Petrogenesis and geodynamic evolution of Neoproterozoic Abu Dabbab Albite Granite, Central Eastern Desert of Egypt: Petrological and geochemical constraints

摘要

Gebel Abu Dabbab, which is located at 50 km NW of Marsa Alam city, represents an unique and specialized stock-like felsic intrusion of rare metals and Sn bearing albite granite. This granitic stock was emplaced along two intersected major faults and/or tensional shear zones trending NE and NW-SE relevant to the Najd Fault system. Petrographically, the albite granite is composed mainly of albite, quartz and microcline-microperthite and muscovite, in association with accessories; cassiterite, tantalite-columbite, zircon, allanite and apatite. The studied albite granite is enriched in Na2O, HFSEs, Ta and Nb, but it is poor in MgO, CaO, Fe2O3, TiO2, Ba, Sr, rare earth elements and radioelements (U, Th). Geodynamic modelling reveals that Abu Dabbab albite granite was generated as a result of partial melting of oceanic crust due to the interaction of primitive basaltic melts-derived from the mantle source. The resultant hybride melts were subsequently fractionated to tonalitic melts giving rise to the Al-subtype granite, which was emplaced within the intraplate environment at the later phase of the Pan African Orogeny. Moreover, the fractional crystallization and reworking of plagioclase were suffered from alkali mtasomatism after extraction of alkali feldspar granite melts.