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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2 resultados
Resultados da Pesquisa
Item Sedimentary provenance and role of tectonic inheritance on the control of the Macaúbas group, eastern margin of São Francisco Craton (SE Brazil).(2021) Oliveira, Rosana Gonçalves; Martins, Maximiliano de Souza; Queiroga, Gláucia Nascimento; Souza, Maria Eugênia Silva de; Lana, Cristiano de Carvalho; Alkmim, Ana Ramalho; Silva, Marco Antônio Leandro da; Bueno, Cássio; Linhares, DavidsonThe Neoproterozoic Macaúbas Group represents the precursor basin system of the Araçuaí–West Congo orogen, located in the southern margin of Sao ̃ Francisco Craton, and records a Tonian volcano-sedimentary succession, at the base, overlain by a Cryogenian sequence related to the Neoproterozoic global glacial event. Detailed strat- igraphic surveys along the Tonian units allowed the identification of two lithofacies associations related to al- luvial fan and braided river environments, while the three Cryogenian lithofacies associations indicate a glaciomarine environment associated with extensive tectonics that has evolved into a marine environment. The results show that the age spectra of the Tonian and Cryogenian units are similar, differing mainly for an increased peak in the Cryogenian sample in ca. 1.0 Ga, where the primary source is probably related to those magmatic rocks associated with the Stenian-Tonian extensional breakup of the Sao ̃ Francisco-Congo paleocontinent. The KS-Test shows that not all the Tonian samples are similar to each other, as in all the Cryogenian samples. The detailed stratigraphic and structural surveys associated with the geochronological U–Pb data allow us to interpret that the Tonian and the basal Cryogenian sequences were deposited in two episodes of an active intracontinental tectonic context related to fault reactivations along the WNW-ESE Pirapora aulacogen structures in superimposed basin-cycles, the middle-to late-Cryogenian sequences extrapolated the WNW-ESE boundaries while the basin local depocenter and its surroundings expanded to a large depocenter during the basin evolution.Item Record of Early Tonian mafic magmatism in the central Espinhaço (Brazil) : new insights for break-up of the Neoproterozoic landmass ancestor of São Francisco-Congo paleocontinent.(2020) Moreira, Helen Fonseca; Danderfer Filho, André; Costa, Alice Fernanda de Oliveira; Bersan, Samuel Moreira; Lana, Cristiano de Carvalho; Queiroga, Gláucia NascimentoPetrological characterization, U–Pb geochronology, Lu–Hf analyses and major and trace element data from mafic intrusions in the Central Espinhaço (central portion of the Brazilian shield) are used here to investigate the geological significance of the Early Neoproterozoic magmatism in the context of the S~ao Francisco-Congo paleocontinent. These mafic bodies are represented by medium to coarse-grained metagabbros with plagioclase, amphibole and clinopyroxene. Zircon U–Pb isotopic data from two samples yielded weighted mean 206Pb/238U ages of 895 3.4 Ma (MSWD ¼ 1.7) and 896 2.4 Ma (MSWD ¼ 0.64), regarded as the best estimates for the crystallization age of these mafic rocks. Major and trace element data (including REEs) show that the gabbros originated from a subalkaline tholeiitic magma, typical of intraplate magmatism. Such rocks are slightly enriched in LREEs and LILEs and depleted in HFSEs. Our new isotope and geochemical data, along with regional knowledge, indicate that these metagabbros mark the beginning of an important Tonian-age extensional tectonic event of the landmass of which the S~ao Francisco-Congo paleocontinent was part (Rodinia supercontinent or Central African block?). We furthermore suggest that these rocks belong to a prominent suite of Tonian-age mafic rocks that mark a diachronic breakup attempt of this landmass which may have occurred from south to north along the Espinhaço mountain range.