EM - Escola de Minas
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6
Notícias
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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8 resultados
Resultados da Pesquisa
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 Geochemistry and U–Pb zircon ages of the metamafic-ultramafic rocks of the Riacho dos Machados metavolcanosedimentary sequence : evidence of a late rhyacian back-arc basin during the assembly of São Francisco-Congo paleocontinent.(2021) Leal, Victor Luiz Silva; Amaral, Matheus Henrique Kuchenbecker do; Barbuena, Danilo; Queiroga, Gláucia Nascimento; Pinheiro, Marco Aurélio Piacentini; Freimann, Marcelo de AlmeidaThe São Francisco paleocontinent comprises Archean nuclei and Paleoproterozoic magmatic arcs which were amalgamated during Siderian to Orosirian thermal-tectonic events (ca. 2.4–2.0 Ga). Located in the Porteirinha domain, one of these Archean segments, the Riacho dos Machados metavolcanosedimentary sequence encompasses metamafites and metaultramafites intercalated with metasedimentary rocks. The metamafites clustered in the Type I category are tholeiitic, present MORB-like affinities and flat REE patterns with enrichment in La, Rb, and Cs. The metamafites from Type II are calc-alkaline, showing arc signatures with enrichment in LILE (Cs, Ba, U, Rb, K) and LREE, and depletion in the HFSE. The associated metaultramafites were classified as high-Mg ultramafic rocks similar to Barberton-Type komatiites, with enrichment in LILE and LREE, Al2O3/TiO2< 16 and Gd/Yb(N) > 1. U–Pb (LA–SF–ICP-MS) zircon analyses were carried out on the Type II hornblendite, unraveling a concordant crystallization age of 2071 ± 9 Ma. Inherited zircons yield a discordant age of 2922 ± 22 Ma and a lower intercept at 473 ± 48 Ma. The hybrid magmatism of the studied metamafites coupled with the inherited zircon grains, indicate that this metavolcanosedimentary sequence was developed in an intracontinental back-arc basin. The rocks from Type I have been originated from MORB-like source with a slightly input of subduction-derived fluids. In its turn, Type II samples represent melts more influenced by the fluids from the dehydrated slab. This assumption implies that the São Francisco paleocontinent, in the region of the Porteirinha block and surroundings, were under an accretionary stage at the late Rhyacian. During this orogenic process the metamorphic PT conditions reached lower-amphibolite facies. Moreover, this thermaltectonic event in likely responsible for the auriferous fluid percolation of the Riacho dos Machados Gold Mine.Item Paleoproterozoic sources for Cordilleran-type Neoproterozoic granitoids from the Araçuaí orogen (SE Brazil) : constraints from Hf isotope zircon composition.(2020) Schannor, Mathias; Lana, Cristiano de Carvalho; Mazoz, Ariela Oliveira; Narduzzi, Francesco; Cutts, Kathryn Ann; Fonseca, Marco AntônioThe Araçuaí orogen of SE Brazil exposes numerous amounts of magnesian, metaluminous, calc-alkaline, and medium- to high-K granitoid batholiths that were emplaced during early convergence between the São Francisco and Congo cratons during West Gondwana assembly in the late Neoproterozoic. Previously proposed sources for these pre-collisional granitoids include the Paleoproterozoic basement and mantle-derived magma based on isotopic signatures, abundant microgranular enclaves and contemporaneous mafic intrusions. Zircons from migmatitic basement gneiss, a noritic intrusion and five granitoid intrusions were analysed for U–Pb–Hf isotopes to evaluate their magma source. Paleoproterozoic migmatites represent addition of juvenile crust in an accretionary orogenic setting at ca. 2.2–2.0 Ga evidenced by their positive zircon εHf values. The Hf isotopic composition of zircon from pre-collisional granitoids has a large range of negative εHf values between −28.8 and −1.7 indicating crustal protoliths. This range of unradiogenic Hf isotopic compositions is explained by inefficient mixing of magmas derived from felsic and mafic Paleoproterozoic sources that hybridised during incremental growth of the plutons. Zircon grains of contemporaneous mafic intrusions display slightly higher, yet enriched, Hf isotopic compositions consistent with crustal contamination of mantle magmas. The new Hf isotope data, integrated with other chemical and isotopic evidence, suggest derivation of the pre-collisional granitoids from lower crustal sources of the Paleoproterozoic basement, with only minor contributions from mantle-derived magmas. Thus, magmatism of the Araçuaí orogen related to the assembly of West Gondwana was dominantly a crustalreworking event.Item The kinematic evolution of the Serra Central Salient, Eastern Brazil : a neoproterozoic progressive arc in northern Espinhaço fold-thrust belt.(2017) Bersan, Samuel Moreira; Danderfer Filho, André; Lagoeiro, Leonardo EvangelistaConvex-to-the-foreland map-view curves are common features in fold-thrust belts around cratonic areas. These features are easily identifiable in belts composed of supracrustal rocks but have been rarely described in rocks from relatively deeper crustal levels where plastic deformation mechanisms stand out. Several local salients have been described in Neoproterozoic marginal fold-thrust belts around the São Francisco craton. In the northern part of the Espinhaço fold-thrust belt, which borders the eastern portion of the São Francisco craton, both Archean-Paleoproterozoic basement rocks and Proterozoic cover rocks are involved in the so-called Serra Central salient. A combination of conventional structural analysis and microstructural and paleostress studies were conducted to characterize the kinematic and the overall architecture and processes involved in the generation of this salient. The results allowed us to determine that the deformation along the Serra Central salient occur under low-grade metamorphic conditions and was related to a gently oblique convergence with westward mass transport that developed in a confined flow, controlled by two transverse bounding shear zones. We propose that the Serra Central salient nucleates as a basin-controlled primary arc that evolves to a progressive arc with secondary vertical axis rotation. This secondary rotation, well-illustrated by the presence of two almost orthogonal families of folds, was dominantly controlled by buttress effect exert by a basement high located in the foreland of the Serra Central salient.Item 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 LavalleDescribed 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.Item P-T path reconstruction in neoproterozoic garnet-bearing paragneisses from a metasedimentary succession of the south western Araçuaí Orogen, Minas Gerais, Brazil.(2015) Degler, Reik; Novo, Tiago Amâncio; Schulz, Bernhard; Queiroga, Gláucia NascimentoEste estudo foca analises de caminhos de pressão e temperatura em paragnaisses de sucessão metassedimentar (SMS) da região sudoeste do Orógeno Araçuaí. A área de amostragem é limitada pela zona de cisalhamento de Abre Campo a oeste e pelo Arco Magmático Rio Doce a leste. A região é rica em rochas metamórficas de alto grau ortoderivadas (complexos Mantiqueira e Juiz de Fora do embasamento) e paraderivadas; incluindo paragnaisses intercalados a quartzitos, que formam o SMS. As rochas amostradas são compostas por quartzo, plagioclásio, granada, feldspato potássio, ortopiroxênio e sillimanita. Perfis de pontos de análise em porfiroblastos de granada mostram certo zoneamento caracterizado pela redução de piropo e por aumento de almadina do núcleo para borda; isto implica em crescimento de cristal sob condições de metamorfismo retrógrado. Condições metamórficas são de fácies anfibolito alto a granulito com um máximo de pressão de ca. 6 kbar e com temperatura máxima de ca. 700°C. Os dados sugerem que porfiroblastos de granada da SMS têm nucleação e início de crescimento durante o final da etapa deformacional principal compressiva do Orógeno Araçuaí (região sudoeste do orógeno); o evento de descompressão captado em bordas dos porfiroblastos foi relacionando ao colapso gravitacional no Cambriano.Item 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 AntonioThe 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.