The late Precambrian to early Paleozoic age rock units of the Pampean ranges, the Puna, and the North Patagonian massif of southwestern South America constitute the Famatinian orogenic belt. They are interpreted as an Ordovician collisional belt between the Occidentalia terrane and the Gondwana craton. They include mafic and ultramafic belts of Neoproterozoic to early Paleozoic age. An intense tectonothermal event resulted from the collision; syntectonic granitoids represent crustal melting. In that collision syntectonic to late-tectonic foreland basins developed. The recently proposed juxtaposition of Laurentia and East Antarctica-Australia in the Neoproterozoic raises the possibility that Laurentia and western South America were close together in the early Paleozoic, and therefore that the Famatinian belt resulted from Laurentia-Gondwana collision. Occidentalia, which is bordered by a Cambrian carbonate platform similar to that of eastern North America, may be a sliver detached from Laurentia during Late Ordovician time.Facultad de Ciencias Naturales y Museo