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Metamorphism and Metamorphic Rocks

Metamorphism and Metamorphic Rocks. Dr. R. B. Schultz. Metamorphic Rocks

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Metamorphism and Metamorphic Rocks

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  1. Metamorphism and Metamorphic Rocks Dr. R. B. Schultz

  2. Metamorphic Rocks Metamorphic Rocks form from pre-existing rocks subjected to high temperatures and/or pressures. High temps and pressure can cause significant chemical and physical changes. Metamorphism usually occurs 10-30 km below surface where temperatures range about 300-800 C. Factors that influence metamorphism: 1. Temperature -- causes recrystallization; speeds up reactions 2. Pressure -- two types: Confining pressure - due to overburden Directed pressure - pressure in a particular direction; can produce Foliationis the preferential alignment of mineral grains due to compression, and tension, caused bystress andstrain Introduction of new chemical entities -can change bulk rock composition; chemicals are brought in by fluids Fluids -- hydrothermal (hot water) fluids are hot water solutions derived from magma or pore water. They can cause metasomatism (change in bulk composition) and also speed up reactions.

  3. Metamorphic Grade Refers to broad ranges of temperature and pressure 1. Low grade -- low T & P (200-400 C) 2. Intermediate grade -- moderate T, P (400-600 C) 3. High grade - high T, P (600-800 C) Types of metamorphism Regional metamorphism -- affects a large area; commonly due to mountain building; foliated rocks common Contact metamorphism -- rocks near igneous intrusion get baked; produces non-foliated met. Rocks Less Common types: 1. Burial metamorphism -- very low grade; results from deep burial 2. Hydrothermal metamorphism -- due to hot, watery solutions; common along mid-ocean ridges. 3. Cataclastic metamorphism -- due to high pressure along a fault; produces distinctive rock called mylonite

  4. Contact metamorphism Regional metamorphism

  5. Metamorphic Rocks in Relation to Plate Tectonics

  6. Classification of metamorphic rocks Foliated vs. non-foliated Foliated metamorphic rocks: ---increasing grade--------> slate, phyllite, schist, gneiss Non-foliated rocks: quartzite (met. sandstone) marble (met. limestone) Metamorphic mineral assemblages Metamorphic rocks contain certain minerals formed through the process of metamorphism. This depends on original rock composition and metamorphic grade. One can see changes in mineral composition in contact metamorphosed zone near intrusion. Mineral assemblages characteristic of metamorphism at a particular grade Low grade Medium GradeHigh Grade TEXTURETYPE OF METAMORPHISM FOLIATED REGIONAL METAMORPHISM NON-FOLIATED CONTACT METAMORPHISM PARENT ROCKRESULTING METAMORPHIC ROCK Contact Metamorphism: LIMESTONE MARBLE BITUMINOUS COAL ANTHRACITE COAL SANDSTONE QUARTZITE GRANITE GRANITIC GNEISS Regional Metamorphism: SHALE SLATE, PHYLLITE, SCHIST, GNEISS ("NICE")

  7. Non-Foliated Texture Foliated Texture Contact Metamorphism (due to heating) Regional Metamorphism (due to pressure)

  8. Key Terminology Metamorphism Confining pressure Directed pressure Foliation Metamorphic grade Foliated texture Non-foliated texture Parent rock (protolith) Regional metamorphism Contact metamorphism Burial metamorphism Cataclastic metamorphism Hydrothermal metamorphism

  9. Pertinent Web Sites Metamorphic Rock Classification A great site dealing with the classification and identification of metamorphic rocks hosted by James Madison University, Virginia. Metamorphic Rocks (University of Oxford) An extensive listing of metamorphic rock and related sites. Metamorphic Rocks Links (Houghton Mifflin) Links to several metamorphism and metamorphic rock sites, including class lecture notes, arranged by topic. Metamorphic Rocks Links (NAGT) An extensive listing of metamorphic rocks links arranged by topic from the National Association of Geology Teachers (NAGT). Metamorphic Rocks (UBC) An overview of metamorphic rocks from the University of British Columbia. Mineral and Rock Description (National Park Service) Mineral and rock photographs and descriptions from the National Park Service. Online Rock Tutorial from W. H. Freeman Company An introduction to rock identification online tutorial. Rock and Mineral Collecting (USGS) Selected references on rocks, minerals, and gemstones from the United States Geological Survey (USGS). Rock Classification and Identification A good tutorial on the classification and identification of common rocks from the Ministry of Energy and Mines, British Columbia, Canada. Rock Cycle (Mineralogical Society of America) The Mineralogical Society of America site offers a good, general description of the rock cycle directed toward elementary school students. Rock Cycle—University of British Columbia A general introduction to the rock cycle. Rocks and the Rock Cycle Links (NAGT) An extensive listing of rocks and the rock cycle links arranged by topic from the National Association of Geology Teachers (NAGT).

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