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Thick-Skinned, South-Verging Backthrusting in the Felch and Calumet Troughs Area of the Penokean Orogen, Northern Michigan

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Thick-Skinned, South-Verging Backthrusting in the Felch and Calumet Troughs Area of the Penokean Orogen, Northern Michigan Thick-Skinned, South-Verging Backthrusting in the Felch and Calumet Troughs Area of the Penokean Orogen, Northern Michigan U.S. GEOLOGICAL SURVEY BULLETIN 1904-L AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY Instructions or. ordering publications of the U.S. Geological Survey, along with the last offerings, are given in the current-year issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Survey publications released prior to the current year are listed in the most recent annual "Price and Availability List" Publications that are listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and Availability List" are no longer available. 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Subscriptions to periodicals (Earthquakes & Volcanoes and RESTON, Virginia-National Center, Rm. 1C402,12201 Preliminary Determination of Epicenters) can be obtained ONLY Sunrise Valley Dr. from SALT LAKE CITY, Utah-Federal Bldg., Rm. 8105, 125 South State St. Superintendent of Documents U.S. Government Printing Office SPOKANE, Washington-U.S. Courthouse, Rm. 678, West Washington, DC 20402 920 Riverside Ave. WASHINGTON, D.C.-U.S. Department of the Interior Bldg., (Check or money order must be payable to Superintendent of Rm.2650,1849CSt.,NW. Documents.) Maps Maps Maps may be purchased over the counter at the U.S. Geolog­ For maps, address mail order to ical Survey offices where books are sold (all addresses in above list) USGS Map Distribution and at the following Geological Survey offices: Box 25286, Building 810 Denver Federal Center ROLLA, Missouri-1400 Independence Rd. Denver, CO 80225 FAIRBANKS, Alaska-New Federal Building, 101 Twelfth Ave. Residents of Alaska may order maps from U.S. Geological Survey, Map Sales 101 Twelfth Ave., Box 12 Fairbanks, AK 99701 Chapter L Thick-Skinned, South-Verging Backthrusting in the Felch and Calumet Troughs Area of the Penokean Orogen, Northern Michigan By J.S. KLASNER and P.K. SIMS U.S. GEOLOGICAL SURVEY BULLETIN 1904 CONTRIBUTIONS TO PRECAMBRIAN GEOLOGY OF LAKE SUPERIOR REGION P.K. SIMS and L.M.H. CARTER, Editors U.S. DEPARTMENT OF THE INTERIOR MANUEL LUJAN, JR., Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government UNITED STATES GOVERNMENT PRINTING OFFICE: 1993 For sale by USGS Map Distribution Box 25286, Building 810 Denver Federal Center Denver, CO 80225 Library of Congress Cataloging-in-Publication Data Klasner, J.S. Thick-skinned, south-verging backthrusting in the Felch and Calumet troughs area of the Penokean Orogen, northern Michigan / by J.S. Klasner and P.K. Sims, p. cm. (Contributions to Precambrian geology of Lake Superior region ; L) (U.S. Geological Survey bulletin ; 1904-L) Includes bibliographical references. 1. Thrust faults (Geology) Michigan 2. Geology, Structural Michigan. I. Sims, P.K. (Paul Kibler), 1918- . II, Title. III. Series. IV. Series: U.S. Geological Survey bulletin ; 1904-L. QE75.B9 no. 1904-L [QE606.5.U6] 557.3 s dc20 [551.8'7'09774] 92-23138 CIP CONTENTS Abstract LI Introduction LI Acknowledgments L2 Regional tectonic setting L2 Bedrock geology L2 Regional structure and metamorphism L5 Kinematic data in the structural domains L5 Bush Lake trough L7 Dickinson Group, South Felch, and Toby Lake blocks L7 Felch trough L8 Toby Lake trough L13 Calumet trough L13 Carney Lake block L20 Summary of kinematic analyses L21 Structural interpretation L23 Style of Penokean tectonism L24 References cited L26 FIGURES 1. Regional tectonic map showing location of study area L3 2. Map showing general geology of the Felch and Calumet troughs area, Michigan L4 3. Map showing detailed rock attitudes and location of detailed study areas L6 4. Sketch and stereoplot of structure near Bush Lake fault L8 5. Map and photograph illustrating flat-lying foliation in Archean rocks adjacent to Felch trough L9 6. Sketch of asymmetric fold in Archean rocks, South Felch block L10 7. Sketch and stereoplot of structure at Rian quarry, south edge of Felch trough Lll 8. Structure map and cross section of Felch trough near Rian quarry L12 9. Sketch and stereoplot of structure in Sturgeon Quartzite at north edge of Felch trough L13 10. Structure maps and cross sections of Felch trough near old Highway 69 and 569 L14 11. Cross section of structure at Groveland mine L15 12. Bouguer gravity profile and geologic section, western Felch trough L15 13. Structure map and cross section of Toby Lake trough L16 14. Stereoplots showing structure in Calumet trough L17 15. Structure map and Stereoplots of outcrop area along west branch Sturgeon River L18 16. Stereoplot showing structure in Archean gneiss, Carney Lake block L19 17. Field sketch and Stereoplots showing structure in Sturgeon Quartzite, west side Carney Lake block L19 Contents III 18. Map showing orientation of mafic inclusions in gneiss of Carney Lake block L20 19. Map showing structural vergence of rocks in the Felch and Calumet troughs area L22 20. Cross sections comparing structure in Felch and Calumet troughs area with that in southern Alps L24 TABLE 1. Explanation of alphanumeric symbols used to describe deformation events and struc­ tural features in the Felch and Calumet troughs area L5 IV Contents CONTRIBUTIONS TO PRECAMBRIAN GEOLOGY OF LAKE SUPERIOR REGION Thick-Skinned, South-Verging Backthrusting in the Felch and Calumet Troughs Area of the Penokean Orogen, Northern Michigan By J.S. Klasner1 and P.K. Sims Abstract INTRODUCTION The Felch and Calumet troughs area of northern Michi­ gan is part of the Penokean fold-thrust belt of the continental Geologic mapping and related studies of the Precam- foreland of the Superior craton. The area lies immediately brian rocks in northern Michigan, done mainly during and north of the Niagara fault zone, the north-verging suture shortly after World War II, have provided excellent detailed between the continental foreland and the Early Proterozoic geologic maps that can be reinterpreted in terms of modern Wisconsin magmatic terranes to the south. Accretion of the structural analysis. In this study we have utilized the magmatic terranes to the continental margin -1,850 Ma pro­ geologic maps of the area comprising the Felch and Calumet duced south-verging backthrusting and backfolding in this troughs (Gair and Wier, 1956; Bayley, 1959; James and region involving both Archean basement and Early Proterozoic others, 1961; Bayley and others, 1966; Dutton, 1971) to supracrustal strata. reinterpret the structural evolution. These maps show Evidence for backthrusting exists throughoutthe Felch and outcrops and numerous faults, most of which were Calumet troughs area. The backthrusting is characterized by interpreted originally as high-angle normal faults. Many of southward-overturned bedding and small-scale, south-verging these faults are here reinterpreted as thrust and reverse faults. asymmetric folds with a subhorizontal axial-planar foliation. In a recent structural study, Maharidge (1986) sug­ The Carney Lake Archean block appears to be a crystalline-core gested that the Early Proterozoic stratigraphy in the Felch nappe wherein the Sturgeon Quartzite of the Chocolay Group trough is inverted and possibly represents the lower limb of forms the lower overturned limb. The deformation probably a crystalline, basement-cored nappe. (See also Sims and started as a north-verging foreland thrust event, but out-of- others, 1987.) Maharidge pointed out that the rocks in this sequence south-verging backthrusts and backfolds developed to accommodate abrupt changes in crustal thickness along the area have been subjected to at least two phases of continental margin. deformation. The first phase produced a north-verging The backthrusting in the Penokean orogen resembles that crystalline-cored nappe with subhorizontal foliation; the in the younger rocks of the southern Alps. Proceeding inward second phase produced upright folds having a steeply from the continental margin, both orogens have accreted oce­ dipping foliation. Hoist (1982, 1984) has suggested that anic crust, indicated by the presence of ophiolite, that is thrust similar north-verging nappes exist in the Early Proterozoic onto the continental margin; a zone of thick-skinned complex continental foreland in east-central Minnesota. deformation characterized by backthrusting and backfolding; a In this report we point out that although the Bush Lake marginal basement arch; and, inboard of the arch, a fold-thrust fault is a major north-verging structure, consistent with the belt that mainly involves thin-skinned deformation.
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