Geology 100
Introduction to Geology Telecourse
|
Geology 100 |
|
UNIT 4 |
||
Mountain belts can evolve from marine-deposited rocks to towering peaks during periods of tens of millions of years. Ultimately the peaks are eroded to plains and become part of the stable interior of a continent. To appreciate the long and complex process of mountain building, you need to know much of the material covered in previous chapters. For instance, you must understand structural geology to appreciate what a particular pattern of folds and faults can tell us about the history of mountain building in a particular region. To understand how the rocks formed during the various stages of a mountain belt's history, you must know about volcanism, plutonism, sedimentation, and metamorphism. Your earlier study of weathering and erosion will help you understand how mountains are worn away. Plate tectonic theory has been strikingly effective in helping geologists make sense of all the complex aspects of mountain belts and the continental crust. For this reason, you need to thoroughly understand the material in chapter 19 before you can appreciate how continents evolve.
In this chapter, we first point out what geologists have observed in mountain belts. Next, we describe how these observations are interpreted, particularly in light of plate tectonic theory. Finally, we discuss current perceptions of how continents change and grow.
In previous chapters we have discussed how rock at Earth's surface is affected by erosional agents such as wind and water. We now shift our focus to changes in bedrock caused by powerful forces originating deep within Earth. In this chapter, we explain how rocks respond to these tectonic forces.
The main purpose of this chapter is to help you recognize certain geologic structures, understand the forces that caused them, and thus determine the geologic history of an area. Some principles discussed in chapter 8 should help you interpret the way structures develop in an area and the sequence. Recognition of unconformities as well as the principles of original horizontality, superposition, and cross-cutting relationships are as important to structural geology as they are to determining relative time.
Subsequent chapters will require an understanding and knowledge of structural geology as presented in this chapter. To understand earthquakes, for instance, one must know about faults. Appreciating how major mountain belts and the continents have evolved (chapter 5) calls for a comprehension of faulting and folding. Understanding plate tectonic theory as a whole (chapter 4) also requires a knowledge of structural geology. (Plate tectonic theory developed primarily to explain certain structural features.) In areas of active tectonics, the location of geologic structures is important in the selection of safe sites for schools, hospitals, dams, bridges, and nuclear power facilities.
Also, understanding structural geology can help us more fully appreciate the problem of finding more of Earth's dwindling natural resources. Chapter 21 discusses the association of certain geologic structures with petroleum deposits and other valuable resources.
E-mail your instructor: John McNamara
Copyright © 2003 by Debbie Secord. All rights reserved.