3D constrained inversion of gravity and magnetic data to image basement and plutonic bodies: A case study from Dood Arale Basin, eastern Somaliland

We present 3D inversion models derived from airborne gravity and magnetic data, which are constrained by seismic and well data, in the eastern Somaliland. The density model reveals a NW-SE trending basin, 125 km long and 25 km wide and named here as the Dood Arale Basin. The basin comprises two sub-basins separated by a basement high and is infilled by up to 2500 to 3200 m of sediments. Smaller and shallower sub-basins are also identified to the west of Lafaweyne and northeast of Dararweyne. The density model shows that the top basement in the platform areas is at about 1500 to 1700 m depth and shallows to around 300 m at Bur Anod, Hagraajin and Hagrin Ranges as well as northwest of Eil Afwein. The basement depths in these areas are more uncertain and could be deeper since they occur in areas of high gravity anomalies caused by a combination of near-surface high density sediments and high-density plutonic bodies within the basement. The susceptibility model indicates the basement consists of very weakly magnetized metasediments of the Inda Ad Complex intruded by three NE-SW trending magnetic bodies with upper surfaces at depths of about 300 to 3000 m. These magnetic bodies are interpreted as plutonic complexes of similar age and composition to the Lower Cretaceous syenite intrusions outcropping at Gorei in the Shilah Madu Range. Seismic reflection profiles image the sedimentary sequences but do not clearly map top basement or detect any of the plutonic bodies. The plutonic bodies could have controlled the location of the basin’s border faults and contributed to the high geothermal gradient recorded at the Faro Hills-1 well. The Upper Cretaceous Gumburo and Jesomma Formations in the basin could potentially have reached maturation close to and above the plutonic bodies within the center of the basin.