NEOTECTÔNICA DA REGIÃO DO ALTO ESTRUTURAL DE QUELUZ (SP-RJ, BRASIL)

Abstract

The region of the Paraiba do Sul River Valley between the cities of Cruzeiro (Sao Paulo) and Itatiaia (Rio de Janeiro), in Southeastern Brazil, comprises the eastern and western terminations, respectively, of the Cenozoic Taubate and Resende rift basins, as well as the Precambrian terranes of the Queluz Structural High separating these basins, and includes much evidence of recurrent or resurgent tectonic movements that have been active until recent times. The morphostructural analysis of this region, combined with the characterization of the Quaternary sedimentary deposits and brittle tectonic structures, has permitted the recognition of three phases of neotectonic movements. The oldest movements were related to a NW-SE compressive stress field, during the Pleistocene, associated with an E-W right-lateral transcurrent binary. The structures related to this phase affected colluvium and stone-line deposits, which are often overthrust by blocks of basement rocks along faults trending NE to ENE. Probably in the beginning of the Holocene the stress regime changed to an E-W (WNW-ESE) extension, responsible for the generation of N-S-trending grabens with syntectonic sedimentary filling. Finally, a new change in the stress field is recorded by conspicuous and widespread families of shear joints, systematically orientated ENE and WNW, that affect colluvium, colluvium-alluvium and alluvium deposits. The accute bissectrix of the families of joints indicate an E-W direction of compression. The reliability of the neotectonic data presented in this study and the proposed neotectonic model are particularly significant due to important human activities in the region, including such major engineering projects as a radioactive fuel factory, a hydroelectric power station and reservoir as well as a nuclear power plant.