Serpentinized Peridotites at the North Part of the Wadi Allaqi District (Egypt): Implications for the Tectono-Magmatic Evolution of Fore-arc Crust

The Neoproterozoic Allaqi‐Heiani suture (800–700 Ma) in the south Eastern Desert of Egypt is the northernmost linear ophiolitic belt that defines an arc‐arc suture in the Arabian‐Nubian shield (ANS). The Neoproterozoic serpentinized peridotites represent a distinct lithology of dismembered ophiolites along the Allaqi‐Heiani suture zone. The alteration of peridotites varies, some contain relicts of primary minerals (Cr‐spinel and olivine) and others are extremely altered, especially along thrusts and shear zones, with development of talc, talc‐carbonate and quartz‐carbonate. The fresh cores of the chromian spinels are rimmed by ferritchromite and Cr‐magnetite. The fresh chromian spinels have high Cr^# (0.62 to 0.79), while Mg^# shows wider variation (0.35–0.59). High Cr^# in the relict chromian spinels and Fo content in the primary olivines indicate that they are residual peridotites after extensive partial melting. The studied ophiolitic upper mantle peridotites are highly depleted and most probably underwent high degrees of partial melting at a supra‐subduction zone setting. They can be produced by up to ～20%–22% dynamic melting of a primitive mantle source. The mineralogical and geochemical features of the studied rocks reflect that the mantle peridotites of the north part of the Wadi Allaqi district are similar to the fore‐arc peridotites of a supra‐subduction zone.