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What is it?

What is it?. What is it? (Quiz).

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What is it?

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  1. What is it?

  2. What is it? (Quiz)

  3. AnnouncementsFault paper- keep the first draft and submit with final draft!!!!!!!!!!If you take into consideration the comments, you will get a higher grade- if you disregard comments, you will get a lower grade.general suggestion: follow the guidelines closely!

  4. Today: Deformation mechanismsReading: Chapter 4 of Davis and Reynolds

  5. Rocks may behave in an elastic or plastic manner- but how? Deformation mechanisms: Processes that permit rocks to deform at the microscopic and atomic scale

  6. Crystal Structure Crystal Lattice: systematic array of atoms or moleculesBonds (covalent, ionic, metallic) are due to attractive forces between atoms/molecules

  7. Elastic Deformation of a Lattice

  8. Crystal Structure and StrengthDifferent minerals/rocks have different strengths- due to differences in bonds, atom spacing and charge, and crystal symmetry

  9. Observed strength of rocks/minerals in lab is order of magnitude lower than theoretical strength- WHY??

  10. Imperfections lead to beautiful structures- but unfortunately, still termed "flaws" and "defects": deviations from ideal crystalline structure

  11. Deformation mechanisms take advantage of defects, but vary as a function ofs, T, P, and other

  12. (1) fracturing and frictional sliding- due to the linking of microcracks

  13. (2) Kinking – bending rather than breaking the crystal lattice- takes advantage of planes of weakness

  14. (3) Pressure solution (a.k.a., Dissolution creep)– distortion by dissolution and recrystallization of material- aided by presence of fluid activated by pressure

  15. (4) Grain boundary diffusion : Same as pressure solution, but purely in solid state (no fluid) activated by temperature

  16. (5) Volume diffusion : movement of material within a crystal by taking advantage of point defects: missing (vacancies), extra (interstitial), or terrorist (impurities) atoms in a lattice

  17. (6) Dislocation creep : deformation by slip within the crystal lattice Dislocations: linear defects of pent up energy

  18. Dislocation creep cont.: at any single moment, only portions of slip plane are slipping- hence "creep"

  19. What happens when differential stress decreases at high temperatures? Recovery and Recrystallization- ahhh releases stored energy in crystal and rock Recovery: rearranges and removes dislocations Recrystallization: smaller grains into larger grains and straightening of grain boundaries

  20. undulatory extinction dynamic recrystallization during deformation "annealing" after deformation

  21. Relationships between deformation and metamorphism time

  22. Next Lecture: Deformation, Metamorphism, and Time

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