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Metamorphic Rocks

Metamorphic Rocks

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Metamorphic Rocks

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  1. Metamorphic Rocks Chemical cooking and crystal crushing

  2. Metamorphism • The transition (transformation) of one rock into another by temperatures and/or pressures unlike those in from which it formed • Metamorphic rocks are produced from • Igneous rocks • Sedimentary rocks • Other metamorphic rocks

  3. Metamorphism • Metamorphism progresses incrementally from low-grade to high-grade • During metamorphism the rock remains essentially solid

  4. Metamorphic Environs • Contact or thermal metamorphism – driven by a rise in temperature within the host rock • Hydrothermal (hydro = water, thermal = hot) metamorphism – chemical alterations from hot, ion-rich water

  5. Contact

  6. Hydrothermal

  7. Metamorphic Environs • Regional metamorphism • Occurs during mountain building • Produces the greatest volume of metamorphic rock • Rocks usually display zones of contact and/or hydrothermal metamorphism

  8. Regional

  9. Agents of metamorphism • Heat • Most important agent • Recrystallization results in new, stable minerals • Two sources of heat 1) Contact metamorphism– heat from magma 2) An increase in temperature with depth due to the geothermal gradient

  10. Agents of metamorphism • Pressure and differential stress • Increases with depth • Confining pressure applies forces equally in all directions • Rocks may also be subjected to differential pressure (which is unequal in different directions)

  11. Pressure in metamorphism

  12. Agents of metamorphism • Chemically active fluids • Mainly water with other volatile components • Enhances migration of ions • Aids in recrystallization of existing minerals

  13. Agents of metamorphism • Sources of fluids • Pore spaces of sedimentary rocks • Fractures in igneous rocks • Hydrated minerals such as clays and micas

  14. Agents of metamorphism • The importance of parent rock • Most metamorphic rocks have the same overall chemical composition as the parent rock • Mineral makeup determines the degree to which each metamorphic agent will cause change

  15. Metamorphic textures • Texture refers to the size, shape, and arrangement of mineral grains • Foliation– any “planar” arrangement of mineral grains or structural features within a rock

  16. Metamorphic textures Examples of foliation: • Parallel alignment of platy and/or elongate minerals • Parallel alignment of flattened mineral grains and pebbles • Compositional banding • Slate cleavage

  17. http://seis.natsci.csulb.edu/bperry/metaconglStan2.JPG

  18. http://www.beavton.k12.or.us/greenway/leahy/00-01/rocks/gneiss.jpghttp://www.beavton.k12.or.us/greenway/leahy/00-01/rocks/gneiss.jpg

  19. Foliation - directed stress

  20. http://seis.natsci.csulb.edu/bperry/slatesideview2.JPG

  21. Metamorphic (foliated) textures • Platy minerals are discernible with the unaided eye and exhibit a planar or layered structure • Rocks having this texture are referred to as schist

  22. http://www.pitt.edu/~cejones/GeoImages/6MetamorphicRocks/Schist/SchistGarnetMuscRusty.jpghttp://www.pitt.edu/~cejones/GeoImages/6MetamorphicRocks/Schist/SchistGarnetMuscRusty.jpg

  23. Gneissic • During higher grades of metamorphism, ion migration results in the segregation of minerals • Gneissic rocks exhibit a distinctive banded appearance

  24. http://content.answers.com/main/content/wp/en/thumb/0/04/180px-Skagit-gneiss-Cascades.jpghttp://content.answers.com/main/content/wp/en/thumb/0/04/180px-Skagit-gneiss-Cascades.jpg

  25. Metamorphic rocks that lack foliation are referred to as nonfoliated • Develop in environments where deformation is minimal • Typically composed of minerals that exhibit equidimensional crystals or • Single mineral composition

  26. http://resourcescommittee.house.gov/subcommittees/emr/usgsweb/photogallery/images/Quartzite%202_jpg.jpghttp://resourcescommittee.house.gov/subcommittees/emr/usgsweb/photogallery/images/Quartzite%202_jpg.jpg

  27. The Rock Cycle