Geo 320 Exam 2

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scngk2011
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265040
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Geo 320 Exam 2
Updated:
2014-03-04 13:42:29
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geochemistry mineralogy
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  1. How do you differentiate the liquidus, solidus, and solvus?
    Liquidus: phase boundary that separates the all liquid stability field from stability fields that contasin at least some solids.

    Solidus phase boundary that separates the all solid stability field from stability fields that contasin at least some liquids.

    Solvus: phase boundary that separates conditions in which complete solid solution occurs within a mineral series from conditions under which solid solution is limited
  2. How are the euctectic and peritectic conditions different? Which describes the composition of the last gasp ofmelt present with two solids? Summarize what you think happens as a system approaches the peritectic, encounters theperitectic, and passes to temperatures lower than the peritectic.
    • Peritectic: A  reaction that is a reaction where a solid phase and liquid phase will together form a second solid phase at a particular temperature and composition.
    • Eutectic: A eutectic system is a mixture of chemical compounds or elements
    • that have a single chemical composition that solidifies at a lower temperature than any other composition made up of the same ingredients.
  3. What's the difference between invariant and incongruent melting?
    Incongruent Melting: occurs when a solid mineral phase melts to produce a melt and a different mineral with a different composition from the initial mineral.

    Invariant: occurns when melts of the sample composition are produced by melting rocks of different initial composition.
  4. What's the difference between continuous and discontinuous reactions? Which limbs of Bowen's reaction series represent each reaction type?
    Continuous: mineral crystals and melt react to continuously and incrementally change the composition and of both; requires a mineral solid solution series

    Discontinuous: mineral crystal and melt react to co produce a completely different mineral; negligible solid solution exists between the minerals 

  5. List the polymorphs of SiO2. Which are the highest pressure phases? Which are the highest temperature phases that exist prior to crossing into the liquid field?


    Nepheline, Albite, Silica
  6. What are the chemical compositions and melting points of the feldspars: anorthite, albite, orthoclase?
  7. How are tie lines useful in determining for a given system: (a) the compositions of coexisting solids andliquids, and (b) the proportions of solid and liquid?
  8. What are the chemical compositions and melting points of forsterite, diopside, enstatite, nepheline, and quartz?In what kinds of rocks do they typically occur?
  9. What is a xenolith?
  10. What is a phase diagram?
  11. What are the three stable isotopes of oxygen, and which are most useful in gleaning paleoclimate information?
  12. What is per mil notation, and what is the conventional isotopic standard for O? …for C?
  13. What are the three isotopes of carbon that occur naturally in Earth materials? Which is radioactive, and what isits half-life? Which isotope is preferentially taken up in biotic processes?
  14. What was the Paleocene Eocene Thermal Maximum, and when did it take place (in Myr)? What commonalities does itshare with modern global warming trends?
  15. What are the three types of radioactive decay? Define them. Sketch the particles transferred, and know thedifferences in atomic number and mass number that result.
  16. What relationship governs radioactive decay? What is t? What is lambda?
  17. How are the systematics of the uranium-lead decay chain useful to geochronology? What are some of theradioactive parent isotopes? What are some of the radiogenic daughter isotopes?
  18. How are the systematics of the rubidium-strontium decay chain useful to geochronology? What is the primaryradioactive parent-radiogenic daughter pair?
  19. What is a concordia plot? What does it mean when data fall on the concordia? What does it mean when the datafall off the concordia?
  20. Why are zircons useful minerals for study in the context of concordia plots? What does age zonation in a zirconimply?
  21. For a rubidium-strontium system considered for different minerals in the same rock (as in F3.15), why do thelines showing the age of the materials migrate upwards on this plot? Why don't minerals 1, 2, 3, and 4 all fall inthe same place on the x-axis?
  22. What is an isochron?
  23. List the phaneritic and aphanitic rock types that are considered ultramafic, mafic, intermediate, and felsic.
  24. Arrange the following rock types in terms of increasing SiO2 content, increasing MgO, and increasing FeO:peridotite, gabbro, diorite, granodiorite, and granite.
  25. Use F7.1 to determine which rock types (a) bracket the onset of alkali feldspars in rocks, (b) bracket the~50/50 split of plagioclase and alkali feldspars in rocks, and (c) occur where ferromagnesian predominate?
  26. Define porphyritic, phaneritic, aphanitic, and groundmass.
  27. What is the difference between anhedral and euhedral minerals?
  28. What is a pegmatite?
  29. What different factors determine mineral textures in rocks?
  30. What is the Phase Rule?
  31. How does the proportion of melt change in a system passing from the liquidus to the solidus? In other words,could you shade in regions on a phase diagram (such as F3.9 or 7.9) where there is ~25% melt and ~75% melt?
  32. What is undercooling, with reference to the plagioclase phase diagram (or F7.9)?
  33. Between 1000 and 1500 degrees Celsius, the viscosities of magmas ranging in composition from rhyolitic tokomatiitic vary by many orders of magnitude. Provide an estimate in absolute terms for the viscosities of these 5main magmatic types, and explain WHY the differ so.
  34. The addition of a few wt% water to a magma drives down the viscosity. Is the water-driven viscosity shift moreimportant for rhyolitic or basaltic compositions? What is your evidence for this?
  35. By the way, I think there is an error here in F7.10 and the y-axis unit should be pascal-second. What is thatunit, anyway?
  36. What are the 8 most abundant element in Earth's crust, in wt%?
  37. Describe in general how major element oxides shift along the spectrum of basaltic to rhyolitic compositions?
  38. What is element compatibility? What do D values greater than, equal to, or less than 1 indicate?
  39. What is restite?
  40. What is the difference between ultramafic and ultrabasic rocks?
  41. Summarize the major igneous minerals/mineral groups that host the compounds MgO, FeO, Al2O3, CaO, Na2O, K2O, andSiO2.
  42. You are looking at a rock. How would you know if the associated magma had been oversaturated with respect toSiO2?
  43. …how would you know if a magma had had more Al2O3 than the combined inventory of CaO, Na2O, and K2O?
  44. In the IUGS classification system, what do the apex labels Q, A, P , F, and M mean?
  45. What is a foid? Hint: in this class, it's not "Firearm Owners Identification."
  46. Be able to plot a given rock compositon on F7.20, F7.21a, F7.22a, and F7.24a.
  47. Define anatexis, equilibrium melting, and disequilibrium melting.
  48. Give three ways to enhance melting, and describe geologic settings that give rise to these melt environments.
  49. Describe in your own words the melting shown in F8.1, and identify the geologic setting to which this ispertinent.
  50. Describe in your own words the melting shown in F8.2, and identify the geologic setting to which this ispertinent.
  51. What is a chondrite, and what are chondrules? Why would we normalize igneous rock data to chondriticcomposition?
  52. In terms of the load of incompatible elements, how are melts typically different from parent rocks?
  53. How could you monitor changing concentrations of rare earth elements in igneous rocks formed by partial meltingof a mantle source and estimate the degree of partial melt?

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