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

这项研究将研究在阿法尔地区（东非）的结构和晚新生代构造作用，努力破译一个活跃的裂谷-裂谷-裂谷三联点的新构造框架。亚丁湾和红海裂谷之间的相互作用可能导致了一个大规模的调节带的发展，目前在阿法尔中部以半地堑和倾斜断块为标志。了解阿法尔裂谷伸展的划分将提供对裂谷-裂谷-裂谷三结点和大陆裂谷作用演化的一般认识。长期（第四纪）变形与近期运动学（例如，从晚更新世地貌和可用的GPS观测）提供了评估调节带的演变的初始手段（例如，同轴应变与渐进应变和旋转）。将通过遥感数据和实地研究调查阿法尔中部的结构和构造，以更好地了解红海和亚丁湾裂谷传播物与阿法尔中部之间的联系。特别是，该研究将侧重于阿法尔类层状火山岩（约4.0至1.0 Ma），这是一个区域性的广泛熔岩表面，早于阿法尔中部地堑的形成。ALOS PRISM PALSAR数据将用于生成高分辨率数字地形底图，ASTER AVNIR-2图像将用于区分地貌和岩性特征。实地观察将为基于遥感的区域制图提供地面实况核查。调查将涉及地质结构，第四纪地质和地貌的当地测绘。这种活动将限制断层相关地貌和其他景观元素的几何形状，这些地貌和景观元素可以提供近期构造活动的标志。实地调查还将记录和测量基本结构数据。结合构造和新构造分析，我们的目标是完成以下工作：1）确定扩展的红海和亚丁湾裂谷之间的调节带的存在; 2）限制结构几何形状和恢复区域基准面的可行性; 3）记录小断层对区域应变的贡献; 4）估计横跨阿法尔中部部分地区的水平延伸;阿法尔地区包含唯一的断裂-断裂-断裂三联点的近空中暴露，因此，提供了一个不寻常的机会来研究从大陆早期分裂到海底扩张的伸展构造作用。现今阿法尔地区的延伸受到岩浆、轴向裂谷带（红海和亚丁湾传播带以及主要的埃塞俄比亚裂谷）的影响，其间的无岩浆延伸则跨越了中间区域。作为一个探索性项目，这项工作将促进美国大学与埃塞俄比亚和吉布提同事之间新的国际合作的发展。与新构造学研究一样，总体而言，研究结果将有助于对该区域的地震危险进行更知情的评估，尽管实施这种联系超出了本试点研究的范围。虽然阿法尔地区人口稀少，但城市和基础设施的发展，包括水坝和灌溉计划，大规模的商业农场，道路和铁路线已经发生。过去的地震，包括Serdo（1969年）和Dobe（1989年）在阿法尔中部的地震，破坏了埃塞俄比亚通往海洋的道路网络。

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.