Browsing by Author "Dussin, Ivo Antonio"

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    A-type Medina batholith and post-collisional anatexis in the Araçuaí orogen (SE Brazil).
    (2018) Serrano, Paula; Soares, Antônio Carlos Pedrosa; Medeiros Júnior, Edgar Batista de; Boa, Tobias Fonte; Araujo, Cristina; Dussin, Ivo Antonio; Queiroga, Gláucia Nascimento; Lana, Cristiano de Carvalho
    The Medina batholith and its host granitic migmatites record intriguing plutonic processes in the northern Araçuaí orogen (SE Brazil). This orogen shows a long lasting (630–480 Ma) succession of granite production events from the earliest pre-collisional plutons to the latest post-collisional intrusions. The Medina batholith includes granite intrusions ascribed to the post-collisional stage. They show high alkali and halogen contents, low CaO (at SiO2=71%:Na2O+K2O=7 to 9%; CaO=1.6%), and high FeOt/(FeOt+MgO) ratios (0.78 to 0.92). The Medina granites are metaluminous to weakly peraluminous, with ASI (molecular ratio Al/(Ca-1.67P+Na_K)) values of 1.76 to 2.07, and have high concentrations of high field strength elements (Zr+Nb+Ce+Y N 700 ppm), as well as high Ga/Al ratios. Accordingly, the Medina intrusions are typical ferroan A-type granites. U\\Pb ages fromzircon (501±2 Ma) and monazite (497±2 Ma) constrain the emplacement timing of theMedina batholith. Surprisingly, all monazite ages from host rocks also cluster around 500Ma, despite their nature and distance from the batholith, suggesting that they would have shared a same thermal process. The studied host rocks are granitic migmatites varying from patch metatexite to nebulitic diatexite, comprising paleosome of foliated sillimanite-garnet-biotite metagranite to gneiss, and non-foliated garnet-cordierite neosome poor to free of biotite. A metatexite (R14) located relatively far from the Medina batholith, and a diatexite (M26) found at the batholith contact were sampled for detailed studies. The paleosome of foliated metagranite (R14A) only shows zircon grains with igneous features and Th/U ratio from1.64 to 0.26. Although the spreading of zircon spots, themain cluster yields a Concordia age at 556±6 Ma, constraining the protolithmagmatic crystallization. A minor cluster furnishes a Concordia age at 499±7 Ma, in agreement with the U\\Pb monazite age at 501±2Ma. Extracted from the same metatexite sample, the non-foliated garnet-cordierite neosome (R14B) shows both igneous and metamorphic zircon domains with Th/U ratios ranging from 1.47 to 0.00. Again, the U\\Pb spots cluster at two distinct Concordia ages (562±3Ma and 499±3Ma). The youngest of them, fitting with themonazite age (495±3Ma), constrains melt crystallization,while the oldest age suggests paleosome inheritance. The nebulitic diatexite (M26) showsmonazite (497±2Ma) and zircon (Th/U=1.7 to 0.0; Concordia ages at 564±2Ma and 507±3Ma) populations similar to themetatexite neosome, alsowith the youngest ages bracketing themelt crystallization process around 500 Ma. Accordingly, all those ages at around 500Ma disclose a partial melting episode coeval with the Medina batholith emplacement. Phase equilibrium modeling on a garnet-cordierite neosome furnished P-T conditions of 750–840 °C at 2.4–3.5 kbar for that post-collisional anatexis. Evidence for such a late thermal event are common in the Araçuaí orogen, even far from the post-collisional batholiths. Thus, a possible major heat source can be envisaged, like a mantle plume triggering crustal anatexis and regional fluid circulation during the gravitational collapse of the Araçuaí orogen.
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    An Early Tonian rifting event affecting the São Francisco-Congo paleocontinent recorded by the Lower Macaúbas Group, Araçuaí Orogen, SE Brazil.
    (2019) Castro, Marco Paulo de; Queiroga, Gláucia Nascimento; Martins, Maximiliano de Souza; Alkmim, Fernando Flecha de; Soares, Antônio Carlos Pedrosa; Dussin, Ivo Antonio; Souza, Maria Eugênia Silva de
    After it had been assembled in the very early Orosirian, the western São Francisco–Congo Paleocontinent experienced several rifting events since the Statherian (ca. 1750 Ma) to Cryogenian (ca. 700 Ma). Records of anorogenic magmatism and/or associated sedimentation from those events have been found in the Neoproterozoic Araçuaí–West Congo orogenic system (AWCO), located between the São Francisco (eastern Brazil) and Congo (central Africa) cratons. Based on detailed field studies and data from lithochemistry, zircon and titanite U-Pb dating, whole-rock Nd and Hf-in-zircon isotopic analyses, we characterize a previously poorly described Early Tonian, rift-related, volcano-sedimentary succession in order to decipher the evolution of the AWCO precursor basins. That volcano-sedimentary succession, found in the Capelinha Formation type-area, now assigned to the Lower Macaúbas Group, includes quartzites with lenses of ortho-amphibolite (metabasalt) covered by pelitic schists. Zircon grains from ortho-amphibolite samples yielded ages of 957 ± 14 Ma and 576 ± 13 Ma, constraining their magmatic crystallization and regional metamorphism, respectively. These mafic rock show ƐNd(t) from −3.64 to +0.21 and Nd TDM ages from ca. 1.4 to ca. 1.7 Ga. Positive covariation of FeOtot/MgO + FeOtot, TiO2, P2O5, V and Zr, enrichment in light rare earth elements, slightly positive Eu/Eu* anomaly and depletion of high field-strenght elements, suggest tholeiitic protolith related to a continental rifting setting. The metasedimentary rocks show broad spectra of detrital zircon ages from the Early Tonian (ca. 940 Ma) to Paleoarchean, with wide-ranging ƐHf values from predominantly negative (as low as −10.76) to positive (+9.94), evoking well-known sediment sources in the São Francisco–Congo Paleocontinent. The youngest age peak (949 ± 12 Ma) constrains a maximum sedimentation age coeval with the basaltic volcanism represented by the ortho-amphibolite. The Capelinha volcano-sedimentary succession nearly correlates in age and origin with other anorogenic units (e.g., Ilhéus and Pedro Lessa dike swarms, Salto da Divisa granitic suite, Gangila basaltic and Mayumbian felsic volcanisms) found in a large region covered by the AWCO and neighbouring cratonic region. However, the Capelinha magmatism seems to preceed by some 20–30 m.y. the main peak (930–900 Ma) of this Early Tonian anorogenic magmatism, suggesting a long-lived and complex rift system.
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    Caracterização geocronológica U-Th-Pb de zircões detríticos na porção nordeste do sinclinal Gandarela – implicações para evolução sedimentar e geotectônica do Quadrilátero Ferrífero.
    (2017) Dutra, Luiz Fernandes; Martins, Maximiliano de Souza; Lana, Cristiano de Carvalho; Martins, Maximiliano de Souza; Dussin, Ivo Antonio; Fonseca, Marco Antônio
    Localizado na região sudeste do Brasil, o Quadrilátero Ferrífero constitui uma das principais províncias minerais do país, principalmente pela expressão dos depósitos de Au, Fe e Mn nele contidos. Caracteriza-se, também, por uma conformação tectônica peculiar, materializada por estruturas sub-regionais de alta complexidade, fruto da interação diferencial dos vários ciclos geotectônicos que o consolidaram como um segmento crustal da porção sul do cráton São Francisco, com registros que vão do Paleo/Mesoarqueano até o final do Neoproterozoico. Ocupando a porção nordeste do Quadrilátero, o sinclinal Gandarela é uma dobra em forma de gota, orientada na direção ENE-WSW e com adelgaçamento para ENE. É flanqueada por uma sequência de natureza vulcanossedimentar arqueana (Supergrupo Rio das Velhas), encerrando em seu núcleo os protolitos sedimentares paleoproterozoicos do Supergrupo Minas. Apesar do aumento significativo dos estudos de proveniência sedimentar que se vem sendo realizados no Quadrilátero Ferrífero nos últimos anos, ainda pouco se conhece sobre as idades de sedimentação e fontes sedimentares das unidades que edificam o sinclinal Gandarela. Este trabalho compreende estudos litoestratigráficos, do arcabouço estrutural e geocronológicos da sucessão estratigráfica que compõe a região próxima à cidade de Barão de Cocais, leste do sinclinal Gandarela. Da base para o topo, a área-alvo é constituída pelo Complexo Caeté, pelo Grupo Nova Lima (Supergrupo Rio das Velhas), pelo Supergrupo Minas (grupos Caraça, Itabira, Piracicaba e Sabará) e Grupo Tamanduá; suíte(s) magmática(s) de idades incertas e coberturas sedimentares recentes. As quatro seções litoestruturais realizadas indicam que o sinclinal Gandarela é uma dobra de segunda fase, com flancos mergulhando para SE e vergentes para NW, associado a um sistema de falhas paralelas aos flancos, responsáveis pelo intenso estiramento ou mesmo omissão das unidades que compõem os grupos Caraça (principalmente) e Itabira. Preservados desta deformação no interior do sinclinal, as unidades de topo do Supergrupo Minas, a Formação Cercadinho (Grupo Piracicaba) e o Grupo Sabará, indicam a sobreposição de dois sistemas turbidíticos distintos e separados por uma discordância angular de baixo ângulo. O primeiro é de natureza arenoargiloso, ao passo que o segundo é predominantemente argiloso. Os resultados U-Th-Pb em zircões detríticos desse trabalho apontam que (i) o alto índice de dados discordantes obtidos nas amostras dos grupos Nova Lima e Caraça evidenciam a forte influência metamórfica/hidrotermal associada ao desenvolvimento do sistema de falhas paralelas aos flancos do sinclinal Gandarela; (ii) a geocronologia da Formação Cercadinho não lança luz sobre sua idade de sedimentação, apresentando idades relacionadas principalmente aos eventos Santa Bárbara e Rio das Velhas I e II. Os zircões mais jovens foram datados em ca. 2561 Ma, idade atribuía a deposição da Formação Moeda (base do Supergrupo Minas); (iii) a sedimentação do Grupo Sabará se estendeu, ao menos, até ca. 1990 Ma, em regime colisional; (iv) o Grupo Tamanduá se firma como o registro do sistema Espinhaço no nordeste do Quadrilátero, com idade máxima de deposição de 1770 Ma em regime extensional.
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    Contrasting provenance and timing of metamorphism fromparagneisses of the Araçuaí-Ribeira orogenic system, Brazil : hints for Western Gondwana assembly.
    (2017) Degler, Reik; Soares, Antônio Carlos Pedrosa; Dussin, Ivo Antonio; Queiroga, Gláucia Nascimento; Schulz, Bernhard
    The Araçuaí orogen and the Ribeira belt make up a complex Neoproterozoic-Cambrian orogenic system, the Araçuaí-Ribeira orogenic system(AROS) located fromthe eastern to southeastern Brazil. Along the AROS, the Ediacaran Rio Doce magmatic arc represents a geotectonic connection between the Araçuaí and the Ribeira orogenic domains. Although the nature and evolution of the Rio Doce plutonic rocks is regionally well established, it lacks detailed studies on the paragneisses found along the western and central regions of this magmatic arc. Besides information on the nature and provenance of their sedimentary protoliths, the paragneisses provide data to unravel the palaeogeographic scenario fromthe precursor to arc-related basins. Six samples of Al-rich gneisses covering a large AROS region were selected for electron microprobe (EMP) mineral analyses in order to obtain geothermobarometric data and monazite ages, as well as for Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) isotopic analyses on zircon (U-Pb, Lu-Hf) and monazite (U-Pb). The different age spectra fromdetrital zircon grains and contrasting Hf isotopic signatures suggest a complex sedimentary history. Located in thewestern sector of the study region, the samples RC-02 and RC-34, with an 80% age peak of detrital zircon grains from 2158 Ma to 1830 Ma, εHf(t) from −2.2 to −22.7, and Hf TDM model ages from 3530 Ma to 2440 Ma, suggest sediment sources located in the São Francisco craton basement. The samples RC-03, also fromthewestern sector, and RC-46 fromthe southern sector, have a more complex assemblage of detrital zircon grains with an 87% age peak from 987 Ma to 592 Ma, εHf(t) from +14.9 to −2.9, and Hf TDM model ages from 2220Ma to 720 Ma, indicating provenance from mainly juvenile sources of distinct ages. Candidates to be juvenile sources for RC-03 and RC-46 sedimentary protoliths are the Rhyacian Juiz de Fora and Pocrane complexes in the basement of the Rio Doce arc, the Neoproterozoic Rio Negro arc systemof the Ribeira belt, and AROS ophiolite complexes. Samples RC-30 and RC-38 from the eastern sector of the study region, with most detrital zircon ages between 650 Ma and 552 Ma and very negative εHf(t) (−25.3 to −16.5), suggest main sediment sources in the Rio Doce arc. By extending U-Pb analyses on metamorphic zircon and monazite, we have identified a complex timing of metamorphism, represented by metamorphic ages ranging from 621 Ma to 480 Ma, with the main collisional activity between 580Ma and 540 Ma. Geothermobarometric studies on garnet porphyroblasts, syn-kinematic to the D2 regional foliation, show a retrograde metamorphic path typical of continental collision belts, starting with P-T conditions of Tmax = 733 °C and Pmax = 6.43 kbar. Our data also suggest: i) the studied paragneisses represent distinct Neoproterozoic basin stages, shifting from passive to active margin settings; ii) if the Rio Negro arc system really provided sediments for the basin stage represented by the RC-03 and RC-46 paragneisses, it would have amalgamated with the AROS before 614 Ma; iii) the final amalgamation of Western Gondwana took place around 540 Ma in the focused region; iv) an important re-heating period (520–480 Ma) can be related to the AROS gravitational collapse, afterWestern Gondwana assembly.
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    Geocronologia U-Pb de minerais hidrotermais : materiais de referência, métodos e aplicações.
    (2018) Gonçalves, Guilherme de Oliveira; Cipriano, Ricardo Augusto Scholz; Lana, Cristiano de Carvalho; Cipriano, Ricardo Augusto Scholz; Zincone, Stéfano Albino; Queiroga, Gláucia Nascimento; Valeriano, Claudio de Morisson; Dussin, Ivo Antonio
    Fluidos possuem um papel importante na evolução da crosta continental. Uma forma de investigar estes fluidos é o estudo de veios de quartzo, já que representam sistemas hidrotermais fossilizados. Estes veios podem conter fases minerais portadoras de U, podendo ser utilizadas para definir o tempo de geração e colocação destes fluidos. Para estudar estes minerais, faz-se necessário a utilização de técnicas de alta resolução espacial, como o LA-ICP-MS. Como minerais hidrotermais normalmente possuem baixo conteúdo de U, é necessário utilizar um equipamento de maior sensibilidade de forma a obter acurácia e precisão satisfatórias. Aqui é descrito o método de geocronologia U-Pb de alta-precisão utilizando o LA-MC-ICP-MS na UFOP. A maior estabilidade e sensibilidade do sistema LA-MC-ICP-MS permite acurácia e precisão das razões isotópicas de interesse ficarem entre 0.5 e 1.0% (2s), mesmo quando é analisado o zircão de baixo-U Rio do Peixe. Ainda, a utilização de materiais de referência (MR) matrizcompatíveis é necessária de forma a reduzir fracionamentos induzidos pelo laser. Desta forma, são aqui caracterizados megacristais de monazita hidrotermal (Diamantina) e xenotima aluvial (hidrotermal?; Datas) como potenciais MR para utilização como matriz-compatíveis na geocronologia U-Pb por LAICP-MS e/ou SIMS. As amostras são provenientes da Serra do Espinhaço (SE), porção externa do Orógeno Araçuaí (AO; 630-480 Ma), na borda leste do cráton São Francisco, onde diversos veios de quartzo cortam as rochas de baixo grau deste domínio. A monazita Diamantina possui uma idade 206Pb*/238U média ponderada de 495.26 ± 0.54 Ma (95% c.l.; ID-TIMS). A xenotima Datas (cristais XN01 e XN02) possui uma idade 206Pb*/238U média ponderada entre 513.4 ± 0.5 Ma e 515.4 ± 0.2 Ma (2s; ID-TIMS). Idades adquiridas por diferentes métodos (LA-(Q,SF,MC)-ICP-MS e/ou SIMS) concordam, dentro do erro, com os dados de ID-TIMS. Rodadas U-Pb por LA-ICP-MS utilizando Diamantina e Datas como MR primário reproduziram, dentro do erro, idades de outros MR com < 1% de desvio. Finalmente, amostras de monazita, rutilo e xenotima de outros veios de quartzo da borda leste cratônica (QF, SE, Novo Horizonte) foram utilizadas para determinar o tempo, distribuição regional e inferir possíveis fontes destes fluidos. Idades U-Pb por LA-ICP-MS ficaram entre 515-495 Ma. Composição isotópica Sm-Nd das amostras de monazita estão entre εNd500Ma -16.8 e -17.8, com uma amostra menos evoluída em εNd500Ma = -5.9. Compilação de idades de monazita do OA produziu um pico mais jovem em uma curva de densidade relativa, similar ao pico produzido pelos minerais hidrotermais. Estas idades podem ser relacionadas ao colapso do orógeno. A composição Sm-Nd das monazitas hidrotermais indicam uma fonte relacionada ao Supergrupo Espinhaço e possível contribuição de fluidos magmáticos. Este evento de fluxo de fluidos foi canalizado, com alto fluxo integrado ao tempo, oxidante, ácido, rico em ETR, P e Ti na borda cratônica. O sistema U-Pb de monazitas do núcleo orogênico foi reiniciado neste mesmo período, possivelmente pela exsolução de fluido magmático supercrítico dos magmas pós-colisionais. A reorganização de calor e massa devido ao colapso do OA produziu fluidos de múltiplas fontes e mineralizações, de níveis crustais profundos a mais rasos, afetando uma área de mais de 400.000 km2 ao longo da borda leste do cráton São Francisco.
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    Granites of the intracontinental termination of a magmatic arc : an example from the Ediacaran Araçuaí orogen, southeastern Brazil.
    (2016) Gonçalves, Leonardo Eustáquio da Silva; Alkmim, Fernando Flecha de; Soares, Antônio Carlos Pedrosa; Dussin, Ivo Antonio; Valeriano, Claudio de Morisson; Lana, Cristiano de Carvalho; Tedeschi, Mahyra
    The Araçuaí orogen of southeastern Brazil together with the West Congo belt of central West Africa form the Araçuaí–West Congo orogen generated during closure of a terminal segment of the Neoproterozoic Adamastor Ocean. Corresponding to an embayment in the São Francisco–Congo Craton, this portion of the Adamastor was only partially floored by oceanic crust. The convergence of its margins led to the development of the Rio Doce magmatic arc between 630 Ma and 580 Ma. The Rio Doce magmatic arc terminates in the northern portion of the Araçuaí orogen. Granitic plutons exposed in the northern extremity of the arc provide a rare opportunity to studymagmatismat arc terminations, and to understand the interplay between calc-alkalinemagma production and crustal recycling. The plutons forming the terminus of the arc consist of granodiorites, tonalites and monzogranites similar to a magnesian, slightly peraluminous, calcic- (68%) to calc-alkaline (24%), with minor alkali-calcic (8%) facies, medium- to high-K magmatic series. Although marked by negative Nb–Ta, Sr and Ti anomalies, typically associatedwith subduction-relatedmagmas, the combined Sr, Nd and Hf isotopic data characterize a crustal signature related to anatexis of metamorphosed igneous and sedimentary rocks, rather than fractional crystallization of mantle-derived magmas. Zircon U–Pb ages characterizes two groups of granitoids. The older group, crystallized between 630 and 590 Ma, experienced a migmatization event at ca. 585 Ma. The younger granitoids, emplaced between 570 and 590 Ma, do not show any evidence for migmatization. Most of the investigated samples show good correlation with the experimental compositional field of amphibolite dehydration-melting, with some samples plotting into the field of greywacke dehydration-melting. The studied rocks are not typical I-type or S-type granites, being particularly similar to transitional I/S-type granitoids described in the Ordovician Famatinian arc (NW Argentina). We suggest a hybrid model involving dehydrationmelting of meta-igneous (amphibolites) and metasedimentary (greywackes) rocks for magma production in the northern termination of the Rio Doce arc. The real contribution of each end-member is, however, a challenging work still to be done.
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    Idade máxima de sedimentação e proveniência do Complexo Jequitinhonha na área-tipo (Orógeno Araçuaí) : primeiros dados U-Pb (LA-ICP-MS) de grãos detríticos de zircão.
    (2011) Dias, Tatiana Gonçalves; Soares, Antônio Carlos Pedrosa; Dussin, Ivo Antonio; Alkmim, Fernando Flecha de; Caxito, Fabricio de Andrade; Silva, Luiz Carlos da; Noce, Carlos Maurício
    O Complexo Jequitinhonha, situado no nordeste de Minas Gerais, é uma das unidades metassedimentares mais extensas do Orógeno Araçuaí. Na área-tipo, situada na região de Jequitinhonha -Almenara, este complexo consiste de paragnaisse peraluminoso (kinzigítico) migmatizado, com intercalações de quartzito, grafita gnaisse e rocha calcissilicática. Os dados isotópicos U-Pb (LA-ICP-MS) de 80 grãos detríticos de zircão de uma amostra de quartzito, coletada em corte da BR-367 cerca de 12 km a SW de Almenara, permitem identificar seis principais intervalos de idades, cujas médias das modas sugerem as seguintes fontes de sedimentos: o embasamento São Francisco-Congo (2541 ± 8 Ma e 2044 ± 6 Ma), o sistema Espinhaço-Chapada Diamantina (1819 ± 6 Ma, 1487 ± 5 Ma e 1219 ± 3 Ma) e o sistema de rifteamento Noqui-Zadiniano-Mayumbiano-Salto da Divisa (956 ± 4 Ma). A idade máxima de sedimentação em 898 ± 8 Ma é dada pelo zircão mais novo. Os espectros de idades desta amostra do Complexo Jequitinhonha e de rochas do Grupo Macaúbas são muito similares, indicando correlação entre estas unidades. Contudo, no Complexo Jequitinhonha inexiste evidência de glaciação. Assim, o Complexo Jequitinhonha na área-tipo é interpretado como depósito de margem passiva da bacia precursora do Orógeno Araçuaí, mais novo que a glaciação Macaúbas e, portanto, equivalente às formações Chapada Acauã Superior e Ribeirão da Folha.
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    Late Neoproterozoic–Cambrian granitic magmatism in the Araçuaí orogen (Brazil), the eastern brazilian pegmatite province and related mineral resources.
    (2011) Soares, Antônio Carlos Pedrosa; Campos, Cristina Maria Pinheiro de; Noce, Carlos Maurício; Silva, Luiz Carlos da; Novo, Tiago Amâncio; Roncato Júnior, Jorge Geraldo; Medeiros, Silvia Regina de; Castañeda, Cristiane; Queiroga, Gláucia Nascimento; Dantas, Elton Luiz; Dussin, Ivo Antonio; Alkmim, Fernando Flecha de
    The Araçuí orogen extends from the eastern edge of the São Francisco craton to the Atlantic margin, in southeastern Brazil. Orogenic igneous rocks, formed from c. 630 to c. 480 Ma, cover one third of this huge area, building up the Eastern Brazilian Pegmatite Province and the most important dimension stone province of Brazil. G1 supersuite (630–585 Ma) mainly consists of tonalite to granodiorite, with mafic to dioritic facies and enclaves, representing a continental calc-alkaline magmatic arc. G2 supersuite mostly includes S-type granites formed during the syn-collisional stage (585–560 Ma), from relatively shallow two-mica granites and related gem-rich pegmatites to deep garnet-biotite granites that are the site of yellow dimension stone deposits. The typical G3 rocks (545–525 Ma) are non-foliated garnet-cordierite leucogranites, making up autochthonous patches and veins. At the post-collisional stage (530–480 Ma), G4 and G5 supersuites were generated. The S-type G4 supersuite mostly consists of garnet-bearing two-mica leucogranites that are the source of many pegmatites mined for tourmalines and many other gems, lithium (spodumene) ore and industrial feldspar. G5 supersuite, consisting of high-K–Fe calc-alkaline to alkaline granitic and/or charnockitic to dioritic/noritic intrusions, is the source of aquamarine-topaz-rich pegmatites but mainly of a large dimension stone production.
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    Magmatic diversity in continental rifts : a case study on the Early Tonian, plutono-volcanic Salto da Divisa Complex, Araçuaí Orogen, Eastern Brazil.
    (2022) Victoria, Anderson Magalhães; Soares, Antônio Carlos Pedrosa; Cruz, Simone Cerqueira Pereira; Lana, Cristiano de Carvalho; Dantas, Elton Luiz; Dussin, Ivo Antonio; Borges, Ramon
    Exposures from plutonic roots to volcanic roofs in deeply eroded regions may disclose the architecture and igneous processes in ancient metamagmatic edifices, like it is the Early Tonian Salto da Divisa Complex (SADICO) of Eastern Brazil. Field, petrographic, lithochemical and isotopic (in-zircon U-Pb and Lu-Hf, and whole-rock Sm-Nd) studies were conducted on the SADICO, an anorogenic plutono-volcanic complex located in the northeast Araçuaí orogen. The SADICO magmatic record comprises (with U-Pb crystallization ages, and isotopic Hf and Nd data): i) pyroxenite (εNd(t): +2.2 to −5.3; Nd TDM: 1.2–1.7 Ga); ii) mafic-intermediate dykes (εNd(t):+2.1 to −5.9; Nd TDM: 1.2–1.8 Ga) and enclaves with OIB-like signature; ii) ferroan, A-type granitoid with mafic-felsic mingling-mixing features (885 ± 9 Ma; εHf(t): −5 to −7, Hf TDM: 2.0–2.1 Ga; εNd(t): −3.2 to −4.3, Nd TDM: 1.5–1.7 Ga); iii) fluorite-bearing, metaluminous to peraluminous, ferroan A-type granites, including biotite-amphibole granite (915 to 875 Ma; εNd(t): −2.8 to −5.8, Nd TDM: 1.6–1.9 Ga), biotite granite (894 ± 10, εHf(t): −4 to −11, Hf TDM: 1.9–2.3 Ga; εNd(t): −1.6 to −8.0, Nd TDM: 1.4–2.2 Ga), and amazonite-bearing two-mica granite (εNd(t): −4.0; Nd TDM: 1.7 Ga); iv) rhyolite (905 ± 24 Ma; εHf(t): −1 to −8.7, Hf TDM: 1.8–2.2 Ga; εNd(t): +3.1, Nd TDM: 1.1 Ga) and subvolcanic silica-undersaturated trachyte (912 ± 13 Ma, εHf(t): −14 to −18, Hf TDM: 2.5–2.7 Ga; εNd(t): +0.3, Nd TDM: 1.2 Ga), also with ferroan A-type signature. Our integrated petrogenetic model envisages mantle-derived magmas (ultramafic and mafic rocks) evolved by assimilation-fractional crystallization to felsic subvolcanic and volcanic rocks, interacting with granitic magmas produced by crustal anatexis (biotite-amphibole granite) and subsequently fractionated (biotite granite) and highly fractionated (two-mica granite) with the involvement of F-rich fluids up to subvolcanic levels.
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    Paleoenvironment, sediment provenance and tectonic setting of Tonian basal deposits of the Macaúbas basin system, Araçuaí orogen, southeast Brazil.
    (2019) Souza, Maria Eugênia Silva de; Martins, Maximiliano de Souza; Queiroga, Gláucia Nascimento; Leite, Mariana; Oliveira, Rosana Gonçalves; Dussin, Ivo Antonio; Soares, Antônio Carlos Pedrosa
    The Neoproterozoic Macaúbas Group represents the main precursor basin system of the Araçuaí orogen, including a Tonian volcano-sedimentary succession, at the base, overlain by a Cryogenian sequence. Belonging to the Tonian succession, the Matão – Duas Barras Formation, exposed at the southern border of the Porteirinha basement block in the proximal (western) Araçuaí orogen, represents the very first stage of rifting ever recorded in the Macaúbas basin system. Sedimentological analysis on that formation has revealed two distinct and consecutive facies associations, both indicating half-graben sedimentary filling: i) fault-sourced alluvial fans; and ii) fluvial deposits associated with braided rivers. U-Pb ages of detrital zircon grains from the Matão – Duas Barras Formation and its underlain unit (ascribed to the Espinhaço Supergroup) uniformly show a dominant Rhyacian to Orosirian peak at ca. 2182 Ma – 1863 Ma, as well as several minor Archean age peaks from ca. 3186 Ma to ca. 2655 Ma. The Matão – Duas Barras fluvial deposits also show two Mesoproterozoic age clusters at ca. 1520 Ma and ca. 1156 Ma. Together with sedimentological features, the Archean and Paleoproterozoic zircon ages indicate sediment provenance from the granite-gneiss sources located in the neighboring Porteirinha block, which would have acted as a basement high (a large horst) at least during the initial filling of the Early Tonian Macaúbas rift. The ca. 1520 Ma and ca. 1156 Ma peaks are in good agreement with the Calymmian and Stenian development stages (II and III) of the Espinhaço Supergroup, which acted as an important secondary sediment sources for the basal Macaúbas Group. This also suggests that the Mesoproterozoic sources were exposed by the Porteirinha block uplift coeval with the Matão – Duas Barras basin filling. The maximum sedimentary ages given by the youngest zircon grains, together with a thorough literature compilation, bracket a depositional interval for the basal Macaúbas deposits from 1000 Ma to 933 Ma. Changes in sedimentary style and geochronological spectra suggest variations in the tectonic activity and subsidence rates of the Early Tonian Macaúbas basin, marking its first stage as an entirely siliciclastic sedimentation.
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    Petrogenesis and age of skarns associated with felsic and metamafic dykes from the Paraíba do Sul Complex, southern Espírito Santo State.
    (2017) Mesquita, Raissa Beloti de; Evangelista, Hanna Jordt; Queiroga, Gláucia Nascimento; Medeiros Júnior, Edgar Batista de; Dussin, Ivo Antonio
    This paper concerns the study of petrography, mineral chemistry and geochronology of skarns generated at the contact of marbles of the Paraíba do Sul Complex with felsic and metamafic dykes in the southern Espírito Santo State. The marbles were metamorphosed under P-T granulite facies conditions during the syn-collisional stage of the Neoproterozoic Araçuaí orogen. Metamafic bodies are composed of amphibolite and hornblende granofels, while felsic dykes consist of alkali-feldspar granite, monzogranite or syenogranite. From marble towards the dyke, skarns related to the metamafic bodies are composed of carbonate + olivine and diopside + hornblende zones. Skarn associated to the granitic dykes are composed of three different zones: carbonate + tremolite, diopside, scapolite + diopside. Variations in mineral chemical compositions along the metasomatic zones suggest introduction of Mg and Ca from the marbles, Fe from the metamafic dykes and Na from the granitoids. The presence of spinel in the metamafic dykes and their skarns indicates that both were metamorphosed under granulite facies conditions during the 580–560 Ma syn-collisional stage. U-Pb zircon geochronology (LA-ICP-MS) of an alkali-feldspar granite dyke resulted in a crystallization age of ca.540 Ma, which suggests that its skarns are therefore younger than skarns associated with the syn-collisional metamafic dykes.
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    Protracted zircon geochronological record of UHT garnet-free granulites inthe Southern Brasília orogen (SE Brazil) : petrochronological constraints onmagmatism and metamorphism.
    (2018) Tedeschi, Mahyra; Soares, Antônio Carlos Pedrosa; Dussin, Ivo Antonio; Lanari, Pierre; Novo, Tiago Amâncio; Pinheiro, Marco Aurélio Piacentini; Lana, Cristiano de Carvalho; Peters, Daniel
    The investigation of ultrahigh temperature (UHT) metamorphic rocks, and their corresponding (pressure)-temperature-time (P-T-t) history is critical to distinguish between arc- or collision-related metamorphism. This isa very challenging task if mineral assemblages are highly retrogressed and isotopic systems are disturbed.Garnet-free granulites lacking accessory minerals (chronometers) and metamorphic index minerals (thermo-barometers) located in UHT domains are examples of such complex systems. In such cases, zircon may be themain chronometer, although isotopic U-Pb data outline protracted records, making the interpretation of the datacomplex. This study focuses on the timing of magmatism and metamorphism, as well as on the thermal meta-morphic conditions of garnet-free UHT granulites of the Guaxupé nappe, southernmost Brasília orogen, locatedclose to the Paranapanema cratonic block. It presents U-Pb dating, Lu-Hf isotopes and trace element signatures ofzircon, and thermometry on metamorphic clinopyroxene and orthopyroxene from granulites. Steady176Hf/177Hf(t)in zircon cores exhibiting U-Pb dates spreading in the Concordia suggest post-crystallizationdisturbance. From those disturbed granulitic systems, minimum crystallization ages of ca. 2550 Ma, ca. 790 Ma,ca. 690 Ma and ca. 660 Ma can be retrieved. The juvenile ca. 2.55 Ga granulite is thefirst evidence of an exposedrock of the Paranapanema cratonic block, previously only inferred from geophysical data. The Guaxupé napperecords arc-related magmatic episodes in the range of 790–640 Ma, partially coeval with a long-lasting(∼80 m.y.) metamorphic event (670–590 Ma) and intrusion of basic magma (ca. 660 Ma). Thermometry onzoned clinopyroxene and orthopyroxene yields UHT conditions around 900–1000 °C. Comparing the distributionpatterns of metamorphic zircon rims and newly formed grains, we suggest two distinct metamorphic stages: i) anarc-related metamorphism (670–640 Ma), recorded by domains possibly formed by subsolidus recrystallization;and ii) a continental collision to decompression involving partial melting (630–590 Ma) associated to extensivezircon crystallization. The temporal relationship between magmatic and metamorphic ages suggests an ultra-high-temperature metamorphic event related to a magmatic arc. This arc was afterwards involved by theGuaxupé nappe stacking during the collisional stage of the southernmost Brasília orogen.
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    Provenance and paleogeographic reconstruction of a mesoproterozoic intracratonic sag basin (Upper Espinhaço Basin, Brazil).
    (2014) Santos, Marcelo Nascimento dos; Chemale Júnior, Farid; Dussin, Ivo Antonio; Martins, Maximiliano de Souza; Queiroga, Gláucia Nascimento; Pinto, R. T. R.; Santos, A. N.; Armstrong, Richard
    The Mesoproterozoic Conselheiro Mata Group is the uppermost sequence of the Proterozoic intracontinental Espinhaço basin that developed on the Congo-São Francisco Paleoplate. This sequence is represented by amarine shallow-water platform that experienced a sag phase followed by a rift phase in the Upper Espinhaço.We used combined sedimentological-stratigraphic descriptions of sections, whole-rock (WR) geochemistry and U-Pb detrital zircon dating to develop a regional paleogeographic evolution model of the sag phase. The succession corresponds to transgressive-regressive cycles in the following ascending order: 1) offshore to lower shoreface facies represented by quiescent periods and episodic sediment supply (Santa Rita Formation); 2) upper shoreface to foreshore and coastal desert facies with a reworking of the underlying units (Córrego dos Borges Formation); 3) lower shoreface with fallout of suspended fine sediments and a combination of unidirectional and oscillatory flows generated by storm waves (Córrego da Bandeira Formation); 4) tidal-influenced upper shoreface to foreshore facies with the migration of subaqueous dunes, wave swash in a beach environment and cycles of neap-spring tides (Córrego Pereira Formation); and 5) the resumption of lower-shoreface sedimentation and the subsequent development of a stromatolitic carbonate-siliciclastic platform (Rio Pardo Grande Formation). The geochemical data indicate that the studied units contain input from felsic rocks and sedimentary rocks. The basal marine to eolian sediments of the Galho do Miguel Formation are dominated by Rhyacian sources (2.1 Ga). The basal and intermediate units of the Conselheiro Group contain Archean, Rhyacian, Statherian and Calymmian-Ectasian (1.6–1.33 Ga) zircon grains, whereas Orosirian (1.9–2.0 Ga) sources dominate in the upper strata of the group. The study of this Stenian (Mesoproterozoic) intracratonic sequence provides clues to understanding the history of sedimentation and the potential source areas on the São Francisco Craton and adjacent areas, which are very useful for comparison to Phanerozoic intracratonic basins and the reconstruction of Paleoproterozoic and Mesoproterozoic supercontinents.
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    Rochas charnockíticas do sudeste de Minas Gerais : a raiz granulítica do arco magmático do Orógeno Araçuaí.
    (2010) Novo, Tiago Amâncio; Soares, Antônio Carlos Pedrosa; Noce, Carlos Maurício; Alkmim, Fernando Flecha de; Dussin, Ivo Antonio
    Os orógenos Araçuaí e Ribeira constituem sistema orogênico neoproterozóico-cambriano que se es-tende da borda oriental do Cráton do São Francisco até o Oceano Atlântico, a sul do paralelo 15°. A zona de fronteira entre esses orógenos situa-se em torno do paralelo 21°. A região meridional do Orógeno Araçuaí, no sudeste de Minas Gerais, é caracterizada pela exposição de rochas metamórficas de alto grau, ortoderivadas e paraderivadas, refletindo o profundo nível crustal ali exposto. Uma associação de rochas charnockíticas máficas a félsicas, metamorfisadas na fácies granulito, recebeu a designação de Suíte Divino. Esta tem características de série cálcio-alcalina expandida, metaluminosa a ligeiramente peraluminosa, com padrão de elementos traços ca¬racterístico de magmatismo de arco de margem continental. A assinatura isotópica de Nd evidencia significativo envolvimento de fusões derivadas do embasamento paleoproterozóico. Datações U-Pb (LA-ICPMS) de rochas da Suíte Divino (592±7 Ma e 603±4 Ma) indicam idade compatível com o estágio pré-colisional (acrescionário) do orógeno. Desta forma, sugere-se que a Suíte Divino representa a raiz granulítica do arco magmático do Orógeno Araçuaí, cuja eventual continuidade para sul seria importante elo de ligação com o Orógeno Ribeira.
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    Sedimentological and paleoenvironmental constraints of the Statherian and Stenian Espinhaço rift system, Brazil.
    (2013) Santos, Marcelo Nascimento dos; Chemale Júnior, Farid; Dussin, Ivo Antonio; Martins, Maximiliano de Souza; Assis, Tiago A. R.; Jelinek, Andréa Ritter; Guadagnin, Felipe; Armstrong, Richard
    The Espinhaço Basin in eastern Brazil contains depositional sequences developed in the São Francisco paleoplate and its margins. Detailed mapping was conducted and combined with U–Pb detrital zircon dating to determine the sedimentological-stratigraphic framework, provenance and minimum and maximum ages of the syn-rift-deposits. The two cycles have minimum ages of 1192 and 923 Ma and maximum ages of 1785 and 1685 Ma. The first depositional cycle, represented by the Bandeirinha and São João da Chapada formations, is marked by contributions of Neoarchean and Paleoproterozoic detrital zircons. The second cycle, the diamond-bearing Sopa-Brumadinho Formation, also contains Mesoproterozoic zircons formed between 1300 and 1190 Ma, which suggests an additional external source of Grenvillian age, that was not previously recorded in the São Francisco Craton. The investigation of such Mesoproterozoic intraplate sedimentary records, provides clues to understanding the history of the Rodinia active margins and, therefore, the kinematic reconstruction of its paleoplates.
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    A suture–related accretionary wedge formed in the Neoproterozoic Araçuaí orogen (SE Brazil) during Western Gondwanaland assembly.
    (2015) Peixoto, Eliza Inez Nunes; Soares, Antônio Carlos Pedrosa; Alkmim, Fernando Flecha de; Dussin, Ivo Antonio
    The Araçuaí orogen represents a branch of the Brasiliano orogenic system developed between the São Francisco and Congo cratons in Neoproterozoic time.Weconducted detailed studies on a complex schist belt located to the west of the Rio Doce magmatic arc, along the assumed suture zone of the Araçuaí orogen. This 30 km-wide and 100 km-long, NS-trending belt includes pelitic schists with intercalations of quartzites, metaultramafic schists and diopsidites, intruded by collisional granites. U–Pb ages from detrital zircon grains point to distinct provenances for different portions of the schist belt. The lower succession shows an age spectra and maximum depositional age (819 Ma) similar to passive margin deposits of the precursor basin. The upper succession yielded a maximumdeposition age around 600 Ma, pointing toward the Rio Doce arc as the main sediment source. Thrust to thewest onto the Guanhães basement and separated on the east fromthe Ediacaran Rio Doce magmatic arc by reverse–dextral faults, the schist belt exhibits the architecture of an asymmetric flower structure developed in transpressional regime. The distribution of metamorphic assemblages across the schist belt characterizes a collisional, Barrovian-type metamorphic zoning, in which the sillimanite, kyanite, staurolite and garnet zones are locally duplicated by thrusts. P–T conditions range from 700 °C at 7.5 kbar, at the western base of the pile, to 550 °C at 5.5 kbar, at the eastern top of the package. Zircon U–Pb ages record metamorphic overprinting on the sheared top of the basement at 560 ± 20 Ma and crystallization of collisional granites at 544 ± 10 Ma. Our results allow us to interpret the schist belt as a suture-related accretionary wedge and suggest that basin closure during the assembly ofWest Gondwanaland lasted to the Ediacaran–Cambrian boundary in the Araçuaí orogen.
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    The Ediacaran Rio Doce magmatic arc revisited, Araçuaí-Ribeira orogenic system, SE Brazil.
    (2016) Tedeschi, Mahyra; Novo, Tiago Amâncio; Soares, Antônio Pedrosa; Dussin, Ivo Antonio; Tassinari, Colombo; Silva, Luiz Carlos da; Gonçalves, Leonardo Eustáquio da Silva; Alkmim, Fernando Flecha de; Lana, Cristiano de Carvalho; Dantas, Elton Luiz; Medeiros, Silvia Regina de; Campos, Cristina Maria Pinheiro de; Corrales, Felipe; Heilbron, Monica da Costa Pereira Lavalle
    Described half a century ago, the Galil eia tonalite represents a milestone in the discovery of plate margin magmatic arcs in the Araçuaí-Ribeira orogenic system (southeastern Brazil). In the 1990's, analytical studies on the Galil eia tonalite finally revealed the existence of a Late Neoproterozoic calc-alkaline magmatic arc in the Araçuaí orogen. Meanwhile, the name Rio Doce magmatic arc was applied to calc-alkaline plutons found in the Araçuaí-Ribeira boundary. After those pioneer studies, the calc-alkaline plutons showing a pre-collisional volcanic arc signature and age between 630 Ma and 585 Ma have been grouped in the G1 supersuite, corresponding to the Rio Doce arc infrastructure. Here, we revisit the Rio Doce arc with our solid field knowledge of the region and a robust analytical database (277 lithochemical analyses, and 47 UePb, 53 SmeNd, 25 87Sr/86Sr and 7 LueHf datasets). The G1 supersuite consists of regionally deformed, tonalitic to granodioritic batholiths and stocks, generally rich in melanocratic to mesocratic enclaves and minor gabbroic to dioritic plutons. Gabbroic to dioritic enclaves show evidence of magma mixing processes. The lithochemical and isotopic signatures clearly reveal a volcanic arc formed on a continental margin setting. Melts from a Rhyacian basement form the bulk of the magma produced, whilst gabbroic plutons and enclaves record involvement of mantle magmas in the arc development. Tonalitic stocks (UePb age: 618e575 Ma, εNd(t): 5.7 to 7.8, Nd TDM ages: 1.28e1.68 Ga, 87Sr/86Sr(t): 0.7059e0.7118, and εHf(t): 5.2 to 11.7) form the northernmost segment of the Rio Doce arc, which dies out in the ensialic sector of the Araçuaí orogen. At arc eastern and central zones, several batholiths (e.g., Alto Capim, Baixo Guandu, Galil eia, Muniz Freire, S~ao Vítor) record a long-lasting magmatic history (632e580 Ma; εNd(t): 5.6 to 13.3; Nd TDM age: 1.35e1.80 Ga; 87Sr/86Sr(t): 0.7091 e0.7123). At arc western border, the magmatic evolution started with gabbro-dioritic and tonalitic plutons (e.g., Chaves pluton, UePb age: 599 ± 15 Ma, εNd(t): 4.8 to 6.8, Nd TDM ages: 1.48e1.68 Ga, 87Sr/86Sr(t): 0.7062e0.7068, and εHf(t): 4.3 to 9.7; and Brasil^andia pluton, UePb age: 581 ± 11 Ma, εNd(t): 8.2 to 10.2, Nd TDM ages: 1.63e1.68 Ga, 87Sr/86Sr(t): 0.7088e0.7112, εHf(t): 12.3 to 14.9),followed by late granodioritic intrusions (e.g., Guarataia pluton, UePb age: 576 ± 9 Ma, εNd(t): 12.52 to 13.11, Nd TDM age: 1.74e2.06 Ga, 87Sr/86Sr(t): 0.7104e0.7110, εHf(t): 12.9 to 21.6). The Muria e batholith (UePb age: 620e592 Ma, εNd(t): 8.2 to 13.6, Nd TDM age: 1.41e1.88 Ga) and the Conceiç~ao da Boa Vista (586 ± 7 Ma) and Serra do Valentim (605 ± 8 Ma) stocks represent a segment of the Rio Doce arc correlated to the Serra da Bolívia and Marceleza complexes, making the link between the Araçuaí and Ribeira orogenic domains. We suggest three phases of arc development: i) eastward migration of arc front (632e605 Ma), ii) widespread magma production in the whole arc (605e585 Ma), and iii) late plutonism in the western arc region (585e575 Ma). Usual processes of volcanic arc development, like subduction of oceanic lithosphere under a continental margin, followed by asthenosphere ascent related to slab retreating and break-off may explain the Rio Doce arc evolution.
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    The hot back-arc zone of the Araçuaí orogen, Eastern Brazil : from sedimentation to granite generation.
    (2014) Mendonça, Camila Bassil Gradim; Roncato Júnior, Jorge Geraldo; Soares, Antônio Carlos Pedrosa; Cordani, Umberto Giuseppe; Dussin, Ivo Antonio; Alkmim, Fernando Flecha de; Queiroga, Gláucia Nascimento; Jacobsohn, Tânia; Silva, Luiz Carlos da; Babinski, Marly
    Este artigo apresenta novos dados litoquímicos e geocronológicos obtidos de rochas gnáissicas e graníticas da zona de retroarco situada imediatamente a leste do Arco Rio Doce (630 – 580 Ma), no orógeno Araçuaí. O Complexo Nova Venécia é a mais importante fonte de fusões graníticas peraluminosas na região. Este complexo consiste, essencialmente, de paragnaisses peraluminosos migmatíticos que variam entre gnaisses ricos em biotita e cordierita-granulitos livres de biotita, cujos protolitos foram sedimentos grauvaquianos. Uma seção E-W no setor norte do retroarco revela uma zona rica em cordierita-granulito, na base, seguida por paragnaisses migmatíticos do Complexo Nova Venécia que passam, gradativamente, a granitos foliados ricos em enclaves de rochas metassedimentares (Suíte Ataléia), os quais estão sobrepostos pelo Batólito Carlos Chagas. Ao sul deste batólito, rochas a hercinita e ortopiroxênio são freqüentes no Complexo Nova Venécia e Suíte Ataléia, indicando nível crustal mais profundo. Nossos dados U-Pb evidenciam que processos anatéticos tiveram início no Complexo Nova Venécia ainda durante o desenvolvimento do Arco Rio Doce, em torno de 590 Ma, originando fusões graníticas relacionadas à Suíte Ataléia. A progressiva produção de magma granítico e sua acumulação atingiram o clímax no intervalo 575 Ma, em pleno estágio sincolisional, resultando na edificação do Batólito Carlos Chagas. Em torno de 545 – 530 Ma, adveio novo processo anatético, que originou granada-cordierita leucogranitos a partir da fusão parcial de granitos da Suíte Ataléia e Batólito Carlos Chagas. Finalmente, um marcante plutonismo pós-colisional (520–480 Ma) do tipo I causou importante re-aquecimento regional. Esta longa história (ca. 110 Ma) de produção de magmas graníticos na zona de retroarco requer diferentes fontes de calor, tais como ascenção astenosférica sob a região de retroarco durante o estágio pré-colisional, cavalgamento da base quente do arco sobre o retroarco, liberação de calor radiogênico da pilha crustal espessada no estágio colisional e, finalmente, ascenção astenosférica durante o colapso gravitacional do Orógeno Araçuaí.
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    Time and isotopic constraints for Early Tonian basaltic magmatism in a large igneous province of the São Francisco – Congo paleocontinent (Macaúbas basin, Southeast Brazil).
    (2022) Souza, Maria Eugênia Silva de; Martins, Maximiliano de Souza; Queiroga, Gláucia Nascimento; Soares, Antônio Carlos Pedrosa; Dussin, Ivo Antonio; Castro, Marco Paulo de; Serrano, Paula
    The Neoproterozoic Macaúbas basin (southeast Brazil) provides key hints to unravel the history of the São Francisco – Congo paleocontinent before its amalgamation as part of Gondwana. Among the several Proterozoic taphrogenic events and anorogenic igneous episodes documented for the São Francisco – Congo paleocontinent, Early Tonian event has been particularly focused on in the literature owing to the large production of bimodal (felsic-mafic) magmas now found in the Araçuaí (SE Brazil) – West Congo (SW Africa) orogenic system (AWCO) and neighboring cratonic regions. Aiming to examine the stratigraphic relations, timing and isotopic signatures of extensive basaltic magmatism related to the Macaúbas basin, we carried out detailed field, lithochemical, isotope (whole-rock Sm-Nd and Lu-Hf in zircon) geochemistry and zircon U-Pb geochronological studies on the Pedro Lessa suite and Planalto de Minas Formation, located in the central-western Araçuaí orogen. The studied Pedro Lessa suite consists of a series of mafic dikes that crosscut the lowermost units of the Macaúbas Group but not the Planalto de Minas Formation. The Pedro Lessa suite yielded zircon U-Pb ages between 951 ± 54 Ma and 939 ± 7 Ma. The Planalto de Minas Formation comprises volcaniclastic rocks crystallized at 889 ± 10 Ma, and sedimentary rocks with maximum depositional age of 867 ± 10 Ma. The lithochemical and isotopic datasets (Pedro Lessa dikes: εNd(t) = +0.60; εHf(t) = –22.21 to +4.66; Planalto de Minas volcanism: εNd(t) = +0.76 to +0.78; εHf(t) = − 19.27 to +10.03) indicate predominantly continental tholeiite and minor enriched MORB-type mantle magmas with variable amounts of crustal contamination. The (La/Sm)N ratios indicate a theoretical partial melting (1–7%) of the spinel-lherzoite lithospheric zone for the Pedro Lessa suite, and of the spinel-garnet transition zone (3–10%) for the Planalto de Minas metamafic rocks, in accordance with La/Nb and La/Ba ratios. The new and complied isotopic and lithochemical data suggest a time-dependent evolution of magma sources, with lithospheric mantle sources for the Early Tonian dike swarms (Pedro Lessa and correlatives) evolving to predominantly asthenospheric mantle sources for the late basaltic volcanism recorded in the Planalto de Minas Formation. Such an extensive and long-lasting anorogenic magmatism of Early Tonian age (c. 965 – 870 Ma) found in the AWCO and São Francisco – Congo craton likely records more than one extensional event and related aborted continental rifts, altogether driven by the same mantle plume. Although long-lived, this mantle plume acted beneath a strong continental lithosphere so that it was unable to break up the São Francisco – Congo paleocontinent into two completely separated landmasses. Highlighting the main stages of anorogenic magmatism, we also present an updated barcode for the São Francisco – Congo paleocontinent.
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    Unravelling a Proterozoic basin history through detrital zircon geochronology : the case of the Espinhaço Supergroup, Minas Gerais, Brazil.
    (2012) Chemale Júnior, Farid; Dussin, Ivo Antonio; Alkmim, Fernando Flecha de; Martins, Maximiliano de Souza; Queiroga, Gláucia Nascimento; Armstrong, Richard; Santos, Marcelo Nascimento dos
    New U–Pb in situ zircon dating provides a new approach for the study of the Espinhaço Supergroup units exposed in the São Francisco Craton and Araçuaí Orogen. Located in Southern Espinhaço, Minas Gerais, the following two basins were formed in intraplate conditions: (i) the Lower Espinhaço Basin is marked by a volcano-sedimentary sequence with alluvial, fluvial and eolian deposits that were formed from 1.68 Ga to 1.80 Ga; (ii) the overlying sequence, called the Upper Espinhaço Basin, is a rift-sag basin that presents basal diamond-bearing continental deposits (the Sopa–Brumadinho Formation) with a younger zircon peak at 1192 Ma, which is the maximum age for deposition of the upper units. The obtained U–Pb detrital zircon data of the studied units show age groupings related to the orogenic cycles of Jequié (Neoarchean) and Transamazonian (Paleoproterozoic), which are associated with the stability period from 1.8 Ga to 0.91 Ga in the São Franscico Craton, and record deposition during at least the three basinal cycles. The Stenian–Tonian ages of the Upper Espinhaço Basin units (906 Ma to 1192 Ma) suggest a direct link with the evolution of the Rodinia Supercontinent and represent a marker for Mesoproterozoic to Early Neoproterozoic evolution in the São Franscico Craton and adjacent areas.