Thermodynamic calibration of geobarometers based on the assemblages garnet-plagioclase-orthopyroxene (clinopyroxene)-quartz

Abstract

Two mineralogic geobarometers based on the assemblage garnet-plagioclase-pyroxeneqvartz, common in granulite-grade quartzofeldspathic and basic lithologies, have been calibrated almost entirely from measured thermodynamic quantities, especially enthalpy of solution and heat capacity measurements. For the continuous reaction: CaAl2Si2O6 + Mg2Si2O6: l/3Ca3Al2Si3O12 * 2/3Mg3Al2Si3Or2 + SiO2 (A) (plagioclase) (opx) the resulting geobarometric expression is: (quartz)