Glacial geologic confirmation of an intraplate boundary, in the Paraná basin of Brazil

The predrift fit of South America and Africa remains problematic given the inability to match all parts of the coastlines simultaneously. Early opening of the South Atlantic Ocean may have been facilitated by intraplate deformation in either South America or Africa, but the location of such deformation is controversial and poorly constrained. Broad-scale remote sensing has suggested an intraplate boundary in South America, stretching from the Cochabamba bend in the Andes to the Rio Grande-Walvis rise, but the inferred boundary crosses the Paranaá basin of Brazil where any evidence of deformation is obscured by Late Jurassic flood basalts. A subsurface study of the upper Paleozoic glaciogenic infill of the Paranaá basin (the 1300-m-thick Itarare Group; ca. 300-260 Ma) identifies repeated episodes of intracratonic rifting on either side of an accommodation zone crossing the basin along the trend of the inferred intraplate boundary. Renewed influence of this zone during the opening of the South Atlantic is suggested by the asymmetric distribution of successive magma units within the Serra Geral lava pile and by the trend of dike swarms. The intraplate boundary identified within the Paranaá basin may extend westward along the northern margin of the Chaco basin in Bolivia.