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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Resultados da Pesquisa
Item Implications for the refinement of the São Francisco Craton magmatic barcode and the North China link.(2022) Mendes, Mônica de Cássia Oliveira; Lobato, Lydia Maria; Caxito, Fabrício de Andrade; Rosière, Carlos Alberto; Lana, Cristiano de Carvalho; Silva, Rosaline Cristina Figueiredo eLate Archean to Paleoproterozoic dike swarms crosscut the basement and supracrustal sequences of the São Francisco Craton. Their spatial distribution and orientation patterns, as paleomagnetic signature, provide key evidence to the positioning of the cratonic area in ancient paleocontinental reconstructions through the refinement of the “magmatic barcode”. Zircon U–Pb data from dikes in the cratonic domain of the Quadrilátero Ferrífero Mineral Province, in the southern of São Francisco Craton, allowed the recognition of two magmatic stages: a Rhyacian-Orosirian pulse, belonging to the Paraopeba swarm, and a Statherian pulse that belongs to the Pará de Minas II swarm. The Ediacaran Brasiliano Orogeny later affected dikes from both swarms. The Paraopeba swarm consists of pulses related to the Rhyacian-Orosirian orogenic cycle, with dikes providing U–Pb zircon ages of 2019 + 23–11, 1944 ± 29 and 1918 ± 12 Ma. The zircon εHf values from these dikes are predominantly negative, suggesting reworking of preexisting crust, whereas the TDM ages vary from 4000 to 2500 Ma, which can be interpreted as a long period of crustal residence. The Statherian Pará de Minas II swarm, with a U–Pb zircon age of 1717 ± 9 Ma, is chronocorrelated to the lower stratigraphic sequence of the Espinhaço rift basin. Zircon grains from this dike have predominantly positive εHf values and TDM model ages between 3050 and 1950 Ma. Unlike the Paraopeba swarm, the Pará de Minas magmatism is marked by a striking input of juvenile mantle material with minor crustal contamination. The Ediacaran Brasiliano tectono-thermal event caused isotopic disturbance in both Paraopeba and Pará de Minas II swarms, resulting in lower intercepts at 595 ± 65 and 584 ± 27 Ma, respectively. Our data pinpoint dike emplacement related to tectonic events described in the southern of São Francisco. In the final stages of Rhyacian orogenic cycle, at ca. 2019–1918 Ma, data suggests an important crustal contamination. Thereafter, a crustal rifting event at ca. 1717 Ma involved dike swarm emplacement with magmatic source from a mantle plume. The Rhyacian-Orosirian ages obtained here are the first zircon U–Pb geochronological data presented for the Paraopeba dike swarm and allow for a refinement of the São Francisco Craton barcode, reinforcing previous suggestions of proximity with the North China Craton crosscut by the similarly aged Hengshan and Xiwangshan/Xuwujia dike swarms, whether or not those two cratonic pieces were part of the Columbia supercontinent.Item Metallogenetic Mn-model of the Rhyacian-aged Buritirama Formation, Carajás domain (Amazon Craton).(2021) Salgado, Silas Santos; Caxito, Fabrício de Andrade; Silva, Rosaline Cristina Figueiredo e; Uhlein, Gabriel Jubé; Nogueira, Leonardo Brandão; Nalini Júnior, Hermínio Arias; Aranda, Ramon de OliveiraThe Mn-bearing Buritirama Formation is composed of clastic and chemical metasedimentary rocks representing a Rhyacian platformal basin (ca. 2.18–2.06 Ga) that limits the northern border of the Archean-Paleoproterozoic Caraj ́ as domain with the Paleoproterozoic Bacaj ́ a domain in the southern Amazon Craton, northern Brazil. The Buritirama Formation is divided into three main stratigraphic units. The Lower and Upper units consist of a basal quartzite followed by carbonate–silicate rocks (marls), dolomitic marbles (dolostone) and minor biotite schist while the Intermediate Unit consists of Mn-carbonate rocks topped by a supergene Mn-oxide deposit (Cenozoic age). These rocks were deformed and metamorphosed during the Transamazonian event (ca. 2.06 Ga). Geochemical data from dolomitic marbles (Lower Unit) exhibit negative Ce anomalies, high Y/Ho ratios (ca. 48) and seawater-like REE + Y patterns that reinforce an open platform setting for the Buritirama basin. Positive δ13C values (+3.2‰ to +5.0‰ V-PDB) for dolomitic marbles are considered to be an expression of the Loma- gundi Carbon Isotopic Excursion. The metallogenesis of Mn-carbonate rocks is evaluated based on redox- sensitive trace elements (e.g. Zn and Ni), PAAS-normalized REE + Y patterns and δ13C values (− 2.56‰ to +0.15‰ V-PDB) and point out to a classical multi-stage redox-controlled Mn-model involving: i) a primary hydrothermal fluid source related to ocean vents and/or normal faults; ii) microbially-mediated reduction of Mn- oxides particles at the ocean bottom; and iii) reactions between Mn2+ and CO3 2− (organic matter and seawater related), giving rise to diagenetic Mn-carbonates. The Rhyacian age, Mn deposits, and presence of Lomagundi- like δ13C allows to correlate the Buritirama Formation with the Aguas ́ Claras Formation within the Caraj ́ as domain further south, thus establishing an important metalliferous event that was up to now largely overlooked within the southern Amazon Craton.Item Provenance of the Buritirama Formation reveals the Paleoproterozoic assembly of the Bacajá and Carajás blocks (Amazon Craton) and the chronocorrelation of Mn-deposits in the Transamazonian/Birimian system of northern Brazil/West Africa.(2019) Salgado, Silas Santos; Caxito, Fabrício de Andrade; Silva, Rosaline Cristina Figueiredo e; Lana, Cristiano de CarvalhoThe Mn-bearing Buritirama Formation along the homonymous ridge consists of a 40 km long by ca. 3 km wide NW-SE trending unit that limits the northern border of the Archean Carajás domain with the Paleoproterozoic Bacajá domain in the southeastern Amazon Craton. The Buritirama Formation type section is arranged in four imbricated thrusts that individualize three main stratigraphic units: Lower Unit, Intermediate Unit and Upper Unit. Detrital U-Pb zircons ages from the Lower Unit and Upper Unit record the prevalence of Neoarchean populations, suggesting the Carajás block as the main sedimentary source for the Buritirama basin. However, minor Paleoproterozoic populations attributed to the Bacajá block are also recognized, defining a maximum depositional age at ca. 2186 Ma. The anorogenic Buritirama metagranite occurs at the local basement, represents a probable precursor stage of the Buritirama rift and yielded a Concordia age of 2549 ± 5.9 Ma (U-Pb). Supported by these new geochronological data, a framework model for the evolution of the Buritirama basin is proposed. Contrary to previous interpretations, the basin was active until at least the Rhyacian, representing a platformal setting fringing the northern margin of the Carajás block. A regional metamorphic event (ca. 2.06 Ga) records the closure of the basin during the Transamazonian Orogeny and the amalgamation of the Bacajá and Carajás blocks. The depositional age bracketed in between 2.3 and 2.1 Ga links the Buritirama Mn deposit (southeastern Amazon Craton) with those of Serra do Navio (Amapá Block, northeastern Amazon Craton) and Nsuta (West African Craton), suggesting: (i) widespread chronocorrelation of Mn-bearing sequences in the continental-scale Rhyacian Transamazonian/Birimian orogenic system, and (ii) formation of the primary carbonate ores under the influence of a major global manganese deposition episode.