Lineamento Iúna: origem, significado e reativações

• Ano de defesa: 2016
• Autor(a) principal: Gomes, Bruno Lopes
• Orientador(a): Nunes, Rodrigo Peternel Machado
• Banca de defesa: Negrão, André Pires , Mendes, Julio Cezar
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade do Estado do Rio de Janeiro
• Programa de Pós-Graduação: Programa de Pós-Graduação em Análise de Bacias e Faixas Móveis
• Departamento: Centro de Tecnologia e Ciências::Faculdade de Geologia
• País: BR
• Palavras-chave em Português: Lineamento Iúna; Zona de Cisalhamento; Reativação; Falhas; Diques
• Palavras-chave em Inglês: Iúna Lineament; Shear Zone; Reactivation; Faults; Dykes
• Área do conhecimento CNPq: CNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS
• Link de acesso: http://www.bdtd.uerj.br/handle/1/7155

The Iúna Lineament (LI) extends for more than 180km and traverses parts of three states, being the southeast of Minas Gerais (MG), the north of Rio de Janeiro (RJ) and the southern portion of Espírito Santo (ES). The LI is most expressive close to the city of Iúna is in ES. The LI forms part of a group of lineaments with NNW-SSE to NW-SE orientations that cut across ES, and includes the Vitória-Colatina and Piúma Lineaments. Theses lineaments and other tectonic elements characterise the Araçuaí-Congo Orogenic system, an accretionary orogen active during the final of the Neoproterozoic until late Cambrian. The Araçuaí orogeny can be divided into four stages: a pre-collisional stage represented by the G1 igneous suite (630-580 Ma), the syn-collisional granitoides (G2 suite - 582-575 Ma), a late collisional stage and associated G3 igneous suite (545-520 Ma). This third stage was followed by the post-collisional magmatism (535-490 Ma) of the G4 & G5 suites and extensional processes related to the gravitational collapse of the Araçuaí orogeny. The Iúna Lineament is best identified in areas of outrcopping Neoproterozoic-Cambrian rocks between the Chalé (MG) and Mimoso do Sul (ES) municipalities. However a large part of this region is covered by paleogene to recent sediments, hampering the identification of the lineament in digital elevation models. In such areas, NNW-SSE orientated drainages and valleys permit the identification of the LI, as collaborated by previous studies. The LI is considered to have formed during the late collisional phase of the Araçuaí orogeny, at the same time as the formation of the four main dextral shear zones, (Abre Campo, Manhuaçu, Guaçuí and Batatal), in the central part of the orogeny. Early ductile structures were observed along the Iúna Lineament during field work, in the form of centimetric to meters wide, subvertical, NNW orientated shear zones, dipping to the ENE and displaying sinistral transcurrent movements. The LI was later reactivated at least four times, the first reactivation during the gravitational collapse of the Araçuaí orogeny with associated the bimodal magmatism. Further ruptile reactivations are related to the Cretaceous opening of the Atlantic Ocean, with the generation of fractures and faults; and the intrusion of dolerite dykes along the Iúna Lineament. Brittle-ductile and brittle, normal faults and associated fractures were observed in the field, often filled by quartz, and dipping to the ENE. Gabbro dykes up to 20m wide and thinner (up to 10m wide) dolerite dykes were also encountered, both striking to the NNW and with subvertical dips to the ENE. Evidence for these reactivations is best observed in the north (sector A & B) of the area, where Neoproterozoic-Cambrian rocks outcrop well. In contrast the south (sector C) of the area is dominated by Cenozoic sediments, where NNW-SSE & NW-SE orientated faults and fractures along the LI were observed to affect the Barreiras Formation and Quaternary gravels. This indicates that at least another two neotectonic events reactivated the Iúna Lineament. The onshore exposure of LI terminates in the region of São Francisco do Itabapoana, where the coastline parallels the lineament until the Cape of São Tomé. From here it is likely that the Iúna Lineament continues offshore onto the continental platform where it may have exerted a control on the structural architecture of the areas of the oil-producing.