Listric growth faults in the Kenya Rift Valley |
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| Institution: | 1. IPL, ISEL - Instituto Superior de Engenharia de Lisboa, Physics Department, Lisboa, Portugal;2. Instituto Dom Luiz (IDL - Universidade de Lisboa), Portugal;3. Paléomagnétisme, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, University Paris Diderot and UMR 7154 CNRS, 4 Av. de Neptune, 94107 Saint-Maur cedex, France;4. Faculdade de Ciências da Universidade de Lisboa, Lisboa, Portugal;5. GEOPS, Univ. Paris-Sud, CNRS, Université Paris-Saclay, Rue du Belvédère, Bât. 504, 91405 Orsay, France;6. Instituto Português do Mar e da Atmosfera, Lisboa, Portugal;7. Centro de Geofísica de Évora and Dep. de Geociências da Univ. de Évora, R. Romão Ramalho, 59, 7000-671 Évora, Portugal;8. Estrutura de Missão para a Extensão da Plataforma Continental, Paço de Arcos, Portugal;9. University of Azores, Department of Geosciences, Rua da Mãe de Deus, 9501-801 Ponta Delgada, Portugal;10. Institute of Geophysics, Acad. of Sci. of the Czech Republic, Prague, Czech Republic;1. Geology Department, Macalester College, St. Paul, MN 55105, USA;2. Department of Geography-Geology, Illinois State, University, Normal, IL, USA;3. School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, AZ, USA;4. Department of Natural & Applied Sciences, University of Wisconsin-Green Bay, 2420 Nicolet Drive, Green Bay, WI 54311, USA;5. ExxonMobil Exploration, Houston, TX, USA;6. Department of Geography-Geology, Illinois State University, Normal, IL, USA;7. Department of Geology, University of Alberta, Edmonton, Alberta, Canada;1. Centre for Tectonics, Resources and Exploration (TRaX), School of Physical Sciences, University of Adelaide, SA 5005, Australia;2. Petroleum Geophysics MSc Program, Department of Geological Sciences, Chiang Mai University, Chiang Mai, Thailand;1. Department of Earth Sciences, HPT laboratory, Utrecht University, The Netherlands;2. School of Earth & Ocean Sciences, Cardiff University, UK;3. Geography and Earth Sciences Department, University of Malawi, Zomba, Malawi;4. Department of Earth Sciences, Malawi University of Science and Technology, Limbe, Malawi |
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| Abstract: | Many of the major faults in the Kenya Rift Valley are curved in section, were active over considerable periods and form sets which are related in space and time. They can, therefore, be regarded as systems of listric growth faults. The Elgeyo Fault marks the western limit of rift structures at this latitude and displaces the basement surface by up to about 6 km. The Kamasia Hills are a block rotated above this fault plane. Movement on the Elgeyo Fault has been grossly continuous since at least 16 Ma ago but deposition of volcanics and sediments has generally kept pace with the growth of the escarpment. The Kaparaina Arch is a rollover anticline on the downthrown side of the Saimo Fault on the eastern side of the Kamasia Hills. On the eastern side of the rift, the block between the Bogoria and Wasages-Marmanet Faults has shown continued rotation since about 15 Ma. The Pleistocene lavas on the rift floor here show rollover into the Bogoria Fault and have formed a facing near the top of the escarpment. Area balancing calculations suggest depths to décollement of 25 km for the Elgeyo Fault, 6 km for the Saimo Fault and 12 km for the Bogoria Fault. The most direct evidence for the listric nature of the faults is provided by microearthquakes near Lake Manyara which appear to lie on fault planes connected to surface escarpments. |
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