Evolution of Eastern Afar and the Gulf of Tadjura

Abstract The structure of the Gulf of Tadjura has previously been interpreted in conformity with a model derived chiefly from seismic and magnetic data. This model comprises an en-echelon axial valley of ENE-WSW, Gulf of Aden trend, offset by NE-SW transform faults. Such a structure implies a transition between the Gulf of Aden oceanic ridge and an emerged rift system in Central Afar. This model is now questioned. It is suggested, based on tectono-volcanic features which have been mapped and dated onshore and which extend offshore into the Gulf of Tadjoura, that continental crust underlies the Gulf as well as the surrounding area of Eastern Afar. Each of the main events in the geodynamic evolution of this area has created a set of brittle structures with a specific trend. NNW-SSE (Red Sea) and associated NE-SW trends have a Miocene age. Some of the NE-SW trending fractures were reactivated by shearing during Lower Pleistocene time, creating a NW-SE horst-and-graben block system. An E-ENE (Aden rift) trend controls the Middle Pleistocene to Recent geodynamics, both on and offshore in the Gulf of Tadjura. This new analysis of the structural evolution of Eastern Afar provides further evidence for a 3-stage evolutionary model of the region, with the Pleistocene events now more clearly defined.