Pan African magmatism in the Zabara District, Central Eastern Desert, Egypt: Geochemistry and Petrogenesis

Abstract

The rocks of the Zabara district include ophiolitic and non-ophiolitic sequences. The ophiolitic ones are metagabbro and metabasalt associated with metasediments, whereas the non -ophiolitic sequence includes intermediate to acidic metavolcanics and two -mica younger granites. The metasediments are felsic with Si02 ranging from 68 to 72 wt% with relatively low Cr and Ni contents (51 ppm and 16 ppm, respectively), which suggest that felsic rocks were predominated in their source area. The Zabara metasediments are characterised by slightly flat REE patterns and have geochemical features similar to those of the ocean island arc metasediments. The ophiolitic metagabbro and metabasalt are similar in their major and trace element contents and show a tholeiitic affinity. The ophiolitic sequence exhibits geochemical characteristics on N-MORB with very low levels of K20, Nb, Zr, Rb and Ba and flat REE patterns. The REE modelling reveals that the ophiolitic sequence could be derived by non-modal batch partial melting of spinel Iherzolite source followed by subsequent fractional crystallization of olivine, clinopyroxene and plagioclase. The non-ophiolitic metavolcanics cover the entire spectrum from medium-K meta-andesite to high-K metadacite with calc-alkaline affinity. The metavolcanics have slightly fractionated LREE and unfractionated, flat HREE. The non-ophiolitic metavolcanics represent cogenetic fractionated sequence. The highly evolved post-orogenic alkaline two mica granite exhibits peraluminous character and shows close similarity with the metarhyolite with repeat to major and trace elements. The granite could be modelled by about 70% fractional crystallisation of plagioclase, alkali feldpar, biotite, titanite and zircon from the dacitic magma.