Geochemistry and tectonic evolution of Neoproterozoic Wadi Kid Dokhan volcanics, Southeast Sinai, Egypt

Abstract

The debate revolves around the tectonic setting and petrogenesis of the Neoproterozoic Dokhan volcanics in the Egyptian Shield (ca.610–560 Ma by whole rock Rb–Sr and ca. 600–590 Ma by sensitive high-resolution ion microprobe SHRIMP U–Pb zircon), which formed during the transition from convergent to extensional, possibly after the collision of east and west Gondwana. The Dokhan volcanics suite in Egypt is undisturbed and geographically connected to immature clastic deposits from the Hammamat molasse-type sediments. These volcanics consist of basic, intermediate, and acidic rocks. The basic and intermediate Dokhan volcanics are represented by basalts and andesites, which are less common, while the acidic Dokhan volcanics are represented by rhyodacites, which are considered the main rock units encountered in the studied area. The geochemical values reveal broad trends of decreasing concentrations of compatible elements with MgO, Fe₂O₃, FeO, MnO, CaO, Co, Sr, and Zn, as well as increasing amounts of incompatible contents (Al₂O₃ and Na₂O) with increasing SiO₂ content. These geochemical characteristics are shared by Dokhan volcanics and associated Hammamat clastic sediments from Sinai and the Eastern Desert of Egypt. The geochemical behavior of Wadi Kid Dokhan volcanics is characterized by both orogenic arc-type and anorogenic within-plate tectonic environments. The magma types of Dokhan volcanics tend to have metaluminous to peraluminous, medium- to high-K calc-alkaline affinities. Meanwhile, the basaltic rocks are of tholeiitic origin. The lava flow of the medium- to high-K calc-alkaline post-collisional Dokhan volcanics shows a tectonomagmatic transition between the calc-alkaline arc-related magmatism and the alkaline anorogenic magmatism. The Dokhan volcanics in Sinai that were the focus of the inquiry exhibit a broad, evolving compositional range (rhyolite-basalt). A typical rhyolitic composition with an average silica concentration (69.5–70.9 wt%), an average andesitic content (57.3–58.6 wt%), and an average basaltic content (47.8 wt%) is also present in the Dokhan volcanics from the Eastern Desert of Egypt.