Temperature changes affect the chemical equilibrium or cation balance in minerals. Temperature measures a substance’s energy-an increase in temperature represents an increase in energy. Rock texture is changed by heat, confining pressure, and a type of pressure called directed stress. During metamorphism, protolith chemistry is mildly changed by increased temperature (heat), a type of pressure called confining pressure, and/or chemically reactive fluids.
Most metamorphic processes take place deep underground, inside the earth’s crust. Metamorphic source rocks, the rocks that experience the metamorphism, are called the parent rock or protolith, from proto– meaning first, and lithos- meaning rock. Metamorphism occurs when solid rock changes in composition and/or texture without the mineral crystals melting, which is how igneous rock is generated. Because metamorphism is caused by plate tectonic motion, metamorphic rock provides geologists with a history book of how past tectonic processes shaped our planet. And metamorphic rocks themselves can be re-metamorphosed. The rock cycle shows that both igneous and sedimentary rocks can become metamorphic rocks. Metamorphic rock material has been changed by temperature, pressure, and/or fluids. Metamorphic rocks, meta- meaning change and – morphos meaning form, is one of the three rock categories in the rock cycle (see Chapter 1). Rock cycle showing the five materials (such as igneous rocks and sediment) and the processes by which one changes into another (such as weathering). Describe the role of hydrothermal metamorphism in forming mineral deposits and ore bodies.Describe what a contact aureole is and how contact metamorphism affects surrounding rock.Explain how metamorphic facies relate to plate tectonic processes.Explain the relationships among slate, phyllite, schist, and gneiss in terms of metamorphic grade.Explain what foliation is and how it results from directed pressure and recrystallization.Describe what recrystallization is and how it affects mineral crystals.Identify and describe the three principal metamorphic agents.Describe the temperature and pressure conditions of the metamorphic environment.6 Metamorphic RocksĬontributing Author: Dr. 6 Metamorphic Rocks Painted Wall of Black Canyon of the Gunnison National Park, Colorado, made of 1.7 billion-year old gneiss intruded by younger pegmatites.
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