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

NSFGEO-NERC合作研究：肯尼亚和埃塞俄比亚图尔卡纳凹陷地壳和地幔结构及伸展表现

• 批准号: 1824199
• 负责人: Rebecca Bendick
• 金额: $ 35.51万
• 依托单位: University of Montana
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-09-01 至 2022-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1824199&HistoricalAwards=false
• 关键词: NSFGEO; NERC; Collaborative; Research; Crust

The basic idea of plate tectonics is built on a simplified view that the lithosphere (the outermost layer of the solid earth) is broken into rigid pieces that drift around relative to each other without deforming internally, like puzzle pieces that are moved around to make a picture but don't themselves change shape or size. 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. This experiment is focused on quantifying the role of three different factors in influencing plate break-up: preexisting structures in the lithosphere; present topography; and the convecting mantle beneath. The Turkana Depression of northern Kenya and southern Ethiopia is an ideal place to investigate these issues: it is probably the location where anomalous mantle first interacted with the African lithosphere to produce magma, it has considerable inherited structure, and it has very little topography compared to adjacent parts of the rift. The scientific and broader impacts of this project are significant. An international team supported by the U.S. National Science Foundation and the U.K. Natural Environment Research Council and including scientists from the US, UK, Kenya, and Ethiopia will undertake both field observations and scientific computing. The work will support graduate and undergraduate students at the two collaborating US institutions. Knowing how new plate 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 East African Rift System (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. This project involves a multi-method geophysical 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. Systematic comparisons of the data products to one another, combined with 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. Such constraints on the dynamics of rifting will, in turn, enable a better understanding of 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.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

板块构造学的基本思想建立在一个简化的观点上，即岩石圈（固体地球的最外层）被分解成刚性的碎片，这些碎片相互漂移，内部不会变形，就像拼图一样，它们被移动来制作图片，但本身不会改变形状或大小。 一旦碎片的边界发育良好，这可以很好地捕捉碎片的运动，但不能解释碎片是如何首先形成的，例如非洲碎片是如何沿着东非裂谷系统分成几个部分的。 这个实验的重点是量化的三个不同的因素在影响板块分裂的作用：岩石圈中的预先存在的结构，目前的地形和对流地幔下面。 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问题的理想地点：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地方，它具有相当大的继承性结构，与裂谷的邻近部分相比，它的地形非常小。 该项目的科学和更广泛的影响是重大的。一个由美国国家科学基金会和英国支持的国际团队自然环境研究理事会和包括来自美国，英国，肯尼亚和埃塞俄比亚的科学家将进行实地观察和科学计算。 这项工作将支持美国两个合作机构的研究生和本科生。了解新的板块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、和岩浆作用决定了大陆板块边界如何随时间演化。 东非裂谷系统（EARS）是裂谷过程的理想天然实验室。 例如，由于整个EARS的远场边界条件相同，因此对富熔体和贫熔体部分的应变调节进行系统比较，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。该项目涉及对图尔卡纳凹陷进行多种方法的地球物理调查，结合地震成像、震源机制、地表运动学、地壳应变率和结构体系的地震和大地测量数据收集。系统的数据产品相互比较，结合大地测量，结构和地震数据的逆模型和有限的正向数值模拟裂谷地形和应变模式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。这种对裂谷动力学的制约反过来又能更好地理解岩石圈和地幔之间的物质和热量交换，长时间尺度的大陆构造板块和边界行为，该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识产权进行评估来支持。优点和更广泛的影响审查标准。

项目成果

Accommodation of East African Rifting Across the Turkana Depression

图尔卡纳凹陷东非裂谷的调节

• DOI: 10.1029/2019jb018469
• 发表时间: 2020
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: Knappe, E.;Bendick, R.;Ebinger, C.;Birhanu, Y.;Lewi, E.;Floyd, M.;King, R.;Kianji, G.;Mariita, N.;Temtime, T.
• 通讯作者: Temtime, T.

Body‐Wave Tomographic Imaging of the Turkana Depression: Implications for Rift Development and Plume‐Lithosphere Interactions

图尔卡纳凹陷的体波断层成像：对裂谷发育和羽流与岩石圈相互作用的影响

• DOI: 10.1029/2021gc009782
• 发表时间: 2021
• 期刊: Geosystems
• 作者: Kounoudis, R.;Bastow, I. D.;Ebinger, C. J.;Ogden, C. S.;Ayele, A.;Bendick, R.;Mariita, N.;Kianji, G.;Wigham, G.;Musila, M.
• 通讯作者: Musila, M.