Fluid Inclusion Evidence for Amphibolite-Granulite Facies Transitional Metamorphism in Delhi Supergroup of Rocks

The Deri-Ambaji massive sulphide deposits are associated with the Precambrian rocks of Delhi Supergroup. Detailed fluid inclusion studies of quartz associated with the host rock of sulphide deposit as well as with ores show high density CO₂ (1.05-1.08 g/cm³) as the dominant fluid phase and C0₂-H₂0 (0.94-0.98 g/cm³) and minor H₂O inclusions are also present. The isochore for the high density fluid inclusions indicate the pressure limit of 7.5 Kbars, at the upper temperature limit 800°C, which is in accordance with the estimation by mineralogic thermobarometery. The lower P-T limit is of 2.5 Kbar at 500°C, which indicates that the transition of upper amphibolite to granulite facies of metamorphism has taken place in the area. The P-T path delineated from combined mineralogical and fluid data is characterised by T-convex nature, which is indicative of isothermal crustal uplift, probably promoted by extensional tectonics.