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

这项研究将研究阿法尔地区(东非)的构造和晚新生代构造作用，以努力破译活动的裂谷-裂谷-裂谷三联结的新构造格架。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可容纳带的发展，目前该带的特点是阿法尔中部的半地块和倾斜的断块。了解跨越阿法尔裂谷的伸展划分，将有助于洞察裂谷-裂谷-裂谷三重结合部和大陆裂谷的总体演化。长期(第四纪)形变与较新运动学的比较(例如，来自晚更新世地貌和现有的GPS观测)提供了评估调节带演化的初步手段(例如，同轴应变与渐进应变和旋转)。将从遥感数据和实地研究中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者进入阿法尔中部之间的联系。特别是，研究将侧重于阿法尔层状火山岩(约4.0至1.0 Ma)，这是一个区域广泛的熔岩表面，早于阿法尔中部地块的形成。ALOS PRISM&AMP；PALSAR数据将用于生成高分辨率数字地形图，ASTER&AMP；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测绘提供地面真实核实。调查将涉及地质结构、第四纪地质学和地貌的局部测绘。这一活动将限制与断层相关的地貌和其他景观要素的几何形状，这些要素可能提供最近构造活动的标志。实地调查还将记录和衡量基本的结构数据。结合构造和新构造分析，我们的目标是：1)确定红海和亚丁湾裂谷之间存在调节带；2)约束构造几何和区域恢复基准的可行性；3)记录小断层对区域应变的贡献；4)估计阿法尔中部部分地区的水平伸展；5)评估晚更新世构造地貌作为运动学指标和估算速率的潜力。阿法尔地区包含唯一的裂谷-裂谷-裂谷三合部的空中暴露，因此为研究从大陆早期解体到海底扩张的伸展构造作用提供了一个不同寻常的机会。今天跨越阿法尔河的延伸包括岩浆、轴向裂谷带(红海和亚丁湾传播带以及埃塞俄比亚的主要裂谷)，以及介于两者之间的岩浆延伸。作为一个探索性项目，这项工作将促进美国大学和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，总的来说，结果将有助于对该地区地震危险的更知情的评估，尽管实施这一联系超出了这项试点研究的范围。尽管阿法尔地区人口稀少，但包括大坝和灌溉计划在内的城市和基础设施发展，也出现了大规模的商业农场、道路和铁路线。过去的地震，包括阿法尔中部的Serdo(1969)和Dobe(1989)，扰乱了埃塞俄比亚通往大海的公路网。该项目得到了地球科学部构造计划和NSF国际科学与工程办公室的支持。

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.