METAMORPHIC 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
• geothermal gradient; large bodies of intrusive rock

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


  geothermal gradient
• due to differential or confining stress

  pressure
• speeds up reaction rates as catalyst; deposits/removes certain elements


  chemically-active fluids
• water source can be from pore fluids, released from mineral dehydration, or from magmatic bodies

  chemically-active fluids
• "contact" of magmatic bodies with pre-existing rocks

  contact metamorphism
• zone of alteration


  aureole
• creates aureole


  contact metamorphism
• the closer to the contact, higher the grade of metamorphism; results in non-foliated rocks

  contact metamorphism
• extensive large areas; produces foliated rocks

  regional metamorphism
• some rocks formed by regional metamorphism may not exhibit foliated texture like quartzite and marble

  regional metamorphism
• high-temperatures and moderate pressure catalyzed by hot, ion-rich (hydrothermal) fluids

  hydrothermal metamorphism
• high pressure of extraterrestrial meteorite impacts; SiO2 polymorphs: stishovite and coesite


  shock (impact) metamorphism
• metamorphism can be classified through?


  texture, size, shape, and relationship of constituent minerals
• exhibits a pervasive planar structure

  foliated
• types of foliation?


  slaty cleavage, phyllitic texture, schistosity, and gneissic texture
• no preferred mineral orientation; may contain large crystals (porphyroblast) in fine groundmass; may also form crenulations (folds)


  non-foliated
• naming of metamorphic rock is based on mineralogical assemblage
• pertains to a group of minerals that form under similar temperature and pressure conditions

  metamorphic facies
• areas where metamorphism occurss

  metamorphic environments
• metamorphic environments :

  trenches - high pressure, low temperature

  volcanic arc - low pressure, high temperature

  subduction zones - high pressure, high temperature
• metamorphism can be classified based on texture, protolith, and mineralogy