Precambrian Basement Complex of Egypt

Abstract

Surface exposure of the Egyptian Precambrian basement complex covers ca. 100 000 km². Outcrops of the basement rocks extend over extensive areas in southern Sinai, the Eastern Desert south of latitude 29°N and the Western Desert south of latitude 24°N between the Nile valley at Aswan in the east to Gabal Uweinat, near the Egyptian-Libyan-Sudanese border, in the west. Apart from the rejuvenated Paleoproterozoic to Archean rocks of Gabal Uweinat-Gabal Kamil inlier (charnockitic, TTG and gabbro-diorite gneisses), belonging to the Saharan Metacraton, the Precambrian basement complex of Egypt, in Sinai and the Eastern Desert, belongs to the juvenile Neoproterozoic (550–900 Ma) crust of the Arabian-Nubian Shield (ANS). The Uweinat-Kamil inlier rocks have been reworked by several events at 3.1–2.55 Ga ago and 2.0 Ga ago. In the southern Western Desert, midway between Aswan and Uweinat-Kamil inliers, there exist three Precambrian inliers; Gabal-Umm-Shagir, Gabal-El-Asr and Bir Safsaf that contain Neoproterozoic Pan-African granitoids and remnants of the pre-Pan-African crust, probably representing the eastern transition between the Paleoproterozoic to Archean terranes of the Sahara Metacraton (i.e. Uweinat-Kamil inlier) and the juvenile Neoproterozoic terranes of the Arabian-Nubian Shield. The evolution of the ANS juvenile crust took place during most of the Neoproterozoic time (900–600 Ma) throughout three major stages, namely: (1) accretion stage (~870–670 Ma) including the formation of island arc volcano-sedimentary sequences and plutonic rocks and amalgamation of these accreted terrains onto east Gondwana continental block; (2) collision (~650–640 Ma) between the juvenile accreted ANS crust with the older pre-Neoproterozoic continental margin of West Gondwana (Saharan Metacraton) along arc-arc and arc–continental sutures, which prompt crustal thickening, and (3) post-collisional stage (630–550 Ma), which commenced after termination of collision, and encompassed extensional collapse of the thickened lithosphere, inducing extension and thinning of the ANS crust, which lasted until about 550 Ma. The main lithologies of the Egyptian part of the ANS include low- to medium-grade metamorphosed volcanosedimentary successions, dismembered ophiolite sequences, metagabbro–diorite complexes and calc-alkaline granitoids formed during the island arc (i.e. subduction) stage. Also, a substantial volume of undeformed late-collisional more evolved calc-alkaline granitoids were emplaced, subsequent to crustal thickening phase and preceding the onset of crustal extensional phase (630–590 Ma). A major period of mafic to felsic, high-K, Dokhan volcanics (610–580 Ma) and high-silica A-type granites and rhyolites (610–560 Ma) is associated with escape tectonics and crustal extension in the post-collisional stage.