Abstract
Calculated phase equilibria among the minerals amphibole, chlorite, clinopyroxene, orthopyroxene, olivine, dolomite, magnesite, serpentine, brucite, calcite, quartz and fluid are presented for the system CaO−FeO−MgO−Al2O3−SiO2−CO2−H2O (CaF-MASCH), with chlorite and H2O−CO2 fluid in excess and for a temperature range of 440°C–600°C and low pressures. The minerals chosen in CaFMASCH represent the great majority of phases encountered in metamorphosed ultramafic rocks. The changes in mineral compositions in terms of FeMg-1 and (Mg, Fe)SiAl-1Al-1 are related to variations in the intensive parameters. For example, equilibria at high \(X_{{\text{CO}}_{\text{2}} } \) in the presence of chlorite involve minerals which are relatively aluminous compared with those at low \(X_{{\text{CO}}_{\text{2}} } \). The calculated invariant, univariant and divariant equilibria are compared with naturally-occurring greenschist and amphibolite facies ultramafic mineral assemblages. The correspondence of sequences of mineral assemblages and the compositions of the minerals in the assemblages is very good.
Published Version
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