Electron microprobe U–Th–Pb monazite dating of the Transamazonian metamorphic overprint on Archean rocks from the Amapá Block,southeastern Guiana Shield,Northern Brazil |
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| Institution: | 1. Companhia de Pesquisa de Recursos Minerais (CPRM) – Geological Survey of Brazil, Avenida Dr. Freitas 3645, Bairro do Marco, CEP 66095-110 Belém, Pará, Brazil;2. Pará-Iso Laboratory, Universidade Federal do Pará, Belém, Brazil;3. BRGM, BP 6009, Orléans, France;1. Observatório Sismológico, Universidade de Brasília, Campus Darcy Ribeiro, SG-13, Brasília – DF, 70910-0900, Brazil;2. IAG – USP, Rua do Matão 1226, Cidade Universitária, São Paulo, SP, 05508-090, Brazil;1. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China;2. Hubei Key Laboratory of Wetland Evolution and Eco-Restoration (WEER), China University of Geosciences, Wuhan 430074, China;1. Centro de Tecnologia e Geociências, UFPE, Av. Acadêmico Hélio Ramos, s/n Cidade Universitária, 50740-530, Recife, PE, Brazil;2. Instituto de Geociências, UFPA, Rua Augusto Correa 1, 66075-110, Belém, PA, Brazil;3. Centro de Ciências da Natureza, UFPI, Ininga, 64049-550, Teresina, PI, Brazil;4. Departamento de Paleontologia e Estratigrafia, UFRGS, Avenida Bento Gonçalves 9.500, 91501-970, Porto Alegre, RS, Brazil;5. Centro de Pesquisa de História Natural e Arqueologia do Maranhão, CPHNAMA, Rua do Giz 59, Praia Grande, 65010-680, São Luís, MA, Brazil;6. Programa de Pós-Graduação em Sociedade, Tecnologia e Meio Ambiente, UniEVANGÉLICA, Av. Universitária, Km 3,5, Anápolis, GO, 75070-290, CP 122 e 901, Brazil;7. Associação Bacelarense de Proteção ao Meio Ambiente, Duque Bacelar, MA, Brazil;1. Museu Nacional/UFRJ, Quinta da boa Vista S/N – São Cristovão, 20940-040 Rio de Janeiro, RJ, Brazil;2. TEKTOS – Geotectonics Research Group, Faculdade de Geologia, Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier 524/4006-A, Maracanã, 20559-900 Rio de Janeiro, RJ, Brazil;3. LAGIR – Isotope Geology and Geochronology Laboratory, Faculdade de Geologia, Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier 524/4006-A, Maracanã, 20559-900 Rio de Janeiro, RJ, Brazil;4. Petrobras S.A. – Ilha do Fundão, Quadra 7, 20179-900, Rio de Janeiro, Brazil;1. Paleontología, Instituto de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), Centro Científico Tecnológico CONICET Mendoza, Avenida Ruiz Leal s/n, 5500, Mendoza, Argentina;2. Centro de Investigación Esquel de Montaña y Estepa Patagónica (CIEMEP), CONICET, Gral. Roca 780, Esquel, Chubut, Argentina;3. Departamento de Ciencias Aplicadas, Instituto de Investigaciones Geológicas, Universidad Nacional de La Rioja, Ciudad Universitaria, Avenida René Favaloro s/n, 5300, La Rioja, Argentina |
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| Abstract: | The Amapá Block, southeastern Guiana Shield, represents an Archean block involved in a large Paleoproterozoic belt, with evolution related to the Transamazonian orogenic cycle (2.26 to 1.95 Ga). High spatial resolution dating using an electron-probe microanalyzer (EPMA) was employed to obtain U–Th–Pb chemical ages in monazite of seven rock samples of the Archean basement from that tectonic block, which underwent granulite- and amphibolite-facies metamorphism. Pb–Pb zircon dating was also performed on one sample.Monazite and zircon ages demonstrate that the metamorphic overprinting of the Archean basement occurred during the Transamazonian orogenesis, and two main tectono-thermal events were recorded. The first one is revealed by monazite ages of 2096 ± 6, 2093 ± 8, 2088 ± 8, 2087 ± 3 and 2086 ± 8 Ma, and by the zircon age of 2091 ± 5 Ma, obtained in granulitic rocks. These concordant ages provided a reliable estimate of the time of the granulite-facies metamorphism in the southwest of the Amapá Block and, coupled with petro-structural data, suggest that it was contemporaneous to the development of a thrusting system associated to the collisional stage of the Transamazonian orogenesis, at about 2.10–2.08 Ga.The later event, under amphibolite-facies conditions, is recorded by monazite ages of 2056 ± 7 and 2038 ± 6 Ma, and is consistent with a post-collisional stage, marked by granite emplacement and coeval migmatization of the Archean basement along strike-slip shear zones. |
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