Post-Collisional Volcanism in Ediacaran NeoProterozoic Northeast Egypt

Edicaran post-collisional volcanism in the Arabian-Nubian Shield: The high-K calc-alkaline Dokhan Volcanics of Gabal Samr El-Qaa (592±5 Ma), North Eastern Desert, Egypt
Authors:

Eliwa et al

Abstract:

The late Ediacaran Dokhan Volcanics (592 ± 5 Ma) of Gabal Samr El-Qaa are exposed in the northern part of the Arabian–Nubian Shield. They constitute a lava-dominated stratified succession that has been distinguished into a lower mafic unit comprising basaltic andesite and andesite lavas grading upward into more evolved felsic lavas (dacites, trachydacites and rhyolites) that are locally interstratified with ignimbrite sheets. Accessory opaque minerals hosted in these lavas are exclusively Fe-Ti oxides, namely; magnetite (titanomagnetite) and ilmenite, with the predominance of the former in all lava types. The chemical composition of the analyzed pyroxene and biotite phenocrysts match those crystallized in calc-alkaline volcanics. The studied volcanics belong to the high-K calc-alkaline series and are metaluminous to slightly peraluminous. Estimated saturation temperatures have indicated the earlier separation of apatite (839-1002 °C) from the melt, followed by almost simultaneous crystallization of monazite and zircon. The studied Dokhan Volcanics evolved mainly through fractional crystallization, even highly likely have experienced limited crustal contamination by older continental crust. These volcanics have combined geochemical characteristics of both orogenic arc-type and anorogenic within-plate environments, suggesting eruption in a transitional post-collisional setting, during the extensional collapse of the Arabian-Nubian Shield following continental collision between its juvenile crust and the pre-Neoproterozoic continental blocks of west Gondwana. The Dokhan magmas were generated by melting of mafic lower crustal source rocks, belonging to earlier accreted arc sequences of the juvenile Arabian-Nubian Shield crust, without or with slight addition from the underlying upper mantle as a consequence of decompression following delamination of the lithospheric root.