The deep structure and dynamics of the East African Plateau, the Kenya Dome and the Gregory Rift

Abstract

Evidence relating to the topography, structure and origin of the East African Plateau, the Kenya Dome and the Rift Valleys between 5°N and 10°S is reviewed. Recent activity of the region is indicated by various data, including oceanic magnetic anomalies, transform fault trends, seismicity, volcanicity, and the warping of erosion surfaces. Global analyses of plate motions show that the African plate has been moving NE for the last 5 my at about 1 cm/yr. It is more difficult to estimate the rate of separation across the African Rifts but it is clear that it is much lower. The study of palaeoerosion surfaces shows that there has been uplift of up to 1500 m in at least three phases since the Cretaceous. The quality and distribution of seismic and gravity data for the region are uneven but suggest that the crustal structure outside the Eastern Rift is normal, but is anomalous along the axis of this rift which is at its optimum development where uplift is greatest. The region of plateau uplift is associated with a long wavelength negative gravity anomaly which is most easily explained in terms of a thinned lithosphere. Uplift, rifting and associated seismicity at the edges of the plateau may be attributed to convection in the asthenosphere and/or deviatoric stesses caused by lithospheric thinning.