Metamorphic Petrology Study Notes

Introduction to Petrology

Learning Objectives

  • Define metamorphism in mineralogy and fabric changes.
  • Describe limits of metamorphism.
  • Explain types and processes of metamorphism.
  • Discuss the role of fluids in metamorphism.
  • Classify metamorphic rocks.
  • Identify common metamorphic rocks in hand specimen.

Metamorphism

  • Solid-state changes in a rock's mineralogical composition.
  • Protolith: Original rock (can be sedimentary, igneous, or metamorphic).

Limits of Metamorphism

  • Defined by boundaries of diagenesis (low-grade) and metamorphism (high-grade).
  • Low-grade minerals: albite, muscovite, chlorite, etc; requires temperatures 150−2000°C150-2000°C.
  • Upper limit: begins melting; various rock types have different melting points.

Types of Metamorphism

  1. Contact or Thermal Metamorphism: Caused by heat from magma/lava.
  2. Dynamic Metamorphism: High differential pressure in fault zones; produces mylonites.
  3. Regional Metamorphism: High temperature and pressure over large areas; occurs at convergent boundaries; forms foliated rocks.

Metasomatism

  • Involves chemical active fluids replacing minerals at the atomic level.
  • Types: hydrothermal, pneumatolytic, additive, expulsive.

Classification of Metamorphic Rocks

  • Based on texture, protolith, mineral assemblage, and bulk chemical composition.
  • Textural changes: porphyroblasts, foliation, non-foliated textures.
  • Foliated textures: slaty, phyllitic, schistose, gneissic.

Parent Material and Metamorphic Equivalents

  • Protoliths are classified based on type:
    • Clay-rich sediments -> metapelites
    • Sandstones -> metapsammites
    • Basalts -> metabasite
    • Limestones -> marble

Metamorphic Grade

  • Describes temperature during metamorphism:
    • Low grade: 150−300°C150-300°C
    • Medium grade: 400−650°C400-650°C
    • High grade: above 650°C650°C

Index Minerals

  • Indicators of metamorphic conditions.
  • Isograds: lines indicating the same grade of metamorphism.

Additional Concepts

  • Prograde metamorphism: changes in response to increased temperature.
  • Anatexis: partial melting within high grade metamorphic rocks.

Reminder for Study

  • Understand the relationships between protoliths and their metamorphic equivalents, the effects of temperature and pressure on mineral formation, and the classification criteria for metamorphic rocks.