The geologic history of South America can be summarized in three different developmental stages, each corresponding to a major division of geologic time. The first stage encompassed Precambrian time (about 4 billion to 540 million years ago) and was characterized by a complex series of amalgamations and dispersals of stable blocks of protocontinental crust called cratons. The second stage coincides with the Paleozoic Era (about 540 to 250 million years ago), during which time the cratons and material accreted to them contributed to the formation first of the supercontinent Gondwana (or Gondwanaland) and then of the even larger Pangaea. The third stage, in which the present continental structure emerged, occurred in the Mesozoic and Cenozoic eras (about the past 250 million years) and includes the breakup of Pangaea and Gondwana, the opening of the South Atlantic Ocean, and the generation of the Andean cordillera.
The present tectonic framework of South America consists of three fundamental units: the ancient cratons, the relatively recent Andean ranges, and a number of basins. Five cratons—Amazonia, São Francisco, Luis Alves, Alto Paraguay, and Río de la Plata—represent the Precambrian core of South America, and (with the exception of the Alto Paraguay craton) these now appear as upwarped massifs arrayed from north to south in the immense eastern portion of the continent; a number of other Precambrian crustal blocks also were accreted along the margins of South America over geologic time. The lofty ranges and intermontane plateaus of the Andes rise along the entire western margin of the continent and represent the collision in the Cenozoic Era (about the past 65 million years) of the Pacific and South American plates brought about by the opening of the South Atlantic. Finally, vast, downwarped, sediment-filled basins are found between the cratons and along the entire eastern margin of the Andes. "South America" © Emmanuel BUCHOT, Encarta, Wikipedia
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