Geologia USP. Série Científica (Dec 2011)
Structural analysis of the Rio Pardo Group - southeast of Bahia state
Abstract
The Meso- to Neoproterozoic Rio Pardo Group is located in the southeastern region of the Bahia State and consistsof low-grade metasedimentary rocks deposited on Paleoproterozoic to Archean basement. From the base to the top, themetasedimentary rocks are grouped into the following sequences: Panelinha Formation consisting of coarse-grainedimmature clastics; the overlying Itaimbé Subgroup which is made up of the Camacã Formation (metapelites with localcarbonates), the Água Preta Formation (fi ne-grained metapsamites and local carbonate lenses), Serra do Paraíso Formation(metacarbonates and quartzites) and the Santa Maria Eterna Formation (metaconglomerates and metacarbonates). TheSalobro Formation was deposited unconformably on this sequence and consists of coarse-grained immature and local fi negrainedclastic rocks. The Rio Pardo Group was affected by three successive folding events, which were recorded in twolitho-structural units. The litho-structural unit 1 is located in the northeastern part of the basin, and the litho-structural unit2, in the southwestern part of the basin. These units are separated by the Rio Pardo-Água Preta inverse fault, trending NWSEand dipping SW. The fi rst unit is autochthonous and monophasic and displays open folds and slaty cleavage, changinggradually towards southwest into large overturned folds with axial plane schistosity. The second unit is polyphasic andshows large folds with NE vergence. A third folding is represented by folds and foliations present at the western marginof the basin. The NE vergence of the Rio Pardo Group can be explained by changes in the deformation regime and in thedirection of the principal axis of deformation in the north sector of the Araçuaí belt during the Brasiliano collision orogen.The tectonic transport to the north could be the cause of deformation of the Rio Pardo Group.
