Geochemistry and Sm–Nd isotope characteristics of the Neoarchean I- and S-type granitoids of Nalgonda region, Eastern Dharwar Craton, India: petrogenesis and geodynamic implications

Situated in the Eastern Dharwar Craton, the Nalgonda granitoid suites consist of Tonalite Trondhjemite Granodiorite (TTG), biotite and two-mica granites, sanukitoids and hybrid granites. The petrography, whole-rock geochemistry and the Sm–Nd isotope geochemistry of the studied granitoids were done. The rocks are mainly made up of quartz, K-feldspar, plagioclase and biotite ± apatite. The biotite and two-mica granites are exclusively peraluminous in nature with S-type affinity, while the sanukitoids and the hybrid granites display both the I- and S-type characters with the metaluminous and peraluminous nature. The studied granitoids present negative anomalies in Nb–Ta, Pb and Ti suggesting the arc environment and the possible involvement of the subducted crust component to their formation. The isotope geochemistry results indicate heterogeneous source characteristics for the studied granitoids. The biotite and two-mica granites are from typical felsic crustal source, while the sanukitoids and the hybrid granites are from mixed older mafic crustal source with mantle component. The hybrid granites are formed due to interactions between the biotite and two-mica granites, the sanukitoids and the TTG. The geochemical and isotope systematics support a two-stage emplacement model for the Nalgonda granitoids as in the entire Eastern Dharwar Craton. The first stage is long process forming the TTG basement, and the second stage is short process generating the other three variants. This implies that, the subduction-collision tectonic setting is the principal tectonic model that permitted the emplacement of the Nalgonda granitoids.