The Neoproterozoic Abu Dahr ophiolite, South Eastern Desert, Egypt, is one of the best preserved and least dismembered ophiolite successions in the Arabian-Nubian Shield. It contains a Penrose-type ophiolite sequence from mantle section below mafic crust upward to oceanic sedimentary cover overlying mafic volcanics, although the original magmatic (stratigraphic) contact between the mantle and crustal sections is disrupted by tectonism. The Abu Dahr ophiolite is metamorphosed under greenschist facies conditions, and low-temperature alteration is widespread. Petrography reveals that: (i) the mantle is homogenous, serpentinized, and dominated by harzburgite and less abundant dunite; (ii) the cumulate ultramafics are represented by wehrlite and pyroxenite; and (iii) the crustal section is represented by metagabbros, meta-anorthosites and metabasalts. The Abu Dahr serpentinized peridotites show high Mg# (0.92-0.93), with enrichment of Ni, Cr and Co, and depletion of Al 2 O 3 and CaO, and nearly flat and unfractionated REE chondrite-normalized pattern. Major and trace element characteristics of the Abu Dahr metagabbro and metabasalt (crustal section) indicate a tholeiitic to calc-alkaline affinity. Units of the crustal section have low-Nb and Zr concentrations, low Dy/Yb and relatively elevated La/Yb ratios, high U/Yb and Th/Yb ratios, and LREE enriched chondrite-normalized pattern. All of the Abu Dahr ophiolite units have trace-element signatures characterized by enrichment of LILE over HFSE. Rare and trace element patterns indicate a genetic link between the Abu Dahr mantle, cumulate ultramafics, and crust. Chromian spinel has survived metamorphism and is used as a petrogenetic indicator in the Abu Dahr serpentinized peridotites. The spinel is homogeneous with a limited composition, and shows high-Cr# (>0.6) combined with low-TiO 2 character (mostly <0.1 wt.%). The Abu Dahr ophiolite is interpreted as a fragment of depleted oceanic lithosphere that experienced high degrees of partial melting (up to 35 %) and originated in a fore-arc setting. Such interpretation contributes to the body of evidence suggesting that tectonomagmatic processes of the Neoproterozoic were largely similar to those of the Phanerozoic, implying little, or no significant, change in the geothermal regime of Earth since the Neoproterozoic.

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Field and geochemical observations of the granitoids of the Homrit Waggat area in the central Eastern Desert of Egypt reveal two magmatic phases. The early phase of weakly deformed subduction-related calc-alkaline rocks includes tonalite and granodiorite. We name the later phase the Homrit Waggat Pluton (HWP); it includes undeformed syenogranite, alkali feldspar granite, and minor albitized granite. The tonalite and granodiorite have distinct negative Nb-Ta anomalies and lower alkalis, REE, Nb, Zr, and Hf than the HWP. The early magmatic pulse is a subduction-related suite, likely generated by underplating of mantle-derived magmas that triggered partial melting of mafic lower crust; mixing of these melts led to intermediate magma that further fractionated to tonalite and granodiorite. The HWP granites of the late magmatic pulse are transitional from a subduction-related to an anorogenic within-plate environment, plausibly generated by post-collisional lithosphere delamination. Although the parent magma of the HWP was I-type, extensive fractional crystallization produced residual liquids with A 2 -type character. Albitized granites are found only along the outer margin of the HWP, and contacts with the alkali feldspar granite are gradational, suggesting fluid interactions at a late stage of crystallization. The original textures of the albitized granites are preserved, but their bulk composition was modified by the production of Narich minerals and the removal of K, REE, and some trace elements by fluids.

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.