THE EAST AFRICAN RIFT SYSTEM

The East African Rift System is one of the most outstanding and significant rift systems on Earth and transects the high-elevation Ethiopian and East African plateaux. Rifting putatively developed as a result of mantle plume activity that initiated below East Africa. The rift is traditionally interpreted to be composed of two distinct segments: an older, volcanically active Eastern Branch and a younger, much less volcanic Western Branch. Rift-related volcanism commenced in the Eocene and a major phase of flood basalt volcanism occurred in Ethiopia by 31-30 Ma. Rift development in the Eastern Branch has a distinct northward progression with a juvenile rifting stage in northern Tanzania, well advanced rifting in Kenya and the transition of continental rifting to incipient sea-floor spreading in Ethiopia and Afar. The Western Branch in general has not yet progressed to an advanced rifting stage and rift basin architecture retains a pristine geometry. The onset of topographic uplift in the East African Rift System is poorly dated but has certainly preceded graben development. It is widely believed that topography has been caused by plume activity. The uplift of the East African Plateau might be connected to African Cenozoic climate change and faunal and human evolution.