The relation of mesozoic-cainozoic volcanism to tectonics in the Afro-Arabian dome

The Mesozoic-Cainozoic volcanism of NE Africa and Arabia is described in terms of four major magmatic provinces. These are dominantly basaltic and vary in general composition from strongly alkaline to tholeiitic, with some overlap between provinces. Most, but not all, of this volcanism has taken place within the confines of the Afro-Arabian dome and its attendant rifts, but the magmatism is not explicable in terms of a 'mantle plume' beneath Afar because such a plume explains neither the spatial nor temporal distribution of volcanicity. Instead, I propose a multi-stage model in which basaltic magmas of transitional composition were generated in Paleogene time as a response to regional extension. With subsequent evolution of the Red Sea and Gulf of Aden into proto-oceans, these magmas took on the character of oceanic tholeiites. In the Neogene, alkalic activity related to epeirogenic doming was superimposed on this extension-related volcanism. A third, independent magma-generating mechanism appears to have operated NW of the Afro-Arabian dome, where small volumes of alkaline basalt magma have been erupted intermittently since early in the Cretaceous. This activity may result from periodic tapping of deep asthenosphere by tensile fracturing and upwarping of the northward-drifting African plate.