Significance of contrasting magmatism in North East Africa and Saudi Arabia

The Red Sea is a north–south rift that split the Arabian–Nubian shield into eastern (Arabian) and western (Egypt and Sudan) segments by seafloor spreading less than 30 Myr ago 1 . Because geological studies in the region have generally have confined by national frontiers, a comparative study of magmatic evolution on either side of the Red Sea has not, so far as we are aware, previously been undertaken, and current models for Arabian–Nubian shield evolution suggest broadly similar histories for the basement on both sides of the Red Sea. However, although the igneous rock geochronology on both sides of the Red Sea indicate that Precambrian magmatic histories were broadly similar, since then they have been quite distinct in that the African crust has been invaded episodically by quartz syenites, nepheline syenites and peralkaline granites between 500 and 80 Myr; no such igneous activity is evident in Arabia (Fig. 1). We propose here that the Red Sea line has had structural significance from at least the end of the Cambrian though whether it defines a line of contrasting upper mantle or lower crust geochemistry, or of contrasting crustal rigidity cannot yet be established.