Geology

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Author:
lolita91
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43151
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Geology
Updated:
2010-10-18 20:05:54
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Geology Metamorphic Rocks
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Test 3
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  1. Metamorphism is a __________________ that involves no melt phase.
    solid-state recrystallization
  2. The protolith of a metamorphic rock is the
    parent
  3. Fabric refers to the way ____________ in a rock are arranged.
    minerals
  4. Foliation is defined by the _______________arrangement of minerals.
    plane or planar
  5. Typical platy minerals (sheet silicates) defining a foliation include
    chlorite,muscovite & biotite
  6. Directed pressure during metamorphism produces a _________________.
    foliation
  7. If elements do not enter or leave a rock during recrystallization, then the rock system is
    described as ___________ or __________________.
    closed, isochemical
  8. Marble is a metamorphic rock composed of coarse-grained
    calcite
  9. Quartzite is a metamorphic rock composed of a dense network of interlocking
    quartz
  10. Basalts when metamorphosed at temperatures of ~500oC or higher are transformed into
    __________________________.
    amphibolite
  11. Slates are characterized by a tendency to break into even-parallel sheets due to the parallel
    alignment of the flat crystal faces of
    chlorite and muscovite
  12. The foliation in a slate is called slaty
    cleavage
  13. Assuming a mudstone protolith, the transformation to a slate occurs at ~________ oC.
    300
  14. Phyllites are _________________ grained than slates, and when held up to the sunlight exhibit
    a marked ____________, as rays of light reflect off the aligned crystals of ______________
    and _________________.
    coarser, sheen, chlorite, muscovite
  15. Assuming a mudstone protolith, the transformation to schist occurs at temperatures between
    about _______ and ______ oC. The resulting foliation is called ___________________.
    400, 500, schisosity
  16. Schist derived from a mudstone at temperatures between about 500 oC and 650 oC will consist
    of quartz, feldspar, muscovite, biotite, garnet, and _____________. Such a rock would be
    ___________________ grained than a phyllite.
    staurolite, coarser
  17. The coarsest grained metamorphic rock is a
    gneiss
  18. A foliation in gneiss would be called ___________________. It forms as ions migrate over
    microscopic distances at temperatures above ______ to ______ oC.
    gneissosity, 600, 650
  19. Metamorphic grade refers to the broad pressure conditions of metamorphism. True or false
    • False, metamorphic grade refers to the relative temperature conditions under which rocks were
    • metamorphosed
  20. In general, metamorphic grade is dependent upon the
    geotherm
  21. Given a specific geotherm, low metamorphic grade rocks occur in the ___________________
    part of the crust while higher grade rocks will occur at _________ levels.
    upper, deeper
  22. Given a mudstone protolith, and a geothermal gradient typical of arc-continent collisions, at
    temperatures over 700 oC, the stable metamorphic mineral assemblage will consist of quartz,
    feldspar, and ______________.
    sillimanite
  23. Isotherms are curves or surfaces of equal
    temperature
  24. Isotherms bend downward within
    subduction zone settings
  25. In volcanic arc settings, isotherms bend downward due to the introduction of hot magma. True
    or false
    False
  26. An envelope of recrystallized rock surrounding a pluton is called a
    contact metamorphic aureole
  27. Non-foliated rocks found in contact metamorphic aureoles are called
    hornfels
  28. Phase diagrams depict the PT conditions under which various minerals are stable. True or false
    True
  29. Is andalusite a low or high pressure phase relative to kyanite?
    low pressure
  30. Is sillimanite a low or high temperature phase relative to andalusite?
    high temperature
  31. Which of the following metamorphic facies represent rocks that were metamorphosed under the
    lowest PT conditions recognized by geologists?
    zeolite facies
  32. Which of the following metamorphic facies represent rocks that were metamorphosed under the
    highest pressure conditions recognized by geologists?
    eclogite
  33. The hornfels facies forms during ____________________ metamorphism.
    contact
  34. In subduction zone settings the geotherm is _________.
    10oC/km
  35. The geotherm in collisional zones and active regions of continents is about __________.
    25o - 35oC/km
  36. The geotherm in island arcs is about _________.
    50oC/km
  37. Why do isotherms bow upward in island arcs and mid-ocean ridges?
    • Isotherms bow upward in island arcs and mid-ocean ridges because hot magma is introduced in
    • these regions.
  38. Why do isotherms bend downward in subduction zone settings?
  39. Isotherms bend downward in subduction zone settings because the cold subducting lithospheric
    • plate descends at a rate faster than it can equilibrate (warm up) to the temperatures of the over
    • ridging plate.
  40. How would describe the distribution of metamorphic facies within a zone of collision between
    an island arc and a passive continental margin?
    • Zeolite and prehnite-pumpellyite facies would occur along the flanks. Moving progressively
    • toward the interior of the zone of collision, you would encounter greenschist, amphibolite, and
    • granulite facies.
  41. What would happen to a mudstone if it were metamorphosed at temperatures in excess of
    700oC under wet conditions?
    The mudstone probably would melt.
  42. Using the illustration shown below, please answer the following questions.
    (a) What minerals would be stable at temperatures around 400oC, 600oC and 710oC?
    (b) What is the relationship between textural type of metamorphic rock and metamorphic
    grade?
    (c) What is the relationship between metamorphic grade and facies development?
    (d) What is the average temperature for the onset of metamorphism?
    (e) If a mudstone undergoes metamorphism under wet conditions at temperatures above
    ~700oC, then what will happen?
    • (a) @ 400oC chlorite, muscovite, and biotite would be stable
    • @ 600oC quartz, feldspar, muscovite, biotite, garnet, and staurolite would be stable
    • @ 710oC quartz, feldspar, biotite, sillimanite, and possibly muscovite would be stable
    • (b) Low grade rocks are going to be composed largely of slates, phyllites, and schists while
    • intermediate grade rocks are going to be schists and gneisses. High grade rocks are going to
    • consist primarily of gneisses.
    • (c) Greenschist facies rocks will be composed primarily of slates, phyllites, and schists.
    • Amphibolite facies rocks will be mostly schists and gneisses, while high grade metamorphic
    • rocks will be dominated by gneisses.
    • (d) ~300oC
    • (e) It will melt
  43. In the illustration shown below, the continental geotherm is broadly representative of
    collisional and other active regions of the crust. Please answer the following questions.
    (a) What is the metamorphic facies series for a geotherm typical of subduction zone settings?
    (b) What is the metamorphic facies series for a geotherm typical of continental regions?
    (c) What is the metamorphic facies associated with geotherms around cooling magma?
    • (a) Zeolite, blueschist, ecologite facies
    • (b) Zeolite, prehnite-pumpellyite, greenschist, amphibolite, and granulite facies
    • (c) Contact
  44. In the following illustration what do the fields labeled A, B, and C represent?
    A = kyanite. B = sillimanite. C = andalusite.

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