514' 514' --- ) ) 236-1903' ? --- 659—697' 659-697' granite 490' 3019—3119'' 3019-3119 3119—3176' 3119-3176' tonalite 2810' 421' 421' �—41— -41- PALMER GNEISS UPDATE Thomas Waggoner and Thomas Mroz Thomas Cleveland-Cliffs Cleveland—Cliffs Iron Company Ishpeming, Ishpeming, Michigan Michigan 49849 49849 ABSTRACT The Palmer Palmer Gneiss Gneiss is The is somewhat of a misnomer for for an an Early Early Precambrian Precambrian formational unit composed primarily of quartz quartz chiorite—sericite chlorite-sericite schists. schists. The unit unit contains The contains thin beds of orthoquartzite and and slate, slate, along along with with aa typical typical Archean magnetite/pyrite chert iron—formation. iron-formation. The gneiss has been intruded intruded by granite with small small amounts amounts of of calcite, calcite, ankerite, ankerite, pyrite pyrite and and chalcopyrite. chalcopyrite. The preference of the intrusive granites for for foliation foliation planes planes indicates indicates deformation prior prior to to the the granitic granitic episode. episode. In Sections Sections 25, In 25, 26 and 27, 27, T47N, T47N, R27W, R27W, the the northern limit limit of of the the Palmer Palmer 0 Gneiss the east-west to Gneiss is is the east—west Palmer Palmer Fault Fault that that dips dips fairly fairly uniformly uniformly at at 58 580 to the north. north. The gneiss is is in in direct direct contact contact with with the the middle middle and and upper upper portions portions of the Negaunee Iron—Formation. of Iron-Formation. Both the Palmer Gneiss and and the the Negaunee Negaunee Iron— IronFormation have been offset by northwest—trending northwest-trending near—vertical near-vertical faults. faults. The terminus of the Palmer Gneiss is is gradational gradational into into the the pegmatitic pegmatitic southern terminus granite. Assimilation of of the Palmer Gneiss into into granite granite has has produced produced comcomthat make determination determination of of the the original original rock rock extremely extremely positional variations that difficult. The Palmer Gneiss contains numerous east—west The east-west vertical vertical faults faults that that further confuse the further the lithologic lithologic sequence. sequence. The foliation trends N N 700_800 70 0 -80 0 W W with northerly northerly attitudes attitudes varying varying between between Where bedding was observed, was N N 720 W with a observed, the trending was 72 0 W a northeasterly dip dip of of 610. 61 0 • 3500 35 to 85°. 85 0 • The Palmer Gneiss is is a Lower Precambrian Precambrian meta—sedimentary meta-sedimentary sequence sequence that that has by Lower Lower Precambrian Precambrian pegmatitic pegmatitic granite granite whose whose abundance abundance has been intruded by increases to to the the south. south. Assimilations and and post—intrusion post-intrusion progressively increases shearing have caused extensive silicification, shearing silicification, carbonization carbonization and and sericitization. sericitization. �—42--42- STRUCTURAL GEOLOGY OF OF AMPHIBOLITIC AMPHIBOLITIC GNEISSES, GNEISSES, NORTHEAST CHIPPEWA CHIPPEWA COUNTY, COUNTY, WISCONSIN WISCONSIN Stephanie Wurdinger Wurdinger Department of Geology University of Minnesota Duluth, Duluth, Minnesota, 55812 ABSTRACT ABSTRACT Precambrian amphibolites, amphibolites, hornblende schists and and intrusive intrusive units units are exposed along the the Chippewa and Fisher rivers rivers near near Holcombe, Holcombe, Wisconsin. Wisconsin. the northern boundary of of the the Chippewa Chippewa These rock formations occur near the Amphibolite Complex and are judged judged to to be Archean Archean (?) (?) in in age. Exposures of in order order to to determine determine the the stages stages of of of the rocks were investigated in deformation and and their their relative relative ages. ages. The major rock units units in the the area are quartz—biotite quartz-biotite amphibolite amphibolite at at Holcombe dam, dam, and interbanded amphibolite gneiss gneiss and and tonalite tonalite along along the the Fisher River. River. Intrusives into into the quartz-biotite include Intrusives quartz—biotite amphibolite include dikes, and and aa hypabyssal hypabyssal coarse grained granodiorite and associated dikes, andesite intrusive. intrusive. The two two amphibolite units are are separated separated by by aa zone zone of mylonite mylonite at at least least 300 300in m wide. Banded gneiss gneiss along the the Fisher River displays displays three three periods periods of of An early phase of folding. of deformation, deformation, Fi, Fl, produced produced isoclinal isoclinal folds folds in in A tonalite banding banding and and aa mineral mineral lineation in zones of amphibolite. tonalite amphibolite. A penetrative axial planar foliation, foliation, S1, Sl, trending trending east—west east-west was was also also During FI F1 deformation, deformation, ptygmatic folds During folds formed in in response response to to produced. the closely spaced spaced S1 Sl foliation. foliation. During aa later later deformadeformathe development of closely tion, F2, F2, large large folds, folds, possibly possibly isoclinal, isoclinal, refolded earlier mineral tion, lineations and along aa great great circle circle distribution. distribution. and minor minor fold fold axis axis lirieations lineations along The axial planes of F1 Fl and F2 are believed to to be be coplanar. coplanar. A A third third fold fold deformation, F3, deformation, F3' produced broad, broad, open open folds folds with north—south north-south axial axial planes planes at a a high angle angle to to earlier earlier fold fold axes. axes. At Holcombe dam the the first and third third fold fold deformations deformations can can be be Late synkinematic granitic in the the quartz—biotite quartz-biotite amphibolite. amphibolite. Late observed in intrusives foliation parallel parallel to to S1. Sl. The hypabyssal andesite andesite intrusives show a faint foliation intrusive faint intrusive exhibits exhibits aa strong, strong, steeply-plunging steeply—plunging lineation and a faint foliation which also also parallels parallels S1. Sl. The quartz—biotite quartz-biotite amphibolite was later later converted converted to to hornblende hornblende A schist along a shear zone zone which is is exposed exposed along along the the Chippewa Chippewa River. River. A penetrative lineation plunges plunges moderately to to the the west. west. Late movements along the zone zone formed formed small pods pods of of brecciated mylonite along along foliation foliation along the planes. the rocks in in the the area area were crosscut crosscut by by aa series series of of closely—spaced, closely-spaced, All the steeply-dipping faults. Strike separation along the the faults faults is is dominantly steeply—dipping faults. right lateral, right lateral, and offset offset does does not not exceed exceed ten ten feet. feet. � https://digitalcollections.lakeheadu.ca/files/original/29d12afcf47b7c5708ec5c269de2bd74.pdf 7ce48d615fb442ba698f3fd3d1fd53cb PDF Text Text u.a.eX UNIVERSITY OF WISCONSIN-EXTENSION GEOLOGICAL AND NATURAL HISTORY SURVEY Meredith E. Ostrom, State Geologist and Director MIDDLE PRECAMBRIAN GEOLOGY OF NORTHERN WISCONSIN Prepared for: TWENTY-FIFTH ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY UNIVERSITY OF MINNESOTA-DULUTH DULUTH, MINNESOTA MAY 8-13,1979 FIELD TRIP GUIDE BOOK NUMBER 4 1979 �-{ffr _____ Tuesday May 8 Route .......... Wednesday May 9 Route 5 I " 0 " I 10 I I miles 20 I I �Field Trip Guidebook Number 4 University of Wisconsin-Extension GEOLOGICAL AND NATURAL HISTORY SURVEY Meredith E. Ostrom, State Geologist and Director MIDDLE PRECAMBRIAN GEOLOGY OF NORTHERN WISCONSIN Road Log and Geological Stop Descriptions Gene L. LaBerge and M.G. Mudrey, Jr. Edited by M.G. Mudrey, Jr. Geological and Natural History Survey Prepared for Twenty-Fifth Annual Meeting INSTITUTE ON LAKE SUPERIOR GEOLOGY University of Minnesota-Duluth Duluth, Minnesota May 8 - 13, 1979 (meeting concurrently with the Thirteenth Annual Meeting, North-Central Section, Geological Society of America) David G. Darby, Chairman, Field Trip Committee University of Minnesota-Duluth Available from the Wisconsin Geological and Natural History Survey, University of Wisconsin-Extension, 1815 University Avenue, Madison, Wisc.onsin 53706. 1979 �CONTENTS INTRODUCTION by M.G. Mudrey, Jr. ........................................................................ 1 TUESDAY, May 8, 1979 Geologic Road Log for Ashland, Bayfield, Iron, and Vilas Counties .... 6 WEDNESDAY, May 9, 1979 Geologic Road Log for Oneida, Price, and Sawyer Counties .......•..... 9 GEOLOGICAL STOP DESCRIPTIONS Stop 1 - Grand View Quarry by G.L. LaBerge ..•••.•.•.....••..•....... Stop 2 - Mount l~itt1esey by G.L. LaBerge . Stop 3 - Pence by G. L. LaBerge ....•....••........................... Stop 4 - Hurley Overpass by G.L. LaBerge ...•.........•.•............ Stop 5 - Bear River by G.L. LaBerge .............•................... Stop 6 - Monico East by M.G. Mudrey, Jr . Stop 7 - Monico Gravel Pits by M.G. Mudrey, Jr . .....•............... Stop 8 - Witte Farm by M.G. Mudrey, Jr . Stop 9 - Monico West by M.G. Mudrey, Jr ...•......................... Stop 10 - Beck Tower Wayside Park by M.G. Mudrey, Jr . Stop 11 - Jump River at Big Falls County Park by G.L. LaBerge ......•. Stop 12 - Arpin Dam in Radisson by M.G. Mudrey, Jr . 12 15 20 23 27 30 32 34 36 38 40 43 ILLUSTRATIONS Figure 1. Figure 2. Table 1. Map of northern Wisconsin showing distribution of various lithologies in the Middle Precambrian ................•.... Schematic cross sections showing inferred lithologic -structural relations during the "Penokean event of Middle Precambrian age ........•......................•.... Time-stratigraphic framework of Precambrian rocks in Wisconsin ............•..•................................. Highway map showing route of excursion 5 2 inside front cover SPECIAL EVENT TUESDAY, May 8, 1979 - Evening Field trip banquet at Holiday Acres, Rhinelander, t..Jisconsin After dinner addresses: Discussion of Massive Sulfide Deposits by J.M. Franklin Discussion of the Crandon Deposit by E.R. May and Paul G. Schmidt i 4 �INTRODUCTION M.G. Mudrey, Jr. l Northern Wisconsin is blessed with an abundance of sand and gravel resources deposited by the last major glacial advance. This is a mixed blessing, in that bedrock exposures are few and far between. A fair average would be about one small outcrop per township. Since the 1920's and extensive exploration for iron deposits, bedrock studies in northern Wisconsin have been few. In the late 1960's, Gene LaBerge and Paul Myers working for the Geological and Natural History Survey initiated detailed-reconnaissance mapping in the central part of the state. Renewed interest in the Precambrian geology of northern Wisconsin was spurred in 1968 with the discovery near Ladysmith in Rusk County of a small, but rich massive sulfide ore body. Additional discoveries since then include the Pelican River deposit near Rhinelander in Oneida County, and the Crandon deposit in Forest County. In addition, numerous theses and dissertations have studied the various Precambrian and Pleistocene units. Although present detailed coverage is sparse (less than five percent of Wisconsin is mapped in any detail), the general framework and distribution is known or can be inferred from geophysical studies. This trip is designed to show the lithologies which illustrate changing environments in the Middle Precambrian, with predominantly sedimentary rocks in the north, and extrusive and intrusive igneous rocks in the south. Classical localities of Middle Precambrian iron-formation, conglomerates within the Middle Precambrian, the environment of volcanogenic massive sulfide accumulation and granitic plutons will be visited in road cuts, quarries, and natural exposures. To cover the terrane, we must travel over 500 miles. Some of the exposures are well studied, whereas others are having been identified in the past few years. Because of the non-ferrous base-metal interest in northern Wisconsin, several of the stops will concentrate on the general rock types infue volcanic pile, and their relation to known ore deposits. In addition, at the field trip banquet Tuesday evening in Rhinelander Jim Franklin of the Geological Survey of Canada will give a general summary on Precambrian massive sulfide deposits and their enclosing rocks and Ed May and Paul Schmidt of Exxon, U.S.A., will present their observations on the largest zinc-copper find to date in Wisconsin, the Crandon deposit near Little Sand Lake in Forest County. The weather this time of year can be nasty, but usually is crisp and invigorating. Stops will not be particularly strenuous. We will assemble for prompt 8:00 a.m. departure on Tuesday, ~fuy 8, 1979, and proceed with field stops to Rhinelander, Wisconsin, for an overnight stop, and journey back to Duluth with field stops the next day. We plan on returning to Duluth about 6:00 p.m. on Wednesday, in time for you to join the activities of the Twenty-Fifth Annual Institute on Lake Superior Geology and the Thirteenth Annual North-Central Section of the Geological Society of America. Monday evening, before the trip, an informal technical/social gathering is scheduled in Duluth. The geologic framework will be discussed, and all participants will have the opportunity to get acquainted before the Tuesday morning departure. WELCOME TO BADGER LAND! 1 �Table 1. Era System Paleozoic Time-Stratigraphic Framework of Precambrian Rocks in lVisconsin Stratigraphic Units Intrusive Rocks Approximate Age -----------------------------::-:::7':::-~::::_::_;:_"i:'_:;;:_~::::1;'~------------------66O:T:"iiDO-;;~;_:_ semimature at base grading 600-1,100 m.y. Bayfield Group upward to mature clastic rocks deposited mainly in shallow water Oronto Group immature clastic rocks deposited mainly in shallow water Upper Keweenawan ·--disconformity-- Middle Keweenawan c co N Lithology and Depositional Environment ... .0 E co t) Q) ... 0- Lower Keweenawan Portage Lake and Powder Mill volcanics south of Lake Superior and Chengwatana volcanics in northwest and along St. Croix River --disconformity-Bessemer Quartzite along Gogebic Range mafic and intermediate lavas and interbedded sedimentary rocks 600-1,100 m.y. gabbroic and granophyric complexes near Mellen and Mineral Lake south of Lake ~uperior immature clastic rocks deposited mainly in shallow water 1,120 m.y. 1,200 m.y. Q) +-' rapakivi massif and associated granite, syenite and anorthosite in northeast (Wolf River area) co ....J --unconformity?-Quartzite at Baraboo, Barron and as isolated outliers in north --unconformity-- clastic rocks deposited mainly in shallow water rhyolite inliers in south subaerial tuffs and breccias --regional unconformity-- 1,500 m.y. 1,765 m.y. epizonal, Dost-tectonic granite in south and isolated plugs in north 1,765 m.y. epizonal to mesozonal, syntectonic granites 1,880-1,820 m.y. 1,800 m.y. �positions uncertain - - - - - - - - - - - - - - - - - - - - - - - - - - - - - basaltic to felsic volcanic and volcaniclastic rocks in north c eo ..... ..a E eo submarine flows, tuffs, and volcanic sediments model lead ages from massive sulfide deposits are l,830 m.y. Physical correlation with other units is difficult at best. May correlate with Tyler Formation in north. metamorphic studies suggest 685 0 C at 7.5 RDars. This area has been correlated with the Gogebic Range. kyanite-staurolitegarnet bearing schists and associated quartzo-feldspathic gneiss near Park Falls to Mercer (including Powell kyanite locality) u Q) ..... a. ~ "'C "'C ~ basaltic to felsic volcanic and volcaniclastic rocks in extreme northeast (Florence area) submarine flows, tuffs, and volcanic sediments uranium-lead ages on zircon from gneisses are around l,850-l,900 m.y. Some volcanic rocks (Quinnesec) have been correlated with the Lower Precambrian and with the Middle Precambrian. Stratigraphic relations in this area are not clear. Tyler Formation on Gogebic Range clastic rocks deposited mainly in deep water (=Baraga v.> ~roup of Michigan) 0. :l >. I: 0,.... l-i <1l c.:J .u --local unconformity?-- (1) ..... Ironwood Iron-formation on Gogebic Range iron formation Palms Formation on Gogebic Range immature clastic rocks deposited in shallow water (=Menominee Group of Michigan) 1.1'\ 00 (1) ..::< e ..... e S ..... ."<1lC ,..,I <t<.u (1)0 ."e ::;:: II ....... 0 ~ .uo ~I.I'\ U ~ eN :l >. (1)"" --regional unconformity?-Bad River Dolomite on Gogebic Range o o (/J cc..o stromatolitic dolomite C1l (=Chocolay Group of Michigan) <1l ..0 ---------::~~::~::~.::::~----------------~ --regional unconformity-- 2,600 m. y. c eo ..a E eo u volcanics and associated sediments south of Gogebic Range submarine flows, tuffs and agglomerates ..... >- ..... eo L.LJ epizonal granite south of Hurley 2,710m.y. --unconformity?-- Q) a. gneiss, migmatite and amphibolite in south and western end of Gogebic Range o l-i 0. high-grade migmatites 2,800 m.y.+ �---------~---~-~~- MIDDLE PRECAMBRIAN ROCKS IN WISCONSIN Geology modified from Sims 11976) Figure 1. IX'ii'l Granitic Rocks Ii>! Metasedimentary Rocks [:,/:',:::':] Metavolcanic Rocks Map of northern Wisconsin showing distribution of various lithologies in the Middle Precambrian. Metasedimentary rocks include slates, conglomerates, iron-formations, and carbonates. These rocks are least deformed and metamorphosed in the extreme northwest. To the south, these rocks contain kyanite and various other higher metamorphic grade minerals. The metavolcanic rocks include mafic to felsic lavas and associated pyroclastic and epiclastic materials. The granitic rocks include epizonal granodiorite to granitic plutons, and alkali-rich post-tectonic granites. 4 �WAUSAU . .. ". " 1900 m·y· LAKE SUPERIOR m.y. ... .'. ... tsJ B MIDDLE GLL PRECAMBRIAN GRANITIC ROCKS SEDIMENTARY ROCKS EARLY PRECAMBRIAN ~ 15?:1 ~ ~I"GREENSTONE" ~ VOLCANIC ROCKS ~ DOLOMITE, ETC. Figure 2. GRANITIC ROCKS Schematic cross sections showing inferred lithologic -- structural relations during the "Penokean" event of Middle Precambrian age. The upper diagram illustrates a north (right-side) -- south (leftside) section from Lake Superior to central Wisconsin near Wausau during the Middle Precambrian about 1,900 m.y. ago. To the north, platform sediments including carbonates and iron-formation were deposited, while to the south, deeper water sediments and volcanics were accumulating. The lower diagram illustrates the cross-section after cessation of tectonism about 1,800 m.y. ago. To the north the sequence is little deformed, whereas to the south the sequence is folded, and in the extreme south the sequence was moved to shallow structural levels along major faults or shear zones in an apparent host-graben arrangement. 5 �Tuesday, May 8, 1979 Geologic Road Log for Ashland, Bayfield, Iron, and Vilas Counties This leg of the trip visits the dominantly sedimentary part of the Middle Precambrian. The first stop is about two hours after starting. Lunch will be at Stop 2 on Mt. Whittesey. The last stop will be about 4:00 with a 90 minute deadhead trip to Holiday Acres in Rhinelander. Mileages 63 Follow U.S. 2 from Superior to the intersection with U.S. 63 turn right (south) on U.S. 63. 14 Proceed on U.S. 63 to intersection with Bayfield County D in Grand View. Turn left (south) on County D. Note: There are several approaches to stop 1. Directions are given for the best route, however roads may be closed by washouts. The alternate direction given below is longer, but is generally a better maintained road. 3.2 Proceed on County D to intersection with U.S. Forest Rd. 377 at Chequamegon National Forest Sign. Turn left (east) on Forest 377. 2.6 Proceed on Forest 377 to intersection with Forest 378. right (south) on 378. 3.1 Proceed on Forest 378 intersection Forest 198 (straight ahead) and 202 (cross road). Continue straight ahead (east) on Forest 198. 1.3 Proceed on Forest 198, crossing Marengo River and then turning right onto unmarked road parallel to Forest 198. 0.2 Proceed on unmarked road to bridge with gate over Marengo River. Park vehicles in area left (north) of road. 1900 ft. Cross bridge on foot, entering private land. Follow quarry road, keeping to right at branches of road, into quarry. Stop 1. 10.4 Turn Grand View Quarry -- Bad River Dolomite Return to Grand View. 6 �Alternate Route From Grand View to Stop 1 4.8 Proceed on County D to intersection with Forest 201 (Atkins Lake Road). Turn left (east) on Forest 201. 4.0 Proceed on Forest 201 to intersection with Forest 202. left (north) toward Marengo Lake on Forest 202. 1.5 Proceed on Forest 202 to intersection with ~orest 198 (right) and 378 (left). Turn right (east) on Forest 198. 1.3 Proceed on Forest 198, crossing Marengo River and then turning right onto unmarked road parallel to Forest 198. 0.2 Proceed on unmarked road to bridge with gate over Marengo River. Park vehicles in area left (north) of road. 1900 ft. Cross Bridge on foot, entering private land. Follow quarry road, keeping to right at branches of road, into quarry. Stop 1. 11.8 Turn Grand View Quarry -- Bad River Dolomite Return to Grand View. 4.8 Follow U.S. 63 north from Grand View to intersection with County E. Turn right (east) on County E. 7.4 Proceed on County E to intersection with Ashland County C (E turns left). Continue straight ahead on County C. 1.3 Proceed south on County C to crossroad intersection with Midway Road. Turn left (east) on Midway Road. 2.3 Proceed east on Midway Road and rejoin County C. straight ahead (east) on County C. 2.4 Proceed east on County C to intersection with State 13. Turn right (south) on State 13. 9.9 Proceed south on State 13 to intersection with State 77 in Mellen south of railroad tracks. Turn left (east) on State 77. 0.4 Proceed east on State 77 to intersection with County P (Lake Drive). State 77 turns left (north) over railroad tracks. Continue straight ahead on County P (Lake Drive). 1.6 Proceed on Lake Drive. Road jogs left. Stay on Lake Drive. Road jogs left. Stay on Lake Drive towards Camp Galike. Turn left on third dirt road to left (east). This may be marked "Mellen Fire Tower Road." 7 Continue �1.5 Proceed on dirt road to flagged area. Hike 100 yards north of road into cleaning. Note: There is a locked gate on the Fire Tower Road. The key is available from the Head Ranger, Copper Falls State Park, about 3 miles northeast of Mellen on State 169. Stop 2. Mt. Wittlesey. Ironwood Iron formation Afternoon, May 8 3.1 21 Return to County P and State 77 in Mellen. Follow State 77 east from Mellen to Pence (mileage that follows is calculated from sign on west city limits of Pence. 0.4 Proceed into Pence on State 77 to intersection with Spruce St. Proceed south one block, and park on Whiteside Street. Out crop is located on south side of Whiteside Street, at the intersection with Spruce Street, under a large tree. 5.1 Return to State 77, and continue east towards Hurley. Enter Hurley. Stop sign at intersection of State 77 and Fifth Ave. Turn left (north) onto Fifth Avenue. 0.5 Follow Fifth Avenue to intersection with U.S. 51. (west) onto U.S. 51. 1.1 Follow U.S. 51 northbound, taking overpass towards U.S. 2 westbound. Stop at large outcrop on right (east) side of road immediately after crossing the overpass. 2.5 Return to southbound U.S. 51 by taking U.S. 2 westbound to cross-over (about 0.5 miles) and reverse direction to eastbound U.S. 2, and taking the exit ramp to southbound U.S. 51. Next leg of trip mileage is measured from intersection of U.S. 51 and State 77 in Hurley. 26.6 Turn left Proceed south on U.S. 51 to intersection of U.S. 51 and State 47 in Manitowish. Turn right (south) on State 47. 3.9 Follow State 47 to intersection with State 182. (west) on State 182. 1.2 Follow State 182 to large outcrops on both sides of road. Stop 5. 1.2 50 Turn right Bear River - Powell Kyanite Return to State 47. Turn right (south) on State 47. Follow State 47 southbound towards Rhinelander and intersection U.S. 10. 8 �Wednesday, May 9, 1979 Geologic Road Log For Oneida, Price and Sawyer Counties This leg of the trip visits the dominantly volcanogenic part of the Middle Precambrian basin near Monico in Oneida County, with incidental stops at granite localities. We will start with a short trip to Monico and examine volcanic rocks, and spend the last half of the morning deadheading to our lunch stop in Price County. One afternoon stop will be made in Sawyer County. We plan on arriving in Duluth - Superior around 6:00 p.m. Morning, May 9 Mileages 14 1.0 Follow U.S. 8 east from Rhinelander to the intersection with U.S. 45 and U.S. 47 south in Monico. Continue east on U.S. 8, crossing on bridge over Chicago and Northwestern Railroad tracks and U.S. 45 to north. About 0.2 miles east of intersection of U.S. 45 to north, take. County V to the right, and park. Outcrop is located at intersection of U.S. 45 and County V. Stop 6. Monico East - Mafic Pillow Basalt. 0.2 Return westbound on U.S. 8 to intersection with U.S. 45 north. Turn right (north) on U.S. 45. 0.5 Proceed to Lake Road, and turn left (west) onto Lake Road. 0.6 Proceed on Lake Road, crossing Baade Road and stopping behind house on left (south). Stop 7. Monico Gravel Pits (Baade and Lake Roads)--Intermediate to felsic pillow lavas. 0.6 Return to U.S. 45 and turn left (north) on U.S. 45. 0.9 Proceed to small, abandoned farm on right (east) side of road. Stop 8. Witte Farm - Coarse Felsic Agglomerate. 1.4 Return south to U.S. 8. 2.4 Proceed west on U.S. 8 to intersection with old U.S. 8 and Leith Road. Proceed on old U.S. 8. 0.7 Proceed to flagged area. road. Stop 9. 0.7 Turn right (west) on U.S. 8. Small outcrops on both sides of Monico West -- Section 26 - pyritic tuff. Return to U.S. 8 and proceed east on U.S. 8. 9 �1.6 Proceed east on U.S. 8 to intersection U.S. 45 (southbound). Turn right (south) on U.S. 45. 2.5 Proceed to Wayside on west (right) side of highway. in wayside. Stop 10. 2.5 Outcrop Beck Tower Wayside Park - Late red granite. Return north to U.S. 8. Turn left (west). 14 Proceed on U.S. 8 west to Rhinelander. 44 Continue west on U.S. 8 to Prentice. 18 Continue west on U.S. 8 to junction with Price County N near Kennan. Turn left (south) on County N. 10.2 Proceed on County N to junction with road to Big Falls County Park road. Turn right (west). 1.0 Proceed on park road to park entrance and turn left (south) into park. 0.2 Proceed to pavillion. Outcrops in river west of pavillion. Stop 11. Big Falls County Park on the Jump River, Price County - Granite and Pyritic tuff. Afternoon, May 9 11.9 0.9 Return to Kennan and junction of County J and N. (west) on County J. Follow County J to U.S. 8. Ladysmith. Turn left Turn left (west) on U.S. 8 to 27 Follow U.S. 8 through Ladysmith to intersection with State 77. Turn right (north) on State 27. 23 Follow State 27 to Ojibwa to intersection with State 70. Turn left (west) on State 70. 4.4 Follow State 27 and 70 west. road. 0.7 Proceed on gravel road. cross bridge. 0.4 Proceed to junction with Swede Road. Turn right. 0.25 Proceed to junction with Birch Lane. Turn right. 0.6 Follow Birch Lane. Turn right crossing bridge and park. Walk 350 feet along trail to river. Stop 12. Turn left (south) on gravel Turn left (east) on asphalt road, Arpin Darn in Radisson - Late Porphyritic Granite. 10 �1. 25 Return to intersection 1 Continue west on asphalt road into Radisson and intersection with State 40. Turn right (north) to intersection with State 70 and 27. with asphalt road. 29 Follow State 27 to Hayward. 77 Follow State 77 to Minong and U.S. 53 to Duluth. 540.2 mi. End of Log GEOLOGICAL STOP DESCRIPTIONS Page Stop 1 - Grand View Quarry - Bad River Dolomite ..........•......... 12 Stop 2 - Mount Whittlesey - Ironwood Iron-formation ...........•.... 15 Stop 3 - Pence - Basal Palms Formation ........•.................... 20 Stop 4 - Hurley Overpass - Tyler Formation Stop 5 - Bear River - Powell Kyanite •.............................. 27 Stop 6 - Monico East - Mafic Pillow Basalt 30 Stop 7 - Monico Gravel Pits - Andesite Pillow Lava 32 Stop 8 - Witte Farm - Coarse Felsic Agglomerate 34 Stop 9 - Monico West - Section 26 Pyritic Tuff 36 Stop 10 - Beck Tower Wayside Park - Jennings Granite 23 , 38 Stop 11 - Jump River at Big Falls County Park - Granite 40 Stop 12 - Arpin Dam in Radisson - Late Porphyritic Granite 43 11 �BA 44/5W/22 Title: Grand View Quarry -- Bad River Dolomite Location: Johnson & Johnson Quarry, Grand View. NW~, NW~, NW~, Sec. 22, T.44N., R.5W., Bayfield County. (Chequamegon National Forest, 1 mile, 1968) ~ inch o Author: Gene L. LaBerge (1978) Description: This quarry provides one of the largest and most excessible exposures of the Bad River Dolomite in IVisconsin. The formation was named by Van Rise and Leith (1911) from exposures along the Bad River at Penokee Gap southwest of Mellen. According to Aldrich (1929), it unconformably overlies the Lower Precambrian greenstones and granites to the south. In the eastern part of the Gogebic Range the Sunday Lake Quartzite conformably underlies the dolomite, but both the dolomite and quartzite are missing in the central part of the district, presumably due to erosion prior to deposition of the overlying Palms Formation (Irving and Van Rise, 1892). Thus, there appears to have been gentle folding or arching along a north-south axis causing erosion of the Bad River Dolomite and Sunday Lake Quartzite prior to deposition of the Palms Formation, the basal unit of the Animikie Series (James, 1958) in this area. 12 �BA 44!5W!22 (2) The exposures in the quarry are fairly typical of the formation. The bedding dips 35 0 - 75 0 north, along with all other Middle Precambrian units on the Gogebic Range in Wisconsin. Komatar (1972) estimates a minimum thickness of 550 feet in this area, thinning to about 310 feet eight miles to the east. Aldrich (1929) reports that the lower part of the formation is mainly a dolomitic limestone with a much more siliceous upper part. The silica occurs as lenses of sandy dolomite or cross-bedded sandstone (now quartzite), and as beds, pods and irregular masses of chert (Komatar, 1972). The chert ranges in color from light gray to black, presumably due to included organic matter. Algal structures up to nearly 1 meter in diameter, some with black chert layers alternating with dolomite, are present in the formation (Figure 1). Figure 1. Algal structures in the Bad River Dolomite. Photo is of a large glacial erratic near Clam Lake, about 10 miles southeast of Grandview. Several mafic dikes striking N.80oE. and dipping 84°S. are exposed in the quarry (Komatar, 1972). These are presumably Keweenawan diabase dikes. Mineralogically, the formation consists of medium-grained granular carbonate with lenses, pods and patches of quartz. A reaction rim of pale green tremolite typically occurs between the quartz and carbonate. The tremolite is also present in layers of massive, randomly oriented crystals and as radial aggregates several inches in diameter. The mineral assemblage in the Bad River Dolomite and associated Palms and Tyler Formation indicate that the area was metamorphosed to greenschist facies during the Penokean orogeny about 1700 m.y. ago (Komatar, 1972). He reports that the metamorphic grade increases from quartz-albite-muscovite-chlorite subfacies on the east to quartz-a1bite-epidote-almandine subfacies in the Grandview area. This metamorphism was associated with only slight deformation. 13 �BA 44/5W/22 (3) Intrusion of the Mellen gabbro produced widespread contact metamorphism superimposed on the earlier regional metamorphism. K/Ar ages (Komatar, 1972) date this event at 1050±40 m.y. Discussion: The Bad River Dolomite was deposited on an erosion surface of Lower Precambrian greenstones and granites. The presence of algal structures, sandy dolomite and interbedded layers of sand indicate deposition in a shallow marine environment. The increase in sand content upward in the formation suggests either a shallowing of the basin or a change in source area providing more coarse clastics to the basin. The unit is similar in all respects to the Kona and Randvi11e dolomites in the Marquette and ~1enominee districts of Michigan respectively, with which it is generally correlated. The absence of the Bad River Dolomite in the central part of the Gogebic suggests a gentle upwarp in that area resulting in erosion of the formation prior to deposition of the overlying Palms Formation. Gentle folding and greenschist facies metamorphism occurred during the Penokean orogeny. The major northward tilting of the units and contact metamorphism associated with emplacement of the Mellen gabbro occurred during Late Precambrian time. References Citied: Aldrich, H.R., 1929, The geology of the Gogebic Iron Range of Wisconsin: Wisconsin Geological and Natural History Survey, Bulletin 71, 279 p. Irving, R.D., and Van Rise, C.R., 1892, The Penokee Iron-bearing Series of Michigan and Wisconsin: U.S. Geo1goical Survey Monograph 19, 534 p. James, R.L., 1958, Stratigraphy of Pre-Keweenawan rocks in parts of northern Michigan: U.S. Geological Survey Professional Paper 314-C, p. 27-44. Komatar, F.D., 1972, Geology of the Animikian metasedimentary rocks, Mellen Granite, and Mineral Lake Gabbro west of Mellen, Wisconsin: Unpub. M.S. Thesis, University of Wisconsin-Madison, 70 p. Van Rise, C.R., and Leith, C.K., 1911, The geology of the Lake Superior Region: U.S. Geological Survey Monograph 52, 641 p. 14 �AS 44/2H/9B Title: Mount Hhittlesey - Ironwood Iron-formation Location: Author: Berkshire Mine, SH\, SW\, sE\, Sec. 9, T.44N, R.2W., Ashland County. (Mt. Hhittlesey 7~-minute topographic quadrangle. 1967) (Get key from Ranger at Copper Falls State Park) Gene L. LaBerge (1978) Description: The Ironwood Iron-formation ranges from about 450-950 feet in thickness and extends for approximately 60 miles across Michigan and Hisconsin in a west-southwesterly direction from west of Lake Gogebic, Michigan, to west of Mineral Lake in Wisconsin. It lies conformably between the Palms Formation and the Tyler Formation. The prominent hill here (Mt. Whittlesey) results from the resistant nature of the exposed metamorphosed iron-formation. The lowlands west and east of the hill are the result of cross-faults of Late Precambrian age that offset the Middle and Upper Precambrian strata (Aldrich, 1929). The iron-formation exposed here shows the bedding characteristics typical of Middle Precambrian iron-formations of the Lake Superior region. Two basic styles of bedding are readily apparent -- one is a laminated rock consisting of alternating layers about 1 cm thick of recrystallized chert and iron oxides. This is commonly referred to as "banded" or "even-bedded" or "slaty" ironformation. The other bedding type present is a thick and irregularly-bedded variety with beds up to 15 cm or more thick. The thicker beds are cherty with abundant sand-size clasts (granules or oolites) of chert in a chert matrix. The clasts commonly are somewhat ferruginous, whereas the matrix is more pure 15 �AS 44/2W/9B (2) :oj ~ .., <1J . 0 o o ~. o o .... .., _ . - , - 6 - - --l - -~ - Volcanics along Powder Mill Creek Intermediate to felsic lava flows unco!Or1Ol1 basdlt flows;except in I Lower 5000 ft thin basalt flows with a few intermediatG flows . Pillow lavas at base ~ N .n a. S a. ~ :l 0'-' ..,:.J o o 0.. Bessemer Sandstone of Seaman (1944) Quartz arenite with abundant matrix; congLunLeratic at base '" C1l ~~_---.-f-..-~/'-r---u-"1""-':"';;"~~~"--~~--+------------------------1 f-.- a. £i :l 0 .., -.-; Cl >< :l E C1l - C1l If) (:Q - -- - S C1l 00 C1l .., - 0 0 - - a-. - - - ---- - Tyler formation Light - to dark - gray pl&gioclaserich fine-grained sandstone, argillaceous siltstone, and argillite. --Lowermost 1000 [t is partly ferruginous and has len~es of lean cherty iron-formation - ~~= 0. :l X C ..,0 C1l ..-4 r--. <lJ Cl -< .n "0 «> .., E C1l u ..,<lJ 0.. "U -.-; E '-' ~ C -aor, a-. -a I If) ~ -.-; E 0 c <lJ ?-: 0. :l ..,o Cl I -0 0alf) ',-..'-_ Anv il"M~~be~ ..:::.:;--\ Ironwood Iron-Formation .....- -- -_...:.---.;.. ==-=:=-'?ence Membcl- ~-'--:'~MostlY thin-bedded cherty carbonate ~ ;:-" - -_- ::.. -, "." -.. =,-;; i.ron- forma t ion --::'-Norr ie Member ~ ~ ~~":>l" fj er---I ~-': Mostly thick wavy bedded cherty iron----.a .: ..---.-- - -e - r'Cr1 - .. " '. ~ ,,"'~' forma tion :- ~ym-;:;uth M~m:,~r ./ Palms Formation Sericitic argillite; red-brown '"~ ~-~~.*~~~~~~ quartzite at top Bad River Dolomite / Gray to buff dolomite and cherty doloo mite. Stromatolitic structures common. a in both east and west parts of Found '" Gogebic district, absent in center ':-~-=- - ~ '-- -=---- --- >. C1l --i o u o ..c: u a If) rl .... Sunday Quartzite Mainly white, gray, and red vitreous quartzite, and conglomerate at the base. Known only in the eastern Gogebic Precambrian W(lower)complex Sedimentary-volcanic ("greenstone") sequence, partly metamorphosed to foliated hornblende gneiss, intruded by quartz monzonite and pegma t i te Figure 1. Generalized stratigraphic section in central and western Gogebic Range (from Schmidt and Hubbard, 1972, p. A3). 16 �AS 44/2W/9B (3) chert. These cherty units are highly irregular in shape and are separated by layers composed mainly of iron oxides. Intra-formational conglomerates are relatively common in the "wavy" or "irregularly" bedded or "cherty" ironformation. These different bedding styles represent different intensities of wave action in the basin during iron-formation deposition. Or alternatively, they represent alternately shallow and deep water conditions, with the thin-bedded variety representing deep (quiet) waters and the wavy bedded units indicating shallow (agitated) waters. These bedding differences were used by Hotchkiss (1919) as a basis of subdividing the formation into five members based on the dominant bedding style. He recognized three units with dominantly wavy bedding (Plymouth, Norrie, and Anvil) separated by two units of mainly thin-bedded iron-formation (the Yale and Pence). These units can be recognized over much of the 60-mile length of the range, and are roughly correlative with the lower cherty, lower slaty, upper cherty and upper slaty members of Biwabik Iron-formation in Minnesota. The iron-formation here has been metamorphosed to grunerite grade, and consists of quartz, grunerite, magnetite and minor hematite and garnet, with minor dolomite, ankerite and siderite co-existing with the grunerite (Laybourn, 1979). Minnesotaite is the stable iron-silicate present in the iron-formation east of Ballou Creek (about 2 miles east of here), and iron-rich pyroxenes (ferrohypersthene and ferroaugite) appear from Mellen westward (Laybourn, 1979). The metamorphic facies are produced by contact metamorphism related to the Mellen and Mineral Lake gabbro complexes. Economic Geology: Iron ore was discovered on the Gogebic Range at Bessemer, Michigan in 1873, and over 300 million tons of natural ore was mined before operations ceased in 1966 (Schmidt and Hubbard, 1972). Most of the mining operations were done ,between Hurley, Wisconsin, and Wakefield, Michigan, on the eastern part of the range. Natural ores that are economically exploitable have been worked out. Marsden (1978) reports that major reserves of taconite ore in the Ironwood Iron-formation remain on the western end of the Gogebic range where the rocks have been more highly metamorphosed. The intensity of metamorphism increases progressively westward from biotite grade to pyroxene grade (Marsden, 1978). The area of interest for development of magnetite taconite extends from near Upson southwestward for 21~ miles to just west of Mineral Lake. Outcrop width of the iron-formation is 1000-1500 feet over much of this length, but folding in the }1t. vfuittlesey area produce an outcrop width of 2500 feet locally (Marsden, 1978). Marsden (1978) estimates the total reserves of magnetic taconite in Wisconsin to be 4,171,000,000 metric tons, of which 3,711,000,000 metric tons are in the Ironwood Iron-formation of the Gogebic Range. The other taconite reserves are the Agenda deposit (Sec. 22, 23, 24, T.42N., R.IE.), 160,000,000 tons; the Butternut deposit (Sec. 20, 21, 28, 29, T.49N, R.1W), 48,000,000 tons; and the Pine Lake deposit (Sec. 21, 22, 23, 26, 27, 28, T.44N, R.3E.), 184,000,000 tons. The latter three deposits are not in the Ironwood Ironformation, but appear to be in lateral equivalents (Allen and Barrett, 1914). 17 �AS 44/2W/9B (4) Thus, the Middle Precambrian of northern Wisconsin contains one of the largest undeveloped taconite reserves in North America. Discussion: Mineralogically, the iron-formation is generally referred to as "oxide facies," implying that it was deposited as oxides with the chert. LaBerge (1964) showed that the magnetite is almost entirely secondary. Dimroth (1975) points out that the mineral facies are diagenetic (or metamorphic) and do not reflect the depositional environment. Thus, unless we can prove that the present mineralogy is the original mineralogy, there is no basis for interpreting the depositional environment from the mineralogy. The Facies concept of James (1954) should be restricted to a descriptive rather than interpretative concept. The present mineralogy of iron-formations is the product of the depositional, diagenetic, metamorphic, and in many cases, the weathering environment; it should not be assumed that the present mineralogy is the original mineralogy. The subdivision of the Ironwood into members based on the dominance of granular (cherty) or laminated (slaty) iron-formation (Hotchkiss, 1919) works well in the eastern two-thirds of the Gogebic. However, subdivision of the formation into the various members in the western third of the district is difficult. In part, this may be due to the highe~ metamorphic grade in the western end of the district, but there seems to be a real change in the stratigraphy as well. Morey (1972, p. 209) shows a similar relationship for the western Mesabi, where subdivision into the cherty and slaty members is difficult. This may suggest a change in the Animikie Basin to the southwest. The presence of a thicker succession, interbedded clastics and volcanic rocks in iron formation in the Cuyuna district (Marsden, 1972) may indicate a change from platform to deeper basin to the southwest. References Cited: Aldrich, H.R., 1929, The Geology of the Gogebic Iron Range of Wisconsin: Wisconsin Geological and Natural History Survey, Bulletin 71, 279 p. Allen, R.C., and Barrett, L.P., 1915, Contribution to the pre-Cambrian geology of northern Michigan and Wisconsin: Michigan Geological Survey Publication 18, Geologic Series 15, p. 13-164. Dimroth, E. 1975, Paleo-environment of iron-rich sedimentary rocks: Geologischen Rundschau, v. 64, p. 751-767. Hotchkiss, W.O., 1919, Geology of the Gogebic Range and its relation to recent mining developments: Engineering/Mining Journal, v. 108, p. 443-452, 501-507, 537-541, 577-582. James, H.L., 1954, Sedimentary facies of iron-formation: v. 49, p. 235-293. Economic Geology, LaBerge, G.L., 1964, Development of magnetite in iron-formations of the Lake Superior Region: Economic Geology, v. 59, p. 1313-1342. Laybourn, D.P. 1979, Geology and metamorphism of the Ironwood Iron-formation, Gogebic Range, Wisconsin: Unpub. M.S. Thesis, University of MinnesotaDuluth, 223 p. , s:l �AS 44/2W/9B (5) Marsden, R.W., 1972, Cuyuna District: in P.K. Sims and G.B. Morey, editors, The Geology of Minnesota (G.M. Schwartz Volume): Minnesota Geological Survey, p. 227-239. Marsden, R.W., 1978, Iron ore reserves of Wisconsin -- A Minerals Availability Systems Report: in Proceedings of the 51st Annual Meeting, Minnesota Section AIME and 39th Annual Minnesota Mining Symposium, p. 24-1 -- 24-28. Morey, G.B., 1972, Mesabi Range: in P.K. Sims and G.B. Morey, editors, The Geology of Minnesota (G.M-.-Schwartz Volume): Minnesota Geological Survey, p. 204-217. Schmidt, R.G. and Hubbard, H.A., 1972, Penokean Orogeny in the central and western Gogebic Region, Michigan and Wisconsin: Field Trip A, 18th Annual Institute on Lake Superior Geology (Roughton, Michigan). 19 �Ir 46/2E/32 Title: Pence--Basal Palms Formation Location: Author: Intersection of ~~iteside Street and Spruce Street in Pence, Wisconsin. SE~, SW~, Sec. 32, T.46N., R.2E., Iron County. (Iron Belt 7~-minute topographic quadrangle, 1956). Gene L. LaBerge (1978) Description: The Palms Formation is the basal unit of the Middle Precambrian Animikie Group (James, 1958), and unconformably overlies the Bad River Dolomite and Sunday Lake Quartzite of the Chocolay Group (Cannon and Gair, 1970). According to Aldrich (1929), the Palms is continuous throughout the Gogebic range, averages about 450 feet in thickness, and contains a basal conglomerate, a "quartz-slate" unit, and an upper quartzite unit. At this locality the basal Palms rests on Lower Precambrian granite, the older Bad River Dolomite and Sunday Lake Quartzite evidently having been removed by post-Bad River - pre-Palms erosion. Both west and east of here the Bad River Dolomite and Sunday Lake Quartzite are present between the Palms and the underlying Early Precambrian granite and greenstone. The following generalized description is taken mainly from Aldrich (1929). The basal conglomerate of the Palms is up to about six feet thick and appears to be derived mainly from the immediately underlying rock types (Aldrich, 1929). It was deposited on an uneven erosion surface, and thus varies in thickness locally. The larger clasts are well rounded at some localities, and very angular 20 �Ir 46/2E/32 (2) at others according to Aldrich (1929). Here the clasts consist of quartz, chert, granite, and felsic and melfic volcanics, are moderately well rounded and range up to about 8 cm in ~iameter. The outc~op is slightly phosphatic. Overlying the basal conglom~rate~ and comprising about 400 feet of the formation is the thin-bedded "quartz-slate" unit characteristic of the Palms. It consists of alternating quartz-rich and argillaceous beds 1-3 cm thick with ripple marks, cross-bedding and scour-and-fill features common. The quartz-rich beds are composed mainly of quartz, although some are quite feldspathic. 0uartz grains range from angular to well rounded, with the larger grains generally the most rounded (Aldrich, 1929). Argillaceous layers consist mainly of fine sericite, chert, ~hlorite and magnetite. A general coarsening of grain size of argillaceous materials and the appearance of octahedra of magnetite west of the Tyler Forks River is evidently due to contact metamorphism produced by the Upper Precambrian Mellen Gabbro. The uppermost 50 feet of the Palms consists of a vitreous quartzite composed of medium-grain, well-rounded quartz. Minor mica is present on bedding planes. The quartzite varies from white, green, brown to red (Aldrich, 1929). The Palms is overlain conformably by the Ironwood Iron-formation. This represents an abrupt transition from clastic sedimentation in the Palms to chemical sedimentation (with virtually no clastics) in the Ironwood. A similar abrupt transition is present throughout most -- but not all -- of the Lake Superior region. Discussion: The Palms Formation is an important part of understanding the geometry of the Animikie Basin. It is genetally correlated with the Pokegama and Kakabeka Formations of the Mesabi and Gunflint districts respectively on the north shore of Lake Superior, and the Siamo and Ajibik Formations of the Marquette district (Cannon and Gair, 1970). The Kakabeka Formation is mainly a conglomerate and generally only a few feet thick (Goodwin, 1954). The Pokegama is mainly a quartzite and up to 167 feet thick (Morey, 1972). These formations underlie the iron-formation in their respective districts. The general thickening of the clastic sequence beneath the iron-formation suggests a deeper (or older) basin to the south, or alternately that the sea was transgressing northward onto the craton at the onset of iron-formatin deposition. In the ~1arquette district, the Siamo Slate and Ajibik Quartzite are 1,000 feet thick in the Neguanee area, but thin markedly to only about 100 feet near Michigamme at the western end of the district (Boyum, 1970). Thus, the nature and thickness of the formations underlying the major iron-formation differs from place to place within the basin and must reflect local differences in the pre-iron-formation history of the Animikie basin. In the Gogebic district, the Palms has some features typical of shallow water deposition, and some (the quartz-slate) which appears to have similarities to deeper water deposition, perhaps transitional into a graywacke-type environment farther south. References Citied: Aldrich, H.R., 1929, The geology of the Gogebic Iron Range of Wisconsin: Wisconsin Geological and Natural History Survey, Bulletin 71, 279 p. Boyum, B.H., 1970, the Marquette Mineral Range, Michigan: Geological Society of America, Field Trip to Marquette Iron Range, }1ichigan, 21 p. 21 �Ir 46/2E/32 (3) Cannon, W.F., and Gair, J.E., 1970, A reVlSlon of stratigraphic nomenclature for Middle Precambrian rocks in northern Michigan: Geological Society of America, Bulletin, v. 81, p. 2843-2846. Goodwin, A.M., 1954, Facies relations in the r,unflint Iron-formation: Geology, v. 51, p. 565-595. Economic James, H.L., 1958, Stratigraphy of pre-Keweenawan rocks of northern Michigan: U.S. Geological Survey Professional Paper 3l4-C, p. 27-44. Morey, G.B., 1972, Mesabi Range: in P.K. Sims and G.B. Morey, editors, The Geology of Minnesota (G.M. Schwartz Volume): Minnesota Geological Survey, p. 204-217. 22 �IR 46/2E/14B Title: Hurley Overpass. Location: Tyler Formation. Junction U.S. Highway 2 and U.S. Highway 51 north of Hurley, Wisconsin. SE~, SE~, NE~, Sec. 14, T.46N., R.2E., Iron County. (Ironwood 7~-minute topographic quadrangle, 1975) 77 Author: Gene L. LaBerge, 1978 Description: This exposure is characteristic of most of the Tyler Formation which conformably overlies the Ironwood Iron-formation, and is the youngest Middle ~re­ cambrian unit recognized on the Gogebic Range. The unit is generally referred to as the Tyler "slate," although Alwyn (1976) reports that the formation is about one-third slate and two-thirds graywacke sandstone. Alwyn (1976) reports that the Tyler formation is approximately 7,000 feet thick in this area, but increases in thickness westward to about 12,000 feet near Mellen. Schmidt and Hubbard (1972) report that the Tyler has been completely removed by pre-Keweenawan erosion to the east. Because of its stratigraphic relations, the Tyler is generally correlated with the Virginia and Rove formations in Minnesota and with the Michigamme formation in Michigan (Leith, Lund, and Leith, 1935; James, 1960). Sedimentological studies led Alwyn (1976) to conclude that the Tyler formation was derived mainly from a granitic terrane and that sediment transport was northward into the Animikie basin. Thus, he postulates a granitic landmass south of the Gogebic range shedding abundant clastics. The presence of probable Middle Precambrian submarine volcanics near Mercer approximately 20 miles to the south 23 �IR 46/2E/14B (2) PREeM"R IAN Y ROCKS r- I PRECAMflRIAN X ROCKS SOUTH + 2000 FEET + + + + + + + + + + 2000 FEET + + ... ... + + + ... + ... + + + + + ... ... + + + + + + + + +- + ++ ... + + + ... + + + + + + + + + + PRECAMBRIAN W ROCKS Generalized diagram of the relationship of Precambrian rocks in the central Gogebic district EROSION SURFACE NORTH SOUTH + 1- + + + + 1- +. + + ... + <- + 1- +- + +. + ... + ++ t- + + + ... + + + +- + +. + + + + + + + + + + + + + t ++ + Hypothetical post-Penokean pre-Keweenawan cross-section on same surface as front of block diagram above 24 + + �IR 46/2E/14B (3) (Allen and Barrett, 1914; Dutton and Bradley, 1970) suggest that the granitic landmass must have been narrow. Assuming that the volcanics near Mercer are correlative with those in the Ironwood Iron-formation in the eastern Gogebic range (Aldrich, 1929), limits on the size of the landmass would suggest that it must have been tectonically uplifted to continue to provide the source of sediments for the Tyler Formation. The dip of the Tyler Formation at this location is 70 0 N\~. Graded beds and other primary structures indicate that the beds are right-side up (Schmidt and Hubbard, 1972). Cleavage in the shaly layers dips less steeply than the bedding (about 30 0 NW). According to Schmidt and Hubbard (1972), this cannot be a Keweenawan axial plane cleavage because that cleavage would dip more steeply than the bedding. If this is an axial plane cleavage, it must have formed during an earlier deformation, presumably the Penokean Orogeny. Discussion: Schmidt and Hubbard (1972) point out that the basal Keweenawan dips more steeply northward than the Middle Precambrian Tyler and Ironwood Formations, suggesting that the Middle Precambrian was dipping south'during early Keweenawan time. The cleavage to bedding relationship at this stop also suggests that the Tyler Formation was dipping south at the time the cleavage formed. Thus, the present orientation of the units is a result of subsidence of the Lake Superior syncline during Keweenawan time, as shown for most of the Gogebic range, suggesting that a block approximately 60 miles long and perhaps 10-15 miles wide rotated northward nearly 90 0 with no obvious internal deformation. The tilting of this block occurred after deposition of the Oronto Group (of early Late Keweenawan time (Craddock, 1972)) because of the Freda sandstone dips near vertically along the Montreal River on the Michigan-Wisconsin border. This suggests that the Tyler and other Middle Precambrian rocks were buried beneath at least 12 miles (20 kms) of Keweenawan basalts and sandstones during the Late Precambrian. However, the low metamorphic grade of the Tyler at this locality is difficult to reconcile with the interpretation of having been buried to a depth of 12 miles. Either an unusually low geothermal gradient of burial was too short to affect much recrystallization, or heretofore unrecognized structures in the Keweenawan sequence give an exaggerated apparent depth of burial. The last alternative seems most likely. Most recognized faults (and the most obvious ones) on the Gogebic are cross-faults; however, mine mapping (Hotchkiss, 1919) has demonstrated the presence of bedding faults and strike faults in the Ironwood Iron-formation. The strike faults duplicate the section in places. I suggest that strike faults (or perhaps thrust faults) exist in the Keweenawan duplicating the section to give an exaggerated thickness of Late Precambrian rocks and therefore an exaggerated apparent depth of burial for the Tyler Formation in this area. Perhaps the question should be raised whether the cleavage may be related to these postulated thrust faults, and therefore of Keweenawan age. Resolution of this problem is pertinent to an understanding of both the Middle and Late Precambrian geology of the Lake Superior region. References Cited: Aldrich, H.R., 1929, The geology of the Gogebic Iron Range of Wisconsin: Wisconsin Geological and Natural History Survey Bulletin 71, 279 p. 25 �IR 46/2E/14B (4) Allen, R.C., and Barrett, L.P., 1915, Contributions to the pre-Cambrian geology of northern Michigan and Wisconsin: Michigan Geological and Biological Survey, Publication 18, p. 65-129. Alwyn, B.W., 1976, Sedimentation of the Middle Precambrian Tyler Formation of north-central Wisconsin and northwestern Michigan: Unpub. M.S. Thesis, University of Minnesota-Duluth, 175 p. Craddock, C., 1972, Late Precambrian - Regional geologic setting: in P.K. Sims and C.B. Morey, editors, The Geology of Minnesota (C.M. Schwartz Volume): Minnesota Geological Survey, p. 281-291. Dutton, C.E., and Bradley, R.E., 1970, Lithologic, geophysical and mineral commodity maps of Precambrian rocks of Wisconsin: U.S. Geological Survey Miscellaneous Geological Investigation Map 1-631, 1:500,000, 6 sheets, separate text. Hotchkiss, W.O., 1919, Geology of the Gogebic Range and its relation to recent mining developments: Engineering/Mining Journal, v. 108, p. 443-452, 501-507, 537-541, 577-582. James, H.L., 1960, Problems of stratigraphy and correlation of Precambrian rocks with particular reference to the Lake Superior Region: American Journal of Science, v. 258-A, p. 104-114. Leith, C.K., Lund, P.J., and Leith, A., 1935, Precambrian rocks of the Lake Superior Region: U.S. Geological Survey Professional Paper 184, 34 p. Schmidt, R.G., and Hubbard, H.A., 1972, Penokean Orogeny in the central and western Gogebic Region, Michigan and Wisconsin: Field Trip A, 18th Annual Institute on Lake Superior Geology (Houghton, Michigan). 26 �IR 42/4E/28B Title: Bear River-Powell Kyanite Location: On State Hwy. 182 approximately 1 mile west of State Hwy. 47. SE\, SW\, Sec. 28, T.42N., R.4E. (Wilson Lake, 7Yz-Minute Topographic Quadrangle, Vilas County). 47 Author: Gene L. LaBerge (1978) Description: This exposure is part of a sequence of upper amphibolite facies gneisses and schists that occur as widely scattered outcrops along the Flambeau River flowage. Magnetic surveys and diamond drilling suggest that this sequence of rocks continues eastward into northern Michigan, and the occurrence of iron-formation, pellitic rocks and volcanics has served as a basis for correlating these rocks with the much lower-grade rocks on the Gogebic range (Allen and Barrett, 1915). James (1955) includes this area in the core of his "Watersmeet node," an elongate area of high-grade regional metamorphism, and Dutton and Bradley (1970) show that metamorphic intensity decreases in directions from this high-grade center. l1ain lithologies present include amphibolites, quartzo-feldspathic gneisses and schists, some of which contain staurolite and kyanite ±sillimanite (Black, 1977). Exposures here are mainly garnet-staurolite-kyanite-bearing schists, although sillimanite is present in small amounts. The sillimanite occurs as incipient crystal clusters in the kyanite. Black (1977) concluded that 27 �IR 42/4E/28B (2) the mineral assemblage kyanite-staurolite-muscovite + sillimanite suggests metamorphism at 685 0 C and a pressure of about 7.5 Kb. This indicates that the rocks were metamorphosed at a depth of 25 kilometers and at temperatures at or near minimum melting range (Black, 1977). The rocks have been intensely folded about an east-northeast trending fold axis with a prominent east-northeast foliation. Quartz boudins, intrafolial folds, disconnected fold hinges and limbs, and augen and other features of transposed bedding are common and obliterate most primary features of the rocks (Black, 1977). The sequence probably represents a highly deformed and metamorphosed pile of mafic to felsic volcanic rocks and graywackes. The high-grade rocks are bounded on the north by a sequence of less deformed, and less metamorphosed mafic-intermediate volcanics, iron-formation and slate (Allen and Barrett, 1915; Black, 1977). The boundary between these sequences contains a prominent zone of electrical conductivity called the flambeau Anomaly (Sternberg and Clay, 1977). The anomaly is evidently produced mainly by highly graphitic rocks that extend a minimum of 17 kilometers into the crust. The conductive zone extends west-southwesterly more than 100 km to near Couderay in Sawyer County. Discussion: Allan and Barrett (1915) interpreted the boundary between the greenstones on the north and the high-grade rocks on the south as an unconformity. Black (1977) interprets the boundary as a major fault with the south side uplifted. The proposed fault may correlate with Sims' (1976) postulated boundary between a 2650-2700 m.y. old granite-greenstone terrane to the north and an older gneiss terrane to the south (Black, 1977). The Flambeau Anomaly appears to be in-folded or in-faulted along the boundary between the greenstones (of unknown age) and high-grade metamorphic rocks (also of unknown age). Thus, the more recent interpretations of the geology in this area raise the question of whether the high-grade metamorphic rocks exposed here are really correlative with the Tyler Formation of the Gogebic. The stratigraphic position of the greenstones to the north is also debatable. Alwyn's (1976) interpretation of a granitic landmass south of the Gogebic as a source area for the Tyler coupled with the recent recognition of major faults and the Flambeau Anomaly suggests that the geology may be far more complex than heretofore recognized. References Citied: Allen, R.C., and Barrett, L.P., 1915, Contributions to the pre-Cambrian geology of northern Michigan and Wisconsin: Michigan Geological and Biological Survey, Publication 18, p. 65-129. Alwyn, B.W., 1976, Sedimentation of the Middle Precambrian Tyler Formation of north central Wisconsin and northwestern Michigan: Unpub. M.S. Thesis, University of Minnesota-Duluth, 175 p. Black, F.M., 1977, The geology of the Turtle-Flambeau area: Iron and Ashland Counties, Wisconsin: Unpub. M.S. Thesis, University of Wisconsin-Madison, 150 p. 28 �IR 42/4E/28B (3) Dutton, C.E., and Bradley, R.E., 1970, Lithologic, geophysical and mineral commodity maps of the Precambrian of ~~isconsin: U.S. Geological Survey Miscellaneous Geologic Investigation }1ap 1-631, 1:500,000, 6 sheets, separate text. James, H.L., 1955, Zones of regional metamorphism in the Precambrian of northern Michigan: Geological Society of America Bulletin, v. 66, p. 1455-1487. Sims, P.K., 1976, Presidential address - Precambrian tectonics and mineral deposits, Lake Superior Region: Economic Geology, v. 71, no. 6, p. 1092-1118. Sternberg, B.K., and Clay, C.S., 1977, Flambeau Anomaly: Ahigh-conductivity anomaly in the southern extension of the Canadian Shield: in J.G. Heacock, editor, The Earth's Crust: American Geophysical Union Monograph 20, p. 501-530. 29 �ON 36/llE/29 Title: Monico East - Mafic Pillow Basalt Location: Intersection of U.S. 8 and County V, center of Sec. 29, T.36N., R.llE., Oneida County (Monico 7Yz-minute topographic quadrangle, 1965). 45 8 & 8 47 Author: M.G. Mudrey, Jr. (1978) Description: A large outcrop is in the southwest corner of the intersection. The rock consists predominantly of sulfide-bearing, gray-green, chloritic pillow basalt trending N. 85 0 E., and dipping 80 0 SE. The two-foot thick by three-foot long pillows are slightly stretched and top to the south. Original pyroxene has altered to hornblende and chlorite. Plagioclase is extensively altered. The southeast edge of the outcrop is a ten-foot thick massive flow or sill. Diabasic texture in this unit is well developed. Discussion: Two supracrustal sequences characterize the Middle Precambrian succession in northern Wisconsin and Michigan, a dominantly sedimentary unit including iron formations to the north, and a dominantly volcanic sequence including massive sulfide deposits to the south. Inasmuch as bedrock exposures are poor south of the Gogebic Range area, geologic maps of northern Wisconsin are based dominantly on geophysical interpretation. Units defined in the few areas of outcrop are extrapolated into the poorly exposed areas. The belt of rocks from Ladysmith on the west to Pembine on the east appears to be dominantly volcanic, with few intrusives. The volcanics in the Monico area are among the least deformed and better exposed in this belt. Pillows and other indicators of subaqueous deposition are evident in the volcanic rocks exposed in the Monico area. These features are well preserved because of the low metamorphic grade. The sequence around Monico appears 30 �ON 36/llE/29 (2) to young to the south, and the sequence is known to be repeated by faulting that trends east-northeast. This particular outcrop appears to lie stratigraphically above the massive sulfide deposit at Pelican River to the west, and possibly above the Crandon deposit to the east. It is representative of the basaltic rocks in the Monico area. �ON 36/llE/30 Title: Monico Gravel Pits - Andesite Pillow Lava Location: Exposures are at the top of the hill behind houses on Baade and Lake Roads, and on the north side of the gravel pit to the west, NE~, NE~, Sec. 30, T.36N., R.llE., Oneida County (Monico 7~-minute topographic quadrangle, 1965). Author: M.G. Mudrey, Jr. (1978) Description: The outcrops consist of pillowed. fine grained. light gray andesite with sparse to abundant quartz and plagioclase phenocrysts. The pillows appear to top south. Schriver (1973, p. 25) describes the rocks as amygdaliodal basalt. In the gravel pit, the amygdule fillings have weathered out, leaving a pockmarked vesicle texture. Amygdules constitute up to three percent of the rock. range in size up to three mm, and have a ~lobular shape, but are generally undeformed. A chlorite rim encloses the amygdule filling of epidote or epidote and quartz. The groundmass consists predominantly of epidote and actinolite less than 0.05 mm in size. Plagioclase phenocrysts are largely altered to epidote and calcite and appear to be around AnZ5-30' Schriver (1973, p. SO, no. 16) reports the following chemical data: SiO Z TiOZ Al Z0 3 FeO T MuO 53.5 0.7 14.0 9.3 0.1 Molecular Norm (Irvine-Baragar) Q ZO.5 Or 0.3 Ab 10.1 An 15.3 Ho 12.9 3Z �On 36/llE/30 (2) MgO CaO Na20 K20 6.9 10.6 2.1 0.1 Total 97.3 En Fs Mt II 25.5 12.0 2.1 1.3 Other analyses of this unit several miles to the southwest contain more silica and potassium, and might more properly be termed dacite. Other outcrops of this unit may be found on the hills to the southwest and to the northeast. Mapping in 1978 by Mudrey suggests that this unit can be traced along an east-northeast strike about 3/4 mile. Mapping also suggests that this unit overlies the tuffaceous agglomerate unit to the east and south. Discussion: Intermediate to felsic Middle Precambrian volcanism characterizes the northern Wisconsin volcanic belt. May (1977) describes the host rocks associated with the Flambeau deposit near Ladysmith, and Schmidt and others (1978) describe similar rocks associated with the Crandon deposit. Recently, Bowden (1978) described a similar sequence of rocks at the Pelican River deposit. Present mapping and geophysics suggest that the sequence of volcanic rocks immediately around Monico are close to the same stratigraphic position as the rocks at Pelican River. This exposure probably lies stratigraphically beneath the Pelican ore body, although definitive mapping has not been completed. References Cited: Bowden, D.R., 1978, Volcanic rocks of the Pelican River massive sulfide deposit, Rhinelander, Wisconsin: A study in wallrock alteration: Unpub. M.S. Thesis, Michigan Technological University, 62 p. May, E.R., 1977, Flambeau - A Precambrian supergene enriched massive sulfide deposit: Geoscience Wisconsin Vol. 1, p. 1-26. Schmidt, P.G., Dolence, J.D., Lluria, M.R., and Parsons, G., III, 1978, Geology of the Crandon massive sulfide deposit in Wisconsin: Skillings' Mining Review, v. 67, no. 18, p. 1, 8-11. Schriver, G.H., 1973, Petrochemistry of Precambrian greenstones and granodiorites in southeastern Oneida County, Wisconsin: Unpub. M.S. Thesis, University of Wisconsin-Milwaukee, 83 p. 33 �(00 Title: Witte Farm - Coarse Felsic Agglomerate /"" ON 36/11E/2l "'~ Location: 1.4 miles north of intersection of U.S. 8 and U.S. 45. Outcrop located 400 feet east of highway behind abandoned house. SE~, NW~, Sec. 21, T.36N., R.llE., Oneida County (Monico 7~-minute topographic quadrangle, 1965). Author: M.G. Mudrey, Jr. (1979) Description: Three-foot long, angular, dacite clasts range in size from inches to several feet are set in an amphibole-bearing tuff or graywacke. Within the clasts, sparse euhedral plagioclase phenocrysts (An20) up to 1.8 mm in maximum dimension are set in a flow banded matrix which wraps around the crystals. The rock is intensively altered, and sericite extensively replaces plagioclase. The groundmass consists predominantly of quartz, muscovite, and calcite. Blood red hematite is present, along with local concentrations of epidote and chlorite. The matrix for the clasts consists of altered mineral grains 0.3 to 0.4 rnrn in size. A few relict (? pyroxene (?) and amphibole crystals remain, but the grains in the matrix consist predominantly of epidote-chlorite-muscovite-quartz granules. Calcite occurs abundantly as granules and in veins. Blood red hematite is sparse, and reflict glass shards can be seen in thin sections. The trend of bedding is N. 70 0 -75 0 W. and dips 85 0 SW. About 700 feet to the northeast, intermediate pillow lavas appear to top south, however the bedding trend at this locality is N. 60 0 W. This is the only area of the quadrangle in which folding has been suggested. 34 ) �ON 36/llE/2l (2) A small body of intrusive granodiorite can be found about one thousand feet north. Discussion: Sangster (1972) noted the close spatial association between felsic agglomerates (or coarse pyroclastics) and massive sulfide ores, and that these agglomerates were a characteristic feature of many mining regions. Sangster (1972, p. 3) remarks that "the author L-Sangster=/ once remarked to his colleagues that whenever he stood on the outcrop containing the largest fragments of acid pyroclastic in any given mining camp, he could invariably hear the mine mill nearby. His colleagues immediately dubbed this distinctive lithology 'millrock' and since then, 'millrock' has been observed close by most massive sulfide deposits in Precambrian volcanic rocks." The interpretation of this distinctive lithology is still open. Millrock is generally found in, or close to volcanic units in which the massive sulfides occur. The belt of rocks from the Pelican deposit, about 7 miles west, to several miles east of this locality has been extensively explored since the early 1970's. Although only the Pelican deposit has been announced as a possible massive sulfide deposit, the intensity of exploration attests to the favorable terrane. References Cited: Sangster, D.F., 1972, Precambrian volcanogenic massive sulfide deposits in Canada: A review: Geological Survey of Canada Paper 72-22, 44 p. 35 �ON 36/10E/26 Title: Monico West - Section 26 Pyritic Tuff Location: Old U.S. 8 west of Monico, SE~, NW~, Sec. 26, T.36N., R.IOE., Oneida County (Monico 7~-minute topographic quadrangle, 1965). 8 & 47 8&47 Author: M.G. Mudrey, Jr. (1978) Description: The low outcrop on the north side of the road is a fine, light-gray, pyritic, indistinctly bedded lithic-crystal tuff which trends N. 60 0 -70 0 E. and dips vertically. The crystals consist of millimeter-sized, sericitized plagioclase. Most of the crystals are euhedral and embayed and corroded. Less altered lithic fragments contain minor amphibole. Actinolite, chlorite, and epidote are the dominant alteration minerals. Prehnite (?) and hematite are sparse. The low ledge on the south side of the road consists of beds of gray, finegrained, chloritic crystal tuff and bedded, light gray, aphanitic ash. The tuff is similar to the tuff on the north side, but matrix is more abundant, and the crystals sparser. Chlorite in the ash is berlin blue in thin section. This volcaniclastic unit varies considerably from fine tuffs and ashes to lapilli tuff. The unit is 3,000 to 4,000 feet thick and can be traced along strike at least three miles. Discussion: Massive sulfide are bodies consist mainly of sulfide-rich tuff, and grade distally into pyritic tuffs. These lithologies usually do not crop out because the sulfides weather readily. Therefore, the sulfide-rich outcrop here is unusual. It illustrates the general lithology and composition of the distal ends of a massive sulfide are body. Some outcrops in the area contain more 36 �ON 36/l0E/26 (2) sulfide than this One. A recent road cut in Sec. 21, T.36N., R.llE. contains abundant sulfidic and sericitic schists, and may represent the lateral equivalent of the mineralized zones at Little Sand Lake. The trend of bedding at this locality and at the Crandon deposit near Little Sand Lake in Forest County is slightly north of due west, and on projection this locality could be essentially the same stratigraphic horizon as that at Little Sand Lake. Intervening between the two, however, is the granite body at Jennings (exposed at Beck Tower Wayside). Wisconsin aeromagnetic data suggest a northwest-trending fault immediately west of the Little Sand Lake deposit, therefore, this particular exposure probably is not directly correlatible with Little Sand Lake, but does illustrate many of the rock types spatially associated with the host rocks for the massive sulfide deposit. 37 �On 35/llE/6 Title: Beck Tower Wayside Park - Jennings Granite Location: 2~ miles south of Monico on U.S. 45 and State 47 S\V~ SEY. Sec 6 T.35N., R.llE., Oneida County (Monico 7~-minute topographic'qua~;ang;~, 1965)~ Author: M.G. Mudrey, Jr. Description: This outcrop is a coarse, red, biotite granite and exhibits spheroidal weathering. Another outcrop is present 500 feet to the northeast in a railroad cut. Fresher outcrops of the same granite are found near Jennings, about 6 miles east. According to Venditti (1973, p. 46), the rock contains euhedral orthoclase, microcline and microperthite (40 percent), subhedral to euhedral oligoclase (An27, 23 percent), anhedral quartz (31 percent), and minor amounts of interstitial biotite (3 percent). The biotite is pleochroic and light brown to dark brown, is sagenitic, and altered to chlorite. The grain size is 4-5 mm and shows no cataclastic textures at this outcrop, although outcrops near Jennings show narrow, well developed mylonitic zones. Venditti (1973, p. 90, no. 24) reports the following analysis: 73.1 tr 15.5 1.5 tr tr Si02 Ti02 A1 2 0 3 FeaT MnO MgO 38 �On 35/llE/6 (2) CaO Na 2 0 1.5 3.0 4.3 Total 98.9 K2 0 Van Schmus and others (1975, p. 1259, no. D1356) report a Rb-Sr age of 1,580 m.y. from this locality. Van Schmus (in press) reports a U-Pb zircon age of 1,765± 10 m.y. from this locality. Discussion: The potassic granitic intrusives in the Middle Precambrian of northern Wisconsin are all post-tectonic, and their ages cluster around 1,765 m.y. The younger 1,600 m.y. Rb-Sr age represents a wide-spread alteration of Rb-Sr ages that is not fully understood. Van Schmus (in press) has divided the Middle Precambrian igneous activity into two pulses. The older one began with mafic to felsic volcanism 1,850~ 20 m.y. ago, and was followed immediately by tonalitic to granitic plutonism 1,840 1,820 m.y. ago. Structural studies by Maas (1977) indicate that these rocks were emplaced during the main phase of the Middle Precambrian thermotectonic event. The second pulse consisted predominantly of phyolitic and granophyric granite and occurred about 1,765± 10 m.y. ago. No plutonic units have been found so far with zircon ages in excess of 1,850, nor have any been found with ages on the order of 1,615 - 1,630 m.y., the time of widespread alteration of the Rb-Sr isotopic systems in the region. After emplacement of the late granites, major faulting occurred (LaBerge and Myers, 1976 and LaBerge, 1977), and has been recently studied to the south in Marathon County. Late faulting is recognized in north-central Wisconsin as seen in the mylonitic samples from Jennings. Extent and magnitude of the faulting in north-central Wisconsin is not known. References Cited: LaBerge, G.L., 1977, Major structural features in central Wisconsin and their implications to the Animikie Basin (abs.): 23rd Annual Institute on Lake Superior Geology (Thunder Bay, Ontario). LaBerge, G.L., and Myers, P.E., 1976, The Central Wisconsin Batholith (abs.): 22nd Annual Institute on Lake Superior Geology (St. Paul, Minnesota). Maas, R.S., 1977, Structure and petrology of an Early and ~iddle Precambrian gneiss terrane between Stevens Point and Wisconsin Rapids, Wisconsin: Unpub. M.S. Thesis, University of Wisconsln-Madison, 128 p. Van Schmus, W.R., in press, Chronology of igneous rocks associated with the Penokean orogeny in Wisconsin: Geological Society of America Memoir. Van Schmus, W.R., Thurman, E.M., and Peterman, Z.E., 1975, Geology and Rb-Sr chronology of Middle Precambrian rocks in eastern and central ~visconsin: Geological Society of America Bulletin, V. 86, p. 1255-1265. Venditti, A.R., 1973, Petrochemistry of Precambrian rocks in southeastern Oneida County, Wisconsin: Unpub. M.S. Thesis, University of WisconsinMilwaukee, 93 p. 39 �Pr 34/2W/20 Title: Jump River at Big Falls County Park Location: Along the Jump River in NE~, NE~, Sec. 29, and SE~, Sec. 20, T.34N., (Jump River Fire Tower, Topographic Quadrangle, R.2W., Price County. 1970). N N Author: Gene L. LaBerge Description: The main rock type exposed here is a weakly foliated quartz monzonite of presumed Middle Precambrian age. Foliation strikes approximately east-west and dips vertically. Late stage aplite dikes along with minor pegmatite and vein quartz cut the main quartz monzonite body. DO\Vllstream from the main park area the rock has been extensively sheared to f1aser gneiss and mylonite. The main catac1astic foliation is oriented approximately east-west with a vertical dip and is about one-half mile wide. Within the catac1astic zone are smaller mylonitic zones that strike N.30 o E. and about 40 o SE. Pyritic tuffaceous andesitic(?) greenstone crops out at the major bend in the river approximately three-quarters of a mile downstream from the park. ~ood preservation of primary textures suggests the rocks have undergone only greenschist or lower amphibolite facies metamorphism. A number of exposures of mafic rocks are present along the river between the tuffaceous greenstone and quartz monzonite. They appear to be somewhat metamorphosed and sheared. 40 �Pr 34/2W/20 (2) Discussion: This exposure is along a major structural feature in Wisconsin, the "Jump River lineament" (Myers, 1974). The lineament is expressed topographically and on both the Bouguer anomaly gravity map (Ervin and Hammer, 1974), and the aeromagnetic map (Zietz, Karl, and Ostrom, 1978). Where exposed, the lineament consists of cataclastic rocks. North of the lineament of the rocks are dominantly volcanic rocks in the greenschist and/or lower amphibole facies with numerous more or less foliated granitic plutons. This forms a major east-west volcanic belt of Middle Precambrian rocks across Wisconsin from the Michigan border westward to the Keweenawan overlap (Sims, Cannon, and Mudrey, 1978). (Note that the "Jump River Fault" of Sims, Cannon, and Mudrey (1978) does not coincide with the "Jump River lineament" of Myers (1974).) South of the lineament, gneisses, amphibol~tes, schists and migmatites are the predominant rock types for nearly 30 miles. Relatively unmetamorphosed volcanic and plutonic rocks are common in Marathon County and are in fault contact with the gneisses (LaBerge, 1977). Little or no work has been done on the high-grade rocks; however, they appear to be mainly amphibolite grade with few, if any, primary features preserved. Cummings and Myers (1978) and Myers (1977) have studied similar rocks in the Eau Claire area that are evidently part of this terrane, and they concluded that the rocks are at least in part Early Precambrian. Probable Middle Precambrian granitic rocks intrude the highergrade rocks, and isolated patches of low-grade metavolcanic and metasedimentary rocks are present in places (Myers, 1978a, b). The low grade metamorphic rocks are probably Middle Precambrian in age, but no age determinations are available on the higher grade rocks. Thus, we do not know whether the high-grade rocks represent an Early Precambrian basement on which simply more highly metamorphosed Middle Precambrian rocks. The "horst-graben" pattern in Central Wisconsin is suggestive of basin and range structure. The implications of this structure, as well as its timing, has important bearing on our interpretation of the tectonic development of the Animikie Basin. As indicated here, the emplacement of at least some of the granitic plutons occurred prior to final displacement along the fault zones. If this is a Penokean age pluton, the faulting must be either late Penokean or post-Penokean in age. References Citied: Cummings, M.L., and Myers, P.E., 1974, Eau Claire River at Big Falls: Wisconsin Geological and Natural History Survey, Geology of Wisconsin Outcrop Description EC 27/8W/13, 10 p. Evin, C.P., and Hammer, S., 1974, Bouguer anomaly gravity Map of T..visconsin: Wisconsin Geological and Natural History Survey, scale 1:500,000, 2 sheets, separate text. LaBerge, G.L., 1977, Major structural features in central Wisconsin and their implications on the Animikie Basin (Abs.): 23rd Annual Institute on Lake Superior Geology (Thunder Bay, Ontario), p. 23. Myers, P.E., 1977, Eau Claire River at Little Falls: Wisconsin Geological and Natural History Survey, Geology of Wisconsin Outcrop Description EC 27/8W/19, 6 p. Myers, P.E., 1978a, North Fork of the Eau Claire River at Knight Pool: lJisconsin Geological and Natural History Survey, Geology of Wisconsin Outcrop Description EC 26/5W/lO, 2 p. 41 �Pr 34/2W/20 (3) Myers, P.E., 1978b, Eau Claire River at Confluence of North and South Forks: Wisconsin Geological and Natural History Survey, Geology of Wisconsin Outcrop Description EC 26/5W/29, 2 p. Sims, P.K., 1976, Presidential address - Precambrian tectonics and mineral deposits, Lake Superior Region: Economic Geology, v. 71, no. 6, p. 1092-1118. Sims, P.K., Cannon, W.F., and Mudrey, M.G., Jr., 1978, Preliminary geologic map of Precambrian rocks in part of northern Wisconsin: U.S. Geological Survey Open-file Report 78-318, scale 1:250,000, 2 sheets. Zietz, I., Karl, J.H., and Ostrom, M.E., 1978, Preliminary aeromagnetic map covering most of the exposed Precambrian terrane in Wisconsin: U.S. Geological Survey Miscellaneous Field Study MF-888, scale 1:250,000. 42 �SW 38/7W/23 Title: Arpin Dam in Radisson - Late Porphyritic Granite Location: River channel downstream from Arpin Dam, one mile southeast of Radisson, NW\, SE\, Sec. 23, T.38N., R.7W., Sawyer County (Radisson 7~-minute topographic quadrangle, 1972) Author: M.G. Mudrey, Jr. (1978) Description: Outcrops are reasonably abundant in the vicinity of Radisson. The bedrock consists of a coarse, hornblende-granodiorite with inch-sized microcline megacrysts generally aligned N. 50o~E. Medium-granied aplite dikes up to onefoot wide trend N. 15 0 -35 0 E. The granodiorite consists of subhedral to euhedral microcline set in a groundmass of sutured quartz grains, subhedral plagioclase (An 15-20), minor brown biotite slightly altered to chlorite, and green hornblende with trace amounts of apatite, epidote and zircon are found. The aplite dikes consist of equal amounts of subhedral plagioclase (An 20), microcline, and anhedral quartz. Trace quantities of muscovite, chlorite and zircon are present. Van Schmus (in press) reports an U-Pb zircon age of 1,765 10 m.y. for a sample from Grimh Flowage, about 0.6 miles west of this locality. Discussion: This granodiorite, the Jennings granite, other alkalic granites, and the rhyolites of south-central Wisconsin are all late Penokean and yield ages around 1,765 m.y. For the most part, the granitic rocks are little deformed, but all yield Rb-Sr ages around 1,600 m.y. The 1,600 m.y. age is widespread. However, there appears to be no rock units or major structures related to this resetting in northern Wisconsin. Smith (1978) has determined that the Baraboo 43 �SW 38/7W/23 (2) Quartzite and the rhyolites of southern Wisconsin were metamorphosed and deformed about this time. The 1,600 m.y. age is pre-Wolf River and associated rapakivi granites, syenites and anorthosites. Some of the faulting in the area may be related to this 1,600 m.y. thermal event. The Radisson granodiorite is similar to the Rockville Granite of Minnesota, both in petrography and in age (Keighin and others, 1972, p. 240). References Cited: Keighin, C.W., Morey, G.B., and Goldich, S.S., 1972, East-Central Minnesota: in P.K. Sims and G.B. Morey, editors, The Geology of Minnesota (C.M. Schwartz Volume): Minnesota Geological Survey, p. 240-255. Smith, E.I. 1978, Precambrian rhyolites and granite in south-central Wisconsin: Field Relations and geochemistry: Geological Society of American Bulletin, v. 89, p. 875-890. Van Schmus, W.R., in press, Chronology of igneous rocks associated with the Penokean orogeny in Wisconsin: Geological Society of American Memoir. 44 600-3 J 9T025-79 � https://digitalcollections.lakeheadu.ca/files/original/eec5ad95f486276a3fc18dd307239f9b.pdf 8d0703cdf8c8bf578aa79690dfd9c0ec PDF Text Text DEPARTMENT OF GEOLOGY, UNIVERSITY OF MINNESOTA AT DULUTH QUATERNARY GEOLOGY OF THE DULUTH AREA BY CAROL M. MOSS, RANDEE J, ZARTH CHARLES L. MATSCH AND --------- I PREPARED FOR FIELD TRIP N0.3 OF GEOLOGICAL THE NORTH-CE:·!TRA.L SECTIO~! SOCIETY OF AMERICA 13TH ANNUAL MEETING AND INSTITUTE OF LAKE SI.IPERIOR GEOLOGY MAY 3-12, 1979 DULUTH, MINNESOTA MAY 12, 1979 25TH i'1EETING THE �DEPARTMENT OF GEOLOGY, UNIVERSITY OF MINNESOTA AT DULUTH QUATERNARY GEOLOGY OF THE DULUTH AREA BY CAROL M. MOSS, RANDEE J, ZARTH AND C!1ARLES L. MATSCH CHARLES L. MATSCH, FIELD TRIP LEADER PREPARED FOR FIELD TRIP N0.3 OF THE NORTH-CENTRAL SECTION GEOLOGICAL SOCIETY OF AMERICA 13TH ANNUAL MEETING AND THE INSTITUTE OF LAKE SUPERIOR GEOLOGY 25TH MEETING MAY 12, 1979 ��1 PHASES OF GLACIAL ¾; ACTIVITY IN NNESOTA .,_ 1 1-------,;i;_ ·--·T-.i.., ! \. j r,.c\i>- i ·-·- ""o -- 4ss,~ ---=- · lae•c" ~_,_.__.,,,__, ~•-T£.-~,· ~ 4o I, ,s.. r· . ,. • • ! I -- LAKE '----·-·-\ ~ :-=-=== ,. .--;ro~ , . b -- R LAKE DULUTH LEGEND AGE OF ICE •Dc~rOldHI □ ~ I] • ■ ~ - SCALE ,o v......,. ,. -WUN Source: Geology of Minnesola: A Cen1t,nn1 ■ f Volume Frontispiece drafted by Mark Zwaschka; reproduced through the courtesy of the Department of Geography, UMD. ��QUATERNARY GEOLOGY OF THE HEAD OF LAKE SUPERIOR REGION Regional Setting Bedrock The northwestern shore of Lake Superior lies generally parallel to the strike of a southeastward dipping sequence of lava flows and mafic intrusive rocks emplaced about 1.2 b.y. ago (Fig. 1). This Keweenawan volcanic pile called the North Shore Volcanic Group is composed mainly of basalt, but includes significant volumes of rhyolite and lavas of Fig. 1. General geologic map of Minnesota and adjacent states. 1 �intermediate composition. The flows are estimated to be over 20,000 feet thick (Green, 1972). The largest of the associated intrusive bodies is the Duluth Complex, a meld of mafic material, mainly gabbro and anorthosite, but including the felsic rock granophyre. Smaller intrusions in the form of dikes and sills lace the entire section. Geophysically, rocks of similar density are traceable as a gravity high southwestward as far as Kansas, region (Fig. 2). and elsewhere in the Great Lakes The belted configuration as well as the composition of the rocks suggests that the entire sequence represents an episode of crustal rifting and insipient sea-floor spreading. That the process aborted is indicated by the insignificant width of the mafic rock belt. 0 0 Miles 250 Kilometers 400 Minnesota \ Wisconsin Nebraska Fig. 2. The mid-continent gravity high outlines the distribution of basaltic rocks emplaced during a rifting event about 1. 1 b. y. ago. 2 �Following the cessation of volcanic activity, the last to occur in this part of the earth's crust, subsidence of the area resulted in the tilting of the entire sequence gently eastward. sediments accumulated in the subsiding basin. A thick wedge of elastic These Late Precambrian sediments include the arkosi.c Fond du Lac Formation and the Hinckley Sandstone. Paleozoic marine transgressions either did not reach the western Lake Superior region, or the sedimentary record of such activity has been completely removed by erosion since deposition. Atop the Precam- brian, and separated from it by a profound unconformity, is the Quaternary System. Quaternary Geology The structure and differential erosion of the Precambrian bedrock in the Lake Superior region resulted in the development of a pre-glacial lowland which had a direct effect on ice movement in northeastern Minnesota. The lowland channeled ice from the Laurentide Ice Sheet into individual lobes which periodically invaded the western Lake Superior region from the north and northeast. Multiple glaciation of ~he region is evident from stratigraphic, geomorphic, and lithologic relations. The Superior Lobe generally moved southwest along the axis of the Lake Superior basin and west onto the upland, transporting sediment derived from the North Shore Volcanics, Duluth Complex, and Precambrian sandstones. Another ice mass, the Rainy Lobe, invaded from the north-northeast and deposited fragments of Precambrian crystalline rock (granite, gneiss, and gabbro), meta-sedimentary rocks, and iron formation. 3 �Four main advances during the Wisconsin Glaciation are recognized and shown in Figure 3 (Wright, 1972). The earliest, or St. Croix Phase, involved concurrent movement of the Rainy and Superior Lobes in a southwesterly direction, with deposition of a sandy-matrixed till and formation of the St. Croix moraine in south-central Minnesota. The formation of the Toimi Drumlins in northeastern Minnesota, composed of gray to brown sandy till with a large percentage of gabbroic fragments, is attributed to this phase of the Rainy Lobe. A period of glacial retreat followed, and a vast system of tunnel valleys was eroded in the glacial drift by subglacial streams flowing in a southwesterly direction. 100 Miles 0 100 Kilometers 0 A Silver Say I St. Croix Phase ' ·..... •· '\ Automba Phase . Split Rock Phase \ @ Nickerson \ ' Fig. 3. Phase '' . Minneapolis~.···. ' , ...... . . Outline of ice margins during successive phases of the Superior Lobe during Late Wisconsin glaciation. (From Wright, 1973.) 4 �The second, or Automba Phase, brought a readvance of the Superior Lobe out of the basin, this time in a more westerly direction. Movement continued as far west as the Mille Lacs Moraine, which borders the west and south sides of Mille Lacs Lake. The Automba drumlin field in western Carlton County is associated with this advance, as is the Highland moraine, which marks the northernmost extent of the lobe as it moved laterally out of the basin. The Rainy Lobe again advanced across the upland from north- east to southwest, forming the Vermilion moraine. After this phase, the Superior Lobe retreated far enough into the Lake Superior Basin to allow proglacial lakes to form around its margins. These lakes were sufficiently deep to allow deposition of silt and clay which was incorporated into glacial till during the next advance, or Split Rock Phase. The third, or Split Rock Phase of Wright (1969) is marked by the advance of a small tongue of ice which moved southwestward in the Denham area, depositing a discontinuous-layer of red clay-rich till on some of the eskers and tunnel valleys associated with earlier phases. A small field of drumlins was also formed in the Split_ Rock River Valley near Barnum. Late-glacial and early postglacial activity- is represented by extensive glaciolacustrine deposits and shoreline features at various levels, which developed during successive glacial lake stages as the Superior Basin was uncovered by melting of the Laurentide Ice Sheet. Winchell (1901) distinguished three lake levels in the western Lake Superior region: (1) "Glacial Lake St. Louis" at 345 m, (2) a lower, but more distinct level, Glacial Lake Nemadji (324 m), and (3) Glacial Lake Duluth 4 m lower than Glacial Lake Nemadji. 5 Glacial Lake Nemadji �was recognized from lacustrine clays, beach features, and a channel at roughly 321 m, which drained by way of the Kettle and St. Croix River systems. In Winchell's view, Glacial Lake Duluth covered approximately the same area as Glacial Lake Nemadji but had an outlet at 316 m and drained by way of the Brule-St. Croix River system. Leverett (1929) in addition to mapping Superior Lobe moraines, discussed the development of proglacial lakes. In his view, Glacial Lake 2 Nemadji was a small lake, covering a maximum area of 130 km, at an elevation of 321 m. It was bound on the northwest by the Thomson moraine and by the ice margin as it stood at the Fond du Lac moraine (Leverett, 1929). With further ice retreat, Lake Nemadji merged with several other small, proglacial lakes and eventually stabilized as Glacial Lake Duluth. Beach elevations at the western part of this lower lake range from 305 m to 318 m (Leverett, 1929). G. M. Schwartz (1949) delineated strandline features of Glacial Lake Duluth at elevations of 325 m. He also noted the extensive clay and silt deposits associated with the lake plain, especially the varves found at the Wrenshall clay pits. W. R. Farrand (1960) integrated much of the earlier shoreline data and added new observations in an attempt to correlate strandlines basinwide. His results are shown in Table 1. Farrand considered the shorelines of Glacial Lake Nemadji, as described by Leverett, to be associated with Glacial Lake Duluth. The term Glacial Lake Duluth was modified " ... to include all those major water bodies which occupied the southwestern part of the Lake Superior basin and which discharged into the St. Croix River system via either the Moose Lake outlet or the Brule-St. Croix outlet or both." (Farrand, 1960). 6 �TABLE 1--LAKE STAGES. (after Farrand,· 1960). LAKE STAGE ELEVATION AGE OUTLET (B.P,) (ft) Sault Lake Superior Sub-Sault Sault Beach 1000 2000 602 602 602 St. Marys River St. Marys River St. Marys River Algoma 3200 595-596 St. Marys Strait Ni pissing Great Lakes 4100 605-607 St. Marys StTait Houghton Low Stage 8500 360 Post-Minong series 90008500 ? Minong Post-Duluth Beaver Bay Manitou Washburn 9200 proto St. Marys R. St •. Marys Str,:lit : I St. Marys Strait &Au Train-Whitefish Strait . 420? 470? I 650 765 850 Au Train-Whitefish I Strait? Marquette Marquette 10,000 ' 870 Moquah Highbridge Sub-Duluth Duluth Epi-Duluth 10,220 920 955 1007 Marquette Huron Mts. Huron Mts. 1035 1060 1070 1085 Brule-St. Croix R. 1100 10, 700. 10,500 Moose Lake and Brule-St. Croix Moose Lake; Brule-St. Croix Recent work by H. E. Wright has contributed to working out stratigraphic sequences and relationships among ice lobes. In his interpre- tation of the development of glacial lakes following ice wastage, Wright supported the sequence proposed by Leverett: (1) the highest lake level of Glacial Lake Nemadji (318 m) and (2) the lower level of Glacial Lake Duluth near 305 m (Wright, 1972). 7 �Quaternary Stratigraphy, Sedimentology and Geomorphic Features Introduction Surficial sediments in the western Lake Superior region can be broadly grouped into three types: those deposited during advances of the Superior Lobe, those resulting from retreat and stagnation of the glacial ice, and and sediments associated with the formation of Glacial Lake Duluth. Lodge- ment till, deposited by actively advancing glacial ice is exposed in, or underlies, most of the region. In a generally NE/SW-trending belt roughly parallel to- Lake Superior, ice disintegration features of till and interbedded or associated sands and gravels predominate. A similarly trending belt of ground moraine parallels the present shoreline along the southern edge of the stagnant ice features. Lake clays with varying amounts of pebbles and boulders cover much of the remaining southern parts of the region. Tills Two tills of different ages, representing· separate advances of the Superior Lobe are extensively exposed along the Lake Superior shoreline and in some of the deeper stream valleys. Visually and texturally, the tills are very similar, and unless seen in their stratigraphic sequence, it is difficult to distinguish the two. The contact between the ~Jo tills is generally sharp and commonly a stone line or a gravelly or sandy layer separates them. Lower Till The lower till is generally dark reddish-brown, silt-rich, stony and very compact. Fissility is developed locally. 8 Although texture �varies, most of the samples analyzed fall into the loam category (U.S. Department of Agriculture Soil Classification). Analysis of 9 samples from exposures northeast of Duluth averaged 36% sand, 46% silt, and 18% clay. Basalt fragments comprise greater than 50% of the 1-2 nnn sand fraction, with gabbro and "red rock" fragments being the only other rock types of significance. boulder size. Up to 25% of the clasts by volume are cobble or This till is correlated with the St. Croix phase of the Superior Lobe as described by Wright (1969). Upper Till The upper till is the predominant surface material in upland areas away from the lake plain, including the Highland moraine. Its color is similar·to the lower till, although in many exposures it appears to be more red-brown. Compactness varies among localities; in places, the sediment is as highly compacted as the lower till, while in other areas, the material is easily disaggregated by the fingers. Although the same Lake Superior region rock fragments are present (basalt, gabbro, "red rock" sandstone, etc.) and in the same general percentages as in the lower till, this till varies considerably in the amount of pebbles, cobbles and boulders which are present from locality to locality; some sections are extremely stone-poor. Although variable in texture, the younger till is generally somewhat siltier than the lower till. Analysis of 28 samples from the Duluth vicinity shows an average composition of 30% sand, 50% silt and 20% clay (Fig. 4). Clasts of cobble or boulder size comprise at most 20% of the volume of the sediment. The textural variability may be due in part to the position of this till in the stratigraphic section; it 9 �CLAY Figure 4 Grain Size Disf ribuf ion in Tills I I \ @ Upper till average ... Lower f i II average 0 \ A I \ clay I ("'\ silty clay I I-' 0 sandy clay sandy clay \ \ \ \tlty clay loam clay loam O ("\ a._O mcf' ?o I /~ loam 6. J. sandy 1oam I \ ~ ~ 0 e - 0 0 0 silty loam 00 00 I I). I SAND 0 A I 0 .I s i It 0 SILT �was probably partially derived from the various sediments left by the preceding glacial advance. Thus, reworked older drift of varying composition may comprise most of this till rather than material eroded directly from bedrock sources. Th_is till has been attributed to advance of the Superior Lobe during the Automba phase (Wright, 1969). Stratigraphic Type Sections Although the two tills can be seen superimposed at many locations, probably the two best exposures are on McQuade Road in the French River quadrangle and in the City of Duluth along the shoreline at Leif Erikson Park (Stop No. 1 on the road log). At Leif Erikson Park the lower till is a sandy, dark brown to dark red-brown, fissile sediment with abundant boulders. the Superior Lobe are present. Clasts typical of The upper till is more red-brown in color, more silt-rich, and at this location more cohesive than the lower till. A discontinuous boulder line marks the generally sharp contact between the two tills. This may represent an erosional surface developed between glacial advances. At this location the textural difference between the two tills is easily distinguished. Along McQuade Road at the Sucker River, the same sequence is again exposed, although less textural difference is apparent between the two tills. The lower till at this location lacks the fissility of that at the Leif Erikson exposure; both tills at the McQuade location are compact and stony. Fabric Studies Orientation of the long axis and dip of elongated stones were measured for both tills at the McQuade Road location (Fig. 5). 11 The majority of �oo 00 f--' N 0 A. 1so FIGURE 5: B. 1so 0 Orientations of longest axes of elongated stones in McQuade Road exposure. Each circle equals one stone. A) Upper till, B) Lower till; average regional striation direction associated with the deposition of this till is approximately N65°E. �elongated stones dip in an upglacier direction. In general, the long axes of stones in the lower till tend to lie approximately 45° from the direction of ice flow as inferred from the regional striation pattern. In the upper till, a similar pattern is evident, with a large concentration of stones lying nearly transverse to ice flow as inferred from regional features such as the Highland flutes. Both tills also show a slight concentration of elongated stones in the direction parallel to inferred direction of ice flow. Clast Composition At both the Leif Erikson Park and McQuade Road exposures, grain counts of three size ranges were studied: clasts larger than 2 mm (up to and including roughly 4 cm), the 1-2 mm fraction, and the fraction less than 1 mm (Figure 6). Basalt is the predominant rock type in the 1-2 mm fraction as well as in the greater than 2 mm fraction. This is due in part to the abundance of basalt as the predominant bedrock type at and upglacier from the sample site. rock are also important. Physical characteristics of the bed- The abundance of joints and vesicles makes the basalt flows more susceptible to breakdown by abrasion, plucking and grinding during a glacial advance. The gabbro and diabase with their more widely-spaced joints and fractures are more resistant to plucking and crushing. abundant. The less than 1 mm fractions show quartz to be extremely Granite from sources still farther northeast as well as sand- stone from within the Lake Superior Basin are probably the source. little sandstone in the larger size range is an indication of its "crushability." 13 Very �80 BO LE 2 60 60 i/ 40 40 20 20 I :~:=:: / ,/{ /f~-, R,G B LE 6 GB 0 Q,F R,G B GB 0 I-' +' 80 60 ' 40 1\}:: ! 80 N25-1 N25-2 60 :::::: (ti~ 40, ,, .·.·-· 204::: 20 •••••••• B .-.·.· It? 1-:-:-:-: R,G GB Q,F ss 0 FIGURE 6: Percent composition of sand fractions in lower (LE 2, N25-l) and upper (LE 6, N25-2) tills. B=basalt, R,G= red rock or granite, GB=gabbro, QF= quartz or feldspar, SS=sandstone, O=other. B □ < l mm R,G GB □ 1-2 mm ss Q,F [ill ' ' > 2 mm 0 �Ice Disintegration Features In the areas west of the broad band of lacustrine clays, most of the topography reflects ice-marginal deposition of material from active as well as stagnant ice. A distinctive geomorphic feature, the Highland moraine, marks the northernmost edge of the Superior Lobe at its maximum advance during the Automba phase, and the Thomson moraine developed in the later Nickerson phase. Both features display great variability in sediment types over very short distances, and the landforms also indicate varying environments of deposition. The following studies of a part of the Thomson moraine near Wrenshall, Minnesota are presented as an introduction to terrains originating from ice disintegration. The moraine is a hulIDllocky complex of kames, kettles, disintegration ridges, and eskers. to 20 m. Local relief is varied but may be up These features are typical of an ice-disintegration environment. Ice-disintegration describes the processes involved in the break-up of a stagnant, wasting glacier. Ice-disintegration features are of two maj.or types: (1) controlled ice-disintegration and (2) uncontrolled ice-disintegration (Gravenor and Kupsch, 1959). Uncontrolled ice-disintegration results from equal forces acting in all directions forming unoriented features, such as kames, kettles, and general hummocky terrain. Controlled ice-disintegration occurs when there is break-up along fractures in the ice and when deposition is localized to form linear disintegration ridges and eskers. Uncontrolled Ice-disintegration Features Karnes Kames are conical hills or mounds of any size consisting of stratified sand and gravel. Kames are abundant in the northwest portion of 15 �the Wrenshall quadrangle and are associated with the Thomson moraine. There they are generally small, reaching maximum dimensions of up to 0.5 km in length and 20 min elevation. They have flat to rounded tops and varying slopes according to the texture of the underlying material. The kames are found to occur both as single, isolated hills and as composite hills which merge to produce ridge-like landforms. Texturally, these kames consist of poorly to moderately sorted, stratified sand and gravel, with boulders. The sand and gravel is in some places capped with fine sand to silt. Kettles Kettles are small basins created by the ablation of buried ice. Kettles found in the Thomson moraine area vary in size but are generally small, less than 1 km in diameter. Some display irregular shapes but most kettles tend to approach circularity. Kettles that are associated with kames tend to give a "pitted" appearance to the landscape and this "kettle and kame" topography is characteristic of ice-disintegration complexes. F. G. Driscoll (1976) in a study of moraine lakes at the Klutlan Glacier, Yukon Territory, suggests lake development may be the result of (1) the melt-out of ice containing differing amounts of debris, resulting in an irregular depositional surface; or (2) uneven surface debris accumulations due to topographic reversals, resulting from slumping of sediment. Superglacial lake development on a stagnant debris-covered surge lobe proceeds in five distinct stages as the buried ice melts (Driscoll, 1976): (1) accumulation of meltwater in low areas on the moraine; (2) expansion of the lake basin by both lateral and vertical melting, and the establishment of inlet and outlet streams; (3) accumulation of melt-out debris along lake perimeter, vegetation cover, and mass-wasting along steep shore areas; 16 �(4) stabilized slopes, rounded lake bottom, areal expansion ceases, significant life in lake; (5) reduction in enclosing slopes, heavy vegetation on periphery, decrease in lake depth and areal extent, final melt-out of buried ice, increase in biomass. Controlled Ice-disintegration Features Linear Disintegration Ridges The term linear disintegration ridge pertains to a ridge that originates during ice stagnation (Gravenor and Kupsch, 1959). Ridges of varying sizes, up to 12 min height and several kilometers in length, are found within the Thomson nroraine. Although these ridges are related to controlled disintegration, they appear gradational with uncontrolled features and are found with kettles and kames. The linear ridges vary in composition from medium and fine sand to sandy gravels, although the latter is predominant. The stratified nature of the drift contained in these ridges suggests that they were open crevasses in the stagnating ice which provided a site for the accumulation of stratified sediments. Sedimentology The sediments associated with ice-disintegration in the Duluth area exhibit a wide variety of textural characteristics, geometries, and sedimentary structures. The sediments are generally poorly to moder- ately sorted, stratified sand and gravel. The geometry of the units varies from sheet deposits to pods and lenses. The grain size distri- bution shows abrupt changes and an extreme range of sizes from boulders to clay. The sediments are thin to thickly bedded, with some cross- bedding, faults, current and gravity structures. 17 The clasts,generally �surrounded, are composed of Precambrian sandstone, basalt, rhyolite, gabbro, granite, gneiss, iron formation, slate, and graywacke. The sediments can be divided into five units based on their internal and external characteristics. These are (1) gravel, (2) horizontally- bedded sand, (3) cross-bedded sand, (4) silt and clay, and (5) diamicton. A gravel pit along West Alcohol Road, SW½, SE½, Sec. 19, T48N, RJ.6W, (Stop in road log) reveals good exposures of these sedimentary units and their structures. The exposures generally show abrupt vertical changes with an overall fining upward sequence in most sections. One locality in the pit near the entrance shows fine to medium sand overlain by very coarse sand, gravel, and boulders, occasionally with mudballs. These units are overlain by laminated silt and clay which show discontinuous beds that are gently contorted in the lower 0.5 m. Lobes of overlying fine sand protrude downward into the silt and clay unit. The fine sand shows small scale cross-laminations with sets 2 cm in thickness. The sand is overlain by another silt and clay unit which shows load structures into an overlying medium to fine sand. Another location, approximately 75 m to the northwest, shows the gravel to be the predominant sediment with lesser amounts of crossbedded sand, horizontally-bedded sand, and diamicton. gravel occurs in the basal 4.5 m of the section. The The unit shows crude cross-bedding with sets to 0.5 min thickness and often containing interstratified sand, less than 0. 3 min thickness. Overlying the gravel are ' the horizontally-bedded and cross-bedded sand units. bedded with gravel-boulder lenses. These are inter- Horizontally-bedded sand has bed thicknesses from 2-3 cm to 2 mm and the cross-bed sets are up to 0.5 m 18 �thick. The sand exhibits scour and fill features in some localities, in addition to normal faults. Cross-bedding measurements, from both the cross-bedded sand and the gravel unit, show that paleocurrent directions (n=l2) for the WestAlcohol Road Gravel Pit are generally to the northwest, but there is a considerable amount of scatter in the orientations. Depositional Environment The ice-disintegration complex west of Wrenshall is characterized by hummocky, kettle-kame topography, consisting of a wide range of sediment types and structures. The extreme range of grain size along with abrupt changes in texture and slump structures indicate that these • sediments were deposited in close contact with stagnant ice (Flint, 1971). Sediment supplied to the complex originated from the stagnating ice mass. The abundance of granite and iron formation clasts (typical of Rainy Lobe sediment) suggests that there has been reworking of the older, underlying drift. The depositional environment of the sediment was one of large velocity fluctuations of the meltwater, which must have varied considerably as indicated by the rapid change in grain size. In the west central portion of the Wrenshall quadrangle, the very hummocky terrain was the result of deposition in ice-walled basins and later wastage of the sediment-covered ice. There was abundant meltwater available which allowed the sorting and stratification of the sand and gravel. An esker depositional environment is also observed. The esker was probably formed in a tunnel in the stagnant ice as evidenced by a single, steep-sided ridge containing longitudinally continuous sedimentary units 19 �(Banerjee and McDonald, 1975). Current flow appears to have been to the southeast with the esker terminating in a delta in a lacustrine environment. The sediments of the West Alcohol Road gravel pit may have been deposited in an ice-walled, fluvial environment, possibly by braided streams. The fining upward sequence, sand and gravel lenses, apparent channeling, scour and fill features, and floodplain silt and clay tend to support this hypothesis. Paleocurrents indicate major flow N60W with some directional variations which would be expected in a braided stream environment. Another possibility is that the sediments were deposited in a large ice-walled basin. The predominance of gravel and boulders indicates the need for a proximal source of sediment. Slump structures, faults, and a diamicton support an ice-contact origin. The laminated silt and clay would have been deposited in a quiet water pool or lake, with an increase in current velocity or loading from overlying material causing convolutions. In general, these sediments were deposited on, against, or under stagnant, wasting ice, and according to R. F. Flint (1971): "In such a place (ice-contact environment) anything can happen and it often does." 20 �GLACIOLACUSTRINE ENVIRONMENT The western tip of the Lake Superior Basin contains geomorphic features and sediments associated with a glaciolacustrine environment. The morphology, stratigraphy, and spatial occurrence of various sedimentary facies are ascribed to the activities of Glacial Lake Duluth, which had a high-stand above 1100 feet. Geomorphic features and sedimentary deposits of Glacial Lake Duluth are well-displayed in the Wrenshall and Frogner 7-1/2 minute quadrangles, and the following discussion is largely concerned with that area. Geomorphology The lacustrine environment in the Wrenshall and Frogner quadrangles is characterized by well-developed beach landforms and extensive lake plains. These features may be compared to the marine shoreline profile typical of sandy, mainland coasts. Coastal areas are divided into three morphologic zones: (1) mainland, (2) nearshore, and (3) offshore. The mainland area consists of older features, such as ancient strandplains, alluvial plains, lagoons (or shallow, restricted bodies of water), or bedrock. Dunes are common, as a result of a large supply of loose sand, and are found bordering the beach. The nearshore area, in a marine environment, extends seaward from the mainland and consists of two main zones: (1) backshore and (2) shoreface. The backshore is the area which is subjected to wave action only during extreme high water, usually generated by storms. ward, the profile shows the shoreface zone. 21 Continuing sea- The shoreface is defined as �a submerged zone which extends to a depth where sand size material is not moved by normal currents (Harms and others, 1975). It is the shoreface that is affected by swash and backwash, breakers, and longshore currents, which transport sand across the entire zone. The offshore area is not affected by normal wave action. Coarse sediment is transported into the offshore zone only under extraordinary conditions, such as storms or density currents (Harms and others, 1975). The lacustrine complex in Wrenshall and Frogner quadrangles is divided into two main morphologic groups: (1) nearshore and (2) offshore, which are separated by a narrow transition zone. shows two zones, the backshore and the shoreface. usually less than 120 min width. The nearshore profile The backshore is narrow, This merges with the hummocky terrain of the ice-disintegration complex previously discussed. The backshore is relatively flat, but in some places is marked by small discontinuous beach ridges. The shoreface in these quadrangles is expressed as a north- east trending belt, approximately 1.8 km in width. The shoreface here is basically a surface of no relief, sloping gently, 3 to 8 degrees, to the southeast and east. The shoreface zone is influenced by current action which is reflected in the presence of beach scarps, spits, an offshore bar, and a delta at elevations near 330 m. Wave-cut beach scarps in the shoreface dip 5 to 8 degrees to the southeast and are underlain by medium to fine sand with boulders and gravel concentrated at the base of the slope. The largest spit trends north-south and is located at the center of Sec. 1, T47N, Rl7W. It is 1.3 km in length and 0.5 km in width with side slopes of 3 degrees. The spit curves to the southwest indicating longshore currents flowing to the southwest. Several smaller spits are located in section 2. 22 �An offshore bar, with up to 6 m of relief is found in SW¼, Sec. 11, and W½, Sec. 4, T47N, Rl7W. It generally lies parallel to the former shore- line, 0.8 km lakeward, and extends for 2.4 km. Paleocurrent directions (four measurements) to the northwest indicate shoreward growth of the bar. A fan-shaped form, located in Sec. 31, T48N, Rl6W, is interpreted to be a delta. It is roughly 2.6 km 2 in area, relatively flat-surfaced in the north portion, with a foreset slope of 4 degrees to the southeast. A former ice tunnel, now containing an esker found to the northwest in the ice-disintegration complex, appears to have supplied the delta with meltwater. Lakeward of the nearshore area nearshore and offshore environments. is a transition zone which separates The transition zone occurs as a northeast trending scarp between 300 and 309 min elevation which slopes 3 degrees to the southeast. The sediments of this zone are transitional in nature between the nearshore sands and the offshore clays, with the sands and clays interfingering. This feature was misinterpreted by Leverett, Farrand, and Wright to be a strandline feature of Glacial Lake Duluth. It appears instead to be a depositional feature associated with the higher (330 m) elevation of Glacial Lake Duluth. The offshore environment is represented by an extensive lake plain that covers the southeast quarter of the Wrenshall quadrangle and most of the Frogner quadrangle. southeast A profile of the offshore from northwest to shows it to be gently dipping to the east-southeast at less than 3 degrees. Two weak scarps are seen on the profile at elevations of 288 and 264 m, which may represent lower lake levels of the Highbridge and Washburn stages respectively (Farrand, 1960). 23 The offshore area has �been deeply dissected by the Nemadji River and the Red River, a tributary of the St. Louis River. These streams have downcut as much as 42 m into the offshore sediments. Extensive slumping is very common along the stream valleys, indicating the instability of the underlying material. Sedimentary Units The sediments of the glaciolacustrine environment may be divided into four units: (1) horizontally-bedded sand, (2) cross-bedded sand, (3) laminated silt and clay with dropstones, and (4) massive clay with dropstones. Horizontally-bedded Sand This sand occurs widely throughout the nearshore zone as a sheetlike deposit, with a minimum thickness of 6 m. The grain size distri- bution shows moderately sorted sand with gravel and a mean grain size of 20 (O.25 mm, medium-fine sand). Sedimentary structures are not abun- dant in the horizontally-bedded sand. nated to medium bedded. The sand varies from finely lami- The bedding planes are faint and difficult to recognize, giving a massive appearance to the sand. Heavy mineral laminae are present and help to distinguish bedding planes. Slightly inclined bedding at one locality gives a general paleocurrent direction to the south-southwest. The only other direction indicator available is a general fining of the sand on the shoreface from medium to very fine sand, suggesting currents flowing to the south. The presence of a plane bed structure associated with the medium to fine grained, horizontally-bedded sand indicates an upper flow regime (Reineck and Singh, 1973). In the upper flow regime the main mode of 24 �sediment transport is via continuous rolling of grains in sheets several grains thick (Reineck and Singh, 1973). Accordingly, the sediment trans- port is large. Cross-bedded Sand The cross-bedded sand occurs as ribbon type deposits. These deposits are generally small, less than 1.5 km in length and 0.5 km in width. The grain size distribution for cross-bedded sand shows that this is moderately sorted. The mean grain size is 1.50 (0.35 mm, medium sand), although there is locally coarse sand and gravel. sedimentary structures found in this unit. Cross-beds are the main These occur as planar or tabu- lar forms with sets up to 0.5 min thickness. The cross-beds show good topset, foreset (inclined 25 degrees), and bottomset beds with laminae comprised of gravel, fine sand, or heavy minerals. Paleocurrent directions indicate (1) current flow to the east-southeast (lakeward) and (2) current flow to the northwest (shoreward). The shore- ward current direction is observed in the area of the offshore bar and indicates a shoreward growth of the bar. Bedforms of small ripples and mega-ripples associated with the crossbedded sand indicate transport and deposition in the lower flow regime (Reineck and Singh, 1973). The cross-bedding developed as a result of the migration of small current ripples and megaripples. In the lower flow regime, the resistance to flow is large and the sediment transport is small. Laminated Silt and Clay The laminated silt and clay occurs as extensive sheet-like deposits which are also associated with massive clay. nated silt and clay varies from 0.5 to 15 m. 25 The thicknesses of the lami- �Texturally, two distinct populations are observed: high silt content and high clay content. The silt layer is moderately sorted with a mean grain size of 5.80 (0.02 mm, medium silt). The unit is pale brown (Munsell color: 10 YR 6/3, dry) and consists of greater than 55 percent silt. The clay layer is reddish brown (Munsell color: 5 YR 4/4, dry) is ang_/composed of greater than 75 percent clay, with silt generally less than 10 percent and sand Oto 2 percent. In a few locations, carbonate concretions are found within the clay layers. The sedimentary structures associated with the silt and clay are very thin to thin bedding, discontinuous and distorted bedding. The silt and clay beds vary from several millimeters to several centimeters in thickness, and change considerably within a stratigraphic section. Discontinuous bedding is contorted, showing small scale recumbent folds and lenses of silt. The laminated silt and clay are rhythmites, alternating layers of different compositions, which may be varves if each couplet represents a single year of deposition (Reineck and Singh, 1973). These appear to have been deposited in the quiet water, deep portion of the basin. The abundance of clay indicates that the main mode of deposition was from the falling out of fine particles from suspension. The presence of silt would indicate more competent currents or turbulence, possibly during the summer thaw, which would periodically transport and deposit the silt. Massive Clay The massive clay, with the laminated silt and clay, comprises the major portion of the lake basin. Massive clay appears as a thick, sheet- like deposit which has lateral continuity. 26 The exposed thickness of the �clay is up to 20 m. Texturally the clay content is greater than 75 per- cent with several samples showing greater than 90 percent. prises the remaining 10 to 25 percent of the sediment. Silt com- The clays are reddish brown (Munsell color: 5YR 4/4, dry) to dark reddish gray (Munsell color: 5YR 4/2) where unoxidized and have a general massive appearance. There are no visible laminae of coarser or different colored material, however in some exposures, the clay does show minor fissility, indicating an internal structure. The presence of massive clay suggests quiet, deep water deposition without apparent current activity. Drops tones Scattered within the massive clay and laminated silt and clay are individual clasts up to 10 cm or more in length. These stones are thought to have originated as ice-rafted material as evidenced by their sporadic occurrence, in addition to their large size which would otherwise require a competent current for transport. Clay Mineralogy Four samples from the laminated silt and clay and massive clay were analyzed by x-ray diffraction. These include a red clay lamina, a gray silt lamina, reddish gray massive clay, and reddish brown massive clay. There is little difference in composition, other than peak intensities, among these samples. The samples contain (1) quartz, (2) calcite, (3) dolomite, (4) plagioclase, (5) k-feldspar, (6) montmorillonite-illite mixed layer, (7) chlorite, and (8) possible hematite. This mineral group is consistent with those determined by Mengel and Brown (1976) for other clay samples in the Wisconsin portion of the lake basin. 27 �These minerals were derived from the underlying weathered bedrock and older glacial sediments. The abundance of calcite and dolomite indicates a source in the drift of the St. Louis Sublobe to the northwest of the study area. Calcite is commonly found as vein fillings and amygdules in the flows of the North Shore Volcanics and could have been incorporated into the drift of the Superior Lobe. Another possible source for the carbonates is the Hudson Bay area with glacial transport of the sediment into the Wrenshall and Frogner area (Mengel and Brown, 1976). Stratigraphy Exposures along roadcuts and stream valleys in the lacustrine complex allow the stratigraphic relationships of the sedimentary units to be worked out. Subsurface data are available only for the area near Wrenshall and show the drift to be up to 115 m thick. Various sections are summarized in a schematic north-south cross-section (Figure 7 ). The section shows the basal unit as older drift or bedrock. These older units are overlain by (1) moderately sorted, probable nearshore sand, (2) massive clay with laminated silt and clay, and including dropstones, and (3) moderately sorted, fine to medium grained, horizontally- and I cross-bedded sand. The presence of shallow water sand over deepwater silt and clay suggests progradation resulting in nearshore facies over offshore facies. Depositional Environment As shown on a surface plot of the sediments (Fig. 8 ), the mean grain size distribution changes depending on the distance from the shoreline. The nearshore facies is shown to be composed primarily of medium sand. The sand consists of both horizontally-bedded and cross-bedded units. Shoreface activity includes upper and lower flow regimes, as indicated by 28 �w m ,'1 i i 'f j J: . ~ ~ •• ~ ~ ~ I r :z 0 1-1 E--< r--r--- u CJ\ .--l V'") ..c .j.J tU I Cl) ti) H (1j N ,~ ., 0 0- u µ~ (/J I ;'!: z u I-< I ,-.. ~ '-' l I ~ I E:-< ii «:: f ;::;..: IJ.l ~ ct :.e • u ·¥ t/J t l ~ ,-... : • ~ lJ 4> k ;: i ::; "1• t,;(j •T"l Gt. i 1 1 j ·'ii ~ i Cl I ::z: < E- ....:1 s2 '!i ';l 0 z < CJ) I $, 1l ;;, 1~: ~ i:i I i: $ ill i f 1': ,:: 29 J.... t .!'/ i �H I I I I I ! i' I Y"\r~ • ,. ! 1 /] / H : • ' .¼ . i I ! ~ I : /. fI ~ -~ 1 1 m·1 ~: I · . --~ -,-- -- ---•-,· - -- - ... L ~ -· : : I ' [I ' : f I ~ ~~ : , .. I ~:::.,..,,r ~ I . r-,""~--f .... ,..,,.. • .,. .. I I ! 3 ~ 4 I I 4 1 _,,.., ~.....---...i-6 , 3;)· • ! I · ~--- ~ ~ ! A ' I I I I I ! ~-~_.. - / ~ - ..... t: _ _..,_nn-1,---n--.,~ .. I ~?'I I I e 1 I I U )/,#' f : D IQ ,P--1 • I I, : I 3 H: I r. 1 I I II l I I 1/, I I I _, ~ I )efjY #r ~~ 1 I 3g : I I __ I lJ - I I : I I • llot I I . . 0, l I I 14 , I I <:'lii~OV---,,.,_C'C'- I 1 1,I I I !l I I f I I . ·an : 1 I · I f91 t : l II t l l ~ ' 'vsM{.I ~ - - .;:- ........... ~ ~-'I., .... ~ ., ...~~ -: I I • I : . I ,,,.. , .cJ__j I II I . , ' I "d I /:I ti I AA · - I' M n I . (.'I • ...... ,.. .... "' ..,, ,.., .., ... " .., ... ,., - - - ..,. I I · . I ., • +,:I •rl ~ I . @ {h ·1 j t! 1 LI I 1 II fI I !l a, ' ! 1 :I I' I :.~ / , ,, I I I i I JI • I I I I t j II • : D I ' 1 I ' ·1 M I - - - ... - " ... I :1 f I I 2,0=,25mm J,0=., 125mm 4%~o062.5mm j;J= ') OJ1 Jmm 6f1cn01,56mm 7Jo=,,0078mm i l I ~ I 4 - - - - .. - - ...... ~ - . . . - - - - .I' I ,:i. I 1 1jli:::; ~ 5mm. --1-"""t'l'lt"I"" I I lI.........,.~, - ) . .· ~ ' I l I I . .., • I im 0%::::lmm I • A "I - - - - I l'.tl~- A3 I I I , l ao .. a~ o - I I I I' ...,.J _ _.. ,,._.,.. __ 1--ll'la""""''"--11"'1"'..,.. ___ i:-,,J._,,_::::rT __ ~/._yJ-' H 111 II i I ... I Shoreline Contour Interval:1% I t .J"""' ...,,..._r.)_,..., s.. • r.o, 1' II I I I I U-1...-l....W I I I ~n'7.,.~ I •a " ,~ MEAN GRAIN SIZE DISTRIBUTION :--= . . . . . .,,.-r .. ----r . . ~~ . ., ~1-==--.-"'-:~- --~1~~- -~-I I -----,-. ,iI' I I I ~ I ~ I - .. -:~ - _., - ~ ' I I .~ 1· I IJ G :1.,- "''"n,:, ~l"Y\()~:--..":') ~.., --"""'-.-'-"" ..,.,~-j11"'!1 .... ,.... ..... ~-- o;; I C I . = I A i '" • I I I I I ; f.11 II : l l 1 w I -'t---~~-,,,. -'"Y'~ r- - -----1•~M-- .. --r---~--:-n-•fl·---L.------ :I ~-I~~: :I II ____ _.,~. . , __ .,.,.,._~, - -- ..-.-~--,...---··t- ___ ,. __ - ..J,. .. 0 I 1 • . , 1 I ai I ,.,,,..---;. ~~ ~11.\1. 1 ....__--,..__-,--..;r _.-,,_ le, : ' I I I U 0 ' " J lL 10 1111 m I II , -•r'"•. r ~ ~ 4 I -r--, 1.',, ; • • • I• , I , 1 •t-------~..,.,_•r.tJIID-1•_,.,.,_ ... m.L•-•••• I I m ,... n- • I .--.,.,,,_= 1 llln P ~ 31! 1 ,_.,r.-•1.-.,.,..o• '1 f"ltl)'lar-o- . . • I t I I iI M I I ~ .,J, ' i 'j_f,J~ ..... ..... ! M~ f0j -,Wt•t•r.tct•c.-ee-,.•, . :· ,' a A I I A:! 0 ,· lfJ • l I I I •n--,-ro..,.c:"»•-"""'• nt <"a ! : ,, . ,. • -c n ~ .,. - . I Rt i I Ir"' ,. .. f/ JV u ~ I ·-•• ... •'--~--.., ; n~ ~ "' • = .... ., ~ ......... Figu:re 8 --DISTRIBUTION OF MEAN GRAIN 0 l1 mile size;· f J (R.J.· Zarth, 1977) M,!,tih;~J,-~iy-,X',.b/ ',"'°' a;,,.,;.~t 1 ~•,-+''4 , , 1,1, •<~•·.1.1,. •-· ... _.,, ,, .. ,:,~ ,., ~.•. , ~,/ L..,-, ,;, ,t• .,• ....., .... ,.,,:.,...,.t, ...\>-&.1h:...1-•".,h;,.-,.i,.~L~~lc.biW,4r.,)·,~1~il•t',,/ll~h.-H.. ''•~,;: .- ,ih\1:.c,"'..t':;(~.r,.-\~•,.i,~1-,9i'.rn,,J,1d"J,,-4,1...,,v.,,,;,.1.,-J. ..,1,.;;,,. ,,,.., .,, ,•... •• • �f._ 1? ·i ' '~ -.~ ' -~ ,....__ r-• r-~ O'\ <,...; :;: ~ f.() '.5 1-4 Ci) tJ'.J ;... ~ _,j i i{ ' .i C) N ' -< t.t., '"1 'l ...J~ < ~ ~ :z ~ C,!l O"\ Q h ;:l bQ ...: '""' 31 i! l J ''' �bedforms. The current directions to the southwest parallel the shoreline, causing the formation of spits (Figure 9 ). The offshore bar formed sub- aqueously and paleocurrents show a shoreward growth, possibly due to storm waves. The north-central portion of the study area has very fine sand and silt relatively close to the shoreline, suggesting lower current strength. Deltaic sedimentation shows an upper surface of sand, with very fine sand and silt on the prodelta slope. and west from the feeding esker. Two narrow valleys radiate south These may represent remnant distributary channels cut into the delta, with the silt and fine sand as floodplain deposits, as suggested by their standard deviations (Folk and Ward, 1957). -There is an abrupt grain size change in the lake basin from predominantly sand to predominately silt and clay (Fig. 8). This boundary, which can be traced laterally, occurs between 300 and 309 min elevation and is represented by a northeast trending scarp, The zone shows varying textures with interfingering sand, silt, and clay. The variety in sediment type reflects the changes in current strength. This abrupt change in slope and sediment type is here interpreted to represent the depositional front of a coarse grained shelf of Glacial Lake Duluth. The offshore facies occurs south and east of the transition zone (Fig. 8). It is composed of laminated silt and clay, massive clay, and dropstone deposits. These sediments were derived from the wasting ice lobe and meltwater streams draining the ice-disintegration complex. Offshore sedimentation must have occurred primarily as the settling of sediment from suspension as evidenced by massive appearing clays. 32 �The rhythmite couplets (silt and clay layer) are not gradational but occur as distinct layers. This would suggest deposition by two sedimentation pulses and modes of deposition (Ashley, 1975). The normal suspension sedimentation may have been periodically interrupted by density currents as underflows, interflows, and overflows. These flows result from the high suspended sediment content of meltwater streams from the ice-disintegration complex and ice lobe entering the lake. These flows have been described in present day Glacial Lake Malaspina, Alaska, by Gustavson (1975). These currents provide a mechanism for the deposition of the silt layers of the rhythmites during the summer months. This would result in clay being deposited continuously in areas not reached by current flows, and massive clays would form (Gustavson, 1975). In add~tion, offshore occurrence of dropstone deposits, interbedded with silt and clay, suggest ice rafting of sediments as a depositional mechanism. The ice dammed Glacial Lake Duluth,with calving of the ice front,would produce massive icebergs which would release sediment over the lake basin as the ice would melt. Vegetational History Cores from bogs and lakes contain a history of plant succession in the form of pollen and macro-fossils, including seeds, woody fragments, and leaves. Studying quantitatively the contents of such cores at a particular site allows the determination of the time of arrival of plant migrants, as well as the reconstruction of the fabric of the plant communities at different times. All of these studies lead to the fuller view of the vegetational history within the time represented by the sediment core. As a data proxy for climate, the pollen record is 33 �then transcribed into a history of climatic change. Sampling along the proper traverses allows the monitoring of the march of vegetation in the wake of retreating glaciers. Most ponds and lakes in glaciated terranes deep enough to accumulate a significant sediment record originated as kettles on ice-cored end moraines. The vagaries of down-wasting of buried stagnant ice decree a complex natural history for the surface features of such a terrane. Topographic reversals are common because the hillslopes are extremely unstable: debris flows and slumps denude sediment-mantled slopes, fill depressions with colluvium, and thereby redistribute the insulation on the stagnant ice surface. slopes and hilltops. Melting proceeds more rapidly on the bared Differential melting transforms ice-cored hills into holes, and vice versa. In such an unstable environment lakes and ponds are ephemeral. Sediment, including pollen and plant macro-fossils is not collected into a continuous and permanent record until a stable basin is formed, generally near the demise of the ice core. Melting to that point in the moraine's history may take thousands of years. Therefore, radiocarbon dates on bottom sediments in such lakes can be significantly younger than dates obtained from beneath basal till in the same moraine. For the same reason, cores contain an incomplete record of revegetation-generally the earliest part is missing. It follows that the best lakes for pollen studies are those that formed early in the history of deglaciation and that continued as stable catchments to the present. In broad outline, the pattern of plant succession in Minnesota during the Late Wisconsin and post glacial is similar to that of the 34 �entire Great Lakes region (Wright, 1976). Minnesota (see Fig. Wolf Creek in central for location WC) and Weber Lake in northeastern Minnesota are two sites that have been especially useful to reconstructing the vegetational history • . ·1. i r.. ,, ti \ .. . .. \. 0 KILOMETERS Figure 10. Major phases in the Wisconsin glaciation in M:lnnesota. Approx1rrate dates 1n thousands of yeal's. Note the non-synchronous maxima of the SL1perior and ~s 1·-:0ines lobes. Locations of Wolf Cr~~k .:ind Weber I,'1.lw al.'c sho~m. The oldest pollen zone at Wolf Creek represents an herb tundra, which prevailed from 20,500 yr BP until about 14,700 years ago. was followed by shrub tundra and forest tundra. This Spruce expanded into the area about 13,600 years ago and was the dominant species for about 35 �4,000 years. Then, spruce was replaced by pine about 10,500 years ago. Cores from Weber Lake, situated farther northeast in the Toimi drumlin field, indicate that herb tundra persisted there until about 11,000 yr BP, with a rapid transition to shrub tundra and then spruce and finally pine. A summary of the changes in major vegetation types and their relationships to glacial phases is shown in Figure NORTH 2000 RAINY 20 0 !:J Stagnant ice Figure 11. 40 ♦ LOBE SUPERIOR LOBE 60 ,co 80 ,20 Ro.c.iacarbon do.le, wit!\ one <10.nd<1t"d c!ev1<11ion 14() 160 180 ZOOmdtt • Rejected r<1d10c<1rbon d.<11e Transect from north to south in eastern Minnesota, showing times and areas of ice-lobe advance, as well as the changes in major vegetation types since glaciation, as inferred from pollen and seed analyses of lake sediment cores. (Courtesy. H. E. Wright). 36 �Glacial Materials and Soil Profiles by Royce Lewis, Soil Conservation Service The kind of soil horizons and their sequence formed on well drained sites in the Duluth area generally can be correlated with the kind of glacial materials. as examples. The Ahmeek, Duluth and Ontonagon soils may be used See Figures 1 through 6 for some physical and chemical properties of these soils. The Ahmeek soils are formed in noncalcareous, reddish brown, sandy loam till. Their sequence of horizons may be interpreted as A , A , 2 1 Bhir, B, and C. X X The Duluth soils are formed in noncalcareous, reddish brown, loam till and have a sequence of horizons of A , A , Bhir, A , BT, 2 2 1 and C. The Ontonagon soils are formed in calcareous reddish brown, lacus- trine sediment and have a sequence of horizons of A , A , BT and CCA' 2 1 The A horizons of these soils have higher accumulation of organic 1 carbon, lower bulk density and higher porosity than other horizons in the pedon (area of about l square meter). They are higher also in available water capacity (1/3 minus 15 bar water). They generally are higher in base saturation and pH than the horizons immediately below. They cotmnonly are black. The A2 horizons generally are discontinuous within a pedon of Ahmeek and Duluth soils and are continuous in the Ontonagon soils. They are horizons of maximum removal of clay, iron or aluminum, which results in a concentration of quartz or other resistant minerals in the sand and silt size. They are lighter in color than the underlying B horizons. The Bhir horizons have significant accumulations of organic carbon, iron and aluminum coatings on sand and silt particles. 37 They are low in �bulk density, base saturation and pH. They have also a higher cation exchange capacity per unit of clay than the underlying horizons. They are commonly reddish brown. The BT horizons have appreciable accumulations of translocated silicate clay particles as contrasted to the B horizons (in the Ahmeek X soils); however they have higher bulk density and lower porosity than BT horizons. The base saturation of the B horizons, and content of clay range widely among these soils. They seem to be a mark of the kind of glacial materials along with the properties of the C horizons. The C horizons are presumed to be relatively little affected by biological activity and include accumulation of calcium and magnesium carbonate (CCA horizons) and high bulk density (Cx horizons). 38 �.&IIKEEJ:l'ElXJ11' J'art:l.oJ.. Siu Dutz:1.bution ('6) 2 l)optb so ail1: l'vtiolA Sue D1atr..bution ('6) 2S 50 75 l!ue S&turation JO 50 Co) 70 pf! (~0) 6,6 7.0 .4 2S Sill: Clq so lllJLll'm PEllOI hrt:l.olA Siu ll1atribut1on (1') 2 0 7, .. l)optb 2S so olq 1111: llua· S&tun.tian (1') 10 50 70 pf! (CaCl) .4 �REFERENCES CITED Ashley, G.M., 1975, Rhythmic sedimentation in Glacial Lake Hitchcock, Massachusetts-Connecticut, in Glaciofluvial and Glaciolacustrine Sedimentation, A.V. Jopling and B.C. McDonald, eds.: SEPM Special Pub. 23, Tulsa, p. 304-320. Banerjee, I. and McDonald, B.C., 1975, Nature of esker sedimentation, in Glaciofluvial and Glaciolacustrine Sedimentation, A.V. Jopling and B.C. McDonald, eds., SEPM Special Pub. 23, Tulsa, p. 132-154. Driscoll, F.G., 1976, Formation and wastage of neoglacial surge moraines of the Klutlan Glacier, Yukon Territory, Canada, Unpub. PhD Thesis, U of Minnesota, 309 p. Farrand, W.R., 1960, Former shorelines in western and northern Lake Superior Basin, Unpub. PhD Thesis, U. of Michigan,. Ann Arbor, 226 p. Flint, R.F., 1957, Glacial and Pleistocene Geology, Wiley and Sons: New York, 553 p. Folk, R.L., and Ward, W.C., 1957, Brazos River bar: a study in the significance of grain size parameters, Jour. Sed. Pet., Vol. 27, p. 3-26. Gravenor, C.P., and Kupsch, W.O., 1959, Ice-disintegration features in western Canada, Jour. Geol., Vol. 67, p. 48-64. Green, J.C., 1972, General geology, northeastern Minnesota and North Shore Volcanic group: in Geology of Minnesota: A Centennial Volume, Minnesota Geological Survey, p. 291-332. Gustavson, T.C., 1975, Sedimentation and physical limnology in proglacial Malaspina Lake, southeastern Alaska, in Glaciofluvial and Glaciolacustrine Sedimentation, A.V. Jopling and B.C. McDonald, eds., SEPM Special Pub. 23, Tulsa, p. 249-263. Harms, J.C., Southard, J.B., Spearing, D.R., and Walker, R.G., 1975, Depositional environments as interpreted from primary sedimentary structures and stratification sequences, Short Course #2, SEPM, Dallas, 161 p. Leverett, F., 1929, Moraines and shorelines of the Lake Superior basin, U.S. Geol. Survey, Prof. Paper 154-A, 72 p. Mengel, J.T., and Brown, B.E., 1976, Final report: red clay slope stability factors, Little Balsam Creek drainage, Douglas County, NW Wisconsin, U.S. E.P.A. and Red Clay Project# G-005140-01. Moss, C.M., 1977, The Surficial and Environmental Geology of the French River Quadrangle, St. Louis County, Minnesota: unpub. MS Thesis, University of Minnesota, Duluth, 69 p. 40 �Reineck, H.E., and Singh, I.B., 1973, Depositional Sedimentary Environments, Springer-Verlag: New York, 439 p. Schwartz, G.M., 1949, The geology of the Duluth metropolitan area, Minn. Geol. Survey Bull. 33, 136 p. Winchell, N.H., 1901, Glacial lakes of Minnesota, Geol. Soc. Amer. Bull., Vol. 12, p. 109-128. Wright, H.E., Jr., and Watts, W.A., 1969, Glacial and vegetational history of northeastern Minnesota: Minnesota Geological Survey, Spec. Publ. SP-11, p. 1-23. _ _ _ _ _ , 1972, Quaternary history of Minnesota, in The Geology of Minnesota: A Centennial Volume, P.K. Sims and G.B. Morey, eds., Minn. Geol. Survey, p. 515-547. Ice retreat and revegetation - - -Area, - - , in1976, Quaternary Stratigraphy of North in the Western Great Lakes America, W.C. Mahaney, Editor: Dowden, Hutchinson, and Ross, Inc., Stroudsburg, Pa. Zarth, R.J., 1977, The Quaternary geology of the Wrenshall and Frogner quadrangles, northeastern Minnesota: unpublished M.S. thesis, University of Minnesota, Duluth, 93 p. 41 �II! \ Ill I I I I Ii i ) 0 l\l Ol 1I111 \1111'. -.... ' s. c·. A. ,L, 'i'. 111 \I\ 111111111111 I11 \ ci 2 4 6 b-3 b-3 I;....., E-3 b3 j i\\ !\lli\\1\11. 111I L .. .. . ......... I ii I , B 10 MILES \ '\ □ -J DenhClJll.', s I I I I ' llll i l\llltl \ l!,., . 0 N (JI l\1AP OF A PART OF NORTI1 ~42 �' ,/ . ~- ,., ,, ...... ' ' ' ~~, ~ II ,. ," # I ... J11 47• io· ' &., . ,(o/ ..) ~v QI I Ol ,-. ..!..~~•:=~~ ~· •~ 1TASCA ca.f I l I ' I :f" QI p..i I 0 e: .~--.., :.,.-;::;_.;f...,,a..-i-:-..c_4-+_ _-,.._ _..,....--,-~f,;''7'-__; I S C A. L E ,o...,.,..,.;o.,.._..•0==20;..._.,;3.;0==40 m,1.. INDEX TO QUADRANGLES :,A STERN MINNESOTA SHo,vING l\'IAJOR GEOIVIORPHIC FEATURES From: Wright, H.E., Jr., and Watts, W.A., 1969, Glacial and Vegetational History of Northeastern Minnesota, Minn. Geol. Survey Special Publication No. 11, 59 p. 43 STUDIED �ROAD LOG AND STOP DESCRIPTIONS Mileage o.o 0.0 Start. Normandy Village, Superior St., Downtown Duluth. Proceed to 3rd Ave. W., turn right. Proceed 2 blocks to 2nd St. W. Turn right. Proceed to 10th Ave. E. Turn right and continue to London Rd. Turn left and proceed to Viking ship at Leif Erikson Park on Lake Superior. 1.5 1.5 STOP 1. Leif Erikson Park. Exposures along the waveeroded shoreline of Lake Superior show two different tills atop the striated and polished Keweenawan lava flows and interflow sediments. The unconformity between the Precambrian and Quaternary Systems encompasses over one billion years. Continue east on London Road 4.7 6.2 Lester River. Rocks are lava flows. A wellstriated whaleback is exposed at the mouth of the stream. The river is popular with smelt and steelhead fishermen. 0.5 6.7 Turn right onto Lake Superior Scenic Drive. Many miles of shoreline were given to the City of Duluth by the Congdon family to be developed as public recreational areas. Notice the effects of recent wave erosion. 2.3 9.0 City of Duluth Water Supply Plant. On the left is the newly constructed filtration plant necessitated by the high amounts of fine-textured fibrous amphiboles suspended in the lake water. Source of the minerals is a taconite (low grade iron ore) processing plant at Silver Bay, which disposes of tailings into Lake Superior. 0.5 9.5 STOP 2. Turn right into scenic pull-out near Duluth Tent and Trailer Camp. Proceed along path to Lake Shore. A variety of glacial sediments, including tills and possibly glaciolacustrine sediments, is exposed along the shore, resting atop lava flows of the North Shore Volcanics. Continue east on Scenic Drive 1.7 11.2 Turn left onto McQuade Rd. (St. Louis Co. Rd. 33) 44 �0.6 11.8 Intersection with Hwy 61 Expressway. Continue north on McQuade Rd. Exposures along the route are pebbly mud deposited in Glacial Lake Duluth. The road transects several flat benches that may be shoreline features. 2.9 14.7 Junction with Lismore Rd. McQuade Rd. 0.7 15.4 Continue north on STOP 3. Gravel pit on the right exposes a complex of cross-bedded outwash interpreted to be a delta constructed by a meltwater stream at its junction with Glacial Lake Duluth's highest stand in the area. Thin diamictons may be debris flows from high-standing ice-cored topography near the shoreline. Continue north on McQuade Rd. 0.9 16.3 STOP 4. Sucker River. Two tills exposed in the stream bank correlate with those along the Lake Shore. Here the upper, fine-textured till is far above the level of Lake Duluth, eliminating the possibility that it is of glaciolacustrine origin. Both tills contain a fabric resulting from the preferred orientation of elongate clasts. See general text for details. Make a U-turn carefully and return south on McQuade Rd. 3.5 19.8 Turn right onto Lismore Rd. 2.9 22.7 Outcrop on right is a coarse-textured felsic intrusive called "granophyre". In one view this rock type, which is common in the Duluth Complex, is a late-stage magmatic differentiate derived from basaltic magma during the crystallization of the Duluth gabbro. 3.4 26.1 Turn left onto Jean Duluth Rd. 5.2 31.3 Large outcrop of granophyre on right. 1.3 32.6 Intersection with Glenwood Ave. Duluth Rd. and Skyline Pkwy. 1.0 33.6 Turn left onto Woodland Ave. 0.1 33.7 Turn right onto Arrowhead Rd. 1.5 35.2 Turn left onto Kenwood Ave. 45 Continue on Jean �1.1 36.3 0.7 37.0 Turn right onto Skyline Pkwy. STOP 5. Turn left into parking lot of First Methodist Church. View of Duluth-Superior harbor. The outer natural barrier at the head of Lake Superior, called Minnesota and Wisconsin Point, is the largest fresh water bar in the world. Sand derived from till bluffs to the east along the south shore is moved to the lakehead by beach drifting. It began to form about 3,000 years ago. Segments of an inner bar are also visible. This feature was constructed during the slightly higher Nipissing level of the lake about 4,000 years ago. Continue west on Skyline Pkwy to Hwy 2. Numerous outcrops of gabbro along the route. 8.3 45.3 0.3 45.6 Junction Hwy 2. Proceed through intersection to Thompson Hill Information and Rest Area. Gabbro bedrock along Hwy 2 is abraded and plucked into whaleback forms. STOP 6. Thompson Hill Rest Area and lunch stop. Good views of the estuary of the St. Louis River. Very accessible are outcrops of the so-called layered series of the Duluth Complex, the result of episodic crystallization of different minerals in the magma chamber. Remember Bowen's reaction series? Exit on northeast side to Hwy 2 and Interstate 35 North. 2.1 47.7 Exit right onto Central Ave and Hwy 2. 0.2 47.9 Turn right onto Central Ave. 0.3 48.2 Stop sign. Turn right onto Raleigh St. 0.6 48.8 Stop sign. Turn left onto Grand Ave, and Hwy 23 8.0 56.8 Fond du Lac village limit. French fur traders were the first white men to see the "head of the lakes" region, about 1659. Twenty years later Daniel de Greysolon Sieur de Lhut raised the French flag on the shores of Lake Superior. In 1817 John Jacob Astor established one of his fur trading posts on the banks of the St. Louis River at Fond du Lac. 0.5 57.3 Junction Hwy 210. 0.5 57.8 Excavation on right exposes glaciolacustrine sediments associated with Glacial Lake Duluth. 46 Keep left on Hwy 23. �2.3 60.1 STOP 7. Turn right into scenic overlook. The St. Louis River and its tributaries have entrenched deep valleys into the sediments of Glacial Lake Duluth. Mass-wasting of the fine-grained sediments results in a distinctive rounded topography. Watch for bald eagles--an active aerie is a few miles upstream. Continue south on Hwy 23. (Following road log is approximated from topographic maps.) 1.7 61.8 Turn right onto Carlton Co. Rd 18 to Wrenshall. The route crosses the nearshore "continental shelf" of Lake Duluth. 2.2 64.0 Turn right into Wrenshall. 0.5 64.5 Turn left onto West Alcohol Rd. The route will climb gradually across nearshore glaciolacustrine sediments onto a hurmnocky bounding stagnation moraine, a part of the Thomson moraine. 1.3 65.8 STOP 8. West Alcohol Rd. gravel pit. Exposures show the sedimentary complexities of a moraine resulting from the stagnation and melting of dirty glacier ice. Return to Wrenshall 1.3 67.1 Turn left to Carlton. The lake plain narrows to a long embayment. Outcrops are Thomson Formation, a Middle Precambrian metasiltstone-slate. 4.2 71.3 Carlton. Continue north on Hwy 45. Numerous outcrops of Thomson Formation striking generally east-west in the form of miniature hogbacks (piggy backs?). 2.4 73.7 Junction Hwy 45 and I-35. Hwy 45. 0.3 74.0 Stop sign. Continue to Scanlon on Turn left on Hwy 45 toward Cloquet. Prepare for sharp left turn 0.3 74.3 Turn left onto Washington Ave. (Carlton Co. Rd. 16) 1.4 75.7 Junction Hwy 33. lane. 47 Turn right and proceed into left �0.3 76.0 Turn left onto service road fronting National Guard Armory, then right toward Armory entrance. 0.1 76.1 Stop sign. 0.4 76.5 Turn left into City of Cloquet Public Works Dept. gravel pit. 0.1 76.6 STOP 9. Cloquet esker. Gravel pit exposes the internal structure of the highest esker in Minnesota. See the Wrenshall Quadrangle topographic map. Mixed bedrock lithology suggests erosion of older tills before final deposition of esker gravel. Turn left to Pine Valley Park. Retrace route to Armory 0.5 77 .1 Turn left to Hwy 33 via service road to Pizza Hut. 0.2 77 .3 Turn left (north) onto Hwy 33. 0.7 78.0 Junction Hwy 33 and Hwy 45. Hwy 33. 0.1 78.1 St. Louis River. 0.9 79.0 Turn right onto North Rd (Carlton Co. Rd. 2) 1.7 80.7 STOP 10. Pit on left exposes the southeast end of a drumlin-like landform ascribed to the Automba phase of the Superior Lobe. Reworked clay displays slickensides produced by "drumlin-forming processes." Continue north on Continue east on County Rd 2 7.0 87.7 Junction Midway Rd (St. Louis Co. Rd 13). right to I-35. 1.9 89.6 Junction I-35. Turn left to I-35 northbound to Duluth. Rock outcrops are lava flows near the bottom of the North Shore Volcanics, of Late Precambrian age. 9.9 99.5 Exit from I-35 onto Superior St. in Duluth. 0.6 100.1 Normandy Inn. End of field trip. 48 Turn �DIAGRAM SUPPLEMENT TO ROAD LOG 8·12" LAKE CLAY 6• 10' UPPER LE t3 LE 5 TILL LC 4 LE 3 5-s' LOWER TILL LE 2 LE 1 lava flows Stratigraphic section at Leif Erickson Park; Duluth,Minnesota. S]%, S\'l¼, Sec. 23, T5ON, Rl4W. Textural composition of samples: LE 1, 34% sand, 45% silt, 21% clay; LE 2, 49% sand, 42% silt, 9% clay; LE 3, 39% sand, 43% silt, 18% clay; LE 4, 23% sand, 74% silt, 3% clay; LE 5, 20% sand, 65% silt, 15% clay; LE 6, 24% sand, 47% silt, 29% clay. c~ M., Moss, 1977 HIGHLAND MORAINE 1400' f ICI DISINTIOaAr I O N - - - - - - . flATUUS LAKI SUPERIOR ------? ---UPPU TIU LACUSUINI 7 Dll'OSITS ,===---------- ? =-----' DIAGRAMMATIC CROSS SECTION LOWU JILL IIDaOCIC • 49 FRENCH RIVER QUADRANGLE 1200' ? -- 1000' aoo' ooo' £LIV. C. M. Moss, 1977 �O lacustrine clay or silt Figure 12 • average, 22 samples Cl ccmpaci, pebbly clay Grain Si%e Oistri but ion in Lacustrine Deposits 0 0 □ □ Cl (C. M. Moss, 1977) 0 LO 1.1 1.2 0 1.3 A 0 0 Cl 0 C A A A A A 1. 4 1.5 l. 6 1.7 1.8 1.9 2.0 Bulk Density; g/cc FIGURE 14: Comparisons of bulk den3ities of glacial sediments: □ = pebbly, compact clay O= laminated or massive pebble-free clays A= sand- or silt-rich. till (C.M. Moss, 1977) 50 �INLAND AREAS L. SUPERIOR BASIN GLACIAL LAKE DULUTH PEBBLE•FREE CLAY DEPOSITION ICEBERGS -0- -- ------... , •o " a·· .. _ .- - RETREATING ICE ' DROPSTONES DEBRIS WASHED OR SLUMPED FROM ICE A M I XE D P £ 8 BL E • f REE CLAY & DROPS TONE DEPOSITS I RETREATING ICE DEBRIS SLUM PED ,FROM ICE .t B Model for deposition of clay facies in Glacial Lake Duluth. (A) earliest stages of deposition with material supplied from icebergs and retreating ice. Clays are carried away from the ice and are deposited in deeper water. (B) later stages of deposition; pebble-free clays continue to settle over slumped debris and icebergs drop coarser material over scattered areas. (Moss, C.M., 1977) 51 �FIGURE 15: Composite stratigraphic section for locations below 115or in French River quadrangle. {C. M; Moss, 1977) 0 360 I 0 270- Measurements of planar cross bedding in deltaic sands and gravels. Section 31; 'I'52N, Rl2W; 24 observations. (C. M. Moss, 1977) 52 �N25-2 N2S-1 Stratigraphic section, McQuade Road at Sucker River; SW 1/4, NW 1/4, Sec. 30, T 52 N, R 12 W ~d SE 1/4, NE 1/4, Sec. 25, T 52 N, R 13 W. Textural composition of samples: N 25-1, 32% sand, 44% silt, 24% clay; N 25-2, 26% sand, 46% silt, 28% clay. (C. M. Moss, 1977) ·"· . BAY-HEAD. BARS IN LAKE -SL'PERIOR Tilll La ke Superior DULUTH Aerial oblique map of the Duluth-Superior Harbor (From Loy, W. G., 1963, The Evolution of Bay-head Bars in Western Lake Superior, Publ. No. 10, Great Lakes Research Di¥ision, Univ. of Michigan) 53 �29? 1:1 295 m SILT-FINE SANO 290 m CLAY SILTY CLAY WITH SILT LAYERS 285 nt CLAY, MASSIVE 280 m CLAY WITH SILT LAYERS 275 m SANDY GRAVEL GRAVELY CLAY SANO 270 CLAY WITH PEBBLES Ill SANO, i-lEDIUM 265 m SILT-;INE SAND WITH CLAY LAMINAE 260 m f,AMINATEO CLAY AND SILT ~55 m HNE SAND 250 m ----------------------------------------------------- CLAYEY SILT SILTY CLAY WITH PEBBLES Wayside Rest, Esko Quadrangle, SW 1/4, SW 1/4, Sec. 13, T 48 N, R 16 W. (Zarth, R. J., 1977) \ ' I ~ \'-----. ..___ Striated bedrock from I-35 Thomson Fm outcrop. Sketc- =C from photograph. North is towards to~ of figure; scale ~s approx. 1.5. --- J ~fi / ) Y,1 1 (A. Norton) � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1979 Description An account of the resource Institute on Lake Superior Geology. University of Minnesota, Duluth, Minnesota. May 8-12, 1979. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1979 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/47fb6d5d027e7e529543644a84d9e3f3.pdf 2e63fed116258cab9c6032555b496100 PDF Text Text �PROCEEDINGS AND AND ABSTRACTS ABSTRACTS PROCEEDINGS the for the 26th 26th ANNUAL ANNUAL INSTITUTE ON ON LAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY held held at THE DAVIES CENTER CENTER THE DAVIES UNIVERSITY UNIVERSITY OF OF WISCONSIN WISCONSIN -- EAU EAU CLAIRE CLAIRE May May 66 -- 10, 10, 1980 1980 sponsored by sponsored by The University University of Wisconsin The Wisconsin - Eau Eau Claire E. Myers Program Paul E. Myers Program Chairman Chairmanand andEditor, Editor, Paul Activities Chairman, Nancy Nancy Jo Activities Chairman, Jo Pickett Geology Geology Department Department University of of Wisconsin Wisconsin - Eau Eau Claire �SALES SALES Proceedingsand andAbstracts Abstractsand andfield field trip Proceedings tripguidebooks guidebooks may be purchased purchased (@ (@$5.00 $5.00each eachU.S.) U.S.) from may be from the the Depart-. Depart- ment of Geology, University of Claire, ment of Geology, University of Wisconsin-Eau Wisconsin-Eau Claire, Eau Claire, Claire, WI checks or money Eau WI 54701. Make Make checks money orders payable to to 26th Institute on payable 26th Annual Annual Institute on Lake Lake Superior Superior Geology. Field trip tripguide guidebooks booksmay may also also be be purchased purchased from from the the Wisconsin History Survey, Survey, PubPubWisconsin Geological Geological and and Natural Natural History lications Sales lications Sales Division, Division,1815 1815University UniversityAvenue, Avenue,MadMadison, WI WI 53706. i-Ili �Of' COTTS TAL Or Dedi cati on Dedication • General Information Informationand andAcknowledgments Acknowledgments General iv iv Vi vi Directors Board Board of Directors 11 SessionChairmen Chairmen Technical Session 2 2 Activity ActivitySchedule Schedul e 3 3 Schedule Schedu 1e of Papers Papers 4 4 Abstracts 9 9 Poster Papers Papers 65 Index 75 111 iii �DEDICATION DEDICATION Ralph will thismonth, month, May May 1980, 1980, as as Professor Professor of of Ralph W. W.Marsden Marsden willretire retire this only his Geology atat the ofMinnesota, Minnesota, Duluth. Duluth. Duluth Duluth has has been been only Geology the University of most recent long career careerdevoted devoted totomining miningand and geology. geology. Because most recent stop stop in aa long Ralph on Lake Lake Superior Superior Ralph has haslong long been beena astaunch staunchsupporter supporterofofthe the Institute Institute on Geology sinceits its inception friend of Geology since inception in in 1955, 1955, and and because because heheisisaa friend of every every geologist geologist in in the the Lake Lake Superior Superior region, region, this this volume volume is is dedicated dedicated to to him. him. Ralph geology degrees of Wisconsin, Wisconsin, Ralph received received his his geology degreesfrom fromthe the University University of He then thenwent wenttoto the the Philippines as completing his graduate graduate work work in 1939. 1939. He as completing a as Chief Chief of of the Geological Division of the a geologist and and served served as Geological Survey Survey Division the Unfortunately, the the last Philippine Bureau Bureau of ofMines Mines from from 1940 1940 to to 1945. 1945. Unfortunately, Philippine three years in this role were served in civilian internment camps three years this role were served in civilian internment campsunder under guidance of of the theJapanese. Japanese. the guidance After aa few few years years with with the theJones Jones &&Laughlin Laughlin Steel Steel Corporation, Corporation, he he moved to the United States Steel Corporation. He became manager of Geomoved to the United States Steel Corporation. He became manager of GeoInvestigations in in 1953, 1953, aa post post he he retained retained for 11 11 years years until he he logical Investigations became manager of ofU.S. became manager U.S.Steel·s Steel 'siron iron ore ore operations. Ralph has haslong long had hadaa love love for Ralph for academia, academia, having having taught taught at atWisconsin Wisconsin while student, at the while aa graduate graduate student, the University UniversityofofOklahoma Oklahoma for one one year, and the Internment Internment Camp Camp School 1967 the and even evenin in the Schoolininthe the Philippines. Philippines. In 1967 University of of Minnesota, Minnesota, Duluth, Duluth, was was able him back back to the uniuniable to to entice him to the versity vers ity environment. envi ronment. He He served the Geology Geology Department Depa rtment for served as as head headof of the for 77 years, leading it italong along aa path path of ofspecialization specializationininPrecambrian Precambrian studies. studies. years, leading Ralph has as one one of ofthe themost mostknowledgeable knowledgeable "iron "ironmen" men" Ralph has aa reputation as Foreign governments, the United Foreign governments, the United Nations and foreign companies companies have have sought advice. His knowknowNations and several several foreign sought his his advice. ledge ores, and and especially especially those those of of the theLake Lake Superior Superior region, region, ledge of of iron ores, is encyclopedic. encyclopedic. His His latest latest major major undertaking undertaking was was aa review reviewof of the the iron ore Wisconsinfor for the U.S. ore reserves reserves of of Minnesota Minnesota and and Wisconsin U.S. Bureau Bureau of Mines, Mines, aa knowsRalph Ralphrealizes realizes that project recently recentlycompleted. completed. Yet, everyone everyone who who knows his expertise is far broader broader than he is inhis expertise is far, far than his his specialization, specialization, for for he is indeedaageologist geologistinIn all all respects. deed respects. the world, world, and and is widely widely traveled. traveled. in the He served the AIN1E AIME and asaswell He has has long long served andSEG, SEG, wellasasother other professional perspective, his organizations, in in aa number number of His broad broad perspective, his organizations, of capacities. His unimpeachable integrity, and his steady hand hand are unimpeachable integrity, and his steady are appreciated appreciated by by all. all The fortunate Ralph's prespresThe ILSG ILSGhas hasbeen been fortunatetotohave havehad hadthe thebenefit benefit of of Ralph's ence and entireexistence, existence,and andwe weknow know we we shall enjoy enjoy ence andsupport supportfor for its its entire that benefit benefitforfor manymore more years years totocome. come. Remember, Remember, Ralph, many Ralph,that that with an ILSG volumededicated dedicated you,you youcannot cannoteasily easilyforget forget this this unique an ILSG volume to toyou, unique We thank thank of which which you you have have long been been an organization of an important important part. We you! iv �Dr. Ralph Ralph W. W. Marsden Marsderi v V �GENERAL INFORMATION GENERAL INFORMATIONAND ANDACKNOWLEDGEMENTS ACKNOWLEDGEMENTS We welcome This is our first, first,but buthopefully hopefully not not We welcomeyou youtoto Eau EauClaire. Claire. This is our Wehope hopeyou youenjoy enjoy yourselves and attempt at at playing playing host host totoILSG. ILSG. We and last attempt return with others others to tohelp helpususcontinue continue our ourstudies studiesofofthe thePrecambrian Precambrian return geology the region. region. geology of of the We haveattempted attemptedtoto make makeyour yourstay stay here here as as convenient convenient as as possible. We have The excellent conference facilities ofof thethe Davies The excellent conference facilities DaviesCenter Centerhave havebeen been gengenerously provided provided by by the the University of erously of Wisconsin Wisconsin - Eau Eau Claire. All arrangements arrangements for space, space, food, food, and and transportation transportationwere werehandled handled by Nancy Pickett. Students by Nancy JoJo Pickett. theGeology GeologyDepartment Department Students and arid faculty faculty ofofthe have donatedmuch muchtime timeand andeffort effort to assure have donated assure the the success success ofofthe theconfer— conference. Manuscripts were typed typed by Hoitomt and and Gail Gail Wirz. Coordinator Manuscripts were by Penny Penny Hoitomt visual aids aidsisisDr.Dr.James James Wilson. Wilson. of visual of WisconWisconConference Conferencevehicles vehicles have havebeen beenprovided providedbybythe theUniversity University of - Oshkosh, Survey, the the sin — Oshkosh,the the Wisconsin WisconsinGeological Geologicaland andNatural Natural History History Survey, University Center Valley, at andby by the the University University Center System, System, Fox Fox Valley, at Menasha, Menasha, and of Wisconsin Special thanks thanksare aredue due thefield field trip trip Wisconsin - Eau Eau Claire. Special to tothe leaders: Randy Maas, Manmohan leaders:Michael MichaelCumings, Cummings, Randy Maas, ManmohanSood, Sood,Randy RandyVan Van Schmus, Schmus, and Stephanie Wurdinger. and Wurdinger. have had had the enthusiastic support support ofofcolleagues colleagues and and ILSG ILSG friends I have the enthusiastic havehelped helpedmake makethe thejob throughout the and region. region. You You have ..job easier. throughout the state and Thankyou you a11 all Thank ~ E. Myers Paul E. Myers Conference Director Conference Director vi �26th 26thANNUAL ANNUAL INSTITUTE INSTITUTE ON ON LAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY sponsored by sponsored by University of ofWisconsin Wisconsin - Eau Eau Claire Eau Claire, WI Eau Claire, WI 54701 May 10, 1980 1980 May66 -- 10, INSTITUTE INSTITUTE BOARD BOARD OF OF DIRECTORS DIRECTORS D. D. M. M. Davidson, Davidson, Jr., Jr.,Department Department of ofGeological Geological Sciences Sciences University of Paso, Texas ofTexas, Texas, El El Paso, Paso, El El Paso, Texas (1979) (1979) M.F. Kehlenbeck, M.F. Kehlenbeck, Department Department of of Geology Geology Lakehead University, Thunder Bay, Ontario (1977) Lakehead University, Thunder Bay, (1977) G. of Geological G. Mursky, Mursky, Department Department of Geological Sciences Sciences University University ofofWisconsin, ~Iisconsin,Milwaukee, Milwaukee, Wisconsin t~isconsin (1978) (1978) P.E. Myers, Myers, Department Department of of Geology Geology P.E. University University ofofWisconsin, Wisconsin, Eau Eau Claire, Claire,Wisconsin Wisconsin (1980) (1980) R. C. Reed, Reed, Geological Survey Division R. C. Geological Survey Dept. of Dept. ofNatural NaturalResources, Resources,Lansing, Lansing,Michigan Michigan(Permanent (PermanentMember) Member) M. M. Walton, Walton, Minnesota Minnesota Geological Survey Survey University ofofMinnesota, University Minnesota, Minneapolis, Minneapolis,Minnesota Minnesota (1976) (1976) 1. �TWENTY-SIXTH ANNUAL MEETING MEETING TWENTY-SIXTH ANNUAL INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY -- 1980 1980 INSTITUTE TECHNICAL SESSION CHAIRMEN CHAIRMEN TECHNICAL SESSION Bruce Brown Brown Dr. Bruce Wisconsin Geological History Survey Survey Wisconsin Geological and and Natural Natural History 1815 Avenue 1815 University University Avenue Madison, WI WI 53706 Dr. Dr. William William S.S. Cordua Cordua Department of and Earth Earth Sciences Sciences Department of Plant and University of ofWisconsin Wisconsin River River Falls, Falls, WI WI 54022 Dr. I. Smith Dr. Eugene Eugene I. Smith Division ofofScience, Science,Earth EarthScience ScienceProgram Program University of of Wisconsin Wisconsin - Parkside Parkside Kenosha, WI Kenosha, WI 53141 53141 Dr. Donald Davidson, Jr. Jr. Dr. Donald M. M. Davidson, Departmentof of Geological Department Geological Sciences Sciences University of ofTexas Texas at at ElE1 Paso Paso El E1 Paso, Paso, TX TX 79968 Dr. Jeff Dr. JeffGreenberg Greenberg Wisconsin Geological and and Natural Natural History HistorySurvey Survey Wisconsin Geological 1815 University University Avenue 1815 Avenue Madison, WI WI 53706 Dr. Gene Gene LaBerge LaBerge Department of Geology Department of Geology University University ofofWisconsin Wisconsin Oshkosh, WI WI 54901 Dr. Michael Michael Mudrey Mudrey Dr. Wisconsin Survey Wisconsin Geological Geological and and Natural Natural History Survey 1815 University Avenue 1815 University Avenue Madison, WI WI 53706 Richard Ojakangas Ojakangas Dr. Richard Geology Department Department of Geology University of ofMinnesota Minnesota Duluth,MN MN 55812 55812 Duluth, 2. �TWENTY-SIXTH TWENTY-SIXTH ANNUAL ANNUAL INSTITUTE INSTITUTEON ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY ACTIVITY ACTIVITYSCHEDULE SCHEDULE TUE, MAY 66 TUE, MAY a.m. 8:00 a.m. FIELD TRIP TRIP #1, CHIPPEWA VALLEY: Departurefrom from north north FIELD CHIPPEWA VALLEY: Departure entrance, entrance, Davies Davies Center, Center, University UniversityofofWisconsln-Eau Wisconsin-Eau Overnight in in Eau Eau Claire Claire(accommodations (accommodations not Claire. Overnight included included in in fee). WED, MAY 77 WED, MAY 8:00 a.m. a.m. FIELD CHIPPEWA VALLEY--DAY 2: 2:Departure FIELD TRIP TRIP #1, CHIPPEWA VALLEY--DAY Departure from north entrance, entrance, Davies Davies Center. Center. Return Return at 5:30 5:30 p.m. p.m. 7:00 a.m. a.m. THU, MAY 88 THU, MAY FRI, MAY MAY 99 FIELD TRIP TRIP #2, #2, BLACK RIVERVALLEY: VALLEY: Departurefrom fromfront front FIELD BLACK RIVER Departure Return Return by by entrance, Midway Midway Motor Motor Lodge, Lodge, Eau Eau Claire. Claire. 6:00 p.m. p.m. 4:00 p.m. p.m. REGISTRATION BEGINS: WillowLounge, Lounge,Davies Davies Center, UWREGISTRATION BEGINS: Willow UWEau closes at at 10:00 10:00 p.m. p.m. Eau Claire. Claire. Registration closes p.m. 7:00 p.m. SMOKER: SMOKER: 8:15 a.m. a.m. TECHNICAL SESSIONS I AND Council Fire Fire Room, TECHNICAL SESSIONS I AND II: II:Council Room, Davies Davies Center, 8:15 8:15 a.m.-12:O0, a.m.-12:00, and and 1:40-5:00 1:40-5:00 p.m. p.m. Center, 8:45 a.m. a.m. POSTER SESSIONS: Alumni Room, Davies Center, p.m. POSTER SESSIONS: Alumni Room, Davies Center,toto 5:00 5:00 p.m. 7:00 p.m. p.m. CASH BAR: Blackhawk Lounge, Davies Center,until until 7:00 CASH BAR: Blackhawk Lounge, Davies Center, 7:00 p.m. p.m. 8:00 p.m. 800 p.m. ANNUAL Council Room, Davies Davies ANNIJALINSTITUTE INSTITUTEBANQUET: BANQUET: CouncilFire Fire Room, Dr. Ralph Marsden,University University of Center. Speaker, Speaker, Dr. Ralph Marsden, Minnesota -- Duluth. Minnesota Duluth. 8:00 a.m. a.m. TECHNICAL SESSIONS AND Council Fire Fire Room, TECHNICAL SESSIONS III III AND IV:IV:Council Room, Davies Davies Center, 8:00-12:00 and and 1:20-5:00 1:20-5:00 p.m. p.m. Center, 8:00-12:00 8:45 a.m. a.m. POSTER POSTER SESSIONS: Ojibwa Room, Davies Center, UW-EC Ojibwa Room, Davies UW-EC toto 10:00 p.m. p.m. Alumni DaviesCenter Center to to 3:00 Alumni Room, Room, Davies 3:00 p.m. p.m. 12:15 p.m. p.m. SYMPOSIUM LUNCHEON LUNCHEONFOR FORAUTHORS AUTHORSAND ANDCOORDINATORS: COORDINATORS:PresPresSYMPOSIUM ident's Room ($2.00) ($2.00) ident's Room 3:20 p.m. p.m. PRESENTATION PAPER AWARD: Council PRESENTATIONOFOFBEST BESTSTUDENT STUDENT PAPER AWARD: CouncilFire Fire Room, Room, Davies Davies Center. 6:00 p.m. p.m. CARAVAN DEPARTURE WAUSAU--FIELD AND 4: 4: CARAVAN DEPARTUREFOR FOR WAUSAU--FIELDTRIPS TRIPS33 AND Entrance, Davies DaviesCenter, Center,UW-EC UW-EC North Entrance, — SAT, MAY 7:30 a.m. SAT, MAY 10 10 7:30 a.m. 8:00 a.m. a.m. FIELD TRIP WAUSAU SYENITE: Departure Boy FIELD TRIP #3, WAUSAU SYENITE: Departurefrom from Big Boy Restaurant ofRoutes Routes 29 29 and and U.S. U.S. 51. 51. Restaurant near near intersection intersection of Return restaurant for lunch lunch at at noon. noon. Participants Returnto to the the restaurant will return the trip. trip. will returntotothe therestaurant restaurantupon upon completion completion ofof the FIELD TRIP TRIP #4, COUNTY: Departurefrom from Holiday Holiday FIELD #4, MARATHON MARATHON COUNTY: Departure Inn, Wausau, Wausau, WI. WI. Return Returnthere thereatat end endofof trip. trip. Shuttle bus will be available to to take take participants participants toto Centrdl Centil bus will be available Wisconsin Airport Airport at Wisconsin atMosinee. Mosinee. 3. �SCHEDULE OF OF PAPERS PAPERS SCHEDULE SESSION SESSION II Thursday, May Thursday, May 8, 1980 1980 Morning ~rning Session Session PRECAMBRIAN GEOLOGY GEOLOGY Co—chairmen: Co-chairmen: 8:15 8:20 8:40 D.M. D.M. D<lvidson. Davidson,Jr. Jr. and and R.R. Ojakangas Ojakanq P.E. Myers Myers Opening remarks Opening remarks *B. Van Van de de Voorde Voorde && *6. P. P. Ervin Ervin N.M. M.M. Kehienbeck Kehlenbeck Geophysical study of aaPrecambrian Precambrian Geophysical study of boundary in Minnesota boundary Minneso~ Regional structure,metamorphism metamorphism and and Regional structure, stratigraphy of of the theQuetico Quetico Gneiss Gneiss Belt, Thunder Bay, Ontario Thunder Bay, 9:00 *R.S. Maass, Maass, 9:20 *J.'; . Goodge Migmatites from Granitic Migmatites from the the Vermilion Vermilion Granitic Complex, Minnesota CompleK, Minnesota 9:40 9:40 A. Fleming, Fleming, A. M. "C. Heinz, Heinz, R. Lee R. Lee && H. H. Woodard Wloodard Geology of the southeastern Geology of southeastern contact contact zone zone of the the Vermilion Vermilion batholith, batholith,Minnesota Minnesota *K.H. Poulsen Poulsen && M.M. Kehienbeck "I,M. Kehlenbeck Overturned Archean Archean successions successionsand andtheir their Overturned significance 10:00 10:00 • Medaris, J, L.G. Jr.. & L.G. Medaris, W.R. Van W.R. Schmus V" Schmus 10:20 Coffee Break Break 10:40 10:40 *C.N. Brandon, Brandon, EoI. Smith smith && E.I. F.R. F.R. Luther Luther Archean andEarly Early Proterozoic Proterozoic tectonic Archean and ofnorth—central north-central Wisconsin history of isconsin The Precambrian PrecambrianWaterloo Waterlooquartzite, quartzlte, The southeastern southeastern Wisconsin: Wisconsin: evolution evolution and and significance 1l:00 11:00 E.t. Eo!. Smith Smith Rare earth element the elementdistribution distribution in the Rare Precambrianrhyolites rhyolites and and granites granites of Precambrian south—central Wisconsin Wisconsin south-central 11:20 1l:20 M.L. Cummings Cunmings Geochemistry andvolcanic volcanicstratigraphy stratigraphy of Geochemistry and of west-central ~est·central Marinette MarinetteCounty, County, Wisconsin Wisconsin 11:40 11:40 W.F. W.F. Cannon Cannon && M.G. M.G. Mudrey Mudrey Where Where isis the the source sourceof of Wisconsin Wisconsindrift drift diamonds? di amnds? There ~ill be aaluncheon luncheon r:eetjng meeting of of the theBoard Board There will be of Directors Directorsininthe theHeritage HeritageRoom, Room, Davies Davies Center Center * student student paper paper 4. �SESSION SESSION III! May 8, 1980 1980 Thursday, May Thursday, Afternoon Session Session PRECAMBRIAN GEOLOGY GEOLOGY Co-chairmen: 1:40 1: 40 Greenberg and and 6. G. LaBerge LaBerge J. Greenberg V.W. V.W. Chandler Chandler Correlation of and ofgravity gravity andmagnetic magneticanomalies anomalies in east-central east-centralMinnesota Minnesota and and northwestern northwestern Wisconsin <Ii sconsi n 2:00 2:00 *R.S *R.S. Maass Maass &~ L.G. L.G. Medaris, Medaris, Jr. Metavolcanic rocks rocksat at Eau Claire Dells, Eau Claire Oells, Metavolcanic Marathon MarathonCounty, County,and andananevaluation evaluation of the zone" hypothesis hypothesis infnWisconsin :.Iisconsfn the "shear "shear zone" 2:20 ILL. LaBerge G.L. LaBerge Were there two Middle Mfddle Precarthrian Precambrian orogenies orogenies Were there two 2:40 2:40 MA.. M.L. CurFillings Ctlllt1lings Volcanic plutonic rocks Volcanic and and plutonic rocks ofofthe theJump Jump and and Yellow River Valleys, north-central Yellow River north-centralWisconsin Wisconsin 3:00 Coffee Break Break 3:20 *1. *T. Ernst, Ernst, J. Markert Markert &to M. M. Montz Montz In the the Lake lake Superior Superior region? region? in Heavy ofPrecambrian Precambrian rocks rocks Heavymineral mineral analysis analysis of in Rusk Rusk County, County, Wisconsin Wisconsin 3:40 P.A. P.A. Daniels Daniels &to Depositional setting of Depositional ofaastromatolite— stromatoliteacute alluvial fan oolite facies faciesonona aKeweenawan Keweenawan alluvial fan 4:00 R.J. Shegelskl R.J. Shegelski Stratigraphy Stratigraphy of the the Gunflint GunflintFormation, Formation, Current River River area, area, Thunder Thunder Bay 8ay 4:20 N.W. N.W. Jones Jones Petrology of some Logandiabase diabasesills sills from Petrology some LOgan from Cook Minnesota Cook County, County, Minnesota D.R. D.R. Elmore EllOOre 4:40 *P. Morton 5:00 Adjourn sills Differentiating ultramafic ultrall\lfic flows flows from from sills in the Mine area, area, northwestern theShebandowan Shebandowan Mine northwestern Canada Ontario. Ontario, Canada 5. �SESSION III SESSION III Friday, Friday, May May 9, 9, 1980 1980 Morning Session SYMPOSIUM BASIN - -AA REVIE~ SYMPOSIUM- -TECTONIC TECTONICHISTORY HISTORYOFOFTHE THELAKE LAKESUPERIOR SUPERIOR BASIN REVIE Coordinator: Co-chairmen: ~. W. Richard Wold Richard J. Wold Cordua Smith Cordua and and E. E. Smith 8:00 J, . Dii. D.M. Davidson, Oavj dson, Jr. Geological evidencerelating relatingtoto the the interpreGeolo9ical evidence tation of of the theLake Lake Superior Superior basin basin structure 8:20 J.S. asner, J.S, Kl Klasner, The Pre-Keweenawan tectonichistory history of of the The Pre-Keweenawan tectonic the north-central United and central central United States States and Canada andhow how influenced formation formation of Canada and it itinfluenced Mid-Continent Rift the Mid—Continent Rift W.r. Cannon && W.F. Cannon W.R. W.R. Van Schnius Schmus 8:40 8:40 J.C. Green Green Keweenawan volcanism Keweenawan volcanismand andthe thenature nature of of Keweenawan rift Keweenawan rift tectonics tectonics 9: 00 9:00 R.W. R.W. Ojakangas, ~ak.angas , Upper Precambrian the Upper Precambriansedimentary sedimentaryrocks rocksof of the Lake Superior region region Lake G.B. G. B. Morey, rey, P.A. .A. Daniels && P Kalliokoski J. Kal1iokosk.i 9:20 Geochronology of Keweenawan rocks: Geochronology of Keweenawan rocks: aa review W.R. Van Schmus, M. R. Van Schmus, Green && J.C. J. C. Green H.C. Hallss Hall 9:40 Break Coffee Break 10:00 10:00 W.J. W.J. Hinze, Hinze, R.J. Wold Wold && and magnetic magnetic anomaly anomaly studies Gravity and studies of Lake Superior Lake 10:20 10: 20 V.W. V. W. Chandler, P.L. P.L. Boman, Boman, W.J. Hinze && W.J. Hlnze N.W. N. W. O'Hara Long wavelength gravity gravity and Long wavelength and magnetic magnetic anomalies anomalies of the theLake Lake Superior SuperiorRegion Region of 10:40 J . H. Luetgert Luetgert && J.H. R.P. Meyer Meyer Seismic refraction studies Seismic refraction studies of ofLake Lake Superior Superior structures crustal structures 11:00 ll:OO R.J. R,J. Wold, Wol d, D.R. O. R. Hutchinson Hutchinson & T.C. Johnson Johnson Topography and surficial structure of Topography and surficial of_ake lake Superior basedononseismic seismicreflection reflection Superior bedrock bedrock based profiles 11:20 J.H. Karl, J.H. Karl, M.P. M. P. Bernardin, R.P. R. P. Meyer, Meyer, M.E. M. E. Bengtson Bengtson & H.C. H. C. Halls Hall s Geophysical studies Islands, Geophysical studiesof of the the Slate Slate Islands, Lake lake Superior N.W. N.W. O'Hara O'Hara , • 6. �SESSION III III (CONTINUED) SESSION (CONTINUED) 11:40 12:00 12:15 12: 15 Lake Superior Superior red clay l6ke clay niineralogy: mineralogy:car— cor· relation relationwith withmechanical mechaniC61 behavior behavior J.T. J. T. Mengel Mengel && B.E. B.t. Brown Brown P61eomagnetism of ofKeweenawan Keweenawan rocks rocks Paleomagnetism I#J.C. t1 •• C, Halls && L.J. L.J. Pesonen Pesonen Adjourn lunch Adjourn for for lunch There Symposium Luncheon 6nd coordinators coordin6tors There will will bebea aSymposium Luncheonfor for 6uthors authors and at 12:20 the Davies 0avis Center 12:20 p.m. p.m. in in the the Presidents Presidents Room Room ofof the Center ($2.00) ($l.OO) I'd SESSION IV Friday, May May 9, 9, 1980 1980 Afternoon Session Session GENERAL GENERAL Co—chairmen: Co-chairmen: 8. B. Brown Brown and and M. M. Mudrey Mudrey 1: 20 1:20 *T.J. Grundi, Grundl, E.C. Perry, Perry, Jr. && LC. R.H. R.H. Gilkeson Gllkeson Stable isotope tracer Stable tracerstudies studiesIninthetheCantro— Cambro· Ordovicianaquifer aquiferofofnorthern northernIllinois Illinois Ordovician 1:40 1: 40 *L.I. Kelley & *L.I. Kelley" F.R. F.R. Karner Kamer Kaoliniticweathering weatheringzone zoneononPrecambrian Precambrian Kaolinitic basement of southeastern North North Dakota Dakota and and basement of western Minnesota Minnesota 2:00 W.R. ifI.R. Rehfeldt Hydrogeologic investigationsatataalandfl'l landfill Hydrogeologic investi~6tions site in in the the red red till till(Valderan) {Valderan) region region of eastern Wisconsin Wisconsin 2:20 T.D. Vick T.O. Vick Seismic survey surveyofof aa i:lJried bjried river Seismic riverchannel channel 2:40 3:00 *W.M. Lucko &" kW.M. S.A. S.A. Kissin Kissin The Quetico gneiss The pegmatites pegmatitesofof the the Quetico gneiss belt, belt, northwestern Ont6rio, and their theiruranium uranium northwestern Ontario, and potential COffeeBreak Break— also - also BEST STUDENT PAPERAWARD AWARD Coffee BEST STUDENT PAPER CASH PRIZE PRIZE $200 CASH SYMPOSIUM SYMPOSIUM -—URANIUM URANIHfl IN IN WISCONSIN WISCONSIN AND AND THE THE UPPER UPPER MIDWEST [DWEST CD\ I INUED ON CONTINUED ON NEXT NEXT PAGE PAGE 7. 7. �SYMPOSIUM URANIUMIN IN WISCONSIN SYMPOSIUM·—URANIUM WISCONSIN AND AND THE THE IPPER UPPERMIDWEST MIDWEST Coordinator: M.G. M.G. Niudrey, Mudrey, Jr. Jr. 3:20 G. Mursky G. Mursky Relationship of ofCanadian Canadian uranium uranium deposits deposits to to the the geologic geologic setting settingofofWisconsin Wisconsin 3:40 J.K. J. K. Greenberg Greenberg Uranium provinces: Uranium provinces:enrichment enrichmentinin granitic granitic rocks relations totoWisconsin rocks and and relations Wisconsin 4:00 W.B. Coker && W.B. Coker J.M. J.M. Franklin Franklin Regional Regional geochemistry geochemistry and and metallogeny metallogeny 4:20 J.J. J.J.Mancuso Mancuso && R.H. Motten R.H. Motten Geology of the Geology of the NicCaslin McCaslin Range, Range, northeastern Wisconsin 4:40 T.J. T.J. Evans, Evans, J.K. Greenberg Greenberg && M.G. Mudrey, Mudrey, Jr. M.G. isconsin Wisconsin interest interestin1nradiological radiologicalimpacts impacts from uranium uranium exploration resulting from exploration(drilling) (drilling) 5:00 5:00 Adjourn lake Superior, Ontario Ontario north shore shore of Lake north 8. �This page has no number in original. Appears between 8 and 9 ABSTRACTS �GEOPHYSICAL STIJDY GEOPHYSICAL STUDY OF OF AAPRECAMBRIAN PRECAMBRIANBOUNDARY BOUNDARY IN MINNESOTA MINNESOTA IN Barbara VanDeVoorde aridC.C.Patrick Patrick Ervin Barbara VanDeVoorde and Department of Geology Department Geology Northern University NorthernIllinois Illinois University DeKaib,Illinois Illinois 60115 DeKalb, West-central West-central Minnesota Minnesotaisis divided divided by by aa northeasterly northeasterly trending trendingboundary boundary an older older gneiss terrane to the separating two Early Early Precambrian Precambrian terranes: an gneiss terrane the separating two south south and and aa younger youngergranite-greenstone granite.-greenstoneterrane terranetoto the the north. The The nature, location, and and origin of ofthis thisboundary boundary is is aamatter matter of ofconjecture. conjecture. During of 1979, 1979, COCORP a deep-crustal,sei seismic reflecDuri ng the summer summer of COCORP ran ran a deep-crustal, smi c refl ecMinnesota Geological Survey tion profile profileacross acrossthe theboundary. boundary. The The Minnesota Survey conducted conducted a gravity survey utilizing the a concurrent concurrent gravity survey utilizing theelevation elevationpoints pointssurveyed surveyed by by the the crew. A corresponding should be be completed completed seismic crew. corresponding aeromagnetic aeromagneticprofile profile should before meeting. before this meeting. This discuss only This paper paperwill will discuss only the the modeling modelingofofthe thegravitational gravitationalfield, field, which is bei-ng using a two-dimensional modeling algorithm. algorithm. which being done done using two-dimensional modeling 9. �REGIONAL STRUCTURE, AND STRATIGRAPHY REGIOI~AL STRUCTURE, METAMORPHISM METAMORPHISM AND STRATIGRAPHY OF OF THE THE QUETICO GNEISS BELT, THUNDER QUETICO GNEISS THUNDER BAY, ONTARIO ONTARIO M.M. Kehienbeck M.M. Kehlenbeck Fold axes Structurally therocks rocksform formaacomplex complex domical domical feature. Fold axes plunge plunge Structurally the gently andaxial axial surfaces surfacestrend trendparallel parallel to the gently to the the east east or or west, west,and the long long axis axis of the thedome. dome. Metamorphic mineralsare aredistributed distributed in zones which parallel the Metamorphic minerals zones which thedomindominant planar gradeincreases increases from from greenschist greenschist facies ant planar structures, structures,and and metamorphic metamorphic grade on the margins granulite fades on the margins toto granulite facies near near the the center centerofofthe thedome. dome. In several several places places near near the center of the the structure structureevidence evidence indicates indicates In the center that rocks rocks become become younger and south. south. younger toward toward the the north and Boundarieswith with the Wabigoon Belt to the Belt to Wabigoon Belt the north northand andShebandowan Shebandowan Belt Boundaries the south south are are transitional. transitional. the 10. �ARCHEAN AND AND EARLY EARLY PROTEROZOIC TECTONIC HISTORY ARCHEAN PROTEROZOIC TECTONIC HISTORY OF OF NORTH-CENTRAL NORTH-CENTRAL WISCONSIN WISCONSIN R.S. Maass Maass and R.S. andL.G. L.G. Medaris, Medaris, Jr. Department Geology and and Geophysics Geophysics Department of Geology University ofWisconsin Wisconsin University of Madison, WI 53706 53706 Madison, WI W.R. Van W.R. Van Schmus Schmus Department Department of Geology Geology University Kansas University ofofKansas Lawrence, Kansas Kansas 66044 Four field seasons anddetailed detailedstructural structural studies Four field seasons of reconnaissance reconnaissance and studies cocoordinated with geochronologic in portions investigation have have been been undertaken undertaken in ordinated geochronologic investigation of Waupaca, Waupaca, Portage, Wood, Jackson, Eau Claire, Claire,Chippewa, Chippewa, Marathon, Marathon, Portage, Wood, Jackson, Clark, Clark, Eau Lincoln, and and Price Price counties counties ininan an attempt attempttotodecipher decipherthe theArchean Archean and and Early Early Proterozoic tectonic history of ofnorth-central north-centralWisconsin. Wisconsin. Proterozoic tectonic Archean gneisses been identified in Portage, Portage, Archean gneissesand andmiqmatites migmatiteshave have been identifiedsosofar far in Wood,Jackson, Jackson,and andClark Clark counties. Gneisses Wood, Gneisses containing in containingsimilar similar structures structures in Waupaca Claire countiesare arealso alsobelieved believed to to be in age, Waupaca andand EauEau Claire counties be Archean Archean in age, although although zircons from the Eau Claire county countylocality locality yield from the Eau Claire yieldan an Early Early Proterozoic Proterozoic age. age. zircons This This unit isis one one of of the the most most thoroughly thoroughly recrystallized recrystallized rocks rocks in the the terrane terrane and weare aretherefore therefore considering consideringthe the possibility possibility that and we thatthe thezircons zirconshave havebeen been reset. The The Archean Archeangneisses gneissesare areofofvolcanic, volcanic, plutonic, plutonic, and and sedimentary sedimentary origin, and and generally generally exhibit exhibitstructures structuresindicative indicativeof of polyphasedeformation. deformation. origin, polyphase Theoldest oldest recognized recognizedEarly Early Proterozoic Proterozoic rocks rocks in Wisconsin are mafic mafic to The Wisconsin are felsic volcanicswhich whichwere wereextruded extruded atatthe thebeginning beginningof of PenokeanOrogeny, Orogeny, felsic volcanics thethe Penokean about Conipressionaldeformation deformationfollowed followedshortly shortly thereafter thereafter 1860 m.y. m.y. ago. ago. Compressional about 1860 resulting resulting in in vertical vertical and and near near vertical vertical dips dips for forthese these rocks. rocks. Medium-grained granitic tona1itic plutons were emplacedthroughout throughoutthe theterrane terranebetween between granitic tototonalitic plutons were emplaced 1840and and1830 1830 m.y. ago, followed finer-grained granitictototonalitic tonalitic 1840 m.y. ago, followed by by thethe finer-grained granitic plutons along between plutons along the the southern southern margin margin ofofthe theterrane terrane between1830 1830and and 1820 1820 m.y. m.y. these plutonic plutonic rocks rocks contain contain aapronounced pronounced lineation ago. The The vast vast majority majority of these lineation which is commonly, but not always, weaktotomoderate moderatefoliation. foliation. which commonly, but always, accompanied accompanied bybyaaweak Catac1astic textures textures are are present present in in all alldeformed deformed rocks, rocks, but butthey theyare aresubordinate subordinate Cataclastic to recrystallization textures. textures. Cataclasis Cataclasis occurred occurred simultaneously simultaneously with to recrystallization recrystallizationduring during Penokean deformation deformation and and amphibolite amphibolite facies facies metametarecrystallization Penokean morphism regionalextent, extent, rather rather than being restricted totolocalized morphism ofofregional than being localizedzones zones of shearing. shearing. The plutonic rocks are generally synkiriematic synkinematic toto late kinematic, kinematic, but but aa The plutonic rocks are generally the basis basis of radiometric few kinematic. On On the radiometric ages ages ititappears appears that thatsome some few are are post kinematic. the undeforrned undeformed units are older than than deformed deformed units elsewhere, thus thus defordeforof the units are units elsewhere, mation terminated at different the terrane. terrane. mationmay mayhave have terminated at differenttimes timesin indifferent different parts parts of of the However, thisconclusion conclusionmust must viewed caution lightofofthe the level level of However, this be be viewed withwith caution in in light precision the radiometric radiometric ages, ages, especially especially when when attempting precision of the attempting to to distinguish events so closely spaced events so spaced in time. time. Penokean the emplacement emplacement of 1760 m.y. old Penokearideformation deformationhad hadended endedprior prior to to the of 1760 m.y. old Subsequently these these rocks and rhyolites rhyolites ininsouthern southernWisconsin. Wisconsin. Subsequently rocks were were granites and folded, whereas rocks the state state were were folded, whereas rocksofof the the same sameage ageininthe thenorthern northernhalf half of the 11. �(Maass, continued) (Maass, Medaris Medaris and and Van Van Schmus, Schmus, continued) Throughout the the Lake Superior region, not. Throughout Lake Superior region, Rb-Sr Rb-Srsystematics systematicshave havebeen been reset at at approximately approximately 1630 1630 to to 1615 1615 m.y. m.y. It It appears appears likely that this this likely that event responsible for forthe thefolding folding metamorphism of the the southern southern event is responsible andand metamorphism Wisconsingranites, granites, rhyolites, rhyolites, and and quartzites, quartzites, but buthad had only only aathermal thermal Wisconsin expression in northern northern Wisconsin. Wisconsin. expression 12. �MIGMATITES FROM THE VERMILION MIGMATITES FROM THE VERMILION GRANITIC GRANITICCOMPLEX, COMPLEX,MINNESOTA MINNESOTA John ~J. Goodge Goodge John W, Carleton College Carleton College Northfield, Minnesota 55057 Northfield, Minnesota Archean migmatiticrocks rocksdated datedatat 2.7 2.7 b.y. b.y. from Archean migmatitic from the the Big Biq Falls, Falls,Minnesota Minnesota area were wereinvestigated investigated in in order Vermilion Graniarea order to to further furtherknowledge knowledge of the the-Vermilion Granitic tic Complex, Complex, particularly particularlyininthose thosewestern westernportions portionswhich whichhave have been been less less The Vermilion Vermilion Granitic Granitic Complex lies in in north-central extensively studied. The Complex lies north-central extensively studied. Minnesotaand andisiscomprised comprisedprimarily primarilyofof pink pink leucogranite leucogranite with with substantial substantial Minnesota rocksofof the the Vermilion Vermilion Distportions of migmatite migmatite throughout. throughout. Volcanogenic Volcanogenic rocks portions of rict ofofMinnesota parent rocks rocks for for the rict Minnesota are arebelieved believedtotobebethe themetamorphosed metamorphosed parent the regional scale scale rocks migmatites in the the Vermilion Vermilion Granitic GraniticComplex. Complex. On On aa regional rocks in migmatites the Big Big Falls Falls area are grouped groupedasasmigmatites, migmatites, locallydistinct distinctdifferdifferthe area are butbut locally encesinin structure structure and andfabric fabric permit permit the the subdivision subdivisionof of the the rocks rocks into into four ences four gneiss, mixed and units: tonalite, tonalite,garnet-biotite garnet-biotite gneiss, mixedtonalite tonalite andgneiss gneissand and grangranitic dikes. itic dikes. Structurally, Structurally,the thegneissic gneissicportions portionsappear appear as as rafts raftsupuptoto2Oni 20m size which which are are enclosed enclosed by by both the tonalite tonaliteand and mixed mixed rock. rock. Orientations in size both the of foliation one raft raft to foliationand andbanding banding in in the the gneiss gneiss are are consistent consistent from from one to another, another, which thatthey theyhave have not notbeen been extensively extensivelymoved moved during migniatization. migmatization. which indicates that The tonalite tonalite exhibits the form of n.ebulitic The exhibits compositional compositional inhomogeneities inhomogeneities inin the form of nebulitic structures shown shown bybydifferences concentrations. The structures differencesinin biotite biotite concentrations. Themajority majority of migmatite appears and gneiss, migmatite appearstotobebea amixture mixtureofoftonalite tonalite and gneiss, displaying displaying aa variety o-F structures including including complex folds and andswirls, swirls, boudinage, dilation and of structures complex folds boudinage, dilation and to nebulitic nebuliticstructures structures indicative of high-grade metamorphismand and schlieren to indicative of high-grade metamorphism Several pegmatitic pegmatiticdikes dikescutting cutting both both the the tonalite severe deformation. Several severe plastic plastic deformation. and gneiss represent represent the the youngest youngestrocks rocks in in the area. dikes are and gneiss area. The The dikes are up up to meter in in cross section, straight 1 meter cross section, straight and and in in sharp sharp contact contact with with the the gneiss. gneiss. 1 The tonalite isiscomposed The tonalite composed of ofmediummedium- to coarse-grained coarse-grained (3-7mm) (3-7mm) plagioclase, quartz quartz and and biotite biotitewith withminor minormicrocline microclineand andmuscovite, muscovite, and and accesaccessories of In several sories of zircon, zircon,sphene, sphene, apatite apatiteand andananopaque opaque mineral. mineral. In several samples, samples, plaqioclase of microcline. The gneissisis well-foliated, well-foliated, plagioclase contains contains small small patches patches of The gneiss medium-grained (0.5-2.0mm)and and composed plaqioclase,quartz quartzand andbiotite biotite medium-grained (0.5-2.0mm) isiscomposed of of plagioclase, with minor Plagioclase, biotite biotite and cordierite (?) minor garnet garnet and and microcline. Plagioclase, and cordierite (?) have replaced replaced subhedral subhedralgarnet garnetto to form form fine-grained aggregates, have aggregates, and and replacement grades from from minor minor to complete. granitic dikes ment grades complete. The The granitic dikes contain contain coarse-grained coarse-grained (4-6mm) microcline,quartz quartz and andmuscovite muscovitewith withminor minorplagioclase plagioclaseand andbiotite. biotite. ~-6mm) microcline, Plagioclase and gneiss oligoclase. The Plagioclase composition compositionininboth bothtonalite tonalite and gneiss is is oligoclase. gneissic of the therocks rocks and and composition composition of plagioclase indicate gneissic fabric of of the the plagioclase indicate that metamorphism reached amphibolite facies, thethebiotite, garnet and and niicrocmicrocmetamorphism reached amphibolite facies,and and biotite, garnet line content metamorphic content isisconsistent consistentwith withthis this metamorphic grade. grade. Modal Modal mineral mineral analysis of these these rocks rocks reveal reveal that that the the tonalite tonaliteand and gneiss gneiss are are similar similarinincomposicomposisis of content (average tion, despite despite aa significant significantdifference differenceininthe thebiotite biotite content (average15% 15% in tonalite; tonalite;28% 28% in in gneiss). gneiss). 13, 13. �(Goodge, continued) (Goodge, Models genesis of the the migmatites migmatites near near Big Big Falls Falls must must consider consider Modelsfor for the the genesis the following: the the strong structures in in the the strong fabric of of the the gneiss, gneiss, complex complex structures the mixed and gneiss, mixedrock, rock,mixing mixingofofthe thetonalite tonalite and gneiss,aa late-stage late-stage injection injection of granitic granitic material, material,compositional compositional similarities similaritiesbetween between the the tonalite tonaliteand and gneiss gneiss and consistencies the plagioclase plagioclase composition. composition. Further petrographic petrographic and and and consistencies in In the geochemical analysis willlead leadtotoananinterpretation interpretation of of the geochemical analysis will the relationship between the tonalite tonalite and between the and gnelss. gneiss. 14. �GEOLOGY OF THE GEOLOGY OF THE SOUTHEASTERN SOUTHEASTERN CONTACT CONTACT ZONE ZONE OF OF THE THE VERMILION VERMILION BATHOLITH, BATHOLITH, MINNESOTA MINNESOTA Anthony Dion Heinz, Heinz, Anthony Fleming, Fleming, Dion Lee and and Henry HenryWoodard Woodard Robert Lee Department Geology Department of Geology Beloit Be1oit College College Beloit, Beloit, Wisconsin Wisconsin mapping in in the theFourtown Fourtown Lake Lake quadrangle quadrangle and and reconnaisreconnaisDetailed geologic geologic mapping sance mapping mappinginin the Friday sance FridayBay, Bay,Iron IronLake Lakeand andAngleworm AnglewormLake Lake quadrangles quadrangles was was 1979field field seasons order to to better carried out out during during the the 1978 1978 and and 1979 seasons inin order better underunderstand the complex natureof of the the southeastern contact zone of the stand the complex nature southeastern contact zone of the Vermilion Vermilion Batholith. The The oldest schist oldest rock rock units units are are layered layered amphibo1ites, amphibolites,biotite biotite schist and aa complex complexunit unit which which may mayhave haveoriginally originally been and been aa volcanic volcanic agglomerate. agglomerate. These rocks by hornbJende hornblende adamellite andmigmatized migmatized by by an an These rocks are are intruded by adamellite sills sills and early episode episode of anatexis. anatexis. These These processes processeshave haveobscured obscuredthe thestrati9raphic stratigraphic relationships theearlier earlier rock relationships between between the rock units. This wasregionally regionally folded folded to This entire entire assemblage assemblage was to produce produce the the northeastnortheastThe detailed detailed mapping in the trending outcrop outcrop belts belts that thatare arenow now observed. observed. The mapping in the trending Fourtown Lake confirms that on the the southern southern Fourtown Lakequadrangle quadrangle confirms thatmost mostofofthe thearea arealies lies on limb of aa major 'major synform. synform. The of the the Friday FridayBay Bay quadrangle quadrangle probproblimb of The southern southernhalf half of The entire ably is underlain by the northern limb of this same structure. ably underlain by the northern limb of this same The entire region was subjected to to passive the Vermilion Vermilion Batholith and region was subjected passive emplacement emplacement ofofthe and the contact zone, zone, which the contact whichisis several several miles miles wide, wide, appears appearstotobebethe theresult result of aa second intense migmatization migmatization and and anatexis. secondstage stageof of intense The then cutcut by by a giant horsetail-like Theregion regionwas was then a giant horsetail-likesplay splayofofleft left lateral faults extending extending northeastward northeastward fro'm zone to the south. south. fromthe theVermilion Vermilionfault fault zone to the The episode episodeof of faulting faulting was hydrothermalalteration alteration of the The was accompanied accompanied bybyhydrothermal the fault fault zone zone rocks rocks and and by by the the development development of of quartz quartz and and epidote epidote veins. veins. mapping will extend both both north north and and east east from from Future Future detailed detailed structural mapping will extend the Fourtown the Fourtown Lake Lake quadrangle. quadrangle. Petrologic studies of of the the contact contactzone zone rocks rocks Petrologic studies are now now in progress. progress. Many Manyimportant importantquestions questionsconcerning concerningthe theorigin origin of these these are be answered answered by rocks remain to be rocks remain by these these continuing continuing studies. 15. �OVERTURNEDARCHEAN ARCHEANSUCCESSIONS SUCCESSIONS AND THEIRSIGNIFICANCE SIGNIFICANCE OVERTURNED AND THEIR K.H. Poulsen Poulsen and and M.M. M.M. Kehienbeck Keh1enbeck K.H. Lakehead University Lakehead University Thunder Bay, Thunder Bay, Ontario Nunerous separated Nunerousexamples examplesofofoverturned overturned Archean Archeansuccessions successionsfrom from widely widely separated Recognition of these cratons have these cratons havebeen beenreported reportedininthe therecent recentliterature. literature. Recognition phenomena in in North America is is still limitedtototwo twosuch suchexamples examples from from the the phenomena North America still limited Superior structural province; province; one one near near Red Red Lake, the other other at at Rainy Rainy Superior Lake, Ontario, Ontario, the Lake, In the the latter latterexample, example,the theoverturned overturnedsuccession succession includes includes Lake, Ontario. In strata which which have have been long standing standing controversy: controversy: the beenthe the subject subject of aa long it can and Keewatin Keewatin Groups Groups of of A.C. A.C. Lawson. Lawson. At At Rainy Rainy Lake Lake it can be be Coutchiching and demonst~ated succession is overturned overturned for for distances distances demonst'atedthat thatthe the stratigraphic stratigraphic succession 15 km km and the deformation deformation which which produced produced the took place place of 15 and that that the the inversion inversion took relatively early ininthe thedeformational deformational history history of of the the region. region. relatively early The thatthe thesequence sequence at at Rainy Rainy Lake Lake isisoverturned overturnedhad had not notbeen been The fact fact that recognized that two two fundamentally fundamentally difThe reason reasonfor forthis this is that difrecognized previously. The ferent approaches approaches totostructural and stratigraphic interpretationhave havebeen been structural and stratigraphic interpretation mapped largeantiforma1 antiformal folds which applied in the the past. past. A.C. A.C. Lawson Lawson mapped large which he he applied assumed totobebeanticlines. As aa result, he interpreted interpretedthe theCoutchiching Coutchiching assumed anticlines. As result, he metasedimentary forms toto be metasedimentaryrocks rocksnear nearthethecores coresofofthese theseanti antiforms be the the oldest in the the region. region. Observations Observations of younging younging using primary primary sedimentary sedimentary strata in and andvolcanic volcanicfeatures featuresatatkey keylocalities localitiesindicate indicatethis this stratigraphic stratigraphic interpretation to be be incorrect. incorrect. F.F. F.F. Grout, Grout, on on the the other hand, hand, interpreted the the pretation stratigraphy from from observations observations of of younging younging in graded graded beds beds near nearstratigraphic stratigraphic result,heheplaced placedthe theCoutchiching Coutchichingmetasedimentary metasedimentary rocks rocks contacts. As As aa result, much stratigraphiccolumn. column. In addition, addition,however, however, Grout Grout used used muchhigher higherinin the the stratigraphic the younging the structure. structure. Anticlines and and synclines synclines the youngingcriteria criteria to to interpret the mapped observed minor such as mappedininthis this manner mannerconflict conflict with observed minor structures structures such as fold It is only by the integrated symmetry and bedding-cleavage relationships. It is only by the integrated symmetry and bedding-cleavage relationships. application of of both both structural structuraland andprimary primaryyounging younging data data that that an an extensive extensive inverted sequence sequence can can be be recognized. recognized. Widespread Archean terranes Widespreadoverturning overturningin in Archean terranes has has mainly mainly been beenattributed attributed structures are to the the existence existence of of large large fold foldnappes. nappes. Such Such structures are normally normally assocassocwith the the concept concept of compressional compressional tectonics the iated with tectonics generally generally related related to the the other other hand it has c10siilg of primitive primitivevolcano-sedimentary volcano-sedimentary basins. basins. On On the hand it has closing of been that in the the developdevelopbeenproposed proposed thatgravity gravitydriven driventectonics tectonics might mightalso also result result in ment of instability near boundariesbetween between ment of nappes, nappes,either either due due to to crustal instability near thethe boundaries Each of of sub-provinces the buoyant buoyant emplacement emplacement ofofgneissic sub-provinces or or to the gneissic diapirs. diapirs. Each these be supported supported by from the Rainy Rainy Lake Lake region. these models modelsmay mayinin part part be by data data from Further documentation documentation ononthe and timing of ofthe thedeformation deformation Further thelateral lateral extent and will be be required required before before a a critical criticalappraisal appraisalofofthese thesemodels models will will be be possible. possible. will 16. �THE THE PRECAMBRIAN PRECAMBRIAN WATERLOO WATERLOO QUARTZITE, SOUTHEASTERN SOUTHEASTERN WISCONSIN: WISCONSIN: EVOLUTION AND AND SIGNIFICANCE EVOLUTION Clifford I. Smith CliffordN.N.Brandori Brandon and and Eugene Eugene I. Smith Division of ofScience Science Wisconsin-Parkside Univ. ofofWisconsin—Parkside Keriosha, WI Kenosha, WI 53141 Frank R. R. Luther Frank Dept. of Dept. ofGeography-Geology Geography-Geology Univ. Univ. of ofWisconsin-Whitewater Wisconsin-Whitewater Whitewater, WI WI 53190 The The Waterloo Waterloo Quartzite Quartzite forms forms aa broad broad asymmetric asymmetric eastward-plunging eastward-plunging syncline that isisa aprominent prominent structural structuraland andtopographic topographicfeature featureofofthethePrecambrian Precambrian basementof of southeastern Wisconsin. basement Wisconsin. If Ifthe thePaleozoic Paleozoic and and Pleistocene Pleistocene overoverburdenwere werestripped stripped from from the the Waterloo area, the the quartzite burden Waterloo area, quartzitewould would stand stand as as an an arcuate ridge arcuate ridge 150 150 toto275 275mmabove above the the surrounding surrounding Precambrian Precambrian surface. surface. A detailed structural structural study studyofofquartzite quartziteexposures exposures reveals reveals two two important important 60 EEwith with variable dip, vertical , The joint joint directions: directions: N 60 dip, and and NN30-40 30-40 W, W, vertical, N 60 interpreted as as the the axial axial plane plane direction for for the the syncline; syncline; 60EEjoint joint set set is interpreted the variable variable dip dip is probably duetoto stress stress refraction refraction in the the probably due the quartzite. quartzite. The N30-40 N30-40Wdirection W direction roughlyperpendicular perpendicular thehinge hingeline lineofof the the fold. The is isroughly to tothe These joint directions are similar to those described by Dalziel and Dott These joint are similar to those described by Dalziel and Dott (1970) (1970) For the Baraboo Quartzlte (which crops crops out out 60 to the The copfor the Baraboo Quartzite (which 60 km km to the northwest). northwest). The lanar attitude thethe Baraboo lanar attitudeofofthe theaxial axialplanes planesof of Barabooand andWaterloo Waterloo synclines synclines suggests thatboth both structures structures formed during the tectonic event. sugge~ that formed during the same same tectonic event. Andalusite wereidentified identified by by petrographic petrographic and and X-ray X-ray Anda1usite porphyroblasts porphyroblasts were diffraction studies diffraction studies ininbeds beds of ofschist schistinterbedded interbedded with with quartzite quartzite (near (near the the nose of the reported nose of the syncline synclineatatGlascow1s G1ascow ' s Farm). Farm). This This is the the first first reportedoccurence occurence medium grade index the Waterloo Waterloo area area of aa medium grademetamorphic metamorphic indexmineral mineralininoutcrop outcrop in in the (Haimson, 1978,identified identifiedandalusite andalusiteinin core core from fromdeep deepwells wellsdrilled drilled into the (Haimson, 1978, the assemblegeandalusite-muscovite-quartz andalusite-muscovite-quartz suggests suggeststhat that the quartzite). The The assemblege quartzite was upper greenschistfacies fadesoror to to the quartzite was metamorphosed metamorphosed to to thetheupper greenschist the lower lower amphibolite facies. In contrast, contrast,the themetamorphism metamorphism of the the Baraboo Baraboo Quartzite amphibolite only reached the facies ony reached thelower lowergreenschist greenschist fades(pyrophyllite (pyrophylliteisis found foundinin phyllite phyllite that either beds interbedded This suggests suggests that either the the thermal thermal beds interbeddedwith withthe the quartZite). quartzite). This event responsible for for andalusite restricted totothe event responsible andalusite growth growth was was restricted theWaterloo Waterloo area area at a deeper level in the or that that the the heat heat source source (intrusive (intrusivebody?) body?) was was at deeper level the Baraboo region. Baraboo ~Je Wesuggest suggestthe thefollowing following scenario scenay,oio involving involvingthree threeepisodes episodesofofmetamormetamorphisni for the phism for the development development of the the Waterloo Waterloo area: area: (1) Deposition Deposition ofofthe theWater-fl Waterlao volcanic-plutonic terrain between loo sediments sediments on on an an eroded eroded volcanic-plutonic terrain between1760 1760and and1630 1630 1630m.y. m.y.ago agoforming formingthe the syncline m.y. ago. m.y. ago. (2) Folding Folding and and metamorphism metamorphism 1630 (3) An and An intrusive event event affecting affectingthe theWaterloo Waterloo andmajor majorjoint joint directions. (3) 17. �(Brandon, Smith Smith.and andLuther, Luther, continued) (Brandon, The andalusite andalusite porphyrob1asts porphyroblasts probably probablyformed formedatatthis this time. Quartzite. The This event haveoccured occuredsoon soon afterthe thefolding folding episode or possibly as This event may may have after episode or as late as as 1500 1500 m.y. the Wolf Wolf River event). The ni.y. ago ago(related (related to to the River intrusive event). pegmatite dike well pegmatite dike on onRocky RockyIsland Islandand andthe theamphibolite amphiboliteidentified identified in in aa well (4) AAretrograde core probably probably formed stage. (4) retrogrademetamorphic metamorphic event event core formedduring during this this stage. producingaaweak weak penetrative foliationthat that is is revealed by aligned aligned sericite sericite producing penetrative foliation revealed by grains within the the andalusite anda1usite porphyroblasts. porphyrob1asts. grains 18. �RARE EARTH EARTH ELEMENT ELEMENTDISTRIBUTION DISTRIBUTION IN RARE IN THE THEPRECAMBRIAN PRECAMBRIAN RHYOLITES RHYOLITES AND AND GRANITES GRANITES OF SOUTH-CENTRAL OF SOUTH-CENTRAL WISCONSIN WISCONSIN I. Smith Smi th Eugene 1. Division of ofScience Science University University ofofWisconsin-Parkside Wisconsin-Parkside Kenosha, WI Kenosha, WI 53141 53141 The rhyolites and The rhyolites and granites granites ofofsouth-central south-centralWisconsin Wisconsin resulted resultedfrom fromanorogenic anorogenic igneous activity 1760+ igneous activity 1760~10 10 m.y. m.y. ago. ago. This This event event occurred occurred after afterthe themagmatic magmatic activity thethe Penokeari activityofof PenokeanOrogeny Orogeny (1850 (1850 m.y.) but but before beforethe theemplacement emplacement of the the Wolf River River Batholith (1500 earth and Wolf (1500 m.y.). Rare Rare earth and trace element element data data suggest suggest that two typesformed formedduring during this this event, two major major magma magma types event, but butpreclude precludea acomagmatic comagmatic The magma types are: are: a peraluminous relationship relationship between between the the type type types. types. The magma types peraluminous suite characterized characterized by bylow lowBa/Sr, Ba/Sr,Rb/Sr Rb/Srand andhigh highCaO CaO and and Al Al?Ol (the Marcellon Marcel10n 0 and Marquette Marquetterhyolites-groups rhyolites-groups22and arid44ofof Smith, Smith, 1978); 1978); aa metaluminous mt1urninous suite suite and characterized by andA1Al 03 (the quartz-aklali characterized by higher higher Ba/Sr, Ba/Sr, Rb/Sr Rb/Sr and and lower lower CaD CaO and 03 (the quart7.-ak1ali feldspar Utley,Berlin, Berlin,Endeavor, Endeavor, 0bservator Observatory2 Hill, Hill,and and Taylor Taylor feldspar rhyolites rhyolites at Uley, Farm; Montello and and Redyranite; Redgranite; and Farm; the the granophyric granophyric granites granites at Montello arid aa porphyritic porphyritic granite dike dike at atFlynn's Flynn'sQuarry-group Quarry-group 33 of of Smith, Smith, 1978). 1978). Both Both suites show light suites show light REEenrichment enrichment(La/Yb-4.7-8.6) (La/Yb-4.7-8.6) and REf and prominent prominent negative negative Eu fu anomalies anomalies (Eu/Eu*= (Eu/Eu*= 0.15-0.4), butthethemetaluminous metaluminous suite suitedisplays displaysuniformly uniformly higher REEabundances. abundances. 0J5-0.4), but higher REE The and granite of of the the metaluminous metaluminous suite the northwest northwest of the The rhyolite rhyolite and suite occur occur to to the of the Thesesuites suites in general rhyolite of ofthe theperaluminous peraluminous suite. These general correspond correspond to those those proposed by J\nderson, Schmusand andCullers Cullers (1978). proposed by Anderson, Van Van Schmus Within the peraluminous peraluminous suite the Marcellon Marce110n rhyolite rhyolitemay mayhave have formed formed from from the the Within the suite the Marquette rhyolite plagioclase, orthoclase orthoclase Marquette rhyolite by bythe thefractional fractional crystallization crystallization ofofplagioclase, and biotite. Within Within the the metaluminous suitethe thequartz-alkali quartz-alkali feldspar feldspar rhyolites and biotite. metaluminous suite and granophyric granites may may have have formed formed from from aa magma magma having and granophyric granites havingthe the composition composition of the Flynn1s Quarry involving two two feldspars, feldspars, the Flynn's Quarrygranite granitebybyfractional fractional crystallization crystallization involving biotite and biotite and hornblende. hornblende. fractional crystallizaEven due to fractional Eventhough thoughthere thereisis wide wide compositional compositional variation variation due the two two suites suites remain remain compositionally compositionally distinct. This indicates indicates differences differences tion, the distinct. This Modelstudies studies suggest suggest that that the suite in crustal crustal source source materials. materials. r~odel the peraluminous peraluminous suite was was generated generatedby by21% 21%nonmoda1 nonmodal fractional fractionalmelting meltingof of aa crustal source source having having an an model source source is intermediate The model intermediatecomposition composition(quartz (quartzdioritic dioritic or or andesitic). The remarkably similar in in composition to the the andesite anddacite dacite dikes dikes that that cut the remarkably similar composition to andesite and the sourcefor for the the metaluminous metaluminous suitewas was difficult to rhyolite exposures. The The source suite difficult to rhyolite exposures. model, since since the the undifferentiated undifferentiated member thissuite suite could could not not be be identified identified model, member ofofthis the source sourceisis rriost probably an an intermediate intermediate rock, rock, but with confidence. confidence. However, However, the most probably but The major abundancesthan thanthe thesource sourcefor for the the peraluminous suite. The with higher higher REE REE abundances peraluminous suite. igneous suites of south-central probably formed formedbybypartial partial fusion igneous suites south-central Wisconsin Wisconsin probably fusion of of The crust was probably tectonically different partsofofa aheterogeneous heterogeneous crust. The crust was probably tectonically different parts thickened during duringthe thePenokean Penokean Orogeny. Orogeny. 19. �GEOCHEMISTRY WEST-CENTRAL GEOCHEMISTRYAND AND VOLCANIC VOLCANIC STRATIGRAPHY STRATIGRAPHY OF OF WEST-CENTRAL MARINETTE COUNTY, COUNTY, WISCONSIN WISCONSIN MARINETTE M. M. L. Cummings Cummings Department of Earth Sciences Sciences Department of Earth Portland State University Portland State Portland,OR OR 97207 Portland, The volcanic volcanic pile The pile ininwest—central west-central Marinette Marinette County, County, Wisconsin, Wisconsin, includes includes mafic to felsic felsicflow flowand andpyroclastic pyroclasticunits, units,and andclastic clastic sedimentary,massive massive mafic sedimentary, The volcanic volcanic belt isisapproximately and iron formation formation units. The approximately 88km km sulfide and wide and is bounded on the north by the Dunbar gneiss and on the south by wide and bounded on the north by the Dunbar gneiss and on the south by the Atheistane quartz North ofGe-l-emn—Lake thebelt belt is is approximately Athelstane quartz monzonite. monzonite. North of~olernan-Lake the approximately 2 km wide where the Twelve Foot Falls quartz diorite occurs to the km wide where the Twelve Foot Falls quartz diorite occurs the north north and and betweenvolcanic volcanic units the Atheistane Athelstane quartz monzonite monzonite to the south. south. Contacts Contacts between the to the are steeply strike north are steeply dipping dipping and and strike north to tonorthwest. northwest. felsiccenter centernorth northofof Coleman Lake Lake contains contains interlayered interlayered andesite andesite A felsic Coleman and massiverhyolite rhyolite flows. and massive flows. Fragmental Fragmental units have not not been been observed. observed. Plagiounits have clase phenocrysts occur in in the quartz and clase phenocrysts occur the andesite andesite flows flows and and abundant abundant quartz and plagiorhyolite clase sparse plagioclase flows. The The rhyolite clase or or sparse plagioclase phenocrysts phenocrystsoccur occurininrhyolite rhyolite flows. flows contain 70 70 to to77% 77% S102 Si0 2 and flows contain contain 57 57 toto60% 60% Si02. Si0 2 , flows contain and the the andesite andesite flows The northwestern underlain by by porphyritic The northwesternportion portionofofthe thevolcanic volcanicpile pile is is underlain dacite and and rhyodacite rhyodacite flows. flows. Basalt flows are are present present locally. Basalt and andrhyolite rhyolite flows locally. The southeastern area is underlain underlain by by clastic clasticmetasediments, metasediments, The southeasternportion portion of of the the area formation, massive massive to semi-massive semi-massive sulfide, and basalt and and dacite flows. flows. iron formation, sulfide, and The composition differenThe compositionofofthe theflows flowsdefine definea adistinct distinct calc-alkaline caic-alkaline differenThe composition compositionof of the tiation trend. trend. All units units are are subaikalic. subalkalic. The the volcanics volcanics suggests island island arc suggests arc volcanism. volcanism. The volcanic volcanic units units of The of westcentral westcentral Marinette Marinette County County are are chemically chemically disdistinct from the thevolcanic volcanicunits units-inineastern easternand andnortheastern northeasternMarinette MarinetteCounty County tinct from includingthe theQuinnesec, Quinnesec,Beecher, Beecher,and andPeniene Pemene Formations. Formations. The The flows the flows in the including study area in general study area general are are higher higher in in TiO TiO?,, K20, K20, A1203 A1 203 and and CaO, CaD,and and lower lower in Na20 and FeO FeOthan than Quinnesec, Quinnesec, Beecher Beecher ana an Pemene Na 20 and Pemene Formations. The The volcanic piTe ininwestcentral westcentral Marinette MarinetteCounty County should should not be be considered considered part the pile part of the Quinnesec Quinnesec Formation. 20, 20. �WHEREIS IS THE WHERE THE SOURCE SOURCE OF OF WISCONSIN WISCONSIN DRIFT DRIFT DIAMONDS? DIAMONDS? W. F. Cannon Cannon W. U.S. U.S. Geological Geological Survey Survey Reston, Virginia Virginia 22092 Reston, M. G. G. Mudrey, Mudrey, Jr. M. Wisconsin Geological and and Natural Natural History Wisconsin Geological History Survey Survey Madison, Wisconsin Wisconsin 53706 Madison, Between 1876and and 1903, dIamonds found in at leastseven sevenlocalities localities Between 1876 1903, diamonds werewere found in at least southern and and central central Wisconsin. Wisconsin. All were were found found in Pleistocene Pleistocene glacial in southern The bedrock bedrockkimberlite kiniberlite source source for for the deposits Holocene river the deposits or or Holocene river gravel. The diamonds but to tobebeininnorthern Canada, the diamondsisis unknown unknown buthas hasbeen beenpresumed presumed northern Canada, the only area north of contain kimberlites. Recently, area north of Wisconsin Wisconsin previously known known toto contain That find a kiniberlite kimberlite pipe pipehas has been been found found in in Iron IronCounty, County, Michigan. Michigan. That causedusustoto consider considerthe the possibility possibility that diamonds caused thatWisconsin Wisconsin drift drift diamonds have have come fromaamore morelocal local source--kimberlites source--kimberlites ininnorthern come from northernMichigan Michigan and and Wisconsin. Wisconsin. The very poorly poorly exposed, exposed, but strong positive The Iron Iron County Countykimberlite kimberlite is is very but aa strong magneticanomaly anomaly indicates thatitit is roughly magnetic indicates that roughly circular circularininplan planand and200-300 200-300 meters meters in diameter. diameter. Although Althoughthe the kimberlite kimberlite is is entirely entirelysurrounded surrounded by by Precambrian rocks, it contains abundant inclusions of fossiliferous limestone, Precambrian rocks, it contains abundant inclusions of fossiliferous limestone, probably from Ordovician Black Black River River Group Group that overlaid the thearea areawhen when probably from the the Ordovician that overlaid the The post-Ordovician post-Ordovicianage ageofof the the kimberlite leads the kimnberlite kimberlite was was intruded. The leads us to suspect that other possible possible cryptovolcanic cryptovolcanic structures in in Paleozoic Paleozoic us to suspect that other rocks overkimberlite kimberlite pipes pipes that are rocks in the the region region were were formed formed over are not not yet yet exposed exposed by by erosion. Such Such structures structures include includeLimestone LimestoneMountain Mountainand andSherman Sherman and Baraga BaragaCounties, Counties,Michigan; Michigan;Glovers GloversBluff Bluff in Hill in Houghton Houghton and in Marquette Marquette County, south of County, Wisconsin; Wisconsin;and andpossibly possiblyan anarea areaalong alongthe the Brule Brule River River south Iron River, Iron River, Michigan. Michigan. No diamonds known IronCounty County kimberlite,but butitit has No diamonds areareknown in in thethe Iron kimberlite, has not not cryptovolcanic structures structures could been been adequately sampled. sampled. The The cryptovolcanic could not not be be the the source of the becauseeven evenifif they source the Wisconsin Wisconsin diamonds diamonds because they are are caused caused by by kimberlites, those kimberlites, those kimberlites kimberliteshave havenot notyet yetbeen beenexposed exposed by by erosion. Elsewhere occur as isolated Elsewhereininthe theworld, world, kimberlites kimberlites rarely rarely occur as aa single single isolated body; bodiesare aremore more common, common, and body; clusters ofofbodies andthe the presence presenceofof one onekimberlite kimberlite makes suspectthat that others others exist nearby. makes usussuspect nearby. The discovery discoveryof of additional additional kirnberlites be very very difficult difficult because The kimberlites may may be because coverof of glacial glacial drift of the the extensive extensive cover driftand andthe theprobable probable small small size of of If all are magnetic, they might be found by detailed kimnberlite bodies. If kimberlite all are magnetic, they might be found by aeromagnetic However, the County kimberlite aeromagnetic surveys. However, the magnetism magnetismofofthe the Iron Iron County kimberlite appears to be by secondary secondarymagnetite magnetiteformed formedduring duringserpentinization serpentinization appeal~s to be caused caused by of olivine, olivine,sosoananunserpentinized unserpentinized kimberlite kimberlitemay may not not be be strongly stronglymagnetic. magnetic. We We suggest suggestthat that one one or or more more diamond-bearing diamond-bearingkimberlites kimberlites may mayexist exist in northern northern Michigan Michiganoror \~isconsin, Wisconsin,but butthe the discovery discoveryof of sLich suchbodies bodiesisis unlikely unless is undertaken. undertaken. unless a a very very thorough thorough search search is 21. 21 �CORRELATION OF OF GRAVITY CORRELATION GRAVITY AND AND MAGNETIC MAGNETIC ANOMALIES ANOMALIES IN EAST-CENTRAL EAST-CENTRAL MINNESOTA MINNESOTAAND ANDNORTHWESTERN NORTHWESTERN WISCONSIN WISCONSIN V.W. Chandler V.W. Minnesota Geological Survey Minnesota Geological Survey 1633 Eustic Eustlc Street 1633 St. Paul, st. Paul,MN MN 55108 55108 Similarities andand magnetic Similaritiesiningravity gravity magneticanomaly anomaly patterns patternsinineast—central east-central Minnesota andnorthwestern northwestern Wisconsin Wisconsinimply imply that that several Minnesota and several Precambrian Precambrian rock rock A broad niagnetic may be between the the two two areas. areas. A magneticmaximum maximum units may be correlative correlative between that isisbounded bounded to the the south south by by east-trending east-trendinglinear linearmagnetic magneticmaxima maxima is an an anomalypattern patternthat that exists exists in anomaly in both both central central Aitkin AitkinCounty, County,Minnesota, Minnesota, and and areas are are characterized characterized by northern Sawyer Sawyer County, County, Wisconsin. Wisconsin. Both Both areas by regional regional gravity maxima. gravity maxima. In Aitkin AitkinCounty, County,Minnesota, Minnesota,the thebroad broadmagnetic magneticmaximum maximum is is associated with the linear associated with the theArchean Archean McGrath McGrath Gneiss Gneiss whereas whereas the linearmagnetic magneticmaxima maxima are apparently related totobelts beltsof of early Proterozoic metavolcanic metaare apparently early Proterozoic metavolcanic andand meta— sedimentary rocks. Similarly, sedimentary Similarly,ininSawyer SawyerCounty, County, Wisconsin, Wisconsin, the thebroad broadmagnetic magnetic maximum associatedwith withArchean Archean graniticand andgneissic gneissicrocks rocks and andthe the linear linear maximum is isassociated granitic magnetic maxima areare believed to to bebe related Proterzoic magnetic maxima believed relatedtotobelts belts of of early Proterzoic east-trendingbelt belt of of irregular metavolcanic and and metasedimentary metasedimentary rocks. An An east-trending metavolcanic magnetic minima minima and Lacs and and Kanabec Kanabec Counties, Minnesota, magnetic and maxima maximainin Mille Mule Lacs Counties, Minnesota, resembles Barron and and Rush Rush Counties, Counties, Wisconsin. Wisconsin. Both resemblesaa magnetic magnetic terrane terrane in Barron regions are characterized characterized by by regional regional gravity gravitymaxima. maxima. This This magnetic magnetic terrane regions are Minnesota corresponds Proterozoic granites granites and and minor minor volcanic volcanic in Minnesota correspondstotoearly early Proterozoic rocks rocks of similar similar age. age. In In Wisconsin, Wisconsin, the the corresponding corresponding niagnetic magnetic terrane terrane is associated with exposures of Barron Quartzite and early associated with exposures of middle middle Proterozoic Proterozoic Barron Quartzite and Proterozoic and volcanic rocks. rocks. Proterozoic granites and In order to to shift shiftthe thediscussed discussed magnetic magnetic terranes terranes of east-central east-central In order Minnesota Minnesota to to match match corresponding corresponding terrances terrances in northwestern northwestern Wisconsin, Wisconsin, aa This distance southeastward transposition 60 km km is required. This distance southeastward transpositionofof at at least 60 is required. is consistent consistentwith withsome some estimates estimates ofofcrustal crustal separation during Keweenawan separation during Keweenawan riftingbut butloss lossofoftypical typical magneticsignatures signatures near near the the rift rift zone,where where riftirig magnetic zone, the Keweenawan clastic make this estimate somewhat somewhat tentative. the Keweenawan clasticrocks rocksare arethick, thick, make this estimate tentative. Clearly, quantitative quantitativeanalysis analysisof of gravity magnetic anomaliescombined combined with gravity andand magnetic anomalies further geologic geologic studies studies Isisrequired requiredbefore beforethe themodel model presented presented in this paper paper in this can be tested. The The results of this thispaper, paper,however, however, demonstrate demonstrate the the results of can be fully fully tested. potential utility gravity magneticdata data ininunraveling unraveling and and correlating correlating potential utility of of gravity andand magnetic complex now separated separated by by the the Keweenawan Keweenawan rift system. complexgeologic geologic features now rift system. 22. �METAVOLCANIC ROCKS ROCKSAT AT EAU EAU CLAIRE DELLS, METAVOLCANIC DELLS,MARATHON MARATHON COUNTY, COUNTY, AND AND AN EVALUATION OF THE AN EVALUATION OF THE SHEAR "SHEAR ZONES' ZONE" HYPOTHESIS HYPOTHESIS IN IN WISCONSIN WISCONSIN R.S. andL.G. L.G. Medaris, Medaris, Jr. R.S. Maass Maass and Department of Geology Department of Geology and and Geophysics Geophysics University of ofWisconsin Wisconsin Madison, WI WI 53706 53706 In years the the interpretation interpretation as of rocks In recent recent years as niylonites mylonites of rocks at the the Dells Dells R1OE) of the the Eau Eau Claire ClaireRiver River(sec. (sec.7, T29N, 7, T29N, R10E)ininMarathon MarathonCounty CountyWisconsin Wisconsin has wide acceptance acceptanceamong amonggeologists geologistsworking workinginin the of has gained gained wide the Precambrian Precambrian of this interpretation interpretation and the Lake the Lake Superior Superior region. region. Based Based ononthis and geophysical geophysical data, data, numerous numerousauthors authors have have drawn d'awn aa major major N2SE N25E to to N3OE N30E trending trending "s 'shear hear zone" zone Therocks rocksatat the the Dells Dells are are aa mafic to felsic through through this this locality. locality. The mafic to felsicmetametavolcanic sequence, sequence, probably probably Early Early Proterozoic Proterozoicininage, age,which whichwas wasdeformed deformed and and metamorphosed amphibolite facies during metamorphosed totoamphibolite duringthe thePenokean Penokean Orogeny. Orogeny. The The inequiinequigranular textures in in these representrelict relict porphyritic granular textures these rocks rocks represent porphyriticfeatures features and and are not the result of of cataclasis. cataclasis. The The metavolcanics, metavolcanics, 'trending ~endingN35E N35E totoN45E N45E are not the with vertical verticaldips, dips,are arebounded bounded on on the the west west and and north north by by the the Kalinke Kalinke quartz quartz monzonite, deformed during thethelater the monzonite, which which was wasemplaced emplacedand and deformed during later stages stages of of the Penokean undeformed 1500 PenokeanOrogeny, Orogeny,and andononthe theeast eastby by the the undeformed 1500m.y. m.y.old old Wolf Wolf River Sa thol ith. Batholith. ll The volcanic sequence sequence theDells Dellsranges ranges from basaltictotorhyolitic; rhyolitic; The volcanic at atthe from basaltic the including feldspar feldspar porphyries, porphyries, quartz quartz porphyries, the latter latter including porphyries,and andlapilli lapilli tuffs. In the feldspar feldspar porphyries porphyries many many of the the feldspar feldsparphenocrysts phenocrysts remain remain In the subhedral to to euhedral, euhedral, and and aa significant significant number not been rotated into subhedral number have have not been rotated the plane planeofof the the foliation. foliation. Some Someofofthe the quartz quartz phenocrysts phenocrystsinin the the quartz the quartz porphyries have beenflattened, flattened, but porphyries have been but others others have have not, not,and and none none are are as as granugranuIn addition, some contain relict lated as as would would be be expected expectedin in a mylonite. In addition, some contain relict embayment unitsare arenow now amphibolites amphibolites containing containingsubhedral subhedral embaymentfeatures. features. Basaltic units euhedral hornblende, hornblende, while contain to euhedral while compositionally compositionally intermediate intermediate units contain subhedral garnet. subhedral Compositionallayering layeringvaries variesinin thickness thickness from frommillimeters millimeters to to tens tens of Compositional distinctive lithologies lithologies down to the meters. Numerous Numerous distinctive down to the millimeter millimeter scale scalecan can be traced across acrossthe theoutcrop outcropwith withlittle little orornonochange be traced change in in thickness. thickness. Crosscutting mafic andfelsic felsic veinlets cutting mafic and veinlets are are tightly tightlyfolded, folded,but butthere thereisisnonoevidence evidence of isoclinal isocJinal folding, folding,and and attenuation attenuation of of fold fold limbs limbs isisminor. minor. Both Both the the micromicroscopic and features of these scopic and mesoscopic mesoscopic features these rocks rocks were were produced produced by by deformation deformation associated middle grades grades of metamorphism associated with with middle metamorphism without withoutsubstantial substantial transpositransposltion tion of of layering. layering. ThroughoutWisconsin, Wisconsin,rocks rocksolder older than than the the 1765 m.y. old old granites 1765 m.y. granites and and Throughout rhyolites rhyolites have have been been subjected subjected to to a widespread widespread brittle brittle deformation deformation event event in nature during the thePenokean Penokean Orogeny. Orogeny. This This deformation deformation was was regional regional in nature rather rather than zones of intense intense cataclasis. cataclasis. We many of the than localized localized in zones Wesuggest suggestthat that many of the localities previously localities previouslydescribed described as as mylonites, mylonites, are are either eithermetavolcanics, metavolcanics, or rocks affected by this thisregional regionalevent, event,and andshould should be be reevaluated reevaluated with with these these rocks affected by alternatives inin mind. mind. 23. �WERE THERETWO TWOMIDDLE MIDDLEPRECAMBRIAN PRECAMBRIANOROGENIES OIOGENIESIN IN THE THE LAKE WERE THERE LAKE SUPERIOR SUPERIOR REGION? REGION? Gene LaBerge Gene L. L. LaBerge Geology Department Department Geology University ofofWisconsin-Oshkosh University Wisconsin-Oshkosh Oshkosh, Wisconsin 54901 Oshkosh, WIsconsin Precambrianrocks rocksinin Central Central Wisconsin Wisconsinoccur occurasaslarge, large, discrete areas Precambrian areas of gneisses, areas of of greenschist gneisses, amphibolites amphibolites and and migmatites, migmatites, and and areas greenschist facies facies Countyisis underlain underlain mainly volcanic volcanic and and plutonic rocks. rocks. Marathon Marathon County mainly by by greengreenfacies volcanic volcanic and and plutonic contact with with gneissic gneissic schist facies plutonic rocks rocks inin fault contact ages suggest suggestthat that both rocks rocks on on the the north, north, west west and and south. south. Radiometric Radiometric ages both the the gneisses and greenschist greenschist facies fades rocks gneisses and rocks are areMiddle MiddlePrecambrian. Precambrian. Fold axes, axes, mineral mineral lineations Fold lineations and and elongated elongated fragments fragments in the the gneisses gneisses However, comparable plunge to the west west at at 200_600 20 0 -60 0 over the region. region. However, comparable plunge to the over most most of of the thegreenschist greenschistfades faciesvolcanic volcanic rocks in MarathonCounty Countyplunge plunge lineations ininthe rocks in Marathon east to northeast Near the fault boundary between east northeast at at 500 50 0 to to near near vertical. Near the fault boundary between vertical. gneissic and andgreenschist greenschistfacies fadesrocks, rocks,the thelineations lineations are are nearly nearly vertical. vertical. gneissic Lineations in greenschlst(?) Lineations greenschist(?) fades faciesvolcanic volcanicrocks rocksIninRusk, Rusk,Price Priceand andOneida Oneida Counties the east. east. Therefore, appears to be a consisconsisTherefore, there appears to be Counties also also plunge plunge to to the tent relationship relationshipbetween between direction directionofoflineations lineations metamorphic grade. grade. andand metamorphic This that the rocks beensubjected subjectedtotodifferent different stresses, This suggests suggests that rocks have have been stresses, and and these these stresses stresses may maybebeofof different different age. age. Myers (1978) rocks folded folded about about Myers (1978)reports reports greenschist greenschlst facies facies volcanic rocks east-plunging axes axes restihg restiHg unconformably unconformably on on gneisses gneisses in western western Clark Clark County. County. Thus, aa period of formation of of the Thus, of erosion erosionmust must have have occurred occurred between between formation the gneisses and rocks. gneisses anddeposition depositionof of the the volcanic rocks. If the If thegneisses gneisses (and (and the thedeformation deformation ininthem) them)are areMiddle MiddlePrecambrian Precambrian and and the the greenschist greenschlst facies fades rocks rocks are are also alsoMiddle Middle Precambrian, Precambrian, then then there must be be two two periods periods of of Middle deformationinIn the the region. These must Middle Precambrian Precambrian deformation two postulated deformations deformations may may be Lake Superior two be recognized recognized elsewhere elsewhereinin the the Lake region. Mild Mild flexuring on the the iron iron ranges after flexuring and and erosion erosion occurred occurred on ranges after deposition of ofthe theChocolay ChocolayGroup Group ofofthe theMarquette MarquetteRange Range Supergroup. Supergroup. Conceivably the gneissic gneissic rocks Conceivably the rocks In in Central Central Wisconsin Wisconsin represent represent aamore more intense intense metamorphi sm associ ated with is unconformity. unconformity. The II Penokean Orogeny," Orogeny, II The 'Penokean metamorphism associated withththis which which occurred occurred after afterdeposition depositionof of thethe Menominee Menomineeand and Baraga Baraga groups, groups, would would then be then be represented represented by by the thegreensch-Ist greenschist fades faciesmetamorphism metamorphism and and widespread widespread ofgranitic graniticrocks rocksIn in muchofofnorthern northernWisconsin. Wisconsin. intrusion of much 24. �VOLCANIC OF THE VOLCANIC AND AND PLUTONIC PLUTONIC ROCKS ROCKS OF THE JUMP JUMP AND AND YELLOW YELLOW RIVER VALLEYS, VALLEYS, NORTH-CENTRAL WISCONSIN WISCONSIN NORTH-CENTRAL M. L. M. L. Cummings Cummings Department of of Earth Department Earth Sciences Sciences Portland State State University Portland Portland, OR Portland, OR 97207 Metavolcanic Metavolcanic rocks rocks are are exposed exposed along along the the Jump Jump River ininsoutheastern southeasternRusk Rusk Countyand andlocally locally along County along the the Yellow Yellow River Rivernear nearGilnian, Gilman, Wisconsin. Wisconsin. Plutonic rocks rocks crop crop out south south of of the theJump Jump River River arid and along along the the Yellow Yellow River. River. The The metavolcanics and and some some plutonic plutonicrocks rockshave havebeen beendeformed deformedand andmetamorphosed metamorphosed under under upper greenschist greenschisttoto lower lower amphibolite amphibolitefacies fades conditions. upper conditions. Schistosity Schistosity is weakly to to strongly developed andisis subparallel subparallel to bedding in the weakly developed and bedding in the volcanics. volcanics. Stratigraphic tops Stratigraphic tops indicate that that the thevolcanics volcanics are are overturned overturned to the the south south and appear have been fold axes. axes. and appearto to have beenfolded folded about about northeast northeast trending trending fold Quartz monzonlteplutons plutonscrop cropout out south south of of the River and and locally locally the Jump Jump River Quartz monzonite The plutons plutons are are weakly weakly foliated foliated and can can be be shown showntotointrude intrude the the volcanics. volcanics. The and quartz monzonite pluton also crops locally display display cataclastic cataclastic textures. textures. A quartz monzonite pluton crops out along north of out along Main Main Creek Creek north of the theJump Jump River. River. The displaysa agrano— granoThe pluton displays phyric texture and phyric and euhedral euhedralquartz quartzcrystals crystals occur occur as as inclusions inclusions in feldspar feldspar crystals. crystal S. A strongly foliated foliatedpluton plutoncrops cropsout out2½ 2~miles miles south south ofofthe theJump Jump River River and similar sirnilarplutonic and plutonic rocks rocks crop crop out out along along the the Yellow Yellow River. River. The The composition of the the plutons plutons Is is granodlorite, granodiorite. An intermediate intermediatecomposition corripositionvolcanic volcaniccenter centercrops cropsout outeast eastofofthe the village village An of Jump Jump River. Volcanic Volcanic blocks blocks to one one foot foot diameter diameter form form massive massive units associated bedded tuffs and massive flows. associatedwith with fine-grained fine-gralned bedded tuffs and massiveporphyritic porphyritic flows. Crystal-lithic tuffsand andintermediate intermediate totobasic basic flows flows crop crop out out at atapparently apparently Crystal-lithic tuffs similar stratigraphic similar, stratigraphic levels levelseast eastand and west west of the the volcanic volcanic center. center. A A prophy.prophyritic with plagloclase phenocrysts riticfelsite felsite with plagioclase phenocrystsoccurs occurs totothe thesouth south ofofthe themain main fragmentalunits units of of the the volcanic volcanic center center and andisis believed believedtoto be bestratigraphically stratigraphically fragmental abovethe the volcanic volcanic center. above The geologic geologic evolution evolution of The of the the area area suggests suggests volcanism volcanism followed followed by by or or Deformation of the Deformation of the area area produced axes. Quartz monzonite monzonite produced recumbant recumbantfolds folds about about Northeast Northeast trending axes. iritrusives were alongthe theaxial axial zones zonesofof the the folds folds producing intrusives were emplaced emplaced along producing linear The metamorphic grade may increase to the south plutonic toward the plutonic belts. The metamorphic grade may increase to the south toward Yellow This interpretation interpretationsuggests suggests that thatthe theproposed proposed northern northern Yellow River. This boundary of the Amphibolite complex and the the Jump River Fault boundary of the Chippewa Chippewa Amphibolite complex and Jump River Fault Zone Zone need to to be need be reconsidered. reconsiderea. associated with, intrusion intrusion of granodioritic associated with, granodioritic plutons. plutons. 25. �HEAVY MINERAL ANALYSIS OF OF PRECAMBRIAN PRECAMBRIAN ROCKS ROCKS IN IN RUSK RUSK COUNTY COUNTY HEAVY MINERAL ANALYSIS * Tom Ernst, cohn Tom Ernst. John Markert, Melissa Melissa Montz Montz * UniversityofofWlsconsln-Oshkosh Wisconsin-Oshkosh University Department Department of Geology Geology Oshkosh, Oshkosh, Wisconsin 54901 The bedrock bedrockin -InRusk RuskCounty County consistsmainly mainlyofofgranitic granitic and The consists and metavolcanic metavolcanic rocks of middle quartzite bodies are believed middle Proterozoic Proterozoic age. age. Several Several quartzite bodies are believed to rocks The age ageof of the various unconformably middle Proterozoic rocks. rocks. The various unconformablyoverlie overlie the the middle quartzltes isisnot quartzites notknown, known, but but they theyhave have been been correlated correlated with with the the middle middle Proterozoic QuartzitebybyDott Dott and andDalziel Daiziel (1970) (1970) and andwith with the the late Proterozoic Baraboo Baraboo Quartzite late Proterozoic Sioux Sioux Quartzite QuartziteofofMinnesota MinnesotabybyCraddock Craddock (1972). (1972). The study determine whether siliceous The study was wasundertaken undertakentototry try to determine whether the the various various siliceous rocks have the same origin and whether Four units rocks have the same origin and whether they they may maybebecorrelative. correlative. Four were sampled sampled for study,the theBarron Barronand andFlambeau Flambeau Quartzites Quartzitesand andtwo twounnamed unnamed were for study, units informally units. informallyreferred referredtotohere hereasasthe theBruce Bruceand and Broken Broken Arrow Arrow units. The BarronQuartzite Quartziteisisnearly nearlyflat-lying flat-lying and The Barron and forms forms aa ridge ridge in the the Petographic show well-rounded, northwestern part the county. county. Petographic studies show northwestern part of the To the south, south, the theFlambeau Flambeau well-sorted grains grains with with quartz quartzovergrowths. overgrowths. To In contrast to the Quartzite forms another contrast to the flat-lying flat-lyingBarron, Barron, Quartzite forms another resistant resistant ridge. In Flambeau Quartzite as as a steeply dipping tightly the the Flambeau Quartziteoccurs occurs a steeply dipping tightly folded folded unit. unit. Thin section similar totothe theBarron Barron although although sorting sorting section analysis analysis reveals reveals aa lithology lithology similar is not not as as complete. complete. Heavy Heavy minerals to toboth minerals common common bothbodies bodiesinclude include apatite, apatite, zircon, corundum, corundum, and and ubiquitous hematite hematite and and niagnetite. magnetite. In In addition addition the the Barron has some some siderite, while the theFlambeau Flambeau Quartzite contains contains Barron Quartzite Quartzite has siderite, wh1e sphene. Between thetwo twoquartzite quartzite ridges ridges lie Between the liethe theBroken Broken Arrow Arrow and and Bruce Bruce units. Examination of These massiveunits unitsare areboth bothfine-grained fine-grained splintery splintery cherts. These massive cherts. Examination thin have undergone shows small small serrated serratedquartz quartzgrains grainsthat that have undergonesome some thin sections sectionsshows Heavyminerals minerals of of metamorphism butbut show no no evidence of aofdetrital metamorphism show evidence a detritalorigin. origin. Heavy the Broken Arrowunit unit include include grossularite, the Broken Arrow grossularite,zoned zoned hematite hematite and and possibly possibly spesspessartite. The very ferruginous ferruginous and and contains contains zircon zircon (malacon), (malacon), The Bruce Bruceunit unit is very and schorl. analcite and We haveestablished establishedthat that the the metacherts metachertsare arenot not detrital detrital and We have and thus thusmay may be related to the the older oldervolcanic volcanicsequence sequence rather than than the the younger younger quartzites. be related to quartzites. Petroqraphic andheavy heavymineral mineralstudies studiesindicate indicateaaseparate separateorigin origin for for the Petrographic and the respective and the metacherts. respective quartzites quartzites and the metacherts. ** Student Paper Paper 26. �DEPOSITIONAL SETTING OF OF STROMATOLITE-OOLITE STROMATOLIIE-OOLIIE FACIES DEPOSITIONAL SETTING FACIES ON ALLUVIAL FAN ON AAKEWEEAWAN KEWEEAWAN ALLUVIAL FAN Paul A. Pau1 A. IJaniels Da ni e1s Dept. Dept. of of Natural Natural Resources, Resources, Geological Geological Survey Survey Division P.O. P.O. Box Box 30028 30028 Larising MI Lansing, MI 48909 48909 R. Douglas Douglas Elniore Elmore R. Dept. Dept. of ofGeology Geology and and Mineralogy Mineralogy The University University of The ofMichigan Michigan Ann Arbor, MI Ann MI 48109 48109 The predominantly consists heavily The Copper CopperHarbor HarborConglomerate Conglomerate(~ (' 1 B.Y.) B.Y.) predominantly consists of of heavily andboulder boulder conglomerates conglomerateswith with subordinate subordinate volcanics oxidized immature immature sandstones sandstones and The unit unit is withthe the volcanics volcanics in in the The is aafining finingupward upwardand and basinward basinward sequence sequence with the lower lower portions. The The sediments (basinward) flowing sedimentswere weredeposited depositedbybynortherly northerly (basinward) streams alluvialfan fanenvironment environment off offthe thebasin basin margin. margin. streamscreating creatingaaclassical classical alluvial 1 Sedimentary structuresand andassociated associatedfeatures, features, including including current crescents, crescents, Sedimentary structures parting lineation, tabular tabular and and trough trough cross-stratification, intraformational parting cross-stratification, intraformational conglomerates, mudcracks,oolites, oolites, cross-stratified cross-stratified boulder conglomerates, mudcracks, boulderconglomerate, conglomerate, large boulders boulders ('-S (~ 70 extensive oxidation, oxidation, and and 70 cm), cm), micro-crass-stratification, micro-cross-stratification, extensive calcite pseudomorphs after probably arid, calcite pseudomorphs after gypsum; gypsurri;allall combine corribirietotoindicate indicate aa probably periodically subject to large periodically dessicated, dessicated, shallow shallow water water environment environment that was was subject large variations variations in in flow flow regime. regime. Seeminglyenigmatic, enigmatic, in in regard of such such an an environment, environment, Is is Seemingly regard to the the harshness harshness of the fan occurrence occurrenceofof algal algal stromatolites. The stromatolites are the medial medial fan The stromatolites arenow now represented laminated carbonates carbonates intercalated intercalatedwith withmudstone mudstone and and represented by by thinly thinly laminated stromatolites are sandstone, and and as as drapes drapes on sandstone, on conglomerate. conglomerate. These These stromatolites are well-preserved well-preserved with the original original depositional early diagenetic with much much ofof the depositional and and early diagenetic fabric being being retained. retained. Various micro-structure Various micro-structuretypes typesand andcements cements can can be be recognized. recognized. Stromatolite morphologiesinclude includelaterally laterally linked morphologies linkedhemispheroids hemispheroids (LLH), (LLH), horizontal horizontal mats, mats, Thin beds and oncoids, and beds containing hematitic hematiticsingle single andcompound compound oncoids, and intraclasts. intraclasts. Thin (grapestone) exhibiting primary radial cortical (grapestone)ooids, ooids,some some exhibiting primary radial corticalfabric, fabric, occur occur interinterbeddedwith withthe the stromatolites. stromatolites. bedded This cyclic three This carbonate carbonatedepositional depositional environment environmentwas was cyclicwith withat at least three thin (< « 25 25 cm) cm) biostromes biostromes present of about about four four presentthrough througha astratigraphic stratigraphic interval interval of meters. Discontinuous exposuresencompass encompass a lateral extent extent of approximately Discontinuous exposures a lateral approximately algal encrusted boulders, up 13 kilometers. Overturned 13 Overturned algal encrusted boulders, up to 50 50 cm cm in diameter, diameter, occur about two two meters rrietersstratigraphically stratigraphically below occur about belowthe thelowest lowestobserved observed biostrome, biostrome, attesting of this facies attesting to to the the exlstance existance of facies at at an an earlier earliertime, time, and and in in aa position position still stillcloser closertotothe thebasin basinedge. edge. The existanceofof the the stromatolite/oolite stromatolite/oolite facies The existance facies indicates indicatessome some of the the complexities should be complexities that that should be addressed addressedininany anyinterpretation interpretation of of the the overall depositional in particular, depositional system, system, in particular,how how aa cyclic cyclic"quiet "quietwater" water"environment environment related totoboulder boulderconglomerates. conglomerates. 27. �STRATIGRAPHY OF THE GUNFLINT GUNFLINT FORMATION FORMATION, STRATIGRAPHY OF THE CURRENTRIVER RIVER AREA, THUNDER CURRENT THUNDER BAY BAY R.J. Shegeiski Shegelski R.J. Department Geology Department of Geology Lakehead University Lakehead University Thunder Thunder Bay, Bay, Ontario OntarioP78 P7B 5E1 5El A total of offourteen fourteen stratigraphic stratigraphicsections sections ofofthe theGunflint GunflintFormation Formation have beenmeasured measured along Current River resultinginin aa section section with aa have been along thethe Current River resulting The composite compositesection sectionfrom fromthis this study lateral extent extent of of 2.6 2.6 kilometers. kilometers. The study thick and containsfive five distinct members. is 43 43 meters meters thick and contains distinctlithostratigraphic lithostratigraphic members. The base baseof of the the Gunflint The Gunflint Formation Formation has has not not been been observed observed in these these sections sections and is is probably below the the level level of and probably below of Lake Lake Superior Superior but there there isisa aconformable conformable contact with overlying asas Rove contact with overlying fissile fissileblack blackshale shaleinterpreted interpreted RoveFormation. Formation. fissile black The are, blackshale shale(450 (450cm, cm, base base The members members are,inin ascending ascendingorder: order: 1. fissile not 2. micrite-siliceous not exposed); exposed); 2. micrite-siliceousgrainstone grainstone (taconite) (taconite)association associationcapped capped by 11 meter of algal algal chert cm); 3. 3. fissile meter of chert (1450 (1450 cm); fissileblack blackshale shale(1250 (1250 cm); cm); grainstone (920 (920 cm) cm) and breccia siliceous grainstone and4.4. an analgal algal chert-intraformational breccia At least association (200 which is overlain association (200 cm) cm) which overlainby bythe theRove Rove Formation. Formation. At 50% this composite thicknessisis fissile 50% ofofthis composite thickness fissileblack blackshale shalebecause because black black shale shale interfingers with and forms a matrix to grainstone lenses as well as occurring with and forms a matrix to grainstone lenses as well as occurring as separate remainderisis predominantly predominantlysiliceous siliceous grainstone. as separatemembers. members. The The remainder grainstone. Micrite and and siliceous grainstone grainstone occur occur as as lenticular lenticulardeposits deposits which which exhibit tabular exhibit tabularand and trough trough cross cross bedding. bedding. The The grainstones contain containsmooth smooth and pustular pustular algal algal laminae, feriestrae and andpisolites pisolites and are locally locally overand laminae, fenestrae and are overlain by by flat-pebble flat-pebbleconglomerates, conglomerates, intraformational breccias breccias and and stromatolite mounds. The The grainstone-algal association isisa achert-carbonate chert-carbonatechemical chemical grainstone-algal association sedimentwhich whichwaswas reworked a littoral-intertidal depositional sediment reworked in ainlittoral-intertidal depositional environenvironmentand andisis analogous analogoustoto the the deposits deposits of Shark Australia. Flatment Shark Bay, Bay, Western Western Australia. pebble conglomeratesand andintraformational intraformatlonal breccias breccias are pebble conglomerates are high-energy high-energy deposits deposits which formed during during periodic storms. fissile shales which formed storms. The The fissile shales associated associated with with these deposits deposits likely likely represent waterdeposits depositsofof clastic clastic these represent lagoonal lagoonal and and deeper deeper water contemporaneouslywith withthe the chert carbonate. debris which which accumulated accumulated contemporaneously carbonate. 28. �PETROLOGY OF SOME SOME LOGAN LOGAN DIABASE SILLSFROM FROM COOK COOK COUNTY, COUNTY, MINNESOTA MINNESOTA ETROLOGY OF DIABASE SILLS Norriss W. Norri W. Jones Jones Department of Geology Department Geology University ofofWisconsln-Oshkosh University Wisconsin-Oshkosh Oshkosh, Wisconsin 54901 Oshkosh, 54901 Four Lower Keweenawan Logan diabase sills between between South South and and Birch Birch Lakes, Four Lower Keweenawan Logan diabase sills Lakes, South Lake Lakequadrangle, quadrangle,northeastern northeasternMinnesota, Minnesota,are arestratified stratified as South as shown shown in Figure ~ (thickness Althoughfabric fabric isis variable, meters). Although variable, the the following following (thickness in meters). general sequence ofof textural general sequence textural zones is is recognized: zones recognized: lower lower chilled, lower chilled, lowerfine—grained, fine-grained, " f}?~~. medi um-grai ned, course—grai ned medium-grained, course-grained :: ~RTIX (except in sill C) (except in sill C), porphyry , porphyry or porphyritic, upper fine-grained, porphyri tic, upper fi ne-grai ned, I::'i'<. upper chilled. upper chilled. ';/--" . r;~ I-~~~~~~~:.~;[)· ~ '62 -,..~ '"! 1S6 ,:,;.-" ..:::•. - lSI ;ooLo. [1.1. B SilL. A CHILLEO MA!tqf,: AND rtNE-r.RAINI::U PORPIlYRY. INTERC.R. ;~2;~~ lJ9 FINt:- to MEDTUM-CRO •• INTER(:R. Ij"-/} -' /I T- lOS~ .. ' — ?IFO.—C,00, OPIIITIC pT:. .' ','-, "','.- ,'.. 'I .. :-tf.OIt'!'<.-<'RA1NFTI, -." SlLl -Ol'HITlC TO I ~: : .. n SURorH IIle . ," ~(lR!-'HR '. ",,' ~ POYrOT,TODIUMAOCO. .':',;<" ;/" ~ ..., ~ :' , ;') 07 99 ~ t) F!NE-CRALNET,OPOITXC nSF.-cR.\[NF.f),nPIlITIC — TO ~TO SUa00000!c SU80PHlTlr /'/ -CIHI.U:O'V.Rc:lN 66 SILl.C .,.... 5) 51 50 __ CHlLl.F.O l(Ml.(:fN 10C-P., IOrERO., ~ ..;. . . ', ~HlE-r.!U)., tNf£R.GR .•FTOP1F909. f[\,' f'lIE~O$. TOO TOO..• 0001TIc. '.',: .~~ ......... I-'EO.-r.RO oPII1TlC. p007IiOoTrTr PORPIIYRITlr ~'~_~".'I _ :<if.DIUl'l-f:RA!':r.n, OPHITIC '" . Both chilled margins Both chilled margins contain contain scattered phenocrysts of plagioscattered phenocrysts of clase in aa matrix clase matrix of of plagioclase, plagioclase, amphiboleand/or and/orbiotite, biotite, quartz, amphibole quartz, and acicular,ororskel skeland granular, granular, acicular, — etal ilmenite. etal ilmenite. The and The finefine- and mediumgrained zones zonesconsist consist of medium-grained plagioclase, augite, plagioclase, augite,interstitial interstitial quartz, acicular quartz, acicul~rapatite, apatite,some some K-feldspar, and and eniLayed, embayed, skeletal or lath—shaoed lath-shaoed ilmenite; ilmenite;pegeo— pegeoEn 2Fs nite Fs nite (ave. (ave.Wo Wo DEn and ) and partially —resbe i n— rich partially-res6rbe~, i~§n-rich, olivine (2 samples, samples, Fo F0 2 and ol i vine (2 in2Oe Fo33 .) are present F0 ~) are present in ~6~esamples. samples . 33 F0TOUFOPOIPLrTO. = Cour—grained zonesare are distingdistingCour~e-grained zones uished by the the abundance abundance and uished by and variety variety of inter-growths inter-growthsbetween between quartz quartz and K-feldspar K-feldspar and/or and/or sodic sodic plagloand plagio1igure Fi gure 1 clase; pyroxene is typically pyroxene is typicallymore more Porphyry zones zones contain contain plagioclase phenoaltered altered than than in in finer-grained finer-grainedzones. zones. Porphyry phenocrysts appeartoto be beslightly slightly more calcic than crysts which which appear more calcic than the the matrix matrix plagioclase; plagioclase; thethe rnedium-grained other aspects aspects of of the the mineralogy mineralogy are are similar similarto to medium-grained zones. zones. Deuteric~lteration alteration was wasextensive extensivein inallall zones, zones,but butthe theintensity, intensity, distribution, distribution, Deuteric andexact exactnature natureofofthe the alteration alteration are the scale scale of of a thin and are variable, even even on on the thin section. ,'.- ~ ... : ~'.'; ~ -:~ :~; ~ 8 :.... :'•. ".:;.;. _ o rI.'l(-r;RAINF:Il. POIKIUTlt' -UlII.U;o ,'lAllf:IN -Q'iF-t:II.O •• I~Tr.RI:'t,. YORl'lIr:. 0 -CHILl,rr} 'Ullt;J~ Fourteen rock ana analyses for major and and microprobe Fourteen rock lyses for major oxides oxi des from from sills sill A s A andB Band m; croprobe analyses of feldspars, analyses of feldspars, pyroxene, pyroxene, and and olivine olivinefrom from1313samples samples (mostly (mostly from from sills AAand B) show showthat: that:(1) (1)there thereisislittle little variation sills and B) variation ininbulk bulkorormineral mineral chemistry zones;(2) (2) chilled chilled margins chemistry in the the finefine-and andmedium—grained medium-grained zones; margins are are notably richer ininSi02 alkalis than notably Si0 2and and lower lower ininCaO CaD and and alkalis than other other zones; zones; porphyry zones zones (based (based on on one one analysis) analysis)are arelower lowerin in FeD, MgO,and andCaO CaD (3) porphyry FeO, MgO, and richer in alkalis, high and richer alkalis,reflecting reflectingthethe highpercentage percentage of ofplagioclase; plagioclase; (4) coarse-grained are enriched enriched in in Si02 alkalis, depleted (4) coarse-grained zones zones are 5i0 2 and and alkalis, depleted ininCaO CaO 29. �(Jones, continued) (Jones, continued) — and MgO,have havehigh highFe20~/FeO Fe2O/FeO ratios,and andcontain containplagioclase plagioclase which which is is notably and MgO, ratios, notably are similar similar throughout, more sodic (5) augite compositions compositions are throughout, more sodicthan thanother otherzones; znes; (5) (6) the of cores mostly in 0En3 - Es WO~O_40En35_4~Fs?n_3n; (6) the composition composition of cores of mostly in the therange rangeWo ; except in the plagioclas~ crystals (excluding pneno~rysts) is An 45 _52 , except the plagioclase (xcudin enryts) is An45_52, course-grained course-gralned zones. zones. These suggest emplacement emplacement of magma containing phenoThese data data suggest of aa magma containing plagioclase plagioclase phenominor assimilation assimilation of ofadjacent adjacent Rove Rove Formation, minerals, crysts, minor Formation,crystallization crystallization minerals, and migration alkalis, water towardthe thecoarse-grained coarse-grainedzones, zones, and migration of of silica, silica, alkalis, andand water toward which werethe thelast lasttoto solidify. solidify. which were 30. �DIFFERENTIATING ULTRAMAFIC FLOWSFROM FROMSILLS SILLS IN IN THE DIFFERENTIATING ULTRAMAFIC FLOWS THE SHEBANDOWANr~INE MINEAREA, AREA, NORTHWESTERN ONTARIO, CANADA SHEBANDOWAN NORTH~~ESTERN ONTARIO, CMADA Penelope Penelope Morton Morton Department of Geology Geology Department Carleton University Carleton Ottawa, Canada Canada Shebandowan Ni-Cu Mine Chico Metals, Ltd.)isisspatially spatially associated Shebandowan Ni-Cu Mine (Inca Metals, Ltd.) associated with ultramafic sill which is is intrusive intrusive into intovolcanic volcanic rocks rocks of with aa thin thin ultramafic sill which A Belt, Superior Province,northwester~ northwester Ontario. A the Shebandowan-Wawa Shebandowan-Wawa Belt, Superior Province, study study of the the volcanic volcanic statigraphy statigraphy ininthe themine minearea area (32 (32 km km )) has has revealed revealed ultramafic the presence ofof conformable the presence conformablelens-like lens-like extrusive extrusive and and intrusive intrusive ultramafic rocks. These These are arenow nowserpentinites serpentinitesand andtalc-carbonate talc-carbonateschists, schists, but but in many instances, relict relict textures many instances, textureshave havebeen been preserved. preserved. In In the the field, field, flows flows are are differentiated differentiatedfrom from sills sinson on the the basis basis of of rock rock association. Ultramafic Ultramafic flows and genetically (?) flows are are spatially spatially and genetically (?) related to related to black black and and white, white, magnetite-chert magnetite-chert iron iron formation formation and and dark dark Youngingdirections directions green, green, iron iron rich rich basaltic basaltichyaloclastite hyaloclastite(17.8% (17.8%FeO). FeO). Younging indicate that that hyaloclastite indicate hyaloclastite sits sits on on top top of ofthe the iron ironformation formation which which in turn Sills, however, relationship however, show show no no such such relationship turn tops tops the the ultramafic ultramafic flows. flows. Sills, and can canbebeintrusive intrusiveinto into either basalts felsic pyroclastic and basalts or more more felsic pyroclastic rocks. rocks. Typical petrochemical plots al.,1977; 1977; Muir, Muir, 1979) 1979) do do not not Typical petrochemical plots (Arndt (Arndt et et al., differentiatethese theseultramafic ultramaficrocks rocksbutbut disseminatedchromites chromites have have differentiate disseminated markedlydifferent different chemical chemicalaffinities. affinities. Chromites Chromitesfound foundinin flows markedly flows are are generally generally lower lowerininA12O A1 0 and Ti0 2 and and MgO MgOcontents, contents,higher higher in TiO and have have higher +2 +2 +Mg and Fe +3 2 3+3 . . Fe /Fe +Mg and Fe /Fe +Al+Cr +Al+Cr ratios than those those chromites chromltes found found in 1n ratios than sills. sills. Analyses Analysesof of chromites chromites from from consecutive consecutivesamples samplesfrom froma athin thinsill sill (every 20 20 feet) and 03 decreases (every and from from a thin thin flow flow(10 (10feet) feet)show showthat thatCrCr?03 decreases and Fe203 Fe2O3increases increasestowards towards topofof both both units. units. But case of and thethetop But in he the case the sill , chromites the siTl, from the immediate immediate top and and bottom bottom have have exactly the chromites from exactly the same Fe203and andCrCr7O2 contents whereas thoseininthe the flow flow are ~ame Fe?03 contents whereas those are markedly markedly differelit, This different. This 8ifferent chemical trend trend might might well be attributed ifferent chemical well be attributed to different cooling cooling histories flows and and sills. histories for flows sills. ° Arndt, Naldrett, A.J., Arndt, N.T., N.T.,.~a~drett, A.J., and and D.R. D.R. Pyke, Pyke, 1977, 1977, Komatiitic I<omatiitic and and FFe Rich Rich e Tholeiit-ic Tholel1t1cLavas Lavas ofofMunro Munro Twp., Twp., Northeastern Northeastern Ontario. Journal of Petrology, Journal Petrology, Vol. Vol. 18, 18, pp. pp. 319-369. 319-369. Muir, T.L., Archean Muir, T.L., 1979, 1979, Discrimination Discrimination Between BetweenExtrusive Extrusive and and Intrusive Intrusive Archean Ultramafic Rocks Rocks in in the theShaw Shaw Dome Major and and DomeArea AreaUsing Using Selected Selected Major Trace Elements. Trace Elements. Can. Vol. 16, 16, pp. 80-90. Can.Jour. Jour.of of Earth Earth Sci., Sci., Vol. pp. 80-90. 31 31. �GEOLOGICAL EVIDENCE EVIDENCERELATING RELATING TO TO THE THE INTERPRETATION GEOLOGICAL INTERPRETATION OF OF THE THE LAKE SUPERIOR LAKE SUPERIOR BASIN BASINSTRUCTURE STRUCTURE Donald M. M. Davidson, Davidson, Jr. Jr. Donald Department of Sciences Department of Geological Sciences University Uni versity of of Texas, Texas, El El Paso The configuration the Lake Lake Superior Superior Basin Basin coincides the regional regional The configuration of the coincides with with the geologic structure and and is isprimarily primarilycomposed composed of of rock rock units unitsofof LakePrecambrian Precambrian geologic Lake (Y) age overlie older (Y) age which which unconformably unconformably overlie olderassemblages. assemblages. Evidence of poorlydeveloped developedininpre-Keweenawan pre-Keweenawan (late Evidence of basin basin formation isispoorly (late Precambrian) and geologic units region. Precambrian) andlower lower Keweenanwan Keweenanwan geologic unitsinin the the Lake Lake Superior Superior region. However,middle middle Keweenawan Keweenawan intrusives,lava lava flows, and However, intrusives, and associated associatedsediments sediments display primary features features such such as flow thickness, thickness, and and crosscrossdisplay primary as mineral mineral layering, layering, flow bedding, whichdirectly directly indicate at that that time. bedding, which indicate basin basin development development. at time. Upper Keweenawan sedimentational patterns delineatethe thebasin basin outline. outline. Keweenawan sedimentational patterns delineate Penetrative and foliation, are well well Penetrativestructures, structures,particularly particularly folds folds and foliation, are developed in Archean and Middle Precambrian rocks, but are generally rare in develvped in Archean and Middle Precambrian rocks, but are generally rare Late Precambrian faults and and joints joints are Precambrian sequences. sequences. Nonpenetrative Nonpenetrative faults are prevalent prevalent allPrecambrian Precambrian rocks rocks in in the the Lake Lake Superior Superior region. region. Curvilinear Curvilinear faults in all east-west trends, trends, prevail prevailin in Archeanand andMiddle Middle Precambrian Precambrian units, units, with east-west Archean although other other trends trends are are to to be noted, particularly particularly ininWisconsin. although be noted, Wisconsin. Northeast-and northwest-trending fractures Northeast-and fracturesare arecommon common in in Late LatePrecambrian Precambrian Faults of units although although regional regional data data are are incomplete. incomplete. Faults of late latePrecambrian Precambrian age age have been the region. region. have beenreported reportedtotooccur occurlocally locally in in the summary, Archean, Archean, Middle Middle Precambrian Precambrian and and pre-Keweenawan pre-Keweenawan geologic In summary, geologic units render little direct over that that time time interinterunits render little directevidence evidence of of basin basin formation formation over val. The The basin basin structure structure appears initiated ininmiddle appears to have have been been initiated middleKeweenKeweenawantime timeasasa acrustal crustalrift. rift. Rifting in awan in the thebasin basin proper proper was was very very likely likely enhancedbybyeast-west east-west structuraltrends trendswithin within older older units. enhanced structural 32, 32. �THE PRE-KEWEENAWAN TECTONICHISTORY HISTORY OF OF THE THE NORTH-CENTRAL THE PRE-KEWEENAWAN TECTONIC NORTH-CENTRAL LINITED UNITED STATES STATES AND AND CENTRAL CANADA CANADAAND ANDHOW HOWITIT INFLUENCED OF THE THE MIDCONTINENT CENTRAL INFLUENCED FORMATION FORMATION OF MIDCONTINENT RIFT u.S. Illinois University J.S. Kiasner, Klasner, Western Western Illinois Universityand andU.S. U.S.Geological Geological Survey Survey Macomb, Illinois 61455 Macomb t Illinois W.F. W.F. Cannon, Cannon, U.S. U.S. Geological Geological Survey Survey Reston, Reston, Virginia Virginia 22092 W.R. Van Van Schmus, Schmus,University University of W.R. ofKansas Kansas Lawrence, Kansas Kansas The Midcontinentrift rift formed about1.1 1.1 b.y. b.y. ago in crust The Midcontinent formed about ago in crust that thathad had aa long long and complex block for for several several hundhundand complexhistory historybut butthat that had hadbeen beena arigid rigid crustal crustal block red million years beforethe therifting. rifting. The rift formed red million years before The rift formed at aa high high angle angle to the the general ENE ENEstructural structural grain of general of older olderrocks rocksand and crossed crossed aaboundary boundary that sepseparates two very different different geologic arates two very geologic terranes terranes near near the the southern southern edge edge of the the Superior Province. Province. North North of crust typical typical of the the boundary, boundary,thetherift rift is is within crust of Superior Superior Province Province that that had had been been deformed deformed only and gentle gentle warpwarponlyby byfaulting faulting and ing 2.6 b.y. b.y. ago; ago; south southofofthe theboundary, boundary, riftisis in in crust that ing after about about 2.6 thethe rift that had longer and more complex complexhistory. history. There, had aa much much longer and more There, rocks rocks as as old old as as 3.8 3.8 b.y. have b.y. (Kenoran (Kenoran have u'ndergone undergonerepeated repeatedtectonism; tectonism;major majorevents eventstook tookplace placeat at 2.6 b.y. orogeny), 1.9 b.y. b.y. (Penokean (Penokean orogeny), (theemplacement emplacement of orogeny), 1.9 orogeny), and and 1.5 1.5 b.y. (the of the Wolf River Wolf River batholith batholithand andsynchronous synchronous volcanism). volcanism). The boundary boundarybetween'the between theSuperior SuperiorProvince-type Province-typecrust crust and and rocks rocks to to the The the south effect the Midcontinent Midcontinent south seems seemstoto have havehad hada apronounced pronounced effectononthe thenature natureof of the rift. Where rift. Where the is ininSuperior Superior Province-type Province-type crust, ititisisabout about150 150km km therift rift is wide andisis complex; whereitit is in terrane to the wide and complex; where in rocks rocks ofofthe themore more complex complex terrane the Its width south, ititisisabout south, about9090kmkmwide wideand and has has aa simpler simplershape. shape. Its widthchanges changes abruptly at the the contact contact of of the the two two terranes. terranes. abruptly Lithologic and/or may Lithologic and/or tectonic tectonicboundaries boundaries within withinthe theSuperior SuperiorProvince Provincemay have the Superior Superior Province, Province, haveaffected affectedthe theextent extentofof the the Midcontinent Midcontinentrift. rift. In the the riftlies lies entirely within the confines of Shebandowan the Shebandowan granite-greengranite-greenthe rift entirely within the confines of the stone belt except 'stone except for for the thepoorly poorlydefined definedarm arm that thatextends extends to toLake Lake Nipigon. Nipigon. Changes composition, structure,ororthickness thicknessofof the the crust crust at the Changes inincomposition, structure, the north north edge of the beltmay mayhave have inhibited the the northward extension of edge of the Shebandowan Shebandowan belt inhibited northward extension of the the.ririft. ft. Orientations arms are are probably probably controlled Orientations of of the the rift rift arms controlled by by older older faults faults or analysis of fractures. Lineament Lineament analysis of gravity gravityand ~ndaeromagnetic aeromagneticmaps maps and and Landsat Landsat images presence of linearzones zones that thatare aremore more than than 1000 1000 km km long. imagesindicate indicate the the presence of linear l~any known faults or zones zones of of crustal crustalweakness. weakness. Manyofof the the lineaments lineaments coincide coincide with with known faults or Geologic data indicate indicate that these Geologic data thes features features formed formed before before 1.1 1.1 b.y. b.y. ago. ago. Conspicuous directions N. 65 65 b W., W., N. N. 45° 45 0 W., W., N. N. 35° 35 0 E., and and N. N. 65° 65 0 E., E., Conspicuous directions are N. the thoseofofindividual individual segments segments therift. rift. the same same asasthose ofofthe 33. �(Klasner, Cannon and and Van Van Schmus, Schmus, continued) (Kiasner, Cannon continued) A large large elliptical elliptical gravity gravitylow, low,more more than than -60 -60 milligals milligals ininamplitude, amplitude, lies ininpart partabove above granitic graniticrocks rocks inincentral centralWisconsin. Wisconsin. This low low suggests suggests the presence of large large volumes subjacentgranitic granitic rocks the presence of volumes ofof subjacent rocks throughout throughout this area. The subsurface granite granite IninWisconsin Wisconsin may may have have played played aa role role The inferred subsurface in localizing because of the the rift rift symmetrically localizing the the rift rift becausethe thearcuate arcuate shape shape of symmetrically of encircles encircles the the gravity gravity low. low. It It may may be be that the the granite graniteformed formed an an area area.of unusually strong strong crust crust through throughwhich whichthe therift rift could unusually could not not form. form. 34. �KEWEENAWAN NATURE OF OF KEWEENAWANVOLCANISM VOLCANISMAND AND THE THE NATIJRE KEWEENAWANRIFT RIFT TECTONICS KEWEENAWAN TECTONICS John C. Green Green John C. Geology Geology Department Department University of ofMinnesota, Minnesota, Duluth Duluth Duluth, Minnesota Minnesota 55812 55812 Since theearly earlyinklings inklingsinin the the '60's '60's of aa rift—tectonic origin for Since the rift-tectonic orlgln for the the Mid-Continent Gravity High, High, aanumber Mid-Continent number of of more more detailed detailedconcepts concepts have have developed. developed. These These include include that of ofWhite White (1972) (1972) who who proposed proposed the the existence existence of of several several separate basins of accumulation of lavas along a tensional zone, contrasting separate basins of accumulation of lavas along a tensional zone, contrasting with modern modern examples such as as thethe East African Rift central graben graben examples such East African Riftwith with its its central and Gilmer Gilmer (1973) and relatively thin and relatively thin volcanics. volcanics. Chase Chase and (1973) subsequently subsequently proposed proposed widens aa strictly strictlyrigid-place rigid-placemodel, model, ininwhich which the the rift rift widens totothe thenorth northfrom from aa pole New pole of of rotation rotationin in NewMexico Mexico and and in in which which mafic mafic mantle-derived mantle-derived rock rock completely completely fills the to widths 80-90 fills therift rift to widthsof of 80-90km. km. Weiblen Weiblen and press) have have since since and Morey Morey(in (in press) suggested Duluth Complex, Complex, and the suggestedthat that the the Duluth andbybyextrapolatio~ extrapolation,other otherparts parts of of the structure, of normal normal faulting faulting ininwhich structure, developed developed through through aa sequence sequence of whichdowndowndropped, rotated blocks wayfor for the the great dropped, rotated blocks of of crust crustunder under tension tensionhave have made made way great volumes intrusions leaving leaving an an intact, intact, horizontal volumes ofofintrusions horizontal carapace carapace of volcanic volcanic rocks. rocks. Green (1977) (1977)elaborated elaborated on on LoJhite's White's model model of of broad Green broad volcanic "pl plateaus." ateaus. 1I The following evidence mapped volcanics tends tends to to The evidence within withinthethe mappedKeweenawan Keweenawan volcanics minimize, thoughnot noteliminate, eliminate,the therole roleof of normal normalfaulting, faulting, particularly particularly minimize, though grabenformation, formation, and andmega-dikes mega-dikes withinthe theLake LakeSuperior Superiordistrict. district. 1. 1. Nograben within No- where are the pre-Keweenawan where are the lavas 1avas seen seen to tobe befaulted faultedagainst aga i nst pre-Keweenawan rocks. rocks. 2. With the exception exception of the the Osler Osler Group Group in Thunder Thunder Bay-Nipigon the basal basal the Bay-Nipigondistrict, district, the Keweenawan lavas erupted onto area relief that was either an Keweenawan lavas areare erupted onto an an area of of lowlow relief was either an erosion surface surfaceoror the the site site of cratonic erosion cratonic deposition deposition of water-laid water-laid quartz quartz arenite. arenite. At of the conglomerate reflect localfault faultrelief. relief. 3. The At the the base base of the Osler Osler aa conglomerate maymay reflect local The stratigraphy thevarious various Keweenawan plateau accumulations is is ininmany many stratigraphy ofofthe Keweenawan plateau lava accumulations cases remarkably remarkablycontinuous, continuous,showing showingboth botha asurface surfaceofoflow lowrelief relief on cases on which which flows could spreadout outfor for many manytens tensofofkilometers, kilometers,and andthe thelack lackofof faulting faulting flows could spread within The major major faults faults now evident show reverse, not not normal within sequences. sequences. The now evident show reverse, normal displacement. 4. Normal Normaldisplacement displacementisis rarely rarely observed rocks on on either either observed between between rocks side of basaltic dikes within andand beyond Keweenawan ~ide ofKeweenawan Keweenawan basaltic dikes (feeders?) (feeders?)both both within beyond Keweenawan volcanic areas. areas. If normal faults faults had had been been prevalent, prevalent, the the feeder feeder dikes dikes could could If normal The small be expected expectedtoto have havefollowed followedthem thempreferentially preferentially or vice be vice versa. versa. 5. The percentage (2-3%) (2-3%)ofof interflow interflow sediments percentage sediments in in most most of ofthe me major major plateau-lava plateau-lava sequencesargues arguesagainst againstlarge large normal-fault normal-fault displacement sequences displacement during during volcanism. volcanism. 6. The The fanning of dips dipsand and down—dip down-dip thickening the Portage Portage Lake Lake Volcanics Volcanics fanning of thickening of the imply warping, warping,not notfaulting, faulting, at at the the edge edge of the the lava lava basin. basin. 7. If mafic imply If mafic magma supply gravityanomaly anomaly were were dominated dominated by by half-graben half-graben magma supplytotothe the crustal crustal gravity faulting leading totointrusions, intrusions, surely manysuch suchfaults faultswould wouldhave havereached reached faulting leading surely many the surface are they? Where are they? 8. The anomalies the surface through through the the lavas. lavas. Where The gravity gravity anomalies (at least leastininwestern westernLake LakeSuperior Superiorwhere wherethe theattempt attempthas hasbeen beenmade: made: White, 1966) can can be be adequately adequately modeled modeledbybythe the known knownlava lavabasins basins without without any 1966) any major major separation of ofmany many tens kilometers. 9. Chase Chase and model crustal separation tens of kilometers. and Gilmer1s Gilmer's rriodel ignores basalts of of Ontario. ignores the thick thickOsler Oslerand and Mamainse Mamainse basalts This of Keweenawan basicallysupports supportsa view a view of Keweenawanniagmatism magmatism in This evidence evidence basically oval basins basins (such (such as as the the Columbia Columbia Plateau sma ler extent extent large, oval Plateaubasalts basalts but but of smaller 35. �(Green, continued) (Green, and thicker) which and thicker) which gradually graduallysubsided subsidedbybywarping warpingwhile whilekeeping keepinga more-or—less a more-or-less level surface. The models of Chase and Gilmer and of Weiben and do not riot level surface. The models of Chase and Gilmer and Wei ben and Morey Morey do fit the the rocks fit thegeology geology ininthe theLake Lake Superior Superior area area where where the rocks actually crop crop out. out. 36. �UPPER PRECAMBRIAN PRECAMBRIAN SEDIMENTARY SUPERIOR REGION REGION UPPER SEDIMENTARY ROCKS ROCKSOF OFTHE THE LAKE LAKE SUPERIOR Rich.rd ofMinnesota, M"lnnesota,Duluth, Duluth,MN MN55812 55812 Richard W. W. Ojikangas, Ojdkangas, University University of G.B. Morey, Minnesota Minnesota Geological St., St. St.Paul, Paul,MNMN55108 55108 GB. Morey, Geological Survey, Survey, 1633 1633 Eustis Eustis St., Paul A. A. Daniels, Daniels, Michigan Michigan Geological Geological Survey, Survey,Box Box 30028, 30028, Lansing, Lansing, MI MI 48909 48909 Paul J. Kalliokoski, Houghton, Kalliokoski,Michigan MichiganTechnological TechnologicalUniversity, University, Houghton,MIMI49931 49931 Quartzose sandstoneunits units which which represent represent parts of Quartzose sandstone ofone oneorormore moresand sand sheets sheets a few few hundred hundred feet in thickness thickness include includethe theBessemer Bessemer Quartzite in a feet or or less in Quartzlte in Michigan Group in Ontario Michigan and and Wisconsin, Wisconsin,the the Pass Pass Lake LakeFormation Formationofofthe the Sibley Sibley Group in Ontario near Thunder Bay, the the Puckwunge Formationininnortheastern northeastern Minnesota, Puckwunge Formation Minnesota, and and the near Thunder Bay, is present Nopeming Quartzite Duluth. A basal basal conglomerate conglomerate is present at at each each Nopeming Quartzitejust just west west of Duluth. localityabove above the the subjacent subjacent unconformity. unconformity. Lava Lava flows succeed succeed the the sandstones sandstones locality except in Ontario overlie the except Ontariowhere where red redmudstones mudstones and and carbonates carbonates overlie thesandstone sandstone and and are in turn are turnoverlain overlainbybyflows flowsand andsedimentary sedimentary rocks rocks of ofthe theOsler OslerFormation. Formation. The immediately overlying overlyingthetheBessemer Bessemerand andNojeming Nopellling are arecommonly commonly pillowed pillowed and and flows immediately the sandstone sandstone appears to tohave been un1ithified volcanism the appears have been unlithifiedatatthe thetime timeofofinitial initial volcanism whereas the Puckwunge Puckwunge appears to have lithified(e.g. (e.g. Mattis, Mattls, 1972). whereas the appears to have beenbeen 1ithified 1972). There is paleomagnetic andradiometric radiometricevidence evidencethat thatthe the lower lower Sibley Sibley is older paleomagnetic and older (1340 (1340 m.y m.y.) (Wanless andLoveridge, Loveridge,1977) 1977)than thanthe thelatter latter two be closer closer to (Wanless and two units units which which may may be to 1100 m.y. m.y. old. Paleomagnetic evidence(e.g. (e.g. Books, 1100 Paleomagnetic evidence Books, 1968, 1968, 1972; 1972; Halls Halls and and Pesonen; inin prep.) thatthe theBessemer Bessemer and are normally normally Pesonen, prep.) indicates that and the the lower lower Sibley Sibley are polarized theother otherunits units are are reversely be interinterreversely polarized polarized and and thus thus can can be polarized whereas whereas the preted to Thequartzose quartzosesandstones sandstones pre-tectonicinin origin, origin, preted to be be younger. younger. The areare allallpre-tectonic although the Sibley although Sibleyrocks rockswere were deposited depositedupon upon aadown-faulted down-faulted block blockwhich whichmay may have been beena afailed failed arm armof of aa 1300 m.y. old old rift effect have 1300 m.y. riftwhich whichcould couldhave have had had some some effect in press). on on sedimentation sedimentation(Kustra (Kustraeteta1., al., 1977; 1977; Franklin Franklin et et al.,, a1., in press). During During many many pauses pausesinin Keweenawan Keweenawan volcanism, volcanism,compositionally compositionally immature immature gravels, gravels, sands, silts, silts, and sands, andmuds, muds, dominantly dominantly derived derived from from intra—basinal intra-basinal volcanic volcanic sources sources but were moved but locally locallyfrom fromextra-basinal extra-basinalolder olderterranes terranesasaswell, well, were moved toward toward the the of the the volcanic volcanicbasin basinbybystreams streams and and deposited deposited -in in stream stream valleys, on on center of alluvial and lakes White, 1970; alluvial plains, plains,inindeltas, deltas, andin in lakes(e.g., (e.g., White, 1970;Merk, Merk,1972, 1972, 1979; 1979; Jirsa, 1979, 1979, 1980). 1980). Jirsa, When volcanism ceased over most area,tectonic tectonicactivity activity associated When volcanism ceased over most of of thethe area, associated with the with the rifting-volcanic rifting-volcanicevent eventcontinued. continued. In In response, response, dominantly dominantlyfluvial fluvial 'redd bed' in the "re bed sedimentation sedimentation began began in the tectonic tectonicbasin basinwhich whichdeveloped developed on on the the site of pfLake Lake Superior, Superior, with with streams streams flowing flowing into intothe thebasin basinfrom frommarginal marginal site portions of of the the basin basin and and from from adjacent adjacent highlands. highlands. The The oldest sedimentary sedimentary portions sequence, the the Oronto Shale, and Group (Copper (Copper Harbor Harbor Conglomerate, Conglomerate, Nonesuch Nonesuch Shale, and sequence, Oronto Group Freda Sandstone present in in northern northern Wisconsin, Wisconsin, western western Freda Sandstoneininascending ascendingorder) order)isis present Upper Michigan, and and on on Isle Royale. Upper Michigan, Royale. The The Copper (to(to7000 ft ftthick) CopperHarbor Harbor 7000 thick) is dominantly fining upward alluvial fan-fluvial fan-fluvial clastic The gray dominantly aafining upward alluvial clasticwedge. wedge. The pyritiferousand andcarbonaceous carbonaceous Nonesuch is isananargillaceous cupriferous, pyritiferous Nonesuch argillaceoussiltsiltstone reducing conditions, conditions, stone unit unit (250—750 (250-750 ftft thick) thick) which which accumulated accumulated under under reducing probably lacustrine(and (anddèltaic) d~.aic)environment. environment. The The Freda Freda(12,000+ (12,000+ftft thick) probably in aa lacustrine is aa fluvian f1uvian and and lacustrine?) lacustrine?) unit. The The source source rocks rocks for for the theOronto Oronto Group Group included both Keweenawan Keweenawan volcanics andand older rocks, with included both volcanics olderbasement basement rocks, withthe thelatter latter most important in the most important the Freda. Freda. - ll 37. �(Ojakangas, Morey,Daniels Danielsand andKa11iokoski, Kalliokoski, continued) (Ojakangas. Morey, continued) In Wisconsin, the the more more steeply dipping Dronto Oronto Group Group is (unconIn Wisconsin, steeply dipping is overlain (unconformably?) by mature (e.g., (e.g., Hite, formably?) by the more more mature Hite,1968; 1968;Myers, Myers,1971; 1971;Craddock, Craddock, 1972), 1972), subhorizontal Bayfield Bayfield Group whichincludes, Includes,inin ascending ascendingorder, order, the the fe1dfeldsubhori~onta1 Group which and the spathic Orienta Orienta Sandstone, Sandstone, the quartzose quartzose Devils Devils Island IslandSandstone, Sandstone, and Chequamegon Sandstone. Sandstone. Geophysical suggests the group group fe1dspathic feldspathic Chequamegon Geophysical evidence evidence suggests may beasasmuch muchasas7000 7000 thick (Mooney, (Mooney,etet a1., al., 1970). The Devils Devils Island may be ft ftthick 1970). The Island (300 ft thick) (300 ft thick) isisapparently apparently the the result result ofofthe thelacustrine lacustrinereworking reworking of of Orienta fluvial detritus in tectonic tectonic activity. Orienta fluvial detritus during during aa significant significant pause pause in The source theBayfield BayfieldGroup Groupwere were dominantly dominantlypre-volcanic pre-volcanicbasement basement The source rocks rocks for the Oronto detritus detritusmay may also also have have been been important. important. rocks, although reworking reworking of Oronto rocks, although In threeformations formationsare arepresent--the present--thefeldspathic-lithic feldspathic-lithic red In Minnesota Minnesota three red Church Formation thered redfeldspathic fe1dspathicFond Fonddu du Lac Lac Solor Solor Church Formation(to (to3200 3200ftft thick), thick), the Formation and the the buff buffquartzose quartzose Hinckley Hinckley Sandstone Sandstone (to Formation(400-1200 (400-1200ftft thick), thick), and (to 500 ftft thick). The the subsurface subsurface (Morey, (Morey, 1972, 1972, 500 The Solor Solor Church, Church, found found only only in the In the 1974) zone. In the 1974) was wasdeposited depositedsouthwest southwestofofLake LakeSuperior Superioralong alongthe therift rift zone. basins flanking the St. St. Croix CroixHorst, Horst,the theSolar SolorChurch Church isisoverlain overlainunconformunconformbasins flanking the ably by duLac Lacwhich whichininturn turnisis gradationally gradationally overlain by ably by the the Fond Fond du by the the contrast the the Solor Solor Church Church conformably conformably overlies rocks Hinckley. In In contrast overlies basaltic rocks on top top of the and in in turn isis unconformably overlain by by the the Hinckley; Hinckley; at at on the HUrst Horst and unconformably overlain places aa regolith regolith separates separates the the two two formations. formations. The The hiatus represented represented by by places this regolith beenofof significant significant duration, regolithmay may have have been duration, for forthe theSolor SolorChurch Church was indurated by by diagenetic or processesprior prior to was indurated or very verylow lowgrade grade metamorphic metamorphic processes to the deposition of ofthe theFond Fond du du Lac. Lac. The The Solor Church Church Formation Formation can can be be correcorrethe deposition lated with du Lac Lacwith with the the Orienta, with the theOronto Oronto Group, Group, the the Fond Fond du Orienta, and and the the Hinckley with the Devils Island. The Solor Church and the Fond Hinckley with the Devils Island. The Church and the Fond du du Lac Lac were were deposited stream-floodplain environment, deposited in aa meandering meandering stream-floodplain environment, whereas whereas the Hinckley Hinckley appears to have beenformed formedbybythe thereworking reworkingofof Fond FondduduLac Lacdetritus detritus in the have been the appears to same lacustrine environment same lacustrine environment in which which the the Devils DevilsIsland IslandSandstone Sandstonewas was formed formed (Tryhorn (Tryhorn and and Ojakangas, Ojakangas, 1972). 1972). In Michigan the feldspathic In Michigan the fe1dspathic to toquartzose quartzose Jacobsville JacobsvilleSandstone Sandstone is aa northward-thickening, fault-borderedwedge wedge regionallyvariable variablefluvial fluvial northward-thickening, fault-bordered ofofregionally sedimentary rocks. The maximum drilledthickness thicknessisis 2845 ft and sedimentary The maximum drilled 2845 ft and the the geogeophysically is 10,000 ft. Most of the physically inferred thickness thickness is 10,000 ft. Most of the conglomerate conglomerate clasts can be be correlated correlated with areas to to the can with deeply deeply weathered weathered source source areas the south south and and southsoutheast, east, confirming confirming paleocurrent paleocurrent data data near near the the base base of of the the section. section. Northeast coarse conglomerate conglomerate(clasts (clasts to near the of Houghtori Houghton aa coarse to 36 36 cm) cm) exposed exposed near KewnawanFau1t interbed highly angular angular basalt basalt fragments KewenawanFault andand an an interbed ofofhighly fragments in the the sandstonewere werederived derivedfrom fromthe the Portage PortageLake Lakefelsic felsic and sandstone and mafic mafic lavas lavas northwest northwest from basement of the the present present fault faultor or from basementhighs highsnow now buried buried under under the the sandstone. sandstone. TheJacobsville Jacobsville is is also found on the the east of Lake Superiorand andisis interinterThe found on east end end of Lake Superior preted to be present a deep deep drill hole ininthe themiddle middleofofthe theMichigan Michigan preted to be present in in a drill hole Basin (Fowler and Basin and Kuenzi, Kuenzi, 1978). 1978). Correlation with with the theBayfield BayfieldGroup Groupremains remains uncertain. Sedimentologicaland andstratigraphic stratigraphic analysis analysis in progress progress will willexpand expand Sedimentological upon earlier work on the the causal upon earlier work (e.g.. (e.g., Fowler Fowler and and Kuenzi, Kuenzi, 1978) 1978) on causal tectonic events and and the the resultant sedimentational within the events sedimentational events events which which occurred occurred within the mid-Continent rift system system in in the theLake Lake Superior Superior region. region. mid-Continent rift 38. �GEOCHRONOLOGY KEWEENAWANROCKS: ROCKS: A A REVIEW GEOCHRONOLOGY OFOF KEWEENAWAN REVIEW W.R. Van Van Schmus, Schmus,Dept. Dept. of of Geology, W.R. Geology, Univ. Univ. Kansas, Kansas,Lawrence Lawrence J.C. Green, Green, Dept. Dept. of ofGeology, Geology, Univ. Univ.Minnesota-Duluth Minnesota-Duluth J.C. H.C. Dept. of of Physics, Physics, Univ. Univ. Toronto, Toronto, Ontario Ontario H.C. Halls, Flails, Dept. There have have been beenmany manyU-Pb, U-Pb,Rb-Sr, Rb-Sr,and andK-Ar K-Argeochronologic geochronologicstudies studies of of There U-Pbdata data of of Silver that most U-Pb Silverarid and Green Green show show that most of the the igneous igneous activity (by activity (byvolume) volume) occurred occurred lllO 1110++10 10m.y. m.y. ago ago ininthe theLake Lake Superior Superior region. region. This age includes rocks of the the upper upper normal normal magnetic magnetic polarity as well well as as upper upper This age includes rocks polarity as polarity sequence, thus dating dating that of the theunderlying underlying reversed reversed magnetic magnetic polarity sequence, thus units of reversed-to-normal reversed-to-normal change change atat1110 1110-1-~ 10 10 m.y. m.y. ago. ago. Keweenawan rocks, Keweenawan rocks. Many results are conconManyofof the the Rb-Sr Rb-Sr and and K-Ar K—Ar resultsononthe the1110 1110m.y. m.y.old old units units are cordant, although in many many instances cleardiscordance discordance with with the theRb-Sr Rb-Sr cordant, although instances there there is clear and ages being too young. young. Many not yet yetdated datedbybyU-Pb U-Pb methods, methods, and K-Ar K-Ar ages being too Manyother other units, units, riot also give give young young ages, ages, suggesting suggesting that thatupper upperKeweenawan Keweenawan igneous may igneousactivity activity may However, review review of paleomagnetic have as young young as as 900 900 m.y. m.y. ago. ago. However, paleomagnetic have extended extended to to as pole positions for such youngcrystallization crystallization forsuch such units unitsshows shows no no evidence evidence for such young pole positions for ages; the data are are consistent consistent with all ages; the paleomagnetic paleomagnetic data allyounger youngerages ages being being about about 1100 m.y. m.y. old. 1100 K-Ar of 1150-1250 m.y.for for older older units (e.g., K-Ar results suggest suggest ages ages of 1150-1250 m.y. (e.g.,Logan Logan Sills) ofofthe and, along along with with Rb-Sr results, for Sills) thereversed reversedsequence sequence and, Rb-Sr results, for riornial normal polarity pole positions positions are polaritydikes dikesofofthetheSudbury Sudburydike dikeswarm. swarm. Paleomagnetic Paleomagnetic pole are also also consistent igneousactivity activity occuring consistent with withearly earlyKeweenawan Keweenawan igneous occuring about about 1200 1200 m.y. m.y. ago. Thus, we conclude concludethat that Keweenawan riftingand andassociated associatedigneous igneousactivity activity Thus, we Keweenawan rifting began began1200-1225 1200-1225m.y. m.y.ago, ago,peaked peakedatat1110 1110m.y. m.y.ago, ago, and andceased ceasedshortly shortly thereafter. 39. �GRAVITY STUDIES OF GRAVITY AND AND MAGNETIC MAGNETIC ANOMALY ANOMALY STUDIES OF LAKE LAKE SUPERIOR SUPERIOR William 3. J. Hinze, Purdue University, West Lafayette, Lafayette, Indiana Indiana47907 47907 Hinze, Purdue University, West Richard Richard J. J. Wold, Wold, U.S. U.S. Geological Geological Survey, Survey,Denver, Denver, Colorado Colorado 80225 80225 Norbert W. W. O'Hara, Inst.ofof Technology,Melbourne, Melbourne, Florida Florida32901 32901 Norbert O'Hara, Florida Florida Inst. Technology, Gravity and magnetic Gravity and magneticanomalies anomaliesininLake LakeSuperior Superiorare areuseful usefulprimarily primarily in out the the extent extentand and near—surface near-surface structure igneous rocks rocks that crop crop tracing out structure of igneous out around the lake lake or or on on islands islands within within the out around the the lake. lake. The the The data data show showthat that the LakeSuperior Superiorstructural structural basin with the the shoreline shoreline of the Lake basin generally generally conforms conforms with the lake. The The limbs the basin basin are aredelineated delineatedbybygravity gravity magneticmaxima maxima limbs of the andand magnetic which occur occur over over the the outcropping and buried buried mafic mafic volcanic volcanic rock. which outcropping and rock. The The limbs coalesce at at the andsoutheastern southeasternends ends thelake lake into into the coalesce the southwestern southwestern and ofofthe the midcontinent and and mid-Michigan mid-Michigan geophysical geophysical anomalies. anomalies. These These geophysical data geophysical data indicate several several faults faults that roughly parallel the indicate roughly parallel the outline outline of of the the basin basin or or transect the the anomaly anomalymaps mapsprovide providenonoindication indication of transect the basin. basin. However, However, the of an an axial graben. Rather, the the inferred inferred axis graben. Rather, axis of of the the basin basin isisgenerally generallyaamagnetic magnetic minimum reflecting the increased minimum reflecting increased thickness thickness of ofsedimentary sedimentary rocks rocks having having low low magnetic susceptability. magnetic susceptability. Gravity and and magnetic magnetic anomalies arecaused caused anomalies locally locally are by and variation variation in by structural deformation deformation and in thickness thickness of of volcanic volcanic and and sedisedimentary rock related relatedtotopre-Keweenawan pre-Keweenawan topography topography and and Keweenawan Keweenawan fault mentary fault blocks major north-northeast north-northeast trending that strike strikeinto intothe thebasin basinfrom fromthe themargins. margins. A major trending fault divides fault divides the thebasin basin into intocontrasting contrastingeastern easternand and western western units. units. By comparisonwith withthe thewestern westernunit, unit, the the eastern eastern unit unit is comparison is characterized characterized by by relatively subdued due to to a combination of relatively subdued gravity gravityand and magnetic magnetic anomalies anomalies due combination of less diastrophism, of volcanic rock, less diastrophism, decreased decreased volume volume of rock, and and more more extensive extensive sedimentary sedimentary cover. cover. Modeling ofofthe constraintsprovided provided by by the the Modeling thegravity gravity data data utilizing utilizing constraints geologic, magnetic, magnetic, and andseismic seismicdata dataindicates indicatesthat that volcanic volcanic units units overlain geologic, by relatively nonmagnetic low-densityclastic clastic sedimentary sedimentaryrocks rocksfill fill the by relatively nonmagnetic low-density the Lake Superior basin. This model showsthe theentire entire crust to Lake Superior basin. This model shows to be be abnormally abnormally This density dense beneath both both eastern eastern and western Lake and western Lake Superior. This density is dense beneath as the the result resultofofextension extensionalong along an an axial axialzone zone associated associated with with interpreted as also indicates aa broad pervasive the mantle. mantle. This This modeling modeling also broad pervasive intrusions intrusions of the thickening the axis thickening of the the crust crust by by aa few few kilometers kilometers along along the axis of of the the basin. basin. W.S. overlapping volcanic volcanic W.S. White Whitedivided divided the the Lake LakeSuperior Superiorbasin basininto into six overlapping basins whose whoseboundaries boundaries closely followfaults faults and andother other structural structural features basins closely follow features Removingthe thegravitational gravitational identified identifiedbybygeologic geologicand and geophysical geophysical data. data. Removing effects of the surficial sedimentary rocks of the Bayfield Group of the surficial sedimentary rocks of the Bayfield Group and and Jacobsville Sandstone gravity anomaly results Jacobsville Sandstone from from aa smoothed smoothed Bouguer Bouguer gravity anomaly map map results mapthat that shows showsonly onlyminor minorvariations variations from from the the original original map. in an an anomaly anomaly map map. The maxima maximaofofthe theanomaly anomalymap map correlatewith withthe the lava lava basins The correlate basins of of White. White. The eastern Lake Lake Superior and have have aa lesser thickness The basins basins of of eastern Superior are are smaller smaller and lesser thickness of volcanic volcanic rocks rocks than than the the basins basins in in the the western western part part of the the lake. lake. These differences differences reflect reflect aa major major division in in the the midcontinent midcontinent rift rift system. system. The of anomalies anomalies extending extending from from central Lake Superior Superior southeast southeast into pattern of central Lake This may Michigan Michigan is is subdued subdued compared compared to tothat thatof of the the western western limb. This may represent aa fundamental fundamental difference limbs with the differenceinin the the degree degreeofof extension extensioninin the the limbs with the eastern subjected to extension, igneous igneous activity, anddiastrophism. diastrophism. eastern limb limb subjected to lesser extension, activity, and 40. �(Hlnze, (Hinze, Wold Wold and and O'Hara, O'Hara, continued) continued) These interpretations of data in the These interpretations of the thegravity gravityand andmagnetic magnetic anomaly anomaly data the Lake Superior Superior basin basin are are consistent with Lake with the theconcept conceptthat thatmid-America mid-America was was subjected time concurrently concurrently with the subjected to tensional tensional forces forcesininKeweenawan Keweenawan time the Grenville These forces forces caused extension of of the Grenville orogeny. orogeny. These caused extension the crust crustwhich whichcaused caused of igneous activity and in aa igneous activity and diastrophism diastrophism that today today is observed observed in aa range range of more dense denseand andperhaps perhapsthickened thickenedcrust crustoverlain overlain by more by volcanic volcanic and and sedimentary sedimentary rock basins basins that rock movements. that have have been been disturbed primarily primarilybybyminor minorvertical vertical movements. 41 41.. �LONG GRAVITY AND LONG WAVELENGTH WAVELENGTH GRAVITY AND MAGNETIC MAGNETIC ANOMALIES ANOMALIES OF THE OF THE LAKE LAKE SUPERIOR SUPERIOR REGION REGION V.W. Chandler, Minnesota Geological Survey, V.W. Chandler, Minnesota Geological Survey, St.Paul, St. Paul ,MN MN P.L. Boman, Boman, Exxon Exxon Corporation, Corporation, Houston, Houston, TX TX W.tJ. Hinze, W.J. Hinze, Purdue Purdue University, University, West West Lafayette, IN IN N.W.O'Hara, O'Hara,Florida Florida Institute N.W. InstituteofofTechnology, Technology,Melbourne, Melbourne, FL FL and particularly particularlymagnetic magneticanomaly anomaly maps maps of the the Lake Lake Superior Superior region region Gravity and are by short short wavelength anomaliesthat that originate originate from are dominated dominated by wavelength anomalies from near-surface near-surface sources country rock. rock. As sourceswhich whichhave havestrong strongphysical physicalproperty propertycontrasts contrasts with with the country a broad, deep deepsources sourceswith withlimited limited physical a result result anomalies anomalies which which have have broad, physical property property This problem contrasts can be bedifficult difficult totodiscern contrasts can discernininthe theanomaly anomaly pattern. pattern. This problem can can be alleviated by upward upward continuation of ofgravity gravityand andmagnetic magnetic data datatotoemphasize emphasize be alleviated by long wavelength wavelength anomaly anomaly components. components. Gravity and and magnetic magnetic data data compiled compiled over over the Superior region continuedtoto levels levels of the Lake Lake Superior region were were upward upward continued of 50, 50, 150, 150,and and 350 350 km km and long wavelength wavelength anomalies and the the resulting long anomalieswere wereinvestigated investigatedfor for significance significance to to crustal crustal structure. structure. '1 ,1 The long wavelength wavelengthgravity gravity anomalies of the The long anomalies of the 50 50 (Figure (Figure 1), 1),150 150and and350 350 km km level data data define define aa continuous, continuous, arcuate arcuate belt beltofofmaxima maxima that that extends extends along along the the St. Croix St. Croix Horst, Horst, into intothe theLake LakeSuperior SuperiorSyncline, Syncline,and andsouthward southward across across the the Michigan Basin. This arcuate Michigan Basin. This arcuate belt reflects reflectsthe theextensive extensiveemplacement emplacement of mafic mafic The 50 50 km rocks into the rifting event. rocks the crust crustduring duringthe theKeweenawan Keweenawan rifting event. The km level concentrationsalong alongthe thearcuate arcuaterift rift gravity data data indicates indicates that thatprimary primary mass mass concentrations occur slightlyoffset offset segments along along the the St. St. Croix CroixHorst, Horst,the theMinnesota Minnesota occur in in slightly segments shore shore of Lake Lake Superior. Superior. The The Keweenaw Keweenaw Peninsula, Lake Michigan, Peninsula,northeastern-most northeastern-most Lake and the central The intense intense gravity and the central Michigan Michigan Basin. Basin. The gravityminima minima which which commonly commonly flank the central the central rift riftanomaly anomaly in in low-level low-level data data are are not notapparent apparent at least leastas as aa concontinuous zone are no tinuous zone in the the upward upward continued continued data. data. There There are no long long wavelength wavelength anomalies whichdirectly directly connect connect with with either eitherthe theNipigon NipigonPlate PlateororthetheKapuskasing Kapuskasing anomalies which feature. In along the the rift rift zone In addition, addition, the thelong longwavelength wavelength gravity gravity maxima maxima along zone do do not display not display aachange change in in character characterupon upon crossing crossingthe theGreat GreatLakes Lakes Tectonic TectonicZone. Zone. Other long long wavelength wavelengthanomalies anomaliesoccur occurinin the the Lake Lake Superior Superior region region that are Other are these anomalies anomalies are are aa apparently not related related totoKeweenawan Keweenawan rifting. Among these apparently rifting. Among : northeast-trending northeast-trendingmaximum maximum over Wisconsin, aa northeast-trending northeast-trending maximum over northern Wisconsin, maximum across Bast, and across the the southern southern Michigan Michigan BasiW, and north-trending north-trendingmaxima maxima over over the the Long wavelength wavelength gravity gravity minima Kapuskasing feature and the the Moose Moose River Basin. Long minima Kapuskasing feature and River Basin. reflecting rocks occur over reflecting aa thickening thickening of offelsic felsiccrustal crustal rocks occur overthe theWisconsin Wisconsin Arch Arch and over over the the Superior Superior Province Provinceadjacent adjacenttoto the the Grenville Grenville Front. and Front. Upward continuationofofthe themagnetic magneticdata datatotolevels levelsof of 50 50 (figure 2) Upward continuation 2) and and 150 km kmreveals revealsseveral several long long wavelength wavelengthanomalies anomaliesthat thatlocally locally show rela150 show aa relationship to to the the corresponding corresponding gravity data. data. The The 50 50 km km level level magnetic magnetic data data reveal an arcuate belt of alongthe therift rift zone reveal an arcuate of maxima maxima along zone which which in in gross gross form form corresponds arcuate gravity gravitymaxima. maxima. However, However, in in the the Lake Lake Superior Superior corresponds to to the arcuate Syncline, the north of of Syncline, the axis axis ofofthe themagnetic magnetic maxima maxima lies approximately approximately 100 100 km km north the gravity gravitymaxima. maxima. The The 50 several 50 and and 150 150 km kmlevel level magnetic magnetic data data reveal reveal several long wavelength wavelength anomalies anomalies that long that are are believed believedtotobebeunrelated unrelated to Keweenawan to Keweenawan rifting. Among theseanomalies anomaliesare are aa regional maximum in northern rifting. Among these maximum in northern Minnesota Minnesota and maximaalong alonga abelt belt extending and maxima extending from from northern northern Lake Lake Huron Huron to to southern southern Upward continued intermediate in these these Wisconsin. Upward continuedgravity gravityvalues valuesare arelow lowto to intermediate areas implying these areas areas is dominated bybyfelsic, but highly highly areas implying the the crust crust in these is dominated felsic, but magnetic, magnetic, rocks. rocks. Long Long wavelength correspond to wavelength magnetic magneticminima minimagenerally generally correspond regional gravityminima minima over over the the eastern eastern Superior Superior Province Province and and over over the the regional gravity 42. �(Chandler, Boman, Hinze (Chandler, Boman, Hinze and and O'Hara, O'Hara, continued) Wisconsin Wisconsin Arch. The 50 and magnetic magnetic data The 50 km kmlevel level gravity and data were weresubjected subjectedtoto quantitative quantitative correlation and analysis indicated indicated that that the correlation and modeling. modeling. Correlation Correlation analysis the majority majority of anomalies inin the related to to long long anomalies the long long wavelength wavelengthgravity gravitydata dataare aredirectly directly related wavelength magnetic magnetic anomalies, anomalies, although although exact wavelength exact spatial spatialcorrespondence correspondencebetween between Keweenawan anomaly peaks notcommonly commonly observed. observed. Poisson Poisson analysis analysisalong alongthethe Keweenawan anomaly peaks is not rift zone rift zone yields yieldsmagnetization magnetization to to density density contrasts contrasts consistent consistent with with mafic mafic Modelingresults results of igneous rocks into intermediate rocks. rocks. Modeling igneous rocksemplaced emplaced intofelsic felsic to intermediate long wavelength anomalydata data along along the the Keweenawan rift zone zoneare are consistent consistent long wavelength anomaly Keweenawan rift with emplacement of ofmafic rocks into the continental continental with emplacement maficigneous igneous rocks intoallall levels levels of the crust. 52 50 4e. 46 44. 42' 40' — — — — CONTOUR CONTOUR Figure 1. INTERVAL INTERvAL'• 55 MILLIGALS "'LLIGALS 0 o 500 500KM KM Central Central North North America America Bouguer Bouguer gravity gravity anomaly upward continued continued to to 50 0 km, anomaly upward km, data data 20 km (flat (flat earth earth asswnption). assumption), interval = 20 43. 43. CONTOUR INTERVAL INTfRVAL' 50GAMMAS GAMMAS CONTOUR • 50 Figure 2. 2. o 0 500 KM ~OKM Central North North Ameri~a America total Central total magnetic intensity anomaly, reduced to the intensity anomaly, the pole, pole, upward continued data interval continued to to 50 50 kin, km, data interval = 20 (flat earth aseumption). assumption). 20 km km (flat �SEISMIC REFRACTION REFRACTION STUDIES STUDIES OF OFLAKE LAKESUPERIOR SUPERIORCRUSTAL CRUSTALSTRUCTURE STRUCTURE J.H. Luetgert J.H. Luetgertand and R.P. R.P. Meyer Meyer Geophysical and Geophysical and Polar Research Research Center Center Department Department of Geology Geology and and Geophysics Geophysics University ofofWisconsin-Madison University Wisconsin-Madison A series series of seismic seismic refraction lines linesshot shotininLake LakeSuperior Superior (Figure (Figure 1) 1) has inversiontechniques techniquesextended extended has been beenanalyzed analyzedusing usingsimple simpletravel-time travel-time inversion Thelines lines were wereshot shotbybyaasingle singleship shipfiring firing by generalized generalized ray by ray tracing. The airguns and and explosives, explosives, with with radio-controlled airguns radio-controlled buoys buoys as as receivers. receivers. The have been been modeled, The upper upper 12 12 km kmofof crust crust have modeled,showing showingthe thevelocity velocity distribution down distribution down to toand and including includingthe theUpper Upper Refractor, Refractor,anananomalouslyanomalouslyshallow, (6.4-6.9 km/sec) km/sec) suite refractors underlying underlying shallow, high high velocity velocity (6.4-6.9 suite of refractors the Lake Superior Basin. Basin. the Lake Profiles inin the thewestern western end end of the lake lake confirm confirm the the essentially synclinal synclinal structure structure ofofthe thecrust crustsuggested suggested by by the the geology geology of the the lake lake margins and by previous previous seismic seismicmeasurements. measurements. margins and Travel-time offsets of the the profiles offsetsobserved observed on on many many of profilesprovide providemore more precise definition crustal faulting faulting inferred inferredfrom from extrapolation extrapolation of precise definition of crustal knownfaults faults on known on land land and and frorri from gravity gravityand andaeroniagnetic aeromagnetic surveys. surveys. Evidence is shown for extension extensionofof the the Isle Royale fault to shown for Royale fault to the the west, west, for forextension extension faulttotothe the east, east, and arid for for the Keweenaw fault the existence existence of the the postulated postulated of the the Keweenaw Thiel fault of Keweenaw faultroughly roughlybetween betweenthe thetiptip of Keweenaw Peninsula Peninsula and and the Slate Slate Islands. 1::= ~ b---. Figure 11 44. 1 -.... 7A �TOPOGRAPHY ANDSURFICIAL SURFICIAL STRUCTURE TOPOGRAPHY AND STRUCTURE OF OF LAKE LAKE SUPERIOR SUPERIORBEDROCK BEDROCK BASED ON REFLECTION PROFILES PROFILES BASED ON SEISMIC REFLECTION Richard J. Wold, Wold, U.S. U.S. Geological Geological Survey, Survey,Denver, Denver,Colorado Colorado 80225 80225 Richard Deborah U.S. Geological Geological Survey, Survey,Woods Woods Hole, Hole, Massachusetts Massachusetts 02543 02543 DeborahR.R. Hutchinson, Hutchinson, U.S. Thomas Minnesota, Minneapolis, Minneapolis,Minnesota Minnesota 55455 55455 ThomasC.C.Johnson, dohnson,Univ. Univ. of of Minnesota, Thickness unconsolidated sediment sediment and underlying Thickness of of the unconsolidated and topography topographyof of the the underlying bedrock surface Lake Superior from 8000 8000 km of bedrock surface of of Lake Superior were were interpreted interpreted from km(kilometers) (kilometers) of high-resolution seismic taken 1966 A seismic reflection reflectionprofiles profiles takenduring during 1966and and1967. 1967. A map was isopach map map of unconsolidepth-to-bedrock depth-to-bedrock map wasconstructed constructed by by combining combining the the isopach of unconsolidated sediments sediments(from (fromour ourprofiles) profiles) with the of the dated the bathymetric bathymetric map map of the lake lake (Canadian 885, 1973). 1973). (Canadian Hydrographic HydrographicService Service Chart Chart 885, Lake Superior Superior can can be be divided divided into Lake into three threemorphologic morphologic regions regionsbased based on on bathymetry region composed longlinear linear bathymetry and and underlying bedrock: bedrock: aa western western region composed ofoflong valleys and gentle changes changesininrelief, relief, aacentral of aa single valleys and gentle centralregion regioncomposed composed of broad depression, and and an an eastern eastern region regioncomposed composed of of aacomplex complex broad bathymetric bathymetric depression, pattern lineartroughs troughsand and shoals. shoals. pattern of linear The western western region region is dominated or less The dominated by by a a more more or less continuous continuous bathymetric bathymetric and bedrock bedrockvalley valley paralleling paralleling the Bay, Ontario, Ontario, to and the north north shore shore from from Thunder Thunder Bay, Duluth, Minnesota, Minnesota, which which reaches reaches depths depths of ofmore more than than 800 800 m m (meters) (meters) below below lake m of of overlying lake level level near nearSilver SilverBay, Bay,Minnesota, Minnesota,and and has has more more than than 500 500 m sediments. This probably resulted unconsolidated sediments. This valley valley probably resulted from fromdifferential differential glacial erosion erosion where where the the relatively relativelyerodible erodible sandstoneofofthe theOronto OrontoGroup Group sandstone comes relativelyresistant resistant underlying Keweenawan volcanic volcanic comesinin contact contact with with the relatively underlying Keweenawan rocks second basement basementvalley valley to to the rocks and and gabbro gabbro of the theDuluth DuluthComplex. Complex. A second southeast the north north shore shore valley valleyand and probably probably represents represents the the contact contact southeast parallels parallels the betweenthe the Oronto Oronto Group Groupsediments sedimentsand andthe theoverlying overlying Bayfield between BayfieldGroup Group sediments. sediments. Thethickness thicknessof of the the Oronto Groupisisabout about1.5 1 .5kmkm thisarea areaof of the the lake, lake, The Oronto Group in inthis linear valley using an assumed the southeast. southeast. Another Another linear valley using an assumedregional regionaldip dipof of 8° 8° to the occurs Isle Royale Royale which close to the the possible possible occurs south southofof and andparallel parallel to to Isle which isis close location thecontact contact betweenthe theFreda FredaFormation Formationand andCopper Copper Harbor Harbor location ofofthe between Conglomerate Conglomerateand andthe theoverlying overlying Bayfield Bayfield Group Group and and Jacobsville JacobsvilleSandstone. Sandstone. The central region The central region is isseparated separated from from the the western western region region by by aa north-south north-south basementridge ridgeand andconsists consistsofofaa broad broadvalley valley with with only only 8-15 8-15 m m of unconsoliunconsolibasement dated bedrock surface. dated sediments sedimentsoverlying overlying the bedrock surface. The complex complexpattern patternofof troughs troughs and andshoals shoalsof of the the eastern The eastern region region form form aa north-south north-south dendritic pattern pattern with withvalleys valleysasasmuch much as as 100 100 km km long, long, but but only The bedrock bedrocksurface surfaceisis more than 600 600mmbelow belowlake lake12vel level in 5 to to 10 10 km km wide. wide. The more than some by 300 300 mmof of unconsolidated unconsolidated sediments. sediments. These someplaces placesand andisis overlain by features are stream erosion, erosion, followed followed by by glacial glacial features are probably probablythe theresult result of of initial initial stream The stream stream erosion erosion may maywell well have scour. The have followed aa system system of of shear shearzones zones which have have been shore exposures exposures of the underlying underlying sediments sediments which beenobserved observedinin the the shore of the of the the Bayfield BayfieldGroup Group and and Jacobsville Sandstone Sandstone to the south. south. All these these bedrock bedrock to the valleys are are truncated truncated about about 15 15 km km north the south south shore shore where valleys north of of the wherethe thelake lake floor floor rises abruptly abruptly to to the the coastline. coastline. rises 45. �(Wold, Hutchinson (Wold, Hutchinson and and Johnson, Johnson, continued) In general of the the bedrock surface in Lake general,, the morphology morphology of bedrock surface Lake Superior Superior probablyreflects reflects the the result of of glacial glacialscour scouralong along pre-existing pre-existing stream stream probably valleys which, which, in in turn, contacts, pre-existing turn, were were controlled controlled by by formation formation contacts, valleys topography, and topography, and shear shear zones. zones. Over theacoustic acousticimpedence impedence contrast across across the the Over most mostof of the the lake, the unconsolidatedsediment-bedrock sediment-bedrockinterface interfaceisis high sothat that the seismic high enough enough so seismic unconsolidated energy energyisis reflected reflected back backwith with little little orornonopenetration penetration into intothe thebedrock. bedrock. Despite this, this, there Despite thereare aresome some places places where where layering within within the thebedrock bedrock can can be be thestructural structural trends trends that identified identifiedand andapparent apparent dips dipsdetermined. determined. Among Among the have have been beendetermined determinedfrom fromthese thesedips dipsare arethe the following: following: aa southwest-plunging southwest-plunging synclinal feature synclinal feature bordering bordering the the Bayfield Bayfield Peninsula; Peninsula; a syncline syncline lying lyingbetween between the Apostle Peninsula, which which probably probably represents represents the the the Apostle Islands Islands and and the theKeewenaw Keewenaw Peninsula, center of center of the the Lake Lake Superior Superior depositional depositional syncline; syncline;a asouth—plunging south-plunging syncline syncline located between between Michipicoten Michipicoten Island and and Superior Superior Shoals; Shoals; and and an an apparent apparent dip dip to the south south of to the region of the of the the bedrock bedrock in the the southeastern southeastern region the lake. lake. 46. �GEOPHYSICAL STUDIES ISLANDS, LAKE LAKE SUPERIOR SUPERIOR GEOPHYSICAL STUDIESOF OFTHE THE SLATE SLATE ISLANDS, J.H. Karl,and andM.P. M.P. Bernardin, Bernardin,Department Department ofofPhysics Physicsand andAstronomy, Astronomy, J.H. Karl, University ofofWisconsin, University Wisconsin,Oshkosh, Oshkosh, Wisconsin Wisconsin 54901 R.P. Meyer, R.P. Meyer, and and M.E. M.E. Bengtson, Bengtson, Geophysical Geophysical and and Polar Research Research Center, Departm~nt of of Wisconsin Wisconsin Department of Geology Geologyand andGeophysics, Geophysics,University University of 53706 Madison, Wisconsin Madison, Wisconsin H.C. of Geology, Geology,Erindale ErindaleCollege, College, University University of Toronto, H.C. Halls, Department Department of Toronto, Mississauga, Ontario, Ontario,Canada Canada L5L1C6 Discussion of origin ofofshock shock features features found found ininthe theCanadian Canadian shield shield Discussion of the the origin has existed the literature literaturefor forperhaps perhaps 20 20 years. years. Several Several well well known known has existed in in the crypto-explosion structure typify typifythis this debatebetween between meteorite meteorite impact impact and and crypto-explosion debate endogenous process such as as thethe Charlesvoix structure, the endogenous process such Charlesvoix structure,the theBrent Brentcrater, crater, the all, Sudbury the Clearwater Clearwatercomplex complex and and the theManicouagan Manicouagan caldera. In In all, Sudbury basin, basin, the The Slate Slate Islands Islands of northern about 79 79 such suchstructures structures have have been beenidentified. identified. The about northern Lake Superior Superior exhibit Lake exhibitshock shockmetamorphic metamorphic features features inincommon common with many many of these these as shatter-cones shatter-conespresent presentlocally locally in host intrusive sites such such as host rocks rocks and and intrusive brecciated clasts, deformation lamellae lamellae in in quartz and brecciated clasts, and and show show deformation and plagioclase grains. In In addition, the central central uplift uplift ofofa acomplex addition, the the islands islands form form the complex crater morphology whichisis ringed ringed by troughand andannular annular ridge ridge with aa morphology which by aa submerged submerged trough diameter of diameter of about about30km. 30km. On the active On the other other hand, hand,the theislands islandsare are located locatedinin aa once oncetectonically tectonically active region associated associatedwith withthe theMichipicoten Michipicoteritriple triple junction and at the region and at the intersecintersection of controls the the location location of late of two two major major regional regional faults, one one of which which controls late Precambrian alkalic magmatism. Precambrian alkalic magmatism. The and deformation deformation The shatter-cone shatter-cone structures and lamellae may be associated associated with with diatreme relatedto to these these regional lamellae may be diatreme emplacement emplacement related features; and thus the the Islands astrobleme-diatreme features; and thus Islands fall fallinto intothethe astrobleme-diatreme controversy. controversy. However, thelocation location of of the However, the the Slate Slate Islands Islands ininthe theLake Lake Superior Superior Basin Basin region the recent recent water water cover cover may may have region with the have reduced reducederosion erosionofof the the structure structure fargreater greaterextent extentthan than for formany many of the the other other cryptoexplosion cryptoexplosion sites. In to aa far addition the the lake lake presents presents the the opportunity opportunityfor formarine marinegeophysical geophysical techniques techniques are not not available available for other other sites. sites. Currently, we we are capitalizing on on that are are capitalizing situationbybyusing using aavariety varietyofofmarine marinetechniques techniques in in association association with with this situation airborne magneticstoto help help identify identify the airborne magnetics the geological geological process process responsible responsible for the the formation formation of the the Slate Slate Islands. Islands. During During July, July, 1979, 1979,we we conducted conducted an an aeromagnetic aeromagnetic survey survey over aa 30 30 XX60 60 km km area over overthe the Islands Islandsusing usingactive activeradar radarpositioning positioningatat1000 1000yard yardflight flight line line area This aeromagnetic data shows clear spacing 1500 surface. This aeromagnetic data shows clear spacing 1500feet feet over over the the lake surface. linear features features which which have have been and linear beenpreviously previouslyinterpreted interpreted as as regional regional faults and long wave-length arcuate apparently related related totoa adeep-seated deep-seated source source long wave-length arcuate trends trends apparently sourcesininthe thevicinity vicinity of centered the Islands. Islands. Shallow Shallow sources centeredatat the the location location of the the Islands centered in in the the Islands produce produce short short wavelength wavelength anomalies anomalies centered the long long wavelength wavelength magnetic magnetic depression. depression. 47. �LAKE SUPERIOR SUPERIOR RED RED CLAY CLAY MINERALOGY: MINERALOGY: LAKE CORRELATION WITH MECHANICAL BEHAVIOR BEHAVIOR CORRELATION WITH MECHANICAL E. Brown T. Mengel Mengel and and B. B. E. Brown J. T. IDS, Minnesota and and IDS, Minneapolis, Minnesota Department of Geological Sciences Sciences Department of Geological University Wisconsin-Milwaukee University ofofWisconsin-Milwaukee Milwaukee, Milwaukee, Wisconsin Wisconsin In threetypes typesof of stratigraphic stratigraphic In the the red red clay clay area area of ofDouglas Douglas County County three successionare areobserved observed from bore hole data: clay(~(c25' 25 thick) thick) over succession from bore hole data: redred clay over older red red clay, clay, red redclay clayover overbrown brown or or gray gray clay, clay,and andred redclay clayover overbrown brown sand. The mean meancontents contentswith withstandard standarddeviation, deviation, of The of sand sand (>44u), ( >44u),silt silt (44-2u), clay (2-O.2u), (44-2u), coarse coarse clay (2-0.2u), and and fine clay clay (<O.2u) «0.2u) of of red red clay clayfrom from 28 28 borehole samples samplesisis 3.5+2.5, borehole 3.5~2.5, 25.6+12.4, 25.6~12.4, 39.8±8.4, 39.8~8.4, and and 28.8+8.2. 28.8~8.2. Smectite clayisisdominant dominant fineclay clayfraction; fraction;illite illite and Smectite clay in in thethe fine and chlorite are dominant in the the coarse are dominant in coarse clays, and and quartz; feldspars, feldspars,and and carbonates, carbonates, Particle size are dominant the silt silt and and sand sand fractions. Particle size distribution are dominant ininthe The equations: and mineral mineralcontents contentscorrelate correlatewith with the the Atterberg Atterberq limit limit values. and values. The limit==10.0 10.0++0.78 0.78 (% (% coarse coarse ++ fine clay) clay) and and Liquid limit Liquid Plasticityindex index == 0.1 0.1 ++0.51 0.51 (% (% coarse coarse ++ fine clay) Plasticity fine clay) have of 0.76 0.76 and and 0.84 this body body havecorrelation correlation coefficients coefficients of 0.84 respectively respectively for this of data. data. The dominant mode inin the LittleBalsam Balsam Creek Creek drainage drainage south The dominantfailure failure mode the Little south of Superior andinin other other similar locales Superior and locales involves involves drying drying and and cracking cracking of of aa surficial layer surficial layerofofclay claywhich whichthen then slides slides as as aadcollement decollement sheet sheet over over the the underlying clay. This failureappears appears totohave havebeen been promoted promoted by This failure by deforestation underlying of the the area. area. 48. �PALEOMAGNETISM PALEOMAGNETISM OF OF KEWEENAWAN KEWEENAWAN ROCKS ROCKS H.C. H. C. Halls Hall 5 Erinda1e College College Erindale Mississauga, Ontario,Canada Canada Mississauga, Ontario, L.J. Pesonen L.J. Pesonen Geological Survey of Finland Geological Survey of Finland Espoo, Espoo, Finland Keweenawan paleomagnetic polesoccur occuralong along aa broad trendingline line Keweenawan paleomagnetic poles broad NW-SW NW-SW trending Stratigraphic and the north north central central Pacific. Pacific. Stratigraphic and radiometric radiometricevidence evidence suggests suggests in the that within within this this polar polardistribution distributionthere thereis is a hairpin-shaped path, path, open open to that a hairpin-shaped the (the so-called so-called Logan Loop)along alongwhich whichthere thereisis aa progressive the SW SW (the Logan Loop) progressive antiThis path clockwise movement poleswith with time. This clockwise movement ofofpoles path which which is only only about about 100 100 of arc in width, afterfiltering filtering ofofthe arc width, emerges emerges after thepole polepopulation population using using certain certain reliability criteria, andthus thusthe the scatter scatter of ofdata data about about this path is reliability criteria, and this path is attributable to uncertainties not to to variations variations in in paleofield table uncertainties in the the data data and and not pa1eofield direction. Late Precambrian poles North America, America, together Late Precambrian poles from from elsewhere elsewhereinin North Keweenawan paleointensity with Keweenawan paleointensityand andpaleosecular paleosecularvariation variation (PSV) (PSV)studies studies further Keweenawan support apparent apparent polar polarwander wander(APW) (APW) as as the theunderlying underlyingcause causeof of Keweenawan There are problems paleopole distribution. problems however: however: more 90% of paleopole distribution. There more than than 90% Keweenawan poles alongthe the western western arm armof of the the Logan Loop; its its apex Keweenawan poles lieliealong Logan Loop; apex remains remains undefined and from aa steeply-dipping steeply-dipping volcanic volcanicsequence sequence define define undefined andonly only two two poles poles from the eastern Furthermore,almost almosthalf halfthe thetotal total length the eastern arm. arm. Furthermore, length of the the loop loop lacks lacks data because Keweenawan igneous unitscontain containasymmetric asymmetricreversals reversals with data because Keweenawan igneous units with inclination differencesaveraging averaging about about 25°, 25 0, across which there across which inclination differences there are are no no interintermediate directions. There are possible explanations explanations of the the reversal reversal mediate directions. There are three three possible (1) APW, (2) regionalsecondary secondary magnetization magnetizationcomponent component superasymmetry: (1) APW, (2) aa regional 0) reversals imposedononoriginally originally symmetric (1800) reversalsor or (3) (3) some intrinsic imposed symmetric (180 some intrinsic property Paleomagnetic, paleointensity andPSV PSV data data propertyofofearth's earth's internal internal field. field. Paleomagnetic, paleointensity and are generally ininaccord accordwith with(1), (1), although volcanic sequenceis isknown knownwhere where are generally although oneone volcanic sequence successive situationthat that posesproblems problemsforforAPW. APW. successive asymmetric asymmetricreversals reversals occur, occur, a situation poses Of Of the the two two remaining remaining explanations explanations (3) (3) cannot cannot be be discounted discounted while while (2) (2) is con con~ sidered the Local overprinting overprinting events events have have recently recentlybeen been sidered the least least likely. likely. Local demonstrated but have different differentages agesand andcauses. causes. They They may may be be demonstrated but they they appear appear to to have due igneousactivity, activity, burial Keweenawan due to Late Late Keweenawan Keweenawan igneous burialof the of the Keweenawansequence, sequence, meteorite impact. impact. emplacement ofofcopper-bearing emplacement copper-bearingores, ores,and andinin one oneinstance instance to to meteorite These Paleozoic or very very late latePrecambrian Precambrian Thesemagnetic magneticoverprints overprints appear appeartoto be be Early Early Paleozoic (500-900Ma) Ma)ininage ageand and arearethus thusimportant importantasasthey theylie lie in in an an age age interval interval poorly poorly (500-900 represented in North represented North American American paleomagnetic paleomagnetic data. data. 49. �STABLE ISOTOPE STUDIES IN STABLE ISOTOPE TRACER TRACER STUDIES INTHE THECAMBRO-ORDOVICIAN CAMBRO-ORDOVICIAN AQUIFER AQUIFER OF ILLINOIS OF NORTHERN NORTHERN ILLINOIS T.J. Grundi Grundl Northern Illinois University Northern Illinois University Dekaib, Illinois Dekalb, Illinois E.C. Perry, Jr. E.C. Perry, Northern University NorthernIllinois Illinois University Dekalb,Illinois Illinois Dekalb, R.H. R.H. Gilkeson Gilkeson Illinois State Illinois StateGeological GeologicalSurvey Survey Oxygenand andhydrogen hydrogen (deuterium) isotoperatios ratios for for water Oxygen (deuterium) isotope water of ofthe theCambroCambro- Ordovician aquifer closelyapproximate approximate the in Ordovician aquiferof of northern northernIllinois Illinois closely the ratios ratios in meteoric water, implying that thatlittle little isotope exchange occuredbetween between meteoric water, implying isotope exchange hashasoccured 180 ofofgroundwater cSlSO groundwaterin in the system groundwater system groundwaterand androcks rocksofofthe the aquifer. aquifer. 0 0/00 (vs. ranges from , characteristic ranges from about about -7 %0 SMOW), characteristic of of modern modernprecipitation precipitation (vs. SMOW) precipitation in in Illinois, in Illinois,totoabout about -12 0/ 00 , characteristic of of modern modern precipitation The implication implication considerably considerablycolder colderclimates climatesthan thanthat thatofofnorthern northernIllinois. Illinois. The some Cambro-Ordovician of of this this Isisthat that someofofthe thewater waterininthethe Cambro-Ordovician aquifer system system of northern Illinois Illinois has northern hasbeen been stored stored since since the the Pleistocene. Pleistocene. oxygenisotopes isotopesininsulfate sulfate of of northern and oxygen northern Illinois Illinoisgroundwater groundwater Sulfur and establish this this sulfate establish sulfate to a mixture ofof2 2end-member end-member compositions. compositions. One One +20, 0IbO0 = = +16) is derived end-member +16) presumably presumably is derived from from Paleozoic Paleozoic end-member( ( 034S 34S = +20, sulfate miners The other other sulfate sulfate miner~!sininrocks rocksassociated associated with the the aquifer. aquifer. The S = 2.6, ol8o component (0 S 018 0 = 1.5) presumably results 1.5) presumably results from from oxidation oxidation of ( pyrite pyrite in in the the glacial glacial drift driftoverlying overlying the the aquifer. aquifer. 9g The presence in the thegroundwater groundwater of northern northern The presenceofofnatural natural isotope isotope tracers tracers in Illinois andadjacent adjacentareas areas should should prove prove useful useful in in establishing establishing recharge recharge Illinois and and flow patterns patterns in in this important and flow important aquifer. aquifer. 50. �KAULINITIC WEATHERING KAOLINITIC WEATHERING ZONE ZONE ON ONPRECAMBRIAN PRECAMBRIAN BASEMENT BASEMENT OF OF SOUTHEASTERN SOUTHEASTERN NORTH NORTH DAKOTA DAKOTA AND AND WESTERN WESTERN MINNESOTA MINNESOTA Keiley Lynn I.I.. KeJley Lynn and and Frank Frank R. R. Karner Karner Department of Geology Geology Department University of ofNorth NorthDakota Dakota Grand Forks, North Grand Forks, North Dakota Dakota 58202 Detailed petrologic petrologicand and geochemical geochemical studies studies have have confirrried confirmed the existence existence weathering profile profile developed deep weathering developed uniformly on on aa variety varietyofofPrecambrian Precambrian of aa deep suite of 26 drill cores basementrocks rocksinin the the southern River Valley. A suite basement southern Red Red River 26 drill cores from aa drilling drilling program from program ininthe theRed Red River RiverValley Valley(Moore, (Moore, 1978), 1978), has has provided provided new information on new information on the the basement basement of eastern eastern North North Dakota Dakota and and western western Minnesota. Minnesota. The Precambrian PrecambrianisIs penetrated penetrated at at an depth of approximately The an average average depth approximately 300 300 m m in The surface dips 5-10 rn/km toward the north and west. the Red River the Red River Valley. The surface dips 5-10 m/km toward the north and west. Different rock mafic metasedimenDifferent rock types types ininthe thecores coresinclude includeintermediate intermediateto to mafic metasedimentary and metavolcanic schists, and intermediate to felsic coarse-grained and metavolcanic schists, and intermediate to felsic coarse-grained Precambrianrocks rocksofofthe the region region are are interpreted massive or rocks. The The Precambrian interpreted massive or gneissic gneissic rocks. to be aa buried buried extension extension of the the Superior Superior Province, Province, and and are to be are divided divided into terranes granitic rock rock and and mafic mafic schist, on on the the basis basis of of patterns patterns seen seen in terranes of of granitic Superior Province rocks which crop out to the east, and regional geophysical Superior Province rocks which crop out to the east, and regional geophysical data (Lidiak, data (Lidiak,unpublished; unpublished;Muehlberger Muehlberger and and others, others, 1967; 1967; Ray Ray and and Karner, Karner, 1979). 1979). In the In the southern southern part part of ofthe theRed Red River River Valley, Valley,aathick thickweathering weatheringresiduum, residuum, up 75 m thick, isisdeveloped developed on on the the upper upper surface surface ofofthe thePrecambrian, Precambrian, up to to 75 wherever it isisimmediately wherever it immediately overlain overlainbybyCretaceous Cretaceous rocks. rocks. Where Where the the deepest, least-weatheredrocks rocksare arefoliated, foliated, ghost-like ghost-like traces traces of the the structures structures can can least-weathered often be be followed followed up up through through all all but butthe themost mostextremely extremely weathered weathered material. Weathered numerous sand-size Weatheredmafic maficand andintermediate intermediaterocks rocksoften often contain contain numerous sand-sizesiderite siderite nodules. The uppermost few meters of some cores is bauxitic in appearance, The uppermost few meters of some cores is bauxitic in appearance, but but aluminum oxides are generally absent. aluminum oxides are absent. Scanning microscope/microprobe Scanning electron electron rnicroscope/microprobe studies that feldspars micas are are altered altered to studies show show that feldspars and and micas to kaolin-group kaolin-group minerals. minerals. rock type, type, the the end end product product of weathering weathering is Regardless Regardlessofoforiginal original rock is generally white to containing suspended aa white to greenish greenish kaolinitic kaoliniticclay clay containing suspended angular angular quartz quartz grains. Trends those reported reported by by Trends in major element in major elementchemistry chemistryare aresimilar similar to those Goldich (1938) Goldich (1938) and and Harriss Harrissand andAdams Adams (1966). (1966). Calcium the early early Calciumisislost lost in in the stages of weathering, stages weathering, followed followedbybysodium sodium and and potassium. potassium. Silicon lost in in Silicon isis lost the parts of of some profiles. Iron values the uppermost uppermost parts some profiles. values are arehigh highwhere wherealuminum aluminum values This is apparently function of of original values are are low low and and vice-versa. This apparently aa function rock type. rock type. The this study study support support evidence evidence for aa pre-Cretaceous pre-Cretaceous kaolinitic The results results of this kaolinitic weathering episode on on the the southwestern part of weathering episode southwestern part of the the Canadian Canadian Shield. This study, variety ofofrock rocktypes types subjected subjected to to identical identicalweathering weathering study, involving aa variety conditions, shows thatdifferent different rock conditions, shows that rock types types alter to to similar similarweathering weathering products. The The pathways pathwaystaken takenbybyfelsic felsic and and mafic mafic rocks rocks may niaydiffer. differ. This study study has has been been supported supported ininpart partbybyananHEW HEW administered administered Domestic Domestic Mining and and Mineral and and Mineral Mineral Fuel Fuel Conservation Conservation Fellowship the Mining Fellowship granted granted to the senior author. author. 51 51. �(Kelley and and Karner, Karner, continued) continued) Reference Cited Reference Goldich, S.S., 1938, A Study Study of of rock rock weathering. weathering. J.3. Geol., Geol., V. V. 46, 46, p.p. 17-58. 17-58. Goldich, 5.5.,1938, Harriss, and Adams, Adams, J.A.S., 1966, Geochemical Geochemical and studies 1-larriss, R.C., and J.A.S., 1966, andmineralogical mineralogical studies Sci,, V. on rocks. Amer. Amer. J.3. Sci., V. 264, 264, p.p.146-173. 146-173. on the the weathering weatheringofof granitic granitic rocks. Lidiak, E.G.,Buried BuriedPrecambrian Precambrian rocks rocks of ofNorth North Dakota. Dakota. unpublished unpublished manuscript. manuscript. Lidiak, E.G., Moore,Walter WalterL., L., 1978, A preliminary preliminary report on Moore, 1978, A on the the geology geology of of the the Red Red River River Valley DrillingProject, Valley Drilling Project, eastern eastern North North Dakota Dakotaand andNorthwestern Northwestern Miflnesota. Minnesota. Prepared for Bendix Prepared for Bendix Field FieldEngineering EngineeringCompany, Company, subcontract subcontract 77-059-E. 77-059-E. 292p. Muehiberger,W.R., W.R., Denison, Denison,R.E., R.E., and Lidiak, E.G. rocks in Muehlberger, and Lidiak, E.G. 1967, 1967, Basement Basement rocks United States. States. A.A.P.G. V. 51, p. 23512351continental continental interior interior ofofUnited A.A.P.G. Bull., Bull., V. 51, p. 2 380. 2380. Ray, and Karner, Karner, Frank Frank R., R.,1979, 1979,The ThePrecambrian Precambrian basement basement of North North Ray, John John T., T., and Dakota(abs.) (abs.) Proceedings, 25th Inst. Inst. Lake Dakota Proceedings, 25th Lake Superior Superior Geol., Duluth, Duluth, p. p. 33-34. 33-34. 52. �HYDROGEOLOGIC INVESTIGATIONS LANDFILLSITE SITE II1 HYDROGEOLOGIC INVESTIGATIONS ATAT A ALANDFILL IN THE THE RED TILL (VALDERAN)REGION REGIONOF OFEASTERN EASTERN WISCONSIN WISCONSIN RED TILL (VALDERAN) Warren R. Rehfeldt Warren R. Donahue&&Associates, Associates, Inc. Donahue 53081 Sheboygan, Wisconsin Sheboygan, The practice practice of of landfllllng thethe most of solid The landfillingis is mostwidely widelyused usedmethod method of waste disposal in waste disposal in Wisconsin. Wisconsin. The The most landfill mostacceptable acceptable landfillisis the the "sanitary sanitary landfill whichrefuse refuseisisplaced placedInintrenches trenches or or other other specific specific locations, locations, , in landfill',"in which then compacted compacted covered daily ordertotoisolate isolate the then andand covered daily withwith soilsoilininorder the solid wastes from the environment. wastes from environment. Evaluation Evaluation ofof the potential of of aa the pollution pollution potential land disposal solid waste management. land disposal site siteisisananimportant importantaspect aspectofof solid waste management. hydrogeologicinvestigation investigation was undertakenatatan anexisting existing sanitary A hydrogeologic was undertaken landfill, located to determine determinethethefeasibility feasibility of of inlandfill, locatedinineastern eastern Wisconsin, Wisconsin, to creasing the the depth site is creasing depth of the the present present operation. operation. The The site is licensed licensed to to operate operate under the the condition that than 10 10 feet feet thattrenches trenches cannot cannot be be excavated excavated deeper deeper than under until an completed until anengineering engineeringstudy studyis is completedand andapproved approvedbybythe theWisconsin WisconsinDepartment Department of Natural Natural Resources. Resources. In eastern which is is underlain In eastern Wisconsin, Wisconsin, which underlain by by sedimentary sedimentary bedrock, bedrock, glacial erosion produced producedtill till that erosion thathas has considerable considerable silt siltand andclay clayand and therefore thereforehas has low permeability. The coefficient of of permeability permeabilityofofthe thesilty silty clay low The coefficient clay soil soil on on the the laboratory as the site sitehas has been been measured measured inin the as being being 22 to to 66XX10-8 10- 8cm/sec. em/sec. the site siteisisunderlain underlainbybymore more than than Analysis geologic borings Analysis of of geologic borings indicate indicate that the 30 metersofofglacial glacial drift 30 meters driftwhich which isisconsidered considered to to function function as as an an aquitard. aquitard. Groundwater the upper upper few few feet, feet, perched perched upon upon the underlying underlying Groundwateroccurs occurseither eitherin in the silty clay, occasional sand silty clay,ororin in occasionalsilty silty sandseams seams or or pockets pockets that are are found found in thetill. till. An evaluation of of the conditions indicates indicates that there the An evaluation the hydrogeologic hydrogeologic conditions there is no no hydraulic hydraulicconnection connection between between the the surface surface and and underlying underlying bedrock bedrock aquifer. aquifer. A thorough hydrogeologic investigation investigation and thorough hydrogeologic and aagroundwater groundwater monitoring monitoring program are of oflandfill program areessential essentialininlocation locationand andoperation operation landfill sites. In addition to. hazards addition to identifying identifying potential potentialpollution pollution hazardsassociated associated with withwaste waste we should should apply knowledge ofof hydrogeologic disposal, we apply our our knowledge hydrogeologicconditions conditions to to promote sitffi andenvironments environments for waste waste disposal disposal where where there safemote sit and there are are natural natural safeguardsthat that will will assure guards assure protection protection ofofhealth healthand and resources. resources. 53. �SEISMIC SURVEY SURVEY OF OF AABUR:[ED BURIED RIVER RIVERCHANNEL CHANNEL Timothy D. 0. Vick Timothy Vick Department Department of Geology Geology Carleton College Carleton College Northfleld, Minnesota, Northfield, Minnesota, 55057 seismic refraction refraction survey River valley A seismic survey of aa portion portion of ofthe theCannon Cannon River cut into Northfield,Minnesota Minnesota revealed revealed a sizable buried buried channel channel cut in Northfield, Prairie du Prairie du Chien Chien bedrock. bedrock. The The buried channel channel begins begins on on the the Carleton CarletonCollege Collegecampus. campus. It It is is cut cut into dolomite dolomite which which varies varies markedly markedly in in hardness hardness from from place place to place. place. The The modern modernriver river channel isis filled withlayers layersofof loam,sand sand and and gravel. gravel. The channel filled with loam, flood courseofofthe the river river is flood plain plain overlies overlies the the buried buried valley; valley; the themodern modern course is offset from offset from the the buried buried channel. channel. the slope the portion portion ofofthe thechannel channel mapped mapped in detail,, the slope of the the chanchanIn the in detail nel is one buried channelbegi begins in a "wa "waterfall' ne1 one to eight ei ght percent. percent. The The buri ed channel ns ina terfa 11 about meters high, then continues continues north north 250 250 meters meters with aa about one one and andaahalf half meters high, then depth of of up depth up to six sixmeters meters and and aa width width ofofalmost almost100 100 meters. meters. The channel The channel the study study area, area, from from wide wide and and changes changescharacter charactermarkedly markedlyininthe the center center of of the gently-sloping to steep narrow;inin this section gently-sloping steep and and narrow; section itithas hasa achannel channel slope slope It then of eight and has hasvertical vertical sides. eight percent, percent, isisabout about 20 20 meters meters wide wide and sides. It then wider (150 (150meters) meters)at at the the end levels off offatat1818meters metersdeep deepand and becomes becomes wider end of the survey tributary buried the survey area. area. A tributary buriedchannel channel joins joinsthe themain main channel channel near near end of the the study study area. area. the the end 1 ' thechannel channelincreases increasesinin depth depth to over A mile downstream downstream the over 30 30 meters. meters. A slope slope of 30 per mil mile 30 meters meters per e is indicated i ndi cated for forthe theburied buri edchannel channel;; the modern slopeofofthe theriver river is modern slope is only onlytwo two meters meters per per mile. mile. Buried channels channelsare arefound foundinInother otherparts partsof of the the Mississippi Buried Mississippi River River Such MinneapolisSuch channels channelshave havebeen beendescribed describedinin the the metropolitan MinneapolisSt. Paul Countyasaswell well as as under under the the Mississippi Mississippi River Paul area area and and in Dakota Dakota County River itself. The buried channel in Northfield may be related in itself. The buried channel Northfield may be related inage ageand andmode mode of formation formation to other other buried buried channels channels in the region. region. in the system. Techniques used survey included included computer computer processing processing of seismic seismic Techniques usedinin the the survey results permitting permitting interpretation interpretation ofofdata data under under conditions conditions of refraction results extremely bedrock topography. topography. extremely irregular irregular bedrock 54. �THE PEGMATITIES OF OF THE THEQUETICO QUETIeoGNEISS GNEISSBELT, BELT, NORTHWESTERN ONTARIO ONTARIO THE PEGMATITIES NORTHWESTERN AND URANIUM POTENTIAL POTENTIAL AND THEIR URANIUM W.M. Lucko Luckoand andS.A. S.A. Kissin W.M. Department of Geology Department of Geology Lakehead University Lakehead University Thunder Bay, P7B 5E1 5El Thunder Bay, Ontario P7B Reconnaissance studiesalong alonga aroughly roughlynorth-south north-south traverse traverse across Reconnaissance studies across the Quetico Gneiss GneissBelt, Belt, utilizing Ontario Highway Quetico utilizingroad-cuts road-cutsin in Ontario Highway527, 527,have havebeen been made inin order characterize uranium-bearing uranium-bearing pegmatites pegmatites in and and adjacent adjacent made order to characterize Analyses of samples to the Gneiss Gneiss Belt. Analyses samples by by the the Geological Geological Survey SurveyofofCanada Canada to the revea 1ed uranium urani urn contents ng from<l:O from < 1:0 ppm ppm UUtoto 36.3 ppm inin the pegmatites. revealed contents rangi ranging 36.3 ppm the pegmatites. The pegmatitesare areofoftwo twodistinct distinct types: The pegmatites types: a granitic graniticpegmatite pegmatiteshowing showing intrusive relationships relationships to to all allother otherrocks rocksininthe thearea areaand and an an anatectic anatectic granitic pegmatite intimately the gneisses gneisses of the the Quetico Quetico Belt. The The granitic pegmatite intimately related related to the pegmatitesare are located located near near the the north and pegmatites and south south margins margins of the the Gneiss Gneiss Belt Belt and Wabigoon andand Shebandowan-Wawa Greenstone Belts. Belts. and extend extend into intothe theadjacent adjacent Wabigoon Shebandowan-Wawa Greenstone The pegmatitesoccur occurasasdikes dikesororlensoidal lensoidal bodies bodiesofof plagioclase-perthiteplagioclase-perthiteThe pegmatites quartz varying amounts amounts of and muscovite. muscovite. Accessory Accessory minerals quartz with varying of biotite biotite and include include zircon, garnet, garnet, tourmaline, tourmaline, and and rare rare hematite. hematite. Apatite occurs in Apatite occurs the most most uranium-rich uranium-rich sample. sample. The pegmatites occur as as lenses lenses and and niigniatite migmatite bands bands most The anatectic anatectic pegmatites most strongly strongly The pegmatites pegmatitesare are feldspar-rich feldspar-rich (ca. in the the center center of of the the Quetico Quetico Belt. The (ca.75%) 75%) consisting of oligoclase consisting oligoclase with with microcline microcline exsolutions, exsolutions,quartz, quartz,muscovite, muscovite, and and Accessoriesinclude includezircon, zircon,cordierite, cordierite,sillimanite, sillimanite, minor corroded minor corrodedbiotite. biotite. Accessories garnet, and chlorite. The garnet, and chlorite. The latter suggests that thatthese thesepegmatites pegmatiteshave have been been latter suggests andptygmatic ptygmatic foldingofof small small dikes dikes is also metamorphosed. Boudinage Boudinage and folding also rrietarriorphosed. observed. Uranium the anatectic anatectic pegmatites pegmatiteswas was fairly uniformly uniformly distributed distributed Uranium ininthe fairly in the the range range of 2-7 2-7 ppm, ppm, but ranges to 36.3 ppm ppm inin the but ranges to highs highs of 36.3 the granitic granitic pegmatites. No No uranium identified, the uraniummineralization mineralizationwas was identified,but but zircon zircon is is the The high high value value was was found foundin in an probable host in most most rocks. rocks. The an apatite-bearing probable host In rock, and andthis this mineral mineral isis a rock, a likely likelyhost host for foruranium, uranium, as as well. well. The The pegmatites pegmatites do not seem likely prospects for for economic economic deposits uranium, owing owing to aa do not seem likely prospects deposits of uranium, lack lack of identifiably identifiablymineralization mineralizationand andlow lowconcentrations. concentrations. They They may, may, howhowever, be ever, be the the ultimate ultimatesource source ofofdisseminated disseminated uranium uranium in the the Sibley SibleyGroup Group sandstonesand andunconformity-vein unconformity-vein type type uranium deposits in sandstones uranium deposits in the theGreenwich Greenwich Lake Lake area. 55. �RELATIONSHIP RELATIONSHIP OF OF CANADIAN CANADIAN URANIUM URANIUM DEPOSITS DEPOSITS TO THE TO THE GEOLOGIC GEOLOGIC SETTING SETTING OF OF WISCONSIN WISCONSIN Gregory Mursky Mursky Departmentof of Geological Department Geological Sciences Sciences University ofofWisconsin-Milwaukee University Wisconsin-Milwaukee Milwaukee, Wisconsin Wisconsin 53201 53201 One analyzing the the uranium uranium potential of Onelogical logical and and preliminary preliminary step step in In analyzing potential of aa region region Is is totoaccess access one one area area against against another, another~ based based on on geological geological data data and the the periods periods of of mineralization. An and An important relates importantcriterion~ criterion, asas it it relates to Wisconsin, Wisconsin, is the the geochronological geochronological position position of of Precambrian Precambrian rock rock units units in in the the Canadian Canadian Shield. Wisconsin Wisconsinand andthe theperiods periodsof of uranium uraniummineralization mineralization in The The overwhelming overwhelmingnumber numberofof Precambrian Precambrianuranium uraniumdeposits deposits and and occurrences occurrences in North the Canadian Canadian Shield often North America Americaare aredistributed distributed within the Shield which which is Is often designated throughoutthe the world world as as distinctive distinctive uranium uranium metallogenetic metallogenetic designated throughout Major uranium uraniumdistricts districts tend province. Major tend totobebeconcentrated concentrated along along the themargins margins the Canadian Canadian Shield (Figure 1) 1) and and include, include,among among others,: others,: the Great Bear Bear of the Shield (Figure the Great Lake area, area, the Great Lake Great Slave Slave Lake Lake area, area, the the Beaverlodge Beaver10dge area, area~ the theAthabasca Athabasca basin basin area, area, the the group of occurrences within the area, the the Wollaston Wollaston Lake Lake area~ group of occurrences within the southern southern part part of the the Churchill Churchill Structural StructuralProvince, Province, the thegroup group of ofoccurrences occurrences within the the western part part of the the Superior Superior Structural Structural Province, Province, the thePort PortArthur Arthur(now (nowThunder Thunder western Bay) area, the Bay) area, the Elliot ElliotLake Lake area, area,the thegroup groupofofuranium uranium occurrences occurrences within the the southeastern part of of the Structural Province distributed near southeastern part the Superior Superior Structural Province distributed near the the Grenville Lake area area and and the the deposits depositsand andoccurrences occurrences Grenville Front, Front,the theMakkovik-Seal Makkovik-Seal Lake within the within the Grenville Grenville Structural Structural Province. Province. Uranium Mineralization and Events within within the Uranium Mineralization and Orogenic Orogenic Events the Canadian Canadian Shield, Shield, the absolute absolute age the age determinations determinations of of the the host host rocks, rocks, and and the the periods periods ofofuranium uranium mineralization revealedaadefinite definite pattern have revealed pattern and and a certain degree degree of mineralization have correlation with with orogenic orogenic events: events: In the Elliot ElliotLake Lakearea area ofofthe theSuperior SuperiorStructure StructureProvince, Province,the theuranium uranium In the m.y. events events and the mineralization belongs to 2,500 to 2,600 m.y. mineralization belongs to 2,500 to 2,600 and relates relates to the Huromian sedimentation~ the Kenoran Kenoran Orogeny, Orogeny, that Huromian sedimentation,which whichclosely closely followed the according to the time according to postasslum-arqon postassium-argon ages ages on on micas micas spans spans the time between between 2,230 2,230 to to 2,730 m.y., with frequency at at 2,480 maximum frequency 2,480 m.y. m.y. 2,730 witha amaximum Within Churchill Structural Structural Province Province during during the the interval intervalbetween between the the Within the the Churchill Kenoranand andHudsonian HudsonianOrogenies Orogeriies(approximately (approximately1,859 1,859and and2,200 2,200 m.y.) m.y.) two Kenoran two periods of of uranium mineralization are are evident, evident, both periods uranium mineralization both of which which correspoid correspond to first period, the periods of the periods ofgranitization, granitization~ metamorphism, metamorphism,and andmetasomatism. metasomatism. The The first period, embracesthe thetime time interval interval around embraces around 2,200 2,200 rn.y., m.y.,and andthe thesecond secondone one around around 1,920 1,920 m.y. m.y. The uranium uraniummineralization mineralization in in the with aa highest highest peak peak at at about about 1,735 1,735 m.y. m.y. The the Beaver10dge Lake northernSaskatchewan, Saskatchewan, took took place placearound around1 1,780 m.y. Beaverlodge Lakearea, area, in northern ,780 m.y. During the interval intervalbetween between the theHudsonian Hudsonian and and Grenville GrenvilleOrogenies Orogenies and and During with Stockwell's Stockwell ISproposed proposed Elsonian E1sonian Orogeny Orogeny (about (about 1,370 1,370 m.y.) coinciding with theGreat GreatBear BearLake Lakearea areashow showaarange rangebetween between 1,200 1,200 uranium uranium mineralization mineralization ininthe to 1,450 1,450 m.y. m.y. 56. �(Mursky, (Mursky, continued, page page b) b) At the the time time of Grenville Grenville Orogeny Orogeny which the time time interval At whichfalls falls within within the of 800 800 to 1,100 1,100 m.y. m.y. and and aa mean mean age 955 m.y., uranium mineralization ageof of 955 m.y., uranium span between between 880 by the occupies aa time time span occupies 880and and1,100 1,100m.y. m.y.and andisis exemplified exemplified by deposits in Lake area, area, Saskatchewan; Saskatchewan; Great Great Bear Bear Lake Lake region, deposits in the theBeaverlodge Beaverlodge Lake N.W.T.; and Ontario. The The uranium Bancroft N.W.T.; and Bancroft Bancroft region, region, Ontario. uraniumdeposits deposits in in the Bancroft area are similar age age as as the the granitic graniticIntrusions intrusionsand andthus thuscorrespond correspond to area are of similar 950 and 950 and1,070 1,070m.y. m.y. interval. interval. Geochronologic results, and geological geological data data show show that thatPrecambrian Precambrian rocks rocks Geochronologic results, and can be begrouped groupedinto intoseveral severaldistinct distinct categories in Wisconsin Wisconsin can categories and and age age patterns: patterns: (1) The 2,500 2,500 m.y. and older orthogneisses, andgranitic granitic The m.y. and orthogneisses, paragneisses, paragneisses, and rocks rocks which which occur occur in in the the western western and and northern northern part of of Wisconsin. Wisconsin. The The gneiss gneiss terraine terraine isiscomposed composed of of several several types types of of migmatic migmatic gneisses, gneisses, including amphibolite related mafic and related mafic rocks, rocks, granitic graniticgneisses gneisses and and including amphibolite and peliticgneisses gneissesand and hybrid hybrid rocks. rocks. The The assemblages assemblages seem seem to granite, pelitic correspond the Kenoran Kenoran Orogeny Province correspond to to the Orogenyininthe the Superior Superior Structural Structural Province Shield and andcoincide coincidewith with the the 2,500 of the the Canadian Canadian Shield 2,500 to 2,600 2,600 rn.y. m.y. old old uranium mineralization region. uranium mineralization in in that region. (2) The 1,850 1,850 to to 1,900 m.y. old volcanic The 1,900 m.y. volcanicand and plutonic plutonicrocks rockswhich whichmake make up up most the basement basement complex and northeastern Wisconsin. Wisconsin. most of of the complexof of northern northern and This suite suite consists consists of of granitic granitic to to dioritic dioriticplutonic plutonicrocks rockswhich which are are This intrusive contemporaneous intrusive into intoa acomplex complexofofessentially essentially contemporaneous volcanic volcanic rocks. The agesand anddistribution distribution of these The ages these rocks rocks suggest suggest that they they directlyrelated relatedto to Penokean Orogeny Orogeny (1,850 1,900 m.y.) m.y.) which, which, are are directly Penokean (1,850 to 1,900 thethe Hudsonian in time, time,coincides coincidesroughly roughlywith with HudsonianOrogeny OrogenyininCanada Canada and and its period its period ofofuranium uranium mineralization mineralization (1,920 (1,920 m.y.) m.y.) as as represented represented in the Churchill Structural Structural Province. Province. the (3) The1,780 1,780toto1,800 1,800m.y. m.y.old oldgranitic granitic and rhyolitic rocks The and rhyolitic rocks which which apapparently constitute constitute most most of ofthe thePrecambrian Precambrian terraine in insouthern southern rocksconsist consistprimarily primarily of of rhyolites Wisconsin. These These rocks rhyolites and and granites. granites. The TherhY81itic rhyolitic units units occur occur in in southern southern Wisconsin, Wisconsin,asasin1iers inliers in in the the Paleozoic rocks, whereas whereasthe theqranitic granitic rocks into central Paleozoic rocks, rocks extend extend into central and and northern Wisconsin. Wisconsin. These These rocks have been deformation rocks have beensubjected subjected to to deformation and whichappears appearstoto be be related related totothe and low-grade low-grade metamorphism metamorphism which thePenokean Penokean In time, Hudsonian Orogeny. In time, these these rocks rocks relate relatetotothethe HudsonianOrogeny Orogeny in in Canadaand andthe the1,780 1,780m.y. m.y.uranium uraniummineralization mineralization which which is represented Canada represented by the the Beaverlodge Beaverlodge area area ofofSaskatchewan. Saskatchewan. by (4) The rocks in central central and and east-central east-central Wisconsin. Wisconsin. The 1,500 1,500m.y. m.y. old old plutonic rocks Some rocks are are composed composed of quartz monzonite monzonite and and show show aa Someofof these these rocks of quartz striking similarity rapakivi massifs Scandinavia striking similaritytotothethetypical typical rapakivi massifsin in Scandinaviaand and in the the Great Great Bear Bear Lake Lake region region ofofCanada, Canada, where where the the associated associated uranium uranium mineralization, and and particularly the isotopic isotopicdata data on on pitchblende, pitchblende, are are mineralization, particularly the grouped m.y. mark. mark. grouped around around 1,400 1,400 m.y. It isistherefore, that thethe considerations thethe Precambrian It therefore,quite quiteclear clear that considerationsof of Precambrian age Wisconsin and the age patterns patterns in in Wisconsin andthe theperiods periodsof of uranium uraniummineralization mineralization in in the CanadianShield Shield would would suggest suggest abundant abundant reason reason to to investigate investigatePrecambrian Precambrian Canadian 57. �(Mursky, continued, page (Mursky, page c) mostlikely likely types terrain ininWisconsin Wisconsin for foruranium uranium as as well as as thorium. thorium. The The most types of deposits deposits Ininthe thePrecambrian Precambrian terraine terraineininWisconsin Wisconsin would would be: be: (1 ) (1) deposits associated associated with igneous igneous rocks. rocks. deposits (2) deposits Precambrian basins. basins. deposits In in clastic clasticsediments sediments ininPrecambrian (3 ) (3) igneouscomplexes. complexes. vein and/or replacement vei nand/or replacement deposits deposits near nearigneous (4) pegmatite pegmatite deposits deposits which whichwould wouldhave havea agenetic geneticrelationship relationship to igneous bodies. igneous bodi es. LaceND , LGo.l"'"HC AND IIU.AflU 1"""'" 0... AI.. ~otr""_., . I,OI,'H O'4'C ..... _ . CONOlOIo4(IMtlC _.-.. . .....'-"), AiH.~'...-('." • ••••• 0 IUl/f'N DC'~"""' . . . T'trc •. , . . . . . . . .'::t~r Ckf...,.., • • .-- ..... , ... ,.---"" ... ~" known Di6tribution of ofpresent prQscntand uncJformer fOrlnururanium uro)niUlll mines mines and oJnd known lyore 11 Distribution occurronces tho Canadian Ciln.JcHcan Shiold Il\ftQr A. h. II. II. Lang. Lung, 1570) 1970). occurrences in in the shield (Cite: I'ltJUfC 58. �URANIUM ENRICHMENT IN IN GRANITIC URANIUM PROVINCES: PROVINCES: ENRICHMENT GRANITICROCKS ROCKS AND AND RELATIONS RELATIONS TO TO WISCONSIN WISCONSIN JeffreyK.K.Greenberg Greenberg Jeffrey Wisconsin Geological Geological and and Natural Natural History Survey Wisconsin Survey Most uranium uraniumdeposits, deposits,but butparticularly particularly granitic Most graniticigneous igneous ones, ones, are are bound by closely bound bytime time(geologic (geologichistory) history) and and space space(tectonic (tectonicsetting) setting) into 'provinces". These "provinces". These provinces original uranium uranium provincesare areproposed proposedasasthe thesites sites of of original No concentration early but but evolved evolvedsialic sialic crustal crustal nuclei nuclei (shields). No concentration ininearly major in inrocks years. major uranium uraniumdeposits depositsare areknown known rocksolder olderthan thanabout about2.8 2.8billion billion years. Since Precambrian time, shieldareas areas have have undergone undergone major Since early Precambrian time, shield major modification, modification, Throughout thermo-tectonic thermo—tectonic events events (orogeny, particularly along along their theirmargins. margins. Throughout particularly etc.), etc.),uranium uraniumbecame became mobilized mobilized and and consequently consequently reworked reworked during each each progresprogressively The enrichment enrichmentofof uranium uraniumand andits its concentration concentration into into sively younger younger event. event. The deposits is an deposits an Important important product product of the the tectonic tectonicreworking reworking and and chemical chemical difdifferentiation ferentiation of of the the crust. crust. The Colorado Colorado Front Front Range Rangeand andEgyptian EgyptianRed RedSea Sea Hillsare are two two plutonic The Hills uranium alkaline uranium provinces. In each each case, case, progressively progressively younger younger and and more more alkaline plutons plutons are are enriched enriched in in uranium. uranium. The The Pikes Pikes Peak PeakBatholith Batholith in inColorado Colorado and and the Younger Granitesofof Egypt Egyptasaswell well as as highly highly urariiferous the Younger Granites uraniferous bostonite bostonite dikes dikes two provinces provinces also also possess in both typify these both areas areas typify these intrusions. intrusions. The The two possess radioIt can genically enriched enriched older older"basement" "basement" rocks. rocks. It can be be concluded concluded that that an an originaluranium uranium concentration concentration ininthese theseareas areaswas wasenhanced enhanced through through tectonic tectonic original and and magmatic magmatic reworking. Many of same rock and geologic environments environments which which are are hosts hosts Many of the the same rock types types and RedSea SeaHills Hills exist exist in for uranium uranium deposits deposits in the the Front FrontRange Range and and Red in Wisconsin. Wisconsin. However, even no However, evenunder underapparently apparentlyideal ideal chemical chemicaland andtectonic tectonic conditions, no major deposits are This absence maybebeinin part major uranium uranium deposits are known known in Wisconsin. Wisconsin. This absence may a it isismost a function function of thick thick glacial glacialblanketing blanketingofofthe thebedrock; bedrock; however, however, it most likely that did not likely thatthe theearly earlyparental parentalcrust crustforforwhat whatisisnow nowWisconsin Wisconsin did not Muchofof that that provide an abundant abundant source eventual uranium uranium enrichment. enrichment. Much provide an source for for eventual enrichment may north in in Canada Canada and Wyoming, but enrichment maybebepresent presenttoto the the north and west west in in Wyoming, but it it decreases the south east away form the the nuclear nuclear shield. decreases toto the south and and east away form shield. 59. �REGIONAL REGIONAL GEOCHEMISTRY GEOCHEMISTRY AND AND METALLOGENY, METALLOGENY, NORTH SHORE SHOREOF OF LAKE LAKE SUPERIOR, NORTH SUPERIOR, ONTARIO ONTARIO W.B. Coker Coker and andJ.M. J.M. Franklin W.B. Geological Survey Canada, Ottawa Ottawa Geological Survey of ofCanada, Ontario, Canada The Proterozoic Proterozoic and Archeanterranes terranes of of the northern The and Archean northern Lake Lake Superior Superior area area include exceptional variety variety of an an accompanying include an an exceptional of lithologles, lithologies,with with accompanying array array of Regional lake sediment water surveys mineral types. Regional sediment and and water surveys were were underundermineral deposit types. taken to obtain the distribution and concentration of selected taken to obtain information information on on the distribution and concentration of selected elementsinin lakes lakes lniiiedlately elements immediately north north of ofLake Lake Superior. Superior. The principal principal Archean lithologic domains, The Archean lithologic domains, with attendant attendant deposit deposit types types are: and examples and examples 1) Supracrustal "greenstone" with massive sulphide Supracrustal "greenstone" sequences, sequences, with massive sul phide (Manitou(Manitouwadge), gold vein and iron formation wadge), gold vein (North (NorthShore Shore Gold) Gold) and iron formation(Wawa (Wawa and and Schreiber areas) types. types. Schreiber areas) 2) intrusions,with with Cu-Moporphyry porphyry type typeoccurrences occurrences (Priske (Priske Twp. Twp. Felsic intrusions, Cu-Mo occurrence) and occurrence) and uraniferous pegmatites pegmatites (Greenwich (Greenwich Lake). Lake). 3) Mafic Intrusions, intrusions,with withCu-Ni Cu-Ni(Nicopor) (Nicopor)and andZn-Cu Zn-Cu(Zenmac) (Zenmac) types. types. Mafic and intrusive units units with with major major Principal Proterozoic stratigraphic and Principal Proterozoic deposit types, and and examples, examples, are: deposit types, 1) Aphebian Gunflint iron formation. Aphebian Gunflint formation. 2) Apheblan Roveshale, shale,with with Ag veins (Creswel). Aphebian Rove Ag veins (Creswel). 3) SibleyGroup Group red-beds, red-beds, with with Pb-Zn-Ba Pb-Zn-Ba veins veins (Dorion) (Dorion) and and Helikian Sibley U+Cu veins(Greenwich (GreenwichLake, Lake,Little Little Bear). U~Cu veins Bear). 4) Heliklan volcanics, with native Helikian Osler Osler Group Group volcanics, native Cu-chalcocite Cu-chalcocite veins veins and and amygdule fillings. amygdule fillings. 5) Helikian He1ikian gabbroic gabbroic intrusions, intrusions,including includingunniineralized unmineralizedLogan Logan diabase diabase sills, and mineralization (Great sills, andthe theCrystal CrystalLake Lakegabbro gabbrowith withNi—Cu Ni-Cu mineralization (Great Lakes Nickel). Lakes Nickel). 6) He1ikian alkalic alkaliccomplex complex (Port (PortColdwell) Coldwell)with witha amagmatic magmatic Cu eu (Ni, Pd, Pd, Helikian zone, Pb-Zn-Ag Pb-Zn-Ag veins veins in in the themetamorphic metamorphic halo, halo, and and UUzones zones near near Pt) zone, the the northeast northeast contact. contact. 7) 7) Prairie Lake) Helikian carbonatite (( Prairie Lake) with with U, U, Nb Nb and and rare earths. earths. Helikian carbonatite Trace element elementpatterns patterns in in lake andwater waterclosely closely relfect'the reirect the Trace lake sediment sediment and chemicalcharacteristics characteristics of the chemical the major major lithologic lithologicdomains, domains, although although glacial overburden andvarying varyinglimnologic limnologicconditions conditions clearly clearly modify overburden and modify the the elemental elemental distributions. The The trace trace element patterns in element patterns in the thelake lakesediments sediments and and waters waters may divided into into three may bebedivided three groups: groups: 60. �(Coker and Franklin, Franklin, continued, (Coker and continued, page page b) b) 1) 2) Patterns related to to bedrock bedrock features, features, as as indicated indicated by byour ourbedrock bedrock Patterns trace element data, which which have haveonly onlymarginal marginalore oredeposit depositsignifisignifitrace element data, cance: (I) (i) Rove shaleisis characterized Rove shale characterized by by elevated elevated Zn, Zn, Ni, Ni, Ag, Ag, As As and and The Ag Ag deposits Hg sediments and lake waters. waters. The Hg in in lake sediments and FF in in lake are not not specifically outlined. are outlined. (ii) (i;) Port Coidwell Alkalic Complex reflected by by FF in in lake Port Coldwell Alkalic Complex isisreflected lake waters sediments; Pb waters and and by by Zn Znand andNiNiinin lake lake sediments; Pbinin lake lake sediments form halo around around the theComplex. Complex. ments form a halo (iii) (iii) Logandiabase diabase sillsare areclearly clearly identified identified by Logan sills by high high Cu Cu levels lake sediments; sediments; Fe in lake Fe ahd ahd Ni Ni levels levels in in the thelake lakesediments sediments reflect the the sills sillstotoa alesser lesserdegree. degree. (iv) In the the Sibley Sibley Group Group the the Kama Kama Hill Formation, and In Hill Formation, and to to aa lesser extent the are reflected the Rossport Rossport Formation, Formation, are reflected by by elevated elevated As As contents contents in the the lake lakesediments. sediments. (v) Wawaarea areavolcanic volcanicand andsedimentary sedimentary strataare are reflected reflected by Wawa strata by elevated Ni Ni in lake lake sediments; sediments; elevated elevatedMn, Mn, Fe, Fe, As, As,Co Co and and Pb in lake reflect the Pb in lake sediments sediments reflect the major major iron formation formation within this thisArchean Archeansequence. sequence. In addition iron formation, formation, certain deposit In addition to to the theWawa Wawa iron deposit types types are are morespecifically specifically reflected more reflectedbybysome some of of the thelake lakesediment sediment and and water water data. For example: example: (1) (i) Manitouwadgemassive massivesulphides sulphidesare arereflected reflected by Manitouwadge by Cu, Cu, Zn Zn and and Pb lake Pb lake sediment sedimentdata, data, as as expected, expected, although althoughin in addition there is significant significantFFininthe thelake lakewaters waters and and U U in the the lake lake there sediments,possibly possibly reflecting reflecting the sediments, the pegmatites pegmatites present present in the the area. area. ((ii) ii) Zenmac are by the the Gabbro-hosted Gabbro-hostedzinc zincdeposits deposits at at Zenmac arereflected refiected by Zn lake sediment Zn and and Co Co lake sediment data. data. (iii) Mo—Cu-bearing felsicintrusions intrusions are are identified MO-Cu-bearing felsic identifiedbybyMoMoand andCu Cu lake sediment sediment data. data. (iv) Pb-Zn-Ba veinsassociated associatedwith with the the Sibley the Port Pb-Zn-Ba veins Sibley Group Group and and the Port Coldwell Alkalic Alkalic Complex are indicated by Coldwell Complex are by the the Pb Pb and and Zn Zn lake sediment sediment data. (i i 1) (v) 3) 3) The zonesofof uraniferous uraniferous pegmatites north of Dorion, The zones pegmatites north Dorion, which which are associated with unconformity are associated with unconformity - related relateduranium uranium occurrences, occurrences, are distinctly distinctlyoutlined outlinedbybythe thelake lake sedimentand and water water UUdata. data. are sediment Finally, under specific specificphysicochemical-limnological physicochemical-limnological conditions conditions an an Finally, under individual trace traceelement, element, ororgroup group ofoftrace traceelements, elements,may may be be conconThe scavenging scavengingeffect effect of centrated to unexpectedly unexpectedly high centrated high levels. The both iron iron and and manganese manganese hydroxide on trace metals metals both hydroxideprecipitates precipitates on (mainly Zn, this area. area. (mainly Zn, Co Coand andNi)Ni)ininlakes lakesisis evident evident in in this hl. �GEOLOGYOF OF THE THE MCCASLIN GEOLOGY MCCASLIN RANGE, RANGE, NORTHEASTERN NORTHEASTERN WISCONSIN WISCONSIN Joseph J. J. Mancuso, Joseph Mancuso, R.H. R.H. Motten* Motten* Bowling Green Bowling Green University University Bowling Green, Ohio Ohio Bowling Green, The McCaslin McCaslinRange Range locatedininportions portions of Forest, The is islocated Forest, Oconto, Oconto, Marinette, Marinette, and northeastern Wisconsin. Wisconsin. It forms forms a a ridge ridge two two to and Lang1ade Langlade Counties Counties in in northeastern to five wide extending an east-west east-west direction. The The major miles wide miles extending 25 25miles miles in in an major geologic thearea areainclude include Lower PrecambrianWaupee Waupee volcanics, volcanics,McCauley McCauley units ininthe thethe Lower Precambrian Granite, and and Hines Hines Quartz Quartz Diorite, Diorite,and andthe theMiddle MiddlePrecambrian PrecambrianBaldwin BaldwinConglomerate, Conglomerate, McCaslin Granite. McCaslinQuartzite, Quartzite, Hager HagerRhyolite, Rhyolite, Belongia Belongia Granite Granite and and High High Falls Falls Granite. On On the the McCaslin McCaslin Range, Range,the the Middle Middle Precambrian PrecambrianMcCaslin McCaslinformation formationconsists consists of of massive red-grey and quartz-pebble quartz-pebble conglomerates conglomerates similar those massive red-grey quartzites quartzites and similar to those found in in the River uranium uraniumdistrict district in found the Elliot ElliotLake—Blind Lake-Blind River in Ontario. Ontario. It It rests rests unconformably unconformably on on Lower LowerPrecambrian Precambriangreenstones, greenstones,granites, granites, and and gneisses. gneisses. The dominant the region region isisthe theMcCaslin McCaslin Syncline Syncline which which trends trends The dominantstructure structure in in the to close close to the approximately east-west. It It plunges plunges 50 5° to to the the west west and and appears appears to the approximately east—west. east but is disrupted east but disrupted by by the the intrusive High High Falls Falls granite. granite. The The northern northern limb and nose of of the McCaslin and nose the syncline synclineare arerepresented representedbybythethe McCaslinRange Range and and Thunder Thunder Mountain, respectively, while Mountain, respectively, while the the southern southern limb limb isisrepresented represented by by the the Baldwin Baldwin Conglomeratewhich whichisis exposed exposednear near the the town town of Mountain, Conglomerate Mountain, Wisconsin. Wisconsin. well-developed metamorphic metamorphic aureole relatedtotothe the High HighFalls Falls granite A well-developed aureole related intrusion can be be traced tracedthrough throughprogressive progressivemetamorphic metamorphic changes changes in the Hager, Hager, intrusion can in the McCaslin, and formations. The metamorphicmineral mineral assemblage indicates McCaslin, and Waupee Waupee formations. The metamorphic assemblage indicates temperature approximatelylOO°C 700°C adjacent thegranite granite intrusion intrusion aa maximum maximum temperature of ofapproximately adjacent to tothe where sillimanite occurs,and andgrades gradeswestward westward through through zones zones of andalusite andalusite and and where sillimanite occurs, muscovite at the theextreme extreme western western end end of the the range. range. muscovitedown downtotosericite sericite at The The lithology lithology and and stratigraphic setting settingofofthe theMcCaslin McCaslin formation formation on on the the McCaslin Range Rangeare aresimilar similar to to those McCaslin those of of uranium uranium producing producing basal basal Proterozoic Proterozoic sedimentsinin Canada, Canada,South South Africa,Brazil, Brazil, and Africa, and Australia. sediments Comparisons with known uraniferous conglomerates: Comparisons with known uraniferous conglomerates: I. Similarities and Similarities and indications indications ofofuranium uranium mineralization: mineralization: A. The McCaslin McCaslin formation formation occurs The occurs immediately immediately above above the the unconunconatthe thebase base ofofa aMiddle MiddleProterozoic Proterozoicsequence. sequence. formity at B. B. The basal basal member member theformation formation is is a quartz-pebble The ofofthe quartz-pebble conconglomerate which is overlain overlainbybya asequence sequence ofofcross-bedded cross-bedded glomerate which and ripple-marked sandstones. and sandstones. C. C. cobble of ore-grade ore-grade conglomerate conglomerate was found in in A cobble was reportedly reportedly found the the drift driftononMcCaslin McCaslinMountain. Mountain. (Wisconsin (Wisconsin Geological Geological Survey) Survey) *Kennecott *Kennecott Exploration, Inc., Inc.,Casper, Casper,Wyoming Wyoming 62. �(Mancusoand andMotten, Motten, continued) (Mancuso D. D. Anomalous concentrations of of uranium Anomalous concentrations uranium were were reported by by NURE NURE inin the McCaslin Hydrochemical& &Stream StreamSediment SedimentSurvey, Survey, Iron McCaslin area. (NURE (NURE Hydrochemical Iron Mountain Mountain Quadrangle; Quadrangle; 1978) 1978) II. dissimilarities: II. Apparent Apparent dissimilarities: A. Uraniferous conglomerates conglomerates Ontario,Brazil, Brazil, Australia, and Uraniferous in inOntario, and South Africa are dated dated at at 2150 2150 to to 2800 2800 m.y. m.y. (Robertson, (Robertson, 1974). 1974). South Africa are The McCaslin reportedly1900 1900m.y. m.y.(Van (VanSchmus, Schmus, 1976). 1976). The McCaslinformation formation is reportedly B. Accessory apparently lacking lacking inin outcrops outcrops ofofthe theMcCaslin McCaslin Accessorypyrite pyrite is apparently formation, but isisaamajor majoraccessory accessory in in the theknown known deposits. deposits. formation, but C. C. Hematite is major accessory accessory in the McCaslin McCaslin formation Hematite is a major in the formation but but is lacking in in the theknown known deposits. deposits. 63. �WISCONSIN WISCONSIN :[NTEREST INTEREST IN RADIOLOGICAL RADIOLOGICAL IMPACTS IMPACTSRESULTING RESULTINGFROM FROM URANIUM EXPLORATION EXPLORATION(DRILLING) (DRILLING) URANIUM Thomas K. Greenberg, Greenberg, and and M.G. M.G. Mudrey, Mudrey, Jr. Jr. ThomasJ.3. Evans, Evans,Jeffrey Jeffrey K. Wisconsin Geological History Survey Survey Wisconsin Geological and and Natural Natural History Recenturanium uraniumexploration explorationactivity activity in Recent in northeastern northeastern and and central central Wisconsin Wisconsin has stimulated assessing potential radiological impacts impacts resulting has stimulatedinterest interest in assessing potential radiological In the from intoa uranium a uraniumorebody. orebody. In the midst midst of far-ranging far-ranging claims claims of from drilling drilling into significantly harmful impacts impacts on on one one hand hand and assertions of of zero zero significantly harmful andthe theflat flat assertions impact on on the the other hand, impact hand, an an informal informal technical technicalworking workinggroup groupwas was formed formed as as a request order to determine a result result of ofaalegislative legislative requestin in order to determinewhat whatfacts factsare areknown known aboutthe theexploration explorationactivity. activity. The about The objectives of ofthe theworking workinggroup group have have been (1) identify been toto (1) identifyexisting existinginformation informationononuranium uraniumexploration explorationimpacts impacts available in in the reliable state, federal, international literature; literature; available the reliable federal, and and international (2) consult (2) consult state, state, federal, federal,and andinternational internationalagencies agencies having having some some experience with issues surrounding uranium drilling impacts; (3) if possible, ience with issues surrounding uranium drilling impacts; (3) if possible, prepare "wors "worst case"estimates estimatesofofradiological radiological impacts ondrillers drillers and prepare t case" impacts on and exexploration geologists, geologists, and and(4) (4)investigate investigatethe thefeasibility feasibility of ploration of low-level low-level radiation monitoring monitoring of of uranium uranium drill sites areas having knownuranium uranium drill sites at at areas having known deposits, exploration sites ininWisconsin. deposits, as as well well as as atatproposed proposed uranium uranium exploration Wisconsin. The report reviews reviewsthe the public public policy policy aspects of investigating potential The report aspects of potential radiological radiological impacts impacts ofofuranium uranium exploration explorationand and the thegeneral general methodology methodology of the working group's approach approachtotoevaluating evaluatingthese thesepotential potential radiological the working group's impacts. Results dateindicate indicate (1) (1) the the literature literature dealing Results toto date dealing with with radiological radiological impacts from drillingisis limited, limited, (2) impacts from drilling (2) interest of of local, local, state, state, ororfederal federal government in in this the governmentagencies agencies thistopic topic ranges rangesfrom fromtotal total indifferences indifferences to the of drilling drillingactivity activity (moratorium),(3)(3) perceivedradiation radiationexposure exposure prohibition of (moratorium), perceived to the driller appears minoratat this this point, to the exploration exploration geologist geologist and and driller appears minor point, and and (4) (4) monitoring of of actual actual drill may monitoring drillsites sites mayprove prove totobe bethe themost most direct directapproach approach to resolving uraniumexploration explorationactivities. activities. The resolving the the issues issues surrounding surrounding uranium The status of the the informal -informal technical technical working working group's group's investigations as as of of early early May, May, 1980will will be 1980 be presented. presented. 64. �GEOLOGIC IN NORTHEASTERN NORTHEASTERN WISCONSIN: AN UPDATE UPDATE GEOLOGIC MAPPING MAPPING IN WISCONSIN: AN B.A. Brown B.A. Brown and and J.K. Greenberg Greenberg Wisconsin Geological and and Natural Natural History Wisconsin Geological History Survey Survey Madison, Madison, Wisconsin Wisconsin Continued reconnaissance reconnaissancemapping mapping reinterpretation of andand a a reinterpretation of geophysical geophysical Continued data signigicantly improved our understanding of the Precambrian data have have signigicant1y improved our understanding of the Precambrian geology geology conceptofoffour four distinct distinct tectonic of northeastern northeastern Wisconsin. Wisconsin. The The concept tectonic regions regions separated west trending boundary boundary structures has not separatedby by three three major major east east to to west structures has changed, boundaries and types present present changed,however howeverthe thenature natureofof the the boundaries and the the rock rock types within the three regions better known result of the southernmost southernmost three regions are are now now better known asasaaresult of exextended mapping and new gravity map. tended geologic mapping and aa new gravity map. The new newgravity gravity data data have haveenabled enabledestimation estimationofof the the extent extent of The of several several known part of ofthe thearea areaand and suggest suggest the the presence presence of knownplutons plutonsinin the the central central part several parts of the several granitic granitic and and mafic mafic plutons plutons in in the thesouthern southern and and western western parts the sheet. The Batholith is and eastern eastern boundaries boundaries of the the Wolf Wolf River River Batholith The northern northern and resulting interinterdelineated by by its itsgravity gravitysignature signatureand andrecent recentmapping. mapping. The The resulting delineated rocks of of the pretation indicates indicates aa sharp sharp contrast contrast between between rocks the Batholith Batholith and and the the granitic graniticterrane terraneofofthe theAmberg-Athelstane-High Amberg-Athelstane-High Falls area. area. The southernmostboundary boundary zone, which followsthe theWolf WolfRiver Rivercontact contact in in The southernmost zone, which follows the to be rilajor fault fault zone This zone the east appears appears to be aa major zone in in the thesouthwest. southwest. This zone truncates northeast trending cates trending cataclastic catac1asticzones zonesknown known from from previous previous mapping mapping in Marathon County. The The central central boundary zone is is marked by east-west east-west trending Marathon boundary zone marked by and cataclastic catac1astic zones zones in the the east, east, but buttotothe thewest westofofthe theCavour Cavourarea area faults and becomesless lessdefined definedand andisischaracterized characterizedbybyaadistinct distinct class becomes class ofofhornblendehornblendebearing intrusions,ranging rangingfrom from gabbro gabbro to granodiorite. granodiorite. These bearing dioritic dioritic intrusions, rocks crop out out in aa band from east east to to west west in in near rocks crop band for over over 100 100 km km from near proximity the central centralboundary. boundary. to the Field work thethe unmapped work in in 1980 1980 will willconcentrate concentratein in unmappedand and poorly poorlyexposed exposed northwestern the sheet. sheet. A program planned northwesternportion portion of the programofoftest testdrilling drilling isisplanned for problem problem areas areas throughout and aa geochronological geochronological study throughout the the area, area, and study of of important rock types important rock types is is now now in progress. progress. 65. �ANALYSIS OF ANALYSIS OF AANEW NEW GRAVITY GRAVITY MAP MAP FOR FOR THE MERRILL-RHINELANDER AREA, AREA, WISCONSIN WISCONSIN THE MERRILL-RHINELANDER C. Ervin and and Kelly Kelly Tuftee Tuftee C. Patrick Ervin Department Geology Department of Geology Northern Illinois University Northern Illinois University DeKalb, DeKalb,Illinois Illinois 60115 The History Survey Survey and and Northern Northern The Wisconsin WisconsinGeological Geological and and Natural Natural History IllinoisUniversity University havecompleted completeda anew new gravity gravitymap map ofofnortheastern northeasternWisconWisconIllinois have sin. Data Data east east of 89 89 degrees degrees longitude and and in in Vilas VilasCounty County were were recompiled recompiled from earlier earlier surveys, from surveys,using usingthe thenew newGeodetic GeodeticReference Reference System System - 67 67 formula formula and the the International International Gravity 71 datum. and Gravity Standardization Standardization Net Net - 71 datum. The The remainder remainder of the the map, map, including including Oneida, Oneida, Lincoln, Lincoln,western westernLanglade, Langlade, and and northern northernMarathon Marathon counties, consists of ofnew new data data on on approximately approximately aa one-mile counties, consists one-mile grid. grid. Preliminary interpretation Interpretation of that a rather ofthe thenew new data data suggests suggests that rather simple, simple, Preliminary qualitative analysis is sufficient totodelineate delineate the the regional regional variations variations in in qualitative analysis is sufficient The gravity gravity data, rock data, used used in conjunction conjunction with with the the aeromatic aeromatic data, data, rock type. The are valuable guide guide for for and and constraint constrainton on the thegeologic geologicmapping mapping of the the hidden hidden are a valuable Precambrian rocks. Precambrian 66. �PETROLOGYOF OFTHE THE BEAR BEAR LAKE LAKE INTRUSIVE, PETROLOGY INTRUSIVE, KEWEENAW KEWEENAW PENINSULA, PENINSULA, MICHIGAN MICHIGAN Institute ofofMineral Allan Johnson, Johnson, Institute MineralResearch Research Michigan Technological Technoloqical University, University, Houghton, Michigan Houghton, Michigan Michigan 49931 Boyd Parker, Parker, Michigan Michigan Geological Geological Survey Boyd Survey Division Department of Natural Natural Resources, Department of Resources, Lansing, Lansing, Michigan Michigan 48906 David Snider, Michigan David Snider, Michigan Geological Geological Survey Survey Division Department of Resources, Lansing, Lansing, Michigan Michigan 48906 Department of Natural Natural Resources, Jack Van Van Alstine, Alstine, Michigan Jack Michigan Geological Geological Survey Survey DNR, DNR,Marquette, Marquette, Michigan 49855 The Bear BearLake Lake intrusiveisisaanearly nearlycircular circular felsic The intrusive felsicplug plugwhich which intrudes intrudes It Keweenaw Itisislocated locatedin the in the KeweenawPeninsula Peninsula miles (13 (13 km) km) north north ofofHoughton, Houghton, Michigan. Michigan. eight miles the Upper Freda formation. formation. Upper Keweenawan Keweenawan Freda Earlier work work on on the the Bear Bear Lake Lake intrusive intrusivebybythe theMichigan Michigan Geological Geological Earlier Survey designed to test aa model model of Surveywas waspart partofofaa larger larger investigation designed to test copper mineralization. Basically, the copper mineralization. the model model suggested suggested that that the the several, isolated isolated intrusive/extrusive intrusive/extrusive bodies bodies of Keweenawan of Keweenawanage ageininthethe Keweenaw Keweenaw Peninsula Peninsula may maybebethe thesource sourcefor for copper coppersulfide sulfide mineralization (Snider (Snider and and Parker, 1979). 1979). The The Bear BearLake Lakeintrusive intrusive appeared appearedtotooffer offer an an opportunity to test test this thismodel. model. Geological Survey Survey in in 1978 indicated the Field work work by by the the Michigan Michigan Geological 1978 indicated poss"ibi1ity coppermineralization mineralizationassociated associated with with the the Bear Bear Lake Lake intrusive. possibility ofofcopper intrusive. Anomalous copper values ofof190 in inthe the presence presence of of two two Anomalous copper values 190ppm ppm theintrusive, intrusive, the VLF-EM conductorsand andanomalous anomalous copper values soil over over these VLF-EM conductors copper values in inthethesoil these conconductors supported this hypothesis. ductors supported this hypothesis. In 1979 1979 the Mineral Research Research joined project. A verIn the Institute Institute ofofMineral joined the the project. The 208 208 feet feet tical diamond drill hole was was put put into into the the largest largestconductor. conductor. The tical diamond drill hole (63 m) deep deephole holepenetrated penetrated8686feet feet (26 (26m)m)ofof glacial glacial overburden, (63 m) overburden, 30 30 feet iii) (9 m) of highly altered 25 feet feet (7.6 (9 m) of altered fragmental fragmental rocks rocks (volcanoclastic?) (vo1canoc1astic?) and and 25 (7.6 m) of clastic clasticsediments sediments ranging ranging from from siltstones siltstones totocoarse coarsearkoses. arkoses. The The bottom bottom 67 feet (20 (20 m) m) cored cored the the intrusive intrusivewhich whichbecame became more with 67 morecoarsely coarselycrystalline crystalline with depth. The The intrusive intrusive has andotherwise otherwisealtered altered the has apparently apparently metasomatized metasomatized and overlying overlying sediments. sediments. These Theseoverlying overlying sediments sediments have have not not been been found found in in outcrop. outcrop. Minor Minor amounts amountsofof native native copper copper were were present present as as finely finely disseminated disseminated grains grains in in quartz quartz veinlets vein1etsbetween between 162 162 and and 180 180 feet (49 (49 and and 55 55 m) m) of of depth. depth. Reference Snider, D.W., D.W., and and Parker, Parker,B.K. B.K.(1979) (1979)Geochemical Geochemical and andGeophysical Geophysical Anomalies Associatedwith with the the Bear Lake Intrusive, Intrusive, Sections Anomalies Associated Bear Lake Sections2424and and 25, 25,TS6N, T56N, R34W, Houghton County, Michigan, on Lake Lake Superior Superior Geology, Geology, R34W, Houghton County, Michigan,25th 25thAnnual AnnualInstitute Institute on Duluth, MN, May p. 38. Duluth, MN, May8-13, 8-13, Abstract, Abstract, p. 67. �THE COSUNA PROJECT -- AANEW THE COSUNA PROJECT NEW CORRELATION CORRELATION CHART CHART FOR FOR THE THE NORTHERN NORTHERN MID-CONTINENT REGION REGION G.B. arid D.J. Bergstrom G.B. Morey Morey and Bergstrom Minnesota Survey Minnesota Geological Geological Survey 1633 Eustis Street 1633 Eustis St. Paul, Paul, Minnesota Minnesota 55108 Late Association of of Petroleum Geologistsinitiated initiated Late in 1976, 1976, the the American American Association Petroleum Geologists North aa national national project project called called 'Correlation "CorrelationofofStratigraphic StratigraphicUnits Unitsofof NorthAmericafl America" (COSUNA), afterward gained officialsupport supportinin this this country (COSUNA), andand soonsoon afterward gained official country from from the the United States and numerous numerous otherprofessional professionalsocirties. socirties. It United States Geological Geological Survey Survey and other It beaaproject project of of voluntary voluntary effort, effort, and is designed designed toto be and the the objectives objectives are are (1) (1) to to develop seriesofof stratigraphic stratigraphic charts charts correlating rock rock units units of of both both the the develop aaseries surface subsurface across acrossgeologic geologic provinces provinces of of the United surface and and subsurface United States, States, and and (2) to thethickness thicknessand and lithologyofofeach eachlithostratigraphic lithostratigraphic unit (2) to summarize summarize the lithology throughout the geologic geologiccolumn, column,asaswell wellasastoto identify identify pertinent throughout the pertinentpaleonpaleonthe data data base basewill will conform and radiometric radiometric data. data. Although Although the conform insofar tological and as possible possible to to the the standards standardsset setforth forth in in the Stratias the International International Code Code ofofStratigraphic Nomenclature Nomenclature will be include information information not not formally formally graphic it itwill be necessary necessary toto include as possible possible for specified within within the theCode Code to to insure insure as as complete complete a data data base base as country. the the entire country. For the the purposes this project, For purposes ofof this project,the theUnited UnitedStates Stateshas has been been divided divided The Minnesota MinnesotaGeological Geological Survey Surveyhas hasvolunteered volunteered to to coorinto 20 20 regions. regions. The dinate the program in the dinate program in the states states ofofMinnesota, Minnesota, Wisconsin, vlisconsin, northern northern Michigan Michigan and eastern eastern South NorthernMid-contintent Mid-contintent and South Dakota, Dakota, which which comprise comprise the theCOSUNA COSUNA Northern Region. The The stratigraphic stratigraphic succession succession in this thisregion regionisissummarized summarized in in approxapproximately 40 columnserected erectedtotorepresent representmajor majorlateral lateral changes changesininlithology, lithology, imately 40 columns structure, This correlation the the other COSUNA structure, and and age. age. This correlation chart, chart,asaswell wellasasallall other COSUNA charts, has constructed following following the for the has been been constructed the general general format format used used for the charts charts of western (Douglas and andothers, others, 1970). Canada (Douglas 1970). The COSUNA charts western Canada The COSUNA chartshave haveaa vertical time units chronostratigraphically. tical timescale, scale,with withthe theArchean Archean and and Proterozoic Proterozoic units Thus they from the the correlation correlationcharts chartspreviously previouslypublished published by by the the Thus theydiffer differ from Geological Society Society of of America depictsstratigraphic stratigraphic Geological America inin that each each column column depicts relationships among rocksofofall all ages among rocks ages rather than than rocks rocks of of only only one one geologic geologic system. Because rocksranging ranainginin age agefrom fromearly early Archean Archean(> (>3,600 m.y.) to Because rocks 3,600 m.y.) Holocene «10,000 Northern Mid-continent Mid-continent Region, Region, aa mixture mixture Holocene (<10,000years) years)occur occurin in the Northern of chronometric andchronostratigraphic chronostratigraphiccriteria criteria of chronometric and ofvarying varying degrees degrees of of acacvery complex complex stratigraphic curacy curacy and andprecision precision were wereused usedtotoportray portray what what is is a very stratigraphic has resulted ininmany many stratigraphic stratigraphicand andcartographic cartographicproblems problems This has succession. This ProjectDirector, Director, that have have not yet yet been been resolved. resolved. Nonetheless, Nonetheless, the the COSUNA COSUNA Project Childs (University of Dr. Orb Orlo Childs of Arizona), Arizona), has has invited invitedany any interested interestedgroups groups or individuals to participate in the review of the geologic or individuals to participate in the review of the geologiccolumns columns ininareas areas Therefore, as as part part of this in which which they they have have expertise. Therefore, thisreview review process, process, weactively actively solicit solicit assistance evaluationofof this this chart. we assistance in in preparation preparation and and evaluation 68, 68. �(Morey and (Morey and Bergstrom, Bergstrom, continued) Reference Reference Cited Douglas, R.J.W., 1970, Geotectonic R.J.W., and and others, others, 1970, GeotectonicCorrelation Correlation Chart Chart for for Western Canada, Douglas, R.J.W., R.J.W., ed., ed.,Geology Geologyand andEconomic Economic Western Canada,inin Douglas, Minerals of ofCanada: Canada: Geological Survey Survey ofofCanada, Canada,Economic Economic Geology Geology ReportNo.1, No. 1,Chart ChartIII. III. Report 69. �MINERALOGY GRANITIC PLUTONIC PLUTONIC MINERALOGYAND ANDCHEMISTRY CHEMISTRYOF OFMIDDLE MIDDLE PRECAMBRIAN PRECAMBRIAN(Xg) (Xg) GRANITIC ROCKS ROCKS FROM FROM NORTHERN NORTHERN WISCONSIN William L. L. Petro* Petro·"" Geology and and Geophysics Geophysics Department Department of Geology University of ofWisconsin Wisconsin Madison, Wisconsin Wisconsin 53706 Madison, study of Middle igneousintrusive intrusive rocks A study Middle Precambrian Precambrian igneous rocks from from northern northern Wisconsin is in progress thethe Penokean Wisconsin is progress to to gain gainfurther furtherunderstanding understandingofof Penokean orogeny. The The rocks rocks are are separated separatedinto into two two suites suites by by radiometric radiometric dating. dating. Van Van Schmus Schmus(in(inpress) press)and andSims Simsand andPeterman Peterman (in(inpress) press)estimate estimatethat that the suite is 1800-1900 m.y. old. The The range rangeof of rock rock types types is older (Penokean) (Penokean) suite 1800-1900 m.y. The older older suite granite-granodiorite-tonalite (IUGS (rUGS classification). classification). The suite has has primary igigPrice,Rusk, Rusk, and and Sawyer Sawyer counties. The The common common primary been been studied studied in Price, neousmineral mineralassemblage assemblage quarz + plagioclase + biotite++alkali alkali feldspar neous is is quarz + plagioclase + biotite feldspar + hornblende. Van Schmus Schmus(in (in press) rocks appear appearto to be be syntectonic. Van hornblende. These These rocks estimates that the suite is 1765 estimates that the younger younger suite 1765 m.y. m.y. old. This This suite suite ranges ranges from toquartz quartzmonzonite, monzonite, and and has has been been studied studied ininSawyer, Sawyer, Oneida, Oneida, from granite to and Marinette Niarinette counties. The primaryigneous igneous mineral mineral assemblage The common common primary assemblage is and quartz feldspar ++ biotite biotite+ +hornblende. hornblende. The quartz ++ plagioclase plagioclase ++alkali alkali feldspar estimates by by powder powder difdifyoungersuite suite appears to be be post-tectonic. From younger appears to From estimates fraction methods,K-feldspars fraction methods,K-feldspars from from both both suites suitesappear appear totobebeordered ordered(between (between Preliminary results of microcline). Preliminary intermediate and and maximum maximum microcline). of mineral mineral chemistry have have been been obtained microprobe. In In the the older older suite, suite, chemistry obtained by by electron microprobe. biotites (total iron determined biotiteshave have0.65-0.73 0.65-0.73wt.% wt.%FeO/FeO+MgO FeOjFeO+MgO (total determined as as FeO), FeO), 0.61-0.76 wt.% wt.% FeO/FeO+MgO, FeOjFeO+MgO, plagioclases normally hornblendes have have 0.61-0.76 hornblendes plagioclases are are normally zoned and have have 31-49 31-49 mole% mole%An, An,and andalkali alkali feldspars feldspars have have 87-92 87-92 mole% mole% Or. Or. zoned and In An,and andalkali alkali fel dIn the the younger younger suite, suite, plagioclases plagioclaseshave have 30-36 30-36 mole% mole% An, feldhave 84-89 84-89 mole% mole% Or. Or. Two geothermometry yields temperatures spars have Two feldspar feldspar geothermometry yields temperatures Major element of 600-800°C 600-800°C (range element rock chemistry chemistry has has (rangefor for both both suites). suites). Major glass beads beads (sample (sample fused fused with been determined been determinedby bymicroprobe microprobeanalysis analysis of of glass Both suites flux). have been been determined determined by by INAA. INAA. Both flux). Some Sometrace trace elements elements have may have have been beenmetamorphosed metamorphosed duringa a1600-1650 1600-1650m.y. m.y.old old regional metamorphic may during metamorphic event which which reset reset Rb-Sr systematics in east-central event Rb-Sr systematics east-central Wisconsin Wisconsin and and the the Fox Fox with Mesozoic-Cenozoic River Vally Vally (Van (Van Schmus Schmus etetal., 1975). Comparison Comparison with Mesozoic-Cenozoic River al., 1975). intrusives ofofknown bebemade known tectonic tectonic setting settingallows allowsinferences inferencestoto made about about the the settingininwhich whichthe theMiddle MiddlePrecambrian Precambrian intrusives intrusiveswere were generated. generated. tectonic setting Chemicaldata dataareareconsistent consistent with(but (butnot notcriteria criteria for) generation Chemical with generation of the the older suite older suite during during plate platesubduction, subduction, and and generation generation of the the younger younger suite This seems be in general related to aa subsequent subsequent collision event. This seems toto be general agreeagreerelated to collision event. ment with with the ment the geologic geologicmodel model presented presented by byCambray Cambray (1978). ** Student Student paper 70 70. �METALLIC MINERALS OF ISLET,LAKE LAKESUPERIOR SUPERIOR METALLIC MINERALS OF SILVER SILVER ISLET, Nancy Scofield Nancy Scofield Institute MineralResearch Research Institute ofofMineral Michigan Michigan Technological Technological University University Houghton, Michigan 49931 Houghton, L.L. Babcock Babcock Tucson, Arizona 85711 Tucson, Isletisislocatedin locatedtn Thunder Bay Bay near near the ofthe the Sibley Sibleypeninsula. peninsula. Silver Islet Thunder the tip of The general Between thetheSilver veinproduced produced $3,260,000. $3,260,000. The Between1869 1869and and1922 1922 Silver Islet Islet vein Themain mainSilver Silver Islet Islet geology of the island island was was described described by by Franklin (1970). (1970). The geology of the vein vein strikes N35°E, N35 QE, dips dips 70 70 to to 80 80 degrees degreestotothe theeast, east, occupies occupiesa afault fault cutting It has widthof of 20 20 feet the Rove formation and a gabbro gabbro dike. It has aamaximum maximum width the Rove formation and (7 whichnarrows narrowstoto8 8toto10 10feet feet (3 (3 meters) in the dike (7 meters) meters) which meters) in dike and and 2 to 44 (1 meter) meter) ininnearby nearby shale, shale, and and has has been been traced depth of 1200 1200 feet feet (1 traced to to aa depth (400 (400 meters). In the In the present present study, study, the the metallic metallic minerals minerals in in polished polished sections sections from from 55 samples (#1-5) from from the the Silver Silver Islet Isletvein veinwere wereanalyzed analyzed by by electron electronmicroprobe. microprobe. samples (#1-5) The presenceofof the the following previously-reported The presence previously-reportedminerals mineralswas was confirmed; confirmed; galena (gn), galena (gn),sphalerite sphalerite(sl), (sl),chalcopyrite chalcopyrite(cp), (cp),nicco1ite niccolite (nc), (nc), gersdorffite gersdorffite (gf), (#3) pink pink dolomite dolomite is cut and native native silver silver (Ag). and (Ag). In one one sample sample (#3) cut by by aathin thin(1(1mm) mm) vein vein of of pyrrhotite pyrrhotite(po) (po)and andpentlandite pentlandite(pn) (pn)which whichappear appeartotoshow showmutual mutual exexsolution Anothersample sample (#5)hashas safflorite (sf) (sf) closely relationships. Another (#5) safflorite closely solution relationships. associated anothersample sample (#1) (#1) associatedwith with Fe-gersdorffite Fe-gersdorffite (Fe-gf). Gersdorffite ininanother Compositional ranges ranges of of major is near near the theNiNiend endmember member (Ni—gf). (Ni-gf). Compositional major and and minor minor elements are are shown in Table shown in Table 1. 1. elements TABLE I1 TABLE Rangesof of Analyses Ranges Analyses (Atomic (Atomic percent) po P0 Fe9S F~95 Fe Fe S S NI Co Co As As Ag Cu Cu Zn Zn Pb Sb Hg Hg Cd 47 47 53 53 po pn (Fe,NI)S (Fe,Ni )5 sf (Fe, Co)As2 Co)As2 - 30—33 30-33 50—52 50-52 14-18 23-26 22 — - 6-7 66-68 - - - 1-2 - — - - — - - — — - - - - - Fe-gf Ni-gf Ni -gf fNi,Co,Fe)AsS Thi,Co,Fe)AsS 24 24 32 32 - 8 36 36 0.5-2 O. :"2 cp CuFeS2 CuFe52 25 51 51 31—35 31-35 25-30 1-3 33-35 0-2 1-2 1-2 — - nc /liAs NiAs Ag Ag Ag Ag - - 05 0-5 - 5-9 43-47 - 50-54 0-0.1 - 13 0.3-4.4 4046 40-46 23 - - - - - - - - - - - - — — — 0.7-2.9 - - - 96-98 - 24 2-4 - 51 si lnS ZnS - "- gn gn PbS PbS - - 44-4A - - 87 87 - - - - (0.5 - The paragenesis is isnot are The paragenesisofofthese theseminerals minerals notsimple, simple,but butthe thepossibilities possibilities are constrained by the analyzed analyzed compositions minerals involved. involved. constrained by the compositionsof of the the minerals REFERENCE REFER E N CE Franklin, J.M., J.M., 1970, 1970, Metallogeny Metallogeny of the the Proterozoic Proterozoic Rocks Rocks of the the Thunder Bay Bay District,Ontario; Ontario;Ph.D. Ph.D.Thesis, Thesis,Western I~estern University, University,London, London, Ontario, Ontario, District, 17 3- 175. pp. 173-175. 71. �GROUNDWATER WATERGEOCHEMISTRY GEOCHEMISTRYASASAN ANAID AID TO GROUND TO GEOLOGIC GEOLOGIC MAPPING OF DRIFT-COVERED MAPPING OF DRIFT-COVERED AREAS: AREAS: TEST TEST CASES CASES ININWESTERN WESTERN MINNESOTA MINNESOTA D.L. and R.S. R.S. Lively Lively D.L. Southwick Southwick and Minnesota Survey Minnesota Geological Geological Survey St. Paul Paul,, Minnesota 55108 Ground water anomaly anomalymaps mapshave havebeen been used decadesasastools tools for for Ground water used forfordecades mineral mineral exploration. In conjunction conjunction with withregional regionalgeophysical geophysicalmaps maps and and whatever direct direct subsurface data are variwhatever subsurface data are available, available,maps maps of of geochemical geochemical variations also appear to be be useful useful for determining ations in in ground ground water water also appear to determining structural structural and lithologic trends beneathglacial glacialdrift. drift. Contoured maps and lithologic trends in in bed bed rock rock beneath maps of alkalinity, alkalinity,specific specific conductivity, dissolved oxygen,and anddissolved dissolved conductivity, dissolved oxygen, radon in ground ground water can be modest cost from from data data radon water can be made madeatatrelatively relatively modest fieldequipment. equipment. Other geochemical geochemical species species such such acquired portable field acquired with with portable as helium, helium, the the metals, metals, and and sulfate sulfate are as are useful useful also, also, but but have have the the disaddisadanalysis. vantage vantageof of requiring requiring laboratory analysis. Because between ground-water ground-water geochemistry geochemistry Becausethe the complex complexrelationship relationship between and bed bedrock rockinvolves involvesgeologic geologicand andhydrologic hydrologic variables thatare aredifficult difficult and variables that to assess, interpretation interpretationofofground-water ground-watergeochemical geochemical maps maps isis rarely to assess, factorsinin interpretation are straightforward. Significant poorly poorly known known factors are drift thickness, thickness, drift drift driftcomposition, composition, and and the the degree degree of hydrologic hydrologic interconinterconHowever,the the coincidence coincidence in in trend nection between drift and bed bed rock. rock. However, trend nection between drift and observed partsofofwestern westernMinnesota Minnesotabetween betweengeochemical geochemical anomalies anomalies and and observed in in parts geophysical anomalies, and, and, less lesscommonly, commonly, between between geochemical geochemical anomalies anomalies geophysical anomalies, and mapped on the and mappedgeologic geologiccontacts contactsstrongly strongly suggest suggest bedrock bedrock influence influence on details of of this influence hydrogeochemical system. The The details influence warrant vlarrant further hydrogeochemical system. investigation and we we intend to to study study the thehydrogeochemical hydrogeochemical interactions investigation and interactions amongground ground water, rock, drift, especially especially as as they they apply among water, bedbed rock, andand drift, apply to the the manyimportant important questions questions remain, distribution radiumand and radon. radon. Though Though many remain, distribution ofofradium maps ofof geochemical help maps geochemicalvariations variationsinin ground groundwater waterhave havethe thepotential potential to help with the the vexing vexing problem problem of of mapping mapping bed bedrock rock beneath beneaththe thevast vast drift-covered drift-covered tracts tracts ofofthe thesouthern southern Lake Lake Superior Superior region. region. 72. �INDEX E.I.,E.I., Luther, F.R., THE PRECAMBRIAN WATERLOO QUARTZ— Brandon, C.N., C.N.,Smith, Smith, Luther, F.R., THE PRECAMBRIAN WATERLOO QUARTZITE, SOUTHEASTERN ANDSIGNIFICANCE, SIGNIFICANCE,p.p. 17. ITE, SOUTHEASTERN WISCONSIN: WISCONSIN: EVOLUTION EVOLUTION AND Brown, B.E., B.E.,Greenberg, Greenberg, GEOLOGIC MAPPING IN NORTHEASTERNWISCONSIN: WISCONSIN: J.K.,J.K., GEOLOGIC MAPPING IN NORTHEASTERN AN (poster 65 AN UPDATE UPDATE (posterpaper), paper), p. p. 65 Cannon, W. W. F., F.,Mudrey MudreyJr.,Jr., M.G., WHERE IS THE SOURCEOFOFWISCONSIN WISCONSIN DRIFT DRIFT M.G., WHERE IS THE SOURCE DIAMONDS?, p. p. 21 DIAMONDS?, 21 Chandler, CORRELATION OF OF GRAVITY AND MAGNETIC Chandler,V.W, V.W., CORRELATION GRAVITY AND MAGNETICANOMALIES ANOMALIES ININEAST-CENTRAL EAST-CENTRAL MINNESOTA WISCONSIN, 22 MINNESOTA AND AND NORTHWESTERN NORTHWESTERN WISCONSIN,p.p. 22 Chandler, V.W., W.J., O'Hara, N.W.,N.W., LONGLONG WAVELENGTH V.W.,Boman, Boman, P.L., P.L.,Hinze, Hinze, W.J., OIHara, WAVELENGTH GRAVITY AND 42 GRAVITY AND MAGNETIC MAGNETICANOMALIES ANOMALIESOFOFTHE THELAKE LAKESUPERIOR SUPERIORREGION, REGION,p.p. 42 Coker, J.M., REGIONAL GEOCHEMISTRY AND AND METALLOGENY Coker, W.B., W.B.,Franklin, Franklin, J.M., REGIONAL GEOCHEMISTRY METALLOGENYNORTH NORTH SHORE 60 SHOREOF OFLAKE LAKESUPERIOR, SUPERIOR,ONTARIO, ONTARIO,p.p. 60 GEOCHEMISTRY Cummings, M.L., M.L., GEOCHEMISTRYAND ANDVOLCANIC VOLCANICSTRATIGRAPHY STRATIGRAPHY OF OFWEST-CENTRAL WEST-CENTRAL MARINETTE COUNTY, 20 MARINETTE COUNTY,WISCONSIN, WISCONSIN,p. p. 20 VOLCANIC Cummings, M.L., M.L., VOLCANICAND ANDPLUTONIC PLUTONICROCKS ROCKSOFOFTHE THEJUMP JUMPAND ANDYELLOW YELLOW RIVER RIVER RIVER VALLEYS, NORTH-CENTRAL WISCONSIN, p. 25 RIVER VALLEYS, NORTH-CENTRAL WISCONSIN, p. 25 Daniels, Elmore, D.R.,D.R., DEPOSITIONAL SETTING OF STROMATOLITE-OOLITE Daniels,P.A., P.A., Elmore, DEPOSITIONAL SETTING OF STROMATOLITE-OOLITE FACIES KEWEENAWAN ALLUVIAL FAN, FACIES ON ON A A KEWEENAWAN ALLUVIAL FAN,p.p. 27 Davidson Jr., Jr., GEOLOGICAL EVIDENCE RELATINGTOTOTHE THEINTERPRETATION INTERPRETATION OF OF Davidson D.M.D.M. GEOLOGICAL EVIDENCE RELAT:[NG THE LAKE THE LAKE SUPERIOR SUPERIOR BASIN BASIN STRUCTURE, STRUCTURE, p. 32 p. 32 Ernst, Ernst,T.,T., Markert, Markert, J., Montz, J., Montz, M., HEAVY M., HEAVY MINERAL MINERAL ANALYSIS ANALYSIS OF PRECAMBRIAN OF PRECAMBRIAN ROCKSININ RUSK RUSKCOUNTY*, COUNTY*,p.p. 26 ROCKS 26 Ervin, C.P., Tuftee, K., ANALYSIS OF A OF NEW GRAVITY MAP FOR Ervin, C.P., Tuftee, K., ANALYSIS A NEW GRAVITY MAP FORTHE THEMERRILLMERRILLRHINELANDER AREA, WISCONSIN (poster 66 RHINELANDER AREA, WISCONSIN (poster paper), paper) , p. p. 66 Evans, T.J., Mudrey Jr.,Jr., M.G.,M.G., WISCONSIN Evans, T.J.,Greenberg, Greenberg,J.K., J.K., Mudrey WISCONSININTEREST INTEREST IN IN RADIOLOGICAL IMPACTS RESULTING RESULTING FROM FROM URANIUM 64 RADIOLOGICAL IMPACTS URANIUM EXPLORATIONS EXPLORATIONS(DRILLING) (DRILLING) ,, p. 64 D., Lee, R., Woodard, H., GEOLOGY OF THE SOUTHEASTERN Fleming, A., A.,Heinz, Heinz, D., Lee, R., Woodard, H., GEOLOGY OF THE SOUTHEASTERN CONTACTZONE ZONEOFOFTHE THEVERMILION VERMILIONBATHOLITH, BATHOLITH,MINNESOTA*, MINNESOTA*, p. p. 15 CONTACT Goodge, J.W., J.W.,MIGMATITES MIGMATITESFROM FROM THE THE VERMILION VERMILION GRANITIC GRANITIC COMPLEX, COMPLEX, MINNESOTA*, Goodge, MINNESOTA*,p.p. 13 13 Green, J.C., KEWEENAWAN Green, J.C., KEWEENAWANVOLCANISM VOLCANISMAND ANDTHE THENATURE NATUREOFOFKEWEENAWAN KEWEENAWAN RIFT RIFT TECTONICS, p.p. 35 35 TECTONICS, Greenberg, J.K., URANILIM Greenberg, J.K., URANIUMPROVINCES: PROVINCES: RELATIONS TOWISCONSIN, WISCONSIN,p.p. 59 RELATIONS TO 59 ENRICHMENTIN IN GRANITIC ENRICHMENT GRANITIC ROCKS ROCKS AND AND Grundi, T.J., Jr.,Jr., E.C.,E.C., Gilkeson, R.H., STABLE ISOTOPE TRACER Grundl, T.J.,Perry Perry Gilkeson, R.H., STABLE ISOTOPE TRACER STUDIES THE CAMBRO-ORDOVICIAN CAMBRO-ORDOVICIAN AQUIFER OF OF NORTHERN ILLINOIS*, p. . 50 50 STUDIES IN IN THE AQUIFER NORTHERN ILINOIS*, Halls, Pesonen, L.J., PALEOMAGNETISM KEWEENAWAN ROCKS, 49 Halls, J. ~. C., C., Pesonen, L.J., PALEOMAGNETISM OF OF KEWEENAWAN ROCKS p. p. 49 *Student paper paper 73. �Hinze, W.J., W.J.,Wold, Wold, O'Hara, N.W., GRAVITY AND MAGNETIC ANOMALYSTUDIES STUDIES Hinze, R.J.,R.J., O'Hara, N.W., GRAVITY AND MAGNETIC ANOMALY OF LAKE LAKE'SUPERIOR, 40 OF SUPERIOR,p. p. 40 Johnson, 4Johnson,A., A., Parker, B., B.,Snider, Snider,0., D., VanVan Alstine, Alstine, 3., PETROLOGY J., PETROLOGY OFOF THE THEBEAR BEAR LAKE LAKE INTRUSIVE, INTRUSIVE, KEWEENAW KEWEENAW PENINSULA, PENINSULA, MICHIGAN MICHIGAN (poster (poster paper), paper),p.p. 67 Jones, N.W., PETROLOGYOFOFSOME SOMELOGAN LOGAN DIABASE DIABASE SILLS SILLSFROM FROMCOOK COOK COUNTY, COUNTY, Jones, NW., PETROLOGY MINNESOTA, p.p. 29 29 MINNESOTA, J.H., Bernardin, Bernardin, M.P., M.P., Meyer, Meyer, R.P., R.P., Bengtson, Bengtson, M.E., H.C., Karl, 3.H., M.E., Halls, H.C., GEOPHYSICAL GEOPHYSICAL STUDIES STUDIESOFOFTHE THESLATE SLATEISLANDS, ISLANDS,LAKE LAKESUPERIOR, SUPERIOR,p. p. 47 47 Keh1enbeck, Kehlenbeck, M.M., M.M., REGIONAL REGIONAL STRUCTURE, STRUCTURE, METAMORPHISM METAMORPHISM AND AND STRATIGRAPHY STRATIGRAPHY OF OF THE THE QLIETICO GNEISSBELT, BELT, THUNDER THUNDERBAY, BAY,ONTARIO, ONTARIO,p. p. 10 QUETICO GNEISS 10 Kelley, Kelley,L.I., L.1., Karner, Karner, F.R., KAOLINITIC F.R., KAOLINITIC WEATHERING WEATHERING ZONEZONE ON PRECAMBRIAN ON PRECAMBRIAN BASEMENT OF OF SOUTHEASTERN NORTHDAKOTA DAKOTAAND ANDWESTERN WESTERNMINNESOTA*, MINNESOTA*, p. 51 BASEMENT SOUTHEASTERN NORTH 51 K1asner, J.S.,Cannon, Cannon,W.F., W.F.,Van VanSchmus, Schmus, W.R. W.R.,, THE THE PRE-KEWEENAWAN PRE-KEWEENAWAN TECTONIC TECTONIC Kiasner, J.S., HISTORY HISTORY OF OF THE THE NORTH-CENTRAL NORTH-CENTRAL UNITED UNITED STATES STATES AND AND CENTRAL CENTRAL CANADA CANADA AND AND HOW FORMATION THE MID-CONTINENT RIFT,p.p. 33 HOW ITIT INFLUENCED INFLUENCED FORMATION OFOFTHE MID-CONTINENT RIFT, 33 LaBerge, WERE THERE TWO LaBerge,G.L., G.L., WERE THERE TWOMIDDLE MIDDLEPRECAMBRIAN PRECAMBRIAN OROGENIES OROGENIES IN THE THE LAKE LAKE SUPERIOR REGION?,p.p. 24 SUPERIOR REGION?, 24 Lucko, W.M., S.A.,S.A., THE PEGMATITES OF OF THE W.M.,Kissin, Kissin, THE PEGMATITES THEQUETICO QUETICOGNEISS GNEISS BELT, BELT, NORTHWESTERN ONTARIO THEIR URANIUM POTENTIAL*,p.p. 55 NORTHWESTERN ONTARIO ANDAND THEIR URANIUM POTENTIAL*, Luetgert, J.H., Meyer, SEISMIC REFRACTION STUDIES LAKESUPERIOR SUPERIOR Luetgert, J.H., Meyer, R.P.,R.P., SEISMIC REFRACTION STUDIES OFOF LAKE CRUSTAL CRUSTALSTRUCTURE, STRUCTURE,p.p. 44 Maass, R.S., R.S.,Medaris Medaris METAVOLCANIC ROCKSATATEAU EAUCLAIRE CLAIRE DELLS, DELLS, Maass, Jr.,Jr., L.G., L.G., METAVOLCANIC ROCKS MARATHON COUNTY, ZONE II HYPOTHESIS HYPOTHESIS IN IN MARATHON COUNTY,AND ANDANANEVALUATION EVALUATIONOF OFTHE THE IISHEAR 'SHEAR ZONE" WISCONS:N*, WISCONSIN*, p.p. 23 23 Maass, L.G., Van Schrnus, W.R., ARCHEAN Maass, R.S., R.S., Meclaris MedarisJr., Jr., L.G., Van Schmus, W.R., ARCHEANAND ANDEARLY EARLY 11 PROTEROZOIC p. 11 PROTEROZOICTECTONIC TECTONICHISTORY HISTORYOF OF NORTH-CENTRAL NORTH-CENTRALWISCONSIN*, WISCONSIN*, p. J.S., Motten, GEOLOGY OF MCCASLIN THE MCCASLIN RANGE, NORTHEASTERN Mancuso, J.S., Motten, R.H., R.H., GEOLOGY OF THE RANGE, NORTHEASTERN WISCONSIN, p. 62 WISCONSIN p. 62 Brown, B.E.,B.E., LAKE LAKE SUPERIOR REDRED CLAY MINERALOGY: Mengel, J.T., J.T., Brown, SUPERIOR CLAY MINERALOGY: WITH MECHANICAL MECHANICAL BEHAVIOR, WITH BEHAVIOR,p.p. 48 CORRELATION G.B.,Bergstrom, Bergstrom, THE COSUNA PROJECT - A NEW CORRELATIONCHART CHART Morey, G.B., 0.3., D.J., THE COSUNA PROJECT - A NEW CORRELATION FOR THE THE NORTHERN NORTHERN MID-CONTINENT REGION (posterpaper), paper), p. FOR MID-CONTINENT REGION (poster 68 p. 68 Morton, DIFFERENTIATING ULTRAMAFIC FLOWS THETHE SHEBANDOWAN Morton,P.,P., DIFFERENTIATING ULTRAMAFIC FLOWSFROM FROMSILLS SILLSIN IN SHEBANDOWAN MINE AREA, ONTARIO, CANADA*, MINE AREA, NORTHWESTERN NORTH~ESTERN ONTARIO, CANADA*, p. 31 31 p. RELATIONSHIP OF Mursky, Mursky, G. G.,, RELATIONSHIP OF CANADIAN CANADIAN URANIUM URANIUM DEPOSITS DEPOSITS TO TO THE THE GEOLOGIC GEOLOGIC SETTING SETTING OF OF WISCONSIN, WISCONSIN, p. 56 p. 56 *Student paper paper 74. �Ojakangas, Ka1liokoski,J.,J., UPPER Ojakangas,R.W., R.W.,Morey, Morey,G.B., GB., Daniels, Daniels, P.A., P.A., Kalliokoski, UPPER PRECAMBRIAN ROCKS OF OF THETHE LAKE SUPERIOR REGION, p.p. 37 PRECAMBRIANSEDIMENTARY SEDIMENTARY ROCKS LAKE SUPERIOR REGION, 37 Petro, W.L., MINERALOGYAND ANDCHEMISTRY CHEMISTRY OF OF MIDDLE MIDDLE PRECAMBRIAN PRECAMBRIAN (Xg) GRANITIC Petro, W.L., MINERALOGY (Xg) GRANITIC PLUTONIC ROCKS FROM NORTHERN WISCONSIN* (poster paper), PLUTONIC ROCKS FROM NORTHERN WISCONSIN* (poster paper),p.p. 70 Poulsen,K.H., K.H., Keh1enbeck, OVERTURNED ARCHEAN SUCCESSIONS AND AND THEIR THEIR Paulsen, Kehienbeck, M.M., M.M., OVERTURNED ARCHEAN SUCCESSIONS SIGNIFICANCE, 16 SIGNIFICANCE, p. p. 16 Rehf1edt, W.R., HYDROGEOLOGIC INVESTIGATIONS INVESTIGATIONS AT LANDFILL SITE IN INTHE THE RED RED Rehfledt, W.R., HYDROGEOLOGIC AT A A LANDFILL TILL (VALDERAN) (VALDERAN) REGION REGION OF OF EASTERN EASTERN WISCONSIN, 53 TILL WISCONSIN,p. p. 53 Scofield, Scofield, N.,N., METALLIC METALLICMINERALS MINERALS OF OF SILVER SILVER ISLET, ISLET, LAKE LAKE SUPERIOR SUPERIOR (poster (posterpaper), paper), p. p. 71 71 Shege1ski, R.J., STRATIGRAPHY GUNFLINT FORMATION,CURRENT CURRENT RIVER RIVER AREA, AREA, Shegeiski, R.J., STRATIGRAPHY OF OF THETHE GUNFLINT FORMATION, THUNDER BAY, p. THUNDER p. 28 28 Smith, E.I., RARE EARTH ELEMENT THETHE PRECAMBRIAN Smith, E.I., RARE EARTH ELEMENTDISTRIBUTION DISTRIBUTIONIN IN PRECAMBRIANRHYOLITES RHYOLITES AND GRANITES GRANITES OF OF SOUTH-CENTRAL SOUTH-CENTRAL WISCONSIN,p.p. 19 AND WISCONSIN, Southwick, Lively, R.S., GROUND WATER GEOCHEMISTRY Southwick,D.L., D.L., Lively, R.S., GROUND WATER GEOCHEMISTRY AS AS AN AN AID AID TO TO GEOLOGIC DRIFT-COVERED AREAS: AREAS: GEOLOGIC MAPPING MAPPING OF OF DRIFT-COVERED MINNESOTA (poster 72 MINNESOTA (posterpaper), paper), p. p. 72 TEST CASES TEST CASES ININWESTERN WESTERN Van Van De De Voorde, Voorde,B.,B., Ervin, Ervin, P., GEOPHYSICAL P., GEOPHYSICAL STUDY STUDY OF AOFPRECAMBRIAN A PRECAMBRIANBOUNDARY BOUNDARY :[N IN MINNESOTA*,p. p. 99 MINNESOTA*, Van Schmus, Schmus, W.,R., W.R., Green, Green,J.C., J.C., H.C., GEOCHRONOLOGY OF KEWEENAWAN Van Halls,Halls, H.C., GEOCHRONOLOGY OF KEWEENAWAN ROCKS: ROCKS: A REVIEW, REVIEW, p. 39 A p. 39 Vick,T.D., T.D., SEISMIC SURVEYOF OF AABURIED BURIED RIVER RIVER CHANNEL, CHANNEL, p.p. 54 54 Vick, SEISMIC SURVEY Hutchinson, D.R., Johnson, T.C., T.C., TOPOGRAPHY ANDAND SURFICIAL STRUCTURE Wold, R.J.,, Hutchinson, D.R., Johnson, TOPOGRAPHY SURFICIAL STRUCTURE Wold, R.J. OF LAKE SUPERIOR SUPERIOR BEDROCK ONONSEISMIC 45 OF LAKE BEDROCKBASED BASED SEISMICREFLECTION REFLECTIONPROFILES, PROFILES,p.p. 45 *Student paper paper 75. � https://digitalcollections.lakeheadu.ca/files/original/f7ae80e1a840559c070a2a1da82925c6.pdf da285056eb25e07a79f0e273fc6f4f63 PDF Text Text 26th 2 6th Annual InstitUteon on Lake Lake Superior SuperiorGeology Geology Institute FIELD TRIP TRIP 1 FIELD 1 Precambrian Geology Geology of the Ohippewa Valley, Chippewa Valley Wisconsin Wisconsin GENERALIZED PRECAMBRIAN GEOLOGY OF THE EAU CLAIRE REGION gO - Di abase I...,! I-,, • I, Gabbro to+ Tonolite tr Trandhjemite I','—,— Volcanics and sediments Amphibolites 4 Shear zone May May 6-7, 1980 1980 Universily Claire University of Wisconsin-Eau Wisconsin-Eau Claire —— - - - — — �PRECAMBRIAN GEOLOGY GEOLOGYOF OF THE THE CHIPPEWA PRECAMBRIAN CHIPPEWA VALLEY VALLEY FIELD GUIDE GUIDE P. E. E. Myers, R. Wurdinger M. L. L.Cummings, C m i n g s , and and S. S. R. Wurdinger P. Myers, M. Prepared ffor Prepared or Twenty-Sixth Annual Twenty-Sixth Annual Meeting Meeting INSTITUTE ON INSTITUTE ON LAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY University of Claire University o fWisconsin-Eau Wisconsin-Eau C laire Eau CClaire, Eau l a i r e , Wisconsin Wisconsin May 6—11, 1980 �26th ANNUAL 26th ANNUAL INSTITUTE INSTITUTEON ONLAKE LAKESUPERIOR SULLRLORGEOLOGY GEOLOGY FIELD TRIP #1 #I May May 6—7, 6-7, 1980 1980 STOP STOP + - DAY DAY Dies. Tues. 5/6 516 LOCATION LOCATION LEADER LEADER SUBJECTS SUBJECTS PAGE PAGE 1 Big B i g FFalls alls Cummings C mings Geochemistryand andPetrology Petrology ooff Geochemistry metamorphosed, layered mtamrphosed, layered gabbros gabbros deformational hhistory deformational istory 23 !3 22 Little L i t t l e Falls Falls Myers Myers Tonalitic T o n a l i t i c intrusion i n t r u s i o n breccia breccia 35 35 3 3 Confluence, Confluence, N. N. Side Side Myers Myers Amphibolite-volcãnic Amphibolite-volcanic contact contact 45 44 Knight Knight Pool Myers Myers Metabasalts, i l l o w breccias(?) b Metabasal t s , ppillow 55 55 Rock Rock Dam Dam Myers Myers Mylonitized rhyol ite 59 59 66 County County Hwy Hwy MM Myers Myers Metasediments. 63 7 7 Confluence, Confluence, S. S. Side Side Myers Myers Younger(?) and volcanics volcanics Younger(?) sediments sediments and 47 88 "Big Bend" Bend" Yellow Yellow River River Myers Myers Cataclastic "dikes" in metadiorite Catacl 67 67 9 9 Cadott Cadott Bridge Bridge Myers Nyers Cataclasis—intrusion—folding Cataclasis-intrusion-folding sequence; multiple sequence; mu1 t i p l e deformations deformations 71 71 75 75 RETURN EAU CLAIRE RETURN TTO O EAU CLAIRE Wed. Wed. 10 10 Wissota WissotaDam Dam Myers Myers IIntrusion n t r u s i o nsequence: sequence: trondh,jemitetrondhjemitetonalite—pegmatite—diabase, etc. etc. tonalite-pegmatite-diabase, 11 11 Jim Jim Falls Falls Myers Myers Amphibolite—granite contacts, Amphi bol ite-grani t e contacts, shearing, cataclasis, cataclasis, folding shearing, folding 5/7 517 12 12 Cornell Cornel 1Dam Dam Myers Myers 13 13 Fisher River River 14 14 81 Relations between Relations between garnet garnet amphiboamphibolite l i t eand andflaser f l a s e rgneisses gneisses 89 89 Myers Myers Tectonic Tectonic oorr Intrusion(?) breccia breccia 93 Holcombe Hol combeDam Dam Wurdingér Wurdinger Intrusion-deformation Intrusion-deformationsequence sequence 97 15 15 Shoulder Shoulder Creek Creek Cummings Cumings Intermediate andf felsic Intermediate and e l s i c volcanics vol canics 1133 11 16 16 Jump River (N. (N. Side) Side) Cuttinings Cumings Jump River ~ntermediatefragmental fragmental volcanics volcanics Intermediate 115 115 17 17 Jump River: Hwy Jump River: Hwy 73 73 Cumnings Cumi ngs Contact metamorphism o foff efelsite lsite Contact metamorphism 117 117 18 18 Sec. Sec. 22, 22,T33N, T 3 3 ,R4W R4W Cumnings Cummings Intermediate c rcrystal-lithic y s t a l - l i t h i c ttuff uff Intermediate 119 119 . * Not Not aall l l of o f the the stops stops described h i s guidebook guidebook w will i l l be i s i t e d . Their inclusion describedi nin tthis be vvisited. inclusion is i s to t opermit permit the theuse use of o fthis t h i sguidebook guidebook after a f t e rthe theconference. conference. , ,,~ >... ,. ..-,',,. , ~,?:.;! L �—1— PRECAMBRIAN GEOLOGY OF THE CHIPPEWA VALLEY - AN INTRODUCTION P. E. Myers Exposures of Precambrian Exposures of Precambrian rocks ini nwest—central west-central Wisconsin Wisconsin are confined confined mainly Valleyand andi tits majort tributaries, mainly to t o the the Chippewa Chippewa Valley s major r i b u t a r i e s , the Yellow, Yellow, Jump, Jump, and Eau Claire rivers, which drain the southwestern and Eau C l a i r e r i v e r s , which d r a i n the southwestern edge edge ooff the the Canadian Canadian Shield Shield in i nWisconsin. Wisconsin. From the Eau Claire dips southFrom the Eau C l a i r e area, area, the thePrecambrian Precambrian basement basement dips south- west west at a t 10 10 feet feet per permile m i l ebeneath beneath aa thickening thickening cover cover of o f lower lowerPaleozoic Paleozoicsandsandstones, shales, and.carbonates. stones, shales, and carbonates. To To the north north and and east, east, the thePrecambrian Precambrian rocks rocks are are overlain o v e r l a i nby byglacial g l a c i adeposits l depositsand andoccasional occasionaloutliers o u t l i e rof s oCambrian f Cambriansandstone. sandstone. Owing outcrop and and sstructural Owing tto o sparseness sparseness oof f outcrop t r u c t u r a l complexity complexity of o f the the rocks, rocks, traditional traditional mapping methods have proven inadequate. mapping methods have proven inadequate. However, However, aaf fair a i r approximation approximation ooff the the regional regional geology geologyhas hasbeen been gained gain through a combination of detailed studies of outcrops outcrops with w i t hpetrographic petrographicand andgeochemical analyses, aeromagnetic and gravity mapping and radiometric radiometric dating. mapping and dating Following of the region by Dutton, I began field Following iinitial n i t i areconnaissance l reconna work with the major problems and working out the work w i t h the the objective o b j e c t i v eofo defining f def geologic geologic history h i s t o r yofo fthe theregion. regionSubsequent publication of Dutton and Bradley's geologic northern Wisc Wisconsin (1970) provided a starting point. Additional geologic maps maps oof f northern specialized specialized studies studiesby bystudents student (Cumings, 1974, 1975, 1978), Maercklein (1974), Piotruscewicz (1979) have greatly accelerated the study (19781, and and Wurdinger kiurd Piotruscewicz (1978), of o f the the region. region. This This guidebook guidebook i is s aa synthesis synthesis ooff available available information information on on the the Precambrian supplementary information Precambrian hhistory i s t o r y of o fthe theChippewa Chippewa Valley. Valley. Relevant, Relevant, supplementary information isi sdrawn Anderson, drawnfrom f r o mimportant importantworks worksbyby Anderson,Van VanSchrnus, Schmus, and and Medaris Medaris (1975), (1975), LaBerge LaBerge (1972, (1972, 1980), 1980),Maass, Maass, Medaris, k d a r i s ,and andVan VanSchmus Schmus (1980), (1980),Maass Maassand andVan Van Schmus Schmus (1980), (1980), Sims Van S i n s (1976), (l976), Smith Smith(1978), (19781,and and VanSchmus Schmus (1974, (1974, 1976 1976 ,, 1980). 1980). Aeromagnetic mapsbybyKarl Karl and and Friedel Friedel (1974-1976) and by by United United States Steel Aeromagnetic maps (1974-1976) and Steel Corp. Corp. (1973) (1973) and and Bouguer Bouguer ggravity r a v i t ymaps maps by by Ervin Ervinand and Hamer Hanrner (1974) (1974)have havebeen been most most useful useful in between i ninterpolating i n t e r p o l a t i ncontacts g contacts betweenwidely widelyseparated separatedoutcrops. outcrops. The The geologic geologic map map presented presented in i n Figure Figure 1is i saa"best "bestapproximation" approximation" of o f the the Precambrian rock uunits Precambrian rock. rock units u n i t sini nthe theChippewa Chippewa Valley. Valley. The The rock n i t s are are ttypically ypically heterogeneous, sot hthat generalize uunits was necessary necessary t to o generalize n i t s by selecting the the heterogeneous, so a t iittwas predominant predominant unit. unit. Its I t spurpose purpose is i s to t oportray portraybroad broad regional regional patterns patterns of o frock rock distribution. d i s t r i b u t i o n . Quality.of geologicinformation informationgenerally generallydiminishes diminishesaway away from fro Qua1i t y o fgeologic the the rivers. rivers. 1 It is emphasized that the interpretations and conclusions in this guidebook are tentative, It is our hope that you will assist us in clarifying the history of these phenomenally complicated rocks. The geologic map (Figure 1) also shows stop locations. Those in parentheses. are optional, ut are included because of their relevance. You are encouvaied to stay and continue your field trip after the conference or to return to Eau Claire soon with your own field trip. t r i p .There Thereremains remains aa large l a r g enumber number oof f tthesis h e s i and dissertation topics. I may be able able to t o assist a s s i s tyou you in i nthe theselection selectionofo fone. one �—2— ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS - We areindebted indebtedt oto the the U University EauCClaire M e are n i v e r s i t y of-Wisconsin Of .Wisconsin — Eau l a i r e ffor o r general general Undertwo tworesearch researchgrants, grants,t hthe sponsorshipooff this e UUniversity n i v e r s i t y aalso lso sponsorship t h i s conference. conference. Under provided M. M. L. L. Cummings Cummings w iwith t h s sumer u m r f ifield e l d and and lab l a b assistants, assistants, and andP.E. P.E. Myers Myers provided chemicalanalyses analysesand andt hthin sections Of of 50 The Wisconsin Wisconsin Geological and 50 rocks. rocks. The chemical i n sections and Natural H History assistedUSusgreatly, greatly, both both through throught htheir e i r pprovision r o v i s i o n of of Natural i s t o r y Survey Survey assisted time, base maps asas well encouragement tthin h i n sections, sections,probe probeanalysis analysis time, base maps w eas l l much as much encouragement throughoutt the termooff tthe We thank Northern throughout h e term h e project. project. W e thank Northern States StatesPower PowerCompany Company the ffor o r permission permission tto o study study and and vvisit i s i ttheir t h e iproperties r propertiesalong along t h Chippewa e Chippewa River River and ffor as possible, possible, outflow and o r consenting consenting tto o reduce, reduce, as outflow from from reservoirs r e s e r v o i r s during during our our visits Holcombe. v i s i t sataLake t LakeWissota, Wissota, Jim JimFalls, F a l l sand , and Holcombe.The TheUniversity U n i v e r s i t yofoWisconsin— f WisconsinOshkoshand andt hthe generously Fox Valley, Val.ley, Menasha Menasha have have generously Oshkosh e UUniversity n i v e r s i t y of o fWisconsin Wisconsin — Fox allowed us the use of their vehicles for the trip. allowed us t h e use of t h e i r vehicles f o r t h e t r i p . - We thank those those ooff our have ooffered W e eespecially s p e c i a l l y thank o u r colleagues colleagues and and students students who who have ffere suggestionsconcerning concerningo uour ttheir h e i r many many hhelpful e l p f u l ideas ideas and and suggestions r i ninterpretations t e r p r e t a t i o n s ooff the th geologyoof Students, as as wwell geology f tthis h i s region. region. Eau Eau CClaire l a i r e Students, e l l as as students students from from other other universities time,t talent, u n i v e r s i t i e s have have generously generously ccontributed o n t r i b u t e d time, a l e n t , and and ideas ideas tto o our our often often Field Mike Mudrey, Weis, ffrustrating r u s t r a t i n gwork. work. F i e l d trip t r i pdrivers d r i v e rare s are Mike Mudrey,Len Len Weis,Gene GeneLaBerge, LaBerge and A1 Al Sun. NanPickett, Pickett, Penny Hoitomt, and andGGail Wirz devoted devoted l long hours tto t and Sun. Nan Penny Hoitomt, a i l Wirz o n g hours o the preparation of Carlson aassisted o f the t h e guidebook, guidebook, and and Diane Diane Carlson s s i s t e d in i n plotting p l o t t i n geochemical g geochemi data. Many Manystudents, students, past past and and present, present, have beeni ninvolved have been v o l v e d wwith i t h various aspects aspe of field and lab preparations. We thank you all sincerely. o f f i e l d and l a b preparations. We thank you a l l sincerely. �—3— - Precambrianrock rockunits units in Distribution of of major Figure 11 —— Distribution major Precambrian in the theChippewa, Chippewa, Yellow, Jump, and Eau Claire river valleys and their major tributaries Yellow, Jump, and Eau Claire river valleys and their major tributaries as as inferred from inferred fromaastudy studyofofsparse sparseoutcrops outcropsand andfrom fromaeromagnetic aeromagneticmapping. mapping. �-4-4- . - GENERAL GEOLOGY GENERAL GEOLOGY (Myers and andothers, others, 1974) The Precambrian Precambrian "Chippewa "Chippewaamphi amphibolite The bol i t e complex' complex" (Myers 1974) iiss megagneissconsisting consistingofof steeply-dipping, steeply—dipping,lensoidal lensoidal screens, aa megagneiss screens, enclaves, enclaves, and and xenolith and schist xenol it h trains t r a i n sofo amphibolitic f amphi bol i t i gneiss c gneiss and s c h i sembedded t embedded subconcordantly subconcordantly iin n (Figure 11). younger, synkinematic syrrkinematicand andl alate kinematictonal tonalite ). younger, t e kinematic i t e and and trondhjemite trondhjemite (Figure The Chippewa amphibolite complex (CAC) forms the core of an eastward-plunging The Chippewa amphibol i t e complex (CAC) forms the core o f an eastward-pl unging Penokeanorogen, orogen,which whichi is and metamorphosed Penokean s overlain overlaineastward eastwardbybyless l e sdeformed s deformed and metamorphosed volcanic and sedimentary rocks of the Flambeau volcani—sedimentary province ttoo volcanic and sedimentary rocks o f t h e Flambeau volcani-sedimentary province the north and the Black River .volcani-sedimentary province to the southeast. the north and the Black River volcani-sedimentary province t o the southeast. Within the region, these these volcanic volcanic and rocks are are represented Within the Chippewa Chippewa region, and sedimentary sedimentary rocks represented by the South Fork volcanic and sedimentary assemblage in the headwaters by South Fork and sedimentary assemblage i n the headwaters oof f the Eau Claire River and the Jump River volcanic rocks to the northeast. The Eau C l a i r e River and the Jump River volcanic rocks t o the northeast. The block diagram(Figure (Figure2)2)i is a generalized representation ooff the the types diagram s a generalized representation types of o f rocks rocks and and structures occurring occurringi in structures n tthis h i s region. region. This This pattern pattern is i s similar s i m i l a rtot oone oneby by Glikson Glikson (1957, p.p. 21) 21) ffor tonalite-trondhjemitessialic (1957, o r Archean Archean tonalite-trondhjemite i a l i c nuclei, nuclei, which which contain contain attenuatedre1 relics xenoliths. GGlikson's i c s of o f supracrustal supracrustal enclaves enclaves and and xenoliths. I ikson's diagram diagram iiss attenuated included pattern to included (Figure (Figure 3) 3) for f o rcomparison. comparison. Probably Probably the the most most conspicuous conspicuous pattern t o be. be seen on onthe the generalized generalized geologic geologic map the region Z—shaped seen map oof f the region (Figure (Figure1)1)is i the s the 2-shaped pattern produced byamphibol amphibolitic mayrepresent representl alarge plunging ffold pattern produced by i t i c enclaves, enclaves, which which may r g e plunging old remnants. Although Althoughthe the ggranitic r a n i t i c rocks, rocks, as asrepresented represented mainly mainly by by trondhjemite, trondhjemite, tonalite, adamellite, tonal i t e , and and subordinate subordinate adamell i t e , llocally o c a l l y intrude i n t r u d e the t h eamphibolites, amphibol i t e s , the the contacts contacts Cataclasis has hascclearly majorr role comnonly sheared. sheared. Cataclasis l e a r l y played played aa major o l e iin n the the are most most commonly deformation and andmetamorphism metamorphism rocksthroughout throughoutthe theregion regi.onduring duringaat deformation o f of thethe rocks t lleast east catathree major major deforniational d e f o m t i o n a l events, events, one oneofo which f whichwas wasthe thePenokean. Penokean. IIn n the CAC, CAC, cata(1)) bending, crushing, and andl elenticulation bending, crushing, nticulation cclasis l a s i s isi smost mostconspicuously conspicuously manifested manifested by: by: (1 development ooff feldspars feldspars with w i t h simultaneous simultaneous development o f of a cahcharacteristic a r a c t e r i s t i c i ninterlensing t e r l e n s i n g f foliaolia(2) laminar transposition ooff originally ttion. i o n . (2) laminar transposition o r i g i n a l l ydiscordant discordantstructures structuressuch such as as dikes, dikes, dikes, and and xenoliths, xenoliths, into mechanical dikes, i n t o the the plane plane of o f cataclastic c a t a c l a s t i cfOliation, f o l i a t i o n(3) , (3) mechanicalhomohomogenizationooff contiguous contiguousrock rocku nunits withoutr recrystallization, genization i t s wwith i t h oor r without e c r y s t a l l i z a t i o n , (4) (4) detachdetachSince tthe ment andtransposition transpositionoof as ttectonic ment and f ffold o l d fragments fragments as e c t o n i c xenoliths. Since h e proper proper off cataclastic iinterpretation nterpretation o c a t a c l a s t i c features features affects a f f e c t s the the interpretation i n t e r p r e t a t i o n of o f geologic geologic sequence, and andsince since there remains sequence, remains considerable considerable debate debate as as tot othe t h mechanisms, e mechanisms, some some goodexamples examples them have included in several stops (mainly 8-ll). good o f of them have beenbeen included i n several o f tof h ethe stops (mainly #8-11). Whereasthe thevolcanic volcanicrocks rocksoof the Jump JumpRiver Riverarea area(Cunnings, (Cumings, p103) p103)have haveaat Whereas f the t l least east locally been metamorphosed to the lower amphibolite grade, those of the South l o c a l l y been metamorphosed t o the lower amphibolite grade, those o f t h e South Fork Fork area (SFVS) (SFVS)are areo of lowermetamorphic metamorphic grade indicatedbybythe theprevalence prevalence area f lower grade as as indicated of ofc hchlorite, lorite, epidote, River volcanics volcanics (JRV) comprisemainly mainlybbasaltic epidote. and and garnet. garnet. The The Jump Jump River (JRV) comprise a s a l t i c tto o One andesitic flows fragmentalvolcanics volcanicso of andesitict to f andesitic o rrhyolitic h y o l i t i ccomposition. composition. One andesitic flows and and fragmental The higher eruptive center was found in the area just east of the town of Jump River. eruptive center was found i n the area j u s t east o f the town o f Jump River. The metamorphic gradeo fofthe theJRV JRVmay may theproximity proximityt oto the the south metamorphic grade be be duedue t o to the south of o f several several large ggranitic Top iindicators large r a n i t i c plutons. plutons. Top n d i c a t o r s in i n the t h eJRV JRV indicate i n d i c a t e the t h esequence sequence iiss overoverthe JRV rocks wwill i l l be beseen seen turned with w i t h beds beds facing facing (younging) (younging) southward.Examples southward.Examples oof f the JRV rocks att stops a stops 15-18. 15-18. Myers Myersand andothers others(1974) (1974)i identified d e n t i f i e daamajor major geophysical geophysical lineament lineament along the Jump River. Sims andMudrey Mudrey(1978) (1978)placed placeda amajor majorf afault along Jump River. Sims and u l t in i n the t h esame same area. area. Cummings (this Cunnings ( t h i s rreport) e p o r t ) suggests suggests that t h a t the thelineament lineamentsimply simplymarks marksthe theboundary boundarybetween between volcanic rocks rockst to the north north and andg granitic rockst to the south, south, and andt hthat i sprobably probably volcanic o the r a n i t i c rocks o the a t iitt is not a fault SFVS rocks mainly andesitic, andr hrhyolitic not f a u l t zone. zone. The The SFVS rocks areare mainly andesitic, d adacitic, c i t i c , and y o l i t i c pyropyroconglomerates, micaceous eclastics l a s t i c s interstratified i n t e r s t r a t i f i ewith d w i tuffaceous t h tuffaceous conglomerates, phyllites, p h y l l i t e sand , and micaceous quartzites. They They have have been beenr regionally uppergreenschist greenschist facies e g i o n a l l y metamorphosed metamorphosed t otoupper and compressed compressed series ooff open open ffolds and i n into t o a aseries o l d s which which plunge plunge gently east-northeastward. east-northeastward. Except where wherethese theserocks rockshave havebeen beensheared, sheared,primary primaryminerals mineralsand andstructures structuresare are wellwellExcept preserved. These Theserocks rocks wwill preserved. i l l be beseen seen at a tstops stops3—7. 3-7. Although Although bedding bedding within w i t h i nthe theSFVS SFVS unit angles,i its u n i t dips dips at a t moderate moderate angles, t s contact contact (at ( a t stop stop 3) 3) with w i t h amphibolitic amphibolltic and and plutonic plutonic Thebest bestt tentative hypothesisi is rocks of CAC is i saahigh—angle high-angle shear shear zone. zone. The e n t a t i v e hypothesis s tthat hat o f the theGAG �F/atnbeaa P/age /1 0 S c. tr;'J L r.i Trondhjemite Shear zone zone FIGURE FIGURE 22--Volconics and sediments Amphibolites GENERALIZED PRECAMBRIAN PRECAMBRIAN GEOLOGY OF THE THEEAU EAUCLAIRE CLAIREREGION REGION �-6- the.SFVS rocksr rest on aa folded, folded, locally uncon— t h e SFVS rocks e s t on l o c a l l ysheared shearedand andrecrystallized r e c r y s t a l l i z eangular d angular uncon-, formity. more detailed field mapping, petrographic and geochemical formity. Considerably Considerably more d e t a i l e d f i e l d mapping, petrographic and geochemical analyses are needed neededt otowork worko uout and genetic genetic rrelationships analyses are t t hthe e s structural t r u c t u r a l and e l a t i o n s h i p s of o f these these rocks. s clear c l e a r that t h a t this t h i sarea area(stops (stops33and and 7) 7) isi sone oneofo fconsiderable considerable rocks. However, However, i tit iis significance. Whereast hthe amphiboliteswweredeformed and significance. Whereas e amphibolites e r e deformed and r e crecrystallized r y s t a l l i z e d aat t lleast east twice before trondhjemite intrusion (Van m.y.ago ago (VanSchmus, Schmus, 1980) 1980) before tonalite t o n a l i tand e and trondhjemite i n t r u s1842—1830 i o n 1842-1830m.y. The amphibolites andvolcanics volcanicswere weresynkinematically synkinematicallyand andl alate The amphibol i t e s and t e kkinematically inematically intruded by trondhjemite, tonalite, gabbro, and adamellite (quartz intruded by trondhjemite, t o n a l i t e , gabbro, and adamell i t e (quartzmonzonite). monzonite). The mostabundant abundant rock type i sisf afaint1yfoliated i n t l y - f o l i a t e dleucotrondhjemite. leucotrondhjemite. At A t Wissota Wissota The most rock type Dam (Stop# #10) Cadott(Stop (Stop#9), #9),and andFisher FisherRiver River (Stop (Stop#13) #13)t hthe trondhjemite iiss Dam (Stop l o ) Cadott e trondhjemite intruded intruded by by hornblende-biotite hornblende-biotite ttonalite. o n a l i t e . At At other o t h e r localities, l o c a l i t i e s ,however, however, the the reverse trondhjemites and and ttonal reverse relationship r e l a t i o n s h i pcan canbe beobserved. observed. The The trondhjemites o n a l i ites t e s are proprobably Thet otonalites bably coeval coeval and and comagmatic. comagmatic. The n a l i t e s ddisplay i s p l a y closer c l o s e r chemical chemical and and mineralogical mineralogical similarities which s i m i l a r i t i e stot the o t hamphibolites e amphibolitesfrom from whichthey theywere were probably probably derived. derived. The The gabbros formpplug—like intrusions, and and although althoughthey they are are younger youngerthan thant hthe gabbros form l ug-1 i k e intrusions, e t otonalites, nal ites, they beeninvolved involvedi in adamellite #8). The they have have been n ccataclastic a t a c l a s t i c deformation deformation (Stop (Stop #8). The adamellite is with i s complexly complexly iintergradational ntergradational w i t h the t h e trondhjemite trondhjemite and and iin n some some l olocalities c a l i t i e s (e.g. (e.g. North North Fork of Eau Claire River) intrudes the trondhjemite. Like the other granitic Fork o f Eau C l a i r e River) intrudes t h e trondhjemite. L i k e t h e other g r a n i t i c rocks, rocks, however, has also a l s o been been cataclastically c a t a c l a s t i c a l l ydeformed. deformed. however, iitt has Almost regardlessoof Almost regardless f oolder l d e r structures, structures, granite g r a n i t epegmatite pegmatite dikes, dikes, usually usual 1y concontaining along aa ppersistent garnet were were iintruded n t r u d e d along e r s i s t e n t east-northeast-northt a i n i n g biotite b i o t i t eand andmuscovite muscovite ++ garnet east east trend t r e n d as as exemplified exemplified aatt Little L i t t l Falls, e F a l l sWissota , WissotaDam, Dam, and and Jim Jim Falls F a l l s as as well w e l l as as many otherplaces. places.Many Manyo foft hthe dikes are are texturally many other e l alarger r g e r dikes t e x t u r a l l yand andcompositionally compositionallyzoned zoned with w i t h quartz quartz cores. cores. At Jim Jim Falls F a l l s(Stop (Stop11—A) 11-A) the t h e pegmatite pegmatite dike d i k e contains containsen enechelon echelon quartz veins as as gash gashf rfracture quartz veins a c t u r e f fillings. i l l i n g s . Microcline Microcline crystals c r y s t a l sini nthese thesedikes dikeshave have been severely bent, broken, and lenticulated. At several locations the dikes been severely bent, broken, and l e n t i c u l a t e d . A t several l o c a t i o n s t h e dikes have beencompletely completely truncated truncated by shearing. Falls have been shearing. At At Jim Jim F a l l s at a t least l e a s t three t h r e e ages ages of of pegmatite pegmatite iintrusion n t r u s i o n can can be be seen. seen. The The older o l d e r dikes dikes are areboudinaged boudinaged in i n the t h e compositional compositional layering pegmatite dikes dikes have been ooffset l a y e r i n g of o fthe t h ebanded banded amphibolite amphibolite host host rock. rock. The The pegmatite have been ffset by Precambrian by north-northwest-trending north-northwest-trending faults f a u l t sofo Late f Late Precambrian age. age. Late Precambrian gabbro—diabase dikes rockswwith Precambrian gabbro-diabase dikes c u t cut a l lallt hthe e o other t h e r rocks i t h strong disdiscordance. chilled (Stop 10) 10) iindicate cordance. Their l e d margins margins (Stop n d i c a t e shallow shallow intrusion intrusion T h e i r conspicuously conspicuously chi1 after The a f t e r aaprolonged prolonged erosional erosional interval i n t e r v a l(1600-1100 (1600-1100 m.y.). my.). The dike d i k e at a tWissota WissotaDam Dam contains large, partially resorbed fragments very coarse—grained contains p a r t i a l l y resorbed fragmentsofo labradorite f l a b r a d o r i tand e and very coarse-grained norite. n o r i t e . This This dike d i k e is i sintruded intrudedby byaathin t h i nleucotrondhjemite leucotrondhjemite dike, dike, which which displays d i s p l a y san an unusual type of crush texture where it is involved in a small fault zone. unusual type o f crush t e x t u r e where i t i s involved i n a small f a u l t zone. The basement was deeply saprolitized (Cumings and and Scrivner, 1980) The Precambrian Precambrian basement was deep1 y saprol i t i z e d (Cutmnings 1980) in timewwith formationooff kkaolinite—rich i n Late Late Precambrian Precambrian time i t h formation a o l i n i t e - r i c h ssoils. o i l s . A distinctive distinctive illitic clay rocks(as (asseen seen i l l i t green i c green c l adeveloped y developedon onthe t h ehornblende—rich hornblende-rich rocks a tatL Little i t t l e Falls). Falls). The clays form markeras ast the EauCClaire River repeatedly crosses The clays form a conspicuous conspicuous marker h e Eau l a i r e River crosses the the unconformity Lak Eau Eau CClaire M t . Simon Simon unconformity between between Lak l a i r e and and Lake Lake Altoona. Altoona. Late LateCambrian Cambrian Mt. Sandstone, which ooverlies knob— Sandstone, which v e r l i e s the t h ePrecambrian Precambrian rocks, rocks, occurs occursabundantly abundantlyasasridge r i d gand e and knobshaped shaped ooutliers u t l i e r s throughout throughout the t h eChippewa Chippewa Valley region. region. Clay Clay and and feldspar content content decrease upwardi nint the formation owing owing tto decrease upward h e formation o reworking reworking of o f the t h esands. sands. Glacial till andand outwash till outwashofot.he f t h Chippewa e Chippewa lobe l o b eofo Wisconsin f Wisconsin glaciers g l a c i e r sare areexposed exposed in Valleynortheast northeasto fofEau Eau Claire.AtAtL Little i n the t h e Chippewa Chippewa Valley Claire. i t t l e Falls F a l l s (Stop (Stop #2) #2) the the tills highly and an oolder t i l l are s are h i g h weathered l y weathered andmay may represent represent an l d e r glaciation. g l a c i a t i o n . Silicified Silicified Cretaceous EauCClaire Cretaceous ttree r e e fragments fragments found found in i noutwash outwash downstream downstream ffrom r o m Eau l a i r e suggest suggest that that Cretaceous sedimentary rocks may underlie deposits iinn the Cretaceous sedimentary rocks may l o clocally a l l y under1 i e g glacial l a c i a l deposits t h e northern northern part p a r t of of the theState, State, oro that r t h aCretaceous t Cretaceousfossil f o s s wood i l woodfrom fromMinnesota Minnesota was was ccarried a r r i e d into into Wisconsin duringanane aearlier Wisconsin during r l i e r gglaciation l a c i a t i o n and and llater a t e r redeposited redeposited iin n this t h i sregion regionduring during Late Lste Wisconsin Wisconsin time. . . �—7— xroiith-gMissmigmatit. zoo. Block Block diagram diagram illustrating illustrating the the concept concept of ofcâivai coevalrelations relation*between between Archaean Archaean gra_nite—greenstone andhigh& high-gradeterrains. terrains. Thà The d diagram represents aa tilted g c 8 n i t ~ ~ t ~ e ntmaina fterrains t o ~ and i i represent> tilted crustal crustal synclinorium (about segment allowing observation observation of of aa major segment allowing major greenstone gneiutonesynclinorium (about mid-way) mid-way)and and aa ultramaflc—mafic high-grade terrain (front left part). Domal tonalites intrude relics of an hiih-gnde terrain (front left part). Domal tonalitec intrude relics of an ultramafic-mafic volcanic volcanic crust crust (early (earlygreenstones) greenstones) (black). (black). The Thetonalites tonalitesbecome becomeincreasingly increasingly gneissose gneisscde (dashed patterns) both toward their margins and with depth. Late greenstone depositories fdsshed oatternst both toward their margins and with depth. Late gmenstone depositories and (hatched (dotted) form (hatched patterns) pattern*) and and sedimentary d i e n t u y sequences se&enc~ (dotted) form unconformably uocoufonnably and parsparalate supraconformably above the tonalites and the early greenstones. L.oci of maximum eonfonnablv abcw the tomtità and the early gmeiutoncs. h i of maximum late supra.. . of crustal synclinoria. Deep-seated crustal deposition deposition coincide coincidewith withinterdomal interdoma1 synclinoria. Deep-seatedgneiss gneissroot rootzones zones of of supracrustal batholiths by aa linear batholiths are are characterized characterized by linear structural structural grain, grain. attenuated attenuated relics relics of supracrustal enclaves andxenoliths. xenoliths, maficÑultramafi mafic—ultramafic intrusion* intrusions and anorthosites. enclaves and and anorthosites. - ~ , .Figure Figure f - 3 Block diagram from GGlikson, 21 3 -— Block diagram from l ikson, 1957, 1957, p. 21 DESCRIPTIONS OF OF MAJOR MAJOR ROCK ROCK UNITS UNITS Introduction Introduction Rocks amphibolite complex complex(CAC) (CAC)consist consistmainly mainly ooff plagioclase Rocks ooff the Chippewa Chippewa amphibolite plagioclase ), amphibole, quartz and biotite. Conron accessory minerals amphibole, quartz and b i o t i t e . Common accessory minerals are are K—feldK-feldspa-, idote, chlorite spa?-!-$dote, c h l o r i t e and and iiron r o n oxides. oxides. Granitoid Grani t o i dcomponents components contain contain the thesame same (An (An essential as the the amphibolites amphibolitesbut buti in essential minerals minerals as n ddifferent i f f e r e n t proportions. proportions. The The apparent mineralogical simplicity of CAC rocks suggests regional metamorphic equilibration, mineralogical s i m p l i c i t y o f CAC rocks suggests regional metamorphic e q u i l i b r a t i o n , following Penokean m.y.j. following the t h emajor majorplutonic p l u t o n iphases c phasesofothe f the Penokeanorogeny orogeny (1840-1830 (1840-1830 m y . ) . By By contrast, the rocks contain contain abundant abundantcchlorite, (JRV) and and South South Fork Fork (SFVS) (SFVS) rocks hlorite, theJump Jump River River (JRV) epidote, and garnet, and andshow show greater 1lithologic epidote, and garnet, s i significantly g n i f i c a n t l y greater i t h o l o g i c and and chemical chemical ddiversity. iversity. (See (See Figures Figures 66 and and 88 ). Amphibolites Amphi bol ites Mafic, intermediate, plutonic Mafic, intermediate, and and feldspathic feldspathic amphibol-ites amphibol-ites ooff volcanic and and p lutonic derivation structures, fabrics, att least derivation contain contain structures, fabrics, and and minerals minerals indicating indicatin a l e a s t three three deformations and (See Stop Stop ##1). and as as many many episodes episodes of o f metamorphism metamorphism (See I . In I n outcrop outcrop the the amphibolites are medium darkgray, gray, commonly comonly laminated laminated and andlineated, lineated, and amphibolites are medium t otodark and cut c u t by by 7 numerous numerous ggranitoid r a n i t o i d veinlets, veinlets, many many of o fwhich whichhave havebeen been strongly stronglydeformed. deformed. The The dominant dominant minerals are Subordinatequartz, quartz,bbiotite, andhornblende. hornblende. Subordinate iotite, are plagioclase plagioclase(An2555) (Annss5 )and �-8trace minerals Common trace minerals are are dd 10 10 percent percent each. each. Comon epidote, and cc epidote, The coarse— sphene,i rand iron oxides,pyrite, pyrite, garnet, garnet,zircon, zircon, apatite, apatite, and coarsesphene, o n oxides, and aallanite. l l a n i te. The grained mafic mafic and andfeldspathic feldspathic amphibolites amphibolitespossess possessstructures structuresi nindicating grained d i c a t i n g dderieriand 2). vation from gabbroicand andanorthositic anorthositicpprotoliths r o t o l i t h s (stops (stops 1 and 2). Textures Textures in in vation from gabbroic fine—grainedmafic maficand andintermediate intermediateamphibol amphibolites indicatet htheir derivation mainly fine-grained i t e s Indicate e i r derivation mainly from basalt basalt flows andesite pyrocl pyroclastics. from flows and and andesite astics. Associated Associated biotite—hornblende— b i o t i te-hornbl endechlorite—epidote schists (Figure 8) probably represent chlorite-epidote schists (Figure 8 ) probabl represent sedimentary sedimentary pprotoliths. rotoliths. The banded bandedamphibolites amphibolitesa tatBig BigFFalls 1) were derived from The a l l s (Stop (Stop 1 were probably probably derived from a a layered layered Although relict garnets occur sparsely throughgabbro (Curnings and Myers, 1979). Although r e l i c t garnets occur sparsely throughgabbro (Cumnings and Myers, 1979). out the the large large hornblendized garnetporphyroblasts porphyroblastsaat Big FFalls CAC, the hornblendized garnet t Big a l l s are are unique. unique. out the CAC, Laminatedamphibolites amphibolites 2) contain Laminated a t at L i Little t t l e FFalls a l l s (Stop (Stop 2) contain ultramafic ultramafic inclusions inclusions (autoliths?). (auto1 i t h s ? ) . Garnetiferous Garnetiferous amphibolites amphibol i t e s ooff the the Cornell Cornell area area are are richer r i c h e r ini nalumina a1 umina The garnets in these amphibolites than those elsewhere in the CAC. than those elsewhere i n the CAC. The garnets i n these amphibolites are are fresh, fresh, show show Plagio— no rotation, and no rotation, and engulf engulf older older laminations laminations produced produced iin n part p a r t by by shearing. shearing. Plagiolaminaeare areaxial-planar axial—planar clase + quartz quartz laminae t ototitight, ht, iisoclinal s o c l i n a l shear shear folds folds(F—l), (F-I), which which clase were locally compressed into small open folds (F—2) with oblique axial trends. were l o c a l l y compressed i n t o small open f o l d s F-2) w i t h oblique a x i a l trends. 1 ! ? Chemical compositionso of the amphibolites amphibolites are are included Chemical compositions f the i n c l u d e din i nTables Tables 1—3, 1-3, and and iinn Figure 5 Figure 5 . Volcanic and and Associated Associated Sedimentary SedimentaryRocks Rocks Volcanics ooff the River area Volcanics the Jump Jump River area (stops (stops 15-18) 15-18) comprise comprise mafic mafic and and intermediate intermediate Relict (basaltic and andesitic) flows flows and andandesitic andesitict otorrhyolitic ict (basaltic and andesitic) h y o l i t i c pyroclastics. pyroclastics. Re1 sedimentary and porphyritic textures are well preserved despite local metamorphism sedimentary and p o r p h y r i t i c textures are well preserved despite l o c a l metamorphism The JRV JRVwere wereintruded intruded by by Penokean(?) Penokean(?)g granitic tto o lower lower amphibolite amphibolite grade. grade. The r a n i t i c plutons plutons along the south side of the Jump River. along the south side o f the Jump River. Basaltic(?) andesitic, andesitic, and andr hrhyolitic volcanic rocks rocksi ninterstratified Basaltic(?) y o l i t i c volcanic t e r s t r a t i f i e d with with siliceous volcaniclastic sediments p h y l l i t e sconglomerates, , conglomerates,and andmicaceous micaceous siliceous volcaniclastic sediments— phyllites, quartzites - are Fork ooff the areexposed exposed along along the the North North Fork Fork and and South South Fork the Eau Eau Claire Claire quartzites River (Stops (Stops 3-7, 3-7, Figure Figure 21). 21). Although Although bedding bedding in i nthe thetuffaceous tuffaceoussandstone sandstone and and conglomeratedips dipsaat moderateangles anglest otothe theeast east and andsoutheast, southeast, contacts contacts w with conglomerate t moderate ith contiguous amphibolite and andplutonic plutonic rocks rocks are steeply dipping contiguous amphibolite dipping and and strongly stronglysheared. sheared. Numerous small exposures of andesitic to rhyolitic volcanic rocks crop Numerous small exposures o f andesitic t o r h y o l i t i c rocks crop out out in EauClaire ClaireRiver River and andJump Jump Riveri ninthe theeast eastside side ooff the region. i n the the area area between between Eau River region. The SFVS Thus is is inferred that the two terranes contain correlative rocks. SFVS Thus i s i s i n f e r r e d t h a t the two terranes contain c o r r e l a t i v e rocks. The ), and rocks show and ttheir heir show a "normal "normal" calc—alkaline calc-alkaline ddifferentiation i f f e r e n t i a t i o n trend trend (Figure (Figure 66 ), compositions areclose closet to those ooff nearby nearby ttonalite compositions are o those o n a l i t e and and trondhjemite. trondhjemite. The The possibility Penokean trondhjemitic and and ttonalittc o n a l i t i c plutons plutons intruded intrudedtheir t h e i rown own b i l i t ythat t h athe t the Penokean trondhjemitic volcanic beexamined, examined, especially volcanic ppiles i l e s should should be especially i ninl i light g h t ooff the the closeness closeness i in n ttheir heir ages (1860m.y. m.y.f ofor the SFVS SFVSand and l840m.y. ages (1860 r the 1840 m y . f oforthe r the plutonic plutonicrocks rocksaccording according to t oVan Van Schmus, 1980.) 1980.) Schmus, - - Plutonic Rocks Plutonic Rocks The ttonalites essentially ooff plagioclase The o n a l i t e s of o fthe theChippewa Chippewa region are composed composed essentially (Ançç),),quartz, Compositionalvariations variations are quartz,hornblende, hornblende, oor r bbiotite, i o t i t e , or o r both. both. Compositional are (An exprsed expressedmegascopically megascopically as as differences differences in i nthe thehornblende—biotite hornblende-biotite ratio r a t i oand andthe the abundanceoof quartz. Mafic tonalites, with abundance f quartz. Mafic tonalites, w i t h total t o t a mafics l maficsini nexcess excess of o f35 35 percent, percent, tend to andare arecommonly comonly associated associatedwwith t o be be hornblende—rich hornblende-rich and i t h mafic amphibolites. Biotite, younger than thethe hornblende, B i o t i t e , which whichisi sinvariably invariably younger than hornblende,produces producesa awell—defined well-defined foliation. weatheredoutcrops, outcrops, iitt f o l i a t i o n . Although Although ffoliation o l i a t i o nmay may not notbe beconspicuous conspicuous on on weathered is i s invariably invariablypresent. present. All A l l tonalites t o n a l i t e sseen seen ini nthin t h i nsection sectionshow show some some eeffects f f e c t s of of cataclasis, mostly and mostly as as interlensing interlensingshear shearsurfaces surfacesalong alongwhich which plagioclase p là i"; .?.' *'9 yas . ".z,*.. i'-,;<*,-. .,*&\.> , t. . :: �—9— quartz Biotite quartz are a r e mylonitized. mylonitized. B i o t i t eflakes f l a k e sare arecrenulated crenulatedbybydisplacements displacements along along shear surfaces during post-metamorphic catashear surfaces d u r i n g cataclasis, c a t a c l a s i s ,a afactor f a c t osuggesting r suggesting post-metamorphiccata— Tonalite cclasis. lasis. T o n a l i t e contacts c o n t a c t s are a r e typically t y p i c a l l ysheared sheared with w i t h considerable considerable mixing m i x i n g ooff contiguous rock rock uunits. contiguous nits. The trondhjemites trondhjemitesaare composed quartz, and andbbiotite. The r e composed e s sessentially e n t i a l l y o f of o loligoclase, i g o c l a s e , quartz, iotite. Epidote, K—feldspar, muscovite, iiron Epidote, K-feldspar, muscovite, r o n oxides, oxides, and and sphene sphene are a r e ubiquitous u b i q u i t o u s accessory accessory minerals. The Thetrondhjemites trondhjemitest etend and minerals. n d t otobebel eleucocratic u c o c r a t i c and o nonly l y f afaintly i n t l y ffoliated. oliated. Theyaare adamellites byaasslight 1i t e s by l i g h t increase increase in in They r e ccontinuously o n t i n u o u s l y i nintergradational t e r g r a d a t i o n a l wwith i t h adamel K-feldspar. The trondhjemites trondhjemitesas asseen seeni nint thin K-feldspar. The h i n section s e c t i o n contain c o n t a i n large, l a r g e , subhedral subhedral margins owing ggrains r a i n s ooff plagioclase p l a g i o c l a s e with w i t h untwinned untwinned margins owing i n in p apart r t t otos tstructural r u c t u r a l ddisisordering under conditions of cataclasis. Quartz ggrains lamellar, o r d e r i n g under c o n d i t i o n s o f c a t a c l a s i s . Quartz l a r , undulatory undulatory r a i n s show show lame1 occuri in eextinction, x t i n c t i o n , are a r e finer f i n e rgrained g r a i n e dthan than the t h e plagioclase, plagioclase, and and comonly commonly occur n cclots lots or ribbons. In contact with K-feldspar grains, the plagioclase is myrmekitic. o r ribbons. I n c o n t a c t w i t h K-feldspar grains, t h e p l a g i o c l a s e i s myrmekitic. Muscovitei is Biotite B i o t i t e isi sconinonly commonly altered a l t e r e d to t o green green chlorite+ c h l o r i t e +muscovite. muscovite. Muscovite s iinvariably nvariably a late mineral , probably formed during retrograde metamorphism of the region. a l a t e m i n e r a l , probably formed d u r i n g retrograde metamorphism o f t h e region. The best exposure exposureo of Dam(Stop (Stopl o10), wherei tit i iss cut cut ) , where The best f t trondhjemite r o n d h j e m i t e i is s at a t Wissota Wissota Dam by dikes and irregular masses of gray tonalite containing amphibolite by dikes and i r r e g u l a r masses o f gray t o n a l i t e c o n t a i n i n g amphibol i t e xxenoliths. enoliths. The aadamellites simply ccontain moreK-feldspar K-feldspar((microcline) than the The d a m e l l i t e s simply o n t a i n more m i c r o c l i n e ) than t h e trondhtrondhjemites. Whereas most of the K-feldspar in the trondhjemites occurs as regular jemites. Whereas most o f t h e K-feldspar i n t h e trondhjemites occurs as i rirregular as ddiscrete occursmore more comonly commonly as i s c r e t e ggrains r a i n s in i n the the iinclusions n c l u s i o n s in i n the t h e plagioclase, plagioclase, iti toccurs adamellites. E a r l y kinematic kinematic veins veins and and dikes dikes of o f adamellite adamell i t e showing showing folding f o l d i n g and and adamell i t e s . Early boudinage, indicate that the sequence of intrusion was complex and not boudinage, i n d i c a t e t h a t t h e sequence o f i n t r u s i o n was complex and n o t confined confined to t o aa single s i n g l e differentiation d i f f e r e n t i a t i o nsequence sequence (as (as at a t Jim Jim Falls, F a l l s , Stop Stop 11). 11). Several as to Several plug-like p l u g - l i k e gabbro gabbro bodies bodies were were seen, seen, but b u t so so poorly p o o r l y exposed exposed as t o render render However,aagabbro gabbrobody bodyi sis wwell along tthe them unmappable. unmappable. However, e l l exposed exposed along h e Yellow Yellow River River The gabbro gabbro has has aa bbrecciated near Stop 88 about about 22 m miles r e c c i a t e d margin margin i l e s eeast a s t of o f Cadott. Cadott. The near Stop Relict against amphibolitic and volcanic(?) rocks in intermediate composition. ict a g a i n s t a m p h i b o l i t i c and v o l c a n i c ( ? ) rocks i n i n t e r m e d i a t e composition. Re1 clinopyroxene clinopyroxene ggrains r a i n s aare r e thickly t h i c k l ymantled mantled by by hornblende, hornblende, which which iiss in i nturn t u r nrimmed rimmed gabbroonont hthe YellowRRiver with (Ans5), The gabbro e Yellow i v e r ccosists o s i s t s ooff plagioclase p l a g i o c l a s e (An55), w i t h brown brown bbiotite. i o t i t e . The hornblende,bbiotite quartz, ppyrite, hornblende, i o t i t e and and accessory accessory quartz, y r i t e , magnetite, magnetite, sphene, sphene, zzircon, ircon, The rock rock is apatite, i s cut c u tby bynumerous numerous shear shear zones, zones, and and ddisplays isplays l l a n i t e t ? ) The a p a t i t e , and and aallanite(?) a TheThe gabbro appears a subtle s u b t l e cataclastic c a t a c l a s t i c foliation f o l i a t i o in n ithin n t hsection. i n section. gabbro appearstot obe beyounger younger than than tthe h e ttonalite o n a l i t e or o r trondhjemite t r o n d h j e m i t e - late l a t ekinematic. kinematic. - Chemical analyseso of Chemical analyses f t the h e pplutonic l u t o n i c rocks rocks are a r e included i n c l u d e d ini ntables t a b l e s5 and 5 and6.6.AnAnAFM AFM diagramf ofor rocks iiss given v a r i a t i o ndiagram diagramshowing showing diagram r t the h e pplutonic l u t o n i c rocks given in i n Figure Figure 77.. AA variation well-defined aa w e l l - d e f i n e d iinterrelationship n t e r r e l a t i o n s h i p of o f the t h e plutonic p l u t o n i c rocks rocks is i s given given in i n Figure Figure 4 . Thessignificance K20curve curvei sisn not exceptt hthat The i g n i f i c a n c e oof f tthe h e double double K20 o t f ufully l l y understood, understood, except a t iitt probably represents representstwo twod distinctly series, which whichaare otherwisei nindistinguishprobably i s t i n c t l y uunrelated n r e l a t e d series, r e otherwise distinguishIt isi ssuggested Morechemical chemicaldata dataa rare needed able. More It suggested that that e needed t o to v everify r i f y t this h i s trend. trend. ont the ffuture u t u r e studies s t u d i e s should should concentrate concentrate on h e aalkali l k a l i ratios r a t i o sini plutonic n p l u t o n assemblages i c assemblages in i n the t h e plutonic p l u t o n i crocks rocksofo the f t h eChippewa Chippewa Valley. �-10- '—S so 60 70 00 •7s;Ot - Variation diagram showingv avariation Figure diagram showing r i a t i o n ooff various various oxides oxides Figure 4 -—Variation in relation to weight.percentage of silica for tonalites, i n r e l a t i o n t o weight ,percentage o f s i l i c a f o r tonal i t e s ,adamellites, adamell i t e s , and Bulkchemical chemical and trondhjemites in i nthe t h eChippewa Chippewa amphibolite amphibolitecomplex. complex. Bulk analyses by Technical Service Laboratories, Mississauga, Ont. analyses by Technical Service Laboratories, Mississauga, Ont. �—11— F AMPHIBOLITES (Fe203+FeO) 0 0 05 0 0 00 0 M (MgO) A (Al 203-Na20-K20) -- Figure 5-Figure 5 AFM AFM diagram diagram f for o r amphibolites.omafic aaphfbolites. o m a f i c amphibolites1 0 intermediate amphibol iites, t e s , and and amphibolites, 0 intermediateamphibol • feldspathic feldspathic amphibo4ites.Plotted amphibolites. - P l o t t e d in i nmolecular molecular proportions. proportions. Total iron i r o noxide oxideexpressed expressedas asFe203 Fe203 F SOUTH FORK SOUTH FORK VOLCANIC AND AND METASEDIMENTARY METASEDIMENTARY ROCKS ROCKS 0 0 A (A1203-Na20—K20) 0 (Fe2O3+FeO) . • NI Figure 66 -— diagram ffor -- AFM AFM diagram o r metavolcanic metavolcanic and and associatedsedimentary sedimentary rocks, •andesite associated rocks, andesite t tuffs, uffs, 0 dacite(fl, d a c i t e ( ? ) , ootuffaceous t u f f a c e o u s conglomerate, conglomerate, o o rhyolite, 0 r h y o l i t e ,Amuscovite—biotite A muscovite-biotite quartzite. quartzite. (MgO) �—12— F (Fe203+FeO) PLUTONIC ROCKS PLUTONIC ROCKS o Trondhjemite 0 Trondhjemite • Tonalite £ A Adamellite Adamel 1i t e Gabbro • Diorite oo a U o AA (Al203—Na20—K20) (A1 n03-Na,0-K,0) M (MgO) -- Figure CompositeAFM AEM p l oplot t o of f pplutonic l u t o n i c rocks rocks Figure 77 -— Composite amphibolite complex, complex,pplotted iinn the t h e Chippewa Chippewa amphibolite l o t t e d in in and 66 ffor molecular proportions. proportions. See o r desdesSee t tables a b l e s 5S and molecular ccriptions r i p t i o n s of o f rocks. rocks. COMPOSITE COMPOSITE PLOT PLOT F - (--C (Fe2O3+FeO) Plutonic P l u t o n i c rocks rocks South Fork volcanic volcanic South Fork O and and sedimentary rocks C__ .— •1 Amphibol ites A (Al 203-Na20—K2 -- (MgO) Composite AFM AFM pplot l o t showing showing compositional compositional Figure 88 -- Composite llimits i m i t s ofo fplutonic p l u t o n i crocks, rocks,South SouthFork Forkvolcanic volcanicand and sedimentary rocks, rocks, and Average ttrend sedimentary and amphibolites. amphibol i t e s . Average rend shownwwith heavyblack black lline. shown i t h aa heavy ine. �—13— - 1 J- - TABLE BULK CHEMICAL CHEMICALCOMPOSITIONS COMPOSITIONS I'FIC AMPHIBOLITES* TABLE I1 — BULK OFOFMAFIC AMPHIBOLITES* 7336 A 7425 177132 77138 77155 7902 A B A B A8 98 52 r28 7927 7908 N-I A 4&30 7941 7950 A A 986609 SiC2 49.06 A1203 15.61 17.12 14.88 13.16 13.30 13.51 19.95 11.06 14.66 13.86 Fe203+ 12.40 11.16 11.12 14.46 13.51 11.59 13.24 11.62 11.09 11.93 1 FeC 9.65 10.90 9.02 9.69 11.87 11.47 12.34 12.10 14.75 5.21 3.19 5.57 7.31 10.85 3.08 2.32 2.32 2.93 1.32 1(20 0.77 0.68 0.85 1.04 0.68 0.31 0.78 Tb2 0,77 öT1 1.01 1.13 MnO 0.19 0.18 0.56 0.14 0.21 P205 0.14 0.12 0,19 0.29 CaD 10.04 MoO 6.60 'rJa2O LOI TOTAL Soec. No. 7336—A 0.64 0.75 1.99 0.60 5.52 15.28 8.11 7,66 2.57 1.18 2.23 1.64 0.70 0.19 0.58 1.00 0.71 0,34 0.90 0.96 0.18 0.21 0.21 0.20 0.19 0,21 0.17 0.00 0.27 0.09 0.08 0.15 0,71 0.37 0.42 0.26 0.56 0.66 0.60 99.28 100.2 100.3 98.28 100.31, 98.31 100.0 99.35 100.1 100.01 Location Eau Claire R. Desc rip U on H—P—8—E—C schist with contorted granitic SE¼S%% Sec.l8; T26N, R5W veinlets in isoclinal folds; banding cut discordantly by granitic veinlets,dikes 7425—B Cornell CornellDam Dam SW¼SE¼Sec.18; T3IN, R6H SMiSEdSec.18; T31N, R6 H—C schist; strongly lineated; isoclinal folds of P 77132 Eau Claire R. Eau Claire R. SW¼Sk SWiSlfc Sec. Sec. 20; 20; T27Nç T Z 7 kRJW R fine—grained schist; stronaly strongly fine-grained H—P H-P schist; 77138—A 771384 Eau Claire R. Eau Claire R. NE¼SE¼ Sec.29; T27N, NWEk Sec.29; T27N. R7W R H—P schist, lineated; lineated; associated H-P schist, associated with with 77155—B Knight Knight Pool; Pool; North North Fork. For 7902—A 1 ineated banded gneiss. banded P—H P-H gneiss. Fine—grained H—P schist (H—60%); thinly Eau Eau Claire ClaireR.R. NW¼SE¼ Sec.IO; T26N. R N W E k Sec.10; T26N. R7W banded with lensoidal lensoidal masses of feldspar banded with masses of felds Little L i t t l eFalls, Falls,Eau EauClaire ClaireR. R. H—rich inclusion of of lineated H-rich inclusion lineatedhornblendite hornblen SW¼NW¼ Sec.19; T27N, S U W Sec.19; T27N. R7W R7W very very tight t i g h t isoclinal i s o c l i n a l folds folds of of PP locally loca 0—B bearing gneissic gneissic H H ttonalite o n a l i t e intrusion intrusion breccia; breccia- H has a pronounced green color color ini nspecimen pronounced green spe and and iinn thin t h i n section. faction. 7908—A 7927—N—i 7941—A Fisher R. Bridge Bridge Fisher R. SWgSW¼ Sec.4; T3IN, SMiSMi Sec.4; T31N. R6W R6H H—P schlst—looksl i like gneissic HHgabbro; H-P schist-looks k e gneissic gabb cut cut by by pegmatite pegmatite veinlets veinletsand andmylonite mylonit 'veinlets" veinlets" with withright—lateral right-lateraldisplacement displac Little L i t t l eFalls, Falls,Eau EauClaire ClaireR. R. Lineated Lineated horrblendite hornblendite xenolith xenolithIn iH— n H- 5W¼NW¼ Sec.19; 19; T27N, SHWIfa Sec. T27B. R7W B71b tonalite t o n a l i t e intrusion intrusionbreccia breccia Knight S. Fk. Fk. Knight Pool; Pool; S. Medium fine—grained H—P schist Hedium fine-grained H-P schist NW¼SE¼ Sec.l0; NUkSEk Sec. 10; T26N, T26N. R7W R7H 7950—A Jim Falls, Falls,Chippewa ChippewaR. R. SW'iE¼.Sec.30; SwaiEii.Sec.30;T3ON, T30N.R8W RBH Medium—grained H—P schist withPPi nIn ttight Mediuei-grained H-P schist with ight isoclinal i s o c l i n a lshear shearfolds, folds,whose ihose limbs limbs impart impart aa pronounced layering iinn the pronounced layering the rock rock * Chemical Chemical analyses analyses by by Technical Technical Service Service Laboratory, Laboratory, Mississaugua, Mississaugua, Ontario, Ontario,Canada Canada ** Mineral hornbiende; Q = quartz; plagioclase-H r a l Abbreviations:P Abbreviati0ns:P ==plagioclase; B == biotite; E = epidote; C = chlorite; biotiteK ; = K K—feldspar; = K-feldspar; NM == muscovite; uu S == sericite; sericite; 6 6==garnet garnet �-14- TABLE 2 — BULK CHEMICAL COMPOSITIONS OF INTEIE0IATE NIPHIB0LITES* 7830 A 5th2 Al203 Fe203+ 7830 — B 7830 7830 6 H 7830 I C . 5.42 4.55 6.13 6.13 MgO 6.10 4.51 3.47 Ma20 3.66 3.16 3.96 3.31 2.69 K20 0.72 1.36 1.89 1.18 0.99 1.00 flO2 0.46 0.61 0.34 0.27 0.22 '1.70 MnO 0.14 0.14 0.06 0.06 0.02 0.13 0.08 0.23 0.11 P2°s 0.03 0.00 0.25 LOI 1.17 1.61 1.53 1.19 0.71 0.80 TOTAL 7830—A 78a-A — 57.08 57.24 57.5k 63.0i 68.42 63.39 15.87 14.89 17.74 l4.3r 14.37 17.22 8.68 9.75 5.80 6.64 3.77 5.28 FeO CaO Spec. & g,g&&NO. 7904 4.94 5.18 1.14 2.20 3.02 4.17 98.41j98.85 98.73 98.94 98.22 !22d - Location Location Confluence off NN&6 SSForks Confluencm o Forts of the of the Eau Eau Claire Claire R. R. 12611, SE¼NE¼SbDS Sec.15; SEkNESR k . 1 6 ; T26N. R5W endoof RW NENEand f outcrop OUtCnIP Descr1otion ~ criotimLineated P—H gneiss withlensoidal lensoidalPPclots. clots, gneiss with Lineated P-H Interlensing shear Interlensing shear surfaces surfaces with with —C E-C laminae; Segmented, lenticulated PP && H. laminae; +nted, lenticulated H. 7830—B 7833-0 2 2 meters meters west westofof7830—A 7833-A Feldspathic gneiss. ~with Feldspathic H—P H-P gneiss, 4 t subhedral hsubhedral PP lineation; Large && H H lineation; Largefl—P Q-P bands bands form f o m bandbanding; EE (10%) layerino. ing; (10%)along along and and across across H—P H-P layerinq. 7830—C 78304 33 meters westof west.of7830—8 7830-8 P—Hgneiss gneissccomposed bent and and crushed P-H w s e d ofofbent crushed lensoldal PP &6 H; lensoidal H; both bothshow show undulatory undulatory extinction and fragmented crystal extinction a d f r a m n t e a c w s t a l bounboundaries; crvss-cuttiig cross—cutting shear shear planes daries d a m s are are E—rich. E-rich. 7830—6 7833-6 15 meters 15 meters west west ofof7830—F 7833-F Medlum—coarse—grained feldspathic P—H gneiss Medim-coarsegrained feldspathic P-H gneiss with lenticular with l m t i m l a rH, H. P. P..and and- subordinate subordinate ffine ine -~~ - - - - -~~ grainS grained(J. 0 . PP wnearly a r l y aall l l altered altered to t o 5; 5 ; HH grains mestly m s t l y converted converted to t o oreen green C. C. H H grains segmented,broken broken{nto into sigmoidal sepented. s i m i d a l lenses lenses which wrap around coarser P lensolds. h i c h wrap a m d coarser P lensoids. Cataclastic lamination N400W, vertical. Cataclastic lamination NW%. vertical. ~ ~ 7830—H 7830-H 5 meters meters west west ofo 7830—6 f 7830-6 Bands P—H gneiss;contains contains abundant abundantpyrite. pyrite. 8anded P-H gneiss; Broken and and bent bent P and P porphyroclasts wr@~ymclasts andlen— lenEmken ticulated, bent, H iin ticulated. bent.segmented semented H na a matrix matrix altered tto E. and ooff fi, Q, E. and P. P. P P altered o 5; S; H H partly partly altered toto C-PE. Tension fractures fractures across altered WE. Tension acms cataclastic laminatio.i, are filled filled with l&aimtim arc withC#E. C+E. cataclastic 7830—I 7830-1 Same location asas7830—6 Sam location 7830-6 Felsic layer fi, less less HH Felsic layerini 7830—G; n 7820-6; more more 0, than 7830—6; muchmylonitization. mylonitization. 7830-6; mch 7904—C 79044 Yellow River, east Yellow River, east of of Cadott Cddott Volcanic (?) (?)Now Now aa fine—grained fine-grained H—B H-E t tonalite onalite or trondhjenite. layering oarallel parallel to or trondhjmite. H H layering to foliation. N No evidenceo of volcanic oriqin. oriqin. 8B foliation. o evidence f volcanic - - - - analysis by * Chemical Chemical analysis by Technical Technical Services Sewices Laboratories, Laboratories, Nississaugua. Mississaugua, Ontario, Ontario.Canada Canada - plagioclase; HH — hornblende; hor,iblende; 0Q quartz quartz Mineral Abbreviations: P P —plagioclase; Uineral chlorite; B biotite;K — K K—feldspar; K-feldspar; P1 tl = muscovite; mscovite; EE = epidote; epidote; C C == chlorite; 8 = biotite; S sericite; 6G = garnet S *= sericite; �—15- - TABLE 33— BULK OF N.IPHIBOLITES* TABLE BULKCHEMICAL CHEMICAl COMPOSITIONS CLWOSXTIONS O F FELDSPATHIC FELDSPATHIC PMPHIBOLITES* 7711 77105 77119 77128 A 5i02 M203 Fe203+ C 48.36 50.51 49.69 57.54 28.48 26.71 24.89 18.80 3.05 3.48 4.18 7.15 FeO CaO 6.72 1.92 0.68 2.94 Na20 3.11 1.67 2.91 4.34 <20 0,28 0.26 0.44 0.25 0.31 MnO 0.18 0.04 0.26 0.49 0.05 P205 0.02 0.06 0.09 0.08 0.12 LOl 0.52 0.02 0.40 0.60 0.60 TiC2 TOTAL Spec. Swc. No. No. 12.99 14.46 13.31 Mg0 2.87 98.96 98.48 99.43 98.96 Location Description Description Strongly P—H—G schist; ragged Stronglylineated lineated P-H-G schist; ragged S G iinn layers. layers. 7711 7711 Cornell NI NE¼ CornellDam D m Nlk N& Sec. Sec. 19; 19; T3IN. T31t1,R6W MU 77105—A 77105-A Eau Claire R. Eau Claire R. ata Nine— t Ninemile Cr. MR NEkSW Sk%Sec. Sec. m i l e Cr. 15; T27N, R8W 15; T27N. RW Strongly lineated gneiss with with folded lineatedP—H P-H gneiss lineatlon lineatim 77119—C 771194 Big B i g Falls, Falls, Eau Eau Claire Claire R. SR Sec. R. 44i4 Wa S& Sec. 13; 13; T27N, R8W T27N. R8U Lineated gneiss ssimilar Lineated P—H P-H gneiss i m i l a rtot 77105—A o 77105-A Eau Claire R. Eau Claire R. Intermediate P—H gneiss; I n t e m d i a t e P-H gneiss; t i gtight h t i sisoclinal oclinal folds folds of o fPPbands bands 77128 77128 * Nlk NW¼ NE¼ Sec. 19; 19; T27N, T27N.R7W R7W NEk Sec. Chemical analysis Services Laboratory, Laboratory, Mississaugua, Mississaugua, Ontario, Ontario,Canada Canada Chemical analysis by Technical Services -- Mineral * ~ i n e r aAbbreviations: 4bbmviations: l - - P == plagioclase; HH = hornblende; hornblende; 0Q = quartz; quartz; BB == biotite; biotiteK ; = K K—feldspar; = K-feldspar; M= nI!scovite; EE epidote; w iwscovite: epidote; C C = = chlorite; chlorite; SS— sericite; sericite;S G—= garnet garnet �-16- - TABLE ROCKS TMLE 44 . BULK SULKCHEMICAL CHWICMCOMPOSITIONS CWOSITIfflSOFOMETAVOLCANIC F M€rAVOLCANAND A MMETASEDIMENTARY IETASEDIMEWARY WCS FROM SOUTHFORK FORKOOF THE EAU EAU CCLAIRE FKU SWTH F THE L A M RIVER* RIVERg ===== == 6 .4l 4 fl6 Y8 fl 7829 7829 A 5102 A1203 B 7829 7830 F E 7831 7832 B 56.84 59.48 48.19 61.76 61.60 75.89 82.64 8.51 6.03 4.08 10.40 UO 1.33 1.33 0.76 0.76 '%a 3.43 3.43 3.10 3.10 Fe203+ 7830 C 7.14 6.80 1.22 2.60 FeO Feo CeO MgO Na20 Ma-0 K2O flO2 0.51 MnO 0.05 P205 0.21 L0I LU TOTAL Spec. No. 7.44 7.44 T7T 7.77 7.77 0.60 0.60 3.65 3.65 4.06 4.06 0.06 0.06 0.00 0.00 8.10 8.10 2.03 2.03 2.25 2.25 0.22 0.22 2.23 2.23 4.68 nnn 4.m 3.29 3 . 8 3.38 3 . 2 ~0.16 0.16 0.08 t26 TT t2 t11 tfl tfl t t 0.49 0.65 0.56 0.51 0.24 0.10 0.04 0.09 0.07 0.00 0.01 0.10 0.27 0.21 0.08 0.25 0.00 0.00 & L80 Th 11 98.11 99.39 99.50 100.1 99.74 96.77 99.72 Location Descriotion Description* (7329) (7323) Confluence N. &&S.S. Forks Forks Confluence of of N. of of Eau Eau Claire C l a i mRiver River 5E¼ T26N.R5W R5U SE4 5E¼ SE4 Sec. Sec. 16; 16;T26N. Chioritized, Chloritized. sericitized s e r i c i t i z e d vitric v i t r i andesite c andsite 7829—A 7829-A Same S m as as 7329 7323above above Feldspathic Feldswthic andeslte(?) a n d s i t e ( ? ) tuff tuff 7829—B 7829-6 Same Sme as as 7329 7323above above Coarse feldspathlc tuff Coarse feldspathic 7829—C 7829-C Same Sam as as 7329 7329above above Coarsest. Coarsest, H—bearing, H-Unring. feldspathlc f e l d s w t h i c andesite andesite tuff; P is and tuftClastic Clastic P ibroken s broken andbent; Wt;rocks mcks have have been been strongly strongly sheared, sheared. locally l o c a l l cata— y cataclasis clasisproduced produced interlensing interlensingshear s h n rsurfaces surfaces along fonTled. alongwhich e t c hC C f o W . Fragmented FragmntedH.H. 7830—E 78%-E tuff tuffwith withlensoidal lensoidalP Pand andclasts clastsini fine— n finegrained graiced tuffaceous tuffaceous matrix; thinly t h i n l ylaminated, laminated. bedded. bedded. (Thin (Thin section sectiononly) only) Eau NE¼ 5W& Eau Claire ClaireRiver: River: NE4 S& Gray Way meta—agglomerate mta-agglomerate ( ?(?) ) ssimilar i m i l a rtot oC C Sec. ovoid clasts clasts of strained Sec. 16; 16;T26N, T26N.R5W; R5U; 44meters meters Rounded, Rounded! ovoid strainedQ, Q,P.P , CC (pennine); (wnnine); devitrified & v i t r i f i e d glass(?) glass(?) Matrix meshwork MdtrixIsi as laminated a laminated m s b r kofoffine— finegrained g n i n eQ+P+E—C. d WM-C. west westofo7830—0 f 7830-0 7830—F 78%-F 55meters 7830—E meterswest westof of 7830-E Coarse, Coarse. sheared sheared dacite(?) dacite(?) with' with. bent, bent, broken matrixooff interlensing broken PP and and Q Q In i n E—C E-C matrix interlensing folla, fine—gralned folia,very very fine-gratned crush crushdebris. debris. Some angular fragments S m angular fragnents of strongly stronglyzoned zoned - P.P. Van — U—Pb VanSchnmjs Schms sample s a w l e for forzircon zircon u-Pb dating m.y.) sample 74—VS—ic. dating(1859±20 (1859220 my.) sample 74-vs-lo. Metatuff? Ntatuff? 7831—B 7831-8 Hay Rock Dam HayCreek Cmekbelow belw Rock Dam 7832 7832 County County Hwy. W . HM at a tEau fau Claire Claire H—C quartzite and andpphyilite M-C quartzite h y l l i t e with w i t h kink kinkfolds folds River NE¼ RiverNENEk NE4Sec. Sec. 1:1: on on the the hats l i n b sofofa small a smallanticline a n t i c l i nwhich e which T26N, ~ 2 6R4W ~R .~ U plunges ENE at about 400 plunges ENE a t about m0 * - 514¼ Sec. 15; S& NE¼ NE4 Sec. 15;T26N, T26N.R4W R4U - Sheared Sheared rrhyolite i t y o l i t e (?) (?Icontains containspolygranular polygranula~ lenses matrix of Q4K+M lensesofo Q f Qini an laminated a laminated matrix of WKM - - Chemical memical Analysis Analysis by by Technical Technical Services Services Laboratory, Laboratory, Mississaugau, Mississaugau, Ontario, O n t a ~ i oCanada , Canada Mineral MineralAbbreviations: Abbreviations P P plagioclase; plagioclase;H — H hornblende; hornblende;Q Q =quartz; quartz; B8==biotite; b i o t i t eK; =KK—feldspar; = K-feldspar; N M= =muscovite; mscovite; E E= epidote; epidote;C C =chlorite; chlorite; SS ==sericite; s e r i c i t e0 ; = G garnet garnet �—17— - TABLE BULKCHEMICAL CHEHICALCOMPOSITIONS CtXPOSITIONS OF OF TONALITES* TWALITES* TABLE S5 - BULK 7906 A 5402 A1203 Fe203+ == 7922 7923 A 7927 7927 0—2 N—2 7952 —— B 64.52 64.71 56.79 61.05 66.81 64.79 16.39 16.56 16.73 16.00 15.18 16.69 4S8 8.40 7.18 tTh FeO 5.93 6.48 4.91 MgO 4.28 2.27 3.43 3.81 1,74 1.82 Na20 3.79 3.89 2.93 3.34 3.98 4.52 (20 T402 2.29 2.11 2.10 1.37 1.23 1.41 0.62 0.43 0.67 0.68 0.06 0.06 0.14 0.11 0.53 0.05 0.36 0.04 9 0.25 0.18 0.11 MnO 0.20 P205 L0I TOTAL 5 0.17 fl 0.19 ] 100.3 99.14 98.23 100.5 100.2 98.07 Wissota Uissota Dam, Dm. Chippewa C h i p w a R. R. NE¼ Sec. 3; NEk NIJJ¼ w% k. 3; T28t1 T2&i 7906—A 7906-A T2 ..ucation a Spec. Swc. No. No. 4.05 4.28 2.24 CaD Description Description ** * B—H tonalite flow lineation; lineation; 6-H t o n a l i t e w with i t h s slight l i g h t flow not not sheared sheared WN R8W Fisher Fishev River River Sec. W . 4; 4; T31N, 131N. 7922 7922 SW¼ Sk% Sl.P Sh R6N R6W Fisher Fisher River River 5W¼ Sec.4; 4; T31N, S+! SSW¼ Uk Sw. T31N. 7923—A 7923-A R6W R6W 7927—0—2 79274-2 Gneissic Gneissic 6B ttonalite o n a l i t e protorriylonite p m t m y l o n i t e with w i t h fljIl blebs (20%); (20%); contains contains occasional occasional xenoliths xenoliths of o f feldspathic feldspathic rock rock (adamellite?) ladamcllite?) - Banded, gneissic H-B H—B tonalite; xenolith xenolith tonalite; Banded, gneissic ( ? ) BB == 10%; 10%; i n adamellite adamellits or o r granodiorite granodiorite (?) in 15%; E = 2% E 2% H = 30%; 30%; P P == 35%; 35%; 0Q matrixf ofor Little L i t t l eFalls, Falls,Eau EauClaire Claire Gneissic Gneissic P—H—B P-H-B t o ntonalite a l i t e matrix r iintrusion ntwsion H— River Sec. 19; River SW¼ Sbh ti%W4 Sec. 19; breccia brecciacontaining containingabundant, abundant,elongated elongated HT27rJ, T27tl. Rib! R7U rich r i c h xenoliths xenoliths - 7927—N—2 7927-N-2 Little ( 7 ) PP L i t t l eFalls, Falls,Eau EauClaire Claire Massive tkssive HHt otonalite n a l i t e or o r trondhjemite t m n d h j m i t e (?) matrIx (63%) not twinned; twinned; QQ = 21%; 21%; H = 13%; 13%; matrix (63%) River River SW¼,NbP, Sec.l9, T27N,R7W W.W, Sec.19. T27N.R7M for f o r H—rich H-rich xenoliths xenoliths 7952—B 7952-6 gnelssic H-B H—B tonalite; llocally Jim Jim Falls; Falls;Chippewa Chippewa River River Sheared Sheared gneissic tonalite; o c a l l yconcontainslenses lensesand andbands bandsofofH—schist H-schist and anddike— dikeME¼,NEk. NE¼.Sec. Sec. 30; N&, 30; 13CM, TDN, tains pegmatite p e g m t i t emasses musses Ren R8W * Chemical analyses Sewice Laboratory, Laboratory, Mississaugua, Mississaugua, Ontario, Ontario,Canada Canada Chemical analyses b.v by Technical Technical Service ** * Mineral Abbreviations: Abbreviations: P P = plagloclase; plagiwlase; HH==hornblende; hornblende; 0Q = quartz; quartz; B = bbiotite: i o t i t e : KK == Kfeldspar; K.fe1dspar; NI4 == muscovite; muscovite; EE epidote; epidote; C C = chlorite; S S = sericite; sericfte; SG= garnet garnet -- - - �-18- - TABLE OF TABLE 66— BULK BULKCHEMICAL CHCNICAl ANALYSES PNALYSES O F TRONDHJEMITES, TROtJDtUEMlTES,, ANDDlQRlTE* DI0RITE* ADNIELLITES. XMELLITES.GABBRO • AND ~~, — — — — 'a aaaa——a AOMLLITE TRONOHJEMITES 7335 7337 77131 7713617830 7905 Al203 Fe203+ 70.22 13.85 70.97 7901 7942 A D C 5102 7906 7425 A GABBRO & DIORITE 7904 A 7945 A 5i 70.62 72.36 71.18 78.27 65.66 72.20 49.45 52.33 15.50 14.10 15.13 13.75 15.52 14.59 15.54 12.00 16.69 14.02 16.30 20.27 3.12 2.09 2.97 2.17 2.49 2,54 2.11 1.68 3.S 2.04 9.11 6.75 FeO Cia 2.95 1.12 2.71 MgO 1.03 Na20 4.39 0.56 4.57 0.96 4.59 3.11 1.34 fl 1.51 K20 7107 Ibt 0.05 P205 0.06 ti 05 29 0.03 0.04 0.01 0.04 1.44 2.61 2.90 2.56 2.56 2.6 2.04 0.42 0.97 0.81 0.71 0.44 2.l 0.68 9.53 8.45 3.05 4.45 4.62 4.84 3.33 4.Of 3.07 2.88 3.59 4.33 1.43 1.45 2.39 tY 1.22 4.05 3.96 0.86 0.96 0.04 0.03 0.03 0.02 0.10 0.02 0.05 0.09 0.09 t fl fl Th Th i fl 0 fl fl Th tä o.3 tTh 0.01 0.05 0.03 0.16 0.00 0.25 0.05 0.25 9.86 5.13 0.24 LOl Th TOTAL 99.57 100.2 99.44 98.54 99.30 100.0 100.0 99.99 100.2 99.01 98.75 100.2 Location Spec. Mo. 0.21 0.59 Descri pti 0n TROMD}43EMITES 7335 Eau Claire River Ew Claire Rivernear m a rmouth mth of d *ippoonqill lhiPPMlWfl1Creek Creek Sit W 5E¼ SE& kSec.18; . 1 8 ; T26M, T2ffl. R5W R5U Gnelssic Leucotonal I te; gteissosity gneissoslty Gneissic LeucotoMlim produced by elmgation elongation of Pmduced by o fAb—rim,*d A b - r i m d PP 7337 Eau Claire River Eau Claire River at a tmouth muth of t.thippoorwill of lhippoolWfl1Creek CNek St Mt Sec.18; T26N, R5W SWa N!& *.I& , l fn f Rm Highly sheared, chloritized, gneissic Highly s h ~ m d .chloritized. gneissic trondhjauite; mcct m m i h j a i t e ; banded. b a M . nylonitized, aylonitized, mechanically intermixed with H—P schists. hanically intemixed with H-P schists. 771 31 EauClaire Claire River Eau River Foliated, Foliatsd, fine—grained, fine-grained, aaplitic p l i t i c BR mu SR Sit WS SPASec.20; SSC.~;127N, 1 2 7 ~RTh . trondhjemi te. tmndhjmite. Eau Claire River Eau Claire River Foliated. H—B Foliated. n-B ttrondhjemite mndhjmite Eau Claire River Eau Claire 0.5 meters 0.5 m t m of of 7830-C 78244 HR SWa St Sec.l6 Ek b . 1 6 west west T26t1. R5W Rm m. Coarse, feldspathic trondhjemites ((Oligoclase O l i w l a s e porphyroclasts p r ~ h m l a s in ~ fine—grained - fim-grained i n matrix m t r l x of of strained strainedQ; Q; laminated) I d n a t e d l Feldspars Feldswrs bent, broken, and Intruded by Q—rich mylonite. h t , bmken. and i n t M by Q-rich aylonite. Cadott Bridge, Yellow Riv. W tt Bridge, Yellan Riv. St MR SWI NEkSec.31; Sec.31;T29N 12%R6W R6U Trondhjnite protomylonite with pmtcwlmite gneiss gndss w ith Trnrdhjcmite E+M+B. and N H altered alteredtoto E m . ovoid PP and Wissota Dam, Riv. Dam. Chippewa Chippea Riv. Uissota trondhjemite: nmjor major rock Gneissic B—H B-M tmndhjmite: rack ttype mbelow belcuWissota MissotaDam. Dm. 7907 Fisher River Fisher River Nit Nit NWa N!&Sec. Sec. 9;9;T3IM, T31N.R6W R6U Gnelssic h e i s s i c M-leucotrondhjmnite. ble!4cotmndhjmite. Accessory Accessory B and andE£ ffort, throughgoingfoliation; foliation; cono m throughwing conB tains round zircons. tains mund zircons. 7942—A Knight Pool, Pool, North off might Nwth Fork Fork o Eau Claire River M u Claire SR NE Sec.l0; SEk See.10; T26H. TZffl.R5W Rm 8—trondhjrclte or granodiortte geiss. 77136 MR St m s!& Sec.20; Sec.20; T27N, n7NR7W . R7U 7830—0 7905-C 7906—D MR N P' Nt nw' Sec.3; sec.3; T28M, T r n ,R8W m m ADAJIELLITE A MLLITE 742S-A Cornell Dam, 7425-A Come11 Dam. Chippewa Chippewa Riv. SR MR SEk NEkSec.l8; See.l& T31M, T31N.R6W MU GAB8i0 W B R O AMU AfiD DIORITE DIDRITE 7904—A Big Bend, 7904-A Bend, Yellow Yellow River River NR NEkSE¼ S& Sec.33; Sec.33; T29H, T29N.R6W R6U LLittle j t t l eFalls, Falls,Eau Eau Claire Claire River SWaNit NWaSec. See. 19; 19: River St T27N. R7W T27N. R7U 7945—A 7945-A * * B—H flaser gneiss gneiss oorr mylonite E M a dadamellite a m l l i t e maser mylonite gneiss with lensoids gneiss lensoid* of of PPand and KKini nQ—rich Q-rich mylonitic matrix; withwith H—P—C mylonitic matrix;interlensed interlensed H-P-6 gneiss and and schist schist gneiss Sheared,foliated, foliated, cataclastic Sheared, cataclasticH—dlorite H-diorite with w i t h B ffoliation o l i a t i o ncut cutbybycataclastic cataclastictone— h a llite i t e"dikes 'dikes. B—H quartzgabbm; gabbro; pmbably probably aa contaminated 0-H quartz antaminat& for,,, ?om of o f H—tonalite. H-halite. chemical analyses by Technical Technical Sewices Services LLaboratories, Ontario, ~ m i c aanalyses l by & x a t o r i e s , Mississaugua, Missjssaugua, Ontario, Canada Canada Mineral Abbreviations: P == plagiwlase; plagioclase; HH = hornblende; quartz; Abbmviations: P hornblende; Q Q == quartz; muscovite; EE a epidote; CC = cchlorite = =K—feldspar; BB == bbiotite; i o t i t e ;K K K-feldspar; NM = mscovite; hlorite sericite; BG •= garnet sS = sericite; garnet - .- �-19— GEOPHYSICS GEOPHYSICS Aeromagnetic quadranglemaps mapsbybyKarl Karl and and Friedel Friedel (1974-1976) Aeromagnetic quadrangle (1974-1976) have have not not been been published published i in n ffinal i n a l form. form. However, maps show However,the the preliminary preliminary maps showimportant important trends, trends, and the patterns patterns help help ttoo identify and the i d e n t i f yand andcorrelate c o r r e l a t eaeromagnetic aeromagnetic signatures signatures with with mapping on the ground. Steep-sidedridges ridges and andtroughs troughselongate elongatepparallel mapping on ground. Steep-sided a r a l l e l to to sstructural t r u c t u r a l grain graincharacterizes characterizesareas areasunderlain underlainbybyscreens screensand and enclaves enclaves of of amphibolite. The The amphibolite amphiboliteterranes terranesare arei in sharp contrast contrast wwith n sharp i t h the splotchy splotchy contour patterns and andlow lowr relief by ggranitic contour patterns e l i e f of o f areas areas underlain underlain by r a n i t i c rocks. rocks. These maps maps were considerable help i n compiling compiling the the generalized generalized geologic geologic map map iin n Figure Figure 1. 1. were ooff considerable help in portion off Wisconsin AA p o r t i o n of o fthe theBouguer Bouguergranity g r a n i t yanomaly anomalymap map o Wisconsin by Ervin Ervin and and Hamer Hamner (1974) has been included included (Figure g )) ffor Note the pronounced (1974) has been (Figure 9 o r reference. reference. Note pronounced ggravity ravity Extendedalong alongi its the "lineament" slope along the t h e Jump Jump River. Extended t s trend trend southwestward, southwestward, the "lineament" follows the t h enorth n o r t hshore shoreofoLake f LakeHolcombe Holcombe and and along the south south side sideofo Flambeau f Flambeau Ridge, whereBarron-type Barron-typeqquartzite are thrown thrown iinto Ridge, where u a r t z i t e conglomerates conglomerates are n t o large l a r g eopen open folds The Barren Barronquartzites quartzites northwest northwest ooff f o l d s which which plunge plunge northwest northwest at a t about about 55°. 55O. The Flarnbeau Ridgeare aret typically Flambeau Ridge y p i c a l l yundeformed. undeformed. lineament trending trending northwesterly AA strong aeromagnetic aeromagnetic lineament northwesterly across across the themouth mouth ooff the the Yellow Yellow River Riveron on the theeast eastend endofo Lake f LakeWissota Wissota isi smatched matched by by aa major major shear shear zoneoof (1976) shows showsseveral several major major northzone f ssimilar i m i l a r trend t r e n d in i n the the rocks rocks there. there. Sims Sims (1976) west-trendingf afaults The Bouguer Bouguer ggravity west-trending u l t s ooff similar s i m i l a r trend. trend. The r a v i t yanomaly anomalymap map shows shows aa maybe bef afaultultllarge a r g e "positive" " p o s i t i v e "anomaly anomaly just j u s t east eastofo Lake f LakeWissota. Wissota. This anomaly anomaly may bounded on tthe bounded on h e west. GE OC H RON OL OGY GEOCHRONOLOGY Major events events iinn the Major the geologic geologic history h i s t o r yofothe f t hChippewa e ChippewaValley Valleyregion regionhave havebeen been compiled Itisi semphasized emphasized t hthat a t t this h i s is is compiled iin n the the chronology chronology presented presented iinn Table Table 7. 7. It Only those thoseage agerelationships relationshipsf ofor whichthere therei sis ffield a tentative t e n t a t i v echronology. chronology. Only r which ield evidence have been included. Zircon U/Pb UIPb dates dates have have been been published published(Van (VanSchmus, Schmus, evidence have been 1980 and Maass Maassand andVan Van Schmus, 1980) rocksi in Valley: (1) 1980 and Schmus, 1980) f o rfor f o four u r rocks n tthe h e Chippewa Chippewa Valley: (1) sheareddacite(?) dacite(?) from volcanic and sedimentaryrocks rocksaatt llocation sheared from the South South Fork Fork volcanic and sedimentary ocation 7830-F (SeeTable Table4 4f ofor description). Age ± 20 m.y.; (2) 1860 + 20 my.; (2)banded banded amphibolite amphibolite 7830-F (See r description). Age == 1860 Age==1850 1850+ +20 m.y.;(7) (3) ffoliated Stop 1. from Big Falls, Stop f r o m Big 1. Age 20 my.; o l i a t e d hornblende hornblende ttonalite onalite Age == 1847 1847+ 10 m m.y.; ffrom r o m LLittle i t t l e Falls, Falls, Stop Stop 2. 2. Age + 10 y . ;and and (4) (4) trondhjemite trondhjemiteataChippewa t Chippewa Age == 1830 Falls 1830 j^± 15 m.y. m.y. F a l l sDam. Dam. Age amphibolite( u(unit Cumings)i sis only only 1850 1850m.y. m.y.old, old,iitt IIffthe t h e banded banded amphibolite n i t ##1 l oof f Cuimn'ngs) whenwhen two two episodes of metamorphism wwill i l lbe bevery verydifficult d i f f i c utol texplain t o explain episodes o f metamorphismand and deformation deformation Van Schmus Schmus(1980, (1980, p. 3) precedingi nintrusion the LLittle preceding t r u s i o n oof f the i t t l eFp.lls F a l l s Tonalite Tonalite took took place. place. Van states that, "In theBig BigFFalls thep opossibility states that, " I n the the case case oof f the a l l s z zircon i r c o n the s s i b i l i t y s still t i l l exists exists m.y. ago tthat h a t they theyare aremetamorphic, metamorphic, formed formedduring duringthe thePenokean PenokeanOrogeny Orogeny about about 1850 1850 m.y. ago (Van Schmus, Schmus,1980) 1980)and and thegneiss gneiss iis (Van t hthat a t the s Archean, Archean, bbut u t for f o rthe thepresent presenta Penokean a Penokean are iinclined We are n c l i n e d from from abundant abundant ffield i e l devidence evidenceata many t many primary age agei is preferred." We primary s preferred." other places places tto o support support the contention contention tthat h a t the t h e age age of o f the the amphibolites amphibolites at a t Big Big Falls F a l l s - and andelsewhere elsewhere throughout throughout the the CAC CAC - is i sArchean. Archean. - - - BIG FALLS LITTLEFALLS FALLSAREA AREA- INTRODUCTION - INTRODUCTION FALLS - LITTLE generalized geologic geologic map mapo of the Big Big FFalls—Little AA generalized f the a l l s - L i t t l e Falls F a l l sarea area(Figure (Figure10) 1 0 )shows shows that the rock units occur in bands trending west—northwest. It is suggested t h a t the rock u n i t s occur i n bands trending west-northwest. It i s suggested t hthat a t iiff the mafic mafic hornblende hornblende sschist c h i s t underlies the the feldspathic feldspathichornblende hornblende gneiss gneiss (layered (layered gabbro), the symetry of the units indicates an overturned anticline gabbro), the symnetry o f u n i t s indicates an overturned a n t i c l i n e cored cored iin n part part by the hornblende tonalite intrusion breccia. Later faulting has modified this by the hornblende tonal i t e i n t r u s i o n breccia. Later f a u l t i n g has modified t h i s The biotite-hornblende-epidote-chlorite biotite-hornblende-epidote-chlorite schists structure. The schistsmay may be be the the substrate substrate for f o r the thelayered layeredgabbro. gabbro. - �0 -- - - - IA C F(amo au R /1/ d N r1 }4 • '[ P-2- E-W-CA -l • ::\- tesafs __ç'.- TEt C1T r / L2) /• A /çL•.Zt_C Figure 9 —--—( • R E \N // -__ -__ / -:\ , } 2O ) 7 •7/ /r7, -- Bouguer anomaly gravity map of the Chippewa Valley region from Ervin and Hamer, 1974. �—21— - TABLE TABLE 77 - TENTATIVE CHRONOLOGY THE CHIPPEWA TENTATIVE CHRONOLOGY FFOR OR THE CHIPPEWA VALLEY VALLEY REGION REGION ———UNCONFORMITYUNCONFORMITY— Erosion, regional Erosion, j o i n t ijointing, n g , regional up1uplift ift —————--——--'-———"— I Fourth Deformation, Deformation,Block Blockf faulting Fourth a u l t i n g along along northwest-trending northwest-trending faults. Holcombe Taults. HolcombeDam, Dam, Lake Lake Wissota. Wissota. - IIntrusion n t r u s i o n of o fleucotronchjemite leucotronchjemiteveins, veins, Lake LakeWissota ~issota 1100mm.y. IIntrusion n t r u s i o n of o fgabbro-diabase gabbro-diabase dikes dikes throughout throughout region; region; ENE ENE trends trends (?) 1100 y . (?) C.UNCONF0RMITY Erosion — removal severalkilometers kilometers of Erosion removal o f ofseveral o f rock UNCONFORMITY —.r IThird T h i r d Deformation, Deformation, Cataclasis, Cataclasis,and andGreenschist GreenschistFacies FaciesMetamorphism Metamor~hism Largescale scale open openf ofolding ancfTical drag ffolding associated with Large l d i n g a n d x c a l drag o l d i n g a s s .------mylonitization; formation s t r i ke-sl i p faulting f a u l t i n gand and widespread widespread mylonitization; formation of andSouth South o f garnet, garnet, chlorite, c h l o r i t e ,and andepidote epidoteini amphibolites n amphibol itesand P Fork, Jump River volcanic volcanic and sedimentary series. series. I Fork, Jump River and sedimentary Aplite pegmatited idike A p l i t e and and pegmatite k e i nintrusion t r u s i o n ( L(Little i t t l e Falls, F a l l s , Jim Jim Falls) Falls) 25 m.y.* 1824 Fa1I sWissota , WissotaDam Dam (dikes) (dikes) IIntrusion n t r u s i o n of o f "Lineated "Lineated tonalite", tonal i t e " ,Jim JimFalls, Late Kinematic Kinematici intrusion Late n t r u s i o n of o f gabbro, gabbro, Yellow Yellow River River (Stop (Stop 8) 8) S 1830 ± 15 p•y* IIntrusion n t r u s i o n of o f trondhjemite, trondhjemite, granodiorite, granodiorite, adamellite, Lake adamel 1ite, Lake Wissota, Chippewa ChippewaFa1 Falls, Fisher River River (leucotrondhjemite) Wissota, l s , Fisher (leucotrondhjemi t e ) Main Main Cpulse ooff pplutonic pulse l u t o n i c aactivity. c t i v i t y . Intrusion I n t r u s i o nofo composite f composite batholiths batholiths along the axis along axis ofo the f thePenokean Penokean orogen. orogen. .4 CBreccia, LLittle 1842 ± 20 m.y.* Intrusion I n t r u s i o n ooff "Foliated "Foliated Tonalite" Tonalite" Breccia, i t t l e Falls, Falls, Cadott. Cadott. Synkinematic intrusion under high compression and the prepreSynkinematic i n t r u s i o n under compression and i nin the sence of a steep geothermal gradient. Formation of Little sence o f a steep geothermal gradient. Formation o f L i t t l e Falls Falls and Fisher Fisher River River breccias, breccias, and and possibly possibly the the breccia breccia aatt Cadott. and Cadott. 20 m.y.* Volcanism Volcanism and andSedimentation: Sedimentation: deposition deposition of 1860 o fSouth SouthFork Forkand andJump Jump River volcanic volcanic and and sedimentary sedimentary rocks rocks as as part p a r t of o fthe theFlambeau Flambeau and Black Black River River volcanic volcanic provinces. and provinces. - 0 - a UN CONFORMITY SecondDeformation, Deformation, Cataclasis, and Second andRegional RegionalMetamorphism Metamorphism Strike—slip S t r i k e - s l i ~f afaulting, u l t i n g . iocaliized l o c a l l i z e d cataclasis, cataclasis. formation formation ooff tectonic open (F-2) (F-2) open open folds, folds, development development oof fte ctonic ttight, i g h t , open breccias by differential breccias d i f f e r e n t i amovement l movement along along shear shear planes; planes; iintrafolial n t r a f o l i a folds.Subsequent l folds.Subsequent erosion. erosion. IIntrusion n t r u s i o n of o f trondhjemite trondhjemite (Cadott, (Cadott, Jim Jim Falls) F a l l s )and and Granite Granite ((Little L i t t l e Falls) Falls) First F i r s tDeformation Deformationand andMetamorphism Metamorphism w i t haxial a x i aplane l planeshearing, shearing, displacement; displacement; IIsoclinal s o c l i n a l folding f o l d i n g(F—i) (1-1 ) with formation ooff garnet (Big FFails). formation garnet porphyroblasts porphyroblasts (Big alls). Intrusion I n t r u s i o n and and ggravity r a v i t y ddifferentiation i f f e r e n t i a t i o nof o fBig BigFalls F a l l sgabbro gabbro For details, see For see Table Table 8. 8. —1 * Van Van Schmus, Schmus , 1980 1980 Basaltic Volcanism Basaltic Volcanism and and Sedimentation Sedimentation �IA ib '7 b 1'. A 9 P. E. Myers Mat Ic hornblende schist ? Kilometers BiotUe - hornbIende — epidote—chiorite schist Feidspothlc hornblende gneiss Hornblende tonolite Intrusion breccia Pegmotite Diabase EXPLANATION Figure 10-- Geologic map of the Eau Claire River including the Big Falls and Little Fans areas. thg SI N) N) �-23- —23— STOP STOP #1 fl :\T: TITLE: TITLE: - GEOLOGY BIG FALLS GEOLOGY OOF F BIG FALLSCOUNTY COUNTY PARK, PARK, EAU EAUCLAIRE CLAIRECOUNTY, COUNTY,WISCONSIN WISCONSIN LOCATION: LOCATION: Eau Claire ¼, SEC. SEC.13, 13, T. T. 27N., Claire Eau C l a i r e River, River,NW NH ¼, %, SE SE \, 27N., R. R. SW, 8U, Eau Eau C laire County County I935 - 925 ..Tiii 1 1' \:. :f t—\ / \C AUTHOR: AUTHOR: M.L. M.L. Cumings Cunnings DATE: DATE : - March, March, 1980 1980 -/———r i / - / - -— - — — — -r - SUMMARY OF SUIWARY O F FEATURES: FEATURES: The rocks aatt BBig Falls Parkare areppart The rocks ig F a l l s County County Park a r t oof f aa ddifferentiated i f f e r e n t i a t e d mafic mafic intrusive igneous compositional compositional banding banding i n t r u s i v eofo Early f E a r lPrecambrian y Precambrianage. age. Primary igneous is Rocks iinn the thearea areahave havebeen beendeformed deformed and and metametai s present present iin n aall l l units. u n i t s . Rocks morphosed three times times producing producing complex morphosed three complex rrelations e l a t i o n sbetween between primary primary igneous igneous structures structures and and structures structuresformed formed by by tectonic t e c t o n i cprocesses. processes. INTRODUCTION: INTRODUCTION: The outcroppings ooff Precambrian rocks aatt Big northThe outcroppings Precambrian rocks B i g Falls F a l l sCounty County Park Park ini nnorth— central Eau Claire County, Wisconsin, record a complex geologic Eau C l a i r e County, Wisconsin, record a complex geologic h history i s t o r y ffor or the west-central west-central Wisconsin Wisconsin area. area. Although Although on on ffirst i r s tinspection, inspection, the thegeology geology seems seems r erelatively l a t i v e l y straightforward, aacloser closerexamination examination reveals reveals evidence evidence ffor or possibly three periods of deformation and metamorphism and three possibly three periods o f deformation and metamorphism and three llate a t e stage stage apparentlong longgeologic geologichhistory recordedi inthe fault f a u l t sets. sets. The The apparent i s t o r y recorded n t h e rocks rocks sugsuggests that the Big Falls area and at least parts of the west-central gests t h a t the B i g F a l l s area and a t l e a s t p a r t s o f the west-centralWisconWisconsin s i n area area are are underlain underlainby byrocks rocksofo Archean f Archean age, age, possibly possiblyearly e a r l yArchean Archean age. age. �Figure 11 -- Outcrop geologic map of the Big Falls area, Eau Claire County, Wisconsin 6' 4Oteet transitional gnelss teldspathic gneiss omphlboflte schlst diobose dike bonded ntIbd lie gneiss EXPLANATION I a �-25- The outcrops aatt Big The outcrops B i g Falls F a l l sare arethe themost mostextensive extensiveand andbest bestexposed exposed outcrops of a differentiated mafic intrusive of unknown size. o ~ t c r o p so f a d i f f e r e n t i a t e d mafic i n t r u s i v e o f unknown size. Outcrops Outcrops of 3.5 km km up up river r i v e rfrom from Big Big of the the intrusive i n t r u s i v eare arefound foundfor f o approximately r approximately 3.5 Falls F a l l s tot oapproximately approximately44km kmdown down river r i v e r(Cumings (Cumingsand andMyers, Myers, 1978). 1978). The The intrusive contains anorthosites, gabbroic anorthosites, gabbros i n t r u s i v e contains anorthosi tes, gabbroic anorthosi tes, gabbros and and mafic mafic cumulates. cumulates. Mostly Mostly anorthositic a n o r t h o s i t i c rocks rocks crop crop out out down down rriver i v e r from from Big Big Falls; Falls; Besides representing gabbroic to mafic cumulates crop out upstream. gabbroic t o mafic cumulates crop out upstream. Besides representing the the best the intrusive, include examples best exposures exposures oof f the i n t r u s i v e , the theBig BigFalls F a l loutcrops s outcrops include examples of rock uunits o f the the major major rock n i t s ooff the the intrusive. intrusive. PREVIOUS PREVIOUSWORK: NORK: Big studied in west—central B i g Falls F a l l swas was one one of o f the the first f i r sareas t areas studied i n west-centralWisconsin Wisconsin mappedi ninddetail (Cummings, (Cumings, 1971). 1971). The The area area was was mapped e t a i l and and preliminary preliminarychemical chemical data data was was presented presented by byCumings Cumingsand andMyers Myers(1974) (1974)and andCummings Cummings (1975). (1975). An An expanded studya1along theEau EauC Claire RiverVal Valley the extent expanded study ong the l a i r e River 1ey iin n which which the extent of of exposure mapped, exoosure ooff the differentiated d i f f e r e n t i a t e dintrusive i n t r u s i vwas e was mapped, was was reported reportedby by these eearlier Cummings and Myers Myers (1978). This Cumings and This paper paper has has drawn drawn ffrom r o m these a r l i e rworks works but b u t also also presents presents new new interpretations i n t e r p r e t a t i o n sand andreexamines reexamines eearlier a r l i e r conclusions. conclusions. ROCK ROCK UNITS: UNITS: The byf four lithologies The ddifferentiated i f f e r e n t i a t e d intrusive i n t r u s i v e is i srepresented represented by o u r 11 thologies at at Big Big Falls F a l l s (Figure (Figure11). 11).The Theunits u n i t sare arerecognized recognizedby bythe thepercentage percentage of of hornblende and pplagioclase, hornblende and l agiocl ase, and and the the prominence prominence of o f compositional compositional banding. banding. hornblende—rich alternating Unit t e r n a t i ng U n i t 11 is i sdistinctly d i s t i n c t banded l y bandedwith with hornblende-rich bands bands a1 with The unit u n i thas has been been called c a l l e daabanded banded amphibolite amphibolite w i t h plagioclase-rich plagioclase-richbands. bands. The gneiss Myers, 1974) emphasized gneiss (Cumings, (Cumings, 1975, 1975,Cummings Cumings and and Myers, 1974) but b u t iti must t mustbebe emphasized that to tmetamort h a t the the banding banding is i s inherited i n h e r i t e dfrom from the the protolith p r o t o l i t and h andisi not s n odue t due o metamorphic differentiation. f r o m local local phic d i f f e r e n t i a t i o n . Unit U n i t one one is i s found found only only at a t Big Big Falls F a l l sand and from relationships bei ninf fault with the other other three three uunits r e l a t i o n s h i p s appears appears t otobe a u l t contact contact w i t h the n i t s at at garnet porphyroblasts porphyroblastsare areprominent prominenti nin the the uunit Big Coarse garnet n i t occurring occurring Big Falls. Falls. Coarse both both in i nhornblende—rich hornblende-rich and and plagioclase—rich plagioclase-rich compositional compositional bands. bands. Units Units 2, 2, 3, 3, and and 44 are are stratigraphically s t r a t i g r a p h i c a l lcontinuous y continuousand andare arerepresenrepresen- tative compositional banding t a t i v eofoapparent f apparentmesoscopic mesoscopicand andmegascopic megascopic compositional banding iinn the the intrusive. intrusive. Unit i sdark dark green green to t o black, black, finely-banded finely-banded amphibolite amphibolite sschist c h i s t of OT U n i t 22 is unit The tthird h i r d unit u n i t is i s .2.3 2.3 m m thick thick unit 2 2 to t o an an anorthositic a n o r t h o s i t i c uunit n i t in i n unit u n i t 4. 4. The and has sharp sharp contacts contacts against against units and has u n i t s 22 and and 4. 4. The The uunit n i t isi sbest bestexposed exposed on on the island i.suniform uniform along along sstrike, t r i k e , however however iitt isi sabsent absent i s l a n d where where i its t s width is or greatly disrupted on the north and south banks of o r g r e a t l y disrupted on the north and south banks o f the river r i v e rbecause because of of faulting. faulting. The The tthird h i r d unit u n i t is i stransitional t r a n s i t i o n a lfrom fromthe the amphibolite amphibolite sschist c h i s t ooff unit u n i t 22 to t o an an anorthositic The tthird h i r d unit u n i tisi s2.3 2.3m mthick t h i c and k andhas hassharp sharp concona n o r t h o s i t i c uunit n i t in i n unit u n i t 4. 4. The on the the island The uunit n i t is i sbest bestexposed exposed on i s l a n d where where iits ts tacts t a c t s against against units u n i t s 22and and 4. 4. The width i sabsent absent or o r greatly g r e a t l ydisrupted disrupted on on the the width is i s uniform uniform along along sstrike, t r i k e , however however iitt is north and south banks banksoof the rriver and south f the i v e r because because oof f ffaulting. aulting. The The ffourth o u r t h uunit, n i t , previously previously referred r e f e r r e d to t o as as aa feldspathic feldspathic gneiss, gneiss, is i san an The uunit n i t ranges ranges anorthositic a n o r t h o s i t i c unit u n i tthat t h adisplays t displaysdiffuse d i f f u scomposition e compositionbanding. banding. The from anorthosite to from aa gabbroic gabbroic anorthosite t o an an anorthosite. anorthosite. Oneo of themajor majord idifficulties Big One f the f f i c u l t i e s in i n interpreting i n t e r p r e t i n g the the geology geology oof f B i g FFalls a l l s iiss deciding which which structures structures and andtextures texturesare aremetamorphic metamorphic and and which which are are primary primary igneous featuresformed formed during andd idifferentiation f f e r e n t i a t i o n ooff the the intrusive. intrusive. igneous features during c r ycrystallization s t a l 1i z a t i o n and �—26- IGNEOUS FEATURES: PPRIMARY. R I N A R Y . IGr4EOUS FEATURES: The most prominentigneous igneousfeature feature iiss compositional All The m s t prominent compositional banding. banding. All rock units display such banding and each of the rock units is, in rock units display such banding and each o f the rock u n i t s i s , i n i titself, self, a compositional layer layer ooff the a compositional the larger l a r g e r intrusive. intrusive. Individual horn— Compositional bandsare arebest bestdisplayed displayedi ninuunit hornCompositional bands n i t 1. 1. Individual blende-rich bands range from 0.6 cm to nearly 20 cm thick and alternate alternate blende-rich bands range f r o m 0.6 cm t o nearly 20 cm t h i c k and Bandsare are generally generally with plagioclase-rich thick. Bands with plagioclase-rich bands bands 0.6 0.6 cm cm tto o 30 30 cms cms thick. uniform in thickness along strike but individual bands cannot be uniform i n thickness along s t r i k e but individual bands cannot be traced traced the crude mesoscopic inesoscopic the length length ooff the the outcrop outcrop because because o fofl alate t e ffaults. a u l t s . AA crude banding is also present; feldspar—rich bands are prominent nearthe ther river, banding i s also present; feldspar-rich bands are prominent near iver, but thickness of but the the number number and and thickness o fhornblende—rich hornblende-rich bands bands increases increases away away from from the river. the r i v e r . Compositionalbanding banding not as as obvious obviousasasi ninuunit Compositional i n in u nunit i t 2 2i sis not n i t 1, 1, but but Fine—scale banding (<.5 cm) may be metamorphically iiss nonetheless nonetheless present. present. Fine-scale banding (< .5 cm) may be produced, however howeverbands bands greaterthan than15 15cm cmt hthick are believed primary. i c k are primary. The The produced, greater more mafic layers, possibly representing clinopyroxene olivine m r e mafic layers, possibly representing clinopyroxene o l i v i n ecumulates, cumulates, contain 60 contain 60 to t o 90 90 percent percent hornblende. hornblende. Cumingtonite—garnet—hornblende Cumningtoni te-garnet-hornblende layers may represent olivine, m y represent olivine, orthopyroxene orthopyroxenecumulates. cumulates. The The mesoscopic inesoscopic Someoof compositional bands can be easily traced through the park. f the compositional bands can be e a s i l y traced through the park. Some mesoscopic bands are characterized by fine-scale bands of plagioclase msoscopic bands are characterized by fine-scale bands o f plagioclase Suchfine-scale fine—scale bands alternating bands areare d i fdifficult f i c u l t tto o trace trace a1 ternating with w i t hhornblende. hornblende. Such becauseooff deformation. because deformation. - The percentage percentage ooff hornblende The fourth fourth unit The u n i tisi sweakly weaklybanded. banded. The hornblende varies varies from band bandt to band, generally generally composing less than than 15 15 percent percent ooff aa given from o band, composing less given band. band. The contact contact zone zonebetween betweenu nunit anduunit The i t 22 and n i t 3 is i sremarkable remarkable for f o raanumber number During crystallization of the intrusive of apparently primary features. During c r y s t a l l i z a t i o n o f the intrusive o f apparently primary features. blocks ooff already already ccrystallized to the the ffloor blocks r y s t a l l i z e d material material apparently apparently dropped dropped t o loor by crystals accumulating there. of the intrusive and were buried by the c r y s t a l s accumulating there. Three Three i n t r u s i v e and were buried o f the exampleso of blockshave havebeen beenfound. found.Figure Figure1212i sisaafeldspar-rich feldspar—richcclast examples f blocks l a s t that that The iinternal displays internal displays i n t e r n a lcompositional compositional banding. banding. The n t e r n a l banding banding iiss truncated truncated by banding bandingi in the more moremafic maficenclosing enclosingrock, rock, folds folds in by n the i n the theclast c l a smay t mayhave have Two examples examplesoof hornblende—richcclasts been produced producedbybyl alater been t e r deformation. deformation. Two f hornblende-rich lasts casethe the cclast have been been discovered. discovered. IInn each have each case l a s t is i s clearly c l e a r l ymore m r e mafic mafic than than the enclosing rock. banding iiss not n o t present present in i neither e i t h e rsample. sample. the rock. Internal banding Although the clasts clasts have havebeen beenf l aflattened in the the plane planeooff sschistosity Although the ttened i n c h i s t o s i t y they they can can of be recognized recognizedas asclasts clasts formed formed during during magmatic magmaticc rcrystallization. Blocks of be y s t a l l i z a t i o n . Blocks earlier r o m ddifferent i f f e r e n t sstratigraphic t r a t i g r a p h i c units u n i t s of of e a r l i e r crystallized c r y s t a l l i z e d materials materials ffrom differentiated differentiated mafic maficintrusives intrusiveshave havebeen been noted noted in i nmajorcomplexes, m j o r complexes, including including the Bushveld the Stillwater Bushveld Complex Complex (Willemse, (Willemse, 1969 1969 )) and and the S t i l l w a t e rComplex Complex (Hess, (Hess, 1960). 1960). Anotherfeature featurenear nearthe thecontact contactbetween between and Another u nunit it 2 2 and u nunit i t 3 3i sisi illusllusstrongly contorted trated 3. AA strongly contortedband band approximately approximately 0.3 0.3 mm wide wide can. can t r a t e d in i n figure f i g u r e 3. be traced across the island. The width and andthe ther relative be traced across the The width e l a t i v e stratigraphic axesoof approximately uniform. uniform. The level of o fthe theband bandare areapproximately The axes f ffolds o l d s in i nthe theband band are apparently random,and andlimbs limbsare arecomnonly comonlytruncated truncated against against limbs limbs of are apparently random, of other folds. The other The ffold o l d axes axes do do not coincide coincide with w i t h any any deformation d e f o m t i o n features features observedi in the enclosing rocks. Apparently Apparently the the material material represents soft observed n the reoresents soft sediment thecrystals crystals tthat thef lfloor sediment ddeformation e f o m t i o n o fofthe h a t accumulated accumulated ononthe o o r ooff the the magma chamber during crystallization. magma chamber during crystal1 ization. Slumpage Slum~ageo of f eearly a r l y formed formed ccrystals rystals on havebeen beentriggered triggeredby by convection convection iin n the cooling cooling on the chamber chamber f lfloor o o r may may have magma earthquakes during the intrusive. magma o r or earthquakes during c r ycrystallization s t a l l i z a t i o n oof f the �-27— The apparentlyprimary primary cclasts features in The abundance abundance o of f apparently l a s t s and and slump slump features i n the the contact betweenu unit anduunit lack of n i t 33 and and the the apparent apparemt lack o f such such features features contact zone zone between n i t 22 and in outcrop i n the the rest r e s tofo the f the outcroparea areasuggests suggests either e i t h e raaslow slowrate r a t eofoaccumulation f accumulation of o f crystals c r y s t a l sononthe thechamber chamber floor f l o o rallowing allowingsuch suchfeatures featurestot appear o appearconcenconcen- trated off tect r a t e d over over a a thin t h i n stratigraphic s t r a t i g r a p h i c zone, zone, or o r might might indicate i n d i c a t e aa period period o tectonic t o n i c instability i n s t a b i l i tduring y duringwhich whichblocks blocks of o fcrystalline c r y s t a l l i n material e materialdropped dropped to t o the the floor chamber f l o o rofo the f the chamberand and slumpage s l umpage ooff unconsolidated unconsolidated ccrystals r y s t a l s occurred. occurred. TECTONIC TECTONIC FEATURES: FEATURES: Polymetamorphism and make the geologic p opolydeformation l y d e f o m t i o n make i n t interpretation e r p r e t a t i o n oof f the geologic Polymetamorphism and the rocks evolution evolution oof f BBig i g FFalls a l l s ddifficult. i f f i c u l t . The The response response ooff the rocks to t odeformation deformation and metamorphism under varyingconditions conditionshas hasproduced produceda awide widev variety and metamorphism under varying a r i e t y ooff structural s t r u c t u r a land and mineralogical mineralogical features. features. One the important features of One oof f the important features of the the rock rock is i s that t h a t the the intensity i n t e n s i t yofo dislocative f d i s l o c a t i v edeformation deformation is i snot n o tconstant constant rocks are are adjacent throughout throughout the the area. area. Intensely Intensely deformed deformed rocks adjacent to t o rocks rocks conconThe deformational and metamorphic taining primary igneous features. t a i n i n g primary igneous features. The deformational and metamorphic history h i s t o r yofo fthe thearea areahas hasbeen been reconstructed reconstructed from from tthin h i n section section analysis analysis coupled with interpretation of structures observed in l e d w i t h i n t e r p r e t a t i o n o f structures observed i n outcrop. outcrop. The features are are the the coarse garnet porhe oldest apparent apparent metamorphic metamorphic features coarse garnet phyroblasts whichoccur occuri nin uunit prominentlyi in The garnets garnets and prominently n uunit n i t 1. 1. The phyroblasts which n i t 2 and are are believed believed to t obe beoldest oldestbecause because they theyappear appear to t ohave have been been present present while while younger structures and mineral textures were developing in the younger structures and mineral were developing i n the rocks. rocks. have formed formed aatt the Highly elongatedi sisoclinal Highly elongated o c l i n a l ffolds o l d s in i n unit u n i t11 may may have the same same time. time. The The aaxial x i a l planes planes of o f such such folds f o l d s are are typically t y p i c a l l ysheared sheared(Figure ( ~ i g u r14.) e14. )Some Some of the structuresfound foundi ninu unit the well—developed well-developed f o fold l d structures n i t 2,2, pparticularly a r t i c u l a r l yon on the the island, island, may may be be of o fthe thesame sameage. age. Folding preceded preceded f faulting. a u l t i n g . The The ffaults aults cross lowangle angle(probably (probablyemphasized emphasized by by cross the the compositional compositional banding banding at a taalow later l a t e r flattening) f l a t t e n i n g )producing producing aa pattern pattern that t h a t resembles resembles ccross-stratification r o s s - s t r a t i f i c a t i on (Figure features appear appeart oto be bethe the remnants remnantso of theeearliest (Figure 15). 15). The The above above features f the arliest deformation Deformation, although although intense intense deformation and and metamorphism metamorphism oof f the area. area. Deformation, and pervasive, ddid not features iinn the main and pervasive, id n o t destroy destroy primary primary features the rock. rock. The main deformational features are are found found iin with deformational features n rocks rocks w i t h aa relatively r e l a t i v e l yhigh highpercentage percentage gradeapparently apparentlywas wasi nin the the garnet garnet amphibolite of o f plagioclase. plagioclase. Metamorphic Metamorphic grade a more morebbrittle Faulting late l a t eini nthe thedeformational deformational period period suggests suggests a rittle facies. facies. Faulting behavior behavior iinn the the rock rock after a f t e rhaving havingbehaved behaved in i n aa ductile d u c t i l emanner manner during during the the peak peak of o fmetamorphism. metamorphism. The metamorphism-deformationd idid develop as as extensive aa The second second metamorphism-deformation d nnot o t develop main structures structures appear The main appear to t o be be associated associated suite s u i t e of o fdeformational deformational features. features. The with and eearly w i t h flattening f l a t t e n i n gasasindicated indicatedbybycompositional compositional banding bandin9 and a r l y ffault a u l t planes planes zonesooff ddislocation wrapped aroundgarnet garnet porphyroblasts. Major wrapped around Major zones i s l o c a t i o n are are aa occurs iinn unit minor minor feature of o f the thedeformation; deformation; one one occurs u n i t22where where aashear shear zone zone zonepresents presentsan anexcellent excellent .example exampleoof cuts f ttransposition ransposition The zone cuts the schist. schist. The of compositionally banded o f foliation, f o l i a t i o nwhere , wherepre-existing pre-existing compositionally bandedrocks rocksoccur occuras as tectonic tectonic inclusions inclusions oorr rootless rootless intrafolial i n t r a f o l i afolds l f o l d sin ian strongly a s t r o n g ldeformed y deformed deformational zone meters wide. wide. Locally Locally matrix. The The deformational zone iiss approximately approximately 22 meters matrix. and 2 and foliation some openf ofolds havedeveloped developedi in units some open l d s may may have n u n i t s 11 and 2 and f o l i a t i o ndeveloped developed under amphibolite amphibolite The rock rock was was metamorphosed metamorphosed under particularly p a r t i c u l a r l y in i n unit u n i t 2. 2. The producedaacoarse coarse grained plagioclase— The metamorphism metamorphism produced plagioclasefacies conditions. conditions. The hornblende assemblage and recrystallization of the hornblende assemblage and r e c r y s t a l l i z a t i o n o f the f afault u l t planes planes ooff earlyI n unit u n i t 11 coarse coarse garnet porphyroblasts porphyroblasts apparently apparentlybecame became formed ffaults. a u l t s . In formed �-28- unstable unstable in i n the thepresence presence of o f plagioclase plagioclaseunder underthe thenew newmetamorphic metamorphic conditions conditions and reaction rims of a highly aluminous hornblende developed and reaction rims o f a highly aluminous hornblende develooedbetween between the the two ~ W Ophases. phases. Similar Similar alteration a l t e r a t i o nofo fgarnet garnettot ohornblende hornblende also also occurs occurs iinn unit unit 22 but but is i snot n o tas asreadily r e a d i lobserved y observedini noutcrop outcropbecause because of o fthe thehigh highpercentage percentage of o f amphibole amphibole iin n the the rock. rock. The sequencei sis associated associated w with The tthird h i r ddeformatlonal—metamorphic d e f o m t i o n a l - m e t m r p h i c sequence i t h developdevelopment ment ooff intense intense zones zones ooff deformation defonnation that t h a t occur occur on on the the south south bank bank and and island island and the development weaksschistosity and the development oof f aa weak c h i s t o s i t y oriented orientedNN55 55W. !4. The The main main deformdefomation beenbefore beforer erecrystallization a t i o n appears appears tto o have have been c r y s t a l l i z a t i o n since sinceshear shear zones zones that that developed onthe thei island and south south bank bankare arethoroughly thoroughlyrrecrystallized developed on s l a n d and e c r y s t a l l i z e d and and fine f i n e pervasive pervasive shear shear zones zones iin n unit u n i t11 are are not not only only recrystallized r e c r y s t a l l i z e dbut b u tserved served Although deforas the locus for crystallization of fine—grained garnet. as the locus f o r c r y s t a l l i z a t i o n o f fine-grained garnet. Although deformation features are are not not prominent, prominent,recrystal recrystallization mation features 1i z a t i o n textures textures are areextensive. extensive. The coarse grained The main new mineral to appear was euhedral epidote. The grained The main new mineral t o appear was euhedral plagioclase that t h a thad hadformed formed during during the thesecondmetamorphism second metamorphism r recrystallized e c r y s t a l 1ized grains tthat to clusters ooff fine t o form form clusters f i n e polygonal polygonal grains h a t preserve preserve the the outline o u t l i n eand and recrystallized twinning twinning ooff the original o r i g i n a l plagioclase plagioclase grains. grains. The The recrystal 1ized plagioclase plagioclase is as 10 10 percent percent aanorthite i s variable variableini ncomposition compositionranging rangingas asmuch much as n o r t h i t e content content within I n unit u n i t22the thedevelopment development of of w i t h i n aa single single relict r e l i c tplagioclase plagioclase grain. grain. In prismatic was prismatic hornblende hornblende and and locally l o c a l l yeuhedral euhedralepidote epidote wasaccompanied accompanied by by crystallization c r y s t a l l i z a t i o nofo ffine—grains fine-grains of o f ilmenite ilmenite in i nrelict r e l i ccoarse t coarsehornblende hornblende ilmenite inclusions inclusions are are hhighly the old crystals. Such Such ilmenite i g h l y concentrated concentrated i in n the old grains but but aanarrow narrow inclusion—free inclusion-free band band surrounds surrounds each each grain. Apparently Apparently the third metamorphism occurred under epidote amphibolite facies conditions t h i r d metamorphism occurred under epidote amphiboli t e facies conditions that extensiver recrystallization t h a t produced produced extensive e c r y s t a l l i z a t i o n but b u tdid d i dnot n o completely t completely destroy destroy the coarse second metamorphism. coarse grained grainedtextures texturesproduced producedduring duringthethe second metamorphism. All with A l l younger younger sstructural t r u c t u r a l features features in i nthe therocks rocks are are associated associated w i t h late late casethe thef fault are nnot faults. In I n each each case a u l t planes planes are o t recrystallized r e c r y s t a l l i z e d and and are are the the sites s i t e s of o f alteration a l t e r a t i o n of o fthe therock. rock. A deformation and metamorphism theBig Big FFalls A sunuiary s u m r y ooff deformation and metanmrphism f ofor r the a l l s outcrops outcrops groupingoof deformationalfeatures featuresi sis different different is The grouping f deformational i s presented presented in i n Table Table 1. 1. The than the interpretations presented by Cunrings (1975) in that growth than the interpretations presented by C m i n g s (1975) i n t h a t growth of of garnet porphyroblastsand and therock rock garnet porphyroblasts f o lfolding d i n g o f of the i n into t o t i tight g h t i isoclinal s o c l i n a l folds folds Also the second deformation are included in the first deformation. the second deformation is is are included i n the f i r s t deformation. interpreted more as aa fflattening more as l a t t e n i n g event event than than an an intense intense folding f o l d i n g event event as as previously. the interpretation threemajor majordeformational deformational I n any any case, case, the i n t e r p r e t a t i o nof07three previously. In and metamorphic events has m e t m r p h i c events has not n o tchanged. changed. Relating the events recorded recorded aatt Big the deformational deformational and and metamorphic m e t m r p h i c events Big Falls frameworko fofregional regionaltectonic tectonicaactivity F a l l s to t o the the broader broader framework c t i v i t y is i s not not an an Penokean easy easy task. The The tthird h i r ddeformation deformationisi sapparently apparentlyyounger youngerthan thanthe the Penokean zonesand andr erecrystallization found aatt Big Falls Orogeny. Cataclastic Cataclastic zones c r t a l l i z a t i o n found F a l l s are are also also present present aatt LLittle i t t l eFalls F a l l s(stop (stop2),2 one , onemile m i l east, e east,where whereaa1842 1842 ±2 10 mm.y. 1980)t otonalite y . (Van (Van Schmus, Schmus, 1980) n a l i t e intrusive i n t r u s i v ehas hasexperienced experiencedthe thesame same the tthird deformation andr erecrystallization. deformation and c r y s t a l l i z a t i o n . Possibly Possibly the h i r d event event coincide coincide with with widespread low-grade m.y. (Van widespread low-grade metamorphism metamrphism at a t 1650—1700 1650-1700 m.y. (Van Schmus, Schmus, 1976, 1976, structures Sims, Sins, 1976 1976 i nthe theLake LakeSuperior SuperiorRegion. Region. The The structures )) reported in developed developed aat t tthat h a t time, time, as as seen seen at a t Big BigFalls, Falls,may maynot n obe t beprominent prominentand and shear zones, although althoughpreserving preservingcataclastic cataclastic textures shear zones, textures ini nhand handsample sample are are Big FFalls thoroughly recrystallized. Structures thoroughly recrystallized. Structures produced produced aat t Big a l l s during during the the third be eeasily without great great aattention t h i r d deformation deformation could could be a s i l y overlooked overlooked without t t e n t i o n to to ? �—29— TABLE TABLE 1: 1: Chronology Chronology ffor o r Big Big Falls F a l l sCounty CountyPark Park Intrusion I n t r u s i o n and and ddifferentiation i f f e r e n t i a t i o n of of a a mafic mafic intrusive. intrusive. Slump structures develop developon onthe thef floor Slump structures l o o r of o f the the magma magma chamber chamber and autoliths are produced by tectonic activity. and a u t o l i ths are produced by tectonic a c t i v i t y . First and metamorphism F i r s deformation t deformation and metamrphism Crystallization Crystal1i z a t i o nofofcoarse coarsegarnet garnet porphyroblasts porphyroblasts iinn units units 1 1 and and 2. 2. Isoclinal I s o c l i n a lfolding f o l d i n gand andshearing shearing of o f axial a x i a l planes planes of o f the the developing d e v e l o ~ i n afolds. folds. Faulting. Second Second defdrmation deformationand andmetamorphism metamorphism Flattening F l a t t e n i n gand and development development ooff local l o c a l intensely intenselysheared shearedzones. zones. Minor Minor open open folds f o l d sproduced. produced. Crystallization C r y s t a l l i z a t i o nofofcoarse coarsegrained grainedhornblende hornblende and and plagioclase. plagioclase. Alteration to tan aluminous A l t e r a t i o nofogarnet f garnet o an aluminoushornblende hornblendebecause because of of incompatability between plagioclase p l agiocl ase and and earlier e a r l i e rformed formed garnet. garnet. incompatabil itybetween Third metamorphism T h i r ddeformation deformationand and metamorphism Local deformation,c crystallization Local intense intense cataclasis cataclasis and and deformation, r y s t a l l i z a t i o n of of NS5W N55W s schistosity. chistosity. Growth euhedralepidote, epidote,r erecrystallization Growth oof f euhedral c r y s t a l l i z a t i o n of the the rock rock but but textures are not destroyed. texturesproduced produced during duringthe the2nd 2ndmetamorphism metamorphism are destroyed. Late Late faulting faulting Development lens shaped, fault—boundedstructures structuresi in Development oof f lens shaped, fault-bounded n unit u n i t11 as as unit u n i t11 is i sfaulted f a u l t e dinto i n t oplace placeagainst against unit u n i t2.2. Right—lateral Right-lateral faults faults Left-lateral L e f t - l a t e r a l faults faults �-30- the ffine The second deformation and the i n e details d e t a i l s In i n the the rock. rock. The second deformation and metamorphism metamorphism aatt Big Falls plutonism and metamorphism Big F a l l s coincides coincideswith w i t hregional regional plutonism and metamorphism associated associated with the with thePenokean PenokeanOrogeny. Orogeny. Intense Intense folding folding does does not n o tappear appear to t ohave have occurred occurred aatt Big Big Falls F a l l s at a t this t h i s time. time. Instead Instead aa pronounced pronounced f lflattening a t t e n i n g and and the the developdevelopment The ffirst ment ooff local l o c a lshear shearzones zones are are recorded. recorded. The i r s tdeformation deformationproduced produced 'the the pervasivei sisoclinal pervasive o c l i n a l folding f o l d i n g at a tBig B i gFalls F a l l sand andappears appears tto o represent represent llate ate Archean deformation. Thus Thusthe thei nintrusion andddifferentiation Archean deformation. t r u s i o n and i f f e r e n t i a t l o n of o f the the mafic mafi c intrusive appears to have been an earlier Archean event. i n t r u s i v e appears t o have been an e a r l i e r Archean event. SUMMARY: S UMMARY : The outcropsa at BigFFalls areppart The outcrops t Big a l l s are a r t oof f aa ddifferentiated i f f e r e n t i a t e d mafic mafic intrusive intrusive Claire The iintrusive tthat h a t crops crops out out along along the the Eau Eau C l a i r e River. River. The n t r u s i v ewas was emplaced emplaced during the Archean. Differentiation Archean. D i f f e r e n t i a t i o nproduced produced compositional compositional layering layering and and possible possible tectonic tectonic activity a c t i v i t yduring duringcrystallization crystal 1i z a t i oproduced n producedslump slump structures structures and and autoliths. Three deformational and and metamorphic metamorphic, periods resultedi ninfolding, folding, autoliths. Three deformational periods resulted The first deformation appears faulting and recrystallization of the rocks. f a u l t i n g and r e c r y s t a l l i z a t i o n o f the rocks. The f i r s t deformation appears beenArchean Archean ageand and produced structuresi in ttoo have have been i ninage produced i s o cisoclinal l i n a l f ofold l d structures n aalll l The second deformation occurred during the Penokean Orogeny rock units. rock units. The second deformation occurred during the Penokean Orogeny and The tthird and i is s primarily p r i m a r i l y associated associated wwith i t h fflattening l a t t e n i n g of o f the the area. area. The h i r ddefor— deformation is with regional low—grade i spossibly possiblyassociated associated w i twidespread h widespread regional low-grademetamorphism metamorphism iinn the theLake Lake Superior SuperiorRegion. Region. �—31— I I 2.'.' -- Figure 12 Anorthositic cclast schist. Figure 12 -—Anorthositic l a s t enclosed enclosed iin n amphibolite amphibol i t e schist. betweenuunit and uunit on the the island. island. between n i t 22 and n i t 33 is i s exposed exposed on Contact zone zone I -- 13 -- Possible Figure 13 structure iinn amphibolite Figure Possible slump slump structure amphibolite schist in i n the the contact contact zone zone betweenuunit and uunit as exposed exposedon onthe the island. island. between n i t 33 and n i t 44 as �—32— C Ifl - hornblende— Figure fold structure structure from Figure 14 14—- Sheared Sheared fold from unit u n i t 1. . Black Blackareas areasare are hornblendeporphyroblast rich bands and round object in lower right corner is a garnet rich bands and round object in lower right corner i s a garnet porphyroblast 1 a—- —a- — — w_ — - -c 1.d - -- 15 cn, . Note the similarity similarityto tcross— o crossFigure Earlyformed formedf afault in unit u n i t 1 . Note Figure 15—— 15-- Early u l t in has s t r a t i f i c a t i o nfound foundinin sediments. The The fault f a u lplane t plane hasbeen beenwrapped wrappedaround around stratification sediments. garnet blackroughly roughly circular circular features. garnet porphyroblasts porphyroblasts shown shown asasblack features. 1 �—33— ACKNOWLEDGEMENTS: ACKNOWLEDGEMENTS: The presenti ninterpretation the geology geologyoof BigFFalls The present t e r p r e t a t i o n oof f the f Big a l l s iis s the the result result of with o f years years ofofwork workand anddiscussions discussionswith w i t hmany many people. people. Discussion P. Myers, Myers, Discussion w i t h P. R. Maass, 3. Grant, D. Davidson and participants on several field trips R. Maass, J. Grant, D. Davidson and p a r t i c i p a n t s on several f i e l d t r i p shave have influenced thinking. influenced my my thinking. REFERENCES REFERENCES CITED CITED Cummings, M.L., 1971, 1971, Geology Geologyoof Cumings, M.L., f BBig i g Falls, F a l l s , Wisconsin: Wisconsin: Guidebook, Guidebook, 3rd 3rd Annual Wisconsin State University Geology Field Conference, Annual Wisconsin State University Geology F i e l d Conference, p. p. 13—20. 13-20. Cumings, Cutmnings, M.L., M.L., Myers, Myers, P.E., P.E., 1974, 1974, Geology Geology ooff the the Big Big Falls F a l l sArea: Area: book, Tn-State Geological Conference. book, 38th 38th Annual Annual Tri-State GeologicalField F i e l d Conference. , GuideGuide- Cummings, M.L., 1975, 1975, Petrology Petrology and and sstructure Cumings, M.L., t r u c t u r e of o fPrecambrian Precambrian gneisses gneisses at at Big thesis, University B i g Falls, F a l l s ,Eau EauClaire C l a i r eCounty, County,Wisconsin: Wisconsin: M.S. M.S. thesis, U n i v e r s i t y of of Minnesota, Minnesota, Duluth. Dul uth. Cummings, M.L., Myers, Myers,P.E., P,E., 1978, Cumings, M.L., 1978, Petrology and and geochemistry geochemistry ooff Amphibolites, Amphibolites, Eau Claire Eau C l a i r e River, River,Eau EauClaire C l a i r eCounty, County,Wisconsin: Wisconsin:Cabs) (abs)24th 24thAnnual Annual Institute Lake I n s t i t u t on e on LakeSuperior SuperiorGeology. Geology. Hess, America, Hess, H.H., H.H., 1960, 1960, Stillwater S t i l l w a t eIgneous r IgneousComplex: Complex: Geological Geological Society Society of of America, Memoir 80, p. Memoir 80, p. 225. 225. Sims, 1976, Precambrian Precambrian Tectonic Tectonic and and Mineral Mineral Deposits, Deposits, Lake Lake Superior Superior Sims, P.K., P. K., 1976, Region: Geology, V.V. 71, Region: Economic Economic Geology, 71, p.p.1092-1118. 1092-1118. Van Schmus,1976, 1976,EEarly andMiddle MiddleProterozoic Proterozoic hhistory Van Schmus, a r l y and i s t o r y of of the theGreat GreatLakes Lakes Area, Area, North NorthAmerica: America: Phil. P h i l .Trans. Trans. R.R. Soc. Soc. Long. Long. A. A. 280, 280, p.p.605-628. 605-628. Van 1980, Geol. Geol. Soc. Paper, #180, #180, Goldich GoldichVolume. Volume. Soc. Amer. Amer. Spec. Spec. Paper, Van Schmus, Schmus, 1980, Willemse, J., 1969, 1969,The Thegeology geology ofo fthe theBushveld BushveldIgneous Igneous Complex, Complex, the largest largest Willemse, 3., repository of magmatic ore deposits in the world: in Magmatic repository o f magmatic ore deposits i n the world: i n Magmatic ore ore deposits: GeologyPublishing Publishing Co. Co. p. 1-22. Economic Geology 1-22. deposits: Economic �-35-35STOP STOP #2 #2 TITLE: TITLE: - LITTLE LITTLEFALLS FALLSBRECCIA BRECCIA LOCATION: LOCATION: County HighwayKKaat EauCClaire 1/4, NW 1/4, Sec. t Eau l a i r e River; SW SW 114, NW 114, Sec. 19, 19, County Highway T27N, Fall Creek 77 1/2' T27N. R8W R8W Fa1 1 Creek 1/2' Quadrangle Ouadranal e - T - J' '7. - • AUTHOR: Paul E. Myers DATE: February, 1980 SUMMARY OF FEATURES: Archean basalt, vo.lcanogenic sediments,and andgranite, granite, aafter ? ) basalt, volcanogenic sediments, f t e r being being Archean ((?) deformed andr erecrystallized deformed and c r y s t a l l i z e d aatt least l e a s t twice, twice, were were synkinematically synkinematically intruded intruded by hornblende tonalite about 10m.y. m.y. hornblende tonal i t e tto o form form the t h e Little L i t t l eFalls F a l lbreccia s breccia about1842 1842++10 A f t e r intrusion i n t r u s i o nofo fgranite g r a n i t epegmatites, pegmati t e s , tthe h e rocks rocks ago ago (Van (Van Schmus, Schmus, i in n press). After were again: deformed deformedbybyshearing, shearing,wwith widespread development developmento of were again i t h widespread f ccataclastic atacla s t ic rocks narrow, interlensing,'ENE Most ooff these these rocks and and narrow, i n t e r l e n s i n g , ' ENE to t oWNW-trending WNW-trending ffaults. a u l t s . Most Shallow iintrusion n t r u s i o n of o fdiabase diabase about about faults f a u l t s at a t Little L i t t l eFalls Fa11s are are right-lateral. r i g h t - l a t e r a l . Shallow 1100 m.y. ago agofollowed followedprolonged prolongedup1 uplift the erosion erosion ooff several kilometers 1100 m.y. i f t and and the several kilometers green cclay remaining i in on tthe Pockets oof f green l a y remaining n low low places places on h e amphibolitic amphibolitic o f rocks. rocks. Pockets of terrane were were buried during during marine marine deposition deposition of o fthe t h eMt. Mt.Simon SimonSandstone Sandstone in in Deeply weathered till and outwash southwest the Cambrian time. Deeply weathered t i l l and outwash southwest ooff the Late Cambrian bridge bridge aatt Little L i t t l eFalls Fa11may s mayrepresent represent aa pre-Wisconsin pre-Wisconsin g glaciation l a c i a t i o n oof f tthis h i s region. region. DESCRIPTION: DESCRIPTION: The complexstructures structuresand and texturesi nint hthe The complex textures e L Little i t t l e Falls Fa11s breccia breccia are are mainly a manifestation of a variation in the proportions of plagioclase, mainly a manifestation of a v a r i a t i o n i n the proportions o f plagioclase, B i o t i t e , epidote, epidote,and andchlorite c h l o r i t eare aresparse sparseaccessories. accessories. and hornblende. hornblende. Biotite, quartz, and �-36- Banded amphibdilte, amphibdiite ,composed composed of of45-70% 45-70% hornblende hornblende and and 20-40% 20-40% pl agi ocl a s e plagioclase Banded e xenoliths t h e breccia. breccia. Many make up make upabout about90% 90%ofoft hthe xenol.iths in in the Many of the t h ebanded banded amphibol i t e xenoliths xenoliths contain contain folds foldswhich whichwere were detached detached dduring u r i n g tonalite tonal i t e amphibolite intrusion. However, mostofofthe thexenoliths xenolithsaare elongatedparallel parallel tto intrusion. However, most r e elongated o ttheir heir lamination. ItI tisisnoteworthy xenoliths aat noteworthy that t h a t the t h e amphilolite amphilolite xenoliths t LLittle i t t l e Falls Falls lamination. do not not contain contain garnets, garnets, although a1 though garnetiferous garnetiferousamphibolite amphibol i t eisi sexposed exposed 1/4 1/4 mile mile do enveloping r a r eini the n t h xenoliths e xenoliths(<5%) ( 4 5%)as as iti tisi in s ithe n the enveloping downstream. Biotite B i o t i t eisisrare downstream. tonal i t e tonalite. . U l tramaficxenoliths, xenol i ths,which whicharea rcomposed e composed ofofover over90% 90%greenish greenish gray gray Ultramafic Mg-rich hornbiende hornblende wwith i t h accessory accessory epidote-cl inozoisi t e , and and plagioclase, plagiocl ase, Mg-rich epidote-clinozoisite, make up e s s than t h e breccia. breccia. Their make upl less than 5% 5%ofofthe the xenoliths xenoliths iinn the Theirangular angularshape shape l u s t e r s indicate fragmentation fragmentation and a r t i a l dispersal dispersal of of and occurrence and occurrencei nin cclusters andppartial d u r i n g ttonalite o n a l i t e intrusion. intrusion. This This feature f e a t u r e of of fragmentation fragmentation is is l a r g e r blocks blocks during larger we1 1-displayed at a t Location Location 7927-D 7927-D (Figure 1Q. Some Some ofof tthe h e ultramafic u l tramafic well-displayed (Figure1. xenol i ths show show relict re1 i c tgabbroic gabbroictextures textureswith w i t hprimary primarypyroxene pyroxene apparently apparently xenoliths 7927-N-1) rep1 aced by by metamorphic metamorphic hornblende. (Tab1e 11,,7927-N-i) replaced hornblende. (Table tabular xenolith xenol i t h (?) ( ? ) of offine-grained, fine-grained, foliated f o l i a t e dhornblende hornblende tonalite tonal i t e AA tabular (Table 55 , , 7927-N-2). occurs just east e a s t of ofthe thebridge. bridge. (Table 7927-N-2). occurs aatt the location just AA large of -foliated, bliated, porphyroblastic large fragment fragment of porphyroblastic biotite b i o t i t egranite graniteis iexposed s exposed wasmapped mapped a t Location Location7927-V. 7927-V. The The fragment fragment was i n ind edetail t a i l (Figure 4). 4 ) . The The at granite granite contains contains 1-3 1-3cm cm porphyroblasts porphyroblasts of K—feldspar K-feldspar i nin aa ffoliated o l i a t e d granoblastic granoblastic Sodic piagioclase plagioclase isi s matrix matrix of of microcline, microcline, quartz, quartz, and and brown brown bbiotite. i o t i t e . Sodic Lenticular Lenticular form form of ofthe theK-feldspar K-fel dsparporphyroblasts porphyrobl a s t s indicates indicates The gradational contact contact recrystallization beforeand/or and/or during during cataclasis. catacl asi s . The recrystal 1 i z a t i onbefore between the fragment fragment and andenclosing enclosing breccia breccia iiss marked by an an inward inward substitution substitution marked by between the of of K—feldspar K-feldspar ffor o r plagioclase plagioclase and and bbiotite i o t i t efor f ohornblende r hornblendeand and by by an an increase increase in in gradational contact contact along along aatt lleast abundance of quartz. The The gradational e a s t the the west west side s i d e of of abundance of quartz. the indicatest hthat i s aa xenolith xenolith and and not not aa ffault a u l t slice, s l i c e , although although its its the fragment fragment indicates a t iitt is shape andposition position were probably modified modified by by post-intrusive post-intrusive shearing. shape and were probably shearing. accessory. accessory. about30% 30% The tonalite plagioclase (An_5), ),about The tonal i t eisi composed s composed of 35-40% 35-40% plagiocl ase (An bluish quartz,5-101 5-10% Id aaccessory bl u i s h green green hornblende, hornblende, 25-30% 25-301 quartz, b i biotite, otite, % 5 a c c e ~ ~ epidote, ~epidote, ry is displaysanani nindistinct i sflow-laminated, flow-laminated, and and commonly commonly displays d i s t i n c t lineation 1ineationproduced produced plagioclase/hornblende Large variation ini nplagiociase/hornblende mainly by by hornblende hornblende alignment. a1 ignment. Large mainly The plagioclase plagiocl ase ratio r a t i oindicates indicatesconsiderable considerablecontamination contamination by by amphibolite. amphibol i t e . The commonly displays bent albite twin lamellae, while associated, polygonal commonly displays bent a l b i t e t w i n lame1 l a e , while associated,polygonal crude, transgressive B i o t i t ecommonly commonly produces produces aa crude, transgressive quartz grains grains are a r e unstrained. unstrained. Biotite quartz The biotite may have formed from hornblende during ater f o l i a t i o n . The b i o t i t e may have formed from hornblende during aa llater foliation. deformation. deformation. �—37- EXPLANATION EXPLANATION Hornbrnnd. tonolits QMiS$ Gnsissic tonalit. bmcclo Ultromofic brenda Linuoldal ompitibolite Porpflyroblasllc gmnit• gnslos Bonded oinphibolits Trace of vertical flow lamination Shear zone ihowing dl1acament Plunge of minor fold P E. Myers Figure 16-- Geologic map pointsoof Figure 16-Geologic map o foft hthe e L Little i t t l e Falls F a l l s area area showing showing points f iinterest nterest �:: .,- L ' S , —. -,- \ '- " - 0' -: : — - — — — - .- — -. - - - --.--— - - - — 5— S — — - . -• ,c• - - o — -- - - — ——-—S. - - - -- -O• — — _c. — - —r -_ 0 - — -— . a— - 00 - - .— --:: - -2 - — — - — -- - —\ tonalite biotite granite gneiss in hornblende Figure 17 -- Deformed xenolith of porphyroblastic drag along both in the xenolith shows intrusion breccia (Location 7927-W on Figure 16). Foliation relative Porphyroblasts to the xenalith. edges; indicates north-northeast flowage of tonalite magma are microcline. .. 4r '0 �-40STAGES STAGES IN I N BRECCIA BRECCIA FORMATION: FORMATION: study ooff outcrops showst hthat intrusion AA study o u t c k p s 1like ike that t h a t ata tLocation Location7927-C 79274 shows at in t r u s i o n ooff haveinvolved involved anatexis anatexis i in ttonalite o n a l i t etook tookplace placeunder under stress stress and and may may have n the amphibolite amphibol it e wwith i t h formation formation ooff aa mobile mobile phase phase oof f ttonalite o n a l i t e composition. composition. The following sequence is suggested: The f o l 1owl ng sequence i s suggested : 1) 1) Formationooff veined amphibolitic Formation veined amphibol i t i c gneiss gneiss by bysegregasegregattion i o n (?) ( ? ) of o ffeldspathic feldspathic lamlnae laminae subparallel subparallel to to 7927—C) ooriginal r i g i n a lbanding banding ini nthe theamphibolite amphibo1it (Location e (Location 79274) with w i t h local l o c a l accumulation accumulation ofoft otonalitic n a l i t i c clots c l o t s and and dikedikellike i k emasses, masses, blocks blocks ofo famphibolite amphibol i t became e becamedetached. detached. 2) 2) Partial P a r t i a l fusion fusion of of quartz—feldspar quartz-feldspar ffraction r a c t i o n to t o form form aa tonalitic t o n a l i t i ccrystal c r y s t amush l mushwhich which intruded intrudedacross across ooriginal r i g i n a l layering l a y e r i n gtot oform formbreccia brecciadikes dikes(Location (Location7927-C, 7927-C, Figured 18-A). Figure1'8-A). 3) 3) Detachment,r orotation, and mixing mixing ooff blocks; blocks; throughDetachment* t a t i o n y and throughgoing flowage* flowage,l elenticulation, and ppartial a r t i a l assimilation assimilation going n t i c u l a t i o n * and of Fluidization o f xenoliths xenoliths(Figure (Figure18 18CC and and D). D). F l u i d i z a t i o n of of the xenoliths-rich stress rresulted xenol i t h s - r i c h mixture mixture under under stress e s u l t e d in in development steeply p1 plunging development o of f steeply unging fflow 1ow ffolds. olds . AGE AGE OF OF THE THE BRECCIA BRECCIA A A rrelatively e l a t i v e l yxenolith-free xenol it h - f r e esample sample of o fhornblende hornblende tonalite tonal it efrom f r o m Location Location 7947 was recently recently dated 7947 was datedusing usingU—Pb U-Pb methods methods by Van Van Schmus Schmus ((1980) 1900) . at at If gneissi sis ttruly 1842 ++ 10 m.y. 1842 m.y. I fthe t h e porphyroblastic porphyroblastic gneiss r u l y a xenolith x e n o l i t h in i n the the breccTa, breccTa and and episode episode of o fgranite g r a n i templacement e emplacementand andsubsequent(?) subsequent (?)metamorphism metamorphism must have have preceded precededt hthis The ggranite therefore represent represent aa fragmust i s date. The r a n i t e may may therefore mentoof Archeanc rcrust upfrom fromaaggranitic thetonal tonalite ment f Archean u s t c carried a r r i e d up r a n i t i c basement basement i ninthe it e magma. This This could could indicate i n d i c a t e that t h a t granitic g r a n i t i crocks rocksmay may underlie underliethe theamphibolites amphibolites at a t Little L i t t l e Falls. Falls. PEGMATITE DIKES PEGMATITE DIKES Blotite-muscovite K-feldspar B i o t i te-muscovi t e ggranite r a n i t e pegmatite pegmatite wwith i t h K-fel dspar ccrystals r y s t a l s up up tto o 30 n maximum dimension c u tcut a t at nearly g h t angles 30 cm cmi in maximum dimension nearlyr i right angles across across flow flow lamination in i n enclosing enclosing breccia. breccia. Orientation of o f the the dikes d i kessuggests suggests. that t h a t they theywere were intruded during stress stress release and/or thermal thermalcontraction contractionooff the the intrusion intruded during release and/or intrusion Quartzveins veinsand andlenses lenseso of breccia. Quartz f ssimilar i m i l a r oorientation r i e n t a t i o n and and oorigin r i g i n are are exposeda tatthe theeast eastend endo fofthe theoutcrop outcrophere here Falls. The exposed a tatL iLittle t t l e Falls. The best pegmatite exposurei is where the the one one tto pegmatite exposure s aa Location 7927-Z, 7927-Zy where o three-meter three-meter dike dike contains very contains very large, 1arge bent bent and and marginally marginal 1y crushed crushed K-feldspars. K-fe1 dspars Although A1 though not vvisibly i s i b l y offset o f f s e tby by shear shear zones zones aat t LLittle i t t l e Falls, F a l l s ythe theinternal i n t e r n a deformation l deformation not iinn the the dike' dike indicates indjcates it i twas was intruded intruded prior p r i o rtot omajor majorshearing shearing in i nthe t h eMiddle Middle Precambrian. . , �B. C. D. -- Figure showing textures and theLLittle Figure 18 18 -- Outcrop Outcrop photographs photographs showing textures and s t rstructures u c t u r e s i ninthe ittle Falls Fa11s breccia.(A) breccia. (A) Tonalite Tonal it e breccia breccia dike d i k e cutting c u t t i n g lamination lamination in i n amphibolite amphibol it e at at Location seedetailed d e t a i l e dgeologic geologicmap map in i nFigure Figure19. 19. For detail, detai 1 ,see Location 7927-C. 7927-C. For (B) andsegmented segmented mafic byminor minorfa,ult fault along (B) Sheared Sheared and mafic x exenolith n o l i t h c cut u t by along which which quartz quartz later l a t e r crystallized. c r y s t a l l i z e d . View View east at a tLocation Location7927-W. 7927-W. (C) (C) Mafic Mafic amphibolite amphibolite xenoliths xenoliths in tonalite 7927-W. i n flow-laminated flow-laminated hornblende hornblende tonal it e20 20feet feetnortheast northeastofoLocation f Location 7927-W. XenoXenoliths feldspar content commonly l i t h swith wita h higher a higher feldspar content commonlyshow show more more plastic p l a s t l cdeformation deformationand and veining. beenfolded foldedpprior veining. The The llarger a r g e r xenolith x e n o l i t h appears appears tto o have have been r i o r to t o its i t sengulfment engulfment in suggestsddifferential We1 1 developed developed f1flow ow 1lamination aminati on suggests i f f e r e n t i a1 i n the thetonalite tonal itmagma. e magma. Well movement between magma xenoliths bedofre and detachment. (D) (D) Mafic and movement between magma andand xenoliths bedofre and a fafter t e r detachment. and u l tramafic xenoliths l a t i v e l y 1i t t l e assimilation a s s i m i l a t i o n in i n the the tonalite. tonal ite.Mixing Mixing ultramafic xenoliths show showr erelatively little of suggests 1itho1ogi es suggestsconsiderable considerable turbulence t u r b u l ence and and vvertical ertical o f diverse d i verse xenolith xenol it hlithologies flow within high proportion proportion of w i t h i nthe t h etonalite t o n a l i tmagma, e magma, which which probably probably contained contained aa high of Location 7927-X. 7927-X. xenocrystic as we1 well xenocrysti c hornblende hornblende as 1 as as xenoliths. xenol iths. Location �-42- SHEAR ZONES ZONES invol v i ngmodest, modest, I n t e r 1ensing, west-northwest-trending west-northwest-trendi ngshear shearzones zones involving Interlensing, r i g h t - l a t e r adisplacement l d i s p l acement andconspicuous conspicuousdrag dragfolding f o l d i n(Locations g (Locations 7927-X right-lateral and 7927—X have segmented segmented and flow and Figure 22. have andtransposed transposed primary primary flow and Y,Y, Figure lamination small shear 1amination iin n the t h e intrusion i n t r u s i o n breccia. breccia. Where Where small shear zones zones converge, converge, the breccia is with i sconverted converted to t oaazoned, zoned, laminated laminated dike—like d i k e - l i k e body body w i t h walls of hornblende core of of quartz-epidote hornblende sschist c h i s t and and aa core quartz-epidote mylonite mylonite up up tto o 1.5 1.5 meters wide. this wide. If If t h i ssmall smallscale scaletransposition transposition ofo fprimary primary lamination lamination is is expanded mapscale, scale, one one can can rreadily expanded t oto map e a d i l y see see how how primary layering 1ayeringmay may be be ami nation para1 1e l to to t o t a l l yobliterated obl i t e r a t e dand andreplaced rep1aced by by aa secondary secondary 1lamination totally parallel shear dislocation iinn the the iinterlensing shear dislocatton the rock. rock. Many Many o of f the n t e r l e n s i n g structures structures of of the Precambrian terrane of of west-central Wisconsin represent 1largePrecambrian terrane M i sconsin may may represent argescale scale tectonic transposition transposition by byshearing. shearing. • The The ffault a u l t seen seen at a tLocations Locations7927-X 7927-X and and Y Y probably probably ooffsets f f s e t s pegmatites pegmatites but not not the the diabase diabase dikes. dikes. Its I t sage age isi stherefore thereforeprobably probablyLate LateMiddle Middle Precambrian Precanbrian (Penokean?) ( Penokean?) A mucheearlier producedi sisoclinal A much a r l i e r deformation deformation produced o c l i n a l folds f o l d s and and banding banding in in the amphibolites before iintrusion +10 10m.y. m.y. ago. ago. atnphibolites before n t r u s i o n of of the thetonalite t o n a l i t e1842 1842+DIABASE DIKES DIKES East-northeast-trending, Late Precambrian basaltLate Precambrian(Keweenawan?) (Keweenawan?) basalt~ast-'northeast-trending , diabase dikes ccut Q. Their Their chilled chilled diabase dikes u t the the breccia breccianear near locations, locations,7927-Z 7927-Zand andQ. margins shallow iintrusion margins i indicate n d i c a t e shallow n t r u s i o n after a f t e rconsiderable considerable erosion. erosion. THE THE PRECAMBRIAN-CAMBRIAN PRECAMBRIAN-CAMBRIANUNCONFORMITY UNCONFORMITY A and erosion erosion wwith A surface of o f deep deep weathering weathering and i t h about about 20 20 meters meters ooff relief gently west—southwest Cambrian re1i e dips f dips gently west-southwestbeneath beneathLate Late CambrianMt. Mt Simon SimonSandstone Sandstone throughout Eau CClaire throughout the region. region. The The Eau l a i r e River River flows flows approximately approximately down down the the dip d i p of o f this t h i smajor majorunconformity. unconformi t y . Chemical weathering of of underlying Chemical weathering underlyingampamphibolitic impermeable green, hibol i t i crocks rocksengendered engendered aahhighly i g h l y impermeable green, i l l illitic i t i c clay. clay. Some this mayhave haveoccurred occurreda fafter deposition ooff the Some o of f th i s weathering weathering may t e r deposition t h e sandsandstone by reaction of stone by o fcirculating c i r c u l a t i ngroundwater g groundwaterwith w i t hferromagnesian ferromagnesian minerals mineral s in through the Mt. Groundwater ccirculating i r c u l a t i n gdownward downward through Mt i n the the amphibolites. amphibol ites. Groundwater Simon Sandstone flows along theclay Simon Sandstone flows l a t laterally e r a l l y along the c l a y l alayer y e r uuntil n t i l iti tcomes comes out out at a t the the surface surface as as aa spring. spring. Since the the Precambrian-Cambrian Precambrian-Cambrian unconformity unconformity is the llevel i s generally generally just j u s t above above or o r below below the e v e l ofthe of theEau Eau Claire C l a i r e River, River, the the river's r i v e r ' smajor majordischarge dischargeisi major s majorfrom fromgroundwater groundwatersystems. systems. Its I t sdischarge discharge varies .only •only sslightly, l i g h t l y ,even evenduring duringprolonged prolonged periods periods of o f drought. drought. . . �'979 Felsic LI mylonite amphibolite folds q - C • • 5Feet i bo% Figure 19 -- GEOLOGIC MAP OF LOCATION 7927-C, LITTLE FALLS Bonded Ultramof Ic, hornblendlte xenoflths Veined and lensoldal omphibolite Hornblende tonolite gnelss Breccia Quartz L1. EXPLANATION E. Myers (A) �-44CHRONOLOGY CHRONOLOGY FOR LITTLE FALLS FOR LITTLE FALLS AREA AREA 1. 1. Basaltic Basal t i cvolcanism volcanismand and sedimentation sedimentation 2. Intrusion I n t r u s i o n of o f Big B i g Falls F a l l s gabbro; gabbro; ddifferentiation i f f e r e n t i a t i o n with w i t h deposition deposition of o f ultramafic u l tramafic autolfths. auto1 i'ths. Mineralogical Mineralogical and and chemical chemical ssimilarity i m i l a r i t y of o famphibolites amphi bol ites at a t Big Big Falls thoseaat F a l l s (Unit (Unit 2) 2) and and those t LLittle i t t l eFalls F a l l ssuggest suggest their t h e i r close close relationship. relationship. 3. Isoclinal ~ s o c l i n afolding lf o l d i n gand andshearing shearing 4. Intrusion 7927W) I n t r u s i o n of o (porphyritic?) f ( p o r p h y r i t i c ?granite ) g r a n i t(Location e (Location 7927W) 5. Catalasis folding. Catalasis and and regional regionalmetamorphism, metamorphism, folding. 6. Intrusion +20 m.y. to tVan Schmus, I n t r u s i o nofo fhornblende hornblendetonalite t o n a l i t(1842 e (1842 + 20 m.y.according according o Van Schmus, 1980) 1980) 7. Intrusion I n t r u s i o nof o fgranite granitepegmatite pegmatite(Location (Location7927Z) 79271) 8. Strike—slip trend) and and1locallized S t r i ke-sl ip faulting f a u l t i n g(WNW (WNW trend) ocal 1ized cataclasis catacl a s i s 9. 9. Prolonged erosionwwith formationoof surface ooff low relief Prolonged erosion i t h formation f aa surface low topographic topographic re1 i e fand and aa soil s o i l rich r i c hini green n greenclay c l a yononthe themafic maficamphibolites amphibolites I 10. 10. Intrusion ?) I n t r u s i o nofo fdiabase diabase dikes dikes(Location (Location7927R) 7927R) (1100 (1100 m.y. m y . ?) 11. 11. Erosion Erosion 12. 12. Marine Marine deposition deposition ofo fMt. Mt.Simon SimonSandstone Sandstone - Late LateCambrian Cambrian - �-45- -- THE FORK AREA AREA -- INTRODUCTION THE SOUTH SOUTH FORK INTRODUCTION Figure2l Figure21 is i s aa geologic geologic strip s t r i pmap map of of the theSouth South Fork Fork area area in i n eastern eastern Eau Claire Claire and Eau and western western Clark counties counties (Stops (Stops3—7). 3-7). An An examination examination of of the map should reason forfor d i difficulties f f i c u l t i e s in interpolating interpolatingbedrock bedrock units units map shouldreveal revealone one reason between exposuresinint hthis between exposures i s region. If cataclastic I f the theexposed exposed contact contact betweeh between catacl astic gneiss and and metatuff a t Stop Stop 33 is i s representative representativeofofconcealed concealed feldspathic gneiss metatuff at contacts iin n the the area, area, iti tcan can be be inferred inferred that thatcontacts contacts are are typically typicallysheared sheared contacts andnearly nearly vertical vertical and lensoidal fault and and that t h a t they they enclose enclose lensoidal f a u l t slices s l i c e swhich which have have been juxtaposedmainly mainlybybystri strike-slip ke-sl i p displacement displacement (Figure 20). 20). Although A1 though the the been juxtaposed metavolcanic and and metasedimentary South Fork Fork area area (SFVS) (SFVS) are are metavolcanic metasedimentaryrocks rocks of of the South commonly foliated foliated(as ( aat s aRock t RockDam Damand and Mead Mead Dam) l l show show excellent comonly Dam)they theya all excellent Garnet, chlorite, chlorite, preservation preservation of primary primary minerals mineral s and and sedimentary sedimentary textures. Garnet, epidote, and muscovite indicate indicate attainment and muscovite attainment of upper upper greenschist greenschist fades faciesmetametamorphismunder underconditions conditions of of moderate SFVSrocks rocksa are interlayered morphism moderate stress. SFVS r e interlayered aatt Stop Stop 33 with w i t h sheared sheared mafic mafic and and feldspathic feldspathicplagioclase-hornblende plagioclase-hornblende gneisses gneisses contactsaare nearlyvvertical, of the theChippewa Chippewa amphibolite amphibolitecomplex complex (CAC). (CAC). The The contacts r e nearly ertical, northwest-trending. In contrast northwest-trending. contrast with w i t hthe theCAC CAC rocks rocks which were were deformed deformed and and metamorphosed threetimes, times,the theSFVS SFVS rocks Stop displayre1 relict metamorphosed a t at l e aleast s t three ro.cks a t atStop 7 7display ict upright SFVS upright bedding bedding which which dips dips ata tmoderate moderate angles. angles. It I t isi sbelieved believedthat t h athe t the SFVS rocks were were deposited deposited unconformably unconformably upon upon eroded, eroded, twice-deformed twice-deformed and andmetamormetamormetatuff from phosedArchaen Archaenamphibolites amphibolites about 1860 phosed 1860 m.y. m.y. ago. ago. Andesite Andesite metatuff from the confluence area (Stop 3, Station 7830-F), as dated by Van Schmus (1980), is confluence area (Stop Station 7830-F), as dated by Van Schmus (1980), is greenschistgrade grademetamorphism metamorphism and these After greenschist and some somefolding, folding, these 1860 m.y. After 1860 + m.y. rocks wereimbricated imbricatedbybystrike-slip strike-slip displacement alongnearly nearly vertical, vertical, rockswere displacement along trondhjemi t i c The imbrication i t i cand and trondhjemitic interlensing imbrication also also involves involves tonal tonalitic interlensing faults. The intrusive m.y. old old but b u t not not intrusive rocks rocks about about 1840 1840 m.y. Present Erosion Surface Surface faults Figure 20 Figure 20 --Block Blockdiagram diagramshowing showing hypothetical hypotheticaldisplacement displacementmechanism mechanism which which best explains of SFVS and best explains the distribution distributionand andspatial spatialrelations relations of SFVS andCAC CAC rocks rocks in the the South South Fork Fork area. area. �EXPLANATION EXKANATION Gneissic granodiorite granodiffite Gneissic wj Foliated Foliated ml biotite biotite tonolite tondite Foliated trondhjemite trondhjemite w Volcanics [ Voicanics wl Metasedirnents m g A5 Metasediments Mafic omphibolites amphiMites Mafic Reid Field trip trip stop stop 2 milss Fairchild, 6 mi. ,p Figure -- Geologic Fork of 0f the Figure 21 21 -Geologic strip s t r i pmap map of of the t h eNorth North Fork Fork and and South South Fork t h e Eau Eau Claire River River in ineastern eastern Eau Eau Claire Claire and western Clark counties. and western counties. �-47-47STOPS #3 and #7 STOPS #3 #7 TITLE: CONTACT BETWEEN BETWEEN CHIPPEWA AND SOUTH SOUTH FORK FORK VOLCANIC VOLCANICROCKS ROCKS CONTACT CHIPPEWA AMPHIBOLITES AMPHIBOLITES AND LOCATIONS: LOCATIONS: Stop #3, T26N, #3ÂSE SE 11/4, / 4  SE SE 1/4, 114 Sec. Sec. 16, 16 TZ6N,R5W: R5W: Field F i e l d Loc. LOC.7830 7830 Stop #7, NE 1/4, Sw 1/4, Sec. 16, T26N, Stop #7, NE 114, SW 1/4 Sec. 16, T26N9R5w: R5W: Field Fie1d Loc. LOC.7329 7329 AUTHOR: AUTHOR : P. P. - March, March, 1980 1980 DATE: DATE : E. E. Myers Myers SUMMARY SUMMARY OF OF FEATURES: FEATURES: The The llithology i t h o l o g y and and contact contact relations r e l a t i o n sofo fsheared sheared metatuffs, metatuffs, tuffaceous tuffaceous sedimentary rocks and and pplagioclase-hornblende gneiss are are well-exposed, sedimentary rocks l a g i o c l ase-hornbl ende gneiss we1 1-exposed9 but but difficult d i f f i c u l ttot ointerpret i n t e r p r e at t a Stop t Stop 3. 3. Tuffaceous Tuffaceous conglomerate, conglomerate9sandstone, sandstone, and and s f 1 tstonewith w i t hwell-preserved we1 1-preservedprimary primarydepositional depositionalfeatures features l p 45-60 SSW siltstone dipd45_600 SSW at a t Stop Stop 7. 7. DESCRIPTION: DESCRIPTION: Stop Stop 3: 3: Four Four nnearly e a r l y vvertical e r t i c a l rock rock units u n i t s here here (Figure (Figure 22) 22) are are listed 1i s t e d from from northeast northeast to t osouthwest southwest : : (1) (1 ) banded, banded, mafic, mafic, hornblende-plagioclase hornblende-plagioclase gneiss Table88 (#7830-A (#7830-Aand andB),B),(2) (2)andesite andesitet tuff u f f and and quartzo-feldspathic quartzo-feldspathic gneiss and and Table volcaniclastic v o l c a n i c l a s t i csedimentary sedimentary rocks rocks (#7830-D,E, (#7830-D9 E, and and F), F) (3) ( 3 )mafic mafichornblende hornbl ende tonalite tonal it e (no (no analyses), analyses), and and (4) ( 4 ) feldspathic f e l dspathi c tonalite tonal it egneiss. gneiss. Discordant Discordant leucotrondhjemite dikeswwith concordant all1 units. leucotrondhjemi t e dikes i t h concordant c a cataclastic t a c l a s t i c f ofoliation l i a t i o n ccut u t a1 units. Sericitization S e r i c i t i z a t i o nofoplagioclase f plagioclasewas was followed followed by by small small scale scale faulting f a u l t i n gand and chlorite with adjacent ttoo the c h l o r i t evein veinemplacement emplacement w i t h conversion conversion of o f hornblende hornblende adjacent the veins veins to Garnets and l a s t s in i n the t h emetatuff metatuffwere were almost almost andmafic mafic cclasts t o chlorite c h l o r i t eand andepidote. epidote. Garnets completely basic questions questions aarise completely cchloritized h l o r i t i z e d at a t this t h i stime. time. Two Two basic r i s e here: here: (1) (1 ) which which o0ff the t h e units u n i t s is i sofo fvolcanic vo1 canicorigin, o r i g i n ,and and(2) (2)tot what o whatextent extentand and in metamorphism i nwhat what sequence sequence were were primary minerals minerals and and textures texturesmodified modifiedbyby metamorphism and and ccataclasis a t a c l a s i s in i neach each unit? unit? �-48- TABLE TABLE 88 MODAL AND CHEMICAL ANALYSES ANALYSES OF OF ROCKS ROCKS FROM FROM THE THE CONFLUENCE CONFLUENCE AREA AREA MODAL AND CHEMICAL I MÔdãl. Analyses Analyses Modal I MIN* MIN* Plag M ag 7829 7829 7829 B B A A 7929 7929 C C 78 65 65 Hb Hb Qtz Q tz Chi. Chl. 6? 6? 4? 4? 28 16 16 7830 7830 7830 7830 AA 58 58 BB 29 30 30 63 77 6 24 55 1 Trr T Tr Tr 1 Tr Tr 1 2 2 Ep. EP 1 <11 4 Op. OP I 7830 7830 17830 7830 17830 7830 7830 7830 7830 7830 7830 DD H .1I E F E F G ' H 61 78 68 53 61 ' 7711 78 69 69 68 53 8 11 11 66 9 9 6 6 14 14 32 32 16? 16? 13 13 4 4 33 5 17? 17? 66 33 11 33 5 2 2 * Minerals: Minerals :Plagioclase, PI agi o c l ase, Hornblende, Hornblende, Quartz, Quartz, Chlorite, Chl or1te, Epidote, Epi dote, Muscovite Muscovite Modal analysesusing using1000-point 1000-point counts.I dIdentification uncertain ffor Modal analyses counts. e n t i f i c a t i o n uncertain o r very very fif i nne-grai ned vvarieties e - g r a i ned arieties Chemi cal Analyses Analyses Chemical Si02 . 56.84 59.48 48.19 57.08 57.24 70.62 61.76 61.60 57.58 63.03 68.42 A1203 19.46 20.41 20.54 15.87 14.89 15.52 17.56 17.18 17.74 14.35 14.37 Fe2O 6.03 * 4.08 10.40 8.68 9.75 2.49 7.14 6.80 5.80 6.64 3.77 CaO 1.33 0.76 0.60 6.10 5.42 2.61 3.65 4.06 6.13 6.13 494 MgO bIg0 3.43 3.10 8.10 4.51 4.55 0.97 2.03 2.25 3.47 3.31 1.74 Na20 Na20 7.44 7.77 •4.68 3.66 3.16 4.45 3.29 3.38 3.96 2.69 3.02 K20 K2 0.71 1.26 1.51 0.72 1.36 1.43 2.02 2.11 1.89 1.18 0.99 Ti02 1102 0.51 0.49 0.65 0.46 0.61 0.28 0.56 0.51 0.34 0.27 0.22 MnO MnO 0.05 0.04 0.09 0.14 0.14 0.03 0.07 0.08 0.08 0.11 0.06 P25 2' 5' 0.21 0.10 0.27 0.02 0.13 0.05 0.21 0.25 0.23 0.03 0.00 LLOl OI 2.11 1.89 4.47 1.17 1.61 0.84 1.80 1.52 1.53 1.19 0.71 TOTAL TOTAL 98.11 99.39 99.50 98.41 98.85 99.30 100.1 99.74 98.73 98.94 98.22 * Includes IncludesFeO. FeO. �-49- banded, mafic banded, m a f i c hornblende— hornblende- plagioclase gnei1 fedspath1c hornblende tonaflte gnelsS edge of / C'. No. 7830). Figure 22-22-- Outcrop Outcropmap map showing showing geology geology and andsample sample llocations o c a t i o n s (Field (Fie1 d No. 7830). Chemicalanalyses analysesf ofor these rocks rocks are are tabulated tabulated in Chemical r these i n Tables Tables 2 and and 4. 4. Unit U n i t #1 # I consists consists of o faligned, aligned, dark darkgreen green("1), ( Y ),subhedral subhedralhornblende hornblende and and crush debris debris llenticular e n t i c u l a r plagioclase plagioclase laths l a t h s or o r its i t smylonitized myloni t i z e dequivalent equivalent - aa crush Although the the existence existence of o f anhedral, anhedral, bent, bent, and andbroken broken plagioclase plagioclasefragments. fragments. Although of and shadowy o f large, large,ovoid ovoidplagioclase plagioclasegrains grains and shadowy darker darker patches patches (best (bestseen seen on on weatheredsurfaces) surfaces) suggests rock, thin weathered suggests a va o lvolcaniclastic c a n i c l a s t i c p r oprotolith t o l i t h f ofor r t this h i s rock, thin section showst hthat laminationi is section study study shows a t aat t lleast e a s t some some o of f t hthe e lamination s ooff cataclastic cataclastic themalong alongsmall smallf afaults, all Thin seams seams o fofcchlorite, h l o r i t e , some some oof f them u l t s , ccut u t a11 origin. o r i g i n . Thin and chlorite c h l o r i t become e becomemuch much other sstructures other t r u c t u r e s i in n aall l l four f o u r rock rock units. u n i t s . Epidote and more abundanti ninhornblende hornblendenear nearthese thesec hchlorite veinlets. The more abundant l o r i t e veinlets. The cchloritization hloritization (Figure 23.) 23. ) and eepidotization was, therefore, therefore, post-kinematic. and p i d o t i z a t i o n ooff these these rocks rocks was, post-kinematic. (Figure - Unit about3030t oto60 60percent percente ellipsoidal U n i t #2 #2 is i s composed composed o of f about l 1 i p s o i d a l plagioclase plagioclase clasts c l a s t s in i n aa foliated, f o l i a t e d ,fine-grained fine-grainedmatrix m a t r i xofo plagioclase, f plagioclase, epidote, epidote, and and Chlorite-mantled garnets make upup about 0.5% cchlorite h l o r i t e(Figure (Figure24). 24). C h l o r i te-mantled garnets make about 0.5%ofo specimen f specimen 7830-E (Figure25). 25).Cataclastic Cataclasticfo1 foliation 7830-E (Figure i a t i o n is i s manifested manifested llocally o c a l l y by by interlensing interlensing plagioclase cclasts and tthinly chlorite c h l o r i t e folia. f o l fa. The The plagioclase l a s t s are a r e well-rounded we1 1-rounded and h i n l y coated coated with with chlorite c h l o r i t eor o rvery veryfine-grained fine-grainedquartz quartzand andcontains containszoned zoned inclusions i n c l usionsofo brown f brown L i t h i cfragments fragments and/or and/or glass glass shards shards were were apparently apparently biotite b i o t i t e and and pyrite. p y r i t e . Lithic (1980) at replaced by by cchlorite. replaced h l o r i t e . This unit u n i twas wasU-Pb U-Pb dated datedby byVan Van Schmus Schmus (1980) a t 1860 1860 m.y. m.y. Unit U n i t #3 #3 is i saahornblende—rich hornblende-rich ttonalite o n a l i t e with w i t hconspicuous conspicuous lamination but but I t s composition composition iiss similar s i m i l a r to, to,but b umore t more mafic mafic than, than, obvious llineation. less obvious i n e a t i o n . Its 7830-A. 7830-A. �-50- Unit U n i t #4 =4 iiss light l i g h tgreenish greenish gray gray feldspathic feldspathic tonalite tonalitegneiss gneisswhich which closely closely resembles thefeldspathic feldspathic amphibolites amphibolitesofof the the Big Big Falls area. resembles the area. However, Howevery iits ts cataclastic fabric color of the give tthis fabricand and the the deep deep green green color the hornblende hornblende give h i s rock rock quite aa different n thin t h i n section. section. Lensoidal differentappearance appearance iin Lensoi dal plagioclase plagiocl ase porphyroporphyroclasts post-kinematicálly c l a s t s are are surrounded surrounded by by fine finegrained grainedquartz quartzwhich whichmay may have have been been post-kinematically introduced. All cataclastic fabric A1 1units unitsdisplay displaya apronounced pronounced cataclastic fabric characterized characterized by by bent, benty broken, and1lenticulated and inter1 interlensing broken, and enticul ated plagioclase plagiocl ase and ensing foliation fo1 iationaccentuated accentuated by by accumulations chlorite and accumulations ofof chlorite and quartz-feldspar quartz-fe1 dspar crush crush debris. debris. Late kinematic kinematic leucotrondhjemite cut the the layering layering and and cataclastic cataclastic foliation leucotrondhjemi t e ddikes i kes cut fol iationbut b u themselves t themsel ves possess weak parallel to possess a aweak folfoliation iation parallel t o that t h a t Ini nthe theenclosina enclosina rocks. rocks. The The finefinegrained matrix of of the for concentration of cataclasis grained matrix the metatuff metatuff allowed allowed for concentration of cataclasis with with little l i t t l abrasion e abrasionand andfragmentation fragmentation of the the insulated insulated feldspar feldspar clasts. c l a s t s . This T h i s may may explain preservation of of primary textures in explain the the unusually unusually good good preservation primary textures i n these these rocks: rocks. A A profile profileofofminor minorelement element variation variation .across .across this t h i s outcrop outcrop isi sshown shown in in Figure 26. 7830D,aa rock rock composed composed coarse,lenticulated lenticulated plagioclase 26. Rock Rock 7830Dy of ofcoarse, clasts has c l a s t s ini naafine-grained fine-grainedquartz quartzmatri,ç matrih hasanananomalously anomalously low low V, V y Cr, Cryand andZn Zn content. The rock has has the the composition compositionb but not the the texture texture of aa trondhjemite. The rock u t not trondhjemite. The protolith of unknown. The protolith of this t h i srock rockis is unknown. Its I t s relatively relativelycoarse coarse grain grain size size suggest intrusive origin. suggest ananintrusive Stop 7: small outcropson onthe the south southside side of oftheEau Three smal 1 outcrops the Eau Claire River River 7: Three about 1/2 mile mile east 100-foot sequence sequence well-stratified, about 112 e a s t of Stop Stop 33 expose expose aa 100-foot ofofwell-stratified, but andsisiltstone b u t poorly poorly shorted shorted volcanic vo1 canic conglomerate conglomerate and 1tstone (Figure 8). 8). The The 1-7 1-7 m mplagioclase plagioclase and and blue quartz quartz clasts c l a s t s are are well wellrounded, rounded, and and quite quite evenly evenly distributed in i n aa well-stratified, we1 1- s t r a t i f i e dfine—grained y fine-grained plagioclase-chiorite plagioclase-chlori t e matrix. matrix. These rocksshow show onlylocalized localizedeeffects of cataclasis, These rocks only f f e c t s of cataclasis, and and most most closely closely resemble specimen 7830-F 7830-Faatt Stop 3. thebasis basisofof1lithologic similarity, resemble specimen 3. On On the ithologic similarityy the volcanic w i t h those those of of Unit U n i t #2 #2 at a tStop Stop 3.3. volcanic rocks rocks at a t Stop Stop 7 are correlated correlated with -- Figure 23 -—Chlori Chlorite-epidote veinlet (upper (upperl left te-epidote veinlet e f t to to Figure 23 lower lower right) r i g h t )cutting cuttingepidotized epidotizedplagioclase-hornblende plagioclase-hornblende gneiss. polars. Width gneiss. Location Location G. G. Crossed Crossed polars. Width of of photo photo == occurrenceofof epidote epidote iinn veinlet 4.2 4.2 m. mm. Note Note occurrence veinletwhere where iti tcrosses crosses hornblende hornblende crystals. crystals. �—51— - Figure 24 24 -— Rounded plagioclase n aa foliated foliated Figure Rounded plagioclaseclasts clastsi in and epiepimatrix of offine—grained fine-grained plagioclase, chlorite,and matrix plagioclase, chlorite, dote. chioritized dote. Location Location E. E. Small Small chlori tized garnet garnet right-center right-center and llithic i t h i cfragment fragment (dark) (dark) on on left. l e f t .Photo Photo width w i d t h is i s4.2 4.2 and mil 1imeters. Textural Textural lamination lamination (relict (re1i cbedding) t bedding) occurs occurs millimeters. in i nother otherspecimens specimens from from this thissame same location. location. -- Figure garnet in isheared and Figure 25 25 -- Chioritized Chloritized garnet n sheared andmetametamorphosed andesite tuff tuff or morphosed andesite o rtuffaceous tuffaceoussediment sedimentfrom from Location Location E.E. Note Noterounded rounded outline outlineofofpseudomorph. pseudomorph. Relict Relict garnet (g)remains remains inincore. core. Ordinary Ordinary illumination. i 11umination. garnet (g) Photo width is Photo width i s 4.2 4.2 millimeters. millimeters. �11 H G 0 5m. Distance F F 0 B N E— A SAIIPLE LOCATION C) L&i z C) z0 I- z 0 2 0 Figure 26 -- Major and minor element variations across outcrop at Stop #3. diagram are shown to scale. (Figure 22.) LOCATIONS SAMPLL.—I L) 0 C 0 0 U) 4-, 0 C 0) 4-, 00) I- U Sample numbers along base of each 5m. N.) U, �—53— - Figure 27 -- Relict Figure 27 R e l i c tbedding bedding in i n andesite andesite metatuff m e t a t u f f from from r t i n g . PlagPlagLocation 7829—C 7 8 2 9 4 (Stop (Stop#7) #7)showing showingpoor poors osorting. ioclase i o c l a s e clasts c l a s t sshow showconsiderable considerablebending bendingand and marginal margi nal fragmentation. s 4.2 fragmentation. Crossed Crossedpolars. polars. Photo Photowidth widthi is 4.2 mm. m. DISCUSSION: DISCUSSION: The pprotolith The r o t o l it hfor f o the r t h hornblende-bearing e hornblende-bearing gneisses gneisses which which enclose enclose the the The hornblende-bearing volcanic rocks rocks at a t Stop Stop 33has has not n o tbeen been established. established. The rocks rocks aatt this t h i slocation l o c a t i o nare areintermediate intermediatebetween between the t h e mafic mafic and and ffeldspathic eldspathic hornblendei sisaadeep deepgreen green( 7 ())) to The hornblende to amphibolites terrane. The amphibolites of o f the t h eCAC CAC terrane. moderate yellow-green 4C). Since Sie the thechemical chemicalanalyses analyses in i nFigure Figure 26 26 do do not not moderate yellow-green ddistinguish i s t i n g u i s hbetween between Fe Fe and Fe Fe ,, iittisi simpossible impossibletot ospeculate speculateOn on the the p). The anomalous partitioning anomalous p a r t i t i o n i n g of o firon i r o nini nthe thehornblende, hornblende, chlorite c h l o r i t eand andepidote. epidote. The eextinction x t i n c t i o n colors c o l o r s of o f chlorite c h l o r i t e minerals minerals comonly commonly rreflect e f l e c t differences differences in in yellow-gray is aluminian composition: yellow-gray i scommonly commonly a1 uminian pprochiorite; r o c h l o r i te; chocolate chocolatebrownbrownpurple purple iiss comonly commonly ferroane ferroane prochiorite; p r o c h l o r i te; deep deep (Prussian) (Prussian) blue b l u e is i spennine. pennine. In I n the the rocks rocks at a t Stop Stop 3, 3, pennine pennine is i s confined confined to t o hornblende hornblende aalteration, lteration, whereas whereas a1aluminian uminian p rprochiorite o c h l o r i t e i is s found found iinn the the mafic-poor mafic-poor volcanic volcanic rocks, rocks, although pennine pennineaalso occurs iinn these although l s o occurs these rocks rocks as as aa replacement replacement of o f garnets. garnets. Thus twochiorite Thus two c h l o r i t e minerals minerals coexist c o e x i s t in i n the t h evolcanic volcanic rocks, rocks, apparently apparently as as aa function of function o f the thechemical chemical composition composition ooff the t h e host host mineral. mineral. Structural age rrelationships amphibolitic S t r u c t u r a l and and age e l a t i o n s h i p s ooff volcanic volcanic and and amphibol i t i c rocks rocks at at The these llocations be cconfidently extrapolated rregionally. these o c a t i o n s cannot cannot be o n f i d e n t l y extrapolated e g i o n a l l y . The eastward increase iinn the increase the proportion proportion of o fvolcanogenic volcanogenic rocks, rocks, and and the t h e virtual v i r t u a disappearance l disappearance of amphibolitic rocks suggests a major transition, which might of amphi bol it i c rocks suggests a major t r a n s i t i o n , which mightbe beaasheared sheared and folded folded angular as suggested here, oorr possibly aa northwestand angular unconformity unconformity as suggested here, northwestIt should It should be be noted noted tthat h a t the the foliation f o l i a t i o nataStop t Stop#3#3bends bends trending trending ffault. ault. abruptly north-northwesterly, wwhile area, ffoliation abruptly north-northwesterly, h i l e eelsewhere l sewhere i nint hthis i s area, o l i a t i o n trends trends The relative freshness of cataclastic features might The r e l a t i v e freshness o f c a t a c l a s t i c features might west-northwesterly. west-northwesterly. work, pparticularly More ddetailed e t a i l e d f ifield e 1 d work, articularly support the cross-fault hypothesis. More support the cross-faul t hypothesis. wwith i t h small-scale smal 1-scale structures and and ppetrofabrics e t r o f a b r i c s will w i 11be benecessary necessary to t o resolve resol ve the problem. problem. �-55STOP STOP TITLE: #4 #4 KNIGHT POOL POOL META-BASALT META-BASALT KNIGHT LOCATION: Pool, Channey Channey Road, Road, North Fork Fork Qf o f Eau Eau Claire C l a i r eRiver, River, SE%,NE¼ NE% Knight Pool, SE¼, Sec. 10, 10, T26N, T26N, R5W, R5W, FFairchild a i r c h i l d 15' 15'Quadrangle. Quadrangle. Sec. AUTHOR: Paul E. Myers Paul E.Myers DATE:: DATE - March, 1980 March, 1980 SUMMARYO OF SUMMARY F FEATURES: Fine-grained, 1lineated amphibolite containingre1 relict Fine-grained, ineated amphi b o l it e containing ic t pillow p i 11ow structures(?) s t r u c t u r e s ( ? ) and and amygdules is cut discordantly by aplite veinlets which show different amygdules i s c u t discordantly by a p l i t e v e i n l e t s which show d i f f e r e n ttypes typesand and rocks, because evidenceooff several several ages off deformation, ages ooff deformation. ages deformation. These These rocks, because oof f evidence ages o deformation, including an eearly phaseo of are tentatively assigned i n c l u d i n g an a r l y phase f i sisoclinal o c l i n a l folding, f o l d i n , are t e n t a t i v e l y assigned to t o the the Chippewaamphibol amphibolites and younger(?) volcanicst to Chippewa i t e s and n onot t t otot hthe e younger ? ) volcanics o tthe h e east. east. ? DESCRIPTION: Fine-grained, mafic, mafic, epidote epidote amphibol amphibolites Fine-grained, i t e s wwith i t h r relict e l i c t pillow p i 1lowstructures structureswere were f i r s tisoclinally i s o c l i n a l lfolded y folded (Figure 28C),intruded intrudedby byaplite apl it eveinlets v e i n l e t s(Figure (Figure28A) 28A) first (Figure 28C), and then thenby byaabody bodyo of and f bbiotite i o t i t e granodiorite. granodiorite. Shearing Shearing iin n and and along along the t h e contact contact ooff the the granodiorite g r a n o d i o r i t econverted converted the t h e massive massive iintrusive n t r u s i v e rock rock to t o aamylonite mylonite gneiss. gneiss. This andcataclasis cataclasisfolded foldedt hthe This late l a t e episode episode ooff shearing shearing and e aaplite p l i t e vveinlets e i n l e t s in i n the the mafic amphibolite amphibolite (Figure (Figure28B). 28B).AAvveinlet of laminated mylónitegneiss gneissl ilies e i n l e t of laminated mylonite e s iin n the the mafic plareof planeof foliation f o l i a t i o nofo the f t h eamphibolite amphibolite(Figure.28B). (Figure28B). This This gneiss gneiss consists consists of o f eyeeyeshaped asts o of f pplagioclase l agiocl ase enveloped i o t i t e and and siliceous s i 1iceous shapedporphyrocl porphyroclasts envelopedi ninmantles mantleso fofbbiotite mylonite. Theplagioclase plagioclasei sis sstrongly myloni te. The t r o n g l y ssericitized. e r i c i t i z e d . Quartz-epidote-filled Quartz-epidote-fi 1l e dgash gash fractures perpendiculart otof ofoliation f r a c t u r e s developed developed perpendicular l i a t i o n during during stress stress release. release. The sheeting and andbbiotite The llineated i n e a t e d mafic mafic amphibolite amphibolite here here displays displays aapronounced pronounced sheeting iotite foliation form the the 1limbs f o l i a t i o naccentuated accentuated by by plagioclase plagioclase laminations laminations which which form imbs ooff highhighsmall fold Hornblende 1lineation i n e a t i on and and small f o l daxes axes plunge p l unge amplitude amp1 itude i sisoclinal o c l inal folds. f o l ds. Hornblende east at northeast aatt location east a t 50-75° 50-750 near the t h e bridge bridge and and 80° 80' northeast l o c a t i o n 7941 7941 (Figure (Figure 29.) 29. ) The offset sides The l lineations i n e a t i o n s are are o f f s e t by by east-west east-west vvertical e r t i c a l faults, f a u l t s ,north north sidesdown. down. �-56- - Figure Figure 28-28 Near-vertical Near-vertical face face of o fan an outcrop outcrop of of fine—grained amphibolite (dark)c cut byvei veinlets f i n e - g r a i ned amphi b o l it e (dark) u t by n l e t s ooff aplite a p l i t e veinlets, veinlets,one oneofo which f whichshows shows aa cataclastic cataclastic foliation f o l i a t i o n parallel p a r a l l e l to t o its i t swalls w a l l s(A). (A). The The aplite aplite vveinlets e i n l e t s cut c u t older 01der isoclinal i s o c l i n a lfolds f o l d sshown shown at a t C. C. AA catacataclastic c l o s e l yresentles resembles•the t h e granograno* c l a s t i c veinlet v e i n l e tata B t Bclosely diorite out jjust d i o r i t e which which crops crops out u s t north n o r t h of o f here. here. This This outcrop iiss at outcrop a t location l o c a t i o n 7941 7941 (Figure (Figure 29) 29 ) . �—57- Lc. 794Z 9P0'noo'/e rife k (Q'Pflphióo///e LOC 794/. / / -'I 'S / / 'I Oi Id 7938 • OC 7940 7939 P. Myers Figure 29 29 ----Geologic Geologicmap map of o f the theKnight Knight PoolArea. Area. Note s t e e p Figure eastward t o east-northeastward plunge oPool f small f o l d sNote and steep lineation. eastward to east—northeastward plunge of small folds and lineation. �________________ —59- STOP #5 TITLE: ROCK DAM DAM META-RHYOLITE ROCK LOCATION: LOCATION: Hay Creek 0.15 0.15 mile SE1/4, 1/4, NW 1/4 Sec. NW 1/4 Sec. 15, 15, Hay Creek m i l e downstream downstream from Rock Rock Dam, Dam, SE T26N, R4W; R4W;FFairchild T26N, a i r c h i l d 15' 15' Quadrangle Quadrangle . 9 -'c:i; ' I •.-— - ' -- AUTHOR: AUTHOR: Paul Paul E. E. Myers Myers DATE: DATE : - February, February, 1980 1980 SUMMARYOF OF FEATURES: SUMMARY Debate continuesonon significance Debate continues t h the e sig n i f i c a n c e o fofc criteria r i t e r i a used used tto o distinguish distinguish this "metamorphosed" rhyolitic volcanics ffrom "mylonitized" "metamorphosed" rhyol it i c volcanics r o m "myloni t i z e d " leucogranites. 1eucograni tes. IIff this stop doesnnot solve the the ""rhyolite-granite may at a tleast l e a sadd t addmore more stop does o t solve r h y o l i t e - g r a n i t e problem," problem," iti tmay fuel f u e l to t o the t h e ffire. ire. AA ffoliated, o l i a t e d , muscovite-bearing muscovi te-bearing ffelsic e l s i c mylonite myloni t e containing containing eyes eyes ooff strained strained quartz quartz in i n aa very very fine-grained fine-grained matrix rnatri xofofK-feldspar, K-fel dspar,quartz, quartz,and andmuscovite muscovite crops crops Dam,where wherei itt unconformably underlies conglomeratic oout u t below below Rock Rock Dam, unconformably underlies conglomeratic Mt. M t . Simon Simon is iN87°W, 31 ). Foliation F o l i a t i o n ini nthe thefelsic f e l s iniylonite c mylonite s N87OW, 85°N. 85ON. Sandstone (Figure (Figure31. Sandstone Complimentary and N77OE, N77°E,8's 8°Saccount accountf ofor Complimentary j ojoint i n t sets sets at a tN18°W, N18OW, 73°E 73OE and r tthe h e blocky The exposed exposedangular angularunconformity unconformity has has aa llocal appearanceoof appearance f tthe h e outcrop here. here. The ocal relief re1 i e fofo about f about55meters. meters. DESCRIPTION: DESCRIPTION: The mylonite mylonite iiss pale eyesoof The pale pink pink and and contains contains conspicuous conspicuous eyes f sstrained t r a i n e d quartz The rock clearly resembles a porphyritic rhyolite 1.0 2.5 mm long. 1.0 - 2.5 mm long. The rock c l e a r l y resembles a p o r p h y r i t i c r h y o l i t e with with quartz I n thin t h i n section, section, the thequartz quartz eyes eyes aresubare. subquartz phenocrysts phenocrysts oor r clasts. In rectangular commonly u r e NThey ) . They commonlypossess possess crush crush rectangular to t o lenticular l e n t i c u l ain r ioutline. n o u t l i n(Figure e . ( F i g30). trails: t h a t is, i s ,the t h ecoarse-grained coarse-grained cores cores display d i s p l a yan anoutward outward decrease decrease iin n grain grain t r a i l s : that contain coarse, size The quartz eyes eyes commonly commonly contain coarse, s i z e into i n t o the t h e fine-grained fine-grained matrix. matrix. The S t r a i n is i s indicated indicated pale high birefringence. birefringence. Strain pal e green green muscovite muscovite wwith i t h anomalously anomalously high matrix The m a t r i x is i scomposed composed ooff very very by the conspicuous lamellar, wavy by conspicuous lamellar, wavy eextinction. x t i n c t i o n . The ffine-grained i ne-grained K-feldspar K-fel dspar (microcline), (mi c r o c l i n e ) ,quartz, quartz, muscovite, muscovite, biotite, b i o t i t e ,and andmagnetite. magnetite. The magnetite magnetiteoccurs occursasasstreaks streaksalong alongf foliation The o l i a t i o n and and in i nmuscovite muscovite grains, grains, where where �-60appears to t o have have formed formed w i t h muscovite muscovite aat t the expense oof f primary iotite. iti tappears with the expense primarybbiotite. Estimated mineral composition Estimated mineral composition iis: s : K-feldspar, 57%';quartz, quartz, 35%; 35%;muscovite, muscovite, 3%; 3%; K-fel dspar, 57%; magnetite, and bbiotite, magnetite, 2%; 2%; and i o t i t e , 1%. 1%. In I n addition a d d i t i o n to t o the t h e quartz quartz eyes, eyes, this t h i s rock rock contains occasional e n t i c u l a r clusters c l usters of of relatively re1a t i vely coarse-grainedmuscovite, muscovi te, contains occasionall lenticular coarse-grained 30). qquartz, u a r t z , and and bbiotite i o t i t e(Figure (Figure30). A thet hbase of oRock A muscovite-rich muscovite-rich phyllite p h y l l i t ecrops cropsout o unear t near e base f RockDam. Dam. The The rock rock is i s composed composed oof f K-feldspar, K-fel dspar, quartz, quartz,and andmuscovite muscovi t e(approximately (approximately20%). 20%). The The quartz quartz eyes andb biotite are absent, absent,factors factorssuggesting suggesting eyes and i o t i t e are a a d i different f f e r e n t p protolith r o t o l i t h ffor o r this this rock. Since K-feldspar could not petrographically, Since the abundance abundance oof f K-fel dspar could n o t be be determined determined petrographically, comparison comparison wwith i t h the previous previous rock rock isi sbased basedmainly mainlyon onhand hand specimen specimen descriptions. Cataclastic of granite Catacl as ti c degradation degradation of g r a n i t e to t o mylonjte mylonj t e produces produces ssimilar, i m i l a r , but b u thopehope- fully f u l l ynot n o t identical, i d e n t i c a l ,features. features. The The cchief h i e f differences differences are: are: (1) (1 ) mylonitization myloni t i z a t i o n of rockst ytypically mylonitizes quartzf first; o f quartzofeldspathic quartzofel dspathic rocks p i c a l l y myloni t i z e s tthe h e quartz i r s t ; feldspars feldspars thus porphyroclasts; (2) sheared shearedgranites granitesare arecharacterized characterizedby by i interthus become become porphyrocl asts; (2) nterlensing with lensing slip s l i p planes planes coated coated w i t h phyllosilicates p h y l l o s i l i c a t e ssuch such as as mica mica oorr chlorite c h l o r i t eand and mylonite; and the the ffelsic (3) transitions t r a n s i t i o n sbetween between relatively r e l a t i v e l yunsheared unsheared ggranite r a n i t e and elsic mylonite; (3) mylonite can be be seen seeni ninthe the ffield. quartz eyes mylonite can i e l d . The The quartz eyes iinn the t h e absence absence ooff feldspar feldspar porphyroclasts suggestsa aprimary primaryo rorigin the quartz quartz - either e i t h e r as as porphyroclasts sstrongly t r o n g l y suggests i g i n f ofor r the phenocrysts other primary phenocrysts o or r asasc clasts l a s t s i in.a n a ttuff. u f f . No No other primary volcanic volcanic textures t e x t u r e swere were - observed observed here. here. The chemical composition compositionoof The chemical f tthis h i s rock rock (7931-B) (7931-B) as as presented presented in i nTable Table 11 on on page 13 shows showst this page 13 h i s rock rock to. t o contain containanomalously anomalously high high K,00and andanomalously anomalously low low A1203. themicrocline microcline and and mus musovite. A1203. The The K20 K20 iis s consumed consumed bybythe ovite. '2 0 -- Figure Micro9raph showing raph showing l e nlenticular t i c u l a r ccluster l u s t e r of of Figure .30 30 -—Micro strained magnetite s t r a i n e d quartz quartz (q), ( q ,muscovite muscovite Cm), (m) , bbiotite i o t i t e (b), (b) , magnetite 7 (black), epidote (black) ,and and epi dote ((e) e ) iin n texturally t e x t u r a l l ylaminated, 1ami nated, finefine- .grained m i c r o c l ine. grained quartz quartz and and microcline. . �N.) -0-0 0' U) • a. 'CD —a. a. -a CD -1)1 .. c-P 01 -s N .0 a.oC -' 01 mm c* —a- -• 0:3_ U)-1)-a. a. —' c-P 0 0-so U)OO U) CDX -s -sCD -a -a -I. o c-i- .JQi (a 0 (<mo -s 01-'. oi —JrI- 'a c-I-fl CD 01 a. 'a (a a. -I CD 01—J. c-P I <3 I 000' mm 3a. 'a -- Cl) 1 (I) ?I -fl <0' ..a. c-f u0t) 0.-,. c-I-CD 0(0 U) 0 0 :3 U) 0—' 0 1. 11 I a.n CD a. CD ci- 1 :3 c-I00 In ri-N :3- (D-a.c+ 0' InQa 10.0 :3•c-IC c- -'- —4 CD 0' CD PaCD U) 0 0'. 0 00 03cP3 CD -a U)--'. (a:3 J :3_:3 a. O I35CD 3 0 'a CD 0 S< (0 W (D0 0'< c-IG)< -J.:3 CD CD U) c+< :3-5 ci- 'aCD —-a 0 CD .a-5 a. Q,-a. .a. ç- (D c-P 01:3 CD a CD 00-0 3 —a U) Qk .4. c-P 0-< < c-POPi 03 U) CD a. c-I-CD ci-'. • CD —s a. --a.-'U)In0'. c-P o:3:3:3 c a .3 C -a.—' a. CD QICD a :3 V)c+1< U) 3 < CD i)(0 OOCDCDc - • Figure 32 Micrograph showing lensoid cored by i n a finegrained, laminated, f o l i a t e d m a t r i x o f s t r a i n e d quartz, K-fel dspar, muscovite, and nearly col or1ess c h l o r i t e . 0101(0 -s -'• C -- • -i-a• In (0 -Ii -a Figure 31 F o l i a t e d metarhyol i t e composed o f quartz, K-feldspar, muscovite, b i o t i t e , epidote, and magnetite. Steeply dipping s c h i s t o s i t y s t r i k e s N870W here. The metar h y o l i t e i s unconformably o v e r l a i n by conglomeratic M t . Simon Sandstone. Photo by Gene LaBerge, UW Oshkosh. �-63TITLE: METASEDIMENTARY ROCKSO OF THE SOUTH METASEDIMENTARY ROCKS F THE SOUTH FORK FORK AREA AREA LOCATION: Clark M; NE T26N,R4W: R4W: NE l1/4, / 4 , Sec. Sec. 1,1,T26N, C1 ark County County Highway Highway M; quadrangle, quadrangl e , Field F i e l d Location Location7832 7832 AUTHOR: Paul E. Myers DATE : - February, 1980 February, 1980 DATE: Stanley 15' 15' SUMMARY O OF SUMMARY F FEATURES: FEATURES: Mica-chlorite schist exemplify thet hmetasediments s c h i s tand and quartzite q u a r t z i t eata this t t h iquarry s quarry exemplify e metasediments Features ooff multiple m u l t i p l edeformation, deformation, and and high-grade high-grade metametaooff the t h e South South Fork Fork area. area. Features morphic minerals, which which ttypify amphiboliteterrane terrane tto morphic minerals, y p i f y the the Chippewa Chippewa amphibolite o the west west are absent iinn these age absent these rocks, rocks, aafactor f a c t o suggesting r suggestinga agreater greater ageand/or and/ormore morecomplex complex hhistory i s t o r y for f o r the theamphibolites. amphi bol ites . DESCRIPTION: DESCRIPTION: Metasediments exposed here(Figure (Figure33) 33)i ninclude: Metasediments exposed here c l ude: (1) (1 ) coarse coarse tot omedium-grained, medium-grained, with ffoliated, o l iated, müscovite-biotite muscovite-bioti t e qquartzite uartzite w i t h indistinct i n d i s t i n c trelict re1i ccross-bedding, t cross-bedding, (2) quartz-chlorite—biotite (2) q u a r t z - c h l o r i t e - b i o t i t eschist s c h i sshowing t showingspectacular spectacularkink—banding, kink-banding ,and and (3) lenticulated subordinatebbiotite (3) l e n t i c u l ated quartz-muscovite quartz-muscovi t e sschist c h i s t wwith i t h subordinate i o t i t e and and cchlorite. hlorite. On the basis basis ooff aa strong O n the stronggeophysical geophysical anomaly, anomaly, North North Central Central Mineral Mineral Ventures Ventures cores were werel later (1973)ddrilled (1973) r i l l e d two two cores cores aatt aa site s i t e 3.7 3.7 miles miles west west of o f here. here. These These cores ater studied petrographically by M.A. M.A. Piotruszewicz Piotruszewicz (1978) (1978) as as ppart. studied petrographically and and geochemically geochemical l y by art . of aa Masters of Masters tthesis h e s i s at a tthe t h eUniversity U n i v e r s i t yofoWisconsin-Milwaukee. f Wisconsin-Milwaukee. The The f first i r s t hole hole penetrated fine—grainedg rgraphitic schists; the hole from of the penetrated fine-grained a p h i t i c schists; the second second hole from the base base of the Mt. Sandstone 180 feet,t oto aa depth depth ooff 1075 M t . Simon Simon Sandstone a t at180 feet, 1075 ffeet e e t cut c u t through through quartzquartzmuscovite-chlorite-garnetsschist accessoryb ibiotite, muscovite-chlorite-garnet c h i s t wwith i t h accessory o t i t e , aactinolitic c t i n o l it i chornblende, hornblende, pyrite, p y r i t e , and and ccalcite. alcite. Small outcrops outcrops ooff fine—grained quartz-muscovite Small fine-grained quartz-muscovi t e sschist c h i s t along along South South Fork Fork 2 miles miles west ooff here Dam milest otothe the northeast northeast suggest suggestwidespread widespreadd idistriwest here and and at a t Mead Mead Dam 22 miles stribution of o f the the metasediments metasediments i in n tthis h i s area. area. �-64- The of quartz (84%), (12%), The qquartzite u a r t z i t e isi scomposed composed of (84%), muscovite muscovite (1 2%), bbiotite i o t i t e(2%) (2%) and accessoryplagioclase, plagioclase,ppyrite, and accessory y r i t e , and and cchlorite. h l o r i t e . The quartz is The quartz i s equigranular equigranular and and forms forms polygranular polygranular pods pods enclosed enclosed in i n muscovite. muscovite. The pods may maybeber relict The pods elict detriral d e t r i r a l grains. grains. The The rock lacks lacksbanding bandingand andisi squite q u i thomogeneous. e homogeneous. Sparse Sparse shreds shreds ooff fine-grained fine-grained brown brown bbiotite i o t i t eare areInterspersed interspersedwith w i t hthe t h emuscovite. muscovite. The kink-banded u a r t z - c h l o r i t e - b i o t i t e isi sa aspectacular spectacularrock rock whenseen seen The kink-bandedqquartz—chlorite-biotite when in Brown bbiotite i o t i t e flakes f l a k e shave have been been kink-folded, kink-folded, i n thin t h i nsection. section. (Figure (Figure 35) 35) Brown locally rep1aced l o c a l l yrotated r o t a t e dwith w i t hcleavage cleavage perpendicular perpendicular t to o ffoliation, o l i a t i o n , and and partially p a r t i a l l yreplaced by 1.0 m. Kink folds f o l d s have have an an amplitude amplitude ooff approximately approximately 1.0 mm. The by the the chlorite. c h l o r i t e . Kink The composition composition ofof tthis h i s rock rock is: i s : chlorite c h l o r i t e(57%), (57%),quartz quartz(38%), (38%),opaque opaque(3%), (3%),and and biotite The cchlorite h l o r i t e has has unusually unusually high i e f , isi spale palegreen, green, nonnonhigh re1 relief, b i o t i t e(1%). (1%). The pleochroic, yellow—gray p l eochroic, and andshows shows anomalous anomalous ye1 low-gray e xextinction t i n c t i o n colors. are with are interleaved interleaved w i t h the the folded folded cchlorite. hlorite. Quartz grains grains Quartz The The llenticulated, e n t i c u i a t e d , fine-grained fine-grainedquartz—muscovite quartz-muscovite sschist c h i s t has has essentially essentially the mineralogyasasthe thequartz, quartz,bbut higher rratio the same same mineralogy u t wwith i t h higher a t i o of o fmuscovite muscovite to t o quartz. quartz. AA chemical a specimen chemical analysis analysis ofo fthe t h emicaceous micaceous quartzite q u a r t z i t was e wasobtained obtainedfrom from a specimen taken (See Table 4; 4; 7832) 7832) A. (See taken at a t Location LocationA. Figure33-at aHighway Figure 33 --Geologic Geologicmap map of o fcounty countyquarry, quarry,Eau EauClaire C l a i r eRiver River t HighwayM.M. REFERENCE: REFERENCE: Piotruszewicz, analysis of of aa drill from western M.A., An An analysis d r i lcore l core from western Piotruszewicz, M.A., Clark Clark County, County, Wisconsin. Wisconsin. Unpub. thesis, University Unpub. M.M.S. S. thesis, U n i v e r s i t y of of Wisconsin, Wisconsin, Milwaukee, Milwaukee. 1978. 1978. �_______ ___ *:jfl C — — Pr — — ; — - r— — — - - j - a r — a" < -w- r— t — - - Figure Kink folds u a r t z - c h l o r i t e - b i o t i t e sschist chist Figure 34 34 —— Kink foldsi ninq quartz-chlorite—biotite PhotobybyGene GeneLaBerge. LaBerge. from f l o o r ,Location LocationC.C.Photo from quarry quarry floor, -- Figure 35 showingkink kinkfolds folds in 35 -- Photomicrograph Photomicrograph showing in Figure chlorite-quartz-biotite schist, Location B. c h l o r i te-quartz-bioti t e s c h i s t , Location B. BBiptite, iotite, now altered now ppartly a r t l y a1 t e r e d to t o chlorite, c h l o r i t e ,has hasbeen been folded folded also. also. �-67STOP STOP #8 #8 TITLE: - CATACLASTIC VEINLETS INHORNBLENDE-BIOTITE HORNBLENDE-BIOTITE METADIORITE METADIORITE CATACLASTIC VEINLETS IN LOCATION: LOCATION: Yellow River miles EE of of Cadott; Cadott;NW NW 1/4, 114, SE SE 1/4, 114. Sec. Sec. 33, 33, T29N, T29NY R6 R6W Yellow River 2 miles W Cadott 15' quadrangle Cadott 15 ' quadrangle I rç j - AUTHOR: AUTHOR: Paul Paul E. E. Myers Myers DATE: DATE : - March, 1980 March, 1980 '—_-__--——- I —r SUMMARY OF OF FEATURES: SUMMARY FEATURES : This contactbetween between foliated hornblende-bioti hornblende-biotite diorite This enigmatic enigmatic contact f a ifaintly n t l y foliated t e diori te and foliated metadacite(?) and strongly deformed, deformed, foliated metadaci t e ( ? ) (Figure 36)exemplifies 36) exempl i f i e s the themany many problems workingout out sequence sequencei ninrocks rocksaffected affected by by recurrent recurrent cataclasis, problems ofof working intrusion, folding, andand metamorphism. intrusion, folding, metamorphism. Field Fie1 d and and petrographic petrographic evidence evidence here, here, and places throughout throughoutthis this region, region, stron.gly the hypothesis and aatt most most places strongly support support the hypothesis tthat hat intrudedinto into more moreb brittle cataclastic veinlets veinlets and and dikes dikes are are synkinematically synkinematically intruded rittle rocks rocks at a t sub-anatectic sub-anatectic temperatures. temperatures. The The basic basic question question here here is, i s , "Under "Under what what conditions, and andaat whattime timewere werethethecataclastic cataclasticb ibiotite tonalite veinlets conditions, t what o t i t e tonalite veinlets (7904-B) emplaced?" empl aced?" DESCRIPTION: DESCRIPTION: chronologyf ifield on ffield AA chronology e l d sstation, t a t i o n , based based on i e l d relations relationsand and features features seen seen in in three, t h r e e tthin h i n sections sections(Myers (Myers7904-A-C) 7904-A-C) isi sproposed proposed below. be1 ow. Three Three pre-catacl pre-cataclastic astic protoliths protol i ths exist: exist:(1) Hornblende-biotite dacite dacite or o r tonalite, tonal i t e , (2) ( 2 )pegmatite, pegmatite, (1 )Hornblende-biotite and metadiorite. and (3) hornblende—biotite hornblende-bioti t e metadiori te. o r metatonalite(?) metatonal i t e ( ? ) iiss composed The foliated metadacite(?) of approxiThe foliated metadaci t e ( ? ) or composed of mately 50% plagioclase (An42), 50% plagioclase (An42),10% 10%fragmented fragmented and and altered a1 tered hornblende, hornblende,25% 25% fine-grained, fine-grained, polygonized, polygonized, strained quartz, quartz, and and 5% 5% bbiotite. i o t i t e . Plagioclase, hornblende, and arep apartially altered epidote, prochlorite, prochlorite, calcite, hornblende, and b i biotite o t i t e are r t i a l l y a1 tered tto o epidote, cal c i t e , The metadaci rnetadacite metatonalite(?) The t e oor r metatonal i t e ( ? ) has and magnetite(?) magnetite(?). has a conspicuous and conspicuouscata— catabent andand fragmented cclastic l a s t i cfoliation; foliation; bent fragmentedplagioclase plagioclaseporphyroclasts porphyroclastshave have ovoid ovoid outlines and outlines and fragmented fragmented hornblende hornblende crystal crystal remnants remnants have have been been dispersed dispersed along interlensing coarse, polygonal polygonal form form of of the quartz interlensing shear shear surfaces. surfaces. The The coarse, quartz and and the the replacement of hornblende by bbiotite cataclasis. replacement of hornblende by i o t i t esuggest suggest metamorphism metamorphism a after f t e r cataclasis. This isoclinal fold 36-E) . This rock rock contains contains several several detached detached isoclinal fold hinges hinges (Figure (Figure 36-E). . �_______________ -68- a granite g r a n i t e in in The pegmatite( n(not studiedi in The pegmatite o t studied n tthin h i n section) section) is i s probably probably a andand composed and quartz. quartz. composition: iti tisi leucocratic, s leucocratic, composed of o f pink pink feldspar feldspar and the quartz Feldspar el dspar cleavage cleavage planes planes are are conspicuously conspicuously bent, bent, and and the quartz locally l o c a l l yhas has been been llenticulated e n t i c u l a t e d by by cataclasis. cataclasis. The sheared hornbl hornblende-biotite The sheared ende-bioti t e meta—diorite meta-diori t e isi scomposed composed ooff reverse-zoned, reverse-zoned, strained, marginally (39%),fragmented, fragmented, subhedral subhedral marginal l ycrushed crushedplagioclase plagioclase(An54) (Ans4)(39%), green (54%),pale paleye1 yellow-brown green hornblende hornblende (54%), low-brown bbiotite i o t i t e in i nrandom random orientation o r i e n t a t i o nand and andpprochiorite, by a1 alteration Epidote and r o c h l o r i te, formed formed by t e r a t i o n ofo fhornblende hornblende distribution d i s t r i b u t i o n(3%). (3%). Epidote include coarse Accessories include coarse aapatite, patite, make up approximately approximately 3% 3%oof make up f the rock. rock. Accessories sphene, and magnetite magnetite (?). (?). sphene, and . Figure 36 36shows showsthe ther erelations The following f o l l o w i n gsequences sequences l a t i o n s ooff these these three rocks. rocks. The subsequent are possible: possible: (1) are I n t r u s i o n ofo ftonalite tonal it into e i n diorite t o d i o rand i t e and subsequentdeformation deformation ( 1 ) Intrusion with w i t h most most intense cataclasis c a t a c l a s i s and and development development o foff ofoliation l i a t i o n in i nthe t h emetadacites; metadacites; (2) subsequent (2) intrusion i n t r u s i o nof of diorite d i o r i t into e i n dacite t o daci tand e and subsequent deformation deformation wwith i t h localizalocal ization t i o n of o f isoclinal i s o c l i n a lfolding f o l d i n gand and cataclasis c a t a c l a s i s in i n the the dacite, dacite, possible possible Injection i n j e c t i o n of of Note felsic blocksoof moreb rbrittle f e l s i c "cataclastic " c a t a c l a s t i c dikes" dikes" into i n t othe thebroken broken blocks f more i t t l e ddiorite. i o r i t e . Note that the rrelative t h a t these these alternatives a1 t e r n a t i v e s reverse reverse the e l a t i v e ages ages ooff the the diorite d i o r i t e and and the the dacite. dacite. The curvatureofofthe thec cataclastic "veins" ccutting the ddiorite The curvature a t a c l a s t i c f ofoliation l i a t i o n near near tthe h e "veins" u t t i n g the iorite (B) the ddiorite andppulled apartt to (B) suggests suggests t that h a t the i o r i t e was was broken broken and u l l e d apart o aallow l l o w iintrusion n t r u s i o n of of Itisi sclear, clear,however, however, that t h a tcataclasis c a t a c l a s i saffected a f f e c t e dboth both the the the t h e more more ffelsic e l s i c rock. rock. It Note that t h a t the t h e folds f o l d s are diorite d i o r i t eand and the the dacite d a c i t e with w i t h its i t spegmatite pegmatite dikes. dikes. ftote detached, rootless, a factor suggesting considerably chaotic internal detached, rootless, f a c t o r suggesting considerably chaotic i n t e r n a l displacedisplace- are ment during or after folding ment during o r a f t e r folding. -.Metatonal i te with folded >'m//OLA/ q Ye//<? w ^?. . . . / Figure 3636---- BBiotite i o t i t e tonalite tonal i t e flaser f l a s e rgneiss gneiss veinlets v e i n l e t s (B) (B) cutting c u t t i n gmetadiorite metadiori t e (A) (A) Figure Antiformal hinges hinges in i n metadacite(?) metadacite(?) or o r metadiorite(?) metadiorite(?) plunge plunge steeply steeply northeast. northeast. Antiformal Fol i a t i o n in i nmetadacite(?) metadaci t e ( ? ) bends bends i into n t o ccataclastic a t a c l a s t i c veinlets v e i n l e t s(B). (B).Outcrop Outcrop slopes slopes Foliation gently toward toward tthe h e bottom f t the h e pprofile. rofile. gently bottomoof �-69 - -- Figure 37 A x i a l portion p o r t i o n of o fhinge hingeof o fdetached detached isoclinal isoclinal Figure 37 -- Axial fold Location E. E. Scale Scale iiss 66 inches inches long. long. f o l d segment, segment, Location Figure 38--- Nearly Nearly vvertical e r t i c a l cataclastic c a t a c l a s t i c veinlets v e i n l e t s cutting cutting . Figure 38 faintly f a i n t l yfoliated f o l i a t ehornblende d hornblendemetadiorite m e t a d i o r i t enear near location l o c a t i o nA. A. Note zoningoof with coarsel lentiNote zoning f vveinlet einlet w i t h concentration concentration ooff coarse enticular c u l a r feldspar feldspar porphyroclasts porphyroclasts near near the t h e center; center; quartzoquartzofeldspathic on photo photo f e l d s p a t h i c layers layersalong alongoutside outsideedges. edges. Line on is i s analogous analogous i in n location l o c a t i o n to t o veinlet v e i n l e tmargin margin described described in in Figure 39. 39. �-70- Biotite tonalite tonal i t eflaser f l aseraneiss aneiss Lenticular pl agiocl ase i n biot i t e f o l i a w i t h qiartz. P l agi ocl ase Quartz Biotite Hornblende -- 65% 20 15 0 Banded 1eucotrondhjemi eucotrondhiemi ttee Hornblende d i ori t e Banded Very coarse pl agi ocl ase w i t h shears and drag w i t h bent t w i n lamellae surrounded by f i n e r grained quartz - 40% 55 5 0 45% 5? 5 40 Figure 39 39 -- Cross section of of zoned cataclastic veinlet veinlet (Location Figure Cross section zoned cataclastic (Location B). B). Width Width of section section fromhornblende hornblende centerofofveinlet veinlet ((left) from d i odiorite r i t e ( r (right) i g h t ) t otocenter l e f t ) isi s7.0 7.0cm. cm. �-71— STOP STOP #9 #9 TITLE:: TITLE CADOIT INTRUSION CADOTT INTRUSION BRECCIA BRECCIA AND AND CATACLASTIC CATACLASTICROCKS ROCKS LOCATION: SW¼, T29N, R6W: Cadott quadrangle;F Field Locatiion 7905 LOCATION: SW s, NEs,NE¼, Sec.Sec. 31, 31, T29N, R6W: Cadott 15' 15' quadrangle; i e l d Locatiion 7905 AUTHOR: P. P. E. E. Myers Myers DATE: DATE : - February, 1980 February, 1980 SUMMARY OF SUMMARY O F FEATURES: FEATURES: Mafic amphi amphibolites andf ofoliated hornblendetonal tonalite containingi sIsoclinally l i a t e d hornblende it e containing o c l i n a l l y folded folded Mafic bol it e s and quartz, as angular angularxenoliths xenolithsi in quartz, aplite, apl ite, and and pegmatite pegmatite vveinlets e i n l e t s eexist x i s t as n aa 1lighter ighter biotite Folds iin n the the xenoliths xenoliths and and l lineations i n e a t i o n s iinn the t h e enclosing enclosing ttonalite onalite b i o t i t e tonalite. t o n a l i t e . Folds southeast (Figure 40) contains aa pervasive pervasive cataclastic cataclastic pplunge l unge southeast 40) The The bbiotite i o t i t e tonalite tonal it econtains ffoliation o l i a t i o n which which was was locally l o c a l l ybuckled buckled into i n t ochevron chevron folds, folds, which which plunge plunge steeply steeply northwest. The Thef first byby a second west. i r s t cataclastic c a t a c l a s t i cfoliation f o l i a t i o is n truncated i s truncated a secondone one (Location (Location A A in in discardat vveinlets The llater a t e r cataclastic c a t a c l a s t i c event event produced produced discordant e i n l e t s of o f leucoleucoFigure 40 40 ). The Figure trondhjemite gneissw iwith strong cataclastic parallel trondhjemi t e f lflaser aser gneiss t h a astrong catacl a s t i c f o lfoliation ' i a t i o n para1 l e l t to o ttheir heir walls (Figure of walls (Figure 42 42 ).). The The second second ccataclastic a t a c l a s t i c event event included included ssignificant i g n i f i c a n tamounts amounts of trendingf faults. sstrike-slip t r i ke-sl ipdisplacement displacement along a1ong west-northwest west-northwest trending aults. DESCRIPTION DESCRIPTION , The predominant predominantrock rocktype typehere herei sis ffoliated The o l iated tonalite tonal it ecomposed composed ooff plagioclase p l agi ocl ase 30-55%), quartz quartz (10-40%), hornblende (0-25%) (0-25%)and andbbiotite 30-55%), (10-40%), hornblende i o t i t e (0-15%). (0-1 5%). These ((An An minal' are partly min&?$'are p a r t lreplaced y replacedby by chlorite c h l o r i t e(of ( o several f several varieties), v a r i e t i e s ) ,epidote, epidote, and and Magnetite (1-5%) (1—5%) by-producti ninthe thecchioritization ssericite. e r i c i t e . Magnetite i s is i sisa aby-product h l o r i t i z a t i o nofo fhornblende. hornblende. The tonalites beenmyloni mylonitized and1ocal locally ites have have been t i zed and l y rrecrystallized e c r y s t a l I i z e d (Location (Location A). A). The tonal At A t locations locations A-D A-D (Figure (Figure 40) 40) bbiotite i o t i t e tonalite t o n a l i t e with w i t h an an older o l d e r ccataclastic a t a c l a s t i c ffoliaoliation containsl elenticular xenoliths of of chlorite.and t i o n (NlO-20°W) (N10-20OW) contains n t i c u l a r xenoliths c h l o r i t e a n d epidote-rich epidote-rich metameta- volcanic(?) rock.The The01older cataclastic vo1 cani c ( ? ) rock. der catacl a s t i c f o foliation l ia t i on i sis aaxial-planar x i a1 -planar t to o iisoclinally socl inal l y These rocks rocks are are ccut folded pegmatite, pegmatite, apl aplite, u t by by folded i t e , and and quartz quartz layers layers (Location (Location A). A). These a pervasive trendingf ofoliation pervasive N65-75°W N65-75 W trending l i a t i o n and and mylonitic m y l o n i t i cshear shear zones. zones. �-72- STRUCTURE SYMBOLS SYMBOLS STRUCTURE go0 80 c. compositional compositional layering 1ayeri ng 600 60" mica mica ffoliation oliation 70' 70. \ cataclastic c a t a c l a s t i c ffoliation, oliation, lenticulation 1enticul a t i o n "5oplunge of lineation G -- Figure Outcrop structure s t r u c t u r e map map of the the Yellow Yellow River River bridge bridge area, a r e a , Cadott Cadott Figure 40 40 -- Outcrop Figure -- Folded Folded iisoclinal s o c l i n a l folds folds Figure 41 41 -in mafic xenolithinin ffolmafic amphibolite amphibolite xenolith oliated i a t e d bbiotite t o t i t e tonalite. tonal i te. Lineation Lineation on on left l e f tside s i d eofofthe thexenolith xenolithplunges plunges550 55O southeast. southeast. Location EE -- Figure Figure 42 42 -- Folds Folds ini nbanded banded mafic mafic tonalite t o n a l i t e cut c u t by by aplite a p l i t e veins veins (left ( l e f tand and right) r i g h t )and and by by coarser coarser tonalite t o n a l i t e vein vein to with w i t h cataclastic c a t a c l a s t i c ffoliation o l i a t i o n parallel para1 1el to its i t swalls walls(center) ( c e n t e r )Location LocationG. G. �-73— West River bridge, bridge, ffoliated West oofthe f t h e Yellow Yellow River o l i a t e d biotite b i o t i t etonalite t o n a l i tencloses e enclosesangular angular xenoliths tonalite o fmore more mafic mafi c hornblende hornblende tonal it e or o r amphibolite amphi bol it e containing containing strongly strongly xenol iths of 43 ) Xenolith deformed aaplité p l i t e and and pegmatite pegmatite sstringers t r i n g e r s (Figure (Figure41 41 and and 43 Xenolith orientation orientation deformed Small Small ffolds o l d s within w i t h i n the the xenoliths xenoliths NIOOW. here (as (as at a t Little L i t t l eFalls) F a l l sis) about i s about here NlO°W. plunge southeast southeast at a t lO_600 10-60 (See (See Figure 40 40 ).). plunge CHRONOLOGY CHRONOLOGY The baseds osolely ont hthe cross-cutting rrelationships The ffollowing o l l o w i n g sequence sequence i sis based l e l y on e cross-cutting e l a t i o n s h i p s of of •features out features aatt this t h i s location, location,but b uthey t theycorrelate c o r r e l a t well e w e with l l w i tsquences h squencesworked worked o u t for for o t h e r areas. areas. other 1. maficp rprotolith coarse, tonal tonalitic it i camphibolite amphibol it e 1. (Oldest) (Oldest) Metamorphism Metamorphism o f of mafic o t o l i t h t to o coarse, accompanied segregation(?) stringers, quartz accompanied byby segregation(?) o f off efelsic l s i c stringers, quartz veins. veins. 2. with 2. Shear Shear ffolding olding w i t h formation formation oof f iisoclinal s o c l i n a l folds. folds. 3. 3. Intrusion I n t r u s i o n ooff light-colored 1ight-colored bbiotite i o t i t e tonalite tonal i t e ("foliated ( " f o l i a t e d tonalite") tonal i t e " ) with with formation formation of o f an an intrusion i n t r u s i o nbreccia breccia(Figure (Figure41 41 ). ). 4. 4. Cataclasis, Cataclasis, formation formation of o f more more isoclinal i s o c l i n a l folds f o l d s (Location (Location D). D). Cataclasis Cataclasismay may have accompanied t r u s i o n . (Figure 45). 45). have accompaniedi nintrusion. 5. 5. Local Local chevron chevron f ofolding l d i n g oof f ccataclastic a t a c l a s t i c ffoliation o l i a t i o n(Location (Location E, E, Figure Figure 44 44 ). 6. 6. Intrusion I n t r u s i o n of o fdarker darker tonalite t o n a l i t e(Location (Location 0) D) with w i t h formation formation of o f intrusion intrusion breccia containing xenoliths xenoliths ooff catacl cataclastically tonalite. breccia containing a s t i c a l l y deformed deformed 1ilighter g h t e r tonal ite. 7. 7. Intrusion I n t r u s i o n of o faplite a p l i t and e andpegmatite. pegmatite. 8. G Gand 8. Formation Formation oorr jntrusion(?) i n t r u s i o n ( ? ) of o fcataclastic c a t a c l a s t i cveinlets v e i n l e t(Locations s (Locations andH,H, Figures Figures 42 and and 45 45 ).). Strike-slip S t r i k e - s l i pdisplacement displacement along along west-northwest-trending west-northwest-trending ffaults. aults. 42 Figure -- Intrusion amphibolite iin Figure 43 43 -I n t r u s i o nbreccia breccia of o fbanded banded amphibolite n biobio- foliated f o l i a t e d biotite b i o t i t etonalite t o n a l i t eata Location t Location H. H. �-74- -- Figure 44 44 -- Chevron-fol Chevron-folded tonalite Figure ded f o lfoliation i a t i on i ninbbiotite i o t i t e tonal it e which contains contains tthe mafic amphi amphibolite xenoliths at which h e mafic bol it e xenoliths a t Location Location here plunge plungesteeply steeply nnorth(?) Horizontal outcrop. outcrop. E. Folds Folds here o r t h ( ? ) Horizontal -- Figure 45 -- Isoclinally I s o c l i n a l l yshear shear folded folded bbiotite i o t i t e tonalite tonalite Figure 45 tonalite. Cataclastic sstringers t r i n g e r s in in darker darker tonal it e . Location Location D. D. Catacl astic View north-northeast. foliation is N80°E, 750N. fo1 i a t i o nhere here i s N80OE, 75ON. View north-northeast. - �—75- STOP STOP #10 #10 TITLE: DIKES AT AT WISSOTA WISSOTA DAM DAM LOCATION: LOCATION: NNW W 1/4, T28N, R8W, R8W, Lake Quadrangle 1/4, Sec. Sec. 3, T28N, Lake Wissota Wissota 77 1/2' Quadrangle Field location, location,7835 7835++7906 7906 AUTHOR AUTHOR:: Paul E. Paul E. Myers Myers DATE: DATE : - December, 1977, and March, December, 1977, March, 1980 1980 SUMMARY OF FEATURES: FEATURES: SUMMARY OF A intrusion sequence exposedi in A complex complex intrusion sequence exposed n aa large outcrop outcrop (Figure (Figure47). 47) below below Wissota DDam (2.5m imi.) northeast of of Chippewa is: (1) protoclastic Wissota am 4.04.0kmkm(2.5 . ) northeast Chippewa F Falls a l l s is: protoclastic pegmatite bbiotite i o t i t e trondhjemite, trondhjemite, (2) (2) biotite b i o t i t etonalite, tonal i t e(3) , (3) pegmatiteand andquartz quartz veins, veins, and((5) trondhjemite ((4) 4 ) gabbro-diabase, gabbro-diabase, and 5 ) trondhjemi t e veinlets. A A ccataclastic a t a c l a s t i c zone zone cuts cuts and shows showsl eleft-lateral 40-50 meter through 33 and f t - l a t e r a l displacement. displacement. The The 40-50 meter gabbrogabbrounits 11 through diabasedike dike grades gradesinward inwardfrom fromaphanitic aphaniticbasalt basaltalong alongi its diabase t s walls to t o coarse coarse Inclusions of very very coarse coarse norite n o r i t e and and plagioclase plagioclase pyroxene gabbroi niniits pyroxene gabbro t s core. core. Inclusions occur along alongthe thenorth north wall wall of of the crystal fragments fragments occur the dike. dike. The The gabbro-diabase dike is i s intruded intruded by by coarse, coarse, pink p i n k trondhjemite trondhjemite (quartz (quartz + oligoclase) 01 igoclase) which which is is dike Thesemiddle middlet to rocks are smallffaults. ooffset f f s e t by by numerous numerous small a u l t s . These o llate a t e Precambrian Precambrian rocks are gravels and and ssilts t h i n outwash outwash gravels i l t s ofofPleistocene Pleistoceneage. age. overlain here here by by thin DESCRIPTION: DESCRIPTION.: Trondhjemite and Tonal Tonalite: Trondh jemi t e and ite: Theooldest rock aatt Wissota WissotaDDam gneissic bbiotite The l d e s t rock am i s isf afaintly i n t l y gneissic i o t i t e trondhjemite trondhjemite composed (50%),quartz quartz(35%), (35%),m microcline (5%),bbiotite composed of of01oligoclase i gocl ase (SO%), i crocl ine (5%), i o t i t e (5%), (5%), muscovite Weakf ofoliation muscovite (5%), (5%),and and abnormally abnormallyabundant abundant sphene. sphene. Weak l i a t i o n srikes s r i kesNl5°W N15OW and and (N2O-5O°W) G,D) The gneissic adamellite adamelliteisi cut s cut (N20-50°Wby by dikes dikes(Loc. (Loc.G,D) dips d i p s steeply steeply east. e a s t . The darkergray graybbiotite and and iirregular r r e g u l a rmasses masses (Loc. (Loc. I and and J) of of medium-grained, medium-grained, darker iotite tonalite t o n a l i t e (Loc. (Loc. D), D ) , which which locally l o c a l l y (Loc. (Loc. G) G ) contains contains llenticular e n t i c u l a r xenoliths xenoliths of of �___"ft. -76- bandedamphibol amphibolite Big The t tonalite o n a l i t e intrusions intrusions banded i t e s i similar m i l a r t oto tthat h a t seen seen aatt B i g Falls. F a l l s . The show nograin grainssize diminution along along contacts, contacts, and show no i z e diminution and tthe h e amphibolite amphi bol i t e xenoliths Someo foft hthe tonalite areoof such i irregular e tonal i t e masses masses are f such rregular are are relatively r e l a t i v e l yunaltered. unaltered. Some shape doubteexists as tto they are are iintrusions shape t hthat a t doubt x i s t s as o whether whether they n t r u s i o n s or o r segregations segregations in in sphene,sosoc hcharacteristic the trondhjemite trondhjemite. Euhedral Euhedral sphene, a r a c t e r i s t i c oof f the trondhjemite is is the trondhjemite. tonalite absent iin n tonalite tonal it esections sectionsexamined. examined. The The tonal it e isi scomposed composed ooff plagioclase p l agiocl ase absent (An-38), bbiaxial A l l minerals minerals ini nthese theserocks rocksshow show (An-38), i a x i a l quartz, quartz, biotite, b i o t i t e , and and epidote. epidote. All internal textures ccharacteristic f r a c t u r i n g and and dislocation, dislocation, although a1though the t h e mortar mortar textures haracteristic . i n t e r n a l fracturing of mylonitized of mylonitized plutonic p l u t o n i c rocks rocks are are absent. absent. The trondhjemite andtonal tonalite The trondhjemi t e and it e are cut c u t by by east-northeast-trending east-northeast-trending pegmatite, pegmatite, pegmatites showc rcrystal quartz and epidote vein1 veinlets. The pegmati t e s show y s t a l oorientation r i e n t a t i o n perpenperpenquartz and epidote ets. The ddicular i c u l a r to t o their t h e i rwalls--a w a l l s--afactor f a c t oindicating r i n d i c a t i nemplacement g emplacement underconditions undercondi t i o n s ooff no iisotopic tension oorr thermal tension thermal contraction. contraction. Although Although no s o t o p i cdates dateshave have been been obtained obtained from these rocks, it is probable that by correlation with similar from these rocks, i t i s probable t h a t by c o r r e l a t i o n w i t h s i m i l a r rocks rocks elseelsewhere, ttheir 1845mmillion where, h e i r age age is i sbetweer between 1820 1820 and and 1845 i l l i o n years. years. A discordant sheet sheetoof A tthin, h i n , branching branching discordant f ffoliated o l i a t e d biotite b i o t i t etrondhjemite trondhjemite (Loc. (Loc. D)-here cuts cuts and andooffsets the oolder by lleft-lateral here f f s e t s the l d e r rocks rocks by e f t - l a t e r a displacement l displacement (Figure (Figure 46) 46) The The ffoliated, o l i a t e d , mylonitized mylonitizedtrondhjemite trondhjemite layer l a y e risi 1-3 s 1-3meters meterswide wideand and trends trends Dragfolded foldedf ofoliation rocksi nindicates Drag l i a t i o n iin n the t h e enclosing enclosing rocks d i c a t e s 1eleft-lateral ft-lateral N55°W. N55OW. S l ickensi ded ffault a u l t surfaces surfaces elsewhere e l sewhere iinn this t h i soutcrop outcrophave have ddisplacement. i spl acement. Slickensided similar s i m i l a r strike s t r i k eand anddip d i pand and slickensides slickensides plunging plunging 5°NW, 5ONW, aaf afactor c t o r iindicating ndicating nearly horizontal, horizontal, lleft-lateral nearly e f t - l a t e r a l strike-slip s t r i k e - s l i displacement. p displacement. / -, / / —..g .- . .z- / '/ ,- I-—', —, d.. granite ,Pmati tei - I' ' drag folds rod\S%'SZ ? drag f o l d s roduce by sinistra s i n i s t r a displacement' displacemen — foliated f o l i a t e d biotite b i o t i t etrotIdhjen p / ,v/,ra ', , I 80' / -- i e l d sketch y l o n i t i c vveinlet e i n l e t in i n foliated f o l i a t e dtrondhjemi trondhjemite Figure Figure46 46 -- FField sketchooff mmylonitic te Location Location FF Diabase Diabase Dike: The rocks described described above abovewere werei nintruded shallow depth The rocks t r u d e d aatt shallow depth in i n Late Late Precambrian time (Â¥^I10 ("1100 m.y. dikes, one B.P. )by bynumerous numerous gabbro-diabase gabbro-diabase dikes, one ooff Precambrian time m.y. B.P.) Thevvertical e r t i c a l dike dike strikes strikes which iiss superbly which superbly exposed exposed i nin tthis h i s outcrop. outcrop. The Numerous apophyses apophyses N20—60°E margins aphanitic basalt. basalt. Numerous N20-60° andand hashas c h ichilled l l e d margins o fofaphanitic extendalong alongj ojoints extend i n t s iin n the the enclosing enclosing ggranitic r a n i t i c rocks rocks (Loc. (Loc. A, A, Figure Figure 47). 47). AA narrow zone ooff plagioclase xenoliths narrow zone p l agioclase and and hypersthene hypersthene gabbro gabbro xenol iths occurs occurs about about one one The llabradorite a b r a d o r i t e (An60) (An6,,) meter the nnorth wall of meter i inside n s i d e the o r t h wall o f the the dike dike at a tLocation Location B. B. The fragments are up up tto 20 centimeters centimeters long long and and are are ooriented with fragments are o 20 riented w i t h long long �-.77- -- Figure 47 47 -- Geologic Geologicmap mapofo Wissota f WissotaDam Dam area. area. Figure �-78- - were ffirst The fragments fragments were i r s trounded rounded by by directions parallel d i rections para1 1e l to t o the.dike the dike wall. wall . The corrosion during ddike ? ) and and llater a t e r broken broken iin n transit t r a n s i tupwards upwards during i k e intrusion. intrusion. corrosion ((?) Closely angular hypersthene hypersthene(C?) gabbroo rornnorite ? ) gabbro o r i t e xenoliths up up Closely associated associated angular to long cconsist t o 40 40 centimeters centimeters long o n s i s t of o f very very coarse, coarse, dark dark brown brown tto o dark dark olive olive gray hpersthene,now' now mostly gray hpersthene, mostly a1taltered e r e d t otot atalc, l c , iiddingsite, d d i n g s i t e , and and chlorite, c h l o r i t e , which which is i s intimately i n t i m a t e l yintergrown intergrown with w i t h very very coarse coarse plagioclase plagioclase llaths a t h s up up to t o 15 15 centicentiandhow how thesexenol xenoliths meters meters ini nmaximum maximum dimension. dimension. Where Where and d i did d these it h s ccrystallize? r y s t a l 1i z e ? (They gabbrosfound foundnear neart hthe baseo foflayered layeredi nintrusions (They cclosely l o s e l y resemble resemble gabbros e base t r u s i o n s llike ike those along the the nnorth those along o r t h shore shore of o f Lake Lake Superior.) Superior. ) Why Why aare r e tthe h e xenoliths xenol i t h sconcenconcentrated t r a t e d only only along along one one wwall a l l of o f the t h e intrusion? i n t r u s i o n ? How How ddid i d tthe h e dike d i k e form? form? The diabaseddike wassampled sampled contact with s contact w i t h gneissic gneissic The diabase i k e was a t at l o clocation a t i o n B Ba tati tits The trondhjemite, att distances trondhjemite, and and a distances of o f 6, 6, 25, 25,50, 50,and and120 120cm cm from from the t h e contact. contact. The rock almost plagioclase(An(An7_)) enstatite, rock iiss composed composed almost e n tentirely i r e l y o fofplagioclase e n s t a t i t e , and and (mostly magnetite,y pyrite, andi%@i hmtite) Opaques (mostly magnetite, r i t e , and t e )decrease decrease in in pegeonite. pegeoni te. Opaques 7 abundance inward(See (SeeTable Table9). 9). Plagioc Plagioclase abundance inward ase occurs occurs as anhedral anhedral to t osubhedral subhedral -- COMPOSITIONOF OFDIKE DIKE BORDERPHASES PHASES TABLE BORDER TABLE 99—- COMPOSITION MINERALS MINERALS Contact Contact 66 cm cm 25 cm cm 50 50 cm cm P l ag Plag 68% 68% 63% 63% 48% 48% 53% 53% 52% 52% 7+ 7+ 12+ 12+ 28 28 27 27 28 28 33 44 66 14 14 10 10 99 1 33 22 22 . --- Biotite Biotite --- Opaques Opaques 15 15 16 16 —— -— --- 99 8 8 44 1 1 1 1 -- Olivine 01 ivine Chlorite Chlorite Accessories 1 -- - 1 1 120 120 cm cm 1 22 1 i. -- TABLE 10-- SIZE SIZE VARIATION VARIATIONINWARD INWARD IN I N DIKE DIKE TABLE 10 o 40 80 20 40 80 (cm) Contact Distance from from (cm) 100 126 cm �-79- laths with m at w i t h size s i z eranging ranging from from 0.13 0.13 mm a t the the contact contact to t o 0.75 0.75 m mm at a t aa distance distance of of 120 m. An 120 mm. content in the An content the plagioclase plagioclaseincreases increases inward. inward. Enstatite Enstatite forms forms blocky blocky wedge-shaped, i ninterstitial t e r s t i t i a lgrains, grains,has hasa a2V2Vofof50-60°, 50-60° anda asize s i zfrom e from 0.10 mrn wedge-shaped, and 0.10 mm at of 120 m. (Table a t the the contact contact to t o0.50 0.50 mm mm aat t a a distance distance of 120 mm. (Table 10.) 10.) Finer Finer grained grained pigeoni t e forms forms pale i n k , weakly pigeonite pale greenish greenishbrown brownt otop pink, weaklypleochroic pleochroicfibers. fibers. Biotite Biotite increases in i n abundance abundance tto o about percent at a t aa distance distanceofof120 120mm mm from from the conconincreases about 66 percent tact. tact. -- Figure Figure 48 48 -- Intrusive Intrusivecontact contactbetween between chilled chilled basalt basalt (center) (center) and and anorthositic anorthosi t i c gabbro gabbro inclusion incl usion at a tLocation Location C. C. Note Note llate, a t e , fault-related faul t-related fracturing. fracturing. Photo Photo width width is i s 4.2 4.2 millimeters. millimeters. At A t location 1ocation B, B, the thediabase diabase dike d i ke is is cut cutby by aa 3-5 3-5 centimeter centimeter vein vein of of coarse-grained trondhjemite (oligoclase The rock rock isisunusual unusual coarse-grained trondhjemi t e (01 igoclase + quartz). quartz). The because of the the pervasive orange-red color color of the because of pervasive orange-red the plagioclase pl agiocl ase(dispersed (dispersed iron the degree t h i n section section by by the the iron oxides) oxides) and and the degree ofof sstrain t r a i n exhibited exhibited iinn thin quartz, an unusual unusualfeathery, feathery, lamellar lamellar undulatory extinction. undulatory extinction. quartz, which which shows shows an The plagioclase i n aa Since the vein vein occurs occurs in is locally locallybent bentand andcrushed. crushed. Since The pl agiocl ase is north—northwest zonewhich whichcuts cutsthe thediabase diabase dike,i tit is is not surprising surprising north-northwest f afault u l t zone dike, to strongly developed t o see see strain s t r a i n features, features, but b u t iti is t iunusual s unusualtot osee seeit iso t so strongly developed in in Late this rock Late Precambrian Precambrian rocks. rocks. Since Since the mineral mineral composition composition ofof this rock is isso so simple, an approximate The simple, iti twould wouldnot notbe be difficult d i f f i c uto l t calculate t o calculate an approximatenorm. norm. The quartz-plagioclase The trondhjemite trondhjemite dike offset by by dike is offset about 0.8. 0.8. The quartz-plagioclase ratio r a t i o isisabout small subsequently fibrous calcite, small faults f a u l t s which which were were subsequently f i lfilled l e d wwith i t h fibrous c a l c i t e , an an indication indication of considerable considerable post-diabase post-diabase aactivity c t i v i t y in i n this thisarea. area. . of �-80- - OOLOGY - WISSOTA ;-i?O:;OLOGY WISSOTADAM DAMAREA AREA 1 1 Metamorphism formation amphibolite tonalite) . Metamorphism andand formation of of amphibolite ( x e(xenoliths n o l i t h s i nintonal it e ) 2. emplacement 2 . Synkinematic Synkinematic emplacement of of f o lfoliated i a t e d b biotite i o t i t e trondhjemite trondhjemi t e with with development ooff foliation development f o l i a t i oNlO—15°W. n N10-1 OW. 3. (?) of of biotite 3. Intrusion I n t r u s i o n (?) b i o t i t e tonalite t o n a l i t e roughly roughly pparallel a r a l l e l tto o foliation foliation iinn the t h e trondhjemite trondhjemite (Location (Location G, G, D) D) 4. Left-lateral L e f t - l a t e r a l strike-slip s t r i ke-sl ifaulting p f a u l t i nand g and development of o f cataclastic cataclastic 4. development veinlets F, P, v e i n l e t s N45-55°W. ~ 4 5 - 5 5 O ~ (Locations .(Locations F, P, and and 0) 5. Intrusion 5. I n t r u s i o nofo fpegmetite pegmetite dikes dikes associated associated with w i t h thermal thermal contraction contraction and/or ccrustal r u s t a l tension. tension. (Location '(Location E.) E. ) and/or 6. E' 6. Jointing, J o i n t i n g , deposition deposition of o fepidote, epidote, and and small-scale small-scale faulting. fau 1t i n q . (Locatioii (Loca t 7. froma addifferentiatinç 7. Intrusion I n t r u s i o nofo fdiabase diabase with w i t hmagmaderived magma derived from ifferentiatino ) adepth. t depth.(Locations (Locations A, A, B, B, C, C, H) H) ssill(?) i l l ( ? at 8. Intrusion 8. I n t r u s i o nofo leucotrondhjemite f leucotrondhjenn'te dike dike (Location (Location B) B) 9. Faulting 9. F a u l t i n g and and development development o of f sstrain t r a i n features features in i n leucotrondhjenite leucotrondhjerii t e 10. 10. Precipitation P r e c i p i t a t i o n of o f calcite c a l c i t eveinlets veinletsini nthe thefault f a uzone.(LoCation l t zone.(Location B) B) 11. Erosion. 11. Erosion. , �- -81 -81- STOP STOP #11 #11 TITLE : TITLE: AMPHIBOLITES OF AMPHIBOLITES AND AND GRANITES GRANITES O F JIM JIM FALLS FALLS LOCATION: LOCATION: EE 1/2 Quadrangle 1/2 Sec. Sec. 30, 30, TT30 30N, N, RR77W, W , Jim JimFalls, F a l l sBloomer , Bloomer15" 15''Quadrangle AUTHORS: AUTHORS: DATE: DATE : Paul E. E. Myers Myers and and Douglas Doug1as R. R. Maercklein Maerckl e i n February, February, 1980 1980 SUMMARY O F FEATURES: FEATURES: SUMMARY OF Banded amphibolites, probably probably derived derived from from mafic mafic volcanicsand Banded amphibolites, volcanics and assocassociated intruded by by granites of i a t e d sediments, sediments, were were intruded o f diverse diverse composition composition and and ttheir heir cogenetic cogeneti c pegmatites pegmati t e s aatt several several times times ini nMiddle MiddlePrecambrian Precambrian time. time. Cataclasis, Catacl a s i s , folding produceda ahhighly deformedsystem systemo of f o l d i n gand andmetamorphism metamorphism produced i g h l y deformed f t tectonically ectonically interlensing only ppartial i n t e r l e n s i n g rock rock units u n i t s showing showing only a r t i a l preservation preservation ooff older o l d e r structures. structures. Prevailing Prevail i n g regional regional structural s t r u c t u r a lgrain g r a i nisi ENE. s ENE. Late Late Precambrian Precambrian diabase diabase dike dike i n t r u s i o n(1100 (1100 - 900 900m.y.?) my.?) followed followedprolonged prolonged erosion. erosion. intrusion - DESCRIPTION: DESCRIPTION: Garnetiferous gneissand andsschist with h i gh-amp1 itude Garneti ferous hornblende hornblende gneiss chist w i t h folded, f o l ded ,high-amplitude isoclines, i s o c l i n e s , (Figure (Figure49)persistent 49)persistentENE ENE strike s t r i k eand and steep steep dip d i pare arecut c u tsubconsubconcordantly from leuco-tonal leuco-tonalite cordantly by granitic g r a n i t i c rocks rocks ranging ranging in i ncomposition composition from it e to to occurred aatt several granite. Pegmatite Pegmatite ddike i k e i intrusion n t r u s i o n occurred several stages stages ooff "granite" "grani tell granite. i n t r u s i o n . The The oolder l d e r ggranitic r a n i t i c rocks rocks are are foliated f o l i a t e d and and locally l o c a l l ymylonitized. myloni t i z e d . intrusion. Shearing and boudinage boudinageofofpegmatite pegmatitesstringers themi into Shearing and t r i n g e r s transposed transposed them n t o oblique oblique concordance lamination iin concordance wwith i t h lamination n the t h e enclosing enclosing rocks rocks (Figure (Figure 51). 51 ). AArough rough correlation c o r r e l a t i o ncan canbe bemade made between between r relative e l a t i v e age age and and concordance concordance o of f vveinlets. einlets. At A t location l o c a t i o n A, A, thinly t h i n l laminated y laminatedamphibolite amphibolite was was intruded intruded by by granite g r a n i t e so so that lenticular slices of the amphibolite were dragged en echelon away t h a t l e n t i c u l a r s l i c e s of the amphibolite were dragged en echelon away from from coarse ggranite t h e wall w a l l (Figure54). (Figure54). The T h e coarse r a n i t e pegmatite pegmatite intruded intruded under under stress stress the �-82- contains en enechelon echelonfractures fracturesfi filled The amphi amphibolitecontains 11ed with w i t h very very coarse coarse quartz. q u a r t z . The bol itegranite (trondhjemite) contact is sheared, cataclastically blended, and regrani te (trondhjemi t e ) contact i s sheared, c a t a c l a s t i c a l l y blended, and Since the the ggranite r a n i t e intrusion i n t r u s i o nwas was apparently apparently crystallized crystal 1ized -- "granitized". "grani tized". Since guided bylamination laminationi ninthe the amphibolite, amphibolite,t the effects of guided by h e effects of cataclasis cataclasis In i nmodimodifying the the contact contact could could be be easily e a s i l yoverlooked. overlooked. Small (F-2) (F-2) folds at plunge gently gently east-northeast. east-northeast. These These are are a tLocation Location CC plunge Small folded F-i isoclinal folded F-1 i s o c l i n a lfolds, folds,and anda afew fewhinges hingescan can be be found found In i n the the outcrop. outcrop. The The geometryo fofthe thei sisolcinal folds, not by F-2 F-2 ffoldlng.ls geometry o l c i n a l folds, not modified modified by o l d i n g i s best best displayed displayed unusual nature nature of of the a t Location Location B. B. The The unusual t h e F—2 F-2 f ofolds l d s iIs s shown shown iin n Figure Figure 50. 50. at Since pegmatiteveins veinswere werec clearly involved iin Since aaplite p l i t e and and pegmatite l e a r l y involved n the t h e F-i F-1event,, event, and and since theseveins veinsalso alsocut cutt hthe appears tthat h a t the the since these e ggranitic r a n i t i c iintrusives n t r u s i v e s here, here, iittappears F-2 ffolding F-2 o l d i n g was was qqu.ite u i t e llate. ate. The The deformational sequence sequence is i ssuninarized summarizedon onpage page 83. of iisoclinally 83. Xenoliths Xenoliths of s o c l i n a l l yfolded folded amphibolite amphibolite occur occur iin n the the granite g r a n i t e (Figure (Figure 52). 52). The aeromagnetic aeromagnetic map map (Figure (Figure 55) The 55) shows shows aapronounced pronounced V-shaped V-shaped westward westward concon- vergence Jim Falls. Falls. The The low low magnetic magneticrrelief vergence aat t Jim e l i e f ofo fthe thebedrock bedrockbetween between these these two two magnetic (amphibolite) ridges iiss probably eastwardextension extensionoof the ggranitic magnetic (amphi bol i t e ) ridges probably an an eastward f the ranitic rocks exposed exposed iInn the and the thedam. dam. theChippewa Chippewa River Riverchannel channel between between Location LocationAA'and A well-defined, arcs southwestward map A we1 1-defined, discordant discordantridge ridge arcs southwestwardacross acrossthe the mapand andcrosses crosses the "amphibolite ridg&' about miles east east ooff the the "amphibol i t e ridge" about 22 miles the bridge bridge at a t Jim Jim Falls. Fa11s. The The feature dike ooff considerable size, possibly possibly the the dike that feature is i s probably probably a diabase diabase dike considerable size, that is i s exposed exposed at a tWissota WissotaDam. Dam. Petrography and and Geochemistry Geochemistry In I n contrast contrast to t o the the alumina-rich, a1 umina-rich, garnetiferous garnetiferous amphibolites amphibol ites of o f the t h e Cornell Cornel 1 area, the the amphibolites Falls area, amphibolites aatt Jim Jim F a l l s are are chemically chemically indistinguishable indistinguishable from from those those of o f the the Eau Eau Claire C l a i r eRiver Riverarea, area.and andare arecomposed composed of o f hornblende hornblende (45-65%), (45-65%), plagioclase p l agioclase (25-50%), epi epidote (5—15%) and ubiquitousaccessory accessory quartz,magnetite, magnetite,ppyrite, (25-50%), dote (5-1 5%) and ubiquitous quartz, yrite, Epidote iiss the sphene,and andcchlorite. sphene, h l o r i t e . Epidote t h e alteration a l t e r a t i o nproduct productofo hornblende. f hornblende. which which is tot omoderate (M) moderate bluish b l u i s h green green (v), ( V and ) , andshows shows aapronounced pronounced aalignligni s pale pale green green (o() The lamination lamination rresults lamination. The e s u l t s mainly mainly ments the plane ments i in n the plane of o f compositional compositional lamination. from changes o f hornblende hornblende and and plagioclase. p l agiocl ase. The The pplagioclase l agiocl ase occurs occurs from changesi nin proportion proportion of as betweenthe thewell-oriented well-oriented hornblende as "windows" "windows" between hornblende laths. IIts t s average average ssize i z e is is More than 95% of the less the hornblende, hornblende,and andi tit iiss typically t y p i c a l l yanhedral. anhedral More than 95% of the 1ess than than the Relict permits measurement e l i c t twinning twinningini na few a fewgrains grains permits measurement no twinning. twinning. R plagioclase shows shows no of By tthis h i s method method the the approximate approximate An An content was was found found to to of extinction e x t i n c t i o n angles. angles. By be betweenAnAn. and andAn An. With be between WithaaCaO:Na20:K20 CaO:Na20:K20 r aratio t i o ooff 86:10:4 86:10:4 (Table (Table 1) 1 ) such such aa compositions&ld st1u1dbebeanticipated. flticipated. composition . . As the oldest oldest recognizeable As iiss the the case case at a tCadott Cadott and and Wissota Wissota Dam, Dam, the recognizeable iintrusive ntrusive It Itisi sintruded intrudedby bydarker darker bbiotjte-hornblende i o t i te-hornblende tonal ijte t e and and aa later l a t e rtrondhjemite trondhjemite with w i t hpegmatite pegmatite segregations. segregations. Even the the pegmatites pegmatites are are K-feldspar K-feldspar iiss aa very very rare r a r econinodity commodity in i n these these rocks. rocks. Even adamellites, contain approximately equal parts parts K-fel K-feldspar sodic adamel 1ites , and and contain approximately equal dspar and and sodi c pplagioclase. l agiocl ase. The lack ooff K20 amphibolitessuggests suggestsf i rfirst-cycle The lack K20 iinn the the Chippewa Chippewa amphibolites s t - c y c l e reworking reworking of p r i m i t i v ebasaltic basal t i cbasement basement rocks. rocks. primitive rock herei sis aa ffoliated, rock here o l i a t e d , light l i g h tgray gray biotite b i o t i t etrondhjemite. trondhjemite. No rock rockseen seena at JimFFalls dikes) is No t Jim a l l s ((with w i t h the exception exception ooff the the diabase diabase dikes) i s devoid devoid the contacts contactsare aree ieither of of cataclastjc cataclastic fabrics. fabrics. Most Most oof f the t h e r t ototally t a l l y oor r ppartially artially modified by shearing shearing and andmechanical mechanicalintermixing intermixingoof contiguous rock rock units. units. modified by f contiguous �-83Chronology C h ronol ogy Based cross—cutting Based ononcross-cutting andand s t rstructural u c t u r a l r erelationships, l a t i o n s h i p s , tthe h e following chronchronology has been beenworked worked JimF Falls area: (1 (1) Archean( ?(?) basaltic ology has outout f ofor r t hthe e Jim a l l s area: ) Archean ) basal t i c vol- canism andassociated associated sedimentation, sedimentation, (2) converting the cani sm and (2) regiona.l regional metamorphism metamorphism converting the volcanics andi sisoclinal f o l d i n g , (3) ( 3 )cataclasis catacl a s i sforming formingultra— ultrao c l i n a l folding, vol canics tto o amphibolites amphi bol ites and mylonite zones,( (4) myloni t e zones, 4 ) ffaulting a u l t i n g and and bbrittle r i t t l edeformation, deformation, (5) ( 5 ) successive successive iintrusion ntrusion of with of at a t least l e a s tfour f o u rgranitic g r a n i t imagmas c magmas w i t h intervening i n t e r v e n i n g episodes episodes oof f ccataclasis'as a t a c l a s i s as evievidenced byt hthe occurrenceo of folded mylonite mylonite xenoliths in denced by e occurrence f folded i nsome some of the t h e younger younger prolonged Late Precambrian iintrusives n t r u s i ves (Figure (Figure52), 52).(6)(6) prolongederosion, erosion,and and(7)(7) Late Precambriandiabase diabase ddike i k e intrusion. i n t r u s i o n . This sequence sequence iiss modified modified from from Maercklein, Maercklein, 1974, 1974,p.p.16—20. 16-20. At least l e a s tthree t h r e edeformational defonnational episodes episodes can can be be distinguished here here as as they they can. can. eelsewhere l sewhere iinn the t h eChippewa Chippewa amphibolite amphi bol it e complex. complex. -- 15_200east-northeast. east-northeast. The The hinges hinges ooff Figure 49 -- F-2 F-2 folds f o l d shere hereplunge plunge about about 15-20' Figure 49 Throughgoing ccataclasis a t a c l a s i s and and iisoclinal s o c l i n a l F-i F-1folds f o l d scan canbe befound found in i n this, t h i s outcrop. outcrop. Throughgoing associated thesesstructural associated f faulting a u l t i n g have have llocally o c a l l y broken broken these t r u c t u r a l blocks blocks into i n t o lensoidal 1ensoi dal and bbrecciation seen i in blocks. Drag Drag ffolding o l d i n g and and and r e c c i a t i o n can can be be seen n the t h e limbs limbs of of some some ooff the F-2 F-2 folds. REFERENCES: Maercklein, 1974, Analysis Analysis ooff deformation Maercklein, Douglas Douglas R.,R., 1974, deformation aatt Jim Falls, F a l l s , Wisconsin, Wisconsin, unpublished M.S. thesis, thesis, University unpublished M.S. U n i v e r s i t yofo Wisconsin f Wisconsin-. Milwaukee. Milwaukee. - , Myers, Paul Paul E., E., and R., 1974, Myers, and Maercklein, Maercklein, Douglas Douglas R., 1974, 38th 38th Annual Annual TTn-State ri-State Geological Book, p. p. 35-42. F i e l dConference Conference Guide Guide Book, 35-42. Geol ogi c a l Field �-84- EXPI.MATION Diaba,. Oranit. p.g,iatit. EE Granit. Ultruylonit• I K 1.ldsp.r—nid ylonit. ,iul.s auphibolitic Wl.nLt* g,siai lopidholit. m u - 0'S'—. Xnfarr.d Dontact Vault _ ' 4- alic,of.ult.d a. utov*nq .txik. and .xt.nt Approxiont. fault Strik. anddip dipOf of f011mtionm foliation. 8trika and •trik. dip of of urti-1 ,sxtionl loliationa 8 t r h.and .ud dip foliation@ l.uinq and plunga of linantian lorisontal lin.ation phoning axial tra.. and bs.zinq and ping, of axis Mtifogn loon of unli antiloxos and .ynfos phowing atrik. of axial ira.. and .xtant CRH IIPPEWA C PPEWA A RRIVER I V E R link. and dip of ointa * Sink. •f vertical joint. — Sink, and dip of aultipla joint ayatan. 9 '9 aç Figure 50 of the Figure 50 --- Geologic Geologic map map of the Jim Falls area Jim area by by D.R. D.R. Maercklein, Maercklein, 1974 showinglocations locationsofof principal 1974 showing stops. �-85- -- Figure 51-51 Interlensing Inter1 ensingshear shear cutting c u t t i n ggranite g r a n i t epegmatite pegmatite at at Figure Location A. Lenticular white areas a r e q u a r t z , which tends Location A. Lenticular white areas are quartz, which tends t obe be locallized l o c a l l i z e dalong alongsurfaces surfacesofofmajor majorslippage. slippage.Sketch Sketchby by to Maercklein (1974, p. 61) Maercklein (1974, p. 61) 52-- P aPartially r t i a l l y assimilated and granitized g r a n i t i z e d amphibolite amphibolite Figure 52—— Figure assimilated and xenoliths i n b i o t i t e adaniellite(?) Contact is l o c a l l y disdisxenoliths in biotite adarnellite(?). Contact is locally cordant. Biotite-rich bands extend i n t o the adamell i t e ( ? cordant. Biotite—rich bands extend into the adamelltte(?)) from the the large l a r g e xenolith. xenolith. Location: Location: halfway halfway between between the t h edam dam from and bridge on west s i d e of t h e Chippewa River. and bridge on west side of the Chippewa River. �-86- Figure Boudinage structuresi ninpegmatite pegmatiteddikes Figure 53—— $3-- Boudinage structures i kes ccutting utting thinly t h i n l ylaminated laminated amphibolite amphibolite jjust u s t north north of o f the the bridge. bridge. Note Note accumulation accumulation ooff quartz quartz at a t points pointsofo fpegmatite pegmatiteseparation. separation. Sketch by Maercklein Maercklein (1974, (1974, p. p. 65) 65) Sketch �-87- i ibol.ite I I boflte amphibol ite .4 pegmat i te f granite-amphibolite ibolite 0 5m —4 granite amphibol ite ,/,* Figure 54—54-- Detailed geologic map map showing showing sheared n t r u s i v e contact contact Figure Detailed geologic shearedi intrusive o f "granite" i n t h i n l y banded amphibolite. Lenses o f amphibolite of granite" in thinly banded amphibolite. Lenses of amphibolite were carried c a r r i e d away away from by the the granite. granite. En En echelon echelon fractures fractures were fromthe the wall wall by were f i l l e d by quartz during contraction o f the pegmatite. Location were filled by quartz during contraction of the pegmatite. Location AA ��-89STOP #12 STOP TITLE:: TITLE CORNELL FLASER FLASER GNEISS GNEISS AND CORNELL AND AMPHIBOLITE AMPHIBOLITE LOCATION: A A BB SE%, West side Cornell SE¼,NE%, NE¼,Sec. Sec.18, 18,T31N, T31N,R6W: R6W: West sideo fofHwy. Hwy.64 64Bridge, Bridge, Cornell SWk, i4E¼,Sec. T31N, R6W: f Hwy. SW¼, Sec. 18, 18, T31N, R6W:East Eastside sideoof Hwy.64 64Bridge, Bridge, Cornell, Cornell, Cornell Cornel 1 15' 15' quadrangle. quadrangle. im, Photo taken 9/17/74 during duringdam dam Photo taken 9/17/74 repairs. repai r s . AUTHOR:: AUTHOR P.E. Myers P.E. Myers DATE:: DATE - September, 1974, September, 1974, March, March, 1980 1980 SUMMARY OF SUMMARY O F FEATURES: FEATURES : F'laser gneiss composed composed mica,quartz, quartz, feldspar feldspar and garnets is Flaser gneiss o fofmica, and sparse sparse garnets is tectonically fine—grained t e c t o n i c a l l yinterlensed i n t e r 1ensedwith w i t hthinly t h i nlaminated l y 1aminated fine-grainedbanded banded garnet garnet Although granite, granite, which which became became t hthe e f lflasergneiss, a s e r gneiss, was was probably probably amphibolite. Although Rocks aatt intruded iinto intruded n t o the t h e amphibolite, amphibolite, its i t scontact contacttoday today isi saashear shear zone. zone. Rocks stage iin tthis h i s locality l o c a l i t yshow show an an intermediate intermediate stage n the the tectonic t e c t o n i c interlensing i n t e r l e n s i n g shear shear and ccataclasis followed byby metamorphism and a t a c l a s i s of o f rocks rocks of o f disparate disparatelithology 1itho1ogy f o l 1owed metamorphism tto o garnet grade. grade. -- GARNETIFEROUSADAMELLITE ADAMELLITE FLASER FLASER GNEISS GNEISS LOCATION LOCATION AA -- GARNETIFEROUS 56) near water l level Garnetiferous, Garnetiferous, bbiotite i o t i t e flaser f l a s e rgneiss gneiss (Figure (Figure 56) near water e v e l aatt the the northwest corner corner of Cornel 1bridge bridgeis icomposed s composed ofo fcoarse coarselenses lensesand andzoned zoned northwest o f the t h eCornell Polygranular lensoids and and layers layers of of a r lensoids feldspar in mylonitic feldspar i n aamicaceous micaceous myloni t i c matrix. Polygranul untwinned untwi nned pplagioclase l agiocl ase (41%) (41 %) intergrown intergrown and and mantled mantled by anhedral anhedral microline m i c r o l ine(18%) ( 18%) Polygranular, strained strained are encased crush debris. Polygranular, are encased i in n a laminated, laminated, micaceous micaceous crush quartz (32%) forms long, long, thin quartz (32%) wwith i t h sutured sutured boundaries boundaries forms t h i nlaminae laminae and and lenses lenses which which impart the lamination seen seeni nin outcrop. outcrop. Very Very dark dark oolive impart t h e conspicuous conspicuous lamination l i v e green green to to pale yellowish with pale y e l l o w i s h green green biotite b i o t i t e(5%) (5%) w i t hcoarse coarsemuscovite muscovite(3%) (3%)and and occasional occasional �-90-- -- grains of o f epidote epidote and and garnet o the o l i a t e d crush crush debris. debris. This grains garnet are are confined confinedt to the ffoliated This rock morebbiotite less garnet garnet than than fflaser r o c k contains contains more i o t i t e and and less l a s e r gneiss gneiss aatt Locality L o c a l i t y B. B. Interlensing i n v o l v eseveral severalstages stages l&rlensing shear. shear ddislocation i s l o c a t i o n and and cataclasis normally normal l y involve of displacement, andand ablation of differential d i f f e r e n t i agrain l g r afracture, i n fracture, displacement, a b l a t i oaccompanied n accompaniedby by laminar flow of laminar flow o f crush crush debris debris with w i t h lateral l a t e r adisplacement, l displacement, ablation a b l a t i o nand andmixing mixing o f rocks. rocks. The The rock from from which which this t h i sgneiss gneissformed formed was was probably a coarse-textured' coarse-textured of componentmineral minerali nin aa ggranitic Each component r a n i t i crock rockbehaves behaves biotite b i o t i t equartz quartzmonzonite. monzonite. Each differently d i f f e r e n t l yunder undershearing shearing stress. stress. -- Stage 11 -- Protomylonite Protomylonite Stage Early Early strain s t r a i nisi expressed,as. s expressed as progressive progressive microscopic microscopic crushing of o f minerals, minerals , The lens is an first at corners, then on edges, and last on faces. f i r s t a t comers, then on edges, and l a s t on faces. The lens i s an equilibrium equilibrium accumulates form aatt all a l lscales. scales. Quartz Quartz is i s easily e a s i l yfractured f r a c t u r eand d and accumulates with w i t hfragmented fragmented form feldspar ani ninsulating rockoor mylonite encasing i l m ooff crushed crushed rock r llmylonitel' encasing rrelict elict feldspar as. as. an s u l a t i n g f film rock i is by aa ffaint lenses or o r °porphyroclasts". llporphyroclastsll. Such Such aa rock s characterized characterized by aint feldspar lenses textures are are sstill conspicuous. Primary textures t i 11 conspicuous. foliation f o l i a t i o nand andovoid ovoidshape shape of o f feldspars. feldspars. Primary -- Stage 22 -— Flaser FlaserGneiss Gneiss Stage With deformation, re1 relict With continued continued deformation, i c tfeldspar feldsparlenses lensesbecome become decidely lenlenmicai sis rreoiriented interlensing Primary mica e o i r iented along a1ong i n t e r l e n s i n g slip s l i pplanes, planes, soi dal (Figure (Figure 56). 56). Primary soidal micamay maybegin begint otoccrystallize and the becomes conspicuously l i a t e d . New New mica rystallize --and the rock becomes conspicuouslyf ofoliated. proportion ooff mylonite a t this t h i sstage. stage. The The proportion my1oni t e to t o surviving s u r v i v i n ggrains grainsincreases increases while while at re1i c feldspar t feldspar 1ensesbecome become thinned thinned by by ablation. ablation. Crenulatlon Crenulation or o r microfolding microfol d i ng relict lenses "tectonic xenoliths" xenoliths1' or o r lenlenor o r residual residual rock rock lenses lenses is i s comon common at a t this t h i sstage. stage. "tectonic ticular t i c u l a rfragments fragments of o f non-mylonitized non-mylonitized rock rock are are carried c a r r i e d along along in i n the the flowing flowing Drag ffolds o l d s and and ptygmatic ptygmatic folds f o l d sshow show differential d i f f e r e n t i amovement l movementand and granularmass. mass. Drag granular alongt hthin, Most ooff the the displacement displacement becomes becomes l olocalized, c a l ized along i n , interlensing i n t e r 1ensing turbulence. Most turbulence. zones ooff slippage s l ippage (Figure (Figure 59 59 ). ) zones . Figure -- Biotite from Figure 56 56 -B i o t i t etonalite tonal i tprotomylonite e protomyloni t e f r o mHamilton Hamil tonFalls, Fa1l s Eau , EauClaire C l a i r eCG. CO. Ends Ends ooff lenticulated l e n t i c u l a t e dplagioclase plagioclaseporphyroclast porphyroclastshow show no no twinning. twinning. Note Notecrushed crushed grain boundaries. boundaries. grain P=plagioclase, P=p1agiocl ase, B=biotite, B=bioti te,Q=quartz, Q=quartz,E=epidote, E=epi dote,Sp=sphene. Sp=sphene. - - �-91-. Stage 33 -Ul tramylonite Stage -- Ultramylonite Reductionofof relict relict rock ultimately Reduction rock and and mineral mineral lenses lenses by by ablation may may ultimately or in crystallization or i n crystal1 ization result in i n aa thinly t h i n l y laminated, laminated, fflinty l i n t y ultramylonite, u l tramylonite, result Relict feldspar lenses become mantled by new feldspar. Relict feldspar lenses become mantled by new feldspar. of new feldspar. new rock at Reversed zoning isi scommon. common. The The rock a t this thisstage stagebecomes becomes a blastomylonite blastomylonite. Reversed The The ppoint o i n t at a t which which feldspar feldspar regrowth regrowth begins begins varies even even from from one one part of of an an outcrop outcrop to to another. another. Reaction rates accelerate accelerate wwith: (1 )increased increased surface surfacearea area ini naccumulating accumulating i t h : (1) Reaction rates frictional heat and (3) pressure of mobilized water. frictional heat and (3) pressure of mobilized water. (2) (2) mylonite. myloni te. Anhedral form form of of the garnets of deformation them ininAnhedral garnets and and absence absence of deformation around around them Freshgarnet garneti is relatively rare s aa relatively raremineral mineral dicate their their late-kinematic late-kinematic age. age. Fresh Big Falls Fa1 1s are are Large, rrelict e l i c t garnets garnets at a t Big in rocks rocks of of the the Eau Eau Claire region. region. Large, altered altered totohornblende. hornblende. With W i t h rocks rocks that thathave havebeen beendeformed deformedand andmetamorphosed metamorphosed difficult totodiscriminate aatt least least three three times, times, iti tbecomes becomes difficult discriminatebetween between surviving surviving Urelictul 're1 ict" minerals minerals and and those those produced produced during during later 1atermetamorphism. metamorphism. FQliation and compositionallayering layering iinn rocks rocks at a t Cornell Cornell strike strikeN80°E ~80'~ Foliation and compositional samestructural structural elements elementsaat Fisher River 4 km northeast of N80 W. These These same t Fisher km northeast to to N80"W. here trend NN40°-50°E, factortaken takentoto indicate indicate aa major major flexure flexure in ~ o O - ~ O O E , a afactor i n the the rocks rocks here trend north of Cornell. north Cornel 1. -- LOCATION GARNETAMPHIBOLITE AMPHIBOLITEAND ANDSHEARED SHEAREDPEGMATITE PEGMATITE LOCATION B -- GARNET Laminatedgarnet garnetamphibolite amphibolitea tatLocation LocationB Bi sis representative representative of of the the Laminated "Cornell amphibolite" which crops out almost continuously for 4 km down the 'Cornell amphibolite" which crops out almost continuously for 4 km down the The amphibolite could also be classed as a gneissic, mafic Chippewa River. Chippewa River. The amphibol i t e could a1 so be classed as a gneissic, mafic hornblende tonalite composed of subhedral subhedral to to hornblende tonal i t e or orhornblende hornblende gneiss. gneiss. ItI tisi scomposed anhedral, lensoidal hornblende clusters (54%) with coarse, lensoidal anhedral , 1ensoi dal hornblende (54%) w i t h coarse, lensoidal porphyroporphyrofine-grained quartz. clasts of of twinned twinned plagioclase plagioclase (28%) (28%) and and fine-grained quartz. The The hornbleñde hornblende pale yellowish yellowish green; green; "7= 7= dark is i s strongly stronglypleochroic pleochroic(OC= (a=pale dark bluish green). green). Bandingi nin the the amphibolite amphibolite iIs s cut by by lenticular lenticularsegments segments of granite granite and and quartz quartz Banding Thepearly nearlyvertical vertical banding is thinly thinly interlensing veinlets. The banding is interlensingini n3 3dimensions, dimensions, Small, isoclinal and strikes strikes N80°E and N80 EtotoN800W. ~ 8 0 ~Small, ~ . isocl inal folds foldsplunge plunge at a t low low angles angles in in n the amphibolite amphibolite tend tend to to be be Garnets iin the plane plane of of compositional compositional banding. banding. Garnets evidence of of garnet porphyroNo evidence porphyrorandomly clustered and randomly clustered and have have ragged ragged borders. borders. No Thedistribution distribution of clusters shows showsl ilittle blasts rotation rotationwas was seen. seen. The of garnet garnet clusters ttle The garnets garnets appear relation totobanding relation banding or orfold foldmorphology. morphology. The appear to t o have have formed formed after most after most of the the particulate particulateflowage flowageofofthe therocks, rocks,asasevidenced evidenced by by the thegood good preservation of garnet the amphibolite. amphibol i te. preservation garnet crystal crystalapophyses apophyses iinn the Coarse,garnetiferous garnetiferous ffelsic are iinn Coarse, e l s i c flaser flasergneiss gneissand and sheared sheared pegmatite pegmatite are commonly intrudes amphi bol i t e intrudes amphibolite contact wwith contact i t h amphibolite amphibol i t e iin n this this outcrop. outcrop. Granite cormnonly relations ofofmost most granite granitebodies bodies aatt other other locations locations (Jim (Jim Falls). Intrusive relations i n the the area area are are obliterated obliterated by by shear shear displacement displacement and partial 1ization. in and partialrecrystal recrystallization. The occurrenceofofgarnet garneti in the flaser flaser gneiss n the gneiss indicates indicates that thatboth both rocks rocks were were The occurrence metamorphosed aftertectonic tectonic imbrication. metamorphosed after imbrication.An An excellent excel lentexample exampleog ogsheared sheared pegmatite pegmatite and rocks can the east east end end and other other coarse-grained coarse-grainedgranitic granitic rocks can be be seen seenjust just north north of the 64 bridge bridge aatt Location Location B B (Figure 58). Coarse, Coarse, bent, of the the Hwy. Hwy. 64 bent, lenticulated lenticulated and porphyroclasts are and fractured fractured feldspar porphyroclasts are enclosed enclosedinin aa fine-grained fine-grained matrix matrix of quartz-feldspar-muscovite quartz-fel dspar-muscovite crush crush debris. Some n the mylonite myloni t e Someflow flowfolds folds can can be be seen seeni in in some of these some of these rocks. rocks. �-92- -- Figure 57 57 -— Garnetiferous i o t i t eadaadaFigure Garnetiferous bbiotite A) m e l l i t e flaser gneiss (Location mellite flaser gneiss (Location A) Lensoidal feldspars feldspars1are are enclosed enclosed in i n aa Lensoidal recrystal 1 ized, f o l i a t e d matrix. recrystallized, foliated matrix. \ - Figure 58 58 -- Sheared Sheared pegmatte pegmatite (Location (Location BB Figure near eastern eastern bridge bridge abutment) abutment) Lensoids Lensoids of of near coarse K-fel dspar iin n matrix matrix of o f crush crush debris. debris. coarse K-feldspar �-93-93STOP #13 #13 STOP TITLE:: TITLE FISHER RIVER FISHER R I V E R BRECCIA BRECCIA LOCATION: LOCATION: NW¼.SW%, SW¼, Sec. T31N,R6W, R6W, Chippewa County, Cornell 15' 15' quadrangle NW*. Sec. 4, 4,T31N, Chippewa county, Cornell quadrangle AUTHOR:: AUTHOR P.E. P. E. Myers Myers DATE: DATE : - February, 1980 February, 1980 SUMMARY SUMMARY OF O F FEATURES: FEATURES: This unusual, This unusual, hheterolithic e t e r o l i t h i c breccia breccia contains contains clasts c l a s t s of o frock rocktypes types not n o tseen seen elsewhere elsewhere i in n tthe h e region, region, such such as as porphyritic p o r p h y r i t i cgabbro, gabbro, greenstone, greenstone, metapyroxenite(?), metapyroxeni t e ( ? ) , breccia iiss andesitic a n d e s i t i c ttuff, u f f , and and cataclastically c a t a c l a s t i c a l l ylaminated laminated granitic g r a n i t i c rocks. rocks. The The breccia enclosed onthe the nnorth and south south sides sides by by ffoliated enclosed on o r t h and o l i a t e d trondhjemite trondhjemi t e and and on on the t h e west west by gneissic obiotite-hornblende tonalite. by gneissic i o t i te-hornbl ende tonal ite. The The gneissic trondhjemite trondhjemi t eelsewhere e l sewhere metadiorite and tonal tonalite it e iinn the t h e area area (Fisher (Fisher River River Bridge) Bridge) contains contains abundant abundant metadiori t e and xenoliths which whichare areelongated elongated plane xenoliths i n in t h ethe plane of fof o l ifoliation. a t i o n . ItIt i is s ttentatively entatively proposedt hthat brecciau nunit, other xenoliths, xenoliths, iiss an proposed a t t hthe e breccia i t , l ilike k e tthe h e other an iinclusion n c l u s i o n in in trondhjemité, and andt hthat by ffaulting. was ooriginally r i g i n a l l y formed formed by aulting. tthe h e gneissic gneissic trondhjemite, a t iitt was DESCRIPTION: Reconnaissance scoured meitwater channeloof Fisher River Reconnaissance a1along ong t hthe e scoured g l glacial a c i a1 me1 twater channel f Fisher R i ver indicates tthat (Figure 59 h a t the t h e area area is i s underlain underlain by by gneissic gneissic tonalite t o n a l i t e and and (Figure 59 ) indi.cates trondhjernite and tonal tonalite. trondhjemi t e containing abundant abundant xxenolithic e n o l i t h i c masses masses oof f mmetadiorite e t a d i o r i t e and ite. The breccia breccia uunit, by ffoliated The n i t , which which is i s apparently apparently enclosed enclosed by o l i a t e d trondhjemite trondhjemite and and tonalite, non-sortedcclasts containsangular an u l a r to t osubrounded, subrounded, non-sorted l a s t s ooff ultramafic u ltramafic tonal ite, contains rock rock (metapyroxenite?), (metapyroxeni te?), massive massive and and porphyritic p o r p h y r i t i chornblende hornblendegabbros, gabbros ,hornblende hornblende , greenstone, andesite andesi t e tuff, tuff, and andmassive massi ve and and ccataclastically a t a c l a s t icall y bbiotite i o t i t etonalite, tonal it e greenstone, 1laminated aminated ggranitic r a n i t i c rocks rocks - probably probablytrondhjemite trondhjemi t e and and adamellite adamel 1it e (quartz (quartzmonzonite). monzoni t e ) - The dominantmineralogy mineralogy theserocks, rocks,i nincluding thosei in the breccia, The dominant of ofthese c l u d i n g those n the breccia, is (An2_),)quartz, , quartz,hornblende, hornblende, biotite, b i o t i t e ,and andK-feldspar. K-fel dspar. Accessory i s plagioclase plagioclase (An epidote, epi dote, cchlorite, h l o r i t e , * kaetite @ e t i tand/or e and/orpyrite p y r i t eare i r eubiquitous. ubiquitous. . �-.94- 90 0.5 mile mile 0.5 Figure 59 ---Geologic Geologic map map ooff the the Fisher Fisher River Riverarea. area. htg htg ==hornblende hornblende Figure 59 tonalite tonalite gneiss; bhtg bhtg == biotite-hornblende b i o t i te-hornbl ende tonal it e gneiss; gneiss; trg t r g==trondhtrondhtonal it egneiss; jemite d i o r i t e ;brb = r =breccia. breccia.Note Notefairly f a i r l gentle y gentlenorthwest northwest jemite gneiss; gneiss; di d i == diorite; plunge p l unge oof f 1lineation ineation in i n the the tonalite t o n a l i t egneiss. gneiss. �-95- Characteristics of Characteristics o f the t h e Breccia: Breccia: The breccia is of angular angular tto non-sortedcclasts of The breccia i s composed composed o-F o subrounded, subrounded, non-sorted l a s t s of chioritized massive tonalites, c h l o r i t i z e dultramafi u l t r a m a f irocks, c rocks, massiveand andlaminated laminated gabbros, gabbros, tonal i t e s , and and The ffine i n e tot omedium medium grained grained granitic andccrystal g r a n i t i c rocks, rocks, greenstones, greenstones, and r y s t a l ttuffs. u f f s . The Chlorite hlorite matrix plagioclase,quartz, quartz, and andbbiotite. m a t r i x is i s composed composed e sessentially s e n t i a l l y oof f plagioclase, iotite. C Epidote seams cutthrough throughthe the breccia breccia fragments andmmatrix seams cut fragments and a t r i x aatt high high angles. angles. Epidote occurs as as j joint occurs o i n t coatings coatings and and as as a a partial p a r t i a lreplacement replacement ooff mafic mafic minerals minerals in in the breccia. breccia. Clast size s i z e ranges ranges from f r o m 11 -- 20 20 cm cm with w i t h an an average avera e of about about 44cm. cm. The fragmentsshow show preferredo orientation (Figure 60 60),, which here iiss which here The fragments a a s usubtle b t l e preferred r i e n t a t i o n (Figure about N50°E,v vertical. no post-deposi post-depositional rounding oor fragabout N50°E e r t i c a l . The The clasts c l asts show show no t i o n a l rounding r fragmentation, as as would wouldbe beexpected expected breccia. Chalcopyrite mentation, i nina af afault u l t breccia. Chalcopyrite occurs occurs iinn the the matrix. ? Photographo of Fisher River River breccia breccia at Figure 60-60-0 Photograph f t hthe e Fisher at Figure widev variety tthis h i s location. location. Note Note wide a r i e t y oof f cclast l a s t llithology ithology tthe h e relatively r e l a t i v e l y high high clast/matrix c l a s t / m a t r i x ratio, r a t i o ,and andthe t h ecrude crude orientation off clasts. nnear-vertical e a r - v e r t i cal o rientation o c l asts . Chronology the Fisher Chronology oof f the Fisher River River Area: Area: chronologycan canbe besynthesized synthesizedfrom fromf i field observations iin AA chronology e l d observations n the t h e Fisher River River area. Table 7. area. Compare Compare wwith i t h Table *1. IIntrusion mafic hornbldnde gabbroand andddiorite *l. n t r u s i o n of o f mafic hornbldnde gabbro iorite *2. IIntrusion adamellite *2. n t r u s i o n of o f adamel 1it e and and trondhjemite trondhjemi t e probably 3. Shearing and 3. and cataclasis, cataclasis , probablyaccompanied accompaniedby byregional regionalmetamorphism metamorphism *4 Extrusion off basalt andesite(?)ttuff *4. Extrusion o b a s a l t and and andesite(?) uff 5. Intrusion mafic hornblende-bioti hornblende-biotite tonalite I n t r u s i o n of o f mafic t e tonal ite 6, Faulting 6. F a u l t i n g and and brecciation b r e c c i a t i o n - formation formation of o f the t h eFisher FisherRiver River breccia breccia 7. Intrusion I n t r u s i o n of of leucotrondhjemi leucotrondhjemi ttee 8. 8. Cataclasis, Cataclasis, metamorphism, metamorphism, l elenticulation n t i c u l a t i o n of o f pegmatites, pegmati tes, mylonite myloni t e '"veinlets" v e i n l e t s " with w i t h right-lateral r i g h t - l a t e r a displacement l displacement 9. 9. Intrusion I n t r u s i o nof o ftonalite tonal i t and e anddiabase diabase dikes dikes (Late (Late Precambrian) Precambrian) f e r r e d on h e basis breccia clast clast *posjtjon ini nsequence known.I nInferred ont the basis ofof breccia *Position sequence nnot o t known. 1lithology ithology and and structures. structures. - �-96Although u t the t h e trondhjemite trondhjemite Althoughno notrondhjemite trondhjemitedikes dikeswere wereseen seent otoc cut the breccia, breccia, the off iiss in i ncontact contact with w i t h the t h ebreccia breccia along along its i t snorth n o r t hand andsouth south sides. sides. The The ttrend rend o the breccia the breccia unit u n i t isi sN550E; ~ 5 5 its i~t sdip ~d i;pisi unknown. s unknown. At several locations l o c a t i o n s along along the the At several Fisher River River (south (south of here), here), the t h egneissic gneissicleucotrondhjemite leucotrondhjemi t econtains containsabundant abundant Fisher schistose mafic mafic i inclusions and1large xenoliths ooff metadiorite. xenoliths schistose n c l usions and arge xenoliths metadiori te. The it h s The xenol are elongated elongatedi nint hthe planeofoff ofoliation. are e plane l i a t i o n . It Itisi stherefore t h e r e f o r etentatively t e n t a t i v e l concluded y concluded t h a t the t h e breccia breccia uunit n i t iitself t s e l fisi sa alarge l a r g elensoidal lensoidalxenolith x e n o l i t hini nthe t h egneissic gneissicleucoleucothat trondhjemite. trondhjemi te. The leucotrondhjemite c l o s e l y resembles resembles that t h a tata Wissota t WissotaDam. Dam. The leucotrondhjemite here closely 1ocal ity, the t h etrondhjemite trondhjemi t e Is i s cut c u t by by gray gray tonalite tonal it e dikes. dikes. locality, As aatt that that As - Modeo fofFormation Formation FisherRiver RiverBreccia Breccia -PPossibilities, Mode of oft hthe e Fisher o s s i b i l i t i e s , Evaluations: Eva1uations: 1. Pyroclastic 1. P y r o c l a s t i c Breccia: Breccia: Fisher River breccia breccia (FRB) (FRB) contains contains mainly mainly. matrix, metamorphic and u t o n i c cclasts. l a s t s . The metamorphic andp lplutonic The matrix, now now rrecrystallized, e c r y s t a l 1ized, might might be be aa metatuff. metatuff. 2. Intrusion 2. I n t r u s i o n Breccia: Breccia: Matrix M a t r i x in i n not n o t discernably discernably aa plutonic p l u t o n i cigneous igneous rock; matrix m a t r i x lacks lacks flow flow fabric f a b r i c around around cclasts; lasts; 3. TTillite: 3. illite: Clasts in are too too angular; Clasts i n FRB FRB are angular; do do not not show show eevividence of transport. dence o f 4. Fault 4. Fault Breccia: Breccia: Recrystallized matrix doesnnot containre1 relict Recrystal 1i z e d m a t r i x does o t contain ic t The absence absenceooff post-depofault f a u l t gouge gouge texture. The post-depositional s i t i o n a lfragmentation fragmentation makes makes t the h e ffault a u l t breccia breccia hypothesis aa bbiti tshaky. hypothesis shaky. 5. 5. Talus Talus Breccia: Breccia: The1lithologic The it h o l o g i c heterogeneity, heterogeneity , aangularity n g u l a r i t y ooff The1likelyclasts, clasts, favor f a v o r this t h i s interpretation. i n t e r p r e t a t i o n . The ikelyhood hood f for o r preservation preservation of o f aa Precambrian Precambrian ssurficial urficial feature feature is i snot n o tgreat, great,however. however. Whatare aresome someother otherp possibilities? What o s s i b i l i t i e s ? How could the the mystery be How could be solved? solved? �—97— -97- STOP #14 STOP #14 TITLE: STRUCTURESI N IN QUARTZ QUARTZDIORITE, DIORITE, GRANITIC GRANITIC INTRUSIVES INTRUSIVESAND AND META-. METASTRUCTURES ANDESITE AT AT HOLCOMBE HOLCOMBE DAM. DAM. LOCATION: Holcombe Dam,SW Sw1/4 1/4 Sec. Sec. 28, T32N, T32N, R6W, R6W, Chippewa Chippewa County, Holcombe Dam, Cornell 15" 15" quadrangle. quadrangle. AUTHOR: AUTHOR: Stephanie Wurdinger,UUniversity Stephanie R.R. Wurdinger, n i v e r s i t y of o f Minnesota, Minnesota, Duluth Dul u t h DATE: DATE : - February, 1980 1980 SUMMARY OF SUMMARY O F FEATURES: FEATURES : Synkinematic quartz quartz ddiorite the lower lower amphibolite Synkinematic i o r i t ewas was metamorphosed metamorphosed t otothe amphibol it e facies during during F1 F folding. Granitic G r a n i t i c intrusives i n t r u s i v e sand anddikes, dikes,and anda ahypabyssal hypabyssal andesite wereintruded intrudedduring duringF F.,f ofolding thequartz quartzddiorite. andesite were l d i n g o of f the i o r i t e . These These rocks rocks were llater a shear zone exposed were a t e r converted converted to t oschist s c h i s1ong t along a shear zone exposedalong alongthe t h eChippewa Chippewa River. AA system systemofofN50W N5OW a dominantly f a u lfaults t s w i twith h a dominantly r i g hright t l a tlateral e r a l s tstrike r i k e ooffffset later major ffold l a t e rsegmented segmented aall l 1 rock rock units. The The major o l d deformations, deformations, and and thus thus the rock rock units u n i t sataHolcombe t HolcombeDam, Dam, are believed believed to t obe bePenokean Penokean in i n age. age. DESCRIPTION: DESCRIPTION: Holcombe IInn order order of o f decreasing decreasing age, age, the the rock rock units u n i t sofothe f the Holcombe area area are: are: banded gneissaat the Fisher River, Dam, banded gneiss t the River, quartz quartzdiorite d i o r i tat e Holcombe a t Holcombe Dam, and. and amphibolite River (Figure 61). amphi bol i t e schist s c h i s t along along the theChippewa Chippewa River 61 ). Gneissic quartz quartz diorite Gneissic d i o r i t eand andassociated associatedmeta-igneous rota-igneous rocks crop crop out out Ultramafic In age,the the l latter I n order order of o f decreasing decreasing age, a t t e r are: are: U1 tramafic and spotted i o r i t e , quartz quartz ddiorite i o r i t e gneiss, gneiss, and spottedmafic maficxenoliths xenolithsi ninthe thequartz quartzd diorite, g r a n i t e and and associated associated granite g r a n i t e dikes, dikes, and andmeta-andesite meta-andesi t e (Figure (Figure62). 62).These These granite u n i t s were were converted converted tto o schist s c h i s t along alongshear shear zones zones which which cross cross the t h e outcrop. outcrop. units below Holcombe HolcombeDam. Dam. below The quartz i o r i t e contains contains two two types types ooff inclusions: inclusions: hornblende The quartz ddiorite hornblende rrich ich u l t r a m a f i c inclusions, inclusions, and and spotted spotted mafic mafic inclusions. inclusions. Ultramafic ultramafic Ultramafic inclusions occur along along the the northwest northwestpportion quartzddiorite. occur o r t i o n ooff the t h e exposed exposed quartz i o r i t e . These These are are generally less l e s s than than 0.5 0.5 meters meters iin n length, length, although although one one iis s at a t least l e a s t22meters meters generally . ' l tramafi cinclusions in c l u s i ons composed f 75-85% hornblende 11-1 3% 1long. ong U Ultramafic areare composed of o75-85% hornblende andand 11—13% biotite b i o t i t ewith w i t ha asmall smallamount amount of o f plagioclase. plagioclase. C h l o r i t e occurs occurs as teration Chlorite as an an a1 alteration product of o f biotite b i o t i tand e and less commonlyofohornblende, f hornblende,and and can composemore more less commonly can compose than the rock. than 20% 20% oof f the Spotted mafic mafic inclusions inclusions occur occur along along the the southeast southeast section section ooff the Spotted the exposedquartz quartzddiorite. range from from aa few few centimeters centimeters to exposed i o r i t e . They They range t o more more than 66 meters iin meters n length. length. The i nthe. thebanded banded gneiss gneiss The same samerock rocktype type occurs occurs as as dikes in arecomposed composed of o f hornblend hornblend aatt the the Fisher Fisher River. River. Spotted Spotted mafic xenoliths xenol ithsare cclots l o t s to t o33mm mm iin n size s i z e in i naafine-grained fine-grained matrix m a t r i xofoplagioclase f plagioclaseand andhornblende. hornblende. A spotted iinA few few hornblende hornblende cclots l o t s are arepseudomorphs pseudomorphs aafter f t e r pryroxene. pryroxene. The The spotted nclusions are surrounded whiter i rinds plagioclase and quartz, are commonly commonly surrounded byby white n d s oof f plagioclase and quartz, probably due duet otothe the ppreferential probably r e f e r e n t i a l nucleation nucleation of plagioclase p'iagioclase on on the the inclusions inclusions during during iintrusion n t r u s i o n ooff the the quartz quartz ddiorite. iorite. . �-98- 2 27 A 34 3$ 0 - Figure 61-61 Geologic Geologicmap mapofo Holcombe f Hol combe area. area. Figure diorite, amphibol it e schist. d i o r i te.ams ams == amphibolite .5m1 bgn gneiss,, qd = quartz bgn = banded banded gneiss quartz The quartz diorite The quartz d i o r i t eisi as medium-grained, a medium-grained, dark darktot omedium medium grey grey rock rock Itisi sfaintly f a i n t l foliated y f o l i a t eand d andhas has white white disdiswith w i t h rusty r u s t yweathering weathering surfaces, surfaces. It continuous bandsand andl elenticles whichare aremore morequartz quartzr irich thant the continuous bands n t i c l e s which c h than h e rrest e s t of of Quartz diorite d i o r i t eisi composed s composed of o fplagioclase p l agiocl ase(32-51%), (32051%),quartz quartz(11-31%) ( 1l-31%) rock. Quartz the rock. range from from entirely e n t i r e l yhornblende hornblende and mafic minerals minerals (12-33%). (12-33%). Mafic minerals range and t o entirely e n t i r e l y biotite. biotite. to The quartz ddiorite medium-grained The quartz i o r i t eisi scutc uby t by medium-grained granite g r a n i t epods pods with w i t h migmigmatitic m a t i t i ccontacts contacts and and by by finer-grained finer-grained dikes dikes with w i t hsharp sharp contacts. contacts. The The granite rock g r a n i t e is i s aa pink, pink, faintly f a i n t l yfoliated foliated rockwhich which locally l o c a l l ycontains contains porphyritic porphyritic microcline grains grains reaching reaching 11 cm cm iin n size. size. Granitic G r a n i t i c rocks rocks consist consist of o f plagioplagioclase, of biotite, c l ase. microcline m i c r o c l ineand and quartz, quartz, with w i t hminor m i noramounts amounts of b i o t i t e .muscovite muscoviteand and epi dote. epidote. �LJ inclusions ITI Quartz diorlte Granite a Meta across the top of the outcrop in this figure. 0 Figure 62 -- Outcrop map of quart diorite gneiss at Holcoithe Granite dikes are unpatterned, and trend northeast Dam. Fault — Shear zones Strike of foliation N 100 ft '.O ',O �-100- The youngest n t r u s i v eunit u n iat t aHolcombe t HolcombeDam, Dam, aa hypabyssal hypabyssal andesite, andesite, The youngest iintrusive intrudes the t h e quartz quartz diorite d i o r i t eand and granite g r a n i t edikes dikes with w i t hsharp, sharp, steeply steeply dipping dipping intrudes contacts. It Itconsists consistsofo about f about10% 10% lineated l i n e a t e d hornblende hornblende grains n aa finefinegrainsi in grained Where the r a n i t e dikes, grained pale gray gray matrix. matrix. Where theandesite andesitecuts cutsthe theg granite dikes, iitt contains numerous numerous pale epidote. contains pale green green veins veins ooff epidote. Shear zones t the i o r i t e gneiss gneiss are long, long, narrow, narrow, Shear zoneswhich whichc ucut thequartz quartzddiorite sinuous zones f schist, containing pods pods ooff quartz y r i t e or o r of of quartz quartz sinuous zonesoof schist, containing quartz and and ppyrite and feldspar. and feldspar. The The shear i l l i m e t e r s to t o 1.5 1.5 meters meters wide wide shear zones zonesare areaa few fewmmillimeters and and aa few few centimeters centimeters to t o 60 60 meters meters long. long. They They ccut u t both iorite both the the quartz quartz ddiorite gneiss gneiss and and the t h e andesite. andesite. Schistose Schistose rocks rocks in i n the theshear shear zones zones are a r e thoroughly thoroughly recrystallized r e c r y s t a l l i z e d and and display d i s p l a y no no cataclastic c a t a c l a s t i c textures. textures. A A shear shear zone zone aatt the the northwest corner corner of o f the the outcrop outcrop isi scataclastic c a t a c l a s t iand c and mayhave have formed formed during during northwest may the t h e late l a t estages stagesofo fshear sheardeformation. deformation. Large, Large, unsheared unsheared lenses the lenses iinn the shear zone zone give give the t h eappearance appearance of o fhaving havingundergone undergone spheriodal spheriodal weathering. weathering. shear The three intrusive Dama lall containrrelict The three i n t r u s i v e rock rock units u n i t sata Holcombe t Holcombe Dam l contain elict igneous subhedral subhedral and and all a11have havemetamorphically metamorphically igneous and euhedral euhedral feldspars feldspars,,and induced induced ffabrics, a b r i c s , imparted imparted dominantly dominantly by by the the mafic mafic minerals. minerals. All A l l of o fthe the above mentioned i t s have r t i a l l y tto o thoroughly thoroughly recrystallized r e c r y s t a l 1ized above mentionedrock rocku nunits havep apartially in facies. i n the thelower loweramphibolite amphi bol it e facies. Late Late hydrothermal hydrothermal aalteration l t e r a t i o n occurred occurred along along fracture fracture systems systems to t o aa width width of o faafew few centimeters. centimeters. In I n altered a l t e r e d zones, zones, plagioclase plagioclase iiss altered a l t e r e d to to sericite s e r i c i t eor o rsaussurite, saussuri te, and and biotite b i o t i t eisi sconverted converted to t o chlorite. c h l o r i t e . Quartz Quartz is is partially and/or hornblende p a r t i a l l yreplaced replacedby byalbite a1b i t e and/orcalcite, c a l c i t eand , and hornblendehas has overovergrowths pale aactinolite. t e r a t i o ncould could alteration growths ofof pale c t i n o l i t e . This This type type of of hydrothermal hydrothermal a1 be metasomatismalong alongw with be produced produced by hydrogen hydrogen metasomatism i t h t hthe e iintroduction n t r o d u c t i o nofo Na20 f Na20 and andCO2. CO., STRUCTURAL STRUCTURALGEOLOGY: GEOLOGY : AA sumary affected rocks summary of o f deformations deformations which which affected rocks in i nthe t h eHolcoithearea Holcombe area is i s presented presented in i n Table Table 11. 11. The The only rock rock showing showing aall l l the the fold f o l ddeformations deformations isi sthe thebanded banded gneiss gneiss at a t the t h e Fisher FisherRiver. River. . F1 F folding f o l d i n gproduced produced aa dominantly dominantly east—west east-west f ofoliation, l i a t i o n , S,. S The quartz quartz The diorité showsananeast-west east-west d i o r i t at i aHolcombe t Holcombe Dam Dam shows f ofoliation, l i a t i o n , but b u t there t h e r eare areno noFF folds. F1F1even folds. This This suggests suggests iintrusion n t r u s i o n of o f the t h equartz quartz diorite d i o r i t eduring duringthe the event. S, F folding. S foliation f o l i a t i o nini nthe thequartz quartzdiorite d i o r i t gneiss e gneisswas was folded folded during d u r i n g Fà folding. F9 are ttight layering F ffolds o i l s are i g h t to t o isocljnal i s o c l i n a l folds f o l d sini nfoliation, f o l i a t i o ncompositional , compositional layering ahd fold a d iin n felsic f e l s i cveins. veins. F9 F fold F folding f o l d i n g occurred occurred aatt a a low, Ion, oblique oblique angle angle to t o F1 trends modrate ttoo steep westerly pplunging trends and and produced produced moderate steep (6O_800) (60-80° westerly l unging 1lineations. in e a h o m . Granite Granite intrusives i n t r u s i v e sand andthe thehypabyssal hypabyssal andesite andesi t e display d i s p l a y east-northeast east-northeast foliations f o l i a t i o n sand andsteep steeptot omoderate moderate lineations, 1ineations, suggesting suggesting that t h a t they they were were inintruded truded during during the theF2 F2event. event. During FF. folding, f o l i a t i o nand and fold f o l daxial a x i a lplanes planes in i nthe thegneissic gneissic During folding, foliation rocks at a tHolcmbe ~ o l c & n b were ewere broadly broadly warped warped along dippingnorth-south north-south rocks along aa steeply dipping axis. A t Holcombe Holcombe Dam, e aaxial x i a l planes planes of o fF2 F2folds, folds,and and metasomaticbands bands axis. At Dam,t hthe metasomatic of granite g r a n i t ewere were affected affected by bythe theF3 Fgevent. event. of �-101TABLE TABLE 11 11 Banded GneissBanded Fisher River River Quartz io r it e Quartz DDiorite Gneiss-Ho1 combe Gneiss-Holcombe Amphibolite Amphibol Ite Schist -Chippewa River -Chippewa Dam - - Isoclinal Isocl inal folds folds F1 Fl . Penetrative Penetrative S1 D1 £ foliation and Penetrative ffoliation ol iation lithologic layer- trending E-W ing trending E-W L1 L Penetrative ffold Penetrative old axis and and mineral mineral ineations 1ineations • Tight to Tight Isoclin- Tight Tight to to lsoclinal isoclinal folds a1 folds, folds, folding folding Isoclinal folds F2 F1, and L folding S1 F2 Fl,Sl,andLl foldingSl 1%' Penetrative Penetrative lineatlons in lineations in graniteand and andesandesgranite Ilife Ite £ I I F3 Broad warping Broad N-S trend trend along N-S . Broad warping Broad warping along N-S along N-S trend Folding ooff 54 Folding S4 and and shearing fonu form rootless folds folds Shear Shear zones zones crosscross- Schistosity Schistosit y and and cut aalll l rock Compositional cut rock units units Compositional at Late cataa cata- 1layering, &yering, N7OE WOE N70E. Late a t N7OE. clastic c l a s t i cshearing. shearing, Penetrative Penetrative lineation at llneation at about about 400 40ÂSw SW Faulting along Faul ting a1 ong discrete discrete planes and P120W aat tP150W N50W and N20W Faulting Faulting along a1ong discrete discrete planes p l anes at a tP150W N50W and andN2OW N2W Penetrative lineation at at about 400 about 40ÂSW SW Faulting along Faul t i n g a1 ong discrete discrete pplanes l anes at and P120W a tP150W N50W and N20W Late Late faulting S4 planes along 84 att N7OE a N70E I �-102- An extensiveperiod periodofof shearing shearingaffected affectedthe the quartz quartz ddiorite An extensive i o r i t e gneiss gneiss A series of of small small shear shear zones zones formed formed iinn the the gneiss, gneiss, and and intrusives. A coincident with the the formation formation of of the theamphibolite amphiboliteschist s c h i salong t alongthe theChippewa Chippewa amphiboliteschist schist displays displays aall The amphibolite l l the the same same structural characcharacRiver. The teristics the quartz quartz ddiorite t e r i s t i c sas asthe thesmaller smaller shear shear zones zones i in n the i o r i t e gneiss. gneiss. For this schist is this reason, reason, the the amphibolite amphibolite schist is interpreted interpreted tot orepresent represent aamajor major shear which crosscuts crosscuts the area. shear zone zone which area. Shear Shear zones zones iinn the thearea areatrend trendN7OE N70E and have lineations lineations which SW. A A linear linearnegative negativeaeromagnetic aeromagnetic and have whichaverage average400 40ÂSw. anomaly whichtrends trendsN70E N7OE across area probably resultofof this this anomaly which across thethe area i s is probably a aresult major shear shear zone. zone. The final phases of b rbrittle i t t l e faulting throughThe final phases of deformation deformationproduced produced faulting throughout the area. Faults trending trending N5OW N50W offsets l other features offsetsa lall other structural structural features the area. Faults i n the the area area (Figure (Figure 63). f t llateral ateral in 63). These Thesefaults faultsdisplay displayboth bothright rightand andl eleft s t r i k e separation, separation, although a1though right o f f s e tisi dominant. s dominant. strike right lateral offset Figure 63 NW-trending f afault u l t offFigure 63 --- NW-trending offsets i n forefores e t s of granitic granitic dikes. dikes. Dike Dike in ground is about 2 feet feet wide. wide. ground is about �-103- TITLE: PRELIMINARY ON THE THE GEOLOGY OFTHE THE JUMP JUMP RIVER VALLEY PRELIMINARY REPORT: REPORT ON GEOLOGY OF VALLEY LOCATION: LOCATION: Jump County Park Price County County to to JumpRiver Rivervalley valley from from Big Big Falls County Park iinn Price the east eastend end ofofHolcombe Hol combe Flowage Flowage in i n northeastern northeas ternChippewa Chippewa County. County. AUTHOR: AUTHOR: M.L. M. L Cummings Cummi ngs DATE: DATE: - March, March, 1980 1980 . SUMMARY OF FEATURES: FEATURES : SUMMARY OF Intermediate Intermediate tto o basic basic flows flows and and fragmental fragmental volcanic volcanic rocks rocks crop out along along the Riverand andi tits tributary valleys. volcanic blocks blocks and and aa plagiothe Jump Jump River s tributary valleys. Coarse Coarse volcanic clase porphyritic porphyritic felsite w i t h aa volcanic volcanic center center east east of clase f e l s i t eflow floware areassociated associated with the village granitic plutons an intrusive the villageofofJump Jump River. River. Several Several granitic plutons appear appear tto o form form an belt Oneofofthe theplutons plutonsisist otonalitic belt immediately immediately south south of of the theJump Jump River. One n a l i t i c in in composition and andwas wasemplaced emplaced before deformation thegranitic granitic plutons are composition before deformation b ubut t the are llate a t e or or post post kinematic. kinematic. INTRODUCTION: INTRODUCTION : Geologic mappingalong alongthe theJump JumpRiver Riverand andtributary tributary streams Geologic mapping streams in i n southwest southwest completed iin Price, southeast southeastRusk Rusk and and northeast northeastChippewa Chippewa Counties Counties was was completed n the the summerof of 1979. The mapped mapped areaextends extends from mileseast eastofof Big Big Fa1 Falls summer 1979. The area from 33 miles 1s County County Park in i n Price PriceCounty, County,west, west,tot Holcombe o HolcombeFlowage Flowage ini nnortheastern northeasternChippewa Chippewa County. County. Park Searchesfor for outcrops outcrops were werecarried carried out on Searches on the the North North and and South South Forks Forks of the the JumpRiver, River,Levi Levitt ShoulderCreek Creekand and Main Creek; tributaries of of Jump tt Creek, Creek, Shoulder Main Creek; a l l alltributaries the Jump Jump River. Localized Localized searches searchesf ofor outcropswere werecarried carriedout outononthe theLLittle r outcrops ittle Jump River and andthe the upper upper reaches reachesof of the North Jump River North Fork Fork ofofthe theJump Jump River Riverand andMain Main �-104- The search search ffor head—waters o r outcrops outcrops centered centeredon onstreams streamsthat t h ahave t have head-waters r ree•.. e o ; . The north n o r t h of o f Highway Highway 3 8 since these these streams streams served served as as major major channels channels for f o rmelt—water melt-water during deglaciation comunication, Adam Cahow, degl a c i a t i o n ofo fthe thearea area(personal (personal communication, Adam Cahow, 1979) 1979)and and thus were niore probably scoured to bedrock than other streams in the area. thus were more probably scoured t o bedrock than other streams i n area. This report This r e p o r t is i s based based primarily p r i m a r i l y on on field f i e l drelations r e l a t i o nand s andhand handsample sample descripdescripsamplesbbut section studies studieshave havebeen beencompleted completed on on some some samples u t are not not tions. Thin section available for all Further thin t h i n section sectionstudy, study,chemical chemicalanalyses analyses available a1 1samples. samples. Further and and sstructural t r u c t u r a l analysis analysisare arepresently presentlyunderway. underway. PREVIOUS WORK: WORK: The geology f t the h e Jump l l e y has o nonly l y b rbriefly i e f l y iinn The geologyoof JumpRiver Riverv avalley hasbeen beenreported reported area northwest northwest ooff the the i t e r a t u r e . The the lliterature. map The area t h e study studyarea areawas was included in i naamap ffor o r aa discussion discussionofo the f the FlambeauCopper Copper Deposit at a t Ladysmith Ladysmith (May, (May, 1977) 1977) but but Flambeau the discussion discussionooff tthe the h e rock rock uunits n i t s was was llimited i m i t e d to t o the t h eregional regional geology geology section section of description o f the the paper. paper. A A ffield i e l dtrip t r i stop p stop d e s c r i p t i owas n wasincluded includedini nthe theguidebook guidebook f o r the the1979 1979 meeting meeting of o f the t h eInstitute I n s t i t u on t e on Lake Superior GeologybybyLaBerge LaBerae for Lake Superior Geology (1979) ffor o r Big B i g Falls F a l l sCounty County Park Park aatt the t h e eastern eastern end end of the the present present study study area. area. (1979) Wurdinger 1980) and and Myers, Myers, (1974, (1974, 1980) 1980) have have mapped mapped southwest the Wurdinger (1979, (1979, 1980) southwest ooff the study River Valley. Valley. study area area along the the Chippewa Chippewa River ROCK ROCK UNITS: The rocks along along the t h e Jump Jump River n t a t i v e l y divided The volcanic volcanic rocks River have havebeen beent etentatively i n t o 1) 1) mafic mafic to t ointermediate intermediateflows flows and and 2) 2) basic basic tot ointermediate intermediatefragmental fragmental into volcanics (Figure 64). volcanics 64). Two areasoof mafic and and intermediate intermediate flows flows have havebeen beeni didentified. Two areas f mafic e n t i f i e d . The irst Thef first underlies area of o f the t h e Jump Jump River t h e confluence confluence ooff the the North North underlies the area River Valley Valley west west ooff the and f t the h e Jump f the i l l a g e ofo fJump Jump River. River. and South SouthForks Forkso of JumpRiver Rivert oto4% 4½miles mileseast eastoof the vvillage The second secondarea area1ilies southeast ooff the The e s southeast t h e village v i l l a g eofoSheldon f Sheldonalong alongShoulder ShoulderCreek Creek and west west along alongtthe JumpRiver Riverf for 2 miles. and h e Jump or 2 The fragmental volcanic volcanic rocks The fragmental rocks crop out o u t along along the t h e South South Fork Fork of o fthe t h eJump Jump River near 4½miles miles east east of of near Big B i g Falls F a l l s County County Park Park in i n Price P r i c eCounty County and and from from 4^ the River tto mileseast easto of thevvillage f the i l l a g e ooff the village v i l l a g e of o fJump Jump River o approximately approximately 3 3miles Sheldon. A coarsefragmental fragmentaluunit occursimmediately immediatelyeast easto fofthe thevvillage off A coarse n i t occurs illage o JumpRiver Riverand andappears appearst otorepresent representan anexplosive explosivevol volcanic center. Jump canic center. Since River flows approximately p a rparallel a l l e l t o to the r i k e ofof l lithologic ithologic Since the the Jump Jump River flows approximately thes tstrike units, the the stratigraphic s t r a t i g r a p h i cthickness thickness exposed exposed along e r iriver v e r iis s not n o t great. great. It units, alongt hthe It would a t f for o r the t h e area area east east of o f Sheldon Sheldon tthe h e fragmental fragmental volcanic units would appear appeart hthat volcanic units are underlain underlain by basic flows. The are u n i t smay may extend extend west west The fragmental fragmental volcanic volcanic units of Sheldon Sheldon as r y s t a l ttuffs u f f s that t h a t are are overlain o v e r l a i nby byintermediate intermediate flows flows of asfine-grained fine-grainedc crystal however a apossible u l t east Sheldon provides ambiguity t o to t hthis i s i ninterterhowever possiblef afault east ooff Sheldon providessome some ambiguity pretation. In i tappears appears tthat h a t basal t i c flows flows are are overlain o v e r l a i n by by iinternterI n general, general, It basaltic mediate o mafic fragmental volcanic rocks that t h a t were were deposited deposited from f r o m aa volcanic volcanic mediate tto mafic fragmental volcanic rocks center iinn the t h e area area east of o f the the village v i l l a g eofoJump f Jump River River and and this t h i s ini nturn t u r nwas was center buried by by intermediate buried intermediate flows, flows. Top i n d i c a t o r s in i n the the fragmental fragmental uunits n i t s indicate indicate lop indicators t h a t the the stratigraphic s t r a t i g r a p h i c section section isi soverturned overturned with w i t h tops tops facing facing south. south. Thus that Thus the proposed t r a t i g r a p h i csequence sequence is1ssouthward southwardyounging youngingsequence. sequence. proposedsstratigraphic The basic basic volcanics volcanics aatt the lowestsstratigraphic The the proposed proposed lowest t r a t i g r a p h i c level l e v e lofo the f t h eexposed exposed volcanic The fflows vol canic pile p i 1eare aremassive massive with w i t hlocally 1ocal ldeveloped y developedamygdaloidal amygdal o i d a l zones. zones. The 1ows �-n .1. (0 01 CD -.5 C Figure 64 rf -I 0 0 (0 -I. 0 -t 0 CD C, -- Geologic Map of CD -S -S CD -I. 3 CD the Jump River area. 'I •lt_. I / Ku:K — — _L±L_ —R —. I DIASASE SIRES FOlIATED TONALITE FLOWS COARSE TO FIRE FRAGMENTAl. VOLCANICS OVER TUNNED •EDDINS SIIEAR o FAULT ZONE STRIKE S DIP OF STRIKE $ DIP OF FOLIATION STRIKE S DIP OF WEDDING CONTACTS. INFERRED LOCATION OF OUTCROPS S TM SO L8 METASEDINENTART ROCKS Hf 1.1. IIJWINTERNEDIATE I SASIC METAVOLCASIC ROCKS ' RSQUARTZ MONZONITE, GSAP)PHYRIC 5 QUARTZ MONZONITE dl ROCKS LEGEND INTRUSIVC -t Ui CD �-106- are fine-grained and and weakly o c a l l y aa well we1 1developed developed sschistosity chistosit y are fine-grained weaklyschistose schistosebut butl locally i s found found to t o coincide coincide with w i t h late l a t eshear shearzones. zones. The e uunits n i t s iinnis Themineralogy mineralogyofoft hthe cludesactinolitic-hornblende, actinolitic-hornblende, plagioclase, plagioclase, epidote epidoteand andl olocally cludes c a l l y cchlorite. hlorite. . Overlying tthe basaltic Overlying h e basal t i c flows flows are are fragmental fragmental intermediate intermediate tto o basic basic volcanics. vol canics Theuunits includec rcrystal andc r crystal-lithic The n i t s include y s t a l and y s t a l -1 it h i c ttuffs u f f s and and 1lapilli-sized a p i l l i - s i z e d to t oblockblocksized The coarsest coarsest fragment fragment sizes sizes occur sized fragmental fragmental units. The occur from from immediately immediately east of the 16) tto miles up up rriver. east of the village v i l l a g eofofJump Jump River River (Stop (Stop 16) o 2 2 miles i v e r . Apparently this t h i s area area Is i s near near an an iirruptive r r u p t i v e center center since since llithic i t h i cblocks blocks to t o11foot f o o tIni ndiameter diameter are found found llocally. The ssize andt hthe are o c a l l y . The i z e ooff lithic l i t h i cfragments fragments decreases decreases and e r ratio a t i o of of ccrystal r y s t a l fragments fragments to t o lithic lit h ifragments c fragmentsincreases increasesaway away from from the volcanic center. center. Fine—grained beddedt utuffs and ash ash beds bedsoccur occur interbedded interbedded wwith Fine-grained bedded f f s and i t h coarse coarse fragmental fragmental beds i in Coarsec clasts beds n tthe h e area area ooff the t h e volcanic volcanic center. center. Coarse l a s t s ooff volcanic volcanic debris debris apparently ffell apparently e l l into i n t othe t h eaccumulating accumulating fine f i n e grained grained materials materials allowing a1lowing deterdeterminationoof top ffor Suchtop top iindicators mination f tthe h e sstratigraphic t r a t i g r a p h i c top o r the the volcanic volcanic ppile. i l e . Such ndicators havebeen beenfound foundi ninthe thearea areaoof the coarsest coarsest fragmental fragmental rocks rocksand andi in have f the n ccrystalrystalcase the the top top ooff the lithic I n each each case the l i t h i ctuffs t u f faway s awayfrom fromthe t h evolcanic volcanic center. center. In Sulfide mineralization m i n e r a l i z a t i o n up up to to volcanic pile volcanic p i l e isi ssouth southfacing f a c i n gand and isi soverturned. overturned. Sulfide 10 volumepercent percent (estimated (estimated iin sample)i is 10 volume n hand hand sample) s particularly p a r t i c u l a r l ycommon common iinn the the A pporphyritic o r p h y r i t i c ffelsic el s i c fragmental fragmental uunits, n i t s , 1locally ocal l y defining d e f i n i n g sulfide-rich sul f i d e - r i c hbeds. beds. A flow f l o w also a l s o occurs occurs In i n the t h e area area of o f the the volcanic volcanic center center along along with w i t h intermediate intermediate flows. The fine-grained The ffelsic e l s i c flow f l o wcontains containsplagioclase p l agiocl asephenocrysts phenocrysts ini na afine—grained m a t r i x and and may may be flow f l o w banded banded (Stop (Stop 17.). 17). The The f felsic e l s i c fflow l o w iis s the the only only ffelsic elsic matrix unit u n i t found found in i n the thestudy study area. area. The The volcanic center centermay may represent represent aacollapsed c o l l apsedsubmarine submarine caldera calderacomplex complex in fragmentaluunits representppart i n which which the coarse coarse fragmental n i t s represent a r t ooff tthe h e rims of o f the the caldera. caldera. The center center ooff the caldera wasf filled The caldera was i l l e dby byintermediate intermediate flows flows and and Intermediate intermediate to to Thef felsic representa ar hrhyolitic f e l s i cfragmental fragmental rocks. rocks. The e l s i c rocks rocks in i n the the area area may may represent yolitic felsic domedeveloped developedduring during caldera caldera resurgence supplying dome resurgence producing the t h e dome dome and and supplying felsic f e l s i cpyroclastic p y r o c l a s t i cmaterial m a t e r i a to l t othe t h caldera e calderacomplex. complex. The area south south ooff Sheldon on Shoulder ShoulderCreek Creeki sis underlain underlain by The area Sheldon on by an an intermediate prominently prominently pporphyritic o r p h y r i t i c fflow l o w uunit n i t that t h a t apparently apparently overlies over1 i e s the the fragmental fragmental uunit. nit. Westoof Sheldonand and apparently underlyingt hthe West f Sheldon apparently s t rstratigraphically a t i g r a p h i c a l l y underlying e f lflow o w uunit n i t are are fine f i n e grained grained intermediate intermediate crystal c r y s t a l tuffs t u f f sthat t h amay t maybe bethe thewestward westward extension extension ooff A fault occurs, A f a u l t occurs east east the crystal and crystal-lithic tuffs found to the east. t h e c r y s t a l and c r y s t a l - l i t h i c t u f f s found t o the east. of andmay mayhave have displaced area bbut o f Sheldon Sheldon and displaced u nunits i t s i nin tthe h e area u t the nature nature and and extent Locally along Shoulder Creek of thef afault ntero f movement movement ononthe u l t is i snot n o known. t known. L o c a l l y along Shoulder Creek i inter- mediatet oto ffelsic mediate e l s i c tuffs t u f f sappear appear to t o be be interlayered i n t e r l a y e r e d with w i t h the t h eintermediate intermediate flows flows (Stop 15) suggesting coeval eruption of flows and pyroclastics. (Stop 15) suggesting coeval eruption o f flows and pyrocl a s t i c s . Throughout thevolcanic volcanic sequence sequence Throughout the o fofs tstrike r i k e ooff bedding bedding i in n fragmental fragmental uunits nits Thesstrike units and and contacts between between units u n i t sranges rangesfrom fromN5OE N50E to t oN75E. N75E. The t r i k e ooff u n i t s in in the t h e area area ooff the t h e volcanic volcanic center center are are more more iirregular. rregular. INTRUSIVE UNITS: The iintrusives The n t r u s i v e s (Figure (Figure 64) 64) ini nthe t h eJump Jump River River Valley Valleyare arepoorly p o o r l yexposed exposed and and are represented by small small outcrops, outcrops, iinn cases outcrop iiss known are represented by cases only one one outcrop known ffor o r aa mostextensively extensivelyexposed exposed cropsoout pluton. The The most i n intrusive t r u s i v e crops u t aat, t , and and tto o the t h e east east occurs southeast southeast ooff the second occurs the of, Big B i gFalls F a l l sCounty County Park Park in i nPrice P r i c eCounty. County. AA second The River and and iiss best exposed vvillage i l l a g e of o fJump Jump River exposed onona at rtributary i b u t a r y ooff Levitt L e v i t tCreek. Creek. The �-107- same plutonintrudes intrudes volcanic volcanic units same pluton u n i t s at a tthe thewayside wayside park park ini nJump Jump River. River. AA t h i r dintrusive i n t r u s i v eis iknown s knownby byonly only2 2oro3r small 3 smalloutcrops outcropsin i an wooded a woodedarea area about about third ½m mile h i l e south south of o fShoulder ShoulderCreek Creek along alongCounty County highway highway H. H. A A ffourth o u r t h intrusive intrusive crops crops out o u t along along Main Main Creek Creek north of of the theJump Jump River. River. The The iintrusives n t r u s i v e s are are granitic A ffifth i f t hpluton p l u t o nisi exposed s exposed g r a n i t i cand and have have variable variable mineralogies mineralogies and and textures. A iinn low low outcrops outcrops south south of ofthe theJump Jump River Riveron onShoulder Shoulder Creek. Creek. The The i intrusive n t r u s i v e iiss tonalitic. Unmetamorphosed dikes crop outi ninthe the area area and and generally generally tonal i t i c . Unmetamorphosed b a sbasalt a l t dikes crop out strike N70E. s t r i keN7OE. The pluton pluton at The a t Big B i g Falls F a l l sCounty County Park Park isi sa amassive massive pink pink quartz quartzmonzonite monzonite cut c u t byminor by minor aplitic ap1i t i cand andpegmatitic pegmati t i c dikes. dikes. The The iintrusive n t r u s i v e has has also been desalso been described The ppluton contains subhedral subhedralgrains grainsooff pplagioclase, c r i bed by by LaBerge LaBerge (1979). (1979). The i uton contains l agiocl ase , anhedralorthoclase, orthoclase, quartz quartz and andbbiotite. anhedral i o t i t e . The plagioclase grains contain The plagioclase contain subsubhedral epidote; h l o r i t e is i s interlayered i n t e r l a y e r e d with w i t h biotite b i o t i t esuggesting suggesting that t h a t the the pluton p l uton hedral epidote; cchlorite has been weakf ofoliation been metamorphosed. metamorphosed. Locally L o c a l l y the t h e rock rock has has a weak l i a t i o n but b u t in i ngeneral general metamorphicf afabric metamorphic b r i c is i sweakly weakly developed. developed. AA w well zone cuts cuts the e l l developed developed shear shear zone iintrusive n t r u s i v e in i nthe thepark parkarea area (will ( w i lbe l bediscussed discussed below). below). One i l e west Onemmile west ooff the park the quartz quartz monzonite monzonitei sisi in park the n iintrusive n t r u s i v e contact contact with w i t h the the volcanic volcanic rocks rocks and contact contact metamorphic metamorphice feffects are observed observedi in the volcanics. and f e c t s are n the The pluton exposed exposedalong alongLevi Levitt Creek appears appearst otobe bemore moreg rgranitic The pluton tt Creek a n i t i c iinn composition. Thin sections ooff tthe unit Thin sections he u n i t indicate i n d i c a t e k-feldspar k-feldspar greater greater than than plagioclase. The occursasassmall smallgrains grainsi in the k-feldspar. The pplagioclase l agioclase occurs n the k-fel dspar. Muscovite occursi ninterstitially Muscovite occurs t e r s t i t i a l l ytot ofeldspars feldsparsand andquartz quartzand andappears appears to t o be be of of igneousoorigin. rep1aces k-feldspar k-fel dspar near near ssericitic e r i c i t i cmicroshears. igneous r i g i n . Fine Fine ssericite e r i c i t e replaces m i croshears Chloritized andt to extent iinn C h l o r i t i z e d biotite b i o t i t eisi sprominent prominent ini nthe themicroshears microshears and o aa llesser e s s e r extent the Handsamples samples of the areas the fresh rock. rock. Hand o f the i n t intrusive r u s i v e i n in areas t h athat t i n indicate d i c a t e l i little ttle deformation contain contain more morebbiotite. deformation iotite. . The pluton pluton south south ooff Shoulder Creekhas hasn not beenstudied studiedi nint thin The Shoulder Creek o t been h i n section at Theggranitic a t this t h i s time. time. The r a n i t i c intrusive i n t r u s i v e contains contains small small zzenoliths e n o l i t h s of o f volcanic volcanic rocks. A.fabric A. f a b r i cdue due to t ometamorphism metamorphism i is s nnot o t present present or o r isi sweakly weaklydeveloped. developed. Outcrops aresmall smalland and Outcrops are d i fdifficult f i c u l t tto o find. find. The along Main Creek Creeki is i uton exposed exposed a1 ong Main s a quartz monzonite monzoni t e characterized characterized The ppluton by granophyric on subhedral subhedral pplagioclase by granophyri c intergrowths developed developed on l agiocl ase grains. grains The feldspars are rred colored due duet to inclusions and andaalteration feldspars are e d colored o ffine i n e hematite hematite inclusions l t e r a t i o n of of the pluton pluton iiss locally Epidote iiss aa corrwon the l o c a l l y intense. intense. Epidote common aalteration l t e r a t i o n mineral. northare known known wwithin i t h i n aa mile m i l e both both southeast southeast and and northOutcrops ooff volcanic volcanic rocks rocks are west west ooff the t h e intrusive i n t r u s i v eoutcrops outcropsononMain MainCreek. Creek. . The The t tonalitic o n a l i t i c intrusive i n t r u s i v e isi snot notonly onlyunique unique in i nits i t scomposition composition but b u t also also Outcrops are are low, low, flat f l a tand andsmooth smooth and and have have in i n its i t sstrong strong foliated f o l i a t e d fabric. f a b r i c . Outcrops been found found iinn only Handsamples samples been o n l y one one area area along along Shoulder Shoulder Creek. Creek. Hand i n indicate d i c a t e bbiotite iotite and plagioclase are the main minerals while quartz is apparently minor.. and plagioclase are the main minerals w h i l e quartz i s apparently minor. Thin Thin The iintrusive section study has nnot beeni ninitiated. section study has o t been i t i a t e d . The n t r u s i v e is i sclearly c l e a r l pre—kinematic. y pre-kinematic. Contactswwith other iintrusive andso sothe the rrelation Contacts i t h other n t r u s i v e rocks rocks havenot have not been been found found and elation ooff the t h e tonalite tonal it eand andquartz quartz monzonite monzoni t e iintrusives n t r u s i v e s in i nthe thearea area isi snot n oknown t known but but textural the differences differencesi in the ttonalite t e x t u r a l relations r e l a t i o n s and and the n ffoliation o l i a t i o n suggests suggests tthat h a t the onalite intrusive i n t r u s i v e is i searlier e a r l i ethan r thanthe thequartz quartzmonzonite monzonite intrusives. intrusives. �-108- STRUCTURAL FEATURES: STRUCTURAL FEATURES: The sstructural The t r u c t u r a l elements elements of o f the the area area are areboth bothcontinuous continuous and and discontinuous. discontinuous. The main continuous structural element is schistosity. Commonly The main continuous s t r u c t u r a l element i s s c h i s t o s i t y . Commonly s cschistosity h i s t o s i ty iiss found found to t o be be parallel p a r a l l e to l t compositional o compositionalbanding, banding, contacts contacts and and bedding bedding iinn the the volcanics. i n t r u s i v discussed e discussedabove above is i s subsubvol canics. The t y iin n the the tonalitic tonal it i cintrusive Theschistosi schistosity Schistosity ty iiss locally l o c a l l yinfluenced influenced pparallel a r a l l e l to t o the the schistosity s c h i s t o s i t y ini nthe thevolcanics. volcanics. Schistosi by faults by f a u l t s and andyounger younger shear shear zones zones and and also appears appears to t o be be warped warped by large l a r g e open open ffolds. olds . The with The sschistosity c h i s t o s i t y associated associated w i t h discontinuous discontinuous sstructural t r u c t u r a l elements elements crosscrosscuts eearlier cuts a r l i e r schistosity s c h i s t o s i t y and and is i s often o f t e nrelateI r e l a t e dtot local o l o c ashear l shearzones zonesand/or and/or faults. Important faults. Important ffault havebeen beeni didentified areas, 1) Big a u l t zones zones have e n t i f i e d i in n 33 areas, B i g Falls Falls CountyPark, Park,2)2) east east ooff the County the village v i l l a g eofo fJump Jump River, River, and and 3) 3) east east of o fSheldon. Sheldon. casethe thef afault associatedwwith strongddisruption IInn each each case u l t zone zone i is s associated i t h strong i s r u p t i o n ofof eearlier arlier formedtextures textures and and fabrics. fabrics. formed AAtt Big Big Falls F a l l s the thefault f a u lhas t hasproduced produced aa significant s i g n i f i c a n zone t zoneofo myonite f myonitewhich which has subsequently subsequentlybeen beenrecrys recrystallized. The best exposed developmentooff the exposed development has t a l l ized. The mylonite side ooff the myloni t e iiss on on the south south side the river r i v e rini na anearly nearlycontinuous continuous group group of of outcrops. IInn the the outcrops outcrops the theprogressive progressivedevelopment development from from unsheared unsheared quartz monzonite mylonite quartz monzoni monzonite occursi nin aa distance distance ooff monzonit e t to o myloni t e ttoo unsheared unsheared quartz t e occurs about quartz monzonite monzoniteonone ieither sideoof the ffault about 500 500 feet. The The quartz t h e r side f the a d tappears appears to to be rock uunit. be the same same rock nit. Thef fault The a u l t east east of o f the the village v i l l a g eofoJump f Jump River River is i sspectacularly spectacularlyexposed exposed iin n the south bankoof the rriver. volcanics are are iintensely folded locally the south bank f the i v e r . The The volcanics n t e n s e l y folded l o c a l l yand and possible l large dragf ofold occursi ninthe thevolcanic volcanict utuffs the ssite. The ffault aa possible a r g e drag l d occurs f f s aat t the i t e . The ault area iiss also The geology geologyofofthe the ffault area also the the site s i t eofo an f anold o l dcopper coppermine. mine. The a u l t zone zone is is not andwwill n o t clearly c l e a r l y understood understood and i l l be be investigated investigated in i n thin t h i nsections sectionsand and by by analysis analysis of the ssite. o f structural s t r u c t u r a l data data from from the ite. The ffault The a u l t that t h a toccurs occurs south south of o fSheldon Sheldon is i s poorly poorlyexposed exposed iinn the the bed bed of of outcropsi nin the themiddle middleoof the rriver the Jump Jump River. Small Small outcrops f the i v e r are strongly s t r o n g l y dedeformedand andconsiderable considerablea lalteration occurs iin formed t e r a t i o n occurs n the the volcanic volcanic along along the the shore shore above bbut u t the fault f a u l titself i t s eis l f not i s nexposed o t exposed abovewater watereven even during during periods periods of o f low low stream flow. stream The sense senseoof displacementoor magnitudeo of displacementf ofor the three major The f displacement r magnitude f displacement r the major north to north t o northeast northeast trending trending fault f a u l tstructures structuresare arenot n o known. t known. However, However, i in n aall ll casesthe thef faults boundariesbetween between different cases a u l t s do do nnot o t form form boundaries different l i tlithologic h o l o g i c uunits n i t s oorr are characterized gradeacross acrossthe the ffault characterized by by aa change change in i n metamorphic metamorphic grade a u l t zone. zone. DISCUSSION: The onf field andl limited The ffollowing o l l o w i n g discussion discussion iiss based based on i e l d work work and i m i t e d thin t h i n section section and chemicalstudy studyand andi sistherefore thereforepreliminary preliminary iin and subject subject tto and chemical n nature nature and o reThe i intent so as as ttoo vision. The vision. n t e n t is i s to t ostimulate stimulatediscussion discussionon on the t h eproblems problems rraised a i s e d so improvei ninterpretation River Val Valley. improve t e r p r e t a t i o n of of the t h egeology geology of o f the theJump Jump River ley. The geologic geologic evolution evolution of The o f the theJump Jump River valley v a l l e y must must be be viewed viewed iinn terms terms of boundary between o f the the location l o c a t i o nand andnature natureofofthethe boundary betweenthe theChippewa Chippewa amphibolite amphi b o l it e �-109- complex volcani-sedimentaryprovince provincetto complex t to o the south south and and the Flambeau Flambeau volcani-sedimentary o the north north of the The boundary boundarywas waso roriginally theJump Jump River. The i g i n a l l y placed placed at a t the the Jump Jump River by by Myers (1974) based basedononthe thel olocation Myers (1974) c a t i o n of o f gravity g r a v i t yand andaeromagnetic aeromagnetic anamolies anamolies iinn the area, the nature area, however however the nature of o f the theboundary boundary was was not n o t defined. defined. Part P a r t of o f the the intent i n t e n t of o fthe thepresent present study study was was tto o investigate i n v e s t i g a t e the the field f i e l devidence evidence that t h a tmight might shed shed llight i g h t on on the thenature natureofo the f theJump Jump River Riverlineament lineament (Myers, (Myers, 1974) 1974) and and to to ' attempt to boundary t o define definethe thenature natureofothe f the boundarybetween between the the two two major major geologic geologic provinces provinces iin n the the west-central west-central part p a r tofo fWisconsin. Wisconsin. LaBerge (1979)pointed pointedout outtthat LaBerge (1979) h a t the lineament 1ineament is i s expressed expressed topographically, topographically , in patterns(Ervin and Haniuer, i n Bouguer Bouguer anomaly anomaly patterns (Ervin and Hammer,1974) 1974)and andononaeromagnetic aeromagneticmaps maps (Zietz, ( Z i e t z , Karl, Karl,and andOstrom, Ostrom, 1978). 1978). The The lineament has has comonly commonlybeen beenassumed assumed to to be by aa major major ffault be produced produced by a u l t zone zone (Cumings, (Cunnings, 1975) 1975) and and recently r e c e n t l ythe theJump Jump River Fault Faulthas hasappeared appeared in i nreports reports(Sims, (Sims,Cannon, Cannon, Mudrey, Mudrey, 1978). 1978). From From f field i e l d relations r e l a t i o n sthe theJump JumpRiver Riverlineament lineamentmay may be be shown shown t to o rresult e s u l t from from contrasting geophysicalc hcharacteristics andthe the gglacial contrasting geophysical a r a c t e r i s t i c s o of f 1lithologles itho1ogies and l a c i a l history h istory of topographicexpression expressionofof the the lineament lineament i is o f the the area. area. The The topographic s evident in.stream i n stream patterns patterns in i n the the area area and and by the valley v a l l e y of of the theJump Jump River. River. In I n the the field f i e l d the the course River can can be be shown shownt otobe beccontrolled course ooff the the Jump Jump River o n t r o l l e d by by bedding bedding iinn the the volcanic strong alignment volcanic rocks rocks along along the river r i v e rbanks. banks. The The strong a1 ignment of of stream stream valleys valleys in i n aa northeast-southwest northeast-southwest d idirection r e c t i o n i siscclosely l o s e l y rrelated e l a t e d t to o tthe h e gglacial l a c i a l history history of River and and 1local o f the thearea area(Cahow, (Cahow, personal personal coninunication, communication, 1979). 1979). The The Jump Jump River ocal streams servedasasmajor majorf l flood channelsf ofor waterduring during deglaciation deglaclation of of streams served o o d channels r mmelt e l t water the area area in i n the theprocess process carving carving large l a r g evalleys valleysand andscouring scouringtot obedrock bedrockini many n many places. The Riveri siscclearly than the the rriver The vvalley a l l e y ooff the t h e Jump Jump River l e a r l y llarger a r g e r than i v e r that that flows flows iinn the the valley. valley. Thus Thus iittwould would appear appear tthat h a t the the topographic topographic expression expression of of lineament may o t be o n t r o l l e d by major ttectonic e c t o n i c boundary boundary bbut u t by by the the the lineament maynnot beccontrolled by aa major in f l uences exerted l a c i a l run-off r u n - o f f and and bedding bedding sstructures t r u c t u r e s In i n the t h e volcanic vol cani c influences exerted by by gglacial rocks rocks ooff the the present present valley. The anamoly map mapfor for the area The Bouguer Bouguer anamoly areashows shows aa distinct area d i s t i n c tchange change in i n the the gravity g r a v i t yofothe f the areaacross acrossthe theJump Jump River River Valley. Valley. The The gravity maybebedue duet otothe thec contrasting g r a v i t y change change may o n t r a s t i n g ddensities e n s i t i e s ooff volcanic rocks rocks north north of belt of the of the the river r i v e r and and the the b e l t of of granitic g r a n i t i cplutons plutons south south of the river. r i v e r . It Itmust must be be emphasized t hthat a t the r a n i t i c rocks t otobebei nintrusive t r u s i v e i into n t o the t h e volvolemphasized theggranitic rocks can can be beshown shown canic andare arennot canic rocks rocks and o t i in n ffault a u l t contact contact with w i t h the the volcanics. volcanics. The aeromagnetic aeromagnetic anomaly the area sulfide-bearing anomaly f for o r the area can can also be be explained by contrasts between between sulfide-bearing tuffs northeastsstrike t u f f s and and sulfide—free sul f i d e - f r e e ggranitic r a n i t i c rocks. rocks. The The northeast t r i k e of of volcanic volcanic units units and the northeast and the northeast trends trends of of basalt b a s a l t dikes dikes ini nthe thevolcanic volcanicrocks rockswould wouldexpectedly expectedly produce some type magnetic contrast rockssouth southofof tthe produce some type o fofmagnetic con t r a s t t o to g rgranitic a n i t i c rocks h e rriver. iver. The JumpRiver River1lineament cant hthusly beexplained explainedbybythe thegeologic geologic features features iinn The Jump ineament can u s l y be rocks and and does does nnot o t necessarily r e q u i r e aa major major tectonic t e c t o n i cboundary boundary along along the the rocks necessarily require Jump River o explain the the observed observed geophysical Jump Rivert to geophysical and and topographic topographicfeatures features ooff the linearnent. lineament. The River Fault Mudrey, 1978) 1978) has The Jump Jump River Fault Zone Zone (Sims, (Sims, Cannon Cannon and and Mudrey, has also also been been placed placed iinn the the general general study study area, area, however however the presence presence ooff aa major major ffault a u l tzone zone of significant s i g n i f i c a ndisplacement t displacementdoes doesnot n o tappear appear tot obe besupporte.d supported by. b y ffield i e 1 devidence. evidence. It Itmay may be be argued argued tthat h a t the the plutonic p l u t o n i crocks rockssouth southofofthe theJump Jump River Riverwere were intruded intruded along such a fault zone, this would require the fault to be Middle Precambrian along such a f a u l t zone, t h i s would r e q u i r e the f a u l t t o be Middle Precambrian in River are are probably probably rrelated i n age age since since the the plutons plutons along along the the Jump Jump River e l a t e d tto o the the plutonic development The development o fofa af afault u l t aafter fter p l u t o n i cphase phaseofo the f t hPenokean e PenokeanOrogeny. Orogeny. The emplacement theplutons plutonsi is questionable since since the the plutons plutons can emplacement o fofthe s questionable can cclearly l e a r l y be be shown the vol volcanics suggesting1ilittle shown i nintrusive t r u s i v e i into n t o the canics suggesting t t l e post post intrusive i n t r u s i v e displacedisplacement ment along the the zone. zone. �-110- An aalternate l t e r n a t e hypothesis i s t o r y ofof the area iiss An hypothesist oto expain expainthe thegeologic geologich history the area t h a t the the Jump Jump River does nnot o t represent a major major tectonic t e c t o n i c boundary boundary but but that River Valley does represents u t o n i c a activity c t i v i t y during f t th h e volcanic volcanic rocks rocks representsnormal normalp lplutonic during deformation deformationoof in i n the thePenokean Penokean Orogeny. Orogeny. The The pplutonic l u t o n i c rocks rocks may may be n t e r p r e t e d as as forming forming be iinterpreted a roughly l linear i n e a r bbelt e l t of o f intrusives i n t r u s i v e s that t h a tisi ssub-parallel sub-paralleltot the o the beddingand and a roughly bedding possible ffold possible o l d structures s t r u c t u r e s in i n the the volcanic volcanic rocks. rocks. The chistosity The development developmento fofsschistosity pparallel a r a l l e l to t obedding bedding In i n the t h evolcanics volcanics can can be be interpreted i n t e r p r e t e d as as suggesting suggesting northnortheasterly trending major f o l d structures i n the area i f t h e c h i s t o s i t y is is easterly trending major fold structures in the area if the sschistosity axial planar to the folds. a x i a l planar t o t h e folds. Thus emplacement ooff plutons plutonsmay may have have been been Thus the emplacement guided by o l d crests c r e s t s and and troughs troughs that t h a thad had already a1 ready developed developed iin n the the guided by the the ffold volcanics. vol canics. Tonalitic Tonal it i cintrusives i n t r u s i v e swere wereemplaced emplaced pprior r i o r to t odeformation deformation and and the the sameoorientation same r i e n t a t i o n of of schistosity s c h i s t o s i t ywas wasimposed imposed on the t o n a l i t e as on the volcanics. on the tonalite as on the volcanics. IIn n an an attempt o further resolve the the disputes disputes over h e ssignificance i g n i f i c a n c e of the attempt tto further resolve over tthe of the geology the Jump Jump River Valley Valley aareconnaissance reconnaissance survey survey was was undertaken n tthe he geology ooff the undertakeni in Gilmanarea areaalong along tthe Yellow River River (Figure Gilman h e Yellow (Figure 64 metavolThe area area contains metavol64 ). The it e facies conditions but butsome some canic rocks rocks that t h a twere weremetamorphosed metamorphosed under underamphibol amphibolite facies conditions primary volcanic volcanic structures primary s t r u c t u r e s are arepreserved. preserved. The The local l o c a lmetamorphic metamorphic grade grade may may havebeen beeninfluenced influencedbybyi nintrusion and gabbroic gabbroici nintrusives have t r u s i o n ooff intermediate intermediate and t r u s i v e s that that have well1 developed have we1 developed sschistosity. c h i s t o s i ty. Basalt Basalt dikes dikesare areunmetamorphosed unmetamorphosed and and trend trend northeasterly. Since northeasterly. Since tthe volcanic rocks rocks sstill h e volcanic t i l lpreserve preserveprimary primary textures textures they they are i m i l a r to t o the t h e volcanic volcanicrocks rocksalong alongthe theJump Jump River River than than the the amphibolites amphiboli tes are more moressimilar exposed along tthe River aatt Jim Falls gneisses exposed along h e Chippewa Chippewa River F a l l soro rthe the gneissesat aHolcombe t HolcombeDam Dam exposed oorr Cornell. Cornell. The The ssimilarity i m i l a r i t yofo fthe t h evolcanic volcanicrocks rockstot those o those exposed ini nthe theJump Jump River Valley Valley would would argue argue against against a major major ffault a u l t zone zone or o r tectonic t e c t o n i cboundary boundary existing existing greater incidence incidence ooff plutonic betweenthe the Ye1 Yellow between low River and and the t h e Jump Jump River. The The greater plutonic rocks along the the Yellow River may mayr reflect rocks along Yellow River e f l e c t proximity proximity to t othe thecore coreofothe f t hPenokean e Penokean Orogenic Someo of Orogenic bbelt e l t rrather a t h e r than than a different d i f f e r e n tgeologic geologic province. province. Some f tthe h e questions questions about the the rrelation about e l a t i o n of o fthe thevolcanic volcanicrocks rocksini the n t hYellow e Yellowand andJump Jump River River Valleys Valleys will w i l lhopefully h o p e f u l l ybeberesolved resolvedbybymajor majorand andminor minorelement element chemistry chemistry presently p r e s e n t l y being being Theppossibility thetwo twor river prepared. The o s s i b i l i t y of o ffinding f i n d i n goutcrop outcropareas areas between between the i v e r valleys valleys i s dampened dampened bybythe o f swamps and and apparently t h i cthick k g l aglacial c i a l d rdrift i f t tthat hat is theexpanse expanseof swamps apparently lies iesbetween. between. 1 SUMMARY: SUMMARY: perplexing questions IInn sumary, summary, several several difficult d i f f i c u and l t and perplexing questionshave havebeen been raised raised about the nature of the boundary between the Chippewa Amphibolite complex about t h e nature o f the boundary between t h e Chippewa Amphibolite complex and and the Flabeau volcani—sedimentary province studies In Flabeau volcani-sedimentary province byby f i field e l d studies i n the t h eJump Jump River River andppetrologic Valley. AAtt present present the the available a v a i l a b l emapping, mapping, chemical chemical and e t r o l o g i c data data are not not As further study of materials collected able ttoo provide able provide definitive d e f i n i t i v eanswers. answers. As f u r t h e r study o f m a t e r i a l s c o l l e c t e d However, on on tthe he from on the the issues. from tthe h e area area continues, continues, new new 1light i g h tmay may be be shed shed on issues. However, basis of present information, a Jump River lineament may be reasonably accepted o f present information, a Jump River 1ineament may be reasonably accepted as markingthe thedifferences differences iinn geophysical as marking geophysical pproperties r o p e r t i e s ooff volcanic volcanic and and plutonic plutonic evidencei nin tthe rocks bbut not rocks ut n o t as as a major major tectonic t e c t o n i c break. break. The The evidence h e ffield i e l d does does not not appear to support a major Jump River Fault in the area. appear t o support a major Jump River Faul t i n area. ACKNOWLEDGEMENTS: ACKNOWLEDGEMENTS: study was was funded 102-155 f from r o m the niversity This study funded by by research research grant grant number nunter 102-155 the U University of Wisconsin Wisconsin - Eau Eau Claire. V. Lueth, R. R. Weegman, Weegman, and V. Lueth, andC.C.Lutzewitz Lutzewitz assisted assisted iinn field f i e l dmapping mapping and and L. Prueher, and i n sections r tthis his L. Prueher, andJ.J. Lauer Lauerprepared preparedt hthin sectionsf ofor study. All A l l were were students students in i nthe t h eDepartment Department of o f Geology, Geology, University U n i v e r s i t y of of WisconsinWisconsinEau Claire. Claire. Discussion Eau Discussion iin n the the field f i e l dwith w i t R. h R.Maass Maasswere were helpful helpful and andappreciated. appreciated. - �—111— REFERENCES CITED REFERENCES CITED Cumings, , M.M.L., L. , 1975, 1975, Petrology Petrology and and structure structure ofofPrecambrian Precambrian gneisses gneisses aatt Big Big Cummings M.S. Thesis, University of Falls, Eau Claire County, Wisconsin: Fa1 l s , Eau Claire County, Wisconsin: M.S. Thesis, ofMinnesota, Minnesota, Duluth uth Dul gravity map of Wisconin: EErvin, r v i n , C.P., C. P., Hammer, Hammer, S., 1974, 1974, Bouguer Bouguer anomaly anomaly gravity map of Mi sconin: Wisconsin Geological and Natural History Geological and Natural History Survey, Survey, Scale Scale 1:500,000 1 :500,000 LaBerge, G.L., G.L., 1979, River aatt Big Falls TripGuidebook Guidebook LaBerge, 1979, Jump Jump River FallsCounty County Park: Park: Field Trip No. 4, 4, University Natural History No. University of ofWisconsin Wisconsin - Extension, Extension, Geological Geological and and Natural Survey, p. Survey, p. 40-42 40-42 - - May, E.R., E.R., 1977, Supergeneenriched enrichedmassive massivesulfide sulfide 1977, Flambeau Flambeau - A A Precambrian Precambrian Supergene May, Wisconsin,V.V. 11,, p. 1-26 deposit: Geoscience Geoscience Wisconsin, 1-26 Myers, P.E., P.E., 1974, 1974, Precambrian Precambrian geology stop descriptions descriptions iinn the geology andand f i e field l d t r trip i p stop the Myers, Guidebook,38th 38thAnnual AnnualTri Tn-State Guidebook, -State Geological Geological Field Fiel dConference Conference Myers, P.P.E., Fieldtrip E., 1980, 1980, Fiel d t r i pstops stopsand and general general geology geology section section ini nthe theGuidebook, Guidebook, Myers, 26th 26th Annual Annual IInstitute n s t i t u t eononLake LakeSuperior SuperiorGeology Geology Sims, P.K., P.K., Cannon, W.F., Mudmy, Mudrey,M.G. M.G.J rJr., Sims, Cannon, W.F., . , 1978, 1978, Preliminary geologic geologic map map of Precambrian rocksi nin part part of northern northern Wisconsin: Wisconsin: UU.S. .S. Geological Geological Survey Survey Precambrian rocks Open-file Open-fi 1e Report Report 78-318, 78-31 8, Scale Scale 1:250,000 1 :250.000 Wurdinger, 1979, Structural Structural geology R. , 1979, geology of amphibolitic amphibol i t i c gneisses, gneisses ,Northeast Northeast Wurdi nger, S.S.R., Chippewa County,Wisconsin: Wisconsin:(abs) (abs)25th 25thAnnual AnnualI nInstitute Chippewa County, s t i t u t e on on Lake Lake Superior Superior Geology, Geol ogy , p.42 p .42 Wurdinger,S.R., S.R.,1980, 1980,Structures Structures quartzdiori diorite, granitic intrusives i n inquartz te, granitic intrusives and and Murdinger, 26thAnnual AnnualI Institute Guidebook, 26th n s t i t u t e on on Lake Lake meta andesites meta andesites ata Holcombe t HolcombeDam: Dam: GuIdebook, Superior Superior Geology Geol ogy Ztetz, I.,I . Karl, J.H., Ostrom, M.E., Preliminary aeromagnetic Zietz, , Karl, J .H., Ostrom, M.E.,1978, 1978, Preliminary aeromagneticmap map covering covering U.S. Geological Geological most of the Terrane in most theexposed exposed Precambrian Precambrian Terrane i n Wisconsin: Wisconsin: U.S. Survey Survey Miscellaneous Miscel 1aneous Field FieldStudy StudyMF—888, MF-888, Scale 1:250,000 1 :250,000 . �-113-1 13STOP STOP #15 #15 TITLE:: TITLE INTERMEDIATE PORPHYRITIC PORPHYRITIC FLOWS FLOWS AND AND TUFFS TUFFS LOCATION: LOCATION: Shoulder Creek SW¼, bridge. SWk,SW¼, SW%, Creek ata tRusk RuskCounty CountyHighway HighwayHHbridge. Sec. 33N.,R.R.4W, 4W,Sheldon Sheldon7½ 7%minute minutequadrangle quadrangle Sec. 29, 29, 1. T. 33N., / AUTHOR: AUTHOR : M.L. M.L. Cuninings Cumnings DATE: DATE : - March, March, 1980 1980 U SUMMARY OF SUMMARY O F FEATURES: FEATURES: Intermediate Intermediate pporphyritic o r p h y r i t i c flows flows are are interlayered i n t e r l a y e r e d with w i t hpossible possibleintermediate intermediate fine-grained developmento of fine-grained ttuff. u f f . Local stretched stretched phenocrysts phenocrysts and and development f sschistosity chistosity appears to rreflect rocks are are ccut appears t o e f l e c t late l a t eshearing. shearing. The The rocks u t by a northeast northeast trending trending basalt b a s a l t dike. dike. DESCRIPTION: DESCRIPTION : The Creeki is subparallel to The vvalley a l l e y of o f Shoulder Shoulder Creek s subparallel t o the t h e valley v a l l e yofo the f t h Jump e Jump River off topographic River which which iiss one one mile m i l e north. north. Study Study o topographic maps maps suggests suggests that t h a t Shoulder Shoulder Creek mayhave havebeen beena amelt-water melt-waterchannel channelduring duringdeglaciation deglaciation ooff the Creek may t h e area area and and may haveformed formeda apparallel may have a r a l l e l channel channel to t o the t h eJump Jump River. River. Shoulder Creek Creek provides provides several key exposures exposuresi nint hthe volcanics stratigraphy andi nintrusive several key e volcanic t r a t i g r a p h y and t r u s i v e hhistory i s t o r y ooff the t h e Jump Jump River Valley. Valley. Several Several 1lithologic it h o l o g i cunits u n i t scrop cropout outalong alonga a½4mile m i l elength l e n g t hofo Shoulder f ShoulderCreek. Creek. The mostprominent prominentrock rocktype typei sis an an intermediate intermediate pporphyri Phenocrysts The most o r p h y r i ttic i c flow. Phenocrysts �-114- of feldspar occur occuri in of plagioclase pl agioclase feldspar n aa sstrongly t r o n g l y rrecrystallized e c r y s t a l 1ized matrix. matrix. The The recrystallization due tto r e c r y s t a l l i z a t i o nmay may be be due o aa bbasalt a s a l t dike dike that t h a t intrudes intrudes the the outcrop. outcrop. The flow unit The flow u n i t isi sexposed exposed at a tthe thebridge bridgeononcounty countyhighway highwayH. H. Intermediate non-porphyri t i c uunits n i t s are nterlayered w i t h the flow flow Intermediate non-porphyritic are iinterlayered with unit be fine-grained fine-grained ttuffs. u n i t and and appear appear t to o be u f f s . Although Although a contact contact between between the the two two rock types i s not notexposed exposed iittappears appears tthat h a t the the contact contact has has aa sstrike t r i k e of o fNN 60 60 E. E. rock typesis A weakly o r p h y r i t i c , pinkish-gray pinkish-gray ffelsite e l s i t e crops crops out outini nthe thepasture pasturearea areawest west A weaklypporphyritic, o f the the highway highway and t o to bebe e i teither h e r a af l o w u nunit i t o or r aafine-grained uff. of andappears appears flow, fine-grainedt tuff. An uninetamorphosed unmetamorphosed b abasalt s a l t d idike k e crops o f highway highway H, H, however however the An cropsout out east east of contacts contacts of o f the t h edike dikeand andcountry countryrock rockare arenot n o exposed. t exposed. The The prominent inting prominentj ojointing i n the the dike dike that t h a tstrikes s t r i k e sapproximately approximately N75E N75E i sis believed o be t r i k e of of in believedt to be the the sstrike the dike. dike. A granitic g r a n i t i cintrusive i n t r u s i vcrops e crops i nwooded a woodedarea areaapproximately approximately½b mile mile A outout in a to NE¼,Sec. Sec.32, 32,T.1. 33 33 N., N., R. R. 44 W). W). The The ggranite r a n i t e contains contains t o the thesoutheast southeast(SW¼, ( S h , NEg, small xenoliths volcanic rock rock suggesting a t the r a n i t e i is s iintrusive n t r u s i v e into into small xenoliths ooff volcanic suggestingt hthat theggranite volcanics but b u t the contact contact of o f the the intrusive i n t r u s i v eand andvolcanics volcanics isi snot notexposed. exposed. the volcanics A shear zone zone iiss exposed approximately 3/8 3/8 mile A narrow narrow shear exposed approximately m i l e west west of of highway highway HH at zonehas hasaasstrike a t aa sharp sharp northward northward bend bend iin n the the creek. creek. The The zone t r i k e of o f NN 65 65 £E and and iis s vertical. v e r t i c a l . Alteration A l t e r a t i o n along along the thezone zone is i sprominent. prominent. The The sschistosity chistosity in volcanic rocks rocks has hasaasstrike and i is i n the the enclosing, enclosing volcanic t r i k e of ofN N 70 70 E E and s vertical v e r t i c a l and and may be rrelated the ffoliation may be e l a t e d to t o the theshear shear zone. zone. Often Often the o l i a t i o n ini nthe theintermediate intermediate flow units u n i t s isi sassociated associatedwith w i t hstretched stretchedfeldspar feldsparphenocrysts. phenocrysts. DISCUSSION: DISCUSSION: The interbedded ttuffs The interbedded u f f sand andintermediate intermediateflows flowsexposed exposedalong alongShoulder ShoulderCreek Creek and the Jump JumpRiver Riveri ninthe thevvicinity appeart otoeeither. and the i c i n i t y of o f Sheldon Sheldon appear i t h e r . sstratigraphically tratigraphical l y overlie the fragmental fragmentalc rcrystal andc rcrystal-lithic o v e r l i e or o r are are interbedded interbedded wwith i t h the y s t a l and y s t a l - 1 i t h i c tuffs tuffs that of intermediate t h a t crop crop out out to t o the the east. east. Eruption Eruption of intermediate flows flows in i nthis t h i sarea areamay may have beenroughly roughlyconcurrent concurrentwwith continuederuptions eruptionsaat the volcanic center have been i t h continued t the center which is exposed 7 miles to the east. eruptions may which i s exposed 7 miles t o east. These These eruptions may have have produced produced the the fine-grained fine-grained tuffs t u f f s that t h a tare areinterbedded interbedded with w i t h the the flows. flows. �-115- STOP #16 #16 STOP TITLE : TITLE: COARSE FRAGMENTAL FRAGMENTAL INTERMEDIATE INTERMEDIATE VOLCANIC VOLCANICROCKS ROCKS COARSE LOCATION: LOCATION: One mmile i l e east t h e village v i 1lageofoJump f Jump River River on on County CountyHighway HighwayMM. MM. One east ooff the S i t e of o l d highway 73 bridge. G. Smith Smith property. property. NE¼, NE$, NE¼, NE$, Site of old highway 73 bridge. G. R. 33W., W . , T.T.33N. 33N. Jump Jump River 7% minute minute quadrangle, quadrangle, 1971 1971 Sec. 7, 7, R. Sec. River 7½ i _ tii2 %/' ---, I •...;._,-___• .—. — ,—.--u-- -: _- __/ _/ / AUTHOR : AUTHOR: M.L. Cumings Cumings M.L. - March, 1980 1980 March, DATE: DATE: SUMMARY OF FEATURES : SUMMARY OF FEATURES: Coarse volcanic u nunits i t s t hthat a t are t e r l a y e r e d wwith i t h ffinely inely Coarse volcanicblocks blocksform formmassive massive arei ninterlayered The intermediate intermediate fragmental fragmental volcanics vol canics are a r e associated associated with w i t h porporThe p h y r i t i cintermediate intermediate flows flows inlilediately immediatelytot othe theeast eastofo the f t h emain mainoutcrop outcroparea. area. phyritic bedded tuffs. bedded tuffs. DESCRIPTION: DESCRIPTION: The most i s t i n c t rock rock unit u n i tini nthe thearea areais icomposed s composed of o f volcanic volcanic blocks blocks The mostddistinct Fragment s i z e i s v a r i a b l e b u t most fragments are f o o t i n diameter. up t o 1 up to 1 foot in diameter. Fragment size is variable but most fragments are inch in i ndiameter. diameter. The The volcanic rock fragments are t y p i c a l ly llarger a r g e r than than 11 inch volcanic rock fragments are typically touching and m a t r i x between c l a s t s i s sparse. The l i t h i c fragments range from touching and matrix between clasts is sparse. The lithic fragments range from b a s a l t i c t o fragments of exceptionally high plagioclase content. Clasts o basaltic to fragments of exceptionally high plagioclase content. Clasts off Vesi c l es d i f f e r i n gcomposition compositionappear appear to t o form form crude crude localized 1ocal i z e dconcentrations. concentrations. Vesicles differing are prominent i n many fragments and the vesicles are now f i l l e d by c h l orite are prominent in many fragments and the vesicles are now filled by chlorite �—116— and epidote. Porphyritic P o r p h y r i t i c clasts c l a s t scontain containplagioclase p l a g i o c l asephenocrysts. phenocrysts. Although A1 though and the clasts vary in textures and mineralogy they all are the clasts vary i n textures and mineralogy they a l l are intermediate in i ncomcomposition. The coarse coarsefragmental fragmentaluunits are interbedded interbeddedwwith fine-grained tuffaceous The n i t s are i t h fine-grained tuffaceous tuffaceous rocks rocks are are rich materials that t h a t are arecommonly commonly ddistinctly i s t i n c t l ybedded. bedded. The The tuffaceous rich tend ttoo be fine-grained. The The ffineineiinn epidote epidote and and feldspar and and tend be extremely extremely fine-grained. grained which is 10 W W which i s anomalous anomalous iin n the the Jump Jump River area. area. grained beds beds sstrike t r i k e NN 10 The The vvolcaniclastic o l c a n i c l a s t i c units u n i t s are are spatially s p a t i a l l yassociated associated with w i t h weakly weakly porphyritic porphyritic flows which which crop crop out out as as low low outcrops outcropsimmediately Immediatelyupupstream stream from flows from t h this i s l olocality. cality. Possible fragmental fragmentalu units arei ninterlayered the flows flows but Possible n i t s are t e r l a y e r e d wwith i t h the b u t textures textures are are poorly developed. poorly developed. Prominentveins veinscross-cut cross-cut the the coarse coarse fragmental fragmental uunits are to Prominent n i t s and and are t o varying varying degrees degrees deformed. deformed. The The tthickest h i c k e s t veins veins are areusually usuallyundeformed. undeformed. Thin sections sections of the wwalls r o m the a l l s ooff the the o f the the veins veins indicate i n d i c a t eeuhedral euhedral epidote epidote developed developed i in n ffrom vein quartz ffilling vein and and quartz i l l i n gthe t h eremaining remainingspace. space. DISCUSSION: DISCUSSION : The coarseness coarseness volcanicblocks blocksa at The of ofvolcanic t t hthis i s llocation o c a t i o n suggest suggest tthat h a t the the outoutcrops are are near nearaassignificant crops i g n i f i c a n t explosive explosive volcanic volcanic center. center. Similar S i m i l a r coarse coarse fragmental rocks rocks interbedded interbeddedwwith fine-grained ttuffs mental i t h fine-grained u f f s occur occur approximately approximately 2 miles mi 1es area between appearst to be underlain underlain by east oof f tthis h i s site. s i t e . The The area between appears o be by massive massive east intermediateflows flowsand andintermediate intermediate r i t i c , tuffs t u f f sand and possibly possibly intermediate t o to f e lfelsic, s i c , o often f t e n ypyritic, Less than ½ mile south (Stop 17) are outcrops of aa llapilli-sized a p i l l i - s i z e d tuffs. t u f f s . Less than h m i l e south (Stop 17 are outcrops of l o w or. o r possibly a felsite f e l s i t edome. dome. A A posposmassive,weakly weaklyp oporphyritic massive, r p h y r i t i c f felsite e l s i t e fflow sible interpretation of the volcanic rocks in the immediate area is a submarine s i b l e i n t e r p r e t a t i o n o f the volcanic rocks i n the immediate area i s a submarine collapsed caldera complex complexi nin which whichthe the coarse coarsefragmental fragmentalrocks rocksare areppart of the collapsed caldera a r t of the rim of the complex and the interior of the collapsed structure filled with rim of complex and the i n t e r i o r o f t h e collapsed s t r u c t u r e f i l l e d w i t h massivef efelsite flows and andintermediate intermediatet otof efelsic flows l s i c pyroclastic p y r o c l a s t i c materials. materials. The The massive lsite may representaaf felsite formedduring during aa caldera caldera resurgence stageaafter may represent e l s i t edome dome formed resurgence stage fter resurgent caldera complexes are possibly possibly Such resurgent complexes are the main main collapse had had occurred. occurred. Such Such an an environment has has mineralization. Such important in i n development development ooff economic economic mineralization. been suggestedf ofor Kuroko deposits deposits (Kouda, Korde, 1978) 1978) and andpossibly possibly the been suggested r Kuroko (Kouda, Korde, massive Noranda district deRosen—Spence, massive ssulfide u l f i d e mineralization mineral i z a t i o nin ithe n the Noranda d i s t r(Spence, i c t (Spence, deRosen-Spence, 1975). ? REFERENCES. CITED REFERENCES CITED Kouda, Korde,H.,H., 1978, 1978, Ring Ring structures, structures, resurgent resurgent cauldron, cauldron, and and ore Kouda, R.,R., Korde, Mining deposits iinn the the Hokuroku Hokuroku volcanic i e 1 d, northern northernAkita,, Aki ta, Japan: Japan: Mining deposits volcanic ffield, Geology, V. 28, Geology, V. 28, p. p. 233-244 233-244 Spence,D.D., D.D., deRosen-Spence, deRosen-Spence, A.F., 1975, The place mineralization A. F. , 1975, The place o f ofs usulfide lfide m ineralization Spence, EconomicGeology, Geology, V.V. 70, iinn the thevolcanic volcanicsequence sequenceata Noranda, t Noranda,Quebec: Quebec: Economic 70, p. 90-101 p. 90-101 �—117— STOP STOP #17 #I 7 TITLE: TITLE: PORPHYRITIC PORPHYRITIC FELSITE FELSITEFLOW FLON LOCATION: LOCATION : Along on the James James M i 1l e r A1 ong Levitt Levi ttCreek Creek south south of of County CountyHighway Highway DD on Miller Farm. SE¼,Sec. Sec. 7, NE& SEQs 7  R. R. 3 W., W e s T. T. 33 33N. N. Jump Jump River 7½ 7% minute minute Farm. NE¼, quadrangle, quadrangle 1971 1971 -, /'-- / :i ( _ -- / "I _I \/ -. 1Z14 - .. -*—___ i.J, •* — 220 - fr I, if jump-1 AUTHOR: AUTHOR : M.L. M.L. Cummings Cumnings DATE: DATE : - March, March 1980 1980 SUMMARY OF FEATURES: SUMMARY OF FEATURES : A fine-grained, fine-graineds weakly weakly porphyritic porphyritic felsite f e l s i tflow e flow formsmassive massiveoutcrops outcrops A forms along along Levitt LevittCreek. Creek. The The fel i t e contains contains aa possible possible metamorphic metamorphic fabric fel ssite fabric or relict by.bya alocal locally E-W shear shear zone zone which which 10 r e l i c tprimary primaryflow flowstructure structureand andisi cut s cut localE-W produces lineation iinn the produces aalineation the rock. rock. DESCRIPTION: DESCRIPTION : Two outcropsofof aa ffelsite Two outcrops e l s i t eoccur occurwest west ofofthe thefarm farmbuildings buildingsononthe theJames Jams Miller i nthe thebed bed of of Levitt LevittCreek. Creek. The The ffelsite e l s i t eisispink p i n kand andmassive. massive. Miller farm farm in Small to anhedral Small subheadral subheadral to anhedral plagioclase p1 agiocl ase phenocrysts phenocrysts occur in in aafine—grained f i ne-grained matrix dominated apparentlyby byquartz quartz and andfeldspar feldspar bbut sericite bands dominated apparently u t sericite bands with with minor chlorite define minor chlorite define aa fabric in i n the the rock. rock. . The irregular clots of The ffelsite e l s i t e isi scut cutbybya ashear shear zone zone containing containing irregular of white white quartz in i n an an outcrop outcrop immediately immediately west west of the the barn. barn. The The shear shear zone zone superimposes superimposes �-118aa secondary secondary sschistosity c h i s t o s ~ t yon on the the earlier e a r l i e r fabric f a b r i cand andlocally l o c a l l yproduces produces aa lineated lineated I fabric fabric iin n the the ffelsite. elsite. DISCUSSION: massivef efelsite AA massive l s i t e crops crops out out west west of of the thewayside wayside park parkalong alonghighway highway 73, 73, the ffelsites but but the the unit u n i t isi scoarser coarser grained grained than than the e l s i t e s at a t this t h i s location, location, possibly possibly becauseo fofcontact contactmetamorphic metamorphic effects from material. because effects from g r granitic a n i t i c i nintrusive t r u s i v e materi a1 . The bandingi in the massive The banding n the massive ffelsite e l s i t e may may be be aa metamorphically metamorphically induced induced ffabric abric or represent primary flow o r may may represent flow banding. banding. The e l s i t e s are are apparently apparently closely closely The ffelsites related to t o coarse coarse intermediate intermediate fragmental fragmental volcanic volcanic rocks rocks which which crop crop out o u t along along the Jump River approximately approximately %½mmile Possibly tthe Jump River i l e nnorth o r t h (Stop (Stop 16). 16). Possibly h e ffelsites elsites form a t e rhyolitic r h y o l i t i dome c dome formed formed during during caldera caldera resurgence resurgence iin n a large l a r g e collapsed collapsed form aa llate caldera complex. Stratigraphic suggestt hthat felsites t o p indicators i n d i c a t o r s would wou1 d suggest a t t the h e fe1 s i tes complex. S t r a t i graphi c top stratigraphically s t r a t i g r a p h i c a l 1yoverlie over1 i ethe t h ecoarse coarsefragmental fragmental rocks rocks exposed exposed tto o the the north. The intruded by by ggranitic The ffelsites e l s i t e s have have apparently apparently been been intruded r a n i t i c rocks rocks which which are. are. exposed t the terexposeda at the wayside waysidepark parkalong alonghighway highway7373t otothe thewest westand andalong alongan ani nintermitent m i l esouth south rnitent tributary t r i b u t a r ystream stream which which flows into i n t oLevitt L e v i tCreek t Creekless l e s sthan than¼%mile of development shearzone zone thef felsite o f the the present present ssite. i t e . The The development of oft hthe e shear c ucutting t t i n g the elsite appearst otobebel alater thant hthe appears t e r than e i nintrusion t r u s i o n ooff tthe h e granites granites since since ssimilarly i m i l a r l y oriented oriented shear zones zonesccut the ggranite park to shear u t the r a n i t e exposed exposed iin n the the wayside wayside park t o the the west. west. i I i 1 1 I �—119- STOP #18 STOP #18 TITLE:: TITLE CRYSTAL AND AND CRYSTAL-LITHIC CRYSTAL-LITHIC TUFFS CRYSTAL TUFFS LOCATION: LOCAT ION : Section line sections 15 22, T. Section line between between sections 15 and and 2Z9 T. 33N., 33N. R. R. 44W. W. along River behind behind the the farm Edwin and and*Gerald Gerald Ahlers. Jump the Jump Jump River farm of Edwin 7% minute quadrangle, quadrangle, 1971 1971 River 7½ AUTHOR: AUTHOR: M.L. M.L. Cuniings Cumings DATE:: DATE - March, 1980 1980 SUMMARY OF OF FEATURES: SUMMARY FEATURES: .W e11-bedded crystal -1 i t h i c tuffs tuffsare arebeautifully beautiful l exposed y exposed along along Well-bedded crystaland andcrystal crystal-lithic south bank the south Impact structures structures produced larger cclasts bank of the the Jump Jump River. Impact produced bybylarger lasts fall ing into materialsindicate indicate that that the the stratigraphic falling into finer finergrained grained bedded bedded materials unitsare areoverturned. overturned. tops of the the volcanic volcanic pile pileare aretot othe thesouth southand and that that the the units DESCRIPTION: DESCRIPTION: Well-exposed, streampolished polishedoutcrops outcropsofof tuffaceous tuffaceous of of various rocks Well-exposed9 stream rocks characteristics 0.75miles milesalong alongthe theJump Jump River River characteristics crop cropout outfor forapproximately approximately0.75 west of the Since the the river river flows west theEdwin Edwin and and Gerald Gerald Ahlers Ahlers property. Since flows approximately parallel to approximately parallel t o the thebedding bedding in i n the thevolcanics volcanicsthe theexposures exposures do do not provide aa thick stratigraphic nearly one one stratigraphic stratigraphic provide stratigraphicsection sectionand andmay may represent represent nearly level. level . �-120- Thelowest lowests stratigraphic The t r a t i g r a p h i c uunit n i t is i s farthest farthest north n o r t hand and isi sfine—grained, fine-grained, massive,l ilight green, intermediate intermediatec rcrystal tuff. Bedding Bedding iiss massive massive, g h t green, y s t a l tuff. massive and and can can be iidentified be d e n t i f i e d by by faint f a i n t bands bands that t h a t have have a a higher higher percentage percentage oof f sslightly l i g h t l y coarser coarser phenocryststhan than the the surrounding phenocrysts surrounding rock. The mainrock rocktype typei sisananintermediate intermediate rock iiss The main c r ycrystal-lithic s t a l - l i t h i c ttuff. u f f . The The rock prominently beddedw with the sstrike and dipping dipping 72' 72 N. prominently bedded i t h the t r i k e of of bedding bedding NN 60E 60E and N. AA coarse, approximately approximately44 inches incheslong, long, volcanic volcanic clasts coayse, c l a s t s has has been been found found that that apparently produced apparently ffell e l l into i n t othe theaccumulating accumulating finer-grained finer-grained tuffs t u f fand s and producedan an impact feature feature ffrom which aa sstratigraphic rom which t r a t i g r a p h i c top t o pdeterinatlon d e t e r i n a t i o can n canbebemade. made. The impact top of o f the the volcanic volcanic unit u n i tappears appears to t o be be to t o the the south south indicating i n d i c a t i n g that t h a tthe thebedding bedding top iiss overturned. overturned. Beds of. c r y s t a l tuff are interbedded interbedded w with i t h c rcrystal-lithic y s t a l - 1 it h i c tuff t u f falong along the the Beds of.crystal tuff are i n c h in i ndiameter diameter outcrop area. area. T y p i c a l l y lithic l i t h i fragments c fragmentsare areless l e s sthan than½ inch Typically and.are areofof intermediate composition. and composition. The The ttuffs u f f s contain contain plagioclase plagioclase crystals crystals and pyroxene ccrystals r y s t a l s that t h a tare arepseudomorphically pseudomorphica11y replaced rep1aced by byamphibole. amphi bo1e. and possible possible pyroxene The plagioclase plagioclase ccrystals Epidote also The r y s t a l s contain contain subhedral subhedral to t o anhedral anhedral epidote. epidote. Epidote a1so forms a r t of the matrix matrix between between ccrystal r y s t a l and and lithic l i t h i cclasts c l a s tin s isome n somesamples. samples. forms ppart of the Hornblende porphyrobl asts are f i de minerals mineral s are Hornblende porphyroblasts areprominent prominenti nin most mostbeds, beds,and andsu1 sulfide found ocal 1y in i nconcentrations concentrations of o f 22 percent. percent. found 1locally + DISCUSSION:: DISCUSSION , The The ttuffs u f f s exposed exposed aat t tthis h i s stop stop are are believed believed to t o be be related r e l a t e d to t oaacaldera caldera complexexposed exposed east thev ivillage JumpRiver River( 3(3miles milest otothe the east, east, Stop Stop 16). 16); complex east o f of the l l a g e oof f Jump Thet tuffs The u f f s in i n this t h i sarea areaare arepossibly possibly stratigraphic s t r a t i g r a p h i cequivalents equivalents of of the thecoarse coarse fragmental uunits fragmental n i t s at a t Stop Stop 16. 16. The The ggrain r a i n size size ofo ffragments fragments decreases decreases and and the proportion of lit h fragments i c fragmentsincreases increasesaway away from from the the proportion o f crystal c r y s t a lfragments fragments to t olithic volcanic center. To tthe westo of andl ilithic volcanic center. To h e west f t hthis i s ssite i t e the the ttuffs u f f s are are fine-grained fine-grained and thic fragments have not n o t been been observed. observed. The The rocks rocks have havebeen beenmetamorphosed metamorphosed under under fragments have epidote—amphibolite facies conditions buta aschistosi schistosity not strongly epidote-amphiboli t e facies conditions but t y i is s not strongly devel aped. developed. �-121— BIBLIOGRAPHY BIBLIOGRAPHY I u t o n i sm in* the Anderson, and Medari s, 1975 "Proterozoic r a n i t i c PPlutonism Anderson, Van VanSchmus, Schmus, and Medaris, 1975, "ProterozoicGGranitic in the Lake Superior Region and its Tectonic Implications," (abs). 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Myers, P.E., P.E., 1980, andf i efield Myers, 1980, General General i nintroduction t r o d u c t i o n and l d t trip r i p descriptions descriptions iin n Field Field Trip T r i p Guide Guide Book Book ffor o r 26th Annual Annual IInstitute n s t i t u t eon onLake LakeSuperior Superior Geology Geology Field Field Trip T r i p #1. #l. Myers, P.E., P.E., Cuniriings, M.L.,May, May,E.R.9 E.R.,Kopp, Kopp,R.A., R.A.,MWillis, i n i s , R.P., R.P., Bergstrom, Bergstrom, J. J. Myers, Cunnings, M.L.9 R., 1974, R., 1974, 38th 38th Annual Annual Tn-State Tri-State Geological GeologicalField F i e l dConference ConferenceGuidebook, Guidebook, 125 125 p. p. Piotruszewicz, M.A., M.A., 1978, "An Analysis Analysis ooff aa Drill 1978, "An D r i lCore l Corefrom fromWestern Western Clark Clark Piotruszewicz, County, Wisconsin," Wisconsin," unpub. unpub.M.S. M.S.thesis, thesis, University County, U n i v e r s i t yofo fWisconsin, Wisconsin, Milwaukee. Milwaukee. Sims, P. P.K., Tectonic and Mineral Deposits, K., 1976, 1976, "Precambrian "Precambrian Tectonic and Mineral Deposits, Lake Lake Superior Superior Sims, Region," Economic Geology, v. 71, Region," Economic Geology, 71, p.p.1092—1118. 1092-1118. Sims, P.K., P.K., Cannon, W.F., Mudrey,M.G., t4.G.,Jr., Jr., 1978, Sims, Cannon, W. F., Mudrey, 1978, "Preliminary "PreliminaryGeologic GeologicMap Map of Rocksi in Part of o f Precambrian Precambrian Rocks n Part o f Northern Northern Wisconsin," Wisconsin," U.S. U.S. Geological Geological Survey Open-file Open-file Report Survey Report 78-318, 78-318, Scale Scale 1:250,000. 1:250,000. Smith, E.I., 1978, E. I., 1978, "Precambrian "Precambrian Rhyolites Rhyol it e s and and Granites Granites in i n South-Central South-Central Smith, Wisconsin," Geol. Soc. Bull., v.v.89, Wisconsin," Geol. Soc. America America Bull., 89,p. p.875—890. 875-890. Spence,D.D., D.D., deRpsen-Spence, deRpsen-Spence, 1975, "The place mineralization Spence, A. F.A.F., , 1975, "The place o f ofs usulfide lfide m ineralization in EconomicGeology, Geology, v.v. 70. i n the thevolcanic volcanicsequence sequenceataNoranda, t Noranda,Quebec',' Quebec',' Economic 70. United States States Steel Steel Corporation, mapso of the Jim Jim FFalls 1973, unpi. unpl. aeromagnetic aeromagnetic maps f the alls United Corporation , 1973, area, W i sconsin. area, Wisconsin. . Van Schmus,W.R., W.R.,1974, 1974,"Chrono "Chronology PrecambrianEvents Eventsi in (abs). Van Schmus, W i sconsi dl (abs) 1ogy oof f Precambrian n Wisconsid' EOS.Trans. Trans.Amer. Amer.Geophys. Geophys.Union, Union,v.v. 55, 55, p. p. 465. EOS. 465; Van Schmus, 1976,"Early "Earlyand andMiddle MiddleProterozoic Proterozoic History History of Van Schmus , R.,R.,1976, o f the theGreat GreatLakes Lakes Area, North North America", America", PPhil. h i l . Trans. Area, Trans. R. R. Soc. Soc. Land. Lond. A. A. 280, 280,p.p.605—628. 605-628. f Igneous i t h the thePenokean Penokean Van Van Schmus, Schmus,R.,R., 1980, 1980,"Chronology "Chronologyoof Igneous Rocks Rocks Associated Associated w with Amer. Special Paper, #180, #180, Goldich Go1dichVolume. Vol me. Orogeny i in n Wisconsin", Orogeny Wisconsin",Geol Geol. Society Society Amer. Special Paper, . �-12 3— Willemse, J., J., 1969, 1969, "The "TheGeology Geology of o fthe theBushveld BushveldIgneous Igneous Complex, Complex, the the Largest Largest Willemse, Repository of o f Magmatic Magmatic Ore the World" World" ini nMagmatic Magmatic Ore Ore Repository Ore Deposits Deposits iinn the Deposits, Economic Economic Geology Pub1 i s h i n g Co.Co., , p.p.1l—22 -227 Deposfts, Geology Publishing Wurdinger, S.R., 1979, "Structural Geology Wurdinger, S.R., 197% "Structural Geology ooff Amphibolitic Amphibolitic Gneisses, Gneisses, Northeast Northeast Chippewa County,Wisconsin1', Wisconsin", (abs)25th 25thAnnual AnnualI nInstitute s t i t u t e on on Lake Lake Superior Chippewa County, (abs) Geology, Geology, p. p. 42. 42. Zietz, I.,I., Karl, J.H., Ostrom, M.E., "Preliminary Aeromagnetic Karl, J.H., Ostrom, M.E.,1978, 1978, "Preliminary AeromagneticMap Map Covering Most Ter.ranei in Most ooff the theExposed Exposed Precambrian Precambrian Ter.rane n Wisconsin," Wisconsin, I' U.S. U. S. Geological Survey, 1 :250,000. Survey, Miscellaneous Miscel laneous Field Fie1dStudy StudyMF-888, MF-888, 1:250,000. rkhthui � https://digitalcollections.lakeheadu.ca/files/original/8f32dbdeaf22a4f8e74619ec237c92d9.pdf 0aa27b9ebf391a523fcce1756843d276 PDF Text Text 26th Annual Institute on Lake Superior Geology FIELD TRIP 2 Precambrian Tectonic History of the Black River Valley GENERALIZED PRECAMBRIAN GEOLOGY OF THE EAU CLAIRE REGION Diabase + Gabbro Tonalite Trondhjemi te Volcanics and sediments Amphibolutes Shear zone May 7, 1980 University of Wisconsin-Eau Claire �_____ ___________ ___ : _______ _________ :. Chippe I A - A — Cjrtiss N cony a — NiII v — — — .— — aA+_4./ 2J ( r S 53 Ck Atr MeIose p0 r K SON A 2 NATPONA. 71 M c,u 0N R 0E N A / vv N E4R I 4 3 — 2 7 tevUe / ' - C — &H Wyele Ii - •1 yZLA 4rNaIkM La Crescerst ,_ el WIItI1 end1 nMaJto �PRECAMBRIANTECTONIC TECTONICHISTORY HISTORYOF OF THE THE BLACK BLACK RIVER PRECAMBRIAN RIVER VALLEY VALLEY Field Guide Guide Field R.S. Maass and and W.R. W.R. Van Van Schmus Schmus R.S. Maass Prepared for Prepared for Annual Meeting Meeting Twenty-Sixth Annual INSTITUTE ON ON LAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY INSTITUTE University ofofWisconsin-Eau Wisconsin-Eau Claire Claire University Eau Wisconsin Eau Claire, Claire, Wisconsin May May 6-11,1980 6-11, 1980 �CONTENTS CONTENTS Page INTRODUCTION INTRODUCTION (W. (W. R. R. Van Van Schmus) Schmus) IITINERARY TINERARY 1 III • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 44 GEOLOGICAL STOP STOP DESCRIPTIONS DESCRIPTIONS GEOLOGICAL Stop Stop 1. 1. Stop Stop 2. 2. Stop Stop 3. 3. Stop 4. Stop 4. Stop Stop 5. 5. Stop 6. Stop 6. Stop 7. Stop 7. Stop 8. Stop Gnei ss near nearGreenwood Greenwood Gneiss 66 Neillsville Granite.................................. 99 Neillsville Granite Gneiss at atHumphrey Humphrey Farm Farm 12 . Gneiss NeillsvilleAugen AugenGneiss Gneiss 15 Neillsville Lake Arbutus 18 Lake Arbutus Granite 20 Gneiss along Black River River .. 20 Gneiss along East East Fork Fork of of Black 22 Hatfield Gneiss,Arbutus ArbutusDam Dam 22 Hatfield Gnelss, 27 Black River Granite 27 Black River Falls Granite • SUPPLEMENTAL LOCALITIES LOCALITIES SUppLn~ENTAL 29 29 DISCUSSION Maass) DISCUSSION(R. (R. S. S. Maass) 40 40 ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS 42 REFERENCES REFERENCES 43 �INTRODUCTION INTRODUCTION W. R. Van Schmus Schmus R. Van W. The along The Precambrian Precambrianbedrock bedrockexposed exposed alongthe theBlack BlackRiver River iR iR west-central Wisconsin, River Falls to tonorth consists primarily primarily Wisconsin,from fromBlack Black River Falls northofofNeillsville, Neillsville, consists grieissic rocks plutônlc rocks. Archean gneissic rocks and and early Proterozoic Proterozolc (Penokean) (Penokean) plutonic rocks. of Archean TheseArchean Archeanrocks rocksare are the the westernmost westernmostexposures exposuresofof an an Archean Archeanterrane terrane that These extends River in inthe extendsfrom fromthe theBlack BlackRiver Rivereastward eastwardtotothe theWisconsin Wisconsin River thevicinity vicinity Gneissic rocks of Stevens Stevens Point and and Wisconsin Wisconsin Rapids rocks also occur occur Rapids (Figure (Figure 1). Gneissic to the the northwest, northwest, ininEau Counties(Myers (Myerseteta1., al., 1980), Eau Claire Claireand and Chippewa Chippewa Counties 1980), as theChippewa Chippewa Amphibolite Amphibolite Complex, Complex, but but they they may may not not be be Archean. Archean. as part ofofthe One ofof the One the major major problems problemsininunderstanding understandingthetheolder olderrocks rocksofof the the region region is how they similar rocks rocks ininthe thesouthern southern part partofofthe theCanadian Canadian Shield, Shield, how theyrelate relate to to similar or to to the either to to the thenorth northininnorthern northernWisconsin Wisconsin and and Michigan Michigan or the west west in the Minnesota River the Minnesota River Valley. N RAPIDS MILES I i 16 I KILOMETERS 26 Figure 1. 1. Geologic Geologic map thethedistribution mapofofcentral central Wisconsin Wisconsinshowing showing distribution of presumed Archean Penokean igneous presumed Archeangneiss gneiss(1), (1), Penokean igneous and and metamorphic metamorphicrocks rocks (2), (2), The Hatfield Hatfield 1500 rocks (3), and and Paleozoic Paleozoic cover cover (4). The 1500m.y. m.y.old old plutonic plutonic rocks Gneiss the block block of of gneiss gneiss (D) (D) Gneiss (Stop (Stop7)7) occurs occursalong alongthe thenorthern northernpart part of of the After Van between BlackRiver RiverFalls Fallsand andNeillsville. Neillsville. After between Black VanSchmus Schmus and and Anderson Anderson' (1977) (1977).. 1 �Most of of the Archeanrock rockin in central Wisconsin I~ost the known known Archean Wisconsin consists consists ofofbanded banded gneiss, migmatitic gneiss, gneiss, gneiss, or or niigmatite; migmatite; Archean Archean plutons plutons are are rare. rare. Regional studies (Van andAnderson, Anderson,1977) 1977) have haveshown shownbybyU-Pb U-Pbdating datingthat that the (Van Schmus Schmus and the gneiss and andmigmatite migmatiteinin the the eastern eastern part part of the m.y. old. gneiss the area area are are about about 2800 2800 m.y. Thereisis some someindication indicationfrom fromtheir theirRb-Sr Rb-Srresults resultsthat thatthe theprotolith protolith of the There the migmatitic gneiss gneiss in in the an earlier earlier crustal migmatitic the Dittsville Dittsyillearea areamay may have have had had an crustal history, but loss during during aa later later but the the results resultscould couldalso alsobe be explained explained by by Rb Rb loss metamorphism. Recent studies in Recent studies in the theBlack BlackRiver Riverarea area(Dubois (Duboisand andVan VanSchmus, Schmus, 1978; Van Schmus,unpub.) unpub.)have haveconfirmed confirmed an an Archean Archeanage agefor for those gneisses. 1978; Van Schmus, gneisses. The gneiss The gneissnear nearHatfield Hatfield(Stop (Stop7)7)yields yields zircons zirconsthat that are are analytically analytically indistinct ininage andandthethe Wisconsin indistinct age from from those those of of the the Pittsville Pittsville WisconsinRiver Riverareas areas (Figure the mean mean age samples is 2815 2815 +20 ~ 20 m.y. m.y. The (Figure 2); the age defined defined by by all all samples zircons are are tentatively tentatively interpreted zircon, rather zircons interpreted as as primary primary igneous igneous zircon, rather than than metamorphic orordetrital zircon, so so that thatthe theage ageofof2815 2815m.y. m.y.would would represent represent metamorphic detrital zircon, the time time of of the the protoliths protoliths (plutons, (plutons, volcanics) volcanics) of of the the the of crystallization of respective gneisses gneisses and and migmatites. of ofNeillsville (Stop 4) Zircon Zircon from fromsyenitic syenitic augen augengneiss gneisssouth south Neillsville (Stop 4) yields an age an age of 2535 2535 ÷+ 10 10 m.y. m.y. This This zircon isisalso alsoconsidered considered primary primary igneous igneous zircon, to the augen zircon, indicating indicatTng that thatthe theprotolith protolith to the augengneiss gneisswas was probably probably aa syenitic syenitic pluton pluton intruded intrudedinto intoolder oldergneiss gneissabout about2535 2535 m.y. m.y. ago. ago. a.6 0.6 r----,.-----,---,.------,-------;r------.----------,----,.------, •• Pittsville quarry (VS75-10) Pittsville quarry (VS75—10) Hatfield Gneiss Hatfield Gneiss(VS77—8) (VS77-8) o o Linwood quarry quarry (VS75-6) Linwood (VS75-6) o o Neillsville Auqen Neillsville AuqenGneiss Gneiss (VS76-25) (Vs76-25) - + 0.4 - co M N J ;:::l ........ a _, I 0.'/ /' ttaa ==2815 2815 ÷~ 20 20 m.y. m.y. \.0 o :/ o c'1 N I 1.5 .D 0... 0.2 '-------'-----_ _- L_ _-----l.. 0.2 I 0 a 2 2 I 4 4 6 6 •, o'~ o 0 p'/;' 2. 2.0 / • tb t == 2535 10 m.y. m.y . b 2535 +~ 10 . L -_ _---L-_ _--L I 8 10 12 L -_ _---L------! 14 16 16 Pb-207/U--235 Pb-207/U-235 Figure Figure 2. 2. U-Pb U-Pb plot data for zircon zircon fractions fractionsfrom fromArchean Archean rocks rocks in plot of of data central Wisconsin(Van (VanSchmus Schmus and and Anderson, Anderson, 1977; 1977;DuBois DuBoisand andVan VanSchmus, Schmus, central Wisconsin 1978; Van 1978; Van Schmus, Schmus, unpub.). The The Hatfield Gneiss is from near Stop 7, and and Hatfield Gneiss from near Stop 7, the NeillsvilleAugert Augen Gneiss Gneiss is is from from near near Stop Stop 4. 4. The ages given are the Neillsville The ages given are for for least squares fits to least squares fits to the the data. data. Decay constants as Decay constants asinin Steiger Steiger and and JMger Jger (1977). 22 �So far no other other Archean Archean ages So far no ages have havebeen beenobtained obtainedfor forgneissic gneissic rocks rocks in amphiboittegneiss gneissatatBig Big Falls Falls in Eau Layered amphibolite Eau Claire Wisconsin. Layered central Wisconsin. County yields Penokean age County yields a Penokean ageofofabout about1850 1850m.y. m.y.and andisis indistinguishable indistinguishable from results tonalite atatLittle Little Falls, a few milesaway away (Figure (Figure from results for for foliated tonalite Falls, a few miles 3; see also Myers et al., 1980). In the case of the Big Falls zircon the In the case of the Big Falls zircon the 3; see also Myers et al., 1980). possibilitystill still exists are metamorphic, formedduring during Penokean possibility exists that that they they are metamorphic, formed thethe Penokean Orogeny 1980) andand thatthat thethe protolith the Orogenyabout about1850 1850m.y. m.y.ago ago(Van (VanSchmus, Schmus, 1980) protolith to the Archean, but but for for the thepresent presentaaPenokean Penokean primary gneiss is Archean, gneiss primary age ageisis preferred. Granitic gneiss gneiss near near Greenwood Greenwood (Locality with an an (Locality10) 10)also alsoyields yields zircon zircon with apparent age beginning to appear appear that apparent ageof of 1850 1850m.y. m.y. (Figure (Figure 3). Thus, Thus, it it is beginning the 1850 1850 m.y. ofofNeillsville are indicative indicative the m.y.ages agestotothe thenorth northand andnorthwest northwest Neillsville are So far far younger gneisslc gneissicterrane, terrane,formed formedduring duringthethe PenokeanOrogeny. Orogeny. So of aa younger Penokean no linebetween between no Archean Archeanages agesare areknown knowninincentral central Wisconsin Wisconsinnorth north of aa line Neillsvilleand andStevens Stevens Point, Point, so so that thatthe theArchean Archean terrane terrane of ofcentral centralWisconsin Wisconsin Neillsville may not north (Sims, (Sims, 1976). 1976). This may not be be continuous continuouswith with Archean Archeanrocks rocksto to the the north clearly represents aa fundamental fundamental problem, is hoped hoped present present and and future clearly represents problem, and anditit is WisconsinArchean Archean terrane terrane in in proper proper studies helptotoplace placethe thecentral centralWisconsin studies will will help and geographic geographic perspective. perspective. geologic and 0.35 O. 35 t--------r-----..,.-------r-----...,.--------::-~ * 1.9 I *Gneissic Falls (VS73—25A) Gneissic tonalite, tonalite,Little Little Falls (VS73-25A) o Trondjhemite, Trondjhemite, Chippewa Chippewa Falls (VS77-1A,B) (VS77-1A,B) amphibolite, Big Falls o Layered Layered amphibolite, Falls(VS78-6) (VS78-6) 1.8 .— reference chord = = 1850 1850 m.y. - o— 1.7 0.30 co c 1 (v, M c.'j N * . I :::J --... 1.0 1.5 a c'J N I .0 0.. 0.25 -0.25 _.- * 0.20 0.20 '---------l..-- / 0/ 0. Granite, Neillsville •S Granite, Neillsville(VS76-18; (VS76-18; Stop Stop 2) 2) *Gneiss near *Gneiss nearGreenwood Greenwood (VS76-22; (VS76-22; Loc. Loc. 10) 10) •N Granite, Lake Lake Arbutus Arbutus (VS76-26; (VS76-26; Stop Stop 5) 5) •£ Granite, Granite, Black Black River River Falls (VS73-22; Stop 8) (VS73—22; Stop 8) -..L ..I....- I 3.0 3.5 I 4.0 Pb-207/U-235 4.5 -L- -.l I 5.0 5.5 Figure 3. U-Pb U-Pbplo! plot of data Figure~. data for for zircon zirconfractions fractionsfrom fromPenokean Penokean plutonic and gneissic rocks rocks ln in the and gnelssic the western western part of ofcentral centralWisconsin Wisconsin (Van (Van Schmus, Schmus, 1980, unpub.). Note 1980, N~te t~at Granite appears appears to that the the Neillsville Neillsville Granite to be be distinctly distinctly older than than the the main maln suite sUlte ofofsamples. samples. Decay Steiger and and Decayconstants constantsasas in in Steiger Thger (1977). JMger (1977). 33 �Analytical Analytical results results have have also also been been obtained obtainedfor for zircon zircon from from three three of Penokean granitic The Lake Lake the the Penokean granitic plutons plutons along along the the Black Black River River (Figure (Figure 3). The Arbutus are apparently apparently part of of the themain main Arbutus and andBlack BlackRiver RiverFalls Falls granites granites are 1820-1850m.y. m.y. old old series 1820-1850 series ofofPenokean Penokean plutons plutons throughout throughoutWisconsin Wisconsin (Van (Van Schmus, 1980), butbut thethe results forforthe Granite suggest Schmus, 1980), results theNeillsville Neillsville Granite suggest;tit ;s is slightly older,extending extendingthe thespread spread ofofPenokean Penokean plutonic back slightly older, plutonic activity activity back as far as as about about 1875 1875 m.y. m.y. ago. ago. as far During tripwe we will willstop stopatatseveral severallocalities localities examine Duringthis this field trip andand examine Several aspects representativelithologies lithologies and structures of of this terrane. representative and structures terrane. Several aspects geology will be highlighted, highlighted, including including a) a) the thenature nature and and of the the regional regional geology will be variability theArchean Archean units, units,b)b)comparison comparison of of deformational deformational features features variability ofofthe Archean and Penokean units, chronologies of Archean andof of Penokean units, and andc)c) comparison comparisonofofrelative relative chronologies based on relationships andthose those basedononabsolute absolute agemeasurements. measurements. based on field field relationships and based age In addition scheduled In addition totodescriptions descriptionsforfor scheduledstops, stops,we wehave have provided provided location andbrief briefdescriptions descriptionsofofadditional additionallocalities localities in location information information and Black River River valley ininorder ordertotoprovide provideasascomplete complete aa guide guide as as possible possible the Black the Precambrian rocks. to these these Precambrian ITINERARY ITINERARY ITINERARY Stop Page 1. 1. 2. 3. 3. 4. 4. 5. 5. Gneiss Gne iss near nea r Greenwood Greenwood..... . . . . . . . . . . . . •. . . . . . . . . . . . . . . . . . . . . . 66 Neillsville Granite Neillsville Granite......................................... 99 Gneiss at Gneiss atHumphrey Humphrey Farm Farm...................................... 12 12 Neillsville NeillsvilleAugen Augen Gneiss, Gneiss, Miller MillerFarm Farm 15 Lake Arbutus Arbutus Granite .....•................................... 18 Lake 5a. LUNCH LUNCH 6. 6. East East Fork Fork Gneiss, Gneiss, Black Black River River ..................•.......••.... Hatfield Gneiss, Hatfield Gneiss,Lake LakeArbutus ArbutusDam Dam.........•.................. Black River River Falls Granite. Black Granite.................................... 7. 7. 8. 8. 44 20 20 22 22 27 27 �_ _ : .5 H. - \ I ci /' -- - Ls4 \HY CR \MOS - r '— — R4 0 ilo,d S dl rfl 1 /Ss - \- P' 't ; c/ — FIELD TRIP TRIP STOPS STOPS 55 - —I-: -— T200 -I dl 1.c. Lf 'J y [//5o 1, r :- ci "( - - �STOP STOP 11 TITLE: IITLE: Banded tonaliteatat Greenwood Bandedgneiss gneissand andfoliated foliated tonalite Greenwood Former pit,E½, E~,NW¼, NW\, Sec. Sec. 3, 3, T.26N., T.26N.,R.2W. R.2W.(Owen (Owen Former gravel gravel pit, l5-minute 15-minute topographic topocraphic quadrangle, quadrangle, Clark Clark County). County). Proceed about 0.1 0.1 ml. dirt road, about mi. south south from from County County Highway Highway GGonona adirt road, keepingtotoleft left when roadsplits, splits, to keeping when road to aa small small outcrop outcrop of banded gneiss. gneiss. Continue banded Continueapproximately approximately0.2 0.2mi. mi. further further short trail trail down southonondirt dirt roads andtrails. trails. A short south roads and down to to the the Black River Riverfrom fromthe thecrest crestofofaasmall smallhill hill leads to foliated Black leads to tonalite, and when when water are low low aa peninsula peninsula of tonalite, and water levels levels are The outcrop foliated foliated tonalite tonaliteand andbanded banded gneiss gneiss isisexposed. exposed. The is located jog of the ;s located at at aashort shortwestward westward jog the Black Black River. River. LOCATION: AUTHOR: AUTHOR: SUMMARY: SUMMARY: R. R. S. Maass S. Maass (1980) (1980) The thatcan can be be seen seen are banded banded tonalitic The four four major major lithologies lithologies that tonalitic gneiss, amphiboliticxenoliths xenoljthsininfoliated foliated tonalite, tonalite, and aplitic to gneiss, amphibolitic and aplitic to pegmatitic pegmatitic veins. veins. The The older folded, but butapparently apparently older units units are are isoclinally isoclinally folded, Onthis this basis only one major phase phaseof of deformation deformation is is present. one major present. On basis the the rocks rocks are tentatively are tentativelyinterpreted interpretedasasearly earlyProterozoic Proterozoic(Penokean) (Penokean) rather rather than than Archean in age. age. Archean 66 �DESCRIPTION: The The first first outcrop outcrop isis aa small smallpatch patch(2(2'xx4') 4') of of tonalitic tonalitic Theaxial axial plane planeof of the the fold banded gneiss banded gneisswhich whichhas hasbeen beentightly tightly folded. The the fold axis E. and strikes N. N. 200 20° E. 70° W. W.~ the axis trends trends N. N. 15° 15° E. E. and and and dips 70° plunges 60°. . plunges 1 From oldest oldest Four can be be distinguished Four lithologies lithologies can distinguished along alongthe the river. river. From gneiss,large large amphibolite amphibolitexenoliths xenoliths in to youngest youngest these these are: banded banded gneiss, foliated tonalite, tonalite, foliated foliated tonalite, tonalite,and and aplitic aplitictotopegmatitic pegmatitic granitic granitic foliated veins. The composition, faintly faintly banded,and and conconThegneiss gneissisis tonalitic tonal itic inincomposition, banded, tains long, tains long, thin thin lenses lenses of ofamphibolite. amphibolite. Isoclinal Isoclinal folds foldscan canbebeseen seen on on close examination. examination. Foliation strikes strikesN.N. 20° 20°E.E.and and dips dips 85° 85° W., W., and and aa weakmineral minerallineation lineationinin the the plane plane of of foliation foliation plunges weak plunges steeply steeply to to the the north. The The rock rock consists consists primarily of ofquartz, quartz,andesine andesine (An (An 34-38), 34-38), and and biotite, withminor minoramounts amounts ofofhornblende, hornblende, sphene, sphene, and and epidote. The biotite, with foliation, which which is is parallel paralleltotothe thebanding, banding, isiswell welldefined defined by by the the foliation, orientation of biotite orientation biotitegrains grains and, and, to to aalesser lesser extent extent by by the the orientation orientation of hornblende. hornblende. The with minerals minerals averaging averaging bebeThe gneiss gne-issisis fine-grained, fine-grained, with tween 0.25 0.25 and and 0.75 0.75mm. mm. tween 1 by 30 30') ) Amphibolite Amphibolite of of undetermined undetermined origin origin occurs occursasaslarge large (up (up to to 8' 8 1 by xenoliths in in the the foliated foliated tonalite. This xenoliths amphibolite does does not appear appear to This amphibolite be generation as as the the amphibolite be of the the same same generation amphibolite lenses lenses in in the thebanded banded gneiss, gneiss, The xenoliths xenoliths are are strongly based onstructural structural and based on and mineralogic mineralogic grounds. grounds. The stron91y but only only weakly weakly foliated, foliated,and andininsome some cases cases unfoliated. They lineated, but andesine (An contain approximately approximately 60% 60% hornblende, hornblende, 40% 40% andesine (An 4—5O), 46-50), and and very minor amountsofofbiotite biotite and minor amounts and quartz. quartz. Figure 4. 4. Photomicrograph tonaliteshowing showing Figure Photomicrographofoffoliated foliated tonalite The upper upper and andlower lower halves halves of of the granoblastic the granoblastic texture. The section are are composed composed primarily quartz and and feldspar~ section primarily of of quartz feldspar; aa biotite biotiteand and hornblende hornblende rich rich segregation segregation runs runs through through Foliation trends fromleft left the center center of the the section. section. Foliation trends from the to to right. 77 �The tonaliteconsists consistsofof2 2toto1010mm mm segregations segregations of Thegray grayfoliated foliated tonalite felsic minerals and and similarly similarly sized sized segregations segregations of rnaflc mafic minerals, minerals, in felsic minerals which the grains are are only only 0.25 0.25 toto11mm mm (Figure (Figure 4). The The major which the individual grains minerals andesine (An and hornblende, hornblende, with minerals are are quartz, quartz, andesine (An33-36), 33-36), biotite, biotite, and minor amounts ofof microcline, epidote,and andsphene. sphene. The which minor amounts microcline, epidote, Thefoliation, foliation, which strikes N. N. 20° 20° E. E. and and dips defined by dips 78° 78° W., W., isis defined by the the orientation orientation of individual biotite grains grains and and by by the the orientation strung-out felsic individual biotite orientation of strung-out mineral and mafic mineral mineral and mafic mineral segregatlons. segregations. Small Smallinclusions inclusionsofofdioritic dioritic material are mineral lineation material are also also flattened flattened inin the the plane planeofof foliation. foliation. A mineral in the the plane plane of of foliation foliationtrends trendsN.N.15° 15°E.E.and andplunges plunges 600. 60°. In In addition addition to the the amphibolite amphibolite xenoliths, xenoliths, the the foliated foliated tonalite tonalite concontains small small inclusions inclusions ofofbanded banded gneiss. gneiss. Although contact between between the the Although the contact banded andand thethe foliated not exposed, exposed, the bandedgneiss gneiss foliatedtonalite tonalite is not the available available outcrop the contact contact be be parallel or or subparallel subparallel totothe thebanding banding crop requires requires that that the and foliation the gneiss gneiss and the tonalite. Measureand foliation of the andthe thefoliation foliation of of the ments indicate these two the ments indicatethat thatthe thefoliation foliation in in these twounits unitsisis parallel; the foliation can be be seen seen to change slightly orientationover over large large expoexpofoliation can to change slightly in orientation sures of sures of either either unit. Aplitictotopegmatitic pegmatiticgranitic granitic veins Aplitic veins which thethe banded whichintrude intrude bandedgneiss gneiss and tonalite have have been been openly folded. The planes andfoliated foliated tonalite openlytototightly tightly folded. The axial planes of these these folds the foliation foliation ininthe thesurrounding surrounding unit. folds are are parallel parallel to the The gneiss at atthis may be Proterozoic in age; age; The banded banded gneiss thislocality locality may be early early Proterozoic support thissuggestion suggestioncomes comes from from aa U-Pb U-Pb (zircon) age age of ofapproximately approximately support for this 1850 gneiss at atLocality the south. south. 1850m.y. m.y.from frombanded banded gneiss Locality10, 10,only only 22 miles miles to the In structures ininthe thebanded banded gneiss gneiss appear In addition, structures appeartoto be bethe theresult result of only one one deformation, deformation, whereas whereas gneisses gneisses of know know Archean Archeanage, age, when whensuffisufficently exposed, exposed, reveal indicativeofofpolyphase polyphase deformation. deformation. reveal structures structures indicative Because of of thethe gneiss is ispoor, stated Becauseexposure exposure gneiss poor,itit cannot cannotbebedefinitively definitively stated that itithas hasbeen been deformed deformed only once; and further investigation, perhaps only once; and further investigation, perhaps radiometric, is necessary necessary before age can can be radiometric, is before its its age be stated stated with with certainty. tonalitesoccurring occurringthroughout throughoutcentral centralWisconsin Wisconsinhave havebeen been Foliated tonalites radiometrically radiometrically dated datedatat between between1850 1850and and1830 1830m.y. m.y.(Van (VanSchmus, Schmus, 1980). 1980). The tonalite atatGreenwood Greenwood isis similar composition, texture, Thefoliated foliated tonalite similar in composition, and styletotothose thosedated datedunits unitsand andisisprobably probablythe thesame same and structural structural style general age. If thisis is case, deformationoccurred occurredduring duringthethe Penokean If this thethe case, deformation Penokean general age. Orogeny, east Orogeny, as as has has been beendemonstrated demonstratedalong alongthe theWisconsin WisconsinRiver Rivertoto the the east (Maass andothers, others, 1980). (Maa ss and 1980). B 8 �STOP STOP 22 Neillsville NeillsvilleGranite Graniteand and Granodiorite Granodiorite TITLE: LOCATION: ,LOCATION: Quarry, NW¼, NWl.;;, NWl.;;, Sec.Sec. 20,20, T.24N., R.2W. (Neillsville 15Quarry, NW¼, T.24N., R.2W. (Neillsville 15minute topographic topographic quadrangle, minute quadrangle, Clark County). County). Approximately 1 mile south south of ofU.S. U.S.Highway Highway 10 10 on on east east side sideofofTower TowerRoad. Road. 1 AUTHOR: AUTHOR: R. Van R. Maass and and W. W. R. Van Schmus Schmus (1980) R. S. Maass The Granite isisa atypical typicalPenokean Penokean pluton, pluton, TheNeillsville Neillsville Granite although geochronologic andand structural is probably probably although geochronologic structuraldata dataindicate indicatethat thatitit is slightly older Penokean slightly olderthan thanmost mostofofthethe Penokean Granites Granites ininWisconsin. Wisconsin. At At this lineatiori, but location the the granite graniteshows shows pronounced pronounced lineation, butdoes does not not have have aa SUMMARY: SUMMARY: cross—cutting dacite dacite dike pronounced dike and and overlying overlyingMt. Mt.Simon Simon pronouncedfoliation. foliation. A cross-cutting sandstone are exposed here. here. sandstone are also exposed DESCRIPTION: A recent recent quarrying operation operation has has provided provided excellent excellentexposure exposure of pink pink Neillsville NeillsvilleGranite Granite,cray 9raygranodiorite, granodiorite,aadacite dacite dike, dike, and and the the Precambrian-Cambrian Granite isisexposed exposed Precambrian—Cambrianunconformity. unconformity. The TheNeillsville Neillsville Granite of the at the the southern southern end end of the quarry, quarry, both both in in place place and and as as large large fresh fresh blocks blocks in rubble The blocks blocks provide provide an an opportunity opportunity to examine the strucexamine the in rubble piles. The ture in andclearly clearly show showthat thatthe thegranite granite is is lineated, ture in three three dimensions dimensions and lineated, Measurement thelineation lirieation on but (Figure 5). 5). Measurement ofofthe on three three nonnonbut not not foliated (Figure parallel surfaces, parallel surfaces,combined combined with stereographic stereographic techniques, techniques, reveals reveals aa trend trend of N. N. 25° 25° E. E. and and aa plunge plunge of 82°. 82°. 9 �Figure 5. Two Twofaces faces of aa block Figure.5. Granite, block of of Neillsville Neillsvjlle Granite, approximately nornial approxlmately normal to each each other, other demonstrate demonstrate the the presenceofof lineation lineatjon and ~rese~ce and the the abse~ce absenceofoffoliation foliation in this ln thls unit. unit. Figure PhotomicrographofofNeillsville Neillsville Granite Figure 6. 6. Photomicrograph Graniteshowing showing The section section contains granoblastic texture. The granoblastic contains porphyroporphyroblastic microcline, microcline, large large strained strained quartz quartz grains, grains, and and fine-grained fine-grained quartz, oligoclase, oligoclase, and and microcline. microcline. The fine-grained free. fine-grained quartz quartz in in nearly nearly strain strain free. 10 �The is composed composed of subequal amounts microcline, and and The granite granite is of subequal amountsofofquartz, quartz, microcline, 2%biotite. biotite. Trace oligoclase (An (An 26-28); 26-28); and and approximagely approximagely 2% Trace minerals minerals include muscovite,epidote, epidote,chlorite, chlorite, sphene, sphene,apatite, apatite,allanite, allanite, zircon, clude muscovite, zircon, and trimodal, consisting consisting and opaque opaque minerals. minerals. The Thegrain grainsize sizedistribution distribution is trimodal, highly strained strained quartz; of 22 to to 33nh mm porphyroclastic porphyroclastic microcline; microcline; 1 to 22 mm mm highly and 0.1 to 0.75 rrim quartz, microcline, and oligoclase. and 0.1 0.75 mm quartz, microcline, and The grained The finer finer grained minerals minerals exhibit gently gently curved curved grain grain boundaries boundaries (Figure (Figure 6). The lineaThe linea— tion is defined defined by by the individual biotite biotite grains, grains, aligned aligned tion is the orientation orientation of of individual clusters of of biotite, clusters biotite,and and trains trains of ofquartz quartz grains. grains. The an The absence absence of of an observable foliation foliation on observable on the themesoscopic mesoscopic scale scale is is supported supported by by its itsabsence absence on microscopic scale. scale. on the the microscopic 1 Thenorthern northernend endofofthe thequarry quarryisisaamixture mixtureofofNeillsville Neillsville Granite The Granite and is istexturally andaagray graygranodiorite granodioritewhich which texturallyand andstructurally structurally identical identical to the granite. Unclear contactrelationships relationshipsmake make difficult totodetermine the Unclear contact it itdifficult determine which unit younger. Petrographic the which unit isisyounger. Petrographicrelationships relationshipsare areso sosimilar similar that the trimodal grain grain size distribution two units two unitsmay may be be comagmatic. comagmatic. The The trimodal distributionobserved observed in the the granite granite is is also also present present in in the the granodiorite. granodiorite. The The only only difference biotite, the is that that the the granodiorite granodiorite contains contains twice twice as as much much biotite, the oligoclase oligoclase is An An 28-30, 28-30, and and microcline is less lessabundant. abundant. microcline is Small patches patches of of an Small an oligoclase porphyry porphyry dacite dacitedike dikeare areexposed exposed along along An An approximately trend and from these these scattered scattered exN. N. 35° E. E. trend and steep steep dip can can be be determined determined from 350 posures. The dike contains contains aa foliation foliation which The dike which also also trends trends N. N. 35° E., and E., arid dips steeply; steeply; a mineral lineation lirieation in the dips a strong strong mineral the plane plane of foliation foliationplunges plunges Poor exposure exposure prevents prevents more moreexact exact structural structural measurements, steeply. Poor measurements, but the mineral lineation lineation in the the mineral the dike dike isisprobably probably parallel parallel totothe themineral mineral lineation in in the the granite graniteand and graniodiorite. granodiorite. the wall of the the 350 floor and and wall the central central portion portion of ofthe thequarry. quarry. The composed ofofquartz, and The dike dike is composed quartz,oligoclase oligoclase (An (An 28-30), 28-30), biotite biotite and The texture is trimodal, consisting of 1 to 6 mm minor 6 mm minor microcline. The texture is trimodal, consisting of 1 oligoclase porphyroclasts, porphyroclasts,0.25 0.25toto0.75 0.75mm mm quartz quartz in in trains trainswhich whichmay may represent represent the the remains remains of predeformational predeformational quartz quartz phenocrysts, phenocrysts, and and aa groundground·Microscopic deformation mass are less less than than0.1 0.1mm. mm. Microscopic massinin which which the the grains are and recrystallization textures identical to and recrystallization textures are are nearly nearly identical to those those in the the granite granite The foliation in the dacite is presumed to have formed and granodiorite. The foliation in the dacite is presumed to have formed and granodiorite. during the deformationthat thatleft left the during the same same deformation the granite granite and and granodiorite granodiorite ununfoliated, suggesting foliated, suggesting that that the themechanical mechanical properties properties of the the rocks rocks played played a very very siqnificant role role inindetermining determining the the final structural structuralexpression expression a The Neillsville Neillsville Granite that the the structural Granite demonstrates demonstrates that of the the event. event. The expressionofofthe theevent eventisis also also spatially spatially variable. expression variable. Two the Twomiles miles to to the northeast (Locality 11) northeast 11) the the granite granite crops crops out out ininaanumber number of older older Herethe the granite granite exhibits aa moderately well developed foliaquarries. Here moderately well developed foliation in in addition addition to to aa mineral mineral lineation. tion Zircon has beenseparated separatedfrom from sample Neillsville granite granite colZircon has been a asample of of Neillsville The zircons are euhedral, light brown lected this quarry. quarry. The zircons are euhedral, light brown inin color, lected at at this and stubby (length:width transmitted light and somewhat somewhat stubby (length:widthisis about about 2:1). 2:1). In In transmitted light they show normal igneous igneousgrowth growth zoning; zoning; older cores they show normal cores or oryounger younger overgrowths overgrowths are absent. U-Pb U-Pb analyses onontwotwo fractions analyses have havebeen beenperformed performed fractions so so far, far, are absent. and the the results results (Introduction, (Introduction, Fig. that the the Neillsville Neillsville Granite and Fig. 3) 3) suggest suggest that Granite is slightly granitic plutons so far far dated slightlyolder olderthan thanmost mostPenokean Penokean granitic plutons so dated in moreprecise preciseestimate estimateof of the the age must await await further further analyses, Wisconsin. A more age must analyses, but but a preliminary preliminary estimate estimate isis1875 1875 ±~ 25 25 m.y. m.y. 11 11 �------ -------- - - ---- - - STOP STOP 33 TITLE: LOCATION: LOCATION: Gneiss at atHumphrey Humphrey Farm Farm Gneiss SE~, Sec. l5-minute topographic topographic SE¼, Sec.22, 22,T.24N.~ T.24N., R.2W. R.2W.(Neillsville (Neillsville 15-minute quadrangle, Clark County). County). Discontinuous Discontinuous outcrop outcropfor for 0.5 ml. mi. quadrangle, along the east bank bank of Black River, River, approximately approximately 0.3 mi. mi. along the east of the Black west of State StateHighways Highways 73-95, 73-95,behind behindthe theThomas Thomas E.E.Humphrey Humphrey west of farm (ask (ask permission permission before farm before crossing crossing land). See Stop formap. map. See Stop 2 for AUTHOR: AUTHOR: R. S. S. Maass Maass (1980) (1980) R. SUMMARY: Three types banded gneiss, gneiss, SUMMARY: Three types of of gneiss gneiss are are present: present: tonalitic tonalitic banded mafic to ultramafic orthogneiss, orthogneiss, and "injection gneiss." gneiss." The The mafic to ultramafic andtonalitic tonalitic uinjection have been been subjected polyphase deformation units have subjected to to polyphase deformationand andinterference interference folds folds complex folding are present. The are present. The rocks rocks have havenot not been beendated, dated, but but the the complex folding Archean ages indicates Archean indicates agesfor forthe the older older units. DESCRIPTION: This ofthe theBlack BlackRiver Riverdisplays displaysa adiverse diverseand andcomplex complex This stretch of group of gneisses gneisses plus some some mildly deformed dikes the gneisses. gneisses. group mildly deformed dikes crosscutting the Three sets gneiss are are present; present; the the oldest oldestisisa banded a banded gneiss gneiss thought thought Three sets of gneiss be a paragneiss; paragneiss; the to be the next next youngest youngestisisan anorthogneiss orthogneissofofmafic mafictotoultraultramafic composition; composition; the the youngest youngest is an "injection "injectiongneiss" gneiss"formed formedwhen when leucoleucomafic is an tonaliteintruded intrudedthe theparagneiss paragneiss and and orthogneiss. orthogneiss. The The percentage tonalite percentageof of leucotonalite varies varieswidely widelyininthe thescattered scatteredexposures, exposures,from fromless lessthan than5% 5% tonalite up up to to 100%. 100%. A (now amphibolite) in the thebanded banded A narrow narrow gabbroic gabbroic dike dike (now amphibolite) in gneiss may maybeberelated related to to the gneiss the orthogneiss. orthogneiss. Both Both sets of ofgneiss gneisshave have been been intruded by by diabase diabase and dikes. All All units unitshave havebeen been intruded andporphyritic porphyritic dacite dikes, metamorphosed amphibolitefacies. fades. metamorphosed atatamphibolite Furthest upstream Furthest upstream(to(tothe thenorth), north), the the outcrop outcropconsists consistsofof thin thin to thickly layered banded banded gneiss composition containing containing quartz, quartz, thickly layered gneissofof tonalitic tonalitic composition oligoclase-andesine, banding is is due andhornblende. hornblende. The The banding due to oligoclase-andesine, biotite, biotite, and alternating rich layers with biotite biotite (+(+hornblende) hornblende) rich layers with biotite poor poor layers. layers. alternating biotite The earlist deformation discernible discerniblein inthethe bandedgneiss gneisshas hasproduced produced The earlist deformati6n banded folds, forming forming an an axial planar foliation. Although FF, folds isoclinal folds, axial planar foliation. Although boudinage structures from this thls event event are rarely rarely seen, seen, highly highlyattenuated attenuated boudinage are structures from are abundant. three dimensional dimensional exposure, not abundant. Due Duetoto the the lack lack of three exposure,itit is is not possible measure either axes or the the elongation elongation of of the the boudins. boudins. possible to measure either the the fold axes The foliation, which isisparallel parallelto to banding,has hasbeen been openly openly to to The foliation, which thethe banding, tightly folded the axial planes folds tightly folded during during F!, F? deformation; deformation; the planes of these these folds are at high angle fold axes axes are are not consistently F are at a high angletoto the the foliation. foliation. F oriented, but but their their general general trend trend Is is totohe thesouthwest southwest with with plunges plunges of oriented, 50° to 85°. 50° 85°. The banded end of of the theexposure exposure has has been been intruded intruded by by The bandedgneiss gneissatat this this end to 88inch inchwide wide mafic mafic dike dike which which appears appears to have have been a 66 to beenoriginally originally aa medium totocoarse-grained now aa fine-grained amphibolite. medium coarse-gralnedgabbro, gabbro,but butisis now fine-grained amphibolite. gabbroicdike dike is truncated The dike has been been openly The gabbroic truncated by by aa The dike has openly folded. The 12 15 foot wide wide unfolded unfolded dike which which was 12 to to 15 wasformerly formerly aa diabase, diabase, but but is 12 12 �now also aa fine grained now also grained amphibolite. amphibolite. Despite amphibolite facies Despite the the amphibolite metamorphism, chilledmargins marginscan canstill still be metamorphism. chilled be recognized. recognized. The unThe dike dike is Unfoliated, but minerallineation lineation exists. exists, trendfoliated. butaamoderately moderately well developed developed mineral trending S. S. 500 50° W. 60°. W. and and plunging plunging 60°. The best best exposure exposureofofthe the injection injection gneiss The gneiss occurs occurs a short short distance distance The medium-grained medium-grainedleuco-tonalite leuco-tonalite phase which has has intruded downstream. The phase which the gneiss and andmafic mafic and and ultramafic ultramafic orthogneiss of the banded banded gneiss orthogneiss isiscomposed composed of nearly equal of quartz equal amounts amounts of quartz and and oligoclase (An (An 27-29), 27-29).and and minor minor (2-3%) biotite. The Theoligoclase oligoclase is 1 to 55 mm, andthe thequartz quartzisis 0.1 0.1 to (2-3%) biotite. mm. and but the the quartz appears may 2 rum, mm, but appears granulated; granulated; it it mayhave haveonce oncebeen been the thesame same size as size as the the oligoclase. The now amphibolite, The orthogneiss, orthogneiss, which which is is now amphibolite, is generally gabbroic in composition, but the generally gabbroic in composition, but the leuco-tonalite leuco-tonalite also also contains contains inclusions of ofultraniafic ultramaficgneiss gneisswhich whichconsists consistsof of muchasas99% 99% hornblende. hornblende. as as much Thefoliation foliation in The in the the injection injectiongneiss gneiss isischaotic; chaotic;blocks blocks ofofthe theortho orthoand and paragneisses (withtheir their earlier have paragneisses (with earlier foliation) foliation) havebeen beenrotated rotatedinto intorandom random orientations, and thefoliation foliation in the orientations, and the the leuco-tonalite leuco-tonalite swirls swirls in in almost almost all Thefoliation foliation inin the directions. The theleuco-tonalite leuco-tonaliteappears appears to to be be aa primary primary flow flow foliation. 1 displaying Figure 7. 7. Highly contorted contorted banded banded gneiss gneiss displaying Figure the fol ding of the interference due to the 'folding the axes axes of interference patterns due isoclinal F1 Fl folds. 13 �STOP STOP 44 TITLE: LOCATION: Neillsville AugenGneiss Gneiss Neillsville Augen Black River River at Miller Black MillerFarm. Farm. NW¼, NW~, NW~, Sec. NW¼, Sec.26, 26, T.24N., T.24N., R.2W. (Neillsville 15-minutetopographic topographic quadrangle, quadrangle, Clark Clark (Neillsville 15-minute County). Approximately StateHighway Highway 73-95, 73-95, Approximately 0.1 mi. west west' of ofState 0.1 mi. on the east of the on the east bank bank of the Black Black River. River. Follow Follow a a small small ravine ravine located 0.1 0.1 mi. south farmhouse to the located south of of the theMiller Miller farmhouse down down to the Black River, River, then Black then turn turn upstream; upstream; outcrop outcrop isissemi-continuous semi-continuous for 0.3 0.3 mi. mi. upstream. upstream. See Stop for map. map. See Stop 22 for AUTHORS: AUTHORS: R. Van R. Maass and and W. W. R. Van Schmus Schmus (1980) (1980). R. S. Maass SUMMARY: The Augen Gneiss SUMMARY: The Neillsville Neillsville Augen Gneissisis aa spectacular, spectacular, strongly strongly foliated rock with microcline to 55 cm rock is rock with microcline porphyroclasts porphyroclasts up up to cm in length. length. The The rock syenitic inincomposition composition and and is is interpreted interpretedtotobebederived derivedfrom fromananArchean Archean pluton that was intruded into the pluton was intruded the older older gneisses gneisses of the the region. region. It It is is 10 m.y. m.y. old old and, Archeanrocks rocksidentified identified so and, thus, thus, the the youngest youngest Archean so far 2535 + 10 in central central Wisconsin. Wisconsin. -I- Figure 8. 8. Neillsville NeillsvilleAugen Augen Gneiss. Gneiss. Both Both highly Figure deformed and undeformed microc1ine porphyrodeformed and nearly nearly undeformed microcline porphyroclasts occur in in aa fine—grained fine-grained matrix quartz, clasts occur matrix of of quartz, biotite, biotite,and and feldspar. feldspar. 15 15 �The spectacular NeillsvilleAugen Augen Gnelss, Gneiss, containcontainThe spectacularsyenitic syenltlc Nelllsvllle ing microcline porphyroc1asts crops out along along the the ing microcTine porphyroclastsupuptoto Scm 5 cminin length, length, crops Black River behind behindthe the Miller Miller farm. Black River farm. Many microcline Manyofofthe theoriginal orgtnal microcline have retained their phenocrysts are phenocrysts arehighly highly deformed, deformed,but butsome some have retained theirinitial initial euhedral shape shape (Figure (Figure 8). However, euhedra1 However,thethemajority majorityofofthose thosethat thatstill still appeareuhedral euhedralare areinternally Internally fractured. The appear The porphyroc1asts comprise porphyroclasts comprise as much as 50% 50%ofof the the gnelss. as much as gneiss. The The matrix, which the the minerals minerals are are matrix, in which than 0.2 m mm inindiameter, diameter, consists consistsofofapproximately approximately equal equal generally less than generally less amounts ofofmicroc1ine, biotite,and anduntwinned untwinned amounts niicrocljne, orthoclase, orthoclase, quartz, biotite, plagioclase. DESCRIPTION: DESCRIPTION: addition totothe thepreviously previouslymentioned mentioned minerals, minerals, the the gneiss gneiss conconIn addition tains minor minor quantities ofofepidote epidoteand and sphene sphene and andtrace trace quantities quantities of muscovite, apatite, allanite, allanite,zircon, zircon, opaque minerals. minerals. muscovite,chlorite, chlorite, apatite, andandopaque Quartz grains are coarser coarser than of the the matrix matrix minerals minerals are are Quartz grains that that are than the the rest of found inin "trains11 "trains" which which may may represent the remains of formerly frequently found represent the remains of muchlarger larger quartz quartz grains. Mortar much around the the rnicrocline microc1ine Mortar texture around porphyroc1asts evident, but butrecrystallization recrystallizationhas hashealed healed the the porphyroclastsisisstill still evident, fragments, and and most have gently curved curved grain grain boundaries. boundaries. fragments, most matrix matrix minerals minerals have producedmyrrnekite myrmekite around around the marmarRecrystallizationduring duringdeformation deformationproduced Recrystallization gins of the gins of of some some of the porphyroclasts. porphyroc1asts. The strike thegnelss gneissisisbetween between Thepredominant predominant strikeofofthe thefoliation foliation ininthe N. 75° 75° E. E. and and N. and the 87° to the the south. south. A A strong N. N. 85° 85° E., E., and the average averagedip dipis is 87° mineral lineatlori in the plane of the foliation trends S. 800 W. and mineral lineation in the plane of the foliation trends S. 80° W. and plunges 55° on on the the average, average, but but extremes plunges 55° extremes inin the the plunge plunge of 42° 42° and and 68° 68° have have been been recorded. Three shearing cut across across the Three small small zones zonesof of intense intense shearing inch in width. butthey theyare areonly only8 8Inches, inches,4 4inches, inches,and and 11 inch width. foliation, foliation, but They between N.N.55° three Theystrike strike between 55°E.E.and andN.N.65° 65°E.E.and anddip dipvertically. vertically. All three zones zones have havebeen beenrecrystallized. recrystallized. Zircons have have been Augen Zircons beenextracted extractedfrom fromananoutcrop outcropofofthe the Neillsville Neillsville Augen Gneiss ofHighway Highway 73, just justnorth northof of Cunningham Creek. Creek. Gneiss on on the the west west side of Cunningham The zircons zircons are are brown, euhedral and andshow showigneous igneouszoning; zoning;there thereisis no no evieviThe brown, euhedral analyses on on three dence coresorormetamorphic metamorphic overgrowths. overgrowths. U-Pb U-Pb analyses denceof of relict relict cores an age age of of 2535 2535 ++ 10 age is interpreted interpreted fractions of zircon zircon yield yieldan fractions of 10 m.y.; m.y.; this age as the age ageofofcrystallization crystallization of the as the the protölith proto1ithofofthe thegnelss gneiss and and Is is the the The highly highly deformed youngest Wisconsin. The deformed youngest Archean Archean age agemeasured measuredsosofar far in in Wisconsin. shows thethe Archean state of of this thisrock rockclearly clearly showsthat that Archeanterrane terranewas was subjected subjected major tectonism tectonism in late or orpost-Archean post-Archean time (e.g., <<2535 2535 m.y. m.y. ago). ago). to major in late time (e.g., It notknown known for forcertain certainwhere where ininthe theInterval interval2500-1850 2500-1850 m.y. m.y. ago ago It isisnot that this thisdeformation deformationoccurred occurred(Penokean (Penokean or orpre-Penokean?). pre-Penokean?). Upstream thethe Neillsville a series ofofthin Upstreamfrom from Neillsvllle Augen AugenGneiss, Gneiss, a series thintoto thickly thickly Some to niafic mafic composition composition isisexposed. exposed. Some layered gneisses of intermediate to layered gneisses of intermediate of the the units units are areporphyroclastic, porphyroclastic,but butthe theporphyroclasts porphyroc1asts are are smaller smaller than than those in the augen augen gneiss; they are are far farless lessabundant, abundant, and and they they are are generalgeneralthose in the gneiss they Someofofthe the units, units, both than microcline. microcline. Some both porphyroporphyroplagioclase rather rather than ly plagioclase clast abundant clast bearing bearing and and porphyroclast porphyroc1ast free, free,contain contain abundantmetamorphic metamorphic hornhornthe gneiss gneiss at this this end end of ofthe theoutcrop outcrop makes makes it blende. The The layering layering of of the it 16 �possible to study the style of detail than possible to study the of deformation deformation in more more detail than in the the unlayered augen gneiss. Numerous Numerous small scale andand large scale tight unlayered augen small scale large scale tightfold~, fold, and aa few few isoclinal isoclinal folds, observed Fere. and folds,can canbe be observed here. axes trend S. 80 Their axes trend S. 80 550, W. and and plunge between W. between 500 50° and and 55°, which is parallel totothe thetrend trendand andplunge plunge which is parallel theaugen augen gneiss. gneiss. The axial planes are parallel of the the mineral mineral lineation lineation ininthe The axial planes are dominant direction to the dominant to the directionofoflayering, layering,which whichisisparallel parallel to to the the foliation foliation in the structuresindicate indicatethat that all all units the augen augen gneiss. gneiss. These These structures units were were affected by folding event. fected by the the same same folding event. Downstream from Neillsville Augen AugenGneiss Gneiss biotite schist Downstream from thethe Neillsville is isa abiotite (see Locality Locality 14 (see 14 for for description), description),and andthen thenmore more interlayered interlayered porphyroclast porphyroclast bearing and andporphyroclast porphyroclastfree free units units (see (see Locality 15) 15) similar similarininappearance appearance bearing These upstream upstreamand anddownstream downstreamunits units probably probably represent to those those upstream. upstream. These sedimentaryand andvolcanic volcanic rocks rocks into into which gneiss protolith protolith was which the augen augen gneiss was sedimentary intruded. Near the middle middleof of the the exposure, the Neillsville Neillsville Augen Near the exposure, the Augen Gneiss Gneiss is by aa sizeable sizeable body body of of coarse-grained coarse-grained granitic graniticaugen augen gneiss. gneiss. The The intruded intruded by augen areonce onceagain againmicrocline, microcline,but but they they are are only only half as augen are as large large as as those those in the the older older augen augen gneiss, gneiss, and and the the younger youngerunit unit contains contains much muchless lessbiotite. biotite. Themineral minerallineations lineations in both The both units units are are equally equallywell welldeveloped developed and and parallel to each each other; however, however, the the younger youngerunit unit is only only weakly weakly foliated foliated ororeven even whether present ititisisnotnotclear clear whetherthetheyounger youngerunit unitwas wasememunfoliated. At present placedafter after the the foliation-forming foliation-forming state prior to the placed state of of deformation, deformation, and and prior the lineation-forming stage; it was priorto to the the entire was emplaced emplaced prior lineation-forming stage; or or whether whether it deformation and simply simply responded respondeddifferently differently due dissiniideformation and due to mechanical mechanical dissimiThe granitic granitic augen gneiss is unlike larities. The augen gneiss unlikeany any known known early Proterozoic Proterozoic rocks and and is is petrographically sorriewhat similartoto the the Neillsville Neillsville Augen somewhat similar Augen rocks Gneiss; an Archean Archean age age seems this isisthe thecase, case, Gneiss; therefore an seemsmost mostlikely. likely. If this the structural difference difference isis attributed attributedtotothe themechanical mechanical properties properties of the the rock, the rock, since since structures structuresobserved observed are are thought thought totohave have formed formed during during Penokean Orogeny final the the Penokean Orogeny(see (see final discussion). 17 �STOP STOP 55 TITLE: Lake Arbutus Arbutus Granite Lake NW~, NW~, Sec.Sec. 19,19, T.23N., 7~-minute topoNW¼, NW¼, T.23N.,R.2W. R.2W.(Hatfield (Hatfield 7½-minute Abandonedbridge bridge abutment graphic quadrangle, Clark Clark County). County). Abandoned abutment graphic quadrangle, LOCATION: LOCATION: 0.25 mi. mi. south south of ofState StateHighway Highway 95 95 bridge bridge over Black Black River, River, 0.25 west bank Black River. River. 2 mi. mi. north north ofofLake Lake Arbutus. Arbutus. west bank of of Black AUTHORS: AUTHORS: R. S. R. S. Maass Maass and and W. W. R. R. Van Van Schmus Schmus (1980) (1980) The undeformed, late-tectonic The Lake LakeArbutus ArbutusGranite Graniteisisaa typical typical undeformed, late-tectonic Penokean granitethat that is is intrusive Archean Penokean granite intrusiveinto intothethe Archeangneiss gneisscomplex. complex. StJM!'IARY: SU~1r'1ARY: The Lake LakeArbutus ArbutusGranite Granite is is aa medium-grained reddish granite granite The medium-grained reddish that contains feldspar, andand andesine contains quartz, quartz, perthitic perthiticalkali alkali feldspar, andesine(An (An 31-32) 31-32) in the ratios 1:1.5:1. the approximate approximate ratios DESCRIPTION: The which range range from from 0.5 0.5toto3 mm, 3 mm,have haveragged ragged boundaries boundaries The feldspars, feldspars, which and fractured internally (Figure (Figure 9). 9). A few few quartz quartz grains grains andare aresli9htly slightly fractured which havesurvived surviveddeformation deformation relativelyintact intact are are as as large large as as 22 mm, m, which have relatively but most most of the quartz quartz has has been been granulated less than than 0.5 0.5 imi. mm. Quartz but of the granulated to to less 18 �>~ L .' '~;';\~'ii/¥""i"*i; ......" Figure Figure 9. 9. Photomicrograph Photomicrograph of of Lake Lake Arbutus Arbutus Granite showing granulatedand andrecrystallized recrystallized quartz showing granulated quartz and and moderatelyfractured fractured feldspar. The moderately cloudy The feldspar feldspar is cloudy due sericftization. due toto sericitization. grain grain boundaries boundaries are are generally generally gently curved, curved, indicating indicatingmoderate moderate post post deforrnationalrecrystallization. recrystallization. The deformational free, hut but conconThegranite graniteisis biotite free, approximately 1% 1% chlorite which probably probably represents represents retrograded retrograded tains approximately chlorite which biotite. Alteration of of opaque opaque minerals, the minerals,and andsericitization sericitization of the feldspar feldsparmay may be be weathering weatheringphenomena. phenomena. Although microscopic microscopic textures textures indicate that was Although thatthe thegranite granite wasdeformed deformed andrecrystallized, recrystallized, no foliation ororlineation and no foliation lineationcan canbe be detected detected on on either the microscopic The granite granite appears the microscopic or or mesoscopic mesoscopic scale. The appears to to have have been been emplaced during latestages stagesof of Penokeandeformation deformationand andmetamorphism. metamorphism. emplaced during the late Penokean Zircons ofofthe Zircons were were separated separatedfrom froma asaMple sample thegranite granite collected collected at the of the on the the opposite opposite (east) (east) side side of the the base base of the old old bridge bridge abutment abutment on the river. The The zircons are are euhedral euhedral,, brown brown inin color, and and exhibit exhibitigneous igneous analysisofofone onefraction fraction (Introduction, (Introduction, Fig. zoning. U-Pb U-Pb analysis Fig. 3) 3) indicates indicates that the the Lake Lake Arbutus Arbutus Granite Granite belongs belongs to to the themain main population populationofofPenokean Penokean granite plutons and is about 1840 ± 20 m.y. old. A more percise plutons and is about 1840 + 20 m.y. old. more percise estimate estimate the age age will will have have to to await await additional additionalanalyses. analyses. of the 19 �STOP 6 STOP 6 TITLE: East Fork Gneiss Gneiss East Fork NW~, NW~, Sec.Sec. 4, 4, T.22N., (Hatfield topoNW¼, NW¼, T.22N.,R.2W. R.2W. (Hatfield 7.5-minute 7.5-minute topois along quadrangle, Jackson Jackson County). County). Outcrop Outcrop is along north north graphic quadrangle, shore East Fork the bridge bridge shoreof of the the East Forkof of the the Black Black River, River, east east of the on East Fork Fork Road. Road. on East LOCATION: LOCATI ON: AUTHOR: R. R. S. Maass (1980) (1980) S. Maass from most mostof of the the other SUMMARY: SUMMARY: The gneiss The gneiss exposed exposedhere hereisisdifferent different from gneisses inin the amphibole rich rich rather rather than than biotite gneisses the region regioninin that that ititisisamphibole the gneiss is cut rich. Both present, and and the gneiss is cut by by Both F F1 and F? F,,folding folding are present, 1 and post-deformat1onal dikes and of of diabase. diabase. post-deforrnatlonal d'tkes of of granite and In contrast contrast to to the theother otherbanded banded gneisses gneisses in region, the the In in the region, Someof of the East Fork East ForkGneiss Gneissisisamphibole amphibole rich richrather ratherthan thanbiotite biotite rich. Some layerscontain containasasmuch muchasas70% 70% hornblende. hornblende. In In addition addition to to melanocratic layers DESCRIPTION: hornblende, gneiss contains contains quartz quartz and and andesine andesine (An (An 33-35), 33-35), and and minor minor hornblende, the the gneiss amountsofofmicrocline, microcline, chlorite, amounts chlorite,epidote, epidote,sphene, sphene,and andopaque opaque minerals. minerals. 20 �The middle section of the outcrop is banded gneiss exhibiting large scale tight folds which are attributed to F deformation. The gneiss has been intruded by a diabase dike (which is nw amphibolite) and by a porphyritic dacite dike which is very weakly foliated, but strongly lineated. The foliation in the dacite strikes N, 25° E. and dips vertically, and the mineral lineation trends S. 25° W. and plunges 86°. The 0.5 to 3 mm phenocrysts in the dacite consist of euhedral microcline and andesine and slightly fractured quartz. Grain size in the recrystallized matrix is less than 0.1 mm. Near the downstream end of the exposure the banded gneiss becomes more felsic than usual. Biotite is less abundant, and hornblende rarely ac-irnpanies the biotite. There are small lenses and thin layers of quartzite, wh,ch are not present elsewhere in the gneiss. The banding becomes extremely contorted in this vicinity. F deformation is responsible for the random orientation of the axial plnes of folds, but the folding of axes of isoclinal F1 folds has resulted in interference patterns (Figure 7) and may be interpreted in a number of ways. The four most likely explanations are: 1) F1 folding was inhomogeneous, resulting in curvilinear xes; 2) F2 foldig was inhomogeneous; 3) some intermediate deformation folded the axes of the F folds, prior to F axes (remember that F, axes upstream are very inconsstent in orientatign). At this locality he second explanation is preferred since interference patterns are only ob- served where F? deformation has become unusually convoluted, and inhomogeneous F deformationis also the simplest explanation for the inconsistent oientation of F fold axes upstream. Why folding is so complex only at on small portioh of the outcrop is open to speculation, but one possiity is that we are in the core of a large unrecognized tight fold 1 the Hatfield Gneiss (Stop 7) exposure is complete enough to see an auiple of extreme contortion in the core of a large tight fold. 14 �Green subhedral euhedral hornblende hornblende ranges ranges from from 0.5 0.5 rum rnm to 22 miii; mm; Green subhedral to to euhedral the quartz feldspar are the quartz and and feldspar are 9enerally generally smaller, smaller,from from0.25 0.25toto1.5 1.5mm. rom. Chlorite is present some samples samples ininamounts amounts up up toto5%. 5%. It occurs as as layered layered present ininsome It occurs a~gregates, and and as as an product ofofhornblende, hornblende. The parallel aggregates, an alteration alteration product epidote gneiss varies epidote content content of of the the gneiss varies appreciably, appreciably, from from trace trace quantities, to as as much much as as 5%. 5%. In certain specimens specimens the so thoroughly thoroughly In certain the plagioclase plagioclase is so almostunrecognizable unrecognizable in thin saussuritized and saussuritized andsericitized sericitized that that ititisisalmost in thin section. The Theorientation orientation of of quartz quartz and andchlorite chlorite gra{ns grains defines definesthe thefoliation, foliation, while quartz, chlorite, chlorite,and and hornblende hornblende elongation while quartz, elongation defines defines the the lineation. lineation. Quartz crystallographically Quartzhas hasbeen been crystallographjcallyoriented orientedduring duringrecrystallization recrystallization to the extent extent that that nearly all quartz the nearly all quartz grains grains in some exsomethin thin sections sections go go to to extinction tinction atatapproximately approximately the the same same time. A narrow narrow granite dike dike composed composed of A of subequal subequalamounts amountsofofquartz, quartz, plagioclase, and alkali feldsparhas has intruded intrudedthe thebanded banded gneiss. gneiss. The clase, and alkali feldspar The dike dike also contains approximately approximately 1% 1% chlorite and trace trace amounts amounts of epidote. epidote. The contains chlorite and The granite differsfrom fromboth boththe theLake Lake Arbutus Arbutus Granite Granite (Stop (Stop 5) 5) and and the the Black Black granite differs River Granite (Stop that ititappears appears less less deformed, deformed, but but this River Falls Falls Granite (Stop 8) 8) in that in thin section. only apparent apparent in section. is only A medium-grained medium-graineddiabase diabasecontaining containingpyroxene, pyroxene,plagioclase plagioclaselaths, laths, A sphene, the banded banded gneiss. Based Based on on sphene, and and opaque opaqueminerals minerals has has intruded intruded the scattered exposure, the wide dike dike scattered exposure, the diabase diabase appears appearstotobe beaa 30 30to to 40 40 foot wide with dike is unfoliated, with chilled chilled margins. margins. The The dike unfoliated,unlineated, unlineatect,and andshows shows no no The original original minerals signs deformation inin thin section. section. The mineralshave have been been signs of of deformation The diabase may extensively extensively altered altered toto chlorite~ chlorite, epidote, epidote, and and sericite. sericite. The may be the gabbro gabbro at Stop Stop 7, 7, since since both both are are structurally structurallyand andmineral— mineralbe related related to the ogically similar. thegneiss gneissproduced produced an F folding folding ininthe Isoclinal F, anaxial axial planar planar foliafoliawhich is pafallel to to the the banding, banding, except except in hinges where where itit tion tion which is pai"allel in fold hinges transects banding. banding. The Thefoliation foliation has has been been subsequently subsequentlytightly tightly folded folded F deformation. deformation. FF2 fold axes axes are are nearly nearly horizontal, horizontal, trending trending both both during F2 axes is 25°; N. 70 E. E.2 and and S. S. 70° 70° W. W. The maximum plunge 25°;the themean mean he maximum plungeof of the axes N. 70 axial plane striking plunge is Synformed structures structures with an an average average axial plane striking plunge is 0°. Synformed N. 70° E. and dipping at atthis N. 70° E. and dipping 70° 70°N.N. predominate predominate thislocality. locality. �STOP STOP 77 TITLE: TITLE: LOCATION: LOCATION: AUTHORS: AUTHORS: Hatfield Gneiss,Lake LakeArbutus ArbutusDam Dam Hatfield Gneiss, SE¼, 3, T.22N., SE~, Sec. Sec. 3, T.22N., R.3W. R.3W. (Hatfield (Hatfield7½-minute 7~-minute topographic topographic quadrangle, Jackson Jackson County). County). Outcrop along the Black River quadrangle, Outcrop along the Black below the east half of Arbutus Dam. below the east half of Arbutus Dam. Approach mi. Approachisis on on 0.2 0.2 mi. long gravel gravel road long road that intersects intersects Clay Clay School Road'0.15 mi. School RoadO.15 west tracks. Additional outcrop west of of Green Green Bay Bay and and Western Western RR RR tracks. outcrop occurs mi.downstream downstream from fromdam. dam. occurs for for0.7 0.7mi. W. Van Schnus Schmus and S. l1aass Maass (1980) (1980) W. R. R. Van and R. R. S. SUMMARY: The the The main mainoutcrop outcrop area area immediately immediately below belowthe the dam damisis one one of of the SUMMARY: largest, ififnot notthe thelargest, largest, outcrops outcrops of of Archean Archeanrocks rocksininWisconsin. Wisconsin. The unitisisthe theHatfield Hatfield Gneiss,ananinterlayered interlayeredsequence sequence of of quartzoquartzoprincipal unit Gneiss, The rocks are as and minor amphibolite. The rocks are interpreted as feldspathic gneisses feldspathic qneisses and minor amphibolite. a metavolcanic metavolcanic sequence sequence that that was was formed formed 2815 2815m.y. m.y. ago ago and and deformed deformedatat least twice, with withthe thelatest latest deformation andmetamorphism metamorphism occuring deformation and occurirtg during during the Post-deformational cross-cutting cross-cutting mafic Penokean Orogeny, ago. Post-deformational mafic Penokean Orogeny, 1850 1850 m.y. m.y. ago. dikes dikes are are also also present presentatatthis this locality. locality. 22 22 �tI .....V .r: .., :>. f.il m ,.... :n 'M ::.:: 0 <:( p:) ....l ~ 0 >-:> (j) (j) ..... Q) ~ t:) "0 ...... Q) .... "-< +" oj ::r: r.r; oj CJ <:( 0-':.- !#:~ri (j) D. ..... (j) "0 Q) ::: ...... ..... I Q) +" t:) Q) (j) ...... .....U .., 0 (j) N·.... +" (j) 0 ,D ..... .r: c '"' ~ rot:) a oj ~ D. E h . Cambrian—Recent Cover 'M (j) 0:: I C oj h Q) > 'EU "' 0 ,D oj U I] {rf~~ (j) Q; .0<: 'r< "0 (j) UJ ro ,D ro 'r< 0 Met a—gabbro U 0.. 0 +-' VI E ro Cl +-' Diahase dikes Q) r--.. V1 :::l '-' c: Geologic map of Archean bedrock exposed south of Arbutus Dam. (Stop 7) < Hatfield Gneiss ,D c:: 1.::;?:] :>. t- (:0 Granitic Gueiss to Cue iss b ::> Quartzo-feldspa thic Geology by J. DuBois 1976-77 t- V) ;:J C h ,D ,D oj bJ) I ro +" (j) ::;; :::l .D s... c:( 40 ..c +-' :::l 0 V1 LIJ ~ "II ?~ ~ "'0 Q) V1 0 0.. X Q) ~ U 0 Fold Axes n UJ 0 ~ s... "'0 Q) .D s:: ro Q) ..c U s... c:( 0 c 4- C'J 0 0.. ro E ..., (j) (j) ~ U or- 01 0 r- 0 Q) G z 0 Q) .r: ..., \.. Figure 10. c.D s... ( :::l 01 or- L1.. �The principal unit exposed exposed (Figure the Hatfield HatfieldGneiss, Gneiss, an an The principal unit (Figure 10) 10) is the interlayered sequence ofofgranitic tona1iticgneiss gneisswith withconcordant concordant interlayered sequence granitic to to tonalitic muchofofthe theoutcrop outcropthe the layers layers are are 0.1 Over much 0.1 to to layers of amphibolite. amphibolite. Over layers of 3 cm pink to to gray, graY9 quartzo-feldspathic quartzo-feldspathic qneiss. gneiss. In some some parts cmthick, thick, pink the layers massive gneiss. gneiss. the layers are are thicker, thicker,approaching approaching several several meters meters of ofmassive Folding andfoliation foliation are Folding and are best best displayed displayed ininthe thethinner-banded thinner-banded portions. portions. The and consists consists Thequartzo-feldspathic quartzo-feldspathic gneiss gneiss has has aa granoblastic grarioblastic texture and of subequal subequal amonts and microcline. Mafic amontsofofquartz, quartz, plagioclase, plagioclase, and minerals represent represent less less than than 10% 10% in most most instances. instances. Normative abundances abundances minerals based on chemical analyses show that the quartz quartz abundance abundance is approxapproxbased on bulk bulk chemical analyses show that the plagioclase/orthoclase ratios vary vary from from about about imately constant constant and imately and that that plagioclase/orthoclase 1:1 (adamellite) to plagioclase (tonalite). 1:1 (adamellite) to primarily primarily plagioclase (tonalite). Theamphibolite amphiboliteisis interlayered interlayered with the The the quartzo-feldspathic quartzo-feldspathic gneiss gneiss and consists primarilyofofhornblende hornblendewith withabout about20% 20% epidote. epidote. The and consists primarily amphibolite has has been with the gneiss gneiss and and is is amphibolite beendeformed deformedalong along withthe therest rest of of the interpreted as originally originallyconcordant. concordant. The assemblage isisinterThe entire entire assemblage interinterpreted as preted as as having having formed formed from from an sequence ofof volcanic an interlayered iriterlayered sequence volcanic flows, sills (DuBois VanSchmus, Schmus, 1978). 1978). The The major metametapyroclastics, pyroclastics, ororsills (DuBois andandVan morphism currently amphibolite facies. Relict morphism currentlyrecorded recordedbybythe therocks rocksisis amphibolite pyroxene pyroxene has hasbeen beenfound foundinin some someofof the the quartzo-feldspathic quartzo-feldspathic gneiss gneiss samples, samples, suggesting either primary volcanic pyroxene or an earlier, higher grade suggesting either primary volcanic pyroxene or an earlier, higher grade period ofofmetamorphism. metamorphism. The Gneiss has event TheHatfield Hatfield Gneiss hasbeen beensubjected subjectedtotoananisoclinal isoclinal folding event an an axial planar foliation the layering, (F,) (F1) which whichproduced produced axial planar foliationparallel parallel to to the exept the foliation foliation transects in fold foldhinges hinges where where the transects the the layering. layering. The except in The foliation was then then tightly openly folded folded during during FF deformation; deformation; the the foliation was tightly totoopenly axial planes of these thesefolds foldsare areatathigh highangles angles foliation. F, to toth~th foliation. folds axial planes of F are rarely visible, areare conspicuous are visible,butbutF2F2folds folds conspicuouswherever wherever the the bandig banding is readily readilyapparent. apparent. Lineations (fold axes, crenulations, mineral mineral lineations) lineations) and andfoliafoliaLineations (fold axes, crenulations, tion were thegneiss gneissalong alonga a0.4 0.4mi. mi. long long stretch stretch of the were measured measured ininthe the river. Poles Poles toto foliation define define aa S axis which is identical axis which is essentially identical main grouping grouping of the the linear linear structural structuralelements elements to the the orientation orientation ofofthe themain (Figure 11). Fold (Figure Fold axes, the two two axes, when whenplotted plottedseparately, separately,fall fall into the groups in the quadrantofof the the stereonet, stereonet, with with the groups in the southeast southeast quadrant the vast vast majority majority plotting ininthe themain main group. group. groupof of F F1 fold axes in the A group fold axes in the core core of aa large were large tight FF fold were l clotted from the the rest rest of of th9 plotted separately separately from th~ linear linear structural structural eements. etrments. The The folding folding in in this this vicinity vicinityisishighly highlycomplex, complex, resulting resulting in in numerous numerous and and diverse interference interference patterns patterns from from the the folding folding of diverse of F, F axes. axes. Figure Figure 1? 12 illustrates illustratesone one of of the the simple simple interference interference patterns patterns.l The The axes of these axes these F1 quadrants F, folds folds plot plot ininallallfour four quadrantsofofthe thestereoniet stereonet with with plunges ran~­ olunges rang— irig from horizontal to vertical. ing from horizontal to which would would indicate aa later Girdles which simple folding pattern simple folding pattern of of the the F1 Fl axes axes do do not not exist, exist,and and the the interference theresult resultof of inhomogeneous deforpatterns are are therefore therefore believed believed totohebe the patterns inhomogeneous mation inin the the core core of of the mation the F2 F fold. 2 24 �N N ineation lineation poles to to foliafion poles foliation 485 485measurements measurements contours 0.2,1,3,5,10,15,20,25% 0.2,1,3,5,10,15,20,25%per per1% 1% area area 884 measurements 884 measurements contours % per contours 1,3,5,7,9 1,3,5,7, 9 % per 1% I% area area Lower hemisphere stereGgraphic projectionsofofstructures structures in Lower hemisphere stereographic projections the the Hatfield Hatfield Gneiss. Gneiss. (left) (left)Lineations Lineations defined defined by by fold fold axes, axes, crenulations, crenulations, and mineral elongations. The mean orientation of the lineaUons is S. and mineral The mean orientation of the lineations is S. 84° 84° E. E. with aa plunge plunge ofof51° 51°ESE. ESE. (right) Plot Plot of of poles poles to to foliation foliation yields yields aa mean for ~ trending S. 84° E. with with aa plunge of 52° ESE,virtually virtually identmean for trending S. 84° E. plunge of 52° ESE, identorientation for for the ical to to the the mean mean orientation the lineations. Figure 11. 11. Photo of the Photo of the Hatfield HatfieldGneiss Gneissshowing show~ng interference pattern pattern due duetoto folding folding of of the interference the axis aX1S of of an an The interference interference pattern pattern occurs isoclinal F1 Fl fold. The occurs in the core F2 fold. the core of of aa large, large, tight F2 12. Figure 12. �is inhomogerieous thisrelatively relatively small deformation is inhomogeneous in inthis small Although FF? deformation as a whole deforarea the outrop; outcrop; the the outcrop outcrop as whole exhibits exhibitshomogeneous homogeneous deforarea of the mation, as demonstrated demonstrated tightdistribution distribution of 94.5% the linear mation, as by by thethe tight 94.5% ofof the structural elements. structural elements. F fold axes axes are are never never exposed exposed in in 33dimensions dimensions F the anomalou anomalou~ area discussed), thus thus their their trend trendand and (except in (except in the area just just discussed), ageofofFF, folding is unclear, hut F2 folding plunge are are unknown. unknown. The The age folding unclear, but F folding 1 2 probably Penokean Penokean (see discussion). is probably (seefinal final discussion). Zircon has beenseparated separatedfrom from tonalitic layer of has been a atonalitic of the the gneiss gneiss on on Zircon the west bank bank of the the Black Black River, River,about about0.6 O.nmimidownstream downstrenm from from the the dam. dam. the west The zircons are The zircons are brown, brown, euhedral euhedral crystals crystals with withnormal normal igneous igneous zoning zoning and and no signs of of significant or relict relict cores. no signs significant overgrowths overgrowths or cores. U-Pb U-Pb analyses on on several show that unitisisessentially essentially sameage age(2815 (2815 several fractions fractions show that this unit thethe same + 20 m.y.) as gneissesinin central central Wisconsin (Introduction, 20 m.y.) as other other Archean Archean gneisses Wisconsin (Introduction, Ng. 2). This age ageisis interpreted interpretedasasthe thetime timeofofcrystallization crystallization (vol~ig. 2). This canism) the protolith protolith of canism) ofof the of the the Hatfield HatfieldGneiss. Gneiss. Rb-Sr Rb-Sr analyses analyses from several samples collected in the several samples collected the area area ofofStop Stop7 7and andfurther furtherdownstream downstream do not plot coherently isochrondiagram, diagram,indicatinq indicatinqpartial partial resetdo not coherently on on an an isochron resetting during ting duringsubsequent subsequentmetamorphism. metamorphism. However, However, these theseare are no no indications indications of crustal crustal history historyexceeding exceeding 2.8 2.8 b.y. b.y. 26 �STOP 8 STOP 8 TITLE: LOCATION: LOCATION: Black River River Falls Granite Black Granite NE¼, SE¼, Sec.15, 15,T.21N., T.21N.,R.4W. R.4W.(Black (Black River River Falls 15-minute NE~, SE~, Sec. 15-minute Outcrop occurs topographic quadrangle, Jackson Jackson County). County). Outcrop occurs along along topographic quadrangle, river andnorth north of State riverdownstream downstream from from dam dam and State Highway Highway 54. 54. .1 IA AUTHORS: AUTHORS: R. R. / S. Maass and and W. W. R. R. Van Van Schmus Schmus (1980) S. Maass SUMMARY: The typical,largely largely undeformed TheBlack BlackRiver RiverFalls Falls Granite Granite is is aa typical, undeformed SUMMARY: late-tectonic Penokean Penokean granite intrusive into intothe theArchean Archean gness gneiss late-tectonic granitethat that is is intrusive complex. DESCRIPTION: The The Black Black River River Falls Granite Granite crops crops out outbelow below aapower power gengenerating dam the heart heart of Black River Falls. The erating dam inin the Black River The pink, pink,medium—grained medium-grained biotite granite quartz,alkali alkali feldspar, biotite graniteconsists consists ofofsubequal subequal amounts amounts ofofquartz, feldspar, and normally and normally zoned zoned andesirte—oligoclase andesine-oligoclase (An (An25—33). 25-33). Biotite Biotitecomprises comprises approximately5%5% theunit, unit, 'and andretrograde retrogradechlorite chlorite deriverl derived from from biotite biotite approximately of ofthe constitutes another 1%. 1%. Trace and constitutes another Trace minerals minerals include include sphene, sphene,allanite, allanite, and epidote. 27 �PhotomicrographofofBlack BlackRiver River Falls Falls Granite. 13. Photomicrograph Granite. Figure 13. Nearly euhedral, andesine-oligoclase is Nearly euhedral, zoned zoned andesine-oligoclase is surrounded surrounded by fractured feldspars andrecrystallized recrystallized by fractured feldspars and and granulated granulated and grain is is visible visible ininthe thecenter center of of the the quartz. A biotite grain figure. Thefeldspars, feldspars, which whichoften often exhibit exhibit nearly The nearly euhedral euhedral outlines (Figure (Figure Thealkali alkali feldspars 13) range 13) range from from 11 to 44mm. mm. The feldspars consist consist of of both both microcline microcline and perthite, perthite, with Granulated and andrecrystallized recrystallized and with microcline microclinedominating. dominating. Granulated quartz from 0.1 0.1 to 1 mm, mm, have which quartz grains, grains, from havebeen beenderived derivedfrom from quartz quartz grains which were originally as Anhedraltoto subhedral subhedralbiotite biotite is often were originally as large largeasas2 2mm. mm. Anhedral often partially ororcompletely in chlorite. Selective partially completely replaced replaced in Selective sericitization sericitization of the the feldspars feldspars has has resulted resulted in in extensively extensively altered alteredplagioclase, plagioclase,modermoderately altered altered perthite, perthite,and and nearly nearly unaltered unaltered microcline. microcline. 1 On both microscopic and and mesoscopic Falls On both the the microscopic rnesoscopicscales, scales,the the Black Black River River Falls Granite unfoliated and Granite appears appears unfoliated and unlineated, despite despite microscopic microscopic textures textures which that itithas hasbeen been deformed deformed and the which indicate indicate that and recrystallized. recrystallized. As As with with the LakeArbutus ArbutusGranite Granite (Stop (Stop 5), 5), this Lake thisunit unitwas wasprobably probablyemplaced emplaced during during the late the latestages stages ofofPenokeari Penokean deformation. deformation. ti-Pb analyses on on two two zircon zircon fractions U-Pb analyses fractions('Ian (VanSchmus, Schmus, 19R0) 1980) indicate that the the Black Black River River Falls Granite Granite is is also also part partofofthe themain main population population of Penokean granitic plutons plutons and, and, like the Granite, is Penokean granitic the Lake Lake Arbutus Arbutus Granite, is about about 1840++ 20 20 m.y. m.y. old. 1840 28 �SUPPLEMENTAL LOCALITIES LOCALITIES SUPPLEMENTAL Page Page tonalite, Greenwood Park Park Foliated tonalite, Greenwood 31 31 10. Granitic gneisssouth southofofGreenwood Greenwood Granitic gneiss 31 11. Neillsville Granite, Granite, Neillsville 32 32 12. Gneiss, granite, sandstone sandstone at Sunburst Sunburst Village Village................ Gneiss, 32 32 13. Gneiss and and granite granite at Snyder Dam Gneiss 33 14. and gneiss, Schist and gneiss,Cunningham Creek 33 15, and gneiss, Schist and gneiss, Black River south of Cunningham Creek .. 34 16. Banded gneiss, Banded gneiss, Big Big Spring 34 17. Gneiss Gr,eiss at Morrison Morrison Creek 35 18. Gneiss, Gneiss, Black Black River RiveratatPowerhouse Powerhouse 35 19. Banded quarry near nearPowerhouse Powerhouse Bandedgneiss, gneiss, quarry 37 37 20. Gneiss Gneiss at Halls Halls Creek Creek 37 37 21. Gneiss Black River River Falls Gneissand andtonalite, tonalite, Black 38 38 22. Quartzite, Silver SilverMound Mound....................................... 38 23. Jackson County Iron Mine Jackson County Mi ne. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 39 9. 29 31 �___ _ __ ___ ,W \ Mill '¼3 15 14 JJ - ? )u '/ i1- k kI' -. ' -J-'L- (cLco rv H: R2\. - wgc-,j WI'c;>c-.4.{~ Joy bg • 887 __ r- - I":f~ '~l l \ ~ . ;::. SUPPLEMENTAL LOCALITIES LOCALITIES SUPPLEMENTAL 30 --—_- j1 1W o ÷ �SUPPLEMENTAL LOCALITIES SUPPLEMENTAL LOCALITIES tonalite, Greenwood Park Park Foliated tonalite, Greenwood LOCALITY 9: LOCALITY NW~, Sec. NW¼,NE~, NE¼, Sec.34, 34,T.27N., T.27N., LOCATION: R.2W. R.2W. (Owen (Owen15-minute 15-minute topographic topographic quadrangle, Clark County). See Stop 1 for locality quadrangle, County). See localitymap. map. Exposureisis on on the the west west bank bankof of the the Black Exposure Black River, which which requires requires aa ~/alk wading the the Black Black River River from from walk across across aa farmer's farmer's field field ororwading Greenwood Park. Greenwood 1 AUTHOR: R.S. Maass (1980) (1980) R.S. Maass EIYESCRIPTION: The foliated tonal ite atatGreenwood Parkisis nearly nearly identical OESCRIPTION: The foliated tonalite Greenwood Park to the the foliated foliated tonalite tonaliteatatStop Stop 1, 1,1.2 1.2miles miles to to the the south. south. The to The major difference is that better developed difference is that the the foliation, foliation,which which isisslightly slightly better developed here, here, has beenopen opentototightly tightly folded. has been folded. A fold axis axis trending trendingS.S.700 70 0W. W. and and plunging plunging 75° hasbeen beendetermined determined localitybybyplotting plotting poles polestoto foliation foliation on 75 0 has for for thisthis locality on Mineral lineation lineation in in the aa stereonet. Mineral the foliated foliated tonalite tonalitecould could not not be be accurately measured measured lackofofproper properexposure, exposure, accurately duedue to to lack butbut it it isis roughly roughly parallel to the statistically statisticallydetermined determined fold axis. axis. Granitic ap1ites similar similar totothose those to the Granitic aplites at Stop 1 Small faults with movement Stop 1 have have intruded intrudedthe thefoliated foliated tonalite. Small faults with movement on the the order of on of aafew few inches inches strike strikebetween betweenN.N.5Q0 60 0 E. E. and and N. N. 700 70 0 E. E. and and dip steeply. dip steeply. LOCALITY 10: LOCALITY LOCATION: Granitic Gneiss south southofofGreenwood Greenwood Granitic Gneiss SW~, NW~, Sec.Sec. 15,15, T.26N., R.2W. (Neillsville 15-minute topotopoSW¼, NW¼, T.26N., R.2W. (Neillsville 15-minute for locality See Stop 11 for graphic quadrangle, quadrangle, Clark Clark County). County). See locality graphic map. Rockisis exposed exposedinin bottom bottomof of old sand gravel quarry. map. Rock sand and and gravel Turn west junction ofofState StateHighway Highway 98 98 with Turn west on on gravel gravel road road at at junction ends after1.0 1.0mi.; mi.; turn turn north north for 0.1 State Highway Highway 73. 73. Road Road ends after 0.1 mile quarry. mile to quarry. AUTHOR: W.R. Van Van Schmus Schmus (1980) AUTHOR: W.R. DESCRIPTION: DESCRIPTION: The The exposed exposedbedrock bedrock consists consistsofofgranitic granitic grieiss gneiss with lenses lenses granitic gneiss of amphibolite; amphibolite; a tonal tonalite dike cuts cuts the the gneissic gneissic rocks. rocks. The The granitic gneiss ite dike consists consists of fresh fresh microcline, microcline, plagioclase, plagioclase, and and quartz; quartz; the amphibolite amphibolite is mostly fresh fresh hornblende hornblendewith withquartz quartzand andplagioclase; plagloclase;the thetonalite tonalite consists mostly consists U—Pbanalysis analysis of of of quartz, quartz, plagioclase, plagioclase, minor minor microc1ine, microcline, and andbiotite. biotite. U-Pb one zircon zircon fraction gneiss one fraction from from the thegranitic granitic gneisshas hasyielded yieldeda Penokean a Penokean age age (Introduction, Fig. 3), suggesting suggesting that locality are are (Introduction, FIg. that the the rocks rocksatat this this locality not not part part of ofthe theArchean Archean terrane terrane to to the the south. south. 11 �LOCALITY 11: LOCALITY S. Sec. 10, 10, T.24N., T.24N., R.2W. R.2W.(Neillsville (Neillsville 15-minute S. half, half,SW¼, SW~, Sec. 15-minute topoaraphic topographic quadrangle, quadrangle, Clark Clark County). County). Several quarries Several granite quarries exist in in this thisarea; area;see seeStop Stop 22for fordetailed detailedmap. map. LOCATION: LOCATION: AUTHOR: AUTHOR: Granite, Neillsville Neillsville Granite, R.S. R.S. Maass Maass (1980) (1980) TheNeillsville Neillsville Granite of old DESCRIPTION: The Graniteisisexposed exposed in inaanumber number of old quarries quarries to the Neillsville. The graniteininthis this vicinity differs to the northwest northwest ofofNeillsville. The granite differsfrom from that that at Stop Stop 22 in in that that ititisisfoliated, foliated, whereas whereas the the granite granite at at Stop Stop 22 is not. not. In In all all other otherrespects respects the the granites granites are are identical, identical,and and there there isisno no reason reason to believe that they believe they are are not not the the same same unit. Exposures Exposures here badly here are are too too badly weathered accuratelymeasure measure foliation, but are that weathered totoaccurately thethe foliation, but best best estimates estimates are (+ 100) dips 300 itit strikes strikesNN450 45 0 W 10 0 ) and and dips 30° (+100) (~lOO) to the the southwest. southwest. W (~ LOCALITY LOCALITY 12: LOCATION: LOCITION: AUTHOR: AUTHOR: SunburstVillage; '/illage; gneiss, Sunburst gneiss, granite, granite,sandstone sandstone N. edge edge SW¼ SW~ and S. S.edge Sec.Sec. 15, 15, T.24N., R.2W. (Neillsville N. and edgeNW~, NW¼, T.24N., R.2W. (Neillsville 15-minute topographic topographic quadrangle, quadrangle, Clark County). See Stop Stop 22 for for 15-minute County). See for detailed To get get to the detailed location locationmap. map. To the outcrop, outcrop, go go one one block block south of of U.S. Hwy.1010inin Neillsville Neillsville totoSunburst south U.S. Hwy. Sunburst Village VillageSchool. School. The outcrop outcrop is is both The both north north and and south south of of the theU.S. U.S. Hwy. Hwy. 10 10 bridge bridge over the Black Black River, River, on on the the east east bank. bank. over the R.S. Maass Maass (1980) (1980) R.S. The outcrop outcrop consists consists of massive quartzo-feldspathic gneiss, DESCRIPTION: The massive quartzo-fe1dspathic gneiss, DESCRIPTION: bandedgneiss gneiss tonalitic composition, maficgneiss, gneiss,and andananaplitic aplitic granitic banded ofoftonalitic composition, mafic dike. The gneiss and and banded banded gneiss gneiss appear appear very The massive massivequartzofeldspathic quartzofeldspathic gneiss similar to to the the Hatfield HatfieldGneiss Gneiss (Stop (Stop 7). 7). Isoclinal F1 Fl folds folds and and tight tight F2 F2 F1 folds occur occur throughout throughout the the gneiss. gneiss. F axes cannot cannot be be measured, measured, but but F2 F2 l fold axes axes the northwest northwest and and plunge axes can; can; they they trend trend to to the plungealmost almostvertically. vertically. Themafic mafic gneiss gneiss occurs occursasas large large blocks blocks and and thick thick concordant (?) layers The concordant (?) layers in the morefelsic, felsic, qneiss. Although the the mafic layers in the surrounding, surrounding, more gneiss. Although layers have have been been metamorphosed amphibolitefacies, facies, they they do metamorphosed to toamphibolite do not appear appear as as highly highly deformed deformed or as thoroughly thoroughlyrecrystallized recrystallized as as the the rest of as of the the gneiss. gneiss. One One possibility possibility is of sills, that they they are are remnants remnants of sills,but butthey theyhave havenot notbeen beenstudied studiedininenough enough detail to towarrant warrant any any firm firmconclusions. conclusions. A fine-grained fine-grained biotite-poor granite intruded into the granite dike dike has has been been intruded the banded mineral lineation lineation in banded gneiss. A mineral in the the dike dike trends trends S. S. 450 450 W. and plunges plunges W. and approximately 800,which whichisisclose close enough enoughtotothe theorientation orientation of of the approximately 80°, the F2 F2 fold fold axes to to imply the FF2 folding event and the formation axes imply aa connection connection between between the folding event and formation 2 lineation in of the the mineral mineral lineation in the the granite. granite. The Cambrian CambrianMt. Mt.Simon SimonFormation Formationisis exposed exposedononthe the south south side side of The of U.S. U.S. Hwy. the east east of of the the Black Black River. River. Hwy.10, 10,just just to to the 32 32 �LOCALITY LOCALITY 13: 13: T.24N.,R..3W. R.3W. (Neillsville 15-minute topotopoT.24N., (Neillsville 15-minute graphic graphic quadrangle, quadrangle, Clark Clark County). County). See map. SeeStop Stop22for for locality locality map. Outcrop on the the north northside sideofof U.S.Hwy. Hwy.10,10,along along Wedges Creek, Creek, Outcrop is is on U.S. Wedges just justbelow belowSnyder SnyderDam. Dam. NE~, NE¼, NE~, NE¼,Sec. Sec. 10, 10, LOCATION: LOCATION: AUTHOR: AUTHOR: Gneiss and SnyderDam Dam Gneiss and granite granite atatSnyder R.S. Maass R.S. Maass (1980) (1980) DESCRIPTION: The gneiss below Snyder any other gneiss gneiss The gneiss below Snyder Dam Damisisunlike unlike any observed this point point in observed upuptotothis in the the Black Black River River region. region. It It isiswispy wispy rather rather than banded, banded,and anditit is highly and quartz quartz rich. The than highlymicaceous micaceous and The average average quartz content is over over 50%, 50%, with biotiteand andmuscovite muscovite being being the the other other major major content with biotite constituents. Microcline content content isisgenerally generallybelow below10%. 10%. The The gneiss contains aa well contains well developed developed foliation foliation and and lineation, lineation, but but due due to to its itsunlayered unlayered nature it isis not nature it not possible possible to detect detect isoclinal FF folds, even even though though the the unit was probably subjected subjected to to this was probably this deformation. deformation. Ti~ht Tijht F2 F2 folding folding has has folded folded the the foliation, during F1 foliation,which whichisispresumed presumed to to have have formed formed during F folding. A pink biotite-poor granite pink biotite—poor granite which which has hasintruded intrudedthe the gneiss gneiss isis unfoliated, unlineated, and and as as best best can can be be determined determined in thin section, section,undeformed. undeformed. The The unlineated, in thin age granite is is unknown; unknown; it may be slightlyyounger younger than than the the ageof of the the granite it may be just just slightly 1850 may be be related related to to the the 1765 1765 m.y. m.y. old old granites granites 1850m.y. m.y.old oldgranites, granites, or or ititmay found throughout throughout the the state. found The CambrianMt. Mt.Simon SimonFormation Formation overliesthe the gneiss gneiss and and the the granite The Cambrian overlies along the the west westbank bank ofofWedges Wedges Creek. Creek. LOCALITY LOCALITY 14: 14: LOCATION: AUTHOR: AUTHOR: Schist and gneiss, gneiss,Cunningham Cunningham Creek Creek Schist and NW~, Sec.Sec. 26, 26, T.24N., R.2W. (Neillsville l5-minute topoNW¼,SW~, SW¼, T.24N., R.2W. (Neillsville 15-minute graphic quadrangle, Clark Clark County). County). See graphic quadrangle, SeeStop Stop22for for detailed location Outcrop is is east locationmap. map. Outcrop east of of State State Hwy. Hwy. 73-95, 73-95, on on the the north bank bank ofofCunningham Cunningham Creek. Creek. R.S. Maass R.S. Maass (1980) (1980) DESCRIPTION: Biotite schist,quartzofeldspathic quartzofeldspathicgneiss, gneiss,and andaugen augen gneiss gneiss are are Biotite schist, exposedaa short short distance exposed distance upstream upstream from from the theHwy. Hwy. 73-95 73-95 bridge bridgeover overCunningham Cunningham Creek. The Thebiotite biotite schist primarilyofof quartz quartzand andbiotite, biotite, with schist isis composed composed primarily with subordinate feldspar. Quartzofeldspathic subordinate bands and and augen augen bearing bands bands are are Quartzofeldspathic bands have been interlayered with schist. All ofofthese theseunits units have beenmeta— metainterlayered with the the biotite biotite schist. morphosed totoamphibolite morphosed amphibolitefacies faciesand anddisplay display granoblastic granoblastic textures. Augen Thebiotite biotite gneisses those described described at Stop Stop 44 also also occur occur here. here. The qneissessimilar similar to those beenisoclinally isoclinally folded schist and and interlayered gneisses gneisses have have been folded during during F1 F] F9 axes plunge deformation, folded during during F9 F? deformation. deformation. F fold axes plunge deformation, and andtightly tightly folded steeply inin all directions, trendisisS.S. 50 520W. steeply directions, but but the the dominant dominant trend W. with with aa plunge plunge of 80°. 80 0 . �LOCALITY 15: 15: LOCALITY Center Sec. Sec. 27, 27, T.24N., T.24N., R.2W. R.2W.(Neillsville (Neillsville 15-minute Center 15-minute topographic topographic quadrangle, Clark County). SeeStop Stop22for for detailed location quadrangle, County). See locationmap. map. LOCATION: AUTHOR: AUTHOR: Cunningham Schist and and gneiss, gneiss, Black BlackRiver Riversouth southof of CunninghamCreek Creek R.S. R.S. Maass Maass (1980) (1980) DESCRIPTION: A diverse diverse group group of schists, schists,gneisses, gneisses,and andmetavolcanic metavolcanic rocks rocks occurs along long stretch stretch ofofsemi-continuous semi-continuous outcrop outcrop along along the occurs along aa 0.6 0.6 mi. ml. long Black The same samebiotite biotite Black River, River,downstream downstream from from the themouth mouth ofofCunningham Cunningham Creek. Creek. The schist with interlayered interlayered quartzofeldspathic quartzofeldspathic units Locality 14 14 schist with units as as that that at at Locality appears at the themouth mouth ofofCunningham Cunningham Creek. Creek. Metamorphosed Metamorphosed basaltic basalticand anddacitic dacitic appears dikes crosscut crosscut the the schist; the dikes the basalt basaltisisnow nowan an amphibolite. amphibolite. Mafic banded banded gneisses gneisseswith with augen augenbearing bearinglayers layersand andaugen augen free freelayers layerssimilar similar to those those upstreamfrom fromthe theNeillsville Neillsville Augen upstream Augen Gneiss Gneiss (Stop (Stop 3) 3) crop crop out out mear mear the the major major bend in the Black an augen augengneiss gneiss containing bend in Black River. River. Further downstream, downstream, an feldspar porphyroclasts porphyroc1asts up up to to 44cm cm isisexposed. exposed. The encountered is The next next unit encountered a gneissconsisting consistingofof sharply sharply defined defined quartzite, quartzite, quartzofeldspathic, a banded banded gneiss quartzofeldspathic, and amphibolite layers. The The final final outcrop and amphibolite outcrop is is aalayered layered nietadacite metadacite to metarhyolite sequence, whichononthe thebasis basis of of structural metarhyo1ite sequence, which structural grounds grounds appears appears to be be younger than the gneisses. The dacites dacites and andrhyolites rhyolites are are porphyritic, younger than gneisses. The containing quartz quartz and and feldspar porphyroclasts porphyroclasts up up to 2mm 2mm inin aa matrix grains containing matrix of grains metavolcanicrocks rocks have havebeen beensignificantly significantly granulated less than than 0.1 0.1mm. mm. The The metavolcanic granulated and moderatelyrecrystallized. recrystallized. The and moderately which varies varies from from 11 mm mm to cm The layering, layering, which to 22 cm thick, strikesN.N.40° 40 0E.E.and anddips dips68° 68 0NW. NW. thick, strikes LOCALITY 16: LOCALITY NW¼,SE\, SE¼, Sec. T.23N.,R.3W. R.3W.(Hatfield (Hatfield 7½-minute NW\, Sec. 25,25,T.23N., 7~-minute topographic quadrangle, Clark County). quadrangle, County). The The gneiss along the the gneiss crops crops out out along western shore of Lake Arbutus at Big Spring; a small island western shore of Lake Arbutus at Big Spring; a small occurs offshoreatatthis this locality. locality. See occurs offshore See p. 30 general map map 30 for for general location. LOCATION: AUTHOR: Banded gneiss, Spring Banded gneiss, Big Spring R.S. Maass Maass (1980) (1980) R.S. DESCRIPTION: The bandedgneiss gneissatatBig BigSpring Spring is is mineralogically The banded mineralogicallyand and structurally structurally similar similartotothe theEast EastFork Forkgneiss gneiss at atStop Stop 6. 6. Exposure Exposure here here is poorer than at at Stop Stop 6,6, but but this is;sa amore poorer than more accessible accessible location. The melanoThe nielanocratic bearing, just as cratic layers layers ofofthe thegneiss gneissare arehornblende hornblende bearing, as in in the the East East Fork Fork 0 0 gneiss. F? F9 fold fold axes trend N. 85° E. and S. 85° W. with plunges ranging axes N. 85 E. and S. 85 W. with plunges ranging up up 0 to 35° 35 in in bach ~ach direction. 34 34 �LOCALITY LOCALITY 17: Gnelss at Morrison Gneiss Morrison Creek Creek LOCATION: NE corner, 22, T.22N., T.22N., R.3W. R.3W. (Hatfield (Hatfield7½-minute 7~-minute topographic topographic NE corner, Sec. Sec. 22, occurs in bed Outcrop occurs bed of of Morrison Morrison quadrangle, Jackson County). County). Outcrop quadrangle, Jackson Creek, downstream fromCounty CountyHwy. Hwy.KKbridge bridgeover over the the creek. See Creek, downstream from map, page page30, 30,for for general general location. map, AUTHORS: AUTHORS: W.R. Van and R.S. R.S. Maass W.R. Van Schmus Schmus and Maass (1980) DESCRIPTION: The pink, fine-grained fine-grained quartzofeldspathic quartzofeldspathic gneiss gneiss that Theunit unit is aa pink, is similar Black River downstream similartotomuch muchofofthe thegneiss gneissalong alongthethe Black River downstream from from Arbutus Arbutus Dam. Rb-Sr Creek do Dam. Rb-Sr analyses analyseson onsamples samplesofofgneiss gneissfrom fromMorrison 4orrison Creek do not not define isochron, but but they they appear to be less disturbed good isochron, appear to be less disturbed than than those those from from near near aa good Arbutus Damandand consistent withananage age 2.8b.y. b.y. for for the Arbutus Dam areare consistent with of of2.8 the gneiss. gneiss. It It appears that that the Penokean wereless less severe severe here here with appears the effects effectsof of Penokeanmetamorphism metamorphism were regard to to chemical alteration. The The gneiss gneiss does does have haveaa pronounced pronouncedfoliation, foliation, chemical alteration. regard 0 roughly transverse to the stream with a general strike of N. 160 W. and roughly transverse to stream with general strike of N. 16 W. and aa 0 dip of dip of 78° 78 E. E. LOCALITY LOCALITY 18: 18: LOCATION: Gneiss, on Black Black River Gneiss, Powerhouse Powerhouse on NW~, Sec. sec. NW¼, Sec.16, 16,and andSE~, SE¼, sec.9,9,T.22N., T.22N., R.3W. R.3W.(Black (Black River River Falls Semi— l5-minute topographic quadrangle, Jackson County). 15-minute quadrangle, Jackson County). Semicontinuous exposureoccurs occursononboth bothbanks banksofofthe theBlack BlackRiver River for for continuous exposure powerhouse. See See map map on on upstream of of the thepowerhouse. approximately 11 mile upstream following for detailed detailed location. following page page for AUTHOR AUTHOR R.S. Maass Maass (1980) (1980) PS. DESCRIPTION: DESCRIPTION: This isan anexcellent excellentexposure exposureofof Archeangneisses gneissesand andpresumed presumed This is Archean early Porterozoic Porterozoic andesitic andesitic and and dacitic daciticdikes, dikes,plus plus a gabbroof of unknown age. age. a gabbro unknown The The gneisses gneissesare arethinnly thinnly to massively massively layered, layered, ranging ranging inincomposition composition from from granitic to to dioritic, dioritic,with withtonailtic tonalitic to granodioritic compositionsdominating. dominating. to granodioritic compositions Many Manyofof the the layers layers are augen augen gneisses gneissescontaining containing feldspar feldspar porphyroclasts porphyroc1asts averaging 11 cm cm inin size, but also also containing containing quartz quartz porphyroclasts. porphyroclasts. The size, but gneisses daciticdikes dikeswhich whichhave havebeen been gneisses have havebeen beenintruded intrudedbybyandesitic andesitic to to dacitic A gabbro deformed gabbro deformedand andrecrystallized. recrystallized. Some Someofofthe thedikes dikesare are porphyritic. porphyritic. A near the the powerhouse powerhouse is Is weakly foliated, unit near weakly foliated,but butthe theorigin originofof the the foliation foliation is unclear. unclear. The to to amphibolite but The gneisses gneisses have have been beenmetamorphosed metamorphosed amphibolitefacies, facies, but it cannot be be ascertained ascertained at at what what grade grade the crosscutting crosscutting dIkes dikes were were it cannot recrystallized. Isoclinal F1 F folding folding produced produced ananaxial thegneisses gneisses axial planar planar foliation foliation ininthe which is re1ativ~lyconsistent consistentininorientation orientationin in downstream three-quarters three-quarters which is relatively thethe downstream of the the exposure, exposure, striking N. 450 45 0 W. W. and F2 folds striking N. anddipping dippingvertically. vertically. Tight F2 become more common toward At becomeprogressively progressively more common towardthe theupstream upstreamend endofof the the outcrop. At the upstream end folding is disharmonic (Figure the upstream endofofthe the exposure, exposure,FF2 folding disharmonic (Figure 14). 2 35 �1ap for localities 20 r'~ap for localities 18, 18, 19, 19,20 Disharmonic FF? folding Figure 14. Figure 14. Disharmonic in the the gneiss gneiss at folding in the upstreani end of of the Pwerhouse the upstream end Powerhouse outcrop. Interference patterns patterns here here may maybebedue duetotofolding foldingof of isoference folds, as clinal FF1 as at at Stops Stops 33 and and 7. 7. l folds, 36 36 �LOCALITY 19: LOCALITY NE¼, SE¼, Sec.17, 17,T.22N., T.22N.,R.3W. P.3W.(Black (BlackRiver River Falls Falls 15-minute NE~, SE~, Sec. 15-minute See map map on on preceeding quadrangle, Jackson Jackson County). County). See topographic quadrangle, from PowerhouseRoad Road page. Proceed 0.1 mile milesouth southfrom Proceed approximately approximately 0.1 Powerhouse The dirt dirt on aa gravel gravel and road to to an dirt road. on and sand sand road an overgrown overgrown dirt road. The road leads leads to aa small, small,abandoned abandoned quarry. quarry. road LOCATI ON: LOCATION: AUTHOR: AUTHOR: Banded Bandedgneiss gneiss at at quarry quarrynear nearPowerhouse Powerhouse R.S. R.S. Maass Maass (1980) (1980) DESCRIPTION: A banded consisting of ofalternating bandedgneiss gneiss consisting alternatingthin thin to to thick biotite free and biotite rich free and biotite richquartzofeldspathic quartzofeldspathic layers layers isisexposed exposed in in aasmall small quarry near the the Black near Black River, River. Many and melanocratic melanocratic layers layers contain Manyofof the the 1eucocratic leucocratic and alkali feldspar cminin length. Both alkali feldsparporphyroclasts porphyroclastswhich whichsometimes sometimes reach reach 33 em isoclinal tight F2 isocl inal F1 Fl and and tight F2 folds folds are are present present in in the the gneiss. gneiss. LOCALITY 20: 20: LOCALITY NE¼, NE~, NE~, NE, Sec. Sec. 30, 30, T.22N., T.22N., R.3W. R.3W. (Black (Black River River Falls Falls 15-minute 15-minute See preceeding page topographic quadrangle, quadrangle, Jackson Jackson County). County). See page topographic Outcrop is located for location locationmap. map. Outcrop located along along Halls HallsCreek Creekbetween between and the the Black Black River, River, and County Hwy. Hwy. E and and on on the west west bank bank of the the Black River from the the mouth of Halls Creek. Black River just justdownstream downstream from mouth of Creek. LOCATION: AUTHOR: Gneiss at Halls Halls Creek Creek Gneiss R.S. Maass Maass (1980) (1980) P.S. DESCRJPfION: DESCRIPrION: The basement rocks at at this crop out just justbelow below the the The basement rocks thislocality locality crop They are are micaceous micaceousfelsic felsic Cambrian Mt. Mt. Simon Simon Formation. Formation. They unconformity theCambrian unconformity with the The best best exposures are along units and clayey clayey intermediate "intermediate to mafic units. The exposures are along units and to rnafic Halls Creek where the Mt. Mt. Simon Simon Formation Halls Creek wherethe therelationship relationship with with the Formationisis clearly visible, visible. There Thereare aretwo twopossible possibleinterpretations interpretationsfor for the the rocks rocksat at this locality:a)a)they theyare arelow lowgrade gradeearly ear'lyProterozoic Proterozoicsedimentary sedimentary or volcanic volcanic locality: latter units; extremely weathered units; ororb)b)they theyareare extremely weatheredArchean Archean gneisses. gneisses. The The latter possibility stronglypreferred preferred since, since, 1)1)the therocks rocks appear appear very very similar possibility isisstrongly the deeply deeply weathered weathered portions the Hatfield HatfieldGneiss Gneiss exposed exposed at Stop 7, to the portions of of the at Stop which is also just below the unconformity; 2) some of the units here which is also just below the unconformity; 2) some of the units here consist consist entirely ofofclay entirely clayminerals mineralsplus plusquartz, quartz,which whichsuggests suggests weathering weathering rather rather than than low metamorphism;and andJ)3)there there are are no no known knownlow lowgrade gradeearly early Proterozoic low grade grade metamorphism; sedimentsoror alurnin(1Us aluruiriousvolcanic volcanicr'ocks rockselsewhere elsewhereinin the the Black Black r~iver River reqion. reqion, sediments "J) 3 •7 .J. �LOCALITY 21: LOCALITY 21 Gnelss andtonalite, tonalite, Black Gneiss and Black River River Falls NE~, NE~, Sec. l5-minute NE¼, NE¼, Sec.22, 22,T.21N., T.21N.,R.4W. R.4W.(Black (BlackRiver River Falls 15-minute quadrangle, Jackson Jackson County). County). See topographic quadrangle, SeeStop Stop88for for detailed LOCATION: LOCATION: East bank bankof of the the Black map. East Black River, 0.2 0.2 ml. mi. west west ofofU.S. U.S.Hwy. Hwy. map. 12. Dirt path path statring statringnear nearsharp sharp bend bend in road road leads leads to outcrop. outcrop. AUTHOR: AUTHOR: R.S. Maass (1980) (1980) R.S. Maass DESCRtPTION: The The gneiss banded and plagioclase, gnetss is Is banded andconsists consistsofof quartz, quartz, plagioclase, DESCRtPTION: alkali feldspar, feldspar, blotite, biotite,hornblende, hornblende, chlorite, chlorite,and andepidote. epidote. Thin Thin to to thick in the thegneiss gneissvaries variesprom from compositional compositional extremes extremes of quartzofeldspathic quartzofeldspathic layering in bands containing alkali bands containingas asmuch muchasas40% 40% alkalifeldspar feldspartoto bands bandsconsisting consistingentirely entirely and minor minor quartz. quartz. The The gneiss has been been intruded of hornblende, hornblende, plagioclase, and gneiss has by fine-grained diorite dioriteand anddiabase diabasedikes dikeswhich whichhave havebeen beenmetamorphosed metamorphosed to by fine—grained amphibolite and by by a fine fine grained grained lineated lineatedtonalite tonalitewhich whichwas was probably probably amphiholite facies fades and subjected to to the thesame same grade grade ofofmetamorphism. metamorphism. Age among the Age relationships relationships among units have have not not been been established intrusive units establisheddue duetotolack lackofof suitable suitable field field relationships. Isoclinal F1 F, folding folding produced produced ananaxial axial planar planarfoliation foliation which hasbeen beenopenly openlytototightly tiht1y folded which has folded during during F,F deformation, deformation. F2 F fold fold axes intn the defined /3 p froffl fro~ aa stereographic stereographic 2plot axes the gneiss, gneiss, statistically statistically defined plot of and mineral mineral lineations the Intrusive intrusive units units are are poles to poles to foliation, foliation, and lineations in the essentiallycolinear, co1inear,trending trending southeasterly andplunging plungingbetween between500 50 0 essentially southeasterly and and and 75°. 75°. LOCALITY LOCALITY 22: 22 LOCATION: LOCATION: AUTHOR: AUTHOR: Quartzite, Silver SilverMound Mound NE¼,NW~, NW¼, T.21N., R.3W. (Black River Falls15-minute l5-1nute NE~, Sec.Sec. 20,20, T.21N., R.3W. (Black River Falls See Stop Stop 88 for topographic quadrangle, quadrangle, Jackson Jackson County). County). See topographic map. Follow Follow a dirt dirtroad roadfrom fromBauer BauerRoad Road to to reach reach detailed detailed map. Silver Mound. Silver Mound. R.S. R.S. Maass Maass (1980) (1980) Thequartzite quartzite at Silver is white, nearly DESCRIPTION: The SilverMound Mound is nearly pure, pure~ and and DESCRIPTION: It isispoorly strongly lineated. It poorlyexposed, exposed, occurring occurring mostly mostly as as loose loose blocks blocks strongly lineated, It isisbelieved on of, and and along along the the sides sides of, of,the themound. mound. It believedtotohave haveformed formed on top top of, from chert beds associatedwith with the the Archean volcanic rocks rocks of of the from chert beds associated Archean volcanic the region. region. 38 �LOCALITY LOCALITY 23: LOCATION: LOCATION: AUTHOR: AUTHOR: Jackson County Mine Jackson County Iron Mine SW~, Sec. 15-minute topotopoSW¼, Sec.15, 15,T.21N., T.21N.,R.3W. R.3W.(Black (BlackRiver River Falls Falls 15-minute See p. p. 30 graphic quadrangle, quadrangle, Jackson Jackson County). County). See 30 for formap. map. R.S. R.S. Maass Maass (1980) (1980) DESCRIPTION: DESCRIPTION: The The Jackson in aa banded banded magnetite JacksonCounty CountyIron IronMine Mineisis In magnetite iron formation a alenticular center. The formationwhich whichcontains contains lenticulartalc talc schist schist zone zoneinin its center. iron formation formation isissurrounded surrounded on on both both sides sides by by aluminous aluminous quartzofe1dspathic quartzofeldspathic schists. Previously, magnetite was primary iron iron Previously, magnetite wasbelieved believedtoto be be the the only only primary oxide present hematite due duetoto weathering weatheringcaps capsthe thedeposit), deposit), but oxide present (secondary (secondary hematite but recently primary encounteredinin the the northwest northwest corner corner of of the primary hematite hematite was was encountered pit. The iron-richamphiboles,and amphibo1es,and The other other major major minerals minerals include include quartz, iron-rich garnet. The consists ofofthree threedominant dominantmineral mineralassemblages: assemblages: 1) 1) The schist schist consists quartz-chlorite-muscovite-anda1usite; quartz-chlorite-muscovite-andalusite;2)2) quartz-biotite-chlorite-staurolitequartz—biotite-chlorite-staurolitegarnet-andalusite-muscovite; garnet-andalusite-muscovite; and and3)3) quartz-biotite-plagioclase-muscovite quartz-biotite-placiioclase-muscovlte (Jones, 1978). 1978). (Jones, F folding folding produced produced aapenetrative F Isoclinal F1 penetrativeaxial axial planar planarfoliation. foliation. F1 axes plunge plunge lsteeply steeplyand andare areaccompanied accompanied by by parallel mineral mineral lineation l fold fold axes Axesofofopen opentototight tight FF2 folds defined by by the the orientation orientation ofofamphiboles. amphiboles. Axes folds defined are also parallel parallel to and F, F fold foldaxes axes are are are also to the the mineral mineral lineation; lineation; thus, thus,F,F,and believed be colinear. colinear. Structurally the the iron iron forthation formation 'ts ~s essentially believed to be identical totothe theArchean Archean gnelss gneiss terrane. terrane. Jones Jones (1978) the (1978) concluded concluded that that the does not theearly earlyProterozoic ProterozoicSuperior-type Superior-type model, model, but but iron formation formation does not fit fit the It may rather ititappears appears totobebeofofthetheArchean ArcheanAlgoma-type. Algoma-type. It may have have been been deposited in small basin basin on volcanic center. center. deposited in aa small on the the flanks flanks of aa volcanic Jones (1978) metamorphic events; was Jones (1978)defined definedtwo twodistinct distinct metamorphic events;the the first first was amphibolite fa~ies, thesecond second was was upper upper greenschist Based on on amphibolite fades, the greenschist facies. fades. Based textural features featuresheheconcluded concluded that thatthe thesecond secondevent eventwas was aamajor majorthermal thermal textural pulse, effect. The pulse, not not merely merely aa retrograde retrograde effect. Thepossibility possibility of of an an earlier, much suggested by presence of muchhigher higher grade gradeevent eventthan than these these two two is is suggested by the presence of kyanite, but the phase relationshipsofofthis this mineral mineralare arenot notatat all all clear. phase relationships clear. kyanite, but the 39 39 �DISCUSSION DISCUSSION OF OF THE THE TECTONIC TECTONIC HISTORY HISTORY In recent years years itithas hasbecome become increasingly increasinglyapparent apparent that thatthe thePenokean Penokean In recent Orogeny deformational Orogenywas wasa amajor majorigneous, igneous,metamorphic, rnetarriorphic,and and deformationalevent eventinin central central along the Wisconsin Wisconsin. This has has been been documented documented along Wisconsin River Riverbetween between Stevens Point Point and Wisconsin Rapids Rapids (Maass (Maassand andothers, others, 1980), 1980), and and as as this Stevens and Wisconsin guidebookillustrates, illustrates, along guidebook along the the Black Black River River as as well. Studies Studies in in progress progress indicate that of Wisconsin that the the entire entirecentral centralportion portion of Wisconsinhas hasbeen been subjected subjected folding during to regional regional amphibolite amphibolitefacies faciesmetamorphism metamorphism and and polyphase polyphase folding during the Penokean Penokean Orogeny. Orogeny. Periokeandeformation deformationbegan began withisoclinal isoclinal F, Penokean with F folding foldingwhich whichproduced produced aa penetrative axial axial planar planar foliation foliation parallel penetrative parallel totobanding blnding in in gneisses, gneisses, schists, schists, and iron iron formation, in fold the layering is and formation, except except in fold hinges hinges where where the is transected transected Susequentlythe thefoliation foliation was tightly totoopenly by foliation. was tightly openly folded folded during during by foliation. Susequently axial planes planesofof these thesefolds folds are are at at small F ; the F?; the nonpenetrative nonpenetrative axial small to large large the Wisconsin WisconsinRiver Riverthere thereisisaadistinct distinct angles Along the agles to FF foliation. Along break betwen tight tight and fold styles, break betwe~n and open open fold styles, thus thusfolding foldingcan canbebeseparated separated but along along the the Black Black River River there there is aa complete into F2 F~ and and FF3 phases, phases, but complete con coninto tinuumLfrom to open open folds and no possible. The The nontinuum fromtight tght to folds and no division division is possible. penetrative axial planes planes of penetrative of FF folds along along the the Wisconsin Wisconsin River River are are always always foliation. All fold at aa high high angle angle to the the fOliat1on. foldaxes axes are are colinear, colinear, and and parallel parallel to aa penetrative Archean penetrative mineral mineral lineation lineationwhich which isispresent presentininthethe Archeangneisses gneisses coliriearity of and most mostofofthe the early early Proterozoic Proterozoic intrusive rocks. and rocks. The The colinearity undersimilar similar stress structures suggests suggests that they they were were formed formed under stress conditions conditions deformational and during an an extended extended Penokean Penokean deformational and metamorphic metamorphic event. The complete completePenokean Penokean deformationalhistory history is is recorded The deformational recorded in gneisses gneisses of confirmed confirmed Archean not Archeanage, age,but butthe the presence presenceofofthese thesestructures structures is is rtot sufficient evidence to a rock, sufficient evidence by by itself itselfforforassigning assigningananArchean Archean age age to rock, since since there may also Proterozoic units which which were were subjected there may also be beearly early Proterozoic subjected to to the entire period gneissatatBig Big Falls Falls in entire period ofofPenokean Penokean deformation. deformation. A banded banded gneiss Eau indicative ofofpolyphase polyphase deformation deformation EauClaire Claire County Countycontains containsstructures structures indicative similar to to those those inin Archean Archean rocks rocks elsewhere elsewhereininthe theterrane, terrane,yet yet the the unit yields age (Introduction: (Introduction: Fig. Fig. 3). this yields an an early Proterozoic Proterozoic age 3). However, However, this gneiss is one of the thoroughlyrecrystallized recrystallized units units in the gneiss is one of the most most thoroughly the region, region, anditit isis not and not yet yetclear clearthat thatthe theage ageobtained obtained isisthe theprimary primary age age of the the gnei ss. gneiss. In the In the Black Black River River valley there there isisaastrong strongcorrelation correlationbetween between the the age of emplacement early Proterozoic Proterozoic intrusive intrusive rocks age of emplacement ofofearly rocks and and the the character character of the Theoldest oldest units units are the structure structurepresent present within withinthem. them. The are foliated foliated and and lineated; younger units but are are generally generally only only lineated; younger units may maycontain containa afoliation, foliation, but units tend lineated; and and the the youngest youngest units tend to to be be completely completely devoid devoid of any any prepreferred However,even evenininthe the unfoliated unfoliated and ferred orientation. However, and unlineated unlineated rocks, rocks, microscopic textures reveal microscopic reveal that thatsome someofofthem themhave havebeen been granulated granulated and and recrystallized (Lake Granite, Black recrystallized (Lake Arbutus Arbutus Granite, Black River River Falls Granite). Granite), Post kinematic granitic granitic rocks rocks inincentral centralWisconsin, Wisconsin. dated dated atat1760 1760 m.y., kinematic m.y. , may may or may may not be be assigned assigned totothe thePenokean PenokeanOroqeny Orogeny' structurally they are are structurally they distinctly thethe Penokean distinctlydifferent differentfrom fromthe therest rp.stof of Penokean intrusives intrusives 40 �Emplacement theearly earlyProterozoic Proterozoic intrusive intrusive rocks Emplacement of ofthe rocks occurred occurred throughthroughout the waning stages of F1 deformation and continued beyond the final out the waning stages Fl deformation and continued beyond the final stages stages activity. F1 deformationproduced producedthe thefoliation foliation present of kinematic kinematic activity. F] deformation present in in someofofthe theintrusive intrusive rocIs, some rocRs, and and the the older older intrusives, intrusives,having havingbeen been subsubjected to F1 Fl deformation deformation for greater period period of oftime timethan thanthe theyounger younger jected to for aa greater However, the generally contain contain aa better better developed developed foliation. intrusives, generally foliation. However, Neillsville Granitedemonstrates demonstrates that thatusing using the thedegree degree ofofdevelopment development of Neil]svi]le Granite Jue to foliation an indicator indicatorofof agecan canbebean an unreliable unreliablemethod. method. Due foliation asasan age inhomogeneous deformation graniteisis foliated foliated ininsome inhomogeneous deformation thethe granite some areas areas and and unfoijated in others. In addition, properties of aa given unfoliated others. In addition, the the mechanical mechanical properties given rock significantly significantly influence rock influence its itsstructural structuralresponse responsetotoa adeformational deformational event, event. The The Neillsville Granite, which which is unfoliated at at Stop Stop 2, is is intruded intruded Neillsville Granite, is unfoliated this locality localitybybyaadacite dacite dike dike which which is strongly strongly foliated. at this Although the the vast vast majority of Although of linear linearPenokean Penokean structures plunge plunge steeply, someare arenearly nearly horizontal. horizontal. There some There may mayalso alsobebeconsiderable considerablevariation variation in twomost mostlikely likely the trend of the the structures structures from from outcrop outcrop to to outcrop. outcrop. The The two the trend explanations for this variance are that the fold axes and mineral lineaexplanations for variance are that the fold axes and mineral lineations were foldedduring duringa alater later event, event, or or that that folding was orioinally tions were folded was originally noncylindrical. Stereographic Stereographicplots plots of of linear linear structural structuralelements elements have have not anypatterns patternsofof refolding, refoldino, therefore possibility not revealed revealed any therefore the the second second possibility is preferred. preferred. In In numerous numerous localities noncylindrical folding foldinghas hasbeen been localities noncylindrical observed mesoscopic scale,and andthere thereisis no no reason reasontoto believe believe that observed ononaamesoscopic scale, that it didnot notalso alsooccur occuronona amacroscopic macroscopic scale. scale. Unlike northern northern Wisconsin, Wisconsin, it did wherenortheasterly northeasterly structural structural trends where trendsseem seem to to dominate, dominate, there there isisnonodomdominant structural trend trend in in the the Black Black River River valley. inant structural Oneintriguing intriguing question remains to to be be resolved resolved is whether One question which which remains whether or not deformation occuredinincentral central Wisconsin during the deformation and and metamorphism metamorphism occured Wisconsin during the Archean. Three Three localities suggest that did. A A migmatite of ofArchean Archean localities suggest thatitit did. age (Van Schmusand andAnderson, Anderson, 1977)isisexposed exposedinin aa quarry quarry near age (Van Schmus 1977) near the the Wisconsin Wisconsin River, ininLinwood Linwood Township. Township. A A steeply plunging plunging mineral mineral linea— lineation which which formed formed during during the thePenokean Penokean Orogeny hinges of of tiori Orogenytransects transects the the hinges The relationship gently plunging isoclinal folds in the migmatite. The relationship gently plunging isoclinal folds in the migniatite. requires that the requires that the folds folds be be older older than than the the mineral mineral lineation, lineation, and and the the gentle plunge plunge of does not thepattern patternofofPenokean Penokean folding gentle of the the folds folds does not fit fit the Archean in the the area, area, suggesting suggesting that thatthe thefolds foldsareare Archeanininage age(Maass (Maass and and others, 1980). 1980). The The other are in the the Black Black River River valley: othertwo twolocalities localities are The Hatfield Hatfield in the the Hatfield HatfieldGneiss Gneiss and and ininthe theJackson Jackson County County Iron Iron Mine. Mine. The Gneiss contains contains relict Gneiss relicthypersthene hypersthene(Dubois (Duboisand andVan VanSchmus, Schmus, 1978), 1978), and and the formation contains contains significant quantitiesofofkyanite kyanite(Jones9 (Jones, 1978). 1978). the iron formation significant quantities These Theseminerals, minerals, and andtheir their textures, textures, suggest suggest that thatthere theremight mighthave havebeen been an metamorphic event facies. an earlier earlier metamorphic eventinin the the upper upperamphibolite amphibolitetoto granulite granulite facies. In addition there there is one one unexplained, unexplained, isoclinally In addition isoclinally refolded, refolded, isoclinal fold ininthe theHatfield HatfieldGneiss Gneisswhich which may may be be evidence evidencefor for an an older older folding event. 41 41 �Theselines lines of evidence are not not conclusive, These evidence are conclusive, and and the features features could could be be attributed to to an an early earlyProterozoic Proterozoic event. event. On On the hand, many many of the other hand, of the Archeangneisses gneissesinInthe the Black Black River River Valley Valley were were derived derived from from aa volcanicvolcanicArchean plutonic terrane, to expect and Ititwould would be be reasonable reasonable to expect that the the volcanic volcanic terrane, and rocks were were deformed deformed during during an an orogeny orogeny rocks during emplacement emplacementofofthe the plutons plutons or during associated Finally,most most other otherArchean Archean terranes terranes associatedwith with the the igneous igneousactivity. activity. Finally, Lake Superior Superior region region contain contain significant significant Archeandeformation deformation and and the Lake in the Archean metamorphism, sosothat thethesame is istrue Archean rocks metamorphism, that we weassume assume same truefor for the Archean rocks of the River valley. However, Penokean effectshave havelargely largely obliterated obliterated the Black Black River However, Penokean effects any Archean tectonic features. any Archean tectonic ACKNOWLEDGMENTS ACKNOWLEDGMENTS R. S. Maass hasreceived receivedsupport support for for the R. S. Maass has the work work covered covered here here from from the the Wisconsin Geological and Natural History Survey and the Wisconsin Geological and Natural Survey and the Department Department of Geology, UW-Madison. UW-Madison. W. W. R. R. Van Van Schmus Schmus has has been been supported by byNSF NSF grant EAR75-15007 andbybya agrant grant from from the EAR75-l5007 and the General General Research Research Fund, Fund, University University of Kansas. Much Muchofof the the field field work at Stop Kansas. work and and mapping mapping at Stop 77 was was done done by by 3. J. F. F. DuBois researchproject project at at the DuBois asasaaresearch the University UniversityofofKansas Kansas under under the grants the grants to readearly earlydrafts drafts of the W.R.V.S. L. L. G. G. Medaris Medaris read the text text and and provided provided many many to W.R.V.S. helpful comments. helpful comments. 42 �REFERENCES REFERENCES DuBois, and Van Van Schmus, Schmus, W.R., and geochronology geochronology of DuBois, J.F., J.F., and W.R., 1978, 1978, Petrology and of Archean Lake Arbutus Wisconsin (abs.). Archeangneiss gneissinin the the Lake Arbutus area, area, west-central west-central Wisconsin Program,Twenty-fourth Twenty-fourth Annual AnnualInstitute Institute on Program, on Lake Lake Superior SuperiorGeology, Geology, Milwaukee, 11. Milwaukee, p. p. 11. Jones, 1978, Geology formation and and associated associated rocks rocks of Jones, D.G., D.C., 1978, Geologyofof the the iron formation County Iron Mine, Mine, Jackson Jackson County, County, Wisconsin. Wisconsin. Unpub. M.S. Jackson County the Jackson Unpub. M.S. thesis, Univ. ll7p. Univ. Wisconsin, Wisconsin, Madison, Madison, 117p. Maass, Medaris, L.G., L.G.,Jr., Jr., VanSchmus, Schmus,W.R., W.R.,1980, 1980,Penokean Penokean Maass, R.S., R.S., Medaris, andand Van deformation in central deformation in central Wisconsin. Wisconsin. Geological Geological Society Society of ofAmerica America Special Paper 182, in press. Special Paper 182, press. Myers, Myers, P., Cummings, Cummings, M., M., and and Wurdinger, Wurdinger, S., S., 1980, 1980, Precambrian Precambrian geology geology of Valley, Wisconsin. the Chippewa Chippewa Valley, Wisconsin. Twenty-sixth on Lake Lake Twenty-sixth Annual Annual Institute Institute on Superior Trip No. No.1 Guidebook. Superior Geology, Geology, Field Field Trip 1 Sims, P. K., 1976, 1976, Precambrian Precambrian tectonics and mineral Lake Superior Superior Sims, P. K., tectonics and mineral deposits, Lake region. Economic p. 1092-1118. 1092-1118. EconomicGeology, Geology,v.v. 71, 71, p. Steiger, E., E., 1977, Subcommission Steiger, R.H., R.H.,and andJger, JMger, 1977, SubcommissionononGeochronology: Geochronology: Convention use of decay decay constants constants iningeogeo-and andcosmochronology. cosmochronology. Convention on on the the use Earth 36, p. p. 359-362. 359-362. Earth and and Planetary PlanetaryScience ScienceLetters, Letters, v. v. 36, Van Schmus,W.R!, W.R.,1980, 1980,Chronology Chronologyofofigneous igneousrocks rocksassociated associated with with the Van Schmus, the Penokean orogeny Geological Society of of America, America, Special Special Penokean orogeny in In Wisconsin. Geological Paper182, 182, in in press. Paper press. Van 1977, Gneiss Gneiss and and migmatite of Archean Archean Van Schmus, Schmus,W.R., W.R.,and andAnderson, Anderson,J.L., J.L., 1977, migmatite of age the Precambrian Precambrian basement basement of Wisconsin. Geology, aqe in the of central Wisconsin. v. 5, p.p.45—48. 45-48. v. 43 43 � https://digitalcollections.lakeheadu.ca/files/original/ffb99f6c9aadf623aa9dc3027e119852.pdf 759040e0a41da077762f726d0db4d2b3 PDF Text Text 26th Annual Institute on Lake Superior Geology FIELD TRIP 3 Petrology, Geochemistry, and Contact Relations of the Wausau and Stettin Syenite Plutons, Central Wisconsin GENERALllEO ""EC.....SRIAN GEOLOGY O~ THE [AU CLAIRE REGKlN • f'>:] Gobb'o bil T.oI'ldn,mt. ~~ Volconic. ooa _,,,,,,n,, ~ .o.",ph,Do''''' May 10,1980 University of Wisconsin-Eau Claire �26TH ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY FIELD TRIP #3 THE PETROLOGY) GEOCHEMISTRY AND CONTACT RELATIONS OF THE STETTIN AND WAUSAU SYENITE PLUTONS CENTRAL WISCONSIN by Mohan K. Sood Department of Earth Sciences Northeastern Illinois University Chicago, Illinois 60625 Paul E. Myers Department of Geology University of Wisconsin Eau Claire, Wisconsin 54701 Louis A. Berlin of Earth Sciences Northeastern Illinois University Chicago, Illinois 60625 Departmen~ May 10, 1980 �Additional copies of this guidebook may be purchased for $5.00 (U.S.) from: ILSG 180, Department of Geology University of Wisconsin-Eau Claire Eau Claire, Wisconsin 53706 or Sales, Wisconsin Geoloqic and Natural History Survey 1815 University AvenueMadison, Wisconsin 53706 �CONTENTS Petrology, geochemistry and contact relations of the Stetti n and Wausau Syenite Pl utons 1 Stop Descriptions 7 Stop 1, Rib Mountain 10 Stop 2, Wausau syenite pluton, core rim ...............•............... 12 Stop 3, Wausau syenite pluton, wall zone 15 Stop 4, Employers' Mutual Insurance Co 19 Stop 5, Stettin syenite pluton, wall zone .......•..................... 25 Stop 6, Amphibole syenite, intermediate zone 32 Stop 7, Amphibole syenite, intermediate zone 32 Stop 8, Stettin syen ite pluton, core zone 36 Mineralogy and miner.al chemistry 38 Petrochemi stry." 46 Di scussi on 51 Comparison of the References ~lausau and Stettin Plutons 54 57 �-1- PETROLOGY. GEOCHEMISTRY AND CONTACT RELATIONS OF THE STETTIN AND WAUSAU SYENITE PLUTONS CENTRAL WISCONSIN by Mohan K. Sood Paul E. Myers Louis A. Berlin INTRODUCTION Alkaline igneous rocks are characterized by the presence of a"'kali feldspars, sodic pyroxenes, amphiboles, and feldspathoids or quartz. Generally, a high content of volatiles (Cl, F, H~O, s, CO 2 ), rare elements (Nb, Ti, Zr, REE, Ta, Bi, and Be), and th~ presenc~ of unusual volatile bearing minerals (sodalite, eudialite, aenigmatite, astrophyllite, villaumite, etc.) impart alakline rocks a character of extreme chemical and mineralogical heterogeneity (Sorenson, 1974)--thus representing an interesting physiochemical system of magmatic crystallization. Alkaline rocks commonly occur in the following tectonic settings: a. Tectonically stable regions of the crust--continental platforms and Precambrian shield areas of North America b. Rift zones--East African Rift, Rhine-Oslo Graben, Montregion Province c. The intersection of fault zones--Greenland (Sorenson, 1970, 1974) GEOLOGY AND GEOCHRONOLOGY OF CENTRAL WISCONSIN The work of Weidman (1907) is the first effort to systematically describe the geology of north central Wisconsin. Recent re-examination of the area has been by LaBerge (1969, 1971), LaBerge and Myers (1972, 1973) and Myers (1973) in refinement of geological mapping and interpretation, Medaris et al. (1973) on the geology of the Wolf River Batholith, Van Schmus (1973), Van Schmus et al. (1980) in geochronological investigations of the region. Koellner (1974) on mineral chemistry, Berlin and Sood (1979) on geochemistry and petrogenetic models. �-2- ~ --~ ~ o / 150 :i? 8 ,, ~. ~ 0 60· r" • C) \ v 'P C''? :HIELD .. " ... •• \0 ; 1\ ~ .~BLACK U HILLS \ b.· \ • 130 0 • ... ~ •••• \ • SHIELD --'~-A ......"\ • • ,p rP " " '1'>-01- ." 140 0 0 •• ... • ..... D.·.· I. ~J:2~-~.: '- . ~ · /~ / W'i,~~"au / ~ • WICHITAS / - / ~ / /. ~ frV c~~ ,"- ·0~ 'i>~ ~ • • I ~ &y~-..; \ I :l~,0 Ch I /3) • • u/~ 'v «V 30 0'--. .... / / i. complexesv \ ~ • .. ~30° I 120 0 90 0 110 0 FIGURE 1 Occurrences of Alkaline Rocks of North America. The tectonic boundaries are generalized. ( From Barbee, 1976) �-3- The oldest rocks of the region are basement gneisses, schists, amph-iblites, and migmatites which are exposed in the Wisconsin RapidsStevens Point area (Figure 6b). However, the Central Wisconsin Cornplex (1800-1900 m.y.) composed of metamorphosed basalts, rhyolites and trachytes (Weidman, 1907, LaBerge and Myers, 1973) and associated granitic rocks (Dutton and Bradley, 1970) form the dominant exposures. (Not if you include rhyolite and granite in southeast Wisconsin, Smith, 1978). Intruding the Central Wisconsin Complex are the 1500 m.y. old anorogenic Wolf River Batholith and the two Wausau Syenite plutons (Van Schmus et al., L. Medaris, Jr., et al., 1975). The Wolf River Batholith is dominantly quartz(?) monzonitic with local phases of syenites, granite, and porphyries. Isolated masses of anorthosite occur within the batholith, but their relationship to the main body is not well understood. The Wausau Syenite Complex comprises a silica-rich phase of granitic quartz syenite-pyroxene amphibole syenite associated at Wausau and a nearly contiguous silica-poor (nepheline bearing) phase at Stettin. Both of the plutons have somewhat elliptical concentric zonal structures. (LaBerge and Myers, 1973). The geochronological stratigraphy is given in Table I. Regional geology is shown in Figure 2, Marathon County, Figure 3. Generalized geology of the two plutons is shown in Figure 4. TABLE I GEOCHRONOLOGICAL RELATIONS OF THE PRECAMBRIAN ROCKS OF CENTRAL WISCONSIN Unit Wausau Syenite Complex 1. Stettin body Major Rock Types Age (m.y.) pyroxene syenite, 1,520* amphibole syenite, tabular syenite, nepheline syenite 2. Wausau body granite, quartz 1,520* syenite, pyroxene+25 amphibole syenite Wolf River Batholith quartz monzonite, 1,500 syenite, granite +25 Central Wisconsin Complex basalt-rhyolite, 1,000-1,900** trachyte, quartz monzonite, granite Basement Complex gneiss, migmatite, uncertain, schist, granite 1,900* * Van Schmus, 1980, Chronology of igneous rocks associated with the Penokean orogeny of central Wisconsin, Geol. Society of America, Spec. Pap. 182 in press. �-4- A [XPLANATION PALEOZOIC tCXf~ Sedimentary rocks PRECAMBRIAN 11-. ":.1 II ~ Wall River 8atholith and Wausau Syenite Camp lex 1;+1 Granitic l;v~'tl Metavolcanic rocks B rocks Ar;~'rE:~:~, - 'I migmatite, schisl, granite, amphibolite FIGURE 2 2A--Generalized geochronologic map of Wisconsin showing the location of the Wolf River Batholith and related Wausau Syenite Complex (after Van Schmus et ~., 1975a) 2B--Inset of Figure 2A. Generalized geologic map of part of central Wisconsin (after Van Schmus et~. 1975b). �A. 7E R 5E R.8E R 9E ,.., l5 z ,.., iXl z I <..T1 ....~ .... I z '"N .... Mil . . o I I,! 2 I !5 ,I R.2E. A 3E R.4E R 5E R 6E - R 9E R 7E AlOE EXPLANATION GEOLOGY OF MARATHON COUNTY,WIS. (Interim Copy) D HI -[]illill WISCONSIN GEOLOGICAL AND NATURAL HISTORY SURVEY r==T"7I ~ LATE PRECA-MBRIAN I=--=:I Iiiiiiiil W .. ~ .•,_ ~ '~.:,;j. , ,. ""', -~ MIDDLE PRECAMBRIAN B o o o I , I Z:1 IS ! I I SCALE EITJ 4 r.:::::l ~ To..... nsn'pJR.nge .. 'ne o''''''''OU.'''O'I>'''''_ EARLY PRECAMBRIAN ~ Figure 3 -- Geologic map of Marathon County by LaBerge and History Survey, Interim Copy. Ge<.logy Mye~, b~ G l l.ee,ge ~nd P E fl,4ye,~ 1979 Wisconsin Geological and Natural �-6- m I Wall zone IT] Intermediate m zone core fmassive auartzitelxenolith-rich zone • Granite tI ol::===II mile PAUL E. MYERS 1976 Figure 4 -- Generalized geologic map of the Wausau and Stettin syenite bodies and the Ninemile granite pluton which intrudes the Wausau syenite. Section A-AI is shown in Figure �-7- STOP DESCRIPTIONS NO. TITLE AUTHOR(S) PAGE 1 Rib Mountain Summit Overlook Myers 10 2 Large quartzite and biotite schist xenoliths in the core rim, Wausau syenite pluton Myers 12 3 Flow structure of the wall zone, Wausau syenite pluton Myers 15 4 Lensoida1 quartz syenite, Employers' Mutual Insurance Company Myers &Sood 19 5 Contact relations and minerals in the wall zone, Stettin syenite pluton Myers &Soad 25 6 Amphibole syenite of the intermediate zone Sood &Myers 32 7 Amphibole syenite of the intermediate zone Scad Myers 32 8 The core zone of the Stettin syenite pluton Myers &Scad 36 & �-8- ,,- nv , , -'--";"/-"1"':',,+~...,..;.;.:;.~t+"''''IE~-.......''''~-''''-l .. \ ' r • •. ;-- ~" - p .. .. ,, , ,. ,~ .~-- ~~.: tTW .f ' / ,1 Figure 5 -- Field tr'ip #3 route map. Geological base map by LaBerge and I~yers (1979) . �-9- I fv fv -+---~~~--..L::'f;-~~ qol i : rJ ... ..J Isy \ ~ .- ,vVAUSAU I Iqsy \ "- , ... , ~ JI , Fi gure 6 -- Route map for stops ,1 J : - 4 in the Wausau syenite pluton. tv �-10- STOP #1 TITLE: RIB MOUNTAIN SUMMIT OVERLOOK LOCATION: Rib Mountain State Park observation platfonn, SE~ Section 8, T28N, R.7E., Wausau 15' quadrangle, Wausau west 7~' quadrangle AUTHOR: Paul E. Myers DATE: February, 1980 SUMMARY OF FEATURES: The Wausau syenite-quartz syenite pluton in two segments (Figure 3) and the more alkalic Stettin syenite pluton are exposed west of the Wisconsin River near Wausau in central Wisconsin. These Middle Precambrian (1520+15 m.y., Van Schmus, 1980) plutons are concentrically zoned and show a distinct northnortheasterly elongation. Each pluton has a contact metamorphic zone of syenitized wall rocks, an alkalic laminated, xenolith-rich wall zone, an intermediate zone and a core. Silica content increases inward in each pluton. DESCRIPTION: From this vantage point a good panorama of the region is available. Rib Mountain is the resistant remnant of a large, keel-shaped quartzite xenolith that forms a ring of xenolith five miles in diameter. To the southeast Mosinee Hill and to the southwest, Hardwood Hill are similar xenoliths of this ring structure. The flat, swampy area to the south is underlain by �-11the younger Ninemile pluton which intruded the southern part of the Wausau pluton. Parts of the quartz syenite rim and xenolithic masses are embedded in the Ninemile pluton. The southern segment" of the Wausau pluton is cilrt:ttlar in plan with a diameter of eight miles. Although the core and south half of this calderalike structure were intruded by quartz monzonite of the Ninemile pluton, its structure is preserved as a discontinuous ring of large xenoliths five miles in diameter. The largest of these xeno1iths--Rib Mountain quartzite is over two miles long. Bedding in the xeno1ith dips steeply southward toward the core. The top of the xenolith has been eroded leaving a keelshaped mass, slightly convex northward, and surrounded at depth by quartz syenite of the crescentic intermediate zone. Quartzite xenoliths near intrusive contacts are typically veined and impregnated by K-feldspar. Pyroxene and amphibole syenite, commonly containing volcanic xenoliths, form a discontinuous outer rim (wall zone) of the southern segment. The northern segment of the Wausau pluton is semicircular in plan with its truncated southern edge along the Rib River. The Stettin pluton is contiguous with it on the northwest. Although its size and internal structure are sim"'lar to that of the southern segment, its intermediate zone consists of coarse gray syenite, and volcanic xenoliths predominate. The older northern segment probably represents a caldera structure, which was partially destroyed by intrusion of the southern segment. The more alkalic Stettin pluton, northwest of here, is oval in plan with dimensions of 5.0 x 3.5 miles. Three major zones distinguished in mapping where; (l) a"wall zone comprising aplitic biotite syenite, nepheline syenite gneiss, and "tabular syenite", (2) an intermediate zone consisting of coarse grai~ed amphibole and pyroxene syenite with swirled flow lineation, and (3) a circular core zone one mile in diameter comprising a rim of magnetite-rich nepheline-hedenbergite-fayalite syenite, and an inner core of pyroxene syenite. Both the Wausau and Stettin plutons possess strongly metasomatized, but unassimilated xenolith-rich wall zones. Concentric cataclastic lamination was developed by high-angle displacements accompanying their forceful emplacement. Subsequent, more passive intrusion of the Ninemile granite caused a partial foundering of at least the southern part of the Wausau pluton. �-12STOP # 2 TITLE: Large Quartzite and Biotite Schist Xenoliths in the Core Rim, Wausau Syenite Pluton LOCATION: South end of Mosinee Hill, NE~, NE~ Sec.27, T28N, R7E Wausau 15' and Wausau West 7.5' quadrangles AUTHOR: Paul E. DATE: February, 1980 ~1yers, University of Wisconsin-Eau Claire SUMMARY OF FEATURES: This abandoned 3-M quarry exposes the south end of a large quartzite xenolith and a much smaller xenolith of biotite schist (Figure 1). The lensoidal shape of the large xenoliths is extrapolated from shapes of smaller ones throughout the intermediate zone. Near its contact with quartz syenite the quartzite is impregnated with very fine-grained, interstitial pink microcline which selectively replaced certain layers in the quartzite. The abundance of interstitial K-feldspar diminishes toward the center of the quartzite xenolith. Smaller quartzite xenoliths have been thoroughly granitized. The question of whether these xenoliths were carried up or down along the cylindrical wall of the Wausau syenite pluton is still not answered. The only significant bedrock occurrence of quartzite and biotite schist in this area is as xenoliths in the Wausau syenite pluton. The xenoliths have the following important characteristics: 1. They show concentric, zonal distribution and orientation around the quartz monzonitic corf'--·thf~ Ninemile pluton. �-13- FIGURE 7. Profile of the south end of Mosinee Hill 2. The largest xenoliths occur one mile outside the core. 3. The quartzite xenoliths are the largest because of their lower susceptibility to fragmentation and assimilation. 4. Flow structure in quartz syenite and feldspar lenticulation indicate intrusion of the quartz syenite as a viscous crystal mush. 5. Mafic xenoliths were biotitized, and quartzite xenoliths were granitized through the metasomatic addition of K 0 and Al 0 with selective replacement of quartzite by fine-~rained mfc~o­ cline along bedding planes. 6. Xenoliths north of the Rib River are dominantly metavolcanic rocks, whereas the xenoliths south of Rib River are dominantly quartzite, biotite schist and very subordinate non-foliated metadiabase. 7. Quartz grains in the quartz syenite and the outer part of the Ninemile pluton are granular, subangular, coarse grained and strained. THE NINEMILE PLUTON: The Ninemile pluton has a granite rim containing xenocrystic quartz. Samples taken at one-mile intervals across the pluton from north to south and from west to east show a decreasing percentage of xenocrystic quartz and an increasing amount of plagioclase toward the center of the pluton. The contact at the Ninemile pluton is locally discordant, as at Black Creek 1.7 miles northwest of here. Miarolitic cavities. some filled with large quartz crystals are common along the west side of the Ninem"i Ie pluton. They indicate shallow conditions of crystallization" �-14- Figure 8--Block diagram of the northeastern corner of the southern segment of the Wausau syenite pluton at Mosinee Hill showing abundant, well-oriented quartzite (q) and biotite schist (bs) xenoliths in a flowlaminated, lensoidal quartz syenite (lqsy). The Ninemile quartz monzonite pluton (qm) intruded the quartz syenite with only a local discordance. The lensoida1 s~enite is bounded on the east by a thin wall of amph"ibo1e syenite (asy) which is itself in fault contact eastward with felsic volcanics. These rocks are cut with sharp discordance by a prominent diabase (db) dike which is characterized by a strong reverse polarity. The Qal is Wisconsin River alluvium. The shaded rectangle shows the 1coation of the profile in Figure 1. �-15- STOP #3 TITLE: Flow Structure of the Wall Zone, Wausau Syenite Pluton LOCATION: " >4- " -.....-... 1',/;~';/~~, ..... ,.-~ ! Ha~~;'n~i..' 'j 'p3)t1' AUTHOR: i Paul E. Myers, Department of Geology, UW-Eau Claire DATE: February, 1980 SUMMARY OF FEATURES: An early, medium-grained pyroxene-amphibole quartz syenite containing NW-oriented quartzite, schist, and volcanic xenoliths is cut by coarser-grained, flow-lineated quartz syenite of similar composition (Figure 9). Average xenolith orientation here is structurally continuous with the concentric lamination of the Wausau syenite pluton whose granite core is in Ninemile Swamp 5 miles southwest of here. "Rootless", lenticular pegmatite with walls of coarse K-feldspar and cores of quartz were probably differentiated from the nearly crystallized syenite at places of greatest quartzite assimilation. Thin screens of biotite schist and quartzite were rafted up or dropped down and brecciated in the viscous syenite magma (Figure 10). OESCR! PTION : According to Weidman (1907, p. 203-208) the IVIausau-type" quartz syenite is composed of alkali feldspars (orthoclase, microcline, albite, and microperthite), barkevite, hedenbergite, fayalite. biotite and quartz. Accessories include fluorite. apatite, magnetite. zircon and allanite(?). �Structures and cross-cutting relations of the syenite phases exposed here typify those seen throughout the crescentic northern rim of the Wausau syenite pluton. They are listed and described below in order of decreasing age. 1. The oldest rocks here are xenoliths in the syenite. They include thoroughly recrystallized, schistose, amphibol1tic metavolcanics, quartzite, and virtually unaltered felsic tuff. Note that long dimensions of xenoliths tend to be parallel to lamination and/or foliation and that, despite lithologic disparity, their mutual alignment imparts a distinct structural "grain lt to the enclosing syenite--a factor believed to be of considerable significance in working out an emplacement mechanism for this pluton. 2. An early. fine-grained, flow-laminated lensoidal quartz syenite may represent a chilled phase. 3. Coarse-grained, flow-1ineated pyroxene-amphibole quartz syenite cuts the fine-grained phase with sharp discordance. This unit contains irregular, lensoida1 and tabular inclusions of amphibolite, schist, and quartzite most of which show little assimilation. Although most of these inclusions show northwesterly elongation, the enclosing quartz syenite displays highly discordant flow-lineation with swirls and eddies suggesting considerable turbulence and viscosity in the quartz syenite magma. After gaining access to the xenolith along its banding or schistosity, the magma pUlled loose segments from its surface. With increasing magma/xenolith ratio the xenoliths became plastic and were strongly deformed in the flowing magma. Quartzite xenoliths appear to have been more readily plasticized presumably because of lower melting point. A screen of schistose metadiabase(?) crosses the south end of the outcrop. Its thin western end shows plastic deformation and I pu11-outs", whereas its more brittle eastern end is segmented into many angUlar fragments (Figure ), 4. Late-staget lenticular granite pegmatite veins with quartz cores probably represent residual liquid segregations along incipient contraction fractures in the already crystallized syenite. They appear to be "rootless" and of local derivation--perhaps from zones of abnormally high quartzite assimilation. 5. Coarse, sadie amphibole crystallized along joint surfaces. It is suggested that many of the structures in the syenites and quartz syenites of the Wausau pluton indicate forceful, subvolcanic injection of dry, viscous syenite magma. Detailed structural analysis may in time reveal the mechanisms of magma flow and xenolith mixing within the magma. Do the xenoliths t for instance, represent fragments from a fault breccia formed initially during caldera collapse and later invaded by upwelling syenite magmas? �-17- Figure g--Amphibolite (a) xenolith with swirled lineation and thin Seams of syenite is cut by coarse pyroxene syenite (psy). Lenticular veins with walls of K-feldspar (Kf) and cores of quartz (q) show mutually crosscutting relations with an intervening offset along a small fault. Joint coatings are of coarse, sodic amphibole. �.;18- Fi gure lO--Segmented metadiabase screen in flow-banded lensoidal pyroxene syenite. �-19- STOP #4 TITLE: Lensoidal Quartz Syenite, Employers' Mutual Insurance Company LOCATION: NW~, SE~, AUTHOR: Paul E. Myers, and Manmohan Sood DATE: March, 1980 Sec. 27, T 29 N, R 7 E, Wausau West 7.5' Quadrangle SUMMARY OF FEATURES: Coarse-grained, pink and brownish gray quartz syenite containing up to 60 percent volcanic xenoliths (best seen on horizontal surfaces) is exposed in an old quarry behind the offices of Employers' Mutual Insurance Company. This rock exemplifies contaminated quartz syenite of the lIointermediate zone of the Wausau syenite pluton (Figure 3). Associated quartz syenite elsewhere in this zone contains large, metasomatized quartzite and/or mica schist xenoliths, the most spectacular of which is exposed on the summit of Rib Mountain. The Rib River 1I1ineament separates the two crescentic segments of the Wausau syen i te body. ll ll DESCRIPTION: The quartz syenite at this location is composed of coarse perthite (80%), quartz (10%), and sodic pyroxene partially replaced by mixtures of dark green amphibole, carbonate, and magnetite (10%). Quartz is interstitial. Large magnetite segregations can be observed along the road on the east side of this outcrop. Four facies of quartz syenite were recognized and analyzed chemically (See Table 2). The pink syenite contains up to 60% trachyte or rhyolite (?) xenoliths which are lensoidal with blunt, broken east ends and rounded (assimilated?) west ends. Their orientation is consistently N 7075 0 W, vertical in this area (Figure 10), and they are seen best on horizontal surfaces. Large quartzite xenoliths occur in the quartz syenite along the ridge crest north of here. The crescentic form of this part of the Wausau syenite body also shows as a conspicuous magnetic anomaly owing to the high concentration of magnetite as sheets and lenses in these rocks. The xenoliths �-20R 0 A 0 o o meter (in detailed area) I Figure 11-- Volcanic xenoliths (dotted) in flow-lineated amphibole quartz syenite (white). Outcrops in grassed area between three roads behind Employers' Mutual Insurance Company. show up on fresh surfaces mainly as slightly finer grained, darker colored masses. In addition to the angular volcanic xenoliths, the quartz syenite here contains mafic schlieren and clots showing irregular shape and orientation as well as gradational boundaries, a factor suggesting their more distant derivation and more thorough assimilation. Xenoliths of highly disparate lithology, and metamorphic grade occur side by side in these plutons. Their lenticular shape suggests mechanical segmentation before or during syenite intrusion. Convoluted flow lineation in amphibole syenite (as at the Old Technical Institute in Wausau) indicates viscous flow, probably due to water-deficiency of the magma. At many locations it is very difficult to distinguish the intrusive phase: indeed, one is hard-pressed to find an uncontaminated syenite exhibiting the features of a true intrusive rock. Sillimanite-bearing quartzite occurs as a tabular xenolith in fine-grained hornblende syenite 2.5 km west-northwest of here. The sillimanite suggest considerable upward transport of the xenolith from a high-grade metamorphic basement. The mica schist and metagabbro(?) xenoliths at Mosinee Hill and along the east side of the Wausau syenite body also suggest a deep-seated source. The close-spaced juxtaposition of xenoliths of disparate lithology indicates considerable vertical movement of wallrock fragments. To what degree did collapse modify these intrusive relationships? Does the quartz syenite represent a syenite magma which was contaminated by zenolithic quartzite? To what degree was the syenite able to assimilate xenoliths? Textural relations se~throughout the pluton suggest little assimilation but considerable dilation owing at least in part to explosive eruption. �-21- TABLE 2 Bulk chemical compositions of the four principal quartz syenite facies from Employers' Mutual Insurance Company Quarry. Description - EW-3 (WEST) Brownishgray EW-5 (EAST) Coarse~ dark gray NSI (SOUTH) Pink syenite~ with volcanic xenoliths SEI (NORTH) Medium-grained syenite Si0 2 63.05 63.55 63.90 64.10 Ti0 2 0.78 0.54 0.47 0.48 A1 0 12.60 15.16 14.14 15.17 1.91 1.25 5.42 4.58 FeO 7.72 3.48 1.32 1.44 MnO 0.34 0.16 0.14 0.12 MgO 0.41 0.16 0.45 0.09 CaO 2.66 1.72 1.35 1.50 Na 20 4.80 5.52 6.32 5.17 K20 H2O 4.22 5.67 6.34 5.57 0.76 0.42 0.56 0.26 P205 0.22 0.06 0.05 0.06 CO 2 0.28 1.92 0.62 0.09 BaO 0.094 0.066 0.024 0.036 Zr0 2 0.222 0.114 0.062 0.071 154 118 80 80 78 83 67 42 2 3 Fe 203 Rb Sr ppm In comparison with Nockolds' (1954) average syenite composition (see Table 2)~ these quartz syenites are richer in SiO, and total iron and poor in alkalies and lime. Their Rb and Sr contents are also low compared to other similar rocks. �-22- THE STETTIN SYENITE PLUTON Although Weidman (1907) mapped the geology of north-central Wisconsin and paid special attention to the mineralogy of the syenites near Wausau, Emmons and Snyder (1944) hypothesized formation of the Stettin syenite body by metasomatism of fe1dspathic rocks along shear zones with a1kalirich solutions derived from a subjacent granite batholith. Turner (1948) studied the heavy accessory minerals and radioactivity of the Stettin pluton, and Geisse (1951) described the petrography of this pluton. Petrographic and geochemical investigation of the mafic minerals and nepheline of the Stettin pluton initiated analytical studies which have been extended by the work of Sood and Berlin. The concentrically zoned Stettin pluton (Figure 12) is oval in plan, elongated northeasterly, with a length of 5.5 miles and a width of 4.0 miles. Older volcanic rocks enclosing the pluton have been extensively syenitized. The eastern and southern margin of the pluton is a complexly laminated series of altered volcanic screens and pendants and various, contaminated intrusive phases of the syenite including n~he1ine syenite. The wall zone comprises a discontinuous outer rim of gneissic nepheline syenite, and an inner layer of tabular syenite (Stop #5). The intermediate zone (Stops #6 and #7) is composed of amphibole and pyroxene syenite showing considerable variation in composition and texture. The amphibole syenite is commonly quartz-bearing. The core zone (Stop #8) is one mile in diameter and is located asymmetrically near the north end of the pluton. The core zone comprises a well-defined, cylindrical rim of indistinctly banded nepheline syenite surrounding a core of pyroxene syenite. Field relations indicate the following intrusion sequence: (l)PYr.qxene syenite, (2) nepheline syenite, (3) tabular syenite, (4) amphibole syenite. Numbers 3 and 4 could be reversed. This evidence is based wholly on field relations (Myers). It should also be emphasized that the intrusion sequence may not be the same as the crystallization seqence. Analytical work (Sood and Berlin, this guidebook) suggests a very late age for the nepheline syenite. (See discussion of petrochemistry beginning on page 46 ). A summary tabulation of paragenetic relations of minerals in each zone of the Stettin syenite pluton is presented with modification from Koellner (1974) in Table 3. �-23- -mv o • .... ..... ..... " ... ' ,.'. ," 45 0 00' , MILE I mv EXPLANATION Qal Qgt Alluvium Till Unconformity c gr .Jl psy Pyroxene Syenite aay syap Amphibole Syenite Syenite aplite .g E II v ~ Q. Granite c .g .Jl E II v e Q. tay Tabular Syenite nsy Isy Nepheline Syenite syv mvb fv Syenitized Volcanic S 8reccjated Malic Valtonics mv MalH Volcanics Lensoidal Syenite Felsic Volcanics Figure 12 -- Geologic map of the Stettin complex (after Myers. 1973) including localities of samples and field trip stops. �-24TABLE 3 PARAGENETIC RELATIONS OF MINERALS IN EACH ZONE OF THE STETTIN PLUTON rJONE PARAGENETIC RELATIONS ROCK TYPE Tabu1 ar Syenite (Myers, 1973) - - zircon-/ I pyroxene-! I-alkali feldspar-i ~ opaques-l green amphibole-1 I w z 0 N -l -l o::t: f-biotite~ Nepheline Syenite (Koell ner, 1974, p. 12) - - nephel i ne---j r-alkali feldspar-i ~ol ivine~ :3: I-- pyroxene-f w ropaques-! /- green amphi bo1 e.., f-biotite-i z 0 N w Pyroxene Syen ite 0:: ~alkali feldspar-, rapatite-I 0 u ~opaques-f r-ol i vinew r-pyroxene-t r-green amphibo1e-j z 0 N ~biotite~ karbonate-l ~b1ue amphibo1e- w I0< I-< Cl w :E: 0::: w l- z I-< Amphibole Syenite (Koellner, 1974, p.33) ~a1ka1i feldspar-l I-apa ti tei I-opaques-i I-- pyroxene-f r-- green amphi bo 1e-l I-biotite-l I-b1ue amphibole �-25STOP #5 TITLE: Contact relations and minerals in the Wall Zone, Stettin syenite pluton LOCATION: County Highway 0 at 10146 Stettin Road, Paul Knopp property, SE~, SE~, Sec. 22, T29N, R6E, Marathon 15' quadrangle, (Sample Location 92) AUTHORS: P.E. Myers and M.K.Sood DATE: February 1973, February 1980 SUMMARY OF FEATURES: The outermost rim of the Stettin pluton is gneissic nepheline syenite composed mainly of alkali feldspar, perthite, nepheline, aegirine, sodic amphibole and biotite. It is in sharp contact with, and veined by, tabular syenite composed of coarse, well-oriented laths of perthite, sodic amphibole, pyroxene, and lensoidal mafic inclusions composed essentially of the same minerals but in different porportions and of finer grain size. The mafic inclusions are well-oriented parallel to the tabular fabric of the enclosing syenite and to the wall of the pluton. They contain large perthite porphyroblasts of similar composition and size as those in the enclosing syenite. Zircons were mined at this site in the 1950's. Zircons from this site have given a UjPb age of 1520 + 20 m.y. by W.R. Van Schmus (oral communication). The chief questions to be answered at this site are: (1) how were the nepheline syenite and tabular syenite emplaced, and (2) to what extent is the present mineral assemblage a result of metasomatic replacement? �-26- The abundance of zircon and hastingsite amphibole, biotite and carbonate indicates a miaskitic trend for the nepheline and pyroxene syenites. The compositions of the nepheline and pyroxene syenites are very similar (Table ). According to Koellner (1974, p. 144) the amphibole syenite is agpiatic and could contain a carbonatite body. DESCRIPTION: The nepheline syenite (Figure 13, Tables 4 and 5) is a gray, banded rock composed here of perthitic feldspar nepheline, olivine, pyroxene, magnetite, amphibole, and biotite. Contorted aplitic and pegmatitic bands lie roughly parallel to the wall of the pluton about 1500 feet south of here. The nepheline occurs as blocky, pinkish grains which weather much more readily than the associated minerals, giving the rock a characteristic pitted appearance. Nepheline is partially altered to cancrinite and iron oxides. Banding, and mafic content of the nepheline syenite increase outward toward its contact with syenitized mafic volcanics which tren westnorthwesterly. In addition to the essential minerals listed above, common accessory minerals include zircon and sphene of unusually large size and abundance, apatite, fluorite, allanite, sodalite, pyrochlore and thorogummite(?). U/Pb dating of the zircons from this site by S. Goldich (oral comnunication) gave a minimum age of 1400 m.y. More recent analyses of these zircons by W.R. Van Schmus yielded a U/Pb age of 1520 + 10 m.y. Thus, the Stettin syenite is about 20 million years older than the Wolf River Batholith (oral communication). The gneissosity and isoclinal folding exhibited by the gneissic nephe'line syenite of the wall zone on the south side of the Stettin pluton suggest considerable differential movement of material a'long its outer wall. The extent to which metasomatism was involved during and after emplacement is not known. However, metasomatism was extensive, and that the nepheline syenite may consist in large part of metasomatized wall rocks. Zircon from this locality is deep red-brown, doubly terminated euhedral prisms up to 14 mm in length. Some crystals display geniculate twinning similar to that of rutile. Chemical analyses of three zircons from a nearby site (NW~ of Sec. 22) by F.B. Hall (in Weidman, 1907, p. 313) indicates an A1 03 content of between 4.28 and 7.80 percent and an Fe?03 content between 21.21 and 4.47 percent. Ca, Ti, Th and rare earths were sought but not detected. Brown pyrochlore octahedra up to 2 mm in diameter were found at this location by Weidman (1907, p. 308-309). Allanite is confined mainly to petmatitic portions in the nepheline syenite. Apatite and sphene of unusually large size show affinity for clusters of mafic minerals in the nepheline syenite. Large sphene c~ystals up to 7 mm in length can be collected from nepheline syenite lenses and masses near its contact with tabular syenite, �-27- The tabular syenite (Figure 14, Tables 4 & 5) is composed dominantly of coarse laths of m;croperthite. Vein and patch type perthites predom"inate. Po'ikilitic amphibole (hastingsite) rims pyroxene (intermediate between acmite and hedenbergite according to Koellner (1974, p. 65). The tabular fabric (Figure 15) is characterized by a random orientation of perthitic feldspar tablets in a plane parallel to the outer wall of the pluton and parallel to the long dimensions of mafic inclusions. Perthitic feldspar tablets within mafic inclusions and across their contacts are identical to those in the enclosing tabular syenite. The inescapable conclusions is that the perthitic feldspar is at least partly of metasomatic origin. Veins of tabular syenite locally cut the nepheline syenite gneiss in the old quarry face at this location. Mafic inclusions comprise from 5 to 80 percent of the tabular syenite. As the volume of mafic inclusions increases, the mafic minerals, mianly sodic amphibole, become coarsely poikilitic. Individual amphibole grains up to 12 centimeters long were observed in a small roadside excavation 1.5 miles east-southeast of here. Although the mafic inclusions contain a much higher percentabe of pyroxene and olivine than the enclosing tabular syenite, they are of about the same chemical composition. The tabular syenite forms the outermost layer on the north and west sides of the Stettin pluton where the nepheline syenite is absent. The abundance of mafic inclusions increases outward in the tabular syenite, suggesting considerable contamination by the basaltic wallrock. A unit mapped as lensoidal syenite and a closely associated syenite aplite (Myers, 1973) are found locally where the nepheline syenite is absent. The lensoidal syenite is an aplitic, gneissose rock consisting of mafic inclusions rich in biotite enclosed in an aplitic syenite. The syenite aplite is similar in texture and mineral composition but relatively free of mafic inclusions. �TABLE 4 MODAL COMPOSITIONS OF THE STETTIN ROCKS ROCK TYPE CORE ZONE Amphibole Syenite Pyroxene Syenite Tabular Syenite 6 and 504 65 46 2 92 87.4 80.2 26.4 63.6 17.6 75.7 6.6 61.4 SAMPLE NUMBERS* 10 77 503 108 Quartz Nepheline Perthite Albite Amphibole Pyroxene Biotite Bi 0 t i te (a1ter . ) Zi rcon Apati te Fl uorite Calcite Sphene Opaque minerals Al teration 7.1 6.6 2.9 1.4 80.7 0.5 11.2 83.5 83.0 8.6 90.3 0.2 5.1 0.6 0.2 0.3 0.2 0.5 0.1 0.2 Nepheline Syenite 13.6 0.6 5.5 4.1 0.5 19.1 8.4 4.6 29.5 0.2 0.6 0.4 0.4 0.1 0.4 1.0 0.7 0.1 0.5 0.1 0.4 *Sample numbers shown on Figure 12 0.3 0.2 I N en I 0.2 0.1 WALL ZONE INTERMEDIATE ZONE 0.3 0.1 0.2 0.3 1.3 0.3 1.1 0.5 0.5 �-29- TABLE 5 CHEMICAL COMPOSITIONS OF THE STETTIN ROCKS* CORE ZONE II Pyroxene Syenite INTERMEDIATE ZONE ROCK TYPE Amphibole Syenite WALL ZONE Tabular Syeni te Nepheline Syenite 46 2 92 61. 50** 57.45 56.95 54.10 16.23 16.62 16.93 21.02 16.32 3.13 2.55 5.20 2.58 2.93 3.41 2.10 2.70 5.66 1.68 5.98 2.12 7.08 0.01 0.02 0.08 0.14 0.24 0.21 0.07 1. 22 0.70 0.50 0.95 1. 10 2.15 1.43 2.64 0.51 4.03 Ha 20 5.92 6.92 7.07 6.51 5.97 6.49 6.71 7.81 5.81 ~O 4.31 5.11 5.19 5.51 5.67 5.15 5.02 5.99 4.84 H2O CO 2 0.73 0.83 0.70 logS 0.51 0.63 0.98 1.43 0.77 0.38 0.35 0.36 0.40 0.22 0.17 0.18 0.40 0.09 Ti0 2 0.72. 0.42 0.27 0.32 0.75 0.31 0.59 0.38 1. 32 P205 0: 11 0.04 0.06 0.07 0.13 0.07 0.13 0.50 0.49 MnO 0.23 0.12 0.15 0.18 0.26 0.22 0.30 0.07 0.29 S 0.010 0.004 0.003 0.008 0.034 O.OOg 0.023 0.000 0.044 0.102 0.165 0.260 0.171 0.11 0.100 0.140 0.001 0.079 10 70 503 108 6+504 5i02 66.10 65.20 64.70 61.95 59: 75 A1 203 Fe 203 13.24 15.59 15.86 16.04 2.61 2.36 2.45 FeD 4.12 2.22 MgO 0.43 CaD Samp1 e # zr0 2 Cl BaD { 0.013 0.024 0.071 0.105 0.241 0.143 0.215 0.03 65 0.010 0.010 0.345 0.02 0.150 0.160 0.103 0.086 0.025 0.02 0.208 Rb(ppm) 199. 152. 66. 133. 115. 102. Sr(ppm) 44 105. 17<t . 109. 57. 345. * Ana1yst-K. Ram1al, University of Manitoba **Tabu1ar Syenite �-30- Figure l3--Photomicrograph of nepheline syenite showing euhedral nepheline grains surrounded by a matrix of discrete albite crystals and amphibole. Crossed nichols. Figure l4--Photomicrograph of tabular syenite showing parallel alignment of feldspar crystals. Crossed nichols. �-31- Figure 15-- Typical fabric of tabular syenite showing coarse tablets of microperthite in random orientation parallel to the wall of the pluton. Microperthite laths in the 1ensoida1 mafic inclusions tend to have a preferred orientation parallel to those in the enclosing syenite. Some of the laths crystallized across the edges of inclusions, thus indicating a metasomatic origin of at least part of the microperthite. �-32STOPS #6 and #7 TITLE: Amphibole and Pyroxene Syenites of the Intermediate Zone LOCATION: Stop #6: Stop #7: J NW~, Sec. NW~, SW~, 14, T29N, R6E, Hamburg 151 quadrangle Sec. 14, T29N, R6E, Marathon 15' quadrangle .--' N 1 / 10 '- ". "- .- '0 .Ir/ "l Dr" 20.0."" R"' I"""~ rr AUTHORS: M.K. Sood and P.E. Myers DATE: Februa ry, 1980 SUMMARY OF FEATURES: Massive and flow-lineated, gray to pinkish-orange amphibole syenite (Stop #6) and pyroxene syenite (Stop #7) of the intermediate zone are composed dominantly of alkali feldspar and up to 35% poikilitic arfvedsonite amphibole which encloses nuclei of pyroxene. The amphibole syenite shows considerable variation in composition and texture from pegmatitic clots of quartz-bearing aplitic phases in single outcrops. Clots of coarse feldspar and poikilitic amphibole (up to 12 ern. long) are cornmon. Most outcrops display swirled flow ll'neation similar to that seen in amphibole quartz syenite at Stop #3 (Old Technical Institute, Wausau). The amphibole syenite contains a relatively large percentage of blue (riebeckitic) amphibole. Although the dominant mafic mineral in the pyroxene syenite ;s amphibole, pyroxene occurs in discreet grains not rimmed by amphibole. At a stone quarry 0.2 mile east of here, the pyroxene syenite shows spectacular schiller structure of the feldspar (moonstone). �-33- DESCRIPTION: Whereas the amphibole is characteristically pink in outcrop, the pyroxene syenite is a moderate-to-light olive gray with islands of coarse mafics enclosed in coarse tablets of randomly oriented feldspar. The amphibole syenite shows considerably greater textural variation, even at mesoscopic scale. Although vein-like and irregular masses of zoned pegmatite and aplite are common in all outcrops, the dominant rock type is medium-grained amphibole syenite with a faint to conspicuous lamination, with or without lineation created by alignment of feldspar tablets and lensoidal clots of mafic minerals--mainly amphibole and subordinate pyroxene. Pegmatitic phases of the amphibole syenite contain up to 12% quartz as coarse segregations commonly rimmed by blue (riebeckitic) amphibole. In thin section, mafics are clustered in acicular or radiating fibers. This zone to the southwest contains small sill-like masses of tabular syenite. The major mineral is micro-to mega-perthitic feldspar surrounding the mafic minerals which seemingly are later than the feldspars. The principal mafic mineral is bluish-green arfvedsonite-riebeckite amphibole (Table 8), sometimes mantling minor Fe-augite pyroxene. However, pyroxene is absent in some samples of this zone. Alteration of amphiboles to brown-red biotite is common in patches and along borders. The interesting feature of the amphibole grains is containment of a dark blue riebeckitic phase which is most common only in this unit. Some amphiboles poikilitically enclose euhedral feldspars (Figure 17). Accessories include zircon which is commonly zoned, quartz (up to 12%), fluorite, calcite, FeTi-oxides, apatite and allanite. �-34- Figure 16--Photomicrograph of aplitic syenite showing a fine-grained mass of anhedral perthitic feldspar. Crossed nichols. Figure 17--Photomicrograph of amphibole syenite showing poikilitic texture. Note the euhedral outlines of the feldspar crystals enclosed in the amphibole grain. �-35- Figure 18--Photomicrograph of pyroxene syenite showing zoned grain of aegirine-augite mantled byarfvedsonite. Crossed nichols. Figure 19--Photomicrograph of pyroxene syenite. Patch perthite showing albite twinning. Crossed nichols. �-36- STOP #8 TITLE: The Core Zone of the Stettin Syenite Pluton LOCATION: SW 1/4, SE 1/4 Sec. 2, T29N, R6E; H-amburg151 quadrangle ! I;': \ ,/ \ .t:". o. SIT / 10 08,/ o. ( -.. / / .0 '0 --' AUTHORS: Paul E. Myers and M. K. Sood DATE: February, 1980 ~_~. ~ _,,-,0 -) P 11 ~ I o 0 .... I '. '-----__ --_1\....' • c•. ". \ . SUMMARY OF FEATURES: The core of the Stettin syenite pluton comprises two distinct parts: (1) a cylindrical core margin of indistinctly banded or lineated, mediumgrained nepheline syenite and (2) an inner core of pyroxene syenite. Bent and crushed feldspar grains and a crude southeast-dipping layering were formed during or after emplacement of the core margin. The nepheline syenite core margin produced a pronounced donut-shaped magnetic anomaly about one mile in diameter. Drilling by Bear Creek Mining Company in the southeast corner of the inner core retreived about 250 feet of core classified by company geologists as larvikite. No carbonatite has been found, although the agpaitic trend of the rocks here suggests that such a carbonatite is possible (Koellner, 1974, p. 144). DESCRIPTION: The nepheline syenite of the core margin here is indistinctly banded or lineated. The weathered surface is pale yellowish gray with pitting due to differential weathering of the nepheline. The fresh nepheline is pale greenish brown and occurs as well-oriented, subhedral to euhedral grains enclosed by tablets of feldspar up to 2 em long. The feldspars, nepheline, and islands ofomafie minerals are elongated in a plane dipping southeast at between 60 and 70. This lamination is not parallel to the outer edge of the core margin at this location. Bent and broken feldspar and nepheline grains and lenticulation of mafic mineral clusters suggest shearing during or after intrusion. �-37- The dominant mineral is tabular microperthite (60% orthoclase with 40% rni]oclase ribbons). An additional 25% of the rock is subhedral to euhedral nepheline, which is partially altered to cancrinite. Mg-rich pyroxene and pleochroic, olive brown amphibole are of about equal abundance and make up about 20-30% of the rock. Accessory (2-5%) Mg-rich olivine and dark brown biotite accompany the other mafic minerals in lenticular clusters and islands occurring interstitially in the nepheline syenite. The biotite partially rims the amphibole and was probably formed at a late stage of crystallization. This unit produced a pronounced~ donut-shaped magnetic anomaly about one mile in diameter. Wiedman (1907~ p. 251) reports unusually large and abundant magnetite octahedra from streams northwest of here. The magnetite is apparently associated most closely with the olivine. �-38MINERALOGY AND MINERAL CHEMISTRY (STOP NO·s 5~ 6~ 7 and 8) by M. K. Sood and L. A. Berlin The principal mineral phases in Stettin Complex are perthitic feldspars, nepheline, sodic and calcic pyroxenes~ and sodic amphiboles whose representative chemistry is given in Table 4 and characteristics described below: Fel ds pa rs The major phase of feldspar is a microperthite in uniform veins showing parallel, subparallel~ or wavy lamellar intergrowths~ or as patches of one feldspar in the host (see plate 1). Both perthite and antiperthite are present, although perthite is more common than antiperthite. Frequently the tabular feldspar grains exhibit Carlsbad twinning and less cOll1l1only Mannebach twinn"ing. The perthitic feldspar constitutes 80 to 90 percent of the syenites and 60 to 75 percent of the nepheline syenites (Table 4). Distinct grains of albite have an average extinction angle of 15 0 , but are not common in any of the syenites. Microcline~ also present as distinct grains~ show its characteristic spindle-shaped polysynthetic twinning and wavy extinction, but is less abundant than albite as individual grains. The bulk compositions of the perthitic alkali feldspars were determined for nine samples of three major zones of the Stettin complex. The samples were homoge~ized to a sanidine phase at 1050° in a muffle furnace for 48 hours; then .620 = 201 feldspar - 101 KBr0 CuKa was measured and the molecular percent orthoclase was determined using the3 homogenized natural microcline-low albite x-ray determinative curve of Jones et al. (1969) The compositions are given below in Table 6. ---Table 6 THE MOLECULAR PERCENT ORTHOCLASE OF HOMOGENIZED PERTHITIC ALKALI FELDSPARS OF THE STETTIN ROCKS Sample .629 CuKa Mol %Or Core Zone pyroxene syenite 1.40 0 39 Intermediate Zone amphibole syenite 3 amphibole syenites 1.45 1.40 35 Rim Zone tabular syenite nepheline syenite nepheline syenite 1.43 1. 35 1.39 37 44 41 39 �Plate 1. A. Enlarged section patch perthite of Plate 3B. Crossed nicols B. Photomicrograph of vein perthite in amphibole syenite. Crossed nicols. I W 1.0 I TYPES OF PERTHITIC FELDSPARS IN ROCKS OF STETTIN COMPLEX: c. Enlarged section showing braided perthite. Crossed nicols. (a) PATCH PERTHITE (b) VEIN PERTHITE (c) BRAIDED PERTHITE �-40- The molecular percent orthoclase ranges from 35 to 44%; however, Or% is above 40% for the nepheline syenites and is less than 40% for the nephelinefree syenites. The intensity ratios of the 201 peaks of microcline and albite were determined for the perthitic feldspars by scanning in both directions between 20 0 and 23 0 -20 Cula' at 1/8 0 -28 per minute using 200 counts per full chart scale, a time constant of 5 seconds and a chart speed of 15 inches per hour. The angular positions were averaged from three scans. Then the goniometer was exactly centered on one peak at a time and the intensity was measured using a fixed time of ten seconds with a 2 second time constant. The background intensity was measured at the midpoint between the two peaks. Then: A = number of counts on microcline 201/10 s B = number of counts on low albite 201/10 s C = number of counts on the background/lO s The intensity ratio lalla = (A - C)/(B - C). The intensity ratio and the value of the bulk composition of Or%/Ab% for each of the perthitic feldspars studied were plotted on the granh of Kuellmer (1959)(Figure ~O). From this diagram, implications can be made as to the temperaturestructural state of the feldspars. From the plots a broadening ratio (8) is obtained. The broadening ratio is a measure of the distortion or structural mistakes in the two phases of perthite. The broadening ratio will decrease with slower crystallization and lower temperature since these conditions are favorable for the attainment of an ordered arrangement of Si and Al ions in the tetrahedral sites of the feldspar structure (Smith, 1974). The broadening ratios for the perthitic alkali feldspars of the Stettin rocks range from low (B = 0.30) to intermediate values (B = 0.9). This is an indication of the low temperature-structural state of these perthites, corresponding to the maximum to intermediate microcline-low a"lbite series determined from the positions of the 204 and 060 reflections. �-41- 10 ....T"T""1 r---___r"-~-_r__r_..,.....,.....,r_T'".,.._--......,.-_.,-...,.___r""""T'" 8 / 6 / / / / ~ // / <0"" ,,"" / ~" / o / / 1-4 / .......... o / / H .8 .6 .5 / / / / / / / / / / / / / / / .. / / / / / / / / / / , / f),~ ~. / / / / / / ~. //~ / / / "'~ / / "" <0"" / / / / ~ / // / / / / / / / / / / / .2 / / // / ~ .~. //// / ""~. e/ / / / / ,," '" ~ / ~" " /~" / / / / / / .4 .3 / / / / / /.. / / / ~ / / / / / // / / / / / ~. 2 / / // / / / 3 / / / // / 4 / / / 5 / / / / / / / / / / .2 .4 .6 .8 1 ORrHoe LASE ALBITE 2 6 8 10 % % figure 20 -- Plot of the bulk composition Or%/Ab% versus lolla for the 201 reflections of the two feldspar phases in the Stettin perthite samples for determination of their broadening ratio B (diagram after Kuellmer, 1959). �I TABLE 7 S;02 A1 203 Ti0 2 FeO MnO MgO CaO Na 20 K20 ELECTRON MICROPROBE CHEMICAL ANALYSES OF MAJOR MINERALS OF STETTIN COMPLEX Pyroxene * psy Feldspar tsy Nepheline * Amphiboles nsy 46.5 39.90 50.1 50.8 67.42 68.23 40.45 48.1 0.59 33.1 19.23 8.70 9.28 1.0 1.34 19.72 -0.26 3.17 -0.30 0.1 1. 31 -29.1 23.70 26.40 0.18 34.22 26.8 ---0.81 0.89 0.71 --1.00 1. 52 0.99 2.28 0.73 0.62 4.41 --0.13 11 .00 0.44 0.25 10.3 8.89 17.8 20.30 15.20 0.57 6.80 7.40 11 .23 2.14 3.30 2.40 N.D. 5.46 6.39 N.D. 0.27 1. 57 1. 75 -- ATOMIC PROPORTIONS Si Al Al Ti Fe Mg Ca Na K Fledspars Based on 8 oxygens 2.987 2.988 1.004 1.018 0 0 --- -0.021 0.635 0.361 Ae Di Hd * From Koellner (1974) ---0.012 0.954 0.015 Amphiboles Based on 23 oxygens 6.73 6.43 1. 52 1. 76 0.118 0 0.372 0.147 3.89 4.61 0.515 0.172 1.765 1.536 0.690 1.031 0.323 0.361 2.001 -0.42 0.004 0.930 0.38 0.797 0.194 Pyroxene * Based on 6 oxygens 1.990 0.010 0.017 0.008 0.786 0.261 0.862 0.044 -- -- 16.0 3.5 75.1 3.9 25.2 60.8 2.074 -0.064 0.010 0.902 0.060 0.480 0.538 -47.3 5.3 42.8 Nepheline * Based on 32 oxygens 8.76 7.352 --0.29 0.27 5.52 1 .315 Fe-Ti Oxides 0.44 0.25 7.57 90.40 1.19 Fe-Ti Oxides Based on 24 oxygens 0.119 0.079 1.530 20.310 0.272 I +::> N I �-43- Nepheline Nepheline is characterized by its euhedral rectangular form and parallel extinction in thin section. In hand specimen, crystals may reach 4 or 5 cm. in length and appear gray with a greasy luster. Nepheline grains show alteration along borders and cracks to a colorless mica, possibly paragonite (Deer et~., 1963). According to Koellner (1974) nephelines are enriched in Si by 15% and deficient in alk~ies by about 13% (also see Smith and Sahama, 1954). Figure 21 Photomicrograph of nepheline syenite showing nepheline grains (at left and right edges) in aplitic matrix of perthitic feldspar. Crossed nicols. �-44Pyroxenes Both sodic and calcic clinopyroxenes occur in the various rocks of the Stettin Complex. Representative chemical compositions are given in Table 8. Sodic pyroxenes, aegirine and aegirine~augite, occur as distinct grains as well as crystals rimmed with bluish-green amphibole. Some grains show color zoning with pale cores asd bright green rims. The average eatinction angle (X:C) of the cores is 28 , whereas that of the rims is 13-24 , implying outward increase of the aegirine content. Calcic pyroxenes (diopside-hedenbergite) are iron-rich with aegirine content of up to 10% (Koellner, 1974). In general, Na+Fe+ 3 content of the pyroxenes is highest 'in the rocks of the wall zone. Figure 22 Photomicrograph of pyroxene syenite. Zircon crystals (left of center) surrounded by arfvedsonite (dark) and aegirine-augite. Note biotite near the center of the photograph. Small colorless apatite crystals occur as inclusions in the mafic minerals. Stained alkali feldspar surrounds the cluster. Plane polarized light. �-45Amphiboles The dominant mafic mineral is a bluish green sodic amphibole. The absorption scheme of this mineral closely agrees with arfvedsonite: X = bluish green or greenish blue, Z = greenish brown or light brown. The amphibole grains have an average extinction angle (X:C) of 16 0 ; this corresponds to a composition of 26 Mg: (Mg + Fe+ 2 + Fe+ 3 + Mn) in the eckermannitearfvedsonite ~eries (Deer et a1., 1963). However, the extinction angles vary from 00 to 29. Some amphibole grains exhibit an optical character more closely resembling riebeckite and have an absorption scheme X = deep blue, Z = light blue. The extinction angle of these qrains is approximately 10 . Figure 23 Photomicrograph of bluish green arfvedsonite in amphibole syenite no. 108. Quartz at right edge. Plane Polarized light. X-ray diffraction powder patterns of the riebeckitic amphiboles show a d:spacing of 8.42 oA for the 110 reflection, compared to 8.50 0 A for arfvedson,te. The lower d-spacing is in close agreement with other riebeckite analyses. Both sodic and calcic amphiboles are Fe-rich. Their composition probably reflects differentiation. �-46Biotite It occurs "in small amounts in two distinct varieties. Both have strong pleochroism but exhibit different absorption schemes. One is reddish brown to dark brown, and the other is 1ight brown to dark green. This may suggest possibly reflecting different Ti, Fe+ 2 , Fe+ 3, and Mg contents (Hyama, 1959; Deer , et ~., 1963 ) . Accessory Minerals The only zirconium mineral so far found is zircon which occurs as zones prismatic crystals along clusters of mafic minerals especially in rocks of the Core Zone, e.g., pyroxene syenite. Other accessory minerals are sphene, fluorapatite, fluorite, calcite, Fe-Ti oxides. PETROCHEMISTRY Chemical compositions of the Stettin rocks are presented in Table 8. Table 9 compares average compositions of the Stettin rocks to those of Nockold's (1954). The average of the Stettin nepheline syenites show distinct differences from Nockold's average syenite. These Stettin samples, while only slightly higher in silica, are lower in A1 203 and NA 20 and higher in FeO, CaO and P205. The amphibole and pyroxene syenites, also sTightly higher in silica than Nockold's average syenite, are lower in A1 201 , MgO, CaO and K20, while higher in FeO, NA 20 and MnO. The differentiation i~dices (01 ~ normative quartz + orthoclase + albite + nepheline + leucite + kalsilite) (Thornton and Tuttle, 1960) for these Stettin rocks are given in Table 10. The average 01 for these rocks is 84.7, which represents a high degree of differentiation. However, nepheline syenites have the highest 01 of 88.9 and 93.9 respectively, indicating the greatest extent of differentiation among these rocks. The agpaitic indices of the Stettin samples are shown in Figure 24-A. Rocks of lower Si0 2 content, the nepheline bearing rocks, have lower agpaitic indices than the more silica rich rocks. This is a reflection of the higher alumina content, due to the presence of nepheline, in the nepheline syenites. The ratio Na 20/K?0 versus Si0 2 (Figure 24C) increases with increasing Si0 2 . This diagram shows two trends suggesting that the Stettin rocks belong to two series. Amphibole and pyroxene syenites appear to follow a continuous differentiation sequence. (Figures 24A-F). C.I.P.W. normative compositions are presented in Table 10. The normative compositions of the analyzed Stettin rocks were calculated in terms of NaA1Si0 4 , KA1Si0 4 and Si0;l and are plotted in the systems NaA1Si0 4 - KalSi0 4 - Si0 2 at 1000 bars PH 0 ~Figure 25). All of the rocks fall within the low temperature trough. 2 �-47- TABLE 8 CHEMICAL COMPOSITIONS OF THE STETTIN ROCKS* INTERMEDIATE ZONE 65.20 64.70 61.95 CORE ZONE 59.75 61.50** RIM ZONE 57.45 • 56.95 54.10 Si0 2 66.10 A1 203 Fe 203 13.24 15.59 15.86 16.04 16.23 16.62 16.93 21.02 16.32 2.61 2.36 2.45 3.13 2.55 5.20 2.58 2.93 3.41 FeO 4.12 2.22 2.10 2.70 5.66 1.68 5.98 2.12 7.08 MgO 0.43 0.01 0.02 0.08 0.14 0.24 0.21 0.07 1.22 CaO 0.70 0.50 0.95 1.10 2.15 1.43 2.64 0.51 4.03 Na 20 5.92 6.92 7.07 6.51 5.97 6.49 6.71 7.81 5.81 K20 H2O 4.31 5.11 5.19 5.51 5.67 5.15 5.02 5.99 4.84 0.73 0.83 0.70 1. 95 0.51 0.63 0.98 1.43 0.77 CO 2 0.38 0.35 0.36 0.40 0.22 0.17 0.18 0.40 0.09 Ti0 2 0.72 0.42 0.27 0.32 0.75 0.31 0.59 0.38 1. 32 P205 MnO 0.11 0.04 0.06 0.07 0.13 0.07 0.13 0.50 0.49 0.23 0.12 0.15 0.18 0.26 0.22 0.30 0.07 0.29 S 0.010 0.004 0.003 0.008 0.034 0.009 0.023 0.000 0.044 Zr0 2 0.102 0.165 0.260 0.171 0.11 0.100 0.140 0.001 0.079 0.215 C1 BaO 0.03 0.013 0.071 0.241 0.143 0.024 0.010 0.010 0.345 0.02 0.150 0.160 0.103 0.086 0.105 0.025 0.02 0.208 Rb(ppm) 199. 152. 66. 133. 115. 102. Sr(ppm) 44. 105. 174. 109. 57. 345. * Analyst-K. Ram1a1. University of Manitoba ** Tabular Syenite �TABLE 9 COMPARISON OF CHEMICAL COMPOSITIONS OF STETTIN WITH NOCKOLDS (1954) AVERAGES Average Stettin Nepheline Syenite Average Nepheline Syenite (Nockolds,1954) Average Stettin Syenite Average Syenite (Nockolds, 1954) 5i0 2 56.17 55.38 63.54 61.86 A1 203 Fe 203 18.09 21.30 15.39 16.91 2.97 2.42 2.62 2.32 FeO 5.06 2.00 3.36 2.63 ~~gO 0.50 0.57 0.14 0.96 I +::> co CaO 2.39 1.98 1.08 2.54 Na 20 6.78 8.84 6.49 5.46 K20 H2O 5.28 5.34 5.16 5.91 1.06 0.96 0.94 0.53* Ti0 2 0.76 0.66 0.50 0.58 P205 MnO 0.37 0.19 0.08 0.19 0.22 0.19 0.19 0.11 * includes only H20 I �TABLE 10 C.I.P.W. NORMATIVE COMPOSITIONS OF THE STETTIN ROCKS ROCK TYPE Sample Numbers* Q Or Ab An Ne 01 Hy lAc Di Mt I1 Pr i Ru Hm C Ap Z Hl Tn CC DI *Tabular Syenite 10 CORE ZONE Amphibole Syenite Pyroxene Syenite Tabular Syenite 6 and 504 65 77 503 100 12.44% 25.61 44.05 4.86% 30.06 51.92 2.80% 30.62 52.97 1.79% 32.28 51.92 7.22 5.31 2.36 5.91 1.89 0.51 0.76 0.01 1. 36 5.89 3.88 0.54 0.46 0.01 1. 65 2.70 2.70 3.28 0.61 0.01 1.04 1. 36 0.12 0.02 WALL ZONE INTERMEDIATE ZONE 33.40% 47.72 0.88 1.28 3.41 1.80% 30.62 52.44 2.22 Nepheline Syenite 46 2 92 29.50% 56.48 1.47 7.93 3.00 35.62% 38.39 2.11 14.86 0.96 28.39% 34.16 4.26 8.10 4.67 I +::> UJ 6.66 3.70 1. 36 0.06 5.06 0.61 0.02 9.82 3.70 1. 06 0.06 4. 17 0.76 10.65 4.86 2.43 0.06 0.34 O. 18 0.03 0.91 0.13 0.001 0.06 1.01 0.11 0.04 1. 62 0.34 0.18 0.06 1. 70 82. 1 0.10 0.18 0.02 86.8 0.13 0.37 0.04 86.4 0.17 0.18 0.02 0.34 0.02 0.02 0.90 86.0 0.50 82.4 0.17 0.15 0.58 84.9 93.9 88.9 0.20 70.6 I �-50- '#. I.t 0 2 0 8 Fig. A ~ Fig. B M 0 <'" 1.0 0 .......... 0 >< '" + 'if. 46 7 0 0 46 N O2 0 0.9 0 Z 92 6 0 92 0, '" 0 z 0.8 5 50 60 70 50 70 60 5 i0 2 0/0 5i0 2 % 15 3 Fig. C Fig. D 2 14 0 'if. to 13 0 0 ""'" '" >< 2 503 0 z'" o 0 2 92 46 0 z O~ 65 • lOB 12 '" 46 0 1 ~7 + .......... 0 10 6 65 11 77 0 6 ·10 92 10 50 70 60 50 0 60 5i0 2 5i0 2 % 70 ~ 2 0 2 6 20 Fig. E 0 Fig. F 6 0 46 #. 'if. 0 0 M 5 0 '" 10 4 50 10 50 70 60 77 503 < 92 ~ 6 92 15 5:' 0 >< 65 10 70 60 5i0 2 % 5i0 2 % 5 Fir.. G 92 4 0 3 #. 1.5 0 46 Fig. H 92 0 0 0 v 2 'if. Figure 24, A-H 1.0 0'" 108- 503 0.5 77 • 0 50 60 046 P _10 20 70 •" 10 " 6 I-- 0.0,0 • " " .77 65~OB 60. '.503 " 70 �-51DISCUSSION Due to chemical and mineralogical heterogeneity, the origin of alkaline igneous rocks is, in many cases, very complex and may be the result of several processes. Experimental studies of chemically equivalent synthetic silicate systems (Bailey and Schairer, 1966; Hamilton and MacKenzie, 1965; Schairer. 1967; Sood and Edgar, 1972; Sood, Platt and Edgar, 1970; Tuttle and Bowen, 1958) have provided a physicochemical framework to explain the crystalli'zation behavior of alkali magmas. Any petrogenetic model for the formation of alkaline rocks of the Wausau area must take into account: 1) the zoned nature of the complex 2) the presence of quartz-bearing aplitic and pegmatitic stages in the intermediate ring of amphibole syenite; 3) the fenitized zone surrounding the pluton; 4) the presence of volatile bearing minerals (flourite, calcite, apatite) in most syenites, and in the quartz monzonite II core ll (1) of the Wausau pluton; 5) major and trace element geochemistry of the syenites. Consideration with Respect to the System Nepheline-Kalsilite-Silica In Figure 25 normative composition of the Stettin rocks is plotted in the system Nepheline-kalsilite-silica at lKb PH 0 along with the composition of the rocks from Kangerdlugssuag intrusion, 2 East Greenland (Wager, 1965). These analyses may be interpreted to show a trend of silica depletion away from the Si0 2 apex. Rocks of the Intermediate Zone of amphibole syenite plot in the alkali feldspar-quartz region, near the alkali feldspar join, while pyroxene syenites of the Core Zone plot just below the alkali feldspar join. The positions of these syenites in the field show a silica depletion trend toward the center of the complex. From Figure 25, it appears that the trend of these amphibole anrl pyroxene syenites is up the alkali feldspar surface and "over " the thermal barrier, which is similar to the interpretation by Wager (1965) for the nordmarkites, pulaskites, and foyaites of the alkaline Kangerdlugssuaq intrusion. (In the nepheline-kalsilite-silica system at 5 Kb PH 0' these rock webs plot close to the feldspar cotectic or nephiline-feldspar 2 cotectic. This is in agreement with mineral paragenetic and textural relations.) Further interp~etations await the accumulation of additional data, especially on the Wausau pluton. �-52- 30~_-+. _ _-~---f\70 Feldspar II 30 - - + - - - - - 4 KAISi 2 0 6 Nepheline 1 IS 0 1 ~ ,~ 100 ..- L-_~L-_----':>L-_~ o NaAISi04 10 20 30 Kalsilite IS 1 \/ 40 " so Weight per <en!. \{ 60 1 70 80 90 KAISiO.cj Figure 25 __ Normative compositions of the Stettin rocks (closed circles) and the alkaline rocks of the Kangerd1ugssuaq intrusion, East Greenland (open circles) (Wager, 1965) plotted in the system NaA1Si04 - KA1Si04 Si0 2 at PH20 = 1000 bars (Fuda1i, 1963; Hamilton and MacKenzie, 1965). �-53- How could such inward silica depletion be caused? Two possible explanations are: (1) (2) Loss of the volatile phase in ~uilibrium with the melt. Such a volatile phase has alumina, alkali, and silica in the same proportion as feldspars (Tuttle & Bowen, 1958; Mackenzie, 1960). The presence of aplitic and pegmatitic phases and fenitization of the surrounding volcanics may be a reflection of separation of volatiles into a gaseous phase and eventual loss. The plot of the Stettin rocks close to cotectics in pertinent synthetic systems may be indicative of crystallization of major phases within narrow temperature limits. Short crystallization intervals are also related to silica and alkali content which control volatile distribution in liquid and gaseous phases (Sood & Edgar, 1970; Kogarko & Rhyaschi kov, 1961). The substitution of Fe+ 3 Al+ 3 in feldspars may contribute to silic~3depletion with crystallization of iron-rich albite (NaFe Si 0R). Only a small amount of Fe-Al substitution is necessary 2to fix silica and cause the liquid to shift from silica saturated to silica undersaturated trend (Bailey & Schairer, 1966). The general iron-rich and alumina-deficient nature of the syenites in comparison to Nockold1s (1954) averages and a limited Fe-content of feldspars favor such substitution. The Nepheline syenite in the Stettin pluton may, therefore, represent last residual liquids injected into the sheared wall zone. It may be concluded that alkaline rocks of Marathon County represent a "genetically related comagmatic series. The study of silicate systems and melting relations of rocks have amply demonstrated that magma composition lies close to the univariant lines or the invariant points, and very slight changes in initial liquid composition can give decidedly distinct liquid trends. Compositional differences in these alkaline rocks may be related to slight changes "in magma composition by fractional crystallization or by wallrock assimilation, or both. It is important to further refine their genetic and tectonic relations. Systematic geoche~ical data both on rocks and minerals are needed to assess if these rocks are formed from mantle derived magmas (tentatively note the low Rb and Sr contents for Wausau rocks) which reached crust through recurrent fracture systems. Such information will also be useful in the estimation of economic mineral potential of this area. Such rocks form in environments favorable to the concentration of a wide variety of elements. II �-54Comparison of the Wausau and Stettin Plutons P.E. Myers Despite obvious differences in size, shape, xenolith types, zoning sequences, and silica saturation, the Wausau and St~ttin plut?ns share several significant sinrilarities: (1) the pyroxene and amp~l~ole syen1t~s of the intermediate zone of the Stettin pluton are compos1tlonally equlvalent to the outer wall zone of the Wausau pluton, (2) the lensoidal quartz syenite and probably comagmatic Ninemile quartz monzonite of th~ Wausau,pluton, are probably the silica-rich end-members which would have dlfferen~lated from the Stettin pluton after crystallization of the amphibole syenlte. Koellner (1974, p. 31) reports contents of up to 15% in the pegmatitic p~ases of t~e amphibole syenite. The close spatial association of zoned granlte,pegmatlte veinlets (Stop #3) and quartzite xenoliths suggests at least locallzed . silification of quartzite and other sili-saturated wall rocks. The relatlve silica undersaturation of the Stettin pluton may be due in part to the low silica content of the volcanic rocks which it intrudes. The Wausau and Stettin plutons probably represent the near-surface "roots" of two collapse calderas (Figure 26). Miarolitic cavities in the margin of the Ninemile quartz monzonite indicate that the quartz monzonite intruded the caldera core and part of its rim to within a short distance of the surface. Although probably related in some way to the rapakivi granties of the Wolf River batholith, Van Schmus (1980, in press) has determined that the Wausau syenite plutons were intruded at 1520 m.y. as contrasted with a 1500 m.y. age for the Wolf River batholith. Thus, the syenites appear to represent an early, shallow, volcanic manifestation of Wolf River batholith intrusive activity. Evidence suggesting that the Stettin pluton is the older is: (1) fragments of porphyritic trachyte (?) similar to that now exposed on both sides of the Wisconsin River at Brokaw are found in the Wausau syenite (Stop #3); (2) the Stettin pluton produced a wider halo of syenitization and contains fewer unassimilated xenoliths. Shearing with chaotic vertical displacement and mixing of wallrock fragments greatest in the intermediate zone of the Wausau pluton and less important 1n the wall zone of the Stettin pluton. Semi-detached wallrock slices, partly sheared away from the cylindrical wall, are seen on the east and south sides of the Stettin pluton. By contrast, xenoliths in the contaminated intermediate zone of the Wausau pluton were completely detached and show no essent~al .r~lationship to contiguous wallrocks. Thus, there appears to have been slgnlflcantly greater vertical transport of xenoliths in the intermediate (caldera rim) zone of the Wausau pluton. The occurrence of sillimanite in q~artzite xenoliths at Rib Mountain (3-M quarry) and on a ridge about 1 1/2 mlle northwest of Stop #4 suggests a derivation from a deeper metamorphic basement. However, the possibility of the metasomatic origin of sillimanite should not be ruled out. There is certainly ample evidence of metasomatism - syenitization - of xenoliths throughout the pluton. ~as �-55- There is little doubt of the close genetic relationship of the Wausau, Ninemile, and Stettin plutons. Based on field relations, the cross section reconstruction is proposed (Figure 26). The concentric xenolith-rich zones, which typically show effects of shearing, suggest that the vertical movement, probably up and down, was localized in these caldera rim collapse structures. This suggests that the floor of the Wausau syenite caldera foundered in the upwelling Ninemile quartz monzonite. Our field and laboratory investigations are now focusing on the Wausau syenite and Ninemile plutons. After completion of this work, a much more detailed picture of magma emplacement conditions, sequence, and mechanism as well as its association with volcanism should be possible. �_ ----,/' ....... '/'-''-/''', JV'O... , , ~" ".'" ~~ ;' '" /" ", .... ,'... --_/ .......... ..... '" ~ ..... '" ...... - .......... SOUTHEAST ----.... '- A A' L . ST ETTIN PLUTON----...I '-1 PEI"\-'80 EXPLANATION ~ ~ Ninemile.quartz monzonite ~+ + +J Amphibole syenite +~ • ."'.~:."';"'. .', ~t.·'!:t~'* • .. .,;. ,.. .m ~ Gneissic nepheline and tabular syenite border facies Syenitized volcanic rocks ~ Lensoidal quartz syenite with xenoliths of biotite schist and quartzite ~ Alkalic extrusives, probably pyroclastics and subordinate flows ~L·.1·:~.'"J '.,,'. [±J Fi gure Pyroxene syenite - Quartz diorite Quartzite Older calc-alkaline volcanic rocks, mainly andesite and rhyolite Hypothetical northwest-southeast section across the Stettin and Wausau syenite plutons as they would have appeared about 1450 m.y. ago. Line A-A' represents the present land surface. See Fiqure 4 for location of section A-A'. I tTl 0) I �-57REFERENCES Bailey, O.K., and Schairer, J.F., 1966. The system Na 0 - A1 0 Fe203 - Si0 2 at 1 atms., and the petrogenesis of alkaline 2rocks. 2 3 Journal of Petrology. V.7, p. 114-170. Berlin, L.A., and Sood, M.K. (1979). Alkaline rocks of the Stettin area, Wisconsin Geol. Soc. Am., V. 11, No.5, p. 225-226. Barker, D.S., 1974. "Alkaline rocks of North America' in the Alkaline Rocks. Sorensen, editor. New York: John Wiley and Sons, p. 160-171. Bowen, N.L., 1928. The Evolution of the Igneous Rocks. Dover Publications, INc., p. 332. New York: Bowen, N.L., 1945. Phase equilibria bearing on the origins and differentiations of alkaline rocks. Am. J. Sci., V. 243, A., p. 75-89. Daly, R.A., 1910. V. 21, p. 87-118. Origin of a"lkaline rocks. Geol. Soc. Am. Bull., Deer, W.A., Howie, R.A., and Zussman, J., 1963. V. 2-4. New York: John Wiley and Sons. Rock Forming Minerals. Dutton, D.E., and Bradley, R.E., 1970. Lithologic geophysical and mineral commodity maps of Precambrian rocks in ~Jisconsin. U.S.G.S. Misc. Inv. Map 1-631, p. 15. area: Emmons, R.C., and Snyder, F.C., 1944. A structural sutdy of the Wausau Wisconsin Geological and Natural History survey, unpub. report. Emmons, R.C., 1953. Selected Petrogenic Relationships of Plagioclase. Geol. Soc. Am. Mem., V. 52, p. 142. Fudali, R.F., 1963. Experimental studies bearing on the origin of pseudoleucite and associated problems of alkali rock systems. Bull. Geol. Soc. Amer., V. 74, p. 110. Geisse, Elaine, 1951. The petrography of the syenites, nepheline syenites, and related rocks west of Wausau, Wisconsin. M.A. thesis, Smith college. Hamilton, D.L., and MacKenzie, W.S., 1960. Nepheline solid solutions in the system NaA1Si0 4 - KA1Si0 4 - Si0 2 . J. Petrology, V. 1, p. 56-72. Hamilton, D.L., and MacKenzie, W.S., 1965. Phase-equilibrium studies in the system NaA1Si0 4 (nepheline) - KA1Si0 4 (kalsilite) - Si0 2 -H 2). Min. Mag., V. 34, p. 215-231. Hayama, Y., 1959. Some considerations on the color of biotite and its relation to metamorphism. Jour. Geol. Soc. Japan, V. 65, p. 21. Henderson, J.R., Tyson, N.S., and Page, J.R., Aeromagnetic Map of the Wausau area, Wisconsin, U.S.G.S. Geophysical Investigations Map Gp-401, 1963. Hyndman, D.W., 1972. Petrology of Igneous and Metamorphic Rocks. New York: McGraw-Hill Book Co., p. 533. �-58Jones, J.B., Nesbitt, R.W., and Slade, P.G., 1969. The determination of the orthoclase content of homogenized alkali feldspar using 201 x-ray method. Min. Mag., V. 37, p. 489-496. Koellner, S.E. 1974. The Stettin Syenite Complex, Marathon County, Wisconsin: Petrography and Mineral Chemistry of olivine, pyroxene, amphibole, biotite, and nepheline, unpublished M.S. Thesis, University of Wisconsin - Madison. Kogarko, l.N. and Ryabchikov, 1.0., 1961. 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MacKenzie, W.S., 1960. Review of some contributions of experimental studies to petrology. Liverpool and r~anchester Geological Journal, V.2, p. 369-388. Medaris, Jr., l.G., Anderson, J.L., and Myles, J.R., 1973. The Wolf River Batholith - A late precambrian rapakivi massif in northeastern Wisconsin, in Guidebook to the Precambrian Geology of Northeastern and Northcentral Wisconsin. Wis. Geol. Nat. Hist. Survey, p. 9-30. Myers, P.E., 1973. ·Stettin syenite pluton-wall zone', in Guidebook to the Precambrian Geology of Northeastern and Northcentral Wisconsin. Wis. Geol. Nat. Hist. Survey, 75-76. Myers, P.E., The Wausau syenite of Central Wisconsin, Abs., Institute on lake Superior Geology, p. 42, 1976. Nockolds, S.R. 1954. Average chemical compositions of some igneous rocks. Geol. Soc. Amer. Bull., V.65, p. 1007-1032. Smith, J.V., 1974. p.627. Feldspar Minerals, V.l, New York: Springer-Verlag, Sood, M.K., and Edgar, A.D., 1970. Melting relations of undersaturated alkaline rocks. Meddelelsen Om Gronland. Bd. 181, Nr. 12, p. 41. �-59- Sood, M.K., and Edgar, A.D., 1972. The system diopside-forsteritenepheline-albite-leucite and its implication to the genesis of alkaline rocks. 24th Int. Geol. Congr. Montreal, V. 14, p. 68-74. Sood, M.K., Platt, R.G., and Edgar, A.D., 1970. Phase relations in portions of the system diopside-nepheline-kalsilite-silica and their importance in the genesis of alkaline rocks. Can. Miner., V. 11, p. 380-394. Sorensen, H., 1970. Internal structures and geological setting of the three agpaitic intrusions - Khibina and Lovozero of the Kola peninsula and Ilimaussaq, South Greenland. Can. Min., V. 10, p. 299-334. Sorensen, H., 1974. Sons, p. 622. The Alkaline rocks. New York: John Wiley and Thorton, C.P., and Tuttle, O.F., 1960. Chemistry of igneous rocks. I. Differentiation Index. Am. J. Sci., 258, p. 644-684. Tilley, E.E., 1957. Problems of alkali rock genesis. Lond., V. 113, p. 323-360. Q.J. Geol. Soc. Turner, D.S., 1948. Heavy accessory minerals and radioactive studies of the igneous rocks in the Wausau area: Ph.D. dissertation. Univ. of WisconsinMadison. Tuttle, O.F., and Bowen, N.L., 1958. Origin of granite in the light of experimental studies in the system NaA1Si 308 - KA1Si 308 - Si0 2 - H20. Geol. Soc. Am. Mem., V. 74, p. 153. Van Schmus, W. R., 1973. 'Chronology of Precambrian Rocks in Wisconsin', in Guidebook to the Precambrian Geology of Northeastern and Northcentral Wisconsin. Wis. Geol. Nat. Hist. Survey, p. 1-8. Van Schmus, W.R., Medaris, Jr., L.G., and Banks, P.O., 1975a. Geology and Age of the Wolf River Batholith, Wisconsin. Geol. Soc. Am. Bull., V. 86, p. 907-914. Van Schmus, W.R., Thurman, E.M., and Peterman, Z.E., 1975b. Geology and Rb-Sr Chronology of Middle Precambrian Rocks in Eastern and Central Wisconsin. Geol. Soc. Am. Bull., V. 86, p. 1255-1265. Wager, L.R., 1965. The form and internal structure of the alkaline Kangerdlugssuaq intrusion, East Greenland. Min. Mag., V. 34, p. 487-497. Weidman, S., 1907. The Geology of North Central Wisconsin. Nat. Hist. Survey Bull., V. 16, p. 697. Wis. Geol. Wright, T.L., 1968. X-ray and optical study of alkali feldspars: II an X-ray method for determining the composition and structural state from measurement of 20 values for the reflections. A. Min., V. 53, p. 88-104. Wright, T.L., and Stewart, D.B., 1968. X-ray and optical study of alkali feldspars: II determination of composition and structural state from refined unit-cell parameters and 2V. Am. l\1in., V. 53, p. 38-87. � https://digitalcollections.lakeheadu.ca/files/original/f93951c247fc58cf4b6675df14962fcb.pdf f7cbd59692bd8796e0f6943abbb81322 PDF Text Text 26Th Annual 26th Annual Institute on on Lake Superior Superior Geology Geology FIELD TRIP FIELD TRIP 4 ogy & The Precambrian Geol The Precambrian Geology & Tectonics Tectonics ounly Wisconsin of Marathon Marabon C Couniy Wisconsin P/n.h... P14q GENERALIZED PRECAMBRIAN PRECAMBRIAN GEOLOGY GEOLOGY OF THE THEEAU EAUCLAIRE CLAIREREGION REGICN Diabase Diabase Gabbro Gabbr0 Tonolite Tonolite Trondhjemite Trondhjemiie Volconics Volcanics and and sediments Amphibolites Amphibdiies + Shear zone I; Shear zone 1980 May 10, 10,1980 Claire University of Wisconsin-Eau Wisconsin-Eau Claire �FIELD FIELD TRIP TRIPGUIDEBOOK GUIDEBOOK FOR FOR THE MIDDLE COUNTY, WISCONSIN THE MIDDLEPRECAMBRIAN PRECAMBRIAN GEOLOGY GEOLOGY OF MARATHON MARATHON COUNTY, WISCONSIN Leaders Leaders Gene and EElizabeth Gene L.L. LaBerge LaBerge and l i z a b e t h Palmer Palmer Special Paper Paper THE PRECAMBRIAN AND TECTONICS TECTONICS OF THE PRECAMBRIAN GEOLOGY GEOLOGY AND MARATHON COUNTY, WISCONSIN MARATHON COUNTY, WISCONSIN by Gene Gene LL.* LaBerge LaBerge Prepared Prepared f for o r the t h e 26th 26th Annual Annual Meeting Meeting ooff the the INSTITUTE ON INSTITUTE ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY Eau Eau CClaire, l a i r e , Wisconsin, Wisconsin, 1980 1980 �Co "VA—-.- -- E- 1Le ——-.0 9 C a -S ---A —--4 .0 -a '—i— CIVIL TAMIMS It- 'E' N). VA VA 111DM Il-I 'r • �CONTENTS CONTENTS Page ................................................... 1 ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS ............................................... 1 GENERAL GENERAL GEOLOGY GEOLOGY ................................................ 1 EARLY(?) PRECAMBRIAN ........................................... 44 EARLY ( ? )PRECAMBRIAN Gneisses Gneisses and and Schists S c h i s t s ....................................... 44 MIDDLE MIDDLEPRECAMBRIAN PRECAMBRIAN ............................................. 66 METAVOLCANIC METAVOLCANICROCKS ROCKS ............................................. 6 Mafic M a f i c and and Intermediate I n t e r m e d i a t eMetavolcanic MetavolcanicRocks Rocks .................. 6 Felsic F e l s i cMetavolcanic MetavolcanicRocks Rocks .................................. 7 Metasedimentary MetasedimentaryRocks Rocks ...................................... 9 INTRUSIVE INTRUSIVEROCKS ROCKS ................................................ 10 10 Gabbroic Gabbroic Intrusions I n t r u s i o n s ........................................ 10 10 Ultramafic Ul t r a m a f i c Intrusions I n t r u s i o n s ...................................... 11 Granitic G r a n i t i c Intrusions I n t r u s i o n s ........................................ 11 INTRODUCTION INTRODUCTION 1 1 1 6 6 7 9 11 11 ............................................... 1313 The Wolf R River The Wolf i v e r Batholith B a t h o l i t h ...................................13 13 The The Syenite S y e n i t e Plutons Plutons ........................................ 14 14 Wausau Syenite Pluton Wausau Syenite Pluton ....................................... 14 14 Stettin S t e t t i nSyenite SyenitePluton P h t o n ..................................... 15 15 Diabase Diabase Dikes Dikes .............................................. 15 15 STRUCTURAL STRUCTURALGEOLOGY GEOLOGY ............................................. 15 15 Regional Regional Setting S e t t i n g ........................................... 15 15 Folding F o l d i n g .................................................... is 15 Faulting F a u l t i n g ................................................... 16 16 LATE LATEPRECAMBRIAN PRECAMBRIAN —1— �Page CONTENTS (continued) CONTENTS (continued) Deformed Volcanic Rocks .................................... Deformed Volcanic Rocks . Minor Structure Structure ............................................ Minor 21 21 ...........................................29 SUMMARY ........................................................ 30 REFERENCESCITED CITED ............................................... REFERENCES GEOLOGICALSTOP STOPDESCRIPTIONS DESCRIPTIONS ................................... 33 GEOLOGICAL TECTONICSPECULATION SPECULATION TECTONIC SUMMARY 31 ............................... Rib Falls Falls- -Deformed Deformed intrusion intrusionbreccia breccia ..................... Rib - Pillow Pillowbasalts basalts ArtusCreek Creek — Artus 34 37 - t ofof R i b River River ata tEmory Emory School School - Iiltramafics Ul tramafics at a tcontac contact Rib .........................................39 c gneiss Black Creek, Creek, Athens Athens -- Quartzofeldspathi Quartzofeldspathic gneiss ............ 41 Black eared rocks Athens County County Park Park—-Sh Sheared rocks ......................... 43 Athens - Lineated Lineated andesite andesite ........................... 45 Hamann Creek Creek — Hamann L i t t l e Eau EauP1Pleine River — - Gneiss Gneiss ........................... 47 elne River Little Wild Rozellville - -Ultramafic Wild Creek, Creek, Rozellville Ultramaficrocks rocks ................... 49 gneiss terrane terrane gneiss . . ILLUSTRATIONS ILLUSTRATIONS RouteMap Map Route .........................................Frontispiece Frontispiece Figure1 1 -. Geological map map of of northern northernWisconsin Wisconsin Geological Figure ............ 2 Figure 22- . Geologicalmap mapofofMarathon MarathonCounty County Figure Geological 3 Figure 33 -. Table of ofgeological geologicalevents events Table Figure ............... ...................... 5 ............................ Figure 55 -.Lahar Lahar ........................................... Figure Figure 56 -.Welded Welded ttuff u f f ..................................... Figure 8 Figure 44 -. Flow banded banded rrhyolite hyolite Figure Flow — 11 8 9 �CONTENTS (continued) CONTENTS (continued) ILLUSTRATIONS ILLUSTWTIONS Page continued) (continued) ........ Figure Simplified map of structural Figure 88 — .Simplified map of structural geology geology ............ Figure Aeromagnetic Aeromagneticmap map ................................ Figure 99- . Figure - Flaser Flaser gneiss gneiss .................................. Figure 10 10— Figure Foliated quartz quartz monzonite monzonite cut by by granite granite Figure 77 -.Foliated 12 12 17 17 19 19 20 20 ............... 2020 Figure Figure 12 12 — - Mylonite outcrop outcrop ............................... 22 22 Figure Texture of ofmylonite mylonite ............................ 22 22 Figure 13 13 -- Texture Figure Photomicrographs Figure 14 14 -. Photomicrographs of mylonite mylonite ................... 23 23 Figure Figure 15 15 -- Cataclastic Cataclastic degradation degradation of granite granite ............. 24 24 Figure Photomicrographofof fflaser - Photomicrograph l a s e r gneiss gneiss Figure1111 — Figure Boudinagedphenocrysts phenocrystsininf felsic Figure 16 16 — - Boudinaged e l s i c volcanics volcanics ..... 25 25 ........................... 2626 Figure Figure 18 18 --Diagram Diagram of of graben graben structure s t r u c t u r e .................... 30 30 Pillow Pillowlavas lavasononArtus ArtusCreek Creek ................................ 35 35 North—south cross—section of of northern North-south cross-section northern Wisconsin Wisconsin ............ 35 35 Sketch 43 Sketch map map of of Athens Athens Park Park .................................. 43 North—south North-south cross—section cross-section across acrossMarathon MarathonCounty County ........... 44 44 Photo 46 Photo of lineated lineatedandesite andesite ................................. 46 Figure Figure 17 17 - Deformed Deformed f efelsic l s i c tuff tuff Photo Photo of gneiss gneiss on on Little L i t t l eEau Eau Pleine PleineRiver River — 111 — ................. 48 48 �Special Special Paper Paper THE THE PRECAMBRIAN PRECAMBRIAN GEOLOGY GEOLOGY AND AND TECTONICS TECTONICS OF OF MARATHON MARATHON COUNTY, WISCONSIN WISCONSIN by Gene Gene L. L. LaBerge LaBerge �INTRODUCTION INTRODUCTION This more This paper paper iiss taken, taken, in i npart, p a r t from , froma a moreextensive extensive report r e p o r ton onthe t h egeology geology of by Paul Paul Myers andme mei nin ppreparation o f Marathon Marathon County County by Myers and r e p a r a t i o n for f o r the t h eWisconsin Wisconsin Geological are presented Geological Survey. Survey. More More ddetails e t a i l s on on the t h e geology geology are presented iin n that t h a t paper. paper. The iinterpretations n t e r p r e t a t i o n s expressed expressed here o t nnecessarily e c e s s a r i l y r reflect e f l e c t those those ooff the the The heredodon not Wisconsin Wisconsin Survey. Survey. They They are based based upon upon nnine i n e field f i e l dseasons seasonsofomapping f mappingbybyme me and reconnaissance mapping and six s i x by by Myers, Myers, ini naddition a d d i t i oto n textensive o extensive reconnaissance mappingbybyMyers Myers in i nEau Eau Claire C l a i r eand andChippewa Chippewa Counties. Counties. IIconsider a forum consider this t h i s field f i e l dtrip t r i (and p (andalla others) l l o t h e r sto ) tbe o be a forumfor f o discussion r discussion on on the the geology geology of o f the t h earea. area. This This paper paper and and stop s t o p descriptions d e s c r i p t i o n sare arepresented presented as background material as background m a t e r i a l ffor o r the the discussion. discussion. The The ttrip r i pisi sdesigned designedtot oshow show representative County,pparticularly r e p r e s e n t a t i v e examples examples oof f tthe h e geology geology ooff Marathon Marathon County, a r t i c u l a r l y those those exposures bearon ont hthe Some ooff the the exposures t hthat a t bear e sstructural t r u c t u r a l and and ttectonic e c t o n i c setting. s e t t i n g . Some exposures ande elicit exposures vvisited i s i t e d present present problems problems and l i c i t questions questions regarding r e g a r d i n g the t h e tectonic tectonic setting. problems and questions probably will not be fully answered; s e t t i n g . These These problems and questions probably w i l l n o t be f u l l y answered; however, however, II hope hope tthe h e ttrip r i pstimulates s t i m u l a t e sothers otherstot oponder ponderthese these questions, questions, and and to to propose alternate propose a1 t e r n a t e solutions. solutions. ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS This This paper paper isi sbased basedon on field f i e l mapping d mappingbybyPaul PaulMyers Myersand andme me that t h a thas hasbeen been funded funded by by the t h e Wisconsin Wisconsin Geological Geological Survey Survey since since1969. 1969. Their T h e i r continued continued support support is i s greatly g r e a t l yappreciated. appreciated. Some Some ofof tthe h e ideas expressed expressed hherein e r e i n are a r e the t h e outgrowth outgrowth of discussionswwith Paul Myers Myersdduring course ooff the o f numerous numerous discussions i t h Paul u r i n g tthe h e course t h e project p r o j e c tand and are a r e hereby herebyacknowledged. acknowledaed. Review comentsby byMike MikeMudrey Mudrey and3nane aearlier onon t h this i s and r l i e r vversion e r s i o n of o f the the Review coments manuscript most hhelpful. manuscript have have been been most e l p f u l . Paul Paul Myers Myers also a l s o reviewed reviewed the t h emanuscript manuscript and and offered o f f e r e d helpful h e l p f u lsuggestions. suggestions. Their T h e i r assistance assistanceisi acknowledged s acknowledged with with gratitude. gratitude GENERAL GENERALGEOLOGY GEOLOGY Marathon Countyi is Marathon County s situated s i t u a t e d near near the t h esouthern southernmargin marginofo the f theexposed exposed Precambrian shield^ Its Precambrian Shield. I t sregional r e g i o n a lsetting s e t t i n gin ithe n t hPrecambrian e Precambrianofo fWisconsin Wisconsin is is shown shown iin n Figure Figure 1. l aThe The bedrock bedrock is i spredominantly predominantlyPrecambrian Precambrianigneous igneousand and metamorphic rockswwith fewsscattered metamorphic rocks i t h aa few c a t t e r e d ooutliers u t l i e r s of o fPaleozoic Paleozoic sandstone sandstone that that unconformably rocks (Figure 2 ) . Early unconfomably ooverlie v e r l i e the t h e Precambrian Precambrian rocks ( F i g u r e 2). E a r l yPrecambrian(?) Precambrian(?) gneisses 1900may.) m.y.) vvolcanic gneisses and and Middle Middle Precambrian Precambrian ( (± t 1900 o l c a n i c rocks rocks are a r e intruded intruded by post—tectonic Middle Precambrian (VanSchmus, Schmus, by numerous numerous syn— syn- t to o post-tectonic-Middle Precambrian (+ ( t1850 1850m,y.) m.y . )(Van 1976) ranging iin fromquartz quartzd diorite 1976) pplutons l u t o n s ranging n composition composition from i o r i F e to t o granite. g r a n i t e . The The volcanic v o l c a n i c rocks rocks range range in i n composition composition from from bbasalt a s a l t to t o rhyolite r h y o l i t eand andoccur occuras as isolated andblocks blocksi nin tth i s o l a t e d pendants pendants and h e plutonic p l u t o n i crocks. rocks. Stratigraphic S t r a t i g r a p h i cand and structural s t r u c t u r a l relationships r e l a t i o n s h i p sofo the f t h evolcanic v o l c a n i crocks rockswithin w i t h i nindividual i n d i v i d u ablocks l blocksand and correlation c o r r e l a t i o nbetween between blocks blocks is i suncertain u n c e r t a i nbecause because of o flack l a c kofoexposures f exposuresand and deformation. deformation. Eastern Countyi sisuunderlain byt the Wolf RRiver Eastern Marathon Marathon County n d e r l a i n by h e Wolf i v e r bbatholith, a t h o l i t h , aa large Precambrian (1500 m.y.) ageage (Van Schmus l a r g eanorogenic anorogenic pluton p l u t o nofoLate f Late Precambrian (1500 m.y.1 (Van Schmusand and The circular Wausau and Stettin syenite bodies west others, 1975). others, 1975). The c i r c u l a r Wausau and S t e t t i n s y e n i t e bodies westof oWausau f Wausau —1— �PRECN4BRIAN of WISCONSIN Quartist. ODLE PRECAI4ThRIMI EAJLT PPNMPXMJ4 Gr.nitic P..ck. Qtanitic Packs zrcn—Fo=tion Metavoicanc Mock. Domiftsatly 'Metas.dLm.ntary .cks omAnat1y Metatotcanto Mocks L I oa.i,3.c Mocks Figure 11.. Generalized geological geological map of Precambrian rocks in in northern Generalized map of Precambrian rocks northern MarathonCounty County outlinedininthe thecentral central part part of the Wisconsin. Marathon i s is outlined the (Data in part state. (Data part from from Sims, Sims, 1976.) 1976.) —2— - 2 - �U) g C 0 C) 0 0) -S 0) -h 0 -o 0) 0 pJ -J I0 0 0 CD 0 N) CD 5 C -n —I. (0 wIsl•oNsFNefE,to(;IcALANpNAIUflALHIsIoR SURVEY Interim Copy) MARATHON COUNTY.WIS. OF GEOLOGY n -5-. (AT B PEE CAM BRIE N EXPLANATION EANLY PEECAMOHEAN - LI] — MIDDLE PEE CAMHBIAN SCALE �are related to Several are probably probably related t o the the Wolf Wolf River River batholith batholith (Myers, (Myers, 1976). 1976). Several small quartz monzonite porphyry plugs plugs and anddiabase diabasedikes dikes aare small monzonite porphyry r e aalso l s o of Late Late Precambrian age. Precambrian age. Several large northeast of cataclasis Several northeast and and northwest northwest zones zones of c a t a c l a s i s dominate dominate the the Major shear shear zones zonesand ands pspatially a t i a l l y related related structural geology geology (Figure (Figure 2). 2 ) . Major ultramafic gneissic rocks ul tramafic bodies bodies separate separate gneissic rocks from from the t h e greenschist greenschist facies f a c i e s Middle Middle Precambrian volcanic-plutonic volcanic—plutonic complex. within the Precambrian complex. Similar cataclastic c a t a c l a s t i c zones zones within the Middle Precambrian complexhave havethe the same sameo rorientation Middle Precambrian complex i e n t a t i o n as as the themajor majorboundary boundary fault f a u l tzones. zones. Field relationships suggest suggest aa long long history of of shearing shearing before, before, Field relationships during the plutonic plutonic rocks. rocks. during and and aafter f t e r emplacement emplacement ofofthe Three ages agesofof glacial glacial drift Three d r i fwere t wererecognized recognizedbybyLaBerge LaBerge (1971). (1971). Mickelson and others (1974) (1974) confirmed confirmedthe theexistence existenceofof the the three three drifts and others d r i f t sand andshowed showed tthat hat they range they range in age age from from pre-Wisconsin pre-Wisconsin to t o late l a t eWoodfordian. Woodfordian. Figure 33summarizes summarizes the geological the geological events events recognized recognized in inand and adjacent adjacenttot oMarathon Marathon County. County. EARLY(?) EARLY ( ? ) PRECAMBRIAN PRECAMBRIAN Gneisses and and Schists. Schists. Medium— coarse—grainedquartzofeldspathic quartzofeldspathic Gneisses Medium- t otocoarse-grained biotiteb i o t i t e -and andhornblende-bearing hornblende-bearing gneisses, gneisses, schists s c h i s t s and and migmatites migmatites underlie underlie northwestern MarathonCounty Countyand andoccur occurasasisolated isolated blocks blocks along northwestern Marathon along the the southern southern edge of the gneissic rocks edge of the county. county. The The gneissic rocks are are poorly poorly exposed exposed and and cconsist o n s i s t mainly mainly of large blocks and and widely widely scattered outcrops. The gneisses largefrost—heaved frost-heaved blocks outcrops. The gneisses range iin from ggranite range n composition composition from r a n i t e to t o quartz quartz diorite d i o r i t and e andhave havea aconspicuous conspicuous ffoliation o l i a t i o n and and lineation. l i n e a t i o n . Biotite B i o t i t eoro hornblende r hornblendeoroboth r bothcomprise comprise15—40 15-40 percent percent of the are garnetiferous. garnetiferous. The The common comon occurrence occurrence of of the rock rockand and some some phases phases are hornblende, have been metamorphosed hornblende, and and llocally o c a l l ygarnet, garnet,suggests suggeststhat t h athey t they have been metamorphosed facies. tto o amphibolite amphiboli te facies. Reconnaissance geologicmapping mappingt otothe the west west and and north north of Reconnaissance geologic of Marathon Marathon County County suggests suggests tthat h a t the the gneisses gneisses are a r e part p a r tofofa ahigh—grade high-grade metamorphic metamorphic t terrane e r r a n e tthat hat extends the west. west. Gneissic extends aat t lleast e a s t 60 60 miles miles to t o the Gneissic rocks rocks extend extend in in aa northeasterly direction along Countya tatl eleast along the the northern northern part p a r t of of Marathon Marathon County a s t t to o PPrairie r a i r i e Dells Dells in Lincoln (about 13 13 km kmnortheast northeastofofHMerrill). e r r i l l ) . The Lincoln County County (about The gneisses gneisses closely closely resemble those those of of the Miphibolite resemble the "Chippewa "Chippewa Anphi bol i t e Complex" Complex" described described by by Myers Myers (1974, ( 1 974, and Eau Claire Claire Rivers. theChippewa Chippewa and and Eau Rivers. and tthis h i s conference) conference) from fromexposures exposures along along the Knownexposures exposuresof of Precambrian Known Precambrian rocks between between Marathon Marathon'and and Chippewa Chippewa and and Eau Claire Claire Counties Counties are a r edominantly dominantlyhigh—grade high-grade metamorphic metamorphic rocks. The Eau The gneissic pattern of of gently gneissic rocks rocks have have aa ddistinctive i s t i n c t i v e aeromagnetic aeromagnetic pattern gently curving curving anomalies, compared w iwith t h a ablotchy magnetic highs the anomalies, compared blotchypattern pattern of of magnetic highs and and lows lows in in the remainder of of Marathon County (Figure (Figure 9). The Bouguer Bouguer Anomaly AnomalyGravity Gravity Map Map of remainder Marathon County 9 ) . The Ervin and Haniiier(1974) (1974)shows shows gneisses area of of zero to Ervin and Hammer t h ethe gneisses as as a daidistinct s t i n c t area to minus40 40mmilligals, with minus minus4040t otominus minus9090mmilligals minus i l l i g a l s , compared compared with i l l i g a l s in the the remainder remainder of of Marathon Marathon County. County. Therefore, the t h eknown known geology, geology, aeromagnetics aeromagnetics and gravity all part of aa and gravity a l lsuggest suggest that t h a tthe thegneisses gneisses ininMarathon Marathon County County aare r e part large "block" as shown on Figure 1 "block" as shown on Figure 1 . Gneissic rocks rocks in and and on on the the periphery periphery of ofMarathon Marathon County County aare r e strongly strongly Gneissic lineated, 1ineated, with with mineral mineral lineations lineations and and fold foldaxes axes plunging plunging 20°-60 200-600 west west in in the the plane of the the ffoliation plane of o l i a t i o n (Figure (Figure 8). 8 ) . For For example, example, llineations i n e a t i o n s and and fold foldaxes axes along the Rib west; fold Rib River near near Goodrich Goodrich ((in i n Taylor Taylor Co.) Co.) plunge plunge 30°—40 300-400 west; along the -4- �PERIOD OR OR ERA ERA GEOLOGICAL EVENTS EVENTS Pleistocene Pleistocene Woodfordian Drift (Late Woodfordian Drift (LateWisconsin) Wisconsin) MerrillI Drift Wisconsin) Drift(Early (Early Wisconsin) Merril Wausau Drift (Pre-Wisconsin?) Wausau Drift (Pre-Wisconsin?) - _-- - - — _,jJnconforthfty Un conformity Paleozoic Paleozoic Scattered Outliers Scattered Upper Upper Cambrian(?) Cambrian;?) Sandstone Sandstone Outliers jJnconformity Late Late Precambrian Precambrian Diabase Dikes Dikes (1200 m.y.?) Diabase m.y.?) Quartz Porphyry Porphyry Plugs Plugs Wolf Wolf River Batholith Batholith (1500 (1500 m.y.) m.y.) Unconformity Unconfonnity Emplacement Post-tectonic Plutons (1765 Emplacement ofofPost-tectonic (1765 m.y.) m.y .) Emplacement Syn—tectonicPlutons Plutons (1850 m.y.) Emplacement ofof Syn-tectonic m.y. ) Major Faulting Faulting in Major in Central Central Wisconsin Wisconsin Middle Middl e Precambrian Precambrian Volcanic-sedimentary (1900 m.y.) Vol canic-sedimentarySequence Sequence (1 900 m.y .) •— ? —? Unconfothity __, 7—.-—— 7 I) 7— 4 Metamorphism toto Amphibol i te Facies? Fades? Metamorphism Amphibolite Early Sedimentary-volcanic Early Sedimentary-volcanicSequence? Sequence? Unconformity Early Early Precambrian Precambrian Gneisses, Migmati Migmatites, Amphiboli tes Gneisses, tes, Amphibolites somegreater greater than than 2800 2800m.y. ni.y, old some anoutline outline of Figure 3. 3. Table Table showing showing an of geological geologicalevents eventsrecognized recognized in in central central Wisconsin. Wisconsin. —5— �axes Marshfield plunge about 20' 200west; west; strong strong mineral mineral llineation axes iinn gneisses gneisses near near Marshfield plunge about ineation in amphibolites amphibolites along along the t h e Little L i t t l eEau EauClaire ClaireRiver Riverin isoutheastern n southeasternMarathon Marathon County plunge60 600southwest; southwest;fold fold axes County plunge axes in migmatitic migmatiticgneisses gneissesata Greenwood t Greenwood (in (in Clark 36°west; west;and andfold foldaxes axesa tatNNeillsville e i l l s v i l l e (in ( i nClark ClarkCo.) Co.)plunge plunge Clark Co.) Co.) plunge plunge 35' 70° 70 west. west. . No published radiometric radiometric ages No published ages aare r e available available from fromthe thegneisses gneissesininMarathon Marathon County, andtherefore therefore ttheir County, and h e i r age age is is uncertain. uncertain. However, Van Van Schmus Schmus and and Anderson (1977)reported reported an an age ageof of more morethan than 2800 2800m.y. m.y.ffor Anderson (1977) o r migmatitie migmatitie gneisses gneisses at kmkmsouth Marathon s t u d i e s of of a t Pittsville P i t t s v i l l(25 e (25 southof of MarathonCounty). County). Structural studies gneisses several llocalities centralWisconsin, Wisconsin,and and radiometric radiometric dating dating o c a l i t i e sini ncentral gneisses aat t several led Maass andMedaris Medaris(1977) (1977)t otoconclude concludet hthat gneisses iinn central centralWisconsin Wisconsin Maass and a t tthe h e gneisses are (1978, and a r e mainly mainly of ofMiddle MiddlePrecambrian Precambrian age. age. Myers Myers (1978, and this t h i sconference) conference)showed showed that and Chippewa EauClaire Claire and ChippewaCounties Countieshad hadundergone undergone t h a t amphibolites amphibolitesand andgneisses gneissesini nEau two anddeformation deformationp rprior two periods periods of metamorphism metamorphism and i o r tto o being being included included inin1850 1850m.y. m.y. old than one age of of gneissic T h u s , there appears appears to t o be be more more than one age gneissic rocks rocks old piutons. plutons. Thus, in i n the the region. region. This This point point will willbebediscussed discussed further f u r t h e runder under the thesection sectionon on structure. structure. MIDDLE MIDDLE PRECAMBRIAN PRECAMBRIAN METAVOLCAN IC ROCKS METAVOLCANIC ROCKS Volcanic occur aas xenoliths, screens pendantsi nin iintrusive Volcanic rocks rocks occur s xenoliths, screens and and pendants n t r u s i v e rocks rocks and and and aas s rrelatively e l a t i v e l ycontinuous continuousareas areasini northern n northern andeastern easternMarathon MarathonCounty. County. They rangei nin composition compositionfrom frombasalt basaltt otor rhyolite They range h y o l i t e and and eexhibit x h i b i t aa wide wide variety variety of of textures textures and and primary primary sstructures, t r u c t u r e s , including including pillow pillowlavas, lavas,massive massive flows, flows, flow breccias, volcanogenic breccias, welded welded tuffs, t u f f s ,tuffs t u f fand s and volcanogenicsediments. sediments. The The rocks rocks have except near near llarger have undergone undergone l ilittle t t l emetamorphism metamorphism except a r g e r plutons, plutons, and and consequently, consequently, primary primary textures and and structures s t r u c t u r e s are a r e well well preserved preserved where where the t h e rocks rocks are a r e not not highly has been beenextensively extensively disrupted by by high1 ydeformed. deformed. The The volcanic sequence sequence has faulting f a u l t i n gand and intrusion, intrusion,forming formingisolated i s o l a t e dblocks blockssurrounded surrounded by by plutonic rocks. rocks. This, coupled with i t h the the generally generally poor poor exposure, exposure, precludes precludes establishing the the coupled w original volcanic volcanic stratigraphy. stratigraphy. U/Pb UIPb age n rrhyolite hyolite agedeterminations determinationsononzircons zirconsi in on the the east e a s t edge edge of Wausau indicate a t volcanic t h i sarea areaare a r e1900 1900 m.y. m.y. on of Wausau indicatet hthat volcanic rocks rocks iinn this old old (Van (VanSchmus, Schmus, 1975). 1975). Mafic Mafic and and Intermediate IntermediateMetavolcanic MetavolcanicRocks. Rocks. Basaltic Basaltic rocks, rocks, including including l a r q e areas areas in in t u f f sand and pillowed pillowed and and massive massive flows, a r e exposed exposed iin n several tuffs flows, are several large eastern, northern northern and and southern southern Marathon Marathon county, n aa number number of eastern, County, and and iin of smaller roof i t h i n plutons. plutons. Pillow Pillow lavas lavas are a r e relatively r e l a t i v e lwidespread y widespreadand and roof pendants pendants wwithin indicate subaqueous indicate that t h a tmany many of the the basalts basalts are a r ethe t h eresult r e s u lof t of subaqueous eruptions. eruptions. Although Although pillow pillow lavas lavasare a r ewidespread, widespread, most most outcrops outcrops are a r e frost-heaved frost-heaved and and therefore therefore cannot cannot be be used used ffor o r top top determinations. determinations. Porphyritic Porphyriticand andamygdaloidal amygdaloidal basalts basalts are a r ealso a l s ocoriinon comnon ininthe thesequence. sequence. The The basalts have have been been converted converted to to chlorite—rich chlorite-rich schists s c h i s t salong along zones zones of of intense intensedeformation. deformation. In In thin thinsection sectionthe theundeformed undeformed rocks rocks consist c o n s i s t ofofrandomly randomly oriented oriented epidote, epidote, a c t i n o l i t e ,chlorite, c h l o r i t esodic , sodic plagioclaseand andquartz, quartz,indicating indicatinggreenschist greenschist actinolite, plagioclase facies faciesmetamorphism. metamorphism. Primary Primary textures, including aa fine f i n efelty f e l tgroundmass y groundmass with with textures, including porphyritic porphyritic oro rglomeroporphyritic glomeroporphyritic ororamygdaloidal amygdaloidal textures, textures, are a r epreserved preserved in in places. the the basalts havehave beenbeen metamorphosed places. Adjacent Adjacent to t o larger l a r g e rgranitic g r a n i tplutons i c plutons basalts metamorphosed -6— �to I n some some roof roof t o aniphibolites amphibol i t e s or o rhornblende hornblende or o r pyroxene pyroxene hhornfelses o r n f e l s e s in i n others. o t h e r s . In pendants andesitesoccur occurbetween betweenb abasaltic andr hrhyolitic pendants t the h e andesites s a l t i c and y o l i t i c rocks. rocks. Because Because the t h e original o r i g i n a l extent e x t e n tand and the volcanic v o l c a n i c rocks rocks aare r e ppresent r e s e n t iin n scattered s c a t t e r e d blocks, blocks, the are llocally t h i c k n e s s of o f units u n i t sisi unknown. s unknown. Andesites Andesites are o c a l l y interbedded interbedded with with thickness "graywacke" suggesting subaqueous graywacke" and and conglomerate conglomerate suggesting subaqueous ddeposition. e p o s i t i o n . In I n eastern eastern Marathon Countyt hthe andesites aare with Marathon County e andesites r e interbedded interbedded w i t h dacites, d a c i t e s ,and andthe t h esequence sequence becomes more becomes p rprogressively o g r e s s i v e l y more r hrhyolitic y o l i t i c to t o the t h e northwest. northwest. Felsic F e l s i cMetavolcanic MetavolcanicRocks. Rocks. Felsic F e l s i c volcanic v o l c a n i c rocks rocks uunderlie n d e r l i e tthat h a t part p a r t of of Wausau WisconsinRRiver andoccur occure extensively Wausau e aeast s t o of f t the h e Wisconsin i v e r and x t e n s i v e l y tto o the t h e east e a s t and and north. north. They occur iinn several They aalso l s o occur several roof r o o fpendants pendants elsewhere elsewhere i in n tthe h e county county (Figure ( F i g u r e 2). 2). A wide vvariety A wide a r i e t y of o f volcanic v o l c a n i c rock r o c k types types are a r e represented, represented, including i n c l u d i n g water-laid water-laid (bedded) (bedded) t utuffs, f f s , welded welded t tuffs, u f f s , pyroclastic p y r o c l a s t i c breccias, breccias, flow f l o wbreccias, b r e c c i a s ,massive massive and sedimentsooff several several types. and flow—banded flow-banded r h rhyolites, y o l i t e s , llahars a h a r s and and volcanogenic volcanogenic sediments types. Lithic L i t h i ctuff t u fwith f w i some t h someinterbedded interbeddedvolcanogenic volcanogenic sediment sediment is i sthe t h emost mostcomon common with P y r o c l a s t i c breccias breccias w i t h clasts c l a s t s up up to t o at a tleast l e a s 20 t 20cm cm are a r e present present rock type. type. Pyroclastic rock in were i n several several localities, l o c a l i t i e sand , and wereprobably probablydeposited deposited near near vents. vents. Flow-banded Flow-banded r hrhyolite y o l i t e ((Figure F i g u r e 44), ) , lahars l a h a r s (Figure ( F i g u r e 5) 5) and and welded welded ttuffs uffs (Figure and along along tthe Rib 6 ) are a r e well w e l lpreserved preserved ini nWausau Wausau and he R i b River R i v e r east e a s t of o f Athens. Athens. ( F i g u r e 6) Relict Re1 i c t spherulites, s p h e r u l i t e s , perlitic per1 it i cracks c cracksand andintensely i n t e n s e l ywelded welded vitric v i t r i cfragments fragments (Figure probably were wereooriginally ( F i g u r e 6) 6 ) suggest suggest that t h a t some some ooff these these rrocks o c k s probably r i g i n a l l y obsidian. obsidian. Near Brokawv volcanic conglomerate,sandstone, sandstone,and ands siltstone Near Brokaw o l c a n i c conglomerate, i l t s t o n e are a r e interbedded interbedded The conglomerates conglomeratescconsist mainly onsist m a i n l y of o f boulders boulders with w i t h welded welded ttuffs u f f s and and lava l a v a flows. flows. The up cmi in diametero of rocksi ninaammatrix up tto o 20 20 cm n diameter f vvolcanic o l c a n i c rocks a t r i x oof f ffiner i n e r volcanic volcanic boulderso fofqquartzite andggranite However, boulders u a r t z i t e and r a n i t e aare r e aalso l s o present p r e s e n t in in fragments. However, The The vvolcanic o l c a n i c sandstones sandstones cconsist o n s i s t of o fround roundsand—size sand-size vvolcanic olcanic These uunits n i t s range range fragments, fragments, qquartz u a r t z ggrains, r a i n s , and and scattered s c a t t e r e d quartzite q u a r t z i t e pebbles. pebbles. These in i n thickness thickness from from aa few few meters meters to t o several several tens tens ofo meters f metersand and have have aa very very restricted r e s t r i c t e d distribution d i s t r i b u t i o nbetween between the t h e lava l a v a flows f l o w s or o r ash ash flows. flows. some some llayers. ayers. Except areas, tthe Except f for o r local l o c a l development development o of f ssericite e r i c i t e in i ndeformed deformed areas, h e ffelsic elsic extremely ffine volcanic evidence of ometamorphism. v o l c a n i c rocks rocks show show llittle i t t l or e ono r no evidence f metamorphism. The The extremely ine g r a i n size s i z e and and preservation p r e s e r v a t i o n of o f primary primary features f e a t u r e s such such as as shard shard structures s t r u c t u r e s also also grain indicates i n d i c a t e s aa general general l lack a c k oof f rrecrystallization. ecrystallization. Where Where tthe h e rocks rocks have havebeen been deformed, they t otos esericite r i c i t e sschists c h i s t s or o r the t h evolcanic v o l c a n i cfragments fragments deformed, theymay maybebeconverted converted may beeextensively deformed,asasdiscussed discussedl alater under tthe may be x t e n s i v e l y deformed, t e r under h e ssection e c t i o n on on structure. structure. The The ffelsic e l s i c volcanic v o l c a n i c rocks rocks are a r e interpreted i n t e r p r e t e dtot obebemainly m a i n l yaquagene aquagene ttuffs uffs w i t h interbedded interbeddedsediments. sediments. Thus Thus t hthey e y aare r e mmainly a i n l y s isimilar m i l a r i in n oorigin r i g i n to t o the the with weldedt utuffs, subaqueous andi nintermediate subaqueous mmafic a f i c and t e r m e d i a t e rocks. However, However, t hthe e welded f f s , flow flow banded andl alahars probablyoof banded r hrhyolites y o l i t e s and h a r s aare r e probably f ssubaerial u b a e r i a l oorigin. r i g i n . The The volcanic volcanic sandstones and conglomerates north of Wausau are believed to be alluvial sandstones and conglomerates n o r t h o f Wausau a r e b e l i e v e d t o be a l l u v i a l f a c i e s of o f the t h e volcanic v o l c a n i c rocks. rocks. Their T h e i r rrestricted e s t r i c t e d distribution d i s t r i b u t i o n and and iinternterfacies layered weldedt utuffs mayi nindicate l a y e r e d welded f f s may d i c a t e tthat h a t they they aare r e valley—fill v a l l e y - f i l l deposits d e p o s i t s on on Therefore, the subaerial felsic volcanic rocks t h e flanks f l a n k s of o f aavolcano. volcano. Therefore, t h e subaerial f e l s i c v o l c a n i c rocks the may may rrepresent e p r e s e n t vvolcanic o l c a n i c islands i s l a n d s ini na abasin basinofounknown f unknown dimensions. dimensions. The determinations on The oonly n l y age age determinations on volcanic v o l c a n i c rocks rocks ini nMarathon Marathon County County are are from a rhyolite along Wis. Hwy. 52 near the eastern city limits of f Wausau. from a r h y o l i t e along Wis. Hwy. 52 near t h e eastern c i t y l i m i t s oWausau. Van Schmus Schmus and (1975)r ereport U/Pbage ageononz izircons 1900m.y. m.y. ffor or Van and o t hothers e r s (1975) p o r t aaU/Pb r c o n s oof f 1900 I assume the other volcanic rocks are part of the same general these rocks. rocks. I assume t h e o t h e r v o l c a n i c rocks a r e p a r t o f t h e same general these p e r i o d of o f volcanism. volcanism. period —7— �Figure rhyolite Figure 4. 4. Flow Flow banded banded rhyol t e along along Rib Rib River River east e a s t ofofAthens. Athens. Figure Figure 5.5. Volcanic Volcanic mudflow mudflow (lahar) (lahar)deposits depositsataHighland t HighlandGrove Grove School of clasts n Wausau. Note Note the the mixture mixture of c l a s t s in in aafine f i n etuffaceous tuffaceous School ini Wausau. matrix. matrix. -8-8- �Welded t tuff u f f showing showing flattened f l a t t e n e dand andwelded welded shard shard fragments fragments Figure 6. 6. Welded along with w i t h rounded rounded phenocrysts. phenocrysts. Sample Sample is i s from fromWausau. Wausau. Metasedimentary Rocks. Rocks. Graywacke Graywacke and a t e associated i t h vvolcanic o l c a n i c rocks rocks ands lslate associatedwwith in i n north n o r t hcentral c e n t r aMarathon l MarathonCounty County(between (between Athens Athens and and Merrill) M e r r i l l were ) werenamed named the the 'HamburgSSlates' Weidman (1907). Mapping "Hamburg l a t e s " by byWeidman by LaBerge and Myers Myers i indicates LaBerge and n d i c a t e s aa Mapping by much more i t e d ddistribution i s t r i b u t i o n of o fmetasedimentary metasedimentary rocks, u r t h e r indicates indicates much morel i m limited rocks, and andf further that with t h a t they they are a r eextensively e x t e n s i v e l yand and complexly complexly interbedded interbedded w i t h volcanic v o l c a n i c rocks. rocks. Most Most of rocksaare o f the the sedimentary sedimentary rocks r e nnot o t ssufficiently u f f i c i e n t l y exposed exposed tto o aallow l l o w delineation d e l i n e a t i o n of of discrete quartz, d i s c r e t e units. u n i t s . The The coarser sediments sediments are a r e graywackes graywackes composed composed oof f quartz, plagic1ase p l a g i o c l a s e and and rock rock fragments. fragments. The The finer—grained f i n e r - g r a i n e d sediments sedimentswere weremetamorphosed metamorphosed to t o chlorite c h l o r i t e and/or and/or ssericite e r i c i t e slates s l a t e s oorr phyllites. p h y l l ites. Well Well bedded bedded aargillite r g i l l i t eand andgraywacke graywacke wwith i t h interbedded interbedded ttuff u f fisi sexposed exposed along CTH—W Wausau (Sec.12, 12,T.29N., T.29N., R.7E.). CTH-W n onorth r t h o of f Wausau (Sec. R.7E.). The The rock rock isi smedium medium to in thickness from about 1—30 t o fine f i n egrained, grained,with w i t layers h l a y e rranging s ranging i n thickness from about 1-30cm. cm. Excellent E x c e l l e n t examples examples of o f graded graded bedding bedding and and ssoft o f t sediment sediment deformation deformation ("slump ("slump structures") s t r u c t u r e s " ) are a r eexposed. exposed. Several units of rhyolitic lapilli tuff are interSeveral u n i t s o f r h y o l i t i c l a p i l l i t u f f a r e interbedded bedded wwith i t h the t h e graywacke—argillite. g r a y w a c k e - a r g i l l i t e . Some Some ofoft hthe e aargillite r g i l l i t eunits u n i tare s a rcomposed e composed mainly m a i n l y of o f volcanic v o l c a n i c fragments. fragments. Conglomeratic Conglomeratic u units n i t s wwithin i t h i n and h e top t o p of of andaatt tthe this (along tthe west end endooff tthe t h i s sequence sequence (along h e Wisconsin Wisconsin RRiver i v e r aat t tthe h e west h e bridge b r i d g e at at Brokaw) may be be volcanic conglomerates. Brokaw) may conglomerates. Welded Welded t utuffs, f f s , flow f l o wbreccias brecciasand and lahars lahars exposed alongt hthe westsside the Wisconsin (Sections 2,2, 3, 11, T.28N., T.28N., exposed along e west i d e oof f the Wisconsin RRiver i v e r (Sections 3, && 11, R.7E.) Quarry(NWk, (NW¼, Sec. T.28N.,R.7E.) R.7E.)aare R.7E.) and and in i nthe t h e3M 3MCompany Company Quarry Sec. 11,11, T.Z8N., r e iinternterbedded ands tstratigraphically bedded wwith i t h tthe h e conglomerates conglomerates and r a t i g r a p h i c a l l y overlie o v e r l i ethe t h egraywackegraywackeargillite a r g i l l i t sequence e sequence on on the t h e east e a s t side s i d e ofo fthe t h eWisconsin Wisconsin River. River. The The sedimentary sedimentary units, u n i t s , therefore, t h e r e f o r e , are a r eunderlain, underlain,interbedded interbedded with, w i t h , and and overlain o v e r l a i nby by volcanic volcanic rocks. They aare r e iinterpreted n t e r p r e t e d to t o be be facies f a c i e s of o fthe t h evolcanic v o l c a n i csequence sequence iinn the t h e area. area. rocks. They -9— �An isolated isolated area by, and An areaofofmetagraywacke metagraywacke and and conglomerate conglomerate surrounded surrounded by, and interbeddedwith withffelsic of interbedded e l s i c to t o intermediate intermediate volcanics volcanics is i s located located northwest northwest of Stratford (Sections (Sections 34, 34, 35, 35, 36, 36, T.28N., T.28N., R.3E., R.3E., and and Sec. Sec. 31, 31, T.28N., T.28N., R.4E.). R.4E.). A magnetichigh highi sis associated associatedwwith A prominent prominent magnetic i t h tthe h e sedimentary sedimentary uunits. n i t s . The The metagraywacke No o metagraywacke i sis ffine i n e tot omedium medium grained grained and a n d medium medium tto o massively massively bedded. bedded. N conglomeratecontains contains boulders boulders up graded bedding u p to t o 30 30cm cm The conglomerate graded bedding was was observed. The of quartzite, q u a r t z i t e ,iron—formation, iron-formation, felsic f e l s i cand andmafic maficvolcanic volcanicrocks rocksand andsome some plutonic The present present landowner reported that rocks. The landowner reported t h a t aamining miningcompany company from from Michigan Michigan ddrilled r i l l e d exploratory exploratory holes holes ffor o r iron iron ore ore in i nthe t h earea area during during the t h e late l a t e1950's. 1950's. Thus, sedimentaryrocks, rocks,mainly mainlygraywackes graywackes Thus, sedimentary andand s l aslates t e s o rora rargillites, gillites, are widely widely ddistributed county and andaare are i s t r i b u t e d throughout throughout tthe h e county r e ccharacteristically haracteristically nol alarge, area of associated with with volcanic rocks. associated rocks. However, However, no r g e , continuous continuous area The sedimentary rocks rocks was demonstrated iinn the sedimentary was demonstrated t h e present presentmapping mapping program. program. The widespreadassociation associationof of sediments volcanic rocks, rocks, however, widespread sediments wwith. i t h t hthe e volcanic however, iiss thethe environment helpful inininterpreting interpreting environmentini which n whichthe therocks rocksaccumulated. accumulated. INTRUSIVE ROCKS INTRUSIVE ROCKS The volcanic rocks The volcanic rocks have have been been intruded by by more more than than twenty twenty stock—like stock-like Most of of the plutons i nMarathon Marathon County. County. Most plutons range range in i n composition composition from from plutons in quartz ddiorite quartz i o r i t e to t ogranite; g r a n i t e ;however, however, several several gabbroic gabbroic intrusions are a r e also also Discordanceofof the the plutons, plutons, low gradeofof the the volcanic volcanic present. Discordance low metamorphic metamorphic grade rocks, and contactmetamorphic metamorphic suggestsc rcrystallization rocks, and generally meagre meagre contact e f feffects e c t s suggests ystallization of the of the intrusions intrusions at a t shallow shallow llevels e v e l s iin n the t h e earth's e a r t h ' s crust c r u s t with w i t h little l i t t lsubsequent e subsequent erosion. The The plutons would would probably probably be be classed classedasasupper uppermesozonal mesozonal. Gabbroic Intrusions. Several small gabbroic gabbroic intrusions intrusions of diverse diverse Gabbroic Intrusions. Several small texture, of diverse t e x t u r e , and and presumably presumably of diverse age, age, are a r e present presentininMarathon Marathon County. County. Most intrusions are intrusions a rmetamorphosed e metamorphosedand andsomewhat somewhat deformed. deformed. 2 A of metagabbro underlying approximately km2 iiss exposed A mass mass of metagabbro underlying approximately 20 20 km exposed along along the the EauClaire Claire River River in in the Wausau). Most of of the Eau the vicinity v i c i n i t yofofGallon Callon(east ( e a sof t of Wausau). Most the intrusion isi smassive massive gabbro gabbro with w i t h aa sub—ophitic sub-ophitic ttexture, e x t u r e , but b u tconspicuously conspicuously layered gabbro gabbroi is present llocally. the flanking flanking volcanic volcanic and layered s present o c a l l y . Although Although the and ggranitic ranitic rocks rocks are a r e extensively extensively deformed, deformed, the t h egabbro gabbro mass mass iiss largely largelyundeformed. undeformed. Inclusions of schistose occur in in the Inclusions schistose volcanic volcanic rocks rocks and and deformed deformed ggranite r a n i t e occur the gabbro suggesting suggestingt hthat the gabbro than the gabbro a t the gabbro iiss younger younger than the deformational deformational event event the surrounding surrounding rocks. rocks. aaffecting f f e c t i n g the Several are present in Several gabbroic gabbroic masses masses are insouthwestern southwesternMarathon Marathon County. County. mass northofofMarshfield Marshfield cconsists AA rrelatively e l a t i v e l yunmetaniorphosed unmetamorphosed mass s i tsituated u a t e d north o n s i s t s of coarse—grainedo pophitic gabbro and andaanorthositic coarse-grained h i t i c gabbro n o r t h o s i t i c gabbro. gabbro. This mass mass produces produces prominent oval oval aeromagnetic aeromagnetic anomaly. anomaly. aa prominent A gabbroic mass massalong alongthe theLLittle Pleine River A gabbroic i t t l e Eau Eau Pleine River (Secs. (Secs. 23, 23, 24, 24, T.26N., T.26N., R.3E., and Secs.17, 17, 18, 18, 19 19 && 20, 20, T.26N., T.26N., R.4E.) R.4E.) cconsists R.3E., and Secs. o n s i s t s of granular granular plaqioclase and hornblendewith with numerous numerousstrongly stronglyf ofoliated of plaqioclase and hornblende l i a t e d zones zones of amphibolite. This gabbroic gabbroicmass mass isi much s muchmore moredeformed deformedand andmetamorphosed metamorphosed than the one than the one nnorth o r t h of Marshfield, Marshfield, and and therefore therefore appears appears tto o be be older. older. - 10 - �Several small, small, widely Ultramafic U l t r a m a f i c Intrusions. I n t r u s i o n s . Several w i d e l y scattered s c a t t e r e d ultramafic u l t r a m a f i cbodies bodies composed serpentine are composed m amainly i n l y o foft atalc l c and and serpentine a r e located l o c a t e d ini nMarathon Marathon County. County. The ultramafic exposed,r erendering i f f i c u l ttot odetermine determine u l t r a m a f i c rocks rocks aare r e ppoorly o o r l y exposed, n d e r i n g i titddifficult their t h e i r size s i z eand andshape. shape. They They aare r e llocated o c a t e d along along major major zones zones ooff cataclasis, c a t a c l a s i s , and and thus thus iitt is i slikely l i k e l that y t h athe t t h bodies e bodiesare a r e elongated elongated pparallel a r a l l e l tto o the t h e sstrike t r i k e of o f the the zones. small ultramafic massalong alongt hthe AA small u l t r a m a f i c body body occurs occurs with w i t h the t h emetagabbro metagabbro mass e LLittle ittle Eau PPleine SE¼,Sec. Sec.20, 20, T.26N., T.26N., R.3E,). IIttisi scomposed composed mainly mainly Eau l e i n e River R i v e r (NE¼, (NEk, SEk, R.3E.). andt talc, olivine ooff serpentine serpentine and a l c , but b u t contains c o n t a i n s numerous numerous r e relict 1 i c t 01 i v i n e crystals. c r y s t a l s . The main exposure exposureo of main f t hthe e sserpentinite e r p e n t i n i t e is i s ini na apitp where i t wherequarrying q u a r r y i n gwas wasattempted. attempted. Themineralogy mineralogyand and hasnot n o tbeen been as as The t e texture x t u r e o foft hthe e r orock c k i nindicate d i c a t e tthat h a t iti thas intensely as the i n t e n s e l ymetamorphosed metamorphosed oorr deformed deformed as t h e associated associatedmetagabbro. metagabbro. Therefore, iti tprobably probably represents represents a a separate separate iintrusion n t r u s i o n rather r a t h e r than than an an ultramafic u l tramafic i m i l a r serpentine-talc s e r p e n t i n e - t a l cbody bodyexposed exposed ddifferentiate i f f e r e n t i a t e ofofthe t h egabbroic gabbroicmass. mass. AA ssimilar NW¼, Sec. 27, 27, T.26N., iinn aa roadcut roadcutsouth southofo Rozellville f R o z e l l v i(NW¼, l l e (NU%, NWk, SW¼, SWk, Sec. T.Z6N., R.4E.) R.4E.) Thus, also a l s o contains contains abundant abundant r relict e l i c t olivine o l i v i n eand andhas has only o n l y39.4 39.4 percent percent Si02. 3 0 2 . Thus, pyroxenites Feldspathic pyroxeni t e s cconsisting o n s i s t i n g of of it i tisi sprobably probablyaaserpentinized s e r p e n t i n i z e d dunite. duni t e . Feldspathic andp plagioclase andr eretaining sserpentinized e r p e n t i n i z e d pyroxene pyroxene and l a g i o c l a s e and t a i n i n g ttheir h e i r igneous igneous texture texture Sec. 2, NE¼, aare r e exposed exposed iinn the t h eSE¼, SEg, SE¼, SEij, Sec. 2, T29N., T.29N., R.3E. R.3E.and and NE%,NE¼, NEk, 5E¼, SEk, Sec. Sec. 27, 27, T.30N., T.30N., R.4E. R.4E. along aa major major fault f a u l tzone zoneini northwestern n northwesternMarathon MarathonCounty. County. Therefore, thant the Therefore, they they appear appear lless e s s deformed deformed than h e uultramafic l t r a m a f i c bodies bodies in i nsouthern southern and eastern Marathon and Marathon County. County. Granitic G r a n i t i c Intrusions. Intrusions. The volcanic-sedimentary sequence sequence and gneisses gneisses The volcanic—sedimentary Most ooff the have beeni nintruded by numerous numerouss tstock—like have been t r u d e d by o c k - l i k e p lplutons u t o n s o of f ggranite. r a n i t e . Most the composit'ional1.y zoned zoned and and contain c o n t a i n pendants, pendants, screens screens and and xxenoliths enoliths pplutons l utons are a r e compositionally ooff volcanic v o l c a n i c and and oolder l d e r plutonic p l u t o n i c rocks. rocks. Quartz heterogeneous Q u a r t z ddiorite i o r i t e intrusions i n t r u s i o n sare a r etypically t y p i c a l lsmall, y small, heterogeneousand and generally generally highly contaminated with inclusions of volcanic rocks, gabbro, pyroxenite, h i g h l y contaminated w i t h i n c l u s i o n s o f v o l c a n i c rocks, gabbro, p y r o x e n i t e , and metasedimentary rocks. AA conspicuous conspicuouse aeast s t t oto nnortheast o r t h e a s t ttrending r e n d i n g ccataclastic ataclastic and metasedimentary foliation is present in most of the plutons. Mineralogically, f o l i a t i o n i s present i n most o f the p l u t o n s . M i n e r a l o g i c a l l y , they they contain contain strongly s t r o n g l y zoned zoned plagioclase p l a g i o c l a s e (about (about An30), 20-30 20-30 percent percent quartz, q u a r t z , 10-30 10-30 percent percent hornblende hornblende o or r bbiotite i o t i t e or o r both, both, and and minor minor rnicrocline. microcline. Intrusions I n t r u s i o n s ranging ranging in i ncomposition composition from from quartz quartz monzonite monzonite tto o granite granite andddioritic Typically, iintrude n t r u d e the the volcanic v o l c a n i c rocks rocks and i o r i t i c bodies. bodies. T y p i c a l l y , the t h emargins margins are are highly quartz h i g h l y contaminated, contaminated, but b u t the t h e cores cores are a r erelatively r e l a t i v e homogeneous. l y homogeneous. Some Some quartz monzonitesappear appear quartzd idiorites, monzonites t o to bebe g r gradational a d a t i o n a l i n into t o quartz o r i t e s , but b u t dikes dikes of o f quartz quartz monzonitei nint hthe monzonite e ddioritic i o r i t i c rocks rocks suggest suggest ffracturing r a c t u r i n g and and iintrusion n t r u s i o n ooff the the The quartz pperipheral e r i p h e r a l ddioritic i o r i t i c rocks rocks by by later l a t e r phases phases oof f tthe h e intrusion. i n t r u s i o n . The monzonites havea apervasive pervasive monzoni t e s g egenerally n e r a l l y have c acataclastic t a c l a s t i c f ofoliation l i a t i o n which, which, in i n places, places, iiss truncated truncated by by non—foliated non-fol i a t e d ggranites r a n i t e s ((Figure F i g u r e 77), ) , suggesting suggesting tthat h a t the t h e granites granites are llater. are ater. The Many have have The ggranitic r a n i t i c plutons p l u t o n srange range ini nsize s i z efrom fromabout about5-130 5-130km2. km2 . Many concentric zoning wwith quartzddiorite c o n c e n t r i c zoning i t h aa ggranitic r a n i t i c core core and and quartz q u a r t z monzonite monzonite t oto quartz iorite Narrow bbut u t ddistinct i s t i n c contact t c o n t a cmetamorphic t metamorphichalos haloswere wereobserved observed around around border. Narrow several iintrusions werer recrystallized several n t r u s i o n s where where t hthe e f felsic e l s i c volcanic v o l c a n i c rocks rocks were e c r y s t a l l i z e d to t o aa massivesaccharoidal saccharoidalrock rockand andmmafic rockswere werer erecrystallized massive a f i c v volcanic o l c a n i c rocks c r y s t a l l i z e d to to Excellent x c e l l e n t examples examples oof f iintrusion n t r u s i o nbreccias brecciasare a r eexposed exposed hornblende hhornfelses. hornblende ornfelses. E on on tthe h e margins margins ooff some some i intrusions. ntrusions. — 11 �t a,- Figure Foliated quartz quartz monzonite g h t (with oliation monzoniteononr i right (with ffoliation Figure 7. 7. Foliated parallel on lleft. w i t h the the pencil) pencil)cut cutby by aamassive massive ggranite r a n i t e on e f t . The parallel with The pencil approximately on on the the contact. contact. pencil point point isi sapproximately The texturesand andmineralogy. mineralogy. The ggranitic r a n i t i c intrusions intrusions exhibit e x h i b i ta awide wide variety v a r i e t yofoftextures Quartz monzonitestend tendt otobe beporphyritic porphyritic with phenocrysts Quartz monzonites phenocrysts of plagioclase plagioclase (An20-30) o rormicrocline i n e r matrix of quartz, q u a r t z , feldspar feldsparand and (An20_30) microclineo rorboth bothi ninaa ffiner mafic minerals. minerals. Hornblende Hornblende iis s comon common in i n quartz quartzmonzonites, monzonites, comprising comprising as as much as20 20percent percentof of the rocks. much as rocks. Biotite B i o t i t eis ialso s a l sconvuion. o common. Granites Granites generally generally contain most conunon variety. most common v a r i e t y . Individual contain fewer fewer mafic mafic minerals, with with biotite b i o t i tthe e the Individual plutons berecognized recognizedbybytheir their mineralogy, mineralogy,oor plutons may may be r ttexture, e x t u r e , or o r both. both. The The intrusions intrusions aalso l s o ddiffer i f f e r in in color. color. Quartz Quartz monzonites r e ttypically y p i c a l l y gray gray and and monzonitesaare weather from ppink weather tto o a a buff buff color colorwhereas whereas granites range range from i n k to t o deep deep brick red. red. The variety of textures The variety textures exhibited exhibited by by the the granitic g r a n i t i crocks rockspresumably presumably reflects reflects differences ininthe t h eenvironment environment(temperature (temperatureand and pressure) pressure) and and chemistry chemistry differences (especially the time timeofof crystal1 crystallization. ization. (especially H20) H20) aat t the The Middle Precambrian volcanic-plutonic of Marathon Marathon County County is is The Middle Precambrian volcanic—plutonic portion portion of situated of the s i t u a t e d on on one one of the major major gravity gravity lows t h e state s t a t e(up (uptot ominus minus 90 90 ows in in the milligals) Rammer, mill i g a l s(Ervin ) ( E r vand i n and Hammer, 1974). 1974). The gravity low low iis The gravity s significantly s i g n i f i c a n t l ygreater greater than than that t h a t over over the thegneissic gneissicarea areadescribed describedabove. above. This This indicates indicates that t h a t the the area area is i s underlain underlain mainly mainly by by granitic g r a n i t i c rocks. rocks. The The general gravitylow lowsuggests suggests general gravity that t h a t the the volcanic volcanic pendants pendants ((at a t least l e a s t the the mafic mafic ones) ones) are a r e relatively r e l a t i v e l yshallow shallow features features in i n the the granitic g r a n i t i crocks. rocks. The mapofof the the area area (Zeitz ( Z e i t zand and The aeromagnetic aeromagnetic map others, others, 1977) 1977) iis s consistent consistent wwith i t h tthis h i s interpretation. i n t e r p r e t a t i o n . The The granites graniteshave have aa 1 low, low, flat f l amagnetic t magneticexpression expressionwhereas whereas the t h egabbros gabbros and and volcanics volcanicsproduce produce magnetic magnetic highs. highs. (This (This is i sthe t h ereverse reverseofofthe t h emagnetic magnetic pattern pattern described described elseelsewhere and Karl Karl (1977).) (1977).) The where in northern northern Wisconsin Wisconsin by by Mudrey Mudrey and The blotchy blotchymagnetic magnetic - 12 - �rocks in an area composed ppattern a t t e r n indicates i n d i c a t e s aa patchy patchy distribution d i s t r i b u t i o nofovolcanic f volcanic rocks i n an area composed largely l a r g e l y of o f granitic g r a n i t i c rocks. rocks. Only aa few few rradiometric agesaare from pplutonic Only a d i o m e t r i c ages r e aavailable v a i l a b l e from l u t o n i c rocks rocks in in Marathon Schmusand ando tothers (1976) obtained obtained a U/Pb Marathon County. County. Van m.y. Van Schmus h e r s (1976) U/Pb age age of o f 1850 1850 m.y. on on zircons z i r c o n s from from the t h e Kalinke K a l i n k equartz quartznionzonite monzonite ini nnortheastern northeasternMarathon Marathon County. County. The ggranitic off the The r a n i t i c rocks rocks in i nMarathon Marathon County County ((with w i t h the t h e exception exception o t h e Wolf Wolf River R i v e r Batholith Bath01 4 t hand andsyenite syeni t ebodies bodiesnear nearWausau, Wausau, described below) below) are a r e believed be1ieved tto o be be related r e l a t e d to t o aasingle s i n g l eigneous igneous event. event. All A l l are a r e intruded i n t r u d e dinto i n t owhat whatmay may reasonably be be iinterpreted reasonably n t e r p r e t e d as as aasingle s i n g l e(but ( b ucomplex) t complex)volcanic—sedimentary volcanic-sedimentary sequence. The various plutons plutons show shows isimilar, widespreadc acataclastic The various m i l a r , widespread t a c l a s t i c f ofoliation, liation, and many have gradational contacts from quartz diorites to is and many have g r a d a t i o n a l contacts from quartz d i o r i t e s t o granites. g r a n i t e s . IItt is conceivable conceivable tthat h a t the t h e various various granitic g r a n i t i crocks rocksare a r co—extensive e co-extensive at a tdepth depth and and form I f this t h i s interpretation i n t e r p r e t a t i o n is i s correct, c o r r e c t , the the form aa large l a r g e composite composite bbatholith. a t h o l i t h . If various plutons may maybebecupolas cupolasonont hthis various stock—like s t o c k - l i k e plutons i s l large a r g e bbatholith. a t h o l i t h . Numerous Numerous 1850m.y. m.y.oold l d pplutons l u t o n s aalso l s o intruded i n t r u d e d the t h e gneissic g n e i s s i c rocks rocks in i ncentral c e n t r a lWisconsin Wisconsin 1850 (Van Schmus, (Van Schmus, 1976). Chemical analyseso of 19ggranitic Chemical analyses f 19 r a n i t i c rocks rocks and and 88 vvolcanic o l c a n i c rocks rocks from from the the Becauset the county iindicate county n d i c a t e that t h a t they they are are calc—alkaline. calc-alkaline. Because h e vvolcanic o l c a n i c and and pplutonic l u t o n i c rocks rocks have have aa similar s i m i l a r age, age, have have undergone undergone a as similar i m i l a r sstructural tructural andaare suggest tthat hat hhistory, i s t o r y , and and are a r e chemically chemically ssimilar i m i l a r and r e sspatially p a t i a l l y related, r e l a t e d , II suggest they may be co-genetic. co-genetic. may be LATE PRECAMBRIAN PRECAMBRIAN The Late Precambrian The Late Precambrian i is s represented represented in i nMarathon Marathon County County by widely widely r a n i t e s ,syenites, syenites , ddistributed i s t r i b u t e d igneous igneous rocks, rocks, including i n c l u d i n g quartz q u a r t z monzonites, monzoni t e s , ggranites, and several several types types ooff diabase and ggranites The qquartz u a r t z monzonites monzonites and r a n i t e s are are and diabase dikes. The part small, circular p a r t of o f aa large l a r g e batholith b a t h o l i t hwhereas whereas the t h e syenites s y e n i t e s aare r e small, c i r c u l a r bodies. bodies. The diabase diabase ddikes mayrepresent represent tthe youngest Precambrian Precambrianrocks rocksi in The i k e s may h e youngest n tthe h e area. area. Wolf River RiverBBatholith The Wolf RRiver Batholith. The Wolf iver B a t h o l i t h . The The Wolf a t h o l i t h is i s aa major major Late Late Precambrianbbatholith Precambrian a t h o l i t h underlying u n d e r l y i n g at a tleast l e a s3500 t 3500km2 km2 ini neastern easternMarathon Marathon County County and aadjoining and others, others, 1975). and d j o i n i n g parts p a r t sofo northeastern f northeasternWisconsin Wisconsin(Van (VanSchmus Schmus and 1975). U/Pb ageononz zircons is i1500 m.y. Schmus U/Pb age i r c o n s i indicates n d i c a t e s that t h a t the t h ebatholith batholith s 1500 m.y.oldo (Van l d (Van Schmus western margin margin ooff the The western t h e batholith b a t h o l i t hwas wasmapped mapped during during and others, others, 1976). and 1976). The this t h i s survey. survey. The major major rock rock ttype The y p e of o f the t h eWolf Wolf River R i v e rBatholith B a t h o l i texposed h exposedini Marathon n MarathonCounty County iiss aa coarse—grained coarse-grained pporphyritic o r p h y r i t i c quartz quartz monzonite monzonite which which extends extends from from the the northeastern corner ooff the northeastern corner t h e county county approximately approximately ttwo-thirds w o - t h i r d s of o fthe t h eway way across across The southeastern southeasternppart off Marathon Countyi is underlain t h e county. county. The art o Marathon County s u n d e r l a i n by by aa the medium—grained quartz monzonite monzonite which which extends extends southwest southwest as as ffar medium-grained p oporphyritic r p h y r i t i c quartz ar Anderson (1975) (1975) and and Anderson Andersonand andCCullers as as Stevens Stevens Point. P o i n t . Anderson u l l e r s (1978) (1978) concluded concluded River chemicallyr related tthat h a t the t h e Wolf Wolf R i v e r BBatholith a t h o l i t h iis s chemically e l a t e d t to o aalkalic l k a l i c intrusions, intrusions, and thus is significantly different from the Middle Precambrian and thus i s s i g n i f i c a n t l y d i f f e r e n t from t h e Middle Precambrian plutons p l u t o n s to to the t h e west. west. The westernedge edgeo of Wolf RRiver Batholith The ccontact o n t a c t between between t hthe e western f t the h e Wolf iver B a t h o l i t h and and Precambrian rocks tthe h e Middle Middle Precambrian rocks i s is, , i in n ppart, a r t , aa major major fault f a u l tzone zone along along the the - 13 - �Claire Dells A t Eau Eau Claire Dells and and to t o the the northeast northeastnear near Hogarty Hogarty Eau Claire River. Eau Claire River. At hashas metamorphosed (Figure 1), I ) ,the theWolf WolfRiver RiverBatholith Batholith metamorphosed the sheared sheared volcanic and plutonic rocks and plutonic rocks (discussed (discussed later) l a t e r )tot ohornblende hornblendeand and pyroxene pyroxene hornfelses. hornfelses. However, southwestalong alongthe thecontact contacta azone zone However, f afarther r t h e r southwest of ofc acataclastic t a c l a s t i c f foliation oliation The sstrike morethan than1.5 1.5 km kmwide widecuts cutsthe theWolf WolfRiver RiverBatholith Batholith (Figure 2). 2 ) . The trike more and dipofof the the ffoliation w i t h that t h a tini nthe theolder olderrocks rocksand and and dip o l i a t i o n isi sconsistent consistent with suggests recurrence of of the deformation of the the Wolf suggests aa recurrence deformation after a f t e remplacement emplacement of Wolf River Batholith. Bath01 i t h . Twoe elliptical, l l i p t i c a l , concentrically concentricallyzoned zoned alkalic a1 kalic The Syenite Syenite Plutons. Two The plutons intruded the Middle Precambrian volcanic—plutonic complex just west west ~ l u t o n sintruded the Middle Precambrfan volcanic-plutonic comvlex just These plug—like plutons are i ke plutons-are These ~ l u ~ l of Wausau (Myers, 1976, this conference). Wausau (Myers, 1976, t h i s conference). about 1500m.y. m.y.old old and andaare chemicallyrelated related tto about 1500 r e chemically o the Wolf Wolf River Batholith Batholith (Van Schmus and others, 1976). (Van Schmus and others, 1976). Wausau syenitepluton pluton iiss approximately The Wausau syenite approximately WausauSyenite Syenite Pluton. Pluton. The Wausau 12 xx 27 kminin plan, plan, elongate concordantly northeast, northeast, and and consists consists of of aa wall 12 27 km elongate concordantly wall xenol i t h r i r zone of foliated amphibole syenite, an intermediate zone of xenolith—rich zone of f o l i a t e d amphibole an intermediate quartz syenite syenite and and aa core core of of quartz quartz monzonite monzonite( t(the "Ninemileg granite). quartz h e "Ninemile ranite"). southern half half of the syenite~pluton wasintruded intrudedand andp partially K wWausau a u s a u svenite l u t o nwas artially The The southern nearly complete completering ring of of very A nearly very large, larie, assimilated by by the the Ninemile Ninemile pluton. plut&. A lensoidal quartzite xenoliths the outer lensoidal xenoliths marks marks the outer part part of of the theintermediate intermediate zone. zone. The larger quartzite quartzite xenoliths xenoliths form ring of prominent The larger form aa ring prominent hhills, i l l s , including includingRib Rib Mountain, MosineeHill Hill and An intrusion breccia breccia marks marks the the Mountain, Mosinee and Hardwood Hardwood HHill. i l l . An contact ther eresistant on tthe tops of of the contact between between the s i s t a n t qquartzite u a r t z i t e on h e tops the hills h i l l sand andthe themore more readily on the lower readily eroded eroded syenite syenite exposed exposed on lower slopes. slopes. Quartzite Quartzite isi saccompanied accompanied schistosemetavolcanics metavolcanics and and metadiorite(?) The by l e r xenoliths of of schistose by smal smaller metadiorite(?).. The northern part of northern ofthe theWausau Wausau syenite pluton appears appears to t o be be repeated repeated (by (by low low Xenolith lithology, lithology, angle ffaulting?) sides of of the angle a u l t i n g ? ) on on opposite opposite sides the Rib Rib River. River. Xenolith size varyextensively extensivelywwithin i t h i n the pluton, pluton, although although s i z e and and rrelative e l a t i v e abundance abundance vary metavolcanicrocks, rocks, qquartzite, metavolcanic u a r t z i t e , schist s c h i s tand and metadiorite metadiorite are a r edominant. dominant. Xenoliths of contrasting contrasting lithology 1ithology are are chaotically chaotically mixed, mixed, especially especially in in the theintermediate intermediate Mixing probably probablyinvolved involvedconsiderable considerablevertical verticaltransport transport of of clasts zone. Mixing clasts during interpretation iiss significant during intrusion. (This (This interpretation s i g n i f i c a n t and and will will be be referred referred Longdimensions dimensionsofofxenoliths xenoliths aare concentric about the core. r e concentric about the tto o later.) l a t e r . ) Long Biotitized mafic mafic xenoliths xenoliths are a r e ubiquitous ubiquitous in the the quartz quartz syenite. syenite. The The amphibole andpyroxene pyroxene syenites thewall wall zone zonepossess possessa ad idistinct amphibole and syenites ofofthe s t i n c t flow lineation ininmost most places. places. The Ninemile Ninemile pluton pluton forms The forms the core core ofofthe theWausau Wausau Syenite Syenite and and appears appears ttoo have breached the southern part of the circular complex and spread have breached the southern part of t h e c i r c u l a r complex and spread iinto n t o aa Although the contact between the quartz large oval area to the southwest. between large oval area t o the southwest. Although the monzonitecore coreand andthe thesurrounding surrounding syenitei sisdiscordant, discordant, iitt appears monzonite syenite appears to be be Quartz monzonite in the space formerly occupied Quartz monzonite in space formerly occupied gradational in most places. gradational i n most places. by the the circular mafic xenoliths. by c i r c u l a rcore coremargin margin contains contains abnormally abnormally abundant abundant mafic It xenolith—contaminated I t isi sprobable probablethat t h athe t the xenol ith-contaminated "caldera—rim"(?) "caldera-rimt'(?) persisted within withoutappreciable appreciablel alateral w i t h i n the the upwelling upwelling magma magma without t e r a l dispersal or orcomplete complete assimilation. The Ninemile pluton pluton iiss aa coarse, The Ninemile coarse, equigranular equigranularhornblende—biotite hornblende-biotite quartz quartz The pluton pluton is monzonite similar in the Wolf monzonite similar in appearance appearance tto o the Wolf River Granite. Granite. The is A peripheral zone zone 2-3 2-3 km km wide wide isi smarked marked by by eelliptical l l i p t i c a and l andunderlies underlies218 218km2. km2. A - 14,- �numerous "rottengranite" granite"quarries quarriesindicating indicating tthat numerous "rotten h a t in i n this t h i szone zone the the rock rock has has almost completely llost almost completely o s t its i t scoherence. coherence. Stettin TheSStettin syenite pluton pluton iiss oval S t e t t i n Syenite Syenite Pluton. Pluton. The t e t t i n syenite oval in plan plan with with dimensions km; iitt isi sconcentrically dimensions ofof66xx 99 km; concentricallyzoned zoned and and elongate elongate northeasterly. northeasterly. The pluton intruded intruded mafic mafic volcanic volcanic rocks on the the west west and andffelsic The pluton rocks on e l s i c volcanic volcanic rocks rocks The pluton is divided into and associated sedimentary rocks on the east, and associated sedimentary rocks on the e a s t . The pluton is divided i n t o lensoidal syenite, syenite, (2) ( 2 )nepheline nepheline syenite, syeni t e , ffive i v e main, main, subconcentric subconcentric units: (1) lensoidal (3) tabular ( 4 amphibole ) amphibole syenite, syeni t e , and and (5) ( 5 )pyroxene pyroxene syenite. syenite. ( 3 ) tabular syenite, syenite, (4) Lensoidal syeni syenite, nepheline syenite andtabular tabular syeni syenite Lensoidal t e , banded banded nephel ine syeni t e and t e are a r e confined confined and pyroxene pyroxenesyenites syenites of of the Flow lineated amphibole amphibole and the tto o the the wall -wall zone. zone. Flow intermediate zone zoneenclose enclosea anearly nearlyc icircular coreof of pyroxene pyroxenesyenite syenitet hthat intermediate r c u l a r core a t iitt pluton was intruded two northeastrrimed i m e d by by nepheline n e p m n e syenite. syenite. The The pluton wasm r u d e d between between two trending shear extendingoutward outwardalong alongthe thef ofoliation. i t h apophyses apophyses extending liation. trending shear zones, zones, wwith The concentriccylindrical cylindrical structure subvolcanicintrusion intrusion of of the The concentric s t r u c t u r e suggests suggests subvolcanic the . Stettin plutons. S t e t t i nand andWausau Wausau pl utons pyroxeneand ando olivine diabase dikes dikes aare Diabase Diabase Dikes. Both Both pyroxene l i v i n e diabase r e present present in They are are characteristically andand unmetamorphosed Marathon c h a r a c t e r i s t i c a l undeformed l y undeformed unmetamorphosed Marathon County. County. They and may mayrepresent representthe theyoungest youngestigneous igneousrocks rocksbecause because they intrudea11 all older older and they intrude The dikes dikes range range uup wide, and rocks iinn the rocks the area. area. The p tto o 30 30 meters meters wide, and those those with with diabase dikes have have no no Most diabase exposedcontacts contactstrend trend eeast exposed a s t oorr northeast. Most magnetic "signature," but one prominentdike dikeexposed exposedi ninthe the"rotten "rotten granite" magnetic "signature," one prominent R i bMountain Mountain has has an an associated associated aeromagnetic aeromagnetic low that t h a t can can be be quarries south south of of Rib traced for kmfrom fromnorthern northernShawano Shawano County County westward westward across across most most f o rmore morethan than100 100km of Marathon Thus,aat Marathon County. County. Thus, t lleast e a s t this t h i s dike dike is i sreversely reversely polarized. polarized. Where Where exposed, iittisi a pyroxene diabase diabase about about 15 15 meters meters wide wide wwith exposed, s medium—grained a medium-grained pyroxene ith fine—grainedoolivine aa chilled c h i l l e d margin. margin. AA fine-grained l i v i n e diabase diabase is is exposed exposed in i n the thenorthwestern northwestern corner of the The rrelative e l a t i v e age age of of the theolivine o l i v i nand e andpyroxene pyroxenediabases diabases corner the county. county. The aare r e not not known. known. STRUCTURAL GEOLOGY GEOLOGY STRUCTURAL RegionalSettinq. Settin. Marathon MarathonCounty Countyi sison on the the southern southern margin marginof of a Regional a large large Middle Precambrian volcanic—sedimentarybasin basint hthat extends across across northern Middle Precambrian volcanic-sedimentary a t extends Wisconsin Although Middle Precambrian rocks are Wisconsin into i n t o Minnesota Minnesota and and Michigan. Michjgan. Although Precambrian rocks are widely widely distributed over over the t h e area, area, their t h e i rrelationship r e l a t i o n s h i pfrom fromone onearea area to t oanother another Sedimentaryrocks rocksaare dominantononthe theiron iron ranges iiss largely largelyunknown. unknown. Sedimentary r e dominant ranges tto o the the north, but b u trelatively r e l a t i v e lunmetamorphosed y unmetamorphosed volcanic and and plutonic plutonicrocks rockspredominate predominate rocks and iinn Marathon Marathon County. County. The The contacts between between these these low—grade low-grade rocks and gneisses, migmatites and amphibolites amphibolites extensively extensively developed migmatites and developed i in n central Wisconsin Wisconsin are are exposedin. in several several places places iin andMedaris Medaris(1977) (1977)i interpret exposed n the t h e county. county. Maass Maass and nterpret the gneisses in age, gneisses ttoo be be mainly mainly Middle Middle Precambrian Precambrian in age, also. a l s o . Contacts between between the Middle rocks,the the 1500 1500m.y. m.y.old old Wolf Wolf River River Batholith, Batholith, and the Middle Precambrian Precambrian rocks, and related syenite syenite plutons plutons are a r ealso a l s owell wellexposed exposedininMarathon MarathonCounty. County. Therefore, an understandingofofthe thes structural geologyofof tthis an understanding t r u c t u r a l geology h i s area area is i s important important to t o aa wide variety variety of rocks wide rocks over over a large large region. region. Folding. Although Although nearly nearly 4500 4500 km2 km 2 are a r e mapped mapped in Marathon Marathon County, County, no no Foldin%. clear—cut structural evidence clear-cut structural evidence for f o r large—scale large-scale folding folding was was established. established. In muchofofthe thecounty countythe thetrend trendofofd idistinctive i n the thevolcanic volcanic rocks rocks much s t i n c t i v e llithologies i t h o l o g i e s in topindicators indicators aare lacking in most of the However, top r e lacking most of the N . ~ O O E . to t oeast—west. east-west. However, iiss N.600E. - 15 - �volcanic rocks, rocks, and and the t h emassive massive nature nature and and broken broken surfaces surfaces of of most most outcrops outcrops and/or the dip dip and and sstrike and/or ffoliation o l i a t i o n prevents prevents determination determination ofof the t r i k e of the the layering. layering. Minor folds were observedinina afew fewwidely widelyscattered scatteredlocations, locations,and andininddifferent Minor folds were observed ifferent roof pendants, so ttheir folding is roof pendants, so h e i r significance significance regarding regarding pre—intrusive pre-intrusive folding is b u ttop topdeterminations determinations can can uncertain. Pillow lavas lavas are a r e widely distributed, distributed, but be madeonly onlya at twol olocalities. otherpillow pillow occurrences occurrencesa rare be made t two c a l i t i e s . The The other e a lall l ffrostrostheaved blocks, oor boulders picked picked from from ffields heaved blocks, r boulders i e l d s and and piled piled by by area area farmers. farmers. The general distribution distribution ofofvolcanic n MarathonCounty, County,however, however, The general volcanicrocks rocksin iMarathon In the the eastern eastern ppart a r t of the the county basalts are abundantt otothe the southeast southeast (near (near Ringle) Ringle) (Figure 2) county basalts a r e more more abundant 2) with toward Wausau. w i t h an an increase increase in i nintermediate intermediateand andfelsic f e l s irocks c rocks toward Wausau. Rhyolites Rhyolites predominate intermediate and predominate at a tWausau. Wausau. North North and and northwest northwest of of Wausau Wausau intermediate and mafic rocks of Wausau pillow lavas rocks again again predominate. predominate. West West of Wausau pillow lavas exposed exposed along along Artus Artus Creek (NE¼,NWk, NW¼, T.29N., R.6E.) indicatetops topst to the southeast, Creek (NEk, Sec.Sec. 29, 29, T.29N., R.6E.) indicate o the southeast, suggesting thethe Wausau suggesting tthat h a t the basalts basalts dip d i p beneath beneath the t h e rhyolites rhyolitesinin Wausau area. area. Assuming t hthat a t t hthe e basalts i s t r i b u t i o n of of volcanic volcanic Assuming basaltsunderlie underliethe therhyolites, rhyolites,the the ddistribution rocks suggestsaanortheast-trending northeast—trending synclinalstructure structurew with rocks suggests synclinal i t h i its t s axis axis approximately the mafic mafic tto approximately ata tWausau. Wausau. However, However, the o felsic f e l s i csequence sequence appears appears to to have beenduplicated duplicatedaat have been t lleast e a s t twice twice by by faulting f a u l t i n gsoutheast southeastofofWausau. Wausau. One One proposed .5 km km west west of the the Eau Eau Claire proposed f afault u l t is i s parallel paralleltot and o andapproximately approximately11.5 River, juxtaposing basalts on the west with rhyolites on the east. on the e a s t . The sequence sequence River, juxtaposing basalts on t h e west w i t h also appears along aa ffault appears tto o be be repeated repeated along a u l tzone zone extending extending from from Rothschild Rothschild northeasterly along complexpattern pattern of of volcanic along Little L i t t l Sandy e SandyCreek. Creek. The The complex volcanic rocks west of the Wisconsin River suggests that the succession rocks west t h e Wisconsin River suggests t h a t the successionhas hasbeen been repeated faulting ((or folding) in i n that t h a t area area as a s well. well. repeated bybyfaulting o r folding) may ther eresult of aa large large synclinal synclinal fold. may bebethe s u l t of fold. In addition folding and and ffaulting, addition to t o the thelarge—scale large-scale folding a u l t i n g , the the volcanic volcanic rocks rocks have beenextensively extensively segmented anddisrupted disruptedbybyintrusions. intrusions. However, have been segmented and However, the the general sequenceofofvolcanic volcanicrocks rocksinin roof roof pendants consistent with general sequence pendants i is s consistent w i t h the the broad pattern outlined broad pattern outlined above. above. This suggests suggests tthat h a t the t h e intrusions intrusionshave have engulfed engulfed the without extensively extensively aaltering the rocks rocks without l t e r i n g the t h e general general fold pattern. pattern. Faulting. The Marathon The Middle Precambrian vol canic-pl utonic complex complex ini nMarathon Middle Precambrian volcanic-plutonic County boundedonona lall sides by by major majorzones zonesofofccataclastic 8). County i is s bounded l sides a t a c l a s t i c rocks rocks (Figure 8). A of cataclastic from the the northeast A zone zone of c a t a c l a s t i c rocks rocks 1-5 1-5km km wide wide extends extends from northeast corner corner of the county downthe theEau Eau ClaireRiver Riverand andLLittle county southwest southwest down Claire i t t l e Eau Eau Claire River River Valleys about km tto o Lake Lake DuBay DuBay near county. There about 61 61 km nearthe the south south edge edgeof of the county. There curvesnorthwesterly northwesterlyand and continues continues northwest northwest up up the the Eau Eau Pleine Pleine River River Valley Valley iti tcurves about 32 km kmt oto Stratford Stratford where whereiitt curves againtoward towardNeil Neillsville. about 32 curves southwest southwest again 1svi 11e . Thus, large sygmoid sygmoidcurve curvet that been traced traced ffor Thus, the zone zone makes makes aalarge h a t has has been o r over over 120 km. Wolf River River Batholith lies and has metamorphosed km. The The Wolf l i e seast e a sof t of and haslocally locally metamorphosed area of of gneisses, the defoned deformed rocks. rocks. A A complex complex area gnei sses, migmatites migmati t e s and and amphibolites amphi bol i t e s (and local local low—grade low-grade metamorphic i e south south of of the thesegment segment along along the the (and metamorphicrocks) rocks)l lie Eau Pleine River. A t least l e a s t five f i v eultramafic ul tramafic bodies bodies occur occur along h i s be1 of alongt this beltt of Eau Pleine River. At cataclastic c a t a c l a s t i c rocks. rocks. A of cataclastic A similar similar broad broad zone zone of c a t a c l a s t i c rocks rocks extends extends in in aa southwesterly southwesterly direction direction along along the the northern northern edge edge of the the volcanic-plutonic volcanic-plutonicterrane terraneininMarathon Marathon County. County. It, I t ,too, too,separates separatesgneisses, gneisses,inigmatites, migmatites, and and amphibolites amphibolites on on the the north north from rocks to from the low-grade low-grade rocks t o the the south. south. The The ffault a u l tzone zone has has been been traced traced from from near Merrill southwest Athenst oto Milan Milanwhere wheref ofoliation near Merrill southwest through through Athens ~ l i a t i o ncurves curves in aa - 16 - �GREENSCYIST I RIVER F - —. I sr I GOODRICH MEDEORDS - I SNEISS —J r—-—-—-— r AND I . , I r si — zo• --- MARSAFIELD N 1 Cl . . •'21- ROZELLVILLE I I '# FAdES •GREENWODD • '— 30 ' (* _',- 2. .224; A> . S L .z t I-> ,,'P p. J7<v1 •poINT -s PITTSvILLE KM :: :4'"RhI/ER c414 > '' ICA4 . 4r. I NEILLsvILLg o N /pATwoLITH.n i<'< 1,41)b I — —.--— — — — -- -, WAU$AU:::LNj,tt44A< — # I so. 4v,',A I I I— ANTIGO I i/I, _....;.>GRtENSCNISt..:/Yv WOLF. 61.M. .' (::.;:::c:::::::. '4.4 /' AMPH/BOLITff 25 !J-!r MERRILL• _€.t — c ',aj7.N WISCONSINT C71j RAPIDS : Figure Figure 8. 8. Simplified S i m p l i f i e d map map oof f sstructural t r u c t u r a l relationships r e l a t i o n s h i p s in i n central central Wisconsin showingt h the Wisconsin showing e o rorientation i e n t a t i o n o of f 1linear i n e a r features f e a t u r e s in i n the the gneissic g n e i s s i c rocks rocksand andlow lowgrade grademetamorphic metamorphic rocks. rocks. Boundary Boundary ffaults aults are a r e shown shown iinn dashed dashed llines. i n e s . Outliers O u t l i e r s of o fgreenschist greenschist facies facies volcanic widely volcanic rocks rocks aare re w i d e l y ddistributed i s t r i b u t e d in i n the t h e areas areas labelled label led gneiss amphi bol it e . gneiss and and amphibolite. more more ssoutherly o u t h e r l y ddirection. i r e c t i o n . Several Several ultramafic u l t r a m a f i c bodies bodies also a l s o occur occur along along this this northern n o r t h e r n zone zone ooff cataclastic c a t a c l a s t i c rocks. rocks. Cataclastic C a t a c l a s t i c foliation f o l i a t i o nin i southwestern n southwestern Marathon Countysstrikes Marathon County t r i k e s nearly n e a r l y north—south, north-south, suggesting suggesting that t h a t the t h etwo twomajor major bounding corner of bounding ffault a u l t zones zones may may j join o i n near near the t h e southwest southwest corner o f the t h e county. county. However, combinationoof However, t the h e combination f gglacial l a c i a l and and Paleozoic Paleozoic cover cover effectively e f f e c t i v e l ymasks masks the the Precambrian themmmigmatitic, Precambrian i in n tthat h a t area. area. Gneisses, Gneisses, some some oof f them i g m a t i t i c , are a r e exposed exposed at at Greenwood, approximately22 22km kmwest westo of low-grade rocks rocks at f t the h e low-grade a t the thewestern western Greenwood, approximately edge T h i s suggests suggests that t h a t the t h elow lowgrade grade rocks rocks do do not not edge of o f Marathon Marathon County. County. This extend These two a t a c l a s t i czones zones coincide c o i n c i d ewith w i t haero— aerotwo major major ccataclastic extend to t o the t h e west. west. These magnetic lows and andl local magnetic and and ggravity r a v i t ylineaments. lineaments. Magnetic Magnetic lows o c a l highs highs parallel parallel - 17 - �the the structures (Figure (Figure 9). 9 ) . The The northern a t a c l a s t i czone zone separates separates aa northern ccataclastic prominent gravity low (over County)from fromsi.gnificant1y significantly higher prominent gravity (over Marathon Marathon County) higher gravity values values over over the the gneisses, gneisses, suggesting suggesting tthat h a t the structures structures involve involve gravity considerable thickness of of crust. considerable thickness crust. In addition additiontotothe themajor majorboundary boundary fault f a u lzone t zonenumerous numerous cataclastic c a t a c l a s t i czones zones are Their trend to trend iiss parallel to w i t h i n the t h evolcanic—plutonic volcanic-plutonic terrane, terrane. Their a r e present present within the major zones range range uup p tto o several km km wide wide and and consist consist major bounding bounding ffaults. a u l t s . The The zones of zonesofof intensely deformed rocks, including of branching branching and and recombining recombining zones deformed rocks, including mylonites, within w i t h i naabroader broader zone zone of of less l e s sdeformed deformed rocks. rocks. Cataclastic zones zones ccut u t the gneissic gneissic rocks rocks at a tGoodrich Goodrich Dells Dells on on the the Rib Rib River Thus, ccataclasis a t a c l a s i s in in River (Elizabeth (ElizabethPalmer, Palmer, verbal verbalcommunication, conimunication, 1979). 1979). Thus, the s not not restricted r e s t r i c t e d totothe t h eboundary boundary fault f a u l tzones. zones. ItI tappears appears to to the gneisses gneisses iis be zonesthroughout throughoutthe thearea, area,cutting cutting greenschist facies be present present in i n numerous numerous zones facies volcanics, plutons plutonsand and gneisses. gneisses. Therefore, Therefore, recognition recognitionand andan anunderstanding understanding of cataclastic the structural and c a t a c l a s t i crocks rocks are a r e important important to t ounderstanding understanding the and tectonic tectonic history history of ofcentral centralWisconsin. Wisconsin. Cataclastic resemblance metamorphosed Cataclastic rocks rocks have have aa superficial superficial resemblancetot oregionally regionally metamorphosed rocks, for which they are often mistaken. They differ in several important They d i f f e r i n several importantways: ways: rocks, f o r which they a r e often mistaken. (1) they have a linear distribution and cut non—deformed rocks; (2) they grade ( 1 ) they have a l i n e a r distribution and c u t non-deformed rocks; ( 2 ) they grade across numerous across sstrike t r i k e into i n t orocks rocksthat t h aare t a r not e notcataclastically c a t a c l a s t i c a ldeformed, l deformed, numerous examples of which which are are present i n Marathon Marathon County; County; (3) ( 3 they theypossess possess aaweak weak to to examples of present in prominent ( 4 )they theyare a r emarkedly markedly inequigranular inequigranular with with prominent ffoliation o l i a t i o n and and lineation; lineation; (4) shattered grains, and rocksshow show the ffine shattered grains, and some some rocks r e crecrystallization r y s t a l l i z a t i o n ofof the i n e matrix. matrix. 7 The typically consist The ccataclastic a t a c l a s t i c zones zones typically consist ofofa anetwork network ofofbraided braidedzones zones of of intense intense cataclasis c a t a c l a s i sseveral severalmm mtot omany many meters meters wide wide bordering borderinglens-shaped lens-shaped pods pods of of relatively r e l a t i v e lundeformed y undeformed rock. rock. Therefore, there iiss aa wide Therefore, there wide ddisparity i s p a r i t y in in the degree degree of cataclasis cataclasis over overshort shortdistances distancesalong alongand andacross across the t h ezones. zones. The lensoidal pattern pattern is The lensoidal t h i nsection sectiontot omap map i s present present on on all a l l scales scales from from thin units. The cross plutonic plutonic and and volcanic volcanic rocks rocks aalike, The ccataclastic a t a c l a s t i c zones zones cross l i k e , with with the the result r e s u l tthat t h a an t anextremely extremely wide wide variety varietyofofcataclastic c a t a c l a s t irocks c rockshave havebeen been produced. major rock types mapped produced. A A brief brief description descriptionofofthethe major rock types mapped isi spresented presented here. here. Flaser coarse grained grained rock rock wwith Flaser gneiss gneiss is i s aamedium medium tto o coarse i t h foliation f o l i a t i o nproduced produced by by the cataclastic c a t a c l a s t i c degradation degradation of plutonic plutonic rocks. rocks. It I tisi scharacterized characterized mesoscopically by aa pervasive pervasive lensoidal lensoidal structure mesoscopically by structure produced produced by by intersecting intersecting shear (Figure 10). Microscopically, the shear planes planes (Figure the rock rock isi smarkedly markedly inequigranular inequigranular fine with relatively r e l a t i v e l yundeformed undeformed porphyroclasts porphyroclasts of feldspar and and quartz with of feldspar quartz iinn aa fine grained grained matrix of of crushed crushed material material . Individual Individual fragments fragments tend tend tot obebecrushed crushed and with larger fragments and boudinaged, boudinaged, with fragments typically typicallyassuming assuming aalensoidal lensoidalshape shape (Figure andand magnetite Biotite,chlorite, c h l o r i t eepidote, , epidote, magnetiteformed formed during during (Figure 11). 11 ) Biotite, cataclasis along braided braided surfaces surfacest that cataclasis are a r e concentrated concentrated along h a t iintersect n t e r s e c t at a tangles angles of of10—30 10-30 degrees. degrees. This This imparts imparts aa streaky streakyappearance appearance tto o the the rocks. rocks. Lineation Lineation due of mineral theplane planeofofffoliation. due tto o elongation elongation of mineral grains grains is i s common common ininthe oliation. Flaser into undeformed plutonic rocks, Flaser gneiss gneiss grades grades on on one one hand hand into undeformed plutonic rocks, and and with with continued cataclasis into mylonite continued cataclasis mylonite or o r phyllonite. phyllonite. . - 18 - �Figure of the of central central Wisconsin. Figure 9. 9. Photograph Photograph of the aeromagnetic aeromagnetic map map of Wisconsin. Note Note the coincidence coincidence of the the major major boundary boundary faults f a u l t s (dashed (dashed white white lines) the ddistinctive w i t aeromagnetic h aeromagneticlineaments. 1 ineaments. Note Note aalso l s o the istinctive l i n e s )with magnetic pattern of Marathon magnetic pattern of that t h a tportion portionof of MarathonCounty Countyenclosed enclosed within within (Magnetic data data from from Karl, Karl,1973—75.) 1973-75.) the the dashed dashed llines. i n e s . (Magnetic — 19 - �— - . Quartz monzonite monzoni t e fflaser l a s e r gneiss gneiss showing showing typical typicallensoidal lensoidal Figure10. 10. Quartz Figure structure structureproduced produced by by intersecting intersectingshear shearplanes. planes. p 4, 2mm typical flaser Photomicrograph ofofaa typical f l a s e rgneiss gneissshowing showing the the Figure11. 11. Photomicrograph Figure fractured fractured porphyroclasts, porphyroclasts, matrix matrix and and lensoidal lensoidal structure. structure. -- 20 20 -- �Mylonite iiss typically typicallyaaflinty, f l i n t laminated y , laminated rock (Figures1212and and13) 13) Mylonite rock (Figures consisting mainly 14), and mainly of of finely finelycrushed crushedmaterial material(Figure (Figure 141, andmay maybe be compositionally compos~tionall ybanded. banded. Like flaser f l a s e r gneiss, gneiss, mylonite mylonite is i svery very inequigranular, inequigranular, but b u t has has a greater greater percentage percentage of crushed crushed matrix. Foliation Foliation surfaces surfaces are are closely spaced andtypically typically intersect spaced and i n t e r s e c t ata tless l e s sthan than1010degrees, degrees. Streaky Streaky lineation in by ""trains" i n the the direction direction of oftectonic tectonictransport transport isi sproduced produced by t r a i n s " of fine mineralsi in the plane planeofofccataclastic f i n e grained grained minerals n the a t a c l a s t i c ffoliation. o l i a t i o n . Detached Detached fold fold axes andi nintrafolial w i t h i n mylonites mylonites indicate indicate local folding. folding. axes and t r a f o l i a l folds folds within Polygonization andincrease increasei ningrain grains size of tthe i z e of h e ffine i n e matrix matrix indicates indicates Polygonization and recrystallization of ofmylonites mylonjtes locally. l o c a l l y . While While the parent parent rock rock for f o rmost most flaser determined, the the protolith protolith for f l a s e r gneisses gneisses can can be be determined, f o mylonites r mylonitesis imuch s muchmore more difficult MarathonCounty Countyhave have been been d i f f i c u l to t t oascertain ascertain(Figure (Figure 15). 1 5 ) . Mylonites Mylonites ini nMarathon derived wide variety variety of volcanic derived from from aa wide volcanic and and plutonic plutonic rocks. rocks. Whereas Whereas f felsic elsic mylonite hard,f flinty mylonite iis s comonly comonly aahard, l i n t y rock rock owing owing t to o iits t s high high silica s i l i c acontent, content, mylonite derived derived from from intermediate intermediate and o be hloritic mylonite and mafic mafic rocks rocks tends tends tto be more morec chloritic and Felsic and and intermediate intermediatetot omafic maficmylonites mylonitesarea rcommonly e comonly and schistose. schistose. Felsic intercalated. intercalated. Deformed Volcanic Rocks. rocksreact reactddifferently Deformed Volcanic Rocks. Volcanic Volcanic rocks i f f e r e n t l y to t o stress stress than do plutonic rocks. than do rocksa Indeed, Indeed, the l i t e r a t u r eonondeformed deformed volcanic volcanic rocks rocks is is the literature extremely presenceofofaawide widevariety variety of volcanic extremely vague vague and andmeagre. meagre. The The presence volcanic rocks rocks interspersed w i t h cataclastically c a t a c l a s t i c a l l ydeformed deformedplutonic plutonicrocks rocksin iMarathon n MarathonCounty County interspersed with provides an excellent opportunity to compare features in deformed volcanic provides an opportunity t o compare features i n deformed volcanic and volcanic rocks and plutonic rocks. rocks. Most Most of the t h e deformed deformed volcanic rocks are a r e strongly strongly foliated layer ssilicates. f o l i a t e ddue due to t o the theextensive extensive development development ofoflayer i l i c a t e s . Felsic Felsic volcanic volcanic rocks andmafic maficrocks rocksa are rocks tend tend tto o be be sericitic s e r i c i t i cwhereas whereas intermediate intermediate and r e c chloritic. hloritic. In some rhyolites the the phenocrysts phenocrystsa rare rotatedi ninto planeof of ffoliation some rhyolites e rotated t o tthe h e plane o l i a t i o nand and boudinaged (Figure 16). O e f o m t i o n of ofrhyol i t i c t tuffs u f f s rresults e s u l t s iinn flattening boudinaged (Figure 1 6 ) . Deformation flattening rhyolitic and/or and/or elongation elongation of the t h e volcanic volcanic fragments fragments (Figure (Figure 17). 17). In In some some rhyolites rhyolites the strain takenuup byrrecrystallization p by e c r y s t a l l i z a t i o n and and flowage flowage of s t r a i nappears appears to t o have have been been taken the matrix, leaving highly foliated n aa highly fol fated leaving relatively r e l a t i v e l yeuhedral euhedral phenocrysts phenocrysts i in sericitic s e r i c i t i cmatrix. matrix. Evidently Evidently the the nature nature of ofthe t h epre—existing pre-existing volcanic volcanic rock rock (e.g. a tuff (*a t u f f vs. vs. aa lava lava flow, flow, or or aa porphyritic porphyriticvs. vs.a anon-porphyritic non-porphyritic rock) rock) affects a f f e c t s the thebehavior behavior of ofthe t h erock rockduring duringdeformation. deformation. Deformation Oeformation of of fragmental fragmental andesites andesi t e s has has produced produced spectacular spectacular examples examples of elongated el ongated fragments. fragments. In areasthe the long long dimension dimensioni is 10 times times the the cross-sectional cross-sectional diameter In some some areas s 10 diameter of the hornblende and and plagioclase plagioclase phenocrysts the lineated lineatedfragments. fragments. Boudinaged Boudinaged hornblende phenocrysts accompany lineatedfragments fragments severall olocalities, accompany thethe1ineated in inseveral c a l i t i e s , suggesting suggesting dislocation dislocation rather than than simple simple fflattening. lattening. Minor structures are Precambrian Mesoscopic structures a r ewidespread widespread ini nPrecambrian Minor Structure. Structure. Mesoscopic rocks rocks in central central Wisconsin, Wisconsin, and and ttheir h e i r pattern pattern isi sinformative informativeregarding regarding the the structure mappingnorth, north, west west and and south south of Reconnaissance mapping structure of of the thearea. area. Reconnaissance Marathon County( (in Wood, Marathon County i n Lincoln, Lincoln, Taylor, Taylor,Clark, Clark, Wood,and andPortage PortageCounties) Counties)and and farther f a r t h e rwest westini nChippewa Chippewa and and Eau Eau Claire Counties Counties (Myers, (Myers, 1974, 1974, 1978, 1978, and and this this conference) discloseaa consistent consistentpattern pattern of of llinear i n gneissic gneissicrocks rocks conference) disclose i n e a r features features in in of minor minor ffolds, lineationsand and elongation elongation Axes of o l d s , mineral mineral lineations in central centralWisconsin. Wisconsin. Axes of of mafic mafic xenoliths(?) xenoliths(?) plunge plunge aatt a a relatively r e l a t i v e l y low low angle angle to t o the the west west ininmost most of In gneisses gneisses ini nand andnear nearMarathon Marathon County, County, 8 ) . In of the the gneissic gneissic rocks rocks (Figure (Figure 8). fold lineations plunge westa at 30-40°i ninthe theplane planeofofthe theffoliation. oliation. fold axes axes and and lineations plunge west t 30-40 Maass andMedaris Medaris(1977) (1977) iinterpret Precambrian Maass and n t e r p r e tthese thesetot obebeMiddle Middle Precambrian(Penokean) (Penokean) structures. Lineations in in the thegneisses gneisses steepen steepen tto o near near vertical near near the the s t r u c t u r e s . Lineations - 21 - �m y l o n i t e about about 1.6 1.6 km km southwest southwest of o f Athens Athens Figure Outcrop ooff rnylonite F i g u r e 12. 12. Outcrop along betweent hthe gneissesand andggreenschist along the boundary boundary between e gneisses r e e n s c h i s t ffacies a c i e s rocks. rocks. Figure F i g u r e 13. 13. Photograph ooff myloni Photograph m y l o n ite t e showing showing tthe h e ttypical y p i c a l streaky s t r e a k y and and lensoidal l e n s o i d a l character. character. - 22 — �-l.-i' fl - ;; r— flrSa 7we ac' afr*.e Figure 14a. typical mylonite 14a. Photomicrograph Photomicrograph ofof typical mylonitefrom fromMarathon Marathon Countyshowing showingt hthe abundance material and and tthe County e abundance of off ifine n e material h e close spacing of of shear spacing shear planes. planes. Photomicrographofoftypical typical mylonite Figure 14b. mylonite from from the the Brevard Brevard 14b. Photomicrograph Zone iin n the the southern southern Appalachians. Appalachians. Zone -—2323 -- �i'a:i T aAi• rT ., - L - -- 4j4 Figure the progressive Photographs showing showing the progressive cataclastic cataclastic gure15. 15. Photographs degradation granite (top) to undefomed granite t o mylonite mylonite(center) (cent( !gradation from from an an undefonited to Iultramylonite ultramylonite(bottom). (bottom). The The protolith protolithforf othe r the mylonitecan canbe mylonite established itablished where where the the transition t r a n s i t i o nis iexposed. s exposed. - -24 24- - �2 nun Figure Figure 16. 16. Deformed Deformed f efelsic l s i c volcanic rocks rocks showing showing aa ffoliated oliated s e r i c i t imatrix c matrix boudinagedphenocrysts phenocrysts that t h a thave havebeen been rotated rotated sericitic andand boudinaged into of ffoliation. i n t o the the plane plane of o l i a t i o n . Note crenulation folds folds in i n the the Note tthe h e crenulation matrix matrix of ofthe thelower lowerphotograph. photograph. - 25 - �: -- j,-- :tc '"r p. - t r 4, — tr -—-'I ; .WL'tfra 7tr *a L.4 a*2S' — Figure 17. 17. Photographs Photographs o foff efelsic l s i c tuff t u f f showing showing the t h e elongation e l o n g a t i o n of of deformed photo i is deformed fragments. fragments. Upper Upper photo s undefornied undeformed t utuff f f with w i t h angular, angular, equant photoshows shows equant cclasts. l a s t s . Lower Lower photo t y ptypical i c a l l elenticular n t i c u l a r longitudinal longitudinal section deformed ttuff. uff. s e c t i o n in i n aa deformed - 26 - �major boundary boundaryf fault wherethe thegneisses gneissesare arei in contact wwith major a u l t zones zones where n contact i t h greenschist greenschist facies volcanic-plutonic volcanic-plutonic rocks rocksininMarathon MarathonCounty. County. Lineations are Lineations are also present present in i n the thedeformed deformed volcanic volcanic and and plutonic rocks. rocks. Elongated cclasts phenocrystsplunge plungee aeast 5Q°or or steeper steeper in Elongated l a s t s and and boudinaged boudinaged phenocrysts s t aat t 50 in minor fold axes most of of the most the volcanic volcanicpendants. pendants. Several Several minor axes also plunge plunge steeply steeply Lineations including streaking east streaking and and elongation elongation of e a s t tto o nearly nearly vertical v e r t i c a l .. Lineations minerals and and xenoliths xenoliths are plutonic rocks. i n many many plutonic rocks. Boudinaged minerals are also present present in measuredlineations lineations Most measured quartz veins veins occur occur iinn both both volcanic volcanic and and plutonic rocks. rocks. Most quartz however, some somew with steep easterly easterly in plutonic i t h aa steep plutonic rock rock are are nearly nearly vertical v e r t i c a l;; however, Crenulationfolds foldsaare locally present, dip were were recorded. recorded. Crenulation r e locally present, indicating multiple dipping 1lineations absent iinn the the deformation. Westerly Westerly dipping ineations are are conspicuously conspicuously absent the orientation of low-grade low-grade rocks. Thus, Thus, the of minor minor structures structures suggests suggests tthat h a t the the two terraneshave haved idifferent structural histories. two terranes f f e r e n t structural Furthermore, Myers(1978) (1978)shows showsisolated isolated patches patchesof of volcanic rocks Furthermore, Myers rocks and and volcanogenic sedimentslying lying unconformably onthe the amphibolite amphibolite facies rocks volcanogenic sediments unconformably on rocks along the Eau Claire River i neastern easternEau Eau Claire Claireand and western western Clark Clark Counties. Counties. Eau Claire River in along (Note tthat River one Marathon n eastern Marathon (Note h a t this t h i s isi sa adifferent d i f f e r e nEau t EauClaire Claire Riverthan thanthethe onein i eastern The unconformi unconformity the amphibolite County.) t y between between the amphi bol i t e facies faciesgneisses gneissesand andgreen— greenCounty. ) The schist s c h i s t facies faciesvolcanogenic volcanogenic rocks rocks has has been been folded folded about about an an axis that t h a tplunges plunges 3Qoeeast This indicates indicates that t h a tthe thelow-grade low-grade rocks rockswere were deposited deposited 30 a s t (Myers, (Myers, 1978). 1978). This Furthermore, iitt argues on amphibolite facies facies rocks. argues against a ainst on aa basement basement ofofamphibolite rocks. Furthermore, kthe suggestion andMedaris Medaris(1977) (1977)t hthat the amphibolite amphibolite facies rocks suggestion by by Maass Maass and a t the roc s are simply equivalentsofofthe the greenschist greenschist facies are simply more more highly metamorphosed metamorphosed equivalents facies rocks rocks in inMarathon Marathon County. County. While the the minor minor structures in i n the thevolcanic—plutonic volcanic-plutonic terrane terrane have have aa While different surrounding rocks, the n the surroundinghigh—grade high-grade rocks, the d i f f e r e n torientation orientationthan thanthose thoseini the nature of the deformation within the low-grade rocks must be considered. nature the deformation w i t h i n the low-grade rocks must be considered. For example,the the deformation deformationi in the volcanic-plutonic terrane For example, n the terranemay may be be due due tto o (1) theplutonic plutonicrocks, rocks,oor 2 ) deformation deformation llater a t e r than, than, and and not not ( 1 ) emplacement emplacement of ofthe r ((2) necessarily relatedt to, the plutonic plutonic aactivity. necessarily related o , the c t i v i t y . If I f the the deformation deformation is i s related related to theplutonic plutonic rocks, rocks, cataclasis t o emplacement emplacement ofofthe c a t a c l a s i s around around each each intrusion should should be related related sspatially in orientation be p a t i a l l y and and in orientation to t o that t h a t pluton. pluton. Foliation Foliationtrends trendsmay may be expected expected tto around" the the plutons. IIff the the deformation deformation iiss not not related related be o "wrap "wrap around" to the deformation would be through—going the plutonic plutonicactivity, a c t i v i tthe y , the deformation would be through-going and and have have aa consistent pattern throughout consistent throughout the the terrane. Strike and and dip dip of ofnumerous numerous ccataclastic a t a c l a s t i c zones zones within the the volcanic—plutonic volcanic-plutonic terrane Cataclastic zones terrane are are similar to t othose those of ofthe themajor major boundary boundary ffaults. a u l t s . Cataclastic zones with a consistent plutonic rocks with consistent trend trend cut volcanic volcanic and and plutonic rocks aalike. like. A A pervasive pervasive ccataclastic a t a c l a s t i c foliation f o l i a t i o nwith w i t haaconsistent consistent regional regional trend trend (east ( e a s t or o r northeast) northeast) is is present i n most most of of the theMiddle MiddlePrecambrian Precambrian plutons plutons ini nMarathon MarathonCounty. County. The present in absenceofofpervasive pervasivec acataclastic plutons iiss aa absence t a c l a s t i c ffoliation o l i a t i o n ininLate LatePrecambrian Precambrian plutons major distinction major distinctionbetween betweenthem themand and Middle Middle Precambrian Precambrian rocks. rocks. Theage ageofofthe thedeformation deformation The i s isd idifficult f f i c u l t to t o establish. e s t a b l i s h . However, However, aa general general pattern of of deformation deformation and and intrusion intrusionwas was recognized recognized by by LaBerge LaBerge (1976), in in which the oldest oldest plutons plutons (quartz (quartz diori diorites) which the t e s ) typically typicallyare a r emore more intensely intensely deformed than quartz quartz monzonites monzonitestthat deformed than h a t intrude intrudethem. them. Granitic plutons plutons are are generally less l e s s cataclastically c a t a c l a s t i c a l l deformed y deformedthan thanquartz quartzmonzonites, monzonites, and and in i n places places — 27 — �(Figure 7) truncate ( F i g u r e 7) t r u n c a t e ccataclastic a t a c l a s t i c foliation f o l i a t i o nini quartz n quartzmonzonites. monzonites. IInn eastern eastern Marathon Countya ac acataclastic m.y.old o l(Van d (VanSchmus, Schmus, 1975) 1975) Marathon County t a c l a s t i c ffoliation o l i a t i o nini 1900 n 1900m.y. thethe 1850 rrhyolite h y o l i t eisi struncated truncatedbyby 1850m.y. m.y.old o l(Van d (VanSchmus, Schmus, 1976) 1976) Kalinke Kalinke quartz quartz westernmargin margin monzonite. The The western o f of t hthe e p lpluton u t o n i sisnnot o t ffoliated, o l i a t e d , but b u t the t h eeastern eastern margin iiss extensively margin e x t e n s i v e l y foliated f o l i a t e dalong alongthe t h eEau Eau Claire C l a i r eRiver R i v e rshear shear zone. zone. South- east plutons e a s t ooff Wausau Wausau g r agranitic n i t i c plutons c ucut t t h the e c acataclastic t a c l a s t i c f ofoliation l i a t i o n i in n aa similar similar foliated f o l i a t e dquartz q u a r t zmonzonite. monzonite. Similar S i m i l a r relationships r e l a t i o n s h i p sthroughout throughoutthe t h ecounty countysuggest suggest that over an an extended extendedpperiod time, and t h a t deformation deformation occurred occurred over e r i o d oof f time, and intrusions i n t r u s i o n s were were emplaced emplaced d during u r i n g t this h i s time. time. The The ccataclastic a t a c l a s t i c rocks rocks of o f the t h eEau Eau Claire C l a i r e River R i v e rzone zone were metamorphosed metamorphosedbybyt hthe 1500m.y. m.y.oold andothers, others, 1973) Wolf were e 1500 l d (Van (Van Schmus Schmus and Wolf 1.5 km widezone zoneo of River Batholith. km wide f ccataclasis a t a c l a s i s wwithin i t h i n the t h e Wolf Wolf River River R iver B a t h o l i t h . AA 1.5 Batholith B a t h o l i t h along along the t h e Little L i t t l Eau e EauClaire C l a i r River e R i v esuggests r suggestssubsequent subsequent deformation deformation of of the Since tthe EauCClaire zonei sispparallel h e Eau l a i r e RRiver i v e r zone a r a l l e l tto o other other the bbatholith a t h o l i t h as as well. w e l l . Since as much muchasas3636kmkm west Wolf River ccataclastic a t a c l a s t i c zones zones as west o f of t h ethe Wolf River B aBatholith, t h o l i t h , i tit iiss unlikely waswas produced by by emplacement u n l i k e l ythat t h a significant t s i g n i f i c a cataclastic n t c a t a c l a sdeformation t i c deformation produced emplacement ooff that t h a t batholith. batholith. Thus, I I believe b e l i e v e the t h e deformation deformation wwithin i t h i n tthe h e vvolcanic-plutonic o l c a n i c - p l u t o n i c tterrane e r r a n e is is Thus, a tectonic t e c t o n i c event eventcontemporaneous contemporaneous wwith i t h bbut u t not n o t necessarily n e c e s s a r i l y related r e l a t e dtot emplacement o emplacement Thecconsistent of o f the the plutons. p l u t o n s . The o n s i s t e n t oorientation r i e n t a t i o n of o f minor minor structures s t r u c t u r e s suggests suggests tthat hat iti tisi sa aregional r e g i o n aorogenic l orogenicdeformation deformationthat t h apre-dates t pre-datesemplacement emplacement ooff the t h e Wolf Wolf This deformation doesnnot appeart to be rrestricted River Batholith. deformation does o t appear o be e s t r i c t e d tot oMarathon Marathon River B a t h o l i t h . This County,f for County, o r lineations l i n e a t i o n s ini ngreenschist greenschistfacies f a c i e svolcanic v o l c a n i crocks rocksexposed exposed along along the the Jump NW Athens)aalso Jump RRiver i v e r iin n northwestern northwestern Taylor T a y l o r County County (40 (40 km km N W o of f Athens) l s o ddip i p steeply steeply Mudrey(1979, (1979,wwritten o m u n i c a t i o n ) also a l s o recorded recorded east-plunging east-plunging tto o the the east. east. Mudrey r i t t e n ccomunication) This llineations i n e a t i o n s ini nvolcanic v o l c a n i crocks rocksnear nearMonico Monicoini nOneida Oneida County. County. T h i s iis s similar similar Countyb but tto o the t h e lineations l i n e a t i o n s ini nMarathon Marathon County u t d distinctly i s t i n c t l y different d i f f e r e n tfrom from the t h e shallow shallow westerly Therefore, iitt w e s t e r l y ddip i p ooff lineations l i n e a t i o n s in i nthe t h eintervening i n t e r v e n i n ggneissic g n e i s s i c rocks. rocks. Therefore, appears haver eregional appears t to o have g i o n a l s significance i g n i f i c a n c e i in n tthis h i s part p a r tofo fthe t h eLake LakeSuperior Superior region. region. Xenoliths in Xenoliths i n some some iintrusions n t r u s i o n s also a l s o have have a bearing bearing on on the t h e possible p o s s i b l e age age of of the Biotite t h e gneissic g n e i s s i c rocks. rocks. B i o t i t e schist s c h i s tand and quartzite, q u a r t z i t e , mixed mixed in i nvarious various proportions proportions with mafic anduultramafic rocks, occur as xxenoliths n t r u s i v e rocks, occur as e n o l i t h s in in w i t h volcanic v o l c a n i c and and m a f i c and l t r a m a f i c i intrusive the Syeniteand andl eless abundantlyi nin oother t h e Wausau Wausau Syenite s s abundantly t h e r plutons. Quartzite Q u a r t z i t e inclusions inclusions are restricted m.y. oldo(Van Schmus, Wausau are r e s t r i c t e dto tthe o t h1500 e 1500 m.y. l d (Van Schmus,1976) 1976) Wausau Syenite Syenitecomplex. complex. A syenite km northwest of Wausau (5E¼, A quartzite q u a r t z i t exenolith x e n o l i t hin iquartz n quartz syeni3.2 t e 3.2 km northwest o f Wausau (SEk,SW¼, SWg, Sec. 21, 21, T.29N., T.29N., R.7E.) R.7E.) contains containsup upt to 12 percent percentssillimanite. Sec. o 12 i l l i m a n i t e . Xenoliths Xenoliths of of volcanic volcanic and and pplutonic l u t o n i c rocks rocks in i nthesame t h e same intrusion i n t r u s i o nare a r evirtually v i r t u a unmetamorphosed, l l y unmetamorphosed, suggesting suggesting tthat h a t the t h e sillimanite s i l l i m a n i tmay e mayhave havebeen beenproduced produced by by an an earlier e a r l i e rmetamorphic metamorphic event, and byt the event, and not n o t by by contact c o n t a c tmetamorphism metamorphism by h e ssyenite. y e n i t e . This suggests suggests an an upward upward transport t r a n s p o r t of o f the t h equartzite q u a r t z i t efrom froma ahigh-grade high-grademetamorphic metamorphic tterrane e r r a n e aatt depth, depth, perhaps onwhich whicht hthe The absence perhaps tthe h e basement basement on e vvolcanic o l c a n i c rocks rocks were were deposited. deposited. The absence m.y. old) o l d ) plutons p l u t o n s suggests suggests eeither i t h e r aa ooff quartzite q u a r t z i t e xenoliths x e n o l i t h s ini nolder o l d e r(1850 (1850 m.y. very very rrestricted e s t r i c t e d occurrence occurrence ooff the t h e quartzite q u a r t z i t e ini nthe t h ebasement basement oor r that t h a t the the qquartzite u a r t z i t e isi syounger younger than than the t h e 1850 1850 m.y. m.y. old o l d plutons plutons and and was was intruded i n t r u d e d only o n l y by by the t h e syenite. s y e n i t e . In I n the t h e latter l a t t e case, r case,quartzite q u a r t z i twould e wouldrepresent representfoundered foundered blocks blocks from aboveand andt hthe would nnecessarily bet the from above e s isillimanite l l i m a n i t e would e c e s s a r i l y be h e rresult e s u l t of o f contact contact However,i tit seems seemsu nunlikely metamorphism syenite. l i k e l y t hthat a t qquartzite u a r t z i t e (with (with metamorphism bybyt hthe e syeni t e . However, a a specific s p e c i f i c gravity g r a v i t yofo f2.7) 2.7)would wouldsink s i n kini na amagma magma tthat h a t ccarried a r r i e d ultramafic u l tramafic xenoliths x e n o l i t h s (with ( w i t h aa specific s p e c i f i c gravity g r a v i t yofo about f about3.4) 3.4) upward. upward. Therefore, Therefore, IIfavor favor the the interpretation i n t e r p r e t a t i o n that t h a tthe t h esillimanite-bearing s i l l i m a n i t e - b e a r i n gquartzite q u a r t z i twas e wascarried c a r r i e dupward upward from aa high—grade metamorphic basement basementalthough although II recognize recognizet that an aalternative h a t an lternative high-grade metamorphic -28- �Since tthick iinterpretation n t e r p r e t a t i o n is i s possible. p o s s i b l e . Since h i c k quartzites q u a r t z i t e sare a r euncommon uncommon iin n Early Early Precambrian sequences, theq uquartzite Precambrian sequences, the a r t z i t e iis s more more llikely i k e l yMiddle MfddlePrecambrian. Precambrian. The question then then aarises deeper level level The question r i s e s whether whether the t h e gneisses gneisses represent r e p r e s e n t aa deeper (higher ( h i g h e r pressure-temperature) pressure-temperature) ooff the t h e volcanic v o l c a n i c sequence, sequence, or o r whether whether they they represent an on which which tthe an older o l d e r basement basement on h e volcanics were were deposited. deposited. Mapping Mapping by andMyers Myersi in and around aroundMarathon MarathonCounty Countyshows shows LaBerge and n and t h that a t s structures t r u c t u r e s in in by LaBerge the haveaa ddifferent t h e gneisses gneisses have i f f e r e n t orientation o r i e n t a t i o nthan thanthose thoseini the n t hlow—grade e low-grade volcanic volcanic rocks. The The general general wwesterly plunge ooff lineations e s t e r l y plunge l i n e a t i o n sini the n t hgneisses e gneissescompared compared with rocks iindicates w i t h easterly e a s t e r l y plunging plunging lineations 1i n e a t i o n sini nthe t h elow—grade low-grade rocks n d i c a t e s tthat h a t the the gneisses and andlow-grade low-graderocks rockshave havebeen been subjected gneisses subjected t otod idifferent f f e r e n t stresses. stresses. While iittisi spossible p o s s i b l ethat t h aboth t bothstrain s t r a ipatterns n p a t t e r nmay s maybe beproduced produced by by a a single single While e l f e v e tthe h e differences d i f f e r e n c e s in i n regional r e g i o n a l patterns p a t t e r n s and and pperiod e r i o d of o f deformation, deformation, II bbelieve unconformabler erelationships (1978) aare unconformable l a t i o n s h i p s described described by by Myers Myers (1978) r e best explained explained by assuming assumingtwo twoperiods periods ooff deformation by deformation separated separated by by erosion. TECTONIC SPECULATION SPECULATION Precambrian IIffthe t h egneisses gneissesare a r eMiddle Middle Precambrian(as (assuggested suggestedbybyMaass Maass and and Medaris, 1979, oral Medaris, 1977, 1977, and and Van Van Schmus, Schmus, 1979, o r a l cormiunication) c o m u n i c a t i o n )and andthe t h elow—grade low-grade Precambrian Van a l s oMiddle Middle Precambrian(as (asdated datedbyby VanSchmus, Schmus, vvolcanic—plutonic o l c a n i c - p l u t o n i c terrane t e r r a n e isi salso 1975, 1976) 1976)and andi iff the weresubjected subjected 1975, t h e two two sequences sequences were t otod different i f f e r e n t periods periods of of deformation, deformation, then then there t h e r eare a r etwo twoperiods periodsofometamorphism f metamrphism and and deformation deformation represented I f this t h i s interpretation i n t e r p r e t a t i o n is is County. If represented iinn the t h e rocks rocksofo Marathon f E a t h o n County. hasconsiderable considerable regional r e g i o n a l significance. significance. ccorrect, o r r e c t , iti thas The ppostulated Middle Precambrian deformations in be The o s t u l a t e d two two Middle Precambrian deformations be represented represented throughout muchoof Superior region. region. It throughout much f tthe h e Lake Lake Superior I thas haslong l o n gbeen beenrecognized recognized that t h a t aa mild m i l d flexuring f l e x u r i n gand anderosion e r o s i o n occurred occurred during d u r i n g deposition d e p o s i t i o n of o f the t h eMiddle Middle - Precambriansedimentary sedimentaryrocks rocksexposed exposed variousi riron Van Precambrian onon t hthe e various o n ranges ranges ((cf. c f . Van Hise and and LLeith, For example, sequenceo of rocks ccontaining Hise e i t h , 1911). 1911 ). For example, tthe h e sequence f rocks o n t a i n i n g the the Kona, Randville River Kona, R a n d v i l l e and and Bad Bad R i v e r Dolomites Dolomites (the ( t h e Chocolay Chocolay Group Group ooff the t h eMarquette Marquette Range Supergroupo fofCannon Cannon and Gair,1970) 1970)underwent underwentg egentle Range Supergroup and Gair, n t l e f flexuring l e x u r i n g and and erosion rocks of othe e r o s i o n prior p r i o rtot odeposition d e p o s i t i o of n othe f t hless e l e deformed s s deformed rocks f t hMenominee e Menomineeand and Baraga The deformation deformationf following Baraga Groups. Groups. The o l l o w i n g deposition d e p o s i t i o n of o fthe t h eBaraga Baraga Group Group is is generally (Goldich, 1961). Deformation 1y referred r e f e r r e dtot oasasthe t hPenokean e Penokean Orogeny Orogeny (Goldich, 1961 ) . Deformation general increasesi nini intensity aattributed t t r i b u t e dtot othe t h ePenokean Penokean Orogeny Orogeny increases n t e n s i t y southward southward iin n the the Lake Superior Superior region. Precambrian If,indeed, indeed,two twoperiods periodsofoMiddle f Middle Precambriandeformation deformation Lake r e g i o n . If, are present, are present, the t h e gneisses gneisses and and amphibolites amphibolites in i ncentral c e n t r a Wisconsin l Wisconsinmay may be be aa manifestation post-Chocolay--pre-Menominee deformation deformation and and the the m a n i f e s t a t i o nofo fthe t h epost-Chocolay--pre-Menominee deformation in deformation i n the thelow—grade low-grade vvolcanic—plutonic o l c a n i c - p l u t o n i c rocks may may rrepresent e p r e s e n t the the "Penokean Orogeny." Orogeny." IIffonly deformation iiss present, o n l yone oneMiddle MiddlePrecambrian Precambrian deformation present, "Penokean the be E Early This t h e gneisses gneisses would would presumably presumably be a r l y Precambrian Precambrian iinn age. age. T h i s problem problem Regardlesso of ageo of gneisses,i itt is remains i s probable probable remains unresolved. Regardless f t hthe e age f t hthe e gneisses, which tthe tthat h a t they they represent represent the t h ebasement basement on on which h e volcanic v o l c a n i c rocks rocks were were deposited, deposited, for of of low-grade f o r relatively r e l a t i v e l small y smallisolated i s o l a t eareas d areas low-gradevolcanogenic volcanogenic sediments sediments (of (of Middle Precambrian age?)occur occurwwithin an area area of of dominantly Eau Middle Precambrian age?) i t h i n an dominantly gneisses gneisses in i nEau Claire I believe Therefore, I C l a i r e County. County. Therefore, b e l i e v e that t h a t the t h e volcanics volcanics are a r e a discrete, discrete, younger than the younger sequence sequence than t h e high—grade high-grade rocks. - 29 - �SUMMARY SUMMARY Gneissic rocks rocks ininnorthwestern northwesternand andextreme extremesouthern southernMarathon MarathonCounty County are n o tbeen been dated dated a r e probably probably tthe h e oldest o l d e s t rocks rocks in inthe t h earea, a r e a ,although althoughthey theyhave havenot Theymay maybe, be,a at t l least e a s t in part, p a r t ,Early EarlyPrecambrian Precambrian (more (more than than radiometrically. They 2500m.y. m.y.) 2500 ) or earlier e a r l i e rMiddle MiddlePrecambrian Precambrian rocks rocks that t h a tunderwent underwent amphibolite amphi bol i t e and deformation. deformation. IIff the thehigh-grade high-grade rocks rocks are a r e Middle Middle ffacies a c i e s metamorphism metamorphism and Precambrian,as assuggested suggestedbybyMaass Maass Medaris (1977), they z.ccorrelate Precambrian, andand Medaris (19771, they o r r e l a t e with with rocks of the Supergroupf afarther rocks theChocolay Chocolay Group Group of the the Marquette Marquette Range Range Supergroup r t h e r north Deformationof of these these rocks rocks would would then then be be postiinn the the Lake Lake Superior Superior region. region. Deformation The more more intense metamorphism and deformation metamorphism and Chocolay-.-pre-Menominee Group. Chocolay--pre-Menominee Group. The in central mayc ocorrelate regional flexuring flexuring of i t h t the h e ggentle e n t l e regional of central Wisconsin Wisconsin may r r e l a t e wwith Chocolay Group Grouprocks rocks(LaBerge (LaBergeand andMudrey, Mudrey,1979) 1979)t hthat occurred on on tthe Chocolay a t occurred h e iron iron ranges tto ranges o the the north. north. Erosion Erosion of these these gently gently deformed deformed rocks occurred occurred on on the the erosion must must have haveoccurred occurredi in b u t much much deeper deeper erosion n central Wisconsin Wisconsin iron ranges, ranges, but the amphibolite-facies amphibolite-facies gneissic rocks. tto o expose expose the rocks. The deposition of Groupsedimentary sedimentaryrocks rocks on on tthe h e iron iron ranges ranges The deposition ofMenominee Menominee Group may correlate with the onset of volcanism in central Wisconsin, where may c o r r e l a t e the onset of volcanism i n central Wisconsin, wheregreen— greensschist c h i s t facies f a c i e s volcanic volcanicrocks rocks rest r e s tunconformably unconformably on on amphibolite amphibolite ffacies a c i e s rocks. rocks. Most of of the volcanic indicating the Most volcanic rocks rocks are a r e subaqueous, subaqueous, indicating t h e presence presence of one one or or The volcanic rocks were then extensively intruded by granitic more basins. The volcanic rocks were then extensively intruded by g r a n i t i c more presenceofof high-grade high-grade rocks rocks juxtaposed plutons and and deformed. deformed. The The presence juxtaposed with with greenschist ffacies rock and and tthe preponderance greenschist a c i e s rock h e preponderance of of v evertical r t i c a l l ilineations, n e a t i o n s , including including boudinage boudinage s tstructures r u c t u r e s tthat h a t indicate indicate vertical v e r t i c amovement l movement on on the boundary boundary ffaults, aults, suggests gneisseswere wereu puplifted alongl large Then the general suggests t that h a t tthe h e gneisses l i f t e d along a r g e ffaults. a u l t s . Then general synclinal structure Marathon s t r u c t u r eofofthe t h evolcanic volcanicrocks rocksin in MarathonCounty County may may rresult e s u l t from from of tthe volcanic rocks rocks iinto graben—like' sstructure rrelative e l a t i v e subsidence subsidence of h e volcanic n t o aa "graben-like'' tructure ofnumerous numerous plutons plutons and and deformation deformation of those those plutons plutons (Figure 18). (Figure 1 8 ) . Intrusion of volcanics volcanics volcanios m lcanics / fit Oneisses .Migmatites Amphiholites Outliers of low— Graben Generally low—grade metamorphism Epizonal Plutons It Amphibolitee Migmatitee Some younger piutons grade rocks Some younger plutons north-south cross-section cross-section across acrosswestern western Figure 18. Figure 18. Idealized north-south Marathon Countyshowing showingthe thepostulated postulated graben graben sstructure. Marathon County tructure. - 30 - �suggests tthat h a t the t h e major major deformation deformation of the the area area continued continued throughout throughout most most of suggests of the plutonic activity. the plutonic a c t i v i t y . This This deformation deformation and c t i v i t ymay may correlate correlate andplutonic plutonic aactivity Penokean Orogeny 1961). with the thepost—Menominee post-Menominee event with event known knownas as the Penokean Orogeny(Goldich, (Goldich, 1961). Presumably the Presumably thearea areawas wasagain againelevated elevatedabove abovesea sealevel level and and subjected subjected ttoo i n the the area. a r e a . Emplacement erosion although f ofor r t hthis i s iis s largely lacking lacking in erosion althoughevidence evidence the anorogenic anorogenic Wolf and rrelated e l a t e d syenite syenite intrusions intrusions about about of the Wolf River River Batholith Batholith and 1500 m ~ y .ago n the area. a r e a . The The ffinal i n a lPrecambrian Precambrian 1500 m.y. agowas wasthe thenext nextmajor majorevent event iin event recorded t h e intrusion intrusionofofpyroxene pyroxene and and olivine o l i v i n ediabase diabase event recordedinin the the area area iiss the dikes, dikes, which which ccut u t aall l l older olderrocks rocks in inthe t h ecounty. county. REFERENCES REFERENCES CITED CITED a , 1975, 1975, Petrology Petrology and and geochemistry ith, Anderson, J3. . LL,, Anderson, geochemistryofofthe the Wolf Wolf River River Bathol Batholith, Unpublished Wisconsin—Madison, Unpublished Ph.D. Ph.D. Thesis, University Universityof of blisconsin-Madison, 297 297 p. p. Anderson, JJ. . LL.. and and Cullers, R. R . L., L . , 1978, 1978,Geochemistry Geochemistry and the Anderson, and evolution evolution of of the Wolf River Batholith, rapakivi massif massif in north Wolf River Bathol i t h , aa Late Late Precambrian Precambrian rapakivi north Wisconsin, Wisconsin, U.S.A., U.S . A * , Precambrian Precambrian Research, Research, vol. vol .7,7,pp. pp.287—324. 287-324. Cannon, andGair, Gair,J 3. Cannon, W W. . F.F.and . EE., . , 1970, 1970, AA revision of of stratigraphic s t r a t i g r a p h i nomenclature c nomenclature for rocks in in northern Geol. SOC. Soc. hAmer. Bull., f o r Middle Middle Precambrian Precambrian rocks northern Michigan, Michigan, Geol. e r . bull^, vol. V O .~81, Bl ,pp. pp.2843-2846. 2843-2846. Ervin, C. C. P. P. and and Hanwier, H a m r , S., 1974, Bouguer Bouguer anomaly map of Wisconsin, Wisconsin, S., 1974, anomaly gravity gravity map Wis. Wis. Geol. Geol. Nat. Nat. Hist. Hist.Survey. Survey. Goldich, S. S. S., S., Nier, Nier,A.A.0.,O .Baadsgaard, , Baadsgaard, H., H . , Hoffman, Hoffman, 3. J . H., H . , and andKrueger, Krueger, H. H . W., W., Goldich, 1961, The The Precambrian Precambrian geology Minnesota, Minn. Minn. Geol. Geol. 1961, geology and and geochronology geochronologyof of Minnesota, Survey, Bull. 41, Survey, Bull 41 ,193 193 p. p. . LaBerge, LaBerge, G. G. L. L . in i n LaBerge, LaBerge, G. G . L. L . and and Myers, Myers, P. P . E., E., 1971, 1971, 1971 1971 Progress Progress report report Marathon County, County, Wisconsin, Wisconsin, Wis. Wis. on mapping mappingTf Precambrian geology on of Precambrian geology iinn Marathon Geol. File Report, 28 28 p. p. Geol. Nat. Nat. Hist, Hist.Survey Survey Open Open F i l e Report, . LL., . , 1976, 1976, The The Central Central Wisconsin Wisconsin Batholith, 22nd Ann. Ann. Inst. I n s t . on on LaEerge, GC. LaBerge, Batholith, 22nd Lake Superior Geol., Geol., S St. MN, p. 36. 36. Lake Superior t . Paul, Paul, MN, LaBerge, Major sstructural LaBerge, G.C.LL., . , 1977, 1977, Major t r u c t u r a l features f e a t u r e s in i n Central Central Wisconsin Wisconsin and and ttheir heir implications on on the the Animikie Animikie Basin, Basin, 23rd 23rd Ann. Ann. Inst. I n s t .on onLake Lake Superior Superior Geol., Bay, OOnt., Geol., Thunder Thunder Bay, n t . , p. p. 23. 23. LaBerge, G. G . L. L . and and Myers, Myers, P. P a E. E. (in ( i n preparation), preparation),The Thegeology geologyofofMarathon Marathon County, Wisconsin, Wisconsin Wisconsin Geol. Geol. Nat. Nat, Hist. Hist. Survey. Survey. County, Wisconsin, LaBerge, C., 1979, LaBerge9C. G. L. L . and and Mudrey, Mudrey, MM. e G., 1979, Stratigraphic Stratigraphicframework framework of of Middle Middle Precambrian rocks iinn Wisconsin, Precambrian rocks Wisconsin, Wis. Wis. Geol Geol .. Nat. Nat. Hist. Hist. Survey. Survey. Maass, andMedaris, Medaris, LL. and plutonic plutonic rocks Maass, RR. . and . C., G . , 1976, 1976, Penokean Penokean s structures t r u c t u r e s and rocks in Counties, Wisconsin, Wisconsin, 22nd 22nd Ann. Ann. IInst. in Portage Portage and and Wood Wood Counties, n s t . on on Lake Lake Superior S t . Paul, Paul,MN, M N , p. p. 38. 38. Superior Geol., Geol ., St. . C., G . , Jr., J r . ,Anderson, Anderson, 3. J . L., L . , and andMyles, Myles, 3.J .R., R : , 1973, 1973,The The Wolf Wolf River River Medaris, LL. Medaris, Batholith Batholith -— -- AA late l a t ePrecambrian Precambrian rapakivi massif massif ini nnortheastern northeasternWisconsin Wisconsin - — 31 31 - - �in Guidebook of Northeastern Guidebook to the the Precambrian Precambrian Geology Geology of Northeastern and and North North Central Central Wisconsin, Wis. Wis. Geol. Geol. Nat. Nat. Hist. Hist. Survey, Wisconsin, Survey, pp. p p . 9-29. 9-29. Mickelson, 0. D. M. M. and and Knox, Knox, J3.. C., C . , 1974, 1974, Late LateQuaternary Quaternary environments environments of Mickelson, Wisconsin, Wisconsin, Amqua--Third Anqua--Third Biennial Meeting, Meeting, Madison. Madison. Mudrey,M.M. G., G., Jr. Mudrey, J r . (Ed.), (Ed.),1979, 1979,Middle MiddlePrecambrian Precambrian Geology Geology of of Northern Northern Number4,4,Wis. Wis,Geol. Geol.Nat. Nat. Hist. Hist. Survey, Wisconsin: Field Trip TripGuidebook Guidebook Number Survey, p. 44 P. Mudrey,M.M.G., G., JJr., Aeromagnetic 1977, Aeromagnetic map map of northern northern Mudrey, r . , and and Karl, Karl,3.J .H.,H.,1977, Wisconsin, Wisconsin, 24th 24th Ann. Ann. Inst. I n s t .ononLake LakeSuperior SuperiorGeology, Geology,Milwaukee, Milwaukee, WI, MI, p. 27. 27. p. Myers, PP. geologyjt~ in Guidebook 38th Ann. Ann. Tri-State Tn-State Myers, . E., E . , 1974, 1974, Precambrian Precambrian geology Guidebook f ofor r 38th Geological Geological Field Conf., Conf., Eau Eau Claire, Claire,WI, WI,pp. p p .1—3. 1-3. Myers, P. E., Syeniteofof Central Central Wisconsin, Wisconsin, 22nd Ann. IInst. Myers, P. E . , 1976, 1976, The The Wausau Wausau Syenite 22nd Ann. nst. on LakeSuperior SuperiorGeol., Geol., SSt. on Lake t . Paul, Paul, MN, MN, p. p . 42. 42. Myers, P.P. E., E., 1978, Structures iinn mica 1978, Structures mica schist s c h i s t and and quartzite q u a r t z i t e of ofthe theYounger Younger Myers, MetasedimentarySeries, Series, Geology GeologyofofWisconsin WisconsinField Field Trip Trip Stop, Metasedimentary Stop, Wis. Wis. Geol Geol . Nat. Hist. Survey. Nat. Survey. Myers, P. E., 5., 1980, E . , Cumings, Cumings, M. M. and and Wurdinger, Nurdinger, S., 1980, Early Earlyand and Middle Middle Myers, P. Precambrian amphibolites, Precambrian amphibol i tes, plutonic plutonicrocks, rocks,rnetavolcanics metavol canicsand andrnetasediments metasediments Valley, Wisconsin, 26th Annual Annual IInst. the Chippewa Chippewa Valley, Wisconsin, Guidebook Guidebook f ofor r 26th n s t . on on of the Lake Superior Geol., Geol., Eau Claire, WI. Lake Superior Eau Claire, WI. Van Hise, C.C. R. R. and and Leith, Leith, C. Van Hise, C. K., K . , 1911, 1911, Geology Geology of the the Lake Lake Superior Superior region, U.S.G.S. U.S.G.S. Mono. Mono. 52. 52. W . W. Van VanSchmus, Schmus, Medaris,L .L.GG., R.,R.,Medaris, . , JJr., r . , and and Banks, Banks, P. P. 0., O., 1975, 1975,Geology Geology and and age of the River Batholith, Wisconsin, Geol. Soc.hAmer. Bull., vol vol. age of the Wolf Wolf River Wisconsin, Geol . SOC. e r . Bull., 86, pp. pp.907—914. 907-914. Van Schmus, Schmus,W W. Thurman,E E. andPeterman, Peterman,ZZ. Van . R.,R.,Thurman, . M.M.and . EE., . , 1975, 1975, Geology Geology and and Rb/Sr Rb/Sr chronology of Middle Precambrian rocks in eastern and central Wisconsin, chronology of Middle Precambrian rocks in eastern and central Wisconsin, Geol. Bull., vol. e r . Bull., vol 86, 86,pp. pp.1255-1265. 1255-1265. Geol. Soc. SOC. hAmer. . VanSchmus, Schmus, 1976,Early Earlyand andMiddle MiddleProterozoic Proterozoichistory history of of the Van W. W. R.,R.,1976, t h e Great Great Lakesaarea, North America, America,PPhil. Lakes r e a , North h i l . Trans., Trans., Royal Royal Soc. SOC.London, London, vol. vol. 28Q, 280, pp. 605-628. pp. 605-628. Van Schmus, Schmus,W.W.R .R.and andAnderson, Anderson,J .3.L., L., 1977, Van 1977, Gneiss Gneiss and and migmatite of 6fArchean Archean age basementofofCentral Central Wisconsin, Wisconsin, Geology, Geology,vol. vol. 5, the Precambrian Precambrian basement 5, age in the pp. 45-48. pp. 45-48. Weidman, 1907, The Thegeology geologyofof North North Central Central Wisconsin, Wisconsin, Wis. Wis. Geol. Weidman, S .5., , 1907, Geol. Nat. Nat. Hist. Survey Survey Bull. 16, 16, 697 697 p. p. Zeitz, I.,I .1978, A new , 1978, A newdetailed detailedaeromagnetic aeromagneticmap map covering most most of the the PrecambrianShield Shieldinin Wisconsin, Wisconsin, 24th 24th Annual AnnualIInst. Precambrian n s t . on on Lake Lake Superior Geol., Milwaukee, WI, p. Geol., Milwaukee, WI, p . 41. 41. -- 32 32—- �C-EOLOG G E O L O G II CAL C A L STOP S T O P - 33 — DESCRIPTIONS D E S C R I P T ~ O ~ ~ S �Title: Title: - Artus Creek Artus Creek -- Pillow basalts. basalts. Location: In pasture pasture along along the the east e a s t side s i d e of of Artus Artus Creek. Creek. NE¼, NEk, NW¼, NW&, NW¼, Nl&i, (Marathon 15 minute quadrangle, (Marathon quadrangle, Marathon Marathon Sec. Sec. 29, T.29N., T.29N., R.6E. R.6E. (Get permission permission from from Harold Harold Theis Theis (pronounced (pronounced ""Tice"), Tice"), County.) (Get R. R. R. R. 2, 2,Marathon, Marathon, WI, MI,Phone: Phone: 715-845-2667.) 715-845-2667.) Author: Gene Gene LL.. LaBerge LaBerge (1980) (1980) This stop contains Description: This contains the the best pillow basalts best exposures exposures ofofpillow basalts in in Marathon County. Due Due t to o tthe h e iirregular rregular Marathon fracture f r a c t u r e pattern pattern on on the t h e surface surface of the the outcrop, •the pillows pillows are outcrop,.the a r e not not very very evident. they aare evident. However, However, they r e well exposed on several several small exposed on small south—facing south-facing ledges ffarther the road. road. ledges a r t h e r from from the The pillows pillows range in size The range in s i z e from from onef foot lless e s s than than one o o t tto o aatt least l e a s t three three Pillows are a r e widely widely i n diameter. diameter. Pillows ffeet e e t in used ffor used o r top top determination determination ini nmapping mapping volcanic rocks. volcanic rocks. The accompanying accompanying photo, taken taken aatt this photo, t h i s stop, s t o p ,shows shows the the cclassical l a s s i c a l domal domal top top and and pointed pointed bottom bottom of the 4fp of of the of the pillow. While While tthe he 9 the flows is is readily readilydetermined determined from from flows pillows, they they do do not not show show tthe h e sstrike. trike. This must by tracing aa must be be determined determined by ddistinctive i s t i n c t i v e lithology lithology (or ( o rpillowed pillowed unit). Where exposures aare Where exposures r e as as u nit) limited limited as as they they are a r eininMarathon Marathon County,i itt iiss extremely County, extremely d difficult ifficult thesstrike tto o determine determine the t r i k e of the t h e basalts. basalts. . The greenstones greenstoneshere here sodicplagioclase, plagioclase,a cactinolite, The c oconsist n s i s t of ofsodic t i n o l i t e , epidote, epidote, chlorite, anda actinolite c h l o r i t e ,and andminor minorcarbonate carbonate and and quartz. quartz. Epidote Epidote and c t i n o l i t e are a r e the the dominant minerals minerals ininsome t h e time time of of formation fornation the t h eselvages selvages dominant some samples. samples. AAtt the the pillows were hydratedbbasaltic glass (palagonite); ((rinds) r i n d s ) around around the were probably probably aa hydrated a s a l t i c glass (palagonite); however, they they aare dominantly quartz quartz and however, r e now now dominantly and epidote. The The mineralogy suggests suggests tthat h a t the therocks rockshave haveundergone undergone greenschist greenschistfacies f a c i e smetamorphism. metamorphism. ananeast—west Pillowed basalts basalts are a r e widely widely distributed d i s t r i b u t e dinin east-west trending trending Significance: Significance: Pillowed They are abundantly 'belt" across "belt" across northern northern Wisconsin. Wisconsin. They abundantly exposed exposed near near Pembine Pembine in in Marinette andsporadically sporadically exposed exposedt otot hthe westofoft there, Marinette County, County, and e west h e r e , including the the Monico area in Gravity Map The Bouguer Bouguer Anomaly Anomaly Gravity Map Monico area in Oneida Oneida County County (Mudrey, (Mudrey, 1979). 1979). The of Wisconsin 1974)suggests suggestst hthat theserather rather heavy rocks (a of Hamer, 1974) a t these heavy rocks h'isconsin (Ervin (Ervin && Hammer, resulting resulting gravity gravityhigh) high)extend extendalmost almostcontinuously continuouslyfrom fromthe theMichigan Michigan border border west Rhyolites are are also a l s o present present at a tmost most west beyond beyond Ladysmith Ladysmith in in Rusk Rusk County. County. Rhyolites localities l o c a l i t i e s along along tthis h i s belt, b e l t , indicating indicating aa long long belt b e l t of of volcanic volcanic aactivity. c t i v i t y . The The widespread occurrenceofofpillows pillowsindicates indicates aa submarine origin ffor widespread occurrence submarine origin o r most most of the the vol canics.. volcanics - 34 - �____ Middle Precambrian pillow lavas along Middle Precambrian pillow along Artus Artus Creek. Creek. aatt the the top top of of the the pillow. pillow. Pencil points Pencil points LLAKE AKE SUPERIOR WAUSAU WAUSAU MIDDLE PRECAMBRIAN PRECAMBRIAN GRANITIC Rocks GRANITIC ROCKS EARLY PRECAMBRIAN SEDIMENTARY ROCKS SEDIMENTARY ROCKS EARLY PRECAMBRIAN - -- VOLCANICROCKS ROCKS IYYI VOLCANIC GRANITIC ROCKS GRANITIC ROCKS DOLOMITE, D O L O M I T E , ETC. ETC. u"GREENSTOtjt' ~ ~ ~ & ~ s ~ o Generalized north-south north-south cross—section Generalized cross-section in in northern northernWisconsin Wisconsin showing showing the postulated volcanic rocks rocks iinn north the postulated relationship between between volcanic north central central Wisconsin and iron-formations iron—fonnationsand andother other sediments sedimentstoto the the north. Wisconsin and - 35 - ~ ~ m �Radioactive age dating dating on on these these rocks rocks indicates that Radioactive age t h a tthey theywere wereformed formed between 1900 1900 m.y. m.y. and between and about about 1825 1825m.y. m.y. ago ago(Van (VanSchmus, Schmus,Thurman Thurman and and Peterman, Peterman, ageas asthe the ironThus, they they are a r e approximately approximately the the same same age 1975; Sims, 1975; Sims, 1976). 1976). Thus, formation and on the the Gogebic Range,and andmust, must, therefore, therefore, have and graywacke graywacke on Gogebic Range, have formedas aspart part of of the basinof of deposition deposition --- the theAnimikie AnimikieBasin Basin (LaBerge, (LaBerge, formed the same same basin 1977) 1977) (see diagram). diagram) . The volcanic volcanic rocks have been beenextensively extensively intruded intruded by The rocks in i n Marathon Marathon County County have by volcanic belt ggranitic r a n i t i crocks rocks and and are a r e separated separated from from the main main volcanic b e l t by by aalarge largewedgewedgeshaped massofofgneisses gneissesand andamphibol amphibolites appear tto However, the ites t hthat a t appear o be be older. older. However, shaped mass volcanic rocks rocks here hereaare believedt otobe berelated relatedtto those ffarther r e believed o those a r t h e r north north in in volcanic Wisconsin because becausethey theyaare of the same age, and and were were formed formedmainly mainly iin Wisconsin r e of same age, n aa stops, we will examine subaqueous environment. At subaqueous environment. A t the the succeeding succeeding stops, we will examine the the relationships between these various variousrock rocksequences. sequences. relationships between these References: Gravity Map of Wisconsin; Ervin, C. C . PP.. and and Haniner, Hamer, SS., . , 1974, 1974, Bouguer Bouguer Anomaly Anomaly Gravity Map of Wisconsin; Wis. Geol. Geol. Nat. Nat. Hist. Wis. Hist. Survey. Survey. LaBerge,GG. Structural Features LaBerge, . LL., . , 1977, 1977, Major Major Structural Features ini nCentral CentralWisconsin Wisconsin and and Their Implications on the Animikie Basin; 23rd Annual n s t . on on Lake Lake Their Implications on the Animikie Basin; 23rd Annual IInst. Superior Geology, Geology, Thunder Thunder Bay. Bay. Mudrey, . , JJr. r . (Ed.), ( E d . ) ,1979, 1979,Middle MiddlePrecambrian Precambrian Geology Geology of of Northern Northern Mudrey, M.M. GG., Field Trip No.4,4, Wis. Wis. Geol. Geol. Nat. Nat. Hist. Wisconsin: Field Trip Guidebook Guidebook No. Hist. Survey, Survey, 44 p . 44 p. Sims, P. Sulfide K., 1976, 1976,Middle MiddlePrecambrian Precambrian Age Age of Volcanogenic Volcanogenic Massive Massive Sulfide Sims, P . K., Deposits Annual IInst. Deposits iinn Northern Northern Wisconsin; Wisconsin; 22nd 22nd Annual n s t . on on Lake Lake Superior Superior Geology, S St. Geology, t . Paul, Paul ,MN. MN. Van Schmus,WW. Thurman,MM. and Peterman, Peterman, Z.Z. E., E . , 1975, 1975,Geology Geologyand and Van Schmus, . R R., . , Thurman, . E.E. and Rb/Sr Chronology Chronology ooff Middle Precambrian Rocks iin Precambrian Rocks n Eastern Eastern and and Central Central Rb/Sr Geol. SOC. Soc. America AmericaBull., Bull., Vol. Wisconsin: Geol. Vol. 86, 86,pp. pp.1255-1265. 1255-1265. — 36 — �Title: Title: Rib intrusion breccia. Rib Falls --Deformed Deformed intrusion breccia. Location: West side of CTH-S w i t h0TH—U CTH-U ononnorth Rib West side CTH-S aatt ju junction nction with north side side of Rib River, corner, Sec. NE corner, Sec. 28, 28, T.29N., T.29N., R.5E., R.5E.,Marathon MarathonCounty County(Marathon (Marathon River. NE 15 minute quadrangle). quadrangle). Author: Author: Gene Gene LL.. LaBerge LaBerge (1980) (1980) Description: extensively Description : The The volcanic volcanic sequence sequence in i n Marathon Marathon County County has has been been extensively invaded by zoned zonedstocklike stocklikeggranitic invaded by r a n i t i c intrusions. intrusions. Many Many intrusions show extensive extensive intrusions show development intrusion breccias. development ofof intrusion breccias. The exposureconsists consists mainly mainly of quartz The exposure quartz diorite w i t habundant abundant quartz, quartz, plagioclase plagioclase and and chloritized chloritized mafics. mafics. Mafic diori t ewith Mafic to to intermediate volcanic(?) volcanic(?) xenoliths xenolithsranging rangingfrom fromabout about2 2cm cm tot oseveral severalmeters meters intermediate are a r e present present in i n several severalzones. zones. The The xenoliths show show aa wide n assimilation wide range. range i in in readily recognizable i n the the intrusive intrusivephase. phase* Some Some aare r e readily recognizable as asfine—grained fine-grained volcanic(?) i n the the quartz quartz volcanic(?) rocks; rocks; others othersare a r eexpressed expressed as a s mafic—rich mafic-rich cclots l o t s in Several late l a t egranitic g r a n i t i c(less ( l e s smafic) mafic)dikes dikes cut c u tthe the quartz quartz diorite d i o r i t eand and diorite. d i o r i t e . Several the the volcanic volcanic xenoliths. xenoliths. Plagioclase the quartz quartz diorite d i o r i t eranges ranges from from An2035 An20-35 and and shows shows prominent prominent Plagioclase iinn the zoning, resorption rims. rs as zoning, and and some some resorption rims. Quartz Quartz occu occurs a s ±+5—8 5-8 m grains grains (phenocrysts?) (phenocrysts?) and as similar sized and as sized clots c l o t s of offinely f i n e l ypolygonal polygonal quartz. quarty. Much the quartz quartzddiorite pervasivec cataclastic Much ofof the i o r i t e has has aa pervasive a t a c l a s t i c ffoliation o l i a t i o n that that strikes dips vvertically. N.45oE. and and dips e r t i c a l l y . Several s t r i k e s N.450E. Several prominent prominent vvertical, e r t i c a l ,N.45°E. 1 . 4 5 ' ~ .shear shear zones cross the outcrop zones cross outcrop area. area. They They appear appear to t o be bemost mostpronounced pronounced where where mafic mafic - 37 - �rocks Someofof the the zones maybe be sheared shearedmafic mafic dikes. rocks are are more more abundant. abundant. Some zones may However, in other zones the mafic material is extensively mixed with lensoidal However, in other zones the mafic material i s extensively mixed with lensoidal patchesofofplutonic plutonic rock, rock, suggesting suggestingt hthat theywere werei ninitially patches a t they i t i a l l y mafic-rich mafic-rich Lensoidal (boudinaged) blocks of of relatively intrusion breccias. breccias. Lensoidal (boudinaged) blocks r e l a t i v e l yunsheared unsheared plutonic rocks rocks are are separated separated from from one one another another by by aa network network of braided braided shear shear planes. planes . Features exposed exposedhere hereand andvariations variationson ont this h i s theme theme aare r e typical Significance: Features of many Middle Precambrian plutons in Marathon County. Intrusion breccias many Middle Precambrian plutons i n Marathon County. breccias country rocks aare r e comon comon and and widespread. widespread. Xenoliths and and country rocks are a r e generally generally Plutons aare typically zoned, metamorphosed onlyt otogreenschist greenschist facies. facies. Plutons with metamorphosed only r e typically zoned, with aa xenolith-rich quartz quartz diorite d i o r i t emargin margin and and aa more more ggranitic r a n i t i c core. core. Inner portions portions multiple of plutons plutons comonly commonly intrude intrude outer, outer,more more mafic mafic zones, zones, suggesting suggesting multiple common injections from from aa differentiating d i f f e r e n t i a t i nmagma. g magma. Quartz Quartz ddiorite i o r i t eisi the s the common intrusive phase in intrusion breccias phase in breccias into i n t o mafic/interinediate mafic/intermediate volcanics volcanics whereasgranite granite iiss more common volcanic xenoliths. xenoliths. This suggests w i twith h f efelsic l s i c volcanic suggests whereas more common of the the magma magma tthat h a t the the composition composition of i s is a tatl eleast a s t ppartially a r t i a l l y controlled controlled by by assimilation assimilation of intruded intruded material. material. Individual mineralogically ddistinct Individual plutons plutons aare r e rrelatively e l a t i v e l y small, small, and and aare r e mineralogically istinct from neighboring neighboring plutons, plutons, and from and roof pendants pendants of volcanic volcanic rocks rocks more more than than ten tenkms kms long are long a r e present. present. Most of Marathon MarathonCounty County includedi ninaamajor majorgravity gravity low low iinn central Most of i s isincluded Wisconsin This suggests the area suggests t that h a t the area iiss underlain underlain Wisconsin (Ervin (Ervinand andHammer, Hamer, 1974). 1974). This predominantlybybyg rgranitic rocks, probably probablyaalarge large batholith. batholith. The predominantly a n i t i c rocks, The ssurficial urficial geology suggests suggestsa acomposite compositebatholith batholithjjust geology u s t being being unroofed unroofed by by erosion. erosion. The The markedlycross-cutting cross—cuttingrelationships relationships of of the intrusion breccias, markedly the plutons, plutons, common comon intrusion breccias, low-grade metamorphism of ofthe n the low-grade regional regional metamorphism thevolcanics, volcanics, prominent prominentzoning zoning iin plagioclases aalll l indicate of the plagioclases indicateemplacement emplacement of the batholith batholithataupper t uppermesozonal mesozonal depths iin n the the crust. crust. tto o epizonal epizonal depths References: C. P.P .and andHammer, Hammer, S., 1974, 1974,Bouguer Bouguer Anomaly Anomaly Gravity Map Map of Wisconsin: Wisconsin: Ervin, C. Wis. Wis. Geol. Geol. Nat. Nat. Hist. Hist. Survey. Survey. - 38 - �Title: Title: Rib Ultramafics at a tcontact contact ofofgneiss gneiss Rib River Riverata Emory t EmorySchool School -- Ultramafics terrane. terrane. Location; SW¼, Sec.30, 30, T.30N., T.30N., R.5E., NW%, SW%, Sec. R.5E., Hamburg Hamburg 15' quadrangle. Location: NW¼, 15' quadrangle. Author: Author: Paul Claire (1978). Paul E.E.Myers, Myers,UW—Eau UW-Eau Claire (1978). (Revised (Revised by byLaBerge LaBerge &&Palmer, Palmer, 1980.) 1980.) Summary of Features: Summary of Features: AA small, small,ENE—trending, ENE-trending, llenticular e n t i c u l a rbody bodyofofmassive massive hornblende-biotite-tonalite-gneiss to t othe the north north metaperidotitet?)separates separates hornblende-biotite—tonalite-gneiss metaperidotite(?) from sedimentary from phyllites p h y l l i t e sofof sedimentaryparentage parentage to t othe thesouth. south. The The ultramafic ultramafic rock rock was alongaa major major ffault emplaced along a u l t which which raised raised more more highly highly was apparently apparently emplaced metamorphosed tonalite metamorphosed tonal i t e gneisses gneisses on on the the north. north. Discussion: Discussion: Muscovite Muscovite pphyllite h y l l i t e with w i t h foliation f o l i a t i o nand andsubparallel subparallel relict r e l i cbedding t bedding N74OE, 75°N 75ON and and subordinate cleavage cleavage N350E, N35CJE, 74°NW 74ONW i is s probably derived derived from from N74°E, aa felsic f e l s i cvolcanic volcanicrock. rock. Relict Relictquartz quartzand and feldspar feldsparclasts c l a s t s(staining ( s t a i n i nshow g show presence presence of both both potassium potassium feldspar feldspar and and plagioclase) plagioclase)and and bedding bedding are a r e best best seen horizontal surfaces towardtheir their fault seen on on horizontal surfaces toward f a u l t contact contact with w i t h the t h eultramafic ultramafic rock. The phyllites p h y l l i t econtain s contain streaked lensoids of K-feldspar diamondrock. The streaked lensoids of K—feldspar andand diamond— shaped shaped hematite hematitereplacements. replacements. AA conspicuous conspicuous lineation l i n e a t i o nformed formed by by the the intersection foliation plunges N360W at 68—74g. i n t e r s e c t i o of n of f o l i a tand i o n cleavage and cleavage plunges N36OW a t 68-74O. Bioti te-hornblende tonalite tonal i t epencil pencilgneisses gneissesalong alongRib RibRiver Rivernorth northofofhere here Biotite-hornblende have N50—650W ata~55—65°. have lineations l i n e a t i o nplunging s plunging ~50-65O t 55-650. Foliation, Foliation,where wherepresent, present, dips dips steeply NNW. steeply NNW. - 39 — �The coarse-grained coarse—grained ultramaficrock rocki is The ultramafic s composed composed ofofr relict e l i c t pyroxene(?) pyroxene(?) which appears tto beenaaltered andcchlorite. which appears o have have been l t e r e d to an an amphibole amphibole and h l o r i t e . The The presence plagioclase suggests suggestst that be aa feldspathic pyroxenite. presence ofof plagioclase h a t tthis h i s may may be pyroxenite. Another massive massivemafic mafic unit unit Some specimensa rare neargabbro gabbroi in Some specimens e near n composition. composition. Another composedofofamphibole, amphibole,epidote, epidote, and outcrops 6.6 6.6 km km southwest southwest of composed and sphene sphene outcrops here (NW¼, Sec.33, 33,T.30N., T.30N., R.4E.). At A t both both localities l o c a l i t i e sthe t h emafic mafic rocks rocks here (NWk, Sec. parallel between p a r a l l e l the thefault f a u lcontact t contact between gneissic gneissic rocks rocks on on the the north north and and lowlowgrade metavolcanic metavolcanic and metasedimentaryrocks rocks on on the the south. The The rrestricted estricted grade and metasedimentary occurrenceofof ultramafic rocks the two two terranes terranes suggests occurrence rocks between between the suggests tthat h a t they they lie along major high-angle faults and were emplaced during or after l i e along major high-angle f a u l t s and were emplaced during o r a f t e r ffaulting. aulting. Their lack lack of of foliation the llatter. the ultramafic ultramafic body a t t e r . Although Although the body iiss Their f o l i a t i o n suggests suggests the about 300 300meters meterswide widehere, here,iitt was about was not observed observed iinn outcrop outcrop along along the the Rib Rib River just just east Shapeand andextent extent of the River e a s t of of here. here. Shape thebody bodyare a r eunknown. unknown. A magneticlow lowp parallels A prominent prominent magnetic a r a l l e l s the fault f a u l tcontact contactbetween between the the gneisses gneisses and low—graderocks rocksf ofor nearly 60 along the km along t h e northern northernedge edge ofofMarathon Marathon and low-grade r nearly 60 km known County ((Zeitz, I tisi snot not knownwhether whether the themagnetic magnetic County Z e i t z , Karl, Karl,and andOstrom, Ostrom, 1977). 1977). It 'demagnetization'ofof rocks rocks along along the the ffault low iiss due low due to t o "demagnetization" a u l tzone, zone, or o rwhether whether aa numberofof reversely-polarized reversely—polarizedmafic maficand andultramafic ultramafic rocks rocks are number a r e present. present. References:: References J. H., andand Ostrom, M.M.E.,E 1977, Preliminary aeromagnetic I . ,Karl, Karl, J . H., Ostrom, . , 1977, Preliminary aeromagneticmap map Zeitz, I., covering terrane iinn Wisconsin: U.S. Geol. Geol. Wisconsin: U.S. covering most most of the t h e exposed exposed Precambrian Precambrian terrane Survey Misc. Field Survey Misc. Field Studies StudiesMap Map 888. 888. -40- �Title: Title: Black Q u a r t z o f e l d s p a t h i c gneisses. gneisses. Black Creek, Creek, Athens Athens - Quartzofeldspathic Location: Location: Along Along Black Black Creek a l l e y west west of o f Wis. His. Hwy. Hwy. 97 97 in i nAthens. Athens. NE¼, Creek vvalley NEi,, SW¼, Sec.31, 31, T.30N., T.30N., R.4E. SWi, Sec. R.4E. (Marathon (Marathon County) County) (Athens 15 15 minute minute quadrangle). Authors: Authors: Gene L. LaBerge and EElizabeth LaBerge and l i z a b e t h Palmer, Palmer, 1980. 1980. Gene L. Description: gneisses ooff variable D e s c r i p t i o n : Quartzofeldspathic Q u a r t z o f e l d s p a t h i c gneisses v a r i a b l e composition composition crop crop out o u t at at aa number number ooff places places ini nnorthwestern northwesternMarathon MarathonCounty. County. This T h i s exposure exposure i illustrates llustrates several several phases phases of o f the t h egneisses, gneisses, but b u numerous t numerous other o t h e r phases phases are a r e present. present. The southeasternend endo foft hthe exposure The southeastern e exposure c oconsists n s i s t s o fofa af efelsic l s i c rock with with lensoidal fragmentsi in medium-grained q uquartz-feldspar a r t z - f e l d s p a r fragments n aa ffiner—grainS iner-grained l e n s o i d a l , , medium—grained micaceous micaceous qquartzofeldspathic u a r t z o f e l d s p a t h i c matrix. m a t r i x . Muscovite and bbiotite Muscovite and i o t i t elaths l a t h swrap wraparound around the t h e lensoidal l e n s o i d a lfragments. fragments. The The rock rock appears appears tto o be be a metamorphosed metamorphosed f e felsic l s i c ttuff uff with planeofof ffoliation. c l a s t s elongated elongated i in n tthe h e plane oliation. A A more more mmafic a f i c ((amphibolitic) amphibolltic) w i t h the t h e clasts rock northwestoof rock occurs occurs northwest f tthe h e ffelsic e l s i c rock. rock. The composition,f fine The composition, i n e grain g r a i n size, s i z e , and and weakly t was derived d e r i v e d from from weakly ffoliated o l i a t e d character c h a r a c t e r of o f the t h emafic mafic rock rock suggest suggest that t h a t iti was aa mafic mafic rock is ont the The m a f i c rock i s bounded bounded on h e nnorth o r t h (near (near the t h e old old m a f i c flow f l o w or o r dike, d i k e . The dam) byaaf felsic dam) by e l s i c rock rock rich r i c hini npotassium potassium feldspar. f e l d s p a r . It I tcontains contains large l a r g e feldspar feldspar fragments and mmicrocline fragments and i c r o c l i n e in i n the t h erecrystallized r e c r y s t a l l i z egroundmass. d groundmass. It I tappears appears to t o be be aa sheared andr erecrystallized sheared and c r y s t a l l i z e d potassic potassic plutonic p l u t o n i c rock rock or o r gneiss. gneiss. Foliation N.~o'E. and and ddips i p s vvertically. e r t i c a l l y . Clasts C l a s t s in i n the the F o l i a t i o n here here strikes s t r i k e sabout about N.70°E. gneissic elongatedv evertically planeoof g n e i s s i c rocks rocks aare r e elongated r t i c a l l y i in n tthe h e plane f ffoliation. o l i a t i o n . Farther Farther - 41 - �from the the ccontact with from ontact w i t h the t h e greenschist greenschist facies f a c i e s rocks, rocks, fold f o l daxes axesand and mineral mineral For example, Dells example, aatt Goodrich Goodrich D e l l s on on lineations l i n e a t i o n s in i nthe t h egneisses gneisses plunge plunge westerly. w e s t e r l y . For the Rib River eight miles northeast of here, mineral lineations, fold axes t h e Rib River e i g h t m i l e s northeast o f here, mineral 1i n e a t i o n s , f o l d axes This is within is and m mafic and a f i c clot c l o tplunge plungewest west ata 350_700 t 35O-70 w i t h i n tthe h e N.85°E. N.8s0E. f foliation. o l i a t i o n . This in contrast to the east-plunging lineations in the greenschist facies i n c o n t r a s t t o t h e east-plunging l i n e a t i o n s i n t h e greenschist f a c i e s rocks rocks along Hamann Hamann Creek which along Creek which we wwe i l l will seesee l a t later e r onon t hthis i s t rtrip. ip. The northwestern northwesterncorner corner ooff Marathon Countyi is Marathon County s uunderlain n d e r l a i n by by Significance: S i g n i f i c a n c e : The aa variety v a r i e t y of o fquartzofeldspathic q u a r t z o f e l d s p a t h i c gneisses, gneisses, amphibolites amphibolites and and locally l o c a l l ymigmatites. migmatites. Reconnaissancemapping mapping westand andn onorth suggestst hthat Reconnaissance t o to t hthe e west r t h suggests a t tthe h e gneisses gneisses are are an extension extension ooff the an the complex complex high-grade high-grade metamorphic metamorphic t eterrane r r a n e tthat h a t extends extends at at l e a s t 60 60 miles m i l e s to t o the t h e west. west. The The llithologies i t h o l o g i e s closely c l o s e l yresemble resemble those those of o f the the least "ChippewaAmphibol Ajnphibolite Complex"described described by by Myers Myers (1974) (1974) from from exposures "Chippewa it e Complex" exposures iinn Knownexposures exposureso of Precambrianrocks rocks iinn Chippewa and l a i r e Counties. Counties. Known f Precambrian Chippewa andEau EauCClaire Clark County Marathonand andtthe Chippewa-EauC Claire area) are Clark County (between (between Marathon h e Chippewa-Eau l a i r e area) are dominantly high—grademetamorphic metamorphic rocks, although dominantly high-grade rocks, although s cscattered a t t e r e d o outliers u t l i e r s of of A ddistinctive istinctive low—grade metavolcanicand andmetasedimentary metasedimentaryrocks rocksaare low-grade metavolcanic r e present. present. A aeromagnetic andg rgravity aeromagnetic and a v i t y ppattern a t t e r n iis s also a l s o present present in i nthis t h i sfour—county four-county area. area. block' Thus, tthe gneisses iin Countyare aree vevidently Thus, h e gneisses n Marathon Marathon County i d e n t l y ppart a r t oof f a a large l a r g e "block" of o f gneisses gneisses as shown shown i in n Figure F i g u r e 1. 1. The age ooff these no rradiometric The age these gneisses gneisses is i s unknown unknown ssince i n c e no a d i o m e t r i c ages ages are are Myers(1980, (1980,t hthis conference) shows showst hthat However, Myers i s conference) a t ssimilar imilar aavailable. v a i l a b l e . However, gneisses iinn the River two periods periods of gneisses t h e Chippewa Chippewa R i v e r valley v a l l e y have have undergone undergone two o f deformation deformation Van Schmus Schmusand andAnderson Anderson (1977)r ereport and metamorphism metamorphismp rprior and i o r ttoo 1850 1850 rn.y. may. Van (1977) p o r t tthat hat similar s i m i l a rgneisses gneisses south south ofo fMarathon Marathon County County have have rradiometric a d i o m e t r i c ages ages ranging ranging from from andMedaris Medaris(1976) (1976)i ninterpret 1850 m.y. to Maass and t e r p r e t the t h e rocks rocks t o more more than than 2800 2800 m.y. may. Maass 1850 m.y. ReconnaissancebybyMyers Myers(1978) (1978)i nindicates d i c a t e s tthat hat to t o be be Middle Middle Precambrian Precambrian in i n age. age. Reconnaissance low rocks unconformably low grade grade vvolcanic o l c a n i c and and sedimentary sedimentary rocks unconformably ooverlie v e r l i e the t h e high h i g h grade grade terrane Claire Thus, the t h e high h i g h grade grade t e r r a n e along along the t h e Eau Eau C l a i r e River R i v e r in i nClark C l a r kCounty. County. Thus, rocks must be beoolder than greenschist greenschist ffacies rocks must l d e r than a c i e s volcanics. volcanics. If area rMiddle Precambrian I fthe t h egneissic g n e i s s i rocks c rocks e Middle Precambrianasassuggested suggestedbybyMaass Maass and and Medaris (1976), they must represent an earlier deformed and metamorphosed Medaris (1976), they must represent an e a r l i e r deformed and metamorphosed sequence thant that which we we ffind sequence than h a t which i n d in i nmost most ofo fMarathon Marathon County. County. References:: References 13., 1976, 1976, Penokean PenokeanS Structures andPPlutonic Maass, R. t r u c t u r e s and l u t o n i c Rocks Rocks iinn Maass, R. and' and Medaris, Medaris, L. G., Portage and Counties, Wisconsin: 22nd Annual AnnualI Inst. and Wood Wood Counties, Wisconsin: 22nd n s t . on on Lake Lake Superior Superior Geology, Geology, SSt. t . Paul, Paul, p. 38. 38. Myers, P. P. E., Myers, E., 1974, 1974, Precambrian Precambrian Geology Geology in i n Guidebook Guidebook ffor o r 38th 38thAnnual Annual Tn—State Tri-State Geological EauCClaire, Geological Field F i e l d Conference, Conference, Eau l s r e , pp. pp. 1-3. 1-3. E., 1978, Younger Myers, P. 1978, Structures S t r u c t u r e s in i nMica Mica Schist S c h i s tand and Quartzite Q u a r t z i t eofo the f the Younger MetaMetaMyers, P. E., Geol. sedimentary Series: Geol . ooff Wis. Idis. Field F i e l d Trip T r i p Stop, Stop, Wis. Wis. Geol. Geol . Nat. Nat. Hist. H i s t . Survey. Survey, sedimentary E. and 1980,EEarly and Middle Middle Precambrian PrecambrianAmphibol Miphibolites, Myers, P. E. and Cummings, Cumings, M.M.L.,L., 1980, a r l y and ites, Myers, P. Plutonic Valley, P l u t o n i c Rocks, Rocks, Metavolcanics, Metavolcanics, and and Metasediments Metasediments ooff the t h e Chippewa Chippewa V alley, 26th Annual Wisconsin: Eau C laire. WisConsin: Guidebook Guidebook f ofor r 26th Annual Inst. I n s t . on onLake LakeSuperior SuperiorGeol Geol ., ., Eau Claire. Van Schnius,W.W.R.,R.,and andAnderson, Anderson,J.J. L.~, L., 1977, 1977, Gneiss Gneiss and and Migmatite Migmatite of o fArchean Archean Age Age Van Schmus, in Geology,vvol. i n the thePrecambrian Precambrian Basement Basement ooff Central Wisconsin: Wisconsin: Geology, o l . 5, pp. pp. 45-48. 45-48. - 42 - �Title: Title: Athens Athens County County Park Park -- Sheared Sheared rocks. rocks. Location: Location: NE¼, NW¼, SW¼, T.29N.,R.4E. R.4E. (Athens (Athens 15 minute quadrangle) NE%, NW%, SM%, Sec.Sec. 6, 6,T.29N., quadrangle) Marathon County. County~ Authors: Authors: Gene LaBerge and and Elizabeth Elizabeth Palmer, Palmer,1980. 1980. Gene LL.. LaBerge Description: diverse lithologies Description: This This stop stop illustrates i l l u s t r a t e some s someofofthe thecomplex complex and and diverse lithologies developed along the major developed along major fault f a u l zones t zonesininMarathon MarathonCounty. County. Movement on the Movement on the f a u l t shave have evidently evidentlyjuxtaposed juxtaposed rocks rocks of ofvaried variedparentage parentage and and in i n various various faults stages c a t a c l a s t i cdegradation, degradation,producing producingextremely extremelyvariable, variable,complex complexzones. zones. stages of of cataclastic At the creek A t the the south south end end of the the exposure exposure aatt the the bend bend i in n the creek (refer ( r e f e r to t osketch sketch map), andand may bebe a metagraywacke. map), the the rock rockisi schistose, s schistose, may a metagraywacke. ItI tisi svariable in variable in composition, composition, with w i t h quartz, quartz, plagioclase, plagioclase, biotite, b i o t i t emuscovite , muscoviteand andhornblende hornblende the the dominant in the dominant minerals, minerals. Exposures Exposures in the small small creek creek entering enteringPotatoe PotatoeCreek Creekfrom from the the south south at a tthe thesouth southedge edge ofofthe themap map appear appear to t o be be deformed deformed ffelsic e l s i c volcanic volcanic rocks. rocks . North from the the schistose schistose rock are North (downstream) (downstream) from a r e several several exposures exposures of of well well foliated lens—shaped f o l i a t e dbiotite—rich biotite-rich flaser f l a s e rgneiss. gneiss. The The biotite b i o t i t encloses e encloses lens-shaped porphyroclasts and porphyroclasts ofofquartz quartzand andfeldspar feldspar andemphasizes emphasizes the thelens—structure. lens-structure. This rock appears to be a highly sheared pluton, or perhaps This rock appears t o be a highly sheared pluton, or perhapsaasheared sheared gneiss. gneiss. The larger grains show cataclastic degradation and alteration The grains show c a t a c l a s t i c degradation and a1 teration tto o sericite serici t e and and carbonate. carbonate. Deformed Deformed f efelsic l s i c volcanic volcanic rocks rocks are intimately intimatelymixed mixed with with the the biotite flaser gneiss. b i o t i t e f l a s e r gneiss. - 43 - �Exposures Exposures o of f f ifine-grained n e - g r a i n e d ppink, i n k , mylonitized m y l o n i t i z e d granitic g r a n i t i cgneiss gneissand and several several large l a r g e quartz q u a r t z veins veins are arepresent present about about 60 60 meters meters northeast northeast of o f the t h epark parkboundary. boundary. These appeart oto have havebeen beenp hphaneritic rocks tthat beenccataclastically These appear a n e r i t i c rocks h a t have have been ataclastically degraded. degraded. Significance: S i g n i f i c a n c e : A major major structural s t r u c t u r a lboundary boundary passes passes through through Athens Athens trending t r e n d i n g about about N600E. N60OE. South South ooff the t h e lineament lineament are a r e volcanic v o l c a n i c rocks rocks and and granites g r a n i t e s that t h a have t havebeen been only o n l y slightly s l i g h t lmetamorphosed. y metamorphosed. North North of o f the t h e lineament lineament the t h e rocks rocks are a r ehigh h i g hgrade grade gneisses, gneisses, amphibolites amphibolites and and migmatites migmatites (LaBerge, (LaBerge, 1977). 1977). Along Along the t h e lineament 1 ineament are a r e mylonites, mylonites, phyllonites p h y l l o n i t e sand and other o t h e r intensely i n t e n s e l ysheared sheared rocks rocks along along with w i t h aa number number oof f mmafic a f i c tto o ultramafic u l t r a m a f i c bodies. bodies. The width The w i d t h of o f the t h eshear shearzone zone ranges ranges up up to braided zones zonesoof km and and consists c o n s i s t s of o fnumerous numerous braided f iintense n t e n s e cataclasis cataclasis t o nearly n e a r l y 22km separated "pods"o fofr relatively separated by by lens—shaped lens-shaped "pods" e l a t i v e l yundeformed undeformed rock. In I n places, places, the deformation deformation affected a f f e c t e dmainly main1ythe t h elow—grade low-grade volcanic v o l c a n i c and and sedimentary sedimentary rocks. rocks. A A variety v a r i e t y of o frocks rocksappear appear to t ohave have been been involved i n v o l v e d in i nthe t h edeformation deformation here. here. AA similar side Marathon County s i m i l a rcataclastic c a t a c l a s t izone c zonealong alongthe t h south e south s i dof e o f Marathon County(see (seeCounty County map) gneisses iinto volcanics and map) bbrings r i n g s gneisses n t o contact c o n t a c t with w i t hlow—grade low-grade volcanics and iintrusions. ntrusions. The metamorphicrocks rocks bounded boundedon ontthe h e north n o r t h and and south south The presence presence of o f low—grade low-grade metamorphic by separated by by broad broadccataclastic by gneisses gneisses and and separated a t a c l a s t i c zones zones containing c o n t a i n i n g mafic m a f i cand and ultramafic scale block block ffaulting. volcanics u l t r a m a f i c bodies bodies iindicates n d i c a t e s llarge a r g e scale a u l t i n g . The The low—grade low-grade volcanics and granites with and g r a n i t e s appear appear tto o occupy occupy aa ggraben—like r a b e n - l i k e s structure tructure w i t h horsts h o r s t s of o fgneisses gneisses uplifted diagrami lillustrates u p l i f t e don on both both the t h e north n o r t hand and south. south. The The diagram l u s t r a t e s these these relationships r e l a t i o n s h i p s across across this t h i spart p a rof t oMarathon f MarathonCounty. County. These large scale faul ts appear to have been active over several hundred million years of time, and represent the major structural features in central Wisconsin. Gn e is see volcanics U Mignatites Amphibolites Outliers of low— grade rocks Some volcanics Graben Generally low—grade metamorphism Epizonal Plutona I Gneisses Ajnphlbolites Migmatites Some younger plutons younger plutons North—south cross-section across Marathon County. References: References : LaBerge, G.G.L., 1977, Major t r u c t u r a l features features in i nCentral Central Wisconsin Wisconsin and heir LaBerge, L., 1977, Major sstructural and ttheir implications imp1 i c a t i o n son on the t h eAnimikie Animikie Basin: Basin: 23rd 23rd Annual Annual IInstitute n s t i t u t e on on Lake Lake Superior Superior Geology, Geology, Thunder Thunder Bay. Bay. -- 44 -- �Title: Title: Hamann Creek-—Lineated Lineated andesite. andesite. Hamann Creek Location: Creeki in SE¼,Sec. Sec. 26, 26, T.28N., R.3E. Location: Along n SEk, R.3â‚ Marathon Along Hamann Hamann Creek Marathon County. County. (Stratford (Stratford15 15minute minutequadrangle) quadrangle) (Get (Get permission permissionfrom fromRoger RogerBohman, Bohman, Rt. 715—687—2343.) R t . 1,1 Stratford; , S t r a t f o rphone d ; phone 71 5-687-2343.) Author: Author: Gene L. LaBerge LaBerge Gene L. Description: is representative Description: This This exposure exposure is representative of the the intermediate intermediate volcanic volcanic rocks rocks ininMarathon MarathonCounty. County. The main rock rock type type iiss aa tuffaceous The main tuffaceous andesite andesite with with clasts c l a s t sabout about11 cm cm iinn diameter, diameter, but b u t .clasts c l a s t sup u p tot o10I 0cm cm long long are a r epresent present aa short short distance distanceupstream upstream from from the t h e bridge. bridge. Sandy Sandy textured "graywacke" isis interintertextured "graywacke" bedded withthe thet tuff bedded with u f f locally. locally. Exposures the pasture n the pasture to t o the the north north are are Exposures i in significantly s i g n i f i c a n t l ymore more siliceous siliceousthan thanthe t h eoutcrop outcropnear near the thebridge. bridge. Phenocrysts Phenocrysts of of plagioclase plagioclase and and hornblende hornblende aare r e vvisible i s i b l e in inplaces. places. The rock displays displays aa prominent prominentf ofoliation l i a t i o n and and llineation. i n e a t i o n . Foliation The rock Foliationand and layering appear to strike about N.85°E. Foliation layering appear t o s t r i k e about N.8s0â‚ Foliationdips dips600_8005. 60°-80° Lineation Lineation' consists consists of of elongation elongation ofofvolcanic volcanicclasts, c l a s t sextreme , extreme"smearing" "smearing" of of mafic mafic minerals plagioclase (Figure minerals and and boudinaged boudinaged plagioclase (Figure 1). 1 ) . Lineation Lineation dips dipsabout about50°E 50° in of foliation. in the the plane plane of f o l i a t i o n . South South of the theroad road exposures exposures along along the the creek creek are are dominantly mile south south along along the creek dominantlygraywacke. graywacke. Approximately Approximately one—half one-half mile creek are are, exposures deformed spectacularly deformedconglomerate. conglomerate. exposures of of aa spectacularly - 45 - �Theexposure exposurei sispart part of of a a large roof roof pendant pendant of volcanics, volcanics, and and Significance: The Siqnificance: exemplifies the type Rocks in in the exemplifies type of of deformation deformation within within the thependant. pendant. Rocks the immediate immediate area and elsewhere in in Marathon Countyhave haveaaconspicuous conspicuousmineral mineral lineation lineation and and area and elsewhere Marathon County boudinaged mineral grains. grains. Volcanic, boudinaged mineral Volcanic, plutonic plutonicand and sedimentary sedimentary rocks rocks are are lineated, suggesting of of thethe deformation post—dates suggesting that t h a t at a tleast l e a s part t part deformation post-dates emplacementofofthe the plutons. The The ffoliation o l i a t i o n and and lineations l i n e a t i o n shave have occurred occurred in in emplacement mappablezones zonest hthat have been beentraced traced ffor These features features mappable a t have o r more more than than 90 90 kms. kms. These are interpreted are interpreted to t o indicate indicatethat t h a the t thearea areahas hasbeen been subjected subjected to t o shearing shearing sstresses t r e s s e s and and tthat h a t the the stress s t r e s swas was taken taken up up along along shear shear zones zones in places, places, and and by pervasive pervasiveccataclasis by a t a c l a s i s iinn other other places. places. The llithologies hereand andt otothe the south southindicate indicate tthat The i t h o l o g i e s exposed exposed here h a t these these are are largely subaqueous volcanics. Welded Weldedr hrhyolitic largely subaqueous volcanics. y o l i t i c ttuffs, u f f s , flow flowbanded banded rrhyolites, hyolites, and lahars(not (notvvisited onthis this ttrip) and lahars i s i t e d on r i p ) indicate indicate that t h a t the the felsic f e l s i cvolcanics volcanics are are The other other supracrustal supracrustal rocks aatt least l e a s t partially p a r t i a l l y subaerial. subaerial. The rocks are a r e probably probably subaqueous,indicating indicating aa sizeable Middle basin in Central subaqueous, Middle Precambrian Precambrian basin Central Wisconsin. Lineated showing alignment and and boudinaging boudinaging of phenocrysts phenocrysts Lineated andesite showing ((the t h e black black lines on on the t h e 'shite white lensoidal lensoidal grains). grains). Note flote also the also the zones of f t and and right r i g h tmargins margins zones of more moreintense intensedeformation deformationnear nearl eleft bounding areas e s s deformation l e f t edge edge and and center photo). bounding areasofof lless deformation((left center of photo). - 46 - �Title: Title: - Little L i t t l eEau Eau Pleine Pleine River River Location: Location: N½, Sec. 31, T.26N. N'5, SW¼, SWi, SeC. T.26N., R.4E. R.4E. Marathon County, Marshfjeld Marathon County, Marshfield 15 15 minute quadrangle. minute quadrangle. (Get from Norbert Norbert Kolbeck, (Get permission permission from Kol beck, RRt. t . 2, 2, Auburndale, Auburndale, WI, MI, Box Box 148; 148; Phone Phone 715-384—8798.) 715-384-8798.) Author: Author: Gene L. LaBerge LaBerge Gene L. - — Gneiss. Gneiss. Description: in Description: Isolated Isolated blocks blocks ofofhigh highgrade grademetamorphic metamorphic rocks a r e present present in rocks are rocks rocks more more typically t y p i c a l l ymetamorphosed metamorphosed tto o greenschist facies. f a c i e s . This Thisexposure exposure represents aa small small block blockofofgneiss gneissand andmigmatite migmatitebounded bounded on on the t h e north northby by aa represents zone several hundred feet wide of ferruginous, sheared(?) quartz. zone several hundred f e e t wide ferruginous, sheared(?) quartz. Across Across the the valley rocks area rnon—foliated monzonites valleytot othe thesouth souththe the rocks e non-foliatedgranites g r a n i t eand s andquartz quartz monzonites that miles south intoi nWood l e a sseveral t several miles south t o WoodCounty. County. Other t h a textend extend ata tleast Other high highgrade grade junction metamorphic blocks an amphibolite amphibolite (metagabbro?) (metagabbro?) mass mass aatt the junction metamorphic blocks include an of contact with ofWis. Wis.Hwy. Hwy.97 97and andCTH—T CTH-T inin contact w i t h aarelatively r e l a t i v eunmetamorphosed l y unmetamorphosedultra— ultramafic major rock rock type type in in the area mafic rock. rock. The The major area is i s aa prominently prominently foliated f o l i a t e dquartz quartz diorite. diorite. This This exposure exposure is i s aa small small block block (lens?) ( l e n s ? )ofofhigh highgrade gradegneiss gneissofofapproximately approximately granodiorite migmatitei is present aatt the Some migmatite s present the western western end end of the the granodioritecomposition. composition. Some exposure. Small scale s c a l e folds folds are a r e relatively r e l a t i v e l coriinon y common in i nthe t h egneiss gneiss with w i t h near near exposure. Small horizontal horizontal fold foldaxes. axes. This This is i s ini ncontrast c o n t r a s t to t othe thenear near vertical v e r t i c a l fold foldaxes axes in in low rocks about about 33 miles miles northeast of low grade grade metasedimentary metasedimentary rocks of here. here. Thus, Thus, iitt isi s anomalous in metamorphic gradeand ands tstructurally with iits anomalous in metamorphic grade r u c t u r a l l y anomalous anomalous with t s surroundings. surroundings. - 47 - �An arcuate arcuate zone zone of of extremely extremelycomplex complex geology geology extends extends along along the the S i g n i f i c a n c e : An Significance: zonecconsists of aa wide wide vvariety The zone o n s i s t s of a r i e t y of of southern boundary boundary of o fMarathon MarathonCounty. County. The southern rock and metamorphic rock types, types, including i n c l u d i n gvolcanic, volcanic,plutonic, p l u t o n i sedimentary c , sedimentary and metamorphic rocks rocks Most ooff the t h e rocks rocks have have a a prominent prominent ffoliation o l i a t i o nand and w i t h no no apparent apparent pattern. p a t t e r n . Most with very different grade aare Rocks oof f very d i f f e r e n tmetamorphic metamorphic grade r e iinn contact c o n t a c t with with l i n e a t i o n . Rocks lineation. one as greenschist one another, another, such such as greenschist facies f a c i e s volcanics volcanics and and sediments sediments in i n contact contact Several ultramafic u l t r a m a f i c bodies bodies (probably (probably dunites) duni t e s ) w i t h gneisses gneisses and and amphibolites. amphiboli t e s . Several with shallow and andvvertical Both shallow e r t i c a l fold f o l daxes axes are a r e present, present, a r e present present in i nthe thezone. zone. Both are along with pervasiveccataclasis (andl olocal along w i t h aa pervasive a t a c l a s i s (and c a l r erecrystallization) c r y s t a l l i z a t i o n ) in i n plutonic plutonic rocks. rocks. The mixture The m i x t u r e of o f lithologies l i t h o l o g i eand s anddisparate d i s p a r a tmetamorphic e metamorphic grade grade in i na abroad broad zone suggestst etectonic zone ooff complex complex ' s•structure t r u c t u r e suggests c t o n i c mmixing i x i n g oof f tthe h e various various rock rock types. types. The area suggestive of o f aa megamelange, megamelange, w iwith t h a ar erelatively l a t i v e l y deep deep llevel e v e l in in The area iiss suggestive the the structure s t r u c t u r eexposed exposed along along the t h e southern southern part p a r tofo Marathon f MarathonCounty. County. Van Schmusand and Anderson (1977) dated gneisses west Van Schmus Anderson (1977) dated m i gmigmatitic m a t i t i c gneisses west o fofPPittsville ittsville The gneisses may The gneisses may be be the the (27 southoof (27 km km south f tthis h i s locality) l o c a l i t yat ) amore t morethan than2800 2800m.y. m.y. However, However, basement onwhich whicht the Middle Precambrian basement on h e Middle Precambrian vvolcanics o l canics were were deposited. the the structural s t r u c t u r a complexity l complexityalong alongthe t h southern e southernedge edgeofo Marathon f Marathon County County indicates indicates aa large-scale large-scale fault f a u l contact t c o n t a cbetween t between the t h e two two terranes. terranes. - - - j4 r I - M i g m a t i t i c gneiss gneiss characteristic c h a r a c t e r i s t i cofo the f t hhigh-grade e high-graderocks rocksexposed exposed Migmatitic along the the southern southernedge edge of o fMarathon Marathon County. County. along References : References: Van Schmus, 1977, Gneiss Gneiss and and Migmatite Migrnatite of o fArchean Archean Van Schmus,W.W.R.,R.,and andAnderson, Anderson,J .3. L., L., 1977, Age iinn the t h ePrecambrian Precambrian Basement Basement oof f Central Wisconsin: Wisconsin: Geology, Geology, vvol. o l . 5, 5, Age pp. 43-48. pp. 43-48. - 48 - �-- Ultramafic U l t r a m a f i c rocks. rocks. Title: T itle: Wild Creek, Creek,RRozeliville Wild ozellville Location: Ditch 1.5 miles D i t c h outcrop outcrop on on east e a s t side s i d e CTH—M CTH-M a t at t h ethe b r ibrink n k o foft hthe e hhill i l l 1.5 miles (Farmhouse d idirectly r e c t l y across across the the road road to t o the the south Rozellville. south oof f R o z e l l v i l l e . (Farmhouse W% corner, T.26N., R.4E., R.4E., Marathon Marathon County County. corner, Sec. Sec. 22, 22, T.26N., west.) west.) W¼ (Marshfield ( M a r s h f i e l d 15 15 minute minute quadrangle) quadrangle) Author: Author: Gene L. L. LaBerge Gene LaBerge The outcropcconsists The outcrop o n s i s t s pprimarily r i m a r i l y ooff a a talc-serpentine t a l c - s e r p e n t i n e rock. rock. Relict A chemical chemicalaanalysis n a l y s i s oof f tthis h i s rock rock R e l i c t olivine o l i v i n eisi svisible v i s i b lin e many i n manysamples. samples. A shows contains only o n l y 39.4 39.4 percent percent Si02, Si02, and and thus thus it i tprobably probably represents represents shows t hthat a t iitt contains intrusions I tisi sone oneofo fata least t l e a sfour t f o usuch r such i n t r u s i o nknown s knownalong along an an aaltered l t e r e d dunite. It Outcropsi in on tthe west sside and iin n tthe h e yyard a r d on h e west i d e ooff the t h e road road and n the the tthis h i s zone. zone. Outcrops creek creek tto o the t h e north n o r t h consist c o n s i s t of o fmafic m a f i cvolcanic v o l c a n i crocks rockswith w i t hpoorly p o o r l ypreserved preserved pillow Exposuresi nint the h e ffields ields p i l l o w structures s t r u c t u r e s indicating i n d i c a t i n g tops tops to t o the t h e south(?). south(?). Exposures quartzd diorite tto o the t h e southeast southeast a are r e a as tstrongly r o n g l y f ofoliated l i a t e d quartz i o r i t e ((tonalite) t o n a l i t e ) that that ( I tcontains c o n t a i n sbraided braided appears appears tto o be be aa relatively r e l a t i v e l yhighly h i g h lmetamorphosed y metamorphosed rock. (It Description: Description: zones zones ooff amphibolite a m p h i b o l i t e up up to t o several several feet f e ewide t widethat t h amay t mayhave havebeen beenproduced produced by by Similar metamorphism shear zones metamorphism of of shear zones i n in t h ethe q uquarz a r p . d idiorite.) orjte.) S i m i l a r quartz quartz ddiorite iorite t h ~area sarea and and is i sassociated associated with with and amphibolite uunderlie and amphibolite n d e r l i e at a t least l e a s t50 50km km iinn this the gneiss exposed at the previous stop. the gneiss exposed a t t h e previous The aaxis xis F o l i a t i o n in i nthis t h i sarea areatrends trendsN.6O°W. N . ~ o O W . and i p s vvertically. e r t i c a l l y . The Foliation andddips plungesv vertically ooff aa minor minor fold f o l dexposed exposed1.2 1.2km kmnorth n o r t halong alongCTH—M CTH-M plunges e r t i c a l l y and and would would suggest rright suggest i g h t lateral l a t e r amovement. l movement. - 49 - �This This and and oother t h e r ultramafic u l t r a m a f i c rocks rocks occur occur along along a a zone zone ooff strongly strongly foliated f o l i a t e d rocks rocks of o f highly h i g h l yvariable v a r i a b l ecomposition. composition. The rocks to The vvolcanic o l c a n i c rocks t o the the north n o r t h are are believed b e l i e v e d tto o be be ppart a r t of of the t h e greenschist g r e e n s c h i s t facies f a c i e s terrane t e r r a n e present present in in most ooff Marathon The f foliated o l i a t e d and and rrecrystallized e c r y s t a l l i z e d tonalites, t o n a l i t e s , quartz quartz most Marathon County. County. The monzonitesand andgneisses gneissest otot hthe southappear appeart otobe beppart e south a r t ooff aa higher h i g h e r grade grade monzonites Significance: Significance: metamorphict eterrahe metamorphic r r a n e t to o tthe h e south. south. However, However, llargely a r g e l yundeformed undefomed (and (and unmetamorphosed?) presentseveral several km unmetamorphosed?) p l uplutons t o n s a rare e present km tto o the t h e southwest southwest ini nWood Wood County, andr erelatively mafic vvolcanic County, and l a t i v e l y low l o w grade grade mafic o l c a n i c rrocks o c k s aare r e aalso l s o present p r e s e n t in in places. Therefore, Therefore, there t h e r e exists e x i s t s here hereaacomplex complex zone zone ooff mixed mixed rrock o c k types, types, which betweent hthe which bbasically a s i c a l l y mark mark tthe h e boundary boundary between e g rgreenschist e e n s c h i s t f afades c i e s tterrane e r r a n e in in MarathonCounty Countyand anda ah ihigher gradet eterrane do nnot Marathon g h e r grade r r a n e tto o the t h e south. south. We We do o t know know the the agesoof anyoof rocks, except ages f any f tthe h e rocks, except tthat h a t all a l lhave have been been interpreted i n t e r p r e t e d to t obe be Middle Middle Precambrian. - SQ - rkinko!J � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1980 Description An account of the resource Institute on Lake Superior Geology. University of Wisconsin, Eau Claire, Wisconsin. May 6-10, 1980. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1980 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/120e905556b72cb3b85c97724adc63b1.pdf f816fd7a26d0eab0f8140bc1a62bda1b PDF Text Text A BSTRACTS a PROCEEDINGS Twenty Seventh Annual Meeting INSTITUTE ON LAKE SUPERIOR GEOLOGY HELD AT THE KELLOGG CENTER MICHIGAN STATE UNIVERSITY EAST LANSING MICHIGAN MAY 14-15, 1981 �Award Guidelines SAM GOLDICH MEDAL Preamble The Institute on Lake Superior Geology was born on or around 1955, as documented by the fact that the 27th annual meeting will be held in 1981. The Institutes are exemplory in their continuing objectives of dealing with those aspects of geology that are related geographically to Lake Superioq of encouraging the discussion of subjects and sponsoring field trips which will bring together geologists from the academia, government surveys, and industry; and of maintaining an exceedingly informal but highly effective mode of operation. During the course of its existence the membership of the Institute (that is, those geologists who indicate an interest in the objectives of the LL.S.G. by attending) has become aware of the fact that certain of their colleagues have made particularly noteworthy and meritorious contributions to the improvement of understanding of "Lake Superior" geology and its mineral deposits. The exemplory award was made by LL.S.G. to Sam Goldich in 1979 for his many contributions to the geology of the region extending over about 50 years. Award Guidelines I) The medal shall be awarded annually by the Board of Directors, I.L.S.G., to a geologist whose name is associated with a substantial sustained interest in, or a major contribution to, the geology of the Lake Superior Region. 2) The Board of Directors, LL.S.G. shall appoint the Nominating Committee. Their annual nominee will be voted on at the annual business meeting. The initial appointment will be of three members, one to serve for three years, one for two, and one for one year, the member with the briefest incumbency to be chairman. After the first year the Board of Directors shall appoint at each spring meeting one new member who will serve for three years. In the third year this member shall be the chairman. The Committee membership should reflect the main fields of interest and geographic distribution of l.L.S.G. membership. 3) The Goldich Medal Nominating Committee shall select the medalist and will make its recommendation to the Board of Directors by November 1 of that year. 4) The Board of Directors normally will accept the nominee of the Comittee, will inform the medalist immediately, and will have one medal engraved appropriately for presentation at the May meeting. 5) It is recommended that the Institute set aside annually from whatever sources, such funds as will be required to support the continuing costs of this award. April 4, 1981 J. Kalliokoski, Chairman Bill Cannon Fred Kehlenbeck Glenn Morey Greg Mursky �ABSTRACTS and PROCEEDINGS Twenty Seventh Annual Meeting INSTITUTE ON LAKE SUPERIOR GEOLOGY I-bid at The Kellogg Center Michigan State Lhiversity East Lansing, Michigan May 14- 15, 1981 Sponsored by DEPARTMENT OF GEOLOGY, MICHIGAN STATE UNIVERSITY East Lansing, Michigan and MICHIGAN DEPARTMENT OF NATURAL RESOURCES, GEOLOGICAL SURVEY Lansing, Michigan F. W. Cambray, B. K. Parker, R. C. Reed, 3. W. Trow, T. A. Vogel 3. T. Wilband and S. E. Wilson Editors Gerraid Bennett Field Trip Coordinator and Director MINISTRY OF NATURAL RESOURCES, SAULTE STE. MARIE MINING DIVISION Saulte Ste. Marie, Ontario ��Thursday May 14, 1981 Session Chairpersons S. S. Goldrich and C. Laberge 1:30 to 1:50 1:50 to 2:10 2:10 to 2:30 A GEOCHEMICAL RECONNAISSANCE STUDY OF GROUNDWATER FROM AN EIGHTEEN COUNTY AREA OF NORTHWESTERN OHIO Mohr, Eileen T., Deering, Mark F., and Carlson, Ernest H. THE DISTRIBUTION OF LITHIUM, RUBIDIUM AND CESIUM IN LAKE MUDS NORTH OF LAKE SUPERIOR M. A. Vos and R. 3. Stevenato THE SIGNIFICANCE OF THE DISTRIBUTION OF CLASTIC LENSES WITHIN THE NEGAUNEE IRON FORMATION AT THE EASTERN END OF THE 2:30 to 3:00 3:00 to 3:20 3:20 to 3:40 PALMER BASIN, MARQUETTE SYNCLINORIUM, NORTHERN MICHIGAN *Mark S. Breithart and F. William Cambray Coffee Break PRELIMINARY ASSESSMENT OF RARE EARTH ELEMENT GEOCHEMISTRY OF VARIOUS IRON FORMATIONS OF THE LAKE SUPERIOR DISTRICT Elaine L. Slaughter, Susan E. Tituskiri, and John T. Wilband LITHOLOGIC AND SEDIMENTOLOCIC CHARACTERISTICS OF THE COPPER HARBOR CONGLOMERATE, NONESUCH SHALE AND FREDA SANOSTONE FORMATIONS OF NORTHERN MICHIGAN AND WISCONSIN Paul A. Daniels, Jr. 3:40 to 4:00 THE ROLE OF HYDROTHERMAL ALTERATION AND TECTONISM IN 4:00 to 4:20 WISCONSIN MOLYBDENITE OCCURRENCES 3. K. Greenberg RETROGRADE PREHNITE-PUMPELLYITE FACIES METAMORPHISM IN THE SOUTHERN VERMILION GRANITIC COMPLEX, NORTHERN MINNESOTA Robert L. Bauer 6:00 pm 7d30 pm Cash Bar Banquet Big TenRoorn Big Ten Room POST PRANDIAL Presentation of the Sam Goldich Medal by Dr. Samuel S. Goldich to Dr. Carl E. Ijutton ADDRESS by F. B. Van 1-buten entitled PHANEROZOIC OOLITIC IRONSTONE - A FACES MODEL (See abstract by F.B. Van Houten and D. Bhattacharyya) �Friday May 15, 198! Session Chairpersons 3. 1. Wilband and C. Anderson Coffee will be available from 8J0 a.m. 8:20 to 9:20 9:20 to 9:30 9:30 to 9:50 9:50 to 10:10 10:10 to 10:30 10:30 to 11:00 11:00 to 11:20 Decade of North American Geology - Open Discussion break WISCONSIN GRAVITY BASE STATION NET WORK--! 980 C. Patrick Ervin PALEOMAGNETISM OF THE MEMESAGEMASING AND CARIBOU LAKES NORITES, GRENVILLE PROVINCE, ONTARIO * S. Dey, D. T. A. Symons, and M. Stupavsky GEOPHYSICAL INVESTIGATIONS OF THE SLATE iSLANDS CRYPTOEXPLOSION STRUCTURE M. E. Bengtson, and R. P. Meyer, H. C. Halls, and 3. I-I. Karl, and D. Dushek Coffee Break JOINT ORIENTATION ANALYSIS IN THE NORTHERN MICI-{ICAN BASIN Timothy B. 1—blst 11:20 to 11:40 I 1:40 to 12:00 IMPACT AS A POSSIBLE ORIGIN FOR SUBSIDED BASINS Jack B. Hartung PRELIMINARY RESULTS OFA GRAVITY SURVEY IN THE EASTERN HALF OF THE IRON RIVER-CRYSTAL FALLS DISTRICT, IRON COUNTY, MICHIGAN * D. R. Paddock, K. Fujita, F. W. Cambray, and H. F. Bennett 12:00 Lunch 5ession Chairpersons Friday afternoon 3. W. Trow and 3. 3. Mancuso 1:30 to 1:50 SUBAQUEOUS PYROCLASTIC FLOW DEPOSITS IN THE VICINITY OF THE HELEN MINE, WAWA, ONTARIO Mark Osterberg and R. L. Morton 1:50 to 2:10 PRE- AND POST-DORE SEQUENCES IN THE WAWA VOLCANIC BELT, ONTARIO 2:10 to 2:30 2:30 to 3:00 3:00 to 3:20 3:20 to 3:40 K. Attoh PETROGENETIC MODELS OF KEWEENAWAN BASALTIC ROCKS, UPPER MICHIGAN John T. Wilband and Pipob Wasuwanich Coffee Break PETROCHEMISTRY AND STRUCTURE OF THE MIDDLE PROTEROZOIC SUCCESSION, HURLEY-TO-MINONG, KEWEENAWAN VOLCANIC WISCONSIN * Hassan Au and Campbell Craddock EARLY PROTEROZOIC GABBROIC, DIORITIC, AND QUARTZ MONZONITIC INTRUSIONS IN THE MINNESOTA RIVER VALLEY: PETROLOGY AND SIGNIFICANCE 3:40 to 4:00 M. Dewitt Daggett THE PETROLOGY AND PETROGENESIS OF THE GAMITAGAMA IGNEOUS COMPLEX, WAWA, NORTHERN ONTARIO * Abdul Choudhry and T. E. Smith �27th Annual INSTITUTE ON LAKE SUPERIOR GEOLOGY Annual Banquet PHANEROZOIC OOLITIC IRONSTONE - A FACIES MODEL Address by delivered by F. B. Van 1—buten (Abstract by Van Houten & D. Bhattacharyya follows) �PHANEROZOIC OOLITIC IRONSTONE - A FADES MODEL F. B. Van Houten and D. Bhattacharyya Department of Geological and Geophysical Sciences, Princeton University Princeton, New Jersey 08544 Almost all of the Phanerozoic ferric oxide-chamosite oolitic ironstones are associated with detrital aeposits that accumulated in low energy, nearshore marine environments, commonly along a broadly embayed coastline. Processes and products were like those on the chenier coast of southwestern Louisiana and the front of the low-energy, wave-dominated Rhone Delta. There were no well-developed tidal features or large, well-winnowed shoreface sandbodies. A subdued, deeply weathered source supplied mature fine-grained sediment composed mostly of quartz, kaolinite, and iron and aluminum oxide. The detrital deposits are arranged in a of asymmetrical, upwardshoaling sequences produced by small- scale Ferruginous ooids formed on detritus-starved mudflats that supported abundant micro-organisms and burrowers. These sites were either mudflats along microtidal coasts protected by breaker bars remote from a prograding delta, or on delta-front and interd istributary coastal flats following delta abandonment. Most of the plastic ooids were carried from their place of origin by coastal currents, and in aecreting, cross-bedded Repeated interruptions in concentrated bars. accumulation of ooids permitted increased burrowing that commonly destroyed the bedding fabric, as well as precipitation of ferric oxide cement. Locally, lapses in bar building led marine mud. to deposition of laminated succession regressions. Each sequence commenced with muddy open shelf deposits locally associated with bioclastic debris, and culminated in either a prograding front of a small delta or a shoreline complex of bars anc lagoons. Waning of cietrital influx was accompanied by development of abundant Commonly ooid bars graded laterally or were succeeded by a thin ferruginous phosphatic intraclast lag deposit developed when waves ana currents of renewed transgression encroached on the detritus-starved mudflats and crests of ooid bars. Each mound of ooids and associated lag deposit was then buried by marine mud into, ooids. that accumulated during an early stage of rapid transgression and renewed supply of Specific control of the prograding sequences has not been established in many sediment. Some may reflect diversion of a major river to a more distant part of the cases. coastal plain while the abandoned muddy shelf continued to subside and was inundated by renewed transgression. Other sequences may reflect more regional control such as tectonic pulses of subsidence or repeated eustatic rise of sealevel. This facies model emphasizes the role of repeated upward-shaling sequences, of abrupt waning of sediment supply, and of renewed rapid rise of sea level as the local framework of accumulation of most oolitic ironstones. A similar sequence of fades dominated the less common development of oolitic ironstone along carbonate coasts. Within this framework both the iron-rich oolites and associated phosphatic intraclast lenses developed at or near the lithofacies discordance between successive sequences. �INSTITUTE ON LAKE SUPERIOR GEOLOGY Annual Goldich Medal Award for 1981 Will be presented to Carl E. Dutton at the Banquet Thursday evening Dr. Carl E. Dutton was born in Dunkirk, Ohio on January 24th 1904. He receivea his B.A. from DePauw University in 1926, his M.A. from the University of Illinois in 1928 and his Ph.D. from the University of Minnesota in 1931. He was a teaching assistant at the University of illinois, an Instructor at Minnesota and an Assistant Professor at Wayne State University and The University of Michigan. He jointed the U.S. Geological Survey in 1943, becoming regional geologist in 1948 and Research Geologist in 1962 and has been based in Madison, Wisconsin where he participated in the Mineral Resources Cooperative Program of the Wisconsin Geological and Natural History Survey and the USGS in addition to teaching some classes at the University. Carl Dutton has had a lifelong interest in the geology of the Precambrian, and particularly in the Great Lakes area. He is widely regarded as an authority on iron formations, he has served on the United Nations Committee on Iron Resources in Geneva in 1953-54 and studied iron ore deposits in Yugoslovia with the AID program in 1961. He is perhaps best known to us for his work in the Menominee District of Michigan and Wisconsin (USGS Prof. Paper 573 and Map 1-466, the Cuycera District, Minnesota (USGS Maps MF-99 & ME 181 the Iron River, Crystal Falls District, Michigan) (USGS Prof. Paper 570 & Map MF-225 and for his series of lithologic, geophysical and mineral commodity maps of the Precambrian Rocks of Wisconsin (USGS Map 1-631). He has written many other papers and particularly field guide books which have opened an understanding of the region for those of us who now try to follow in his footsteps. The members of the Institute are proud to recognize the achievements of one of their distinguished colleagues in the awarding of the 1981 Sam Goldich Medal to Dr. Carl E. Dutton. ��PRE- AND POST-DORE SEQUENCES IN THE WAWA VOLCANIC BELT, ONTARIO K. Attoh Hope College I-blland, Michigan 49423 An unconformity at the base of Dor Fm and equivalent sedimentary rocks marks a significant stratigraphic break on the basis of which the volcanic-sedimentary succession in the Wawa greenstone belt can be subdivided into pre- and post-Dor Sequences. The pre-Dor Sequence includes at least two cycles of mafic-felsic containing iron volcanism, each an formation unit, but only the lower mafic-felsic volcanic cycle which is terminated by an extersive siderite deposit completely preserved. Two post-Dore' Sequences have been identifiea; an older Sequence represented by a mafic flow unit, which directly overlies sedimen tary rocks equivalent to the Doré and a younger Sequence, which is structurally discordant with the underlying rnafic fLOW, is characterized by a distinct b reccia unit interpreted as a debris flaw. Post-Dora' Sequences do not contain iron formation is units. �RETROGRADE PRLHNITE-PUMPELLYITE FACIES METAMORPHISM IN THE SOUTHERN VERMILION GRANITIC COMPLEX, NORTHERN MINNESOTA Robert L. Bauer Department of Geology, Macalester College, and Minnesota Geological Survey St. Paub Minnesota 55105 Regional prehnite-pumpellyite metamorphism (M2) overprinted fades middle Most previous studies describing prehnite in biotite do not ascribe this lenses amphibolite facies (Ml) assemblages in the rocks of the southern Vermilion Granitic occurrence to reactions involving biotite, Complex, but pta-dated dynamic metamorphism associated with (M3) strike-slip displacement on the Vermilion prehnite components along biotite cleavage fault. The M2 event is defined on the basis of the occurrence of various combinations the prehnite, of Ca-Al silicates, pumpellyite, epidote, and grandite garnet along with chlorite, adularia, albite, sericite, sphene, i. calcite in the biotite schists, lamprophryes, and granitic rocks exposed in the area. The M2 phases may pervade a given sample, but are more commonly concentrated adjacent to thin quartz or adularia veins or fractures in the but rather to the introduction of all the traces. Observations made during the present study, including the albitization of plagioclase and the occurrence of prehnite, adularia, and sphene within a single chlorite pseudomorph after biotite, are consistent with following prehnite-forming the reaction: anorthite (component) + biotite + H20 = prehnite + chlorite + adularia + sphene sericite aligned parallel to the cleavage traces in The other Ca-At silicates occuring as lenses in biotite or chlorite may also have formed by similar reactions involving the breakdown of biotite. has a similar mode of occurrence, but also occurs in thin veins ± prehnite. M2 epidote and rare pumpellyite may occur as lenses in biotite or chlorite, but are more commonly associated with sericite or rare calcite as alteration products of plagioclase. M2 stability of the Ca-Al silicates indicate a rocks. The prehnite and grandite occur most commonly as lenses or barrel-shaped grains biotite or chlorite after biotite. Adularia No regional variations in the observed assemblages have been found which might indicate systematic spatial variations in the conditions of M2 metamorphism. Comparison of the coexisting mineral assemblages with experimental data on the occurs as fine-grained granular clusters in chlorite after biotite and is pseudomorphic after rutile needles in probable range of conditions for the metamorphism of 250 to 350 degrees chlorite in some of the lamprophyres. P(H20) = P(total). sphene centigrade and 2 to 4 kilobars at P(fluid) = �GEOPHYSICAL INVESTIGATIONS OF THE SLATE ISLANDS CRYPTOEXPLOSION STRUCTURE M. E. Bengtson, and R. P. Meyer Geophysical and Polar Research Center, Department of Geology and Geophysics University of Wisconsin, Madison, Wisconsin 53706 H. C Halls Department of Geology, Erindale College, University of Toronto Mississauga, Ontario, Canada L5L 1C6 3. H. Karl, and D. Dushek Department of Physics and Astronomy, University of Wisconsin Oshkosh, Wisconsin 54901 A survey of the underwater crater area (defined by an irregular arcuate bathymetric rise) surrounding the Slate Islands of northern Lake Superior is now nearly complete. A close order aeromagnetic survey (l000yd spacing, 425m above lake level) and a set of marine magnetic and high resolution 3.5kc bottom and subbottom profiles taken under flight lines has been acquired. These have revealed several short wavelength anomalies on the east side of the islands. The sources of these anomalies appear to be 1/2 km to 1 km below lake level and none seem to have any bathymetric expression. To the west a longer wavelength anomaly trending NW-SE This feature correlates predicted contact. The islands about a roughly defined arcuate magnetic high. Short wavelength has been delineated. with a igneous-sedimentary seem to be centered well previously anomalies have been found over the islands. A set of marine refraction and reflection records was also obtained. Data was recorded digtally. Large thicknessess (Up to I km) of a '-'3.5km/sec layer underlaid by a —5.5km/sec refractor have been detected exterior to the crater. Inside the crater rim, the 3.5km/sec layer is absent. Here, only a 4.8km/sec refractor, lying directly beneath recent sediments, has been detected. All layers appear to have a gentle southerly dip. �THE SIGNIFICANCE OF THE DISTRIBUTION OF CLASTIC LENSES WITHIN THE NEGAUNEE IRON FORMATION AT THE EASTERN END OF THE PALMER BASIN, MARQUETTE SYNCLINORIUM, NORTHERN MICHIGAN * Mark S. Breithart and F. William Cambray Department of Geology, 206 Natural Science, Michigan State University East Lansing, Michigan 48824 The vertical and horizontal distribution of clastics found within the Negaunee Iron Formation in the eastern end of the Palmer Basin, T47N-R26W sections 26, 27, and 28, was studied to determine the geometry of the region at the time of deposition of the sediments. Previous work by Gair (1975), Davis (1965) and Mengel (1956) has suggested that a relict sedimentary Their conclusions were based upon and textural qualitative sedimentars' descriptions. This study has attempted to test this concept with a quantitative approach based upon the vertical and the Palmer Basin is basin. horizontal variation in amount, type, and grain size of clastics observed in the subsurface. The data indicates that the earlier models are correct and that the Palmer Basin is a relict sedimentary basin. The Palmer Basin is located on the south limit of the Marquette synclinorium in the Upper Peninsula of Michigan. It contains over 2,000 feet of middle Proterozoic age sediments and has been down-faulted along the E-W trending Palmer Fauilt relative to the main synclinorium. This study utilized 84,000 feet of core made available by the Cleveland-Cliffs Iron Company. two main The clastics were divided into matrix composition (chloritic vs. iron oxide). The size distribution was divided into coarse (1.05 ± .l5), medium (1.82 + .28) and fine (2.80 + types based upon .46 ':0. From petrographic analysis of over IOU thin sections of the clastics could best be * Presentation eligible Award for the Student classified as immature sediments of the lithic-quartz wacke clan. The quartz is subangular and is supported by a variable matrix of chlorite and iron oxides with minor cryptocrystalline quartz (chert) and carbonate. The majority of lithic fragments were either rounded chert or chloritic clasts. Feldspar was rarely noted. Most bedding contacts between clastics and iron formation are sharp. The vertical and horizontal variation indicates that: 1) the south margin of the Palmer Basin has a consistently higher percentage of coarse clastics with a chioritic type matrix dominating, 2) depositional centers of clastics varied with vertical position throughout the basin, and 3) the source areas for the clastics is indicated to be to the SW, S or SE. All of this supports the idea of the Palmer Basin being a relict sedimentary basin. The best model for the deposition of the sediments is one involving mass flows and/or submarine fans with migrating feeder channels and depositional centers. This would account for the high percentage of matrix, the immaturity of grains, the wide horizontal and vertical distribution and the sharp bedding contacts. A source area for the clastics low in feldspar is also inferred. The pattern is consistent with the concept of a basin which was progressively subsiding during deposition. The periodic supply of clastics by mass flow being controlled disturbances by perhaps associated with fault movements controlling the subsidence. �MIDDLE PROTEKOZOIC DEFORMATION IN NORTHERN AND CENTRAL WISCONSIN B. A. Brown and .1 K. Greenberg Wisconsin Geological and Natural History Survey, 1815 University Avenue Madison, Wisconsin 53706 Recent mapping and compilation by the Wisconsin Geological Survey has pointed out the compelling need for reinterpretation of the Proterozoic tectonic history of northern and central Wisconsin. Tectonic structures observed in this region were predominantly formed during the Penokean deformationM event, and have been modified locally and possibly on a regional scale by later events. In central Wisconsin, the Wolf River granitic complex of 1500 m.y. age represents a major plutonic event, covering over 3600 km2. A plutonic event of this magnitude would be expected to produce at least locally intense deformation as well as thermal metamorphism. Mapping in the Wisconsin Northeast sheet (Greenberg and Brown, revealed has 1980) metamorphic and deformational various features associated with the Wolf River complex, including: amphibolite-grade (I) metamorphism and intense folding near the northern margin of the Wolf River complex Langlade in and Lincoln Counties; (2) recrystallization and refoliation of the 1850 granitic complex Athelstane in southwestern Marinette County; (3) thermal metamorphism in the Mountain (Lahr, 1972) m.y. and Thunder Mountain areas; (4) crenulation and chevron folding of metavolcanic rocks in the Mountain area where earlier fabrics impinge at high angles to the granite's contact; tectonic reorientation in (5) Marathon and Portage Counties, as shown by (6) intense aeromagnetic trends; deformation observed in metavolcanic units caught between the Wolf River complex and major Penokean pluton in Marathon County (LaBerye, 1980). a eastern Deformation related to the emplacement of the Wolf River complex is restricted to the rocks south of the major structural boundary proposed by Brown and Greenberg (1980) and Greenberg and Brown (1980). Structures to the north of this boundary trend to the northeast in Lincoln County, gradually arching eastward until trends are east-west to slightly southeast in central Marinette County. In south-central Wisconsin, broad, open folding is preserved in widely scattered exposures of quartzite and underlying 1760 m.y. old rhyolites. If the interpretation of Dott and DaIziel (1972) is correct, and the quartzites are correlative over a wide area, considerable strain has been superimposed on the basement rocks of central Wisconsin the 1760 m.y. plutonic-volcanic episode, and the intrusion of the 1500 m.y. anorogenic Wolf River complex. Deformation appears to increase in intensity between from west to east. This is exhibited in contrasting modification minor the of the Sioux structural and Barron quartzites (west) with the obvious folding and metamorphism evident in McCaslin, Thunder Mountain, Baraboo, and Waterloo quartzites (east). The deformation is closely related in time to the resetting of Rb-Sr ages (1600 n.y.) observed widely in northcentral Wisconsin (Van Schmus, 1980; Sims and Peterman, 1980). The 1500 m.y. intrusive episode itself may be envisioned as a result of the 1600 m.y. event, just prior to (and during?) intrusion. Confirmed Archean rocks are known only in northernmost Wisconsin and as limitea exposures Proterozoic surrounded rocks in intruded by and Central Wisconsin. Current data indicate no Archean rocks exposed in the main part of the Proterozoic belt. volcanic The complexity of deformation observed in this belt is probably due to multiple deformation and intrusion during the Penokean event, with local, and possibly widespread overprinting by younger events at 1600 m.y. and associated with the 1500 m.y. Wolf River complex. The apparent absence of Archean ages in the volcanic belt of northeastern Wisconsin better supports this interpretation than alternatic'e interpretations which appeal to Penokean deformation overprinting Archean structures in this region. �THE PETROLOGY AND PETROGENESIS OF THE GAMITAGAMA IGNEOUS COMPLEX, WAWA, NORTHERN ONTARIO * Abdul Choudhry and T. E. Smith Department of Geology Windsor, Ontario, Canada, N9B 3P4 The Gamitagama Lake Complex is a plug-shaped, elliptical gabbroic complex of orthopyroxene Archean the respective parent magmas, at pressures less than 5 Kb, to give calc-alkalic differentiation trends within each series. age (Rb/Sr 2642 Ma), approximately 7 x 10 km in dimensions. It outcrops in the metasedimentarymetavolcanic rocks of the Shebandowan Greenstone Belt of the Superior Province, clinopyroxene + + titaniferous magnetite, crystallized out of Many of the rocks of the complex are cumulative in origin, and their major and approximately 40 km south of Wawa. trace Five intrusive phases are recognized in the complex, four of which are subalkaline. They include an olivine- bearing representative of the liquid line of descent. However, their incompatible element contents may be compared to those of other complexes considered to be cumulate rocks produced during calc-alkaline fractionation. The most basic rocks of each discrete, intrusive event are successively less basic in composition indicating that fractionation inner gabbroic series, partly surrounded by a middle zone of less basic, gabbroic rocks, and an outer group of dioritic rocks. The dioritic group includes hornblende- gabbro, diorite, quartzdiorite, quartzmonzodi orite, and tonalite. Arcuate outcrops of leucocratic granodiorite and granite occur within the diorite zone. The granites and diorites are cut by a large dyke- like body of quartz- monzonite which has alkaline affinities. In the olivine- bearing inner gabbroic series, olivine gabbronorite and gabbronorite dominate, and troctolite, norite, and andesine anorthosite are subordinate. In the middle zone of gabbroic rocks, gabbronorite and amphibole gabbronorite occur with lesser amounts of narita and pyroxene diorite. Late dykes of fine- grained gabbroic rocks with porphyritic amphibole and phlogopite intrude the inner and outer gabbroic series. the inner qabbroic series olivine + + titaniferous magnetite + clinopyroxene + orthopyroxene, and in the In plagioclase eligible for the chemistry Student is not occurring in the source magma chamber, at deeper levels. The late fine-grained gabbroic intrusions in the was complex contain amphibole and phlogopite phenocrysts. This suggests that the differentiation was controlled by the separation of amphibole and phiogopite at more than 10Kb pressure ("-'35 km depth). The complex is compared to several well described hornblende-beari ng gabbroic plutons occurring in the Cordilleran batholiths of North and South America. It is concluded that the Gamitagama Complex is most similar to the Guadalupe Complex in California. Within the Gamitagama Complex there is a complete range of rock types from troctolites, through amphibole gabbros and diorites, to quartz-diorites and granitoid rocks. It is considered to represent an excellent illustration of the fractionation of gabbroic ultimately yield granitoid rocks. middle gabbroic series plagioclase + * Presentation Award element melts to �EARLY PROTEROZOIC GAbI3ROIC, DIORITIC, AND QUARTZ MONZONITIC INTRUSIONS IN THE MINNESOTA RIVER VALLEY: PETROLOGY AND SIGNIFICANCE M. DeWitt Daggett Minnesota Geological Survey, University of Minnesota, St. Paul, MN 55108 present address, Noranda Exploration, Inc., Cobalt, ID 83229 Three, small, early Proterozoic plutons intrude the Archean gneiss terrane of the Minnesota River Valley south of Franklin, Redwood County, Minnesota. The largest is the Cedar Mountain Complex, a composite intrusion consisting of a chilled margin of diabase and microgabbro, a main body of flow-layered hornblende diorite, and a quartz monzonite core. This complex is 600 meters in diameter. Two smaller plugs consisting of 1) diabase and gabbro, and 2) granodiorite, crop out five kilometers east of Cedar Mountain. Cross cutting and orthoclase in diabase indicate that the parent melt was potassic. Assimilation of sialic crust during magma intrusion affected the final mineralogies chemistries of and the Franklin-area plugs. Xenoliths of Archean yneiss occur throughout the Cedar Mountain diorite and the gabbro plug to the east; emplacement of the plugs to a fairly shallow depth proceeded in part by stoping of the country rock. from these rocks suggest that the dioritic, These early Proterozoic intrusives may a part of a limited but widespread shallow level igneous event which occurred in the southern Lake Superior region about 1,760 m.y. ago. The Minnesota River Valley plugs are lithologically somewhat similar to the Fox River rhyolites and related granites of south-central Wisconsin, and to the granodioritic, and differentiated from monzonitic melts common gabbroic Amberg quartz monzonite and related intrusions of northeast Wisconsin. These parent magma by fractional crystallization rocks all occur as small, isolated, epizonal clinopyroxene, of olivine, and calcic plagioclase. Feldspar compositions range continuously from An80 in diabase and gabbro to An2 in quartz monzonite. Olivine in the diabase is Fo53 to Fo6. Clinopyroxene from diabase, gabbro, and intrusions or extrusive flows; they all possess a calc-alkaline chemical character. The presence of rare rhyolite clasts in conglomerate units of the middle-Proterozoic Sioux quartzite indicates the former existence of additional similar rocks in Minnesota. relationships between rock types identify three distinct stages of intrusion: l)gabbro, 2)diorite and granodiorite, and 3) quartz rnonzonite. Petrographic and mineral chemistry data a hornblende diorite is diopside or diopsidic The restricted range of augite. clinopyroxene compositions and the lack of iron enrichment trend for an overall clinopyroxene phenocrysts are evidence for melt with calc-alkaline original an affinities. High modal abundances of biotite be This 1,760 m.y. old igneous event followed the Penokean orogeny but preceded the more voluminous igneous activity which accompanied crustal extension in middleand late-Proterozoic time. �LITHOLOGIC AND SEDIMENTOLOGIC CHARACTERISTICS OF THE COPPER HARBOR CONGLOMERATE, NONESUCH SHALE AND FREDA SANDSTONE FORMATIONS OF NORTHERN MICHIGAN AND WISCONSIN Paul A. Daniels, 3r., Hunt Energy Corporation, Lansing, Michigan The Keweenawan Age Copper Harbor Interfingering with the Copper Harbor Conglomerate, Nonesuch (Shale) Formation, Conglomerate is the Nonesuch (Shale) Formation, an unoxidized sequence of gray-black siltstone, shale, and sandstone and Freda Sandstone formations comprise the Oronto Group and are found in outcrop over some 200 kilometers in northern western Upper Michigan. These formations are part of a volcanic-elastic sequence created in response to the formation of the Midcontinent Rift System. Although intercalated volcanics are found in the lower one-third of this group, the sedimentary depositional regime was dominant. Along the Keweenaw Peninsula three paleocurrent indicators for all formations show that the predominant paleoflow directions were generally in northerly directions. In contrast, sedimentary structures in the Copper Wisconsin and Harbor Conglomerate on the opposite side of the rift (i.e., Isle Royale) indicate stream flow was to the south and east. Harbor Depositionally, the Copper Conglomerate is a basinward-thickening of volcanogenic clastics wedge and subordinate volcanics that decreases in average grain-size upsection. Various facies comprise the Copper Harbor and these have interpreted collectively been as representing a prograding alluvial fan complex. Maximum thickness is on the with a maximum thickness of 215 meters. The Nonesuch contrasts with the redbed sequences, both above and below, by: 1) having been deposited in a reducing environment, 2) increased textural maturity, and 3) hydrocarbon, sulfide and chlorite content. The Nonesuch is interpreted as having been deposited in a rift-flanking lacustrine environment of varying depth. Initiation of lacustrine conditions probably occurred through disruption of existing drainages by alluvial, volcanic, and/or tectonic processes. As with the underlying Copper Harbor, a gradational contact exists with the overlying Freda Sandstone. The Freda Sandstone is a ferruginous, lithic sequence of cyclic sandstone and exceeding 3660 meters in maximum thickness. Although similar in appearance to some sandstones of the mudstone Copper Harbor Conglomerate, the Freda, overall, is of greater compositional maturity conglomerate facies are uncommon. The Freda is dominantly fluvial in origin and appears to have "overridden" the Nonesuch and environments. clast-supported and comprised of volcanic clasts with an overall compositional ratio of mafic to silicic plus intermediate clasts of about 2:1. The heavy-mineral suite for the Copper Harbor (as well as for the Nonesuch and Freda) mainly consists of ilmenite plus Although complex in detail, the overall depositional model for the three formations is one of siomple transgressive-regressive relationships between alluvial fan/ lacustrine/ fluvial environments (Elmore and Daniel; 1980b). Important aspects of such a model are that: I) all the formations are genetically related with no major unconformities between them, and 2) the intervening Nonesuch Formation is, at least in part, equivalent in age to the upper similar opaque minerals, and epidote. Copper Harbor and the lower Freda. order of 1830 meters. Principal lithologies are red-brown, oxidized, lithic graywacke volcanogenic conglomerates. The conglomeratic facies are predominantly and �I PALEOMAGNETISM OF THE MEMESAGEMASING AND CARIBOU LAKES NORITES, GRENVILLE PROVINCE, ONTARIO * S. Dey, D. 1. A. Symons, and M. Stupavsky Department of Geology, University of Windsor Windsor, Ontario, Canada N9B 3P4 The Memesagemasing and Caribou Lake 20 km2 stocks intruding the high rank granitic gneisses in the Crenville Province about 60 km S of the Grenville Front. Five cores yielding 10 specimens were drilled in the stocks at Sch of 24 and 26 sites respectively. Low-field magnetic susceptibility measurements show that both layered norites outcrop as oval, stocks have a central phase with magnetite content. a high their airborne magnetic anomaly pattern rather than invoking a funnel-shape. Anisotropy of magnetic susceptibility measurements show This explains that the norites are strongly layered even though most outcrops appear unbanded, and that the plutons have not been structurally compressed or tilted as previously suggested. AF, thermal, and chemical step demagnetization and general AF cleaning all isolate a stable remanence component with 95 percent confidence of r-.'3l0°, 5l in the Memesagemasing stock using conventional tiered statistical analysis. This component * Presentation eligible Award for the Student resides in titanomagnetite with numerous exsolution lamellae. The same component is isolated in the Caribou Lake stock by point density stereonet contouring only after AF cleaning. Its less stable remanence resides in coarser unexsolved t itanomagetite grains. Eight baked contact tests using more than 100 additional specimens and including 2 profiles show that: I) the norite remanence predates emplacement of the crossing cutting -.s 1250 Ma Sudbury olivine diabase dikes and — 1100 Ma granite pegmatite dikes, and 2) the norite was 2000 when the dikes were cooled to emplaced. The norite pole lies on the -'l760 Ma position of the North American APW path implying: 1) emplacement during the terminal stages of the Hudsonian Orogeny dated by Rb-Sr at r 1800 + 100 Ma ago; 2) possibly comagmatic emplacement with the Sudbury Irruptive which is —90 km NW in the Southern Province; ano 3) the juxtaposition of the Grenville and Southern Provinces as far back as 1760 Ma. �WISCONSIN GRAVITY BASE STATION NETWORK--1980 C. Patrick Ervin Department of Geology, Northern illinois Lkiiversity DeKaIb, Illinois 60115 The Wisconsin Geological and Natural History Survey has embarked regional gravity surveying upon a program. Mapping is being done on a one mile grid insofar as the road system and elevation control permit. The Northeast Wisconsin Sheet is "in press" and was presented at this meeting last year. The rest of the state will be covered in the coming years. A successful field program is dependent on the existence of a high precision, internally consistent base station network. To facilitate field operations, a base station should be readily accessible by auto, no more than 25-30 feet from a road or drive, to locate, permanent, relatively isolated from foot and vehicular traffic, and easy have a stable base on which to set the meter. Additionally, no point in the state should be more than about a 45 minute drive from a base station. A statewide base station network, consisting of 30 stations, was established in 1980 the summer of LaCoste-Romberg model C using two gravimeters. Use of two gravimeters doubles the number of ties between stations and facilitates error detection. The network was designed to include several extant oase stations and is in good agreement with the earlier measurements. �THE PENOKEAN OROGENY Samuel S. Goldich Department of Geology, Colorado School of Mines Golden, Colorado 804131 The Penokean orogeny, which occurred in the Lake Superior district approximately 1800 m.y. ago, was a complex event that involved more than mountain building by uplift followed by erosion. As in the development of the more recent mountain chains, igneous and metamorphic activity on a grand scale characterized the Penokean orogeny. Graywacke-argillite sequences with intercalated volcanic rocks were folded, metamorphosed, and intruded by a variety of igneous rocks ranging from gabbroic to granitic in composition. Published U-Pb zircon ages from Wisconsin and Michigan indicate two pulses of igneous activity. The older, 1835 ± 15 The data available at this time indicate more or less continuous igneous activity in the Lake Superior region between 1850 and 1750 m.y. ago. The 2600-m.y. old McGrath Gneiss of eastern Minnesota was strongly deformed during the Penokean orogeny. The U-Pb ages on zircons from the gneiss are strongly discordant and reflect the 1800-m.y. deformation. Similarly, old rocks in Wisconsin and in Michigan were severely affected by the Penokean orogeny, and the earlier geologic history, as a result, is difficult to decipher. The similarity in lithologic types and structural style of the rocks involved in the m.y. ago, involved a variety of rock types, 1800-m.y., whereas the younger pulse, 1760 ± ID m.y. ago, appears to have been restricted to granite and rhyolite. Unpublished U-Pb analyses of zircon concentrates from a large number of samples representing tonalitic to granitic rocks in east-central Minnesota are closely related in time, 1804÷ 24 m.y. Rb-Sr isochron ages for the rocks of east-central Minnesota range from 1700 m.y. to 1750 m.y. and are distinctly younger orogenic events in the Lake Superior region is striking. In each case metasedimentaryvolcanic accumulations, a variety of igneous intrusive rocks, and migmatitic development were involved. Regional folaing gave way to higher grades of metamorphism accompanying igneous activity, and late shearing with recrystallization are characteristic. Emplacement of pegmatite and aplite dikes followed each major than the corresponding U-Pb zircon ages. the orogenic event. 2600-m.y., and in older �THE ROLE OF HYDROTHERMAL ALTERATION AND TECTONISM IN WISCONSIN MOLYBDENITE OCCURRENCES .1. K. Greenberg Wisconsin Geological Survey Madison, Wisconsin 53706 Molybdenite is known to occur in three places in northeastern Wisconsin. These appear to be situated along a north-south region restricted near 88°W Molybdenum mineralization in longitude. Michigan's Upper Peninsula is also concentrated near the same longitude. In all Wisconsin cases, Penokean-age granite plutons are directly with the mineralization. The best known occurrence, near Middle Inlet in Marinette County, is in quartz veins within the Mount Tom granite body. The other two associated occurrences, near Amberg in Marinette County and in southeast Florence County, are pegmatite mineralizations. Chemically, the granite host rocks are calcalkaline to alkaline, with no "unusual" trace element characteristics. }—bwever, near the site of mineralization in veins or pegmatites, the host rocks show the effects of hydrothermal alteration, especially alkali Dramatic examples of metasomatism. potassium metasomatism are apparent at Middle Inlet and southeastern Florence County. The granite at Middle Inlet has also been albitized and silicified proximal to quartz veins. These alteration effects should be considered as essential guides in exploring for molybdenum in Wisconsin. Wisconsin occurrences of molybdenum are similar to those in older Precambrian terranes of the world, such as in Ontario and Western Australia. However, these cannot be equated with the extensive ore resources porphyry-type deposits represented by typical of younger plate tectonic environments. �IMPACT AS A POSSIBLE ORIGIN FOR SUBSIDED BASINS Jack B. l-brtung NationaL Research Council Senior Post-doctoral Research Associate Code SN6-NASA Johnson Space Center, F-kiuston, Texas 77058 Subsidence of basins, Michigan must basin, circular roughly intracontinental such have mechanism or energy source. as a the driving Mechanisms directly related to plate tectonics do not operate slowly enough to explain a record of almost continuous subsidence of the Michigan basin throughout the Paleozoic Era. Thermal contraction of the lithosphere underlying the basin is another mechanism, but even proponents of this idea recognize "little direct evidence that an initial heating actually occurred in the Michigan basin immediately before the start of subsidence." Another energy source which could lead to a subsiding basin is the impact event of an asteroid or comet roughly ID km in diameter. During such an impact material is excavated from depths of a few tens of km and deposited on the surrounding area. The is filled temporary cavity produced immediately by material that was originally below the cavity. The resulting structure, similar to those observed on the Moon and Mars, is a broad topographic low surrounded by higher rocks capped by ejecta deposits. Of particular importance is the likelihood that a state of isostatic equilibrium will be established or closely approached after motions directly related to the impact have The mass deficiency associated with the topographic low may be expected to be compensated for by excess mass related to more dense rocks centrally uplifted below the basin. Basin evolution ceased. with erosion of surrounding highlands and deposition within the basin. If proceeds it is required that isostatic equilibrium is maintained, the to the basin will subside in and the surrounding highlands will be uplifted. This response sediment load process will continue until the more dense material underlying the basin is returned approximately to its original level or until no topographic difference exists between the basin center and the surrounding area. A significant characteristic of this process is that the rate of subsidence is controlled entirely by the rate of sedimentation, which may be extremely slow or even nonexistent at times. On the Earth an evolved impact basin may take the appearance of a subsided sedimentary basin, something like the Michigan basin. �EVIDENCE FOR MULTIPLE DEFORMATION IN THE MIDDLE PRECAMBRiAN THOMSON FORMATION Timothy B. Hoist Department of Geology, University of Minnesota, Duluth Duluth, Minnesota 55812 The Thomson Formation of East-Central exhibits numerous structural features which have been interpreted to have formed during the Penokean Orogeny. In the Thomson-Cariton-Cloquet area there are open folds on a scale from centimeters to kilometers. The folds are upright, and Minnesota fold axes trend about east-west and are horizontal to gently plunging either east or west. An axial-planar cleavage, vertical or nearly vertical, is present. To the south there is a pervasive bedding-parallel foliation which has previously been interpreted as having formed in a metamorphic event which predated deformation. Evidence of the amount of compressional strain associated with foliation (Wood, 1974) as well as abundant extensional features (boudinage) within the foliation plane in this region suggest that the bedding-parallel foliation is associated with a deformation. Folds are with southern area, present in the geometries and attitudes similar to those in the north. A vertical crenulation cleavage, axial-planar to these folds where both are observable, is also present. The crenulation cleavage can be found even where folds are not found, in the area from Denham to Atkinson. The deformation which caused the bedding-parallel foliation must then pre-d ate that which caused the open, upright, sub-horizontal folds. Isoclinal, recumbant folds, to which the earlier foliation is axial-planar, have been found in several localities. These folds vary in scale from centimeters to meters. Fold hinges are fairly rare because of the isoclinal nature of the folds. The pervasive nature of this earlier foliation suggests that isoclinal, recumbent folds of a large scale also may be present. The deformation history involves an early stage of indicated isoclinal, recumbant folding, with the development of an axial planar foliation. A latter stage of deformation involved the development of open, upright folds, with an axial-planar foliation also, which is a crenulation cleavage where the earlier foliation is present, and a slaty cleavage where the earlier foliation is not present. Evidence for the earlier deformation has been found from Denham to just northeast of Atkinson, whereas evidence for the second deformation can be found in the entire region of Thomson Formation exposure. �JOINT ORIENTATION ANALYSIS IN THE NORTHERN MICHIGAN BASIN Timothy B. 1-blst Department of Geology, University of Minnesota, Duluth Duluth, Minnesota 55812 The orientations of 14,687 joints were measured at 142 locations in the Paleozoic rocks of the Michigan Basin. The data were for each of the four sets. The local variation could not be correlated with taken which ranged from Manitoulin Island on the east, the south Joint set orientation is independent of regional strike around the Michigan Basin Door Peninsula on the west and the northern which varies from about 020 degrees (N200E) to about 115 degrees (N65°W) in an area shore of Lake Superior on the north, the portion of the lower peninsula of Michigan on the south. The rocks at the sample localities range in age from Cambrian to Devonian. Most of the localities are in carbonate rocks, but data were taken from outcrops of sandstone and shale also. Almost all (over 98%) of the joints are vertical or nearly vertical. Four main joints sets are present in the northern Michigan Basin. The largest peak in the data is a joint set with a strike of about 054 degrees (N54°E). The second-largest peak in the data is a set with a strike of about 133 degrees (N47°W). Two peaks of about the same height are joint sets striking 002 degrees (N02°E) and 092 degrees (N88°W). Local mean orientation of any of the sets does vary from location to location, but is relatively consistent over the entire area lithogy, age of rock, or geographic location. across the study area. Possible structural trends in the Precambrian rocks below the Devonian rocks in the area, postulated from geophysical data, do not correlate with any of the joint sets. Trends of axes of folds present in the Paleozoic strata of the lower peninsula average about 135 degrees (N45°W). This suggests that the joint set of nearly the same strike direction may be related to these folds (the b-c joints of Price, 1966). In-situ stress measurements in the Paleozoic rocks of the mid-continent region (summarized in Haimson, 1978) show the maximum principal compressive stress in the horizontal plane to be quite consistent in orientation, averaging 053 degrees (N53°E). This suggests that the joint set with a nearly-idential strike may be extensional, and fairly recent in age. �A GEOCHEMICAL RECONNAISSANCE STUDY OF GROUNDWATER FROM AN EIGHTEEN COUNTY AREA OF NORTHWESTERN OHIO Mohr, Eileen T., Deering, Mark F., and Carison, Ernest H. Department of Geolgy, Kent State Lkiiversity Kent, Ohio 44242 A reconnaissance study of groundwater techniques showed sulfate and silica to be quality in Northwestern Ohio was undertaken in which 100 samples from actively pumping wells were collected. The major supply of groundwater for this area is from carbonate aquifers which locally evaporites contain and epigenetic present in concentrations of 4-1500 ppm and 7.2-29.0 respectively. ppm Fe, also determined spectrophotometri c by a mineralization that may be the source of natural trace element pollution. Major industrial centers and agricultural areas may also be a prime source of pollution. technique, ranged from 0.0 ppm to 11.2 ppm. The concentrations of K (1.0-34.4 ppm), Zn ( less than 40 ppb-l.7 ppm), Co less than 300 ppb), ana Na (5.5-150.6 ppm) were determined by atomic absorption techniques. Other trace elements including As, Cd, On site measurements of static water Cu, Be, Pb and Sr will be measured by level, temperature, (6.85-8.5 5), pH conductivity (100-2500 micromhos), alkalinity (83-580 ppm), F (0.2-2.8 ppm) and Cl (3-230 ppm) were made. Digital graphite furnace techniques, while Hg concentrations will be determined by a flameless AA method. It will be determined titration analyses performed on filtered, acidified samples indicated Ca to be present in concentrations from 27-560 ppm and Mg from 14-192 ppm, while spectrophotometric if any of the trace elements present a health hazard and should, therefore, limit water utilization or require special treatment of water supplies. �RB-SR DATING OF PRECAMBRIAN BASEMENT FROM ILLINOIS DEEP HOLE PROJECT CORE UPH-3 Carla W. Montgomery Department of Geology, Northern Illinois University DeKaib, Illinois 60115 Eble UPH-3 Deep core 840 m approximately of Precambrian granitic basement. Whole-rock samples taken over the full length of the Precambrian portion of the core fit a single Rb-Sr isochron with slope age of 1479 + 10 m.y. and initial 87Sr/86Sr of o.71i12 + .0025 (Iderrors). Mineral isochrons frorii measurements, indicating that these rocks have not been affected by any significant thermal event since that time. The initial strontium isotope ratio reflects some contribution of radiogenic Sr from older crust. The l479-m.y. age is similar to ages several core samples yield essentially the same age within the precision of the region, illinois penetrated reported for granitic rocks in Wisconsin, Missouri, and elsewhere in the mideontinent suggesting widespread activity at about that time. igneous ��PRELIMINARY RESULTS OFA GRAVITY SURVEY IN THE EASTERN HALF OF THE IRON RIVER-CRYSTAL FALLS DISTRICT, IRON COUNTY, MICHIGAN * D. R. Paddock, K. Fujita, F. W. Cambray, and H. F. Bennett Department of Geology, 206 Natural Science, Michigan State University East Lansing, Michigan 48824 A gravity survey was conducted in the eastern portion of the Iron River-Crystal Falls district of Iron County, northern Michigan. Measurements were taken on five profiles, three east-west profiles to the south of Crystal Falls and two north-south profiles to the west of Crystal Falls. The stations along each profile were separated by an average of 750 meters. Altitude control was maintained by an altirrter and 1:24,000 topographic maps. Accuracy of the data after reduction to bouguer anomalies is about plus or minus 1.4 milligals. A maximum amplitude of 34 milligals is observed over the Iron-River Crystal Falls district. Our observed data are in agreement with those obtained by Bacon and Wyble (1952). The anomaly is centered to the south and west of the iron formation The shape of the anomaly indicates that the source is at depth. exposures. Several crustal models were developed to interpret the data. If the stratigraphic section reported in the literature is used, only a 9 milligal anomaly is obtained. * Student Presentation eligible Student Award Linear stretching of the stratigraphic succession requires a sedimentary thickness of greater than 40 km to fit the amplitude of the anomaly. With no stretching of the column, and an iron formation density of gm/cc, an increase of the iron formation thickness from 200 to 1200 meters is required. An increase in the 3.21 density of the Riverton Iron Formation to 3.56 gm/cc would reduce the total sedimentary thickness to the reported 12 km with an iron formation thickness of 600 These iron formation thicknesses greatly in excess of the reported average thickness of 200 meters. An alternative possibility is that the Paint River group and Badwater Greenstone are directly underlain by basalt. This model postulates a sedimentary thickness of 2800 meters (of which 200 is iron formation) and 1800 meters of greenstone. To fit the observed anomaly, an underlying basaltic meters. are layer of between 3200 ana 3900 meters is required. This could be caused by the sub-aqueous emplacement of basalts in a rift basin which has subsequently filled with sediments. for the ��PRELIMINARY ASSESSMENT OF RARE EARTH ELEMENT GEOCHEMISTRY OF VARIOUS IRON FORMATIONS OF THE LAKE SUPERIOR DISTRICT * Elaine L. Slaughter, Susan E. Tituskin, and John 1. Wilband Department of Geology, 206 Natural Science, Michigan State University East Lansing, Michigan 48824 Several samples of banded ironformation (6W) from the Wawa district and the Gunflint, Vulcan, and Negaunee Iron Formations have been analyzed for their patterns to the carbonate samples. investigation to determine the use of REE as indicators of depositional environments and to investigate their mobility during intermediate to these groups. rare earth elements (REE) as part of an metramorphism, oxidation, and leaching. Our preliminary results cannot be interpreted too literally in terms of genetic modeling because the experimental base, such as exists for magmatic rock—forming minerals, is very weak for BIF sedimentary systems. The carbonate rich sediments of the Negaunee I.F. at the Empire Mine show relatively strong fractionation of the light REE (La/SM 3-5x chondrite) and have surprisingly uniform total abundances with respect to depth. The clastic lenses are in total considerably more enriched abundances yet show similar distribution * Student Presentation Student Award eligible for the The "jaspilite" and "hard ores" (Cliffs Shaft) of the Michigan formations are most REE enriched, Vulcan samples the least, and Tilden and Empire Mine oxide ores are We suggest the REE enrichment in the to be a response to solutions migrating through the formations (e.g. oxides Cannon, 1975 - hard ores) or depletions in response to increase in metamorphic grade (Vulcan). In the Empire and Tilden environments where carbonate to oxide reactions are obvious or implied, preliminary data indicate that the abundance of REE in the oxides are similar to that of the carbonates. Cherts, carbonates and oxides do not exhibit a Ce depletion. The Gunflint and Negaunee cherts have "terrestrial" REE patterns similar to other "land exposed" cherts. �THE DISTRIBUTION OF LITHIUM, RUBIDIUM AND CESIUM IN LAKE MUDS NORTH OF LAKE SUPERIOR M. A. yes and R. 3. Stevenato Ontario Geological Survey Oronto, Ontario A study of the distribution of Li, Rb and Cs in lake muds north of Lake Superior is funded by the Ministry of Northern Affairs under the Northern Industrial Mineral Study program, and is supervised by staff of Mineral Deposits Geological Survey. Ontario Section, Centre-lake samples covering an area of 27,700 sq. km. (NTS 42D, 1/2 of 42E, 52A, 1/2 of 52H), originally the Federal-Provincial collected for Uranium Reconnaissance Program of 1977, The primary were used in this study. purpose is to evaluate the geochemical response of lithium and related trace elemental concentrations in lake sediments and determine its potential as a tool for lithium exploration. The lake sediment samples were collected at an average ciensity of sample per 13 sq. km. A total of 1782 samples were 1 analyzed for Li, Rb and Cs by Barringer Ltd. not including randomly control reference and blind duplicate samples. Two hundred and four samples were analyzed for tin and tantalum. Lithium, rubidium and cesium were Magenta inserted analyzed by flame atomic absorption upon reverse HF/HCIO4/HNO3 The detection limits were 1 digestion. ppm, 10 ppm ppm respectively. Tantalum was analyzed by plasma emission upon reverse and a HF/HCIO4/HNO3 digestion The redissolution in 0.5 N HCI/HF. Tin was detection limit was 5 ppm. analyzed colourimetrically upon fusion with ammonium iodide; the detection limit being and 1 I ppm. Control reference, blind duplicate and field duplicate samples were utilized to determine the precision and accuracy of the data. Precision of the four different control samples ranged from 8% to 18% for lithium Blind and from 6% to 10% rubidium. duplicate accuracy was 16% and 20% for lithium and rubidium respectively, while field duplicate accuracy was 7% for Li and 12% for Rb. Cesium was not considered since most concentrations recorded were below the detection limit of the lab equipment. high lithium While generally coincide with concentrations high rubidium concentrations, no large anomalous regions were detected in a preliminary visual examination except in the area southwest of Progress of a detailed Thunder Bay. computer analysis amalgamating the data with major element and base metal values of the lake muds is discussed. �PETROGENETIC MODELS OF KEWEENAWAN BASALTIC ROCKS, UPPER MICHIGAN John T. Wilband and Pipob Wasuwanich Department of Geology, 206 Natural Science, Michigan State University East Lansing, Michigan 48824 Lower Keweenawan diabase dikes from Marquette-Baraga Counties, and middle Keweenawan Portage Lake Lavas from upper Michigan, can each be subdivided into two chemically distinct groups: a low Tb2- P205 group characterized by higher AI2O3 content, higher Mg ratio, and lower total Fe end REE abundances than a high Ti02-P2O5 group. Both groups, which are indistinguishable in the field, are enriched in the LREE relative to the HREE, and have similar normalized REE abundance patterns. respective type. The wide gap between the TiO2-P205 contents of each group cannot be resolved by a simple fractionation or mixing model, especially because the Ti02/P205 ratio remains remarkably constant within each group. We conclude that two sources perhaps from different depths or with separate REE signatures, are required to produce the two groups and suggest each linear trend is indicative of liquids derived by varying degrees of partial melting of these sources. Similar chemical the dikes have been trends within but nonparallel for each subgroup of the interpreted to mean that the magmatic processes must have This correlation can be interpreted to mean that the rocks, regardless of mode of formation, are coeval within their early opening stages of the Keweenawan rift in Michigan. Plots of La/Sm vs. La and Yb are linear basalt. same been operative during their emplacement in the �AUTHOR H. All and C. Craddock K. Attoh R. L. Bauer M. E. Bengtson, R. P. Meyer, I-I. C. Halls, 3. H. Karl, and D. Dushek M. S. Breithart and F. W. Cambray B. A. Brown and 3. K. Greenberg A. Choudhry and T. E. Smith M. D. Daggett P. A. Daniels, Jr. S. Day, D. T. A. Symons, and M. Stupavsky C. P. Ervin H. P. Gilbert S. S. Goldich 3. K. Greenberg 3. 8. Hartung 1. 6. F-blst 1. 8. HoIst E. T. Mohr, M. F. Deering, and F. H. Carlson C. W. Montgomery M. Osterberg and R. L. Morton D. S. Paddock, K. Fujit F. W. Cambray, and H. F. Bennett P. K. Sims and Z. E. Peterman F. L. Slaughter, S. E. Tituskin, and 3. T. Wilband F. B. Van 1-buten and D. Bhattacharyya M. A. Vos and 5. 3. Stevenato 3. T. Wilband and P. Wasuwanich TIME 3:00 to 3:20 Friday 1:50 to 2:10 Friday 4:00 to 4:20 Thursday LOflOto 10:30 Friday 2:10 to 2:30 Thursday 11:00 to 1 iao Thursday 3:40 to 4:00 Friday 3:20 to 340 Friday 3:20 to 3:40 Thursday 9:50 to 10:10 Friday 9ö0 to 9:50 Friday 9•30 to 9:50 Thursday lOdOto 10:30 Thursday 3:40 to 400 Thursday 11:20 to 11:40 Friday 1 h20 to 1 h40 Thursday 11:00 to 11:20 Friday h30 to 1:50 Thursday 11:40 to 12:00 Thursday 1:30 to 1:50 Friday 11:40 to 12:00 Friday 9:50 to 10:10 Thursday 300 to 3:20 Thursday Thursday evening 1:50 to 2:10 Thursday 2:10 to 2:30 Friday � https://digitalcollections.lakeheadu.ca/files/original/e0aa4ed07dd4add1745e0969cdcbfe3d.pdf edcf69eb414fe00bfd52b2bc8c45457a PDF Text Text Twenty Seventh Annual Meeting Institute a Lake Lansing, Michigan Stperior Geology May 11—12, 1981 The Huronian Between Sault Ste. Marie and Thessalon �I I THE HURONIAN ROCKS BETWEEN SAULT STE. MARIE AND THESSALON DISTRICT OF ALGOMA ONTARIO MAY 11-12, 1981 FIELD EXCURSION GUIDE Prepared By Gerald Bennett, Ontario Ministry of Natural Resources �I THE HURONIAN SUPERGROUP OF THE SAULT STE. MARIE AND THESSALON AREAS, ONTARIO I Introduction: Previous Work: The Huronian Supergroup is probably the most studied sequence of rocks in Canada with published observations going back to 1821. Knight (1915) investigated part of the areas and recognized volcanic rocks in the Thessalon area. Collins (1925) memoir included the first accurate geological map of the North Shore of Lake Huron and his stratigraphic subdivision of the Huronian has only recently been supplanted. McConnell (1927) described the rocks of the Sault Ste. Marie area and placed the Huronian rocks in their correct stratigraphic position. Chandler (1973, 1976) did detailed mapping for the Ontario Division of Mines in the area west of Wakomata Lake. Frarey (1977) culminated several seasons of mapping for the Geological Survey of Canada with the publication of a memoir on the geology between Sault Ste. Marie and Blind River. Frarey revised the stratigraphic scheme for the Sault Ste. Marie area and recognized additional Huronian volcanic rocks in the Aberdeen Lake area. The writer carried out ¾ mile to the inch mapping for the Ontario Geological Survey between Sault Ste. Marie and the Aberdeen Lake ares between 1974 and 1977. A study of the stratigraphic relationships of the Huronian volcanic rocks was begun in 1978 (Bennett in preparation). In addition to the above studies there are many studies of specific problems relating to the Huronian geology. Most of the significant theses and publications are given in the references accompanying this field guide. General Geology: The Lower Proterozoic (Aphebian) Huronian Supergroup forms part of the Southern Province of the Canadian Shield. These predominantly clastic sedimentary rocks form an eastwest trending belt about 35 miles (56 km) wide extending along the north shore of Lake Huron as far east as the Quebec border, a distance of approximately 200 miles (320 km). The total stratigraphic thickness of Huronian rocks is about 40,000 feet (12,000 m). �I -2An absolute age for the Huronian rocks has not yet been firmly established. The basal Huronian rocks lie unconformably upon Archean granitic rocks of the Superior Province which give K-Ar ages of 2,500 m.y. Nipissing diabase which intrudes the Huronian sequence has been dated by Sr-Rb methods at 2,150 m.y. (Van Schmus, 1965). The Huronian rocks along the north shore of Lake Huron are part of the Penokean Fold Belt and have undergone varying degrees of deformation and metamorphism. Radiometric dating of metamorphic rocks generally gives ages between 1,600 and 1,800 m.y. In the area between Sault Ste. Marie and the east end of Quirke Lake Syncline Huronian rocks are metamorphosed to lower greenschist facies and strata are deformed into open folds or a south to southwest dipping homocline. Normal fault sets strike northeast and northwest. Most movement occurred along northwest trending thrust faults (Frarey, 1977). East of the Quirke Lake Syncline the metamorphism and deformation is more intense. In the Sudbury-Espanola area dips are generally steep, folds are locally tight and the metamorphic grade is almandine-amphibolite facies (Card et al 1972). Elliot Lake Group: In the Sault Ste. Marie and Thessalon areas the Elliot Lake Group is represented by the Livingstone Creek, Thessalon, and Matinenda Formations. The McKim Formation, a very thick sequence of mudstones, siltstone and turbidites present in the eastern half of the Huronian belt has; not been recognized in the area between Sault Ste. Marie and Thessalon (Frarey, 1977) The Livingstone Creek Formation; The Livingstone Creek Formation is a clastic sedimentary sequence which overlies the Archean basement rocks and which is, in turn, overlain by the Thessalon Formation volcanics. In the Quirke Lake Syncline the Livingstone Creek Formation is missing and the Thessalon volcanics lie directly on the basement. In the Sault Ste. Marie area the Livingstone Creek Formation can be subdivided into a conglomerate member, a sandstone member, and a quartz-arenite member. The conglomerate member of variable thickness is locally present at the base of the formation, although in Morin Township, about 25 miles (40 km) north of the Thessalon area, the conglomerate member occurs at least one hundred feet (33 m) above the base. �I -3— TABLE OF FORMATIONS FOR THE SAULT STE. MARIE AND THESSALON AREAS I PHANEROZOIC (max. thickness in feet) CENOZOIC Pleistocene and Recent Gravel, sand, silt, clay and organic deposits Unconformity Paleozoic Ordovician Limestone, shale, sandstone Unconformity — PRECAMBRIAN LATE PRECAMBRIAN (PROTEROZOIC) Jacobsville Formation (+ 700) Sandstone, shale, conglomerate Unconformity KEWEENAWAN GROUP Mamainse Point Formation Basalt, rhyolite, conglomerate, diabase, felsite dikes Unconformity Olivine diabase dikes, lamprophyre dikes Intrusive Contact MIDDLE PRECAMBRIAN (PROTEROZOIC) Nipissing Diabase Gabbro, diabase, granophyre HURONIAN SUPERGROUP COBALT GROUP Bar River Formation (1000) Quartz arenite Gordon Lake Formation (1000) Siltstone, chert Lorrain Formation (8000) Arkose, quartz arenite, pebble conglomerate, siltstone, mudstone Gowganda Formation (3500) Matrix supported and clast supported conglomerates, siltstone, mudstone, wacke, arkose �-4Dis conformity QUIRKE LAKE GROUP Serpent Formation (800) Subarkose, conglomerate Espanola Formation (650) Grey limestone, siltstone, dolomite Bruce Formation (300) Matrix supported conglomerate Local Disconformity ROUGH LAKE GROUP Mississagi Formation (5000?) Subarkose, pebble conglomerate, arkose Aweres Formation Subarkose, arkose, clast and matrix supported conglomerate, siltstone Pecors Formation (Not recognized in Sault Ste. Marie area) Muds tone Ramsay Lake Formation Matrix supported conglomerate Local Disconformity ELLIOT. LAKE GROUP McKim Formation (Not recognized in Sault Ste. Marie area) Mudstone, siltstone, wacke Matinenda Formation Arkose, subarkose, quartz wacke, uraniferous quartz pebble conglomerate Disconformity Thessalon Formation (3500) Basalt, andesite, rhyolite, basaltic andesite, minor arkose, pebble conglomerate Dis conformity Livingstone Creek Formation (+ 1000) Subarkose, clast supported conglomerate, quartz arenite Unconformity EARLY PRECAMBRIAN (ARCHEAN) Late Intrusive Diabase, Rocks gabbro dikes Intrusive Contact U �-5-Plutonic Rocks Porphyritic quartz monzonite, granitic gneiss, migma t it e Intrusive Contact Metavolcanic-metasedimentary belts Mafic to felsic metavolcanics, metasedirnents, gabbro and porphyry intrusions Sources of Information: Frarey, 1977. Robertson et al, 1969. Bennett et al, 1975. U �1 1 — J LEGEND FOR FIGURE 1 Formation LAKE GROUP — ————— EARLY PRECAMBRIAN BASEMENT Livings tone Creek Formation Thessalon Formation ELLIOT LAKE GROUP Matinenda Formation HOUGH QUIRKE LAKE GROUP Gowganda Formation Lorrain Gordon Lake and Bar River Formations COBALT GROUP DIABASE LATE PRECAMBRIAN AND PALEOZOIC E'H NIPISSING I ____ I 4. Highway — — with number I II a__I h Thrust fault (Hanging wall) Fault Symbols �M. S S Superior Lake - ,' -s-- ...4. .It. Figure I j((tS of jrJortfl2tth &ibI'n pE,L&hy,J.,ord kobertsJA., 919. FrneyMJ-, I?fl s S Jonj. IkIwl.J G3I Field Iip 51095 Souls Ste. MorirthessolOfi Area Geotogy and Field Slops t (if �I —7— The conglomerate member consists of clast supported cobble to boulder conglomerate with coarse sandstone interbeds. The granitic megaclasts are typically pale grey in contrast to the pink to reddish granitic rocks which make up much of the basement. Clasts of diorite, gabbro, quartz and mafic volcanics are subordinate to the granitic component. granite The sandstone member forms the bulk of the Livingstone Creek Formation. This unit consists predominantly of fine to medium-grained, grey subarkose and arkose displaying planar and trough cross-beds. Interbeds of siltstone, mudstone or pebble conglomerate are rare within the sandstone member. The member is locally calcareous. An upper quartzarenite member of the Livingstone Creek Formation, up to 10 meters (30 feet) thick, has been recognized only in the Sault Ste. Marie area where it directly underlies the Thessalon flows. It is a pale grey to white, or yellowish grey, fine-grained, silicious subarkose and quartzarenite. The quartzarenite member is generally well sorted and finer grained than the subarkose member. The Livingstone Creek Formation is up to at least 1,200 feet (350 m) thick in the Sault Ste. Marie area. Frarey (1977) gives the thickness of the Livingstone Creek Formation in the Thessalon area as up to 300 feet (100 m). The Thessalon Formation: The Thessalon Formation (Frarey, 1967) is a predominantly volcanic sequence near or at the base of the Huronian Supergroup west of the nose of the Quirke Lake Syncline. The distribution of the Thessalon Formation is shown in Figure 2. The Thessalon Formation is underlain by the Livingstone Creek Formation as far east as the Crazy Lake area. In the Dollyberry Lake and Pecors Lake areas the Thessalon Formation lies directly on the Early Precambrian basement. Drill logs indicate that the Livingstone Creek Formation is missing throughout the Quirke Lake Syncline. In the Sault Ste. Marie and Aberdeen Townships areas the Thessalon Formation is up to at least 3,500 feet (1000 m) thick. In the Thessalon area the Huronian volcanics are about 1,500 feet (450 m) thick, but may be thicker under Lake Huron. In the Quirke Lake Syncline drill hole data indicates thickness from 0 to about 500 feet (150 m) of Thessalon Formation is present. b �cx 48' I I FEB Ii Paleozoic Rocks Grenville Province Rocks Sudbury Irrupttve Whitewater Group Rocks 10 kitom.tert LN Hutonian Superyroup -1 ftjj Archean Cc,. 0 0 8: Copper (]iIf Fo,r,iolion FEB Huronian Vokonic Rocks El Slobie Formation the Spiogge 111 Solinay I.ole Fotmotion (including and Runt Volcancs) El [Isle Mountain Formal,on Thesso$on Formation FIGURE 2 Presence confirmed by drilling Subsurface EnSenf [I Thenolon [ Dollyberry tale Area Presence assumed [.j Duncan iwp Area [ Aberdeen Twp Area [1 Crazy tale Arm NI Priors Fake Area H Cooper Lake Area Gabbro Anorthosile Rocks ni. 8 a 48 N.' —' lot �I -9Thin lenses of coarse, poorly-sorted arkose and quartz pebble conglomerate are locally present at the base, or intercalated with the lowermost few flows, of the Thessalon Formation. These clastic units are in places pyritic and radioactive. These radioactive quartz pebble conglomerates are not correlated with the uranium bearing Matinenda Formation of the Elliot Lake area because thin elastic units, lithologically identical to these at the base of the Thessalon Formation in the Sault Ste. Marie-Thessalon area, occur at the base of the Thessalon Formation in the Dollyberry Lake and Crazy Lake areas (Figure 2). At the latter location the Matinenda Formation overlies the volcanic rocks and there is evidence of disconformity between them. The available whole rocks chemical analyses suggest that the volcanic rocks of the Thessalon Formation can be subdivided into two groups or members, an (upper) tholeiitic basalt member, and a (lower) mixed member. There is some interfingering of these members, and in the Sault Ste. Marie area the mixed member is locally missing or very thin so that the basaltic member rests on the Livingstone Creek Formation. The mixed member varies in content from area to area. In the Sault Ste. Marie and Aberdeen Lake areas the mixed member is predominantly basaltic andesite with minor hawaiite. In the Thessalon area icelandite, rhyolite, tholeiitic andesite, high-magnesium tholeiitic basalt and mugearite are present. In the Dollyberry Lake area mugearite, hawaiite rhyolite, volcanic breccia and high-magnesium tholeiitic basalt, tholeiitic basalt and andesite have been identified. The (upper) tholeiitic basalt member is prominent in the Sault Ste. Marie and Aberdeen Lake areas where it is about 1,500 feet (500 meters) thick. The basalt member is thinner in much of the Thessalon area and apparently missing in the Dollyberry Lake and Pecors Lake areas of the Quirke Lake Syncline. The Thessalon Formation typically exhibits a greenschist mineralogy. The basalts are made up of albite, clinozoisite epidote, actinolite, chlorite and oxides. Primary clinopyroxene is locally preserved in basalts of the Sault Ste. Marie area. The icelandites and basaltic andesites generally contain biotite and stilpnomelane in addition to albite, chlorite actinolite epidote and quartz. Many, if not all of the volcanic rocks of the Thessalon Formation have undergone varying degrees of metasomatic alteration involving mainly addition of Na20, grain or loss of K)0, and loss of calcium. Spilitization is especially pron&inced in some parts of the Sault Ste. Marie area where metabasalts have soda contents of over 5 percent. �I - 10 Explanation - of Table 2: 1. Average analysis of tholeiitic basalt, Thessalon Formation, Thessalon area. 2. Average analysis of icelandite. Lower mixed member, Thessalon Formation, Thessalon area. 3. Average analysis of high magnesium basalt. Mixed member, Thessalon Formation, Thessalon area. 4. Average analysis of basaltic andesite. Mixed member, Thessalon Formation, Duncan Township area. 5. Average Hawaiite-mugearite. Mixed member, Thessalon Formation, Dollyberry Lake area. 6. Rhyolite. Mixed member, Thessalon Formation, Dollyberry Lake area. �j 1 59.03 50.65 14.26 2.43 S102 A1203 Fe203 1.304 0.174 1.31 0.28 0.02 0.14 0.78 0.89 0.28 7.78 3.31 0.58 1.02 0.13 0.023 0.21 0.20 2.12 0.28 99.32 12 103 81 Na20 K2O Ti02 S MnO CO2 1120+ H20- Total n Cr Ni 5 5 12 99.23 3.01 4.07 3.61 341 885 5 99.28 0.44 1.606 0.38 0.19 0.021 0.78 2.28 9.99 9.38 CaO 1.92 6.01 10.41 Mg0 7.41 10.32 1.94 9.89 50.46 3 FeO 2.47 14.04 2 1 Analysis No. Major Components in Weight Percent Trace Elements in Parts per Million CHEMICAL ANALYSES OF HURONIAN VOLCANIC ROCKS - 42 22 11 99.99 0.43 2.16 0.62 0.19 0.06 0.38 1.99 1.27 4.71 5.54 4.21 9.64 2.69 14.3 51.8 4 TABLE 2 6 5 51 — 8 1 99.8 0.38 0.51 0.09 0.04 0.03 0.23 0.75 4.07 3.66 0.94 0.62 2.23 1.08 14.5 70.5 43 9 100.21 0.41 1.80 0.19 0.17 0.07 0.42 2.27 0.95 5.90 4.65 2.73 9.51 4.15 15.3 51.69 5 �I - 12 - Rock names assigned using the Irvine and Baragar (1969) procedure were scrutinized by examination of immobile elements such as Ti, P, Al, Cr, Ni. A triangular diagram of TiO/P9Oç/ AlO proved useful in grouping the volcanic rocks. th Jener cation plot (Jensen, 1976) aided the classification of subalkaline rocks. The Matinenda Formation: The Matinenda Formation is the host of the major uranium deposits of the Elliot Lake area, and is by far the most commercially significant formation of the Huronian Supergroup. The Elliot Lake deposits and enclosing rocks are described by Robertson (1968, 1976), Roscoe (1969), Piennar (1963), Theis (1973), and others. In the Quirke Lake Syncline the Natinenda Formation overlies the volcanic rocks of the Thessalon Formation or, where the Thessalon Formation is absent, it lies on the Early Precambrian basement (Bennett, 1979a). The writer knows of no specific locality, either in outcrop, in mine workings, (personal communication with mine geologists) or from diamond drilling (Leahy, 1973) where rocks of the Matinenda Formation interfinger with the Thessalon volcanics. In at least two localities a regolith is preserved at the top of the Thessalon Formation in the Quirke Lake Syncline. It is the conclusion of the writer that a significant disconformity exists between the Thessalon and overlying Matinenda Formation. This is in contrast to the view held by Bottrill (1971) that the Matinenda Formation and the Huronian volcanics are essentially coeval. A unit of pale grey to yellowish subarkose overlying the Thessalon Formation in the Thessalon area and at one locality in the Sault Ste. Marie area is assigned to the Matinenda Formation by the writer (Bennett, l977a, l977b) In these areas the nature of the contact with the Thessalon Formation could not be determined. The Aweres Formation: A thick sequence of conglomerates and sandstones which overlie the Thessalon Formation in the Sault Ste. Marie area was termed the Aweres Formation by McConnell (1926) The lowermost member of the Aweres Formation is a discontinuous unit of clast-supported, metabasalt conglomerate up to 300 feet (100 meters) thick. Megaclasts �U - 13 - in the metabasalt conglomerate are more than 807 mafic metavolcanics of the Thessalon Formation with scattered megaclasts of grey sandstone from the underlying Livingstone Creek Formation. With increasing stratigraphic height the granitic clasts become more abundant in the conglomerates and the proportion of arkose matrix generally increases. This polymictic conglomerate member passes upward into a mixed conglomerate-sandstone member and finally into a member comprised mainly of arkose, subarkose with some wacke and siltstone as well as subordinate matrix-supported and clast-supported conglomerates. The total thickness of the Aweres Formation may be as much as 6,000 feet (2,000 meters), but this may be an exaggeration since there may have been a considerable primary dip. The correlation of the Aweres Formation has been a problem for some time. McConnell (1927) placed the Aweres Formation at the top of his "Soo Series" which included the Duncan (Thessalon Formation) and the Driving Creek (Livingstone Creek) Formation. The Soo Series was placed by McConnell directly below the Bruce Group (the present Bruce Formation). Hay (1964) considered the Aweres Formation equivalent to the Serpent Formation; and Roscoe (1967) correlated the Aweres Formation in the Mississagi Formation of the Hough Lake Group, and noted the presence of conglomerates resembling the Ramsay Lake Formation. Frarey (1977) tentatively correlated the lower, conglomeratic part of the Aweres Formation with the Ramsay Lake Formation and the sandstone-rich upper part with the Mississagi Formation. In 1977 the writer found, in the Sault Ste. Marie area, conglomerate resembling those of the Aweres Formation overlying yellowish, sericitic sandstone which he correlated with the Matinenda Formation (Bennett, 1976, l977b) The writer favours correlating the Aweres Formation with the Mississagi Formation and the Ramsay Lake Formation. The Aweres Formation appears to represent an alluvial fan complex formed as a clastic wedge at the base of a prominent fault scarp. The coarse, proximal deposits of the Aweres Formation may pass laterally and vertically into the Mississagi Formation. �U -14- I The Hough Lake, Quirke Lake, and Cobalt Groups: Each of these groups contains a repeated litho— logical assemblage which begins with matrix-supported conglomerate followed by mudstone, siltstone or limestone, and completed with the deposition of a thick sandstone sequence (Table 1) (Roscoe, 1967) The conglomeratic sequences (Ramsay Lake, Bruce, and parts of the Gowganda Formation) contain much matrix— supported conglomerate generally held to be glaciogenic. The only limestone in the Huronian is found in the Espanola Formation which is probably of shallow marine origin (Young, 1973) and represents the earliest record of platform sedimentation (Frarey and Roscoe, 1970). The thick cross-bedded arenite sequences (the Mississagi, Serpent and Lorrain Formations) had sources areas on the Archean craton to the north, northwest, and west (McDowell, 1957, Long, 1978, Hadley, 1968) For the most part these formations are fluvial (braided stream) deposits laid down on a great outwash plain (Frarey and Roscoe, 1970, Long, . 1978) A shallow marine or beach environment of deposition has been advocated for parts of the Lorrain Formation (Hadley, 1968, Pettijohn, 1970). It has been pointed out (Piennar, 1963; Roscoe, 1968; Frarey and Roscoe, 1970) that regoliths developed below the Matinenda Formation are depleted in iron, in contrast to more recent soils. Also, rocks of the lower three groups of the Huronian are drab coloured while those of the Cobalt Group, in particular the Lorrain and Gordon Lake Formations, contain reddish and maroon coloured hematite-bearing beds. Pyrite, apparently of detrital origin, is abundant in parts of the Matinenda Formation and is common in the Mississagi Formation but generally lacking in rocks of the Cobalt Group. These features have been interpreted as evidence for a change from essentially reducing atmosphere to an atmosphere containing free oxygen (Frarey and Roscoe, 1970). The large uranium deposits of the Elliot Lake area are considered by most recent workers to be of a placer or modified placer origin. The transportation of uraninite by surface streams is believed to be possible only under reducing atmospheric conditions (Roscoe, 1968). �U -15II A RIFT MODEL FOR HURONIAN SEDIMENTATION By G. Bennett and D. G. Innes The concept of a rift through Lake Huron is not entirely new. Kumarapeli and Saul (1966) postulated a westward extension of the St. Lawrence Valley rift passing along the north shore of Lake Huron to join the Lake Superior rift. Innes (1977) completed a detailed study of the Huronian volcanics in the Sudbury area and proposed that the volcanics were fissure eruptions associated with cratonic rifting. He noted the significance of the alkalic volcanics in the Dollyberry Lake area. The following is a scenario in an attempt to interpret the features of the Elliot Lake Group in an intracratonic rift environment. Early Rifting Stage: The Livingstone Creek Formation is interpreted as being deposited in a graben or graben complex with a conglomeratic sequence along fault scarps and a more distal sandstone facies. A period of relative crustal stability permitted the weathering and reworking of the Livings tone Creek sands to produce an upper quartzarenite member. a. Tectonic uplift, somewhere east of the present Elliot Lake area, bevelled the Livingstone Creek Formation. The upper quartz arenite member was removed east of the Sault Ste. Marie area and the entire sequence was eroded away in the Quirke Lake Syncline. b. Main Rifting Stage: Volcanism begins initially from central vents to provide the icelandite, rhyolite, tholeiitic and mildly alkalic rocks of the lower part of the Thessalon Formation. c. Rifting and volcanism continues with voluminous eruption of subaerial tholeiitic basalt which forms the upper member of the Thessalon Formation. d. A return of uplift east of the present Elliot Lake area causes a bevelling of the Thessalon Formation. The upper tholeiitic volcanic sequence is removed in the Quirke Lake Syncline and the entire formation is eroded further e. east. �U - 16 - f. Thermotectonic subsidence following the cessation of Thessalon volcanic activity results in an influx of sands and quartz and pyrite-rich gravels of the Matinenda Formation in the Elliot Lake area. In the Massey-Sudbury area volcanism is renewed with the extrusion of thick sequences of tholeiitic basalts of the Elsie Mountain and Stobie Formations, and finally the eruption of rhyolites of the Copper Cliff Formation. g. The gabbro-anorthosite complex (Agnew Lake Formation) between Massey and Sudbury were probably emplaced during one of the volcanic episodes. An earlier statement that the intrusive complex was equivalent to the Thessalon Formation and unconformably overlain by the volcanics of the Sudbury area (Bennett and Innes, 1979) did not stand up under further field investigations (our own) (Bennett, 1979) Late Rifting Stage: The end of Huronian volcanic activity is followed by a period of thermotectonic collapse. Some of the subsidence took place along one of the rift boundary faults which was later reactivated as the Murray Fault. The slowly subsiding basin is filled by fine clastic detritius of the McKim Formation. h. i. This elongate zone of subsidence and structurally weakened crust provides the initial trough for sedimentation from the craton. The basin expands laterally under the continuing load of Huronian sediments now represented by the Hough Lake, Quirke Lake, and Cobalt Groups. Perhaps other equally detailed scenarios may be constructed to account for the observed features of the Huronian Supergroup. However, the writers feel that any scheme to explain the origin of the Huronian basin must place emphasis on the rocks of the Elliot Lake Group, since these are the oldest preserved Huronian rocks. The Elliot Lake Group is atypical of Huronian sequences, since the former contains the only volcanic rocks of the Huronian succession. The volcanic suite contains tholeiitic and alkalic rocks typical of rift environments and large gabbro-anorthosite intrusions (or intrusion) with a stratigraphic position similar to that of the Duluth Complex of the Lake Superior Rift System. The Elliot Lake Group does not contain the conglomeratemudstone-arenite cycle of the overlying grQups. There is evidence of significant erosion intervals within the Elliot �I - 17 - Lake Group, and formations of the oldest Huronian group tend to be discontinuous or more variable in lithology and thickness along strike than formations of the overlying groups. Given a Huronian rifting event it is tempting to look upon the Penokean tectonism and magmatic events as the closing stage of a Wilson Cycle. Unfortunately the area south of the Huronian belt is covered by Phanerozoic rocks and it is not possible to choose between an intracratonic and continental marine environment for the bulk of the Huronian Supergroup. �____ U -17a—I LEGEND FOR FIGURE 3 I MIDDLE PRECAMBRIAN L+1 Nipissing Diabase Gabbro, diabase, granophyre HURONIAN SUPERGROUP Hough Lake Group Mississagi Formation E:::::] Subarkose, arkose, pebble conglomerate Elliot Lake Group Matinenda Formation Su1arkose, grit, conglomerate Thessalon Formation Mafic to intermediate metavolcanics Felsic Metavolcanics Livings tone Creek Formation Subarkose, granite-cobble conglomerate EARLY PRECAMBRIAN kU Felsic plutonic rocks S ymb — 01 S Fault (inferred) Strike and dip of bed or flow Anticlinal axis 0:7 Highway with number Secondary road �— (FJ Field Trip Slops Figure 3 + 4. + • + + + o I. - M11c3 J kdonifre Geology and Field Stops Thessalon Area LAKE HLIRON L----- -. • t I __________ C I. I. I. I. I. I_I. L LA- L LILLLL LL I. I. I. I. I. I. LI. LI. I. I. I. I. I. LI. I LI. I. I. I. I. I. I. LLLLLLLLLL I. I. L L I. L LLL I. I. I. I. L LLLL LLI. L L L L LI. LLLL I. LLLL I. I.I.I.LI.LLLLLLLLLL LLI.LLLLLLLLLI I. C - I. - I. I. I. - I. I. I. L I. I. I. I. I. I. I. I. I. I. I. I. I. I. I. ennefl in prepQrcxhorl Irorey1 1977. L, L, LLL lnformgtIL V'-. I. L L Source5 of 'L.) I. I. I. I. I. LC LI.L LLLLLI.LL LI. LI.LI. I. LI. I. I. LLLLLLI.LLLLLLLLLL LI. LI. I. LLLLI.LLI. I. LLLLLLLI.LI.L LI. LL LI. LI. LI LI. I.LLLI.I.I.LLLLI.LL ILL LI. LLL_r.,CI.LLLLLLI.I. I I. i-LI. .1 I. I LI. LI.I.LI.LLLLI.LLLLLI.LCLLL LLI.LI. LI.LLLCLI.LLLLLI.I.I.LLI L C L C L C C I.I. I.LI.LLI.LLLLLLLLI.LL L L L I. I. L = I. C L I. I. I. LI.LLI.I.I.I.I.L I.LLLI.I.LI.LLI.L LLLLLLI.LLLLLLLI- LI LLLLLLLLLL LI.LI. LLLLLLLL LLLLLLI LI.LL LLI.L LLLLLLLI.LI.LLLLLL LI. LI. i-LI. I. CCLI. LI. I. CLI. LLLI. I. I. LI. LI. CLI LI. I. LI.I.I.LL I. LI.LL I. LLL I. LI- I. I. LI. LI.I I.LLLI.LI.LLLLLLI.LI.LL I. L LI. I. LI. LI. LII. I. I. LI. I. LI. LI. I. I. I. I. LLLLLI. LI. LL L LI. I. LILLL-LLLLI.LLL LLI.LLLLI.I. I. LLLLL LI. LI. LI. LLLLI. LI. I. CLI. LLLL LI. CLLI. LLI.LI.I. - LLI.LI.LI.I. LLLLCLI.I.L LLLLL _LLLLL I.LLL - LI. LI. I. LI. LLLLLL LI. L LI. LI. I-I. LI. LI. I. LI. I. LI. LII. I. LL L LLLLLL L I. LLI. LLLL LLLLI.LI.ILL I. I. LI.:ILLCl LLI./LLLLLLLI.LL LLLLLLLI-LI. I. I- LI. I.LI. LLLLL LI. I. I. LI. LI. _I. LLLLLLLLLI.LI I. L C LL LLLL I. L LL I. LI. LLLLLLLLLL LI. LI. LI. LI. LLI. LI. LL I. LI. LI. LI.L LL I. ri-LI. LCI.LCI.LLLLLLL LI. LI. ILL LI. LI. L ti-I. LLI. I. ILL LI.I LI. L!LI. I. I. LI. LI.LLL LI. I.I. LI.LLLI. I. I. L I. I. I. LI. I. C LI. II.L LLL ILL LLLL I.LLLI.LLA L Kirkwood 1 �I - 18 - Description of Stops and Roadlog for the Huronian Supergroup in the Sault Ste. Marie •and Thessalon Areas Time constraints are uncertain. To allow for flexibility some optional stops have been included. Also included are some locations and very brief descriptions for those following the guide at their leisure. DAY 1: HURONIAN STRATIGRAPHY IN THE THESSALON AREA (Figure 3) The mileage count begins at the intersection of Highway 17 and Highway 129 at the town of Thessalon about 80 km (50 miles.) east of Sault Ste. Marie. KM MILES 00 00 Intersection of Highway 129 and Highway 17. at Thessalon. Continue east on Highway 17. Count begins at 0 km. 6.0 3.7 Pine Ridge Road and Highway17 east. right (south) on to Pine Ridge Road. 8.5 1.6 At Lake Huron.Cross causeway on foot to small, rocky island with boat house. This is private property. You should contact Guaranty Trust Realtor, Sault Ste. Marie, Ontario, for permission to enter. Stop 1 - Livingstone Creek Formation. STOP 1 Turn LIVINGSTONE CREEK FORMATION CONGL0RATE The clast-supported conglomerate is pale-grey to white weathering with megaclasts mainly of grey equigranular and porphyritic granitic rocks and subordinate mafic rocks. The maximum clast size is about 70 cm with most in the 5-25 cm range. The sparse matrix is poorly sorted grey a.rkose. A few arkose lenses are crudely cross-bedded. The gradational contact with the basement Early Precambrian granitic rocks is exposed on one of the small islands about .250 m (800 feet) east of here. At that location massive granite gives way to angular blocks of grey granite separated by sandstone. Over a few meters this regolith zone grades into clasts.upported conglomerate (See Robertson and Card, 1972, p.10). Return to vehicle at northwest end of causeway. �U - 19 KM MILES 00 00 STOP 2 - Outcrop west of road - Stop 2. LOWER (MIXED MEMBER) OF THESSALON FORMATION South end of Pine Ridge Road - Rocks here are dark grey-green, fine-grained tholeiitic andesite with areas of epidote alteration up to a meter across. A chemical analysis from near the shore of Lake Huron, about 100 m (300 feet) west of here, indicates the volcanics are tholeiitic andesite with a low TiO content (O.777). Similar volcanics have been ound near the base of the volcanic sequence in the Dollyberry Lake area. • Proceed north on Pine Ridge Road. .8 .5 Pink to redgranite along the road. Note contrast with colour of conglomerate clasts at Stop 1. 1.1 .7 Partly leichen covered outcrop east of road - Stop 3. REGOLITH BELOW LIVINGSTONE CREEK FORMATION STOP 3 The regolith here is a breccia comprised of blocks of grey granite and gneiss separated by fine-grained grey sandstone. The breccia probably formed as sand sifting down through a coarse rubble or talus. The blocks represent bleached equivalent of red and pink granite and gneiss found nearby. The bleaching is generally considered to be due to reduction of ferric iron under the influence of a reducing atmosphere. 1.7 STOP 4 1.1 Low outcrops along road - Stop 4. THESSALON ARKOSE Along east side of road are low outcrops of grey, coarse, poorly sorted arkose of the Thessalon Formation. Similar sandstones are found in the Sault Ste. Marie, Aberdeen Lake, and Dollyberry Lake areas. The Thessalon sandstones are found as thin discontinuous units between the Livingstone Creek Formation and the volcanics, or intercalated with the lowermost flows. �I - 20 KM - MILES The fine—grained volcanics in the area are icelandite in composition. They can usually be recognized by their very dark colour and faint bluish to purplish tint as a result of abundant, very fine biotite. 2.3 1.4 Highway 17 East. Continue north on Pine Ridge Road. 00 00 2.3 1.4 STOP 5 Weir's Farm. Private land. Inquire at farmhouse before continuing - Stop 5. Continue on foot through farm yard to long outcrop ridges in field to the east. Note: if access to farm is not possible the high magnesium tholeiite described below can be seen on the east side of the road about 300 m (1000 feet) south of farm gate. HIGH MAGNESIUM THOLEIITE OF THE THESSALON FM. An average analysis of this flow is given in Table 2. The high magnesium tholeiite is a relatively pale green colour in spite of its basic composition. The mineralogy is predominantly actinolite with subordinate albite. The normative composition suggests it was originally a clinopyroxene-rich basalt. The high magnesium tholeiite contains many irregular coarse-grained areas (pegmatoid patches). A chemical analysis of one of these patches indicates composition similar to a tholeiitic basalt. High magnesium tholeiite (with pegmatoid patches) have been identified in the Dollyberry Lake and Pecors Lake areas; providing evidence for stratigraphic equivalence with the Thessalon Formation (Bennett, in preparation). Continuing eastward to the furthest outcrop ridge. These are icelandites near the base of the Thessalon Formation. See Table 2 for composition. These flows are similar to those of Stop 4. Continuing southeast along farmers trail. �I - 21 MILES - Low outcrops of Livingstone Creek subarkose. The fine-grained, grey, cross-bedded subarkose is typical of the bulk of the Livingstone Creek Formation. South of the stockyard near Thessalon Station the upper part of the Livingstone Creek sandstone is very pale-grey and yellowish grey. Chemical analysis reveals a composition typical of a Huronian regolith (Bennett in preparation). Return to Pine Ridge Road. Outcrop of radioactive Thessalon Formation pyritic conglomerate in a field west of Pine Private land; obtain permission Ridge Road. at house. Here pale-pink and rusty, pyritiferous quartz-feldspar grit and conglomerate is This unit is at or exposed in a low outcrop. near the base of the Thessalon Formation. Note fresh appearance of pink feldspar ?Iphenocrysts?v as clasts in grit and conglomerate. -Assay indicates the radioactivity is due mainly to Very similar thorium (50 ppm, 0.1 lb./ton). radioactive conglomerate occurs at the base of the Thessalon Formation in the Crazy Lake area. Return to Highway 17 via Pine Ridge Road. Proceed west on Highway 17. 00 00 Highway 17 and Pine Ridge Road. 3.19 2.0 Turn off on to road to south. Field with old barn due south of turn-off. This is private Permission to enter may be obtained property. from owner who resides on north side of road just east of turn-off. Low outcrops in field Stop 6. near barn are rhyolite. STOP 6 RHYOLITE OF THESSALON FORMATION This is pink to grey, fine-grained rhyolite with large flattened amygdules filled with quartz and biotite or stilpnomelane. Dark staining is due to local concentration of The rhyolite consists mainly of a pyrite. fine-grained mosaic of albite, k-feldspar and quartz with very minor green pleochroic biotite. h �U - 22 KM - MILES Since this area is located near the crest of an anticlinal structure we are near the base of the Thessalon Formation. A felsic volcanic center was located in this area or perhaps under Lake Huron to the south. 00 00 Return, to Highway 17. 2.6 1.6 Intersection of Highway 129 and Highway 17. Outcrops of tholeiitic basalt are located just north of Highway 17 on Highway 129. Stop 7. STOP 7 Proceed west. THOLEIITIC BASALT OF THESSALON FORMATION The dark green amygdaloidal metabasalt consists mainly of fine albite, chlorite, epidoteclinozoisite, leucoxene, and minor quartz and oxides. The larger amygdules are generally concentrically zoned with quartz-calcite-epidote being a common sequence. Small amygdules are chlorite, quartz, calcite or epidote. This outcrop is located near the top of the Thessalon Formation. 00 .5 00 .3 Continue north on Highway 129. Low outcrop of very pale sandstone on east side of Highway 129 is Matinenda Formation. Stop 8. STOP 8 MATINENDA FORMATION SANDSTONE Fine-grained,pale pink to pale yellowish sandstone displays well developed trough crossbedding and yellow (sericitic) partings between beds. The trough cross-beds and sericite are typical of the Matinenda Formation but the fine-grain size is not. This rock type occurs as a unit up to a few hundred feet thick directly overlying the volcanics. The contact between the two was not observed in this area. Return to junction of Highway 129 and Highway 17. 00 00 Proceed west (turn right) on Highway 17. Outcrops found along the highway for the next five kilometers, with few exceptions, are Nipissing gabbro and part of a large sill which extends as far west as Bruce Mines-. �U -23MILE S 15.6 9.7 Waltonen Road. Continue on Highway 17. Oi.tcrops of Mississagi Formation on both sides of highway. Stop 9. MISSISSAGI FORNATION STOP 9 This is grey to pinkish-grey cross-bedded subarkose of the Mississagi Formation. Pebbly layers are mainly quartz, black chert and very sparse jasper. Very fine pyrite is concentrated in thin, continuous layers along fore-set beds and in the narrow pebble conglomerate layers. With a hand lens it can be seen that the pyrite is largely crystalline in outline while the distribution strongly suggests a detrital origin. Recently Innes and Colvine (1979) have suggested that the Huronian Supergroup is a potential host of base metal and gold deposits of sedimentary origin. Continue west on Highway 17. Town of Bruce Mines. 20 11.4 Junction of Route 561 and Highway 17. Town of Bruce Mines. Bruce Mines is the location of the first known copper deposits in the north shore region. Development work began on the veins in 1846 and production took place intermittently until 1921. Production statistics are incomplete but the grade appears to have been between 3 and 47 copper over five feet. Some orebodies were continuous for a length of over 1800 feet (550 m) The deposits are fissure veins of quartz, carbonate, chalcopyrite and bornite in Nipissing diabase and related granophyre (Frarey, 1977, Knight, 1915) Mineralized quartz vein in diabase outcrop on north side of Highway in Bruce Mines. Stop 10. STOP 10 MINERALIZED QUARTZ VEIN The vein is about 2 m (6 feet) wide but appears to pinch toward the northwest. It may be divided into three zones which are, from east to west, disseminated bornite and chalcopyrite in quartz, chalcopyrite, bornite, chalcocite and quartz: quartz-diabase breccia. The host �U - 24 - rock is Nipissing gabbro and granophyre. Some of the old workings can be seen just north of the highway. Thanks to the efficiency of the Cornish miners who first worked these veins, there is very little high-grade material left at the surface. YOU ARE THEREFORE ASKED NOT TO TAKE SAMPLES OF THIS VEIN. This is the last stop of Day 1 - Continue west on Highway 17 to Sault Ste. Marie. �____ U - 24a - LEGEND FOR FIGURE 4 —I LATE PRECAMBRIAN I I Jacobsville Formation Sandstone, siltstoné, conglomerate MIDDLE PRECAMBRIAN Nipissing Diabase Gabbro, diabase, granophyre r+ HURONIAN SUPERGROUP COBALT GROUP Lorrain Formation Quartzarenite, quartz-pebble conglomerate, arkose Gowganda Formation Paraconglomerate, siltstone, mudstone, arkose HOUGH LAKE GROUP E: Aweres Formation Arkose, subarkose, paraconglomerate, basalt cobble conglomerate, orthoconglomerate ELLIOT LAKE GROUP kI Thessalon Formation Tholeiitic basalt, basaltic andesite, spilite, arkos Li Livings tone Creek Formation Subarkose, granite cobble conglomerate, quartzarenit EARLY PRECAMBRIAN LLL1 Felsic Plutonic Rocks Quartz monzonite, gneissic granite, rnigrnatite ij1I1th Metavolcanic Rocks Mafic metavolcanics, amphibolite SYMBOLS 'w-' — jiuiu.. Fault Strike (inferred) and dip of bed or flow Highway with number Algoma Central Railway I I I �I CD D_ .O -.-4 — -÷ th O- 3 — 0 00(n C)) -o - 0 a' (I) -'0 (D -o a.°- (DO -' (D Co -a — .--.—_—.I r r r err curl r r r- r ,- r I- r I r . r I C r . - recur -C - . - - r C C r r r r C r rr r I r r r r r r Cr err err rrr rr Cr r CC r r r r I I r r r r r r r e r C C C C rrrrrrrrrrrrrrrrrrr I C Cr cc... rrrr errr -rrrrirrrr ,-rrrrr I I rrrrrr CrrCrr IC rrr CU e r r r rr r rr ruU r rrrrrr run—C r U rrrrrrrrrrr r r r C U r r re r r C e e r I r r - g-rrrrrrrr err errs-err r rrrrrrrr r e rrrrrrr rrrrrrrrrrrrrrrrrrCrrrrrrrrr rrrrrrerrrrrrrrerrrrrrrrrrrr rr r C r r C ci4 I Cr re rrerr r rerrrrrrrr r C t r .rCrCrrrree : rrrernrrrrrrrrrrrrrrrrrrerrrrrrrrr rrr rerr err rr r rrr U rrecur C r rr rrrrrerr rrrrrer rlrlrlrlrrrrrrrrrrrrr errrr r rrrrr rrrr Cr UrC Cr r C C err, r r U rrCrr rrrrl rrrrrrrrrerrrrnrrrrrrrrrrrr rrr rrrCrCrrrrrr C urrrrrrrrrrrrl ref rrrrrrrrrerrr rrrrrrrrrr rrrrrrrrrr,Crrrlrt,Crrerrterrrrrrrerrrrrrrrr,_rrr C C r r C C C r I C r U r C r C C r r r C U C r I r r CrU r C C r C r C r r U r r r r r e r r r r r rn cur freerrrrlr rrerrer rrrrrrrr ruerrrrerrrrrrrrr r rrrrrlI rr r C rrrrrrurrrrrrrf rrrr rrr,rrrrrr rrrrrrrr rrrlurrr r -r C r rrrrCrCrrrrCrrrrrrCrrrCrrr1rrr1rt,frrJT r r r r C r C r r r r CCr C r rr r r r rrrrrrrrrr. . err rrrrrrrrrrrrrrrrrrrrrrrrerrrrrr r r I r r rrrrrrrrerrrrrre rrrrr rr IIrUrrC r r r r C 4 rrrrreerrrr rrrrrrrr errCr errrrrr r err r r err rrC err r err Cr r rr rrCr err r err ref r rrrrrrr err err rrrr rerr rerrrrrrrr errrrrr rrrrrrrrr rrerer rr ricrrrecur rrrrr err rrerreel-u Crc rrrrr rrrrrerrrrrrr rr rrrrr err r rrrrrrrrrrrrr er r r r r r -err rrrrrrrrererrrrrrrrrrrerrr rue r e rrrrr rrrr rrr rr referrer rrrrrr err r r rrrrrr ri-err rrrrr rrr;rrrlrrrrrrrrrrrrrrrrrr ,rrrrrrfrrrrrrrrrrrrrrc err r rrr.-rrrrrrerurrr rrrrrrrl rerrer, rri-rrrrrrrrrrrr - ...., 0 4.. NJ �U - 24c - ISLAND LAKE AREA (FIGURE 4) DAY 2: The mileage log begins at the junction of Highway 556 and Highway 17 in the village of Heyden, about 15 km (10 miles) north of Sault Ste. Marie on Highway 17. KM MILES 00 00 Turn right (east) on Highway 556. 7.4 4.6 Abandoned section of Highway 556 branches off to the right. Turn off onto abandoned The abandoned section is highway and park. washed out about 100 m (100 yards) ahead. Vehicles with very low ground clearance may park a few hundred feet ahead on the right Walk north along old side of the road. highway to washout and from there walk about 500 feet (200 m) through the bush in an easterly to east-southeasterly direction as Ear as theAlgoma Central Railway track. Proceed northeast along the track to outcrops of dark green metabasalts of the Thessalon Stop llA. Formation. STOP hA SPILITES OF THE THESSALON FORMATION Dark green, massive and amygdaloidal spihite of the tholeiitic basalt member is exposed along both sides of the track. Amygdules up to 3 cm across contain quartz, epidote, pink Black chlorite amygdules albite, and calcite. a few millimeters across are characteristic of the mafic rocks of the Thessalon Formation. Amygdaloidal flow tops and flow breccia are found near the southwest end of the outcrop. Thin seams of chalcopyrite occur along fractures and veins of epidote, pink albite, and calcite are common. Primary clinopyroxene are generally presented in the basalts of this area. The soda content is from 3 to over 5 percent. Proceed southwest on the track across a gully which marks a fault between the volcanics and Stop llB. the overlying Aweres Formation. �U - 25 STOP 11B - AWERES FORMATION Clast-supported and matrix-supported conglomerates of the Aweres Formation are exposed in rock-cuts and outcrops along the tracks. The predominant megaclasts are mafic volcanics and granitic rocks with minor subarkose and dark chert in a matrix of coarse, poorly sorted subarkose and subwacke. Bedding planes are poorly defined. Continuing up-section the matrix becomes more abundant and contains many angular, shard-shaped fragments a few centimeters or less in size. A few pyrite nodules up to 12 cm across occur in the upper part of this section. The coarse arkose which makes up much of the upper part of the Aweres Formation is not exposed along the railway track section. A few kilometers south of here in Jarvis and Aweres Townships the conglomerates are found intercalated with coarse, poorly sorted arkose. The writer believes that the Aweres Formation represents a thick clastic wedge deposited along prominent fault scarps. KM MILES Return to Highway 556 either by continuing along the track or proceeding to the right through the bush for a few hundred feet (100 m). Continue east on Highway 556. 9.6 STOP 12 6.0 Rock-cut on the right. Stop 12. GOWGANDA MIXITE AND THESSALON SPILITE This is a good example of matrix-supported conglomerate (mixite) of the Gowganda Formation in fault contact with glomeroporphyritic spilite of the (upper) tholeiite basalt member of the Thessalon Formation. The conglomerate consists of clasts of pink granitic rocks, dark green volcanics and some quartz pebbles in an abundant dark green wacke This type of conglomerate is generally matrix. considered a tillite. �I - 26 - Using Irvine and BaragarTs (1971) procedure, the glomerophyritic volcanic would be classified as hawaiite, as would many of the upper tholeiitic basalts. The low Ti02 (0.7), low P205 content (0.077), and cromium content (110 ppm) shows that it is not. It is a spilite with over 4.87 total alkalis. The mineralogy is clinopyroxene, albite, chlorite, actinolite, epidote, and leucoxene. Turn round and proceed west for about 5 km (3 miles) on Highway 556 to the junction with Highway 552. Park near railway track on Highway 552 and locate a bush road on west side of Highway 552 near railway track. Continue on the bush road or trail which continues west and then turns north, up the A few hill for about 500 m (1500 feet) outcrops of brecciated granitic rocks and a small, low outcrop of fine-grained, red Keweenawan felsite dike is exposed on the One of the mineralized exploration trail. trenches of the Nystedt copper prospect is found near the trail near the crest of the . hill. Stop 13. NYSTEDT COPPER PROSPECT STOP 13 - Chalcopyrite occurs as seams, disseminated grains and massive patches in pink quartz syenite and breccia. Veinlets and disseminated grains of specular hematite are common in the surrounding rocks. This is one of four known major surface showings in the immediate area; a fifth occurs just east of Highway 552. Kennco Explorations (Canada) Ltd. optioned the property in 1965-66, and carried out a diamond drilling program. Assays from one diamond drill hole returned 0.78 copper over 95.3 feet. The copper deposits are set in pink syenite and chloritic granite-breccia consisting of fragments of gneissic and massive granite in a matrix of quartz, chlorite and feldspar. The granite breccia extends to the east of Highway 552 and there is well exposed in rock-cuts along the highway. Return to Sault Ste. Marie. �U - 27 - HURONIAN STRATIGRAPHY EAST OF SAULT STE. MARIE DAY 2 (Figure 1) Proceed east from Sault Ste. Marie on Highway 17 to the town of Echo Bay, a distance of about 25 km (15 miles). Turn left on Highway 638 in Echo Bay. 00 00 Town of Echo Bay. 1.1 1.3 Highway 638 East to Leeburn - 6.5 4.2 Outcrop on south side of highway. One to twofoot (.5 m) quartz-specular hematite vein in white, pale yellow medium-grained quartzarenite of the Lorrain Formation. 10.9 6.8 McCarroll Lake Road - Continue on Highway 638. 11.8 7.4 High rock-cut along both sides of road. turn left. Stop 14. GORDON LAKE FORNATION STOP 14 The rocks here are from the transition zone between the Gordon Lake Formation and the underlying Lorrain Formation. Rocks are pink to white fine-grained, well sorted silicious subarkose to quartzarenite with well developed cross-beds.. Ripple marks and slickensides are found on some partings. Sandstone sequence contains a narrow unit of laminated ferruginous siltstone with green (sericitic) partings. An east-west trending, 1 to 2-foot wide (30-60 cm) hematitic shear zone with wide flanking bleached zones is located near the east end of outcrop. 7.2 10.7 Gordon Lake Road - Continue on 638, left turn. 23.6 14.7 Bass Lake Road - Continue on 638. 24.4 15.1 Village of Leeburn.. 49.7 30.9 Center Line Road - Continue on 638, turn left. 31.8 19.8 Poplar Dale Road - 32.4 20.1 Route 638 - Continue on 638, turn left. MacKay Road - turn turn right on 638. left onto MacKay Road. �I - 28 ai MILES 34.3 21.3 STOP 15 - Proceed about 100 yards (100 m) north on MacKay Road to abandoned farm house on the Harnden farm. This is private property. Obtain permission to enter from resident of house east of Harnden farm. Proceed northwest on foot to pale grey outcrops on hill west of farm house. The outcrops on the north slope of the hill are outcrops of Mississagi Formation. Stop 15. MISSISSAGI, BRUCE, ESPANOLA, AND SERPENT FORMATIONS Pale grey subarkose of the Mississagi Formation display well developed cross-bedding with cosets about a meter thick. These exposures are typical of the upper half of the Mississagi Formation. The lower half of the formation is generally finer-grained, darker grey and approaches a subwacke in composition. A few hundred feet (less than 100 m) to the south is grey weathering, matrix-supported conglomerate of the Bruce Formation. The predominant clasts are granite, mafic metavolcanics, and quartz in an abundant, dark, quartz wacke matrix. This is the second of the extensive mixite units in the Huronian and like the Ramsay Lake and Gowganda mixites is generally considered to be a tillite. Further to the southwest the Espanola Formation is exposed. The Espanola Formation consists of three members: The Bruce limestone, the Espanola siltstone member, and the Espanola dolomite member. Only the Bruce limestone member is exposed here. The Bruce limestone member consists of alternating thin layers of pale grey, white or pink limestone and dark grey argillite and siltstone. The Bruce lime-. stone is generally highly deformed. Some discussion has arisen over whether or not the tight folding is tectonic or syndepositional (Young, 1973a, Frarey, 1977) The distinctive appearance and composition of the Espanola Formation along with its widespread distribution makes the Espanola Formation the most useful stratigraphic marker in the Huronian Supergroup. The Espanola Formation is overlain by the Serpent Formation, the lowermost part of which is exposed on a south-facing steep slope just �I - 29 KM - MILES south of the Espanola Formation outcrops. In this area the lowermost part of the Serpent Formation consists of a thin unit of tightly packed polymictic conglomerate with well rounded cobbles of granite, maic igneous rocks and small fragments of Bruce limestone (Frarey, 1977). Continuing to the south one, comes upon exposures of pale pink, mediurn-grained, well sorted, massive subarkose, which makes up most of the Frarey (1977) gives the Serpent Formation. composition of the subarkose at this location asquartz (807), plagioclase (20%) with traces of chlorite, zircon, tourmaline or hornblende and opaques. 000 000 Return to intersection of Highway 638 and 561. Turn left (south) on 561. 1.1 0.7 Polymictic matrix-supported conglomerate of the Gowganda Formation is exposed on both sides of road. 2.0 STOP 16 1.2 Large outcrop ridge west of road. Stop 16. GOWGANDA FORMATION Near the road thin beds of fine-grained, pink weathering sandstone are interbedded with dark green mudstone and siltstone. The sandstone beds have undergone considerable deformation and disruption which appears to have been the result of syndepositional slumping. A mixite0unit striking about 150° and dipping The about 45 south overlies the mudstone. mixite consists of rounded to angular clasts of granitic rocks up to over a meter (3 feet) long in an abundant dark green, wacke matrix. Just above the mixite unit, mudstone and siltstone contains large, well rounded balls of pink weathering sandstone producing an ttintraformational mixite". A 10-meter 30 feet) wide Nipissing type diabase strikes 140 near the crest of the outcrop. The features and relationships displayed in this exposure are typical of much of the middle part of the Gowganda Formation in the Sault Ste. Marie area. �U - 30 KM MILES Continue south on Highway 561. 7.4 4.6 The rocky, hill ½ to 1 mile to the west of the road reveal four of the six members of The most distant hill the Lorrain Formation. consists of the upper white quartzite member, the pinkish summit of the nearest hill is part of the upper red quartzite member; this is underlain by the jasper conglomerate member (white from a distance) which is in turn underlain by the, mostly tree covered, lower red quartzite member. The remaining purple siltstone and basal arkose members are further to the north but cannot be distinguished from this point. Mount Zion Road - Cotinue on Route 561. 8.1 5.0 Outcrops of jasper conglomerate. Stop 17. JASPER CONGLOMERATE OF THE LORRAIN FORMATION STOP 17 The jasper conglomerate (known locally as "puddingstone") is probably the most distinctive and attractive rock in the north shore area. It consists of rounded to angular pebbles up to 7 cm (3 inches) of quartz and abundant vancoloured Jasper. The jasper conglomerate and intercalated white quartzarenite units make up the jasper conglomerate member of the Lorrain This member is up to 200 m (600 feet) Formation. thick (Frarey, 1977). 8.5 5.3 Large, high outcrop area to the right (west) of Stop 18. Upper red quartzite. the road. UPPER RED QUARTZITE OF THE LORRAIN FORMATION STOP 18 The outcrop consists mainly of well cross-bedded, poorly sorted, reddish quartzarenite, with thin pebble conglomerate interbeds. The red colouring Thin seams of detnital is due to fine hematite. grey hematite can be seen along fore-set beds and within continuous layers of quartz and jasper The upper red quartzite pebble conglomerate. member varies from 260 m (850 feet) to as much as 20 m (1700 feet) (Frarey, 1977) Continue south on Highway 561. 9.5 5.9 Outcrop of white quartzite Ledyit Line Road. on west side of road. Stop 19. �I - 31 KM - I MILES STOP 19 UPPER WHITE QUARTZITE MEMBER OF LORRAIN FORMATION The outcrop consists mainly of white, to pink, medium-to-coarse-grained quartzarenite with scattered pebble layers. This is the uppermost and thickest member of the Lorrain Formation. It is the thickest member, about 740 m (2400 feet) (Frarey, 1977). — 12.8 7.8 Village of Rydal Bank. 00 00 Highway 561 turns left. Plurnmer road straight ahead. Proceed on Plunimer Road. 3.8 2.4 Plummer Road and West Road. Outcrops of Gordon Lake Formation on west side of West Road about 100 m (100 yards) north of junction. Stop 20. STOP 20 GORDON LAKE FORMATION Thinly bedded and laminated, fine-grained sandstone, siltstone, mudstone and chert are exposed here. Frarey (1977) suggests that some chert may be the result of the diagenetic replacement of siltstone. Curving, and branching mud cracks in mudstone beds are filled with fine sandstone. The Gordon Lake Formation contains sedimentary structures indicative of a stable, low energy environment, probably nearshore marine to littoral or in part lagoonal (Frarey, 1977). See Wood (1973) for a discussion of the depositional environment of the Gordon Lake Formation. Proceed northwest on Plummer Road. 7.2 4.5 Center Line Road. 8.3 5.2 Outcrops of white quartzite to the right (north). Continue to top of hill and park. Stop 21. Continue on Plununer Road. BAR RIVER FORMATION STOP 21 Almost all of the Bar River Formation consists of thick bedded, white quartzarenite similar in most aspects to the upper white quartzite of the Lorrain Formation. The rocks here are white to pale yellow quartzarenite with little visible structure. 00 00 Return to Center Line Road via Plunimer Road. Turn right (south on Center Line Road). �• U-s 3 t —— I * I 500 2000 Alteration feet (000 metres 3000 — a rknse • bjacke — GOUCAIIDA FOR1IAT!ON I is tone, conglomerate. EIIT1 titnia tutu' • ci Arkose, quartzite, conglomerate IIURONIA'4 SUPERGLOUP JORRA III FOROATION breccia LEGEND McGreQ 561 /'Highway 4 Radicactive occurrence NIFISSIN(; F ROTE ROZO IC JJj Gahbro, granophyre; diabase dikes 1000 4 't%%, >'—i N p Pyrite occurrence —Geological Sketch Map ol (lie McGregor Road Breccia Zone. FIGURE 5 //// I Fault (defined, inferred) SYMBOLS ::::::::::::::::.,j,,a!I ::::::::::::::::::::::::::::::::::::::: •.::c•:•:': aaaa r1 p fl �I - 32 KM - MILES Turn left (east) on Government 5.4 3.4 Government Road. 00 00 Road. 1.7 00 1.1 00 Caribou Road. 3.7 2.3 Outcrop on left (east side of road is sulfide stained outcrop of McGregor Road breccia. Fragments of Lorrain Formation arkose and quartzarenite are set in a quartz and pyrite Sulfide-rich samples gave values of matrix. 0.20 and 0.34 ounces of silver /ton). 3.8 2.4 This is private Tractor road to the right (west). Inquire at farmhouse directly east of here land. Outcrop area is located for permission to enter. about 100 m (100 yards) west of Caribou Road. (Stop 22, McGregor Road Breccia). STOP 22 Turn right (south) on Caribou Road. McGREGOR ROAD BRECCIA The McGregor Road breccia (Figure 5) is emplaced along the south side of a down-dropped fault block of basal arkose of the Lorrain Formation. The surrounding rocks are part of the Gowganda The breccia consists mainly of Formation. angular to rounded fragments of Gowgands siltstone and mudstone, and arkose, quartzarenite and jaspe.r conglomerate of overlying members of the Lorrain Formation. Fragments of jasper conglomerate are about 1000 m (3000 feet) below their stratiAlthough in places the breccia graphic position. is polymictic, there are localities where the predominant clast lithology varies (from south to north) in a manner corresponding to their original position in the Huronian stratigraphy. Near the west end of the breccia fractured Gowganda argillite is altered to a locally pyritic, hard, pink rock approaching pure albite Small radioactive occurrences in composition. (up to 10 times background) occur in the breccia. The breccia may be a fissure diatreme formed as a result of explosive degassing of magma along Alternatively, the breccia may be the a fault. result of fracturing and spalling along a dilatent zone formed along the down dropped fault block. �I - 33 KM MILES - Just north of the tractor road a Nipissing type diabase dike intrudes breccia consisting of arkose and quartzarenite of the Lorrain Formation along with brown weathering, dark green fragments of diabase. Continuing north the breccia is comprised mainly of fragments, blocks and fractured slabs of Lorrain quartzite. Continuing for about 200-300 m (yards) north and west are outcrops of pink, locally pyritic albitized, laminated mudstone of the Gowganda Formation. Continue south on Caribou Road to the Town of Bruce Mines. Turn right (west) on Highway 17. 00 00 Bruce Nines. 12.3 7.6 Village of Desbarats - Large pink outcrops of basal arkose of the Lorrain Formation just east Stop 23. of the village. BASAL ARKOSE MEMBER OF THE LORRAIN FOPNATION STOP 23 The basal arkose member is up to 500 m (1700) feet thick (Frarey, 1977). In Desbarats well sorted pink arkose of this member are exposed The dark spots in rock-cuts along Highway 17. commonly found in this member are due to fine hematite. Disseminated chalcopyrite and pyrite mineralization occurs in this member about 3 km (2 miles) northThe mineralization may be west of Desbarats. syngenetic but Pearson (1979) suggests a diagenetic origin. 13.3 STOP 24 8.6 Dark red to maroon outcrops of the purple siltstone member of the Lorrain Formation are exposed along the highway. Stop 24. PURPLE SILTSTONE MEMBER OF THE LORRAIN FORMATION This unit is a thick bedded, massive, fine-grained arkose and, silts tone with a hematitic matrix. It appears to be a relatively local, true red bed, and is evidence for an oxygen bearing (The unit is atmosphere during its deposition. about 30 m (100 feet) thick (Frarey, 1977). �U - 34 KM MILES 15.3 9.5 - I "Ripple Rock". Thinly bedded arkosic sandstone of the Lorrain Formation displays excellent examples of asymmetrical ripple marks. This outcrop is a designated historical site and should not be defaced. End of Field Trip - Return to Sault Ste. Marie. i �I - 35 - SELECTED BIBLIOGRAPHY OF THE HURONIAN ROCKS OF THE SAULT STE. MARIE AREA Bennett, G. 1977a: Huronian Volcanism, District of Algoma and Sudbury; pp. 102-103, in Summary of Fieldwork, 1977, by the Geological Branch, edited by V.G. Milne, 0. L. White, R. B. Barlow, and J. A. Robertson; Ontario Geological Survey Misc. Paper 75, 208p. *Bennett, G. 1978: Huronian Volcanism, Districts of Algoma and Sudbury, pp. 105-111, in Summary of Fieldwork, 1978, by the Ontario Geological Survey, edited by V. G. Milne, 0. L. White, R. B. Barlow, and J. A. Robertson; Ontario Geological Survey Misc. Paper 82, 235p. Bennett, G. l979a: Huronian Volcanism, Districts of Algoma and Sudbury; pp. 84-85, in Summary of Fieldwork, 1979, by the Ontario GeologicalSurvey, edited by V. G. Milne, 0. L. White, R. B. Barlow, and C. R. Kustra; Ontario Geological Survey Misc. Paper 90, 245p. Bennett, G. 1979b: The McGregor Road Breccia Zone, District of Algoma; pp.82-83, in Summary of Fieldwork, 1979, by the Ontario Geological Survey, edited by V. C. Mime, 0. L. White, R. B. Barlow, and C. R. Kustra; Ontario Geological Survey Misc. Paper 90, 245p. Bennett, G. 1979c: Geology of the Two horse Lake Area, District of Algoma; Ontario Geological Survey Open File Report 5277, 99p. with uncoloured geological map at 1 inch to ¼ mile. Bennett, G., Hillier, R.D., Nentwich, F., Dupuis, C,P.. and Pucovsky, M. 1975: Jarvis Lake—Garden River Area, District of Algoma; Ontario Div. Mines, Prelim. Map. Pp. 1064, Geol. Ser., scale 1 inch to ¼ mile or 1:15,840. *Bennett, G., Sawitsky, E., and Whittaker, P. 1976: Jarvis Lake-Duncan Township Area, District of Algoma; Ontario Div. Mines, Prelim. Map P1190, Geol. Ser., scale 1:15,840. Bennett, G., and Sawiuk, M. 1979: Jarvis Lake-Garden River Area, Southern Part, District of Algoma; Ontario Geological Survey, Prelim. Map P2241, Geol. Ser., scale 1:15,840. *See Addenda, page 42. �U - 36 - Bottrill, T.J. 1970: Geology and genesis of uranium deposits in the Huronian and associated geology, Blind River, Sudbury, and Gowganda areas, Ontario, (41 I, J, 0, F); in Report of Activities, Part A: April to October, 1969, pp. 57, 58; Geol. Surv. Can., Paper 70—i, pt. A, 25lp. Bottrill, T.J. 1971: Uraniferous conglomerates of the Canadian Shield; PP. 77-83,. in Report of Activities, Part A, Geol. Surv. Canada Paper 71-7; (R.G. Blackadar, editor), 259p. Card, K.D., Church, W.R., Franklin, J.M., Robertson, J.A., West, G.F., and Young, G.M. 1972: The Southern Province; PP. 336-379, in Variation in Tectonic Styles in Canada; edited by R. A. Price and J. W. Douglas, G.A.C. Special Paper No. 11, 688p. Card, K.D., and Pattison, E.F. 1973: Nipissing Diabase of the Southern Province, Ontario; in Huronian Stratigraphy and Sedimentation, pp. 7-37, edited by G. I. Young; Geol. Assoc. Canada Special Paper No. 12, 27 lp. Casshyap, S.M. 1969: Petrology of the Bruce and Cowganda Formations and its Bearing on the Evolution of Huronian Sedimentation in the Espanola-Willisville Area, Ontario (Canada); Palaeography, Palaeoclimatology, Palaeoecology, 6 (1969), PP. 5-36. Casshyap, S.M. 1971: Petrology and Sedimentation of Huronian Arenites, south of Espanola, Ontario; Can. J. Earth Sci., V. 8, pp. 20-49. Chandler, F.W. 1973: Geology of McMahon and Morin Townships, District of Algoma, Ontario Div. Mines CR112, 77p; accompanied by Map 2272, scale 1 inch to ½ mile. Chandler, F.W. 1976: Geology of the Saunders Lake Area, District of Algoma; Ontario Div. Mines CR155, 46p.; accompanied by Map 2331, scale 1 inch to ½ mile (1:31,680). Chandler, F.W., Young, G.M., and Wood, J. 1969: Diaspore in Early Proterozoic Quartzites (Lorrain Formation) of Ontario; Can. J. Earth Sci., v; 6, pp. 337-340. Church, W.R. 1971: The Nature and Evolution of Proterozoic and Phanerozoic Orogenic Belts; Abstract, Geol. Assoc. Canada, Mineral Assoc. Canada, Abstracts and Program, Sudbury, pp. 14-15. �I - 37 - Collins, W.H. 1925: North Shore of Lake Huron; Geol. Surv. Canada Mem. 143, l86p. Douglas, R.J.W. 1980: Proposals for Time Classification and Correlation of Precambrian Rocks and Events in Canada and Adjacent Areas of the Canadian Shield. 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Long, D.G.F. 1978: Deposition Environments of a Thick Proterozoic Sandstone: The (Huronian) Mississagi Formation of Ontario, Canada; Canadian Jour. Earth Sci., Vol. 15, No. 2, pp. 190-206. McConnell, R.G. 1926: Sault Ste. Marie Area, District of Algoma; Ont. Dept. Mines, Vol. 35, Pt. 2, pp. 1-52 (Published 1927). Accompanied by Map 35a, scale 1 inch to 2 miles. McDowell, J.P. 1957: The Sedimentary Petrology of the Mississagi Quartzite in the Blind River Area. Ont. Dept. Nines, Geol. Circ. No. 6, 3lp. McLennan, S.M., Fryer, B.J., and Young, G.M. 1979: The Geochemistry of the Carbonate-Rich Espanola Formation (Huronian) with Emphasis of the Rare Earth Elements; Canadian Jour. Earth Sci., Vol. 16, No. 2, pp. 230-239. Moore, E.S. 1929: Ore Deposits near the North Shore of Lake Huron; Ont. Dept. of Mines, Vol. 38, Pt. 7, (published in 1930). Ovenshine, A.T. 1964: Glacial Interpretation of the Precambrian Gowganda Formation, North Shore of Lake Huron, Canada; Geol. Soc. Am., Abstr. (ann. mtg.), pp. 146. - Palonen, P.A. 1973: Paleogeography of the Mississagi Formation and Lower Huronian Cyclicity; in Huronian Stratigraphy and Sedimentation, ed. G. M. Young; Geol. Assoc. Canada, Spec. Paper 12, Pp. 157-168. Parviainen, E.A.U. 1973: The Sedimentology of the Huronian Ramsay Lake and Bruce Formations, North Shore of Lake Huron; unpublished Ph.D. Thesis, University of Western Ontario, London, Ontario. Pearson, W.N. 1978: Copper Netallogeny, Lake Huron, Ontario; Current Research, Part A, Geol. Surv. Canada, Paper 78-lA, pp. 263-268. �U - 40 - Pearson, W.N. 1979: Copper Metallogeny, North Shore Lake Huron, Ontario; Geol. Surv. Canada, Paper 79-lA, Current Research, pp. 289-304. of Pettijohn, F.J. 1957a: Paleocurrents of Lake Superior Precambrian Quartzites; Geol. Soc. Am., Bull., v. 68, pp. 469-480. Pettijohn, F.J. 1970: The Canadian Shield: A Status Report, 1970 (and discussion); in Symposium on Basins and Geosynclines of the Canadian Shield, ed. A. J. 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Wood, J. 1970: Evidence for a Tropical Climate and Oxygenic Atmosphere in Upper Huronian Rocks of the Rawhide Lake-Flack Lake Area, Ontario (abstr.); in 16th ann. mtg. Inst. on Lake Superior Geol. program (Thunder Bay, Ont.), pp. 45, 46. Wood, J. 1973: Stratigraphy and Depositional Environments of Upper Huronian Rocks of the Rawhide Lake-Flack Lake Area, Ontario; Geol. Assoc. Canada Spec. Paper No. 12, pp. 73-95, edited by G.M. Young. Young, G.M. 1969: Geochemistry of Early Proterozoic Tillites and Argillites of the Gowganda Formation, Ontario, Canada; Geochim. Cosmochim. Acta, v. 33, pp. 483-492. Young, G.M. 1971: Stratigraphic and Sedimentological Framework of the Huronian Rocks of the Southern Province of the Canadian Shield; Abstract, Geol. Assoc. Canada, Mineral Assoc. Canada, Abstracts and Program, Sudbury, 1971, pp. 75-76. Young, G.M. l973a: Origin of Carbonate-Rich Early Proterozoic Espanola Formation, Ontario, Canada; Geol. Soc. Am., Bull., v. 84, pp. 135-160. Young, G.M., and Chandler, F.W. 1968: Possible Glacial Origin for Three Precambrian (Huronian) Conglomerates, North Shore of Lake Huron (abstr.); in 14th ann. mtg. Inst. on Lake Superior Geol. programSuperior, Wis.), pp. 42, 43. �U - 42 - ADDENDA: Bennett, C. 1977b: Garden River Indian Reserve Area, District of Algoma; pp. 104-106, in Summary of Fieldwork, 1977, by the Geological Branch, edited by V.G. Mime, O.L. White, R.B. Barlow, and J.A. Robertson, Ontario Geological Survey Misc. Paper 75, 208p. Bennett, C., and Innes, D.C. 1979: Huronian Volcanic Rocks, North Shore of Lake Huron, Ontario; 25th Annual Institute on Lake Superior Geology, Duluth, Minnesota, pp. 8. Bennett, C., and Innes, D.G. (in preparation): Huronian Volcanism, Ontario Geological Survey, Geological Report. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1981 Description An account of the resource Institute on Lake Superior Geology. Michigan State University, East Lansing, Michigan. May 14-15, 1981. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1981 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English Contributor An entity responsible for making contributions to the resource H. All K. Attoh R. L. Bauer H. F. Bennett M. E. Bengtson D. Bhattacharyya M. S. Breithart B. A. Brown F. W. Cambray F. H. Carlson A. Choudhry C. Craddock M. D. Daggett P. A. Daniels, Jr. S. Day M. F. Deering D. Dushek C. P. Ervin K. Fujita H. P. Gilbert S. S. Goldich J. K. Greenberg H. C. Halls J. B. Hartung T.B. HoIst J. H. Karl R. P. Meyer E. T. Mohr C. W. Montgomery R. L. Morton M. Osterberg D. S. Paddock Z. E. Peterman P. K. Sims T. E. Smith F. L. Slaughter R.J. Stevenato M. Stupavsky D. T. A. Symons, S. E. Tituskin F. B. Van Houten M. A. Vos P. Wasuwanich J. T. Wilband