Tectono-metamorphic evolution of garnet–scapolite-bearing calc-silicate rocks from the Pur-Banera Belt, Aravalli orogen (NW India)

This study presents the first detailed investigation of garnet–scapolite-bearing calc-silicate rocks from the Pur–Banera Belt (PBB) in the Bhilwara region (NW India). These rocks preserve three stages of deformation (S₁, S₂, and S₃) and typically comprise garnet + clinopyroxene + amphibole + biotite + calcite + scapolite bearing assemblages. T–X_CO2 phase equilibrium modelling was carried out in MnO–Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–TiO₂–H₂O–CO₂ (MnNCKFMASTHc) to investigate the mineral paragenesis during metamorphic evolution of calc-silicates. The integration of petrological and phase equilibrium modelling results reveals that the calc-silicate rocks experienced prograde metamorphism from greenschist to upper-amphibolite facies conditions (~515–694 °C, ~9 kbar). Garnet compositional zoning, mineral inclusion patterns and trace element distributions collectively record a sequence of fluid-mediated reactions and episodic mineral growth under varying P–T–X_CO2 conditions as observed from phase equilibria modelling. A comparison between observed and modelled mineral proportions, coupled with the presence of disequilibrium textures, indicates that externally derived fluids with significant hydrous infiltration would have controlled mineral growth in the PBB calc-silicates. U–Pb geochronology of inclusion-type titanite constrains peak metamorphism at ~1280 ± 4 Ma, corresponding to the D₁–D₂ deformation. In contrast, the recrystallized titanite, occurring along the matrix grain margins yielded the timing of retrograde re-equilibration at ~953 ± 7 Ma, which was synchronous with the D₃ deformation. Overall, these results highlight the critical role of externally buffered fluids in driving mineral reactions and geochemical redistribution during the metamorphic evolution of the PBB, linked to basin closure, crustal thickening, and subsequent exhumation associated with the assembly of the Rodinia supercontinent.