Published by the American Geophysical Union as part of the Short Courses in Geology Series, Volume 7.

A renaissance in the study of metamorphic rocks has occurred in the past decade. For a long time (with some notable exceptions) metamorphic rocks were studied as examples of heterogeneous systems at equilibrium and the study of metamorphism was, in effect, a phase equilibria experiment. A major goal of metamorphic petrology was to pigeonhole the types of mineral assemblages encountered into the appropriate metamorphic facies. Indeed, even geothemobarometry, in all its sophistication, is nothing but a quantitative form of pigeonholing. However, all of this has changed recently and today, metamorphic rocks are studied in large part as a means to unravel major tectonic problems during orogenesis.