ORIGIN AND GEOCHEMISTRY OF EGYPTIAN GRANITOID ROCKS IN NUWEIBA AREA, EASTERN SINAI

Geological, petrological and geochemical studies indicate two distinct types of granitoid rocks: an older quartz diorite to granodiorite assemblage and younger granitoids, the latter occurring in two phases. The older granitoids have a calc-alkaline character, with high MgO, (FeO)t, TiO2 and P2O5 and low SiO2, K2O and Rb. Their major and trace elements compositions, together with a low Sr-87/Sr-86 (0.7029 +/- 0.0008) denote 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 Ti2O, and low SiO2, K2O, Zr, Nb and Rb relative to the third phase granitoids. The corundum normative nature and field observations suggest that it was formed by partial melting of the lower crust (S-type). The third phase granitoids are characterized by high SiO2, Rb, Y, Zr and low MgO, CaO, Sr and Ba values than younger granitoid phase II. They show A-type granitoids which are generated from below or within existing continental crust.