Growth of the Egyptian crust in the northern East African Orogen: A review of existing models and proposed modifications

摘要

The crystalline basement complex of Egypt in NE Africa is exposed extensively in the Eastern Desert and Sinai as well as in smaller, isolated exposures in the southern part of the Western Desert extending west of the River Nile to the Uweinat area. The Egyptian crust can be divided into the Eastern Desert terrain which is a part of the Nubian Shield and the Western Desert terrain which is a part of the Saharan metacraton. The two terrains are lithologically, structurally and geochronologically different. The rock assemblages of the Western Desert terrain were produced predominantly by remelting of the older, pre-Pan-African crust, while those of the Eastern Desert terrain exhibit juvenile character. However, the basement complex in the southern Western Desert was strongly reworked by Neoproterozoic thermal and deformational events. The evolution of the Egyptian crust within the eastern Desert can be classified into two main regimes, i.e. an older (780-620 Ma) compressional regime, and a younger (620-450 Ma) compressional/transpressional to tensional regime. During the compressional regime, initial island-arc build-up (780-730 Ma) and arc-splitting and back-arc spreading (730-620 Ma) stages were represented. The first stage is characterised by generation of the intrusive metagabbro-diorite complex, intruding continental shelf facies metasediments, and the early Pan-African Shadli metavolcanics. This stage is followed by arc-splitting and back-arc spreading producing the ophiolite sequences and older granitoids. The final compressional/transpressional to tensional regime (620-450 Ma) was characterised by the evolution of late Neoproterozoic post-orogenic A-type younger granites, the Dokhan volcanics, the molasse-type sediments and exhumation of the metamorphic core complexes. Emplacement of the ring complexes in Egypt is mainly controlled by faults and shear zones and took place during an extended period of time between closing of island arcs at the end of the Pan-African orogeny and opening of the Red Sea Rift.