Gravity study of the crustal structures of Somalia along International Lithosphere Program geotransects

Abstract

Gravity data have been used to examine the crystalline basement morphology along five geotransects in Somalia defined by the Global Geotransect Project (Monger 1989). The gravity data were digitized from the 1:1 000 000 Gravity Anomaly Map of Somalia produced by the African Gravity Project. After the removal of the non-crustal wavelength anomalies from the observed gravity field, the remaining gravity anomalies were interpreted in terms of 2.5D crustal models. Available geophysical and well data, and other geological information, were used as constraints for the construction of the crustal sections. Mean densities varying from 3.30 to 3.15 g cm −3 were used for dense bodies observed on the lower continental crust of the southern Somali basins. A density of 3.00 g cm −3 was given to the oceanic crust offshore. The density of the crystalline basement and the overlying sediments were, respectively, assumed to be 2.85 g cm −3 and 2.46 g cm −3. Coherent and incoherent marine sediments were given densities varying from 1.70 g cm −3 to 2.30 g cm −3. The results of the 2.5D gravity modelling indicate that the basement beneath the southern Somali basins is partially or totally transformed to denser material and that, just a few hundred kilometres offshore from Somalia, the basement is of an oceanic nature.