Calculated phase equilibria for low- and medium-pressure metapelites in the KFMASH and KMnFMASH systems

Abstract

Petrogenetic grids in the KFMASH and KMnFMASH model systems calculated with the software THERMOCALc 3.1 are presented for the P-T range 0.5-12 kbar and 450-900 °C, for assemblages involving garnet, muscovite, chloritoid, biotite, chlorite, staurolite, cordierite, spinel, orthopyroxene, K-feldspar, Al2SiO5 phases, quartz, water and melt. Based on calculated compatibility diagrams and P-T and T-MMn [Mn/(Mg + Fe + Mn)] pseudosections for different metapelitic bulk compositions, the principal conclusions are that the addition of Mn to the KFMASH system: (i) enhances the stability of garnet, and, to a lesser extent, aluminosilicates; (ii) reduces the stability of staurolite, cordierite and, to a ..