Causes / agents of metamorphism

• Heat:  the most important agent
  • Drives chemical reactions at atomic level
    • solid–state diffusion of atoms
  • Internal / geothermal sources of heat
    • increase in temperature with depth (geothermal gradient:  ~ 20 – 30° C / km)
    • contact metamorphism – heat from magma
    • metamorphism occurs at ~ 250 – 850° C
• Recrystallization  => more T–stable minerals  (some new)

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