SMOOTH AND ROUGH PROPAGATION OF SPREADING SOUTHERN RED-SEA - AFAR DEPRESSION

A compilation of the structural history of the southern Red Sea is presented and a new conceptual model for its evolution is suggested. According to this model, three major transverse, pre-rift structures control the "rough" and "smooth" propagations of the spreading axes of the Red Sea and Gulf of Aden and the general pattern of this rift system. In the southern Red Sea, between 15-degrees 30"N and 20-degrees-N, the crustal structure enables "smooth" propagation of spreading because of parallel ancient deep-seated structures. This condition changes at the southern end, where a transverse structure forms a terminus to the "smooth" propagation and the spreading axis "jumps" westward and splits into nine secondary axes; eight axial ranges in the Afar Depression and one south of the transverse structure in the Red Sea itself. The formation of the Afar Depression and the extremely elevated marginal plateaus with intensive fissure volcanic activity expresses the "rough" propagation southward of the spreading axis. The Afar Depression itself is composed of attenuated, partly oceanized, continental crust.