Calculation of Phase Relations Involving Haplogranitic Melts Using an Internally Consistent Thermodynamic Dataset

A simple thermodynamic model is developed for silicate melts in the system CaO–Na2O–K2O–Al2O3–SiO2–H2O (CNKASH). The Holland & Powell (Journal of Metamorphic Geology, 16, 289–302, 1998) internally consistent thermodynamic dataset is extended via the incorporation of the experimentally determined melting relationships in unary and binary subsystems of CNKASH. The predictive capability of the model is evaluated via the experimental data in ternary and quaternary subsystems. The resulting dataset, with the software THERMOCALC, is then used to calculate melting relationships for haplogranitic compositions. Predictions of the P–T stabilities of assemblages in water-saturated and -undersaturated bulk compositions are illustrated. It is now possible to make useful calculations of the melting behaviour of appropriate composition rocks under crustal conditions.