A SEGMENT OF SEA-FLOOR SPREADING IN THE CENTRAL RED-SEA - BASALTS FROM THE NEREUS DEEP (23-DEGREES-00'-23-DEGREES-20'N)

The major element chemistry and Sr-Nd isotope composition of three bas altic glasses and two whole rock samples dredged from the Nereus Deep, in the central Red Sea, were used to constrain the nature of the magm atism in the Nereus axial valley. The glass and whole rock composition s show the tholeiitic character of magmas and their affinity with MORE . The chemical composition of the most magnesian glass (mg# = 69.9) wo uld suggest an origin from a melting event in the mantle at a pressure in the range 8-10 kbar. Magma differentiation modelling using the maj or element chemistry of the more evolved glasses indicates mineral-mel t equilibration at moderate pressure, followed by most of the fraction ation under low pressure conditions. The observed Ti content and Sr is otope composition suggest the occurrence of additional processes besid es fractionation, and could reflect different degrees of partial melti ng of a slightly heterogeneous mantle source. The Sr-Nd isotope compos ition reveals the time-integrated depleted nature of the mantle, and o verlaps the fields of MORE and basalts from the southern Red Sea axial ridge. The Sr isotope data on glasses resemble more closely the compo sitional range reported for the Indian Ocean ridges, and suggest a dom inant asthenospheric source, with minor enriched components, (C) 1998 Elsevier Science Limited.