Deformation of the Crust

Transcription

1 Deformation of the Crust Review Choose the best response. Write the letter of that choice in the space provided. 1. The state of balance between the thickness of the crust and the depth at which it rides on the asthenosphere is called a. stress. b. isostasy. c. strain. d. shearing. 2. The increasing weight of mountains causes the crust to a. sink. b. fold. c. rise. d. fracture. 3. The force that changes the shape and volume of rocks is a. footwall. b. isostasy. c. rising. d. stress. 4. The type of stress that squeezes rock together is a. compression. b. tension. c. shearing. d. faulting. 5. The type of stress that pulls rocks apart, making them thinner, is a. folding. b. compression. c. tension. d. isostasy. 6. Shearing a. bends, twists, or breaks rocks. b. squeezes rock together. c. causes rock to melt. d. pulls rock apart. 7. High pressure and high temperature will cause rocks to a. fracture. b. adjust. c. plateau. d. deform. 8. Upcurved folds in rock are called a. anticlines. b. monoclines. c. fractures. d. synclines. 9. Downcurved folds in rock are called a. fractures. b. monoclines. c. anticlines. d. synclines. 10. Folds in which both limbs remain horizontal are called a. monoclines. b. fractures. c. synclines. d. anticlines. Study Guide 17

2 Choose the best response. Write the letter of that choice in the space provided. 11. When no movement occurs along the sides of a break in a rock structure, the break is called a a. normal fault. b. fracture. c. fold. d. hanging wall. 12. When a fault is not vertical, the rock above the fault plane makes up the a. tension. b. footwall. c. hanging wall. d. compression. 13. A nearly vertical fault in which the rock on either side of the fault plane moves horizontally is called a a. normal fault. b. reverse fault. c. strike-slip fault. d. thrust fault. 14. The largest mountain systems are part of still larger systems called a. continental margins. b. ranges. c. belts. d. synclines. 15. Mount St. Helens in Washington State is an example of a a. folded mountain. b. volcanic mountain. c. fault-block mountain. d. dome mountain. Critical Thinking 1. Suppose glaciers, which are vast fields of slow-moving ice, were to cover much of the earth s surface once again. What would you expect to happen to those parts of the continents that were covered by ice? Explain. 18 Study Guide

3 2. When the Indian plate collided with the Eurasian plate, producing the Himalaya Mountains, which type of stress most likely occurred? Which type of stress is most likely occurring along the Mid-Atlantic Ridge? Which type of stress would you expect to find along the San Andreas Fault? Use your knowledge of stress and plate tectonics to explain your answers. 3. If the force that is causing a rock to be slightly deformed begins to ease, what might happen to the rock? What would happen if the force causing the deformation became greater? 4. Why do you suppose dome mountains do not become volcanic mountains? Study Guide 19

4 Application 1. Suppose that a new highway is being planned. This proposed road would intersect a transform boundary. What would happen to the highway if a strike-slip fault existed along the boundary? Why? 2. A geologist discovers that part of a mountain range along the west coast of the United States contains the fossil remains of animals that do not match any other fossils from North America. What is the most likely explanation for this phenomenon? 3. Construct a concept map that illustrates the relationship between crustal deformation and types of mountains. 20 Study Guide

5 they hung their lamps. Footwall referred to the rock they walked on. Interested students may wish to research the origins of other terms. Pages 88 89: Discussion (Extension) To extend students scientific vocabulary, you may wish to point out that the geologic term for mountain building is orogeny (oro-, from the Greek word oros, meaning mountain, and -geny, from the Greek word gignesthai, meaning act of being born ). Pages 90 91: Science & Technology You may wish to tell students that the word laser is an acronym for light amplification by stimulated emission of radiation. Explain to students that lasers are used to measure the distance to Lageos satellites because laser light has special properties. One property of laser light is that it does not spread out as quickly as ordinary light does. The diameter of a typical laser beam grows by only 1 m for every 1,000 m that the light travels. Page 93: EarthBeat You may wish to point out to students that the Mediterranean Sea is a remnant of the Tethys Sea, which covered most of the Eastern Hemisphere during the Mesozoic Era. Small-Scale Investigation Folds and Fractures (p. 87) Science Process Skills: observing, identifying cause-and-effect relationships Answers to Analysis and Conclusions 1. The dowel bends but regains its original shape when the books are removed. The putty bends, but it does not regain its original shape. The dowel represents rock that is deformed temporarily by stress but regains its shape when the stress is removed. The putty represents rock that permanently folds as a result of stress. 2. Both the dowel and the putty fracture. 3. Two influential factors are the physical properties of material and type of stress. Rocks deep within the earth s crust are made more pliable by the high temperatures. Cooler temperatures at the earth s surface make rock brittle. Rocks deformed by slow, gentle stress may regain their original shape when the stress is removed. Quick, strong stress usually fractures rock. Review Answers to Review 1. b 5. c 9. d 13. c 2. a 6. a 10. a 14. c 3. d 7. d 11. b 15. b 4. a 8. a 12. c Answers to Critical Thinking 1. The continents would sink because the increase in the weight of the crust would trigger an isostatic adjustment. 2. compression, because rock is being squeezed together; tension, because rock is being pulled apart; shearing, because rock is being bent, twisted, and torn apart 3. It would return to its original shape. The rock would become permanently deformed, either folding or faulting. 4. because the weight of the crust above the molten rock prevents it from breaking through Answers to Application 1. The highway would crack apart along its width, and the two sections would be displaced horizontally. 2. Part of the mountain is a terrane that was scraped off the ocean floor as oceanic crust was subducted beneath continental crust. 3. Student concept maps should represent the connections among the types of mountains formed and the process by which they are formed. In-Depth Investigation Continental Collisions (pp ) Approximate time: 1 class period Objectives: to construct a model; to demonstrate with a model how the Himalayas formed as a result of the collision of India with Eurasia Skills: observing, experimenting, constructing and interpreting models, measuring Prelab Discussion Have students describe a convergent boundary and a subduction zone. Stress the nature of the continental and oceanic lithosphere and their respective densities. Also, discuss the idea that the formation of new T44