Western Michigan University ScholarWorks at WMU Master's Theses Graduate College 12-1981 Structural Analysis of Precambrian Metasedimentary Rocks of the Swede Gulch Formation, Nahant, South Dakota Richard G. Cookman Follow this and additional works at: https://scholarworks.wmich.edu/masters_theses Part of the Geology Commons Recommended Citation Cookman, Richard G., "Structural Analysis of Precambrian Metasedimentary Rocks of the Swede Gulch Formation, Nahant, South Dakota" (1981). Master's Theses. 1837. https://scholarworks.wmich.edu/masters_theses/1837 This Masters Thesis-Open Access is brought to you for free and open access by the Graduate College at ScholarWorks at WMU. It has been accepted for inclusion in Master's Theses by an authorized administrator of ScholarWorks at WMU. For more information, please contact [email protected]. STRUCTURAL ANALYSIS OF PRECAMBRIAN METASEDIMENTARY ROCKS OF THE SWEDE GULCH FORMATION, NAHANT, SOUTH DAKOTA by Richard G. Coohman A Thesis Submitted to the Faculty of the Graduate College in partial fulfillment of the requirenents for the Degree of Master of Science Department of Geology Western Michigan University Kalamazoo, Michigan December 1981 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. STRUCTURAL ANALYSIS OF PRECAMBRIAN METASEDIMENTARY ROCKS OF THE SWEDE GULCH FORMATION, NAHANT, SOUTH DAKOTA Richard G. Cookman, M.S. Western Michigan University, 1981 Precambrian X tectonites deformed between thermal domes in the northern Black Hills 1.7 B.Y.B.P. display variably trending isoclinal folds cross-cut by southeast trending slip-folds developed in discrete shear zones. Eugeosynclinal sedimentary rocks consisting of shale, quartzarenite , sublitharenite, and graywacke were meta­ morphosed to phyllite, quartzite, and metagraywacke during two syntectonic phases and one post-tectonic phase. The earliest syntectonic metamorphism was asso­ ciated with development of isoclinal folds and may have produced amphibolite or greenschist facies. It was succeeded by retrograde metamorphism of greenschist facies syntectonic with and post-tectonic to development of southeast trending folds. Mica, chlorite, iron oxides, and graphite are strongly developed parallel to isoclinal' fold axial planes and quartz c-axes display preferred orientation related to isoclinal fold axes. These minerals display weaker preferred orientation related to southeast trend­ ing folds. Chloritoid, Mn-garnet, chlorite, and mica display random orientation and may have developed concur­ rently with ubiquitous post-tectonic quartz veins. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS Although many individuals provided stimulation and assistance in the preparation of this thesis, the respon­ sibility for any errors, misstatements, or misinterpre­ tations is solely my own. I am grateful to the Department of Geology for pro­ viding both financial assistance and opportunity for field work and research necessary for this study,, Dr„ Richard V. McGehee, as thesis supervisor, gave freely of his time and invaluable counsel during preparation of the thesis, and in conjunction with Dr. W.D. Kuenzi and Dr. L.J. Schmaltz critically read the manuscript. Dr. J.D. Grace, Dr. W.D. Kuenzi, and Dr. R.A. Davis provided indispen­ sable advice regarding laboratory research. I thank all for their assistance and advice, and I dedicate this thesis to my wife, Pat, who readily served as instrument man, secretary, campmaker, and inspiration. Richard Gerald Cookman Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 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In all cases we have filmed the best available copy. University Miaorilms International 300 N. ZEEB RD.. ANN ARBOR, Ml 48106 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1317865 CDOKMAN• R1CHARD GERALD STRUCTURAL ANALYSIS OF PRECAM&RKAN HETASEDIMENTARY ROCKS OF THE SWEDE GULCH FORMATION. NAHANT, SOUTH.DAKOTA• WESTERN MICHIGAN UNIVERSITY, H.<U, 1981 University Micrpfilms International 300 N. ZEEB RD„ ANN ARBOR, Ml 48106 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLEASE NOTE: In all cases this material has been filmed in the best possible way from the available copy. Problems encountered with this document have been identified here with a check markV . 1. Glossy photographs or pages______ 2. Colored illustrations, paper or print______ 3. Photographs with dark background ^ 4. Illustrations are poor copy______ 5. Pages with black marks, not original copy______ 6. 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CONTENTS PAGE INTRODUCTION . ........ ...... o.............. 1 Regional Setting .................. 4 Objectives ...................... 5 Previous Wor k ................. 5 Current Work ...................... 7 Geologic Setting ................ .. 8 Economic Geology ........... 11 Stratigraphy ............ 12 METHODS OF INVESTIGATION ..................... 16 Field Procedures .................. 16 Laboratory Procedures ........ 18 STRUCTURAL DAT A .............................. 19 Macroscopic Fabric .............. 19 Description........ 19 Summary and interpretation of macroscopic fabric ............ 23 Mesoscopic Fabric ................. 23 Introduction ........... 23 Fold s t y l e ..... *................ 24 Description— general ............. 30 Description— specific areas ...... 36 iii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PAGE Summary and interpretation of mesoscopic fabric .......... 43 Microscopic Fabric ................ 45 Orientations of quartz a x e s ..... 45 Description ........... 49 Summary and interpretation of microscopic fabric ....... 50 Summary and Interpretation of Structural D a t a ................. 53 STRATIGRAPHY AND METAMORPHISM '........... 57 Description .................. 57 Introduction,...... 57 Poverty#Gulch Slate ............. 58 Unit I ........... 59 Unit II ......................... 64 Unit III ................ 65 Unit I V ......................... 68 Summary and Interpretation of Stratigraphy and Metamorphism .... 69 TECTONIC AND METAMORPHIC HISTORY ............. 78 REGIONAL RELATIONSHIPS ....................... 81 SUMMARY OF GEOLOGIC HISTORY ...... 85 APPENDIX L ............... 88 APPENDIX 2. ..................... 113 APPENDIX 3. .............................. 115 REFERENCES CITED ........................ 116 iv Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ILLUSTRATIONS FIGURE PAGE 1 Index map showing location of the Black Hills and areas mapped in the northern Black Hills . „ . o . <> 2 2 Structural