A MODEL FOR THE 3-DIMENSIONAL EVOLUTION OF CONTINENTAL RIFT BASINS, NORTHEAST AFRICA

Large areas of north-east Africa were dominated by regional extension in the Late Phanerozoic. Widespread rifting occurred in the Late Juras sic, with regional extension culminating in the Cretaceous and resulti ng in the greatest areal extent and degree of interconnection of the w est, central and north African rift systems. Basin reactivation contin ued in the Paleocene and Eocene and new rifts probably formed in the R ed Sea and western Kenya. In the Oligocene and Early Miocene, rifts in Kenya, Ethiopia and the Red Sea linked and expanded to form the new e ast African rift system. This complex history of rifting resulted in f ailed rift basins with low to high strain geometries, a range of assoc iated volcanism and varying degrees of interaction with older structur es. One system, the Red Sea rift, has partially attained active seaflo or spreading. From a comparison of these basins, a general model of th ree-dimensional rift evolution is proposed. Asymmetrical crustal geome tries dominated the early phases of these basins, accompanied by low a ngle normal faulting that has been observed at least locally in outcro p. As rifting progressed, the original fault and basin forms were modi fied to produce larger, more through-going structures. Some basins wer e abandoned, others experienced reversals in regional dip and, in gene ral, extension and subsidence became focused along narrower zones near the rift axes. The final transition to oceanic spreading was accompli shed in the Red Sea by a change to high angle, planar normal faulting and diffuse dike injection, followed by the organization of an axial m agma chamber.