Geochemical constraints on the tectonomagmatic evolution of the late Precambrian Fawakhir ophiolite, Central Eastern Desert, Egypt

The Fawakhir ophiolitic sequence is composed mainly of serpentinites, metag abbros, boninitic metagabbros and metavolcanics. The serpentinites have geo chemical features similar to those of depleted-mantle peridotites. Major an d trace element characteristics show that the ophiolitic metagabbro and met avolcanic rocks are of tholeiitic to calc-alkaline affinity. REE abundances in the metagabbros and metavolcanics are characterised by flat to fraction ated patterns. The Fawakhir ophiolitic sequence shows a spectrum of composi tions ranging from are-type lavas, P-type MORE and boninitic rocks, suggest ing that these rock units developed in a back-are environment. The evolutio n of the Fawakhir ophiolite sequence from early tholeiites to later boninit ic-type magmas may suggests that these rocks could be generated by fraction al fusion and melt extraction during ascent of the magma source within a ma ntle melting column. The boninites were generated from a more refractory ma ntle source relative to the other rocks. (C) 1999 Elsevier Science Limited. All rights reserved.