METAMORPHIC ROCKS

• 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
• heat

  • geothermal gradient
  • large bodies of intrusive rock
• GEOTHERMAL GRADIENT - 20-30 C increase in temperature per kilometer of descent in crust
• PRESSURE - due to differential or confining stress
• CHEMICALLY-ACTIVE FLUIDS

  • speeds up reaction rates as catalyst
  • deposits/ removes certain elements
  • water sources can be from pore fluids, released from mineral dehydration, or from magmatic bodies
• contact metamorphism - “contact” of magmatic bodies with

  pre-existing rock; the closer to the contact, higher the grade of metamorphism
• aureole - zone of alteration
• regional metamorphism - extensive large areas, produces foliated rocks
• HYDROTHERMAL METAMORPHISM - High-temperatures and moderate pressure

  catalyzed by hot, ion-rich (hydrothermal) fluids
• SHOCK (IMPACT) METAMORPHISM - high pressure of extraterrestrial meteorite

  impacts; SiO2 polymorphs: stishovite and coesite
• FOLIATED - exhibits a pervasive planar structure (foliation)
• classification of metamorphism based on texture: size, shape, and relationship of constituent minerals
• types of foliation

  • SLATY CLEAVAGE
  • PHYLLITIC TEXTURE
  • SCHISTOSITY
  • GNEISSIC TEXTURE
• NON-FOLIATED

  • no preferred mineral orientation
  • may contain large crystals (porphyroblast) in fine groundmass
  • may also form crenulations (folds)
• BASED ON MINERALOGY - naming of metamorphic rock is based on mineralogical assemblage
• metamorphic facies - pertains to a group of minerals that form under

  similar temperature and pressure conditions
• metamorphic environments - areas where metamorphism occurs
• CLASSIFICATION OF METAMORPHIC ENVIRONMENTS

  • high pressure, low temperature (trenches)
  • low pressure, high temperature (volcanic arc)
  • high pressure, high temperature (subduction zones)
• RESOURCES FROM METAMORPHIC ROCKS:

  marble - used for statues and building stones

  talcum powder

  slate - used for roofing/flooring

  graphite - pencils

  REEs and precious metals

  anthracite is burned for energy