Abstract
Abstract This paper presents a numerical simulation of the well-documented, fluid-controlled Kabbal and Ponmudi type gneiss-charnockite transformations in southern India using a free energy minimization method. The computations have considered all the major solid phases and important fluid species in the rock - C-O-H and rock - C-O-H-N systems. Appropriate activity-composition relations for the solid solutions and equations of state for the fluids have been included in order to evaluate the mineral-fluid equilibria attending the incipient charnockite development in the gneisses. The C-O-H fluid speciation pattern in both the Kabbal and Ponmudi type systems indicates that CO2 and H2O make up the bulk of the fluid phase with CO, CH4 H2 and O2 as minor constituents. In the graphite-buffered Ponmudi-system, the abundance of CO, CH4 and H2 is orders of magnitude higher than that in the graphite-free Kabbal system. Simulation with C-O-H -N fluids of varying composition demonstrates the complementary role of CO2 and N2 as rather inert dilutants of H2O in the fluid phase. The simulation, carried out on available whole-rock data, has demonstrated the dependence of the transfonnation X(H2O) on P, T, and phase and chemical composition of the precursor gneiss.
Published Version
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