Classification of the Neoproterozoic ophiolites of the Central Eastern Desert, Egypt based on field geological characteristics and mode of occurrence

Abstract

The present work presents new field observations on the geological characteristics of the Neoproterozoic ophiolites of the Central Eastern Desert (CED) of Egypt. Based on mode of occurrences, the investigated ophiolites appear to show characteristics of both MORB-type and SSZ-type ophiolites and classified from oldest to youngest into: (1) MORB intact ophiolites (MIO), (2) dismembered ophiolites (DO), and (3) arc-associated ophiolites (AAO). Ophiolite components include serpentinized peridotite and other metamorphosed ultramafics, metagabbros, sheeted dykes, pillowed and massive metabasalts, minor boninites, and pelagic sediments. The rocks of the MIO and DO were subjected to two main phases of deformation (D1 and D2) and metamorphism, whereas the AAO have been affected only by later phase of deformation (D2). Compositional variation of chrome spinel in blocks of metamorphosed ultramafic and serpentinite of dismembered ophiolites shows three distinct groups (G1, G2, and G3) based on their Cr#. Whereas G1 is similar to abyssal peridotites, G2 and G3 display mainly supra-subduction zone (SSZ) tectonic setting. The ophiolitic metagabbros display both N-MORB and supra-subduction zone tectonic setting (SSZ). The basaltic rocks of the MORB-intact ophiolites (MIO) and blocks of metabasalts in the melanges display N-MORB affinity, whereas the basaltic rocks associated with arc volcanics display SSZ tectonic setting. Collectively, the investigated ophiolites of the Central Eastern Desert (CED) fall into two groups, MORB or BABB and SSZ ophiolites. They are spatially and temporally unrelated, and thus, it seems likely that the two types are not petrogenetically related. Ophiolites occur in different geological settings, and they represent change of the tectonic setting of the ophiolites from MORB to SSZ with time.