The Neoproterozoic–Cambrian Paraguay Belt, central Brazil: Part I — New structural data and a new approach on the regional implications

Abstract

Together with the Araguaia and Brasília belts, the Paraguay belt forms in central Brazil, the Tocantins Province that is one of the largest orogens of western Gondwana. The Corumbá area occupies the site where the northern and southern parts of the Paraguay belt form, together with the Chiquitos-Tucavaca aulacogen (stretching E–W in the adjacent Bolivian territory) an R-R-R basin system opened-filled in the ~700/650–540Ma interval within the Amazon-Rio Apa paleo-continent. The sedimentary (volcanic) rocks of the Jacadigo and Corumbá Groups found around the Corumbá city record part of the Neoproterozoic–Cambrian passive margin precursor of the Paraguay belt. Our pioneer structural analysis reveals that these rocks experienced progressive deformation (phases D1–D2–D3) and low-grade metamorphism during the Brasiliano Cycle (540–513Ma). The crystalline basement was also involved, according to structural data and K–Ar ages in the literature. The paleo-passive margin was thickened during the D1–D2 deformation and was lately shortened (D3) in two orthogonal directions, SE–NW (D3P) and SW–NE (D3T). Developed co-axially and verging to NW, D1–D2–D3P structures record the closure of the basin precursor of the Paraguay belt, whereas D3T structures seem related to the inversion of the aulacogen. Although the tectonic transport to NW, as observed in the Corumbá area, matches the reported transport of Paraguay belt's supracrustal rocks towards the eastern margin of the Rio Apa block and Araguaia belt's rocks towards the Amazon craton, the transport direction is opposite in other parts of the Paraguay belt. Our comprehensive discussion of these facts brings to light profound regional implications.