Petrogenesis of late Precambrian younger granites from southwest Sinai, Egypt.

Abstract

The paper represents the field, petrographic and geochemical characteristics of late Precambrian granites of Wadi Baba-Wadi Seih area in southwestern Sinai. They are composed of biotite granites and leucogranites. The biotite granites are fluorite non-bearing, vary from monzo- to syenogranites, which cut by felsic dykes, and probably correspond to the phase II of Egyptian Younger Granites. The leucogranites are fluorite bearing, range from syenogranites to alkali feldspar granites, cut the phase II and felsic dykes and belong to the phase III granites. Petrographic and geochemical data reveal a peraluminous type and potassic-sodic character of the present younger granites. They were originated at 20->30 km depth as shallow- to moderate-level intrusives. They were mostly originated in intraplate environment with extensional regime. In general, the biotite granites have alkaline character, probably exhibit the features of S-type granite, and are derived by partial melting of the lower crustal materials. On the other hands, the leucogranites have strong alkaline and peralkaline charcters, largely similar to the A-type granite with high silica, alkalis and normative acmite, and were formed through partial melting of lower crustal materials followed by crystal fractionation of a fluorine-rich I-type magma.