Collaborative Research: Dry Rifting In the Albertine-Rhino graben (DRIAR), Uganda

地球表面不断移动，形状不断变化。在一些地方，比如东非，一个大陆延伸到断裂的地步，形成大陆裂缝，经过一段时间，可以形成新的海洋。大量研究表明，大陆裂谷是沿着岩浆深部侵入造成的弱化带发育的。然而，有些大陆裂谷的形成没有岩浆侵入的证据，被称为岩浆贫乏裂谷或“干”裂谷。在这个项目中，对东非裂谷系统的调查将沿着位于东非乌干达的西北分支进行，那里正在发生岩浆匮乏的裂谷作用。将收集广泛的地球物理、地质和地球化学观测资料，并对该地区进行数值模拟，以加深我们对这些岩浆贫乏的裂谷如何形成和演化的理解。在科学调查的同时，乌干达的合作伙伴将参与数据收集技术。乌干达和美国的研究生将参与，代表性不足的学生将得到指导，并将开发几个开放获取的数据集和模型产品。这项研究的社会意义包括用于油气勘探的裂谷模型的进步，对大陆裂谷期间进入大气的二氧化碳通量的改进估计，以及对与活动断层相关的地震危险的新见解。该项目的科学成果将部分通过面向公众的教育短片传播。大陆裂谷作用是板块构造范式的一个组成部分，然而关于岩浆-贫/干裂谷作用的物理过程的猜测仍然存在。该项目的目标是将地球物理、地质、地球化学和地球动力学技术结合应用于乌干达东非裂谷系统的西北分支，以测试3种假设：(1)在岩浆丰富的裂谷中，通过岩石圈熔体的减弱来调节应变；(2)在岩浆贫乏的裂谷中，地表以下存在熔体并使岩石圈减弱，从而在地壳上伸展过程中调节应变；(3)在岩浆贫乏的裂谷中，在深部不存在熔体，应变沿着原有的结构（如继承的成分、构造和流变非均质性）进行调节。本项目的观测方法包括：被动地震约束岩石圈结构和流动模式；重力约束地壳和岩石圈厚度的变化；磁学约束上地壳的热结构；大地电磁学约束岩石圈厚度和熔体的存在；GNSS用于约束地表运动、扩展率和帮助描述地幔流动；地质制图以记录活动断层的几何和运动学；裂谷内断层地震反射分析记录时间应变迁移量化温泉和气体中地幔源流体的地球化学；和地球动力学建模，以开发新的岩浆贫裂陷过程模型。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Earth’s surface is constantly moving and changing shape. In some places, like East Africa, a continent stretches to the point of breaking, forming continental rifts that, after a period of time, can form new oceans. Numerous studies show that continental rifts develop along weakened zones caused by deep intrusions of magma. Some continental rifts, however, form without evidence of magma intrusions and are known as magma-poor or "dry" rifts. In this project, an investigation of the East African Rift System will take place along the Northern Western Branch located in Uganda, East Africa where magma-poor rifting is taking place. A wide range of geophysical, geological, and geochemical observations will be collected, and numerical modeling of the region will be performed to advance our understanding of how these magma-poor rifts form and evolve. In conjunction with the scientific investigation, ]Ugandan partners will be engaged in data collection techniques. Ugandan and US graduate students will participate, underrepresented students mentored, and several open-access data sets and model products shall be developed. Societal implications of this study include advances in rifting models used for hydrocarbon exploration, improved estimates of CO2 flux into the atmosphere that occurs during continental rifting, and new insights into seismic hazards associated with active faulting. The scientific results of this project will be communicated, in part, through short educational videos geared towards public audiences. Continental rifting is an integral component of the plate tectonic paradigm, yet speculation remains about the physical processes involved in magma-poor/-dry rifting. The goal of this project is to apply a combination of geophysical, geological, geochemical and geodynamic techniques to the Northern Western Branch of the East African Rift System in Uganda to test 3 hypotheses: (1) in magma-rich rifts, strain is accommodated through lithospheric weakening from melt, (2) in magma-poor rifts, melt is present below the surface and weakens the lithosphere such that strain is accommodated during upper crustal extension, and (3) in magma-poor rifts, there is no melt at depth and strain is accommodated along pre-existing structures such as inherited compositional, structural, and rheological lithospheric heterogeneities. Observational methods in this project include: passive seismic to constrain lithospheric structure and flow patterns; gravity to constrain variations in crustal and lithospheric thickness; magnetics to constrain the thermal structure of the upper crust; magnetotellurics to constrain lithospheric thickness and the presence of melt; GNSS to constrain surface motions, extension rates, and help characterize mantle flow; geologic mapping to document the geometry and kinematics of active faults; seismic reflection analyses of intra-rift faults to document temporal strain migration; geochemistry to quantify mantle-derived fluids in hot springs and gases; and geodynamic modeling to develop new models of magma-poor rifting processes.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.