Mapping the Crust-Mantle Boundary Beneath Afar Depression

Abstract

The funnel-shaped Afar depression in the Horn of Africa situated at the separation zones of the Nubian, Somalian and Arabian plates, represents a triple junction between the Main Ethiopian Rift, the Red Sea and Gulf of Aden rifts. This depression occupies an important place in that it is the only emerged triple junction in the world. Assuming that the mechanism of compensation is one in which the topography is regionally compensated by the flexuring of the elastic plate and that linear relationship exists between the gravity field of the compensation and the topography isostatic correction, isostatic anomaly and Moho depth maps are computed for the depression. The results show that nonlinear elements are small in Afar and hence the crust-mantle interface beneath Afar modelled using admittance technique compares very well with the existing seismic results. The results also show that there is crustal attenuation to the north and east and that there is an under compensation in the north that may be due to the upwelling of mantle material along the active axis.