Geology 200

Study Guide

Unit 15:
Mountain Belts and the Continental Crust

Overview

In this final unit of Geology 200 you will apply what you have learned in earlier units to a study of the processes of mountain building and continental crust development.

The unit begins with an overview of the general characteristics of major mountain belts. Section 2 discusses the three major types of mountain ranges. The characteristics of mountain ranges that geologists have observed are the basis for a theory about the evolution of mountain belts, which is the subject of Section 3. As you may have guessed, the evolution of mountain belts is explained in terms of plate tectonic theory. Finally, Section 4 explains the growth of continents, again using plate tectonic theory.

Objectives

After completing this unit, you should be able to

  1. describe the origin of the Precambrian shield.
  2. describe the main characteristics of the major mountain belts.
  3. describe and give examples of the three major types of mountain ranges.
  4. describe the three stages in the history of a mountain belt.
  5. describe the process of mountain building and the resulting sequence of rocks in each of the types of plate collisions listed below.
    1. convergence of two oceanic plates
    2. convergence of ocean and continental plates
    3. convergence of two continental plates
  6. Describe two possible origins for the Basin and Range Province of the United States.
  7. Define accretion terrane and exotic terrane.
  8. Define suspect terrane, and explain how such terranes originate.

Section 1: Characteristics of Major Mountain Belts

The reading associated with this section deals with some of the more important characteristics of major mountain belts. Be certain that you can list and discuss the eight features described.

Reading Assignment

Plummer, C. C., Carlson, D. H., & Hammersley, L. Physical Geology (15th ed.).

  • Introduction to Chapter 20: Mountain Belts and the Continental Crust (pp. 485-486).
  • "Mountains and Mountain Building" (pp. 486-489).
  • “Characteristics of Major Mountain Belts” (pp. 489-494).

Study Questions

  1. Are higher mountains always geologically younger than lower mountains?
  2. How can the evolution of a mountain range be dated? Which are older, the mountains on the East Coast of North America (the Appalachians) or the mountains on the West Coast?
  3. What is a Precambrian shield, and how would it originate?
  4. How do sedimentary rocks in cratons differ from sedimentary rocks in a mountain belt?
  5. How does the composition of sedimentary rocks vary throughout a mountain belt?
  6. What kind of stresses do folds and faults characteristic of the interiors of mountain belts represent?
  7. What is the origin of metamorphic rocks found in mountain belts?
  8. What feature of mountain belts suggests that large volumes of magma may have accumulated from partial melting of the lower crust and then welled upward, eventually solidifying?
  9. What evidence suggests that normal faulting occurred after intense deformation in the development of mountain belts?
  10. Outline four other pieces of information that geophysical investigations have given us about mountain belts and the continental crust.

PDF icon Answer Key

Section 2: Types of Mountain Ranges

The textbook mentions mountain ranges, but does not discuss the kinds of ranges in detail or distinguish clearly between a mountain range and a mountain belt. A mountain belt is an elongate series of mountains belonging to a single geologic unit. An elongate unit consisting of numerous mountain ranges, regardless of their similarity or dissimilarity in form or age, is referred to here as a mountain belt; the American Cordillera is an example of a mountain belt.

A mountain range can be classified into one of three types according to the force that is predominantly responsible for its configuration.

  1. Fold-and-thrust mountain ranges, such as the Appalachians, the Alps, the Rockies, the Urals, the Himalayas, and the Carpathians, develop from thick piles of sedimentary strata—predominantly marine strata that have been compressed, faulted, folded, and crumpled. Metamorphism and igneous activity are always associated with fold-and-thrust ranges.

  2. Volcanic mountain ranges are formed through the deposition of new pyroclastic and volcanic rock, not by the deforming of pre-existing crust. Examples of volcanic mountains include Mount Fuji, Mount Etna, Mount Rainier, Mount Mayon, Mount Kilimanjaro, and Mount Garibaldi.

    The four major types of volcanic mountain ranges are

    • submerged seafloor mountains, such as the mid-ocean ridge;
    • partially submerged seafloor mountains, such as the chain of volcanoes that forms the Hawaiian Islands;
    • oceanic island arcs, which are arcuate belts of andesitic and basaltic volcanic islands formed over subducting oceanic crust; for example, the Aleutian Islands from Kamchatka, through the Kurile Islands and Japan; and the islands of Sumatra, Java, Sumba, and Timor; and
    • continental volcanic arcs, which are the andesitic mountain ranges that form where a subduction zone occurs beneath the edge of a continent; for example, the Andes or the Cascades.
  3. Fault-block mountain ranges such as the Sierra Nevada of California and the Basin and Range province of the southwestern United States are isolated mountain ranges that stand abruptly above their surrounding plains and are separated from the lowland areas by normal faults of great displacement. Volcanic mountains or fold-and-thrust mountains once occupied the sites of fault-block mountains, but were worn down by erosion before the block faults formed.

Study Questions

  1. Distinguish between a mountain range and a mountain belt.
  2. Identify three characteristics of fold-and-thrust mountain ranges, and give three examples of such ranges.
  3. List four types of volcanic mountain ranges, and give one example of each.
  4. Identify two characteristics of fault-block mountain ranges.

PDF icon Answer Key

Section 3: The Evolution of a Mountain Belt

Section 3 of this unit describes the observed data that geologists use to classify mountain ranges. Classification, however, is not explanation. To understand how mountain ranges form and develop, geologists have applied the plate tectonic theory. The reading that follows summarizes the plate tectonic interpretation of mountain development.

Volcanic mountains can form at spreading ridges, over hot spots in mid-plate areas, and at convergent margins as island arcs in oceans or as magmatic arcs on continents.

Fold-and-thrust mountain ranges form at convergent boundaries where two continental plates or a continental and an oceanic plate converge. The first three readings in this section discuss continental slopes and plate margins. The fourth reading describes how orogeny can occur in three different settings along plate margins: ocean-continent convergence, arc-continent convergence, and continent-continent convergence. The last part of the reading discusses the final stage in the evolution of a mountain belt: post-orogenic uplift and block faulting. This stage of mountain building occurs after the compressive stress of orogeny ceases. General uplift occurs as the newly-thickened continental crust adjusts isostatically. Fault-block mountain ranges form where greater uplift occurs along normal faults.

Reading Assignment

Plummer, C. C., Carlson, D. H., & Hammersley, L. Physical Geology (15th ed.).

  • “Continental Shelves and Continental Slopes” (pp. 438).
  • “Submarine Canyons” (pp. 439-441).
  • “Passive Continental Margins” (pp. 441-442).
  • “Evolution of Mountain Belts” (pp. 495-503).

Study Questions

  1. What kind of crust underlies the continental shelf?
  2. Describe the sediments deposited in the continental shelf.
  3. How do sediments deposited at converging plate boundaries differ from those deposited in opening ocean basins?
  4. What is an orogeny?
  5. Describe what happens when an island arc collides with a continent.
  6. List the sequence of events that would occur if spreading of the Atlantic Ocean ceased and the ocean began to close.
  7. Give an example of where the ocean has closed to form a new mountain belt and then opened again.
  8. Describe the role of isostacy in the evolution of a mountain belt.
  9. Describe the possible origins for the Basin and Range Province of the United States.

PDF icon Answer Key

Section 4: The Growth of Continents

A continent grows as new material is added to its margins. The formation of a mountain belt accompanies the accretion of new material. The following reading describes how geologists have divided major mountain belts into terranes, or zones of continuity, to enhance understanding of the belts in geology.

Reading Assignment

Plummer, C. C., Carlson, D. H., & Hammersley, L. Physical Geology (15th ed.).

  • “The Growth of Continents” (pp. 503-505).

Study Questions

  1. What is a tectonostratigraphic terrane?
  2. What is an accreted terrane? —an exotic terrane?
  3. What characterizes a suspect terrane? How do geologists prove that a terrane is exotic?

PDF icon Answer Key

Unit 15 Self Test

You have now finished Unit 15, the last unit in Geology 200.

References and Supplementary Material

Barker, D. S. (1983). Igneous rocks. Englewood Cliffs, NJ: Prentice-Hall.

Bell, F. G. (2007). Basic environmental and engineering geology. Boca Raton, FL: CRC Press, Taylor & Francis Group.

Blatt, H. (1992). Sedimentary petrology (2nd ed.). San Francisco, CA: W. H. Freeman.

Bolt, B. A. (1982). Inside the Earth. New York: W. H. Freeman.

Bonatti, E., & Crane, K. (1984). Ocean fracture zone. Scientific American, 250(50), 40-51.

Carrigan, C. R., & Gubbins, D. (1979). The source of the Earth’s magnetic field. Scientific American, 240(2), 118-128.

Cech, T. V. (2005). Principles of water resources: History, development, management and policy. Hoboken, NJ: John Wiley & Sons.

Chernikoff, S., & Whitney, D. (2007). Geology: An introduction to physical geology. Upper Saddle River, NJ: Pearson-Prentice Hall.

Deer, W. A., Howie, R. A., & Zussman, J. (1992). An introduction to the rock-forming minerals (2nd ed.). New York: Wiley.

Dietrich, R. V., & Skinner, B. J. (1979). Rocks and rock minerals. New York: Wiley.

Hamblin, W. K. (1989). The earth’s dynamic systems: A textbook in physical geology (7th ed.). New York: MacMillan.

Hamblin, W. K. (1992). Physical geology: A study guide to accompany the Earth’s dynamic systems (6th ed.). Englewood Cliffs, NJ: Prentice Hall.

Howell, D. G. (1985). Terranes. Scientific American, 253, 90-103.

Kehew, A. E. (2006). Geology for engineers and environmental scientists (3rd ed.). Upper Saddle River, NJ: Prentice Hall.

Klein, C., & Hurlbut, C. S. (1993). Manual of mineralogy (21st ed.) New York: Wiley.

Judson, S., Kauffman, M. E., & Leet, L. D. (1987). Physical geology (7th ed.). Englewood Cliffs, NJ: Prentice Hall.

Lutgens, F. K., & Tarbuck, E. J. (2006). Essentials of geology. Upper Saddle River, NJ: Pearson-Prentice Hall.

Montgomery, C. (2008). Environmental geology (8th ed.). New York: McGraw-Hill.

Murck, B. W., Skinner, B. J., & Porter, S. C. (1995). Environmental geology. Hoboken, NJ: John Wiley & Sons.

Plummer, C. C., Carlson, D. H., & Hammersley, L. Physical geology (13th ed.). New York: McGraw-Hill.

Postel, A., & Richter, B. (2003). Rivers for life: Managing water for people and nature. Washington, DC: Island Press.

Skinner, B. J., & Porter, S. C. (2000). The dynamic earth: An introduction to physical geology (4th ed.). New York: Wiley.

Tarbuck, E. J., Lutgens, F. K, Tsujita, C. J., & Hicock, S. R. (2009). Earth: An introduction to physical geology. Upper Saddle River, NJ: Pearson-Prentice Hall.

Tucker, M. (2001). Sedimentary petrology: An introduction to the origin of sedimentary rocks. Oxford: Blackwell Science.

Vink, G. E., Morgan, W. J., & Vogt, P. R. (1985). The Earth’s hot spots. Scientific American 252(4), 50-58.

Wilson, M. (1989). Igneous petrogenesis. London: Unwin Hyman.

Zumberge, J. H., Rutford, R. H., & Carter, J. (2008). Laboratory manual for physical geology (13th ed). New York: McGraw Hill.

Appendix

PDF icon Interpreting Ternary Diagrams

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