I-type granitoid rocks emplaced during pre-collision stages of the Neoproterozoic Pan-African Orogeny, are widely distributed in the southern Sinai Peninsula and constituting 30% of the basement outcrops. Petrological, geochemical, and mineral chemistry data are presented for a selection of I-type, Wadi El-Akhder tonalite–granodiorite suite, in order to determine their origin and geotectonic implications. Wadi El-Akhder granitic rocks (AGR) have geochemical characteristics of medium-K calc-alkaline, metaluminous to mildly peraluminous granitoids formed in an island-arc environment, which are conformable with well-known Egyptian older granitoids rocks (G1). Wadi El-Akhder granitic rocks have low Al2O3, FeO*, MgO, MnO, CaO, TiO2, Sr, Ba, and V contents, but possess high contents of Na2O, K2O, Nb, Zr, Th, and Rb. The studied AGR are generally characterized by enrichment of LILE and LREE and depletion of HFSE relative to N-MORB values (e.g., negative Nb and Ta
2
anomalies). They follow assimilation and fractional crystallization (AFC) trends indicative of extensive crustal contamination of magma derived from a mantle source. The studied granitic rocks show high CaO/Na2O ratios (0.82-1.54) being a decrease from tonalite to granodiorites to, whereas they have also high Al2O3/TiO2 ratios (16.69-27.61) increasing toward the higher silica granitic type (granodiorites). These features indicate that emplacement of these granitoids were strongly affected by magma mixing of felsic and mafic melts. The chemical characteristics of the AGR are remarkably similar to those of subduction-related granitoids from the Arabian-Nubian Shield (ANS). |
