Metamorphic Reactions in the Kyanite and Sillimanite Zones of the Barrovian Type Area

Metamorphic conditions in the staurolite, kyanite, and sillimanitezones of the Barrovian type area have been calculated usinga variety of equilibria. Temperatures ranged from 550?C (transitionzone) to 650?C (sillimanite zone) with P {small tilde} 6000bars and XH₂O {small tilde} 0?6. Metamorphism was progressive,and the exact nature of the continuous reactions responsiblefor the formation of index minerals was strongly controlledby bulk rock Mg/(Mg + Fe). Thus, in magnesian rocks staurolitebroke down to kyanite + biotite, whereas in iron-rich rocksit broke down to garnet + muscovite and kyanite was not produced.Sillimanite formed both from kyanite and by dehydration reactionsof staurolite and white mica.