Fluid evolution characteristics and piezothermic array of south Indian charnockites

Abstract

The Precambrian granulite fades metamorphism that gave rise to the charnockites of south India involved the activity of chemically distinct fluids that evolved progressively from early high-density carbonic (1.0−0.95 g/cm³) through moderate-density carbonic (0.75−0.65 g/cm³) and mixed carbonic aqueous to low-salinity and moderate-density aqueous (0.88−0.65 g/cm³) types. The pressure-temperature conditions recorded by fluid inclusions define a piezothermic array that is characterized by higher convexity toward the temperature axis than the array defined by the locus of metamorphic geotherms obtained from mineral assemblages. The convexity depicts a fast rate of uplift that exceeded the rate of heat transfer. The carbonic metamorphism resulting in the formation of charnockites was achieved under high P_{CO2 conditions by the transfer of juvenile CO2 from the upper mantle.}