Unraveling the Transcrustal Magmatic Mush and Geothermal Systems of Aluto and Corbetti Volcano in the Main Ethiopian Rift using Magnetotellurics

Active continental rifting in Ethiopia has led to formation of numerous volcanoes and geothermal systems with associated socio-economic potential for generating clean energy.

Aluto and Corbetti are two silicic volcanoes in the Central Main Ethiopian Rift (CMER) that have been closely examined. Past studies provided insights into their formation in the extensional magma-tectonic context of the CMER, into causes of volcanic unrest and surface deformation and seismic activity, as well as their geothermal systems. However, many aspects about the structure of the volcanoes’ underlying transcrustal magmatic system remained unanswered.

Here, we present new 3-D electrical conductivity models of these volcanoes, obtained from inversions of magnetotelluric (MT) data, providing the most detailed images of the associated magmatic and geothermal systems across multiple scales so far.

The models from Aluto and Corbetti provide evidence for several hypothesized properties of the associated magmatic systems. The cross-rift model, enclosing Aluto, shows that the volcano’s lower crustal melt source, west of the rift axis, also feeds volcanos in the western part of the rift, which has been debated in the past.  Our Corbetti model confirms the existence of a shallow magmatic intrusion, as it has been modelled from InSAR and gravimetry studies.

We estimate thermodynamically constrained melt fractions and interpret geothermal flow structures. The inferred melt fractions indicate crystalline magmatic mush systems in rheological lock-up, where melt is extracted slowly through buoyancy processes, while mechanical trapping explains the observed compositional gaps.