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Zwaan, F.; Corti, G.; Sani, F.; Keir, D.; Muluneh, A. A.; Illsley‐Kemp, F.; Papini, M.
Tectonics, July 2020, 2020-07-00, 20200701, Letnik: 39, Številka: 7Journal Article
The Afar region in East Africa represents a key location to study continental breakup. We present an integrated structural analysis of the Western Afar Margin (WAM) aiming to better understand rifted margin development and the role of plate rotation during rifting. New structural information from remote sensing, fieldwork, and earthquake data sets reveals that the N‐S striking WAM is still actively deforming and is characterized by NNW‐SSE normal faulting as well as a series of marginal grabens. Seismicity distribution analysis and the first‐ever borehole‐calibrated sections of this developing passive margin show recent slip concentrated along antithetic faults. Tectonic stress parameters derived from earthquake focal mechanisms reveal different extension directions along the WAM (82°N), in Afar (66°N) and in the Main Ethiopian Rift (108°N). Fault slip analysis along the WAM yields the same extension direction. Combined with GPS data, this shows that current tectonics in Afar is dominated by the local rotation of the Danakil Block, considered to have occurred since 11 Ma. Earlier stages of Afar development (since 31–25 Ma) were most likely related to the large‐scale rotation of the Arabian plate. Various authors have proposed scenarios for the evolution of the WAM. Any complete model should consider, among other factors, the multiphase tectonic history and antithetic fault activity of the margin. The findings of this study are not only relevant for a better understanding of the WAM but also provide insights into the role of multiphase rotational extension during rifting and passive margin formation in general. Plain Language Summary The Earth's continents are in gradual but perpetual motion, driven by large plate tectonic forces in the Earth's deep interior. A crucial process is the stretching and breaking up of continents, initially forming localized rift or graben depressions, followed by the opening of a new ocean flanked by the margins of the newly divided continents (passive margins). Rifts and passive margins are important because of their vast resource potential (e.g., oil, gas, geothermal energy), but pose also severe risks (volcanism, earthquakes, and landslides) since they are often home to large populations. We focus on the Western Afar Margin in Ethiopia, where the African continent is currently splitting apart, providing a unique research opportunity. In the framework of an international collaborative effort, we combined satellite imagery, topography data, field observations, GPS, and earthquake measurements in order to map out the present‐day geology and tectonic activity along the margin. Our results show the complexity of tectonic plate movements: We find evidence for two phases of continental stretching in Ethiopia that both involve the rotation of tectonic plates. We also observe active faulting, which may help to assess seismic risks in the area. Our study helps to better understand passive margins worldwide. Key Points Structural, borehole, and seismicity data from the Western Afar Margin serve to study continental breakup processes and rotational rifting Antithetic faults bounding marginal grabens are currently accommodating significant deformation along the margin Current extension is due to rotation of the Danakil Block; a previous oblique extension phase was likely related to Arabian plate motion
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