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Ductile Deformation Processes

Ductile Deformation Processes. Chapter 9 in Van der Pluijm and Marshak. How can solid rock flow like taffy?. Swiss Alps. Ice is a solid phase that flows when conditions are appropriate and there are forces acting on the material. “g”. Ductile deformation is permanent.

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Ductile Deformation Processes

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  1. Ductile Deformation Processes Chapter 9 in Van der Pluijm and Marshak

  2. How can solid rock flow like taffy? Swiss Alps

  3. Ice is a solid phase that flows when conditions are appropriate and there are forces acting on the material. “g”

  4. Ductile deformation is permanent

  5. Accomplished by these 3 mechanisms: • Cataclastic flow • Diffusional mass transfer • Crystal plasticity

  6. Mechanism is determined by: • Temperature • Stress • Strain rate • Grain size • Composition • Fluid content

  7. Effect of Composition Quartz Plag. Olivine Pyroxene Calcite Halite Gypsum Slow

  8. 1) Cataclastic flow: small pieces sliding past each other

  9. Cataclastic flow: Is it brittle or ductile? Ductile on large scale but brittle on small scale

  10. 2) Crystal Plasticity: The crystal changes shape by movement of lattice defects Point Defects are vacancies or impurities

  11. Dislocations form in 2 ways: • During crystal growth • During deformation

  12. By moving the dislocations, the crystal changes shape

  13. Migrating defects change the lattice shape.Occurs under stress

  14. Line defects in olivine

  15. Twinning also changes the crystal shape

  16. 3) Diffusional Mass Transfer has three mechanisms: • Grain boundary diffusion • Volume diffusion • Pressure solution Low T High T

  17. Grain boundary diffusion Atoms will diffuse along the edges of the grain to create shape changes (strain).

  18. Volume diffusion Atoms will diffuse through the center of the grain to create shape changes (strain).

  19. Pressure solution:Material is dissolved under stress Dissolved rock goes into veins

  20. Deformed Marble

  21. Mylonite

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