The interplay of rifting, magmatism and formation of geothermal resources in the Ethiopian Rift constrained by 3-D magnetotelluric imaging

Abstract

The Main Ethiopian Rift (MER) is accompanied by extensive volcanism and the formation of geothermal systems, both having an imminent impact on lives of millions of local inhabitants. Although previous studies from the region found evidence that asthenospheric upwelling and associated decompression melting provide melt to magmatic mush systems that feed the tectonovolcanic segments in the rift valley, no geophysical model imaged these regional and local scale transcrustal structures within a single comprehensive 3-D model. To fill this gap, we combined regional and local magnetotelluric data sets to obtain the first multi-scale 3-D electrical conductivity model of the central MER. The model clearly images a magma ponding zone with up to 7 vol.% melt at the base of the crust in the western part of the rift, its connection to Aluto volcano via a tectonically controlled transcrustal magmatic mush system and how the melt, stored at shallow crustal depths, supplies heat for Aluto's geothermal system. Our model provides evidence that different volcano-tectonic lineaments in the rift valley share a common melt source, which has been debated in the past. The presented multi-scale model provides new constraints as well as geologic insights into the melt distribution below the rift and will facilitate future geothermal developments and volcanic hazard assessments in the MER.

Role of Metasomatism in the Development of the East African Rift at the Northern Tanzanian Divergence: Insights From 3D Magnetotelluric Modeling

“…Unveiling the nature of magma/fluid infiltration at the trans‐lithospheric scale may help us elucidate the processes related to magma generation, how magmas travel to the surface and what kind of compositional effects magmatic events have on the lithosphere. In our models, the rift zone is electrically heterogeneous (Figure 5), as has been observed in previous MT models of the East African Rift (Dambly et al., 2023; Hübert et al., 2018; Meju & Sakkas, 2007). This may reflect magmas and fluids exploiting pre‐existing, lithosphere‐scale weakness zones (Acocella, 2014; Muirhead & Kattenhorn, 2018).…”