Themes of the Day:

• Metamorphic Changes
• Conditions of Metamorphism
• Settings of Metamorphism

Metamorphic Changes

• Metamorphism includes solid-state changes that can affect any type of protolith (parent rock)
• Types of changes:
  • texture - foliation, recrystallization - cleavage development in slate - Texture-based Classification System
  • mineralogy - changes in mineral type reflecting altered P,T conditions (not requiring changes in bulk rock chemical composition)
  • composition - addition or removal of chemical elements to a rock, especially by fluids (metasomatism)

Conditions of Metamorphism

• Conditions that affect the textural and compositional characteristics of metamorphic rocks
  • composition of the protolith
  • temperature and pressure (T,P)
  • effects of tectonic forces (directed stress)
  • fluids
  • time/rates of change
• Temperature - geothermal gradient - may be perturbed by rising magmas, hydrothermal circulation
• Pressure - difference between confining pressure and directed stress - What happens to a styrofoam cup under deep sea pressures? before & after
• Metamorphic Facies - regions of P,T space - characteristic mineral assemblages (depends on protolith composition and P,T)
• Mineral Zones - ways to map isograds ("equal grade")