Two new geobarometers for garnet amphibolites, with applications to southeastern Vermont

Two new geobarometers for the assemblage garnet + hornblende + plagioclase + quartz have been calibrated on the basis of the equilibrium 6 anorthite + 3 tremolite = 2 grossular + 1 pyrope + 3 tschermakite + 6 quartz and its Fe end-member equivalent. Data representing 37 natural samples that equilibrated at conditions of 2.5 to 13 kbar and 500 to 800°C were fitted to the general equation -RT ln K_eq = A-BT+(P-1)C by using a weighted least-squares method. Application of the calibrations to samples from southeastern Vermont near the Strafford Chester, and Athens domes documents relatively high pressure metamorphism (7 to 10 kbar) for these structures. -from Authors