Ghadir Ophiolites, Eastern Desert, Egypt: A Complete Sequence of Oceanic Crust in the Arabian-Nubian Shield

Abstract

AbstractNeoproterozoic ophiolites are widely distributed in the Central and Southern Eastern Desert of Egypt. The most important and well-known ophiolites of the Central Eastern Desert (CED) are exposed in Ghadir area. They occur as intact ophiolitic sequence of oceanic crust, blocks and fragments in an ophiolitic mélange and as dismembered ophiolite components. The whole rock association is foliated and metamorphosed to the greenschist facies up to lower amphibolite facies. The intact ophiolite sequence is composed mainly of metagabbro, sheeted dykes, and pillow lavas. Exotic fragments of oceanic lithosphere tectonically incorporated in a foliated volcaniclastic matrix forming tectonic ophiolitic mélange. The Ghadir pillowed metabasalts are classified as high-Ti MORB-type, which are comparable to MORB or BABB ophiolites and appear to be derived from an evolved magma in an intra-oceanic back-arc basin. The intact ophiolite sequence is remnants of oceanic crust formed the floor of the basin and became tectonically obducted during the closure of the back-arc basin in which they formed. The formation of the Ghadir ophiolitic mélange by tectonic processes in a back-arc basin is followed by tectonic emplacement of some dismembered ophiolitic rocks along structural contacts. The whole MORB ophiolites of the Eastern Desert (ED) of Egypt were suggested to be formed in a back-arc basin due to collision of an island arc system with the African continent. They occur in different geological settings, and the compositional variation within these rocks was assigned to geochemical variations in a single tectonic setting of back-arc basin rather than to different tectonic settings.KeywordsNeoproterozoicGhadirOphiolitesEastern desertEgyptMORBBABBOphiolitic melange