GEO Chapter 4

5. Despite the fact that the temperatures within Earth are hot enough to melt rock, Earth is mostly solid. Why do the rocks within Earth NOT melt? a. The pressure is too high. c. There is not enough water. b. The pressure is too low. d. They are not in contact with air.

a. The pressure is too high.

50. Which type of plate boundary hosts the most explosive volcanoes? a. convergent only c. transform and convergent b. divergent only d. convergent and divergent

a. convergent only

38. As compared to coarse-grained igneous rocks, fine-grained igneous rocks ________. a. cool and solidify more quickly c. solidify at higher temperatures b. cool and solidify more slowly d. solidify at lower temperatures

a. cool and solidify more quickly

16. Which type of magma has the greatest silica content? a. felsic c. mafic b. intermediate d. ultramafic

a. felsic

22. All other factors being equal, if a body of magma becomes more felsic, its viscosity will ________. a. increase b. decrease c. stay the same d. Chemical composition has no effect on viscosity.

a. increase

45. An oceanic plate subducting under another oceanic plate will create a(n) ________. a. island arc c. continental rift b. continental arc d. transform fault

a. island arc

11. Decompression melting occurs at both ________ and ________. a. mid-ocean ridges; hotspots c. subduction zones; hotspots b. mid-ocean ridges; trenches d. subduction zones; mid-ocean ridges

a. mid-ocean ridges; hotspots

27. Magma tends to ________. a. move upward, away from where it formed b. move downward, away from where it formed c. move laterally d. stay in one place

a. move upward, away from where it formed

6. In Bowen's discontinuous reaction series, the first mineral to crystallize from a mafic melt is ________. a. olivine c. pyroxene b. plagioclase d. quartz

a. olivine

28. Stoping by magmas occurs when ________. a. pieces of surrounding country rock are broken off and assimilated b. the magma stops flowing and starts to solidify c. the magma becomes fully solidified to form intrusive rock d. the magma alters a thin rind of surrounding country rock

a. pieces of surrounding country rock are broken off and assimilated

43. Volcanic eruptions at divergent boundaries generally take the form of ________. a. pillow basalts c.lava domes b. pyroclastic flows d.pyroclastic falls

a. pillow basalts

33. An igneous rock with a mixed texture of coarse crystals (phenocrysts) surrounded by fine crystals (groundmass) is termed ________. a. porphyritic c. aphanitic b. phaneritic d. necrotic

a. porphyritic

19. The composition of magma will ________ when it erupts and turns into lava. a. remain the same c. become more mafic b. become more felsic d. have more silica

a. remain the same

1. The interior of Earth consists almost entirely of ________ rock. a. solid c. sedimentary b. molten d. felsic

a. solid

2. The mantle is composed entirely of ________. a. solid peridotite c. molten peridotite b. solid basalt d. molten basalt

a. solid peridotite

25. A sill is a(n) ________. a. tabular intrusion that lies parallel to surrounding layers of sedimentary rock b. cooled layer of an ancient lava flow c. intrusion formed within the magma chamber of a volcano d. tabular intrusion that cuts across preexisting layers

a. tabular intrusion that lies parallel to surrounding layers of sedimentary rock

35. Most commonly, felsic igneous rocks ________. a. contain more iron and magnesium than intermediate rocks b. are lighter in color than mafic rocks c. are darker in color than mafic rocks d. are found in oceanic crust

b. are lighter in color than mafic rocks

41. Which of the following silicate minerals is often found in granite? a. olivine c. pyroxene b. calcite d. quartz

b. calcite

37. The presence of vesicles in an igneous rock is evidence that the source melt ________. a. had a mafic composition b. contained dissolved volatiles c. underwent fractional crystallization d. was stoping and assimilating wall rock

b. contained dissolved volatiles

21. If the volatile content of magma is increased, its viscosity will ________. a. increase b. decrease c. stay the same d. Volatile content has no effect on viscosity.

b. decrease

31. All other factors being equal (i.e., depth, volume, temperature, etc.), which type of igneous intrusion would cool fastest? a. pluton c. batholith b. dike d. All intrusions cool at the same rate.

b. dike

17. Viscosity controls how ________. a. hot the fluid is c. quickly the fluid cools b. fast a rock will melt d. fast a fluid flows

b. fast a rock will melt

44. Volcanoes whose magma source is NOT linked to a plate boundary are associated with ________. a. continental rifts c. mid-ocean ridges b. hot spots d. subduction zones

b. hot spots

13. If a body of magma is subjected to fractional crystallization, the first rock that is expected to crystallize from the magma will be ________. a. identical in chemical composition to the magma b. more mafic than the magma c. more felsic than the magma d. The composition of the rock is not predictable.

b. more mafic than the magma

24. An irregular-shaped and blob-like igneous rock body that cooled beneath the surface of Earth is a ________. a. dike c. sill b. pluton d. laccolith

b. pluton

3. The extremely high ________ within Earth keeps the rocks solid. a. temperature c. silica content b. pressure d. water content

b. pressure

10. ________ melting occurs at subduction zones because the down-going plate ________. a. Heat transfer; is extremely hot b. Heat transfer; creates abundant friction c. Flux; contains abundant water d. Decompression; rises toward the surface

c. Flux; contains abundant water

48. Which of the places listed below was formed by a hotspot? a. Mount St. Helens, Washington c. Kilauea, Hawaii b. Mount Fuji, Japan d. Mount Pinatubo, Philippines

c. Kilauea, Hawaii

4. Why is the outer core the only layer in Earth that is molten? a. The pressure decreases within Earth, thus allowing iron to melt. b. The pressure increases within Earth, thus allowing iron to melt. c. The temperature is high enough but pressure low enough to melt iron. d. The temperature is high enough but pressure low enough to melt olivine.

c. The temperature is high enough but pressure low enough to melt iron.

26. A batholith is a(n) ________. a. large body of sedimentary rock c. amalgamation of plutons b. large body of metamorphic rock d. amalgamation of aureoles

c. amalgamation of plutons

42. Volcanic arcs form along ________ boundaries. a. transform c. convergent b. transvergent d. divergent

c. convergent

20. All things equal, a magma will have ________ viscosity than a lava. a. the same c. lower b. fractional d. higher

c. lower

15. The difference between magma and lava is that ________. a. magma cools more rapidly than lava b. magma is found at the surface, whereas lava is found below the surface c. magma is found beneath the surface, whereas lava is found at the surface d. There is no difference; the two terms mean the same thing.

c. magma is found beneath the surface, whereas lava is found at the surface

46. The formation of a hotspot is thought to be associated with ________. a. convergent boundaries c. mantle plumes b. divergent boundaries d. mid-ocean ridges

c. mantle plumes

12. Injecting hot fudge into ice cream and causing the ice cream to melt is an appropriate analogy for which cause of magma melt? a. melting due to a decrease in pressure b. melting due to an addition of volatiles c. melting due to heat transfer from rising magma d. melting due to an increase in pressure

c. melting due to heat transfer from rising magma

23. In general, if a body of igneous (source) rock is subjected to partial melting, the magma that is produced is expected to be ________. a. identical in chemical composition to the source rock b. more mafic than the source rock c. more felsic than the source rock d. The melt composition is not predictable.

c. more felsic than the source rock

7. Important volatiles in magmas include ________. a. mafic minerals, such as olivine c. water and carbon dioxide b. potassium and aluminum d. silicon and iron

c. water and carbon dioxide

8. Volatiles refer to substances that ________. a. crystallize most rapidly out of a melt b. remain molten even after lava is erupted at the surface c. melt immediately upon contact with a hot body of magma d. are gases at surface temperature and pressure

d. are gases at surface temperature and pressure

49. Large igneous provinces involve more than just the formation of large volumes of igneous rock. Which of the following global events has NOT been attributed to large igneous provinces? a. sea-level rise c. extinction b. climate change d. large outcrops of granite

d. large outcrops of granite

9. The formation of magma within Earth is NOT caused by which of the following processes? a. decompression (drop in pressure) b. addition of volatiles c. transfer of heat from adjacent magma or very hot rocks d. loss of volatiles to the atmosphere

d. loss of volatiles to the atmosphere

32. Dikes serve an alternate purpose besides being an area where magma solidifies. For what else are dikes used? a. pathways for geyser flow c. storage space for nuclear materials b. linear holes that fill with sand d. magma pathways to surface volcanoes

d. magma pathways to surface volcanoes

34. Ash, and larger fragments of pumice are all examples of ________. a. intrusive igneous rocks c. volatiles b. hot spots d. pyroclastic debris

d. pyroclastic debris

39. Coarse-grained granite is most similar in mineral composition to fine-grained ________. a. andesite c. gabbro b. basalt d. rhyolite

d. rhyolite

40. As compared to mafic igneous rocks, all felsic igneous rocks ________. a. cool and solidify more quickly c. solidify at higher temperatures b. cool and solidify more slowly d. solidify at lower temperatures

d. solidify at lower temperatures

18. Viscosity does NOT depend on ________. a. temperature c. silica content b. volatile content d. volume of the magma

d. volume of the magma