Essentials of Geology (10th Edition)

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Essentials of Geology Metamorphic Rocks Chapter 7
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Metamorphism The transition of one rock into another by temperatures and/or pressures unlike those in which it formed Metamorphic rocks are produced from Igneous rocks Sedimentary rocks Other metamorphic rocks
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Metamorphic rocks are produced from a pre-existing “parent rock”, which can be igneous, sedimentary, or metamorphic Changes occur in appearance, texture, and mineralogy. This rock was This rock was previously a previously a conglomerate conglomerate
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Metamorphism occurs in the crust and upper mantle, and the rocks remain in a solid solid state (200°C to 800°C).
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Metamorphism Metamorphism occurs when pre-existing rock experiences high temperatures and pressures unlike the original formation conditions. The rock typically changes it’s mineralogy and texture (appearance) in response to the new conditions. Metamorphism ranges from minor changes ( low grade ) (ex, shale shale slate slate ) to major changes ( high grade ), and the original “parent rock” may be difficult to identify.
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Metamorphism Metamorphism progresses incrementally from low-grade to high-grade During metamorphism the rock must remain essentially solid Metamorphic settings Contact or thermal metamorphism driven by a rise in temperature within the host rock
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Metamorphic minerals, rocks, and “grade” Metamorphic minerals, rocks, and “grade”
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Metamorphism Metamorphic settings Hydrothermal metamorphism chemical alterations from hot, ion- rich water Regional metamorphism Occurs during mountain building Produces the greatest volume of metamorphic rock Rocks usually display zones of contact and/or hydrothermal metamorphism
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Agents of metamorphism Heat The most important agent Recrystallization results in new, stable minerals Two sources of heat Contact metamorphism – heat from magma An increase in temperature with depth due to the geothermal gradient
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Magma - a local source of heat Granite (formerly magma) Granite (formerly magma) Metamorphosed sedimentary rocks forming a
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Agents of metamorphism Pressure ( stress ) Increases with depth Confining pressure applies forces equally in all directions Rocks may also be subjected to differential stress, which is unequal in different directions
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Sources of heat for metamorphism Figure 8.3 Figure 8.3
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2) Pressure a. confining pressure increases equally in all directions with depth, and will often increase rock density. b. differential stress occurs with directed forces, such as at a convergent margin.
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Agents of metamorphism Chemically active fluid Mainly water with other volatile components Enhances migration of ions Aids in recrystallization of existing minerals
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Agents of metamorphism Chemically active fluids Sources of fluids Pore spaces of sedimentary rocks Fractures in igneous rocks Hydrated minerals such as clays and micas
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1) Chemically reactive fluids – hot, ion-rich water can alter minerals and can accelerate metamorphism
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This note was uploaded on 06/15/2011 for the course GEL 111 taught by Professor Vandevelde during the Spring '11 term at Craven CC.

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Ch07 - Essentials of Geology Metamorphic Rocks Chapter 7...

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