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<p>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&#xa0;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 &lt; 20&#xa0;ppm) contents. They are further characterized by enrichment in LILEs and depletion in HFSEs (Nb &lt; 2.6, Ta &lt; 0.08, and Ti &lt; 53.31&#xa0;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&#xa0;ppm) contents. The alkali metabasalts are strongly enriched in HFSEs (Ti &gt; 14,676, Nb &gt; 28.9, and Ta &gt; 1.7&#xa0;ppm) along with high Cr (up to 337.8&#xa0;ppm) and Ni (up to 245.1&#xa0;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.</p>

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

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  • 发表日期：

    2026年7月14日

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  • Mohamed Zaki Khedr,
  • Mahmoud A. Sayed,
  • Shehata Ali,
  • Mokhles K. Azer,
  • Akihiro Tamura,
  • Tomoaki Morishita,
  • Eiichi Takazawa,
  • Yuji Ichiyama,
  • Ali M. Mahdi

摘要

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.