Lithostructural and tectonic determinants in the geomorphic evolution of the Basalt Plateau - Southern Brazil

摘要

There remains a lack of understanding on the geomorphic setting of the landscapes of the Basalt Plateau of the Paran acute accent a Sedimentary Basin (South Brazil), especially in regard to lithostructural and tectonic influence on the landscapes. Therefore, this article investigates the role of the geological framework in the evolution and configuration of the landscapes of the Basalt Plateau, which encompasses part of southern Brazil. Research is based on data obtained in the field and in the office. In the field, a survey of tectonic structures was carried out, along with differentiation of the lithological members. The structural data served as a basis for the elaboration of stereograms and the calculation of paleostress. Rose diagrams exposing lineament and fault trends were also developed. In the office, cartographic products were elaborated using Geographic Information Systems, resulting in maps of the geology (lithostructure and faults), elevation, knickpoint density, and relief rugosity, besides generating swath profiles of the studied area. Morphometric techniques related to the longitudinal profiles of the rivers, slope-length index (SL), and basin asymmetry factor (AF) were used to evaluate the possible tectolithostructural control in the geomorphic configuration of the drainage basins of the Basalt Plateau. The results showed that massive flood basalts, related to the Toledo and Foz do Iguacu Members, and vesicular flood basalts, especially the Santa Quite acute accent ria Member, together with the faults (NW-SE and NE-SW), strongly influence the landform development. The convex segments of the longitudinal profiles and the high slope length (SL) values (1st order anomalies), associated with the spatial disposition of the faults that cut across the rivers, demonstrate the tectonic action on the regional landscape. This action reactivated strike-slip faults (NE-SW, NW SE, N-S and E-W) in two events from the Eocretaceous: one event prior to the Neogene and another possibly during the current tectonic regime. Thus, it is considered that the current geomorphic configuration of the Basalt Plateau is the result of the interaction of tectonic reactivations, possibly Cenozoic, with the lithostructure, which reacts unevenly to exogenous factors in the sculpting of landforms.