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Incipient Continental Rifting: Insights from the Okavango Rift Zone, Northwestern Botswana

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Incipient Continental Rifting: Insights from the Okavango Rift Zone, Northwestern Botswana Scholars' Mine Doctoral Dissertations Student Theses and Dissertations Fall 2007 Incipient continental rifting: insights from the Okavango Rift Zone, northwestern Botswana Baraka D. Kinabo Follow this and additional works at: https://scholarsmine.mst.edu/doctoral_dissertations Part of the Geology Commons, and the Geophysics and Seismology Commons Department: Geosciences and Geological and Petroleum Engineering Recommended Citation Kinabo, Baraka D., "Incipient continental rifting: insights from the Okavango Rift Zone, northwestern Botswana" (2007). Doctoral Dissertations. 2191. https://scholarsmine.mst.edu/doctoral_dissertations/2191 This thesis is brought to you by Scholars' Mine, a service of the Missouri S&T Library and Learning Resources. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. INCIPIENT CONTINENTAL RIFTING: INSIGHTS FROM THE OKAVANGO RIFT ZONE, NORTHWESTERN BOTSWANA by BARAKA DAMAS KINABO A DISSERTATION Presented to the Faculty of the Graduate School of the UNIVERSITY OF MISSOURI-ROLLA In partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY in GEOLOGY and GEOPHYSICS 2007 _______________________________ _______________________________ ESTELLA A. ATEKWANA, advisor JOHN P. HOGAN, co advisor _______________________________ _______________________________ DAMIEN DELVAUX MOHAMED ABDELSALAM _______________________________ STEPHEN GAO Copyright 2007 BARAKA DAMAS KINABO All Rights Reserved PUBLICATION DISSERTATION OPTION This dissertation is organized into two sections and two journal articles. Section one gives an outline of the dissertation and introduces the problem, tectonic framework, objectives, available data and research plan. The first article “Early structural development of the Okavango Rift Zone, NW Botswana”, from page 14 to 49, has been published in the Journal of African Earth Sciences, volume 48, page 125-136. The second paper “Fault growth and propagation during incipient continental rifting: Insights from a combined aeromagnetic and SRTM DEM investigation of the Okavango Rift Zone, NW Botswana”, from page 49 to 91 has been submitted to Tectonics and is in the second round of review. Section two summarizes the major conclusions and includes recommendations for future work. iv ABSTRACT In this dissertation aeromagnetic, gravity, and Shuttle Radar Topography Mission Digital Elevation Model (SRTM DEM) data from the Okavango Rift Zone in northwest Botswana are used to map the distribution of rift and basement structures. The distribution of these structures provide useful insights into the early stages of continental rifting. The objectives of this study are (1) assessing the role of pre-existing structures on rift basin development, (2) characterizing the geometry of the nascent rift basins, (3) documenting fault growth and propagation patterns, and (4) investigating the border fault development. Potential field data especially aeromagnetic data are used to map out structures in the sediment covered basement, whereas SRTM DEM data express the surface morphology of the structures. The azimuth of rift faults parallel the orientation of the fold axes and the prominent foliation directions of the basement rocks. This indicates that pre-existing structures in the basement influenced the development of the rift structures. NE dipping faults consistently exhibit greater displacements than SE dipping faults, suggesting a developing half-graben geometry. Individual faults grow by along axis linkage of small segments that develop from soft linkage (under lapping to overlapping segments) to hard linkage (hooking, fused segments). Major rifts faults are also linking through transfer zones by the process of “fault piracy” to establish an immature border fault system. The relationships between scarp heights and vertical throws reveal that the young and active faults are located outside the rift while the faults with no recent activities are in the middle suggesting that the rift is also growing in width. This study demonstrates the utility of potential field data and SRTM DEM to provide a 3- D view of incipient continental rifting processes such as fault growth and propagation. v ACKNOWLEDGMENT This research could not have been completed without the support and countless blessings from the almighty God. I would like to thank my advisors, Dr. Estella Atekwana and Dr. John Hogan for their constant inspiration, encouragement, advice, support, and help throughout my studies at the University of Missouri-Rolla (UMR). Dr. Mohamed Abdelsalam taught me everything I needed to know about the Remote Sensing technology. My other committee members Dr. Stephen Gao, and Dr. Damien Delvaux, were always there for me when I needed their intellectual guidance and expertise. Summer Young of the University of Missouri-Rolla writing center generously provided her English language expertise. Partial financial support for this research was provided by the National Science Foundation (NSF-OISE-0217831) and the American Chemical Society (Petroleum Research Fund; ACS PRF 38595-AC8). Other sources of funds include: University of Missouri-Rolla, Geological Society of America student research grant, National Association of Black Geologists and Geophysicists Mark Gipson awards and Society of Exploration Geophysicist Educational Award. The Geological Survey of Botswana provided the aeromagnetic and gravity data used in this study. Thanks to my family for their unwavering support and prayers throughout my life. My sincere and heartfelt gratitude go out to my mother, my father, brothers, sisters and grandparents. I wish to express special appreciation to my wife, Victoria Joshua Mamkwe for the sacrifices she made so that I could realize one of my biggest dreams in life. I love you sweetheart and thanks for the love and support. vi TABLE OF CONTENTS Page PUBLICATION DISSERTATION OPTION.................................................................... iii ABSTRACT....................................................................................................................... iv ACKNOWLEDGMENT......................................................................................................v LIST OF ILLUSTRATIONS...............................................................................................x LIST OF TABLES........................................................................................................... xiv SECTION 1. INTRODUCTION ...........................................................................................................1 1.1. DISSERTATION OUTLINE..................................................................................1 1.2. PROBLEM STATEMENT.....................................................................................2 1.3. THE EAST AFRICAN RIFT SYSTEM.................................................................3 1.3.1. The Southwestern Branch................................................................................ 7 1.3.2. The Okavango Rift Zone… ............................................................................. 8 1.4. AVAILABLE DATA............................................................................................10 1.5. RESEARCH PLAN ..............................................................................................11 1.5.1. Objective 1 – Influence of Pre-existing Structures........................................ 11 1.5.2. Objective 2 – Geometry of Rift Basins.......................................................... 12 1.5.3. Objective 3 - Fault Growth Patterns.. ............................................................ 12 1.5.4. Objective 4 – Border Fault Development.. .................................................... 13 vii PAPER 1. EARLY STRUCTURAL DEVELOPMENT OF THE OKAVANGO RIFT ZONE, NW BOTSWANA…………………………………………………………….14 Abstract..............................................................................................................................15 1. Introduction....................................................................................................................17 2. Tectonic and geologic framework .................................................................................20 2.1. East African Rift System (EARS)...........................................................................20 2.2. Southwestern branch.............................................................................................20 2.3. Okavango Rift Zone ..............................................................................................21 3. Data acquisition and processing....................................................................................24 3.1. Aeromagnetic data................................................................................................24 3.2. Gravity data ..........................................................................................................27 4. Results............................................................................................................................29 4. 1. Structural Elements and Orientations .................................................................29 5. Discussion......................................................................................................................32 5.1. Influence of Pre-existing Basement Fabric...........................................................32
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