Mineral chemistry, geochemistry, Raman spectroscopy and geotectonic significance of Neoproterozoic ophiolitic peridotites and pyroxenites from Kab Amiri district, central Eastern Desert, Egypt

Abstract

The small gold mining Kab Amiri district ultramafic ophiolitic section (central Eastern Desert) comprises highly serpentinized peridotites (serpentinites) and few pyroxenites. It lies within a region of Neoproterozoic ophiolitic rocks and associated derivatives. The chromian spinel textural and chemical compositional features suggest transitional greenschist-amphibolite up to lower amphibolite facies metamorphism and indicates that they represent highly-depleted mantle residues. The presence of the Si-Ob-Si antisymmetric ν1(A1), symmetric ν2(A1) bands and the hydroxyl group (OH) modes are conclusive for the discrimination of antigorite. Furthermore, the speculation of serpentines as antigorite can also be indicated from the hydroxyl group modes. The Kab Amiri ophiolite suite (central Eastern Desert) represents fragments of oceanic lithosphere that are developed in forearc setting in a supra-subduction zone (SSZ) environment. Thus the low TiO2 contents, the enrichment in LILE and LREE and the Nb depletion reflect the remelting of a highly depleted mantle source and suggest their formation in a SSZ environment (i.e forearc).