Neoproterozoic post-collisional granitoids in the Central Eastern Desert of Egypt: Petrological and geochemical constraints

The Um Had and Um Effein (UHUE), Central Eastern Desert of Egypt, are elliptical and circular bodies of monzogranite to syenogranite with subordinate alkali feldspar granite. The UHUE granites are quite evolved (SiO2=67-74wt.%), and have characteristics of high-K calc-alkaline peraluminous rocks. They are relatively enriched in K, Ba, La, Rb, Zr and total REEs, while are depleted in Sr, Y, Ti, HREE. The rocks have LREE-enriched patterns with significant negative Eu anamolies suggesting post-collision granites. The gradual increase of Rb/Sr and Rb/Ba ratios from the monzogranite to the alkali feldspar granites indicates that these granites are genetically related. The various geochemical discrimination diagrams strongly suggest that the studied granitoids were generated from crustal sources through fractional crystallization with some crustal contamination which have played a major role during the magmatic evolution of the plutons. These granites display transitional character from orogenic calc-alkaline arc-type up to subsequent anorogenic within-plate environments, suggesting continuous crystallization of magma in a transitional "post-collision" tectonic setting. This transition from compression to extension was controlled mainly by lithospheric delamination following continental collision in the Eastern Desert of Egypt.