OPTIMIZED STANDARD STATE AND SOLUTION PROPERTIES OF MINERALS .2. COMPARISONS, PREDICTIONS, AND APPLICATIONS

Internally consistent thermodynamic data for endmembers and solid solu tions derived in Part I of this work are used to predict phase relatio nships and compositions of solid solutions in good agreement with dire ct experimental observations that were not used in the calibration. Th is ''external'' consistency with a large body of experimental observat ions increases confidence in applications to both petrogenetic grid an d thermobarometric calculations. The predicted position of the univari ant FMAS equilibrium Gt+Cd=Opx+Si+Qz occurs between 7.8 kbar - 700 deg rees C and 10.6 kbar - 1100 degrees C, in excellent agreement with ava ilable phase equilibrium reversals, and with thermobarometric results for both higher-P Opx+Si+Qz bearing and lower-P Cd bearing granulites. In these assemblages, garnet composition is an excellent geobarometer and Al2O3 content of Opx is an excellent geothermometer, almost indep endent of other compositional variables. Comparison of temperature est imates from different exchange and net-transfer reactions for a number of samples representative of high-grade terranes demonstrates the abi lity of carefully chosen portions of Fe - Mg minerals to preserve info rmation regarding a high temperature steady state during their evoluti on. The equilibrium Fs+Ok=Alm, based on the Al2O3 content of Opx, offe rs the most robust thermometry for the Opx-Gt assemblage because of it s relative insensitivity to late Fe-Mg exchange. Applications of this thermometer indicate that in many samples the Al2O3 content of Opx yie lds very similar temperatures to Gt-Cd Fe-Mg exchange. For some high t emperature samples, these temperatures are up to 150 degrees C higher than calculated with the Gt-Opx Fe-Mg exchange thermometer.