Zona de Cisalhamento de Rio Preto: caracterização geométrica e cinemática

Abstract

The high grade ductile shear zone system of the Paraíba do Sul Middle Valley corresponds to an important corridor of shear zones and configures a bundle of zones parallel to each other, hundreds of kilometers long and hundreds of meters thick, responsible for the lithostructural and tectonic compartmentalization of the Ribeira Central Belt. The Rio Preto Shear Zone (ZCRP) integrates and defines the northwest limit of this System. It is an important regional structure of the Ribeira Belt that limits the Andrelândia and Juiz de Fora domains, even though it was of great expression, it was little studied individually. In this sense, the present work sought to analyze and characterize the geometrical and cinematic aspects of this Zone through the techniques of geological mapping and structural analysis, with field descriptions of the internal structures followed by studies of optical microscopy, with a view to petrological and microstructural characterization. The structural data allowed the individualization of three ductile deformation phases, individualized as D1, D2 and D3. The D1 phase was responsible for the generation of an S1 foliation, observed only in the hinge of folds F2. The D2 event formed an extensive fold, through a compressive strain with transport to NW. The D3 event was responsible for the formation of the Rio Preto Shear Zone, for a directional transpressive deformation. It was found that the Rio Preto Shear Zone has a general NE-SW orientation, being marked by a strong mylonitic foliation of moderate diving for SE and a low stretch angle lineation for ENE, exhibits a distal kinematics in cuts parallel to the stretch lineation Le3. Lineation analysis allowed the identification of directional to oblique lines formed in a single deformation phase through the deformation partitioning. The results arrived at the model proposed by an inclined transpression, the combination of directional and contraction components being common.