Structural evolution and U–Pb SHRIMP zircon ages of the Neoproterozoic Maria da Fé shear zone,central Ribeira Belt – SE Brazil |
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| Authors: | MPS Zuquim RAJ Trouw CC Trouw E Tohver |
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| Institution: | 1. Center for Economics, Management and Social Research, National Polytechnic Institute, Lauro Aguirre 120, col. Agricultura, Del. Miguel Hidalgo, 11360, Mexico City, Mexico;2. Department of Control Automatics, Center for Research and Advanced Studies, Av. IPN 2508, Col. San Pedro Zacatenco, 07360 Mexico City, Mexico;1. Departamento de Cristalografía y Mineralogía, Universidad Complutense de Madrid, Madrid E-28040, Spain;2. Instituto de Geociencias (UCM-CSIC), c/José Antonio Novais, Madrid E-28040, Spain;3. Instituto Madrileño de Estudios Avanzados en Nanociencia, IMDEA Nanociencia, Campus Universitario de Cantoblanco, Madrid E-28049, Spain;1. Geological Survey of Brazil (CPRM), Regional Superintendence of São Paulo, Rua Costa 55, São Paulo, SP 01304-010, Brazil;2. Instituto de Geociências, Universidade de São Paulo, Rua do Lago, 562, Cidade Universitária, São Paulo, SP 05508-080, Brazil;3. Geological Survey of Brazil (CPRM), SGAN 603, Conjunto J, Parte A, 1° andar, Brasília-DF 70830-030, Brazil |
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| Abstract: | The Maria da Fé Shear Zone (MFSZ) is a sinistral strike-slip kilometric-scale structure developed in the late Neoproterozoic during the assembly of Gondwana. The MFSZ development is related to the NW–SE collision between the São Francisco Paleocontinent and the Rio Negro Magmatic Arc, which formed the Ribeira Belt. This paper describes the shear zone in detail, concluding that the orientation and age are consistent with NW–SE shortening during the afore mentioned collision. A U–Pb SHRIMP Concordia age of 586.9 ± 8.7 Ma is reported from zircon grains of a granitic dyke that crystallised synkinematically to the main tectonic activity of the shear zone. Another group of zircon grains from the same sample generated an upper intercept age of 2083 ± 43 Ma anchored in the younger Concordia age. These zircon grains are interpreted as relict grains of the basement from which the granite dyke was generated by partial melting. The temperature during mylonitization in the MFSZ was estimated in the range from 450 to 600 °C, based on microstructures in quartz and feldspar. An earlier collision in the same region, between 640 and 610 Ma, led to an extensive nappe-stack with tectonic transport to ENE, integrating the southern Brasilia Belt. One of the thrust zones between these nappes in the studied area is the Cristina Shear Zone with mylonites that were generated under upper amphibolite to granulite facies conditions. Brittle-ductile E–W metric-scale shear zones are superimposed on the MFSZ, which were active in similar, but probably slightly cooler, metamorphic conditions (≈500 °C). |
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