MESOZOIC-CENOZOIC PALEOGEOGRAPHIC AND GEODYNAMIC EVOLUTION OF SOUTHERN SOUTH AMERICA

Abstract

ln this presentation, we compare the paleogeographie evolution of continental South America with the established plate tectonic history of the oceanic crust of the South American and African Plates. Major paleogeographic changes that have occurred in the last 200 million years are illustrated by reconstructions at 200, 160, 120, 100, 70, 50, 20, and 5 Ma. The se reconstructions show location and type of magmatic activity, types and arnounts of subsidence, and transgressions and regressions of shorelines. The latter are eompared with proposed eustatie sea-Ievel ehanges. The sequence of events documented by the reconstructions begins in the mid-late Triassic with the development of successor troughs and intra-plate domes and sags that represent the prelude to the rupture of Gondwanaland. Extension eontinued through the Late Jurassie resulting in widespread faulting and intra-plate volcanism. Large-seale drift occurred by the Early Cretaceous (late Neocomian) accompanied by the formation of epicontinental rifts and sags, and a well-defined magmatic are along the western margin of South America. In the mid-Cretaceous the Atlantic Basin was well developed and rimmed by trailing-margin sedimentary prisms, and global changes in plate motions led to the reorganization of the subduction system along the Pacific margin of South America. The Late Cretaceous, a time of relative tectonic quiescence in southern South America, recorded the maximum flooding of the continent by Atlantic waters. Plate tectonic reorganization in the Paleogene introduced new patterns of Andean deformation and magmatism, and coincided with general marine retreat. Magmatic arc buildup and renewed marine flooding followed in the early Neogene, with the late Neogene being dominated by pronounced shortening, Cordilleran uplift, and marine withdrawal.