Geochemical, mineralogical and petrogenetic studies of the calc-alkaline younger gabbros, Sinai of Egypt with a special emphasis on the role of hydrous fluids

Abstract

Neoproterozoic younger gabbroic intrusions cropping out in Wadi Watir, Gabal Minadir and Gabal Imleih, southern Sinai, Egypt were investigated. The Imleih gabbros are characterized by fresh mineral constituents while Watir and Minadir gabbros are slightly altered. They are layered and consist of pyroxenites, olivine gabbros, pyroxene gabbros, pyroxene-hornblende gabbros, hornblende gabbros and anorthosites. The clinopyroxenes are of subalkaline affinities and range in composition from augite to diopside, while the orthpyroxenes are clino-enstatite. The primary amphiboles are of mantle origin and represented mainly by pargasite and edenite whereas actinolite and magnesiohornblende represent the secondary one. The investigated gabbros were originated from high Al, hydrous basaltic magmas that were evolved by fractional crystallization at the base of magma chamber to produce calc-alkaline magmas that were emplaced in a transitional stage between volcanic arc and within plate settings. They were crystallized at temperature of ∼800–1200 °C; pressure ∼4.8–6 Kb (∼15–20 km) and high oxygen fugacity. The gabbroic magmas have undergone significant crustal contamination and differentiation which affect on the geochemical characteristics of them. The enrichment of LILE and LREE relative to HFSE and HREE, respectively reflects the effect of slab-derived fluids and metasomatism of their enriched mantle source.