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Earth Systems 3209 Test Chapters 3 & 4 Solutions Name _______________ Multiple Choice. Choose the best answer for the following multiple choice questions. Write the UPPERCASE letter of the correct answer on the answer sheet on page 8. [21 marks] 1. Molten material found inside the earth is called ______ . a) lava b) plasma c) magma d) rock fluid e) mineraloid 2. The process of igneous rock formation is called ______ . a) weathering b) lithification c) foliation d) decomposition e) crystallization 3. Igneous rocks that contain the last minerals to crystallize from magma and consist mainly of feldspars and quartz are said to have a ______ composition. a) granitic b) basaltic c) lithic d) gneissic e) metamorphic 4. When large masses of magma solidify far below the surface, they form igneous rocks that exhibit a ______ texture. a) fine-grained b) coarse-grained c) fragmental d) glassy e) porphyritic 5. Why can two igneous rocks have the same minerals but different names? a) They may have different colors b) Names of igneous rocks are arbitrary c) The rocks may be of different sizes d) They may have different textures e) They may have been found in different places 1 6. Igneous rocks formed from magma that crystallized at depth are called ______ or intrusive rocks. a) plutonic b) volcanic c) foliated d) metamorphic e) porphyritic 7. Most of the earth's seismic activity, volcanism, and mountain building occur along ______ . a) lines of magnetism b) parallels of latitude c) hot spots d) plate boundaries e) random trends 8. During oceanic-continental convergence, as the oceanic plate slides beneath the overriding plate, a ________ is often produced adjacent to the zone of subduction. a) deep-ocean terrace b) transform fault c) divergent boundary d) deep-ocean ridge e) deep-ocean trench 9. The chain of volcanic structures, extending from the Hawaiian Islands to Midway Island and then continuing northward toward the Aleutian trench has formed over a(n) ________ as the Pacific plate moved. a) subduction zone b) island arc c) divergent boundary d) hot spot e) convergent boundary 10. Highly viscous magmas tend to impede the upward migration of expanding gases, which often results in ________ eruptions. a) relatively quiet b) explosive 11. The most violent type of volcanic activity is associated with ______ . a) cinder cones b) composite cones c) shield cones d) sills e) intermediate cones 12. Which one of the following is NOT a factor that determines the violence of a volcanic eruption? a) temperature of the magma b) size of the volcanic cone c) the magma's composition d) amount of dissolved gases in the magma 2 13. The area of igneous activity commonly called the Ring of Fire surrounds the ______ . a) Indian Ocean b) Atlantic Ocean c) Pacific Ocean d) Coral Sea e) Sea of Japan 14. A magma's viscosity is directly related to its ______ . a) depth b) volcanic cone c) color d) age e) silica content 15. Pulverized rock, lava, and glass fragments produced from the vent of a volcano are known as _____ . a) nuee ardentes b) pyroclastics c) pahoehoes d) sills e) craters 16. Which type of volcano consists of interbedded strata of lavas and pyroclastic material? a) cinder cone b) intermediate cone c) pyro-cone d) composite cone e) shield cone 17. Basaltic lava tends to be ________ fluid than granitic lava. a) more b) less 18. Eruptions of fluid basaltic lavas, such as those that occur in Hawaii, tend to be ______ . a) relatively quiet b) extremely violent c) unpredictable d) explosive 19. The type of volcano produced almost entirely of pyroclastic material is the ______ . a) shield volcano b) composite cone c) batholith d) cinder cone e) pyro-cone 20. Which volcanoes are generally small and occur in groups? a) composite cones b) shield cones c) intermediate cones d) laccoliths e) cinder cones 3 21. Intraplate volcanism may be associated with the formation of ________ over rising plumes of hot mantle material. a) hot spots b) subduction zones c) volcanic necks d) dikes e) ocean ridges True/False. For the following true/false questions, if a statement is not completely true, mark it false. Place a T for true and F for False on the answer sheet on page 8. [20 marks] 1. The most common extrusive igneous rock is granite. 2. The rock cycle shows the relations among the three rock types, and is essentially an outline of physical geology. 3. Granite is a classic example of an igneous rock that exhibits a coarse-grained texture. 4. Because magma's density is greater than the surrounding rocks, it works its way to the surface over time spans from thousands to millions of years. 5. The process called weathering, whereby magma cools, solidifies, and forms igneous rocks, may take place either beneath the earth's surface, or on the surface following a volcanic eruption. 6. Molten material found on the earth's surface is called magma. 7. The texture of an igneous rock is based in the size and arrangement of its interlocking crystals. 8. According to Bowen's reaction series, quartz is often the last mineral to crystallize from a melt. 9. Slow cooling of magma results in the formation of small mineral crystals. 10. Older portions of the sea floor are carried into the earth's core in regions where trenches occur in the deep-ocean floor. 11. The "Ring of Fire" is an area of earthquake and volcanic activity that encircles the Pacific Ocean basin. 12. Deep-ocean trenches are located adjacent to subduction zones. 13. Most of the earth's active volcanoes are near divergent plate margins. 14. The more viscous a material, the greater its resistance to flow. 15. The smallest volcanoes are composite cones. 16. The greatest volume of volcanic rock is produced along the oceanic ridge system. 17. Magmas that produce basaltic rocks contain more silica than those that form granitic rocks. 18. A magma's viscosity is directly related to its iron content. 4 19. When subduction volcanism occurs in the ocean, a chain of volcanoes called an island arc is produced. 20. The viscosity of magma, plus the quantity of dissolved gases and the ease with which they can escape, determines the nature of volcanic eruptions. Word Choice. Complete each of the following statements by selecting the correct response(s). Write the correct response on the answer sheet on page 8. [21 marks] 1. The very first rocks to form on the earth's surface were [igneous/sedimentary/metamorphic]. 2. Because a magma body is [less/more] dense than the surrounding rocks, it works its way toward/away from] the surface over time spans of thousands to millions of years. 3. The molten minerals in magma are primarily members of the [carbonate/silicate/sulfide] group. 4. A rock that will effervesce with dilute hydrochloric acid most likely contains the mineral [quartz/calcite/feldspar]. 5. At convergent plate boundaries, oceanic lithosphere is being [created/consumed]. 6. The region where one plate descends into the asthenosphere below another plate is called a [rifting/subduction] zone. 7. At divergent plate boundaries, lithosphere is being [created/destroyed]. 8. Hot spots are believed to be created by [converging plates/mantle plumes]. 9. When spreading centers develop within a continent, valleys called [trenches/rifts] form. 10. The magma produced in a subduction zone often produces [oceanic ridges/volcanic arcs]. 11. The greatest volume of volcanic material is produced along the [ocean trenches/oceanic ridge system]. 12. The magma of spreading center volcanism is produced primarily by the partial melting of [continental crust/upper mantle rock/oceanic crust] and is mostly of [basaltic/granitic] composition. 13. A volcanoes effect on climate, if any, would be caused by ash and [lava/gases] being ejected into the [upper/lower] atmosphere. 14. [Increasing/Decreasing] the silica content of magma will increase its viscosity. 15. The smallest volcanic cones are typically [cinder/composite/shield] cones. 16. The most fluid magmas have a [basaltic/granitic] composition. 17. The most explosive volcanism is associated with [spreading center/subduction zone] volcanism due to the relatively high [crystal/basalt/water] content of the associated magma. 5 Written Questions: Answer all questions on this paper. 1. Explain how each zone of volcanic activity listed below is related to plate tectonics. [6 marks] a) Pacific Ring of Fire At convergent plate boundaries, slabs of ocean crust descend into the mantle, creating an ocean trench. The ocean crust eventually melts and the less dense basaltic or andesitic magma moves slowly upward toward the surface. The volcanoes produced lie in a linear or slightly curved chain and are called continental volcanic arcs if they lie on land and volcanic island arcs if they are formed under the ocean and rise above sea level. Both arcs will lie roughly parallel to the ocean trench (see Figure 4.35 p. 120). Mount St. Helens is part of a continental volcanic arc. b) Mid-Ocean Ridges When two tectonic plates move apart in the ocean, magma rises up into the rift valley created and produces new seafloor on either side of the rift (seafloor spreading). Material builds up on either side of the rift to create an ocean ridge. Iceland was formed when the material on either side of the rift rose above sea level. When two plates move apart on a continent, a similar process occurs. The greatest volume of volcanic rock is produced at divergent plate boundaries. c) Hot Spots These volcanoes do not occur at the plate boundaries (intraplate volcanism). Volcanoes are formed here because the mantle under the crust in this area is hotter than normal so the material moves upward toward the crust and creates a mantle plume. When the magma (basaltic or granitic) reaches the surface, a volcano called a hot spot is formed. The islands of Hawaii are the result of hot spot volcanism. 2. In the table below, place a check mark to indicate which magma has the greater amount of each characteristic. [3 marks] Basaltic magma Granitic magma Silica Content Viscosity Melting Temperature 3. Describe the texture of both granite and basalt. Explain how the texture of each rock was formed. [4 marks] a) Granite: Texture of Granite: course grained (phaneritic) Reason: Molten rock called magma is insulated within Earth and loses its heat slowly to the surrounding rock. This slow cooling allows the crystals within the magma to become relatively large which forms a course texture 6 b) Basalt: Texture of Basalt: fined grained (aphanitic) Reason: Molten rock called lave flows on or near the surface where it loses heat quickly to the surrounding rock or air. This rapid cooling does not allow large crystals to form within the lava and results in the formation of a fine grained texture. 4. Match the description to the corresponding term in the table below. [6 marks] Texture Description A. Openings produced by escaping gases. B. A texture characterized by two distinctly different crystals. C. Obsidian exhibits this texture. D. Crystals are too small to be seen without a microscope. E. Coarse-grained, with crystals of roughly equal size. F. Exceptionally large crystals exceeding 1cm in diameter. __E__ Phaneritic __D__ Aphanitic __A__ Vescular __B__ Porphyritic __C__ Glassy __F__ Pegmatitic 7 Name _______________________ Multiple Choice: 1. 2. 3. 4. 5. 6. 7. ____C ____E ____A ____B ____D ____A ____D 8. ____E 9. ____D 10. ____B 11. ____B 12. ____B 13. ____C 14. ____E 15. ____B 16. ____D 17. ____A 18. ____A 19. ____D 20. ____E 21. ____A 8. ____T 9. ____F 10. ____F 11. ____T 12. ____T 13. ____F 14. ____T 15. ____F 16. ____T 17. ____F 18. ____F 19. ____T 20. ____T True/False: 1. 2. 3. 4. 5. 6. 7. ____F ____T ____T ____F ____F ____F ____T Word Choice: 1. 2. 3. 4. 5. 6. 7. 8. 9. igneous less toward silicate calcite consumed subduction created mantle plumes rifts 10. volcanic arcs 11. ocean ridge system 12. upper mantle rock basaltic 13. gases lower 14. increasing 15. cinder 16. basaltic 17. subduction zone water 8