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Metamorphism

Metamorphism. Changes in Rock Composition or Texture Due to Heat, Pressure and Action of Fluids. We Do Not Live at “Normal” Conditions. By the standards of Earth’s interior, we live in a frozen vacuum Things that look “abnormal” to us are normal behavior for materials Solids can flow

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Metamorphism

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  1. Metamorphism Changes in Rock Composition or Texture Due to Heat, Pressure and Action of Fluids

  2. We Do Not Live at “Normal” Conditions • By the standards of Earth’s interior, we live in a frozen vacuum • Things that look “abnormal” to us are normal behavior for materials • Solids can flow • Solids can react chemically with each other • A given material can have several different atomic structures

  3. Weathering At Surface Diagenesis Sedimentary Rocks Metamorphism Starts about 200 C Outside range of normal near-surface conditions Chemical Changes in Rocks

  4. Where Does the Heat Come from? Uranium and Thorium  Other Elements + Lead + Radiation (about 90%) Potassium-40  Calcium-40 or Argon-40 + Radiation (about 10%)

  5. Where Does the Pressure Come from? • Air Pressure = 14 P.s.i. (1 Atmosphere or 1 Bar) • Pressure Beneath 10 Meters (33 Ft.) Of Water = 1 Atm. = 1 Bar • Same Pressure Beneath 3.5 M (10 Ft.) Of Rock • Pressure in Deepest Part of Ocean = 1000 Bars • Pressure under One Mile of Rock = 500 Bars • 1000 Bars (2 Mi. or 3 km Of Rock) = 1 Kilobar (Kb.)

  6. Contact Around Intrusions Shallow: 0-6 Km Low Pressure Local Regional Wide Areas 5-20 Km, Sometimes 30+ High Pressure Usually Accompained by Deformation Types of Metamorphism

  7. Minerals React to Form New Minerals 2SiO2 + CaMg(CO3) 2 == CaMgSi2O6 + 2CO2 Quartz + Dolomite == Pyroxene Minerals Change Form Al2SiO5 == Al2SiO5 Andalusite == Kyanite New Materials Are Added (Metasomatism) CaMg(SiO2)2 + 2CO2 == CaMg(CO3)2 + 2SiO2 Pyroxene + CO2 == Dolomite + Quartz Minerals in Solution == Ore Bodies Recrystallization What Happens During Metamorphism

  8. Why Don't Rocks "De-metamorphose"? Reactions Can't Reverse Because Ingredients Lost • 2AlSi2O5(OH) == Al2SiO5 + 3SiO2 + H2O • Clay Mineral == Andalusite + Quartz + Water (Lost) • An example of carbonate metamorphism: • CaMg(CO3) 2 + 2SiO2 == CaMgSi2O6 +2CO2 • Dolomite + Quartz == Pyroxene + CO2 (Lost) Reactions "Freeze" Sometimes it Does Happen if Fluids Present • Retrograde Metamorphism • On the surface we call it weathering

  9. Metamorphic Grade - Degree to Which the Rock Has Changed Composition • Can Often See Original Bedding • Can Sometimes Even See Deformed Fossils • At High Grades, Rocks Can Often Lose All Trace of Their Original Appearance

  10. Major Metamorphic Rock Types

  11. Major Metamorphic Rock Types

  12. Major Metamorphic Rock Types

  13. Major Metamorphic Rock Types

  14. Major Metamorphic Rock Types

  15. What About Other Rocks?

  16. Al2SiO5 Andalusite Kyanite Sillimanite Ice - 6 high pressure forms Diamond - Graphite Calcite - Aragonite Quartz - - Tridymite - Cristobalite (increasing temperature) - Coesite - Stishovite (increasing pressure) Polymorphism

  17. Metamorphic Facies

  18. Mantle Rocks

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