Crustal Evolution of the Egyptian Precambrian Rocks

Abstract

Precambrian basement of the Egyptian sector of the Arabian-Nubian Shield are well exposed on the flanks of the Red Sea and along the border with Sudan, making it an excellent place to study Neoproterozoic processes of crustal growth, obduction–accretion tectonics, and post collisional escape tectonics. We review the published field observations, structural geological analyses, and geochemical and isotopic data to provide an up-to-date overview Neoproterozoic and pre-Neoproterozoic crustal formation in Egypt. Egyptian basement exposures are distributed in three major places: southern Sinai, the Eastern Desert and in the southernmost Western Desert. Neoproterozoic igneous rocks dominate basement exposures in southern Sinai, the Eastern Desert, and the eastern part of the SW Desert, although ~1.0 Ga crust is documented from northernmost basement exposures in southern Sinai. Neoproterozoic basement rocks mainly consist of ophiolite associations, calc-alkaline and alkaline, and immature sediments; these rocks are especially well exposed in the Central Eastern Desert. Older Neoproterozoic basement rocks represent juvenile arc terranes that formed during Upper Tonian–Cryogenian time at ~650–750 Ma around the margins of the Mozambique Ocean. Accretion of juvenile arc and backarc basin systems ended by Late Neoproterozoic time (~620 Ma) when large fragments of east and west Gondwana collided, closing the Mozambique Ocean and forming the East African-Antarctic Orogen. Orogenic collapse and escape tectonics to form NW-SE trending “Najd” shear zones was associated with intense igneous activity in Ediacaran time; these igneous rocks are especially abundant in Sinai and the NE Desert. Exposures along the E-W Nubian Swell from Aswan to Uweinat provide a glimpse of the transition from juvenile Neoproterozoic rocks of the Arabian-Nubian Shield westward into Archean and Paleoproterozoic rocks of the Saharan Metacraton. We have much to learn about the formation of Egypt’s crust; the SE Desert is especially poorly known, and there are surprises to be discovered in the NE Desert basement. Future efforts to understand the crust of Egypt will require seismic refraction profiles to resolve its crustal structure; aeromagnetic mapping to resolve its crustal fabric; and drilling to sample basement buried beneath sediments of the vast Western Desert and Mediterranean coast.