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Metamorphic Rocks

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Metamorphic Rocks

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    1. Metamorphic Rocks

    2. Metamorphic Rocks Recrystallization in the solid state Caused by changes in T, P or fluids New environment = new minerals Growing minerals create a new texture

    4. Metamorphism Recrystallization T, P or change in pore fluids initiate change in the mineral assemblage Reaction occur entirely in the solid state

    5. Textural changes occur during metamorphism New minerals grow during metamorphism Precursor rock textures are modified

    9. Origin of Metamorphic Rocks Metamorphism Temperature exceeds 200OC Pressure exceeds 300 M Pa (approx. 10,000 ft deep) Metamorphism ends when melting begins Melting begins at ~700oC

    11. Source of heat Proximity to igneous intrusions Contact metamorphism Different metamorphic grade ring the intrusion Depth of burial 15-30oC increase per km Geothermal Gradient

    19. T & P determine degree of metamorphism Low-grade metamorphism- 200 to 350 OC Intermediate-grade metamorphism-350 to 550 OC High-grade metamorphism - very high temperatures, above 550OC

    23. Metamorphic Rocks Classified by texture and composition Texture is divided into foliated & nonfoliated rocks Mineral composition qualifies textural name

    27. Phyllite Similar to slate More Recrystallization Crystals are larger Common Protolith: shales

    28. Schist Strongly foliated rock Medium to coarse grained -dominated by platy minerals Protoliths: multiple??

    30. Gneiss Coarse grained granular rock Foliation: alternating bands of light & dark minerals Quartz, feldspar, amphibole, biotite Protoliths: ??

    31. Nonfoliated Rocks Marble Interlocking, coarse grained calcite Recrystallization of limestone or dolostone Sedimentary features destroyed

    32. Quartzite Metamorphism of quartz sandstone Entire rock is recrystallized

    33. Amphibolites & Eclogites Metamorphism of mafic rocks Mineral assemblage gives green color

    34. Regional Metamorphic Zones Index minerals A mineral that forms within a specific,often narrow range of conditions Identifies a specific grade of metamorphism Allows further subdivision of rock types

    36. Protolith controls final mineral assemblage Different mineral assemblages form at a given P & T for various parent rocks Metamorphic facies describe a group of minerals formed under similar conditions May be found in different rocks

    39. Metamorphic Rocks & Tectonics Most metamorphic rocks develop due to plate collisions Processes are not observable in the field Conditions at various plate boundaries define possible P & T range Parent rocks present control mineral assemblages

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