Geochronology, geochemistry, and Hf–Sr-Nd isotopes of the Hamisana Shear Zone granitoids in northeastern Sudan: Petrogenesis and tectonic evolution of neoproterozoic juvenile crust in the Nubian Shield

Abstract

We have investigated the petrology, U-Pb zircon ages, whole-rock geochemistry, and Hf–Sr-Nd isotopic compositions of the Hamisana Shear Zone granitoids (HSZG) in the Arabian-Nubian Shield (ANS) in northern Sudan in order to constrain their petrogenesis and tectonic setting of formation. The HSZG rocks consist mainly of granite, quartz syenite, and quartz monzonite that collectively make up two major groups based on their ages and geochemical compositions. The older group (average U-Pb zircon age of ~663 Ma) is represented by calc-alkaline and I-type peraluminous granites, whereas the younger group (average U-Pb zircon age 623.5 Ma) is characterized by A-type and metaluminous monzonitic intrusions. All rocks show high Al2O3, La/Nb, Th/Ta, Ba/Nb ratios, and similar REE patterns indicating enrichment of LILEs (Ba, K, Pb, and Sr) and depletion of HFSEs (Nb, Ta, Sm, P, and Ti), consistent with the characteristics of subduction-related magmas. La/Yb, La/Sm, Th/Nb, Rb/Sr, and Rb/Ba ratios suggest that magmas of the HSZG formed by partial melting of a subduction-modified mantle beneath the ANS. Sr-Nd isotopic compositions of both groups with Nd model ages of 794–877 Ma have εNd(t) values of +5.24 to +6.10. In-situ Hf isotope analyses indicate εHf(t) values of +10.36 to +10.90 for the older granites and +9.9 to +10.73 for the younger quartz monzonites. These isotopic features point to a depleted mantle source of their magmas with no involvement of Pre-Neoproterozoic crust in their melt evolution. The older HSZG granite suites represent pre-collision arc magmatism, whereas the younger HSZG quartz monzonite suites mark post-collisional magmatic units. Both magmatic events contributed significantly to juvenile crust construction during the Neoproterozoic assembly of the ANS.