Classification and origin of the Neoproterozoic ophiolitic melanges in the Central Eastern Desert of Egypt

The Eastern Desert of Egypt is part of the Neoproterozoic Arabian-Nubian Shield and displays different occurrences of Neoproterozoic ophiolitic melanges. The melanges contain exotic and native blocks and fragments of variable sizes and types set in a sheared and schistose volcaniclastic matrix. The main exotic blocks are ophiolitic and include metamorphosed ultramafic rocks, metagabbros, massive and pillowed metabasalts and pelagic sedimentary rocks. Based on the mode of occurrences of the ophiolitic components and the processes of melange formation, the ophiolitic melanges of the Central Eastern Desert are classified and mapped into tectonic melange, olistostrome and olistostromal melange. The whole rock associations of these melanges were subjected to two different events of deformation (D-1 and D-2) and contemporaneous metamorphism (M-1 and M-2). The metagreywackes of the melange matrix are similar to oceanic island arc sandstone and appear to have been deposited in a back-arc or inter-arc basin. The blocks of ophiolitic metabasalts within the melange show tholeiitic affinity and have back-arc basin (BAB) tectonic origins. Metamorphosed ultramafic blocks in the melange display both mid-ocean ridge (MOR) and suprasubduction zone (SSZ) affinities. The ophiolitic components represent fragments of oceanic lithosphere that formed in a back-arc/arc environment, and were incorporated into the melange through tectonic and/or sedimentary processes. Both tectonic and sedimentary processes played a major role during melange formation in a back-arc or inter-arc setting. (C) 2012 Elsevier B.V. All rights reserved.