Helmholtz Centre Potsdam
GFZ German Research Centre for Geosciences
Abstract (EDOC: 11621)
The crustal and uppermost-mantle structure of major units of the Afro-Arabian rift system has been consecutively investigated by seismic-refraction surveys in the Jordan-Dead Sea rift, the Red Sea, the Afar depression and the East African rift of Kenya. With the exception of the Jordan-Dead Sea transform, the entire Afro-Arabian rift system is underlain by anomalous mantle with Pn-velocities less than 8 km/s, while under the rift flanks the velocity is clearly equal to or above 8.0 km/s. Various styles of rifting have been found. Oceanic crust floors the axial trough of the southern Red Sea rift, thinned continental crust underlies the margins of the Red Sea as the Afar depression and the northern Kenya rift. On the other hand, 30–35-km-thick continental crust is found both under the Jordan-Dead Sea rift, where strike-slip rifting is active and thinning towards the Mediterranean occurs, and under the central Kenya rift, where updoming is apparently the controlling feature. While the transition from thinned continental to 5–6-km-thick oceanic crust in the centre of the Red Sea appears to be more gradual, the transition from rift-related structure to undisturbed continental crust of 40 ± 5 km thickness is mostly rather abrupt. The seismic data indicate various stages of rifting evidenced by different styles of crustal strucre and they imply the presence of heated uppermost-mantle under most parts of the rift system, possibly related to plume activity. Local volcanism may disrupt and/or underplate the crust in places, altering in particular the structure of the lower crust. Progressive thickening of the rifted crust away from the oceanized centres in the southern Red Sea and Gulf of Aden towards north and south may be viewed as an evolutionary sequence which, however, may be difficult to explain when viewing the Afro-Arabian rift system as an active rift controlled by plume activity.
(1997): Seismic-refraction studies of the Afro-Arabian rift system - a brief review. Tectonophysics, 278, 1-4, 1-13.