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.

National Science Foundation (NSF)
Division of Earth Sciences (EAR)
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Dennis Geist
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Midwestern State University
Wichita Falls
United States
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