ABSTRACT
Despite what was said in Chapter 1 about the peak metamorphic temperature assemblages usually being preserved, retrograde metamorphic effects are actually almost ubiquitous in medium-to high-grade regionally metamorphosed rocks. This is because it takes a long time for those rocks to reach the surface, so there is a lot of time for them to partially reequilibrate to the new P-T conditions, and to be exposed to fluids, as the rocks are cooling and decompressing (Fig. 22.1A).
