Geophysical controls on sedimentation within the African Rift Systems

Summary Gravity and seismological data are used, together with unpublished oil company data, to investigate the lithospheric structures associated with the East, and the West and Central African Rift Systems. Although these two rift systems are the result of extensional tectonics, they appear to be tectonically very different, with uplift and volcanism in East Africa, and subsidence and sedimentation in West and Central Africa. These differences can be explained in terms of the amounts of crustal extension (and thinning) that these rift systems have undergone and the isostatic response of these crustal structures during, and subsequent to, the extensional phase. In West and Central Africa, gravity modelling indicates crust extensions in the order of 70 km, while in East Africa extension across the Kenya Rift could be as little as 10 km. The implications of these lithospheric models for the formation of sedimentary basins are discussed, as well as how the rift structures relate to the crustal structure of continental margins.