STRUCTURES RELATED TO RED-SEA EVOLUTION IN NORTHERN ERITREA

Structural analysis of remotely sensed images of Eritrea, guided by th e common presence of a mid-Oligocene datum at the base of flood basalt at different elevations, helps to piece together the Tertiary history of the western flank of the Red Sea basin. Many of the Tertiary fault s are reactivated shear zones in the Pan-African basement, the most im portant Tertiary fault at the foot of the Red Sea Escarpment marking t he site of a pre-Tertiary boundary between andesitic island-are crust and deeper, perhaps older granitoid migmatites. The initiation of exte nsional sedimentary basins in Eritrea clearly followed volcanism, as d id doming and uplift. This sequence lends some support to active mantl e upwelling as the primary tectonic impetus, specifically to massive m elting simultaneous with plume impact with the lithosphere. The coinci dence of major Tertiary extensional faults with zones of mid- crustal to lower- crustal silicic basement may indicate that active mantle pro cesses were focused by zones of theologically weak lithosphere, as pos tulated by Dixon et al. (1989).