Metamorphism

• Metamorphism - The process of changing the physical and chemical properties of rocks by heating and pressure.
• Foliation - Where minerals align in parallel layers.
• Non-Foliated - Where minerals are randomly oriented or exhibit equidimensional shapes.
• Agents of Metamorphism

  • Heat (Temperature)
  • Pressure (Stress)
  • Chemically Active Fluids (Hydrothermal Fluids)
  • Time
  • Composition of Parent Rock
  • Tectonic Stress and Shearing
  • Volatiles (Gases)
• Metamorphic processes

  • the geological processes that alter the mineralogical, chemical, and structural composition of rocks in response to changes in temperature, pressure, and chemical environment beneath the Earth's surface.
  • Occurs primarily in the Earth's crust and upper mantle.
• Recrystallization - growth of new mineral grains from existing ones without melting.
• Phase Change - Transformation of one mineral into another stable mineral phase due to changes in temperature and pressure.
• Neocrystallization - The formation of entirely new minerals that were not present in the original rock
• Deformation - involves the mechanical deformation of rocks due to tectonic forces, resulting in the development of structures such as folds, faults, and foliation.
• Foliation - refers to the alignment of mineral grains or the development of preferred orientation planes within the rock, often parallel to the direction of tectonic stress or shearing
• Metasomatism - Introduction or exchange of chemical components between rocks and chemically active fluids during metamorphism.
• Pressure Solution

  • Also known as pressure dissolution or chemical compaction.
  • Occurs when minerals dissolve at points of contact between mineral grains under pressure, and the dissolved ions migrate and recrystallize in regions of lower stress.
• Regional Metamorphism

  • This type of metamorphism occurs over large areas and is associated with tectonic forces and mountain building processes.
  • Typically happens at convergent plate boundaries or in areas of intense crustal deformation.
• Contact Metamorphism

  • This type of metamorphism occurs when rocks are subjected to high temperatures and low pressures due to their proximity to igneous intrusions, such as magma chambers or lava flows
• Dynamic Metamorphism

  • This type of metamorphism occurs along fault zones and shear zones where rocks are subjected to intense pressure and shearing forces.
• Hydrothermal Metamorphism

  • This type of metamorphism occurs when rocks are altered by hot, mineral-rich fluids circulating through fractures and pore spaces. These fluids can introduce new chemical elements and cause changes in mineral composition.
• Shock Metamorphism

  • This type of metamorphism occurs when rocks are subjected to the extreme pressures and temperatures associated with impact events, such as meteorite impacts or nuclear explosions.
• Burial Metamorphism

  • This type of metamorphism occurs when rocks are buried to great depths within the Earth's crust, leading to changes in temperature and pressure.
• Metamorphic zone

  • A region in the bedrock where the same mineral composition has resulted from metamorphism.
• 3 Metamorphic Zones

  • Epizone - Is the uppermost depth zone of metamorphism lies near the earth's crust surface where temperature is low 300°C and directed pressure is high. In this zone, hydrostatic pressures with low to high shearing stress.
  • Mesozone - It is an intermediate zone where temperature is of the order of 300°C to 500°C. Compared to the epizone, there is a higher pressure and temperature.
  • Katazone (Catazone): The lowermost depth zone of metamorphism, where directed pressure is absent, uniform pressure is high, and temperature is also high 500°C to 700°C
• Metamorphic Facies - Defined as a set of metamorphic mineral assemblages that are typical of a specific range of pressure and temperature conditions during metamorphism.
• Some common textures and structures include

  1. Foliation
  2. Lineation
  3. Porphyroblasts
  4. Schistosity
  5. Band-aid Structure
• Slate - a fine-grained metamorphic rock derived from shale or mudstone.
• Schist - characterized by its medium to coarse-grained texture and often exhibits visible mineral grain.
• Marble - is a metamorphic rock formed from limestone or dolostone that has undergone recrystallization due to metamorphism.

  
  

  Limestone/Dolostone - Parent rock of marble.
• Quartzite - is a hard, metamorphic rock primarily composed of quartz grains that have been fused together.