MINERAL REACTIONS IN PELITIC ROCKS - 2. CALCULATION OF SOME P-T-X(Fe-Mg) PHASE RELATIONS.

Abstract

On the basis of predicted phase relations in the system K//2O-FeO-MgO-Al//2O//3-SiO//2-H//2O, attempts have been made to calculate isobaric T-X(Fe-Mg) sections from available experimental and thermochemical data. T-X(Fe-Mg) relations, calculated at PH//2O equals 5 kb, for reactions involving garnet-biotite-cordierite-sillimanite-quartz with muscovite or K-feldspar, are compared with available experimental data and compositions of coexisting phases from different metamorphic environments. These methods allow observed textural relationships between minerals, compositions of coexisting phases, experimental and thermochemical data to be assembled in a coherent framework. They may easily be extended to include other phases (minerals, melts, or fluids) or any other bulk rock composition. Refs.