The ARGeo geophysical model of the Tendaho geothermal field, Ethiopia

The Dubti and Ayrobera geothermal systems are located in the Tendaho Graben (Afar region, Ethiopia). As part of the ARGeo 2014 program, we have integrated the available geophysical data set with new measurements. The new residual magnetic anomaly map has been used to map the younger (<0.78 Ma) normal polarity basalt distribution and infer the location of the main rift axis hindered by sediments. The bedrock surface obtained by 3D inversion of the gravity residual anomaly gives a first order insight on the geometry of the graben. The graben sediments are marked by a shallow electrical conductor, with exceptionally low resistivities <1 Ohm m, mainly ascribed to low temperature clay alteration. Local resistivity variations are due to basalt interlayerings and coarser components. Resistivity 2D inversion models show a deep conductive anomaly that has been previously mapped and interpreted as an upper crustal fracture zone that lies above a 15 km wide area of partial melt . The new magnetotelluric data acquired to the South of Dubti manifestations indicate that the conductive anomaly is shallower and more intense to the South and approximately centred below the anomalous stripe of recent dikes/intrusions.