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CU-Boulder GEOL 1010 - Metamorphism and Metamorphic Rocks

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1Metamorphism andMetamorphic RocksClicker•The transformation of one rock into another by solid-state recrystallization is known as–a) Sedimentation–b) Metamorphism–c) Melting–d) Metasomatism–e) Hydrothermal alterationMetamorphism•Metamorphismis the solid-state transformation of pre-existing rock into texturally or mineralogically distinct new rock as the result of high temperature, high pressure, or both.Metamorphism•The mineralogy of a metamorphic rock changes with temperature and pressure.•In general, the highest temperature mineral assemblage is preserved.•It is possible to infer the highest P-T conditions from the mineralogy.Diamond is Metamorphic2Metamorphic Environments•Regional metamorphisminvolves the burial and metamorphism of entire regions (hundreds of km2)•Contact metamorphism results from local heating adjacent to igneous intrusions. (several meters)Metamorphic Environments•Where do you find metamorphic rocks?•In the mountains and in continental shield areas.•Why?•Because elsewhere they are covered by sediments.Metamorphic EnvironmentsRegional Metamorphism•Because the tectonic forces required to bury, metamorphose, and re-exhume entire regions are slow,•most regionally metamorphosed terranes are old (> 500 MY), and•most Precambrian (> 500 MY) terranes are metamorphosed.Regional Metamorphism•Regional metamorphism is typically isochemical (composition of rock does not change), although water may be lost.•Metasomatism is a term for non-isochemical metamorphism.•Contact metamorphism is typicallymetasomatic.Regional Metamorphism•Regional metamorphism is typically isochemical (composition of rock does not change), although water may be lost.•Metasomatism is a term for non-isochemical metamorphism.•Contact metamorphism is typicallymetasomatic.3Conditions of Metamorphism•Changing the mineralogy of a sediment requires temperature > 300ºC and pressures > 2000 atmospheres (~6 km deep).•Temperature increases downward at ~20ºC/km in crust.•Pressure increases downward at ~1000 atm (1kbar) per 3 km (~330 bar/km).Effect of Increasing Temperature•Increases the atomic vibrations•Decreases the density (thermal expansion)•Increases the speed of reactionsEffect of Increasing Pressure•Increases the density (compression)•Pressure can be hydrostatic (equal in all directions), or•Pressure can be directed as a shearwhich can cause–Foliation (alignment of platy minerals)–Lineation (alignment of needle-like minerals).Temperature and Pressure•Continental temperatures increases by ~30°C / km (90°C = 3 km).•Pressure increases by 330 atm / km (1kbar = 3km).4Metamorphosed Sediments•Conglomerate Metaconglomerate•Sandstone Quartzite•Shale Phyllite / Slate•Shale Schist•Shale Gneiss•Limestone Marble•Gypsum (Anhydrite)Schist: Metamorphosed ShaleBlueschistMarble&Blueschist:MetamorphosedShale + LimestoneMarbleMetamorphosed Igneous Rock•Granite Gneiss•Diorite Gneiss•Basalt/Gabbro Eclogite•All are high-grade•Partial melting Migmatite5Garnet in SchistGneissMigmatite (Partial Melting) Migmatite (Partial Melting)Inner Gorge, Grand CanyonGarnet Amphibolite Gneiss6Garnet Amphibolite Gneiss Garnet Chlorite SchistBlueschistAostaValley,ItalyDiamond in EclogiteBlack Canyon of the GunnisonMetamorphism Terms•Regional Metamorphism•Contact Metamorphism•Isochemical•Metasomatism•Hydrostatic•Foliation•Lineation•Terrane •Quartzite•Phyllite•Slate•Schist•Gneiss•Marble•Eclogite•Granulite•Migmatite7Clicker Question•Which is a term for metamorphism that involves significant chemical change?–A. Regional metamorphism–B. Contact metamorphism –C. Metasomatism–D. Diapirism –E. LithificationClicker Question•Which is a term for metamorphism that involves significant chemical change?–A. Regional metamorphism–B. Contact metamorphism –C. Metasomatism–D. Diapirism –E. LithificationClicker Question•The high grade metamorphic equivalent of limestone is?–A. Eclogite–B. Quartzite –C. Marble–D. Slate –E. GneissClicker Question•The high grade metamorphic equivalent of limestone is?–A. Eclogite–B. Quartzite –C. Marble–D. Slate –E. GneissClicker Question•A shale caught in a subduction zone and carried to high pressures at low temperatures would be a?–A. Blueschist–B. Quartzite –C. Marble–D. Slate –E. AnhydriteClicker Question•A shale caught in a subduction zone and carried to high pressures at low temperatures would be a?–A. Blueschist–B. Quartzite –C. Marble–D. Slate –E.


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CU-Boulder GEOL 1010 - Metamorphism and Metamorphic Rocks

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