GEOL364 Exam Study PDF

Long Answer 3 questions, 30min each for 50% 1. Write an essay on the plate tectonic setting, source materials and melting mechanisms for primitive island arc magmas. Include discussion of relevant phase diagrams, petrographic and geochemical data in your essay 2. Write an essay c...

Long Answer 3 questions, 30min each for 50% 1. Write an essay on the plate tectonic setting, source materials and melting mechanisms for primitive island arc magmas. Include discussion of relevant phase diagrams, petrographic and geochemical data in your essay 2. Write an essay comparing and contrasting differentiation of calc-alkaline magmas in island arcs and continental arcs. Include discussion of relevant phase diagrams, petrographic and geochemical data in your essay 3. The fractional crystallisation process can be illustrated graphically with the use of x-y variation diagrams. Figure 1 illustrates chemical variation of a hawaiian rock suite in terms of selected major elements a. Considering the overall magma chemical character, what mineral(s) would you expect to crystallise from magmas of these compositions? b. Evaluate the fractionating assemblage(s) responsible for the compositional change from A to C using sketched like that in figure 2 c. Describe, in terms of mineralogy, the plutonic rocks that would result from accumulation of the fractionating mineral phases d. Describe, in terms of magma composition and resulting rock texture, the differences between crystallisation, fractionation and accumulation 4. Assume a mantle source consisting of homogeneous lherzolite. a. Discuss and illustrate using labelled diagrams the conditions of partial melting that would result in formation of alkaline vs subalkaline magmas b. Describe the main geochemical characteristics (major elements, trace elements, isotopes) that would enable you to distinguish alkaline and subalkaline basalts. 5. Explain how the plume of an explosive volcanic eruption is formed, and how different aspects of the eruption affect plume height and stability 6. Use labelled diagrams to illustrate an essay about how mafic magma is transported through the cryst, what drives the transport, and what controls whether it reaches the surface to erupt or is instead intruded at shallow levels eg as sills 7. Write an essay comparing and contrasting the petrogenesis of igneous rocks in island arcs and continental arcs. Include discussion of important phase diagrams and geochemical data in your essay. 8. Draw labelled diagrams and use them to: a. Explain the different mechanisms that generate alkaline vs subalkaline (thoeleiitic) basalt in intraplate magmatic settings b. Describe the main petrographic differences that would enable you to distinguish alkaline and subalkaline (tholeiitic) basalts in thin sections  9. Tabulate similarities and differences of submarine eruptions versus subglacial ones for both mafic and silicic compositions, and both explosive and effusive eruption styles. Discuss at least one similarity, and at least one difference 10. Use labelled diagrams to illustrate an essay about how magma both silicic and mafic, is transported through the crust, what drives the transport, and what controls whether it reaches the surface to erupt or is instead intruded at shallow levels. 11. Write an essay on pyroclastic density currents, illustrating different types and their origins and characteristics 12. Consider the Rb/Sr and Sm/Nd isotopic systems. Write illustrated notes on BOTH the following aspects: a. Discuss how variable compatibility of the elements involved influences the evolution isotopic ratios in mantle and crust on Earth. b. Explain how the range of isotopic ratios in OIBs have led to the current model of Earths interior Multichoice 90 questions, 1min each for 50% 1. Which of the following textural terms can refer to a lava rock specimen a. Foliation b. Flow banding c. Bedding d. None of the above 2. Partial melting is caused by mantle peridotite crossing its liquidus to form a basaltic liquid a. True b. False 3. Partial melting of mantle peridotite leaves a solid refractory residue of: a. Lherzolite b. Dunedinite c. Harzburgite d. Gabbro 4. Volcanic glass represents magma major-element composition: a. Never b. Only when it occurs with crystals in the rock c. Only when the rock contains no crystals d. Always 5. Partial melting in intraplate settings can occur by adiabatic decompression because a. Heat conduction is greater than the rate of mantle upwelling b. Subducting plates supply water and fluids c. Thermal equilibrium is slower than the rate of mantle upwelling d. Mantle plumes originate in the inner core 6. Compared to alkaline basalts, tholeiites are generated at lower pressure a. True b. False 7. Compared to alkaline basalts, tholeiites are generated by greater degrees of partial melting a. True b. False 8. Layered mafic intrusions are a good target for REE mineral exploration a. True b. False 9. Compared to syenite, granite contains modal: a. Alkali feldspar b. Quartz c. Feldspathoids d. Amphibole 10. Tin-tungsten deposits are often associated with: a. Carbonatites b. Kimberlites c. Komatiites d. None of the above 11. Diamond deposits often occur within: a. Carbonatites b. Kimberlites c. Komatiites d. The Crown 12. In garnet, HREE are mostly incompatible whereas LILE are mostly compatible a. True b. False 13. Water dissolved in basaltic magma causes suppression of plagioclase crystallisation a. True b. False 14. Which element substitutes for K in alkaline feldspar a. Rubidium b. Strontium c. Europium d. Radon 15. Basaltic magma of the Dunedin Volcano was generated during the Miocene by: a. Decompression melting b. Flux melting c. Solid-liquid immiscibility d. Basaltic underplating 16. Contamination of a basaltic magma by sediments or continental crust tends to decrease the 87Sr/86Sr isotopic ratio a. True b. False 17. Mantle plumes are a window into the lower mantle a. True b. False 18. The study of igneous rocks is fundamental to: a. Understanding earths interior b. Characterizing ore formation processes c. Forecasting volcano behaviour d. All of the above 19. Residual garnet in the source of basalt magma can be inferred by: a. Relative depleting of HREE in the basalt  b. Relative depletion of HREE in the peridotite residue c. Flat REE patterns normalized to chondrite d. Garnet phenocrysts in the basalt 20. Resorbed macrocryst cores are often diagnostic of: a. Phenocrysts b. Autocrysts c. Antecrysts d. Xenocrysts 21. The basal ultramafic portion of an ophiolite is usually composed of basalt a. True b. False 22. Select the most silica-undersaturated rock a. Rhyolite b. Diorite c. Trachyte d. Phonolite 23. Compared to tholeiites, alkaline basalts are generated at greater depth a. True b. False 24. High 143Nd/144Nd and low 87Sr/86Sr ratios characterize depleted MORB a. True b. False 25. Ore deposits in layered mafic intrusions formed early in the crystallization sequence of magmas, and therefore are rich in incompatible elements such as lithium a. True b. False 26. During intracontinental rift development tholeiites are erupted early followed by highly alkaline magmas a. True b. False 27. Rare earth element deposits are often associated with: a. Carbonatites b. Kimberlites c. Komatiites d. Kaiwekites 28. During eutectic crystallisation the temperature of the system decreases a. True b. False 29. The rare earth elements have similar chemical properties because of their similar ionic charge and size a. True b. False 30. Which element substitutes for Ca in plagioclase only if the oxidation state of the melt is reduced: a. Beryllium b. Strontium c. Europium d. Radon Question 31-34 refer to the diagram below: 31. Which of the images, A B or C, might represent either a pyroclastic flow or lahar deposit? a. A b. B c. C 32. Which of the images represents a pyroclastic-fall deposit? a. A b. B c. C 33. Which of the images represents the deposits of a stratified pyroclastic density current, or “surge” a. A b. B c. C 34. Deposits of the sort shown in A characteristically a. Have more ash closer to the vent b. Have larger particles dispersed through the deposit c. Show an exponential thickening trend toward the vent d. Show a linear thickening trend toward the vent 35. Caldera forming eruptions are typically of Plinian intensity a. True b. False 36. Fallout deposits from a Plinian eruption a. Are made primarily of particles dropped from the umbrella cloud b. Contain dense blocks and pumice of the same size c. Have larger particles near the vent because they dont go as high in the column 37. Lava in an a’a flow is too viscous to form a pahoehoe flow a. True b. False 38. When using golden syrup to represent lava in experiments, adding seeds to the syrup mimics the effect in real lavas of a. Mafic crystals b. Felsic crystals c. Interconnected vesicles  d. Mantle xenoliths 39. When using golden syrup to represent lava in experiments, adding sand to the syrup mimics the effect in real lavas of a. Mafic crystals b. Felsic crystals c. Interconnected vesicles d. Sedimentary xenoliths 40. When using golden syrup to represent lava in experiments, the effect of adding abundant seeds to the syrup is more similar to that of adding bubbles, rather than of adding sand. This is because: a. The seeds are spherical b. The sand grains have rough surfaces c. Isolated bubbles interact as though they are solids suspended in the syrup d. The seeds form nuclei for bubbles in the syrup 41. When using golden syrup to represent lava in experiments, mixing citric acid and baking soda into the syrup mimics the effect in real lava of: a. Felsic crystals b. Mafic crystals c. Interconnected vesicles d. Mantle xenoliths 42. Formation of pyroxene or feldspar crystals from a melt can make it less viscous a. True b. False 43. Ropy fold structures can form on lava erupted under water a. True b. False 44. Vesicles in subaerial lavas that cross the shore and flow down the submerged slopes of Mauna Loa have been shown to: a. Increase flow velocity by weakening the lava b. Make the lava stop flowing because the bubbles make it buoyant c. Shrink because of the increased confining pressure d. Get bigger because the high pressure squeezes more gas out of the lava 45. Ice and snow caps on stratovolcanoes increase formation of hydrothermal systems a. True b. False 46. Lava erupting on a stratovolcano can collapse and break up to form pyroclastic density currents a. True b. False 47. Exsolution of water makes melt less viscous a. True b. False 48. Flow of basaltic magma through dikes is commonly laminar rather than turbulent a. True b. False 49. As an eruption under ice progresses, the ice surface sinks as the volcano grows a. True b. False 50. Magma for monogenetic volcano eruptions sometimes comes to the surface in diapirs a. True b. False 51. Higher velocity pyroclastic flows leave behind thicker and more voluminous deposits a. True b. False 52. Dilute pyroclastic density currents (surges) leave deposits that are well-bedded distally but more massive near the source a. True b. False 53. Pahoehoe flows of low-viscosity magma produce only thin lavas a. True b. False 54. To form long lava flows before cooling, lava must flow very quickly a. True b. False 55. Monogenetic volcanoes do not erupt from more than one vent a. True b. False 56. A single monogenetic eruption can produce a scoria cone and lava flow(s) a. True b. False 57. Stratovolcanoes like Taranaki build up as alternating layers of ash and lava a. True b. False 58. In a Plinian eruption, formation of the tall eruptive column requires: a. Enough initial eruptive momentum to carry ash up to the stratosphere b. A volcanic jet that entrains atmospheric air to form a buoyant convective plume c. Magma water interaction, to add a lot of energy to the eruption d. Eruption from tall, high volcanoes, so that the column starts off closer to the stratosphere 59. Volcanic ash is a. Made from the fire in a volcano b. All particles smaller than 2mm erupted from a volcano c. Juvenile particles erupted from a volcano d. Incandescent particles erupted from a volcano 60. Hyaloclastite is a. Any deposit of glassy volcanic particles b. A high-elevation clastic deposit c. A deposit of glassy particles from quenching of magma in water d. The rind of a pillow lava 61. Subaerial volcanoes rarely exceed about 2km height above their base because a. Glaciers erode their summits b. They tend to partly collapse in major landslides c. They spread viscously to form shield forms d. Their height prevents magma from reaching the vent Questions 61-64 refer to the liquidus phase diagram shown below 62. Initial partial melting of a rock with a composition shown by the dot labelled C will produce a liquid with the composition shown by the dot labeled: a. A b. B c. C d. D e. E 63. 25% partial melting of a rock with a composition shown by the dot labeled C will produce a liquid with the composition shown by the dot labeled: a. A b. B c. C d. D e. E 64. 25% partial melting of a rock with a composition shown by the dot labeled C will produce a sold residue with the composition shown by the dot labeled: a. A b. B c. C d. D e. E 65. Initial crystallisation of a liquid with a composition shown by the dot labeled C will produce a solid with the composition shown by the dot labeled a. A b. B c. C d. D e. E Questions 65-68 refer to the liquidus phase diagram shown below. Dry cotectics are shown with solid lines and water-saturated cotectics with dotted lines, both at 2kbar pressure 66. The second mineral to crystallise from a dry magma of composition L will be a. An b. Di c. Fo d. L 67. The third mineral to crystallise from a dry magma of composition L will be: a. An di b. Fo c. L 68. The third mineral to crystallise from a water saturated magma of composition L will be: a. An b. Di c. Fo d. L 69. Fractional crystallisation can change the sequence of mineral crystallisation in this system: a. True b. False Questions 69-70 refer to the liquidus phase diagram shown below for the system Q-Ab-Or at variable pressure. Data plotted as solid triangles and circles are from rhyolitic glass shards of a single eruption from a TVZ caldera 70. The array of glass data indicate: a. Cotectic crystallisation over a range of temperatures b. Eutectic crystallisation over a range of pressures c. Cotectic crystallisation over a range of pressures d. Eutectic crystallisation over a range of temperatures  71. The array of glass data indicate that magma probably erupted from a reservoir that was: a. Shallow with a large height to width ratio b. Deep with a large height to width ratio c. Shallow with a small height to width ratio d. Deep with a small height to width ratio Questions 71-73 refer to the P-T phase diagram shown below: 72. Most granitic magmas are generated by water-saturated partial melting of the continental crust: a. True b. False 73. S-type granitic magmas usually have: a. Temperatures >800c and crystallise at 800c and crystallise at >5km c. Temperatures 5km c. Temperatures