A fore-arc setting of the Gerf ophiolite, Eastern Desert, Egypt: Evidence from mineral chemistry and geochemistry of ultramafites

• Published in: Lithos 2016-10, Vol.263, p.52-65
• Main Authors: Abdel-Karim, Abdel-Aal M., Ali, Shehata, Helmy, Hassan M., El-Shafei, Shymaa A.
• Format: Article
• Language: English
• Subjects: Boninitic magma; Fore-arc; Gerf ophiolite; Mantle rocks; Neoproterozoic
• ISSN: 0024-4937; 1872-6143
• DOI: 10.1016/j.lithos.2016.05.023

The Gerf ophiolite is the largest mantle-derived complex in the Arabian–Nubian Shield (ANS). This ophiolitic complex extends for tens of kilometers in the south Eastern Desert (SED) of Egypt as part of the Allaqi–Heiani and Oneib-Sol Hamed suture zones. The ultramafic section of the Gerf ophiolite comprises serpentinites, serpentinized peridotites and minor pyroxenites. All rocks contain relics of original magmatic phases. The elevated Cr# (>0.84) of Cr-spinels indicates that these rocks represent highly-depleted mantle residues after high degrees of melt extraction. Mineral and bulk-rock chemistry show that the Gerf ophiolite suite represents fragments of oceanic lithosphere that developed in fore-arc setting in a supra-subduction zone (SSZ) environment. The pyroxenites have a LREE-enriched pattern relative to the serpentinites while the serpentinized peridotites display depleted patterns [average (La/Yb)n=0.56)]. Modeling of LREE suggests that the LREE-enriched pyroxenites and serpentinites could have been produced via contamination of their mantle source by crustal material and/or subduction-related slab fluids during the mantle evolution in a SSZ setting or soon after ophiolite assemblage obduction onto the continental crust. In contrast, the LREE-depleted serpentinized peridotites could have been generated through MORB melt/mantle rock reaction. •The Gerf ophiolite is the largest mantle-derived complex in the Arabian-Nubian Shield (ANS).•The Gerf ophiolitic ultramafics comprise serpentinites, serpentinized peridotites and minor pyroxenites.•They represent highly-depleted mantle residues after high degrees of melt extraction [high Cr# (>0.84)].•Gerf ophiolite suite developed in fore-arc setting in a supra-subduction zone (SSZ) environment.