Neoproterozoic concentric intrusive complex of gabbro-diorite-tonalite-granodiorite association, Rahaba area, southern Eastern Desert of Egypt: Implications for magma mixing of arc intrusive rocks

Abstract

We present results from a detailed study of a representative suite of Neoproterozoic concentric intrusive complex, Rahaba intrusive complex (RIC), in the south Eastern Desert of Egypt. It intrudes the island arc volcano-sedimentary successions and serpentinized ultramafic rocks. The RIC is made up of several consanguineous rock types with gradational contacts suggesting that they are genetically related. It is a composite intrusive complex consisting of a mafic core (gabbro and diorite) surrounded by tonalite in the middle to granodiorite at the margin. Abundant of mafic microgranular enclaves (MMEs) are observed within tonalite and granodiorite. The chemical composition of the mafic minerals indicated that they are primary minerals and crystallized from calc-alkaline mafic magma. Geochemically, the gabbroic rocks characterized by low concentrations of alkali contents and high Mg# (40.42 to 58.05) values with enriched contents of large ion lithophile elements (LILEs; Ba, K, Pb, and Sr) and light rare earth elements (LREEs) and depleted in high field strength elements (HFSEs; Nb, Ta, P, Zr, and Hf), reflect their derivation from mafic melt. The tonalite and granodiorite are calc-alkaline, metaluminous and have similar characterization of their LILEs, REEs and HFSEs, suggest their development from the same source magma. The diorites and MMEs are characterized by intermediate compositions between gabbroic and tonalitic rocks, however they have trace element signatures tend to be analogous to those of tonalites. The integrated petrological and geochemical features of the different rock types of the RIC suggest emplacement in an active continental margin setting. The gabbroic rocks originated from hydrous partial melting of a depleted-mantle wedge, metasomatized by aqueous fluids released from the subducted oceanic slab, whereas the diorites and MMEs as well as tonalites were generated due to the mixing of mafic magma related to gabbroic rocks and granodioritic magma.