Origin and geochemistry of Pan-African granitoid rocks in the Gabal Um Shomer area, Southwestern Sinai, Egypt

Geological, petrological and geochemical studies indicated that there are two distinct types of granitoid rocks: older quartz diorites to granodiorite assemblage and younger granitoids, the latter occurring in two phases. The older granitoids have a meta-aluminous chemistry and a calc-alkaline character, with high MgO, Fe₂O₃, TiO₂, CaO, P₂O₅, Sr and low SiO₂, K₂O, and Rb. Their major and trace elements data, together with low ⁸⁷Sr/⁸⁶Sr ratios (0.7029±0.0008) are indicative of I-type affinities. The second- and third-phase granitoids range from calc-alkaline to alkaline, respectively. The second-phase granitoids have a peraluminous chemistry and high Sr, Ba, CaO, MgO, Al₂O₃ and Ti₂ O and low SiO₂, K₂O, Nb, Y and Rb relative to the third-phase granitoids. The corundum normative nature and field observations suggested that it was formed by partial melting of the lower crust. The third-phase granitoids are alkaline in nature and characterized by higher SiO₂, Rb, Y, Nb and lower MgO, Sr and Ba values than the younger granitoids (phase II). They are A-type granitoids which were generated from below or within the existing continental crust.