NEW IDEAS ON THE KENYA RIFT BASED ON THE INVERSION OF THE COMBINED DATASET OF THE 1985 AND 1989 90 SEISMIC TOMOGRAPHY EXPERIMENTS/

A tomographic image of the P-velocity structure beneath the central pa rt of the Kenya rift has been obtained from the inversion of the combi ned data sets of the 1985 and 1989/90 teleseismic experiments. This in vestigation confirms the three-dimensional character of this rift stru cture. In the uppermost mantle a steep-sided low-velocity body indicat es the presence of partial melt. The maximum anomaly is located where the NW-SE-trending Aswa suture zone of Proterozoic age crosses the N-S -oriented Miocene rift in the area of the Kenya Dome. It is suggested that the development of the rift in this area is controlled by two fac tors: (1) the old NW-SE-trending Aswa shear zone and (2) a narrow wedg e of asthenosphere beneath the rift in the area of the Kenya Dome, whi ch is a clear indication of upper mantle dynamics due to asthenospheri c upwelling and which is, at least partially, the driving force of the rift's formation.