University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 1980 Structural investigation of a section through the Seven Devils Mountains Idaho Earl H. Detra The University of Montana Follow this and additional works at: https://scholarworks.umt.edu/etd Let us know how access to this document benefits ou.y Recommended Citation Detra, Earl H., "Structural investigation of a section through the Seven Devils Mountains Idaho" (1980). Graduate Student Theses, Dissertations, & Professional Papers. 7446. https://scholarworks.umt.edu/etd/7446 This Thesis is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. COPYRIGHT ACT OF 1976 Th is is an unpublished manuscript in which copyright sub ­ s is t s . Any further reprinting of its contents must be approved BY THE a u t h o r . MANSFIELD L ibrary Un iv e r s it y of MONTANA Date: 198 0____ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. STRUCTURAL INVESTIGATION OF A SECTION THROUGH THE SEVEN DEVILS MOUNTAINS, IDAHO by Earl H. Detra B.S., Pennsylvania State University, 1974 Presented in partial fulfillment of the requirements for the degree of Master of Science UNIVERSITY OF MONTANA 1980 Approved by: )V. KaLA~tlx.c>i Chairman, Board of Examiners D@mh, Graduate Sctwol /Û - Date Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: EP38247 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UMT OisMftation r\jbiishing UMI EP38247 Published by ProQuest LLC (2013). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProQuest* ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT Detra, Earl H., M.S., Spring, 1980 Geology Structural Investigation of a Section Through the Seven Devils Mountains, Idaho Director: David M. Fountain ‘ Rocks of the Seven Devils Mountains consist of an entire suite of island-arc-type rocks including subvolcanic, volcanic, pyro- clastic, volcaniclastic, and epiclastic rocks, generated during the development of a Permian through Triassic island-arc system. These rocks were subjected to a single major deformational event characterized by east-over-west thrust faulting which was con­ centrated near the east flanking metamorphic-plutonic terrane. From geometric and kinematic arguments, this deformation is pro­ posed to be synkinematic with motion of previously identified thrust faulting related to emplacement of the Idaho batholith. Various structural elements have been analyzed and systematic variation of deformational style has been defined. A model en­ tailing batholithic uplift is favored as an agent of deformation, but subduction cannot be ruled out, and a combination of models may ultimately explain deformation of Seven Devils terrane. 11 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGMENTS I would like to express my sincere appreciation to all of the individuals whose efforts contributed to the completion of this research. Special thanks are due to my thesis committee, especially Dr. David Fountain for his steady encouragement and Dr. Don Hyndman for his thought-provoking comments. Special recognition is also reserved for Katie Marron, whose prompt and diligent typing was absolutely invaluable. Many others, too numerous to mention here, also rendered valuable assistance for which I am extremely grateful. m Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS P age ABSTRACT..................................................................................................... l i ACKNOWLEDGMENTS.............................................................................................. i i i CHAPTER I. INTRODUCTION................................................................................... 1 II. STRATIGRAPHY AND GENERAL GEOLOGY............................................ 7 Seven Devils Group ...................................................................... 7 Martin Bridge Formation .......................................................... 10 Lucile Slate .................................................................................. 11 Intrusive Rocks .......................................................................... 12 Other Rocks .................................................................................. 15 I I I . DEFORMATION AMD STRUCTURE OF THE SEVEN DEVILS GROUP . 17 Faults............................................................................................. 17 Folds ............................................................................................. 19 Analysis of Ductile Zone. ; ................................................. 21 F o lia tio n s .............................................................................. 22 Lineations .............................................................................. 23 Origin of Foliation and Lineation ................................... 25 Second Deformation .............................................................. 27 Third Deformation .................................................................. 31 Timing of Deformation ........................................................... 31 IV. DISCUSSION....................................................................................... 33 Speculative Geologic History ................................................... 35 Summary.......................................................................................... 39 iv Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS (Continued) Page V. CONCLUSIONS.................................................................................. 43 REFERENCES CITED ...................................................................................... 45 APPENDIX I ................................................................................................. 49 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES Page Figure 1. Location Map....................................................... 2 Figure 2. Detailed Location Map .................................. 3 Figure 3. Distribution of Wrangellian Rocks . 4 Figure 4. O rientation Diagram, Poles to Bedding . 20 Figure 5. O rientation Diagram, Poles to F oliation 20 Figure 6. O rientation Diagram, Poles to F o lia tio n , Martin Bridge Formation, Ductile Zone .................................. 24 Figure 7. O rientation Diagram, Poles to F o lia tio n , Seven Devils Group, D uctile Zone .......................................... 24 Figure 8. O rientation Diagram, Lineations, D uctile Zone . 26 Figure 9. S tra in -s lip Cleavage Development .................................. 28 Figure 10. Domainal Analysis, Poles to Bedding, D uctile Zone 29 Figure 11. O rientation Diagram, Kink-fold Axes, D uctile Zone 29 Figure 12. Sketch o f Kink Fold ............................................................ 30 Figure 13. (a,b) Reconstructed Geologic History .......................... 36 Figure 13. (c,d) Reconstructed Geologic History .......................... 37 VI Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES Paqe Table 1. Comparison o f S tructural Elements from Seven Devils and Riggins Group Terranes ..................................................... 40 Table 2, Timing of Geologic Events in Seven Devils Area . 42 LIST OF PLATES Plate 1 ..................................................................................................... In Pocket Plate 2 ..................................................................................................... In Pocket VI 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER I INTRODUCTION The Seven Devils Mountains are situated in west-central Idaho, forming the divide between the Snake and lower Salmon River drain­ ages near Riggins, Idaho (Fig. 1). The most distinctive character­ istics of the range is its extreme relief, rising from about 400m above sea level in Hells Canyon to over 2800m elevation at the Devil Peak, less than 10km away. Rocks underlying much of the Seven Devils Mountains are part of a discontinuous belt of eugeoclinal volcanic and volcaniclastic rocks extending from central Alaska to northern Mexico (Fig. 3). The northern half of this