Abstract
Continental rifting is a critical component of the plate tectonic
paradigm, and occurs in more than one mode, phase, or stage. While
rifting is typically facilitated by abundant magmatism, some rifting is
not. We aim to develop a better understanding of the fundamental
processes associated with magma-poor (dry) rifting. Here, we provide an
overview of the NSF-funded Dry Rifting In the Albertine-Rhino graben
(DRIAR) project, Uganda. The project goal is to apply geophysical,
geological, geochemical, and geodynamic techniques to investigate the
Northern Western Branch of the East African Rift System in Uganda. We
test three 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 asthenospheric 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 identify and quantify
mantle-derived fluids in hot springs and soil gases; and geodynamic
modeling to develop new models of magma-poor rifting processes.
Fieldwork will begin in January 2022 and the first DRIAR field school is
planned for summer 2022. Geodynamic modeling work and morphometric
analyses are already underway.