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Information about Metamorphism

Published on January 10, 2008

Author: Silvestre


Metamorphism:  Metamorphism Changes in Rock Composition or Texture Due to Heat, Pressure and Action of Fluids We Do Not Live at “Normal” Conditions:  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 Chemical Changes in Rocks:  Chemical Changes in Rocks Weathering At Surface Diagenesis Sedimentary Rocks Metamorphism Starts about 200 C Outside range of normal near-surface conditions Where Does the Heat Come from?:  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%) Where Does the Pressure Come from? :  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.) Types of Metamorphism:  Types of Metamorphism Contact Around Intrusions Shallow: 0-6 Km Low Pressure Local Regional Wide Areas 5-20 Km, Sometimes 30+ High Pressure Usually Accompained by Deformation What Happens During Metamorphism:  What Happens During Metamorphism 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 Why Don't Rocks "De-metamorphose"?:  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 Metamorphic Grade -:  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 Major Metamorphic Rock Types :  Major Metamorphic Rock Types Major Metamorphic Rock Types :  Major Metamorphic Rock Types Major Metamorphic Rock Types :  Major Metamorphic Rock Types Major Metamorphic Rock Types :  Major Metamorphic Rock Types Major Metamorphic Rock Types :  Major Metamorphic Rock Types What About Other Rocks?:  What About Other Rocks? Polymorphism:  Polymorphism Al2SiO5 Andalusite Kyanite Sillimanite Ice - 6 high pressure forms Diamond - Graphite Calcite - Aragonite Quartz - - Tridymite - Cristobalite (increasing temperature) - Coesite - Stishovite (increasing pressure) Metamorphic Facies :  Metamorphic Facies Mantle Rocks:  Mantle Rocks

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