Petrogenesis of the Jaisamand sanukitoids and associated TTGs: Constraints on the Neoarchean tectonic evolution of the southern Aravalli-Banded Gneissic Complex, northwest India

The lack of a comprehensive whole-rock geochemical and mineralogical dataset for the Archean granitoids of the Aravalli-Banded Gneissic Complex (BGC), northwest India, results in significant challenges for their correct characterization and assessment of their antiquity. The new field, mineralogical and geochemical data classify the Jaisamand granitoids into sanukitoids, TTGs, and transitional TTGs, which are most likely coeval in nature. The obtained results, in conjuncture with the previously published geochemical and geochronological results of the Aravalli–BGC granitoids, unveil the Neoarchean affinity of the Jaisamand pluton. The TTGs were generated by the melting of a subducting slab (metabasite) at shallow (high-HREE-Y TTGs) to moderate depths (medium-HREE-Y TTGs) above the garnet-in line but still within the plagioclase stability field, with garnet-poor residue. The ascending TTG melts were transformed into sanukitoids through differential interaction with the overlying mantle wedge peridotite. The TTG melts, generated at different pressures, interacted with older TTGs at lower and middle crustal levels to form the transitional TTGs. The coexistence of high-HREE-Y and medium-HREE-Y TTGs and sanukitoids suggests a subduction-related setting for the Jaisamand granitoids. The heat required for simultaneous melting at shallow and deeper depths during the Neoarchean was provided by the upwelling asthenosphere due to slab break-off. The study also revealed the occurrence of altered granitoids in the Jaisamand pluton, showing evidence of albitization and silicification. These rocks do not represent the pristine mineralogy and should be carefully examined to avoid misleading interpretations, particularly for the Archean granitoids.