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Paleomagnetic and Rock Magnetic Analysis of an Ignimbrite Sequence, Yellowstone’S Huckleberry Ridge Tuff, Eastern Idaho

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Paleomagnetic and Rock Magnetic Analysis of an Ignimbrite Sequence, Yellowstone’S Huckleberry Ridge Tuff, Eastern Idaho PALEOMAGNETIC AND ROCK MAGNETIC ANALYSIS OF AN IGNIMBRITE SEQUENCE, THE YELLOWSTONE HUCKLEBERRY RIDGE TUFF, SOUTHEAST IDAHO by April Allen Langhans APPROVED BY SUPERVISORY COMMITTEE: ________________________________________ John W. Geissman, Chair ________________________________________ John F. Ferguson ________________________________________ Robert J. Stern Copyright 2019 April Allen Langhans All Rights Reserved PALEOMAGNETIC AND ROCK MAGNETIC ANALYSIS OF AN IGNIMBRITE SEQUENCE, THE YELLOWSTONE HUCKLEBERRY RIDGE TUFF, SOUTHEAST IDAHO by APRIL ALLEN LANGHANS, BS THESIS Presented to the Faculty of The University of Texas at Dallas in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN GEOSCIENCES THE UNIVERSITY OF TEXAS AT DALLAS May 2019 ACKNOWLEDGEMENTS First, and foremost, I would like to acknowledge John Geissman for accepting me as his student, and his guidance and support in my current and continued research endeavors. Secondly, I am most grateful to Samuel Johnson for his assistance in sample collection, our many enlightening discussions, and for all the valuable resources and input he imparted to me and this project. Thirdly, I am thankful to Collin Wilson for locating the beautifully exposed site, and allowing me to contribute to the understanding of the area’s geology. I am grateful for the help and guidance of Scott Kerstetter, for his unique and valuable insight into structural geology. Additionally, I would like to acknowledge Jordan Newman, Jonathan Stine, Clayton Koop, Jackie Horn, and Ziaul Haque for their contributions. Lastly, I am thankful to Adam Langhans for his unending support and patience. March 2019 iv PALEOMAGNETIC AND ROCK MAGNETIC ANALYSIS OF AN IGNIMBRITE SEQUENCE, THE YELLOWSTONE HUCKLEBERRY RIDGE TUFF, SOUTHEAST IDAHO April Allen Langhans, MS The University of Texas at Dallas, 2019 Supervising Professor: John W. Geissman, PhD Paleomagnetic data collected at four sites in ignimbrite members A and B of the Huckleberry Ridge Tuff in the Teton River Valley area of southeast Idaho, USA, yield ChRM directions in in situ coordinates of south-southwest declination and shallow inclinations that are consistent with previous investigations. Data collection was primarily focused on an exposure of HRT member A on a road cut off of Hog Hollow Road, where the ignimbrite was previously described as being an overturned fold that is reverse faulted. Contrary to this interpretation, the results of this study may imply that the Hog Hollow Road locality is not overturned, but is instead an upright fold that has been normal faulted. Data collected at the Hog Hollow locality indicate that folding and acquisition of compaction fabrics occurred above maximum magnetization blocking temperatures (>580ºC) in the hanging wall of faulted member A, but that deformation of underlying rocks occurred simultaneously with acquisition of remanence. Directional data from hanging wall and footwall rocks do not show significant deviations from each other to support an overturned fault, but instead support the hypothesis that the fold is an upright fold. Preliminary data from other sites may indicate that deformation followed ChRM acquisition at temperatures <580ºC thus during syn-emplacement-tilting. v TABLE OF CONTENTS ACKNOWLEDGEMENTS ........................................................................................................... iv ABSTRACT .................................................................................................................................... v LIST OF FIGURES ..................................................................................................................... viii LIST OF TABLES ......................................................................................................................... ix CHAPTER 1 INTRODUCTION .................................................................................................... 1 CHAPTER 2 GEOLOGIC BACKGROUND ................................................................................. 5 2.1 Geologic Setting............................................................................................................ 5 2.1.1 Huckleberry Ridge Tuff Member Description ............................................... 9 2.1.2 Site Description ............................................................................................ 11 2.2 Paleomagnetism, Background..................................................................................... 15 CHAPTER 3 METHOD ............................................................................................................... 18 3.1 Data Collection ........................................................................................................... 18 3.2 Data Analysis .............................................................................................................. 21 CHAPTER 4 RESULTS ............................................................................................................... 23 4.1 Field Observation ........................................................................................................ 23 4.2 Rock Magnetic Data ................................................................................................... 28 4.2.1 ARM & NRM decay, IRM acquisition, & Backfield demagnetization ....... 28 4.2.2 Susceptibility versus Temperature Experiments .......................................... 30 4.2.3 Anisotropy of Magnetics Susceptibility Data .............................................. 32 4.3 Paleomagnetic Data .................................................................................................... 56 4.3.1 Progressive Thermal & AF Demagnetization Results ................................. 57 vi 4.3.2 Anisotropy of Magnetic Susceptibility Results ........................................... 60 CHAPTER 5 DISCUSSION ......................................................................................................... 78 5.1 Timing and Degree of Deformation ............................................................................ 78 5.2 Tilt Tests ..................................................................................................................... 80 CHAPTER 6 CONCLUSION....................................................................................................... 83 APPENDIX ARM, IRM, AND NRM DEMAGNETIZATION CURVES .................................. 84 REFERENCES ............................................................................................................................. 87 BIOGRAPHICAL SKETCH ........................................................................................................ 91 CURRICULUM VITAE vii LIST OF FIGURES 1) Area Map ..................................................................................................................................4 2) HRT Distribution Map ..............................................................................................................8 3) Stratigraphic Column .............................................................................................................. 11 4) Hog Hollow Road Geologic Map ........................................................................................... 13 5) Bitch Creek Geologic Map ..................................................................................................... 14 6) Bitch Creek Core Samples ...................................................................................................... 23 7) Previous Field Interpretation................................................................................................... 24 8) Member A Ignimbrite ............................................................................................................. 26 9) Field Relations ........................................................................................................................ 27 10) Conglomerate and Breccia ...................................................................................................... 28 11) Normalized ARM/NRM decay curves.................................................................................... 34 12) IRM acquisition and backfield demagnetization curves ......................................................... 36 13) Susceptibility versus Temperature .......................................................................................... 39 14) Magnetic Separates ................................................................................................................. 43 15) Bulk Susceptibility .................................................................................................................. 47 16) Degree of anisotropy (P) versus shape parameter (T) ............................................................ 48 17) In situ AMS susceptibility ellipses ......................................................................................... 51 18) Tilt Corrected AMS susceptibility ellipses ............................................................................. 54 19) In situ orthogonal demagnetization diagrams ........................................................................ 63 20) Tilt corrected orthogonal demagnetization diagrams ............................................................. 69 21) PCA stereonets .......................................................................................................................
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