SOUTH AMERICAN CRATONS AND THEIR ROLE IN PROTEROZOIC SUPERCONTINENTS

The South American platform is composed of four major cratons (Amazon, Sao Francisco, Rio de la Plata and Sao Luis) and other smaller continental blocks and terrains that may have took part in supercontinental assemblages. Here, paleogeographic configurations from the Paleoproterozoic up to the Cambrian are tested through an updated paleomagnetic and geochronologic record of South America, including new high-quality poles from Amazon and São Francisco cratons. These poles are compared to those of other cratons thought to have interacted with South American units in the Proterozoic, such as Baltica and Laurentia. The oldest assemblage of continents to be addressed is the Paleoproterozoic Columbia (~1800 Ma), for which our data support a configuration aligning Laurentia, Baltica and Amazonia through their Paleo-Mesoproterozoic belts. For Neoproterozoic times (~1200-1000 Ma) a connection between Laurentia and Amazonia craton in an evolving configuration (with relative movement between the two units) is supported by a pole-to-pole comparison. In contrast, striking differences in Laurentia's drift history compared to Sao Francisco, Sao Luis(=West Africa) and Kalahari rule-out the effective participation of these cratons in Rodinia. The assembly of Gondwana has probably occurred in different steps, comprising first (~630 Ma) the connection between Sao Francisco, Rio de la Plata, other minor blocks and the African cratons, followed by the collision of these central Gondwanan blocks with the Amazon craton and adjoining blocks by mid-Cambrian times (~530 Ma), after the opening of the Iapetus ocean basin between Laurentia and Amazonia. In this scenario, the West Gondwana was not a coherent tectonic unit before the end of Precambrian times.