Structural geology of northern limb of the Paraiba do Sul river divergent structure: cross-sections Três Rios (RJ) - Matias Barbosa (MG) and Barra do Piraí - Conservatória (RJ) / Geologia estrutural da aba norte da estrutura divergente do rio Paraíba do Sul: seções Três Rios (RJ) - Matias Barbosa (MG) e Barra do Piraí - Conservatório (RJ)
AUTOR(ES)
Leticia Constantino Vicente
DATA DE PUBLICAÇÃO
2008
RESUMO
This study is about the structural geology of a portion of the Central Mantiqueira Province which corresponds to the north side of the structural divergence of the Rio Paraíba do Sul valley. Two geological cross-sections (Três Rios - Matias Barbosa and Barra do Piraí - Conservatória) provided geometrical and kinematics data. Lattice preferred orientation of quartz showed deformation mechanisms that affected these rocks in the lower crust. Three distinct structural domains were recognized in the Três Rios - Matias Barbosa cross-section. They present NE-SW foliation with decreasing dip distant from the shear zone, low dip at domain II and moderate dip at domain III. The mineral and stretching lineation present low plunging at domains I and II and significant NE oblique dip at domain III. In all domains of the meso-scale there are observed distinct geometrically structures. Kinematics indicators are likely in all domains showing horizontal dextral sliding and top-to SW from low dip. Five distinct domains were observed in the Barra do Piraí - Conservatória crosssection. Domains I and V are characterized by NE-SW steeply dipping foliation and strike lineation. Domains II, III and IV show NE-SW foliation presenting NW low dip, subvertical and SE low dip, respectively. Kinematics indicators at domains I, III and V show dextral shear sense, while in the domains II and IV, they were not observed. As in Três Rios - Matias Barbosa cross-section, meso-scale distinct geometrical structure intercalation were observed. Microstructural data and lattice preferred orientation present variation in simple shear and pure shear for different domains. A change on the slip systems can be associated to thermal gradient along cross-section during deformation or to high temperature maintenance after deformation, characterizing an annealing process. Changes on geometrical structures can be characterized as a relationship between simple shear and pure shear. Comparing these structures with theoretical modeling, we can consider them to be kinematics likely in a three-dimensional evolution model. Both crosssections suggest extrusion in transpressional tectonic pattern at domain II in Três Rios (RJ) - Matias Barbosa (MG) cross-section and domains II, III and IV in Barra do Piraí - Conservatória (RJ) cross-section. Lateral changes and structures overlapping are interpreted as a result of spatial and temporal partition of deformation. The presented data suggest that Mantiqueira Province structures in the studied area were generated by a non-confined transpressional deformation pattern in a simple tectonic evolution.
ASSUNTO(S)
transpression kinematics cinturão ribeira extrusion cinemática transpressão ribeira belt extrusão
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