Integrated remote sensing and geochemical data of Shadli mineralized metavolcanics (Egypt): mantle plume-driven magmatism during subduction-rift transition

The Wadi Ranga-Atshan metavolcanic (WRAM) suite in the Southern Eastern Desert of Egypt is part of the Shadli calc-alkaline metavolcanic belt, which is the main crustal part of the Arabian-Nubian Shield (ANS). Integrated remote sensing, mineral compositions, and whole-rock chemical data are used to elucidate the mantle-plume contribution, petrogenesis, and geodynamic evolution of the ~ 739 Ma Shadli metavolcanics. Remote sensing analysis using Landsat-8 and ASTER band ratios in RGB effectively discriminates between the dominant felsic and mafic varieties (bimodal volcanism) and minor intermediate types along with the different alteration zones (e.g., iron- and Al‒OH-rich zones). Its PCA and CEM techniques are used to delineate phyllic, argillic, and propylitic alteration zones and their associated Cu-Fe-Zn sulfides, iron oxides, and malachite mainly along the NW-SE shear zones. The whole rock chemistry indicates that mafic rocks (metabasalts) and felsic to intermediate types (metarhyolites, metadacites, and metabasaltic andesites) show tholeiitic and calc-alkaline natures, respectively. But alkali metabasalts exhibit alkaline affinity. The calc-alkaline metavolcanic protoliths are derived from 10-20% partial melting of a depleted spinel lherzolite mantle source, supported by their low REEs (ΣREEs < 20 ppm) contents. They are further characterized by enrichment in LILEs and depletion in HFSEs (Nb < 2.6, Ta < 0.08, and Ti < 53.31 ppm), suggesting a typical arc-related magmatic signature. In contrast, the alkali metabasalt protoliths are derived from low partial melting (~ 5% melting) of the enriched garnet lherzolite or garnet-spinel lherzolite source in deeper and enriched mantle parts, supported by their high REEs (ΣREEs: 212 ppm) contents. The alkali metabasalts are strongly enriched in HFSEs (Ti > 14,676, Nb > 28.9, and Ta > 1.7 ppm) along with high Cr (up to 337.8 ppm) and Ni (up to 245.1 ppm) relative to calc-alkaline types, consistent with intraplate (OIB-like type) magmatism due to upwelling of mantle plume. The investigated metavolcanics plot in MORB-arc and within-plate/OIB fields, reflecting coexistence of OIB-like (mantle plume-derived melts) and arc/MORB-like basaltic melts, together with arc-like magma signatures; these results indicate tectonomagmatic evolution of the studied rocks from supra-subduction arc magmatism to intraplate rifting transition during the arc assembly of the ANS. Therefore, the different partial melting, magmatic affinity, and magma source (mixed plume-arc magmas) possibly reflect plume-driven magmatism during the subduction-rift transition of the ANS. This transitional environment may be characterized by a sequence of magmatic sulfide mineralization (disseminated pyrite and chalcopyrite) to post-magmatic hydrothermal alteration and supergene oxidation assemblages (gossans, talc-carbonate, malachite, and chrysocolla). These processes were structurally controlled by NW-SE (Najd-related) and NE-SW shear zones that developed during the subduction-rift transition, which facilitated mantle-derived magmatism and fluid migration, thereby generating volcanogenic massive sulfide (VMS) mineralization. The arc-related hydrothermal systems, plume-related ore systems, and later metasomatic overprints may highlight the metallogenic significance of the ANS.