A Quaternary Solution Model for White Micas Based on Natural Coexisting Phengite-Paragonite Pairs

摘要: A thermodynamic model for the quaternary white mica solid solution with end-members muscovite–Mg-celadonite–paragonite–Feceladonite (Ms–MgCel–Pg–FeCel) is presented. The interaction energies MgCel–Pg join, FeCel–Pg join and ternary interactions were obtained from natural coexisting phengite– paragonite pairs. Phengite–paragonite pairs selected based on criteria that their chemical compositions may be represented as a linear combination of end-member respective formation conditions (350–650 � C, 4–21kbar) are accurately known. Previously published excess free energy expressions used Ms–Pg, Ms–MgCel Ms–FeCel binaries. suggested mixing was tested by calculating multicomponent equilibrium phase diagrams. This proved to particularly well suited reproduce compositional variations micas amphibolite-facies metapelites.