Tectonism is the science of Earth movements and the rocks and structures involved therein. These movements build the structural framework that supports the stage on which surface processes, plants, animals and, most recently, people pursue their various roles under an atmospheric canopy. An appreciation of this tectonic framework is thus a desirable starting point for understanding the physical geography of South America, from its roots in the distant past through the many and varied changes that have shaped the landscapes visible today. Tectonic science recognizes that Earth’s lithosphere comprises rocks of varying density that mobilize as relatively rigid plates, some continental in origin, some oceanic, and some, like the South American plate, amalgams of both continental and oceanic rocks. These plates shift in response to deep-seated forces, such as convection in the upper mantle, and crustal forces involving push and pull mechanics between plates. Crustal motions, augmented by magmatism, erosion, and deposition, in turn generate complex three-dimensional patterns. Although plate architecture has changed over geologic time, Earth’s lithosphere is presently organized into seven major plates, including the South American plate, and numerous smaller plates and slivers. The crustal mobility implicit in plate tectonics often focuses more attention on plate margins than on plate interiors. In this respect, it is usual to distinguish between passive margins, where plates are rifting and diverging, and active margins, where plates are either converging or shearing laterally alongside one another. At passive or divergent margins, such as the present eastern margin of the South American plate, severe crustal deformation is rare but crustal flexuring (epeirogeny), faulting, and volcanism occur as plates shift away from spreading centers, such as the Mid-Atlantic Ridge, where new crust is forming. Despite this lack of severe postrift deformation, however, passive margins commonly involve the separation of highly deformed rocks and structures that were involved in the earlier assembly of continental plates, as shown by similar structural legacies in the facing continental margins of eastern South America and western Africa. At active convergent margins, mountain building (orogeny) commonly results from subduction of oceanic plates, collision of continental plates, or accretion of displaced terranes.
South American Tours: Work Relations in the Entertainment Market in South America
