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Recent Faulting and Active Shortening of the Middle Atlas Mountains, Morocco, Within the Diffuse African-Eurasian Plate Boundary

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Recent Faulting and Active Shortening of the Middle Atlas Mountains, Morocco, Within the Diffuse African-Eurasian Plate Boundary RECENT FAULTING AND ACTIVE SHORTENING OF THE MIDDLE ATLAS MOUNTAINS, MOROCCO, WITHIN THE DIFFUSE AFRICAN-EURASIAN PLATE BOUNDARY _______________________________________ A Thesis presented to the Faculty of the Graduate School University of Missouri-Columbia _______________________________________________________ In Partial Fulfillment Of the Requirements for the Degree Master of Science _____________________________________________________ by Michael Rigby Dr. Francisco Gomez, Thesis Supervisor MAY 2008 The undersigned, appointed by the Dean of the Graduate School, have examined the thesis entitled: RECENT FAULTING AND ACTIVE SHORTENING OF THE MIDDLE ATLAS MOUNTAINS, MOROCCO, WITHIN THE DIFFUSE AFRICAN-EURASIAN PLATE BOUNDARY Presented by Michael Rigby A candidate for the degree of Master of Science And hereby certify that in their opinion it is worthy of acceptance. Dr. Francisco Gomez Dr. Robert Bauer Dr. Brent Rosenblad ACKNOWLEDGEMENTS I would like to thank my thesis advisor, Dr. Francisco Gomez, for all of his help throughout the research process. I would also like to thank my thesis committee members, Dr. Robert Bauer and Dr. Brent Rosenblad, for their assistance during the writing process. Also, I want to thank Yousuef Hahou, Zakir Abdelali, Nacer Jabour, and Abdelali Fadil for their assistance during the completion of field work. I would also like to thank the National Science Foundation of the funding of this project (EAR-0408661) and Dr. Rick Allmendinger for the use of his structural programs. Lastly, I would like to thank my family and friends for their continuous support. ii TABLE OF CONTENTS ACKNOWLEDGEMENTS................................................................................ ii LIST OF FIGURES ..........................................................................................v LIST OF TABLES .......................................................................................... vii ABSTRACT ...................................................................................................viii CHAPTER 1 INTRODUCTION AND TECTONIC BACKGROUND..................1 Introduction ..................................................................................................1 Objectives and Justification......................................................................4 Tectonic Setting ...........................................................................................5 Tectonic Evolution of the Atlas Mountains ...................................................6 Triassic through Early Tertiary..................................................................6 Cenozoic Tectonics ................................................................................10 CHAPTER 2 - MIDDLE ATLAS STRUCTURE ..............................................19 Introduction ................................................................................................19 Geologic Mapping of the Folded Middle Atlas............................................22 Stratigraphy............................................................................................23 Triassic ...............................................................................................23 Lower Liassic ......................................................................................23 Middle Liassic .....................................................................................24 Cretaceous .........................................................................................24 Neogene .............................................................................................24 Quaternary..........................................................................................24 Remote Sensing Analysis and Interpretation..........................................24 Data Types .........................................................................................24 Analyses .............................................................................................27 Stereo Photogrammetry ..................................................................27 Multi-spectral image processing and interpretation .........................27 Geologic Map of the Folded Middle Atlas...............................................33 Structural Analyses ....................................................................................35 Balanced Cross-Section of the Folded Middle Atlas ..................................40 Discussion..................................................................................................42 CHAPTER 3 ACTIVE TECTONISM IN THE FOLDED MIDDLE ATLAS MOUNTAINS.................................................................................................45 Longitudinal Stream and Stream Terrace Profiles .....................................46 Quaternary Fault Scarps............................................................................49 Microtopographic Mapping .....................................................................49 Radiocarbon Age Dating ........................................................................57 Fault Scarp Degradation Modeling .........................................................58 Single Event Fault Scarp Degradation Model .....................................59 Composite Fault Scarp Degradation Model ........................................66 iii Discussion..................................................................................................70 Conclusion .................................................................................................72 REFERENCES CITED ..................................................................................74 iv LIST OF FIGURES Figure Page 1.1. Simplified tectonic map of the western Mediterranean. ...........................2 1.2. Topography map of the western Mediterranean. .....................................3 1.3. Tectonic evolution of the western Mediterranean from 200 - 30 Ma. .......7 1.4. Paleotectonic reconstructions of the western Mediteranean..................12 1.5. GPS velocity vector map. ......................................................................15 1.6. Seismicity Map. ....................................................................................16 2.1. Geologic map of the Middle Atlas Mountains..........................................20 2.2. ASTER band combination image with bands 7-3-1. ..............................29 2.3. Shortwave infrared spectral reflectance curves.....................................30 2.4. ASTER image composed of principal components 4, 5, and 6..............31 2.5. Geologic map of the Middle Atlas study area. .......................................34 2.6. Bedding Measurements.........................................................................36 2.7. Exposure of the Ait Oufella Fault in a road cut. .....................................38 2.8. Fault kinematic data ..............................................................................39 2.9. Balanced cross section..........................................................................41 3.1 Longitudinal Stream and terrace profiles ...............................................48 3.2. Field photograph of the composite scarp...............................................51 3.3. Field photograph of the singe event scarp.............................................52 3.4. 1 meter digital elevation model of the composite scarp. ........................54 3.5. 0.5 meter digital elevation model of the single event fault scarp............56 3.6. Single event fault scarp profile 1............................................................62 v 3.7. Single event fault scarp profile 2............................................................63 3.8. Single event fault scarp profile 3............................................................64 3.9. Single event fault scarp profile 4............................................................65 3.10. Root mean square analysis for D variable...........................................68 3.11. Composite fault scarp degradation model ...........................................69 vi LIST OF TABLES Table 2.1 Performance parameters for the ASTER radiometer....................26 Table 3.1 Radiocarbon age data ..................................................................57 vii RECENT FAULTING AND ACTIVE SHORTENING OF THE MIDDLE ATLAS MOUNTAINS, MOROCCO, WITHIN THE DIFFUSE AFRICAN-EURASIAN PLATE BOUNDARY Michael Rigby Dr. Francisco Gomez Thesis Supervisor ______________________________________________________________ Abstract The intracontinental Atlas Mountains of northwest Africa are prominent tectonic elements in the broader, diffuse plate boundary zone between the converging African and Eurasian plates in the western Mediterranean. Cenozoic geology, as well as present-day seismicity, document co-eval tectonism across a zone more than 500 kilometers in width. Hence, quantifying the rates of deformation in the Atlas Mountains is necessary in understanding the distribution of crustal deformation across the entire plate boundary zone. This study focuses on constraining the recent shortening rate across the NE-SW striking Middle Atlas Mountains, which are obliquely oriented to the NNW-SSE direction of Late Cenozoic plate convergence. Both strike-slip and contractional structures are exhibited with apparent slip partitioning: folding and thrusting is concentrated in the Folded Middle Atlas, whereas strike-slip dominates
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