O Complexo Juiz de Fora na Região de Pedra Dourada (MG): litogeoquímica, geocronologia U-Pb, isótopos de Sm-Nd e Sr e implicações na Formação do Paleocontinente São Francisco

• Autor(a) principal: Ferreira, Sandro Lúcio Mauri
• Data de Publicação: 2022
• Outros Autores: [e-mail]
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UERJ
• Texto Completo: http://www.bdtd.uerj.br/handle/1/19169
• topic: Complexo Juiz de Fora; Riaciano; Sanukitoides; Ortogranulitos; Sistema Orogênico Minas-Bahia; Paleocontinente São Francisco; Juiz de Fora Complex; Rhyacian; Sanukitoid rocks; Ortogranulites; Minas-Bahia Orogenic System; São Francisco Paleocontinent; CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA

The Juiz de Fora Complex (CJF) comprises Paleoproterozoic orthogneisses and orthogranulites with a wide compositional variation, interpreted as a product of an arc built between the Siderian and Orosirian (within the Minas-Bahia Orogenic System) and related to the formation of the São Francisco Paleocontinent. This work presents inedited data from zircon U-Pb geochronology (LA-MC-ICP-MS) combined with Sm-Nd and Sr isotopes, lithogeochemistry, petrography, and field observations for the CJF in the region of Pedra Dourada (MG). The data allow the recognition of two main lithotypes: felsic orthogranulite and mafic orthogranulite. The felsic orthogranulite, the predominant lithotype, has intermediate contents of SiO2, high Ba, Sr, Mg#, high La/YbN ratio, and low Na2O/K2O ratio, and these characteristics are compatible with those of sanukitoid rocks. They present crystallization ages of 2175 Ma and initial εNd values between -4.0 and +0.5, TDM ages between 2.57 and 2.12 Ga and initial 87Sr/86Sr ratios between 0.6937 and 0.7137, informing moderately juvenile signatures to slightly evolved, suggesting the origin of magmas originating from a hybrid mantle extensively modified by the assimilation of crustal material (fluids, sediments, melts) by a long period of subduction and/or by previous subductions. The mafic orthogranulite, lithotype of a subordinate character, presents gabbroic composition, high enrichment in REEs, and provides negative Eu anomaly, it is classified as an OIB. It was crystallized in 2102 Ma and the isotopic data (with initial εNd equal to -5.5, TDM of 2.61 Ga and initial 87Sr/86Sr ratio equal to 0.7020) suggest a significant contribution from sources crustal rocks and the origin of this rock in an arc environment through a slab-window. Both mafic orthogranulite and felsic orthogranulite exhibit metamorphic peak paragenesis with Opx + Cpx + Pl with ages between 581 and 605 Ma being obtained for this Neoproterozoic reworking, compatible with the collision of the São Francisco Paleocontinent with the of Inner Arc System during the development of the Brasiliano/Pan-African orogenies. The predominance of felsic orthogranulites with sanukitoid signature in the studied region suggests that the generation of sanukitoid rocks may have been much more expressive in the more central and northern portions of the CJF than in the southernmost portions of it, where sanukitoid rocks are described as subordinate components. Finally, In the southeast of the São Francisco Paleocontinent, the association of sanukitoid rocks with other magmatic arc rocks points to a complex and prolonged Rhyacian accretionary system similar to modern plate tectonics.