The Mesoproterozoic Supercontinent Atlantica in the Brazilian Shield - Review of Geological and U-Pb Zircon and Sm-Nd Isotopic Evidence

Abstract

Supercontinent Atlantica was formed in South America by the orogenies of the Trans-Amazonian Cycle, namely the accretionary Encantadas Orogeny (2250-2100 Ma) and the collisional Camboriú Orogeny (2100-2000 Ma). Large belts 500 to more than1000 km long formed during the Trans-Amazonian Cycle in the three major cratons of South America, in the northern part of the Amazon Craton, in the São Francisco Craton and in the Rio de la Plata Craton. However, other large (1000 km) segments of Archean crust remained little deformed in the cratonic interior of Supercontinent Atlantica, such as a major portion of the Tocantins Province in central Brazil. In addition, smaller fragments, up to 100 km, of Trans-Amazonian Cycle continental crust are present inside the Neoproterozoic Brasiliano Cycle orogenic belts in the eastern half of extra-Andean South America. In contrast, the dominant volume, about 90%, of Neoproterozoic belts was formed by reworking of Archean and Paleoproterozoic crust. Zircon U-Pb geochronology, associated with Nd isotopes, indicates the widespread presence of Supercontinent Atlantica crust in South America and sensitive high-mass resolution ion microprobe investigation of zircons indicates that crust in southern Brazil was formed mostly in the Trans-Amazonian Cycle. Zircon geochronology also reveals that Supercontinent Atlantica was preceded by an intra-cratonic period lasting about 300 my and was succeeded by an intra-cratonic period of about 1000 to 1300 my. Many of the Trans-Amazonian Cycle belts and crustal fragments may have been accreted to South America during the Neoproterozoic. The demonstration that they all were once part of Supercontinent Atlantica must await further multi-technique investigations.