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

Abstract

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.

Multiple Stages of Carbonation and Element Redistribution during Formation of Ultramafic-Hosted Magnesite in Neoproterozoic Ophiolites of the Arabian-Nubian Shield, Egypt

“…In Egypt, exposures of the northwestern corner of the ANS include Neoproterozoic ophiolites that represent fragments of oceanic lithosphere obducted onto continental crust during the collision between West and East Gondwana and the closure of the Mozambique Ocean (e.g., Pallister et al 1988;Stern 1994;Zimmer et al 1995;Stern et al 2004;Azer and Stern 2007). Although generally dismembered and affected by various degrees of alteration and metamorphism (e.g., Stern et al 2004;Azer and Stern 2007;Khalil et al 2014;Boskabadi et al 2017), these ophiolites are among the most distinctive rock units in the basement exposures of the Eastern Desert of Egypt, especially in the central and southern sectors (fig. 1).…”

Geochemistry and Petrogenesis of Late Ediacaran Rare‐metal Albite Granites of the Arabian‐Nubian Shield

“…The Arabian-Nubian Shield (ANS) exposes crystalline rocks of Neoproterozoic age and represents one of the largest tracts of juvenile crust on Earth (Meert, 2003;Johnson, 2003;Stoeser and Frost, 2006;Ali et al, 2010;Khalil et al, 2014;Samuel et al, 2019). It constitutes the northern part of the East African Orogen (Stern, 1994) and is well-exposed in parts of Egypt, Saudi Arabia, Sudan, Eritrea, Ethiopia, Yemen and Somalia (Fig.…”

Genesis and Tectonic Implications of the Kabr El‐Bonaya Ultramafic Rocks, Sinai Peninsula, Egypt: Constraints from Mineralogical and Geochemical Characteristics

“…Mineralogically, the NiO (<0.24 wt%) and Fo (> 81.41) contents of olivines of the studied ultramafic rocks (Table S1) are lower than those of the Egyptian ophiolites (Fo = 92-96, e.g. Abd El-Rahman et al, 2009;Ahmed, 2013;Khedr and Arai, 2013;Khalil et al, 2014;Gahlan et al, 2015;Obeid et al, 2016), but are generally similar to those of the Egyptian Alaskan-type ultramafic rocks (Fig. 5a) (Helmy and El Mahallawi, 2003;Farahat and Helmy, 2006;Abd El-Rahman et al, 2012;Khedr and Arai, 2016).…”