Continental intraplate volcanism in the Sinai subplate: The Oligo-Miocene basalts of the Gulf of Suez rift

Three major Oligo-Miocene basaltic occurrences in Sinai, along the eastern side of the Gulf of Suez rift (Wadi Tayiba, Wadi Matulla and Gabal Abu Durba), have been chosen to reveal the geochemistry and petrogenesis of the magmatism associated with this newly-formed continental rift. They include rift-related basaltic/doleritic dikes and sills and isolated basaltic lava flows, belonging to a prolonged persistent magmatic event occurred around 20 Ma, that crosscut older Phanerozoic strata and Precambrian basement. The Gulf of Suez rift (GSR) volcanics show confined range of SiO2 contents (47.51–52.25 wt%) and Mg# values (31–48) and consist of alkaline basalts, hawaiites, mugearites and transitional tholeiitic basalts. All of the investigated basaltic samples possess explicit Fe-enrichment and sodic nature and are silica-oversaturated (quartz-normative) and metaluminous (diopside-normative and have NK/A<1 and A/CNK <1). The compatible transition elements Ni (9–69 ppm), Cr (14–123 ppm), V(237–453 ppm), Sc (19–43 ppm) are generally depleted relative to primitive lavas, consistent with the evolved nature of these basalts (e.g. low Mg# (<68) and silica-oversaturation). Conversely, these basalts show strong enrichment of most of the incompatible LIL and HFS elements relative to primitive mantle, analogous to ocean island basalts. The GSR basalts have suffered minimal degree of crustal contamination, which was likely a minor contribution from the lower crust that superimposed on crystal fractionation. The Nb/Ta and Zr/Hf ratios of the studied basalts are comparable to those of OIB and enriched MORB and are suggestive of their derivation from mantle source. The GSR basalts were most probably derived via partial melting of quite deep asthenosphere (>70 km) amphibole-bearing garnet peridotite mantle source.