A segment of sea-floor spreading in the central Red Sea:: basalts from the Nereus Deep (23°00′-23°20′N)

The major element chemistry and Sr-Nd isotope composition of three basaltic glasses and two whole rock samples dredged from the Nereus Deep, in the central Red Sea, were used to constrain the nature of the magmatism in the Nereus axial valley. The glass and whole rock compositions show the tholeiitic character of magmas and their affinity with MORE. The chemical composition of the most magnesian glass (mg# = 69.9) would suggest an origin from a melting event in the mantle at a pressure in the range 8-10 kbar. Magma differentiation modelling using the major element chemistry of the more evolved glasses indicates mineral-melt equilibration at moderate pressure, followed by most of the fractionation under low pressure conditions. The observed Ti content and Sr isotope composition suggest the occurrence of additional processes besides fractionation, and could reflect different degrees of partial melting of a slightly heterogeneous mantle source. The Sr-Nd isotope composition reveals the time-integrated depleted nature of the mantle, and overlaps the fields of MORE and basalts from the southern Red Sea axial ridge. The Sr isotope data on glasses resemble more closely the compositional range reported for the Indian Ocean ridges, and suggest a dominant asthenospheric source, with minor enriched components, (C) 1998 Elsevier Science Limited.