Tomography-Based Convection and Melt Generation Beneath the Rungwe Volcanic Province, East Africa

Within the Western Branch of the East African Rift (EAR), volcanism is highly localized, which is distinct from the voluminous magmatism seen throughout the Eastern Branch of the EAR. Voluminous magmatism in the Eastern Branch results from plume-lithosphere interactions, but the origin of magmatism in the Western Branch remains enigmatic. Previous investigations of melt generation beneath the Rungwe Volcanic Province (RVP), the southernmost volcanic center in the Western Branch, suggest plume materials are present. Here, we develop a model of tomography-based convection (TBC) with melt generation to test the hypothesis that melt beneath the RVP is sourced from plume materials. To test our hypothesis, we use seismically constrained lithospheric thickness and sublithospheric mantle structure to develop a fully adiabatic 3D thermomechanical model of TBC with melt generation using ASPECT. We test a range of mantle potential temperatures and find values ranging from 1250-1350 °C are unable to generate melt beneath the RVP. However, when the sublithospheric mantle temperature is increased by ~250 K based on constraints from shear wave velocity anomalies, decompression melt generation occurs at a maximum depth of ~150 km beneath the RVP. Our work suggests that excess sublithospheric mantle temperatures are necessary for melt generation beneath the RVP, and that shear wave velocity anomalies can provide a first order estimate of these anomalous mantle conditions. Excess sublithospheric mantle temperature in the RVP suggests the influence of a plume-source for the seismic anomalies and supports existing geochemical interpretations of a mantle plume contribution to magmatism in the RVP.