Magmatism during extension of the lithosphere:: geochemical constraints from lavas of the Shaban Deep, northern Red Sea

Geochemical and isotopic data of tholeiitic lavas from the northernmost volcanic deep. the Shaban Deep in the Red Sea rift suggest the presence of small-scale heterogeneities in the mantle underneath this part of the rift. The major and rare-earth element compositions indicate less than 10% melting of a variably depleted spinel peridotite. The basalts from the Shaban Deep have significantly higher Sr-87/Sr-86 for a given Nd isotope value than basalts from the southern Red Sea rift. The magmas formed from an asthenospheric source distinct from the Arabian lithospheric mantle and have not assimilated crustal material. The mantle source is enriched in alkali and alkaline earth elements relative to Nh and the rare earth elements and in that respect resembles Indian Ocean MORB. Olivine, plagioclase and clinopyroxene were fractionated and magma mixing occurred in shallow crustal magma reservoirs. The degree of partial melting decreases towards the north along the Red Sea rift due to decreasing spreading rate and colder mantle temperatures. (C) 2000 Elsevier Science B.V. All rights reserved.