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Short circuits

Short circuits. Metamorphic Rocks. form beneath the Earth’s surface heat, pressure and/or fluids on pre-existing rocks exhumed by uplift and erosion Don’t Create / change metamorphism can be: regional fault-related (beside seismic zones) contact (adjacent to igneous rocks).

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Short circuits

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  1. Short circuits

  2. Metamorphic Rocks • form beneath the Earth’s surface • heat, pressure and/or fluids on pre-existing rocks • exhumed by uplift and erosion • Don’t Create / change • metamorphism can be: • regional • fault-related (beside seismic zones) • contact (adjacent to igneous rocks)

  3. Metamorphic rocks • "Changed form" rocks • Produced from preexisting • Igneous rocks • Sedimentary rocks • Other metamorphic rocks

  4. Metamorphism • Original minerals become unstable • new stable minerals form • graphite ---> diamond (MR) • no change in chemistry • all changes occur in the solid state (no liquid involved)

  5. The rock cycle Figure 3.2

  6. “Shields” of the world Canadian Shield ~ 1-3 Ba Exposed now but once must have been 10-30 km below

  7. Origin of pressure in metamorphism Directed stress Figure 3.20

  8. Gneiss typically displays a banded appearance Figure 3.24

  9. End night class

  10. Metamorphic Rocks • form beneath the Earth’s surface • heat, pressure and/or fluids on pre-existing rocks • exhumed by uplift and erosion • metamorphism can be: • regional • contact (adjacent to igneous rocks) • fault-related (beside seismic zones)

  11. Measuring stress directions Figure 3.22

  12. Marble – a nonfoliated metamorphic rock Less directed stress Figure 3.24

  13. Metamorphic rocks • Common metamorphic rocks • Nonfoliated rocks • Marble • Used as a building stone • Variety of colors • Quartzite • Parent rock – quartz sandstone • Quartz grains are fused

  14. Metamorphic rocks • Metamorphic textures • Foliatedtexture • Minerals are in a parallel alignment • Minerals are perpendicular to the compressional force • Nonfoliated texture • Contain equidimensional crystals • Resembles a coarse-grained igneous rock

  15. Metamorphism and Deformation • Metamorphism = new minerals replacing older ones • under these conditions, the rocks may behave plastically • they flow to form folds • metamorphism and deformation are “siblings”

  16. Rock deformation Flowing New Minerals

  17. Folded veins

  18. metamorphism can be: • regional • fault-related (beside seismic zones) • contact (adjacent to igneous rocks)

  19. REGIONAL METAMORPHISM

  20. Metamorphism and plates

  21. Continental collision

  22. Rock deformation Flowing New Minerals

  23. CONTACT METAMORPHISM

  24. CONTACT METAMORPHISM

  25. FAULT-RELATED METAMORPHISM

  26. Fault surface

  27. Metamorphic minerals • Minerals reflect conditions of metamorphism • Mineral content reveal processes occurring within the Earth’s crust • Diamond / graphite • Reaction rates slow with temp

  28. All minerals = Al2Si05 High pressures High T Low pressures

  29. Water

  30. Increasing metamorphism • Increasing grain size, increasing temperature • slate (very fine grained) • schist (visible crystals, coarse grained)

  31. Fault-related

  32. Smearing-Mylonite

  33. Andes

  34. DEFORMATION • accompanies metamorphism • change in shape, geometry • minerals oriented into “fabrics” • folds and fracture on all scales • outcrop to global scale

  35. UNUSED

  36. Melting

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