NSFGEO-NERC: Crust and mantle structure and the expression of extension in the Turkana Depression of Kenya and Ethiopia

板块构造理论建立在一个简化的观点上，即岩石圈（固体地球的最外层）被分解成无限刚性的碎片，这些碎片彼此相对漂移，内部不会变形。一旦碎片的边界发育良好，这可以很好地捕捉碎片的运动，但不能解释碎片最初是如何形成的，例如非洲碎片是如何沿着东非裂谷系统（EARS）分成几个部分的。这个实验的重点是量化的三个不同因素的作用，影响板块的分裂：预先存在的结构和密度差异在岩石圈继承了很久以前的构造过程中，目前的地形，可能会提供潜在的能量分裂，并推动和拉动板块从运动的对流地幔下面。肯尼亚北方和埃塞俄比亚南部的图尔卡纳凹陷是研究这些因素的理想场所，因为它可能是异常地幔与非洲岩石圈相互作用产生岩浆的第一个位置，它有很多继承性结构，与裂谷的邻近部分相比，它的地形非常小。通过使用地震技术测量图尔卡纳岩石圈和地壳的详细特性，同时使用大地测量技术测量拉伸的速率和位置，我们可以比较三个因素中每一个在影响新板块边界的形成和演变方面的重要性。了解新的边界在空间和时间上是如何形成的，可以让我们更好地了解地球在其漫长历史中的构造演化，识别过去、现在和未来的板块边界，了解与构造边界相关的自然灾害，如地震、火山、力学能力、引力势、地幔动力学之间的非线性相互作用和岩浆作用决定了大陆板块边界如何随时间演化。EARS是研究裂谷过程的理想天然实验室。例如，由于整个EARS的远场边界条件是相同的，系统的比较，在熔体丰富和熔体穷人部门的应变调节阐明了加热和成分的作用。比较部门和没有大的横向材料不均匀性揭示了预先存在的岩石圈结构的作用，比较部门与不同的总有限应变可以作为代理的演变。然而，仍然需要考虑的是重力势能（GPE）的作用，通过一个裂谷部门在高地形，一个在低地形的比较。虽然地震和火山活动的图尔卡纳凹陷似乎代表了端员条件非常低的地形，非常高的物质异质性，并提高地幔地热，它还没有被详细调查与现代地球物理方法。我们提出了一个多方法的调查图尔卡纳凹陷，结合地震和大地测量数据收集地震成像，震源机制，地表运动学，地壳应变率和结构体系。这些数据的分析，大地测量，结构和地震数据和有限的正向数值模拟裂谷地形和应变模式的逆模型，将测试基本假设的作用，GPE和地壳结构在大陆裂谷。这样做将有助于解决长期的裂谷演化，特别是一个或两个地幔柱的作用，继承大陆结构从中生代裂谷，地形反馈，在促进和塑造大陆分裂。我们的目标是更好地了解岩石圈和地幔之间的质量和热量交换，长时间尺度的大陆构造板块和边界行为，以及与岩浆裂谷相关的灾害和资源的时空分布。

The theory of plate tectonics is built on a simplified view that the lithosphere (the outermost layer of the solid Earth) is broken into infinitely rigid pieces that drift relative to each other without deforming internally. This works well to capture the motions of pieces once their boundaries are well-developed, but doesn't explain how the pieces are made in the first place, such as how the African piece breaks into several parts along the East African Rift System (EARS). This experiment is focused on quantifying the role of three different factors in influencing plate break-up: preexisting structures and density contrasts in the lithosphere inherited from long past tectonic processes, present topography that may supply potential energy for breakup, and pushes and pulls on plates from motions of the convecting mantle beneath. The Turkana Depression of northern Kenya and southern Ethiopia is an ideal place to investigate the contribution of these factors because it is probably the location where anomalous mantle first interacted with the African lithosphere to produce magma, it has a lot of inherited structure, and it has very little topography compared to adjacent parts of the rift. By measuring the detailed properties of the lithosphere and crust in Turkana using seismic techniques and simultaneously measuring the rate and location of stretching using geodetic techniques, we can compare the importance of each of the three factors in influencing the initiation and evolution of a new plate boundary. Knowing how new boundaries form in space and time allows us to better understand the tectonic evolution of the planet over its long history, to identify past, current, and future plate boundaries, and to understand the natural hazards associated with tectonic boundaries, such as earthquakes and volcanos.Nonlinear interactions among mechanical competence, gravitational potential, mantle dynamics, and magmatism determine how continental plate boundaries evolve over time. The EARS, is an ideal natural laboratory for rifting processes. For example, because the far-field boundary conditions on the whole EARS are the same, systematic comparisons of strain accommodation in melt-rich and melt-poor sectors have illuminated the role of heating and composition. Comparing sectors with and without large lateral material heterogeneities has revealed the role of pre-existing lithospheric architecture; comparing sectors with different total finite strain can be used as proxies for evolution. What remains to be considered, however, is the role of gravitational potential energy (GPE) through a comparison of a rift sector in high topography to one in low topography. Although the seismically and volcanically active Turkana Depression appears to represent the end member conditions of very low topography, very high material heterogeneity, and elevated mantle geotherms, it has yet to be investigated in detail with modern geophysical methods. We propose a multi-method investigation of the Turkana Depression, combining seismic and geodetic data collection for seismic imaging, earthquake source mechanisms, surface kinematics, crustal strain rates, and structural architecture. Analysis of these data, and inverse models of geodetic, structural, and earthquake data and limited forward numerical simulations of rift topography and strain patterns will test basic hypotheses about the role of GPE and crustal architecture in continental rifting. Doing so will help to resolve the longer-term rift evolution, especially the role of one or two mantle plumes, inherited continental structure from Mesozoic rifting, and topographic feedbacks in contributing to and shaping continental breakup. We aim to better understand the exchange of mass and heat between the lithosphere and mantle, long timescale continental tectonic plate and boundary behavior, and the spatial and temporal distribution of hazards and resources associated with magmatic rifting.