Diverse geodynamic settings of the Egyptian ophiolites: Geochemical insights from Wadi Ghadir and Gabal Abu Dahr

Abstract

In the context of the ongoing debate on the genetic aspects of Egyptian ophiolites, understanding the geodynamic setting of significant ophiolitic complexes is crucial. Here, we investigate the Wadi Ghadir (WG) and Gabal Abu Dahr (AD) ophiolites to elucidate their tectonic setting and evolution. Combining whole-rock trace element geochemical data of crustal and mantle section rocks with mineral chemistry analyses of relict clinopyroxene and Cr-spinel, we delineate the geochemical signatures indicative of their tectonic setting. The WG represents a nearly complete ophiolite sequence, while the AD complex is a dismembered ophiolite nappe encompassing serpentinized peridotite, variably sheared metagabbro, and mélange matrix. The trace element patterns of the crustal section rocks in both ophiolites exhibit enrichments in LILE and depletions in HFSE, suggesting formation in a supra-subduction zone (SSZ). The low Ti contents and fractionated chondrite-normalized REE patterns of clinopyroxenes from both studied ophiolites further support the subduction-induced characteristics. The highly elevated Cr# of Cr-spinel in the WG and AD serpentinites, alongside their high Mg# and low TiO2 contents, resemble those of the forearc basalts and boninites, indicative of extensive melt extraction. Despite the shared features of progressive evolution to boninite-similar geochemistry, the AD ophiolite is deemed unlikely to have experienced the MORB or backarc environments. Conversely, the WG ophiolite has geochemical signatures inferring transitioning from back-arc MORB-like lithosphere to the SSZ setting. Although originating from distinct geodynamic settings, these ophiolites can be conceptualized as representing a Tonian-Cryogenian sub-arc lithosphere (∼730–700 Ma) in the Egyptian Eastern Desert, showcasing varied responses to subduction-related processes.