Insights on the Interplay of Rifting, Transcrustal Magmatism and Formation of Geothermal Resources in the Central Segment of the Ethiopian Rift Revealed by 3‐D Magnetotelluric Imaging

Abstract

The East African Rift system (EARS) is a prominent continental rift that shaped the landscape of East Africa, including the East African Plateau, rift valleys and numerous volcanoes. Rifting and rift-related volcanism in East Africa played a role in early human evolution (King & Bailey, 2006) and to this date affect the life of humans due to volcanic hazards (Biggs et al., 2021), but also by providing rift-associated natural resources, including geothermal energy resources (Benti et al., 2023;Burnside et al., 2021). A large number of studies, especially in the northern part of the EARS, which includes the Main Ethiopian Rift (MER), have provided a wealth of information Abstract The Main Ethiopian Rift is accompanied by extensive volcanism and the formation of geothermal systems, both having a direct impact on the lives of millions of inhabitants. Although previous studies in the region found evidence that asthenospheric upwelling and associated decompression melting provide melt to magmatic systems that feed the tectono-magmatic segments in the rift valley, there is a lack of geophysical models imaging these regional and local scale transcrustal structures. To address this challenge, we use the magnetotelluric method and image subsurface electrical conductivity to examine the magmatic roots of Aluto volcano, quantify and interpret the melt distribution in the crust considering established concepts of continental rifting processes and constrain the formed geothermal system. Specifically, we combined regional (maximum 30 × 120 km 2 ) and local (15 × 15 km 2 ) magnetotelluric data sets and obtained the first multi-scale 3-D electrical conductivity model of a segment of the central Main Ethiopian Rift. The model unravels a magma ponding zone with up to 7 vol. % melt at the base of the crust (30-35 km b.s.l.) in the western part of the rift and its connection to Aluto volcano via a fault-aligned transcrustal magma system. Melt accumulates at shallow crustal depths (≥4 km b.s.l.), thereby providing heat for Aluto's geothermal system. Our model suggests that different volcano-tectonic lineaments in the rift valley share a common melt source. The presented model provides new constraints on the melt distribution below a segment of the rift which is important for future geothermal developments and volcanic hazard assessments in the region.Plain Language Summary Continental rifting is a fundamental process of plate tectonics that breaks continents apart to ultimately form new oceans. The landscape of the Main Ethiopian Rift is characterized by abundant volcanism and hot springs, which indicate the presence of geothermal resources formed by magmatic heating of subsurface fluids. Here we present a new 3-D subsurface electrical conductivity image of the magmatic system and geothermal reservoir beneath the Aluto volcano in the Main Ethiopian Rift. The model allows us to estimate the amount and distribution of magmatic melt. This is the first model that provides a high-resolution image of the entire magmatic system below a centr...

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).…”

Role of metasomatism in the development of the East African Rift at the Northern Tanzanian Divergence: Insights from 3D magnetotelluric modelling.

“…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 (Hübert et al, 2018;Meju & Sakkas, 2007;Dambly et al, 2023). This may reflect magmas and fluids exploiting pre-existing, lithosphere-scale weakness zones (Acocella, 2014;Muirhead & Kattenhorn, 2018).…”