Geologia estrutural rúptil na região do Platô do Seival, no município de Caçapava do Sul, RS

Abstract

The Sul-rio-grandense Shield (SrgS) is composed of several petrotectonic associations, formed during the Paleoproterozoic and Neoproterozoic, which register different processes of deformation, magmatism, metamorphism and formation of sedimentary basins. The present work presents a structural analysis of a certain area, observing its geomorphological characteristics and patterns of structural lineaments, acquired by extraction of textural elements by satellite imagery. With this, the brittle structural characteristics and their relationships with field data were delimited, seeking to understand the deformational history of the rocks and related processes, allowing the understanding of tectonic events. The present work focused on the Santa Bárbara Group, specifically where rocks from the Serra dos Lanceiros Formation outcrop, characterized by sandstones with cross-channeled bedding and conglomerates supported by clasts, generally imbricated, from a depositional system of intertwined rivers. In structural terms, the study area is located between two major structural geomorphological lineaments: the Segredo and Perau faults, both northeast (NE-SW) direction, and northwest (NW-SE) direction lineaments. The scarcity of works on the ESrS in a more detailed scale and involving brittle structures boosted the present work, with greater detail and focus on structures in NW-SE directions, from the point of view of brittle structures. The work began with a bibliographical review and delimitation of geomorphological lineaments on a scale of 1:250,000, 1:100,000, and 1:50,000 by remote sensing. From this analysis, it was possible to determine prevailing directions NW-SE, NE-SW and secondary directions N-S and E-W. It was observed that, when the scale of analysis is more detailed, the geomorphological lineaments become more discontinuous and fragmented. What's more, the N-S secondary direction becomes more representative. In the field, it was possible to recognize brittle structures, mainly in the region where a fracture zone was identified in the NW-SE direction. Fracture analysis in almost all outcrops showed a low rate of fracturing in sedimentary rocks, except for the specific region where fracture zones were identified. There was an increase in the number of fractures in this region. Based on the interpretation of field data, the existence of a syncline and anticline fold was identified in the region of the Seival Plateau, in the municipality of Caçapava do Sul. These structures condition the terrain's geomorphology and outcrop patterns. The geometry of the structure, with NESW direction axes, corroborates regional NW-SE compression efforts, consistent with data from the bibliography. A pattern of fractures in a NW-SE direction, also important in the formation of the relief, is related to the system of fractures in a NW-SE direction, conditioned by the Arch of Rio Grande, responsible for the uplift of the ESrg.