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Metamorphic Rocks

Metamorphic Rocks. Fig. 3-CO, p.44. Fig. 3-4, p.46. Metamorphism. The transition of one rock into another by temperatures and/or pressures unlike those in which it formed. Metamorphic rocks are produced from Igneous rocks Sedimentary rocks Other metamorphic rocks. Metamorphism.

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Metamorphic Rocks

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  1. Metamorphic Rocks Fig. 3-CO, p.44

  2. Fig. 3-4, p.46

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

  4. Metamorphism • Progresses incrementally from low to high-grade • Rock must remains essentially solid throughout process • Agents of metamorphism include heat, pressure and chemically-active fluids

  5. Metamorphic settings • Contact or thermal metamorphism – driven by a rise in temperature within the host rock • Hydrothermal metamorphism – chemical alterations from hot, ion-rich water • Regional metamorphism (mountain building)

  6. Agents of metamorphism Heat: The most important agent • recrystallization of mineral grains and chemical precipitates • Formation of new, stable minerals • Two sources of heat • Contact metamorphism – heat from magma • An increase in temperature with depth due to the geothermal gradient

  7. Geothermal Gradient

  8. Agents of metamorphism Pressure (stress) increases with depth • Confining pressure: applies forces equally in all directions • Example: depositional environment • Differential stress: applies unequal forces in different directions • Example: mountain-building environment

  9. Figure 7.3a

  10. Agents of metamorphism Pressure (stress) increases with depth • Confining pressure: applies forces equally in all directions • Example: depositional environment • Differential stress: applies unequal forces in different directions • Example: mountain-building environment

  11. Figure 7.2b

  12. Figure 7.4

  13. Result of differential stress

  14. Role of Parent Rock • Mineral composition of parent rock determines mineral composition of metamorphic daughter rock (often the same or similar: • Sandstone and quartzite • Limestone and marble • Mineral composition of parent rock determines grade of metamorphism that takes place:

  15. Quartz sandstone, sedimentary parent rock of quartzite

  16. Quartzite – Metamorphosed Sandstone

  17. Limestone, sedimentary parent rock of marble

  18. Marble – Metamorphosed Limestone

  19. Low grade to high grade Metamorphism (left-right)

  20. Figure 7.17

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