Quaternary oblique extensional tectonics in the Ethiopian Rift (Horn of Africa)

he Ethiopian Rift extends in a northeasterly direction, from Southern Ethiopia to the Afar region. It shows a complex fault pattern, characterised by the interplay of a N30°E—N40°E-trending border fault system with the Quaternary Wonji Fault Belt, which is constituted by right-stepping en-echelon NS to N20°E trending faults. The Wonji Fault Belt affects mainly the rift floor, but it also overlaps with some segments of the margins. Its en-echelon arrangement indicates a left-lateral component of displacement along the rift trend. The general fault pattern of the Ethiopian Rift, as well as mesoscopic fault analyses and structural features of some key areas, indicate the occurrence of a roughly E—W extension, which is compatible with the sinistral shear component of motion along the rift. This paper proposes that oblique rifting related to the E—W direction of extension has been active since the beginning of the Quaternary and that it came after an earlier phase of roughly pure extension orthogonal to the rift trend.