Investigations Into the Tectonics of Uranian and Saturnian Icy Satellites
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University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Doctoral Dissertations Graduate School 8-2015 Investigations into the Tectonics of Uranian and Saturnian Icy Satellites Chloe Brett Beddingfield University of Tennessee - Knoxville, [email protected] Follow this and additional works at: https://trace.tennessee.edu/utk_graddiss Part of the Tectonics and Structure Commons Recommended Citation Beddingfield, Chloe Brett, "Investigations into the Tectonics of Uranian and Saturnian Icy Satellites. " PhD diss., University of Tennessee, 2015. https://trace.tennessee.edu/utk_graddiss/3395 This Dissertation is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a dissertation written by Chloe Brett Beddingfield entitled "Investigations into the Tectonics of Uranian and Saturnian Icy Satellites." I have examined the final electronic copy of this dissertation for form and content and recommend that it be accepted in partial fulfillment of the equirr ements for the degree of Doctor of Philosophy, with a major in Geology. Devon M. Burr, Major Professor We have read this dissertation and recommend its acceptance: William M. Dunne, Joshua P. Emery, Liem T. Tran Accepted for the Council: Carolyn R. Hodges Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) Investigations into the Tectonics of Uranian and Saturnian Icy Satellites A Dissertation Presented for the Doctor of Philosophy Degree The University of Tennessee, Knoxville Chloe Brett Beddingfield August 2015 Copyright © 2015 by Chloe Brett Beddingfield All rights reserved. ii Dedication To my parents and brother iii Acknowledgements I’d like to express my deepest gratitude to my Ph.D. advisor, Dr. Devon Burr for being an outstanding role model, for teaching me how to be a logical, scientific thinker, and for providing me with the perfect environment for research. I am grateful to my committee members Dr. William Dunne, Dr. Joshua Emery, and Dr. Liem Tran. Thank you Bill for helping me to develop a background in structural geology. Thank you Josh for helping me to develop a better understanding of the outer solar system icy satellites and geodynamics. Thank you Liem for expanding my knowledge of statistics. I am also thankful to Dr. Annie Howington-Kraus and Dr. Raad Saleh for teaching me how to use SOCET SET to create the digital elevation models used in my research. I am grateful for additional support from Dr. Jeffrey Moersch, Dr. Harry McSween, and Dr. Lawrence Taylor. I want to thank my friends at the University of Tennessee in Knoxville, Dr. Arya Udry, Dr. Nicole Lunning, Nina Wong, Nate Wigton, Robert Jacobson, Michael Lucas, Dr. Sean Lindsay, Ashley Dameron, Samantha Peel, Keenan Golder, Emily Nield, Eric Maclennan, Dr. Latisha Brengman, Cameron Hughes, and Dr. Noemí Pinilla-Alonso. I am also thankful to my friends from Texas Tech University, Kevin and Amanda Wertz, Christopher Treat, and Maeghan Brundrett. Thank you all for many wonderful conversations about science, research, classes, teaching, and other things. I am so grateful to my undergraduate advisor, Dr. Aaron Yoshinobu, who helped inspire me to pursue a doctorate degree after college. I’m grateful to my parents, Craig and Christina Beddingfield, and my brother and sister-in-law, John and Ashley Beddingfield who greatly encouraged and supported my dream of pursuing science throughout college and graduate school. I am additionally thankful for the support of other family members, including my grandparents Gary and Heidi Barner, and Willie Mack and Norma Jean Beddingfield. I am especially grateful to Richard Cartwright for tremendous support, for sharing my most memorable and exciting moments throughout graduate school, and for many extensive discussions about science, research, coursework, life, and everything in between. iv Abstract This dissertation reports a range of analyses of tectonic structures on various icy satellites and the implications of these analyses for each satellite’s geologic history. On Miranda, I tested the hypothesis that faults of the Arden Corona boundary and the 340º [degree] Chasma are listric in geometry. A listric fault geometry implies the presence of a subsurface detachment, which likely marked Miranda’s brittle-ductile transition (BDT) at the time of faulting. Results support the hypothesis for the Arden Corona boundary, although not for the 340˚ [degree] Chasma. Using the Arden Corona fault system geometry, the BDT depth, thermal gradient, and heat flux were estimated. Those estimates are consistent with a previously hypothesized heating event associated with an ancient tidal resonance of Miranda with Umbriel and/or Ariel. On the Saturnian satellites Tethys, Rhea, and Dione, I analyzed normal fault slope geometries to test the hypothesis that faults on icy bodies reflect dip values derived from laboratory deformation experiments in cryogenic H2O [water] ice. The results show that faults within Ithaca Chasma on Tethys, Avaiki Chasmata on Rhea, and one scarp within Dione’s Wispy Terrain exhibits scarp slopes that are shallower than these values. Analyses of these fault systems indicate that viscous relaxation is the most viable explanation for these shallow slopes. I modeled the potential role of viscous relaxation in creating these shallow fault slopes. The modeling results support the formation of these faults with steep dips, consistent with deformation experiments, followed by their relaxation due to lithospheric heating events. Finally, I tested for the presence of subtle and/or non-visible fractures within Dione’s Non-Wispy Terrain. A set of statistical analyses of crater rim azimuth data was used to test for polygonal impact craters (PICs) at randomly distributed study locations. The results indicate that PICs are widespread throughout the Non-Wispy Terrain, supporting the hypothesis that fractures are widespread throughout this terrain, despite the lack of visible fractures. These results demonstrate that analysis of crater geometries is a useful tool for identifying and mapping fractures with dimensions below the resolution of available images. v Table of Contents INTRODUCTION 1 CHAPTER I Fault Geometries on Uranus' Satellite Miranda: Implications for Internal Structure and Heat Flow 4 Abstract 5 Introduction 5 Background 7 Miranda’s Coronae and Global Rift System 7 Extensional Tectonism on Other Icy Satellites 9 Normal Listric Fault Geometries 10 Possible Detachment Formation Mechanisms on Icy Satellites 11 Data and Methods 12 Images 12 Digital Elevation Models 12 Criteria for a Listric Fault System 13 Results 16 Analysis 17 Depth to Detachment during Faulting 17 Thermal Gradient at the Time of Faulting 18 Heat Flux at the Time of Faulting 20 Discussion and Implications 20 Comparison of Thermal Results to those of other Icy Satellites 20 Miranda’s Surface Evolution 21 Summary 22 References 23 Appendix I 29 Appendix I-A: ISIS Image Processing Steps 50 Appendix I-B: Ames Stereo Pipeline Processing Steps and Vertical Accuracy Calculations 50 Appendix I-C: Tables I-C1 through I-C6 52 CHAPTER II Shallow Normal Fault Slopes on Saturn’s Icy Satellites 61 Abstract 62 Introduction 62 Background 63 Brittle Deformation Theory 63 Brittle Deformation Experiments in Water Ice 64 Causes of Icy Satellite Extensional Tectonics 65 Data and Methods 65 Ithaca Chasma, Tethys 66 vi Avaiki Chasma, Rhea 66 The Wispy Terrain, Dione 67 Digital Elevation Models 67 Measurement Techniques 68 Statistical Analysis Techniques 69 Results 70 Shallow Fault Slope Development and Icy Satellite Faults 71 Fault Rotation during Offset 71 Stress-Axis Perturbation 72 Material Weakening 73 Regolith Deposition 73 Viscous Relaxation 73 Model Tests for Shallow Fault Slope Formation by Viscous Relaxation 76 Calculation Methods 76 Calculation Results 79 Discussion and Implications 79 Summary 81 Acknowledgements 82 References 83 Appendix II 93 Appendix II-A: SOCET SET DEM Generation 130 Appendix II-B: ASP DEM Generation 133 Appendix II-C: DEM Comparisons 134 CHAPTER III Polygonal Impact Craters on Dione: Evidence for Tectonism outside the Wispy Terrain 139 Abstract 140 Introduction 140 Background 142 Impact Processes 142 Controls on Impact Crater Size and Morphology 142 Models of PIC Formation 143 PICs throughout the Solar System 144 The Geology of Dione 144 Data and Methods 146 Measurement Techniques 146 PIC Identification 147 Comparing PIC and Fracture Azimuths 148 Results 148 Wispy Terrain Results 149 Non-Wispy Terrain Results 149 Implications for the Tectonic History of Dione 151 Orbital Recession 152 Spin-up 152 vii Despinning 153 Volume Contraction 153 Volume Expansion 154 Conclusions 155 Acknowledgements 156 References 157 Appendix III 167 Appendix III-A: Determining Study Locations 189 Appendix III-B: ISIS Image Processing Steps 190 Appendix III-C: Classifying PICs 190 Appendix III-D: Comparing Visible Wispy Terrain Fractures to PICs 192 Appendix III-E: Study Location IDs, Coordinates, and Images Utilized 192 Appendix III-F: Details on Statistical Test Results 204 CONCLUSION 240 VITA 241 viii List of Tables Table I-1. Image information including resolution, area of Miranda covered, and whether or not the image was used