Neotectonics of the Upper Pardo River - Southeastern Brasil

Abstract

The hydrographic basin of the Pardo river (São Paulo and Minas Gerais states, southeastern Brasil), upstream from the Armando de Salles Oliveira dam, has been investigated with the main purpose of recognizing regional features related to neotectonic activity. Studies of structural geology, tectonics and geomorphology carried on two different scales (1:250,000 and 1:50,000) were aimed at estimating seismic risk as well as the evolution of landforms and associated erosive processes. The following topics have been specially taken into account: plateau levels, types of slopes, escarpments, lineaments, rapids, stream captures, terraces, alluvial fans, alluvial and colluvial Neocenozoic sediments, density and structural control of the drainage and brittle structures, such as joints and faults. These structures are scarce and scattered in the studied area so that structural analysis by means of classical methods could hardly be applied to the case; notwithstanding, their association to landforms, specially to the plateau, allowed an interpretation of the principal zones of neotectonic activity. Geomorphological and structural data referred to the 1:250,000 scale proved to be more useful; they indicate stronger tectonic activity in the Paleogene through the deformation of the highest plateau, followed by lesser events whose effects could not be as easily recognized through the landforms. A comparison of these results with structural data obtained from the 1:50,000 mapping displayed patterns of Cenozoic structures oriented to ENE-WSW and NW-SE, which suggests that they are the weakened effects of the tectonic activity related to the rifts of the southeastern Brasilian continental margin