Magmatismo pós-tectônico investigado por meio dos métodos U-Pb e Lu-Hf, Complexo Pedra Branca, Rio de Janeiro - RJ

• Autor(a) principal: Moterani, Ana Carolina Machado
• Data de Publicação: 2021
• Outros Autores: [e-mail]
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UERJ
• Texto Completo: http://www.bdtd.uerj.br/handle/1/17726
• topic: Geochronology; Magmatism; Complexo Pedra Branca; Zircão; Magmatismo – Rio de Janeiro (RJ); Geocronologia; Geologia isotópica – Rio de Janeiro (RJ); Geoquímica – Rio de Janeiro (RJ); Pedra Branca Complex; Zircon; CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS

The Pedra Branca Complex is located at the western region of Rio de Janeiro city. Tectonically it is inserted in the Coastal Domain, which is part of the central segment of Ribeira Belt. The lithologies that formed this rocky complex were generated in events related to the Brasilian-Panafrican Orogeny (~ 600 Ma), thus contains pre- to- post-collisional rocks. The study of post-tectonic granite bodies belonging to Ribeira belt reveals that the magmatism event occurred in two different pulses, a Cambrian pulse (~ 512 Ma), and a younger one, Ordovician (~ 486 Ma) with ~ 30 Ma between them. The Favela and Pedra Branca granites are the representants of the post-collisional magmatism within the Pedra Banca Complex. The Pedra Branca granite is divided in four facies: Média-homogênea, Bandada, Hololeucocrática e Pegmatítica. The use of both U-Pb and Lu-Hf geochronological methods in zircon allows us to generate new ages and isotopic signatures of rocks and it is one of the most used tools in this sense nowadays, due to the high speed, sensibility and relative simplicity of the analysis. The aim of this work was to obtain by way of LA-MC-ICP-MS new U-Pb ages and Lu- Hf isotopic data to rocks of the Complex to reach a better comprehension about the formed magmatism of theses rocks and their evolution to then contribute to a better discussion about its geological context. The studies were based on analysis of seven samples of Pedra Branca, in different facies, (representative of the older magmatic pulse) and two of Favela granite (representative of the younger magmatic pulse. Totalizing 9 samples. The obtained ages of Pedra Branca granite (514,6 ± 6,9 Ma; 503,4 ± 5,3 Ma; 505,3 ± 6,7 Ma; 516,3 ± 7,8 Ma; 496,8 ± 4 Ma; 507,7 ± 5,6 Ma; 504 Ma) and Favela granite (501 ± 3,6 Ma and 489 ± 7,7 Ma) mostly corresponded with the previously published in literature for the respect lithologies (513 ± 5 Ma and 482 ± 6 Ma), however their indicate that the magmatism in the Complex occurred in progressive pulses, causing a low interval (~20 Ma) than what was expected (~30 Ma). The petrogenetic indicator εHf showed crustal and mantellic sources to the magmatism of the area. By means of the εHf was also possible to corroborate with the discussion about the formation of the Hololeucocrática facies, which has their origin related to the Média-Homogênea facies.