Geology 1 MT2: stress/strain, geochronology

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Geology 1 MT2: stress/strain, geochronology
2011-05-09 13:06:57
Geology MT2 stress strain geochronology

Geology 1 MT2: stress/strain, geochronology
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  1. forces applied to rocks that cause deformation
  2. 3 types of stress
    • compression => <= (squish)
    • tension <= => (stretch)
    • shear ^v (twist)
  3. deformation that occurs due to stress
  4. 3 types of strain
    • elastic
    • plastic
    • brittle
  5. plastically deformed rocks
  6. when the limbs of the fold open downward
  7. when the limbs of the fold open upwards
  8. a break in a rock where the two sides have moved relative to eachother
  9. fault surface is ground smooth by fault motion
  10. a description of a rock or geological feature's orientation in space
  11. horizontal compass direction
  12. deviation from horizontal (vertical direction)
  13. a fault that moves horizontally
    strike-slip fault
  14. fault that moves vertically
    dip-slip fault
  15. two walls of a fault that moves vertically
    • hanging wall
    • foot wall
  16. restraining bend
    • compression occurs at the bend
    • leads to reverse faults and mountains
  17. releasing bend
    a basin will form due to normal faults
  18. principle of horizontality
    sediments settle out and are deposited horizontally
  19. principle of lateral continuity
    • all beds will continue in all directions equally until:
    • their edges pinch out
    • they reach the edge of their deposition basin
  20. principle of superposition
    • rocks and seds are generally deposited on top of other deposits
    • without perturbation, younger rocks should be found above older
  21. cross-cutting relationships
    any intrusive igneous body must be younger than the rocks it cuts across
  22. principle of inclusions
    fragments of other rocks found in the host rock must be older than the host
  23. fossils and faunal succession
    a rock's maximum age is the same as the age of its youngest fossil
  24. geologic time scale; oldest to present
    • Precambrian - origin of life; rise of oxygen in atmosphere
    • Paleozoic - age of fish; Pangaea assembled
    • Mesozoic - age of reptile; dinosaurs; Pangaea broke up
    • Cenozoic - age of mammals;
  25. radiometric dating
    numerical method involving the radioactive decay of elements
  26. 3 types of radioactive decay
    • alpha decay
    • beta decay
    • electron capture
  27. alpha decay
    • nucleus emits an alpha particle (2p+ + 2n)
    • alpha particle is a helium nucleus
    • atomic # down by 2
    • atomic mass down by 4
  28. beta decay
    • nucleus emits a negatron (massless negative charge)
    • neutron becomes a proton
    • atomic number up by 1
    • atomic mass unchanged
  29. electron capture
    • an electron is incorporated into the nucleus
    • proton becomes a neutron
    • atomic number down by 1
    • atomic mass unchanged
  30. parent isotope
    original radioactive isotope
  31. daughter
    product of radioactive decay
  32. half-life
    the time it takes for 1/2 of the radioactive parents to become daughters
  33. calculating an age by radioactive decay
    • 1. count the number of parents and daughters
    • 2. add the numbers together to get the starting number of parents
    • 3. divide your number of parents in half repeatedly until you get down to the number of parents in step 1
    • 4. count number of half-lives and multiply by the duration of the half-life
    • 5. that's the age
  34. fission
    the splitting of a nucleus -- Ex: alpha decay
  35. fission tracks
    • if we know the half-life we can determine the amount of time that will pass between decays
    • to get the age, we multiply the number of tracks by the time that passes between fission events
  36. cosmogenic dating
    • radioactive isotopes created by nuclear reactions between atoms and cosmic rays (the sun)
    • useful for dating ice, sediments, exposures, etc.
  37. lake varves
    • alternating layers of seds that develop seasonally
    • summer - high deposition due to river input
    • winter - low deposition (only fines) due to lack of river input
  38. dentrochronology
    tree rings
  39. lichenometry
    lichen: symbiotic organism that is fungus/algae
  40. age bracketing
    combination of numerical and relative dating techniques in order to determine the min/max ages of rocks and geologic features that we cannot directly date
  41. unconformity
    a gap in the rock record due to erosional events
  42. 3 types of unconformity
    • nonconformity - unaltered sedimentary rocks on top of intrusive igneous or highly metamorphosed rocks
    • angular unconformity - horizontal sed beds on top of tilted sed beds
    • disconformity - young sed rocks on top of old sed rocks with erosion found between them
  43. correlation
    determining equivalency in age for geographically distant rocks