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Western Michigan University ScholarWorks at WMU Master's Theses Graduate College 12-1979 Structural and Petrologic Comparison of the Southern Sapphire Range, Montana with the Northeast Border Zone of the Idaho Batholith Stacy Lon Clark Follow this and additional works at: https://scholarworks.wmich.edu/masters_theses Part of the Geology Commons Recommended Citation Clark, Stacy Lon, "Structural and Petrologic Comparison of the Southern Sapphire Range, Montana with the Northeast Border Zone of the Idaho Batholith" (1979). Master's Theses. 1939. https://scholarworks.wmich.edu/masters_theses/1939 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 AND PETROLOGIC COMPARISON OF THE SOUTHERN SAPPHIRE RANGE, MONTANA WITH THE NORTHEAST BORDER ZONE OF THE IDAHO BATHOLITH by Stacy Lon Clark A Thesis Submitted to the Faculty 01 The Graduate College in partial fulfillment of the Degree of Master of Science Western Michigan University Kalamazoo, Michigan December, 1979 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS Dr. Ronald B. Chase, Department of Geology, Western Michigan University, guided the field work and manuscript preparation. Dr. J. Ronald Sides, Department of Geology, Western Michigan University, and Dr. Donald W. Hyndman, Department of Geology, University of Montana provided valuable assistance. The field investigation was financed by the Graduate Research Fund of Western Michigan University, a Montana Bureau of Mines Grant, and research funds from Burlington Northern, Incorporated. Aerial photographs, topographic maps and access to remote logging roads were provided by the U.S. Forest Service. Finally, I wish to acknowledge the ranchers of the Sleeping Child area for their coopera­ tion. Stacy Lon Clark Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. INFORMATION TO USERS This was produced from a copy of a document sent to us for microfilming. While the most advanced technological means to photograph and reproduce this document have been used, the quality is heavily dependent upon the quality of the material submitted. The following explanation of techniques is provided to help you understand markings or notations which may appear on this reproduction. 1. The sign or “target” for pages apparently lacking from the document photographed is “Missing Page(s)”. If it was possible to obtain the missing page(s) or section, they are spliced into the film along with adjacent pages. This may have necessitated cutting through an image and duplicating adjacent pages to assure you of complete continuity. 2. When an image on the film is obliterated with a round black mark it is an indication that the film inspector noticed either blurred copy because of movement during exposure, or duplicate copy. Unless we meant to delete copyrighted materials that should not have been filmed, you will find a good image of the page in the adjacent frame. 3. When a map, drawing or chart, etc., is part of the material being photo­ graphed the photographer has followed a definite method in “sectioning” the material. It is customary to begin filming at the upper left hand comer of a large sheet and to continue from left to right in equal sections with small overlaps. If necessary, sectioning is continued again—beginning below the first row and continuing on until complete. 4. For any illustrations that cannot be reproduced satisfactorily by xerography, photographic prints can be purchased at additional cost and tipped into your xerographic copy. Requests can be made to our Dissertations Customer Services Department. 5. Some pages in any document may have indistinct print. In all cases we have filmed the best available copy. University Microfilms International 300 N. ZEEB ROAD. ANN ARBOR. Ml 43106 18 BEDFORD ROW. LONDON WC1 R 4EJ. ENGLAND Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 131AA66 CLARK, STACY LON STRUCTURAL AND RETROLOGIC COMPARISDN OF THE SOUTHERN SAPPHIRE RANGE, MONTANA WITH THE NORTHEAST BORDER ZONE OF THE IDAHO &ATHOL1TH. WESTERN MICHIGAN UNIVERSITY, M . S . , 1 9 7 9 University Microfilms International 3 0 0 n z e e s r o a d , a n n a r b o r . m m s i o 6 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 mark v ' ' . 1. Glossy photographs ^ 2. Colored illustrations ________ , 3. Photographs with dark background s '4. Illustrations are poor copy________ 5. Drint shows through as there is text on both sides of page__________ 6. Indistinct, broken or small print on severalpages _____________ throughout 7. Tightly bound copy with print lo st in spine_________ 8. Computer printout pages with indistinct print _________ 9. Page(s) _ lacking when material received, and not available from school or author________ 10. Page(s) ________ seem to be missing in numbering only as text follows________ 11. Poor carbon copy________ 12. Not original copy, several pages with blurred type___ 13. Appendix pages are poor copy_________ 14. Original copy with light type_________ 15. Curling and wrinkled pages ________ 16. Other University Microfilms International 300 N Z=== s q .. AW A330S Mi -3*06 '313! 761-4700 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS CHAPTER I. PAGE INTRODUCTION ............................................... 1 General Statement and Purpose ......................... 1 Previous Investigations ................................ 3 Location and Nature of this S t u d y ..................... 5 Regional Tectonic Setting and General Features of the Sapphire Block ....................... 6 Stratigraphy .......................................... 7 Structure ............................................. 7 Metamorphism.......................................... 10 Proposed Regional Tectonic Models ..................... 11 II. PETROGRAPHIC DESCRIPTIONS ................................ 16 Bitterroot Range and Zone of C a t a c l a s i s ............... 16 Noncataclastic interior .............................. 16 Zone of weak cataclasis .............................. 17 Zone of strong cataclasis ............................ 17 Local mylonite l e n s e s ................................ 21 Sapphire Range .......................................... 21 Quartzofeldspathic gneiss ............................ 22 Pelitic schist ........................................ 24 Calc-silicate gneiss .................................. 26 Amphibolite .......................................... 31 Quartzofeldspathic orthogneiss ....................... 31 Quartz diorite ........................................ 32 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER PAGE Isolated granitic intrusions ......................... 33 Volcanic rocks and associated dikes ........... 33 III. METAMORPHISM............................................... 35 Introduction ............................................. 35 Metamorphic conditions ................................ 35 Regional metamorphism ................................ 40 Thermal overprint .................................... 41 Retrograde metamorphism .............................. 42 IV. STRUCTURAL GEOLOGY ........................................ 43 Penetrative and nonpenetrative Structural Features .................................. 43 Planar structures .................................... 43 Lineations............................................. 43 Mesoscopic folds ...................................... 44 Structural History ...................................... 46 F^ f o l d i n g ............................................. 46 T?2 f o l d i n g ............................................. 46 F^ fo] di n g ............................................. 49 Zone of cataclasis.................................... 54 Faul _i n g ............................................... 54 V. INTERPRETATION............................................. 57 Timing of the Sapphire Tectonic Block Movement ........................................ 57 Synopsis of Deformational History of the Sapphire Tectonic Block ....................... 58 Synopsis of Thermal-Structural History of the southern Sapphire Range ....................... 61 iy Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER PAGE Origin of the Quartzofeldspathic Orthogneiss.......................................... 63 Choice of Tectonic Models ............................... 66 VI. CONCLUSIONS.............................................. 68 APPENDIX I ......................................................... 70 REFERENCES CITED .............................................. 83 v Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ILLUSTRATIONS FIGURE PAGE 1 Tectonic map of southwest Montana showing major faults, distribution of granitic plutons and important geological

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