Abstract
Petrologic studies and application of well-calibrated mineralogic thermometers and barometers reveal several important features common to many granulite terrains: (1) Peak metamorphic pressure and temperature conditions cluster around values of $$7.5 \pm 1 kbar$$ and $$800 \pm 50°C$$, implying average geothermal gradients of 30-35°C/km. (2) In comparison with upper amphibolite facies rocks, especially in paired, amphibolite-granulite terrains, it is evident that granulites are distinguished from amphibolites by the former's higher metamorphic temperatures but not higher pressure. (3) Initial cooling of granulite terrains from peak conditions is nearly isobaric. For garnet closure temperatures of $$600 \pm 50°C$$, the dP/dT retrograde paths inferred from compositionally zoned garnet rims are 2-8 b/°C in most granulites. (4) Primary, coarse sillimanite is found in most granulites, and retrograde kyanite is known in a few. These data suggest that granulites form as a result of anomalous thermal gradients...
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