Investigating Potential Melt Sources for the Magma-Poor Albertine-Rhino
Graben of the East African Rift System Using 3D Geodynamic Modeling with
ASPECT
Abstract
The leading paradigm for rift initiation suggests “magma-assisted
(wet)” rifting is required to weaken strong lithosphere such that only
small tectonic stresses are needed for rupture to occur. However, there
is no surface expression of magma along the 300 km long Albertine-Rhino
Graben (except at its southernmost tip within the Tore Ankole Volcanic
Field), which is the northernmost rift in the Western Branch of the East
African Rift System. The two prevailing models explaining magma-poor
rifting are: 1) Melt is present at depth weakening the lithosphere, but
it has not reached the surface or 2) far-field forces driving extension
are accommodated along weak pre-existing structures without melt at
depth. The goal of this study is to test the hypothesis that melt is
generated below the Albertine-Rhino Graben from Lithospheric Modulated
Convection (LMC) using the 3D finite element code ASPECT. We develop a
regional model of a rigid lithosphere and an underlying convecting
sublithospheric mantle that has dimensions 1000 by 1000 by 660 km along
latitude, longitude, and depth, respectively. We solve the Stokes
equations using the extended Boussinesq approximation for an
incompressible fluid which considers the effects of adiabatic heating
and frictional heating. We include latent heating such that we can test
for melt generation in the sublithospheric mantle from LMC. Using
LITHO1.0 as the base of our lithosphere, our preliminary results suggest
melt could be generated beneath the Albertine-Rhino graben given a
mantle potential temperature of 1800 K. These early results indicate LMC
can generate melt beneath the northernmost Western branch of the East
African Rift System.