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

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Presentation on theme: "Metamorphism Changes in Rock Composition or Texture Due to Heat, Pressure and Action of Fluids."— Presentation transcript:

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

2 Take-Away Points 1.Rocks change due to heat, pressure, and fluids 2.Heat in the earth is original heat plus heat from radioactive decay 3.Pressure is simply from the weight of overlying rocks. Pressure = Depth 4.What happens during metamorphism 5.Different metamorphic conditions result in different rocks and minerals 6.Metamorphic rocks reveal temperature and pressure conditions in the earth.

3 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

4 Chemical Changes in Rocks Weathering At Surface Diagenesis Sedimentary Rocks Metamorphism Starts about 200 C Outside range of normal near- surface conditions 1. Rocks change due to heat, pressure, and fluids

5 Where Does the Heat Come from? Some Heat is Probably Original Much heat is from Radioactive Decay –Uranium and Thorium  Other Elements + Lead + Radiation (about 90%) –Potassium-40  Calcium-40 or Argon-40 + Radiation (about 10%) Typical temperature increase –25 C per kilometer near surface –1-2 C per kilometer in deep earth 2. Heat in the earth is original heat plus heat from radioactive decay

6 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.) 3. Pressure is simply from the weight of overlying rocks. Pressure = Depth

7 Types of Metamorphism Contact Around Intrusions Shallow: 0-6 Km Low Pressure Local heat source Regional Wide Areas 5-20 Km, Sometimes 30+ High Pressure Usually Accompanied by Deformation and Mountain Building 4. What happens during metamorphism

8 What Happens During Metamorphism Minerals React to Form New Minerals 2SiO 2 + CaMg(CO 3 ) 2 == CaMgSi 2 O 6 + 2CO 2 Quartz + Dolomite == Pyroxene Minerals Change Form Al 2 SiO 5 == Al 2 SiO 5 Andalusite == Kyanite New Materials Are Added (Metasomatism) CaMg(SiO 2 ) 2 + 2CO 2 == CaMg(CO 3 ) 2 + 2SiO 2 Pyroxene + CO 2 == Dolomite + Quartz Minerals in Solution == Ore Bodies Recrystallization 4. What happens during metamorphism

9 Why Don't Rocks "De-metamorphose"? Reactions Can't Reverse Because Ingredients Lost –2AlSi 2 O 5 (OH) == Al 2 SiO 5 + 3SiO 2 + H 2 O –Clay Mineral == Andalusite + Quartz + Water (Lost) An example of carbonate metamorphism: –CaMg(CO 3 ) 2 + 2SiO 2 == CaMgSi 2 O 6 +2CO 2 –Dolomite + Quartz == Pyroxene + CO 2 (Lost) Reactions "Freeze" Sometimes it Does Happen if Fluids Present Retrograde Metamorphism On the surface we call it weathering 4. What happens during metamorphism

10 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 5. Different metamorphic conditions result in different rocks and minerals

11 Major Metamorphic Rock Types Temp CTemp FCoalLimestoneSandstoneBasaltShale Index Minerals Lignite Bituminous 500Anthracite GraphiteMarbleSlateChlorite 700Greenstone 800QuartzitePhylliteBiotite SchistGarnet 1000AmphiboliteStaurolite Gneiss Kyanite 1200Sillimanite 700 Melting Begins 5. Different metamorphic conditions result in different rocks and minerals

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13 Major Metamorphic Rock Types Temp CTemp FCoalLimestoneSandstoneBasaltShale Index Minerals Lignite Bituminous 500Anthracite GraphiteMarbleSlateChlorite 700Greenstone 800QuartzitePhylliteBiotite SchistGarnet 1000AmphiboliteStaurolite Gneiss Kyanite 1200Sillimanite 700 Melting Begins 5. Different metamorphic conditions result in different rocks and minerals

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15 Major Metamorphic Rock Types Temp CTemp FCoalLimestoneSandstoneBasaltShale Index Minerals Lignite Bituminous 500Anthracite GraphiteMarbleSlateChlorite 700Greenstone 800QuartzitePhylliteBiotite SchistGarnet 1000AmphiboliteStaurolite Gneiss Kyanite 1200Sillimanite 700 Melting Begins 5. Different metamorphic conditions result in different rocks and minerals

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17 Major Metamorphic Rock Types Temp CTemp FCoalLimestoneSandstoneBasaltShale Index Minerals Lignite Bituminous 500Anthracite GraphiteMarbleSlateChlorite 700Greenstone 800QuartzitePhylliteBiotite SchistGarnet 1000AmphiboliteStaurolite Gneiss Kyanite 1200Sillimanite 700 Melting Begins 5. Different metamorphic conditions result in different rocks and minerals

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19 Major Metamorphic Rock Types Temp CTemp FCoalLimestoneSandstoneBasaltShale Index Minerals Lignite Bituminous 500Anthracite GraphiteMarbleSlateChlorite 700Greenstone 800QuartzitePhylliteBiotite SchistGarnet 1000AmphiboliteStaurolite Gneiss Kyanite 1200Sillimanite 700 Melting Begins 5. Different metamorphic conditions result in different rocks and minerals

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21 What About Other Rocks?

22 Polymorphism Al 2 SiO 5 Andalusite Kyanite Sillimanite Ice - 6 high pressure forms Diamond - Graphite Calcite - Aragonite Quartz - - Tridymite - Cristobalite (increasing temperature) - Coesite - Stishovite (increasing pressure) 6. Metamorphic rocks reveal temperature and pressure conditions in the earth.

23 Metamorphic Facies Depth\Temp300C400C500 C600 C700 C800 C 5 kmZeoliteContact Metamorphism - Andalusite forms 10 km - 3 kbGreenschist Chlorite, Biotite form Slate Greenstone Quartzite Marble Amphibolite Garnet, Staurolite, Kyanite form Schist Amphibolite Quartzite Marble Gneiss Granulite Sillimanite forms Muscovite breaks down to K- feldspar Partial Melting Gneiss 15 kmBlueschist 20 km - 6 kb 25 km 30 km - 9 kb 35 km 40 km - 12 kbNot FoundEclogite (Mantle) 6. Metamorphic rocks reveal temperature and pressure conditions in the earth.

24 Mantle Rocks

25 Take-Away Points 1.Rocks change due to heat, pressure, and fluids 2.Heat in the earth is original heat plus heat from radioactive decay 3.Pressure is simply from the weight of overlying rocks. Pressure = Depth 4.What happens during metamorphism 5.Different metamorphic conditions result in different rocks and minerals 6.Metamorphic rocks reveal temperature and pressure conditions in the earth.


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