Metamorphic Rocks and Processes
Metamorphic Rocks and Processes GEOL 101 001
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GEOL 101 001
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This 3 page Class Notes was uploaded by Madeline Wilson on Tuesday February 9, 2016. The Class Notes belongs to GEOL 101 001 at University of South Carolina taught by Dr. Knapp in Spring 2016. Since its upload, it has received 24 views. For similar materials see Introduction to the Earth in Geology at University of South Carolina.
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Date Created: 02/09/16
Metamorphic Rocks and Processes Garnet is commonly used to determine a metamorphic Pressure- Temperature path. Metamorphism: change affected by pressure, heat, and water that results in a more compact and more highly crystalline condition Metamorphic rock: rock that has undergone changes in texture, mineralogical, and/or chemical composition in the solid state (10-30km in the Earth’s crust) How do rocks metamorphose? Through partial or complete recrystallization of minerals over long periods of time Rocks remain in solid state during metamorphism Matrix can melt due to fluids that lower melting temperature Pressure: Greater pressure tends to decrease space available for mineral growth; density Confining pressure is a general force applied equally in all directions Directed pressure is a force exerted in a particular direction (continent- continent boundaries – horizontal pressure) Temperature: Heat greatly affect a rock’s minerology/texture Geothermal gradient: measure of variation of temperature with depth (average 30C/km) Main factors: Internal heat of the Earth Earth’s pressure Earth’s fluids Isotherm – surface of equal temperature Stable Continental Lithosphere will be coolest at 30km deep. Metamorphic Reactions: Prograde: mineral changes that take place during an increase in temperature Retrograde: mineral changes that take place during a decrease in temperature Fluids: Fluids (H2O): act as a catalyst during metamorphism Aid the exchange of ions between growing crystals Metasomatism: change in a rock’s bulk composition by fluid transport of chemical substances in or out of a rock Metamorphic grade: Refers to intensity of metamorphism High grade – high temperature, high pressure Low grade – low temperature, low pressure No rocks at low temperature, high pressure Regional – changes in rocks due to tectonic forces, widespread changes in pressure and temperature Contact – low pressure, high temperature, intrusion of magma against colder rocks Seafloor – low pressure, high temperature, mid-ocean ridges Burial – low pressure, low temperature, due to successive burial Shock – high pressure, low temperature, meteorite impacts Ultra-High Pressure – high pressure, high temperature Amount of change depends on: Grade of metamorphism Duration of metamorphism Composition of rock Low grade, small crystals, low coarseness ----------------------- High grade, large crystals, high coarseness Slate(diagenesis)Phylite(low grade)Schist(intermediate)Gneiss(high grade)Migmatite(high grade) Classification is based on texture Foliation: a set of flat or wavy parallel planes produced by deformation Most minerals are stable over a relatively narrow range of pressure and temperature Stability range of different minerals sometimes overlaps and provides insights into the history of metamorphic rocks Metamorphism occurs at all types of plate boundaries and plate interiors Subducted lighter metamorphic rocks are driven upward by their inherent buoyancy relative to surrounding rocks Boundary between 2 continents colliding is called suture Ophiolites (metamorphosed oceanic crust) are often found near a suture
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