Cenozoic/Mesozoic transcurrent tectonics in the eastern portion of Rio Grande do Sul Plateau, Brazil

Abstract

Structural analysis of faults and fractures were carried in quarries volcanic rocks of the Serra Geral Formation, Paraná Basin, Rio Grande do Sul Plateau. They allowed defining four main families of faults: NE-SW to NNE-SSW, WNW-ESE to E-W, N-S and NW-SE. The tectonic lineaments (392) extracted from Landsat TM7 images and SRTM - digital elevation model, in the 1:250,000 scale, frequently show structures with a preferred WNW- ESE (N60 -80W) trend, and secondarily NE-SW (N30-40E) and NNE-SSW (N0°-10E) trends. The outcrops analysis predominantly showed NE-SW and ENE to E-W trends with dextral strike-slip kinematics, and the presence of microfiber carbonates and iron manganese oxides along fault planes. On the other hand, for the patterns N-S and WNW–ESE, both dextral and sinistral strike-slip kinematics were obtained, without the filling of microfiber. A chronological relation of the different fault families establishes that the NW one is older, probably of Early Cretaceous age, and that the NE-SW and NW-SE ones with dextral and sinistral kinematics, respectively, are younger, with age between Paleogene and Neogene. However, both N-S to NNE (dextral) and ENE-WSW to E-W (sinistral) fault patterns have intermediate age, between Upper Cretaceous and Paleogene.