Age Constraints for Deposition and Sedimentary Provenance of Espinhaço Supergroup and Bambuí Group in Eastern São Francisco Craton

Abstract

The São Francisco Craton corresponds to an inner and stable portion of one of the plates involved in the assembly of Gondwanaland in late Neoproterozoic. To the east, the São Francisco Craton is limited by the Araçuaí-West Congo Orogen, which is composed, in its outer part, by the metasedimentary units of the Espinhaço Supergroup and Macaúbas Group. The cratonic adjacent area is mostly covered by the marine neoproterozoic units of the Bambuí Group, with few exposures of the Espinhaço Supergroup rocks. This paper aims to discuss the available geochronolgicl data and to present five new SHRIMP U-Pb dating on detrital zircons from rocks of the Bambuí Group and upper Espinhaço Supergroup at the eastern São Francisco Craton. The available dataset indicate that, within the São Francisco Craton, the upper portion of the Espinhaço Supergroup was deposited in the Pirapora Aulacogen through, in a period constrained between 1280 Ma (younger zircon population) and 933 Ma (age of the intrusive Pedro Lessa Mataigneous Suit). The cratonic basement highs (Sete Lagoas and Januária) seem to have been important source areas to the Mesoproterozoic units. The ages of the zircons found in the Serra de Santa Helena Formation suggest that its sediments may have come both from the Brasília Belt or the Araçuaí Orogen. On the other hand, zircons as young as 580 Ma, found in the Três Marias Formation sandstones indicate contribution from the Araçuaí Orogen. An important part of the sediment supply for the Espinhaço and Bambuí basins in the studied area could have come from older sedimentary units, as suggested by the great overlap in their detrital zircon age spectra. It demonstrates the remarkable polycyclic nature of the sedimentary processes who took place in the São Francisco Craton evolution Keywords: Geochronology, São Francisco Craton, Pirapora Aulacogen, Bambuí Group, Espinhaço SupergroupResumo: PROVENIÊNCIA SEDIMENTAR E BALIZADORES DE IDADE DE DEPOSIÇÃO DAS ROCHAS DO SUPERGRUPO ESPINHAÇO E GRUPO BAMBUÍ NA PORÇÃO LESTE DO CRÁTON DO SÃO FRANCISCO. O Cráton do São Francisco corresponde à porção interna e estável de uma das placas envolvidas na aglutinação do supercontinente Gondwana, no fim do Neoproterozoico. Em sua borda leste o cráton é limitado pelo Orógeno Araçuaí-Congo Ocidental, que é composto, em sua porção externa, por rochas metassedimentares do Supergrupo Espinhaço e do Grupo Macaúbas. A área cratônica adjacente é, em grande parte, coberta por rochas do Grupo Bambuí, à exceção de grandes anticinórios, como o da Serra do Cabral, que exibem, em seu núcleo, rochas do Supergrupo Espinhaço. Este trabalho objetiva apresentar cinco novas datações U-Pb SHRIMP em zircões detríticos de rochas do Supergrupo Espinhaço e do Grupo Bambuí aflorantes na região da Serra do Cabral, integrando-as com os dados existentes. Em conjunto, os dados indicam que, na área cratônica, a porção superior do Supergrupo Espinhaço foi depositada entre 1280 Ma (população mais jovem de zircões detríticos) e 933 Ma (idade de rochas intrusivas básicas). Os altos de Sete Lagoas e Januária parecem ter atuado como importantes áreas-fonte para as unidades mesoproterozoicas. Os zircões encontrados em siltitos da Formação Serra de Santa Helena apresentam fontes possíveis na Faixa Brasília e no Orógeno Araçuaí, enquanto zircões com c.580 Ma, encontrados na Formação Três Marias, devem ter fonte exclusiva no Orógeno Araçuaí. Grande parte dos sedimentos que preencheram as bacias Espinhaço e Bambuí parece ter origem em unidades sedimentares mais antigas, como sugerido pela grande interseção entre seus espectros de idades de zircões detríticos, o que demonstra o notável caráter policíclico dos processos sedimentares. Palavras-chave: Geocronologia, Cráton do São Francisco, Aulacógeno de Pirapora, Grupo Bambuí, Supergrupo Espinhaço

Integrating geological mapping and geophysical analyses in Southern Espinhaço Range, eastern edge of the São Francisco Craton, Brazil

“…The structural arrangement of the study area is defined by a succession of relatively smooth anticlines and synclines, whose axes have a general north-south direction. Eventually they show culminations of brachanticlines and brachsynclines (Pflug, 1965;Dinis & Pinheiro, 1980;Dossin et al, 1984;Kuchenbecker et al, 2015). The slight asymmetry of the folds and the associated planeaxial cleavage indicate deformation with vergence to the west.…”

The nitrogen biogeochemical cycle on Ediacaran rocks: A study on carbonates from the Bambuí Group, São Francisco Basin

“…During the marine stage of the basin, there were series of regressive-transgressive movements that are registered in the carbonate and siliciclastic rocks of the Conselheiro da Mata Group, which is divided into Santa Rita, Córrego do Borges, Córrego da Bandeira, Córrego Pereira and Rio Pardo Grande formations (Alkmim and Martins-Neto, 2001;Reis et al, 2017). Provenance studies for detrital zircons of the SE at the São Francisco basin indicate that the deposition of the sediments occurred between 1800 and 900 Ma (Chemale et al, 2012;Guadagnin et al, 2015;Kuchenbecker et al, 2015).…”

“…The carbonates from the base of the Sete Lagoas Formation, and within the first 2 nd -order sequence, are interpreted as cap carbonates and they register a Neoproterozoic glaciation whose age is still debated. For instance, Babinski et al (2007) assigned them a Sturtian age; Caxito et al, (2012Caxito et al, ( , 2018, Okubo et al (2018) and Crockford et al (2019) set a Marinoan age; Paula- and Kuchenbecker et al (2015) attributed a late Ediacaran age.…”

Strontium isotope stratigraphy and trace-metal geochemistry of the Ediacaran-Cambrian Bambuí Group, São Francisco Basin

“…The available U−Pb ages on detrital zircons younger than ca. 1.3 Ga extracted from Paranoá−Upper Espinhaço sequence in the São Francisco Basin indicate a time span between ca 1.3 and 0.9 Ga for its deposition (Chemale et al 2012;Lopes, 2012;Kuchenbecker et al, 2014Reis et al, 2014.…”

“…U−Pb ages for detrital zircons of the Bambuí Group range from the Archean to the early Cambrian (Pimentel et al, 2012;Kuchenbecker et al, 2014Babinski et al, 2018). Provenance studies and facies distribution indicate that the two main source areas are the Archean-Proterozoic rocks represented by the basement and older basin−fill units, and the Neoproterozoic orogenic belts, but the current data is insufficient to distinguish between the contribution from sources in the Brasília and Araçuaí belts (i. e., , and The Rio Preto and Riacho do Pontal Belts (i. e., .…”