Petrography and geochemistry of granitic rocks, their origin and tectonic environment in the Wadi Risasa area, Southeastern Sinai, Egypt

Field study of the granitic rocks in the Wadi Risasa area, Southeastern Sinai, Egypt, shows that they comprise three granitic groups namely the older granite, younger granites (phases II & III) and alkali granites. Petrographically, the older granites are mainly granodiorite, while the younger granite and alkali granites are granite. Major and trace element data reveal that the older granites are mainly calcalkaline whereas the younger granites show a gradual increase in alkalinity from phase II to phase III. The granites of phase III are alkaline while the alkali granites are peralkaline. The older granites are formed at high to intermediate vapour pressure, while the younger granites are formed at intermediate to low vapour pressure. Tectonically, the older granites and younger granites are classified as I-type granites which are related to orogenic granite evolved in a volcanic arc. The alkali granites are emplaced in anorogenic belt which reflects continental epeirogenic uplift. They are classified also as A-type granite, originated in a within-plate environment.