EM - Escola de Minas
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6
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A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.
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Item Unravelling the protracted U-Pb zircon geochronological record of high to ultrahigh temperature metamorphic rocks : Implications for provenance investigations.(2023) Tedeschi, Mahyra; Vieira, Pedro Leonardo Rossi; Amaral, Matheus Henrique Kuchenbecker do; Ribeiro, Bruno Vieira; Barrote, Vitor Rodrigues; Reis, Humberto Luis Siqueira; Stutenbecker, Laura; Lana, Cristiano de Carvalho; Soares, Antônio Carlos Pedrosa; Dussin, Ivo AntonioThe assessment of detrital zircon age records is a key method in basin analysis, but it is prone to several biases that may compromise accurate sedimentary provenance investigations. High to ultrahigh temperature (HT-UHT) metamorphism (especially if T > 850 °C) is herein presented as a natural cause of bias in provenance studies based on U-Pb detrital zircon ages, since zircon from rocks submitted to these extreme and often prolonged conditions frequently yield protracted, apparently concordant, geochronological records. Such age spreading can result from disturbance of the primary U-Pb zircon system, likewise from (re)crystallization processes during multiple and/or prolonged metamorphic events. In this contribution, available geochronological data on Archean, Neoproterozoic and Palaeozoic HT-UHT metamorphic rocks, acquired by different techniques (SIMS and LA-ICP-MS) and showing distinct compositions, are reassessed to demonstrate HT-UHT metamorphism may result in modes and age distributions of unclear geological meaning. As a consequence, it may induce misinterpretations on U-Pb detrital zircon provenance analyses, particularly in sedimentary rocks metamorphosed under such extreme temperature conditions. To evaluate the presence of HT-UHT metamorphism-related bias in the detrital zircon record, we suggest a workflow for data acquisition and interpretation, combining a multi-proxy approach with: (i) in situ U-Pb dating coupled with Hf analyses to retrieve the isotopic composition of the sources, and (ii) the integration of a petrochronological investigation to typify fingerprints of the HT-UHT metamorphic event. The proposed workflow is validated in the investigation of one theoretical and one natural example allowing a better characterization of the sedimentary sources, maximum depositional ages, and the tectonic setting of the basin. Our workflow allows to the appraisal of biases imposed by HT-UHT metamorphism and resulting disturbances in the U-Pb detrital zircon record, particularly for sedimentary rocks that underwent HT-UHT metamorphism and, finally, suggests ways to overcome these issues.Item 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, RamonExposures 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.Item Detrital zircon U–Pb analysis constrain the depositional age and provenance of Cryogenian glacial successions of the Macaúbas group in the northeastern Araçuaí orogen, eastern Brazil.(2023) Pacheco, Fernando Estevao Rodrigues Crincoli; Caxito, Fabrício de Andrade; Souza, Maria Eugênia Silva de; Bento, Ciro Couto; Soares, Antônio Carlos Pedrosa; Lana, Cristiano de CarvalhoThe precursor basin of the Araçuaí – West Congo Orogenic System (AWCO) formed a large gulf within the São Francisco – Congo Paleocontinent (SFCP), where the diamictite-bearing Macaúbas Group was deposited during the Neoproterozoic. However, the lack of robust age constraints on the Cryogenian glaciogenic successions prevents correlation to one or both of the Cryogenian Snowball Earth glaciations. The present study introduces new field data and new U–Pb detrital zircon data from diamictite-bearing units on the southern margin of the São Francisco Craton, in the northeastern Araçuaí Orogen. This region is much closer to possible EdiacaranCryogenian igneous rocks of the southern São Francisco craton than other regions previously studied for the Macaúbas Group, enhancing the probability of detecting detrital minerals from those rocks, if they were involved as source areas. In the studied region, the Macaúbas Group is composed of metadiamictite with sparse clasts and schistified metagraywacke with bulk mineralogy similar to the quartz-muscovite-feldspar matrix of the metadiamictites. U–Pb (LA-MC-ICP-MS) dating of 182 detrital zircon grains from the Lower Chapada Acauã Formation forming the syn-glacial sequence yielded main age peaks at 939 ± 3 Ma, 1409 ± 10 Ma, 1822 ± 8 Ma, 2044 ± 7 Ma, 2551 ± 9 Ma and 3103 ± 19 Ma. The youngest concordant zircon grain found in this study aged 753 ± 12 Ma. U–Pb (LA-MC-ICP-MS) dating of 104 zircon crystals from a granitic clast recovered from the diamictite exhibits highly discordant data plotting in distinct Discordia lines with upper intercept ages of 2.0 Ga, 2.5 Ga, 2.6 Ga and 3.2 Ga, indicating derivation from the adjacent cratonic basement. The U–Pb age spectra suggests important contribution from the Archean and Paleoproterozoic basement of the São Francisco – Congo paleocontinent and metamorphic complexes, from the Mesoproterozoic intrusive and volcanic rocks of São Francisco Craton, and from the Tonian Salto da Divisa Suite. Despite the relative abundance of Cryogenian zircon grains in the surrounding prospective source areas, the studied rocks lack this interval age. The glaciogenic events in the Macaúbas basin system probably did not sample rocks with these age intervals due to the general characteristics of this type of deposit or because the sources were not exposed. Thus, the lower diamictite-bearing units of the Macaúbas Group in the northeastern São Francisco craton were deposited after ca. 753 Ma, but their correlation to either the Sturtian or Marinoan global glaciations remain speculative.Item Detrital zircon U–Pb and Lu–Hf constraints on the age, provenance and tectonic setting of arc-related high-grade units of the transition zone of the Araçuaí and Ribeira orogens (SE Brazil).(2022) Mendes, Raíssa Santiago; Caxito, Fabrício de Andrade; Soares, Antônio Carlos Pedrosa; Neves, Aparecida; Calegari, Salomão Silva; Lana, Cristiano de CarvalhoSedimentary basins with epiclastic and volcanoclastic components are important geotectonic components for understanding the complex evolution of orogenic systems. The age, provenance and tectonic setting of ancient basins are, however, often hard to constrain, especially in the high-grade core of ancient mountain belts where original sedimentary and stratigraphic relations have been largely obliterated by deformation and metamorphism. In this case, analytical tools such as whole-rock geochemistry and U–Pb and Lu–Hf analyses on detrital zircon grains can be deployed to unravel the provenance and tectonic setting of high-grade metasedimentary and metavolcaniclastic units. Here, we apply these analytical tools on samples from gneissic paleosomes of migmatites found in the eastern transition zone between the Neoproterozoic–Eopaleozoic Araçuaí and Ribeira orogens (southeastern Brazil). The studied paleosomes comprise peraluminous paragneiss rich in biotite, garnet and sillimanite, metaluminous hornblende-bearing gneiss free of peraluminous silicates, and intermediate terms between these compositions, all of them with geochemical characteristics pointing to sources located in magmatic arc systems. Overall, U–Pb data from detrital zircon grains bracket a maximum sedimentation age for all samples between 600 and 627 Ma, while εHf(t): +5.7 to − 18.7 and Hf TDM model ages of 1.0–2.2 Ga suggest moderately juvenile to evolved sources for the gneiss protoliths. However, despite the similarity in age range, the analyzed samples show contrasting isotope data indicating significant variability in the source areas. Sample 7 only has grains with negative εHf (− 5.9 to − 18.7), most of them ranging in age from 708 Ma to 758 Ma, with very few older (1021–1143 Ma) and younger (642–651 Ma) zircons grains, indicating evolved crustal sources of distinct ages (e.g., the Late Tonian – Early Cryogenian South Bahia Alkaline Province, the Early Cryogenian magmatism found in the West Congo Belt, the Stenian to Early Tonian Espinhaço and Matadi-Noqui igneous rocks, and magmatic rocks of the early Rio Doce arc). Conversely, sample 13 has twenty grains with positive εHf values and ages between 602 and 758 Ma, suggesting sourcing from (meta)igneous rocks of the Rio Negro arc and their remelting products, and forty grains with negative εHf values with ages between 591 and 646 Ma suggesting magmatic sources in the Rio Doce arc. Additionally, the two youngest spot ages (553 Ma and 571 Ma) have highly negative εHf values (− 11.1 and − 16.4) suggesting their origin from collisional anatexis. Similarly, sample 12 shows detrital grains within the consistent time interval (ca. 596 Ma – 798 Ma) of the Rio Negro arc and Rio Doce arcs, reinforcing that the fragments of these arcs, or zircons that were inherited from these terranes, are potential sources to the sedimentary protoliths of the paragneisses. The regional scenario together with our field and analytical data, compared with data available in the literature, suggest the sedimentary protoliths of the studied samples filled orogenic basins related to the Rio Doce magmatic arc. Most detrital zircon ages are close to the maximum depositional age, a classical signature of orogenic basins related to magmatic arcs. The studied paragneiss unit correlates with the Nova Ven´ecia Complex, located on the intra-arc to back-arc zones of the Araçuaí orogen, and with the orogenic succession of the distal Andrelândia Group, shared by both the Araçuaí and Ribeira orogens. Furthermore, our data also suggest the juvenile Rio Negro - Serra da Prata arc system was either amalgamated with the Rio Doce arc or that fragments of these arcs were incorporated as unmelted xenoliths and xenocrystals within the Rio Doce arc rocks before ca. 614 Ma, providing key hints to unravel the evolution of the Araçuaí - Ribeira orogenic system (AROS) and its role in the Gondwana assembly.Item Zircon petrochronology reveals the moderately juvenile signature of a diatexite from the boundary one between the Brasília and Ribeira orogens (SE Brazil) : relict of a Tonian arc?(2022) Costa, Fernanda Moura; Penna, João Lucas Andrade; Martins, Lorena Cristina Dias; Tedesch, Mahyra; Novo, Tiago Amâncio; Araujo, Cristina Santos; Vieira, Pedro Leonardo Rossi; Lana, Cristiano de Carvalho; Soares, Antônio Carlos PedrosaUnraveling the tectonic evolution of Precambrian high-grade rocks is often challenging owing to widespread metamorphic overprint under high to ultra-high temperature conditions. In this scenario, isotopic systems-based investigations constitute an important tool to obtain the time constrains of formation and evolution of rocks.We present a petrochronological investigation using U–Pb and Lu–Hf data of zircon grains extracted from a biotitebearing granitic leucosome from a diatexite found in the boundary zone between the Brasília and Ribeira orogens, SE Brazil. Clusters of 176Hf/177Hf(t) ratio values characterize two distinct zircon data groups, suggesting at least two different crystallization stages. 176Hf/177Hf(t) ratios from group 1 range from 0.28230 to 0.28247 with εHf (t) between +7.54 and − 1.55, representing a moderately juvenile to evolved magma. This group constrains a time interval of ca. 890-540 Ma, and the ancient zircon core (890 Ma) could potentially record the minimum age for the magmatic crystallization of a moderately juvenile protolith, with ϵHf (890) ranging from +8.66 to +0.36. Excluding this ancient zircon (since it is the only date older than 800 Ma), the oldest grain provides a minimum crystallization age of ca. 797 Ma, with ϵHf (797) between +6.73 and -1.61. Group 2, exhibiting 176Hf/177Hf(t) ratios from 0.28214 to 0.28225and negative εHf(t) values (− 3.35 to − 7.53), represents xenocrysts of crustal origin from the protolith or an influx of allochthonous crustal melt during high-grade metamorphism. The age spreading from ca. 890 Ma to ca. 540 Ma along the concordia is consistent with a Pb-loss scenario, with cores locally providing younger ages than rims. This is also consistent with prolonged metamorphism, as newly crystallized domains also present a spread of ages. Our data indicate that the leucosome is the metamorphic product of a moderately juvenile rock. When placed in the regional context, the biotite-bearing granitic leucosome may represent the relic of a magmatic arc, now located in the boundary zone between the Brasília and Ribeira orogens. Its moderately juvenile signature suggests the following tectonic setting interpretations: (i) an intra-oceanic subduction setting similar to modern island arcs or an early stage of continental subduction, formed at ca. 890–800 Ma and, thus could be potentially correlated with juvenile magmatic arcs found in both Brasília (Mara Rosa – Arenopolis ´ arc system) and Ribeira (Serra da Prata – Rio Negro arc system) orogens, suggestive of a large ocean realm to the south of the Sao ˜ Francisco paleocontinental block in Tonian time; and (ii) the most primitive relic of an early stage of the continental magmatic arc installed on the active margin of the Paranapanema paleocontinent.Item Towards an integrated tectonic model for the interaction between the Bambuí basin and the adjoining orogenic belts : evidences from the detrital zircon record of syn-orogenic units.(2020) Amaral, Matheus Henrique Kuchenbecker do; Soares, Antônio Carlos Pedrosa; Babinski, Marly; Reis, Humberto Luís Siqueira; Atman, Dora; Costa, Ricardo Diniz daThe Sao ̃ Francisco craton and its surrounding orogens are some of the most important tectonic elements of South America, and key regions to understanding the assembly of Western Gondwana in the Proterozoic-Palaeozoic transition. During this major tectonic event, diachronic collisions between small continents developed an intricated orogenic system, where several orogens evolved in unique paths through time and space. In such collisional settings, there are some tectonic processes that promote subsidence, thus controlling the formation of orogenic-related sedimentary basins. Furthermore, the tectonic activity in collisional orogens generates dynamic landscapes that usually favor increased erosion and sediment generation to feed these basins, making them key places to seek for clues about the tectonic evolution of their surroundings. On the S ̃ ao Francisco craton, the Bambuí Group records a complex foreland system, which evolved in response to the lithospheric overload exerted by the uplift of both Brasília belt and Araçuaí orogen. In turn, both Salinas Formation and Ibia ́ Group comprise orogenic deposits resting within the Araçuaí orogen and Brasília belt, respectively, whose tectonic significance is still under debate. Here we present new U–Pb (LA-ICP-MS and SHRIMP) and Lu–Hf isotopic an- alyses on a great amount of detrital zircon grains extracted from the rocks of the Bambuí Group and Salinas Formation, together with a thorough data compilation from the literature. The two units present similar prov- enance patterns, sharing the major detrital zircon age peaks (550–650 Ma, 950–1050 Ma, 1750–2000 Ma, 2600–2800 Ma) and maximum depositional age in c. 550 Ma. The Ediacaran zircons recovered from the Bambuí Group show a wide range of the εHf(t), ranging from c. − 17 to +15, which suggest the existence of multiple late Neoproterozoic sources, some of them juvenile and some with a long crustal residence. The variation in detrital zircon age patterns and εHf(t) values from different units within the Bambuí Group provided additional clues of provenance changes occurred during the evolution of the basin. The new data obtained for the Salinas Formation constrain its deposition between 548 and 500 Ma, which have an important implication on its tectonic signifi- cance. We propose that in both Brasília belt and Araçuaí orogen sides, the early foredeep deposits of the Bambuí basin should have been incorporated to the orogenic domains, which could explain the apparent lack of deposits recording the climax of the Brasilia belt uplift (c. 630 Ma) within the cratonic area. In this same direction, we consider that both Salinas Formation and Ibi ́ a Group could represent remnants of these early foreland deposits related to the uplift of Brasília belt and Araçuaí orogen, respectively, incorporated to the orogenic wedges due to the advance of the deformational fronts. Therefore, what we know as Bambuí Group is in fact the remaining record of an advanced stage of the foreland system, when subsidence was already influenced by the two evolving orogens. Altogether, the analyses of the stratigraphic, structural and geochronological data converge towards an integrated tectonic model for the interaction between the Bambuí basin and the surrounding orogens during West Gondwana amalgamation.Item 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, PaulaThe 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.Item The Ediacaran Rio Doce magmatic arc in the Araçuaí – ribeira boundary sector, southeast Brazil : lithochemistry and isotopic (Sm–Nd and Sr) signatures.(2020) Soares, Caroline Cibele Vieira; Queiroga, Gláucia Nascimento; Soares, Antônio Carlos Pedrosa; Gouvêa, Lucas Pequeno; Valeriano, Claudio de Morisson; Melo, Marilane Gonzaga de; Marques, Rodson de Abreu; Freitas, Renata Delicio Andrade deThe Rio Doce magmatic arc, developed from ca. 630 to ca. 580 Ma on an active continental margin, linking the Araçuaí and Ribeira orogens in southeastern Brazil. The arc plutonic portion comprises the G1 supersuite, a calcalkaline, magnesian, I-type pre-collisional rock-assemblage, mostly composed of tonalite to granodiorite, frequently containing dioritic to mafic enclaves, and their metamorphosed equivalents. We carried out field, petrographic, lithochemical and isotopic (Sm–Nd and Sr) studies on a segment of the Rio Doce arc located in the transition region between the Araçuaí and Ribeira orogens. The studied samples include metamorphozed granitic rocks (referred to by their igneous names in the QAP diagram), consisting of syenogranite, monzogranite, granodiorite, tonalite, quartz diorite, orthopyroxene-bearing tonalite and orthopyroxene-bearing quartz diorite. This rock assemblage defines an I-type, magnesian, metaluminous to slightly peraluminous, medium-to high-K, expanded calc-alkaline series. The numerous mafic to dioritic enclaves and related features indicate magma mixing processes. Isotopic data show moderately to strongly negative εNd(t) values (− 2.9 to − 13.6) and intermediate to high 86Sr/87Sr ratios (0.7067–0.7165) suggests assimilation of older crustal material (i.e., the Juiz de Fora and Pocrane complexes, enclosing paragneisses), which is also indicated by Nd TDM model ages from 1.19 Ga to 2.13 Ga. Magmatic orthopyroxene and high content of CaO in garnet suggest magma crystallization in the deep crust. Together, our data point out to a combination of partial melting of mantle wedge in the subduction zone, deep crustal anatexis, host rock assimilation, and crystal fractionation for magma genesis in the southeastern Rio Doce arc.Item Provenance shift through time in superposed basins : from early cryogenian glaciomarine to late ediacaran orogenic sedimentations (Araçuaí Orogen, SE Brazil).(2020) Castro, Marco Paulo de; Queiroga, Gláucia Nascimento; Martins, Maximiliano de Souza; Soares, Antônio Carlos Pedrosa; Oliveira, Leon Dias; Lana, Cristiano de Carvalho; Babinski, Marly; Alkmim, Ana Ramalho; Silva, Marco Antônio daRecords of Precambrian glaciation have been reported from southeastern Brazil for over a century. We present sedimentological, stratigraphic and isotopic (U-Pb and Lu-Hf on detrital zircons, C and O on carbonates) studies on diamictite-rich to diamictite-free successions of the Araçuaí Orogen, the Brazilian counterpart of the Araçuaí – West Congo Orogenic System (AWCO). From base to top, the Chapada Acauã Formation (Macaúbas Group) includes a diamictite-rich unit, with lenses of graded sandstone and clast-supported conglomerate, that gradually passes to graded sandstone, pelite with sparse oversized clasts and rare carbonate lenses on top, representing mass flow and turbidity current deposits of submarine fan, followed by finer-grained turbiditic sedimentation with iceberg discharges along fan fringes, from glaciomarine to post-glacial scenarios. The Salinas Formation comprises a deep-sea sand-mud sequence composed of pelites and pelitic wackes. The Chapada Acauã Formation was deposited in-between 750 and 667 Ma. It shows wide spectra of zircon ages (typical of continental rift to passive margin settings) that start around 3.2 Ga and display main age peaks indicating sediment provenance from the Rhyacian-Orosirian basement (εHf(t) = +14.6 to −18.5) and Early Tonian anorogenic rocks (950–880 Ma; εHf(t) = −3.2 to −23.2) for the diamictite-rich lower unit and, for the upper unit, also in Early Cryogenian anorogenic rocks (ca. 715 Ma, εHf(t) = −9.6). In contrast, the Salinas Formation shows most ages in-between 676 and 620 Ma and a maximum sedimentation age around 551 Ma, with εHf(t) from +6.9 to −18.2, unravelling an important shifting of sediment provenance to sources located in magmatic arcs and collisional granites of the Araçuaí and Ribeira orogens. The Early Cryogenian age and negative Hf signature for the glaciomarine Chapada Acauã Formation point to sediment sources in the 720–670 Ma anorogenic igneous rocks found in AWCO and adjacent Congo – São Francisco Craton, and suggest correlation with the Sturtian global glaciation.Item 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 deAfter 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.