Petrogenesis and tectonic evolution of late Pan-African granitiods in the El Regita area, Central Southern Sinai, Egypt: With a synopsis about Th–U distribution and Cu mineralization

Abstract

The Late Precambrian intrusives in the El Regita area, central Southern Sinai at the northernmost Arabian-Nubian Shield, signify the typical evolutionary Pan-African magmatic stages. Geochemical and mineralogical variation from calc-alkaline (I-type) quartz-monzonite and granodiorite to later mostly A-type monzogranite, syenogranite, and alkali-feldspar granite, indicates high fractionation and extensive magmatic differentiation of the same parent melt, derived from the mantle–crust interaction above the subducted oceanic plate influenced by partial melting processes. The compositional variation is linked to the tectonic evolution from regional compressional deformation to the continental crust's relaxation. The mineralogy of the studied granitoids, which are analogous to similar rocks that crop out in the North-Eastern Desert of Egypt, is consistent with the view that the Sinai region is an eastern extension of the northern Eastern Desert. Results from all geothermometers of the studied granitoids expected decreasing oxygen fugacity in the magma following temperature decrease. Based on the Al-in-hornblende geobarometer, the (I-type) granitoids represents hydrated granites emplaced at lower crustal levels than the monzogranite-syenogranite plutons. The El Regita area is characterized by structurally controlled mesothermal copper mineralization which has epi-genetic origin and is mainly related to the emplacement of granitoids in the late-collisional stage. Abnormal radioactivity levels in the El Regita area are structurally controlled and connected to highly sheared granodiorites. After leaching, uranium was redistributed and finally fixed or adsorbed by Fe-oxyhydroxides to form immobile secondary U-bearing minerals.