Neoproterozoic hybrid forearc – MOR ophiolite belts in the northern Arabian-Nubian Shield: no evidence for back-arc tectonic setting

The Neoproterozoic Arabian-Nubian Shield (ANS) post-dates the Boring Billion (1.85−0.85 Ga), a transition dominated by extensive arc-magmatism, terrane accretion along active subduction zones. Understanding the nature of the oceanic crust fragments preserved in the ophiolite belts is essential in extrapolating the predominant style of plate tectonics during the Neoproterozoic Era. There are two ophiolite belts with controversial genetic models in the Central Eastern Desert (CED) of Egypt, namely Wadi Semna–Fawakhir–Um Gheig belt to the north, and Ghadir–Mubarak–Barramiya belt to the south. Geochemical database and magnetic data are herein integrated to envisage the tectonic setting of the dispersed ophiolite blocks within these two belts. The northern belt is dominated by NW obduction-related thrust faults and is intensely deformed by structures attributed to the Najd fault system (NFS). The southern belt is less affected by the Najd fault with NE obduction-related thrust faults. Based on various discrimination diagrams and REEs pattern, oceanic mafic-ultramafic rocks in these belts can be classified into three types, MOR, forearc and volcanic arc basalt, where the latter is MORB overprinted by arc affinity. Our proposed evolutionary model includes N-dipping subduction zones parallel to the ~ E-W Allaqi-Heiani suture with hybrid forearc-MOR affinities. The data synthesis presented here weighs with advancing accretionary orogeny along the intraoceanic subduction zones as the dominant tectonic style during the Neoproterozoic evolution of the CED rather than the retreating style of the modern western Pacific region.