An Introduction to Structural Geology and Tectonics
19. Perspectives of Regional Geology -- Essays
In Chapters 14 through 18, we have introduced you to the great variety of tectonic settings in which deformation occurs. To put deformation in context, we have not limited the discussion to structural features of these environments, but we also used basic information concerning petrologic and sedimentological features that accompany deformation. Most of our discussion focused on what happens at the three basic types of plate margins, in response to plate interaction, ranging from what happens during the inception of a divergent margin (rifting) to the death of a convergent margin (collision ± strike-slip). Tectonism that occurs in these various settings is dramatic, and results in belts of deformation, metamorphism and igneous activity. These belts are known as orogens, and the processes that create them comprise orogeny. Much of what is known about the plate tectonic processes comes from study of Mesozoic and Cenozoic plate margins, rifts and collision zones. Plate interactions, however, leave a permanent scar in the lithosphere, even long after the associated topography has eroded away, and thus through field study we are able to get a fairly thorough understanding of ancient plate tectonic events in our planet's history (Figure 19.1.1). We feel that to understand the nature and consequences of plate tectonic processes, including orogeny, it is best to study natural examples. Thus, we devote the final chapter of this book to case studies of important deformation belts. Each case study is written by an expert, in his or her own style, so that you will get a flavor of how different geologists think and approach tectonics. When you talk with such seasoned geologists, chances are that they show great excitement about the area in which they work or have worked. This may stem from discovering key outcrops for understanding regional deformation or maybe new insights into an aspect of fundamental significance for crustal evolution. We have tried to capture some of this excitement in the essays, as opposed to offering comprehensive review papers. When you collect additional reading material on these and other areas, you will rapidly learn that views vary and, sometimes, that they contradict. The data, of course, stand, but interpretation always remains open to alternative views, which is especially the case for regional tectonics. You will find that the essays emphasize the large scale, yet the scenarios are generally based on smaller scale observations. This interaction follows the approach we have taken throughout the book: observations on different scales are not separate and unrelated entities; rather, they form part of an integrated framework to study the deformation of rocks and regions.