Postcollisional Ferani Volcanics from North Arabian–Nubian Shield (South Sinai, Egypt): Petrogenesis and Implication for Ediacaran (607–593 Ma) Geodynamic Evolution

Abstract

The Ediacaran (607–593 Ma) Ferani volcanic rocks are exposed in South Sinai, at the extreme northern tip of the Arabian-Nubian Shield (ANS). The studied volcanics constitute a cogenetic continuous intermediate (andesite to dacite) to acid (rhyodacite to rhyolite) lava sequence with a high-K calc-alkaline metaluminous to slightly peraluminous nature. They contain a high concentration of large-ion lithophile elements (i.e., Ba, Rb, Pb, and Th), but lower contents of Nb, P, Ti, and Sr. They also have a general enrichment in light rare earth elements ((La/Sm)N=2.66–4.92), compared to heavy rare earth elements ((Gd/Yb)N=1.10–2.29), with a slightly negative Eu anomaly (Eu/Eu*=0.35–0.94). The cooling of the Ferani magma began at ∼1000°–1100°C and went to ∼700°C at low pressure (<5.1 kbar) and shallow crustal levels (<17 km), according to thermobarometric modeling. The low degree of partial melting of the mafic lower-crustal rocks could have produced the andesitic-dacitic magmas that ascended through the crust and fractionated, leading to the production of the early intermediate Ferani lavas. Progressive fractional crystallization of the intermediate melts could consequently have formed the rhyodacite and rhyolite melts, which were later erupted to form the upper acidic Ferani volcanic sequence. Petrological and geochemical features support a postcollisional setting of the Ferani volcanics. Lithospheric delamination is the main geodynamic process responsible for the formation of the Ferani volcanics during the postcollisional extensional stage in the northern ANS crust.