An Introduction to Metamorphic Petrology

In the previous chapters, the emphasis has been on the attainment of chemical equilibrium in metamorphism, because it is only by identifying assemblages of minerals that have co-existed together in equilibrium that the pressures and temperatures of their formation can be determined. Equilibrium studies alone tell us only about the P–T conditions prevailing when a particular assemblage formed, they cannot tell us anything about the rock’s history before or after the assemblage grew.