Cenozoic volcanism and riftdevelopment in Ethiopia

Abstract

The distribution, K-Ar ages and the chemistry of the Cenozoic volcanic rocksin Ethiopia have been interpreted as indicative of a progressive, lateral migration of volcanism from the bordering plateaux to the Ethiopian Rift, i.e. Afar and the Main Ethiopian Rift (MER), in response to the down-warping of the latter. In this report, it is shown that the volcanism in Ethiopia is fixed in space and that at each place it occurred as a consequence of elongate doming, the longer size of which probably did not exceed 225 km. Rifting may or may not follow the doming depending on the boundary conditions. Four domally uplifted regions have been identified, three of which evolved into the MER. The fourth is a well documented dome that gave rise to the Chew B ahir Rift in southwestern Ethiopia. The presence of other similar structures is discussed and it is concluded that the Ethiopian Rift formed by the coalescence of small and discrete rift systems.