Abstract
Abstract New petrography, geochemistry and Sm-Nd and Sr data from the orthogranulites of the Juiz de Fora complex in southern Rio de Janeiro State and compiled information provide insights on the petrogenetic and tectonic evolution. The complex comprises several geochemical groups including mafic orthogranulites (three tholeiitic and one alkaline) and felsic orthogranulites (three calc-alkaline and one tholeiitic/low K calc-alkaline). New geochemical and isotope data, combined with available U-Pb data suggest a long evolutionary history from the Paleoproterozoic to the Neoproterozoic. The oldest magmatic episode produced juvenile to slightly contaminated arc-type Rhyacian rocks, as well as granitic rocks related to collision or post-collision episodes. Altogether these rocks integrate part of a dismembered Rhyacian orogen within the Ribeira belt. Few TDM Nd model ages yielded 2.75 to 2.58 Ga, suggesting minor Archean contribution for magma genesis. Some of the basic granulites’ bodies yield Meso- to Neoproterozoic TDM Nd model ages, which may refer to an extensional magmatism. Orthogranulites present granulite facies paragenesis, related to the youngest tectonic episode in the Juiz de Fora Complex (Brasiliano Orogeny). The new data are potentially important for Paleoproterozoic reconstruction models, due to the predominantly juvenile character of the Juiz de Fora complex, as similarly worldwide.
Highlights
The São Francisco Paleocontinent (Heilbron et al 2000, 2004, 2008, Trouw et al 2000), is a landmass that encompasses the Archean nuclei within São Francisco-Congo and adjoining Paleoproterozoic belts
The JFC rocks are in tectonic contact with the overlaying orthogneiss of the Quirino Complex and the metasedimentary rocks of the Paraiba do Sul group that make up Paraíba do Sul Terrane (Heilbron et al 2000, Tupinambá et al 2007)
The obtained geochemical and isotopic data reinforce the idea that the orthogranulites of the JFC had a very complex and protracted tectonic evolution, recording several tectonic events throughout the Proterozoic
Summary
The São Francisco Paleocontinent (Heilbron et al 2000, 2004, 2008, Trouw et al 2000), is a landmass that encompasses the Archean nuclei within São Francisco-Congo and adjoining Paleoproterozoic belts. In SE Brazil, the Paleoproterozoic Mineiro, Mantiqueira and Juiz de Fora belts accreted onto the southern São Francisco Archean nuclei in the Siderian to Orosirian (Alkmim & Teixeira 2017, Barbosa et al 2018, Heilbron et al 2010). This important episode of continental crust growth is ascribed to the Minas accretionary orogeny (Teixeira et al 2014, 2015). The São Francisco-Congo Paleocontinent behaved as a stable mass until the Statherian, when an important period of bimodal intraplate magmatism and extensional tectonics resulted in the Espinhaço rift system
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