New Paleomagnetic Constraints on the Proterozoic Supercontinent Evolution: A view from the South

The assembly and disruption of supercontinents is thought to have impacted the long-term evolution of different envelopes of the Earth throughout Precambrian times, from mantle convection dynamics to feedback mechanisms leading to the stepwise change in atmospheric oxygenation. But the timing, duration, the size and the paleogeographic configuration of Precambrian supercontinents is still a matter of discussion. Large South American cratonic units (>30,000 km2) such as the Amazon, Rio de la Plata and São Francisco are usually represented as key pieces of different supercontinental assemblies but their paleomagnetic database is still scarce. The most important advances in the Precambrian paleomagnetic database concerns the Amazon Craton. Recent paleomagnetic studies allows one to track the participation of the Amazon Craton in several supercontinent assemblies from 2.0 Ga up to the end of the Proterozoic era. Amazonia was definitely part of the Columbia Supercontinent as attested by 1.78-1.79 Ga key poles. This supercontinent also comprised Laurentia, Baltica, North China, and Amazonia, forming a long and continuous landmass, linked by Paleo- to Mesoproterozoic mobile belts. Paleomagnetic data for Amazonia support a long-lived connection between Laurentia and Baltica at least until 1.26 Ga ago. However, new paleomagnetic poles from the same craton suggest that Columbia was in fact ephemerous, indicating a changing configuration between Amazonia and Baltica between 1.78 and 1.44 Ma. At the end of the Mesoproterozoic, the Amazon craton is part of Rodinia based on its record of Grenvillian events with overlapping ages with similar orogenic belts in eastern Laurentia. But its relative position in that supercontinent is still intensively debated. Presently only four poles for the Amazonian craton are available for the 1,200-900 Ma interval. Based on these results a dynamic model for the Amazonian craton was envisaged, which considers its oblique collision with southern Laurentia, followed by strike-slip migration along the Grenville belts, but other models are also paleomagnetically viable. During the Neoproterozoic and the Cambrian, the Amazon Craton collided with the São Francisco Craton forming the West Gondwana. The existence of a large Clymene ocean between Amazonian and Congo-São Francisco cratons, implies that these units were not together in a fixed position within Rodinia and were assembled after Precambrian times, along a Cambrian suture zone. During the talk we will present the paleogeographic configurations of the different supercontinents and supercratons allowed by the new paleomagnetic data and also the geochronological and isotopic constraints on the timing of assembly and break-up of continental assemblies.