Geology, geochemistry, and petrogenesis of Jebal Ruro A-type granite, Blue Nile State, Sudan: implications for origin of HFSE mineralization

Abstract

The Jebal Ruro granites occur west of the late Proterozoic Ingessana-Kurmuk suture of the Arabian-Nubian Shield located in the southeastern region of the Blue Nile State of the Sudan. A-type post-collisional granitoids from Jebal Ruro region were here studied through new field, petrographical and whole-rock data. These granitic intrusions comprise alkali granites consisting of aegirine granite, aegirine-arfvedsonite granite, and arfvedsonite granite. Geochemically, they are characterized by high Na2O, K2O, Fe/Mg, Ga/Al, Zr, Y, Nb, and REE (except Eu), and low abundances of CaO, MgO, TiO2, P2O5, and molar (Na2O+ K2O)/Al2O3 ratio ≥ 1 represent their peralkaline affinity. The Jebal Ruro granites show enrichment in Zr, Hf, Y, Nb, Ta, U, Th, Zn, and REE particularly in the aegirine granite and aegirine-arfvedsonite granite. Ruro granites show relatively high ratios of Nb/Ta and Zr/Hf close to that estimated for mantle magma source as well as Th/Ta, Th/U, Zr/Nb, La/Nb, and Rb/Nb. Furthermore, Ta+Yb vs. Gd/Yb, Sm/Yb, La/Yb, and Ta/Yb plots show that Ruro granites have distinguishable characteristics among arc and slab wedge-derived A-type magmas. In this study, we concluded that Jebal Ruro granites are A-type peralkaline to transitional metaluminous granites generated mainly by fractional crystallization from a mantle-derived OIB-like parent magma, emplaced in within-plate post-collisional tectonic environment.