Metamorphic evolution of Neoproterozoic metapelites and gneisses in the Sinai, Egypt: Insights from petrology, mineral chemistry and K–Ar age dating

Petrology, mineral chemistry, and age dating of the metapelitic schists and gneisses in three metamorphic complexes of Sinai have been studied and reported with the aims of characterizing the nature, type, and age of metamorphism as well as the metamorphic evolution of the Sinai metamorphic complexes. Nine representative samples of metapelitic schists, migmatites, and gneisses from the Taba Metamorphic Complex (TMC), the Kid Metamorphic Complex (KMC) and the Feiran-Solaf Metamorphic Complex (FSC) in southern Sinai Peninsula have been analyzed by electron microprobe for their mineral assemblages and K–Ar geochronological methods for biotite separates. Garnet from the metapelites and migmatites are almandine-rich and usually show zoning with variable XFe values.The estimated P–T metamorphic conditions of the TMC range from 560–578 °C/3–4.5 kbar for the metapelitic schists, to 685 °C/5.3 kbar for the migmatites, while those for the metapelitic schists in the KMC are 590 °C/4–5.9 kbar in the Umm Zariq Formation, and 636 °C/4.7 kbar in the northern part of the Malhaq Formation. The P–T metamorphic conditions of the hornblende–biotite gneisses from the SZ of the FSC are 634–641 °C/4–5 kbar. These P–T conditions and mineral assemblages indicate amphibolite facies conditions of the LP/HT-type of metamorphism.The K–Ar biotite cooling ages range from 594 to 617 Ma for the TMC, from 593 to 609 Ma for the KMC, and from 589 to 602 Ma for the FSC. It could be suggested that the cooling metamorphic ages of all complexes lie at approximately 600 Ma, and thus point to a uniform and single metamorphic event for the whole complexes in the southern Sinai Peninsula.The estimated geothermal gradient is in the range of 30–50 °C/km. Such a steep gradient and the LP/HT mineral assemblages suggest that they were formed in an extensional setting and a heat flow was transferred from nearby granite intrusions.