Collaborative Research: Structure and Kinematics of an Accommodation Zone within the Evolving Afar Triple Junction, Central Afar (Ethiopia and Djibouti)

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This study will examine the structure and late Cenozoic tectonism in the Afar region (East Africa) in an effort to decipher the neotectonic framework of an active rift-rift-rift triple junction. The interaction between the Gulf of Aden and Red Sea rifts may have led to the development of a large scale accommodation zone that presently is marked by half grabens and tilted fault blocks in central Afar. Understanding the partitioning of extension across Afar rift will provide insight into the evolution of rift-rift-rift triple junctions and continental rifting, in general. Comparison of long-term (Quaternary) deformation with more recent kinematics (e.g., from late Pleistocene landforms and available GPS observations) provides an initial means of assessing the evolution of the accommodation zone (e.g., co-axial strain versus progressive strain and rotation). The structure and tectonics of central Afar will be investigated from remote sensing data and field studies to better understand the linkage between the Red Sea and Gulf of Aden rift propagators into central Afar. In particular, the research will focus on the Afar Stratoid volcanic rocks (approximately 4.0 to 1.0 Ma), a regionally extensive lava surface that predates the initiation of grabens in central Afar. ALOS PRISM & PALSAR data will be utilized to generate high resolution digital topographic base maps, and ASTER & AVNIR-2 images will be used to discriminate geomorphic and lithologic features. Field observations will provide ground-truth verification for the remote-sensing-based regional mapping. Investigations will involve local mapping of the geological structure, Quaternary geology, and geomorphology. This activity will constrain the geometry of fault-related landforms and other landscape elements that could provide markers of recent tectonic activity. Field investigations will also document and measure basic structural data. Combining structural and neotectonic analyses, we aim to accomplish the following: 1) determine the presence of an accommodation zone between the propagating Red sea and Gulf of Aden rifts; 2) constrain structural geometries and the viability of a regional datum for restoration; 3) document the contribution of small faults to regional strain; 4) estimate horizontal extension across part of the central Afar; and 5) assess late Pleistocene tectonic landforms as kinematic indicators and potential for estimating rates.The Afar region encompasses the only sub-aerial exposure of a rift-rift-rift triple junction and, hence, affords a unusual opportunity to study the extensional tectonism from the early break-up of continents to seafloor spreading. Present-day extension across the Afar is accommodated by magmatic, axial rift zones (the Red Sea and Gulf of Aden propagators and the main Ethiopian Rift), and amagmatic extension across the intervening region in between. As an exploratory project this work will facilitate the development of new international collaborations between US universities and colleagues in Ethiopia and Djibouti. As with neotectonics studies, in general, results will contribute to a more informed assessment of the earthquake hazard in the region, although implementing that link is beyond the scope of this pilot study. Although the Afar region is sparsely populated urban and infrastructure development including dam and irrigation schemes, large scale commercial farms, roads, and railway lines have taken place. Past earthquakes including the Serdo (1969) and Dobe (1989) in central Afar have disrupted road networks that provide Ethiopia access to the sea.This project is supported by the Earth Sciences Division Tectonics Program and the NSF Office of International Science and Engineering.