Tracing final Gondwana assembly: Age and provenance of key stratigraphic units in the southern Paraguay Belt, Brazil

The Paraguay Belt in central South America developed in response to the collision between the Amazonian Craton, the Rio Apa Block, the São Francisco Craton and the Paranapanema Block and marks the final suture of western Gondwana. The traditional 'Brasiliano' age (∼620 Ma) of this belt has recently been questioned by evaluation of the geological record of sedimentation, deformation, metamorphism and magmatism, which indicate the closing stages of orogenesis occurred well into the Cambrian. Here we investigate the time of deposition and source areas for the metasedimentary rocks of the Jacadigo and Corumbá Groups overlying the Amazonian and Rio Apa cratons in the southern part of the Paraguay Belt. 1177 LA-ICPMS and 61 SHRIMP detrital zircon U-Pb ages were analysed from samples taken from both the basement and the sedimentary succession. A new maximum age constraint of 686 ± 10 Ma is presented for the Puga Formation to complement existing work in the region. The youngest ages from our samples are 566 ± 8 Ma and 543 ± 11 Ma. These maximum depositional ages indicate that final sedimentation began no earlier than 543 ± 11 Ma in the southern Paraguay Belt. Given that zircon inheritance in these rocks continues up until this age and that known Amazonian Craton ages are older than ∼950 Ma we discuss other potential sources for these sediments by integrating the U-Pb detrital zircon data with Hf isotopic data. Cumulative proportion analysis of our detrital U-Pb data set indicate a transition from a passive to a collisional setting. Our final conclusions are that sedimentation in the belt transitioned from a passive margin environment to a collisional setting, consistent with an ocean to the east of the present-day Amazonian Craton that did not close until the Cambrian.