Progress relating to calculation of partial melting equilibria for metapelites

摘要: mproved activity–composition relationships for biotite, garnet and silicate liquid are used to construct updated P–T grids pseudosections high-grade metapelites. The biotite model involves Ti charge-balanced by hydrogen deprotonation on the hydroxyl site, following substitution , where HD represents site. Relative equivalent biotite-breakdown melting reactions in K2O–FeO–MgO–Al2O3–SiO2–H2O (KFMASH), those K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O2 (KFMASHTO) occur at temperatures close 50 °C higher. A further consequence of activity models is that spinel-bearing equilibria higher temperature pressure. In contrast, addition Na2O CaO KFMASH make Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O (NCKFMASH) system lowers key space relative KFMASH. Combination KFMASHTO NCKFMASH systems Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O2 (NCKFMASHTO) results occurring intermediate between NCKFMASH. Given such differences, choice will be critical inferred conditions application mineral modelling rocks. Further, constructed KFMASH, NCKFMASHTO several representative rock compositions show substantial differences not only metamorphic assemblages but also overall topology, with calculations more reliably reflecting Application rocks should undertaken most comprehensive possible, if reliable quantitative information derived.