Reorganização da rede de drenagem a par1r de controles morfoestruturais nas subbacias do Alto e Médio Rio Grande (MG)

Abstract

The reorganization of the drainage network and the migration of divides are essential for assessing the influence of tectonics, lithology, climate, changes in base levels, and erosive processes in the evolution of fluvial landscapes. However, most research focuses on areas with tectonic activity, leaving gaps in the understanding of these phenomena in intraplate regions. In South America,some authors explore these issuesin escarpments of passive basinsthat draininto the Atlantic Ocean, but there are few analyses on the rearrangement of drainage and the displacement of basin divides draining into the interior of humid escarpments. Thus, despite some advances, the understanding of drainage reconfiguration in passive zone basins with distinct morphostructural compartments and geological histories remains incomplete. The lack of comparative analyses between mobile belts and cratons in the same fluvial system of tectonically quiescent areas highlights the need for a comprehensive approach. In this context, the research aims to elucidate the evolution of the drainage network and divide migration in a diverse morphostructural setting, considering influences of tectonic legacies in intraplate zones. Using the Upper and Middle Grande River basin in Brazil as a study area, we applied morphometric parameters, evaluated distributions, and investigated key factors related to equilibrium conditions. The analysis involved the application of classic morphometric parameters, identification of knickpoints, evaluation of longitudinal profiles, calculation of the normalized steepness index (ksn), and investigation of drainage divide stability through the chi index (χ). The results enhance that drainage reorganization and topographic rejuvenation are common in tectonically quiescent regions and in exorheic systems on the Brazilian Atlantic margin, due to the influence of morphostructures. Drainage of sub-basins in Neoproterozoic mobile bets is more unstable than those associated with cratons. We observed that material resistance is decisive in differential erosion in plateau landscapes and influences the formation and distribution of knickpoints. In this scenario, knickpoints sustained by resistant layers delay energy propagation effects, create transient zones, favor instability conditions at divides, and rejuvenate the landscape. Additionally, we note that the degree of erosion rate amplification is influenced by stratification dip, layer alternation on slopes, and slope gradient.