3D geological modelling of the Asal Ghoubbet Rift (Djibouti): New insights into fault geometry and stratigraphic formations for better geothermal resource assessment

The Asal-Ghoubbet Rift (Djibouti), less than 1 million years old, is marked by intense tectonic and magmatic activity, a thinned crust, and higher thermal gradients. These characteristics make it a promising target for high-temperature geothermal development, but the lack of sustainable assess to fluids is an important challenge. In this context, building a reliable 3D geological model is an essential first step to characterize the subsurface geometry and support future geothermal assessment. This study integrates borehole data, surface observations, geophysical surveys, and structural interpretations to construct a representative 3D geological model. Due to the uneven spatial distribution of data, the model is also constrained by four representative geological cross-sections that define the geometry of stratigraphic units and faults. Geological features were interpolated using the Discrete Smooth Interpolation (DSI) method implemented in SKUA/GOCAD®. The model identifies 17 steeply dipping normal faults (∼75°), oriented east or southeast, with near-pure extensional motion reaching depths of 3–5 km, consistent with seismological data. These faults divide the rift into structural blocks, which may influence hydrothermal fluid circulation. The modeled volcanic units, predominantly basaltic, generally have thicknesses below 600 m except for the Mabla complex and reflect continuous volcanism. The model also includes the brittle-ductile transition surface, interpreted as a major thermal boundary. Its reduced depth beneath the rift axis suggests a thermal anomaly likely related to crustal thinning and the presence of a shallow magmatic reservoir. This 3D model provides a valuable framework to guide future investigations and support more accurate assessments of the site geothermal potential. • First 3D structural model of the Asal- Ghoubbet Rift. • Construction of geological cross-sections representative of subsurface geological structures. • Identification of major fault zones that may control fluid circulation within the geothermal system. • New support for numerical simulations to enhance understanding of the Asal Rift geothermal system.