Evolução estrutural da borda sul do Gráben da Guanabara

Abstract

This work investigates the Cenozoic tectonic deformations on the southern edge of the Guanabara Gráben from extensive paleo fields in sedimentary rocks, silicified breccias, diabase dikes and gneiss basement rocks. The study area is located in the metropolitan area of the city of Rio de Janeiro. It is bordered on the west by Morro Dois Irmãos (southern zone of the city of Rio de Janeiro) and, on the east, by Serra da Tiririca (oceanic region of Niterói). The southern border of Guanabara graben has NE-SW direction to ENE-WSW and Cenozoic deformations controlled by the Rio Bonito Fault Zone. Regionally it is correlated with the border faults of the basins of São José de Itaboraí and Macacu. In the study area corresponds to the fault of the Paineiras, which deforms the Carioca Coastal Massif. Besides, this fault zone controls the intrusion and deformation of the alkaline massifs, the plug and dikes of Cabuçu, and the plugs of Jardim Cabuçu. These deformations are also recorded in the Tanguá alkaline massifs and Itaboraí plug belonging to the Rio de Bonito high. To the east of the Rio Bonito high, this fault zone has probable continental continuity up to the Cape of São Tomé (Almeida, 1976, Ferrari, 2001), and also probable relation with the deformations in Gráben of Barra de São João and Campos basin. In the distal part of Gráben de Barra de São João, the pinching of the layers towards the continent, and the NE-SW direction of the graben suggest a correlation of this structure with the continental basins of Macacu and São José de Itaborái. The employed method involves the kinematic analysis of fracture failures and characterization of the affected lithology, including minerals newly formed by basement hydrothermal alterations. Five distinct paleotension fields were identified, with the interaction between the upper Cretaceous and the Holocene. The geochronological characterization was made based on the regional events and field criteria such as the overlap of striations, the timing relation of fault movements and hidrotermalized rocks and their mineralizations. The results obtained in the field were correlated to regional tectonic events of a brittle nature deforming the basins and alkaline massifs contained in the Fault Zone of Rio Bonito. The deformations recognized in the study area, the corresponding paleostress field and regional correlation will be listed below:Event 1 – σ3 paleogenic NE-SW: deforms diabase dikes and silicified breccias with percolation of oxidizing fluids. Regionally controls the intrusion of the alkaline massifs and implantation of the São José de Itaboraí basin.Event 2 – σ1 upper neogenic NW-SE formation of low-angle and high-angle dips reverse faults associated with neoformed minerals. Regionally correlated to the second inversion pulse of the Itaboraí basin and control of the formation of fluorite veins in the Tanguá alkaline massif. Event 3 – σ3 E-W forms N-S fractures in NW-SE direction diabase dike. Regionally it forms N-S faults in the Macacu basin. From the correlation of these events with literature data, it was proposed that the tectonic events responsible for the formation and reactivation of the southern border of Guanabara Gráben exerted control in the implantation and deformation of the alkaline bodies contained therein, and inversion of the basins of Itaboraí and Macacu, characterizing a corridor of brittle deformation from the south zone of Rio de Janeiro to the Rio Bonito High.