Metamorphic TOPIC 1 ( METAMORPHISM )

• Metamorphism

  Solid state mineral and/or textural change to a pre-existing protolith due to changes in the condition of surrounding country rock.
• Prograde Metamorphism

  Metamorphism due to increasing P-T over time
• Retrograde Metamorphism

  Metamorphism due to decreasing P-T over time, overprinting earlier mineral assemblages
• Geothermobarometry

  Use of mineral assemblages or deformation characteristics of specific minerals to infer P-T conditions of metamorphism; Index Minerals
• Heat

  Determines which minerals occur in metamorphic rock
• Diagenesis:   150oC – 200oC

  Metamorphism: 200oC – 800oC

  Partial Melting: >800oC
• Chemically-active Fluids

  Chemical reactions result to dissolution and leaching from protolith and later deposited, especially around hydrothermal vents, magma intrusions, fault/shear zones

  Fluids and vapors with H2O, CO2, CH4, K, Na, B, S, Cl
• Deuteric Alteration -Reaction of hot, vapor-rich fluid associated with magmatic intrusions. Minerals from deuteric alteration include albite, calcite, epidote, sericite, chlorite, serpentine, and talc.
• Metasomatism -Hydrothermal fluids exchange chemical components with protolith by leaching and precipitation. 

  Examples are Spilitization of anorthite into albite and submarine hot vent metallic deposits e.g., Co, Cu, Mn
• Pressure -Stress applied to protoliths resulting to a reorientation and/or reshaping of mineral grains.
• Uniform Stress -Stress uniform in all directions.

  Produce changes in Volume

  • equant grains with crystals of same dimensions
  • Non-foliated textures with no metamorphic layering
• Non-uniform Stress -Stress not uniform in all directions.

  Produce changes in Shape

  • Inequant grains with flat or elongate grains
  • Foliated structures