Geochemistry and petrogenesis of a high-K calc-alkaline Dokhan Volcanic suite, South Safaga area, Egypt: the role of late Neoproterozoic crustal extension

The South Safaga area, Central Eastern Desert of Egypt, comprises an undeformed Dokhan Volcanic suite, which is temporally and spatially associated with immature clastic sediments belonging to the Hammamat Group. Undeformed high level leucogranite intrusions and dykes have invaded these volcanic rocks whereas relatively more deformed lithologies, represented by a syn-tectonic metavolcano-sedimentary association and an I-type tonalite–granodiorite underlie them. The Dokhan Volcanic suite consists of two units: (1) a mafic unit composed of basalt, basaltic andesite, andesite, dacite and their pyroclastic equivalents, (2) a felsic unit of rhyodacite and rhyolite composition in addition to welded flow tuffs. The chemical data of the entire suite show general trends of increasing contents of incompatible elements (K2O, Rb, Nb, Y, and Th), and decreasing contents of elements compatible with clinopyroxene, feldspars, and magnetite (e.g. MgO, Fe2O3∗, Al2O3, CaO, TiO2, Ni, Sr, and Ba) with increasing SiO2. Although these variations are consistent with closed system fractional crystallization processes, the slightly wide variation of Rb/Zr and La/Sm in the felsic volcanics may indicate random crustal contamination during the evolution of these rocks. Normalized trace element patterns show enrichment in LILEs (Rb, Ba, K, Th, and Ce) relative to HFSEs (Nb, Zr, P, and Ti) and are very similar to calc-alkaline subduction-related rocks from orogenic belts. However, the stratigraphic position of the Dokhan Volcanic rocks in relation to the major structural features and tectono-metamorphic events in the Eastern Desert of Egypt suggests that these rocks post-date active subduction. They were emplaced during a post-orogenic extensional collapse event that follows continental collision during late stages of the late Neoproterzoic Pan-African crustal evolution. Major and trace element arc signature of these rocks indicate partial melting of a lithospheric mantle enriched during a previous long subduction event in the Arabian–Nubian Shield. Further investigation of the regional significance of the Dokhan Volcanic rocks and their associated clastic sediments shows that the extensional episode during which these rocks were formed is a regional one.