Exam Prep Ch.9 Crags, Cracks, Mountain Building

CHAPTER 9: Crags, Cracks, and Crumples: Crustal Deformation and Mountain Building

LEARNING OBJECTIVES

9A. Distinguish between mountain belts (orogens) and other regions of continental crust.

9B. Define what geologists mean by deformation when referring to rock, and explain how and why rocks undergo deformation and develop geologic structures.

9C. Contrast brittle with plastic deformation, and give examples of each.

9D. Sketch the various kinds of folds, faults, and foliation that develop during deformation, and interpret these structures.

9E. Correlate different kinds of mountain belts with specific geologic settings, in the context of plate tectonics.

9F. Explain why mountain uplift develops, and why topography in mountain belts becomes so rugged.

9G. Explain how a craton differs from an orogen, and show how to distinguish between basins and domes in cratonic platforms.

MULTIPLE CHOICE

1. An episode of mountain building is termed a(n) ________.

2. The majority of the Earth’s mountains occur ________.

3. Which of the following is NOT an example of deformation?

4. A body of rock affected by tensile stress will likely undergo ________.

5. A body of rock affected by compressive stress will likely undergo ________.

6. The term for a change in shape induced by stress is ________.

7. Which of these is NOT one of the components of deformation?

8. How is stress different from force?

9. How is stress different from strain?

10. Under which condition would a body of rock be most likely to exhibit brittle behavior?

11. How does the rate at which a body of rock is deformed affect its behavior?

12. Under which of these conditions would a body of rock be more likely to exhibit plastic behavior?

13. Why are earthquakes on continents most likely to occur above the brittle-plastic transition depth?

14. If compressive stresses acting on a rock are greatest in a north-south direction, the rock will likely deform by shortening in a _________ direction.

15. A mineral-filled crack in a rock is termed a _______.

16. Regularly spaced joints in an outcrop may indicate that an area ________.

17. The distinction between joints and faults is that ________.

18. Normal, reverse, and thrust are all examples of ________ faults.

19. We can describe the orientation of planar features such as faults and joints using measurement of the _______.

20. Movement along faults often produces a rock formed from sharply angled rock fragments termed ________.

21. A polished surface produced by scraping of rock along a fault is termed a(n) ________.

22. If a fault plane is greater than 30° from horizontal and the hanging wall block moves upward relative to the footwall block, the fault is called a ________ fault.

23. In a ________ fault, the fault plane is non-vertical and the hanging wall block moves downward relative to the footwall block.

24. Which type of a fault is the result of deformation to accommodate tensile stresses such as those that occur during rifting?

25. It is possible for offset along an oblique-slip fault to have both ________ and ________ components.

26. If you stand on one side of a strike-slip fault and the block on the other side of the fault has moved to your left, this is known as a(n) ________.

27. A geologist’s compass differs from the more widely known orienteering compass in that the geologist’s compass ________.

28. In the image below, the rocks have been bent into an elongate arch. This is an example of a(n) ________.

29. The portion along a fold where curvature is the greatest is termed the fold ________.

30. What is term for a fold in which layers bend without changing thickness, indicating slip between layers during folding?

31. In the image below, the rocks have been bent into an elongate trough. This is a(n) ________.

32. What is the term for a fold in which layers show thickened hinges and thinned limbs, indicating plastic deformation during folding?

33. On a geologic map, the beds of an eroded anticline will be _________ near the fold hinge compared to further from the hinge.

34. On a geologic map, if the contacts between sedimentary rock units form a bull’s-eye pattern of concentric circles, with the youngest unit in the center, the underlying structure is a(n) ________.

35. On a geologic map, if the contacts between sedimentary rock units form a bull’s-eye pattern of concentric circles, with the oldest unit in the center, the underlying structure is a(n) ________.

36. The sides of a fold, where curvature is at a minimum, are termed ________.

37. On a geologic map, if the contacts between sedimentary rock units form a series of parallel lines, with the oldest unit in the center, the underlying structure is a ________.

38. Mountain ranges formed along subduction zones are formed, in part, by ___________ in the crust.

39. During the formation of Pangaea, Africa collided with North America and created the Appalachian Mountains. Which of the following mountain ranges is a modern analog to the ancient Appalachian Mountains?

40. Normal faulting is most often associated with mountain building along ___________ boundaries, whereas reverse faulting is generally observed at ___________ boundaries.

41. The formation of the Basin and Range Province, a fault-blocked mountain range in Utah, Nevada, and Arizona, is associated with which of the following processes?

42. The accreted terranes that are added to a continent during orogeny are _______ than the cratons of the continent’s interior.

43. __________ is the balance between the weight of a mountain range and the buoyancy provided by the underlying mantle.

44. Which of these properly illustrates the principle of isostasy?

45. What is the primary reason why mountains substantially taller than Mt. Everest are unlikely to arise on the Earth?

46. There are many ways in which uplift can occur, but all of them reflect ________.

47. What can be said about a mountain range that is being uplifted at 2 cm/year but is not growing any taller?

48. Regions of continents that have NOT been subjected to orogeny during the past 1 billion years are termed ________.

49. Regions where Precambrian metamorphic rocks are exposed at the surface are termed ________.

50. On a geologic map, cratonic basins, where thick sequences of sedimentary rocks overly the Precambrian basement, show the _________ rocks toward the center of the basin.

1. What are the three components of deformation? Briefly explain each.

2. What types of geologic structures would you expect to find in an area that had undergone compression?

3. Contrast brittle and plastic deformation. Cite an example of a structure associated with each.

4. What is the difference between a dip-slip fault and a strike-slip fault? Describe each and give specific examples (use sketches if that helps).

5. Draw a cross section of a normal and reverse fault. For each, list the stress involved and change in the length of the crust, if any.

6. Compare and contrast domes and basins. If both are composed solely of sedimentary beds that have been eroded such that the ground surface is level, how would you identify each?

7. What is the plate tectonic setting that formed the mountains of the Basin and Range Province, and what type of faulting has this resulted in?

8. What can be said about the rates of uplift and erosion in a mountain that is gaining elevation? In a mountain decreasing in elevation? What is the ultimate fate of all mountains on the Earth?

9. Compared to the Rocky Mountains, the Appalachian Mountains are a series of lower-elevation hills with more gentle slopes. Have they always had these differences in topography? Explain.

10. Compare and contrast a cratonic shield and platform.