Rodinia to Gondwana evolution record, South Sinai, Egypt: Geological and geochronological constraints

Abstract

The geological history of Sinai is complicated and differs from the other parts of the Arabian Nubian Shield. Some rocks in Sinai have a signature from the Grenvillian crust, as evidenced in Wadi Seih area. The ultimate objective of this research is to clarify the progression of episodic island arc accretion events from the amalgamation of Rodinia to the assembly of Gondwana supercontinent.Geochemical, mineralogical, U-Pb zircon geochronological, and thermobarometric studies are considered to constrain the nature and tectonic evolution of Wadi Seih gneisses. The protoliths of the orthogneisses are tonalite, trondhjemite, granodiorite, and granite, which were derived from metaluminous-calc-alkaline magma and formed during island-arc accretion. The paragneisses originated from immature Fe-sand and arkose that were deposited in active continental margin and back-arc basin. The orthogneisses and orthopyroxene-free paragneisses were metamorphosed under amphibolite to low granulite-facies conditions with temperatures from 530 to 775 °C at pressures of 3–7 kb, while the orthopyroxene-bearing paragneisses were metamorphosed under granulite-facies at a temperature of 870 °C and pressures of 5–7 kb. Zircon U-Pb geochronological data of the orthogneisses yields three distinct ages (i.e., the oldest ages are 994 ± 6 Ma and 976.6 ± 6.2 Ma, the second age is 740 ± 6.4 Ma, and the third age is 619.4 ± 4.2). Similar ages are obtained from detrital zircons in paragneisses: 1039 ± 57 Ma, 643 ± 49 Ma, 628 ± 3.7 Ma, and 627 ± 6.6 Ma. These new U-Pb data delineate three episodic Mesoproterozoic to Neoproterozoic island arc events at 1050–900 Ma, 850–700 Ma, and 650–580 Ma. The oldest 1050–900 Ma arcs potentially formed during the Rodinia supercontinent-arc collision, while the 850–700 Ma arcs may have formed during the closure of the Mozambique Ocean. The youngest 650–580 Ma arcs could reflect the Gondwana assembly. The age of metamorphism in this study is constrained by the low Th/U ratio of a zircon grain at 633 ± 10 Ma, which is consistent with other previous studies in other areas in Sinai.