238 10 13081 https://digitalcollections.lakeheadu.ca/files/original/02ccd22010c6a26959f5b0298d72ee3e.jpg 24a3ff0b407384848e5514576f526843 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 Cairine Budner fonds 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 Kiri Athletic Club Subject The topic of the resource Sports Description An account of the resource Black and white photograph of gymnasts performing a balance routine on stage floor. Men are dressed in the Kiri uniforms for the time Date A point or period of time associated with an event in the lifecycle of the resource c1911 Contributor An entity responsible for making contributions to the resource Donor E. Takala Rights Information about rights held in and over the resource Public domain Format The file format, physical medium, or dimensions of the resource Photograph Type The nature or genre of the resource Still image Identifier An unambiguous reference to the resource within a given context PHIII-0012b (ii) scan#BUD-0029 1911 balance routine E. Takala gymnastics Kiri Athletic Club https://digitalcollections.lakeheadu.ca/files/original/1fd7c945743a19048d401359e5afc5b3.jpg d6812bad613730c89410b0dd4c6037cf 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 Cairine Budner fonds 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 Mixed pyramid Jyru Athletic Club Subject The topic of the resource Sports Description An account of the resource Black and white photograph of the mixed pyramid at the Finnish Labour Temple. Athletic director Heikki Roine is at the base of the pyramid. The group is dressed in Jury uniforms for the time Rights Information about rights held in and over the resource Public domain Format The file format, physical medium, or dimensions of the resource Photograph Type The nature or genre of the resource Still image Identifier An unambiguous reference to the resource within a given context PHIII-0012b (iii) scan#BUD-0030 athletic director Finnish Labour Temple gymnasts Heikki Roine Jyru mixed pyramid https://digitalcollections.lakeheadu.ca/files/original/118f590c7256fda60e65cf070c680ac3.jpg 3b7c20810edae391420d05b01e8dc8bc 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 Cairine Budner fonds 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 Nahjus Athletic Club building gymnastic pyramid Subject The topic of the resource Sports Description An account of the resource Black and white photograph of the Nahjus athletic club men's gymnastics pyramid at the Finn Hall stage Date A point or period of time associated with an event in the lifecycle of the resource 1920s Contributor An entity responsible for making contributions to the resource Donor E. Takala Rights Information about rights held in and over the resource Public domain Format The file format, physical medium, or dimensions of the resource Photograph Type The nature or genre of the resource Still image Identifier An unambiguous reference to the resource within a given context PHIII-0012b (iv) scan#BUD-0031 1920's Finn Hall gymnastics mens' Nahjus Athletic Club pyramides https://digitalcollections.lakeheadu.ca/files/original/4bb0a6fba9bbfb19e411edf5ac90c7da.jpg 4c9f76c5feea071f94ba1e12e3b21d00 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 Cairine Budner fonds 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 Jyru Athletic Club Subject The topic of the resource Sports Description An account of the resource Black and white photograph of Jyru athlete suspending a woman gymnastics with one arm Date A point or period of time associated with an event in the lifecycle of the resource 1920s Contributor An entity responsible for making contributions to the resource Donor E. Takala Rights Information about rights held in and over the resource Public domain Format The file format, physical medium, or dimensions of the resource Photograph Type The nature or genre of the resource Still image Identifier An unambiguous reference to the resource within a given context PHIII-0012b (v) scan#BUD-0032 1920's athletes gymnasts Jyru suspending https://digitalcollections.lakeheadu.ca/files/original/008f2fe217dc97b3cfe51ab8334afc2d.jpg 2ea4b7fbad2ecf02dbbac8beabfaa59f 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 Cairine Budner fonds 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 Kiri Athletic Club gymnasts Subject The topic of the resource Sports Description An account of the resource Black and white photograph of Kiri athletic club men's gymnasts. Athletes are standing and kneeling on one knee posing for the photograph Date A point or period of time associated with an event in the lifecycle of the resource 1920s Contributor An entity responsible for making contributions to the resource Donor E. Takala Rights Information about rights held in and over the resource Public domain Format The file format, physical medium, or dimensions of the resource Photograph Type The nature or genre of the resource Still image Identifier An unambiguous reference to the resource within a given context PHIII-0012b (viii) scan#BUD-0033 1920s athletes gymnasts Kiri Athletic Club 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/19e11aefc78ed911ffd2919a7a4f0e47.pdf 408bdbe9402ec8dd1840b6f48eed31bc PDF Text Text luoty !big Aoooal Meetio Institute on Lake Ihooder Hay, Ootariu Superior Geology �PROCEEDINGS tWENTY - THIRD ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY HELD AT THE AIRLANE MOTOR HOTEL THUNDER BAY ONTARIO MAY 2 — 8, 1977 SPONSORED BY THE ONTARIO DIVISION OF MINES AND LAKEHEAD UNIVERSITY THUNDER BAY.. ONTARIO M.M. Keh1enbeck,:S.A. Kissin, R.H. General Editors Mi t che 11 �This page intentionally left blank �TABLE OF CONTENTS GENERAL INFORMATION . INSTITUTE EOARD OF DIRECTORS LQCAL COMMITTEE Vi . SESSIONS CHAIRMEN . . ANNUAL BANQUET SPEAKER. ACKNOWLEDGEMENTS V . ,.. ... . . . . Vii Viii . ix CALENDAR OF EVENTSAND. PROGRAM ABSTRACTS FIELD TRIPS . . 51 A. COLDWELL COMPLEX, MARATHON, ONTARIO. 51 B. PROTEROZOIC ROCKS OF THE THUNDER BAY AREA 52 MATTABI, IGNACE, ONTARTO 53 C. iii �L GENERAL INFORMATION 23rd "ANNUAL INSTITUTE. ON. LAKE SUPERIOR GEOLOGY AIRLANE MOTOR HOTEL THUNDER BAY MAY 2. -: 8, 1977: SPONSORED BY THE ONTARIO DIVISION OF MINES AND LAKEHEAD UNIVERSITY THUNDER,. BA, 'ONTARIO INSTITUTE BOARD OF DIRECTORS P.E. Giblin, Ontario Division of Mines, Ministry Resources,. Sault Ste. Marie, Ontario. of Natural J.D. Hughes, Department of Geography., Earth .Science,and Conservation, 'Northern Michigan University, Marquette, Michigan. . M.M. $ Kehlenbeck, Department of Geology, L.akehead',Iiniversity, Thunder Bay, Ontario. R.C. Reed' (Secretary-Treasurer), Geological Survey Division, Department of Natural Resources, Lansing, Michigan. M.S. Walton, Minnesota Geological Survey, University of Minnesota, St. Paul, Minnesota. v �Trip C - Mattabi James M Franklin, Geological Survey of Canada, Ottawa, Ontario. WallyGibb, Mattabi Mines Ltd, Ignacé, Ontario. Howard Poulsen, Department of Geology, Läkehead University, Thunder Bay, Ontario. Paul Severin, Sturgeon Lake Mines Ltd. , Ontario. Adel Tammán, Mattabj Mines Ltd. , Ignace, Ignace, Ontario. Banquet Chairman John S. Mothersill, Dean of S,cience, Lakehead University, Thunder Bay, Ontario. Session Chairmen S.S. Goldich1, Department of Geology, University of Northern Illinois, DeKalb, Illinois. H.C. Halls, Dgpartment of Geology, University of Toronto, Toronto, Ontario. Bram Janse, Selco Mining Corp., Tpronto, Ontario. R.H. McNutt, Department of Geology, •McMaster University, Hamilton, Ontario. G.B. Morey, lvlinnesota Geologidal Survey, University of Minnesota, St.: Paul, Minnesota. R.W. Ojakangas, Department of Geology, University of Minnesota, Duluth, Minnesota. H. Walton, Minnesota Geo'ogical Survey, University of Minnesota, St. PaUl, Minnesota. G.M. Young, Department of Geology,. University of Western Ontario, London., Ontario. vii �LOCAL COMMITTEE General Chairman Hanf red M. Kehlenbeck, Department of Geology, Lakehead University, Thunder Bay, Ontario. Technical' Program Stephen A. Kissin, Department of'Geoiogy, Lakehead University,, Thunder Bay, Ontario. Roger H. Mitchell,' Department of Geology, Lakehead University, Thunder Bay, Ontarip; Field Trips Trip A - Coldwell Complex Roger H., Mitchell, Department of Geology, Lakehead University, Thunder Bay, Ontario. R. Garth Platt, Department of Geology, Lakehead University, Thunder Bay, Ontario. Trip B - Proterozoic Rocks of the Thunder. Bay Area Kenneth G. Fenwick, Ontario Division of Mines., Thunder Bay, Ontario. Clarence R.. Kustra,: Ontario Division of Mines, Toronto, Ontario. William " ' H. Mcllwaine, Petrologic 'Ltd. ,,thunder' Bay, Ontario. John F. Scott, Ontario Division Of Mines, Thunder Bay, Ontario. vi �Annual Banquet Guest Speaker Dr. J. Tuzo Wilson, Department of Physibs Geophysics Division, University of Toronto) Toronto, Ontario Acknowledgements The organizing committee for the 23rd Annual Meeting of the Institute on Lake Superior Geology gratefully acknowledges the work of Wendy Bons and Cathy LeBrun for typing the final, manuscripts of the field trip guidebooks and proceedings volume. Special thanks to Sam Spivak wh prepared the many figures, maps, and cover illustrations'. viii �CALENDER OF EVENTS AND PROGRAM MONDAY, MAY 2, 1977 1:00 p.m.- 330 p.m. Early Registration .AirianeMotor Hotel-Lobby 4O0 p.m. Pre—Institute field trip ACoidwell Complex departs from the Airlane parking lot for Marathon, Ontario: 8:00 p.m.—10:00 p.m. Early Registration Airlane Motor Hotel-Lobby TUESDAY, MAY 3, 1977 7:00 a.m.- 8:00a.m. 8:00 a.m. 5:00 p.m. Early RegiStration Airlane Motor Botel-Lobby :pre....Institute fièldtrip B— (part 1)—Proterozoic Rocks of the Thunder Bay area departs from the Airlane parking lot. Field trip B (part 1) returns to Airlane Motor Hotel. ix �WEDNESDAY, MAY 4, 1977 Pre—Institute field trip B (part 2)—Proterozoic rocks 8:00 a.m. of the Thund'ei Bay area. departs Airlane parking lot. 5:00 p.m.— 9: 00 p.m. Registration 5:00 p.m. Pre—Institute Airlane Motor Hotel—Lobby field trip B returns to Airlane (part 2) Motor Hotel. 5:00 p.m. Pre—Institute field trip A returns from Marathon to Airlane Motor Hotel. 8:00 p.m. Conference Smoker (cash bar) Tiberio Room - Airlane Motor Hotel THURSDAY, MAY 7:30 5, 1977 Registration Airlane Motor Hotel-Lobby a.rn.— 9:30 a.m. 8:30 a.m..-12:00 a.m. Technical Session 1 (see page xii) 1:30 p.m.-' 6:00 p.m. Technica' Session 2 (see page xiii) 7:00 p.m.— 8:00 p.m. Cocktail Hour (cash bar) Tiberio 1oom - Airlane Motor Hotel Annual Banquet - 8:00 p.m. x Tiberio Room �- FRIDAY, NAY 6, 1977 - 8:30 a.m.—12:;00 noon Technical Session 3 (seepage. xiv) l:30 p-.m.— 5:40 p.m. Technical Session 4 (see page xv) .1 6: 30 p.m. Post—Institute field trip C— Mattabi. departs Airlane parking lot for Ignace. Trip C will return on Sunday, May 8,1977 by 1:00 p.m. to Airlane Motor Hotel. 8:00 p.m. Northwoods MOtel, Ignace Informal discussion period in preparation for field trip.. xi �$7SSZON 2 1Morning' Thursday, May 5th, 2977 8.20 Opening Remarks 8.30 Meineke, D.G., Valdis, M.K. & Klaysmat. A.W. - 8:30 - 22:00 a.m. Organic-rich lake sediment exploration geochemical survey of eastern Lake Verraillion-Ely Minnesota. area, Northeastern 8.50 Beard, R.C.. Urani'vM deposits of the Kenora area. 9.10 0jakanas, R.W. Proterozoic pitchblende vein potential in Minnesota: Theory and Speculation. 9.36 Cannon, Two-hi 1 lion-year-old sedimentary phosphorite deposits in •the precambrian of northern Michigan. IV. F. 9. 50. - 10.00 t4ôrey, G.B.. Preliminary manganese resource for the Cuyuna District: approach. Mudrey, M.G., Massive sulphide deposits Beltrarne, R.J., I-Ioltzman, 10.20 £offe_ByLeak C. estimates A statistical in Wisconsin. Ostrom, M.E. Reinke, G. 10.40 Booy, E. Engineering problems in glacial soils near the Canadian-United States border. 11.00 Morey, G.B. Stratigraphic and tectonic history of lower and middle precambrian rocks in east-centra7 Minnesota. LaBerge, GIL. Major structural fsatures in Central Wisconsin and their implications on the 11.20 $ Animike Basin. 11.40 Davidson, D.M. 12.00 -. Paleostrain i.30 Lunch jj S analyvis: That, How and Why? �SESSION 2 'A Lt erno on" Thursday, l30 Ma_yb 5th, 19?? Birk, D. McNutt, R .H. - 1.30 - 6.00 p.m1 Rb/Sr geochronolo,yof Wabigoon Belt Granitoids, Northwestern Ontario. Rare earth element geochemistry of 'Archean anrphiboli tes, tona lites, granites and paragneisses in the eastern Lac Seul area, Ontario. 1.50 thou, C.L. 2.10 Mcbennan, S.M., Fryer, B.J. ' An estimate of the rare earth element'' distribution in Post-Kenoran upper crust, Young, north 2.30 G.M. of Lake Huron. The occurénce" and some nobel metal concentrations in selected komatiitic' ultramafic volcanic rocks from Munro McCrae, W.E. & Crocket, J.H. Township, Ontario. 2.50 3.00 3.90 goffe_Bea& Geochemistry of early proterozoic of Lake Huron, Ontario. Fryer, B.J. north 3.20 Longstaffe, F.J.,, 180/160 results for Archean plutonic rocks, Lake Despair 'area, Northwestern Ontario. Schwarcz,H:P. 3.40 4.00 ' 4.20 Review of Occygen isotope geochemistry of Ahinad, SN Perry, E.G. Jr. some precambrian Mitchell, R.H Platt, R.G.' CoQper, ' Mafic iron formations. mineralogy of ferroaugite syenite from the coldwell Complex, Marathon, Ontario. ' Weiblen, P.W. paleosols Shape, sixe, cznd cooling history of trochtolitic—gabbroic rocks in the Duluth E, R.W. complex. 4.40 McMaster, B., 1'icNutt, R.H. Archean volcanism Washeigamaga' Lake area, Wabigoon Subprovince, Northwest Ontario. 5.00 Blackburn, G.E., Identification 5.20 Pilatzke, R.H., Petrology and trend curface,analjgsis of two lake-stage gra'nodioritic plutons, Northern . Er Karner, F.R. Er Peterson, W.M. '5.40 Morris, W.J., E Wilband, J.T, of archean calc-alkaline volcanid centres in the Ma'nitou Lakes, area, Northwestern Ontario Lake of the'Woods region, Ontario. Geochemistry of the Yellow Dog Plains., Marquette County, Michigan. peridotite, xiii �SESSION 3 'Morning,' Friday, May ôf/j, 8.30 Weber, R.E. 1977 — 8.30 - 12.00 a.rn. The petrology and sedimentation of the upper precambrian sioux quartzite. of Minnesota South Dakota, and Iowa. 8.50 Morey, G.B Schulz, K.J. 9.10 Young, G.M., Long, D.G.F Petrographic and chemical attributes of some lower and middle precambrian gray-wacke-shale sequences in northern Minnesota. Deltaid deposits in tlze upper Pecors, Espanola and Gowanda formations (Huronian). McLennan, S.M. 9.30 Mancuso, J.J., Seavoy, R.E. Lougheed, M.S. Strati graphy of tle Baraga Basin metasediment, Michigan; 9.50 - 10.00. Coffle Break Lougheed, M.S. f Mancuso, J.J. Fossil collectibles from the Gunf lint 10.20 Shegeiski, R.J. Evidence fbr archean turbidite and submarine fan sedimentation from the Savant Lake greenstene terrain, N.W. Ontario. 10;40 Frost, B.R. Some comment; on the metamorphism of iron-formati 'n$. 11.00 Gower, C.F. Clifford, P.M. Metamorphism in the English River Feixzn, W.C. The stratigraphy and petrology of the archean volcanic rocks at Jasper Lake, eastern Vermilion District, Cook County, Minnesota. Maas, R.S., Medaris, L.G. El VanSchmus, W.R. Penokean structures and 10.00 Jl.20 11.40 12.00 - formatiiin. sub- province near Kenora, Northwest Ontario. Wisconsin. 1.30 Lunch xiv plutpnic rocks iv �SESSION 4 'Afternoon 1.30 Friday, May 6th, 1977 ' - 5.40 p.m. 1,30 Eyerson.C,I, Drift lithology in relation to bedrothk geology, Long Is land Lake Quadrangle, Cook County, Minnesota. 1.50 Zarth, R. Sedimentary facies associated with late 2.10 2.30 Wisconsin Glacial Lake. Duluth, Wrenshall 'areas Minnesota. Welke, C.J., Nebriga, E.t. Meyer, R.P. Swrficial Green, J.C. Environmental sediment analyse,s offshore of the copper-bearing provinc of Keweenaw Point, geotogy 'of the North Shore'a coastal zone management project. Lso - 3,00 43.00 Upper Michigan. Mothersill, j.s. Coffiae Break Post-glacial Canadian 3.20 the The application of linear topographic features a glaciated precainbiian terráine in Cooper, R.W. e Morey, G.B. t.o structural interpretation of northeas tern 3.40 sediment 'distribution ih of Lake. SuperiorS portion Minnesota. Geophysical' studies of peridotite dikes, Yellow Dog Plains, Northern Michigan. Snider, D.W,, Kiasner, J.S, Quam, S., Lilienthal, R. Geraci, P. G Grosz, A. 4.00 4.20 Dugan, J.P. Jr. Ervin, C.P. Geophysical study 'of a gabbroic' intrusion, Klasñer,' J.S., Bouguer gravity anomaly map of northern peninsula of Michigan, Lake Superior, and Hinze, W.J.,Bacon, L.0. 4.40 E O'Hara, N.W. Chandler, v.w., Hinze, w.j. Braile, L.W. ' ' 5.00 5.20 environs. Analytical'correlation magnetic data in of gravity and the North American Midcontinent. studies of a regional'gravity model anomaly in norther'n'Michigan and Wisconsin, .extent.of anomaly, and its relationship to near surfac geology. D.' Pesonén, LJ . Halls, 4Ij.C. Lake, Wisconsin. Crustal Klasner, J.s. Bomke, Clam " PaleomagnetidAtiñdpaleointensity studies of normal and reversed keweenawan 'rocks - implications North xv for the polar wander path of America. �Str cts �This page intentionally left blank �REVIEW OF OXYGEN ISOTOPE GEOCHEMISTRY OF SOME PRECAMBRIAN IRON FORMATIONS S.N. Ahmad and E.C. Perry, Jr. ABSTRACT A review of published values for oxygen isotope data for quartz and magnetite from the Hamersley Iron Formation and the eastern portion of the Biwabik Iron Formation indicates that consistent trend lines appear if ol8o of quartz and magnetite are plotted v5AQM. This implies that during metamorphism these iron fprmations behaved as closed systems on same scale and that the system as a whole records isotopic information not present iii any one sample. The Hamersley and Biwabik trend lines intersect one another at a olSo for quartz of about 24.0 0/00., a value close to that observed for pure chert horizons in the Hamersley Iron Formation and the Gunflint Iron Formation (correlative with the Biwabik). Subject to certain assumptions, the intersectiônof the Hamersley and Biwabik oxygen isotope trend lines permits us to estimate that the temperature oX precipitation or diagenesis of these iron formations was about 22°C. A continuing study of other iron formations of low metamorphic grade may show whether this temperature estimate is reliable. It may also permit evaluation of reactions proposed by several authors for conversion of iron carbonate to magnetite during diagenesis and metamorphism. 3 �URANIUM DEPOSITS O,F'TH:IENORP AREA R. C. Beard, Ont. Div. of Mines, MNR, Kenora, Ontario Uranium deposits were first recognized in the Kenora area in 1949 and exploration has been carried out on these occurrences during two periods, 1952-57 and 1965-67. Recent increases in the price of uranium have stimulated a new cycle of exploration in the area, and numerous programs, both detailed examinations of previously known occurrences and grassroots exploration for new deposits, are currently under way. Past work on the various properties consisted of tren— ching, geophysical surveys, and diamcnd.drilling. An exception, the flew Campbell Island Mining and Exploration Ltd. deposit in MacNicol Twp., has been explored by underground development on two levels. Over thirty deposits have been documented in the KenoraDryden area; there is evidence to suggest that many more have been discovered which have not yet found their way into the public record. They tend to be concentrated in two general areas: a) near Vermilion Bay, 40 miles east of Kenora, associated with a narrow "greenstone" belt and, b) north of Kenora within the English ,River Gneiss Belt. The uranium occurrences are (typibally) asociated with pegmatitic phases of anatectically—derived, rather than plutonic, granitoid rocks. Supracrustal rocks of Archean age, exhibiting remelting and assimilation features to varying degrees, are associated with almost all deposits. These are quartz-biotite paragneisses of sedimentary derivation although some deposits are associated with amphibolitized mafic volcanic rocks. 'Uranium occurs as fine grains of uraninite disseminated in the granitoid rocks which are usually, but not always, It js frequently associated with one pegmatitic in texture. of the following accessory minerals: biotite, magnetite, sulphides, or apatite. Minor leaching and redeposition as uranophane along near surface fractures is common to many of Grab sample assays from radioactive zones range the deposits. from 0.5 or less to 1.5 'lbs. U 08 per ton; with occasional grab samples assaying over 10 bs. per ton. It is suggested that the urahiferous pegmatites of the area are, to a certain extent, stratigráphically controlled,: having been anatectically derived from supracrustal rocks which contained ahomalous amounts of uranium. Study should be directed toward the identification of these "source beds", so that exploration may then be directed to these more favorable areas. Reconnaissance mapping by the Ontario Div. of Mines (Breaks et al, 1975) suggests one such area near Umfre— ville Lake, north of Kenora. 4 �PRELIMINARY MANGANESE RESOURCE ESTIMATES OR THE CUYUNA DISTRICT: .A STATISTICAL APPROACH R.3. Beltrame, Richard C.' Holtzman, and G.B. Morey, Minnesota Geologiëal Survey, University of Minnesota, St. Paul, Minnesota. The Cuyuna range in east-central Minnesota has produced over 105 million tons of iron ore and manganiferous-iron ore during the past 62 years. Although iron ore reserves are nearly exhausted and all mining activity, has ceased, significant amounts of manganese beating materials are presently available. The occurtence of high-grade rnanganiferous material (>5 weight % Mn) is generally limited to the Emily iron-formation member of the Rabbit Lake Formation and more commonly to the Trommald Formation. In both iron-rich units the manganese is present in both the original protolithic iron-formation (10-30% Fe) and the so-called secondarily enriched "natural ores" (40-60% Fe). In the Trommald Formation of the North range,most of the manganese occurs in the transistion zone between the thick-bedded (granule chert layers 1-100 cm thick) and thin-bedded (laminae ci cm thick) facies rocks. Due to the complexity of the stratigraphic and structural relations and because of the enormous amount of available drill hole data, preliminary manganese resource estimates were statistically calculated for 69 uniquely defined deposits. A deposit was defined, for statistical reasons, as a legal land section. The location coordinates, collar elevations, and chemical assay data for 5,045 drill holes were entered into a computerized storage and retrival system. Statistical methods involved calculating an area of influence for each given Mn assay value for each drill hole. These areas of influence were calculated based on the spatial distribution of drill holes in each deposit and the location of the drill hole relative to the section boundaries. Computer-generated data location and drift thickness maps were produced as were grade-quantity estimates of manganese resources. Manganese quantity resource estimates were calculated for five gcade classes (13%, 3-5%, 5-10%, 10-15%,and >15%) for each of five depth intervals (<30, <60, <90, <120, and < 150 meters below the surface) for each of the 69 deposits.' Resource estimates for three deposits in the Emily district, 39 deposits in the North range, and 27 deposits in the South range accounted for 6%, 77%, and 17% of the total Cuyuna district resource estimate respectively. A total of 22.4 billion metric tons of manganiferous material (>1% Mn) was talculated 'to a depth of 150 meters for the entire Cuyuna district. More realistic values are 2.3 billion metric tons at>5% Mn, and 887 million metric tons at >10% Mn, calculated to a depth of 60 meters. 5 �Rb/Sr GEOCHRONOLOGY OF WABIGOON BELT GRANITOIDS, NORTHWESTERN ONTARIO DIETER BIRK and POI3ERT H. McNUTT Department of Geology, McMaster University. Hamilton, Ontario L8S 4M1 granitoid ThirtyLóne whole rocksamples from five piutons, intrusive intomet- volcanics- of the Wabigoon Greenstone Belt, generate a composite Rb/Sr errorchro (MSWD = 2,34): Age = 2621 ± 42 m.y'. (2°) k0 = :7007 ± 4 (2e) Linear regression of togenetic samples generate Rb/Sr isochrons sensustricto for each pluton as follows: Pluton (No. Of Samples Analysed) Age in m.y. Lithology (± 2a) - Initial Location Ratio (± 2a) (NTS) Burditt Lake (9) granodiorite 2598 ± 45 .7009 ± 6 52C/13 Esox Lake (4) quartz-feldspar porphyry 2572 ± 42 •.7003 ± S -52F/3 Flora Lake (5) granite-monzodiorite 2636 ± 63 .7017 ± 52F/S Taylor Lake (5) granodiori'te-monzonite 2640 ± 31 .7005 ± 3 52F/7E- Ryckman Lake (7) granodiorite-.mónzodiorite 2609 ± 63 :7001 ± 52C/lS 2230 ± 55 Ryckman Lake (5) For the Ryckman Lake Stock, the lower S .7012 ± 2- 52C/1S age, is fro'm a "pseudoisochron" caused- by the fortuitous alignment of five data points beyond that expected from known analytical error. The seven point isochron represents a wider range of rock chemtstry a-nd more meaningful age and-intercept. Isochron data must be tested by several linear regression techniques to expose such "pseudoisochrons'1. i These Wabigoon granitoid isochrons, when compared with published isochrons from the Rainy Lake area, suggest juvenescence of granitoid plutonism from north to south. This may relate genetically to the presence of the Quetico-Wabigoon Belt interface near Rainy Lake. The low 875r/86Sr ratios for all the late-kinematic granitoids implies a source region of low Rb/Sr. Partial melting of upper mantle rather than older sialic material is indicated, 6 �IDENTIFICATION OF ARCHEANS CALC-ALKALINE VOLCANIC CENTRES IN THE MANITOU LAKES AREA,. NORTHWESTERN ONTARIO C. E. BLACKBURN Ontario Division o: Mifles, Queen Park, Toronto A B S T R A C T Centres of felsic to intermediate vo1Oanisn within Archean volcanic-sedimentary belts have long remained enigmatic. In their detection reliance has frequently been made upon physical parameters in pyroclastic rocks (eg. coarsening towards vents), without special attention to overall volcanic and subvolcanic stratigraphy. In the Manitou Lakes area detailed geological mapping has pinpointed a number of vent areas, both simple and compOund. Within the study area a thick submarine basaltic flow sequence of tholeiitic affinity was built up, followed by eruption of a caic—alkaline sequence composed predominantly oE dacitic to andesitic coarse pyroclastics. The tholeiitic baa1t sequence was intruded by quartz-feldspar porphyry plugs, at Sunshine Lake and at Thundercloud and Washeibemaga. Lakes (McMaster and McNutt, this volume). The plug at Sunshine Lake is the subvolcanic equivalent of rhyolitic flows that occur within the pyroclastic sequence. This plug was in turn intruded by irregular lamprophyric dikes and sills that are subvolcanic equivalents of a calc-alkaline to alkaline mafic flow that terminated volcanism in this part of the area. Southwest of Cane Lake, elongate to lenticular quartz-feldspar porphyry bodies within the pyroclastic sequence variously have subvolcanic and volcanic characteristics, suggesting theY. location of a felsic vent in this vicinity. A mafic sill correlatable with the late mafic phase at Sunshine Lake occurs in close spatial association with these porphyries. None of these vents has been directly identified as supplying dacitic to andesitic pyroclastic debris. However, one vent that did supply such coarse pyroclastic material has been identified at Frenchman Island, Upper Manitou Lake, where a. subvolcanic porphyritic to inequigranular plug intrudes coarse pyroclastics of comparable chemical and.. mineralogical composition. 7 �ENGINEERING PROBLEMS IN GLACIAL SOILS NEAR TILE CANADIAN-UNITED STATES BORDER Emmy Booy Department of Geology ar3d Geological Engineering Michigan Technological University Houghton Michigan 49931 ABSTRACT The borderlands of the United States and Canada ranging from Lake Superior eastward to the Gulf of St. Lawrence are characterized by the presence of glacial deposits which cause problems in safe utilization of the land. At various locations, but particularly along the valley of the St. Lawrence River and its tributaries and along the southern margin of Lake Superior, slope failures have caused expensive losses in property and hazards to human life. Because glacial clays in northern climates have been .known for cén— tunes to be prone to failure, they have been studied by engineers and geologists to determine the causes of their failures and means for controlling them. Most of these investigations have concentrated on the so—called "quick clays", glacial clays laid down in marine environments. There have been relatively few studies of fresh—water glacial deposits and their relationship, if any,,to the marine and estuarine deposits. At the present state of knowledge, there is no definitive explanation for the sudden outflows of clay which are characterized as quick clay failures. It should be noted that a variety of types of failures are observad in all the glacial deposits. Many of them appear to be a result f excess hydrostatjc pressure in the coarser strata of varved deposits. These occur in both the fresh water and marine deposits. Classic slump failures have, also been described in both fresh and salt—water deposits. The only major difference in slope stability between the more easterly marine deposits of glacial soils and those deposited in the fresh water predecessors of Lake Superior, is the apparent lack of quick clay flows in the latter. These flows have been reported from Scandinavia, Alaska, and eastern Canada as occurring suddenlyon slopes as low as a few degrees. The failed material has an extremely low viscosity and may require hours to regain significant shear strength. There has been a significant lack of reports in the literature of similar failures in freh—water glacial deposits. It appears likely that there is a significant difference in material between those soils which fail as quick clays and those which do. not. It is generally agreed that there is a major rearrangement of soil fabric during quick clay failure which is held responsible for the variation in shear strength between failed and unfailed portions- of a deposit. Itis equally possible that the "cement" which is alleged to give quick clays their original shear strength is significantly different i-n marine and fresh water glacial deposits. S �Two—billion—year—old sedimentary phosphorite deposits in the Precambrian of northern Michigan 1/ by W. F. Cannon S. Geological Survey Reston, Virginia 22092 U. Abstract Phosphate—rich beds have recently been found at five localities in 2—billion—. year—old metasedimentary rocks of the t4arquette Range Supergroup in northern Michigan (Cannon and Klasner, 1976). All occurrences are near the unconformable base of the supergroup within 100 meters stratigraphically above older gneisè. Four occurrences are in the Michigamme Formation, part of the Baraga Group; the fifth is in the older Ajibik Quartzite, part of the Menominee Group. as The phosphatic minerals occur in two ways: 1) thin beds of apatite, mostly associated with lean carbonate iron—formation, and 2) as pebbles of apatite in conglomerate. Two thin—bedded occurrences in the Michigannne Formation, first reported by Mancuso and others (1975), have not been evaluated for grade and extent. Of the three new occurrences reported by Cannon and Kiasner (1976), two are low grade and consist of scattered pebbles of apatite in basal Michigamme and Ajibik conglomerates, and a few thin beds of apatite generally less than 1 cm thick. The third contains thick conglomerate beds, including a bed about 15 m thick that averages about 15% P205, and many thinner beds of comparable grade. Because outcrops are very limited in *the area, the grade and extent of the deposits are impossible to determine without subsurface data, but the economic potential of these deposits warrants further evaluation. 'The area has never been systematically explored for phosphate minerals. The five known occurrences were found by only a cursory examination of field notes and hand specimens; none of these rather cryptic deposits was identified in the field. Precambrian sedimentary rocks have not been considered a likely host for' economic phosphate deposits in the United States, and these deposits are the richest so far known in the Precambrian of this country. Because five localities have been found without a thorough field search in an area that has very sparse outcrops, a good possibility exists for undiscovered phosphate deposits in the region. - References cannon, W. F., and Klasner, J. 5., 1976, Phosphorite and other apatite—bearing sedimentary rocks in the Precambrian of northern Michigan: U. S. Geol. Survey Circ. 746, 6 p. Mancuso, J. J., Lougheed, M. 5;, and Shaw, R., 1975, Carbonate—apatite in Precambrian cherty iron—formation, Baraga County, Michigan: Econ. Geology, v. 70, no. 3, p. 583—586. 1/ Prepared in cooperation with •the Geological Survey Division, Michigan Department of Natural Resources 9 �ANALYTICAL CORRELATION OF GRAVITY AND. MAGNETIC DATA IN THE NORTH AMERICAN NIDCONTCNtNT V.W. Chandlr, W.J. Hinze and L.W. raile Department of Geosciences Purdue University. West Lafayette, Indiana 47907 The correlation of gravity ane mágñetic data isone of the most commonly used geophysical techniques in basement. This usage is especially vital in the geological studies. Midcontinent area of North America where direct observation of the basement complex is essentially prohibited by a In the past the àorrelation blanket of Phanerozoic strata. of.gravity and magnetic data has usually been carried out by purely visual method:; or by restricted applications of Visual theoretical methods such as Poisson's theorem. methods are hampered by their subjectie nature wherea the classical application of Poisson's theorem is often voided Recent studies have by necessary theoretical assumptions. investigated several computerized apprc'aches to the correlaOne of these recently tion of gravity and magnetic data. developed techniques, internal correspondence, has been investigated through model studies and has been shown to be a potentially valuable supplement to ccmbined gravity and magnetic interpretation. The technique '3 involves a moving window analysis Df anotalies of the fir;t vertical derivative A least squares of gravity and iragnetics reduced to the pole. linear regression is conducted between the two data sets for each window position with a subsequent creation of three Considregression coefficient arrays over the data space. eratic:n of Poisson's theorem shows that the slope coefficient array is equivalent to a continuous estimate of magnetization-density ratios for anomalous sources. The intercept coefficient array yields valuable information regarding The correlation coefficient array anomaly base levels. expresses the significance of the linear fit for each window position. Analysis of gravity and riagnetic data from. the Midcontinent region of North America demonstrate that the internal correspondence approach yieldE useful constraints in local as well as regional geophysical irterpretation of the basennnt complex. - 10 �RARE EARTH ELEMENT GEOCHEMISTRY OF ARCHEAN AMPHIBOLITES, TONALITES, GRANITES AND PARAGNEISSES IN TIlE EASTERN LAC SElL AREA, ONTARIO C.—L. Chou, Department of Geology and Erindale College, University of Toronto, Mississauga, Ontario, Canada LSL1C6 ABSTRACT Using neutron activation techniques twenty samples from the eastern Lac Seul area of the English River gneiss belt have been analyzed for twenty—eight major and 'trace elements (A12O3, total Fe, MgO, CaO, Na2O, K2O, T1O2, MnO, Sc, V, Cr, Co, Zn,'Rb, Zr,. Ba, La, Nd, Sm, Eu, Tb, Dy, Yb, Lu, Hf, Ta and Th). Variations of Mn, Sc, Co and Cr are related to total Fe content, their concentrations decrease in the order of amphibolites, tonalites paragneisses, leucosome, trondhjemite, granites, muscovite granites, and peginatite. Distinct rare earth element (REE) patterns are found for. various rock types. Two amphibolites have flat REE patterns and total REE contents about l0—l2X chondritic abundances, similar to Archean basalts. A third amphibolite (T91) is enriched in La and Ce relative to other amphibolites, probably due to metamorphism. Six tonalites can be separated into two groups based on their REE patterns. Type—A tonalites (4 samples) have smooth and steep—sloped REE patterns with remarkable enrichment of lIght REE and depletion of Ce, heavy REE (LaE F =71—135 and YbE F 3—11). Type—B tonalites (two samples) have higher total REE contents than type—A, negative anomalies and flat heavy REE abundances (LaEF = 106—112 and Type—A tonalites may have derived from garnet = 22—39) . eclogites, with garnet as a residual phase during partial melting, Eu whereas type—B tonalites are probably derived from dioritic source with amphibole and plagioclase as residual phases. Granites have smooth and steep—sloped REE patterns. Muscovite granites have lower light REE contents than granites and negative Eu anomalies. Both granites and muscovite granites may have originated from sedimentary rocks by crustalanatexis. The REE patterns of garnet paragneiss and biotite paragneiss are. similar to type—A tonalites, suggesting that tonalitic rocks are the dominant source of meta— sediments. 'I �THE APPLICATION OF LINEAR TOPOGRAPHIC I'EATURES TO STRUCTURAL INTERPRETATION OF A GLACIATED PRECAMBRIAN TERRANE IN NORTHEASTERN MINNESOTA R.W. Cooper and G.l3. Morey, Minnesota Geological Survey, tiniMersity of Minnesota, St. Paul, Mjnnesota The application of linear topographic features to various kinds of structural interpretations has become increasingly popular since the advent of spacecraft and high-altitude imagery. Although many types of lineaments can be recognized in Minnesota, a major question remains as to their usefulness in structural studies, particularly in areas where glacial activity has obscured many fundamental bedrock attributes. We have analyzed in detail an area of 3600 sq. km. in parts of northern St. any, exists Louis and Cook Counties. Minnesota to determine what correlatAu, between the bedrock geology and topographic linearrients. The bedrock geology of our study area may be divided into four strato-tectonic units: (1) Lower Precambrian metavolcanic and metasedirnentary rocks of Jhe Vernlion distct having a &redeminance of Saults trending approximately N.20 E., (2) Lower Precambrian "granitig" N.33 E., N.55 -6o°E;, N.70 -75 E. and N.85 E.; rocks of the Vermilion massif and Giants Range batholith having faults trending N.20 40 E.; (3) Middle Precambrian sedimentary rocks of the Animikie Group having a few northwest- and north-northeast- trending faults; and (4) various kinds of Upper Precambrian mafic rocks assignable to the Duluth Complex. lm\ addition, the northern part of the study area is covered by thin (c6 meters), discontinuous patches of Quaternary materials, 'whereas a thick, more- or less continuous mantle of these materials obscures bedrock relationships in the southern part of the area. The southern part of ths stu0dy area is characterized by numerous topographic lineãments trending in a N.35 -40 E. direction; a direction parallel to movement of the Rainy lobe in this area. In contrast, lineaments in the northern part of the study area exhibit a number of divora !irect½r.a. ".r.tn alysis o these lineaments indicates that bedrock structural features exerted a profound influence on 8resent-y lend forms. or eample, an excellent correlation exists between N.20 E., N.35 -40 F_.. N.55 -60 E. and N.85 E. trending lineaments and ground-mapped faults in areas underlain by Lower Precambrian metavolcanic and etaedimentary rocks. Similarly there is a marked correspondence between N.25 -40 E. trending lineaments and ground-mapped faults in areas underlain by the Lower Precambrian Vermilion massif and Giant's Range batholith. FUrthermore faulting or fracturing in a northeast direction may be much more prevalent in the "granitic" rocks than present mapping indicates 'ecause of many codirectional lineaments that are not ssociated with areas of known faulting. Previous mapping has documented only a few northeast- and northwest-trending faults in the Duluth Complex. However this part of the study area is characterized by nhim,rn,,c northeast-trending topographic lineaments. Thus an area of approximately 20 sq. km. was mapped in detail to determine if the lineaments could be related to any strtktural features in the bedrock. As a result of this mapping several faults having unknown amounts of displacement were recognized that correspond to major lineament trends. Subsequently it was recognized that many topographic lineaments also coihcide with northeast-trending aeromagnet ic lineaments and with disrupted struc- tural elements such as contacts between, and o1Lsiü .. n vnap units. This suggests that faulting in a northeast direction was a majar tectonic process during and after.intrusion of the Duluth Complex. A few northwest-trending faults have been inferred, primarily on the basis of subsurface inforrnaiiui, tn nit the western margin of the Duluth Complex. In places these faults correspond to mapped faults in the Middle Precambrian Animikie Group, whereas in other places they correspond to well-defined northwest-trending aeromagnetic gradients. However other magnetic gradients have no known geologic expression. We infer from these data that northwest-trending faults may he more numerous than present mapping indicates. The results of our lineament analysis suggest that any pre-glacial topographic expression of the. northwest-trending faults was eliminated by the. southward flow of glatial ice which at the same time enhanced the topographic expression of the northeast-trending bedrock structures. Thus although topographic lineaments are a useful adjunct to structural studies in nqrthern Minnesota, they must be carefully interpreted in terms of the glacial history. �PALEOSTRAIN ANALYSIS: WHAT, HOW AND WHY? Donald M. Davidson, Jr., Geology Department, University of Minnesota,. Duluth, 55812 ABSTRACT WHAT? Several excellent techniquest for 3lantitatively'analyzing natural strain (paleostrain) in deformed rock units have appeared in the geological literature within the past decade. HOW? Samples are collected and slabbed along orthoganal planes ot photographs taken of the unit viewing three such planes. Deformed structures within rocks, such as fossils, oolites, concretions, phenocrysts, or reduction spots, often The major and minor axes of these ellipses may be have elliptical shapes. measured along with angular relationship of the axes (0) to some fundamental directional property in the rock (bedding, cleavage, foliation, lineation). The particular method used in treating the data is dependent upon certain assumptions fundamental to the mathematical techniques employed, although virtually Other all methods assume that deformation involved finite, homogeneous strain. assumptions relate to.knbwledge of the initial shape of the deformed object (circular or otherwise) tr knowledge of the orientation of primary planar features such as bedding ,within the deformed unit. The procedures of Ramsay, Elliott, Dunnet, Hsu and Matthews and a new method currently being developed at the.University of Toronto will be reviewed, WHY? Paleostrain techniques are powerful tools in direcdy analyzing strain history in rocks and shear zones, in preferentially.discriminating between defor— mational models or in treating sedimentary fabrics.. These methods warrant' serious. consideration by geologists working in the Lake Superior region. REFERENCES Barr, M. and Coward, M. P., 1974, A method for the, measurement of volume change, Ceol. Nag., v. 111, p. 293—296. Boulter, C. A., 1976, Sedimentary fabrics and their relation to strain— analysis methods: Geology, v. 4, p. 141—146. Coward, M. P., 1976, Strain within ductile shear zones? Tectonophysics, v. 34', p. 181—197. Coward, N. 1?. and James, P.. R. 1974, The deformation of two' Archaean greenstone belts in Rhodesia and Botswana: Precambrian Res., v. 1, p. 235—258. Dunnet, D. and Siddans, A.W.B., 1971, Non—random sedimentary fabrics and their Tectonophysics, v. 12, p. 307-325. modification by strain: Elliott, D.,' 1970, DeterminatiOn of finite strain and' initial shape from deformed elliptical objects: Geol. Soc. Amer. Bull: v. 81, p. 2221—2236. Hobbs, B. E. and Talbot,' J. 1., 1966, The analysis of strain in deformed rocks. Jour. Ceol: v. 74, p.'. 500—512. Matthews, P. E., Bond, R.A.B; and Van Den Berg, J. J., 1974, An algebraic method of strain analysis using elliptical markers: Tectonophysics, v. 24, p. 31—67. Owens, W. H., 1974, Representation of finite ,strain state by three—axis planar diagrams: G.S.A. Bull., v. 85, p. 307—310. Ramsay, J. G., 1967, Folding and fracturing of rocks: McGraw—Hill, New 'York, p. 103—120, 134—142, 200—221. Talbot, C. J., 1969, The minimum strain ellipsoid using deformed quartz veins: Tectonophysics, v. 9, p. 47—76. Tobisch, 0. T., et al., 1977, Strain' in metamorphosed volcaniclastic rocks and its bearing on the evolutiQn of 'orogenic belts: G.S.'A.B., v. 88, p. 23—40. ' , 1.3 . ' �GEOPHYSICAL STUDY OF A GABBROIC INTRUSION, CLAM LAKE, WISCONSIN Joseph Patrick Dugan, Jr., and C. Patrick Erviri, Dept. of Geology,Northerrt Illinois University, DeKalb, IllinOis 60115 ABSTRACt Aeromagnetic maps recently released by the &Wisconsin Geologiàal àhd Natural History Survey contain a sharp, 7000 gamma magnetic anomaly near the town of Clam Lake, Ashland County, in the northwestern part of the state. The anomaly has a wavelength of only 5.5 km, suggesting a shallow source. A coincident, but less well-defined, Bouguer gravity anomaly of 15-20 mgals is also present. Inland Steel Company drilled a 104 m hole in the center of the anomaly using a diamond drill. The lithologic log shows 29 meters of drift overlying a fresh, unaltered gabbroic sequence with zones containing up to 60% magnetite and ilmenite. Preliminary analysis of the potential field anomalies suggests that the source is a vertical body that is circular-to-elliptical in horizontal section. Since the Mellen Gabbro Complex lies only about 8 •km to the north, the Clam Lake Anomaly may be caused by an intrusive offshoot at depth.. 14 �DRIFT LIThOLOGY IN RELATION TO BEDROCK GEOLOGY, LONG ISLAND LAKE QUADRANGLE, COOK COUNTY, MINNESOTA Curtis I. Everson, Department of Geology, University of .Minnesota, Duluth Lithologic studies in northeastern Minnesota suggest that drift prospecting is a useful tool for mappIng drift—covered bedrock. A detailed study of till clasts composition in the Long Island Lake quadrangle revealed a significant relationship between drift lithology and bedrock geology. The Long Island Lake quadrangle. is a suitable area for this study for 1) outcrops are numerous enough to have allowed the following reasons: the construction of a detailed geologic map, 2) the area contains eight 3) the local bedrock experiended glacial erosion,. distinctive rock unit, indicated by the existence of glacially abraded and quarrIed outcrops. The distribution of glacial sediments, mainly till and outwash,&were mapped,. and one hundred and one samples of drift were collected along traverses parallel to ice flow (perpendicular to strike of the bedrock). Both till and outwash contain a large quantity of local bedrock clasts in the size ranges greater than 2 mm in diameter. Clasts smaller than 2 mm are mainly the mineral quartz, and therefore not so diagnostic of local As a test, boulders greater than 1 meter in diameter were used bedrock. in the field for inferring bedrock contacts. These contacts were found to be within ± 60 meters (200 ft.) of cQntacts placed by outcrop mapping.. tack of local bedrock clasts in the smaller size fractions indicate either high resistance of local bedrock to crushing, or lack of opportunity for crushing because of short residence .time in the glacial system (short distance transport). In either case, the fine—grained fraction therefore represents a eontribution to the glacial load from more distance sources. 15 �THE STRATIGRAPHY AND PETROLOGY OF THE ARCHEAN VOLCANIC ROCKS AT JASPER LAKE, EASTERN VERMILION DISTRICT, COOK COUNTY, MINNESOTA William C. Feirn, Geology Department, University of Minnesota, 55812 Duluth, Minnesota ABSTRACT The Jasper Lake area, located within the eastern Vermilion district in Cook County, northeastern Minnesota, represents the basal portion of a thick metavolcanic-metasedimentary sequence. Gruner (1941) found the area to contain threedominantly.ign'eoas units: a greenstone unit, an "agglomerate-conglomerate" unit, and an "andesite intrusive" unit., These rocks were shown t& have been complexly faulted and isoclinally folded. All units have been metamorphosed to greenschist facies. The oldest unit consists of predominantly massive metavolcanics (including basalt, diabase, andesite, and lesser dacite) and is herein referred to as the Jasper Lake greenstone. Du'e to the presence of pillow structures and quench textures observed at several localities, thse rocks are interpreted, as subaqueous The unit is linear in outline, 1000—1500 meters thick flows. (exposed), and trends east-west, and is probably continuous with the Chub Lake Volcanic Complex of Morey, Weiblen, and others (1971) to the east. The SaganaEa tonalite intruded the greenstone unit along its northern margin, locally metamorphosing it to amphibolite n'ade along a 30-60 meter wide zone. The "agglomerate-conglomerate", herein referred to as the Jasper Lake pyroclastic unit, and the associated "andesite intrusive" conformably overlie the greenstone. The pyroclastip unit consists mainly of volcanic breccias, tuffs, and lesser amounts of epiclastic volcanic breccias, conglomerates,, and metaClasts range from 0.1 mm to 1.2 meters in diameter graywacke. and are composed of dominantly porphyritic andesite with very minor amounts of basalt, dacite, and tuff. Some of the basaltic clasts may have been derived from the older greenstone unit. The Jasper Lake andesite unit (Gruner's "andesite intrusive") is composed of predominantly porphyritic augite andesite with lesser amounts of massive, porphyritic hornblende andesite-dacite. The rock is typically fine-grained to aphanitic, and vesicular to amygdaloidal, thereby representing a shallow hypabyssal intrusion which may have reached the surface locally. These rocks are conformably overlain by a well-bedded, graded graywacke-slate unit, greater than 1.6 kilometers thick. Detailed study in the area shows that the volcanic rocks at Jasper Lake represent the oldest portion of the regional volcanic pile. They trend west-northwest and are faulted off to the west by northeast-trending units which are clearly younger, as they contain clasts of the Saganaga tonalite, which intrudes the greenstone. �SOME COMMENTS ON THE METAMORPHISM OF IRON—FORMATIONS B. Ronald Frost, Department of Geology, University of Minnesota, Duluth, Mn. 55812 ABSTRACT Preliminary work on the metamorphism of iron—formations shows that the rocks can be modeled by the system Fe—Si—O—C—H. In the typical assemblage of Fe—silicate-- quartz—magnetite, the fluid composition is controlled by a reaction of the form: Fe—silicate + 02 = magnetite t quartz ± H2Q When fayalite i present the oxygen fugacity is controlled by the QFM' buffet1 and it deviates increasingly from the buffer when it is controlled by increasingly lower—temperature Fe—silicates. It is conceivable that at very low temperatures, of the range of diagenesis, the oxygen fugacity buffered by the greenalite + those quartz + Fe—oxide assemblage is high enough to make the coexisting Fe—oxide hematite. The presence of siderite requires the consideration of carbon in the fluid Fortunately, the oxygen fugacities of an Fe—silicate—quartz—magnetite rock seem to be high enough to allow CO2 to exist as the major carbon—bearing component in the fluid instead of CH4. Under such conditions siderite will.break down to magnetite by the reaction: phase. 6 siderite 1- 0.2: = 2 magnetite Siderite + 6. CO2 will also react to form an Fe—silicate by the reaction: siderite + quartz +H20 = Fe—silicate Simple topological calculations show that the assemblage siderite ± magnetite + Fe—silicate + quartz will be isobarically, isothermally invariant, indicating that at fixed T and P the fugacities of O2 H2O, and CO2 will be fixed.. Furthermore, the same diagrams show that the breakdown of siderite to magnetite canoccur at constant f0 if there is a gradient of H20 present; 2 model can be used to explain the origin of magnetite in siderite—bearing taconite formations. If the rock originally consisted of alternating layers rich This in siderite with those containing iron—silicate + quartz, each layer would be Equilibration of the fluids across the layers would cause the chemical potential of CO2 in the siderite layer to decrease, and induce the formation of magnetite without introduction of oxygen from outside buffered to a.different. fluid co:mposition. the system. . . 11 . ,. �Geochemistry of Early Proterozoic PaleosoU; North ofLakeHuron,bntir±o B. J, Fryer, Department of Geology University of Western Ontario London, Ontario, Canada The contact between the reHuroniàrI and Hurbniañ tôcks, north pt Lake Huron, Ontario, is often marked byresidual weathering products or paleosols. These -are characterized by extensive leaching of Na, Ca, Mg, Fe, Mn and Si inthOir upper parts and conctmtration of K, Al and Ti. Even-when developed on mafic volcanics, these paleosOls approach a sériciteatitanium dioxide mineralogy. With increasing depth in the páleosois a very iroa—rich chlorite abruptly jOins the sericite and titanium oxide assemblage. This transitionpossIbly represents the permanent paleowater table. The behavior of the rare earth eleMents in these plebsols indicates that the ground waters responsible for these weathered deposits were of significantly higher pH (greater than 8) than at present. A direct consequence of this,is that the-high K contents of these paleosols are almost certainly original features produced during weathering and not a result of later metasomatism. This is substantiated by the behavior of Rh and Ba. The behavior of all elements, whether major or trace, appears to be dominated by the reducing and high pH nature of the ground waters. These results suggest that element solubilities and hence concentrations during Early Proterozoic surficial prOcesses nay have been considerably different: thn previously assumed 18 �?ETAM0PPHISM IN THE ENGLISH rv:u Gower, C.F. ançi SUBPROVINCE NEAP KENORA-,. NOPtHWT ONTAPTO Cliffqrd1 P4M., Dept. of Geplo, MoMaster University, Hamilton, Ontario Detailed petrograpitic investigations on 300 thift sections of gneissic and associated rocks from 200 6q.km. of the EnglIsh River Subprovince near Kenora have enabled two metemorphic episodes to be. defined. N1 metamorphism attained uppermost amphibolite facies and, using mineral assefnbiages together with whole rock chemistry in calcic pods, amphibolites and metasedimgnts, it is estimated that the P-P conditions were 5.25 ±0.75 kb and 650 ± 40 C. Prograde reactions during this metamorphism generated garnet from hornblende and biotite in amphibolite and tonalitic gneisses respectively. The distribution of garnets can be closely correlated with U) alkali feldspar mega-cryst distribution, (ii) lowest Fe20 /FeO bulk composition ratios in amphibolite and tonalitic gneisses, (iii) deepes structural level. The garnets are .undeform— ed and show no correlation with F? fold trends suggesting that the earliet recognizable metamorphism is late or pOst-f2. The N9 metamorphism is retrograde and, using mineral assemblages in amphi— bolites and metasediments, appears to have taken place under greenschist facies conditions. P—T conditions cannot be closely0defined from petrographic evidence but are estimated as 2.25 ± 1 kb and 400 ± 50 C. Potassium has behaved as a mobil,! component during both phases of metamorphism and is extensively involved in (i) asa reactant with hornblende to give biotite and epidote/clinozoisite, (ii) as a product, together with magnetite, from the oxidation of biotite, (iii) as a roduct from the reaction of biotite to give garnet. The presence of megacrysts in both gneisses and granitoid rocks is suggested as an expression of this mobility. 19 �ENVIRONMENTAL GEOLOGY OF THE NORTH SHORE A COASTAL ZONE MANAGEMENT PROJECT by John C. Gren, Gedlogy Department, TJniversity-df Minnesota, Duluth ABSTRACT During the jast two years the Minnesota Geblogicàl -Survey, on contrac -from the State Planning Agency, has undertaken a study of the environmental geology of the state's Lake Superior shore as an element of the Federal Coastal Zone Management Program. Two field seasons were devoted to mapping, with sample analysis, literature research, map development,, and report writing during the academic year. Besides the author, two graduate students (C. Moss and M. Jirsa) and five undergraduates (C. Baker, M. Gasser, K. Husby, and K. Peterson) were involved. The products, are a set of 13 maps,' covering the entire shore at a scale of 1:24,000, of each of 5 types (Bedrock geology, Surf icial geology, Depth t' bedrock, Landforms, and Economic Geology), plus a report which includes interpretations. Geologic processes currently active! geologic hazards, opportunities and resources offered, and land—use constraints are treated for the major surf icial material types and landform units. In this aréa the major geology—basèd lthid—use constraints are imposed by (a) geologic processes such as wave processes-and stream erosion and flooding, (b) soil suitability related to clayey glacial lake deposits and to shallow and exposed bedrock, and (c) economic resource protection, particularly gravel. in abandoned deltas of higher lake levels. 20 �CRUSTAL MODEL STUDIES OFA REGIONAL GRAVITY ANOMALY IN NORTHERN MICHIGAN AND WISCONSIN, EXTENT OF ANOMALY, AND ITS RELATIONSHIP TO NEAR SURFACE GEOLOGY J. S. Kl'asner and D'. Bbmke, Department of Geology, Western Illinois University, Macomb, Illinois 61455 The Bouguer gravity anomaly map oP northern Michigan •and Wisconsin has a broad, long wavelength gravity maximum that extends in an east—west direction for about 800 km from near the eastern end of the northern peninsula of Michigan into north-central Wisconsin. This anomaly may be part of a generally continuous gravity maximum that extends along the Southern Province of the Canadian Shield, except where it is overprinted by the gravity expression of the midcontinent gravity high.. It is truncated in South Dakota by a gravity maximum of similar width and amplitude that extends 'around the western and northern edge of the' Superior province. It is truncated on the eastern end by the gravity expression o'f the Grenville..orogenic belt. Two dimensional gravity models were constructed over the' regional anomaly in The models consider mass variations within the upper 20 km Michigan and Wisconsin. of the crust and consist of primarily two layers with a density of 2.80 gm/cc for the upper layer and 2.94 gm/cc for the lower layer. Th'ey show that the upper layer is thinnest beneath the middle Precambrian (X) basins and troughs such as the Marquette Trough and it reaches a thickness of about 16 km in central Wisconsin. In Michigan and Wisconsin several important geologic and economic features are associated with the regional gravity anomaly. For example, middle Precambrian (X) basins and troughs, which cause relatively short (a few kilometers or less) wavelength gravity anomalies, are located over the regional anomaly. Middle Precambrian (X) volcanic accumulations are generally located along the edge of the regional anomaly or within the middle Precambrian (X) basins. The recently discovered boundary between gneiss and greenstone terrane (Sims, 1976) is located roughly near the northern edge of the regional gravity anomaly. Regional metamorphic zones are generally located near the edge of the gravity anomaly, or, where superimposed upon the anomaly, cause gravity minima within the regional anomaly. The recently discovered massive sulfide deposits in Wisconsin seem to occur ajong the edge of the regional gravity anomaly or along prominent gravity features that cut the regional anomaly. The above data suggest a genetic relationship between the thinning of the uppermost (2.81) gm/cc) crustal layer and the formation of the middle Precambrian (Xe) basins and troughs, the accumulation of volcanic deposits, the formation of regional metamorphic zones, and possibly the accumulation of the sulfide deposits in northern Wisconsin. Perhaps the v,olcanic deposits, the sulfide deposits, and the igneous intrusions that supplied the heat for the formation of the metamorphic zones are all differentiates of the lower (2.94 gm/cc) crustal layer. They were intruded and extruded through fracture zones that formed in the 'uppermost layer during the Penokean orogeny. Sims (1976) has suggested that the middle Precambrian (X) basins were developed over, and approximately parallel to, the boundary between gneiss and greenstone terranes. The regional gravity maxima lie within the eugeosynclinal zone that Sims has postulated for this area'. Sims, P. K. 1976, Precambrian Tectonics and MineràT Deposits, Lake Superior Region, Presidential Address: Econ. Geol. V. .71 , M6, p. 1092-1110. 21 �BOUGIJER GRAVITY ANOMALY MAP OF, NORTHERN PENINSULA OF MICHIGAN, LAKE SUPERIOR, AND ENVIRONS J. S. Klasner, U.S. Geological $urvey and Western Illinois University, "acomb, 61455, William J. Hinze, Purdue University, Lafayette, Indiana 47907, .L. 0. Bacon, Michigan Technological University, Houghton, Michigan 49931, arid N. W. OtHara, Florida Institute 'of Technology, Melbourne, Florida 32901 Illinois ABSTRACT A prepublicatin version of the Boug1uer gravity anomaly map of the northern peninsula of Michigin, Lake Superior, and adjacent parts of Michigan, Lake Huron and Lake Michigan, Ls presented for discussion purposes. The map, which is at, 1:500,000 scale and has a 5-mga. contour interval, is a compilation of data collected since 1951 f±om several sources. Personnel from the U.S. Geological Survey tied each of the individual surveys to the 1971 base reference datum and made additional observations in areas that lacked gravity coverage. Data were reduced and compiled on digital tape by the Defense Mapping Agency, Aerospaae Center, St. Louis, Missouri, using the 1967 international gravity formula, sea-level datum and a 2.67-gm/cc reduction density. Terrain corrections were applied to selected sections in the Porcupine Mountain area only. Because of high station density in the western part of northern Michigan, the Bouguer gravity data were contoured using values selected frpm 1-minute quadrilaterals. On most of the map, station spacing is broader than the 1-minute interval, so that all stations are represented. Although the geologic implications' of many of the individual anomalies on the map h:tve been discussed in the literature, this map provides a comprehensive integrated view of the gravity field, which can be used in geologic and strutural anaLysis. The geologic Fources of a few of the gravity anomalies are discussed in this context. Over the Keweenawan-Lake Superior basin, a pronowiced g .'avity low is found along the center of the lake, and gravity maxima parallel ;he shoreline and join together at both ends of the lake to connect the midcontinent gravity high with the mid-Michigan gravity maxima. In general the gravity maxima reflect near-surface accumulations of relatively dense mafic volcanic and plutonic rock and the gravity mnima reflect thick less dense clastic rock. In northern Michigan, middle Frecambrian (x) basins and troughs such as the Marquette trough have east-trending positive anomalies. Lower Precambrian (W) granitic terranes commonly have gravity minima. A broad gravity maximum extends east across the northern peninsula. It has no apparent surficial origin and is believed to be caused by deep crustal or upper mantle mass variations.. 22 �Major Structural Features in Central Wisconsin and Their Implications on the Animikie Basin by Gene L. LaBerge university of Wisconsin—Oshkosh, Oshkósh, WI, 54901 EXPLANATION Abstract PRECAMBRIAN Paleotoic Niddle Precambrian batholith comprising numerous in composition from quartz diorite to granite intrusive sedimentary pile in Central Wisconsin has been outlined LaBerge and Myers. This batholith lies on the southern west trending sedimentary-volcanic (Animikie) basin. - IN) C.s.) A epizonal plutons ranging into a complex volcanicby recent mapping by margin of the large east— WISCONSIN LATE PREcAMBRIAN I Broad steeply dipping cataclastic zones separate the composite batholith and its greenschist facies roof pendants from upper amphibolite gneisses, migmatites and amphibolites that flank the batholith on the north and south. The scale of cataclasis, presence of ultramafic bodies along the zones, and the marked difference in metamorphic grade across the shear zones indicates deformation on a crustal scale. The gneissic areas appear to be horsts, and the batholith a graben-like structure. Field relations along comparable shear zones within the batholith indicate a long and complex history of cataclasis during emplacement of the batholith, and, by inference, during the history of the Animikie Basin. of [ :::::::::::: Bayf ld Group Oronto Group I! :::: ::::: Wetf RiVer aatholith Qqartslte MIDDLE P}EECLMBRIAN The present distribution of Precambrian rocks in Wisconsin is one of east— west trending belts of Middle Precambrian sedimentary-volcanic-plutonic rocks alternating with Early Precambrian(?) gneissic rocks. This has disrupted the basin into a series of horst-like and graben-like blocks. Field relations in Central Wisconsin indicate that at least part of this deformation occurred during the. tectonic history of the basin, and is consistent with Cannon's (1973) interpretation in the Marquette District. This suggests that the Animikie Basin was characterized by vertically moving blocks, which may have provided local sediment sources within the basin and also produced local strongly reducing troughs, one of which may have resulted in the highly graphitic "Flambeau Anomaly." Granitic Ro49 Iron-Formation Dominantly Matasedimeckary Rocks 1Ta tlyMt 1 Rok EARLY PREcAMBRIAN Granitic Reeks Metavolcanic Rocks GneisSic Rocks (Modified from Sims, 1976) Gee Eases Creenschtst Gneisses kigeaEttas )taa,rphism Pligeatitea MiphtkCliteI Episenal Plutats Asphibolita - Greenschist Matarerphisa Gneisses Pligmatitis Asphibolltss �18 0/ 15 0 Results for Archean Plutonic Rocks, Lake Despair Area, Northwestern Ontario F. J. Longstaffe and R. H. McNutt, H. P. Schwarcz Department of Geology, McMaster University, Hamilton, Ontario An oxygen isotope study of the Jackfish Lake nlutonic complex and the Burditt Lake stock, (Ivabigoon granite-greenstone belt), has indicated the importance of nagmatic-autometasomatic fluid activity and/or hydrothermalmeteoric water interaction in their crystallization and alteration. o18o values of the main phase of the Burditt Lake granodiorite are relatively constant across the stock (8.00 ± 0.33 0/00); microcline megacryst hearing phases, as well as late stage anlitic rocks have higher 6180 values (8.95 ± 0.35 0/00); Depletion in lo occurs in t e volcaniclastic county rocks as the granodiorite contact is approached (11.35 to 8.00 0/00). The movement of mac'matic water unward from hotter, deeper portions of the stock through the roof zone into the country rocks can cause such isotopic variations. The high water/rock ratios required at the contact by such a model appear reasonable, as considerable chemical modifications of the country rock has occurred in the vicinity of the contact. The Jackfish Lake Complex. as exnosed in the Lake Despair area, is composed nrelominantly of diorite and monzodiorite, with lesser volumes of quartz diorite, miaocline megacryst hearing granodierite and soda syenite. The samnles Thich preserve the highest and the most concordant oxygen isotopic terneratures are located within 50 meters of the contact with the mafic amphibnlite country rock (which itself has been enriched in 18o from 5.7 to 8.0 otoo). Apnarently, the oxygen isotopes have been quenched more rapidly and nore comnletely in the outer margins of the body. Elsewhere in the Complex, discordant oxygen isotope mineral-pair temperatures indicate varying degrees of isotopi disequilibrium. Th"se disturbances can he largely attributed to late stage deuterir alteration and continuing subIn snite of such pe'turhations, some primary solidus isotonic exchange. isotopic trends are still discernible; 6180 values of cluartz, plagioclase, hornhlende and hiotite decrease gradually with increa;ing degree of differentiation of the rock type. This hehavinur nrohahly reflects the relative imnoverishment of the remaining melt in ISO as Iarc'e amounts of 180-rich mineral rhases begin to crystallize during the formation of the late stac'e srnll volume granodiorite. The preservntion of citch trends. as ''ll as the nrrnnl a18o enrichnont pattnn from diorite tO granodiorite observed in rock samples swgests cln.scl system isotonic exchange in these rocks. The southern boundary of the Jackfish Lake Complex is formed by a major fault. Cranodiorite located near the shear zone is altered, showing Fe staining arid large scale saussuritization of felclspars. Chemically, such samples are enriched in lirht rare earths, Zr, Ni, Fe. Ti, P, K and Rh, and denleted in Na, Sr and Ha. These rocks are also denleted in 18o (5.41 O/oo The depleted 750 meters from the fault; 7.80 °/oo 2400 meters distant). rocks contain minRral phases which are grossly out of isotopic equilibrium and depleted in 1o0 relative to "unaltered" granodiorites from the Complex. Such behaviour is best explained by hydrot'iermal-meteoric water interaction ir anisotopically open system. 24 �FOSSIL COLLECTIBLES FROM THE GUNFLIN'P FO1MATION S. Lougheed and J. J. Mancuso, Department of Geology, Bowling Green State University, Bowling Green, Ohio 43403 P4. ABSTRACT Iron—formation to be. of economic value is dependent upon a succession of processes that transform the initial biogenic particulate material, produced on a gently sloping marine shelf zone There are five great fossil collectibles into iron-rich, minerals. of initial material bccurring in the Gunf lint; they are, siliceous and carbonate shells, blue—green algae, greenaloid and bacterial framboidal pyrite. Two outstanding areas for collecting fossil materials occur at Kakabeka Falls and in the vicinity of Schreiber. Excellent specimens of ooids are found at the falls, but more remarkably, many chalcedonic chert laminae contain totally or almost completely dissolved ooids so that only the nuclei remain. The nuclei are varied in their structural pattern but commonly appear as ellipsoids, spheres, or as spheres with concentric laminae. The structures are small, generally less than thirty microns in diameter. The ellipsoid structures and probably some of the spherical structures are siliceous shells of microorganisms. Some, if not most, of the spherical nuclei are silicified shells of calcar— Both siliceous and calcareous shells are eous microorgansisms. fairly common in organically pigmented chalcedonic chert. Although bacterial carbonate, is common in specimens from Kakabeka Falls particularly those specimens rich in pyrite, the best specimens are found in the Schreiber area, where the micron sized carbonate crystals occur in the cortex of oncolites. The; carbonate bacteria produce ammonia as a by-product from their metabolism of expired algal laminae in the cortex, and carbonate is therefore precipitated in the microdomain of high alkalinity., The columnar stromatolites in the Sbhreiber area are noted for the fidelity of preservation of the filimentous and coccoid algae in a siliceous matrix and therefore are not associated with bacterial carbonate. We find the best specimens of bacterial carbonate produced in columnar stromatolites occurring in the Biwabic iron—formation, however good specimens 'may be found in the road cut at the junction of highways 590 and 17-11 near Kakabeka Falls. Greenaloid, the gel-like material composed of silica, and sapropel complexed with ferrous iron, is best collebted as matrix material in laminae of ooids or as matrix material occurring with tuffball laminae at Many specimens show transitional steps in the' Kakabeka Falls,. oxidation of greenaloid to greenalite and/or magnetite and less commonly to hematite. 2.5 �PENOKEAN STRUCTURES AND PLUTONIC ROCKS IN WISCONSIN K. S. Maass'and L. G. Nedaris, Jr.,' DepartmerIt'of Geology and Geophysics, University of Wisconsin, Madison 53706 W. R. Van Schmus, Department of Geology, University of Kansas, Lawrence, Kansas 66044 ABSTRACT Last •year we reported on the occurrence of Penokean structures and plutonic rocks in early Precambrian gneiss in Portage and Wood Counties, Wisconsin. We now have completed more detail3d structural and isotopic studies on these occurrences and have extende tour investigations westward about 100 miles to include localities in Clark, Jackson, and Chip— pewa Counties. The Early Precambrian gneiss, formed about 2.8 by. ago (Van Schmüs and Anderson, 1977) and domposed of quartzofeldspathic gneiss, amphibo— lite, and migtnatite, contains three sets of folds: first, penetrative isoclinal folds; second, non—penetrative S-- and Z—folds; and third, non— penetrative broad, open folds. The axial surfaces of the second and third fold sets are discordant -to those of the first set, but the fold axes of all three are colinear, Well developed lineations, defined by the dimensional orientation of elongate minerals and trains of mineral In all the localities examined so grains, are parallel to fold axes. far, fold axes and lineations plunge steeply, from 45° to 900. • The gneiss has been intruded by two different tonalites: an earlier medium—grained tonalite, which contains a strong foliation and lineation, and a later fine—grained tonalite, which contains a weak foliation and strong lineation. Lineations in both tonalites are colinear with those in the gneiss. The tonalites as well as the gneiss have been recrystal— 1ied under middle—grade metamorphic conditions. Petrofabric analyses have been completed for samples along the Wisconsin River, including three samples of quartzofeldspathic gneiss, one Measure—, -of medium—grained tonalite,- and two of fine—grained tonalite. ments of [0001] in quartz have given a similar pattern for all five samples: a girdle normal to the h fabric axis.- Thus, the tonalites contain structural elements in common with some of those in the gneiss, on both mesoscopic and microscopic scales. - U—Pb analyses of zircofl'have yielded ages of 2800'm.y. 'for the gneiss, 1850 ± 25m.y.- for the medium—grained tonalite, and 1800 ± 25 m.y. for the fine—grained tonalite. We believe that the zircon ages for the tonalites represent their times of emplacement and, consequently, that the structures within them and some of the structures within the gneiss were produced during the Penokean orogeny. -Further investigations of this type shouli give a 'more complete un— - derstancling of the Penokean orogeny in Wisconsin and provide a basis for comparison between gneisses of Early Precambrian age in Wisconsin and 'those of the Minnesota River Valley terrane. 26 �THE OCCURENCE AND SOME NOBLE METAL CONCENTRATIONS IN SELECTED KOMATIITIC ULTRAMAFIC VOLCANIC ROCKS FROM MUNRO TOWNSHIP, ONTARIO. ' MacRae, William E., and Crocket, James I-I., Department of Geology, McMaster University, Hamilton, Ontarjo. Munro township, situated in 'the Abitibi volcariic belt, Is the location of a sequence of well documented komatiitic ultramafic voldanics. The rocks are well exposed and the area has been subjected to only very low' grade metamorphism. The Jcomatiitic volcanic rocksrange from peçidotitic through pyroxenitic to basaltic in composition'. Samples taken from peridotitic flows at the base of Centre, Hill have been'analysed for gold, platinum, palladium, and iridium by neutron activation analysis. Four lithologic units were sampled from two flows. The results pf the analysis are summarized below: Lithologic Unit Au 'Pt" Pd Ir 1.6 2.5 8.9 1.1 Spinifex zoné(3) 2.1' 14.3* 10.7' 0.8 Foliated zone(1) 3.3 '— '7.5 0.4 Cumulate zone(4) 3.6 ll,.l. 6.3 1.5. ' (Flow) Chilled marins(3) ' , (ppb) *(3) Number of samples for zone. There appears to be a slight enrichment of'gold in the' cumulate zone as well as'iridium relative to the spinifex zone. This is probably due to the settling of immiscible sulphides as well as olivine before the formation of the spinifex. Platinum and palladium increase in the spinifex zone and were possibly enriched in the molten silicate phase. The average of the cumulate and the spinifex zone for palladium and iridium are the" same as the chilled zone, while the 'values: fr gold and platinum are lower. The latter values are possibly due to seawater leaching. The average concentration of gold (2.7 ppb) is not significantly higher in peridotitic komatiites 'than' in other major rock types and do not appear to contain enough gold to make them a source 'rock for 'gold deposits. 27 �Stratigraph of the Dar1aga' Bain Metasédiments; Michigan J• J. Mncu'èo, R.- E. éavoy, M. S. Louc4heed Bowling Green State University Bowling Green, Dhio 43403 ABSTRACT The BaragaBasin is located- in eastern Baraga and northern Marquette Counties, Michigan. It is 30 miles long by 8 miles wide and is filled with approximately 1400 feet of mildly deformed Middle Precambrian metasediments. Lower Precambrian basement. rocks ecposed around the perimeter of the basin are crystalline granites and gneisses which unbonformably underly the metasediments. The lowermost Middle Precambrian unit in the basin is a white vitreous quartzite which appears to be limited to the western and central portibn of the basin. A basal quartz-pebble conglomerate is exposed at Pikes Peak in sec. 11, T. 51 .N., R. 32 W. Overlying the quartzite is a chert-carbonate iron-formation and a volcaniclastic sequence. Recent phosphate discoveries occur within this unit (Mancuso, Lougheed, Shaw, 1975; Cannon and Klasner, 1976). More than 1100 feet of graphitic slates and a thick meta-arkose make up the rest of the section. Flat lying Cambrian(?) Jacobsville Sandstone unconformably overlies the Precambrian rock section. . -The white basal quartzite -is correlated with the Goodrich Formation while the iron-formation, volcaniclastic. sequence, the. black slates and the meta—arkose are correlative with the Greenwood Iron-formation Member, the çlArksburg Volcanics Member, and the Lower Slate member of theMichigarnme1ormationin.the.western part of the . Marquette Basn,. . . References, Cited. Mancuso, J. •J., Lougheed, M. S., and Shaw,R., l975,Carbonate apatite in Precambrian cherty iron-formation, Baraga County, Michigan: Econ. Geology, v. 70, no. 3, p. 583-586. Cannon, W. F., and Klasner, 3. 5., 1976, •Phosphorite and other apatite bearing sedimentary •rocks in the Precambrian of Northern Michigan: U.S. Geol.. Survey Circular 746, 6 p. 28 �AN ESTIMATE OF THE RARE EARTH ELEMENT DISTRIBUTION IN POST-KENORAN UPPER CRUST, NORTH OF LAKE HURON McLenrian,. Scott M., Fryer,B.J.., and Young,. Grant 1W., Department' of ceology, University of Western Ontario., London, .Qntario., N6A 5.B7. Rare earth analyses havë been made on'.sampls of tillite matrix from the Gowganda' Formation, north of Lake Huron. Agrandmean based on averages.from the. Cobalt, Quirke Lake and Esp-anola'- SudburSr Areas is considered to berepresentative of upper cnistal abundances for a large area. northof Lake Huron. The three districts were given equal weight in the estimate. The ovtrall abundances are('ih ppm): La, 24,;' 'Ce, 55 Nd, 23; Sm, 43; Eu, 1.2; Gd, 3.8; Dy,. 31 Er, 2.0. These data are compatible with analyses of granitic and volcanic rocks typical of the surrounding areas. Values are also in line with estimate's 'pf Canadian Precambrian crust and post-Arch'ean crustal abundance.s in Australia, though relative distributions have significant 'dirferenoes. Analyses of Gowganda argillites and sandy argillites intimately associated with the tillites have- similar patterns tji those of the tillites. Absolute magnitudes, however, are consistentlyhigher(by. a factor of about 1.3) than the tillites. A possible explanation for this could be concentration of clay minerals in the argillites. This may suggest that other estimates of crustal abundances which are based, in part, 'on analyses of fine grained sedimentary rocks are systematically high by a similar proportion. 29 �Archean Volcanism Washeibamaga Lake Area, Wabigoon -ubprovinc?, Northwest Ontario. G.E. McMaster and Departmento R.!J. McNutt Geology, McMaster 'University. The Washeibamaga-Thind'rcloüdtâkes area' )f the Wabigoon Subprovince, can be subdivided into three faàies; I) The Lower volcanic sequence of metabaèalts (lower greenschist facies) is preserved. as a:-stenly-dipping, north-facing- homoclinal volcanic -pile six kilometres thick Nb, rr, Ni,-Ba .Pb, Sri', They show trace, element (Y, geochemical. similrities tomoderxi ocear. --floor. tholeiitic basalts. 2) The Thundercloud Lake Quartz-Porphyry intrudes the lower sequence-and is helieved-to..represent a vent-plug filling a late-stage felsic volcano. Accompanying explosive vojcanism produced 'a threekilometre. thick sequence of coarse pyroclastic rocks an&-tuffs.. Associated dacitic and autobrecciated. rhyolltic flows have calc .alkaline affinties and are chemically 'distinct from both volcanic sequences and appear not to be a differentiated product but to have originated as a seperate magma. 3) The Upper volcanic sequence of metabasalts is composed of tightly folded, massive to pii.lowed flows. The contact with t le unde: 'lying epiclastic and pyroclastic rocks is at ah angle c' thirt-- degrees-, implying either profound angular unconformity or a fau'±t dont ct. -The upper sequence is chemically distinct from the lower sequence. K,-Rb-, Sr, Ba, abundances suggest similariie with rirodern Island Arc'tho3eiites 30 �ORGANIC-RICH 'lAKE SEDIMI4T EXPLORATION GEOCHEMICAL SURVEY OF EASTERN LAKE VERMILION—ELY AREA, NORTIIEASTERN MINNESOTA D. G. Meineke, M. K. Vadis and A. W. Klaysmat Minerals Exploration Section, Division of Minerals, Minnespta Department of Natural Resources, Hibbing, Minnesota 55746 ABSTRACT An organic rich (gyttja) lake sediment geochemical survey was conducted over Lower Precambrian volcanic and associated rocks in northeastern Minnesota for the purpose of determining the applicability of this method for evaluation of mineral resource potential and, reconnaissance exploration. Two hundred and seventy samples were collected from 75 lakes over an area of 200 square miles (520 sq. km.). A weak aqua regia leach on unignited gyttja produced the best contrast over background. Statistical analysis of the data indicates that trace element distributions are greatly dependent upon the limnological environment of each lake; trace elements tend to be concentrated in the organic and/or inorganic fractions of the gyttja; and, of all parameters considered, LOl (loss on ignitipn) is the best single 'indicator of limno— logical environment. Due to the variations in lake environments and trace eLement accumulation inthe gyttja, parameters other than the element concentrations were considered. However, the study indicated, even though a perfect datum for comparing lakes was not possible, •the element concentrations for arsenic, cobalt, copper, nickel,'lead and zinc provided the best datum for comparing all 75 lakes. Several significant anomalieth were located by the survey. Anomalous copper was found in a lake near an interesting copper prospect. Copper, lead, titanium and zinc appear to reflect bedrock composition; chromium, magnesium and nickel reflect bth bedrock domposition ,and glacial dispersion. 31 �MAFIC MINERALOGY OF FERROAUGITE SYENITE PROM THE COLDWELJ1 ALKALINE COMPLEX ROGER H. MITCHELL and R. GARTH PLATT DEPT. OF GEOLOGY LAKEHEAD UNIVERSItY ,. THUNDR BAY ,ONTARIO Plutonic Center 1 of the Coldwell alkaline complex is dominantely ferroaugite syenite associated with minor A c. 2000 m. amounts of earlier hypersthene gabbro. section of ferroaugite syenite exposed on the lake shore between Marathon and the eastern margins of the complex exhibits well defined igneous layering in the eastern portion of the sequence. The layered syenites grade into syenites with poorly defined diffuse turbulent layering and thSe in turn into coarse syenites conCryptic layering taining patch and sheet pegmatites. is well developed in the sequence and indicates this portion of Center 1 ferroaugite syenite is a small intrusion in which crystallization occurred simultaneously Olivines range in composition from at the roof and base. Fa3 to Fa03. Pyroxenes initially belong to the diopside— hedenbergiCe series (Di42HdagAc3.to Di10Hd85Ac5 and grade into members of thp acmie-hedenbergite series (Di10H95 Ac5-Di5Hd45Ac0) Pyroxene c npostional trends are similar to tháse observed in peralkaline igneous rocks and in particular to those of the undersaturated Fivegroups of amphiboles are Ilimaussaq intrusion. present; 1 — ferroedenite-hastingsite; 2 — sub-aluminousr ferroedenite; 3 - aluminous ferrorichterite - ferrorichterite; Amphibole compositional 4 — arfvedsonite; 5 - ferroactinolite. trends parallel those of the pyroxene in showing dcreasing Al and Ca with increasing Na and extreme iron enrichment. Oxides minerals in the earliest stages of crystallization were Fe—Ti oxides and baddeleyite, these were replaced as. liquidus phase by aenigmatite and zircon respectively as Residual liquids, as represented by the magam evolved. the pegmatites crystallized ferrorichterite, feldspar, zircon and quartz. The ferroaugite syenite magma evolved along an oversaturated peralkaline trend characterized by extreme iron enrichment under conditions pf low oxygen fugacity at high silica activity. 32. �STRATIGRAPHIC AND TECTONIC HISTORY OF LOWER AND MIDDLE PRECAMBRIAN ROCKS IN EAST-CENTRAL MINNESOTA G.B. Morey, Minnesota Geological Survey, University of Minnesota, St. Paul, Minnesota It has been recognized for nearly 70 years +that a great diversity of Precambrian rock types crop out in east-central Minnesota. However the rocks are poorly exposed and an understanding of their geologic history has been hampered by a lack of definitive geologic data from which age and spatial relationships can be deduced. Nonetheless, recent geologic studies utilizing conventional mapping techniques in conjunction with subsurface, magnetic, and recently acquired gravity data have more precisely defined the spatial relationships of various rock units and have led to a more complete understanding of their stratigraphic and tectonic histories. The Lower and Middle Precambrian rocks in east-central Minnesota are divisible into three distinct terranes: (I) a diverse Lower Precambrian terrane; (2) overlain on the north by a thick sequence of folded and metamorphosed Middle Precambrian stratified rocks; and (3) intruded on the south by a variety of Middle Precambrian plutonic rocks. All of these rocks are overlain by generally flat-lying sedimentary rocks of Late Precambrian, Cambrian and Cretaceous age. Two presumably high_angle, east-trending faults of Early Precambrian age divide the Lower Precambrian terrane into three lithotectonic segments. The southernmost segment consists dominantly of quartzófeldspathic gneisses metamorphosed to the 'upper. amphibolite or granulite grade. Granite and lesser a,mounts of rnetasedimentary and metavolcanic rocks assignable to the greenstone-granite belts of northern Minnesota comprie the northern mast segment. Substantive data bearing on the lithic attributes in the middle segment are lacking, The segment may consist of either cataclasized gneissic rocks or metagraywacke and slate similar to that in northernmost segment. However, regardlessof their original age and character, the rocks in the middle segmen't forrrt a discrete zbne separating two considerably different Lower Precambrian lithotectonic units. The Middle Precambrian strt-ified 'rocks occur within an intracratonic baih centered over and approximately parallel to the boundary zone between the Lower Precambrian gneissic 'and greenstone-granite segments. The stratified rocks are divisible into two 'groups separated by an unconformity. The older group consists dominantly of quartzose rocks of clastic and perhaps volcanogenic origin. Mappable ynits of metabasalt, mafic 'tuft, oxide- to carbon,ate-facies iron-formation and carbonaceoui mudstone are abundant near the base, whereas carbonate rocks occur as mappable beds near 'the top of the group. The younger group is similar to, an,d correlative with, the well-known Animikie Group of northern'Minnesota and Ontario. Sedimentation was either terminated or cldsely followed by a period of regional deformation and metamorphism assignable to the Penokean orogeny. The dominant Penokean structure is an eastward-plunging synchnorium bounded on the north, west, and.south by"Lower Precambrian rocks. However the extent to which the rocks were' deformed varies from place to place ,within the synclinorium and the style of deformation is attributable to the tectonic behavior of contrasting kinds of Lower Precambrian rocks. Where they overlie granitic basement rocks, the stratified rocks dip gently southward and the basal contact is relatively undisturbed.' ln contrast, where they overlie gneissic or metasedimentarv basement rocks, the stratified rocks are complexly infolded into a number of large anticlines and synclines having numerous coaxial. second- and third-order folds on their limbs. The metamorphic grade of the stratified rocks increases from north' to south. To the north, argillaceous rocks contain minerals indicative of high-grade diagenesis or zeolite-facies metamorphism, whereas to, the south they contain minerals indicative of the lower atnphibolite facies. Metamorphic mineral isograds conform in a general way to the fold geometry, but in detail they transect fold axes implying that deformation ' nd metamorphism were discrete events. - Teètonic instability during the Penokean orogeny was manifested principally by vertical uplift of the gneissic basement rocks and the development of a mantled gneiss dome along the south edge of the Penokean synclinorium. The virtual coincidence of bedding in the stratified rocks that surround the gneiss dome with cataclastic foliations within the gneiss dome suggests that folding and uplift occurred contemporaneously. In addition, the spatial coincidence of high-grade metamorphic rocks along, the flanks of the gneiss dome suggests that the gneissic terrane' was characterized by relatively high heat flow during deformation. The Middle Precambrian plutonic rocks are confined to that part of east-central Minnesota underlain by gneissic rocks. Most' of the plutonic rocks are post-tectonic in. age as evidenced by cross-cutting relationships with the mantled gneiss dome,' and by their relatively homogeneous and undeformed nature. Igneous activity of calc-alkaline affinity began with the emplacement of dike-like bodies of quartz diorite. This was followed by the emplacement of small, to large plutons of granodiorite and quartz monzonite, which in turn was follOwed by the emplacement of various sized plutons.of granite. Quartz monzonitic rocks having rapakivi-like textures occur locally as border phases to some of the granite plutons. . ' Erosion, following uplift along major northwest-trending faults, exposed the 5gneissic and' plutonic rocks prior' to the deppsition of Upper Precambrian sedimentary -rocks. ' - - �PETROGRAPHIC AND CHEMICAL ATTRIBUTES OF SOME LOWER AND MIDDLE PRECAMBRIAN GRAY WACK E-SH ALE SEQUENCES tN NORTHERN MINNESOTA G.B. Morey and NI Schulz, Minnesbta Geological ,$UrVey, University of Minnesota, Si. Paul, Minhesota. Graywacke-shale sequences comprise a significant proportion of the Lower and Middle Precambrian rock record in northern Minnesota. Although the petrographfc character of these rocks has been evaluated in detail, little use has been made oftheir bulk chemical compositions, particularly in classification and provenance studies. We suggest however that the chemical data, when used with petrographic data, provide useful new insights regarding the sedimeritological history of these rocks. According to the classification scheme of Crook (1974), which considers only th framework grains, the Lower Precambrian graywackes are quartz-poor to quartzintermediate in composition and are indicative of a tectonically active island-arc environment. They contain 2 5-50 percent dacitic to rhyodacitic rock fragments, 10-36 percent sodic plagioclase, trace amounts to 12 percent volcanic quartz, and as much as 22 percent labile components such as hornblende. In contrast, the Middle Precambrian graywackes are quartz-intermediate to quartz-rich in composition and are indicative of deposition under tectonically stable conditions. They contain: 15-90 percent plutonic quartz, 1-36 percent feldspar, and as, much as 7 percent rock fragments of mostly granitic composition. The bulk chemistry of the two sequences emphasizes the fact that they are different chemical entities. The_Middle Precambrian graywackes contain more silica (X= 75% vs. 62%) and less K20 (X=l.43% vs. 1.90%) and Na 0 (X=2.42% vs. 4.06) than do the Lower Precambrian graywackes. The former also Jhibit a narrower range of Na2O/K.,O values (1:2'to 2:1) than do the latter (1:1 to 13:1). These differences can be related 'to the, mineralogy of the framework grains. Quartz is the dominant mineralogic variable in the Middle Precambrian gçaywackes, and its abundance exerts a major influence on the amount of Si02 in the analyzed samples. In contrast, dacitiç to rhyodacitic rock fragments dominate the framework grains of ' the! Lower Precambrian graywackes 'and exert a strong influence on the. Na20/K20 ratios. Very little is known about the petrography of intercalated shale units iri either sequence. However the bulk chemical data suggest that the tower Precambrian shales are fine-grained equivalents of the graywackés, whereas the Middle Precambrian shales are discrete chemical entities not related to graywackes simply ,by the relative abundances of framework grains. The bulk chemistry of the Lower Precambrian graywackes suggests that they were derived from: a dacitic to rhyodacitic source with little attendent chemical alteration. Thus these rocks were not 'markedly affected by .post-depositiona . processes; the framework grains reflect the comp'osition of the source area. However neither the Middle Precambrian graywackes nor their' intercalated shales can be derived chemically. from a simple granitic source; chemical-mixing calculations indicate a complex source of consisting of quartz monzqnitic, rhyodacitic, and basaltic1 rocks. The mixing calculations'also imply that the Middle 'Precambrian sediments were, derived from a considerably weathered terrane and subjected to post-depositional processes which considerably modified the original framework mineralogy. 3.4 �-GEOCHEMISTRY OF THE YELLOW DOG PLAINS PERIDOTITE, MARQUETTE COUNTY, MICHIGAN W. J. Norris and J. T. Wilband, Geology Department, Michigan State University, East Lansing, NI 48824; P. W. Snider, Geological Survey Division, Michigan Department of Natural Resources, Lansing, MI. 48909 . A relatively fresh, previously undescribed,.peridotite body outcrops in an area locally known as the Yellow Dog Plains, adjacent to county road MA in the Champion quadrangle, Marquette County, Michigan. A small exposure south of the road and a roughly oval shaped "plug", 120 meters wide by 190 meters long, intrude the Precambrian X Michigaimne Slate which underlies most of the Yellow Dog Plains. The larger outcrop stands 15 meters above the plain at its highest point. Recent paleomagnetic data indiqate the, intrusive is of lower Keweenawan (Precambrian Y) age (K. Books, U.S.G.S., personal 'communication, 1977). The fact that the Yellow Dog Plains peridotite is located in an extensive east—west trending magnetic belt suggests it maybe' genetically related to the exposed east—west,trending Keweenawap diabase dikes to the south -which-haye been saippied and analyzed for comparisons. The peridotite contains up to. 50 percent olivine, as much as 30- percent pyroxene (both clino— and orthopyroxene), approximately 10 percent plagioclase, and less than 10 percent opaque minerals. A dark red pleochroic biotite (Cl percent) is common in most specimens. Preliminary microprbbe analysis of unserpentinized olivine and plagioclase give Fo80 and An8.65, respectively. The sulfide minerals pyrite, pyrrhotite, chalcopyrite, cubanite (?), pentlandite, and bornite are present in small amounts mostly associated wit-h magnetite. Major oxides, Cu, Ni, Cr, Zp,. Co, and several rare earth elements were analyzed from 22 specimens. The average values for the oxides are as follows: 5i02 = 42.46%,' A1203 4.24%, Fé203 = 5.65%, FeO = 8.71%, MgO = 26.19%, CaO = 4.40%, Na20 = 0.49%, K20 = 0.24%, 1120 = 6.72%, Ti02 = 0.71%, P.20s 0.10%, MnO = 0.18%. Samples from a 30'meter vertical drill core in the large exposure show a continuous increase in Ni with depth. MgO, FeO, and Cr have the same trend as Ni., A break' in. the alkali values, which otherwise consistently decrease with depth, suggests. the intrusion maybe layered. Layering has not been confirmed by modal data. - 35 �Post-Glacial Sediment Distribution in the Canadian Portion. of .-Läkë SupérioJ J. S. Mothersill, Lakehead Univerity The Canadian portion of Lake Superior covers an area •of approximately 29,882 km2 -of a -total lake area of 82,375 km2. The drainage area of the Canadian portion of the lake, excluding the lake and the Lake--Nipigon drainage basin, is approximately72,,000 km2. The drainage basin which was covered .by a virgin forest up:until a century ago, is'still mainly covered by boreal forest. Based on radiocarbon dating of the lake-sediments, glacial retreat from the-northern part- of Lake Superior occurred about 11,600 yrs. B.P. Since the time of glacial retreat, approximately 12,545x106 m3 of sediment have been deposited in the lake proper and adjacent -bay areas. The post-glacial sediments tendto have been deposited in topographic basins with the thickest sequences occurring in Thunder Bay, Nipigon Bay and Black Bay where up to 12 m, 12 m and 14 m respectively have been deposited in topographic basins. In the lake proper, the. maximum thickness of post— glacial sediments is only in the -order of S m. The average rate of sediment reaching the. lake since glacial retreat has been about l.08x106m3/yr. The sediments consist ofquartzarenite to arkosic.sandswhich occüradjacent to the shore and the islands-and a silty clay, sequence that occurs in the topographic basins. The bulk of the sediments (>99% percent) are formed of silty- clay'-.which'is comprised of major amounts of quartz, K—feldspar and plagioclase, subordinate amounts of chlorite, ililte and kaolin añd minor amounts of amphibole and an interbedding 'Of vermiculite artdsmectite. - The average sediment yield fromthe drainaqebasin was about 15 m3/km2/yr. or a total-of l74;000 m3/km Sinde- glacial retreat'. 3- �MSSIVE SULFllTh 1)E1OSITh IN WISO0N4TN M. G. Mudres', Jr., K. K. Ostrom, Wiscons in Geological and Na Lu,-a I Ill s)ot'y Survey, l815 University Avenue, Madison, Wisrons in 5371)6, antI Gordon Reinke, Wisconsin Department of Natural Resources, 4610 University Avenue, Madison, Wisconsin 53702. ABS TRACT Since 1968 with tile discovery near Ladysmith in Husk County of n massive sulfide ore body, over three dozen mining conpanies have at one time or another explored for non—ferrous massive sulfide deposits in the Precambrian of northern Wisconsin. The most significant find to date is by the Exxon Company, U. 5. A., of a 60-million ton deposit of zinc and copper south of Crandon in Forest County. Exploration activity has precipitated numerous studies by the state, including geological, geophysical and hydrotogical surveys, review of legislation, and social and economic ,.impact analysis. Exploration has been concentrated in a 100—km wide hand from Ladysmith in the west, through the ghinelander-Crandon area to the Pembine area in the east, a distance of 350 kilometers. Available outcrop data, gravity compilations, and state—acquired aeromagnetic data, coupled with isotopic studies by the U. S. -Geological Survey and the University of Kansas, suggest that this terrane is a middle Precambrian volcanic belt surrounded by early Precambrian gneisses, Detailed geology is known only for the Ladysmith deposit. This deposit, owned by the Kennecott Copper Qorporat ion, is essentially a verti— cally—oriented, lens-shaped pod 15 m wide, 720 m long, and 240 m deep. Country rock consists of intermediate to felsic volcanic rocks of anda— lusite metamorphic grade. Economic minerals found within a pyritized quartz—serieite schist are a supergene enriched blanket of chalcocite and bornite of pre—Late Cambrian age, overlying primary chalcopyrite. The 6-million ton body averages three and one-half to Tour percent copper. Favorable terrane was identified by an INPUT survey in 1967, and follow—up drilling in 1969—1970. sulfidc ore hodics in North A:aerjca. Wisconsin environmental laws are administered by the state Department of Natural Resources. Present regulations require an:environme,ntal impact assessment of all proposed mining operations. Experience has shown that for significant new mines this assessment will invariably result in preparation if an Environmental Impact Stateaent by the Department. New mines are also required to obtain a mining permit which in— Mine operators cludes a reclamation plan approved by the Department. are required to post a bond to cover the cost of reclamation, Uining &mmpanies must also obtain other permits required by thc Department for the protection of the environment. - Several pieces of legislation that were introduced in the spring 1977 legislative session would: (I) replice present mineral taxes with a graduated severance tax on net proceeds; (2) require the registrótion Cf exploration companies in Wisconsin with the additional requirement that some kinds of company—acquired geologic data be turned over to the state after exploration; (3) require the registration of severed mineral rights and ultimate aquisition of orphan mineral rights; (4) set limits on the duration of mineral exploration leases; (5) set a cooling—off peiod during which n exploration lease could be broken; and (6) eliminate the mine'al depletion atlowande. - It is reasonable to expect that more deposits of massive sulfide ore will be identified in future years in Wisconsin. Whether or not the deposits are developed depends on cots, mctal prices,- environmental constraints at each individual prospect, the tax climate, and the mineral policy of the state. - Tn 1974, Noranda Exploration, Ihc. announced the discovery of a small zinc—copper body on 'the Pelican River east of Rhinelander in Oneida County, The deposit consists of three zones. The total deposit consists of 2.3 million tons at an average grade of one percent copper and four and one— half percent zinc. The deposit is 300 a long, 15 m wide and 203 m deep. It was identified by combined geologic and INPiJI' surveys. The generally small- size and uncertain mine development climate, preclude the immediate develop'nent of the property. Noranda is continuing exploration activities in the area. In May 1976, the Exxon-company-U. S. A., announced the discovery of a zinc-copper body south of Crandon. The body appears to be slightly less than 2 km long, at least 480 m deep, and about 69 a wide, Preiiminarv drilling suggests 60—million tops of ore sveraging six and one—half percent zinc and one percent copper, making this nnc of the five largest massive - �PROTEROZOIC PITCHBLENDE flIN POTENTIAL IN MINNESOTA:: THEORY 4ND SPECULATION Richard W. Ojakangas, Department of Geology,.University of Minnesota, Duluth ABSTRACT Several major Proterozbic unconformitie-s are present within the rock column of Minnesota. (1) The MPG Animikian formations (the Pokegama Quartzite and older units) rest upon LPG granitic and volcanic rocks. (2) The UPG Sioux Quartzite overlies LPG rocks in southwestern Minnesota and adjacent South Dakota and Iowa. (3) The UPG Puckwunge Formation overlies the MPG Rove Formation in northeastern Minnesota, and in adjacent Ontario the correlative Sibley Formation overlies the Rove and older Anits. (4) The UPG "Nopeming Quartzite" overlies the MPG Thomson Formation near Duluth. (5) The UPG Fond du Lac Formation rests upon the MPG Thomson Formation in east—central Minnesota. In addition, Upper Cambrian rocks of southeastern Minnesota unconformably overlie LPG, MPG, and UPG units and Cretaceous deposits overlie LPG, MPG and UPG rock units over the westernhalf of the state. Two localities which have abnormal total radioactivity may be related tc nearby unconformities. One is in the LPG McGrath Gneiss, nearly adjacent to moderately dipping unnamed MPG roék units. The second is in a probable shear zone in the MPG Thomson Formation, a few miles from the UPG Fond du Lac Formation. - At Beaverlodge, Northern Saskatchewan, the MPG Martin Formation overlies crystalline basement rocks; pitchblende veins in the area may be related to this unconformity (e.g., Langford, 1977). Further south, the UPG Athabasca Sandstone unconformably overlies a similar basement and uranium mineralization appears to be related to the unconformity. Discoveries in northern Australia are of a similar nature. No promising uranium shows have as yet been discovered in Minnesota. However, the stratigraphic—structural relationships, coupled with the supergene pitchblende vein model, callsforcIetailed exploration along the cited uncon— * formities. Refer en a e Langford, F. F., 1977, Surficial origin of North American pitchbiende and related uranium deposits: American Assoc. Petroleum Geologists Bull., v. 61, p. 28—42. 38 �PALEOMAGNETIC AND PALLOINTENSITY STUDIES OF NORMAL AND REVERSED KEWEENAWAN ROCKS IMPLICATIONS FOR THE' POLAR WANDER PATH OF NORTH AMERICA Lauri J. PeAOnen and Henry C. Halls Department of Geology, Erindale College University of Toronto, TOronto, Ontario KB S TRA c t Paleomagnetic' studies on Keweenawan rocks (1200 - 1000 my) have revealed a well—defined magnetic stratigraphy composed of units with both normal and 'reversed polarity. There are at least two polarity changes in the Keweenawan sequence of which the younger One (from reversed to normal polarity) has been detected throughout the Lake Superior region. A characteristic feature of this reversal is its asymmetry: the reversed magnetization always has a much steeper (upward), inclination than the normal (downward) one; resulting'in a difference of 300 in their paleopoles. Of particular concern in the interpretation of Keweenawan paleomagnetism is whether this asymmetry in reversal is caused by ,a secondary remagnetization component or whether it is the signature of apparent polar wander during Keweenawan igneous activity. , ' , - Detailed thermal and alternating field demagnetizaticin "studies On both igneous and baked Keweenawan rocks do not, however, reveal any systematic secondary component but rather the difference in inclination between reversed and normal rocks A possibility remains throughout the blocking temperature and coercivity spectra. exists that these demagnetization techniques are unable to detect the secondary component. If a 'non—removable' secondary component indeed is present in all Keweenawan rock units", it would result in a lower Thellier-type paleointensity still determination for the reversed rocks compared to that predicted for the normal ones. On the other hand, if the apparent polar wander 'interpretation is correct, and the Earth's magnetic field was dipolar during the Keweenawan, an enhanced paleo— field'value would be obtained for the reversed rocks because they have a significantly higher paleolatitude than do the normal ones. In order to test the credibility 'of the above models, we have conducted about luo Thellier—Thellier paleointensity measurements on Keweenawan intrusives of both polarities, and adjacent baked contact rocks from the Sibley and Rove formations. These results suggest a higher paleo— field for the reversed epoch compared to that for the normal one. Moreover if the paleofield data are reduced to the paleoequator, this difference in paleointensity between reversed and normal rocks disappears. Both paleomagnetic and paleointensity data therefore cast doubt on the hypothesis that a secondary component has caused the Keweenawan asymmetric reversal. The results, however, are 'consistent with apparent polar wander during Keweenawan tin'e. 39 �PETROLOGY AND TREND SURFACE ANALYSIS OF TWO LATE-STAGE GRANODIORITIC PLUTONS, NORTHERN LAKE OF THE WOODS REGION, ONTARIO Pilatzke, Richard H.; Karner, Frank R.; and Peterson, William M., Geolc5gy Department, University of North Dakota, Grand Forks, North Dakota 58202 Trend Surface analysis of modal data for two small plutons in the Keno±a block of the Superior Province show similar concentric patterns of mineral abundance. Alkali feldspa ith concentrated at the margins of the plutons and oligoclase in the cores. The Indian Reserve pluton Outcrops about one km northeast of Kejick at the north end of Shoal Lake at latitude 49°38'N and longitude 95°04'W. the area of exposure is about 6 km2 and has an elliptical shape about 4.0 km by 1.6 km with the major axis trending E-W. •Field study at 60 locations and point-count analysis of 30 thin sections shows that the rock is typically a pink, mediuiñgrained, hypidiomorphic granular granodiorite with minor oligoclase phenocrysts and scattered, small, greenstone xenoliths. The average composition is 50% oligoclase, 26% quartz, 13% slightly perthitic microcline, 4% biotite, 3% sericite, 2% epidote and minor opaque minerals, sphene and apatite. The oligoclase typically contains two or three, thin, euhedral.to subhedral, in€eLrnal alteration zones marked by a concentration of fine—grained sericite and epidot.e. The Dogtooth pluton. outcrops about 16 km east of Kenora at latitude 49°l''N The area studied is 4 km2 and is irregular in shape and longitude 94°l3'W. with its long axis oriented NE—SW. It appears to be a texturally distinct lobe of a larger granodioritic pluton to the east.. Field study at 115 locations and point-count analysis of 86 thin sections indicates that the rock is typically a pink, medium-grained, hypidiomorphic granular granodiorite characterized by polycrystalline quarta aggregates, protoclastically deformed oligoclase, and ve;y low total mafic mineral content. The average composition is 47% oligoclase, 26% quartz, 20% slightly perthitic microcline, 1% biotite and 4% epidote, sericite, chlorite, opaque minerals and accessories. In these rock?s oligoclase typically varies from 40% to 60% and microcline Trend surface analysis of mineral distributions shows similar from. 5% to 25%. NE-SW trends for first and second—order surfaces for oligoclase and alkali feldspar with oligoclase increasing to the SE and inward and alkali feldspar Higher degree surfaces show increasingly increasing to the NW and outward. complex, concentric patterns. Quartz surfaces show mpre irregular patterns with higher order surfaces showing marginal, alternating highs and lows. Biotite surfaces for the Indian Reserve pluton follow the pattern of. alkali feldspar surfaces. We interpret the striking concentric patterns of the feldspar distributions to be related to the cooling and crystallization histories of the plutons. The linear trends for lower order surfaces and the axes of elongation of the The. southeastward concentric patterns ref léct regional structural trends. increase of oligoèlase and the northwestward increase of alkali feldspar shown on lower order surfaces may reflect a fundamental assymmetry of the plutons or their regional tectonic framework relative to the present erosional Both plutons nay be on the, southern lint of major synclinal features. surface. 40 �.EVIDENCE FOR ARCHEAN TURBIDITE AND SUBMARINE FAN SEDIMENTATION FROM THE SAVANT LM GREENSIONE TERRAIN, N. W. ONTARIO R.J. SHEGELISKI LSKEHEAD UNIVERSfl'Y Results from an investigation of vertithliy dipping Archeah netaseditrnts in the Savant area have outlined the presence of four basic sedimentary facies: • 1. 2. 3. 4. Graded-stratified cohglomerates of submarine fan association. Graded greywacke—siltstone beds of turbidite association. Stratified-laminated mudstones of pelitic association. Laminated oxide iron formati6i of chemical association. The graded—stratified conglomerates are corrnDnly associated wfth graded greywacke—siltstone beds and form a coarse-grained l.—2. facies group. The oxide iron formation and mudstones re also associated with greywacke—siltstone sequences and form a finer—grained 2.-3.-4. facies group. The sequence of deposition of metasediments in the north arm of Savant Lake is that of coarse— grained l.—2. facies group overlain by the finer grained 2.—3.—4. facies group, thereby forming a mega—fining upward cycle. Facies Group l.—2. Detailed field mapping of this conglomerate—rich group reveals major fining—upward cycles within the group. Such features nay be indicative of fan—channel abandonment. A predominanbe of well—rounded clasts within the conglomerate suggest efficient abrasion of clasts in a shallow—water, highenergy environment, prior to final deposition, via turbid flow, in a deepwater environment. The l.-2. facies group is therefore considered to represent a portion of a submarine fan systen composed of residimented conglomeratçs and inter layered turbidites. * Facies Group 2.-3.-4. Detailed mapping indicates that the overlying greywacke—silstone and mudstone facies contain several sedimentary structures and textures of the deep—water turbidite association. The presence of interlayered iron—rich and chemical iron formation indicate extrenely quiet periods between mudstones turbidite deposition. This facies group is therefore considered to represent elastic and chemical accumulation in a portion of a restricted, deep—water turbidite basin. The interpretation that the clastic metasec.iments are coexisting proximal coarse—grained submarine fan facies and dist al finer—grained turbidite basin facies requires a deep—water environment for tIe acccmulat ion of oxide iron formation as well. This interpretation sheds dcubt upon the ccrmnn belief that Archean oxide facies iron formations are products of shallow water deposition. 41 �GEOPHYSICAL STUDIES OF PERID0TITE DIKES, YELLOW DOG PLAINS, NORThERN MICHIGAN W. Snider, Michigan Dept. of Natural Resources, Lansing, Michigan 48926, 3. S. Klasner, U.S. Geological Survey and Western Illinois University, Macomb, 61455, S. Quam, Western Illinois University, Macomb, Illinois 61455, R. Lilienthal, Michigan Dept. of Natural Resources, Lansing, Michigan 48926, and P. Geraci and A. Grosz, U.S. Geological Survey, Reston, Virginia 22092 D. Illinois ABSTRACT Very low frequency electromagnetic, gravity, and ground magnetic studies indicate that peridotite exposed in two outcrops within the Pleistocene outwash of the Yellow Dog Plains is part of a dike swarm that extends in a westnorthwest direction for about 20 km beneath the Pleistocene drift cover. Rocks at the two outcrops contain small quantities of copper— and nickel-bearing sulfide minerals and have slightly anomalous copper content. Paleomagnetic studies by Kenneth Books of the U.S. Geological Survey show that the perido- .tite has a remnant pole position typical of lower Keweenawan rocks from throughout the region. Analyses of the three types of geophysical data in sec. 11 and 12, T. 50 N., R. 29 W., where the peridotite crops out, indicate that several dikes are present. The dikes are intruded into middle Precambrian (x) metasedimentary rocks within a structural trough in lower Precambrian (W) rocks. Gravity data suggest that a steep, west-trending fault with the downdropped side to the south lies beneath the southernmost dike in secs. 11 and 12. The fault offsets the contact between lower and middle Precambrian rocks and may have been a channelway for intrusion of the dikes. Northwest-trending faults offset both the dikes and the west-trending fault. Filtered VLF-EM data combined with ground magnetic data suggest the presence of two different types of dikes. Negative VLF-EM anomalies and associated large-magnitude positive magnetic anomalies occur at the peridotite outcrops. In addition, positive VLF-EM anomalies cannot be attributed to nearsurface conductors or fault zones, and therefore suggest the presence of subsurface conductors. Gravity studies indicate the presence of dikes in the NW) 1W* sec. 12 and NW NW sec. 11, T. 50 N., R. 29 W. but no magnetic anomalies were found. Two positive VLF-flt anomalies were also found there. We believe that these are attractive exploration targets for sulfide mineralization and warrant further study. 42 �TIlE PETROLOGY AND SEDIMENTATION OF THE UPPER PRECAMBRIAN SIOUX QUARTZITE OF MINNESOTA, SOUTH DAKOTA, AND IOWA Richard E. Weber, Department of Geology, University of Minnesota, Duluth, Duluth, Minnesota 55812 ABSTRACT The Upper Precambrian Sioux Quartzite.is exposed at along several locations an east—west trend 175 miles long and 30 miles wide between Mitchell, South Dakota and New Ulm, Minnesota. It rests unconformably on Lower Precambrian rocks and is overlain by Cretáceous sediments and Pleistocene drift. The formation consists of over 1600 meters of orthoquartzite sandThe conglomerates stone with minor interbedded conglomerates and mudstones. are present in the lower two—thirds of the section and mipor thin mudstones occur in the upper third. The pebbles of the conglomerates consist of vein A coarse basal conquartz, hematitic chert, iron formation and quartzite. glomerate is exposed at New Ulth, Minnesota where it crops out 110 meters from the underlying granite. The mature orthoquartzite is composed almost exëlusively of well rounded, moderately sorted, monocrystalline quartz. Detrital chert and jasper are common in some samp1e. Grains are coated with a thin film of iron oxide and cemented by quartz overgrowths that are locally partially replaced by secondary diaspore and sericite. Rounded zircon and tourmaline. are the only common nonopaque detrital heavy minerals. Measurements of. 856 cross—beds and 491 ripple marks show paleocurrent directions to the south and southeast; no major vertical or lateral changes in trends were observed. Paleocurrent patterns are unimodal throughout most of the unit but some bimodal patterns occur in the upper part of the section. The crossbedding consists predominantly, of narrow troughs 60 to 140 cm wide and 15 to 30 cm thick. Asymmetric current ripple marks are common, but both small— and large—scale symmetrical ripple marks are also present. The abundance of crossbedding and current ripple marks indicates vigorous current action. Mudcracks and mudchip conglomerates suggest periodic exposure and fluctuating current strength. These structures may suggest in part a fluvial origin but herring—bone cross—beds and reactivation surfaces, structures commonly associated with tidal deposits, are present in a few areas in the upper third of the section. It is intruded by diabase at The Sioux Quartzite is gently folded. Corson, South Dakota. A rhyolite interbedded with the quartzite in a well at Hull, Iowa has been dated at 1470±. 50 m.y. (Lidiak, 1971). REFERENCES Lidiak, E. G., 1971, Buried Precambrian rocks of: South Dakota: Ceol. Spc. America Bull., v. 82, p. 1411—1420. 43 �SHAPE, SIZE, AND;COOLING HISTORY OF TROCTOLITIC-GABBROIC ROCKS IN THE DULUTH COMPLEX by PW. Weiblen and R.W. Cooper Data on mineral proportions and chemistry have been obtained on randomly oriented thin sections of troctolitic-gabbroic rocks along a 10 km traverse normal to the contact in the central part of the Duluth Complex in N.E. Minnesota. The data provide, new insights into the shape, size, and cooling history of individual intrusions. The spread in data at - any locality on olivine (fig. I), plagioclase, and to a lesser extent clinopyroxene may be correlated with degree of layering in the rocks. The data suggest a regular increase in mineral layering away from the contact. Data on biotite (fig. 2) sulfides, iron oxides and orthopyroxene show an expontential decrease away from the contact. These data suggest a diffusion controlled equilibration of basaltic magma with pelitic country rocks and introduction of K, H20, and S into the magma. The above data combined with geological and geophysical data on textural relations, faulting, and aeromagnetic anomalies suggest the shape and size of individual troctilitic-gabbroic intrusions as shown in fig. 3. These intrusions are distinctly asymetric and show a continuous variation betweçn. flow (region A fig. 2) and gravity (region B, fig. 2) layered rocks. HIGHWAY HIGHWAY TRAVERSE I TRAVERSE !! +\ ;L_• :i - Fig. Di%1.r. FaOI C1RC1tVM; I '•' 4+ OSTPtLC( FRO CONTPCT IKM 1. Olivine vs distance. Fig. 2. Biotite - - - vs distance. Inclusions A Curved lines - Flow pattern Blaèk areas 5 KK Fault shown is normal to the probable transform fault direction in the kidcontinent Rift.. IN Fig. 3. Three dimensional view qf proposed magma chamber for troctolitic—gabbroic intrusions in the Duluth Complex. 44- �Surf icial Sediment Analyses Offshore of the Copper—Bearing Province of Keweenaw Point, Upper Michigan C. J. Welkie, E. L. Nebrija, R. P. Meyer, Geophysical and Polar Research Center, Department of Geology & Geophysics, University of Wisconsin, Madison, WI 53706 Surficial bottom samples collected in 1974 and 1975 around Keweenaw Point were analyzed for selected trace elements and textural parameters as indicators of depositional processes following the methods of Moore and Welkie (1976). The distribution of the concentrations of Cu, Zn, Ni, Co, Mn and Fe were compared for Five Mile Point (north of the peninsula) and Bete Grise bay (south). The test of log— normality was applied (Ahrens, 1954) and the number of statistical geochemical populations for each element determined. For Cu, three statistical populations were found in both sites. Regression curves were drawn for all possible pairs of trace elements and a least—squares fit determined. The slopes of the regression lines support the contention of Smith and Moore (1972) that the sediments north of the Keweenaw represent a separate grouping of popuiations from those to the south. The contours fo copper distribution off Five Mile Point generally parallel the shore, with three areas of high concentration (295 to 175 ppm) which are uncorrelated to bathymetry. In Bete Grise, six samples containing anomalous values were found (145 to 175 ppm) and these clustered in two areas, both occurring in an elongate bathymetric low corresponding to a postulated ancient channel of the Montreal River Thus, the samples are anomalous which drains copper—bearing rocks (Goodden, 1974). according to the criteria established by Bolviken (1971), i.e., values exceeding two standard deviations from the arithmetic mean over all samples. After correlation of copper content with all other variables, multiple linear— regression analysis showed 91% of the variation in Cu at Five Mile Point could be and explained by the variables Zn, Ni, Fe, Mn, by percent 3.5 , percent 4.0 At Bete Grise, only 72% of the variation percent 4:5 $ grain size, and by bathymetry. in the copper concentrations could be explained by these variables; either the relationships between these parameters are nonlinear, or other vari4bles as yet undetermined enter into the linear model. 3.5 Kc seismic profiles and towed electrical resistivity profiling and sounding failed to correlate with the areal extent of the placer deposits as determined from physical sampling in Bete Grise, implying that the anomalous values do not continue to depth or that these geophysical techniques as applied had insufficient resolution. References: Ahrens, L. H., 1954, The lognormal distribution of the elements, Geochim. Cosmochim. Açta, 5, 49—73. Bolviken, B., 1971, A statistical approach to the problem of interpretation in geochemical prospecting, Geochemical Exploration (Boyle, Tech. Ed.),Special Vol. No. 11, Canadian Institute of Mining and Metallurgy, 564—567. Goodden, J.J., 1974, Sedimentological aspects of underwater copper exploration in Lake Superior, M.S. Thesis, University of Wisconsin, Madison, Wisconsin. Moore, J. R., and C. J. Welkie, 1976, Metal—bearing sediments of economic interest, coastal Bering Sea, Symposium Proc., Alaska Geol. Society, Recent & Ancient Sed. Envir. in Alaska, pp. K—l to K—17. Smith, P. A., and J. R. Moore, 1972, The distribution of trace metals in the surficial sediments surrounding Keweenaw Point, Upper Michigan, Sea Grant College Reprint, WIS—SG—73—341, 383—393. 45 �DELTAIC DEPOSIPS IN TITLE UPPER PECORS,ESPANOLA AND GOWGANDA FORMATIONS (HIJRONIAN) G. IC Young, D. G. F. Long. ad S. N. NcLennan Dept. of Geology, -University of Western Ontario, London, Ont. The cyclical repetitibn of mixtite, siltstone, sandstone is the hall-mark of much of the Huronian succession. Little attention has been given to the finer grained units (Pecors, Espanola and upper Gowganda Formations). This report deals mainly with the upper parts. of these units in the southern part of the Huronian outcrop belt. The upper parts of the Pecors and Gowganda Formations constitute complex coarsening upward sequences with many of the attributes of the classical prograding deltaic sequence. Both units are composed mainly of muddy and silty argillite. The prodelta deposits consist of laminated, in some cases graded siltstone-mudstone couplets, some of which may be varves. The delta slope is represented by finely interbedded mudstonés and wavy, laminated and cross laminated,siltstones. Slope instability is evidenced by The presence of abundant asymmetrical flame, and ball and pillow structures. Thin—to—thick massive units of siltstone-fine sandstone.with rip-up clasts and erosive bases are considered to have been resedimented by downslope mass movement. Clastic dykes are present in the Pecors Formation. The delta slope deposits pass rapidly upwards into fluvial(?) sandstones of the Nississagi and Lorrain Formations which appear to have been derived predominantly from the northwest. The upper Espanola Formation differs from the other two units in containing much more sandstone3 anc carbonate-rich units.In some areas the upper Espanola Formation contains abundant fining upward sequences(one to seeral metres thick) like those of both fluvial and tidal channel deposits. The interpretation is favoured because of the presence oL bimodal-bipolar(NW-SE oriented) cross bedding distributions in some units. This interpretation is important because it implies a tide-dominated and therefore marine environment in the upper Espanola Formation. This unit passes upward into the fluvial (part eolian?) sandstones of the Serpent Formation. The Pecors and upper Gowganda Formations are interpreted as prograding muddy delta deposits whereas the upper Espanola appears to have accumulated in a higher energy, tide-dominated delta platform. The reasons for this difference are not understood, but might have been caused.by greater rates of subsidence or fluvial advance in the Pecors and Gowganda than in the case. of the Espanola Formation. latter o oO 00 46 �SEDIMENTARY FACIES ASSOCIATED WITH LATE WISCONSIN GLACIAL LAKE DULUTH, WRENSI-LALL AREA, MINNESOtA. Randee Zarth, Geology Dept., University of Minnesota, Duluth, Mn, 55812 ABSTRACT Study of Late Wisconin glacial deposits southwest of Duluth suests a revised model for the late'- and postglacial history of the area. Two major sedimentary environments, are distinguishedi (1) an ice-disintegration environment and (2) a glaciolacustrine environment associated with Glacial Lake Duluth. Sediments produced by ice-disintegration are stratified, 'moderately- to poorly-sorted sand, and gravel, with clasts predominately Of Precambrian. sandstone, volcanics, gr'anite, and slate; and minor bodies of'laminated silt and clay.. Topographically, these sediments comprise a wide belt of 'kettles, kames, disintegration ridges; and outwash plains that are dissected locally by meltwater channels and' tunnel valleys, some of which contain eskers. The lacustrine environment contains the following facies: (1) thick, flat-bedded sands, (2) cross—bedded sands, (3) parallel laminated silt and clay, (k), massive clay, and (5) massive' and stratified drop stone deposits. In the nearshore environment. are found moderately—sorted and well-rounded sand grains (0.25 mm) with boulders at' the shoreline. At 305 to 31k meters in elevätion,,the sand grades rather abruptly to massive clay. The sand facies overlies the silts and clays indidating progradation into Glacial Laket Duluth by nearshóre currents. The highest strandline features occur 'at elevations near 335 meters. They are expressed primarily as beach scarps and other welldeveloped shoreline features, such as several spits and a delta. A prominent linear, northeast trending scarp between 305 and 31k meters previously considered to be a strandline, is here interpreted, to be the depositional front of. a coarse-grained shelf deposited into Glacial Lake Duluth as it stood near its highest stage (335 meters). This indicates what wa previously considered to be two stages Glacial Lake Nemadji and Glacial Lake Duluth is actually a single stage of Glacial Lake Duluth, The following, late- ard early postglacial history is" indcateds (1) Ice from the last advance of the Superior Lobe stagnated along the margin of the Lake Superior Basin, resulting in the development of an ice-disintegration complex and stratified glacial deposits. (2) Meltwater from the disintegrating ice, the retreating Superior Lobe in the basin, and from more distant upland sources, along with runoff from the hydrologic cycle, were ponded in fron.t of the retreating ice to form Glacial Lake Duluth. (3) A lake level rise to 335 meters is represented by a transgressive sequence of sediments. (k) The lake stabilized long enough to develop strong beach features. Sediment supplied, to the lake at this stage appears to have been mainly derived from the ice-disintegration complex with minor contributions 'from ice rafting, (5) Progradation of the shallbw water facies over the deep water facies was the result of sediment laden streams, meltwater, and, other runoff enterinE the lake. '(6) The lack of a regressive facies indicates a rapid drop in the lake level as a lower outlet was uncovered by the retreating ice front.. 47" �!field rs Copies of the guidebooks Department of may be obtained frOm: Geology Lakehead University Thunder Bay, Ontario PTh 5E1 Price $5.90 Canadian. Make checks payable to Lake SUperiOr Institute. �FIELD TRIP A 'COLDWELL COMPLEX LEADERS: R.H. Mitchell and R.G. Platt DATE: May 2 -4, 1977. The Coldwell Complex is a large Proterozoic alkaline igneous complex containing saturated, oversaturated, and under-saturated syenites. Visits will be made to exposures of all the major rock types found within the complex and to areas which illustrate the relationships between the magma types and the mechanisms of intrusion of the. complex. 1. Depart Thunder Bay on Monday May 2 at4:00 p.m. Return Thunder Bay Wednesday May 4 by 5:00p.m. All 'day Tuesday May .3 and the morning of. Wednesday May 4 will be spent examining the complex. 2. The cost is $7O.O0. and includes: a) 2 nights accomodation (double) at Marathon. b) Transportation to and from Thunder Bay and during the. excursion. c) Guidebook. Maximum costs for meals Cost does not include meals. in Marathon are about $12.00 per day,. 3. Accomodation will be in rñotels in Marathon (with restaurants). Costs are based upon double occupancy of motel units. Persons requiring single occupancy must notify the organizers in advance and be prepared to pay $10.00 extra. 4. Limited to a maximum of 45 persons. 51 �FIELD TRIP PROTEROZOIC ROCKS OF THE THUNDER BAY AREA LEADERS: K.G. Fenwick, C.R. Kustra, W.H. Mcllwalne, J.F. Scott. DATE: May 3: and 4, 1977. A two day field trip will cover the Proterozoic (Middle to Lake Precambrian) rocks of the Thunder Bay area. Day one will cover selected stratigraphic units of lower and upper members of the Gunflint Formation and the overlying Rove Formation. On the second day, outcrops of the Sibley Group will be examined. The stops are designed to illustrate the stratigraphic relationships of the three fold division of the Sibley Group into formations. Side trips to Ouimet Canyon and the Thunder Bay Amethyst Mine are also planned. leave the Airlane Motor Hotel, Thunder Bay, on Tuesday May 3rd and on Wednesday May 4th at 8:00 a.m. The bus will return each day by late afternoon. 1. Field Trip B will, 2. The costs for participants is $4O.OQper person. This fee includes bus transportaion, lunch each day, literature, and guide to field stops1. It does not include lodging. 3. Limited to a maximum of 45persons. 52 �FIEL,D TRIP C STURGEON. LAKE LEADERS: W. Gibh, P. Severin, A. Tarnman, H. Poulsen, J. Franklin. DATE: May 6 - 8, 1977. A one ay field trip to the Sturgeon Lake area will include the examination Qf two open-pit mines (Mattabi and Sturgeon Lake Mines Ltd.) and outcrops representative of the volcanic stratigraphy of the lower portion of the pile.. The Mattabi and Sturgeon Lake Mines are typical volcanogenic massive sulphide deposits. Tour stops within the mines will include an examination of both massive and stringer ore and various types of alteration The associated with the footwall stringer suiphides. regional stops will examine a variety of felsic and mafic pyroclastic, flow,, and epiqlastic rocks,. and two subvolcanic intrusive bodies. 1. Participants will depart by bus from Thunder Bay at A approximately.6:30 p.rp. on Friday, May 6. discussion period, will be held in Ignace that evening. As the tour will be rather lengthy, participants will stay in Ignacethe evening of Saturday, May 7. Buses will reach Thunder Bay and Dryden on Sunday, 'May 8 in order to connect with mid-day planes. 2.. A fee of $75.00 will include transportation, accomodatjon,, meals, and guidebook. 3. Limited to a maximum of 45 persons. 53 � https://digitalcollections.lakeheadu.ca/files/original/b2bf913cd5f79f3b89a1b7891165c6b1.pdf c40ef197359f1bb47e247efcc376edec PDF Text Text a I*eHty Third Alinoal MeeliHg Thunder ilay, Ontario Ii r Institute on Lake Superior Geology S I I I I. I I I I I I P.! I Li 1 COLD WELL TRIP COLDWELL U �r I I FIELD GUIDE GUIDE TO TO ASPECTS ASPECTS OF OF THE THE FIELD I GEOLOGY OF OF THE THE COLOWELL COLDWELL ALKALINE ALKALINE COMPLEX COMPLEX GEOLOGY I I ROGER ROGER H. MITCHELL AND R. GARTH PLATT H. MITCHELL AND R. GARTH PLATT I I Department of Geology Lakehead University Thunder Bay I I I I I I I I I Twenty Third Third Annual Annual Meeting, Meeting, Institute Institute on Lake Twenty on Lake Superior Geology, Marathon, May 1977 Superior Geology, Marathon, May 1977 �THE COLDWELL ALKALINE CuwLEX COMPLEX na LULIDWELL ". I I I I I I I I I I I I I I I The Coldwell complex located 1 o - y is 410c-~-d on the north shore shore Superior between the Pie of Lake Superior Pic and and Little Little Pie Pic Rivers. Rivers. The community The community of Marathon rathon is is located located on the the eastern eastern side side of the the complex. complex. This circular complex with a diameter of 25 25 km. of km. is the largest alkaline alkaline intrusion intrusion in in North North America and is is unusual in that oversaturated, oversaturated, under— undersaturated and saturated magmatism magmatism is saturated is present. present. The alkaline (1000 m.y. ) The alkaline rocks rocks are areof ofNeohelikian Neohelikianage. age(1000 m.y.) are emplaced in Archean rocks of the Superior Province and are emplaced in Archean rocks of the Superior Province of Canadian Shield, f the Canadian Shield, which in this area form form an north— essentially east—west trending ssentially east-west trending greenstone greenstone belt. belt. A northeasterly bifurcation of this belt originates originates in the easterly Marathon area area and it is is at this this point that the the alkaline alkaline rocks have have been The Archean rocks, rocks, which rocks been emplaced. emplaced. The include basic and acidic volcanics and greywackes have been metamorphosed to greenschist and amphibolite amphibolite grade, grad been subjected to at least two periods of folding and intruded by Archean granites Little is granites and and syenites. syenites. Little is known of the the Archean geology although although some some information information known can be found in Puskas Puskas (1967) (1967) Milne Milne (1967), (1967), Walker Walker (1967), (1967)., Ayres et al. (1970), (1970), Thompson Thompson (1931), (1931), and Einarsson (1972). (1972). A general geological map of the complex, complex, together together with an aeromagnetic map is figures lA with is given given in infigures 1A and and lB. IB. The geological (1967), geological map is is based on the the work of Puskas Puskas (1967), together with our own observations observations and re—interpretation together re-interpretation of the sequence sequence of igneous It should should be be noted igneous events. events. It that simplication of the geology of hat figure 1A is an over simplication the area. area. In detail, detail, relationships relationships are the are extremely extremely mapping, coupled with complicated and very detailed mapping, extensive mineralogical mineralogical studies, is required required before before studiesis extensive anything approaching an accurate geological map can be nything appr produced. reduced. S- �-2- I - 2 - P I I1 II I I Ij I I I I II I I I I I The structure The structure of of the the complex complex is is poorly poorly known because of insufficient insufficient geophysical geophysical and and structural structural observations. observations. Puskas Puskas (1967) believed that the the complex complex was was aa lopolith lopolith but our recent work does does not support this this concept of a single differentiated intrusion. single differentiated intrusion. Lilley (1964) (1964) considers conside that the bulk of the intrusion intrusion is a funnel funnel shaped shaped body of gabbro gabhro and ferroaugite of ferroaugite syenite syenite which has been intruded intruded by nepheline nepheline syenites. syenites. Our recent studies studies indicate indicate that that several present, and that an several centers centers of intrusion intrusion may be present, an area Pic River, area bounded by the the Little Little Pic River, Redsucker Cove Cove and Geordie Geordie Lake Lake may be be aa downfaulted downfaulted block. block. Rocks Rocks within within this area are characterized characterized by by the occurrenceof occurrerueof multiple this breccias breccias and and metasomatism metasomatism and and may represent represent rocks rocks which which were were originally originally close close to to the the roof roof of of the the complex. complex. Rocks Rocks of the the eastern eastern portion of the the intrusion intrusion are are in in contrast contrast less ss complex complex and and relatively relatively xenolith xenolith free. free. Petrologically we have Petrologically have recognized recognized three three distinct distinct intrusive magmatic episodes, episodes, each being characterized trusive magmatic characterized by In order differentiationtrend. by a distinct differentiationtrend. order of of^ intrusion these are: intrusion these are: CENTER 11 CENTER -— Saturated Saturated rocks with peralkaline alkaline rocks peralkaline oversaturated residua. oversaturated residua. CENTER Miascitic alkaline alkaline rocks rocks with with under— un CENTER 22 -- Miascitic saturated saturated residua. residua. CENTER 3 - Alkaline rocks with oversaturated rsaturate residua. - . ., Gabbro,, ferroaugite ferroaugite syenite I CENTER CENTER 1 - I I I I I I I The The oldest unit of the the complex comulex is is represented represented by by eastern border These rocks the eastern border gabbros gabbros (figure (figure lÀ). 1A). These rocks are Igneous layering layering are intruded intruded by ferroaugite ferroaugite syenites. syenites. Igneous Several centers is characteristic characteristic of of both both units. units. Several centers of o intrusion may be present in in the the ferroaugite ferroaugite syenites syenite , . �r —3— I I 1 I I I 1 I I I I I I I which typically typically exhibit exhibit extreme extreme iron iron enrichment enrichment and and , Characteristic differentiate to quartz differentiate quartz bearing bearing residua. residua. Characteristic minerals of minerals of the the ferroaugite ferroaugite syenite syenite are are fayalite, fayalite, ferroaugite, ferroaugite, ferrorichterite, ferrorichterite, ferroedenite ferroedenite and aenigmatite. aenigmatite. CENTER 2 Biotite gabbro, gabbro, nepheline and natrolite syenites 2 —- Biotite syenites CENTER outcrops is an arcuate Alkaline biotite gabbro outcrops arcuate ring pattern on the Coldwell Penninsula Penninsula and we believe believe that this this together with nepheline syenite syenite defines defines an undersaturated undersaturated nepheline intrusive center center (figure (figure lA). 1A). AA second intrusion intrusion of ne~heline Nepheline syenites syenite may be located syenite located on on Pic Pic Island. Island. Nepheline syenites are are characterised by characterised by moderate moderate iron iron enrichment, enrichment,alurninous aluminous amphiholes amphiboles and acmitic acmitic pyroxenes. pyroxenes. Titanium in these rocks enters amphibole and pyroxenes rather than forming forming aenigmatite aenigmatite as in Center Center 1. 1. of Centers Centers 11 and and The distinctly differentiation differentiation trends trends of 2 are well illustrated illustrated by the trends trends in pyroxene compositions compositions Platt, 1977) illustrated below. illustrated below. (Mitchell and Platt, 1977) ACM ITE ACMITE DIOPSIDE HEDENBERGITE �a -4— ifi I Figure - lÀ - Geological Geological map of thq the Coldwll Coidwell alkaline Department of complex based upon Ontario Department Preliminary Map P114 Mines Preliminary P114 (Puskas (Puskas 1967) 1967) together ogether with our own observations and re—interpretation of the sequence of re-interpretation igneous events. igneous events. 1 ' 1 Figure alkaline Based upon Ontario Department of Mines Aeromagnetic Maps 2146G, 2147G, 2156G, 2157G. I I 1 1 I I I I I I I I I - lB - Magnetic Magnetic expression of the Coldwell r complex. �+ 0 z In -4 C-) + �GEOLOGICAL S— MAP —a I 2 4 I 3 6 4 6 Gabbro Ferroaugite Syenite Biotite-Gabbro +-LIIIJ Acid Metavolcanics & Metasediments LZ1II Basic Vojcanjcs & Metcisediments [±IEI Ultrabasjc Intrusives LII1 Granite Gneisses 1IIIJ Basic Xenoljths (metavolcanics) PAA Nepheline Syenite Syenite - Syenodiorife 2 MILES 8 KILQMETRES 5 ++ Granite ,Quartz - Syerüte, Hybrid Syenites I 2 LEGEND o o MARATHON AREA COLDWELL COMPLEX a VICINITY _____ ______ LAKE SUPERIOR �-7- 1 1 S N 1 I ' CENTER 3 - Syenite, quartz syenites thewestern westernportion portion of ofthe thecomplex complexare arefound founda a InInthe widevariety varietyofofsyenites, syenites,quartz quartzsyenites syenitesand and granitic granitic wide The quartz rockswhose whosepetrology petrologyisispoorly poorlyknown. known. The quartz rocks syenites syeniteshave havebeen beenfound foundto to intrude intrudeall allearlier earlierrocks rocks by an Theserocksare arecharacterized characterized by an Center2.2. These.rOcks ofofCenter abundanceof ofzircon, zircon,paucity paucity of ofpyroxene, arfvedsonitic abundance amphiboles, amphiboles,fluorite fluori and quartz. MINORINTRUSIONS INTRUSIONS MINOR Theplutonic plutonicrocks are cut by two groups of minor The intrusions. (a) (a)diatremes diatremes (b) (b) dikes dikes intrusions. DIATREMES Threediatreifles diatremesare areknown knownin inthe theColdwell Coldwellregion, region Three I oneof ofwhich whichcuts cutsthe the intrusive intrusiverocks rocksof of the the only y one Thisdiatreme diatremelocated locatedon on the the west west side sideof ofthe t complex. This complex. ColdwellPenninsula Penninsulacontains containshornfelsed hornfelsedmetasediments metasediment Coidwell I I I and and inclusions inclusionsof ofCenter Center 22rocks rocksas asxenoliths xenoliths (Balint (Balint rocks, such as Diatremesin inthe theArchean Archean rocks, such.asthe the 1977). Diatremes 1977). be Deadhorseand andMcKellar McKellarCreek Creekdiatremes, diatremes,may may be Deadhorse Coldwell rocks have contemporaneous, yet been been contemporaneous,but but no no Coldwell rocks haveyet amongtheir theirxenolith xenolithsuites. suites. found among DIKE ROCKS s I widevariety varietyofof dike dike rocks rockscut cutthe thecomplex complexand and AA wide of These dikes In order surroundingcountry countryrocks. roc surrounding I vedabundance abundanceare:— are: observed 1 1 I 1) ocellular �--S C 2) analcite tinguaites 1 3) porphyritic (Al—Cr—cpx) lamprophyres 4) 4) glomeroporphyritic glomeroporphyritic and and alkali alkali basaltic basaltic dikes dikes (? Pukasaw swarm) ( ? Pukasaw swarm) . I ' 5) porphyritic (resorbed 5) (resorbed quartz) quartz) lamprophyres lamprophyres 6) nepheline nepheline syenite 6) syenite 7) rhyolitic 7) rhyolitic dikes dikes 8) syenites with a 8 ) syenites a high organic organic content content TECTONIC TECTONIC SETTING SETTING I I I I I I I I The complex The complex is is aa part part of of the the Keweenawan Keweenawan igneous igneous activity activity centered centered around around Lake Lake Superior Superior which which includes includ the Keweenawan basalts, basalts, the Duluth Complex Complex and the the the Logan sills. summary of the the regional regional geology and and Logan sills. A summary tectonic framework is 2. The complex complex tectonic framework is given given in in figure figure 2. is located at the Thinge 'hinge point' of of two two belts belts of of essentially tholeiitic essentially tholeiitic volcanics, volcanlcs, i.e. i.e. the the North North Shore— ShoreOsler volcanics and the Mamainse-Michipicoten Mamainse—Michipicoten volcanics Osier north—south and is itself the southern most member of a north-south trending belt of belt of of trending of alkaline alkaline intrusions. intrusions. A belt alkaline intrusions, alkaline intrusions, some some being being contemporaneous contemporaneous with with the Coldwell Coidwell Complex, Complex, is found along the "Kapuskasing the "Kapuskasing High" but no no petrological or or tectonic tectonic connection connection between these two The tectonic two belts belts is is known known to to exist. exist. The setting and type setting type of of igneous igneous activity activity is is similar similar to to that that found in the Kangerdlugssqaq Kangerdlugssuaq area of East Greenland and the Gregory-Kavirondo Gregory—Kavirondo Rifts the Rifts of of East East Africa. Africa. Both Both of of these areas these areas have been considered considered to to be be the the sites sites of of plume plume generated generated triple triple junctions, junctions, the the alkaline alkaline rocks rocks being associated with the failed ed arm of the spreading center. I I I �1 V I I I i I I 1 I I I I I I I I I I Figure Figure 22 -- Tectonic Tectonic setting setting of of the the Coidwell Coldwell alkaline alkaline from data data given given by by Card Card complex, complied compiled from complex, et et al a1 (1972), (1972). Currie Currie (1976), (1976), Gittins Gittins et et a1 (1967), (1967). Halls Halls and and West West (1971). (1971). Alkaline Alkaline complexes complexes and and carbonatites carbonatites are are designated designated ** and and their their radiometric radiometric ages ages (mostly (mostly K—Ar) K-Ar) are of years. are given given in in millions mill years. ~, �I I! 1 .m A ARCHEAN ARCHEAN 0 50 50 1do 00 150 ISO 00 200 KILOMETRES 200 KILOMETRES 150 MILES Ar, A SOUTH RANGE TRAPS KEWEENAWAN BASIN STRUCTURALAXIS AXIS OF OF STRUCTURAL MAJOR KEWEENAWAN MAmR KEWEENAWAN INTRUSIVES I EARLY EARLY PRECAMBRiAN PRECAMBRIAN UNCONFORMITY UNCONFORMITY A - LOWER KEWEENAWAN LOWER KEWEENAWAN UNCONFORMITY UNCONFORMITY MIDDLE PRECAMBRIAN t MIDDLE KEWEENAWAN LL.. CAMBRIAN CAMBRIAN UPPER KEWEENAWAN UPPER KEWEENAWAN U. U. KEWEENAWAN KEWEENAWAN SILURIAN SILURIAN - U. U. CAMBRIAN CAMBRIAN UNCONFORMITY UNCONFORMITY PRECAMBRIAN f LATE PALEOZOIC - A P LEGEND _7_ Ar NIPIGON NIflGON PLATE PLATE MICHIGAN PUCKASAW :/ / I / j Seabrook Lake 1100 Lackner Lake 1090 SAULT STE. MARIE Mamainse Car gantua F. Ar 1/ " Nemegosenda 1010 Portage 1090 /1 'i/la ía' Is I0Io*I Goldray 1695 Valentine Tp** 4Herman Lake.) Borden * Arg2655 * Sextant Rapids * Teetzel Tp. 1155 GRAVITY HIGH KAPUSKASING CargilI 1740* Clay — Howel Firesand 1048/ lola Lake 1185 1000 Coldwell 1 000 * Chipman Lake see �r I STOP I I ' I I I I I I I 1 Two EXPLOSION DIATREME - DEADHOBSE CREEK small explosion diatremes (Deadhorse Creek & McKeller Creek) are located in the Arehean greenstone belt just to the west of the Coldwell alkaline complex. A third subcircular diatreme (The Neys Diatreme) cuts rocks of the Coidwell complex. Located on the west side of the Coldwell Peninsula, this latter diatreme has been studied by Balint (1977). Neither diatreme in the greenstone belt has been studied in detail. This stop examines the small diatrerne exposed on the Ministry of Natural Resources access road which parallels Deadhorse Creek. Here the diatreme cuts Archean metavolcanics and pyroclastics. cross— The matrix of the diatreme, when unweathered, is dark green in colour and consists of carbonate and a greenish amphibole. Embedded in this are clasts of varying size and angularity. By far the most prominent are fragments from the greenstone belt. Of regional geological interest are occassional clasts of orthoquartzite. Similar clasts, together with red— purple shales, are found in greater abundance in the McKeller Creek diatreme. These clasts closely resemble rocks formed extensively in the paleohelikian Sibley l I I I I Group. Until now, the most easterly extension of this group of rocks was thought to he some forty miles to the west in the vicinity of Rossport. �p —12— I I 1 I I 1 I 1 I I I I I I I I I Fragments similar in appearance to certain felsic Fngments similar in appearance to certain felsic porphyries of the Keweenawan Osier volcanic rocks are porphyries of the Keweenawan Osler volcanic rocks are present. This may indfcate an easterly extension of present. This may indicate an easterly extension of Keweenawan volcanism, although the seeming total lack Keweenawan volcanism, although the seeming total lack Keweenawan basaltic rocks makes this assumption ofof Keweenawan basaltic rocks makes this assumption problematical. problematical �I I I I 1 ' I I I I I I I I I I I I -22 STOP STOP WESTERN MARGIN MARGIN OF OP THE WESTERN THE ALKALINE ALKALINECOMPLEX COMPLEX This stop investigates This investigates the the complexities complexities of of the the western stern contact region of the Coldwell Complex as exposed in the outcrops outcrops and road cuts exposed cuts adjacent adjacent to to Hwy. 17. region, the border intrusive Hwy. 17. In this region, intrusive rocks rocks of the complex are in contact with folded Archean of metasediments. metasediments. The rocks of the intrusion exposed in this region The are extremely extremely varied, varied, ranging ranging from from ultramafic ultramafic cumulates, cumulates, olivine gabbros olivine gabbros and syenodiorites syenodiorites to to nepheline nepheline syenites, syenites, quartz pegmatites with with and without without uartz syenites and syenitic pegmatites natrolite. atrolite. Later diabasic and lamprophyric dykes also cross ross cut the the region. region. The interrelationships interrelationships between these these various rock rock types ypes is still somewhat problematical as as is is their their exact exact relationship to the intrusive history of the complex in general. Webelieve, We believe, however, however, that the geographic general. relationships of the major intrusive relationships intrusive phases of the the contact contact zone are at least in in part fault fault controlled. controlled. It convenient, for the purposes of this stop, stop, to It is convenient, body of the intrusion traverse the contact zone from the body towards the purposes, we out towards out the contact. contact. For descriptive purposes, will consider consider the the rocks rocks exposed exposed in in three three major major zones. zones. These are outlined outlined as the accompanying sketch map map and These described below: below: described Zone 1 The main Coldwell Coldwell rock of this zone The zone is is a banded syenodiorite consisting consisting of subequal amounts of oligoclase syenodiorite and alkali feldspars, feldspars, the latter showing incipient exsolution. Apatite is ubiquitous and the mafic minerals minerals exsolution. consist of ferroaugite, ferroaugite, fayalitic olivine olivine and exsolved' exsolved consist ilmeno—magnetite. Thick ultramafic bands develop by the ilmeno-magnetite. �r I I I I I I I I I 1 I I I I I accumulation minerals, particularly particularly the accumulation of the mafic minerals, ilmeno-magnetite. ilmeno-magnetite. wide Cross cutting the syenodiorite is a relatively wide Cross syenite, most probably dyke or sheet of nepheline syenite, associated with with Center 2. Alkalic feldspar feldspar is is the the preassociated Center 2. dominant felsic phase with nepheline occurring in the interlath regions. interlath regions. Green (acmitic) (acmitic) pyroxene pyroxene is is the the major major mafic phase, while opaque minerals and accessory fluorite mafic phase, fluorite make up the the remaining remaining mineral mineral phases. phases. Cutting both the syenodiorite Cutting syenodiorite and the nepheline nepheline syenite is syenite is a coarse—grained coarse-grained natrolite natrolite syenite syenite pegmatite. pegmatite. In this, this, the natrolite In natrolite is is seen seen as as large large reddish reddish patches. patches. At least two thin lamprophyres intrude the rocks of of At this zone. zone. this These zone These zone 11 rocks rocks have not been recognized along along the the coastal section of the contact region lying lying some some 1 1 mile Here gabbros the south south of our to the to our present present location. location. Here gabbros of of with ferroaugite ferroaugite syenites, syenites, as shown zone 2 are in contact with the geological, map of the margin of themargin of the on the peolWica1 map ofsouthwestern the southwestern complex below below (Aubut (Aubut 1977). 1977). Zone 2 A zone of banded olivine gabbro intruded by syenite natrolite—bearing syenitic and natrolite-bearing syenitic pegmatites. pegmatites. The gabbros show considerable evidence of textural The plagioclase mineralogical readjustment. and mineralogical readjustment. Invariably the plagiocla crystals have been granulated and recrystallized giving crystals olivines rise to microscopic 'augen'—like rise 'augenl-liketextures. textures. The divines by coronas of of amphibole and are commonly surrounded by are mica and in many instances instances the original olivine olivine is is now represented by somewhat rounded replacement zones of 1 I �-15- fl I I green-blue green-blue amphibole amphibole and and pale pale green—brown green-brown mica. mica. Thin Thin , microscopic microscopic shear shear zones zones cross cross cut cut the the gabbro. gabbro. I I I I I I Again, later Again, later lamprophyric lamprophyric dykes dykes intrude intrude the the main main Coidwell Coldwell intrusive intrusive rocks. rocks. Along the Along the coastal coastal section section lying lying to to the the south, south, this this combination combination of olivine olivine gabbro gabbro intruded intruded by syenitic syenitic pegmatites pegmatites can can also also be be identified. identified. Here Here the the gabbros gabbros are somewhat somewhat coarser coarser than than those those seen seen on on the the highway. highway. The The olivines divines in in general are are fresh, fresh, although the the plagioclase crystals crystals still still show show considerable considerable evidence evidence of of readjustment. readjustment. On On the the coast, coast, the the gabbros gabbros are are in in direct direct intrusive intrusive contact contact with Archean metasediments and often often contain contain inclusions inclusions of the the latter. latter. (Aubut, (Aubut, 1977) 1977) The The Highway section section however, however, shows shows aa third third zone zone of of rocks rocks lying lying between between the the gabbro—pegmatite gabbro-pegmatite grouping grouping and and the the Archean Archean country countrv rocks. rocks. Zone 3 I This This zone zone consists consists of of quartz quartz syenite syenite which which is is often often seen seen intruding intruding aa 'hybrid' 'hybrid' rock rock of of overall overall syenitic syenitic mineralogy. mineralogy. I The The quartz quartz syenite syenite is is yellowish yellowish to to pink pink in in colour colour and and consists consists predominantly predominantly of of perthite perthite with with interstitial interstitial quartz quartz and and minor proportions proportions of of biotite, biotite, amphibole, amphibole, zircon zircon and and fluorite. fluorite. As yet, yet, we we do do not know know if if there there is is more I than than one one generation generation of of quartz quartz syenite. syenite. Thin Thin veins veins and and dykelets dykelets are are seen seen invading invading the the country country rock. rock. These These syenites 3. syenites have have been been ascribed ascribed to to Center Center 3. The The colour colour of of the the 'hybrid' 'hybrid' syenite syenite of of this this zone zone is is I I I I generally generally purple—brown, purple-brown, although although this this varies, varies, as as does does the degree to to which which it it is is invaded invaded by by the the quartz quartz syenite. syenite. �— 16 . I I I I I I 1 I I I I I I . - . . This 'hybrid' 'hybrid' syenite syenite is Us This .. . is of problematic problematic origin. origin. Lts:.. ..-$< . , , ' mineralogy is is syenitic syenitic consisting consisting predominantly of perthitic alkali alkali feldspars. feldspars. The large large red—pink red-pink alkali alkali invariably feldspar crystals crystals visible in hand specimens specimens invariably have remnant cores have cores of of plagioclase. plagioclase. The visible mafic spots, common spots, common throughout throughout the the rock, rock, consist consist of of biotite biotite and/or amphibole. Texturally the and/or amphibole. the rock rock is is hornielsic. hornfelsic. No later dykes dykes are are seen seen to to cut cut this this zone. zone. of quartz quartz syenitelhybrid syenite/hybrid We believe that this zone of syenite is in fault contact with the syenite the banded gabbro— gabbropegmatite complex pegmatite complex of of zone dbne 2. 2. We also feel that the the quartz quartz syenite rocks represent a higher structural structural level of the intrusion intrusion and that that the the hybrid syenite syenite represents aa block highlymetasomatised metasomatised country country rock. rock. represents block of ofhighly �I-> I I I S Xs S S I I I I I I I I 1 I I I I 000 0000 000 Syenodiorite iiIlllllIIIii' Nepheline Syenite / I -\ , \\'i../V '-1 I Olivine Gabbro ((banded) " J. Olivine *' Gabbro ban 'I ; Xxxx X X Syenite xx xx Quartz Syenite ¥  •Â0•.•• •0•5 •5 0 ''Hybrid Hybrid Syenite' syenitel -------- - Archean Sediments --- Archean Sediments Dyke(s) D NP NP Natrolife Pegmatite Natrolite Pegmatite (s) sP SP Syenite Pegmafite (s) Syenite Pegmatite ($1 w 'v\/- '\/\- Fault Fault o0 400 400 800 800 2000 FEET 1200 200 1600 600 2000 FEET M 600 METRES 600 METRES 400 200 0 I I I • I I Western Central Stop 2. Stop 2. Western Central Region. Region r %______ �-- I unsubdivided {b) -—--l porphyritic (Al—Cr Augite) (c) 2--—--2 acellular (a) == 4 6--—-6 layering (in intrusive racks bedding laps unknawn (inclined breccia zone (abundant xenoliths) sa L o ke Superior 2.. a SOUTHWEST MARGIN of the COLDWELL COMPLEX Sand and Gravel Pyraxene Horntels (including xenaliths Gabbra Augite Syenite Red Syenile Pegrnatite calloidal residua gabbro Cd) 3—3 parphyritic (resarbed quartz) 4--—--4 porphyritic (feldspar) 5--—-5 lamprophyre DYKES —- _____ ' iaI 23 _ a ac after A. Aubut Z.3 2(0 50 90° 1977 sa 200 METRES . an ;_ a us �I STOP STOP 3 LITTLE LITTLE PlC PTC LOOKOUT LOOKOUT 3 I j Parking Parking Lot Lot To seen cliffs cliffs of of xenolith xenolith free free To the the southwest southwest can can he be seen I .. $ I ferroaugite ferroaugite syenite syenite along along the the west west bank bank of of the the Little Little Plc Pic River. River. The The river river probably probably occupies occupies aa fault fault zone, zone, the down faulted faulted block block of of Center Center -- 22 the east east bank bank being being aa down and and 33 rocks rocks from from higher higher levels levels of of the the intrusion. intrusion. To To the the south south lies lies the the Coldwell Coldwell Penninsula Penninsula and and Pie Pic Island. Island. Densely Densely wooded wooded shores shores are are alkali alkali gabbro gabbro and and nepheline nepheline syenite. syenite. The The distant distant barren barren shores shores are are syenite syenite and and quartz quartz syenites. syenites. I I I I I I I I I I I Highway Highway Cuts Cuts The The highway cuts cuts on on the the north north side side of of highway highway 17 17 provide provide excellent excellent examples examples of of the the complex complex multiple multiple igneous whiah are aTe characteristic characteristic of of the the Little Little igneous breccias breccias which Pie Pic - Redsucker Redsucker Cove Cove block. block. The The oldest oldest breccias breccias are are of of - Center rocks, alkali alkali gabbro gabbro and and nepheline nepheline syenites syenites Center 2 rocks, similar similar to to those those exposed exposed on on the the West West side side of of the the These breccias Coidwell Coldwell Penninsula. Penninsula. These breccia* are are found found as a large large xenoliths xenoliths in in the the later later Center Center 33 quartz quartz syenite syenite Xenoliths Xenoliths in in the the quartz quartz syenite syenite are are oligoclase oligocla basalts basalts showing showing all all stages stages of of assimilation assimilation from from relatively sericitized basalt basalt to to almost almost relatively unaltered unaltered sericitized completely completely digested digested xenoliths xenoliths of of amphibolite amphibolite mineralogy. mineralogy. Development Development of of "clots" r'clots''of of biotite biotite and and amphibole amphibole is is aa breccias. breccias. characteristic characteristic metasomatic metasomatic feature feature of of the the xenoliths. xenoliths. The The oligoclase oligoclase basalts basalts probably probably are are remnants remnants of of Proterozoic Proterozoic extrusives extrusives which which originally originally capped capped the the complex. complex. These outcrops These outcrops demonstrate demonstrate conclusively conclusively that that Center Center 3 quartz syenites syenites are 3 quartz are younger younger than than Center Center 22 undersaturated undersaturated �g I ii I I rocks. rocks. , Two types types of of lamprophyre l a m p r o p h y ~ ecan can be be found found crosscutting crosscutting Two the breccias. the (a) porphyritic porphyritic lamprophyre, lamprophyre, characterized characterized by by (a) greenish phenocrysts phenocrysts of of Al—Cr Al-Cr augite, augite, possibly possibly greenish of high high pressure pressure origin. origin. of (b) ocellular ocellular lamprophyre, lamprophyre, characterized characterized by by ocelli ocelli (b) I 1 I I I I I I 1 I I I I I of carbonate, carbonate, quartz quartz and and fluorite. fluorite. of , �r I I I A A hi, I, I I hi p S p. I I I I Red quartz syenite with angular to rounded xenoliths of oligoclase basalt. Xenoliths show all stages of assimilation from sericitizecj basalt to almost completely digested ,9host xenoliths of amphibolite. Prominent biotite — amphibole clots" of metasomatic origin. Nepheline syenite xenoliths. A p. Large xenolith of Centre 2 rocks, biotite gabbo Large xenolith of Centre 2 rocks, vetned by nepheline syenites, cutbiotite by pegmatitic gabbro veined by nepheline syenites, cut by pegmatitic notrolite syenite dikes. In thin section biotite natrolite syenite In thincorono section biotite gabbro showsdikes. extensie structures. •'55 . gabbro shows extensive corona structures. • •• .S . ' doo_/ a Centre 2 rocks veined by quartz syenite. <0 I. I A I I I I I I I © 4\ ' 4 Red to ye1 low quartz Red to yellow quartz syenite breccia, syenite breccia. ow Porphyritic lamprophyre. Alurninous - Porphyritic lamprophyre. Aluminous in a cpq cpx phemcrysts biotite cpx phenocrysts feldspar matrix. in a cpx — biotite — feldspar matrix. - Ocellular lompophyres. Ocel li ore corbonoteOcellular lamprophyres. Ocelli are carbonate— quartz fluorite, matrix is amphibole, cpx , quartz — fluorite, matrix is amphibole, cpx, feldspar, biotite. feldspar, biotite. - 0 50, 100 200 FEET 150 I- 0 25 50 METRES Stop 3.3. Little Little Plc Pic River River Lookout. Lookout. Stop \ quartz syenites quartz syenites �STOP STOP 44 - - BRECCIA BRECCI DIKES I I I I I I I I I I I I I I At At this this locality locality are are found found several several natrolite natrolite syenite These dikes dikes are are of of variable variable syenite breccia breccia dikes. dikes. These thickness, thickness, they pinch and and swell swell and and terminate terminate in in thin thin natrolite natrolite syenite syenite veins. veins. Bifuroations Bifurcations of of the the dikes dikes are are common. common. The The outcrop outcrop of the the dikes dikes are are sinuous sinuous and give impreesion that they may have been em— emgive the the impression placed placed in in relatively relatively plastic plastic host host rocks. rocks. The The thicker thicker portions of the the dikes dikes are are crowded crowded with dark grey xenoliths xenoliths set set in in aa fine fine grained grained reddish reddish natrolite natrolite syenite. syenite. As the the dikes dikes thin the amount of xenolith decreases decreases and the terminating veins are composed composed of xenolith coarse grained xenolith free coarse grained natrolite natrolite syenite. syenite. The The xenoliths xenoliths are are rounded rounded to to very very irregular irregular in in shape. shape. Crenulated margins Crenulated margins are are typical. typical. No angular angular xenoliths xenoliths are present although the wedging action of the syenite syenite on comonly on the xenolith causing causing further further fragmentation fragmentation is commonly visible. visible. The The shape shape of ~f the the xenoliths xenoliths is is considered considered to to be the result result of brecciation and corrosion both in situ situ and and during during transport. transport. The The xenoliths xenoliths are are of of two two types, types, the the most abundant abundant being being a fine fine grained dark grey rock which in thin section section is seen of amphibole and mica, mica, alkali composedo€amphibo alkali seen to to be be composed sericitized feldspar feldspar and plagioclase. plagioclase. Rare relict sericitized phenocrysts The xenolith xenolith phenocrysts of of plagioclase plagioclase are are present. present. The margins margins are enriched in amphibole and mica relative relative to the 5 mm. in the interior. interior. Rounded aggregates of mica up to 5 diameter diameter are are common. common. Although the the xenoliths xenoliths have have been been bear a resemblance extensively extensively metasomatized they be+r resemblance to the the western end metavolcanic xenoliths metavolcanic xenoliths seen seen at at Stop Stop 3. 3. At the western of of the the outcrop outcrop occur xenoliths which consists consists of rounded aggregates of greenish mica set in a matrix of pale green aggregates pyroxene clinopyroxene and clinopyroxene and minor minor oligoclase. oligoclase. Rare euhedral pyroxen I I -22- �1 -23- I phenocrysts are are found. found. The The mica mica "rosettes" "rosettes" are are the the result result phenocrysts No comparable comparable rocks rocks of intense intense metasomatism metas~matism ofpyroxenite. pyroxenite. No of of I I I I I I I I I I I I I I I are known known elsewhere elsewherein inthe theintrusion. intrusion. are The The matrix matrix of of the the dikes dikes is is aa leucocratic leucocratic natrolite natrolite syenite composed composed of of alkali alkali feldspar feldspar (patch (patch perthites) perthites) syenite with with albite albite replacements, replacements,natrolite, natrolite,minor minor green green alkali alkali amphibole amphibole and and accesory accesory zircon zircon and and fluorite. fluorite. The host host rock rock of of the the dikes dikes is is aa leucocratic leucocratic syenite syenite The composed perthite, minor minor amphibole amphibole and and accessory accessory composed of of patch patch perthite, zircon and and fluorite. fluorite. Although Although natrolite natrolite has has not not yet yet been been zircon observed observed these these rocks rocks bear bear aa remarkable remarkable mineralogical mineralogical These rocks rocks have have similarily to to the the matrix matrix of of the thedikes. dikes. These similarily been been intruded intruded by by aa very very dark dark quartz quartz syenite. syenite. The breccia breccia dikes dikes are are considered considered to to be be intrusive intrusive The breccias,rather rather than than multiple multiple intrusions, intrusions, connected connected breccias, tabular lamprophyre lamprophyre dike dike can can activity. AA tabular with Center Center 22activity. with be be observed observed at at the the eastern eastern end end of of the the outcrop. outcrop. �r STOP STOP 55 - -- MINK MINK CREEK CREEK -- REDSUCKER REDSUCKER COVE COVE -- NEPHELINE NEPHELINE SYENITES SYENITES - -- r This This area area is is located located at at the the eastern eastern margin margin of of the the I I I faulted faulted block block characterized characterized by by extensive extensive igneous igneous breccia breccia development. development. Here Here the the arcuate arcuate structure structure defined defined by by the the gabbros gabbros and and by Center by Center 33 nepheline nepheline syenites syenites of of Center Center 22 is is truncated truncated quartz syenite. quartz syenite. The The Center Center 22 rocks rocks contain contain abundant abundant xenoliths xenoliths of of earlier earlier rocks, rocks, whilst whilst the the Center Center 33 rocks rocks are are relatively relatively xenolith xenolith free. free. Biotite Biotite gahbros gabbros are are the the oldest oldest rocks rocks at at this this locality locality and are found as greenish massive coarse grained to and are found as greenish massive coarse grained to pegmatitic pegmatitic rocks rocks which which in in many many places places are are commonly commonly brecciated brecciated and and veined veined by by natrolite—nepheline natrolite-nepheline syenites. syenites. The The gabbros gabbros are are composed composed of of hortonolitic hortonolitic olivines, olivines,augite, augite, plagioclase plagioclase (andesine—labradotite) (andesine-labradotite) biotite biotite and and alkali alkali feldspar feldspar which which in in some some examples examples becomes becomes sufficiently sufficiently I I I I I I abundant abundant that that the the rocks rocks should should be be termed termedsyenodiorite, syenodiorite. Corona Corona structures structures of of alkali alkali amphibole amphibole and and biotite biotite are are comnionlv developed around commonly developed around olivine olivine and and augite. augite. The The nepheline nepheline syenites syenites are are leucocratic leucocratic rocks rocks containing containing patch patch perthites, perthites, nepheline nepheline and/or and/or natrolite natrolite together together with with acicular acicular crystals crystals of of hastingsitic hastingsitic amphiboles. Quartz Quartz syenites syenites in in this this area area are are reddish reddish rocks rocks which which have have been been extensively extensively brecciated brecciatedand andsheared. sheared. At At the the localities localities shown shown can can be be found found the the following:— following:A. A. of of carbonate carbonate ocelli ocelli into into the the upper upper portions portions of of the the dike, dike, aa characteristic characteristic feature feature of of many many of of the the lamprophyres lamprophyres in in this thisarea. area. I B. B. I AA lamprophyre lamurophyre dike dike which which illustrates illustrates the the segregation segregation AA lamprophyre lampro~hyredike dike which which illustrates illustratesthe the intense intense metasomatism metasomatism associated associated with with many many of of the the Coldwell Coldwell minor minor intrusions. intrusions. The The metasomatism metasomatism is is manifested manifested I I -24- �—25— I C. C. D. D. E. I I I I I I I I I I I I I I by by aa "reddening" "reddening" of of the the host host rock rock feldspars. feldspars. Widths widths & of of the the metasomatic metasomatic zones zones are are commonly commonly much greater greater than than the the width width of of the the dike dike causing causing the the alteration. alteration. Igneous Igneous breccia. breccia. Xenoliths Xenoliths of of greenish greenish biotite biotite gabbro gabbro in in natrolite—nepheline natrolite-nepheline syenite. syenite. Hybrid Hybrid grey grey syenites. syenites. Coarse grained amphibole—nepheline—natrolite syenites. �P I I I I I I I I I I I I I U . .. . . . . .. . . .. .. . . . I 1*: :.•..I QUARTZ SYENITE NEPHELINE SYENITE SYENITE with gabbro gabbro and and NEPHELINE metavolcanic metavolcanic xenohths xenoliths j £j -- BIOTITE GABBRO as massive rock or in nepheline syenite — — Lineaments Lineaments I I I I I 0 - 0 1 200 I 400 I 600 METRES Redsucker Cove Stop 5. Mink Creek — . ..... .. . .. : ., .' ... .. - : . .... .. .. . ..... .. . ... . :.. . . .....1 ' . /2 MILE 1(4 Redsucker Cove. n ' sTS �r STOP 66 -STOP - FERROAUGITE SYENITE SYENITE QUARRY AND ROAD CUTS, HIGHWAY 17 FERROAUGITE - QUARRY AND ROAD CUTS, HIGHWAY 17 -- I I Ferroaugite syenite was formerly quarried at Marathon Ferroaugjte syenite was formerly quarried at Marathon for use use as as aa building building stone stone under under the the name "laurvekite", a for name ttlaurvekite, a term first first used used by by Kerr Kerr (1910) (1910) because because of the supposed term of the supposed I similarity between between the the Coidwell Coldwell complex complex and rocks of the similarity and rocks of the Oslo igneous province. Unfortunately this term has has permeated permeated Oslo igneous province. Unfortunately this term much of of the the geological geological literature literature concerning concerning the Coldwell much the Coldwell I complex.. complex.. j I I U I ~3, The only similarity in fact between the Coldwel The only similarity in fact between the Coldwell ferroaugite syenites and the Oslo larvikites is the ferroaugite syenites and the Oslo larvikites is the presence of cryptoperthitic intergrowths which impart an presence of cryptoperthitic intergrowths which impart an intense schiller schiller to to the thefeldspars. feldspars. The Oslo larvikites intense The Oslo larvikites are monzonitic monzonitic rocks rocks which which grade gradeinto intonepheline nephelineplagi— plagi are foyaite (lardalite). (lardalite). They do not show extreme iron foyaite They do not show extreme iron chment nor nor do do they they differentiate differentiateto tooversaturated oversaturatedresidua. enrichment residua. The quarry at this stop exposes highly weathered The quarry at this stop exposes highly weathered oaugite syenite and illustrates the typical deep1 ferroaugite syenite and illustrates the typical deeply weathered friable friableappearance appearance of of ferroaugite ferroaugite syenite weathered syenite away from the polished glaciated outcrops on the lake away from the polished glaciated outcrops on the lake shore (Stop (Stop8). 8). shore The fresh ferroaugite syenite exposed in the roa The fresh ferroaugite syenite exposed in the road cut to the east east of of the the quarry quarry is is an example of one of cut to the an example of one of I the most highly differentiated .portionsof the ferrothe most highly differentiated portions of the ferroaugitesyenite. syenite. Olivines are fayalite (FaQ4Tp4F02), augite Olivines are fayalite (Fa94Tp4Fo2), pyroxenes are light greenish brown ferroaueite (Di pyroxenes are light greenish brown ferroaugite (Di10Hd85 1oHd85 I I I zoned to to acmitic—hedenlergite acmitic-hedenbergite(Ac50Hd50). (Ac50Hd 50) . Amphiboles Ac 5 ) zoned Ac5) Amphiboles are light green ferrorichterite (Na2CaFe5Si8On2(OH),,) are light green ferrorichterite (Na2CaFe5Si8o22(O}J)2) with minor minor mantles mantles of of arfvedsonite arfvedsonite (Na3Fe5Si8O29(0H)2) (Na3Fe,Si8022(OH)2) with Aenigmatite (Na2Fe5TiSi6O20) is abundant and calcite and quartz can he found as interstitial residual phases. I I I I — 27 — �STOP STOP 77 - - GABBRO GABBRO p I I The The arcuate arcuate mass mass of of basic basic rocks rocks which which define define the the eastern eastern margin margin of of the the complex complex is is commonly commonly referred referred to to as as the the eastern eastern gabbro gabbro to to distinguish distinguish it it from from the the alkaline 2. This This eastern eastern gabbro gabbro is is alkaline gabbro gabbro of of Center Center 2. considered considered to to belong belong to to Center Center 11 activity activity as as it it is is intruded intruded in in many many places places by by ferroaugite ferroaugitesyenite. syenite. The The petrological petrological relationship relationship between between the the two two magmas magmas is is however unclear. however unclear. Ferroaugite Ferroaugite syenite syenite is is unlikely unlikely to to be b aa direct direct differentiate differentiate of of the the gabbro gabbro because because of of the the greater greater volume volume of of the the former former and and lack lack of of mineralogical mineralogical gradations gradations between between the the two two rock rock types. tyoes. The The zone zone of of I I I I I I gabbro gabbro defines defines aa prominent prominent magnetic magnetic low low on on figure figure lB 1B and and is is considered considered by by Lilley Lilley (1964) (1964) to to be be due due to to reversed reversed magnetization magnetization of of the the gabbros. gabbros. The The gabbros gabbros are are composed composed of plagioclase (An6035)) and ) , augite, augite, plagioclase and of olivine olivine (Fo67_43), minor minor orthopyroxene orthopyroxene (Efls5rc) (En55-..c ) (Lum, (Lum,1973). 1973). The The ortho— orthopyroxene pyroxene may may be be aa product product of of assimilation assimilation of of Archean Archean metasediments, metasediments, aa xenocryst xenocryst derived derived frpm from the the pyroxene pyroxene hornfels hornfels thermal thermal aureole aureole or or aa relict relict high high pressure pressure phase. phase. The The gabbro gabbro has has been been extensively extensively prospected prospected with with regard regard to to its its copper copper potential potential as as accumulations accumulations of of pyrrhotite pyrrhotite and and chalcopyrite chalcopyrite with with minor minor pentlandite, pentlandite, cubanite, cubanite, pyrite, pyrite, bornite, bornite, arsenopyrite arsenopyrite and and mackinawite (vatkinson (Watkinsonet et al. al. 1973, 1973, Lum, Lum, 1973) 1973) are are common. common. The The excursion excursion stop stop is is close close to to the the contact contact between between the the gabbro gabbro and and the the ferroaugite ferroaugitesyenite. syenite. Many Many pegmatites pecmatites of of ferroaugite ferroaugitesyenite syenitecut cut the the gabbro gabbroat at this thislocality locality and and demonstrate demonstrate that that the the gabbro gabbro is is the the earliest earliest activity activity present present in in the thecomplex. complex. The The gabbro gabbro is is widely widely variable variable in in appearance appearance due due to to the the presence presence of of variable variable amounts amounts of of Archean Archean xenoliths. xenoliths. At At this this location location the the gabbro gabbro shows shows all all transitions transitions from from massive massive homogenous homogenousgabbro gabbroto torocks rocks I I I -28- �1 I- -3 F-Q CD O P CO -C CD CD CD P o c-f CD 0 0 H- CO C p H- Q o ow ci- CD CD .w wc p P0 <p CO CD H CD H, o ci- H- OqGq lipli (t ci- CD — CD ot (DO -C -C CD CD 0 ci- w CD — — CD P' CD o c-I- c-I-p c* 0 c* Elill — F" tt pa ____ ____ ____ w i t h w e l l developed igneous l a y e r i n g . The l a y e r s a r e not t r a c a b l e o v e r l a r g e d i s t a n c e s and do not s e r v e t o o u t l i n e t h e s t r u c t u r e o f t h e gabbro i n t r u s i o n . �a STOP STOP 88 -- LAKE LAKE SUPERIOR SUPERIOR SHORE SHORE LINE LINE CENTER CENTER 11 - PLUTONIC PLUTONIC - ROCKS ROCKS AND AND MINOR MINOR INTRUSIONS INTRUSIONS I Proceed Proceed fron from the the parking parking lot lot at at the the foot foot of of Howe Howe St., St., Marathon Marathon along along the the trail trail through through the the woods woods to to avoid av the the boulder boulder beach. beach. The The trail trail emerges emerges at at location location F, F , from from that that point point follow foil the coast to to location A. I Location AA Location ~Hornfelsed Hornfelsed Archean Archean metasediment metasediment cut cut by by analcite I , I tinguaite tinguaite dikes. dikes. These These rocks rocks were were initially initially described described by by Coleman Coleman (1900) (1900) as as heronites. heronites. The The tinguaites, tinguaites, after after I lamprophyres, lamprophyres, are are the the second second most most abundant abundant type type of of minor minor intrusion intrusion at at Coidwell Coldwell and and are are probably probably associated associated with magmatism. Xenoliths Xenoliths with the the undersaturated undersaturated Center Center 22 magmatism. I of of coarse coarse grained grained nepheline nepheline syenite syenite can can be be found foundin in some some examples examples at at Heron HeronBay. Bay. The The majority majority of of the the tinguaites tinguaites I I are are intensely intensely hematized hematized and and carbonatized, carbonatized,are are very very fine fin grained grained and and brick brick red red to to dark dark reddish—brown reddish-brownin incolor. color. At At this this locality locality is is found found aa relatively relatively fresh fresh 3—4 3-4 ft. ft. wide vertical vertical dike. dike. Black Black margins margins with with conchoidal conchoidalfractures fractures may may represent represent an an original original chilled chilled glassy glassy margin. margin. The The tinguaite tinguaite is is porphyritic porphyritic with with phenocrysts phenocrysts of of pale pale green green I I ferroaugite ferroaugite with with titan—acmite titan-acmite rims, rims, brown brown hastingsite hastingsite and and anorthoclase anorthoclase set set in in very very fine fine grained grained groundmass groundmassof of apatite, apatite, acicular acicular pyroxene, pyroxene, hematized hematized feldspar, feldspar,fluorite fluorite and and analcite. analcite. I I Location_B Location B - Glomeroporphyritic Glomeroporphyritic diabase diabase representative renresentativeof of the the post-Coldwell post-Coldwell alkali alkali basaltic basalticmagma magma activity. activity. The The glomeroporphyritic glomeroporvhyritic feldspars feldspars are are labradorite labradoriteset set in in aa I groundmass groundmass of of andesine andesine and and aluminous aluminousaugite augite(8% (8%A1203). Alp03). Several Several thin thin ocellular ocellular lamprophyre lamprophyredikes dikescan canbe be I I -30- , �-3'- P observed between locations A and B. I I I Location C Location I Ocelli in these observed between locations A and B. rocks contain quartz plus calcite orOcelli dolomite. in these rocks contain quartz plus calcite or dolomite. Extensive deposits of sand and gravel cover the Extensive deposits of sand and and the gravel contact between the intrusion Archean covercountry the contact between the intrusion and the rocks and no outcrops are found between locations B Archean country rocks and no outcrops are found between and C. The area however presents excellent exposures locations B and C. The area however presents excellent of the lowest of the six beach terraces at exposures Marathon. of the lowest of the six beach terraces at Marathon c Xenolith bearing gabbro considered to be equivalent Xenolith bearinggabbro gabbroobserved considered to be7.equivalent to the hypersthene at Stop to the hypersthene gahbro observed at Stop 7. Location - Location I I I I D 0 Fayalite-ferroaugite syenite with well dev Fayalite_ferroaugite with well developed igneous layering defined syenite by the mafic minerals. Crossigneous layering defined by the mafic minerals. bedding, slump structures, and diffuse turbulentCross— layering bedding, slump structures, and diffuse are all well developed in this area. turbulent layering are all well developed in this area. The mafic minerals ferroaugite, and amphiboles belonging toare thefayalite, ferroedenite-hastingsite amphiboles belonging to the ferroedenite_hastingsite series (NaCa2Fe5Si~102~OH)2-NaCa2Fe5SinA1202(OH)2). series (NaCa2Fe5si7Alo22(OH)_NacaFesiAlo(0H)) Location E Location E Ferroaugite syenites representative of the more I I I I I I Ferroaugite syenites representative of the extreme differentiates of this magma. Pyroxenes more are extreme differentiates of this magma. members of the acmite-hedenbergite series and amphiboles Pyroxenes are members of the acmite_hedenbergite series and amphiboles are subaluminous ferroedenite (NaCa2Fe5Si7.5Alo. are suhaluminous ferroedenite (NaCa2Fe5si7Alo(OH)) or ferrorichterite (Na2CaFe3Si8o2 (OH) (Na2Fe5Tisi6O) is ) abundant. Aenigmatite �— 32 — Location FF Location Ferroaugite syenite cut by very coarse patch and Ferroaugite syenite cut by very coarse patch and I sheet pegmatites. The pegmatites illustrate the oversheet pegmatites. The pegmatites illustrate the oversaturated nature of the ferroaugite syenite differentiation saturated nature of the ferroaugite syenite differentiation trend, and contain ferrorichterite altering to ferrotrend, and contain ferrorichterite altering to ferro— I actinolite, i I I I I I I I I I I I I I C feldspars, quartz and zircon. �I parking lot ii I I I I I I I I I I I I I I I I F FERRQ4UGITE SYENITE C, / / / 0 I- 0 1/2 500 4- J 1000 Mile 1500 Metres 4RCHE4N Stop 8. Layered Ferroaugite__Syenites. �. r ~ . REFERENCES REFERENCES I I • • I I I I I I I I I Aubut, Aubut, A.J. A.J. (1977): (1977): Geology Geology of of the the southwestern southwestern margin margin of of the the Coidwell Coldwell alkaline alkaline complex, complex. Northwestern Northwestern Ontario. Ontario. H.B.Sc. H.B.Sc. Thesis, Thesis, Lakehead Lakehead Univ., Univ., Thunder Thunder Bay, Bay, Ontario. Ontario. Ayres, Ayres, L.D., L.D., Lumbers, Lumbers, S.B., S.B., Mime, Milne,V.G., V.G.,and andRoherson, Roberson, D.W. D.W. (1970): (1970): Ontario Ontario Geological Geological Map. Map. East East Central 2198a. Central Sheet, Sheet, Ontario Ontario Dept. Dept. Mines Mines Map, Map, 2198a. Balint, 1 dwell alkaline Balint,F. F. (1977): (1977): The The Neys Neys diatreme, diatreme, Co Coldwell alkaline complex, o. H.B.Sc. complex, Northwestern Northwestern Ontari Ontario. H.B.Sc. Thesis, Thesis, Lakehead Univ., Thunder Bay, Ontario. Lakehead Univ., Thunder Bay, Ontario. Card, Card, K.D K.D., Church, Church. W.R., W.R., Franklin, Franklin,J.M., J.M., Frarey, Frarey, M.J., M.J., Robertson, J.S., West, West, G.F., G.F., and and Young, Young, G.M. G.M. Robertson,J.S. (1972): hem Province. Variations (1972): The The Sout Southern Province. In In : Variations in in Tectonic Tectonic Style Style in in Canada. Canada. Eds,, Eds., Price, Price,R.A., R.A., and and Douglas, Douglas.J.W. J.W. Geol. Geol. Assoc. Assoc. Canada Canada Spec. Spec. Paper Paper 11, 11,335—380. 335-380. : Coleman, Coleman, A.P. A.P. (1900): (1900): ileronite Heronite or analcite analcite tinguaite. tinguaite. Ann. Rept. Bur. Mines Ontario 9,186—191. 186-191. Ann. Rept. Bur. Mines Ontario 9, Currie, Currie,K.L. K.L. (1976): (1976): The The alkaline alkaline rocks rocksof of Canada. Canada.Geol. Geol. Surv. Surv. Canada CanadaBull. Bull., 239. 239. , Einarrson, G.W. G.W. (1973): (1973): Variations Variations in in the the style styleof of metamorphism in Archean supracrustal units metamorphism in Archean supracrustal units Einarrson, of of the the Superior Superior Province. Province. H.B.Sc. H.B.Sc.Thesis, Thesis, Lakehead Univ., Thunder Bay, Lakehead Univ., Thunder Bay,Ontario. Ontario. Gittins, Gittins,J., J., MacIntyre, R.M., and York, D. (1967): The ages ages of of carbonatite carbonatite complexes complexes in in eastern eastern Canada. J. Earth EarthSci. Sci. 4, 4,651—655 651-655. Canada. Canad. Canad.J. Halls, Halls,H.C., H.C.,and and West, West.G.F. G.F.(1971): (1971): AA seismic seismic refraction refraction survey survey in in Lake Lake Superior. Superior. Canad. Canad. J. J. Earth Earth Sd. Sci. 8, 8,610—630. 610-630. Kerr, Kerr,H.L. H.L.(1910): (1910): Nepheline Nepheline syenites syenites of of Port Port ColdwelL Coldwell. Ann. Ann. Rept. Rept. Bur. Bur. Mines Mines Ontario, Ontario,19, 19,194-232. 194-232. I I I — 33 — �ri Lilley, Lilley, F.E.M. F.E.M. (1964); (1964): An analysis analysis of of the the magnetic magnetic An features features of of the the Port Port Coidwell Coldwell intrusive, intrusive. M.Sc, M.Sc. Thesis. Thesis. Univ. Univ. Western Western Ontario, Ontario. London, London. I I Ontario. Ontario. Lum, Lum, H.K. H.K. (1973): (1973): Petrology Petrology of of the the eastern eastern gabbro gabbro and and associated associated sulphide sulphide mineralization mineralization of of the the Coldwell Coldwell alkalic alkaliccomplex. complex. B.Sc. B.Sc. Thesis, Thesis, Carleton, Carleton, Univ. Univ., Ottawa, Ottawa, Ontario, Ontario. , I ' Milne, Milne,V.G. V.G. (1967): (1967): Geology Geology of of the the Cirrus Cirrus Lake—Bamoos Lake-Bamoos Lake Lake area. area. Ontario Ontario Dept. Dept. Mines, Mines,Rpt. Rpt.43. 43. Mitchell, and Platt, P1att, R.G. Mitchell,11.11., R.H., and R.G. (1977): (1977): Mafic mineralogy mineralogy Mafic of of ferroaugite ferroaugite syenite syenite from from the the Coidwell Coldwell alkaline alkaline I I I I I I complex! complex. 23rd 23rd Ann. Ann. Instit. Instit.Lake LakeSuperior SuperiorGeology, Geology, Thunder ThunderBay Bay (abstract). (abstract). Puskas, Puskas, P.P. F.P. (1967): (1967): The The geology geology of of the the Port PortColdwell Coldwellarea area Ontario .No. Ontario Dept. Dept. Mines Mines Open Open File FileRpt Rpt. No.5014, 5014, Thunder Thunder Bay, Bay,Ontario. Ontario. Thompson, Thompson, J.E. J.E. (1931) (1931)- Geology Geology of of the theHeron HeronBay Bayarea. area. Ann. Rept. Ontario Dept. Mines, 40, 21—39. Ann. Rept. Ontario Dept. Mines. 40. 21-39. Walker, Walker,J.W.R. J.W.R. (1967): (1967): Geology Geology of of the theJackfish-Middleton Jackfish-Middl area, area,Ontario OntarioDept. Dept.Mines MinesGeol. Geol.Rpt. Rpt.50. 50. Watkinson, ,D.H., D.H.,Mainwaring, Mainwaring,P.R., P.R.,and andLum, Lum,H.K. H.K.(1973): (1973): Petrology Petrology and and copper copper mineralization mineralizationof ofthe the Coldwell Coldwellcomplex, complex.Ontario. Ontario. Geol. Geol.Soc. Soc.Amer. Amer. Abs. Abs. Ann. Ann.Mtg. Mtg. 5, 5,856. 856. ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS I I I I Research on the thepetrogenesis petrogenesisof ofalkaline alkalineintrusions intrusions in in Northwestern Northwestern Ontario Ontariois issupported supportedby by the theNational National Research ResearchCouncil CouncilofofCanada. Canada. Sam SamSpivak Spivakis isthanked thankedfor fordrafting draftin services involved in in the theproduction productionof ofthis thisguide guidebook. book. �a 8 (4) a; -- - a__fl -. AIRLANE MOTOR HOTEL LOTUS INN CROSSROADS MOTOR INN RED OAK INN p � https://digitalcollections.lakeheadu.ca/files/original/511ac78db0b56dd6f5327fb751cf7e10.pdf 3e8cc58a84a56f5723808e43eaafc4d9 PDF Text Text Iwety Ihipti Aonoal Institute Meeting Thunder Bay, Ontario Superior PROTEHOZOIC TRIP �PROTEROZOIC ROCKS OF THE THUNDER BAY AREA NORTHWESTERN ONTARIO May 3—4, 11.977 FIELD EXCURSION GUIDE PREPARED BY C.R. Kustra, Ontario Ministry of Natural Resources W.H. Mcllwaine, Petro-logic Limited, Thunder Bay K.G. Fenwick, Ontario Ministry of Natural Resources J. Scott, Ontario Ministry of Natural Resources �1 Guide to the Proterozoic Rocks of the Thunder Bay Area, Northwestern Ontario INTRODUCTION: The Proterozoic rocks of Northwestern Ontario, which form part of the itAnimikiet and !TKeweenawantt units, represent one of the most complete geological records of Middle and Late Precambrian sedimentation and igneous activity in eastern North America. These rocks are virtually unmetamorphosed and relitively undeformed. Mineral depsits in the Proterozoic rocks include silver in Keweenawan dikes and the Rove Formation, iron in the Gunf lint Formation, nickel in mafic intrusive rocks, copper in various volcanic and sedimentary strata, and lead-zinc-barite, amethyst and uranium associated with the Sibley Group. During the last century, the famous Silver Islet mine produced over 2.8 million ounces of silver. REGIONAL GEOLOGY The Proterozoic rocks lie unconformably on the peneplained Early Early Precambrian (Archean) surface of the Superior Structural Province. Precambrian rocks form several northeast-trending "belts" of metamorphosed and complexely deformed metavolcanic and metasedimentary rocks intruded by felsic, and intermediate to ultramafic intrusive rocks. The lithostratigraphy of the Proterozoic rocks is shown in Table 1. API-JEBIAN The Gunflint Formation (Fig. 2) has been studied by Goodwin (1956, 1960) and Moorhouse (1960). The petrology has been studied in detail by Floran and Papike (1975). Detailed descriptions of fossils from the Gunf lint Formation are recorded by Barghoorn and Tyler (1965), Barghoorit (1971) and Edhorn (1973). The Rove Formation has been described by Morey (1969) and Geul (1970, 1972). Much of the descriptive detail is taken from these authors. Gunf lint Formation (adapted from Goodwin, 1956) The Gunflint Formation extends continuously for 110 miles (177km) from Gunflint Lake east to beyond Thunder Bay, from where it can be traced intermittently to the Slate Islands, (Sage et al 1975), southeast of Schreiber. It averages 400 feet (122 m) in thickness (Goodwin, 1956) Except for local faulting and brecciation caused by intrusive activity and slumping, the Gunf lint Formation is structurally simple and uncomplicated, with an average southeast dip of 5°. �2 TABLE 1 Proterozoic Stratigraphy of Northwestern Ontario Neohelikian Osler Group: basalt, minor rhyolite and sedimentary rocks Intrusive Rocks: gabbro stocks undersaturated stocks Iayered bodies northeast trending dykes Logan diabase sills Paleohelikian Sibley Group: Kama Hill Formation Rossport Formation Pass Lake Formation Aphebian Animikie Group: Rove Formation: shale, greywacke Gunflint Formation: iron formation (taconite) algal chert, limestone, tuffaceous shale. TABLE 2 Stratigraphy of the Gunf lint Formation (modified from Goodwin, 1956) Limestone-dolomite Member Upper Member Taconite-chert carbonate submember: taconite (west) facies chert carbonate (east) facies Tuffaceous shale submember Algal chert submember Lower Member Taconite-chert carbonate submember: Tuffaceous shale submember Algal chert submember Kakabeka Conglomerate Member west taconite facies chert carbonate facies east taconite 1 acies �Fig. I LII UPPER TACONITE i — - 5 0 10 10 20 • ••.• I S •••• :.:... •. : : .••: : : SS --- ALGAL CHERT 30 KILOMETRES MILES 0 501 0 I0 1- 20 oo-f 30 F 40 I5O FEET METRES LOWER EAST TACONITE - !JPER CHEAT CARBONATE •: Thunder Bay Slate River UPPER TUFF ARGILL1TE — ... •••• •' ::•::•:••::• •: •s,••••I•s,s••,•• .• • 'a' '::•::: 'c.:.: :•.•.:•: :•.• . ..... fg'\ k'..... IUI Northeast Longitudinal section of the Gunf lint formation. (after Goodwin ,1956).(Rove fm. added by author). Stops described in field guide BASAL CONGLOMERATE MEMBER LOWER WEST TACONITE —urrLn P4L%)ML .ncni-— MEMBER ci'- LOWER MEMBER UPPER Southwest �__ ___ ____ r.fl77' f ////// /////,../// ////. / ______ ____________ ____ ___ + + . + ÷ (4 + + 44+ * + ÷/+ + r+___.r4.m.y4.T.rn Urrn + - ÷ + ÷;' ÷ + + ÷ t-cj_XY +t.tt___ + 4 9....... I + - . ++ I LEGEND I I I j.-I + + I DIABASE I ri ROVE FORMATION THUNDER ÷ ÷ . L9÷.t_t ÷+÷+÷+÷: + + + + + + + + K K FHWH GUNFLINT FORMATION - ÷ . 1'' 1 LH1 I 7' - GRANITE - H + + HH H + H +/i;H I / H 'HJ 0/0 T -- FAULT / N-_--- FaMERS ::-: . + I,Hi NOLKLU : .... I I :'- :- . . T:.. . (I I 7-• :- -. . . . ,- w :' o . .-- -a.- .-'- . .: 1-k .•[ S .. . ,-7 c—cs : - ,j, I . - - :HYl t,-nPY -. . -0 •j/ ) - SLATE RIVER HWY 61, SW. OF CLOUD LAKE ROAD I 2 5 KAKABEKA FALLS (SWIM AREA) KAKABEKA FALLS RIM (WEST SIDE) KAKABEKA FALLS (HYDRO SPILLWAY) 6 DICKSONS QUARRY (BELROSE ROAD) 7 —S, HILLCREST PARK (HIGH STREET) BOULEVARD LAKE ( LYONS BRIDGE) THUNDER BAY LOOKOUT (EXPRESSWAY) 4 8 9 -. -' 0 4 2 6 - 0 . , .7' F7 (. . •----\ STOP LOCATION FIELD STOPS 3 A L- H- •- .-Z,, c-.i U -: ... . Yk * 2 4 6 8 10 12 KILOMETRES L)/ C Fig 2 Geology and Field Stop Locations a �5 Deposition of the Gunflint Formation was in part cyclical. A basal conglomerate member is overlain by two members each composed of chert, tuffaceous shale, and carbonate-taconite submembers. These members are in turn overlain by a discontinuous limestone member, (Fig. 1 and Table 2). Although no isotopic investigation has satisfactorily established the time of sedimentation, various studies suggest that deposition of Animikie sediments took place 2,000 m.y. B.P. (Floran and Papike, 1975). Stratigraphic Descriptions (a) Basal Kakabeka Conglomerate Member This member ranges to five feet (1.5 m) in thickness and is composed of polymictic conglomerLte. Clasts of Archean volcanic rocks, granite and quartz are cemented in a matrix of chlorite and quartz. The unit is highly irregular in thi.kness but persistent. (b) Lower Member The lower algal chert submember (Fig. 1) consists of reef-like mounds of finely banded black, red, and white oolite chert. These mounds This submember forms the are intergrown and cemented in dolomite. western margin of Gunflint outcrop (Fig. 1), but is continuous to just It contains abundant microflora remains west of Kakabeka Falls. (Barghoorn and Tyler, 1965, Barghoorn, 1971, Edhorn, 1973). The lower tuffaceous shale (lower tuff argillite, Fig. 1) submember It overlies the lower algal chert subranges to 20 feet (6 m) thick. member in the area west of Kakabeka Falls and is composed of fissile black shale containing much volcanic ash. The uppermost submunber of the lower member is subdivided into three facies (Fig. 1). The lower west taconite facies, which is 150 feet (45 m) thick, extends northeast from Gunf lint Lake to Kakabeka Falls and is composed of wavy-banded granular chert, carbonate, and oxides. The lower half contains disseminated greenalite granules in pale grey chert; siderite forms local beds. The upper half contains increasing amounts of hematite and magnetite. This facies grades upward into jaspilitic upper algal chert and grades laterally into the lower banded chert-carbonate facies. The lower banded chert-carbonate facies extends from Kakabeka Falls to Thunder Bay city, and consists of 4 to 6 inch (10 to 15 cm) siderite beds, with interbedded 2 to 6 inch (5 to 15 cm) grey cherty beds. Carbonaceous material and pyrite are common in shale interbeds. This facies grades into granular taconite towards the northeast. The lower east granular taconite facies extends from Thunder Bay to The basal 2 to 6 feet (60 to 180 cm) are formed of interbedded granular chert and ankerite. The upper 10 to 20 feet (3 to 6 m) consist of interbedded red to green mottled chert and dolomitic limestone. This facies grades upwards into the tuffaceous shale (upper tuff argillite, Fig. 1) submember of the upper member. Loon Lake. �6 (c) Ujper Member The upper algal c iert submember extends west from Nolalu to Gunf lint Lake and consists of b sal granular chert overlain by algal chert and, in the Mink Mountain area, amygdular basalt flows. The flows and algal chert are overlain by granular chert and bedded jasper. Jasper beds grade into tuffaceous shale of the overlying submember. The upper tuffaceous shale (upper tuff argillite) is the only continuous submember in the Gunf lint Formation and forms a key stratiIt ranges to 100 feet (30 m) thick and thins graphic marker (Fig. 2). laterally in either direction from Kakabeka Falls. It consists of black tuffaceous shale and siltstone with interbedded siderite and pyrite and The ash contains ellipsoidal, aceretionary extensive beds of volcanic ash. lapilli and concentric layers of small angular tuff fragments, arranged Similar lapilli have formed due to the about a larger central fragment. accumulation of volcanic dust in water droplets and on water coated shards (Moore and Peck, 1962). The upper tuffaceous shale submember grades into the upper taconite and chert-carbonate submember. The upper taconite facies extends from Gunflint Lake to Thunder Ba, (Fig. 1), and is composed of wavy bands of granular greenalite-bearing chert. The greenaTite-bearing granules are round to oval, evenly distributed throughout a layer, and appear to have The unit exhibits a rusty weathering, contains abundant formed "in situ". hematite and magnetite in granules towards the top, and grades laterally (Fig. 1) into the upper banded chert-carbonate facies which extends from west of Thunder Bay to Loon Lake. The latter facies consists of interbedded grey chert and brown carbonate (siderite with lesser dolomite arid Brecciation and folding, apparently contemporaneous with ankerite). deposition, are common. (d) Upper Limestone Member The upper limestone member marks the top of the Gunflint Formation. Minor chert beds, illite and volcanic shards are present, and tuffaceous shale is most prevalent in the eastern area of Gunflint outcrop. Stratigraphic Interpretation Goodwin (1956) concluded that Gunf lint deposition occurred in a After shallow basin which had limited circulation with an open sea. initial algal activity in the neritic zone, volcanic activity (tuffaceous Silicate-bearing material shale) was accompanied by sinking of the basin. (taconite) was deposited in the deepest portions while in the neritic, or intertidal zone (between Kakabeka Falls and Thunder Bay) banded chertFarther to the northeast, the lower east taconite facies carbonate formed. formed in agitated, oxygenated waters. As the basin filled, conditions of algal growth returned, initiating the "Upper Gunflint" cycle. Volcanic activity, marked by local basalt flows, terminated the upper algal chert deposition and resulted in widespread distribution of pyroclastics of the upper tuffaceous shale. Downwarping resulted in deposition �7 of granular iron silicate rocks in the deeper, southwest portion of the basin, while on the shallow northeast shore, chert carbonate was deposited. As the basin filled, sporadic but violent volcanic activity was accompanied by the entry of sea water, resulting in formation of the upper limestone. Goodwin (1956) in drawing an analogy with the Santorin volcano of the Aegean Sea, suggests that volcanism was the chief source of iron and silica. Alternatively, Hough (1958) suggests deposition in a fresh water basin, with material derived through weathering of an adjacent landmass, and deposition controlled by limnic cycles. Rove Formation The Rove Formation conformably overlies the Gunflint Formation. In the Thunder Bay and Pigeon River areas, it may attain a thickness of at least 1,250 feet (380 m), and possibly more than 2,000 (610 m), Geul (1970). The formation consists of three lithologic units (Geul, 1970) which are, from base upwards: (1) black pyritic shale and argillite (base) (2) interbedded argillite and greywacke and shale (transition sequence of Morey, 1969) (3) quartzitic greywacke with argillite interbeds (top) The lower argillite is the dominantly exposed unit in Ontario and commonly enclosed carbonate concretions of varying size and complex in The transition sequence consists of thin-bedded greyform and texture. wacke, consisting of grey to pink greywacke and sandstone, is the thickest unit of the Rove Formation and is exposed mostly in northeastern Minnesota. The metamorphic age of the Rove Formation is considered to be 1.7 billion years (Peterman, 1966). Morey (1969) notes that the detrital matenal comprising the Rove Formation was derived from Archean terrain to the north. PALEOHELI KlAN The Sibley Group This section is adapted from Franklin et al (in press). Introduction: The distinctive red and white sandstone and dolomite of the Sibley Group were first described by Logan (1863) who considered them as part of his "Upper Copper-Rearing Series". Logan included the Gunflint and Rove Formations, as well as the Sibley rocks, in this "series". �8 Robert Bell (1872), in completing the first comprehensive description of these rocks, considered them as the Upper Group of the Upper CopperBearing Series. He compared the Sibley Group with rocks of Nova Scotia and concluded (p. 321) that "they (Sibley rocks and the overlying ()sler volcanic sequence) may now be considered as of Permianand Triassic age". Logan (1872), in strongly reprimanding Bell, outlined evidence for a pre-Silurian age. T. Sterry Hunt (1873) divided Logan's Upper Copper-Bearing Series into Animikie (now the Gunflint and Rove Formations) and Keweenawañ Groups, and assigned the Sibley to the latter Group. Uilson (1910, p. 69) indicated that these rocks occupy a "trough-like depression between two areas of Archean rocks" in the western Lake Nipigon area, and tentatively assigned them to the Paleozoic. The name "Sibley" was first assigned to this group by Tanton (1931). Hs description of the "Sibley Series" of the Sibley Peninsula is accurate, but unfortunately he did not have an opportunity to map the more northern areas, and thus his stratigraphic analysis is of somewhat limited value. Although local studies of the Sibley Group rocks were undertaken in subsequent years by Hawley (l)29) and Moorhouse (1960) the first comprehensive mapping was completed by Coates (1972) and Mcllwaine (l971a, 197lb) Recent geophysical studies by duBois (1962) and Robertson (1973) have underscored the need for a comprehensive study of the stratigraphy and paleogeography of the unit. Red-bed sequences like the Sibley Group are important environmental indicators and in addition this occurrence may have tectonic implications. Age: The age of the Sibley Group is a key question with respect to the position of these rocks within the framework of the Keweenawan tectonic event, and the Helikian polar wandering curve. A rubidiumstrontium whole rock isochron was completed in the laboratory of the Geological Survey of Canada. The analytical procedure is outlined by Wanless and Loveridge (1972). The Geological Survey of Canada uses an R87 decay constant of 1.47 x l0-1yr, as physically determined and outlined in the aforementioned paper. The widely used 1.39 x 10-11 yr'. a 'geologically determined' decay constant results in ages approximately 5.75% older. The age, using the 1.47 x l0-11yr constant, is 1294 t 31 m.y. Samples were selected from the Kama Hill and Red Rock formation; the areas near diabase sills were avoided as their metamorphic effects are extensive (Robertson, 1973). The Kama Hill section is cut by multiple thin sills; the data for one of the samples probably reflects this metamorphism, and should be discounted. The Sibley Group is apparently older (by at least 150 m.y.) than the accepted age of the Keiceenawan igneous event as typified by the �9 Duluth complex (1,115 m.y. RbSr, Faure et al 1969) and the.Keweenawan extrusive rocks (1,142 m.y. RbSr Faure and Chaudhuri, 1967). However well documented comparable age determinations have notbeen published on either the Logan sills or the lower Osler group; These latter units are magnetically reversed (duBois, 1962) and are the oldest Keweenawan igneous rocks in this area. K-Ar dates of 1,060 m.y. on Logan sills (Franklin, 1970) probably represent a minimum age due to possible argon leakage. Unpublished RbSr data indicates that the sills may be as old as 1298 ± 33 m.y. (Robertson and Fahrig, 1971), and thus very close in age to the Sibley Group. The Sibley Group exhibits both normal and reversed magnetic polarity (Robertson 1973); igneous rocks of similar paleomagnetic characteristics have a very similar age to that obtained for the Sibley Group (Peterman et al, 1968, Murthey et al, 1968). Thus the determined RbSr age of the Sibley Group is probably reliable. Stratigraphy of the Sibley Group The Proterozoic rocks of the Southern Province of the northern Lake Superior region have been described in a general way by Card et al (1972). Although the Sibley Group has not been heretofore formally subdivided, subdivision into formations is possible. The subdivisions are given in Table and locations of type sections are included in the formation descriptions. The Pass Lake Formation The type section for the Pass Lake Formation is exposed along the Canadian National Railway tracks in southern McTavish Twp. (Mcllwaine, 1974) near the north shore of Pass Lake where it is SO m thick; it continues eastward along the tracks for about 3 kms where it is overlain by the Red Rock Formation. Reference sections are located under the type section of the Red Rock Formation at Red Rock cuesta, at Mousseau Mountain north of Nipigon and on Quarry and Channel Islands in Lake Superior near Rossport. The formation is composed of lensoid basal conglomerate overlain by quartz-rich arenites. It thins rapidly northward; scattered patches are present along the eastern edge of the Sibley basin, but the unit is absent along the western basin margin. The Pass Lake Formation overlies the Rove Formation in the south and to the north lies unconformably on Archean Rocks. The contact with the Rove is exposed over a distance of about 20 m at Pass Lake; the Rove has been altered for about 50 cm from the contact. This normally black shale has been partially oxidized to a dark reddish brown. Where the Pass Lake Formation lies directly on the Archean there is little or no evidence of a reaction; at the site of the old Enterprise Mine in McTavish Township (Mcllwaine 1971b) the sandstone rests directly on quartz monzonite with no apparent affect. �1 U Overlying the basal conglomerate with sharp contact is a succession of arenites which are generally buff to pale pink with a minor number of red interbeds. The arenites are commOnly very thickly bedded (greater than 1 m) at the base of the sequence and range to very thinly bedded (1-3 cm) with increasing stratigraphic height. The sharpness of bedding boundaries also increase with stratigraphic height. They 'are commonly fine-grained (2-3 phi) but are locally very fine-grained (3-4 phi), with generally moderate sorting and locally poorly (especially at Pass Lake) and moderately well sorted (e.g. Mousseau Mountain). There appears to be no systematic variation in grain size or sorting with stratigraphic. height Thin section examination and modal analyses indiëate the rocks range from quartzose arenite to quartz arenite1 in composition. Detrital grains range from angular to well rounded but are generally subrounded with larger grains tending to be more rounded than finer grains. Quartz grains with undulatory extinction are more abundant than quartz with straight extinction. Total quartz at Pass Lake appears to be lower in the upper half than the lower half but this is mainly a function of cement content. For the most part there is little or no cement in the lower half and induration isapparently due to conpaction. Feldspar is a mino:' constituent, especially at Pass Lake. There is a suggestion of a systeiiatic decrease in feldspar with stratigraphic height in the Rossport section. Chert is present in all areas. Chert content is greater in the top half of the formation than in the bottom half at Pass Lake, other sections exhibit no apparent variation. Cementing material includes carbonate, mainly at Pass Lake, Red Rock and Rossport, and silica, which is more common at Mousseau Mountain. The matrix, generaUy fine mica and clay, forms consistently less than 15%; this is the content generally accepted as the dividing line between arenite and wacke. The Rossport Formation The type section of the Rossport Formation, is exposed on the shore of Channel Island, near the Village of Rossport. This formation overlies the Pass Lake Formation disconformably through much of the area, and unconformably on Copper Island near Rossport. In the northern area it lies nonconformably on the Archean basement. The Rossport Formation is distinguished by its brick red color, high dolomite content, and concoidal fracture. The formation maintains a relatively constant thickness of about lOOm in all measured sections except on the Sibley Peninsula, where it thins to approximately 2Om. In the southern area of the basin the formation may be divided into three members (a) lower dolomite, (b) central chert-carb.onate (stromatolite to the north) and (c) upper dolomite. In the northern area these members are less clearly distinguishable due to the lack of exposure. Much of the description is thus based on the more southerly sections. 1 . . . . . The limits used here are based on Pettijohn's (1957) classification but his rock names have been changed. �11 The lower and upper members exhibit enly minor lateral facies changes in the east and west direction, but to the north both members become distinctly more clastic. The central member is lithologically distinct and forms a lateral (east/west) continuous 'marker bed traceable from Rossport to Sibley Peninsula. The upper and lower members can be distinguished on the basis of mineralogical composition and bedding development. The lower member has distinct bedding, whereas the upper is. more massive. The lower is richer in carbonate and quartz whereas the upper member is clearly richer in clay and feldspar. Dolomite is the dominant carbonate mineral present. No easy distinction between the lower and upper members on the basis of calcite-dolomite ratio may be made, although in general. the calcite-dolomite ratio is higher in the upper unit than the lower. iKama Hill Formation The type section of the Kama Hill Formation is located along the northern-most powerline, on the west side of Kama Hill, 17 miles (27 km) east of Nipigon. Reference sections are available at Albert Lake, Stewart Lake and Channel Island. The boundary with the underlying Red Rock Formation is placed at the disappearance of carbonate and the change in color. The maximum preserved thickness is 50 m. The Kama Hill Formation is distinguished by its deep red-purple colour, silt to clay sized particles, thin bedding, moderately well developed fissility, its mineralogy and distinctive structures. Due to its fine-grained nature, mineralogical analysis is possible only by x-ray diffraction. Two clay minerals, quartz, microline and minor calcite and hematite constitute the mineralogy. Colour in outcrop varies from deep red to deep purple and is duç to hematite. The amount of hematite varies widely betweei 'beds from less than 1% in a few course silt beds to over 90% in a fw clay rich layers. It normally constitutes approximately 4% of the rock. The coloration is quite homogeneous within individual beds. Conspicuous "bleaching" is present only along a few bedding plane fractures and joint planes. Microscopic variation in coloration intensity is related to grain size, with finer clay rich beds containing more hematite. The lower portion of the formation has up to 10% white spherical "reduction" spots; these are much less common in the upper portion of the unit. Hematite occurs as evenly disseminated very fine grained aggregates. In the coarse silty beds it forms a coating and is interstitial to the clasts. Bedding is very difficult to distinguish in outcrop but is readily apparent in thin section and cut surfaces. The three types of beds which may be distinguished are: �12 (a) regular finely laminated clay rich regular beds. (b) irregular partially reworked course silty beds. (c) stromatolitic beds. Types (a) and (b) are intermixed but the type (a) beds appear more dominant with stratigraphic height. Bed types (a) and (b) are distinguished by their lack of carbonate. Beds of type (c) are confined to the lower part of the formation. * Sedimentary Structures Mud cracks are pervasive and a characteristic featur• of the Kama Hill Formation regardless of the bed composition (sand, silt, or clay). Linear and polygonal cracks occur on most bed surfaces. Small scale erosional features are common. Disturbed bedding is locally present. Ripple marks are present only in the sand and silt rich beds. These are symmetrical current ripples, with wave lengths of 1.0 to 3.5 cm and amplitudes of 0.5 to 1.5 cm, covered with fine mud; ripple surfaces have small spindle shaped flute casts, superimposed at an oblique angle to the ripple axis. Interference ripples are most common in the more coarse-grained beds on Sibley Peninsula. Rain-print surfaces occur rarely at Kama Hill. Evaporite casts (probably halite) are present, and are particularly evident at Stewart Lake. $ Summary of the Depositional History The Sibley Group was depositod in a elongate, north/south basin The which was initially probably deepest in the south. basin formed relatively rapidly and along its margins fans of locally The derived and rapidly deposited conglomerate formed. initial period of rapid deposition gave way quickly to relatively slow deposition of the arenites of the Pas's Lake Formation. The basin transgressed northwards towards the end of the deposition of the Pass Lake Formation and extended far to the north (at least to southwestern Lake Nipigon) during deposition of the lower member of the Red Rock Formation. Moderately rapid regression marked the middle stage of Red Rock deposition, accompanied by increased clastic deposition and stromatolite growth to the north of Nipigon and chert precipitation to the south. Transgression followed as the basin extended northward at least to Armstrong. The basin depth was relatively constant, and it slowly filled with clay-rich dolomites. * The transition to the Kama Hill Formation marks a change from predominantly sub-aqueous to predominantly sub-aerial deposition. Deposition of the Kama Hill Formation continued in an extremely consistent very quiet mud flat environment. Primitive life flourished during quiescent periods of deposition of the Kama i-Jill sediments. Tectonic Implications $ The relation of the Sibley Group in any tectonic reconstruction can only be reviewed in the context of the entire Helikian history of eastern �13 North America. The dominant tectonic event in the Lake Superior area was the development of the Keweenawan rift zone which forms an inverted U, extending roughly from the northern area of the Michigan basin, around Lake Superior and continuing southwest from Duluth as the mid-continent gravity high. Although nomajor "opening ocean" event has been firmly documented during the Helikian, Baer (1974) in summarizing papers present at the Grenville symposium (Ottawa, Feb. 1974) indicates that a pre-Grenvillian orogenic event may have initiated with a divergent phaseat 1,300 m.y. As part of this rifting, the Keweenawan arm may have developed at this time (Burke and Dewey, 1973). This arm ultimately (at 1,100 m.y.) underwent limited spreading (Burke and Dewey, 1973). It is probable that igneous activity was initially very limited, but rifting occurred by means of crestal rifts about which developed "rrr" triple junctions. These rifts meet at 120°, and are located at major strike changes of a rift valley (Burke and Dewey, 1973). The major flexure in the Keweenawan rift valley occurs immediately south of Nipigon. Should a triple junction have formed in association with the Keweenawan rifting, the Nipigon area would be the most probable area of development. The 'failed' arm would thus extend north from Nipigon. The Sibley group occupies a N-S block which is the result of a failed arm developed about the Nipigon crestal rift. Later reactivation of the Keweenawan rift was accompanied by intrusion of the Logan sills into the same failed arm. Many problems related to the time of development remain unsolved. The Sibley Group is similar in age to the proposed age of initial spreading of the Grenvillian orogen (Baer, 1974). However, little evidence related to time of initial development of the other ultimately actively spreading arms of the Keweenawan rift is available. Minor igneous activity has been recorded at 1400 m.y. (Books 1969). Sibley sedimentation appears to have been controlled by a rapidly developing fault scarp in the southern area, as indicated by a rapid increase in coarse clastic material near the basin margin. Limited exposure of the Sibley Group in the northern area precludes examination of the nature of the basin margins here. The elongate basin shape is suggestive of rift-valley filling, but the possibility remains that the Sibley basin has been preserved in a failed arm, rather than the 'arm' actually controlling sedimentation. �14 Description of Stops and Road Log for the Gunf lint and Rove Formations Time and seasonal water level conditions may prevent access to all stops indicated on Figures 1 and 2. For alternate and addItional stops of the Gunflint and Rove Formations, the reader is referred to Franklin and Kustira (1972). Mileage count begins at the intersection of Highways 11-17 and 61, near the Airlane Motor Hotel, Thunder Bay. Proceed south on Highway 61. Figures in brackets record accumulated mileage. MILES KM. 00. 0.0 The prominent Intersection Highways 17-11 and 61. hill to the southeast is Mount McKay, the most northerly of the "Norwesters" range of hills. Towering over the Kaministikwa River delta, it is 1,581 feet (481 m) above sea level and 978 feet Mount McKay is a large (298 m) above Lake Superior. mesa, made up of shales and greywackes of the Rove Formation overlain by a hard, protective 200 foot (61 m) thick capping of diabase (Pye, 1969, p. 39). The upper half of the mesa is 3,000 feet (914 m) long and has a maximum width of 1,100 feet (336m). A second sill, about 15 feet (4.6 m) thick is found in the Rove sedimentary rocks and is 474 feet (141.5 m) It forms the base of a below the top of the hill. wide and prominent terrace to which the tourist may drive his automobile for a magnificent view of the City of Thunder Bay (Pye, 1969, p. 39). 5.9 9.5 7.1 11.4 20th Si.deroad; turn right (north). Riverdale Road, turn left (west) and follow to end of road. 8.5 13.7 Parking spot; follow cottage road (J.C. Kirkup); this is private property and permission for access to the Slate River must be obtained from the owner. �15 BASAL CONCRETION-BEARING SHALE OF Th ROVE FOkMATION, SLATE RIVER CANYON (FIG. 1). STOP 1 The black, graphitic, fissile Rove shale contains These vary an abundance of carbonate concretions. from a few inches (cm) to 8 feet (2.4 m) in size Although commonly in the shape of in diameter. oblate spheroids, they display a complexity in shape and texture. Some show radial septarian cracks on their surfaces. The concretions form bedded unitsin the canyon walls. They are in various stages of weathering out of the host shale, some slumping into the river bed and many others lying in the river bed arranged in imbriShale bedding is warped around the cate fashion. top and bottom of the cpncretions. Moorhouse (1963) describes these concretions in detail. Return to Highway 61. 0.0 (11.1) 0.0 (17.9) Intersection of Highway 61 and 20th Sideroad. Continue south on Highway 61. The range of hills to the south are the Nor'westers. 5.4 (19.1) 19.4 (33.1) STOP 2 8.7 Highway 130; continue on Highway 61. (30.7) 31.2 (53.3) Entrance to abandoned quarry, west side of Highway 61, approximately 1,600 feet (410 m) beyond Cloud Bay Road. UPPER THICK-BEDDED QUARTZITIC GREYWACKE, ROVE FORMATION, (FIG. 1). Quarry operations have exposed thin to thick bedded quartzitic greywacke interbedded with lesser amounts Greywacke displays sole of black fissile argillite. markings and graded bedding. The quarry walls are bounded by two dikes bifurcating from a single olivine diabase dike of Geul's (1973) Pigeon River intrusions. The west dike is approximately SO feet (15 m) wide and vertically dipping; the narrower east dike dips steeply southeast, its attitude well exposed at the back of the qvarry. �16 Due to the development of a closely spaced fracture pattern in the Rove Formation, the quarry walls and hack may be unstable; extreme caution is advised. Return to Highway 130. (47.1) 0.0 (75.8) Intersection of Highways 130 and 61. Proceed north on Highway 130; continue to end of road. 3.2 (50.3) 5.1 (81.0) Paipoonge Concession 1 Road. Turn left (west). Proceed for 1.8 miles (2.9 km) to unmarked gravel •road; turn right (north). Continue for 3;4 miles (5.5 km) to steel bridge over Kaministikwa River. Turn right and proceed over bridge on paved road (Highway 588) for 1.2 miles (1.9 km) to Highway Turn •left (west) and proceed for approxi11-17. mately 3.5 miles (5.6 km) through village of Kakabeka Falls into Kakabeka Falls Provincial Park. Turn right at the park gatehouse, before crossing the old bridge in the park, and follow road under Highway 17, to its end at the swimming area. Proceed on foot past cabins to the Kaministikwa River shore. 0.0 STOP 3 BASAL CONGLOMERATE AND LOWER ALGAL CHERT, GUNFLINT FORMATION, (FIG. 1). Here, the basal conglomerate and algal chert mounds rest directly on Archean granitic gneiss basement. Basal conglomerate may be seen in place only at very low water. However, large, angular, locally derived Note the blocks of conglomerate are abundant. angularity and polymictic nature of the pebbles. All can be assigned to various Archean rocks to the west and north. The Ep-Archean Note also the absence of a paleosol. interval, here occupying 800 million years, is represented by little or no "in-situ" weathered basement, suggesting absence of normal weathering conditions, or pre-Gunflint strong fluvial or glacial transport action, The algal mounds here are similar to those found 1.8 miles (2.9 km) west of Nolalu (Franklin and Kustra, 1972, p. 31). Return to park gate house, turn right and cross the bridge. Proceed to parking area, thence by foot to the rim of the falls. �17 STOP 4 UPPER TUFFACEOUS SHALE SUBMEMBER (UPPER TUFF ARGILLITE) AND OVERLYING UPPER CHERT CARBONATE, GUNFLINT FORMATION, FIG. i. Kakabeka Falls drops 128 feet (39 m) into a gorge formed in fissile, thinly bedded upper tuffaceous shale submember (Goodwin, 1956) A more resistant massive two-foot bed of thinly banded chert-carbonate caps the escarpment. Note apparent cross lamination in the chert carbonate and the undulating nature of the surface. The chert carbonate capping is overlain by tuff argillite and a second chert carbonate bed, exposed in a parking lot on the east side of the gorge. A bed of lower chert carbonate occurs at the base of the falls, (Fenwick, personal communication). Return to Highway 17, turn right and proceed approximately 1/3 mile (0.5 km) Ontario Hydro station access road imrpediately west of the Kakabeka Falls Motel. Turn right (south) and proceed to parking lot by the generating station. Access to STOP 5 is through the genenting station to its west side. Permission must be obtained from The spillway serves as a the station supervisor. safety feature to bleed off excess water in the event of generator failure at the power station. Follow the river bank for approximately 600 feet (183 mj to the"spillway" cut. Beware of Poison Ivy. STOP 5 UPPER TUFFACEOUS SHALE SUBMEMBER (UPPER TUFF ARGILLITE) GUNFLINT FORMATION (FIG. 1). The best section of upper tuffaceous shale submember is exposed at this locality. Pyrite-bearing chert, possibly of the upper algal chert submember; occurs It is overlain by shale at the base of the section. containing pyrite nodules and calcareoüs concretions, interbedded shale and tuff and a cap of thinly bedded upper chert-carbonate. �_____— 18 One of the best exposures of "mud ball tuff" in the shtle occurs near the bottom of the section; the tuff is formed of closely packed accretionziry lap ill F elongated a long the bedding. ellipsoids contain mdiv idual small, angular fragments of uniform size, grouped concentrically around a larger shard fragment. The remainder of the material comprising the beds consists of volcanic fragments in a groundmass of green illite: Higher than background radioactivity (0.004% U3O8 has been noted in the tuff argillite by Fenwick (personal communication). Note downwarping of beds on the west side of the exposure and the fault filled with quartz-carbonate and anthraxolite for which Kwiatkowski (1975) reported a 0.2% nickel content. Return to Higiway 11-17 and proceed east. 0.0 (64.7) 0.0 (104.1) 9.8 15.8 (74.5) (119.9) 10.9 17.5 (75.6) (l2l7) 16.3 (81.0) STOP 6 26.2 (130.4) Junction Highway 11-17 and Oliver Road (formerly Highway 590),. Proceed on Oliver Road. Thunder Bay city limit. Good ''iew of a series of mesa type hills, the Nor'westers, all capped by Logan diabase. Junction of Oliver Road with Highway 130; continue east. Belrose road. Turn left, proceed 0.5 miles (0.8 knflto quarry on west side of road, (Dickson's Quarry). UPPER TACQNITE SUBMEMBER, GUNFLINT FORMATION, (FIG. 1) In this quarry wavy-banded, red jàspilitic and darker greena],ite-bearing taconite is capped by a Neohelikian (Logan) diabase sill. The taconite contains approximately 50 percent shale, interbedded with 6 to 12 inch (15 to 30 cm) irregular taconite beds that are best exposed at the north end of the outcrop where quarry operations exposed the taconite at a lower stratigraphic level. The diabase sheet displays an irregular, undulating �19 bottom surface at a slight angular discordaneL The upper surface is polygonally jointed and contains occasional patches of a thin veneer of argitlite. Return to Highway 130, turn left (east), and proceed across Highway 11-1.7 and past Lakehead University to High Street. 19.8 31.9 (83.5) (134.4) Intersection Highway.130 (Oliver Road) and High Street. Turn left at the traffic lights and proceed up High Street. 20.4 (84.1) Entrance to Hillcrest Park. 32.8 (135.4) STOP 7 UPPER LIMESTONE MEMBER, GUNFLINT FORMATION, (FIG. 1). Hillcrest Park stands about 160 feet (48 m) above the level of Lake Superior and offers a panoramic view the of Thunder Bay harbour, the Seqping Giant, WelcomeIslands, Pie Island and the Nor'westers. Dolomitic limestone and chert layers arc exposed at the base of the flag pole and bell. Follow stairs to base of hill where fragmental limestone (upper limestone member) is exposed. The rock consists of many angular tci rounded chert fragments in a matrix of coarsely crystalline, iron-bearing carbonate, and thin chert interbeds. Volcanic shards and fragments occur in the limestone (Goodwin, 1956). Proceed north on High Street. 35.2 21.9 (85.6) (137.8) Intersection with Balsam Street: Turn lefton 22.5 36.1 (86.2) (138.7) Huron Street, 300feet (90 m) south of Highway 17-11. Turn right on Huron Street, then Balsani Street. immediate left. 23.9 38.4 (87.6) (141.0) Bridge over Current River, cross bridge, turn right into Boulevard Lake Park and proceed 0.3 miles (0.5 km); park on right side of road. Traverse begins in river bed. �20 STOP S UPPER CHERT CARBONATE FACT ES, GUNFL I N FORMATION (FIG. 1) The upper chert carbonate fades is overlain by the Rove Formation. An upstream traverse encounters ferruginous carbonate, interrupted by thin layers and lenses of granular and algal chert, dark, fissile shale and dolomitic limestone. At the beginning of the traverse, note the rounded chert lenses showing concretionary structures, attributed to action of algae. Features to observe include stylolite surfaces lined with anthraxolite, pyrite veinlets, imbrication of thin chert layers and the striking weathered app3arance of the rock. Under the bridge, a bed of gray, massive limestone, possibly the Upper Limestone member, contains pancake-like lenses of serpentine material, and is interrupted by a thin band of pyritic and pyrrhotitic Note the hununocky upper surface of the chert. limestone at the shale-limestone interface. The overlying shale is probably Rove Formation, Several hundred feet north of the bridge, at the lookout, a diabase sheet caps the shale. Heat from the cooling of this sheet metamorphosed the limestone, forming serpentine and pyrrhotite. East:of the bridge, in the picnic area, several well developed river terraces are preserved. From bridge, proceed east along Arundel Street. 40.7 25.3 (90.0) (144.9) Intersection, Arundel Street and fodder Avenue. Turn left on fodder Avenue at the fodder Avenue Hotel. Highway 17-11: Turn right. 26.9 43.3 (91.6) (147.4) Scenic lookout. Park View of Thunder Bay harbour. car and walk 500 feet (150 m) east to roadcut on north side of road. �21 SioP 9 UPPER LIMESTONE MEMBER, GUNFLINT FORMATION, OVERLAIN BY DJABASE, (PIG. 1). Sill of Logan diabase overlies argillite and fragmental limestone of the upper limestone member; The contact i gently undulating and visible effects of contact metamorphism are little In this section, however, a microporphyevident. roblastic texture is developed in the argillite. Pyrite is altered to pyrrhotite. Note the lenticular chert patches within the limestone, some veined with pyrrhotite, exhibiting agate textures. Additional End of Animikie portion of trip. points of interest concerning a more complete picture of Gunf lint Formation stratigraphy are given in Fra1lin and Kustra (1972), �______ INSET SCALE 4 KM. Stop Locations Pass Lake Railroad tracks east of Pass Lake No. 5 Road (Pass Lake Area) Ouimet Canyon Kama Fiji Thunder Bay Amythest SIBLEY THUNDER - BAY 40 KILOMETRES Locations. �_____ _____ 23 A A an • - . •. -H-—:- + + + - -:- + + + + + + ARCHEAN + + + + + + ÷ + ÷ FT. 00-, t .+ + + + + + + + B ÷ + + + ÷ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + SANDSTONE ÷ + + + + + CONGL)MERATE + + + + +__+ + + + + + 20 KM. I0 0 B' '10 MILES •.7CSLTSTONE_1-SHALE.T . 7 -. . . . BRECCIA . ..... RED' QOLOSTONE / SANDSTONE ONGLOMERATE ROVE FM, KAMA HILL FM. ( Dots indicate increased silt-sand content ROSSPORT PASS Fig. FM. LAKE FM. 4. Longitudinal and Cross-sections of the Sibley Group. t ÷ 25 METRES 'O q ROVE FM + + �24 Description of Stops and Roadlog for the Sibley Groip Mileage count begins at the junction of Highways 11-17 ad 61 near the Thunder Bay Airport. Figures in brackets recprd accumulated mileages. MILES KM. 0.0 0.0 Proceed north along Highway 11-17. * 1.9 3.1 Golf Links. Road. 2.9 4.7 Oliver Road (Highway 130). 4.9 7.9 5.6 9.0 7.1 11.4 Balsam Street. 9.7 15.6 Hodder Avenue. 19.3 16.6 Scenic Lookout. 12.1 19.5 Spruce River Road (Highway 527 - 21.6 34.8 Lakeshore Drive. 31.2 50.2 Highway 587: turn right and proced southeast. 35.0 56.3 A large azea of outcrop extends along the north side of the C.N.R. railway tracks and Highway 587 where they parallel Pass Lake, * John street. Red River Rowi (Highway 102). formerly 800). �25 This cliff is the type section for the Pass Lake Formation. Exposure is almost continuous for about 2 miles (3.2 km) along the tracks and gives a stratigraphic thickness of 164 feet (50 metres). STOP 1 At the western end of this outcrop, a sandstone quarry provides an excellent exposure of Sibley sandstone. In the railway cut at the western edge of the quarry, Rove shale is altered.to a reddish colour. This alteration affected the Rove for several fçet below its contact with the Sibley Group. Also present is a thin lens of basal conlomerate. PLEASE EXERCISE EXTREME CAUTION CLIMBING ON THE DEBRIS. 35.3 56.8 The conglomerate is better exposed behind'the railway shed at the east end of Pass Lake. Clasts in the basal polymictic conglomerate are composed of 93 per cent Gunflint iron formation, 6 per cent quartz and 1 per cent granite. Boulders are of variable size and angularity, The contact and are cemented in a sandy matrix. with overlying sandstone is sharp; only a few pebbles are found in the base of the overlying unit. The sandstone is moderately to poorly indurated, thick bedded at the bottom of the section, and composed of quartz, with minor chert and feldspar, in a calcite matrix. Continue along Highway 587. 35.7 57.5 Pass Lake East road: 37.6 60.5 No. 4 Road: 37.9 61.0 Y Junction - bear left. 38.6 62.1 Field on left side (west) of road: park here and proceed on foot across field and through bush to CNR tracks - about 1/4 jnije (400 metres); turn left and proceed east. turn left and proceed north. �26 this outcrop is red intraformational breccia Angular fragments vary of the Rossport Formation. from 0.4 in. to 15.7 in. (1 cm up to about 40 cm.) Several clastic dikes are also present. STOP 2 Much of' The lithology is generally a red sandy limestone. Return. to No. 4 Road and continue north. 39.9 64.2 Gravel Pit - for turning vehicle around. back to Pass Lake East Road. 42.3 68.1 Pass Lake East Road - turn Proceed left. *********************** 0.0 0.0 Proceed along Pass Lake Eas; Road from Junction with No. 4 Road. 0.8 (43.1) 1.3 (69.4) Right angle bend to left. 1.5 (43.8) 2.4 (70.5) No. S Road - 2.1 (44.4) 3.4 (71.5) Juncticn - 4.0 (46.3) 6.4 (74.5) Area of outcrop. STOP 3 turn turn left. left. KAMA HILL SANDSTONE Poorly exposed reddish-brown to reddish-purple sandstone of theKama Hill Formation. Generally Although fine- to medium-grained sandstone. not evident at this location mudcracks and ripple marks are common in this unit. These occur along the shore of Lake Superior to the east, (see The main difference between Mcllwaine, 1972). this sandstone and sandstone of the Rossport Formation is the lack of carbonate in the Kama Hill Formation. �27 Continue north along No. S Road. 15.9 9.9 (52.2) (84.0) 10.3 (52.6) (84.7) 16.6 Cross CNR Tracks. Highway 11-17 - Turn right. *********************** 0.0 0.0 (84.7) Proceed northeast along Highway 11-17. (52.6) 2.0 (54.6) 3.2 (87.9) Road to Enterprise Mine. 7.8 (60.4) 12.6 (97.2) Road to Ouimet Canyon - Turn left. 8.4 (61.0) 13.5 (98.2) Y Junction - 9.2 (61.7) 14.8 bear left. * Sharp right turn. (99.3) 9.7 15.6 (62.3) (100.3) Sharp left turn. 10.2 16.4 (62.8) (101.1) Junction - proceed straight. 10.7 17.2 (63.3) (101.9) Junction - proceed straight. 12.8 20.6 (65.4) (105.3) Junction - 13.3 21.4 (65.9) (106.1) Turn off to Gulch Lake Picnic Grounds to Ouimet Canyon. 15.2 turn 24.5 (67.8) (109.1) Bridge. 15.4 24.8 (68.0) (109.4) Quimet Canyon. right. turn left �28 Ouimet Canyon, a spectacular steep-walled gorge, is located in a thick Keweenawan (Logan) di;tbase sill. The canyon can be traced for over two miLes (3.2 km) and is approximately 600 feet (183 m) wide at its It has a maximum depth. of 400 feet, southern end. STOP 4 (122 in). Although diabase is the most conspicuous rock type, a pink quartz monzonite occurs in the south central portion of the canyon, and a calcareous red mudstone of the Sibley Group has been noted localLy at the base of the west wall of the canyon (here bleached grey) and surrounding the southern portion of Gulch Lake. Mapping along the western rim and wall oF the canyon indicates the presence of two major, continuous joint sets and three less-continuou.; minor It appears that the canyon sets (Stacey, 1976, p.3). is a deep erosional depression, carved out of the. diabase along two major joints by the action of glacialice, running water and freeze-thaw action. An interesting feature within the canyon is a prominent diabase pinnacle, referred to as the Indian Head, which has been isolated from the west rim by erosion. The canyon has been declared a Provincial, Park under the Quetico Nature Reserves system. Return to Highway 11-17. Highway 11-17 - 38.2 23.8 (76.4) (123.0) turn left. *********************** 0.0 0.0 (76.4) (123.0) 9.0 5.6 (82.0) (132.0) 12.4 7.7 (84.1) (135.3) Proceed northeast along Highway 11-17. . Bridge over Wolf River. Road to Stewart Lake at end of Itinerary)'. (see extra stop descriptions �29' 20.4 32.8 (96.8) (155.8) Highway 627 - proceed straight. 21.3 34.3 (97.7) (157.2) Highway plaque describing Red Rock Cuesta. The cuesta features a thick sequence of red sandy limestone capped by a diabase sill. 22.6 (99.0) 36.4 (159.3) Road cut here shows a diabase sill cutting Archean rocks and Sibley Group. 25.7 41.4. (102.1) (164.0) Road to Mousseau Mountain - (see extra slop descriptions at end of Itinerary). 28.3 45.5 (104.7) (168.5) Junction of Highways 11 and 17, - Proceed straight along Highway 17. 40.6 65.3 (117.0) (187.3) Junction of Domtar Road - (see extra stop descriptions at end of Itinerary). 66.5 41.4 (117.8) (189.6) First Lookout, Kaina Hill. STOP SA ROSSPORT FORMATION OVERLAIN 'BY KAMA HILL FORMATION WITH A CAPPING OF DIABASE. A broad anticline of sandy red carbonate is exposed in the prominent road cut to the north of this lookout. This represents the lowest member of the Rossport Formation. Soft-sediment deformation may have produced this structure. Three thin diabase sheets follow bedding planes; the sills pinch out, and locally Thi: cut across bedding at a high angle homogeneous, calcareous sandy mudstone :orms a distinct horizon at the base of the sand red mudstone unit. Follow the road (south) to the distinctive red and white interbedded sandy mudstone. Sand:.tone beds (white) are lenticular in shape, anti are interbedded with red, sandy mudstone. �30 42.1 67.8 (118.5) (190.7) Second Lookout, Kama Hill. In the roadcut to the north of the second lookout, the following features may be observed: (1) Two thin Keweenawan diabase sills, partially replaced by carbonate, cut across the poorly developed bedding place at a low angle. (2) Finely laminated chert of the chert-stromatolite unit is exposed below the lower sill. Up to six inches (15 cm) of anthraxolite carbonate has accumulated at the base of the chert. An oily smell may be detected when this anthraxolite is freshly broken. (3) Limey red mudstone above this unit is marked by many cream-coloured spots, (average diameter 0.5 inch, 13 mm). Similar spots are evident throughout this unit, and commonly have a small amount of graphite or hydrocarbon at the centre. In thin section, the only apparent mineralogical change in the spots is the lack, of hematite coating on clay and carbonate grains. (4) Irregular, flame-shaped, bleached zones follow structures and bedding plane cleavage in the Leaching of hematite and red limey mudstone. destruction of clay mjnerals and feldspar has occurred along the fractures. (5) Above the road cut and overlying the talus It is slope, the purple mudstone crops out. more highly fissile, and contains approximately 4 per cent hematite, which coats very fine grained corrensite and microcline, and forms Bleaching blades of specularite in tiny vugs. along fractures is common in this rock. Purple mudstone contains abundant syneresis cracks, and to the west, at Stewart Lake, contains thin stromatolite beds. 119.6 192.5 Outcrop on east side of Highway. �31 STOP SB Red Shale of the Kama Hill Formation is exposed here underneath a cap of diabase. Turning Point - Proceed back towards Thunder Bay. * * * * * * * * * * * * * *+ * * * * * * * * * 0.0 0.0 (119.6) (192.5) Proceed west along Highway 17. 55.2 88.8 (174.8) (281.3) East Loon Road - turn right (north) and proceed to end of road to Thunder Bay Amethyst Mining Company Limited. STOP 5 THUNDER BAY AMETHYST MINING COMPANY LIMITED The Thunder Bay Amethyst Mine is the largest producing amethyst mine in Ontario and is open annually to the public, from May 1st to November 1st. The property has been in production since 1962. The number of rockhounds and tourists visiting the mine site has increased steadily from 900 visitors There are in 1967 to 24,396 visitors in 1976. sufficient reserves to give the mine an expected life of 65 years at current mining rates (R. Hartviksen, Mine Manager, personal communication). The amethyst deposit is located in an east-west fault zone cutting an intrusive body of massi'e, mediumgrained, red to pink Archean quartz monzonite. Spectacular breccia is noted in the floor of the quarry and in large blocks in the display area exhibiting fragments of unaltered quartz monzonite and highly silicified dolomite of the Sibley Group. Quarrying, diamond drilling and stripping has delineated the deposit for a length of approximately 1000 feet (305 m) and for a width of over 80 feet (24th). Individual amethyst veins vary in width from 1/4 inch (7.6 mm) to 4 feet (1.2 m) and include numerous cavities lined with purple crystals. Well formed crystals (points) line the cavities and vary in size from 1/4 inch (7.6 mm) diameter to large crystals measuring 9 inches (22.9 cm) from tip to root and 6 inches (15.3 cm) in diameter. �32 Coloration of crystals and-the more massive material is dark purple. Variations in intensity of purple colour occur, and locally, colourless am! smokycoloured quartz is found. Crystals are )ccasionally coated with a reddish brown hematite. The colour of ametht results from substitution of small quantities of ferric iron for silicon followed by irradation, (Dennen and Puckett, 1972, p.448). The deposits of the producing amethyst mLnes in McTavi;h Township are found either in fradtures that extend below the.Sibley-Archean unconformity or. at the coittact of the Sibley Group with Archean granite. END OF ITINERARY For anyone interested in a more complete view of the Sibley Group, the following additional areas may be visited. From Rossport, a boat trip to Quarry Channel and Wilson Islands, which lie one to two miles off shore, will allow the visitor On Quarry to see an almost complete section of Sibley rocks. Island, Rove shale is overlain by a thick section of Pass Lake sandstone. Here, crossbeds and ripple marks are abundant. 1. On Channel Island, the upper part of the sandstone unit, sandy red mudstone units are all exposed. The latter is disconformably overlain by Osler volcanic rocks. The type section of the Kama Hill Formation at the top of Kama Hill. The best access is provided by following the Domtar Logging Road (0.8 mi., 1.3 km west of the first lookout at The Kama Hill) for 0.3 mi (0.5 km) to the first powerline. section is at the top of the hill and is exposed on the powerline. 2. 3. - good section of Pass Lake sandstone is exposed along the road up to Mousseau Mountain. The top of this hill also provides one of the best views of Lake Superior and the surrounding country. A MILES KM. 0.0 0.0 Leave Highway 11-17 point). (see Itinerary fox Junction �33 turn 1.5 2.4 Road junction - 1.9. 3.1 Road junction - turn left. Proceed along this road to Mousseau Mountain (see Coates 1972). left. 4. A further section of Kama Hill Shale may be viewed at Stewart Lake, salt casts may be found here. 5. The stromatolites near Disraeli Lake may be reached by following the Armstrong road north from Hurkett for 21.6 miles, (34.7 kin) to the Disraeli Lake road, which connects the Armstrong road with the Spruce River Road (Hwy. 527). Follow the Disraeli Lake road west for 22.2 miles (35.7 km) past Shillaber and Seagull Creeks to the Disraeli campground road. Proeed for 3/4 of a mile (1.2 km) beyond this, to the first bush ro.sd leading north. Follow this road for two miles (3.2 km). Blocks of stromatolite are strewn along side the road for some distance. Stromatolite blocks are common throughout the Disraeli area, and may be found in outcrop and float along most of :he bush roads. AC KNOWLEDGEMENTS The authors wish to acknowledge the assistance of Mi. S. Spivak who compiled and drafted the figures and Mrs. Cathy LeBnn for typing the manuscript. The cover plate was taken by J.F. Scott. �34 SELECTED BIBLIOGRAPHY OF ThE PROTEROZOIC ROCKS 'OF THE THUNDER BAY AREA * Abelson, P.H. and Hare, P.E. 1968: Recent Amino Acids in the Gunf lint Chert; Carnegie Inst. Washington, Yearbook 67, pp. 208-210. Alexandrov, Eugene A. 1955: Contribution to Studies of Origin of Precambrian banded Iron Ores; Econ. Geol., Vol. 50, pp. 459-468. 40Ar39Ar Studies of Precambrian Alexander, E. Colvin, Jr. 1975: Cherts: An unsuccessful attempt to measure the time evolution of the atmospheric 4OAr/36Ar Ratio; Precambrian Research, Vol. 2, pp. 329-344. Proterozoic Flood Básalts of Eastern Lake Annells, R.N. 1973: Superior: The Keweenawan Vblcanic Rocks of the Mamainse Point Area, Ontario; Geol. Surv. Canada, Paper.72-1O, Slp. Keweenawan Volcanic Rocks of Michipicoten Annells, R.N. 1974: Island, Lake Superior, Ontario; An Eruptive Centre of Proterozoic Age; Geol. Surv. Canada, Bull. 218, PUp. Geoscience Baer, A.J. 1974: Grenville Geology and Plate Tectonics; Canada, 1, pp. 54-60. Diffusion in gatO Point Vitrophyres; Amer. Jour. Sci., Vol. 211, pp. 74-88. Bain, George IV. 1926: Barghoorn, E.S. 1971: No. 5, pp. 30-42. The Oldest Fossils; Sci. Amer., tol. 224, Microorganisms Three Barghoorn, Elso S., Schopf, William, J. 1966: Billion Years Old from the Precambrian of South Africa; Science, Vol. 152, pp. 758-763. * Barghoorn, Elso Microorganisms from S., Tyler, Stanley, A. 1965: the Gunflint Chert; Science, Vol. 147, No. 3658, pp. 563-577. Barghoorn, Elso.S., Tyler, Stanley A. 1965: Mitroorganisms of Middle Precambrian Age from the Animikie Series, Ontario, Canada; Chap. 3, in Current aspects of exobiology, Calif. Technol., Jet PropulsionLab., Fasadena, pp. 93-118. '[he Animikie Sea; a talk given at Institute On Bartley, M.W. 1958: Lake Superior Geology, Minneapolis, Univ. Minn. Center Continuation Study, 9p. * * All * references are on file with Regiona' Geologist, Ontario Ministry of Natural Resources, Ontario Government Building, 435 James St. S., Thunder Bay, P7C 5G6. �35 1960: Magnetization of Volcanic Rocks in the Lake Superior Geosyncline; U.S. Geol. Surv. Prof. Paper 400-B, Bath,. Gordon, D. pp: B'212-B213. Minera1oy and S.tdimentation in the Kama Hill Battrum, D.D. 1975: Formation of the Sibley Group, Northwestern Ontario; unpubl. B.Sc. Thesis, Lakehead University., Thunder Bay, Ontario, 141 p. Bayley, R.W. and James, ILL. 1973: Precambrian Iron-Formations of the United States; Econ. Geol.. Vol. 68, No. 7, pp. 934-959. Paleomagnetism of Keweenawan Intrusive Beck, Myrl E., Jr. 1970: Rocks, Minnesota; J. Geophys. Res., Vol. 75, No. 26, PP.. 49854996, On the Geology and Economic Minerals on the NorthBell, R. 1870: east Coast of Lake Superior and Adjoining Country from Pigeon River to Black Bay, Black Sturgeon River, Nipigon River and Lake Geol. Surv. Can., Report of Progress 1866-1869, Pt. IX. Nipigon; The Iron Formation Syndrome; Econ;.Geol., Beutner, E.L. 1972: Vol. 67, PP. 254-255. Differentiation and Assimilation in the Logan Blackadar, R.G. 1956: Sills, Lake Superior District, Ontario; Amer. Jour. Sci., Vol. 254, pp. 625-645. Metamorphic Pyroxenes and Amphiboles in Bonnichsen, Bill, 1969: the Biwabik Iron Formation, Dunka River Area, Minnesota; Mineral.Soc. Amer. Spec. Paper 2, pp. 217-239. The Duluth Complex; Geo. Soc. America, Bonnichsen, Bill, 1972: Abstracts with Programs, Vol. 4, No. 7, pp. 453-454. Magnetization of the Lowermost Keweenawan Books, Kenneth G. 1968: Lava Flows in the Lake Superior Area: U,S. Geol. Survey Prof.. Paper 600-D, pp. D248-D254. Paleomagnetism of some Lake Superior Books, Kenneth G. 1972: Keweenawan Rocks; U.S. Geol. Survey Prof. Paper 760, 42 p. Further Paleomagnetic Books, Kenneth C. and Green John C. 1972:. Data for Keweenáwan Rocks in the Western Lake Superior Area; Geo. Soc. Amer., Abstracts with Programs, Vol. 4, No. 7 P. 454. Concerning "EvIdence of Liquid. Immiscibility in Bowen, N.L. 1926: a Silicate Magma, Agate Point, Ontario", Jour. Geol., Vol. 34, pp. 71-73. Economic Geology and Stratigraphy of the Broderick, T.M. 1920: Günflint Iron District, Minnesota; Econ. Geol., Vol. 15, pp. 422452. �36 Broughton, Paul L. 1975: The Thunder Bay Amethyst Mine; Rock and Gem, July, pp. 58-62. Burke, K. and Dewey, J.F. 1973: Plume generated triple junctions: Key indicators in applying plate tectonics to old rocks; Jour. Geol., Vol. 81, pp. 406-433. Campling, Neil R. 1973: Some Geological and Environmental Aspects of Remnant Pre-Gunflint and. Pre-Sibley Weathered Profiles; urtpubl. B.Sc. Thesis, Lakehead University, Thunder Bay, Ontario. 43 p. Card, K.D., Church, W.R., Franklin, J.M., Frarey, M.J., Robertson, J.A., West, G.F., and Young, G.M. 1972: The Southern Province; in Variations in Tectonic Styles in Canada, R.A. Price, ed., Geol. Assoc. Canada, Special Paper 11, pp. 336-380. Chase, Clement G. and Gilmer, Todd H. 1973: Precambrian Plate Tectonics: The Midcontinent Gravity High; Earth Planet. Sci. Letters, Vol. 21, pp. 70-78. Cloud, Preston E. Jr. 1942: Vol. 240, pp. 363-379. Notes on Stromalites; Amer. Jour. Sci., Cloud, Preston E. Jr. 1965: Significance of the Gunflint (Precambrian) Microflora; Science, Vol. 148, No. 3666, pp. 27-35. Cloud, Preston E. Jr., and Hagen, Hannelore, 1965: Electron Microscopy of the Gunflint Microflora: Preliminary Results; Natl. Acad. Sci. Proc., Vol. 54, No. 1, pp. 1-8. Cloud, P.E. Jr., and Semikhatov, M.A. 1969: Proterozoic Stromatolite Zonation; Amer. J. Sci., Vol. 267, pp. 1017-1061. Coates, M.E. 1972: Geology of the Black Sturgeon River Area, District of Thunder Bay; Ontario Dept. Mines and Northern Affairs, GR 98, Accompanied by Maps 2233, 2234, 2235, 2236, scale 1 inch to 41 p. 1 mile. Cooke, H.C. 1931: Studies of Physiography of the Canadian Shield: III. The pre-Pliocene physiographies, as inferred from the geologic record; Trans. Roy. Soc. Canada, Vol. 25, Sect. 4, pp. 127-180. Cornwall, HenryR. 1951: Ilmenite, Magnetite, Hematite and Copper in Lavas of the Keweenawan Series; Econ. Geol., Vol. 46, pp. 51-67. Cornwall, Henry R. 1951: Differentiation in Lavas of the Keweenawan Series and the Origin of the Copper Deposits of Michigan; Geol. Soc. Amer. Bull., Vol. 62, pp. 159-202. Cornwall, Henry R. 1951: Differentiation in Magnias of the Keweenàwan Series; Jour. Geol., Vol. 59, pp. 151-172. �37 Courtis, W.M. 1887: The Animikie Rocks and their Vein Phenomena as shown at Duncan Mine, Lake Superior; Amer. Inst. Mi Eng., Transactions, Vol. 15, pp. 671-677. Craddock, Campbell, 1972: StructUral Evolution of the Keweenawan Province; Geol. Soc. Amer., Abstracts with Programs, Vol. 4, No. 7,, pp. 715-716; Davies, F. Bryan, and Windley, Brian, F. 1976: Significance of major Proterozoic high grade linear belts in continental evolution; Nature, Vol. 263, pp. 383-385. Dennen, William, i-I. and Puckett, Anita M. 1972: On the Chemistry and colour of Amethyst; Can. Mineralogist, Vol. 11, No. 2, pp. 448-456. Dott, R.H. 1972: A Post-Animikean - Pre-Keweenawan Transgressive Sand Blanket over the Lake Superior Region; Geo. Soc. Amer., Abstracts with Programs, Vol. 4, No. 7, pp. 490-491. Drever, James I. 1974: Geochemical Model fOr the Origin of Precambrian Banded Iron Formations; Geol. Soc. Amer. Bull, Vol. 85, pp. 10991106. Correlation of Keweenawan Rocks of Lake Superior District by Palaeomagnetic Methods; Geol. Asoc. Canada, Vol. 11, pp. 115-128. flu Bois, P.M. 1959: Palaeomagnetism and Correlation of Keweenawan Rocks; Geol. Surv. Canada, Bull: 71, 75p. flu Bois, P.M. 1962: Further investigations of fossils from the Edhorn, Anna-Stina, 1973: Animikie, Thunder Bay, Ontario; Proc. Geol. Assoc. Canada, Vol. 25, pp. 37-66. Nickeliferous and liraniferous Anthraxolite from Ellsworth, H.V. 1934: Port Arthur, Ontario., Amer. Mm., Vol. 19, No. 9, pp. 426-428. Age and significance of Diabase Fahrig, W.F. and Wanless, R.K. 1963: Dyke Swarms of the Canadian Shield; Nature, Vol. 200, pp. 934-937. Faure, G. and Chaudhuri, 5. 1967: The geochronology of +the Keweenawan Dept. Geol. Rocks of Michigan and Origin of the copper deposits. Ohio State Univ.,Lab. Isotope, Geol. and Gepchem. Dept. No. 1. Ages of the Duluth Faure, G., Chaudhuri, S., and Fenton, M.D. 1969: Gabbro complex and of the Endion Sill, Duluth,Minnesota; J. Geophys. Red., 74, pp. 720-725. The Age of the Gunflint Iron Faure, Gunter; Kovach, Jack, 1969: Formation of the Animikie Series in Ontario, Canada; Bull. Geol. Soc. Amer., Vol. 80, pp. 1725-1736. �38 Faure, Gunter; Kovaçh, Jack, 1969: The Age of the Gunflint Iron Formation of the Animikie Series in Ontario, Canada; Ohio State University, Laboratory for Isotope Geology and Geochemistry, Contribution No. 8, 23p. Floran, R.J. and Papike, J.J. 1975: Petrology of the Low-Grade Rocks of the Gunflint Iron Formation, Ontario-Minnesota; Geol. Soc. Amer. Bull., Vol. 86, pp. 1169-1190. Franklin, J.M. 1970: Metallogeny of the Proterozoic Rocks of the Thunder Bay District, Ontario; unpubl. Ph.D. Thesis, Western Univ., London, Ontario, 317p. Franklin, J.M. and Kustra, C.R. 1970: Proterozoic rocks in the Thunder Bay Area; Institute on Lake Superior Geology, 16th Annual Meeting, Thunder Bay, Guidebook, pp. 48-68. Franklin, J.M. and Kustra, C.R. 1972: The Proterozoic Rocks of the Lake Superior Area, Northwestern Ontario; p.20-46 in Guidebook for Field Excursion C34. International Geological Congress, Twenty-fourth Session, Canada 1972, 74 p. Franklin, J.M., Poulsen, K.H., and Mcllwaine, W.H 1972: Stratigraphy of the Sibley Group, A Helikian Red Bed Sequence; Gecl. Soc. Amer., Abstracts with Programs, Vol. 4, No. 7, p. 509. Franklin, James, H. (in press): Interpretation of the Rb/Sr isochrons of metamorphosed and unmetamorphosed Rove shale. Franklin, J.M. Mcllwaine, W.H., Poulsen, K.H. and Wanless, R.K. Stratigraphy and Sedimentation of the Sibley Group; 37 p. (in prep.): Franklin, J.M. and Mitchell, R.H. (in prep.): Lead-Zinc-Barite Veins of the Dorion Area, Thunder Bay District, Ontario; 25 p. French, Bevan M. 1973: Mineral Assemblages in Diagenetic and Low Grade Metamorphic Iron-Formation; Econ. Geol. Vol. 68, pp. 1063-1074. French, William A. 1976: Silver Mining in the Thunder Bay Region 18451891: An Examination of its Economic Viability; Unpubl. B.A. Thesis, Lakehead University, Thunder Bay, 44p. Garrels, R.M., Perry, E.A. Jr. and MacKenzie. F.T. 1973: Genesis of Precambrian Iron Formations and the Development of Atmospheric Oxygen; Econ. Geol., Vol. 68, pp. 1173-1179. Guel, J.J.C. 1970: Geology of Devon and Pardee Townships and the Stuart Location; Ontario Dept. of Mines and Northern Affairs, GR 87, 52 p. Accompanied by Map 2207, scale 1 inch to 1/2 mile. Guel, J.J.C. 1973: Geology of Crooks Township, Jarvis and Prince Locations, and Offshore Islands, District of Thunder Bay; Ontario Div. Mines, GR 102, 46 p. 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Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1977 Description An account of the resource Institute on Lake Superior Geology. Thunder Bay, Ontario. May 2-8, 1977. 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 1977 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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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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U n i v e r s i t yofo Minnesota f Minnesota Dul uth. uth. Cummings, Myers,P.P.E., Cumings , M.M.L., L., Myers, E. 1978, 1978 "Petrology and and Geochemistry Geochemistry ooff Amphibolites, Amphibol it e s Eau Claire Eau CClaire l a i r e River, River, Eau Eau C l a i r e County, County9 Wisconsin," Wisconsin9" (abs). (abs). 24th Annual Annual IInstitute n s t i t u t eononLake LakeSuperior SuperiorGeology. Geology. Cummings, Cummings, M.M.L., L., SScrivner, c r i vner9 J.V., J. V. 1980, 1980, "The ''Thesaprolite saprol itat e the a t tPrecambrian—Cambrian h e Precambrian-Cambrian Contact, Irvine Transactions, Wisconsin Wisconsin Contact I r v i n ePark, Park, Chippewa Chippewa Falls, Fa11s, Wisconsin." Wisconsin. I'Transactions, Academyo fofAArts, and LLetters. Acadew r t s 9 Sciences Sciences and e t t e r s . IInn press. press. Dutton, Dutton C.E., C. E. and and Bradley, Bradley, R.E., R. E., 1970, 1970, Lithologic, L i t h o l o g i c , Geophysical, Geophysical, and and Mineral Mineral CommodityMaps Mapso of PrecambrianRocks Rocksi in U.S. Commodity f Precambrian n Wisconsin. Wisconsin. U.S. Geol. Geol Survey. Survey. Misc. mv. Misc. Inv.Map Map1—631, 1-631, scale 1:500,000. 1:500,000. . Ervin, Gravity E r v i n 9C.P., C.P., Hammer, Hammer, S., S. 1974, 1974, Bouguer 90uguer Anomaly Anomaly G r a v i t y Map Map ooff Wisconsin, Wisconsin, Wisconsin Geological Geological and andNatural Natural H History Wisconsin i s t o r y Survey, Survey, Scale Scale 1:500,000. 1 :5OO,OOO. Glikson, Tonalite-Trondhjemite G I ikson, A.Y., A.Y. 1979, l979, "Early "Early Precambrian Precambrian Tonal ite-Trondhjemi t e SSialic i a l i c Nuclei," Nuclei, Earth Science Science Reviews, Reviews9 15, 15, 1-73. 1-73. Hess, H.H., Hess, H. H. 1960, 1960, "Stillwater " S t i l l w a t e Igneous r IgneousComplex," Complex9 Geological Geo1ogi c a l Society Society of o fAmerica, America, Memoir80, 80, p. p. 225. Memoir 225. 'I 1974-76ÂAeromagnetic Aeromagnetic map map sseries, e r i e s 9Wisconsin Wisconsin Geological Geological and and Karl and and Friedel, Friedel 1974-76, Natural History H i s t o r ySurvey, Survey9Scale Scale1:62500. 1 :62500. Kouda, Korde, H. 1978Â"Ring "Ring structures, structures,Resurgent Resurgent Cauldron, Cauldron9and and Ore Ore Kouda,R.,R., Korde, H., 1978, Deposits iin n the the Hokuroku Hokuroku Volcanic i e l d, Northern Northern Aki ta, Japan." Japan. Mining Deposits VolcanicFField, Akita, Mining. Geology, v. v. 28. Geology, 28. LaBerge, G.L., 1972, and Mylonite Mylonite Zones LaBerge9 G.L., 1972, "Lineaments "Lineaments and Zones iin n the the Precambrian Precambrian ooff Northern Northern Wisconsin," 18thAnnual AnnualI nInstitute W i s ~ o n s i n : ~18th s t i t u t e on on Lake Lake Superior Superior Geology, Geology, Abs., Abs., paper paper #27. #27. LaBerge, G.L.,. 1979, 1979, "Jump "JumpRiver Riveraat Falls LaBerge9 G.L., t BBig ig F a l l s County County Park." Park." Field F i e l dTrip T r i pGuidebook Guidebook No. 44, University U n i v e r s i t yofo fWisconsin-Extension, Wisconsin-Extension, Geological Geological and and Natural Natural History History No. Survey. LaBerge, G.L. G.L., and E., l980,"Middle 19809"MiddlePrecambrian Precambrian History H i s t o r yofo fMarathon Marathon LaBerge, and Palmer, Palmer, E., County, Wisconsin Wisconsin,"26th 26thAnnual AnnualI nInstitute Superior Geology, Fieldd County, s t i t u t e on on Lake Lake Superior Geology9 Fie1 Trip T r i p Guidebook Guidebook #2. #2. �-122- Maass, andVan VanSchmus, Schmus,W. W.R., 1980,"Precambrian TectonicHistory History. ooff the Maass, R.R.S., S., and R., 1980, "Precambrian Tectonic the Black River River Valley," Valley," 26th Black 26th Annual Annual Institute I n s t i t u t eononLake LakeSuperior SuperiorGeology, Geology, Field F i e l d Trip T r i p#2 #2Guidebook. Guidebook. Maass, R.S., Medaris, Medaris, Jr, L.G., L.G., and andVan VanSchmus, Schmus, W.R., W.R., 1980, 1980, "Archean "Archean and and Early Maass, R.S., Proterozoic Tectonic Proterozoic Tectonic History Hi s t o r y of o fNorth-Central North-Central Wisconsin," Wisconsin ,"26th 26thAnnual Annual MI., Abs. Abs. I n s t i t u t eon onLake Lake Superior Superior Geology, Geology, Eau Eau Claire, Institute Claire, WI., Maercklein, Douglas, Douglas,R.,R., 1974, 1974, "Analysis "Analysis ooff Deformation Deformation aatt Jim Jim Falls, Wisconsin," Wisconsin," Maercklein, Universityofo Wisconsin-Milwaukee. f Wisconsin-Mi lwaukee. unpublished unpublished M.S. M.S. Thesis, Thesis, University E. R., 1977, 1977,"Flambeau——A "Fl ambeau--A Precambrian fide May, May, E.R., PrecambrianSupergene SupergeneEnriched EnrichedMassive MassiveSul Sulfide Deposit," Geoscience Deposit," 1-26. GeoscienceWisconsin, Wisconsin,v.v.1,1, p. p. 1-26. Myers, P.E., P.E., 1974, geology descriptions iinn the Myers, 1974, Precambrian Precambrian geology andand f i efield l d t rtrip i p descriptions the guidebook, Geological Field guidebook, 38th Annual Annual Tn—State Tri-State Geological F i e l dConference. Conference. 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. Dependence of the contents of halogen compounds in the gaseous phase on the chemistry of the magma. Geochemistry, V.12, p. 1195-1201. Kuellmer, F.J., 1959. X-ray intensity measurements on perthitic materials, I: theoretical considerations. J. Geol., V. 67, p. 648-660. laBerge, G.l., 1969. Preliminary report on the geology of the northern part of the Wausau East quadrange, Wisconsin. Wis. Geol. Nat. Hist. Survey Open File Report, p. 13. laBerge, G.l., 1971. Progress report on mapping of Precambrian geology in Marathon County, Wisconsin. Wis. Geol. Nat. Hist. Survey Open File Report, p. 27, maps. laBerge, G.l., and Myers, P.E., 1972. 1971 Progress report on mapping of Precarnbrian geology of I~arathon County, Hisconin. ~Jis. Geol. Nat. Hist. Survey Open File Report, p. 28, maps. laBerge, G.l., and Myers, P.E., 1973. 'Precambrian Geology of Marathon County', in Guidebook to Precambrian Geology of Northeastern and Northcentral Wisconsin. Wis. Geol. Nat. Hist. Survey, p.31-86. 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