A simple thermodynamic model is developed for silicate melts in in the book by Johannes & Holtz (1996). Thermodynamic approaches to calculating melting relations for basic the system CaO–Na2O–K2O–Al2O3–SiO2–H2O (CNKASH). The Holland & Powell ( Journal of Metamorphic Geology, 16, magmas and wet granitic systems have also been made (e.g. Burnham, 1975; Nicholls, 1980; Berman & Brown, 289–302, 1998) internally consistent thermodynamic dataset is extended via the incorporation of the experimentally determined 1987; Stolper, 1989; Nekvasil, 1990; Ghiorso & Sack, 1995). melting relationships in unary and binary subsystems of CNKASH. The predictive capability of the model is evaluated via the exMetaluminous and peraluminous bulk compositions, primarily in the silica-saturated portion of the haploperimental data in ternary and quaternary subsystems. The resulting dataset, with the software THERMOCALC, is then used to granitic system, CaO–Na2O–K2O–Al2O3–SiO2–H2O (CNKASH), will be considered here. These include comcalculate melting relationships for haplogranitic compositions. Predictions of the P–T stabilities of assemblages in water-saturated positions made up of combinations of the end-member components albite (NaAlSi3O8), K-feldspar (KAlSi3O8), and -undersaturated bulk compositions are illustrated. It is now possible to make useful calculations of the melting behaviour of anorthite (CaAl2Si2O8), aluminosilicate (Al2SiO5), quartz (SiO2) and water (H2O). The purpose of this study is to appropriate composition rocks under crustal conditions. extend the thermodynamic dataset of Holland & Powell (1998) to allow prediction of melting relations involving water-saturated and -undersaturated granitic melts. The