Browsing by Author "Heilbron, Monica da Costa Pereira Lavalle"

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    Arco magmático Rio Doce : estudos litoquímicos, petrológicos, isotópicos e cronológicos no limite dos Orógenos Araçuaí e Ribeira.
    (2021) Soares, Caroline Cibele Vieira; Queiroga, Gláucia Nascimento; Soares, Antônio Carlos Pedrosa; Queiroga, Gláucia Nascimento; Alkmim, Fernando Flecha de; Nalini Júnior, Hermínio Arias; Heilbron, Monica da Costa Pereira Lavalle; Novo, Tiago Amâncio
    A porção plutônica do Arco Magmático Rio Doce compreende a Supersuìte G1, uma assembleia de rochas pré-colisionais do tipo-I, cálcio-alcalina, magnesiana, composta principalmente por rochas de composição tonalítica a granodiorítica, frequentemente contendo enclaves dioríticos a máficos. Esse arco foi edificado por uma intensa atividade magmática entre c. 630 e 580 Ma em uma margem continental, ligando os orógenos Araçuaí e Ribeira no sudeste do Brasil. Os estudos no setor limítrofe entre os orógenos Araçuaí – Ribeira consistiram em trabalhos de campo, petrográficos, litoquímicos, isotópicos (Sm – Nd e Sr), caracterização de zircão (isótopos U-Pb e Lu-Hf, e análises ETR) e modelagem de equilíbrio de fases (P-T) de representantes da Supersuíte G1 e de um enclave de silimanita-granada paragnaisse. Os resultados foram comparados com os compilados do mesmo setor estudado, dos setores central e norte do Orógeno Araçuaí e do setor norte do Orógeno Ribeira. As amostras estudadas incluem rochas graníticas metamorfizadas em graus distintos, identificadas por seus nomes ígneos no diagrama QAP, sienogranito, monzogranito, granodiorito, tonalito, quartzo diorito, ortopiroxênio tonalito e de ortopiroxênio-quartzo diorito. Os numerosos enclaves máficos a dioríticos indicam processos de mistura de magma; o ortopiroxênio magmático assim como o alto teor de CaO (9.34 - 10.36 % em peso) da granada sugerem cristalização de magma na crosta profunda. Os valores εNd (t) variam de - 2,9 a - 13,6, razões intermediárias a altas de 86Sr / 87Sr, de 0,7067 a 0,7165 e idades do modelo TDM Nd de 1,19 Ga a 2,13 Ga. Os resultados εHf(t) e as idades modelo TDM Hf exibem um intervalo amplo entre -30.69 a +1.06 e 1.44 a 2.86 Ga. Os resultados isotópicos indicam fusão parcial da cunha do manto na zona de subducção e anatexia profunda da crosta terrestre com assimilação de material crustal mais antigo (os complexos Juiz de Fora e Pocrane, e paragnaisses). Os dados geocronológicos fornecem uma geração de rocha magmática prolongada, divididos em cinco estágios (E1 a E5) considerando as médias das idades de concórdia: c. 638 Ma (E1), c. 622 Ma (E2), c. 606 Ma (E3), c. 590 Ma (E4) e c. 577 Ma (E5). As determinações geotermobarométricas no enclave do paragnaisse anatético (CS19GRT) resultou em condições P-T de metamorfismo de alto grau de c. 765 °C a 775 °C e 7,6 kbar a 9,2 kbar. Considerando que o (meta) granodiorito que encaixa o enclave apresenta idade mínima de c. 630 Ma (E1 e E2) em grãos de zircão com bordas corroídas, o metamorfismo com anatexia deve ter ocorrido após essa idade, a c. 610 Ma, que é a idade máxima obtida em zircão sem indícios de bordas absorvidas. As condições estabelecidas para assembleia ígnea da amostra CS14CPX, um clinopiroxênio tonalito, são de c. 590 °C a 630 °C e 7,1 a 8,05 kbar. De acordo com a idade de cristalização obtida para essa amostra, essas condições foram atingidas a partir do E3 (c. 608 Ma). Ao comparar a evolução do arco magmático registrada nos setores (i) limite Araçuaí-Ribeira (Orógeno Araçuaí) e norte do Ribeira com os (ii) setores central e norte do Orógeno Araçuaí, o amplo espectro de dados isotópicos de Hf e Nd dos setores (i) aponta para a incorporação de embasamento Riaciano - Orosiriano evoluído e envolvimento mantélico mais jovem. Enquanto os resultados dos setores (ii) sugerem um retrabalhamento de um componente crustal evoluído com pouca mistura de reservatórios crustais. Por sua vez, os dados isotópicos U-Pb compilados em zircão, demonstram que o arco magmático do Rio Doce foi mais ativo no período Ediacarano, entre 574 e 625 Ma, com idades Criogenianas-Tonianas mais antigas (dois intervalos, 641 Ma a 651 Ma e 716 Ma a 760 Ma), registrada nos setores (i). Nos setores (ii) as idades são mais jovens e restritas (pico de 576 Ma a 583 Ma) em comparação aos setores (i) (pico de 583 Ma a 597 Ma). Os picos de idades Ediacaranas definem períodos nos quais o magmatismo deve ter sido mais ativo, mas não indicam quiescência magmática, uma vez que os intervalos são separados por lacunas equivalentes aos erros de idade. O final da construção do arco em c. 574 Ma é proposto para todos os setores, no entanto, as idades mais velhas revelam particularidades tectônicas. Em conjunto, os resultados corroboram com o modelo de que a formação do Sistema Orogênico Araçuaí-Ribeira inicia com a subducção da placa oceânica no sul, onde é mais ampla e o Arco Magmático Rio Doce apresenta maior mistura de componentes crustais e envolvimento mantélico.
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    Combined use of Sm–Nd isotopes and lithogeochemistry in the sedimentary provenance of the southern Ediacaran-Cambrian Bambuí foreland basin system, Brazil.
    (2021) Paravidini, Gabriel; Reis, Humberto Luis Siqueira; Heilbron, Monica da Costa Pereira Lavalle; Carvalho, Manuela de Oliveira; Aguiar Neto, Carla Cristine; Valeriano, Claudio de Morisson
    Sedimentary provenance analysis based on lithogeochemistry and isotope data has been extensively applied in the investigation of ancient sedimentary successions. This approach contributes to understand the tectonic setting in which these strata were deposited and to recognize major provenance patterns in time and space. The Ediacaran to Cambrian Bambuí Group is exposed in the Sao ̃ Francisco craton (SE Brazil) and represents the sedimentary record of a foreland basin system developed during the assembly of the West Gondwana. Different lines of evidence indicate that this basin system evolved into a confined setting, due to the overloads imposed on the western and eastern margins of the Sao ̃ Francisco paleoplate by the diachronic Brasília and Araçuaí orogenic systems, respectively. New whole-rock lithogeochemistry and Sm–Nd isotopic data were applied to evaluate the overall sedimentary provenance patterns of the Bambuí strata exposed in the southern portion of the Sao ̃ Francisco craton (i.e., within the Sete Lagoas basement high) and to identify its possible sources. Coupled (La/Yb)n and Th/Sc ratios with 147Sm/144Nd and εNd isotopes allowed the recognition of three contrasting source patterns associated with different 2nd order sequences. The lower sequence comprises carbonate ramp deposits and shows highly heterogeneous and more negative εNd ranging from − 10.5 to − 4.5, as well as Th/Sc and (La/Yb)n ratios between 0.6 and 0.7 and 0.54 and 0.76, respectively. The provenance patterns point toward intermediate-dominated and isotopically evolved crustal sources, with mean TDM model ages between 1.5 and 2.0 Ga. The overlying 2nd-order sequence is composed of fine-to medium-grained siliciclastics grading upward into platformal oolitic calcarenites and calcilutites. This succession exhibits homo- geneous and less negative εNd(t) values between − 6.8 and − 5.2, with low Th/Sc (0.6–0.8) and (La/Yb)n (0.60–0.84) ratios. The uppermost Bambuí 2nd-order sequence, marked by greenish siltstones and arkoses grading upward into storm-bedded arkoses and lithic sandstones, shows homogeneous εNd(t) ranging from − 8.5 to − 6.1, slightly more negative than the underlying successions, and relatively higher Th/Sc and (La/Yb)n ratios ranging from 0.7 to 1.3 and 0.85 to 1.28, respectively. The Sm–Nd isotopic signature of the upper deposits indicates felsic-dominated and more isotopically juvenile crustal sources with TDM model ages of 1.5–1.7 Ga, characteristics compatible with Ediacaran arc-related rocks and post-tectonic granites exposed in the Araçuaí orogen. Our data indicate that the Proterozoic cratonic covers, their correlatives in the surrounding orogens, and magmatic rocks from the Araçuaí orogen acted as major sedimentary sources during the first evolutionary stages of the Bambuí basin-cycle in the Sete Lagoas basement high, which behaved as a forebulge depocenter. During the deposition of the overlying sequences, the Araçuaí orogen rocks became increasingly important in sourcing the Ediacaran- Cambrian foreland system in this depocenter. Besides revealing the major provenance patterns through the evolution of an ancient and partially confined foreland basin system, our data also demonstrates that even minor changes in the Sm–Nd system might be useful as reliable elements on the provenance analysis of sedimentary systems elsewhere.
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    Genesis and evolution of a neoproterozoic magmatic arc : the cordilleran-type granitoids of the Araçuaí Belt, Brazil.
    (2018) Narduzzi, Francesco; Nalini Júnior, Hermínio Arias; Farina, Federico; Lana, Cristiano de Carvalho; Stevens, Gary; Nalini Júnior, Hermínio Arias; Tohver, Eric; Heilbron, Monica da Costa Pereira Lavalle; Queiroga, Gláucia Nascimento; Cipriano, Ricardo Augusto Scholz
    The Araçuaí orogen (SE Brazil) is one of the largest (350,000 km2 ) and long-lived (ca. 630 – 480 Ma) granitic province in the world. The peculiarity of this Orogen is its wide variety of granitoids recording mid- to lower crustal P - T conditions that allow direct investigation of petrological processes occurring in the deepest part of the continental crust. This study investigates the field, textural, geochemical, geochronological and isotopic evolution of the pre-collisional Galiléia Batholith outcropping in the central part of the Araçuaí orogen. This metaluminous to slightly metaluminous (ASI = 0.97– 1.07) batholith, is a large is (ca. 15,000 km2 ), Neoproterozoic (ca. 632–550 Ma) weakly foliated, calc-alkaline, granitoid body characterized by the widespread occurrence of grossular-rich magmatic garnet and magmatic epidote. This is a rare mineral association in Cordilleran-I-type granitoids and of special petrogenetic significance. Field, petrographic, and mineral chemistry evidence indicate that garnet, epidote, biotite as well as white mica crystals (low-Si phengite), are magmatic. There is no difference in bulk rock major and trace element composition between the Galiléia and other garnetfree cordilleran-type granitoids worldwide. Thus the uncommon garnet+epidote parageneses are related to the conditions of magma crystallization, such as pressure, temperature and water content. Comparison between the mineral assemblages and mineral compositions from this study and those recorded in crystallization experiments on metaluminous calc-alkaline magmas, as well as within garnet-bearing metaluminous volcanic rocks and granitoids, indicates that the supersolidus coexistence of grossularrich garnet, epidote and white mica is consistent with magma crystallization at pressures greater than 0.8 GPa (above 25 km depth). This indicates that the Galiléia batholith was assembled in the lower crust during the accretionary/collisional stages of the Neoproterozoic Brasiliano Orogeny. It is evident that this granitic body represents a natural laboratory for studying the history of a lower crustal magma reservoir. Indeed the lifetime of deep magma chambers and the duration of magmatic activity in them remains a puzzle, contrary to young upper crustal magmatic systems. Despite being homogeneous with respect to mineralogy/texture and major/trace elements, all samples from the central part of the batholith record extreme variability in U-Pb magmatic ages from ca. 630 to 555 Ma. Trace element geochemistry and Hf isotopes from the igneous zircons – here interpreted as autocrysts (ca. 555 – 560 Ma) and antecrysts (> 560 Ma) – are all consistent with an open-system crystallization, rather than a simple cooling following fractional crystallization at the level of magma emplacement. We interpret the age variability recorded by the Galiléia samples as the result of a long-lived, uninterrupted injection of magmas of similar composition during assembly of the batholith. Such continuous injections of magma took place in the lower crust, keeping the system above its solidus through the 80 Ma of zircon crystallization. Unradiogenic 176Hf/177Hf and 143Nd/144Nd isotopic values of the Galileía samples indicate no direct mixing with mantle-derived magmas during the assembly and growth of the Galiléia batholith. This explains the scarcity of mafic products in the region. All of these characteristics need a more suitable geodynamic scenario. Indeed mineral textural, geochronological and isotopic similarities with other younger and older granitic plutons constructed within accretionary / fore-arc settings, better explain the characteristics showed by the Galiléia granitoids. Thus it is suggested that this giant batholith was assembled in an accretionary prism during the Brasiliano Orogenic stages. Eventually, it is likely that during the Brasiliano/Pan-African orogeny, accretionary prism, fore- and back–arc setting were sites of voluminous silicic magmatism and commonplaces for the stabilization of continental crust and its differentiation.
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    Rhyacian magmatic arc rocks with sanukitoid geochemical signature from the Juiz de Fora Complex, Minas-Bahia Orogenic System (SE-Brazil).
    (2022) Ferreira, Sandro Lúcio Mauri; Heilbron, Monica da Costa Pereira Lavalle; Bruno, Henrique; Marques, Rodson de Abreu; Neto, Carla; Valeriano, Claudio de Morisson; Bersan, Samuel Moreira; Romero, Luiz Felipe; Geraldes, Mauro César
    Sanukitoid rocks make up a complete magmatic series with distinct geochemical characteristics of TTG suites and granitoids from modern magmatic arcs and are regarded as markers of the transition from typically Archean geodynamics to modern plate tectonics. Although most known sanukitoid suites formed during the Neoarchean and Mesoarchean, numerous papers have characterized Paleoproterozoic magmatic arc granitoid rocks showing affinity with the sanukitoid series. This work presents new data from field, lithogeochemistry, zircon U-Pb geochronology, and Sm-Nd and Sr isotopic studies on granodioritic granulites with sanukitoid signatures from the Juiz de Fora Complex (JFC), one of the Paleoproterozoic tectonic components of the Minas-Bahia Orogenic System (MBOS), southern São Francisco Paleocontinent (southeastern Brazil). These rocks crystallized at ~2175 Ma and present values of εNdt between −4.0 and +0.5, TDM between 2.57 and 2.12 Ga, and 87Sr/86Sri between 0.6937 and 0.7137. We interpret these rocks as the result of crystallization of magmas from a hybrid mantle source extensively contaminated by crustal material during protracted subduction. In southeastern 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.
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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.