A new interpretation for the interference zone between the southern Brasília belt and the central Ribeira belt,SE Brazil |
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| Institution: | 1. Universidade Federal do Rio de Janeiro, Depto. de Geologia, I.GEO, 21949-900 Rio de Janeiro, RJ, Brazil;2. Universidade Estadual do Rio de Janeiro, TEKTOS, Faculdade de Geologia, Rio de Janeiro, Brazil;3. BHP Billiton, Av. Américo Vespucio Sur 100, 10th floor, Las Condes, Santiago, Chile;1. Instituto de Geociências, Universidade de São Paulo, São Paulo, SP, Brazil;2. Department of Geology, The University of Kansas, Lawrence, KS, USA;1. Universidade Federal do Rio de Janeiro, Dep. de Geologia, IGEO, Rio de Janeiro, Brazil;2. Universidade Estadual do Rio de Janeiro, TEKTOS, Faculdade de Geologia, Rio de Janeiro, Brazil;3. Petrobras CENPES, Av. Horácio de Macedo, 950 Cidade Universitária, Ilha do Fundão, Rio de Janeiro, Brazil;1. Depto. de Geologia – IGEO – UFRJ, Cidade Universitária, CEP 21949-900, Ilha do Fundão, Rio de Janeiro-RJ, Brazil;2. Institut für Geowissenschaften – Goethe Universität Frankfurt am Main, Altenhöferallee 1, D-60438 Frankfurt am Main, Germany;3. Depto. de Geologia – UFES – CCA Alto Universitário, s/n – Guararema – CEP 29500-000, Alegre-ES, Brazil;1. Programa de Pós-Graduação em Geologia, Universidade Federal de Minas Gerais, IGC-CPMTC, Av. Antônio Carlos 6627, Belo Horizonte, Brazil;2. Geological Survey of Brazil (CPRM), Avenida Brasil 1731, Belo Horizonte, MG, Brazil;3. Faculdade de Geologia, Universidade do Estado do Rio de Janeiro, R. São Francisco Xavier 524, Rio de Janeiro, Brazil;4. Institute of Geological Sciences, University of Bern, Baltzerstrasse 1-3, Bern, Switzerland;5. Laboratório de Geoquímica Isotópica, Universidade Federal de Ouro Preto, Campus Morro do Cruzeiro, Ouro Preto, Brazil;6. Institut de Recherche en Astrophysique et Planétologie (IRAP), Observatoire Midi-Pyrénées (OMP), CNRS, 14 avenue Edouard Belin, 31400 Toulouse, France;1. TEKTOS Research Group, Geology Institute, Rio de Janeiro State University, Rua São Francisco Xavier 524/4030-A, Maracanã, Rio Janeiro 20550-900, Brazil;2. LAGIR Geochronology and Radiogenic Isotope Laboratory, Geology Institute, Rio de Janeiro State University, Rua São Francisco Xavier 524/4043-F, Maracanã, Rio Janeiro 20550-900, Brazil;3. Geochronology Laboratory, School of Earth Sciences, Australian National University, College of Physical & Mathematical Sciences, Building 142 Mills Road, Acton, ACT 2601, Australia;4. Geochronology Laboratory, Geosciences Institute, Brasília University-UNB, Campus Universitário Darcy Ribeiro ICC – Ala Central 70.910-900, Brasília, DF 70919-970, Brazil;5. Dept. Civil & Environmental Engineering & Earth Sciences, 156 Fitzpatrick Hall, University of Notre Dame, Notre Dame, IN 46556, USA |
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| Abstract: | In southeastern Brazil, the Neoproterozoic NNW–SSE trending southern Brasília belt is apparently truncated by the ENE–WSW central Ribeira belt. Different interpretations in the literature of the transition between these two belts motivated detailed mapping and additional age dating along the contact zone. The result is a new interpretation presented in this paper. The southern Brasília belt resulted from E-W collision between the active margin of the Paranapanema paleocontinent, on the western side, now forming the Socorro-Guaxupé Nappe, with the passive margin of the São Francisco paleocontinent on the eastern side. The collision produced an east vergent nappe stack, the Andrelândia Nappe System, along the suture. At its southern extreme the Brasília belt was thought to be cut off by a shear zone, the “Rio Jaguari mylonites”, at the contact with the Embu terrane, pertaining to the Central Ribeira belt. Our detailed mapping revealed that the transition between the Socorro-Guaxupé Nappe (Brasília belt) and the Embu terrane (Ribeira belt) is not a fault but rather a gradational transition that does not strictly coincide with the Rio Jaguari mylonites. A typical Cordilleran type magmatic arc batholith of the Socorro-Guaxupé Nappe with an age of ca. 640 Ma intrudes biotite schists of the Embu terrane and the age of zircon grains from three samples of metasedimentary rocks, one to the south, one to the north and one along the mylonite zone, show a similar pattern of derivation from a Rhyacian source area with rims of 670–600 Ma interpreted as metamorphic overgrowth. We dated by LA-MC-ICPMS laser ablation (U–Pb) zircon grains from a calc-alkaline granite, the Serra do Quebra-Cangalha Batholith, located within the Embu terrane at a distance of about 40 km south of the contact with the Socorro Nappe, yielding an age of 680 ± 13 Ma. This age indicates that the Embu terrane was part of the upper plate (Socorro-Guaxupé Nappe) by this time. Detailed mapping indicates that the mylonite zone is not a plate boundary because motion along it is maximum a few tens of kilometres and the same litho-stratigraphic units are present on either side. Based on these arguments, the new interpretation is that the Embu terrane is the continuation of the Socorro-Guaxupé Nappe and therefore also part of the active margin of the Paranapanema paleocontinent. The Brasília belt is preserved even further within the central Ribeira belt than previously envisaged. |
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| Keywords: | Brasília belt Ribeira belt Interference zone Neoproterozoic mobile belt Junction between collisional belts |
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