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Morpho-Tectonic Analysis of the East African Rift System

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MORPHO-TECTONIC ANALYSIS OF THE EAST AFRICAN RIFT SYSTEM By LIANG XUE Bachelor of Engineer in Geological Engineering Central South University Changsha, China 2011 Master of Science in Geology Missouri University of Science and Technology Rolla, Missouri 2014 Submitted to the Faculty of the Graduate College of the Oklahoma State University in partial fulfillment of the requirements for the Degree of DOCTOR OF PHILOSOPHY July, 2018 MORPHO-TECTONIC ANALYSIS OF THE EAST AFRICAN RIFT SYSTEM Dissertation Approved: Dr. Mohamed Abdelsalam Dissertation Adviser Dr. Estella Atekwana Dr. Danial Lao Davila Dr. Amy Frazier Dr. Javier Vilcaez Perez ii ACKNOWLEDGEMENTS This research could never have been completed without the support of my mentors, colleagues, friends, and family. I would thank my advisor, Dr. Mohamed Abdelsalam, who has introduced me to the geology of the East African Rift System. I was given so much trust, encouragement, patience, and freedom to explore anything that interests me in geoscience, including tectonic/fluvial geomorphology, unmanned aerial system/multi-special remote sensing, and numerical modeling. I thank my other members of my committee, Drs. Estella Atekwana, Daniel Lao Davila, Amy Frazier, and Javier Vilcaez Perez for their guidance in this work, as well as for their help and suggestion on my academic career. Their writing and teaching have always inspired me during my time at Oklahoma State University. The understanding, encouragement from my committee members have provided a good basis for the present dissertation. Also, I thank Dr. Nahid Gani, of Western Kentucky University for her contribution to editing and refining my three manuscripts constituting this dissertation. It has been four years since I came to Oklahoma State University for my PhD program. I have greatly benefited over that time from interaction with my teachers and colleagues. The professors in Geology and Geography departments prepared me to be a much more balanced researcher. I also wish to express my appreciation to the Boone Pickens School of Geology, for providing the Graduate Teaching Assistant, and fellowships that made my study possible. Further, I would like to thank several communities. This work is partially supported by American Association of Petroleum Geologists’ Grant-in-Aid fund and Geological Society of America’s Graduate Research Funding. I also thank the members of American Geophysical Union Gilbert Club and Community Surface Dynamics Modeling System for sharing their data, code, and helping me with methodologies of this work. To my colleagues and treasured friends in the PhD office (NRC 412) and in the Geodynamic and Geospatial Science lab (NRC 303), Tadesse Alemu, Mercy Achang, Sahar Mohammadi, Jingyao Meng, Pouyan Ebrahimi, Ibukun Bode Omoleye, Zelalem Demissie, Folarin Kolawole, and Andrew Katumwehe, Babak Shabani, Luel Emishaw, I cannot give enough thanks for their supports, encourage, friendship, and good moments. A sincere thank is also due to all members of the Tectonic Group for their intellectual discussions, as well as for collaboration with Steven Johnson and Ines Barrios Galindez in their research projects. Finally, I am grateful to my parents, grandma, and Shaoyi, who supported my efforts throughout this long journey. During my four years in the PhD program, I have only been back home once, so I would also like to thank my family and friends in China who have tolerated my long absence. iii Acknowledgements reflect the views of the author and are not endorsed by committee members or Oklahoma State University. Name: LIANG XUE Date of Degree: JULY, 2018 Title of Study: MORPHO-TECTONIC ANALYSIS OF THE DRAINAGE SYSTEMS IN THE EAST AFRICAN RIFT SYSTEM Major Field: GEOLOGY Abstract: Tectonic uplift of mountain ranges and plateaus have a significant impact on the geological record by influencing drainage systems and sediment supply, and on climate and on biogeography. Recent geomorphological, geochronological and geophysical studies have provided some understanding of time constraints and uplift rate distribution patterns, especially in convergent plate margins. Nevertheless, fewer studies took a comprehensive view over the topographic patterns, rates and changes in rates of tectonic uplift in continental rift systems. We do not know the how ground’s vertical motion is localized along the axis of rift and the relative roles of upwelling of magma and rift extensional processes play in tectonic uplift history. The East African Rift System (EARS) has long served as the ideal example of a continental rift to explore the distribution patterns, rates, and timing of tectonic uplift in the evolution of geomorphology. This work addresses fundamental questions of tectonic uplift and its footprint on the topography associated with rift systems. Specifically, three distinct segments along the EARS, the Rwenzori Mountains in the Western Branch, the southeastern Ethiopian Plateau in the Northern Branch and the Kenyan Rift in the Eastern Branch are investigated. The first chapter evaluated geomorphic proxies in the Rwenzori Mountains. We found that the linear geomorphic proxies (normalized steepness and chi integral) have strong positive correlation with the erosion rates. Additionally, our geomorphic proxy results suggest that the north and south sectors of the Rwenzori Mountains are in relative tectonic quiescence but that the central sector is experiencing higher levels of erosion and rock uplift. The second chapter used morphotectonic analysis to study the tectonic uplift history of the southeastern Ethiopian Plateau (SEEP). We find an increase in tectonic uplift rates from the southeastern escarpments of the Afar Depression in the northeast to that of the Main Ethiopian Rift to the southwest. We identify three regional tectonic uplift events at ~11.7, ~6.5, and ~4.5 Ma recorded by the development of regionally distributed knickpoints. This is in good agreement with ages of tectonic uplift events reported from the Northwestern Ethiopian Plateau. The third chapter examined the tectonic uplift history of the Kenya Rift. This work found that the spatial and temporal pattern of the tectonic uplift inferred from the drainage incision is well-correlated with known phases of magmatic activities. Also, this work found that the rapid increase in drainage incision since ~4.5 Ma correlated well with a major change in vegetation from grassland to woodland. This suggests that the tectonic uplift coupled with Pliocene magmatic activities have caused a major shift in the ecosystem in the region. iv PUBLICATION DISSERTATION OPTION This dissertation has been structured in two sections. The first section (Chapter 1) gives a brief introduction of the dissertation and introduces the scientific questions investigated in this research. The second section (Chapters 2, 3, and 4) also presents three manuscripts including two that have been published and one in preparation for publication. Paper 1: Xue, Liang, Nahid D. Gani, and Mohamed G. Abdelsalam. "Geomorphologic proxies for bedrock rivers: A case study from the Rwenzori Mountains, East African Rift system." Geomorphology 285 (2017): 374-398. Paper 2: Xue, Liang, Alemu, Tadesse, Nahid D. Gani, and Mohamed G. Abdelsalam. "Spatial and temporal variation of tectonic uplift in the southeastern Ethiopian Plateau from morphotectonic analysis." Geomorphology 309 (2018): 98-111. Paper 3: Xue, Liang, Nahid D. Gani, and Mohamed G. Abdelsalam. (Submitted) “Drainage incision, tectonic uplift, and magmatism of the Kenya rift, East African Rift System: a morpho-tectonic analysis approach.” JGR-Earth Surface. v TABLE OF CONTENTS CHAPTER I ............................................................................................................................... 1 INTRODUCTION ...................................................................................................................... 1 1.0. Project Motivation ................................................................................................................ 1 1.1. Objectives ............................................................................................................................ 2 1.2. Significance ......................................................................................................................... 3 1.3. References ........................................................................................................................... 6 CHAPTER II .............................................................................................................................. 8 GEOMORPHOLOGIC PROXIES FOR BEDROCK RIVERS: A CASE STUDY FROM THE RWENZORI MOUNTAINS, EAST AFRICAN RIFT SYSTEM................................................. 8 2.0. Abstract ............................................................................................................................... 8 2.1. Introduction ....................................................................................................................... 10 2.2. Geologic setting ................................................................................................................. 12 2.2.1. The East African Rift system (EARS) .......................................................................... 12 2.2.2. The Rwenzori Mountains ............................................................................................. 14 2.2.2.1. Lithology .............................................................................................................
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