Juvenile contribution of the Neoproterozoic Rio Negro Magmatic Arc (Ribeira Belt,Brazil): Implications for Western Gondwana amalgamation |
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| Authors: | Miguel Tupinambá Monica Heilbron Claudio Valeriano Rubem Porto Júnior Fátima Blanco de Dios Nuno Machado Luiz Guilherme do Eirado Silva Júlio Cesar Horta de Almeida |
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| Institution: | 2. Petrology research group, Universidade Federal Rural do Rio de Janeiro. Instituto de Agronomia, Departamento de Geociências. BR-465, Km 7. Seropédica. Rio de Janeiro RJ Brazil 23890-000;3. Petróleo Brasileiro SA, PETROBRAS. Av. República do Chile;4. Petróleo Brasileiro SA, PETROBRAS., 330/24th Torre Leste Rio de Janeiro RJ Brazil 20031–170;5. GEOTOP, Université du Québec à Montréal, Canada;1. Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto, Morro do Cruzeiro, 35400-000 Ouro Preto, MG, Brazil;2. Research School of Earth Sciences, The Australian National University, Canberra 0200, ACT, Australia;1. Universidade Estadual Paulista (Unesp), Instituto de Geociências e Ciências Exatas, Caixa Postal 178, 13506-900 Rio Claro, SP, Brazil;2. University of Alberta, Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, Edmonton, Alberta T6G 2E3, Canada;3. Universidade Federal dos Vales do Jequitinhonha e Mucuri (UFVJM), Instituto de Engenharia, Ciência e Tecnologia, Av. Um, n 4.050 – Cidade Universitária, CEP 39447-814 Janaúba, MG, Brazil;1. Universidade do Estado do Rio de Janeiro, Faculdade de Geologia, Rua São Francisco Xavier 524/4006-B, Maracanã, Rio de Janeiro, Brazil;2. Universidade Federal do Sul da Bahia, Centro de Formação em Ciências Ambientais, Porto Seguro, Bahia, Brazil;3. University of Portsmouth, School of Environment, Geography and Geosciences, Burnaby Building, Burnaby Road, Portsmouth PO1 3QL, United Kingdom;4. University of Notre Dame, Department of Civil and Environmental Engineering and Earth Sciences, 46556, United States;1. Universidade Federal de Ouro Preto, Programa de Pós-graduação, Departamento de Geologia, Campus Morro do Cruzeiro, Ouro Preto, MG, CEP 35400-000, Brazil;2. Universidade Federal de Ouro Preto, Departamento de Geologia, Campus Morro do Cruzeiro, Ouro Preto, MG, CEP 35400-000, Brazil;3. Sustain Geologia Ltda, Teresa M. Valadares 503/502, Belo Horizonte, MG, CEP 30575-160, Brazil;4. University of Portsmouth, School of Earth and Environmental Sciences, Burnaby Building, Burnaby Road, Portsmouth, PO1 3QL, UK;1. Faculdade de Geologia, Universidade do Estado do Rio de Janeiro (UERJ), Rua São Francisco Xavier 524/4006-A, 20559-900, Rio de Janeiro, RJ, Brazil;2. Programa de Pós-graduação em Análise de Bacias e Faixas Móveis, Faculdade de Geologia, Universidade do Estado do Rio de Janeiro (UERJ), Rua São Francisco Xavier 524/4006-A, 20559-900, Rio de Janeiro, RJ, Brazil;3. Graduação em Geologia, Faculdade de Geologia, Universidade do Estado do Rio de Janeiro (UERJ), Rua São Francisco Xavier 524/4006-A, 20559-900, Rio de Janeiro, RJ, Brazil;1. School of Earth and Environmental Sciences, University of Portsmouth, Burnaby Building, Burnaby Road, Portsmouth, PO1 3QL, UK;2. Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto, Ouro Preto, MG 35400-000, Brazil;3. GEOTOP Université du Québec à Montréal, P.O. Box 8888, Station Centre Ville, Montréal, Québec H3C 3P8, Canada |
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| Abstract: | The ca. 790–600 Ma Rio Negro Complex (RNC) of the Ribeira belt (Brazil) consists of a plutonic portion of a magmatic arc built by the E-vergent subduction of the ESE border of the São Francisco paleoplate during the amalgamation of Western Gondwana.The plutonic series comprises low- to medium-K granitoids (ca. 790–620 Ma) and high-K granitoids and shoshonite rocks (ca. 610–605). The age span of 185 m.y. is suggestive of a long history of arc-related magmatism, continuously or not in time. The Nd isotopic signatures of the RNC consist of εNd(t) ratios from ? 3 to + 5 for the medium-K series shoshonite series and from ? 14 to ? 3 for the younger high-K group. This time-dependent trend of Nd isotopes is indicative of progressive maturity of the arc over time. The same evolution is indicated by Sr data, as the medium-K rocks have 87Sr/86Sr initial ratios < 0.705 while the high-K rocks yield values between 0.705 and 0.710. The predominance of intermediate rocks over mafic ones suggests an initial intra-oceanic to transitional stage, possibly developed in a distal portion of a passive margin, such as the Japanese arc, evolving to a more developed, differentiated felsic rock associations.The role of transform fault zones, such as the Luanda shear zone, is emphasized in order to explain the consumption of a wide oceanic plate in the inner portion of Western Gondwana. |
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