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Paleomagnetism of the Late Cretaceous-Paleocene Adel Mountain Volcanics West-Central Montana

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Paleomagnetism of the Late Cretaceous-Paleocene Adel Mountain Volcanics West-Central Montana University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 1989 Paleomagnetism of the late Cretaceous-Paleocene Adel Mountain volcanics west-central Montana Jay A. Gunderson 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 Gunderson, Jay A., "Paleomagnetism of the late Cretaceous-Paleocene Adel Mountain volcanics west- central Montana" (1989). Graduate Student Theses, Dissertations, & Professional Papers. 8321. https://scholarworks.umt.edu/etd/8321 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 COPYRIGHT ACT OF 1976 Th is is an unpublished m anuscript in which c o p yr ig h t SUBSISTS. Any further r e p r in t in g of it s contents must be APPROVED BY THE AUTHOR. Ma n s f ie l d L ibrary Un iv e r s it y of Montana Date : 1 9 89 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PALEOMAGNETISM OF THE LATE CRETACEOUS - PALEOCENE ADEL MOUNTAIN VOLCANICS. WEST-CENTRAL MONTANA by Jay A. Gunderson B.S., University of Minnesota, Duluth, 1984 Presented in partial fulfillment of the requirements for the degree of Master of Science University of Montana 1989 Approved by Chairman, Board of Examiners Dean, Graduate School J / , r j S - i Date • 7 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: EP39122 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. UMI Oi«MrMtCion Publimhimg UMI EP39122 Published by ProQuest LLO (2013). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLO. 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 4 8 1 0 6 -1 3 4 6 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. You are asking yourself, as all of us must; "Who am I?"... "Where am I?"..."Whence do I go?" The process of enlightenment is usually slow. But, in the end, our seeking always brings a finding. These great mysteries are, after all, enshrined in complete simplicity. - Bill W. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Gunderson, Jay A., M.S., July 1989 Geology Paleomagnetism of the Late Cretaceous - Paleocene Adel Mountain Volcanics, west-central Montana (242 pp.) Director: Steven D. Sheriff (P Accurate apparent polar wander (APW) paths provide an excellent reference frame for delineating tectonic histories of crustal fragments. Yet, cratonic North America’s APW path remains undefined between the Late Cretaceous and Paleocene pole positions. This cusp represents about 13° of apparent motion over ~22 my and coincides with the beginning of Laramide deformation (ca. 80 Ma). A paleomagnetic study of the Late Cretaceous - Paleocene (67-58 Ma) Adel Mountain Volcanics of west-central Montana (lat. 47.20°N, long. 111.85°W) was initiated to refine the North American APW path during this crucial interval. Twenty-six reliable paleomagnetic sites were obtained from the Adel Mountain shonkinite flows, dikes, and laccoliths. Positive fold and conglomerate tests indicate that isolated characteristic remanent directions are primary magnetizations, acquired before the Paleocene folds and thrusts associated with the disturbed belt. Averaging the virtual geomagnetic poles (VGP’s) from these 26 sites yields a paleopole (82.2°N, 209.9°E, «95=6.8°, k=18.4) which is concordant with other Paleocene reference poles. This paleopole appears to have adequately averaged paleosecular variation according to the VGP dispersion predicted by current models. The Adel Mountain VGP’s are combined with other estimates of the Paleocene pole to give a new mean located at 81.8°N, 197.1°E, «95=2.96°. The new mean Paleocene (67-59 Ma) pole suggests that much of the rapid APW had already occurred by the latest Cretaceous (ca. 67 Ma) and further constrains this apparent motion to 12.3° between approximately 87-67 Ma. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS Work on this project was funded in part by NSF grant #EAR-8804126 awarded to Steven D. Sheriff. Pac Gunderson, Sherri Gunderson, Joel Knutson, and Art Jolly provided valuable assistance in the field. Discussions with Bob Swenson regarding local access and geology saved immeasurable amounts of time. I wish to thank Jim Diehl of Michigan Tech and committee members Steve Sheriff, Jim Sears, and Mark Jakobson for their time and effort during the manuscript preparation; particularly committee chair, Steve Sheriff, who offered helpful comments and suggestions throughout every phase of the project. Finally, a special thanks to my wife, Sherri, for her continual tolerance and support during this ordeal. Ill Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS PAGE ABSTRACT ....................................................................................................................... ii ACKNOWLEDGEMENTS ........................................................................................ iii LIST OF TABLES...................................................................................................... v LIST OF ILLUSTRATIONS ..................................................................................... vi INTRODUCTION ...................................................................................................... 1 GEOLOGY ............................................................................................................... 6 FIELD AND LABORATORY TECHNIQUES .................................................... 10 PALEOMAGNETIC RESULTS...............................................................................18 F lo w s .......................................................................................................................... 18 Dikes and laccoliths .............................................................................................25 Conglomerates and breccias .............................................................................. 34 DISCUSSION AND CONCLUSIONS...................................................................35 APPENDIX A. - SITE DATA ...................................................................................45 APPENDIX B. - NRM/lRMs TESTS ...................................................................... 171 APPENDIX C. - VRM ............................................................................................... 225 APPENDIX D. - SITES OF FURTHER INTEREST .........................................235 REFERENCES C ITE D ..............................................................................................237 IV Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES TABLE PAGE 1. Summary of paleomagnetic d a ta ...................................................................15 2. Cretaceous still-stand p o le s ...........................................................................42 3. Paleocene paleomagnetic studies ............................................................... 44 4. Summary of NRM/IRM coercivity te s ts .................................................... 175 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF ILLUSTRATIONS FIGURE PAGE 1. North American apparent polar w ander ................................................ 4 2. Location m ap .................................................................................................. 5 3. Geologic m ap ................................................................................................... 8 4. Paleomagnetic site distribution ..................................................................... 11 5. Site means and a95’s ....................................................................................16 6. Vector diagrams - flow s ................................................................................ 19 7. Intensity decay (M/Mo) - flow s .....................................................................23 8. IRM acquisition - flow s ................................................................................... 24 9. Fold te st ............................................................................................................. 26 10. Intensity decay (M/Mo) - dikes .................................................................. 29 11. Vector diagrams - dikes .................................................................................30
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