8.1: Different Kinds of Metamorphism
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- 17545
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Metamorphic rocks, and the processes that create them, are key parts of the rock cycle that relates igneous, sedimentary, and metamorphic rocks. Most metamorphic rocks form when heat, pressure, or chemically reactive fluids cause changes in preexisting rocks (Figure 8.2). The preexisting, or parent rocks, are called protoliths. Protoliths can be igneous, sedimentary, or metamorphic rock of all sorts. The changes that occur during metamorphism may involve changes in rock texture, in the minerals present, and sometimes in overall rock composition. These changes record geologic processes and events of the past. Consequently, metamorphic petrologists often study metamorphic rocks to interpret rock histories.