![]() ![]() When pressure is exerted from rocks above, it is balanced from below and sides, and is called confining or lithostatic pressure. Pressure exerted on rocks under the surface is due to the simple fact that rocks lie on top of one another. Under directed stress, some stress directions (forces) are stronger than others, and this can deform rocks. Pressure (or confining pressure) has equal stress (forces) in all directions and increases with depth under the Earth’s surface. Confining Pressure Difference between pressure and stress and how they deform rocks. Strain is the result of this stress, including metamorphic changes within minerals. Stress is a scientific term indicating a force. The pressure that affects metamorphic rocks can be grouped into confining pressure and directed stress. Like heat, pressure can affect the chemical equilibrium of minerals in a rock. Pressure is the force exerted over a unit area on a material. Temperature increases with increasing depth in the Earth along a geothermal gradient (see Chapter 4) and metamorphic rock records these depth-related temperature changes. Higher temperatures would create magma, and thus, would no longer be a metamorphic process. Heat-driven metamorphism begins at temperatures as cold as 200˚C, and can continue to occur at temperatures as high as 700☌-1,100☌. The temperatures of metamorphic rock lies in between surficial processes (as in sedimentary rock) and magma in the rock cycle. In other words, this atom swapping can happen while the rock is still solid. At high temperatures atoms may vibrate so vigorously they jump from one position to another within the crystal lattice, which remains intact. 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. Painted Wall of Black Canyon of the Gunnison National Park, Colorado, made of 1.7 billion-year old gneiss intruded by younger pegmatites.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |