Seaward extension of the East African Rift

The continental margin of northern Mozambique is edged by a north-south trending alignment of submarine peaks forming the Davie Ridge (Fig. la). From earlier studies^1-5, the ridge has been interpreted as a remnant transform fault that controlled the late Jurassic/early Cretaceous drift of Madagascar and the opening of the Somali Basin^6-8. During MD40-MACAMO cruise (June 1984), 7,500 km of water gun seismic reflexion lines have been implemented throughout the region where two flat-bottomed troughs, the north-south trending Kerimbas and Lacerda deep grabens, interrupt the continental slope alongside the ridge. These grabens cut into Tertiary sediments correspond westward, to a Miocene tilting or a recent normal fault; and eastward, to an old discontinuity several times reactivated and located above an abrupt uplift of the Moho. The two grabens are separated from each other by a rigid region of thickened crust, affected by intense seismicity and supporting volcanoes. We report here that the eastern branch of the East African Rift joins the submerged grabens across the Tanzanian continental shelf (Fig. 1b).