A CALCULATED PETROGENETIC GRID FOR THE SYSTEM K2O-FEO-MGO-AL2O3-SIO2-H2O, WITH PARTICULAR REFERENCE TO CONTACT-METAMORPHOSED PELITES

A petrogenetic grid is Presented for the system KFMASH (K2O-FeO-MgO-Al 2O3-SiO2-H2O), including biotite, muscovite, K-feldspar, chlorite, chl oritoid, staurolite, cordierite, garnet, orthoamphibole, orthopyroxene , spinel, andalusite, sillimanite, kyanite, quartz and corundum with H 2O in excess, which was calculated using the computer program THERMOCA LC and the Powell and Holland internally consistent thermodynamic data set. By removing the normal constraint of having quartz in excess, bot h quartz-bearing and quartz-absent equilibria are shown. Quartz-absent equilibria are particularly relevant at high-T and low-P conditions, because of their common occurrence at these conditions. The calculated mineral assemblage and mineral compositional variations in terms of F eMg-1 and (Fe, Mg)SiAl-2 exchange vectors are broadly compatible with observations on natural rocks, particularly when non-KFMASH components are taken into account.