P–T–X (Fe–Mg) Relations of Cummingtonite-sillimanite-cordieritequartz-H2O Equilibrium: Implications on Evolution of Metamorphic Rocks

Abstract

Abstract The P–T–X (Fe–Mg) phase relations of the cummingtonitesillimanite-cordierite-quartz-fluid assemblage have been constructed considering the model system FeO–MgO–Al2O3–SiO2–H2O (FMASH) and using available experimental and thermodynamic data. The assemblage represents a divariant reaction: cum + sil+ qtz= crd + H2O, the Fe- and Mg-end member reactions of which have positive slope in P–T space. Isobaric T–X (Fe–Mg) loop and isothermal P–X (Fe–Mg) loop show that,at constant pressure, both cummingtonite and cordierite become Fericher with increasing temperature, whereas, at constant temperature, this assemblage is displaced towards Mg-richer compositions with increasing pressure. The study of the P–T–X relationships of cummingtonite-sillimanite-cordierite-quartz-H2O equilibrium suggests that the cummingtonite–cordierite bearing assemblages are stable at the low-pressure metamorphic environment.