Análise estrutural e modelagem geológica da porção oeste da Janela Bom Jardim, Bacia do Camaquã, Caçapava do Sul – RS

Abstract

The Sul-rio-grandense shield occupies the central region of the state of Rio Grande do Sul and is composed by associations of rocks generated in the time interval between the Paleoproterozoic and the Neoproterozoic. During the final stages of the Brasiliano cycle, in the Neoproterozoic, the Camaquã Basin was filled and deformed. The Camaquã Basin is divided geographically into three sub-basins (Camaquã Occidental, Central and Oriental) that are separated by the tops of the basement. In the Camaquã Central sub-basin, in the Camaquã Mine region, there is a structural window, where older rocks are surrounded by younger rocks called Bom Jardim Window. The rocks that are located inside the structural window belong to the Santa Bárbara Group and the rocks that surround this window belong to the Guaritas Group. The work aimed at the construction of a 3D geological model constructed in the western portion of the Bom Jardim Window from field data (lodging, extension and shear fractures, and lineations), remote sensing, structural analysis of the structures obtained in the field using the Move™ software. Structures were analyzed through structural analysis for their geometry, kinematics and dynamics (when possible). With the results of the structural analysis and the geological model it was possible to make correlations with the main deformer events in the Camaquã Basin and also to better understand the structural relationship between the Santa Bárbara Group and the Guaritas Group. The deforesting events of the Camaquã Basin occur in the time interval between the end of the Neoproterozoic and Cretaceous and correspond to a series of compressive and distensive events. The extension fractures described in the work are classified as joints, because they have little movement perpendicular to the plane and have a preferred direction for NNE and NNW. These directions are similar to the digitized lineaments in the study area, which has preferred directions for NE and NW. For the shear fractures the paleontensores were analyzed and with that two deformation events, one transcurrent and another extensional, were identified. The transcurrent event, with NNE direction structures and hatchet kinematics and structure with NW direction and sinistral kinematics, coincide with two deformer events in the Camaquã Basin. The transcurrent event coincides with what is presented in the bibliography to an NNE compression, which generated transcurrent faults transcurrent faultless NNE and sinister WNW. The extensional event, with NW structure and sinistral kinematics and NE structure with normal obliqua kinematics, coincides with the distending NE event, which may be related to two events of Cretaceous magmatism (Serra Geral volcanism and alkaline dykes of the Piratini Suite). In conjunction with the geological model, it was possible to observe the deformation that is present in the two upper geological units of the Camaquã Basin, where the Santa Bárbara Group is more deformed than the Guaritas Group.