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Concept of

Concept of. Metamorphic Rocks and metamorphism. Concept of metamorphic rocks. METAMORPHIC ROCKS Controls on metamorphism by: P,T, fluids Isotherm Geothermal gradient Confining pressure Directed pressure Regional metamorphism Contact metamorphism High-P metamorphism

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Concept of

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  1. Concept of Metamorphic Rocks and metamorphism

  2. Concept of metamorphic rocks • METAMORPHIC ROCKS • Controls on metamorphism by: P,T, fluids • Isotherm • Geothermal gradient • Confining pressure • Directed pressure • Regional metamorphism • Contact metamorphism • High-P metamorphism • Burial or low-grade metamorphism • Foliated texture • Crystal Growth • Pressure-Temperature Paths (pro-grade and retrograde metamorphism)

  3. Factors that control the type and and degree Metamorphism • Heat • Pressure • Fluids

  4. Temperature increases with depth A typical continental geothermal gradient is 30 degrees C per kilometer Where is the 1300 degree isotherm? Old lithosphere - 150 km New lithosphere (Divergent) - 30 km Volcanic regions (Convergent)- 50 km

  5. 150

  6. Confining Pressure Confining pressure is the same in all directions (incl. 3rd dimension) In water, that is one ton per m2 each meter of depth 10 m ~ 1 atm or 10 tons of pressure Confining pressure implies that there is little more in one direction that in the other directions.

  7. Directed Pressure When one pressure is greater than the other three (incl. 3rd dimension) If directed pressure is great enough rocks can break and/or fold

  8. Fluids • Accelerate chemical reactions • Dissolve ions and move them from one mineral to another • (A change in rock composition by fluid transport is metasomatism)

  9. TYPES OF METAMORPHISM Pressure (Impacts) Subduction Zones Regional Metamorphism Increasing grade Burial (low-P, low-T), low-grade Mountain belts Contact Fluids metasomatism) Temperature

  10. Types of metamorphism shock, contact, regional, and burial

  11. Shock metamorphism Regional metamorphism Depth, km Oceanic crust 0 35 Continental crust Oceanic lithosphere 75 Continental mantle lithosphere Asthenosphere

  12. Regional metamorphism Shock metamorphism Regional metamorphism Depth, km Oceanic crust 0 35 Continental crust Oceanic lithosphere 75 Continental mantle lithosphere Asthenosphere

  13. Regional high-pressure metamorphism Regional metamorphism Shock metamorphism Regional metamorphism Depth, km Oceanic crust 0 35 Continental crust Oceanic lithosphere 75 Continental mantle lithosphere Asthenosphere

  14. Regional high-pressure metamorphism Regional metamorphism Shock metamorphism Contact metamorphism Regional metamorphism Depth, km Oceanic crust 0 35 Continental crust Oceanic lithosphere 75 Continental mantle lithosphere Asthenosphere

  15. Regional high-pressure metamorphism Regional metamorphism Shock metamorphism Contact metamorphism Regional metamorphism Depth, km Oceanic crust 0 35 Continental crust Oceanic lithosphere 75 Continental mantle lithosphere Asthenosphere Burial metamorphism

  16. Regional high-pressure metamorphism Regional metamorphism Shock metamorphism Contact metamorphism Regional metamorphism Depth, km Oceanic crust 0 35 Continental crust Oceanic lithosphere 75 Continental mantle lithosphere Asthenosphere Water Seafloor metamorphism

  17. Textures to distinguish metamorphic rocks

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