University of New Mexico UNM Digital Repository Earth and Planetary Sciences ETDs Electronic Theses and Dissertations Spring 5-8-2018 Birth and Evolution of the Virgin River: ~1 km of post-5 Ma uplift of the western Colorado Plateau Cory J. Walk Follow this and additional works at: https://digitalrepository.unm.edu/eps_etds Part of the Geology Commons Recommended Citation Walk, Cory J.. "Birth and Evolution of the Virgin River: ~1 km of post-5 Ma uplift of the ew stern Colorado Plateau." (2018). https://digitalrepository.unm.edu/eps_etds/232 This Thesis is brought to you for free and open access by the Electronic Theses and Dissertations at UNM Digital Repository. It has been accepted for inclusion in Earth and Planetary Sciences ETDs by an authorized administrator of UNM Digital Repository. For more information, please contact [email protected]. Cory J. Walk Candidate Earth and Planetary Sciences Department This thesis is approved, and it is acceptable in quality and form for publication: Approved by the Thesis Committee: Karl E. Karlstrom, Chairperson Ryan S. Crow Laura J. Crossey Louis Scuderi i BIRTH AND EVOLUTION OF THE VIRGIN RIVER: ~1 KM OF POST-5 MA UPLIFT OF THE WESTERN COLORADO PLATEAU by CORY J. WALK B.S. GEOLOGY BRIGHAM YOUNG UNIVERSITY–IDAHO 2015 THESIS Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science Earth and Planetary Sciences The University of New Mexico Albuquerque, New Mexico July 2018 ii ACKNOWLEDGEMENTS I would first like to acknowledge my graduate advisor, Karl Karlstrom. I had the opportunity to sit outside his office for the past 2 years and witness firsthand his continuous drive to learn, teach, and further the science of geology. He taught me by example how to be productive as a graduate student and as a human being through hard work and collaboration with others. His office door was always open which resulted in spontaneous and insightful discussions regarding not only my research, but also my personal well-being and the well-being of my family. He gave me his time, energy, funding, and advice to ensure my success. I cannot imagine a more influential graduate advisor. Thank you, Karl. I would also like to thank those who were on my graduate thesis committee, including Laura Crossey, Ryan Crow, and Louis Scuderi. Each of these individuals has greatly influenced my academic experience for the last 2 years and played a critical role in my success through their mentorship in the field, classroom, and informal discussions. I express gratitude to Matt Heizler and Lisa Peters at the New Mexico Geochronology Research Center in Socorro, NM. They spent hours in the lab, teaching me and acquiring the results necessary to perform a detrital sanidine analysis using argon geochronology. I also thank Brandon Schmandt for providing the tomographic cross- section that influenced the discussion on potential mantle driven uplift mechanisms. I must also acknowledge the funding that made my fieldwork possible, the National Science Foundation (NSF) EPSCOR award #IIA-1301346 to Laura Crossey and Karl Karlstrom. I need to thank my parents Dirk and Tami Walk, for their continuous love and support throughout my entire life. My two sons, Cooper and Hudson, for always giving me motivation and putting a smile on my face after a long day at the office. Finally, I express my highest degree of gratitude to my wife, Savanah. My success as a graduate student would have been impossible without her sacrifice, support, love, and patience. She deserves the highest of accolades for raising our 2 children at home, while pursuing her own online degree, as I spent many hours on campus. I am grateful for her sacrifice and I am truly blessed to have her as my eternal companion. iii BIRTH AND EVOLUTION OF THE VIRGIN RIVER FLUVIAL SYSTEM: ~1 KM OF POST-5 MA UPLIFT OF THE WESTERN COLORADO PLATEAU By Cory Walk B.S., Geology, Brigham Young University – Idaho, 2015 M.S., Earth and Planetary Sciences, University of New Mexico, 2018 ABSTRACT The uplift history of the Colorado Plateau has been debated for over a century with still no unified hypotheses for the cause, timing, and rate of uplift. 40Ar/39Ar dating of semi-continuous basaltic volcanism over the past ~6 Ma within the Virgin River drainage system, southwest Utah and southern Nevada, provides a way to calibrate differential river incision and compare patterns of basaltic migration, mantle velocity structure, channel steepness, lithology, incision history and the birth and evolution of the Virgin River. New detrital sanidine ages constrain the arrival of the Virgin River across the Virgin Mountains to a maximum depositional age of 5.9 Ma. Incision magnitudes and rates of the Virgin River show a stair-step increase in bedrock incision as the river crosses multiple N-S trending normal faults. Average calculated rates are 23 m/Ma in the Lake Mead block, 85 m/Ma in the combined St. George and Hurricane blocks, and 338 m/Ma in the Zion block. Block-to-block differential incision adds cumulatively such that the Zion block has been deeply incised ~1 km (~315 m/Ma) over 3.6 Ma relative to the Colorado River confluence. We test two hypotheses: 1) observed differential incision magnitudes and rates along the Virgin River system are a measure of mantle-driven iv differential uplift of the Colorado Plateau relative to sea level over the past ~5 Ma. 2) Observed differential river incision relates to river integration across previously uplifted topography and differential rock types with no post 5 Ma uplift. Strong correlations exist between high channel steepness (ksn) and low mantle velocities throughout the Virgin River drainage while weaker correlations exist between high ksn and resistant lithologies. Basaltic volcanism, which has migrated at a rate of ~18 km/Ma parallel to the Virgin River between ~13 and 0.5 Ma suggests a possible mantle- driven mechanism for the combined observations of differential uplift across faults and additional young Colorado Plateau epeirogenic uplift tracked by headward river propagation. Thus, we interpret the Virgin River to be a < 4.5 Ma disequilibrium river system responding to ongoing upper mantle modification and related basalt extraction, which is driving ~ 1 km of young uplift of the western Colorado Plateau. v TABLE OF CONTENTS ACKNOWLEDGEMENTS .......................................................................................iii ABSTRACT ...............................................................................................................iv TABLE OF CONTENTS ...........................................................................................vi LIST OF FIGURES ...................................................................................................viii LIST OF TABLES .....................................................................................................ix PREFACE ..................................................................................................................x INTRODUCTION .....................................................................................................1 GEOLOGIC BACKGROUND ..................................................................................11 METHODS ................................................................................................................16 Profile Analysis .....................................................................................................16 Magmatic Sweep ...................................................................................................19 Differential Incision ..............................................................................................20 Provenance Analysis .............................................................................................23 RESULTS ..................................................................................................................24 Profile Analysis .....................................................................................................24 Magmatic Sweep ...................................................................................................29 Differential Incision ..............................................................................................29 Basalt Paleoprofiles ..............................................................................................34 Provenance Analysis .............................................................................................36 INTERPRETATIONS ...............................................................................................37 Profile Analysis .....................................................................................................37 Magmatic Sweep ...................................................................................................41 vi Differential Incision ..............................................................................................41 Basalt Paleoprofiles ..............................................................................................47 Provenance Analysis .............................................................................................48 DISCUSSION ............................................................................................................50 Evolution of the Virgin River ...............................................................................50 Pre-5 Ma landscape ...............................................................................................51