Magmatic evolution of the area around Wadi Kariem, Central Eastern Desert, Egypt

Abstract

A group of intrusive and extrusive igneous rocks is located around Wadi Kariem, Central Eastern Desert. These rocks have diversed petrographic compositions ranging from gabbros to granites with their volcanic equivalents. They belong to four distinct Neoproterozoic units of the Eastern Desert, namely “metagabbros (MG), older granites (OG), metavolcanics (MV) and younger granites (YG)”. Both major and trace elements are compiled to deduce their genetic relationships. 1/Sr versus Rb/Sr and Rb/Ba versus Rb plots suggest that these rock units exhibit comparative magmatic relationships. The trace element data and the numerical modelling are treated according to the general equation of partial melting (Shaw 1970) and Rayleigh equation of fractional crystallization. These rock types favour complex petrogenetic processes during their generation. The magmatic model is based on “in-sequence” genesis between partial melting and fractional crystallization as well as assimilation and/or magma mixing processes in the late stage. It is evident that these rocks resulted from five essential stages during magmatic evolution of the area: (1) Meta-andesite (MV) was generated throughout partial melting (5 %) of the oceanic crust followed by fractional crystallization (25–50 %); (2) Gabbroic rocks (MG) were derived by partial melting (46 %) of the oceanic crust followed by fractional crystallization (20–40 %); (3) Granodiorite (OG) were derived throughout partial melting (6–6.5 %) of gabbroic parent followed by (5–20 %) fractional crystallization; (4) Alkali-feldspar granite (YG) was derived throughout (45–60 %) fractional crystallization of granodiorite (OG); And finally, (5) the recorded hybrid granodiorite rocks (HG) were generated by partial melting of granodiorite (OG) (24.5 %), assimilation and/or partial melting of metagabbros (MG) (11.7 %), followed by magma mixing and (35–55 %) fractional crystallization.