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<p>In the Brasiliano/Pan-African Orogenic Cycle at the end of the Neoproterozoic (during the formation of West Gondwana), the convergence between the passive margin of the São Francisco-Congo paleoplate (Alkmim et al., In: Dominguez JML, Misi A (Eds), Arcabouço tectônico do Cráton do São Francisco—uma revisão. O Cráton Do São Francisco, Salvador, pp 45–62, 1993; Ussami, Estruturação e limites da placa litosférica São Franciscana: Contribuição Gravimétrica—Thesis for a postgraduate degree. University of São Paulo, 1999) and the magmatic arc domains of the Paranapanema paleoplate (Mantovani and Brito-Neves in Gondwana Res 8:303–315, 2005; Mantovani et al. in Episodes 28:18–22, 2005) and subsequent collision resulted in the structuring of the southern segment of the Brasília Orogen, with deformation of the rocks of these two domains and structuring in a stack of nappes, by thick-skin tectonics (Campos Neto and Caby in Precambrian Res. 97:3–26, 1999; Trouw in Pre-Congress Field Trip.31 International Geological Congress, Rio de Janeiro, Brazil, Field Trip Bft 08, p 45, 2000). The São Francisco paleocontinent, in its southern portion, is today represented by a cratonic region (São Francisco Craton) and a margin reworked in the Neoproterozoic. The study area is situated in the southern portion of the Brasília Belt (SE Brazil), where successions of Proterozoic metasedimentary rocks (Andrelândia Group) occur discordantly with respect to the Paleoproterozoic to Archean basement. The various lithotypes observed during the fieldwork were grouped into five mapping units: (A) Undivided basement—biotite gneiss and talc schist; (B) Ultramafic schist; (C) Campestre Unit, composed of garnet-muscovite schist/graphite phyllite with subordinate intercalations of quartzite with muscovite; (D) Luminárias Unit, composed of quartzite with green mica, with subordinate intercalations of quartz-green mica schist, magnetite-green mica schist and metarenite rich in Fe and/or Ti oxides; (E) Santo Antônio Unit, composed of biotite schist. In this investigation, we propose that the mica-bearing quartzite units, along with their associated rocks, currently included in the São Tomé das Letras Unit, be divided into two separate units. The São Tomé das Letras Unit comprises quartzites with scarce muscovite and subordinate intercalations of muscovite schist, and is present in the homonymous mountain range. Quartzites and schists with green mica and metarenite rich in Fe and/or Ti oxides, present in the Serras da Estância, Campestre, Pombeiro, Carrancas, das Bicas, Chapada das Perdizes, and Luminárias region, are grouped into a new unit of the Andrelândia Group, here named the Luminárias Unit. The samples contain younger zircon, close to the Mesoproterozoic/Neoproterozoic boundary, with ages ranging from 905 to 1047&#xa0;Ma. Lu–Hf isotope data indicate that most populations are grains with positive ɛHf(t) values, suggesting a more significant contribution from mantle-derived rocks. Lu–Hf data present most Mesoproterozoic values with positive εHf, and the studied samples exhibit curve patterns related to a passive margin setting, with an older zircon distribution relative to the metamorphic processes generated during the collisions reported in the amalgamation of Gondwana. Based on data collected during the mapping, petrographic study, and isotopic geochemical analyses of zircon grains by the U–Pb and Lu–Hf methods, it is possible to suggest the existence of a Neoproterozoic/Mesoproterozoic platform basin at the edge of the São Francisco craton.</p>

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The Andrelândia Group as a record of a Neoproterozoic/Mesoproterozoic platform basin in the São Francisco craton (SE Brazil): U–Pb and Lu–Hf results and tectonic implications

  • 期刊论文

  • 发表日期：

    2025年11月3日

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  • Rafael Cardoso de Moraes Telles,
  • Rodrigo Peternel Machado Nunes,
  • Ariane Felix Coelho Azevedo,
  • Pedro Costa Furtado,
  • Marcos Vinicius Ferreira Fontainha,
  • André Campos Rocha Pinto,
  • Felippe Amaral,
  • Armando Dias Tavares,
  • Mauro Cesar Geraldes

摘要

In the Brasiliano/Pan-African Orogenic Cycle at the end of the Neoproterozoic (during the formation of West Gondwana), the convergence between the passive margin of the São Francisco-Congo paleoplate (Alkmim et al., In: Dominguez JML, Misi A (Eds), Arcabouço tectônico do Cráton do São Francisco—uma revisão. O Cráton Do São Francisco, Salvador, pp 45–62, 1993; Ussami, Estruturação e limites da placa litosférica São Franciscana: Contribuição Gravimétrica—Thesis for a postgraduate degree. University of São Paulo, 1999) and the magmatic arc domains of the Paranapanema paleoplate (Mantovani and Brito-Neves in Gondwana Res 8:303–315, 2005; Mantovani et al. in Episodes 28:18–22, 2005) and subsequent collision resulted in the structuring of the southern segment of the Brasília Orogen, with deformation of the rocks of these two domains and structuring in a stack of nappes, by thick-skin tectonics (Campos Neto and Caby in Precambrian Res. 97:3–26, 1999; Trouw in Pre-Congress Field Trip.31 International Geological Congress, Rio de Janeiro, Brazil, Field Trip Bft 08, p 45, 2000). The São Francisco paleocontinent, in its southern portion, is today represented by a cratonic region (São Francisco Craton) and a margin reworked in the Neoproterozoic. The study area is situated in the southern portion of the Brasília Belt (SE Brazil), where successions of Proterozoic metasedimentary rocks (Andrelândia Group) occur discordantly with respect to the Paleoproterozoic to Archean basement. The various lithotypes observed during the fieldwork were grouped into five mapping units: (A) Undivided basement—biotite gneiss and talc schist; (B) Ultramafic schist; (C) Campestre Unit, composed of garnet-muscovite schist/graphite phyllite with subordinate intercalations of quartzite with muscovite; (D) Luminárias Unit, composed of quartzite with green mica, with subordinate intercalations of quartz-green mica schist, magnetite-green mica schist and metarenite rich in Fe and/or Ti oxides; (E) Santo Antônio Unit, composed of biotite schist. In this investigation, we propose that the mica-bearing quartzite units, along with their associated rocks, currently included in the São Tomé das Letras Unit, be divided into two separate units. The São Tomé das Letras Unit comprises quartzites with scarce muscovite and subordinate intercalations of muscovite schist, and is present in the homonymous mountain range. Quartzites and schists with green mica and metarenite rich in Fe and/or Ti oxides, present in the Serras da Estância, Campestre, Pombeiro, Carrancas, das Bicas, Chapada das Perdizes, and Luminárias region, are grouped into a new unit of the Andrelândia Group, here named the Luminárias Unit. The samples contain younger zircon, close to the Mesoproterozoic/Neoproterozoic boundary, with ages ranging from 905 to 1047 Ma. Lu–Hf isotope data indicate that most populations are grains with positive ɛHf(t) values, suggesting a more significant contribution from mantle-derived rocks. Lu–Hf data present most Mesoproterozoic values with positive εHf, and the studied samples exhibit curve patterns related to a passive margin setting, with an older zircon distribution relative to the metamorphic processes generated during the collisions reported in the amalgamation of Gondwana. Based on data collected during the mapping, petrographic study, and isotopic geochemical analyses of zircon grains by the U–Pb and Lu–Hf methods, it is possible to suggest the existence of a Neoproterozoic/Mesoproterozoic platform basin at the edge of the São Francisco craton.