Petrology and geochemistry of the Tertiary Suez rift volcanism, Sinai, Egypt

摘要

The Tertiary basaltic rocks of Southwestern Sinai, situated along the Wadi Nukhul-Wadi Matullah-Wadi El Tayiba join, were selected to study the Gulf of Suez rift related-lavas and their geochemical and petrological relation with the rifting process. Whole rock samples were studied petrographically and analysed for major and trace elements. The samples from dykes, sills and flows from multiple magmatic events display a large variety in texture and in modal mineral compositions. They range from olivine dolerites and olivine-bearing basalts to vitrophyric, texturally heterogeneous basalts and crystal lithic tuffs. The transitional tholeiitic basalts display low compatible element concentrations and an enrichment of the whole spectrum of the incompatible elements. Major, trace and Rare Earth Element data suggest that the melts formed by 5% melting of mantle peridotite at the spinel-garnet transition zone (80-90 km depth), in the presence of 2-4% residual garnet. During the melt ascent, the fractionating phases were olivine, clinopyroxene and, to a lesser extent, plagioclase. Thermobarometric calculations indicate the presence of two crystallization levels beneath the Gulf of Suez rift: a shallower stage at 15-20 km and a deeper stage at depths of 25-30 km. The mantle source consists of streaks and blobs of enriched mantle, preserved in the geochemical signatures of these rocks. The enriched mantle sources melted preferentially compared to the surrounding ambient mantle and thus led to a preferential enrichment of the sources of the Gulf of Suez rift.