GEOS - 6. Metamorphic Rocks

Card Set Information

GEOS - 6. Metamorphic Rocks
2015-02-18 22:07:37
geology metamorphic

For Exam 1
Show Answers:

  1. What is the geothermal gradient?
    rate of increase of temperature w/ depth
  2. What are migmatites?
    Rocks that exhibit characteristics of both igneous and metamorphic rocks
  3. What does metamorphism mean?
    change of form
  4. What does metamorphism involve?
    re-crystallization without heat using heat and/or pressure and/or fluid chemistry
  5. What happens to a parent rock's chemical composition when it undergoes metamorphism?
    it is mostly unchanged.
  6. What happens to a parent rock's structures when it undergoes metamorphism?
    It is mostly destroyed
  7. What is mesatomatism?
    Chemical alteration of a rock by fluids; fluid carries elements into/out of rock
  8. What is an example of mesatomatism?
    Hydrothermal fluid flow creates most metallic ore deposits.
  9. Why are metamorphic rocks at the surface not reverse-metamorphosed?
    Minerals were formed and stable only at depth. Chemistry happens faster when warmer.
  10. What are the four types of metamorphism?
    • regional
    • contact
    • dynamic
    • hydrothermal
  11. What is regional metamorphism caused by?
    Heat & pressure
  12. How deep into the crust must regional metamorphism occur?
    at least 10 km
  13. What plat tectonic settings does metamorphism occur?
    Mountain building, thickening crust, subduction
  14. How/where does contact metamorphism occur?
    When magma is near cooler rock, the edge of the cool rock is heated near the boundary.
  15. What is contact metamorphism caused by?
  16. What plate tectonic settings does contact metamorphism occur?
    Metamorphic aureole = zone of altered rock
  17. How/where does dynamic metamorphism occur?
    Folding & faulting is sufficient to crush and pulverize minerals along a fault plane
  18. What does hydrothermal mean?
    Flow of hot fluids
  19. What plate tectonic settings does dynamic metamorphism occur?
    Fault zones
  20. What is foliation?
    The parallel orientation of mineral grains w/in a metamorphic rock
  21. What is the difference between foliation and bedding?
    Foliation show stresses applied in one direction, not sediment laid on top of one another in layers
  22. What is a geotherm?
    Temp vs. depth profile
  23. Where does high pressure and low temperature occur?
    Subduction zones
  24. Where does high temperature and low pressure occur?
    Near magma
  25. What is the temp vs. depth profile in the upper crust?
    25-30 degrees C / km
  26. What are index minerals used for?
    They tell us what temperature and pressure that the rock was exposed to
  27. What is a metamorphic facies?
    a field in the T vs. P plot - tells us about temperature and pressure; pick up a rock and find its facies to know conditions (T, P, depth) at which it was formed
  28. Describe slate.
    • low grade, most minerals parallel to plane, paper-shaped
    • clays & chlorites are platey minerals
    • Rock can be broken into thin and strong slabs
    • Phyllite included in this grade
    • Common roofing material
  29. Describe schist
    • medium grade
    • coarser grain size than slate
    • paper-shaped
    • big crystals (typically micas)
    • all parallel to one another
    • breaks easily
  30. Describe gneiss
    • high grade
    • foliated, but more rounded than planar
    • bands of dark and light (mafic & felsic)
    • caused by flow of atoms at high temperature and pressure
  31. If a rock has felsic minerals, it will not ___.
    • melt
    • Describe granulite.
    • parent rock: gneiss
    • non-foliated
    • beyond melting point of quartz
  32. Describe quartzite.
    • Parent rock: quartz sand
    • crystals have regrown into each other
    • non-foliated
  33. Describe marble.
    • Parent rock: limestone
    • nothing but calcite
    • Has growing crystals at a solid state
  34. ___ and ___ are the most common nonfoliated metamorphic rocks.
    quartzite, marble
  35. How strong is unfractured metamorphic rock?
  36. Is unfractured metamorphic rock permeable?
  37. How do engineers incorrectly define crystalline as?
    Plutonic and metamorphic = strong (they ignore foliation and fracturing)
  38. Which metamorphic rocks are used as contruction materials?
    Marble, quartzite, gneiss, slate
  39. SLow metamorphic crystal growth creates ___.
  40. What does hydrothermal circulation create?
    Most metals & other ores