|Mountain Belts and the Continental Crust|
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 stuctural 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.