GEO 11 - Met Rocks

• Change undergone by a pre-existing rock (protolith) in the solid rock to another rock


  Metamorphism

  
• Can be igneous rock, sedimentary rock, and even metamorphic rock

  Protolith

  
• Agents of metamorphism


  • Heat
  • Pressure
  • Chemically-active fluids
• Geothermal gradient


  20-30 C increase in temperature per kilometer of descent in crust

  
• Differential or confining stress


  Causes pressure
• Chemically-active fluids


  Speed up reaction rates as catalyst, deposit/remove certain elements, from pore fluids, released from mineral dehydration, or from magmatic bodies
• Contact metamorphism


  1. Contact of magmatic bodies with pre-existing rock

  2. Creates a zone of alteration (aureole)

  3. The closer to the contact, higher the grade of metamorphism

  4. Results in non-foliated rocks

  
• Regional metamorphism


  1. Extensive large areas

  2. Produces foliated rocks

  3. Some rocks formed may not exhibit foliated texture like quartzite and marble
• Hydrothermal metamorphism


  High-temperatures and moderate pressure catalyzed by hot, ion-rich (hydrothermal) fluids
• Shock (impact) metamorphism


  1. High pressure of extraterrestrial meteorite impacts

  2. SiO2 polymorphs: stishovite and coesite
• Foliated metamorphic rocks


  • Exhibit a pervasive planar structure (foliation)
  • Types: slaty cleavage, phyllitic texture, schistosity, gneissic texture
• Non-foliated metamorphic rocks


  • No preferred mineral orientation
  • May contain large crystals (porphyroblast) in fine groundmass
  • May also form crenulations (folds)
• Protolith


  The original rock that underwent metamorphism

  
• Mineralogical assemblage


  Pertains to a group of minerals that form under similar temperature and pressure conditions, used to name metamorphic rocks

  
• Metamorphic environments


  • High pressure, low temperature (trenches)
  • Low pressure, high temperature (volcanic arc)
  • High pressure, high temperature (subduction zones)

  
• Uses of metamorphic rocks


  • Marble for statues and building stones
  • Slate for roofing/flooring
  • Talcum powder
  • Graphite for pencils
  • REEs and precious metals from hydrothermal liquids
  • Anthracite burned for energy
• Metamorphism


  Change undergone by a pre-existing rock (protolith) in the solid rock to another rock

  
• Protolith


  • Can be igneous rock, sedimentary rock, and even metamorphic rock

  
• Agents of metamorphism


  • Heat
  • Pressure
  • Chemically-active fluids
• Geothermal gradient

  20-30 C increase in temperature per kilometer of descent in crust
• Differential or confining stress


  Causes pressure
• Contact metamorphism


  1. Contact of magmatic bodies with pre-existing rock

  2. Creates a zone of alteration (aureole)

  3. The closer to the contact, higher the grade of metamorphism

  4. Results in non-foliated rocks

  
• Regional metamorphism


  1. Extensive large areas

  2. Produces foliated rocks

  3. Some rocks formed may not exhibit foliated texture like quartzite and marble

  
• Hydrothermal metamorphism


  High-temperatures and moderate pressure catalyzed by hot, ion-rich (hydrothermal) fluids
• Shock (impact) metamorphism


  1. High pressure of extraterrestrial meteorite impacts

  2. SiO2 polymorphs: stishovite and coesite
• Foliated metamorphic rocks


  • Exhibit a pervasive planar structure (foliation)
  • Types: slaty cleavage, phyllitic texture, schistosity, gneissic texture

  
• Non-foliated metamorphic rocks

  • No preferred mineral orientation
  • May contain large crystals (porphyroblast) in fine groundmass
  • May also form crenulations (folds)

  
• Protolith


  The original rock that underwent metamorphism

  
• Mineralogical assemblage


  Pertains to a group of minerals that form under similar temperature and pressure conditions, used to name metamorphic rocks

  
• Metamorphic environments


  • High pressure, low temperature (trenches)
  • Low pressure, high temperature (volcanic arc)
  • High pressure, high temperature (subduction zones)