metamorphism

• Lithostatic pressure


  Pressure affecting an object equally in all directions, inducing changes in volume and associated with granular textures
• Changes in temperature induce thermal agitation of ions, leading to breakdown and reassembly of minerals into stable forms
• Changes due to metamorphism

  • Changes in crystal sizes, internal structure, chemical composition of minerals, and texture of rocks
• Possible sources of water in metamorphism

  • Meteoric or connate water
  • Water in hydrous minerals released during reactions
  • Juvenile water from intrusive magma
• Metamorphism


  Adjusting to conditions other than those from which rocks were originally formed
• Two types of pressures in metamorphism: lithostatic pressure and shear stress
• Temperature, pressure, and chemically reactive fluids are agents of metamorphism
• Liquids and gases present in regions of metamorphism can act as solvents and catalysts accelerating metamorphic change
• Agents of metamorphism

  • Temperature
  • Pressure
  • Chemically reactive fluids
• Metamorphism

  Transformation of rocks in solid state with pressures and temperatures as major factors
• Shear stress


  Directed pressure associated with large earth movements, promoting changes in form and orientation of minerals
• Heat from large intrusive bodies is a significant source of heat for metamorphic processes
• Thermal or contact metamorphism is dominated by heat and occurs near the contact between intrusive rocks and surrounding host rocks
• Possible sources of water

  1. Meteoric or connate water

  2. Water in hydrous minerals released during certain reactions

  3. Juvenile water emanating from an intrusive magma
• Type of metamorphic rock is controlled by factors such as starting material, composition of original rock, degree of metamorphism, changes in composition during metamorphism, and amount of deformation
• Dynamic or cataclastic metamorphism results from directed pressures or shearing stresses in folded regions, thrusted terrains, and fault zones
• Chemically active fluids and gases

  • Liquid and carbon dioxide
• Regional metamorphism occurs due to heat, pressure, presence of chemically active fluids, mechanical deformation, and chemical recrystallization
• Development of metamorphic rocks

  1. Undergoes different stages of transformation

  2. Sedimentary rocks formed at greater depths subjected to different conditions leading to the formation of new minerals

  3. Changes occur in solid state

  4. Imprints of change manifested by formation of new mineral assemblages indicative of higher temperatures and pressures, as well as deformation

  5. Textural changes observed with grains becoming coarser and developing parallel structures
• New changes in rock composition and structure can lead to the production of new resources
• Rocks formed in stressed regions

  • Subjected to granulation, brecciation, and pulverization
  • Mineral grains fractured and distorted
  • Usually flinty, fine-grained, with fragments of crushed rocks showing long axes parallel to the direction of movement
• Foliated rocks


  • Slate
  • Schists
  • Gneiss
• Temperature and pressure are major factors influencing metamorphic transformation in rocks
• Recrystallization among textures is evident in metamorphic rocks
• Non-foliated metamorphic rocks


  • Products of lithostatic pressure or thermal metamorphism
  • Exhibit granoblastic textures with equidimensional grains
  • Example: Marble
• Resultant product of mechanical breaking and grinding of rocks

  • Mylonite
• Limestone can transform into marble, an important material in infrastructures
• Mechanical breaking and grinding of rocks due to direct pressure and shearing stresses


  Commonly caused by fault movements
• Types of metamorphism

  • Regional
  • Contact
  • Cataclastic
• Foliated rocks


  • Exhibit foliation, lineation, and banding of minerals brought about by extreme pressures
  • Recrystallization of minerals occurs
  • Preferred orientation of minerals with their greatest dimension at right angles to the direction of pressure
• Metamorphism is a process of transformation occurring mostly in solid state