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Abstract
Based on chemographic relationships and petrogenetic grids in the K2O-FeO-MgO-Al2O3-SiO2-H2O (KFMASH) system, a sequence of prograde (early stage), isothermal decompression (middle stage) and retrograde (late stage) reactions ('back reactions' and hydration reactions) are inferred. Relatively lower P-T estimates (0.35 GPa/550-750 °C) obtained from the different geothermobarometers are attributed to late Fe-Mg re-equilibration during cooling. Therefore, the convergence method has been applied to retrieve simultaneously the P-T conditions of the thermal peak of metamorphism. The near thermal peak condition of metamorphism estimated by the convergence method are 850 °C/0.62 GPa. The P-T estimates define a retrograde trajectory with substantial decompression. [PUBLICATION ABSTRACT]