Paleoproterozoic source contributions to the São Roque Group sedimentation: LA-MC-ICPMS U-Pb dating and Sm-Nd systematics of clasts from metaconglomerates of the Boturuna Formation

Abstract

The São Roque Group is characterized by volcano-sedimentary sequences, in which deposition probably started in the late Paleoproterozoic. U-Pb dating by LA-MC-ICPMS of zircons extracted from predominantly equigranular monzogranites clasts from Morro Doce and Morro do Polvilho regions, yield paleoproterozoic ages of 2199 ± 8.5 Ma and 2247 ± 13 Ma, respectively. These represent the ages for the main source of granite for the metaconglomerates from the Boturuna Formation (basal unit of São Roque Group). Its polycyclic history is reinforced by the presence of inherited Archean zircons (2694 ± 29 Ma) found within the clasts. Moreover, these clasts have also been affected by the Neoproterozoic overprinting event as indicated by their lower intercept Concordia ages. Sm-Nd isotope data for the main clast varieties from the Morro Doce metaconglomerates yield T DM ages of 2.6 to 2.7 Ga, demonstrating that these granites are the recycling products of an Archean crustal component. The metaconglomerate arkosean framework yields slightly lower Ɛ Nd(t) values than those for the clasts, indicating that a younger and/or more primitive source also contributed to the Boturuna Formation.Keywords: São Roque Group; Metaconglomerates; U-Pb dating; Sm-Nd data; Provenance.Resumo O Grupo São Roque é caracterizado por uma sequência vulcanossedimentar com deposição provavelmente iniciada no Paleoproterozoico tardio. Datações U-Pb obtidas por LA-MC-ICPMS de zircões extraídos das variedades predominantes dos clastos de monzogranitos equigranulares, das regiões do Morro Doce e Morro do Polvilho, mostram idades paleoproterozoicas de 2199 ± 8,5 Ma e 2247 ± 13 Ma, respectivamente. Estas representam as idades da principal fonte de granito da Formação Boturuna (unidade basal do Grupo São Roque). A história policíclica deste domínio é reforçada pela presença de zircões arqueanos herdados (2694 ± 29 Ma), encontrados nos clastos. Além disso, tais clastos também foram afetados pelo evento Neoproterozoico, conforme indicado pelo intercepto inferior das idades concórdia. Dados isotópicos Sm-Nd para os principais clastos do metaconglomerado do Morro Doce têm idades T DM entre 2,6 a 2,7 Ga, demonstrando que estes granitos são produtos da reciclagem de um componente crustal arqueano. O arcabouço dos metaconglomerados, quando comparado com os clastos, mostra valores mais baixos de Ɛ Nd(t) , indicando contribuições de fontes mais jovens e/ou primitivas para a Formação Boturuna.Palavras-chave: Grupo São Roque; Metaconglomerados; Datação U-Pb; Dados Sm-Nd; Proveniência.Paleoproterozoic source contributions to the São Roque Group sedimentation: LA-MC-ICPMS U-Pb dating and Sm-Nd systematics of clasts from metaconglomerates of the Boturuna Formation Contribuições de fontes Paleoproterozoicas para a sedimentação do Grupo São Roque: datação U-Pb LA-MC-ICPMS e sistemática Sm-Nd dos clastos dos metaconglomerados daFormação Boturuna

Provenance and sedimentary environments of the Proterozoic São Roque Group, SE-Brazil: Contributions from petrography, geochemistry and Sm–Nd isotopic systematics of metasedimentary rocks

“…14C). One explanation for this coincidence could be the existence of sources with juvenile signature at this age range, therefore with less negative ƐNd(1.75) than the metaconglomerate clasts studied by Henrique-Pinto et al (2012). To our knowledge, such rocks have not yet been documented in the literature so far in the small paleoproterozoic basement nuclei described in the Apiaí Terrane (e.g., the Tigre, Setuva and Betara nuclei in Açungui Domain).…”

“…The SmeNd isotope signature of the oldest (pre-1.4 Ga) passive-margin sequences of the Andrelândia Group (e.g., Campestre Formation; Westin and Campos Neto, 2013) is indeed very similar to that of the SRD metasediments, suggesting that they might be correlative. In this context, it is possible that at least part * ¼ SmeNd isotope data of meta-feldspathic wake (MD-01B) compiled by Henrique-Pinto et al (2012). Fields in gray represent analyses with low Sm/Nd ratios that been excluded from interpretations.…”

“…Our previous works (Henrique-Pinto and Janasi, 2010;Henrique-Pinto et al, 2012) investigated the paleoenvironment and provenance of metaconglomerates and associated metarkoses from exposures of the lower stratigraphic unit (Boturuna Formation) in a restricted area at the NW of the city of São Paulo. Here we use petrography, geochemistry and SmeNd isotope geochemistry as main instruments to extend that study to a broader area that encompasses a large portion of the SRD exposures, including samples of metasandstones.…”

U-Pb dating, Lu-Hf isotope systematics and chemistry of zircon from the Morro do Polvilho meta-trachydacite: constraints on sources of magmatism and on the depositional age of the São Roque Group

“…The LA-ICPMS U-Pb zircon concordia age of 1760 ± 17 Ma obtained for the Polvilho meta-trachydacite in this study confirms previous determinations by ID-TIMS U-Pb in two slightly discordant zircon fractions dated by van Schums et al (1986) and defines the age of deposition of the associated metaconglomerate-metarkose sequence of the São Roque Group. Field evidence favors an origin as rhyolitic deposits of effusive or pyroclastic nature interlayered with metaconglomerates bearing granite pebbles dated at 2.2 Ga (Henrique-Pinto et al, 2012). As direct observation of contacts is not possible, the alternative interpretation that the rhyolites are concordant intrusive bodies cannot be totally ruled out.…”

Dobras poli-harmônicas e estilos de dobramento em rochas carbonáticas da Mina de Salto de Pirapora, Votorantim, SP

“…Dobra de ápice espessado, de escala mesoscópica, em rochas cálcio-silicáticas bandadas da Mina de Salto de Pirapora, Votorantim, SP tido como anterior ao Grupo São Roque. Hackspacher et al (1999Hackspacher et al ( , 2000 efetuaram datações U-Pb em rochas metavulcânicas, indicando que a deposição do Grupo São Roque teria ocorrido entre 0,628 e 0,607 Ga. Henrique-Pinto et al (2012) analisaram seixos e a matriz do metaconglomerado do Morro Doce (Fm. Boturuna), buscando elucidar a proveniência das rochas.…”