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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2017 - 201952020 - 20222

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Autor: search.filters.author.Araújo, Teodoro Gauzzi Rodrigues de

Resultados da Pesquisa

Agora exibindo 1 - 7 de 7
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    Soil-chronosequence and quaternary landscape evolution at the marine terraces of Harmony Point, Nelson Island, Maritime Antarctica.
    (2022) Rodrigues, William Fortes; Machado, Mariana de Resende; Oliveira, Fábio Soares de; Schaefer, Carlos Ernesto Gonçalves Reynaud; Leite, Mariangela Garcia Praça; Michel, Roberto Ferreira Machado; Araújo, Teodoro Gauzzi Rodrigues de
    This study characterized the physical, chemical, macro- and micromorphological soil properties from three successive marine terrace levels from Harmony Point (Nelson Island, Maritime Antarctica) in order to understand the pedological signatures of Quaternary coastal landscape evolution of Maritime Antarctica. Soils were sampled on the Late Holocene beach (current beach) and Mid Holocene marine terraces higher up, at 3, 8, and 12 m a.s.l. At the lower levels, the predominant soils were Gelorthents, whereas Haplogelepts dominate the higher terraces. Soil properties are mostly influenced by parent material and faunal activity, in which cryoclastic (thermal weathering) and phosphatization are the main soil-forming processes. Soils from the upper levels are more developed, deeper with reddish colors, granular structures and incipient formation B horizon. These horizonation features highlight that soils vary according with age of glacier-isostatic terrace uplift, representing a Quaternary soil chronosequence. All marine terrace levels are Ornithogenic soils, at varying degrees. However, the presence of old bird nesting sites for long periods led to formation of phosphatic horizons, stable Fe-phosphate minerals and abundant vegetation in the highest terraces of this part of Maritime Antarctica.
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    Geochemistry of Antarctic periglacial soils from Harmony Point, Nelson Island.
    (2021) Rodrigues, William Fortes; Oliveira, Fábio Soares de; Schaefer, Carlos Ernesto Gonçalves Reynaud; Araújo, Teodoro Gauzzi Rodrigues de; Leite, Mariangela Garcia Praça
    Little is known about the geochemical baseline of Antarctic soils in diferent environments. We investigated the soil geo- chemistry of the two main landscape units of Harmony Point (Nelson Island, Maritime Antarctica): the coastal domain and the upper platform. Fourteen soil samples (seven in each landscape unit) were divided according to depth (hA for surface and hC for subsurface horizons) and characterized by their major, trace elements and REE concentrations. The concentration of major elements (SiO2, TiO2, Al2O3, Fe2O3, MgO, CaO, MnO, and K2O) were determined by X-ray fuorescence, whereas trace elements were quantifed by inductively coupled plasma-optical emission spectrometry (Co, Ni, As, Cd, Pb, Ba, Cr, Cu, V, Zn, and Zr) and REE by inductively coupled plasma mass spectrometry. The results showed geochemical variation with depth, either related to pedological processes (phosphatization, humifcation, podzolization, and cryoturbation), and parent material constitution (andesitic basalt in upper platform and mixed volcanic sediments in coastal domain). The main chemical aspects distinguishing Harmony Point soils from other Maritime Antarctic soils from the vicinity are: (i) higher CIA index; (ii) P2O5 enrichment due to bird guano and enhanced pedogenesis; (iii) REE retention; (iv) enrichment in Fe2O3 and S concentrations. The REE concentration was infuenced by weathering processes combined with allochthonous inputs, such as volcanic ashes and iceberg-transported granitic boulders at the coastal domain. The Harmony Point soils are little subjected to anthropic impacts, so they can be used as a basis for environmental monitoring programs in the Maritime Antarctica region.
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    Soil-landscape interplays at Harmony Point, Nelson Island, Maritime Antarctica : chemistry, mineralogy and classification.
    (2019) Rodrigues, William Fortes; Oliveira, Fábio Soares de; Schaefer, Carlos Ernesto Gonçalves Reynaud; Leite, Mariangela Garcia Praça; Araújo, Teodoro Gauzzi Rodrigues de; Bockheim, James G.; Putzke, Jair
    Soils and landforms of Nelson Island remain one of the least studied in the South Shetlands Archipelago, despite that it is one of the oldest ice-free areas and is strongly vegetated. In this paper, we examine the main processes and factors of soil formation at Harmony Point and the relation of soils to landforms, vegetation and lithology. To achieve the goals, 26 pedons were collected and studied from a 4 km2 ice-free area at Harmony Point (S62°18′; W059°10′) on the southern area of Nelson Island (Maritime Antarctica). The soils were sampled on all representative local landforms, including three levels of uplifted marine terraces up to cryoplanated plateau, waterlogged depressions, rock felsenmeer, debris slopes and patterned ground, and a paraglacial border of the ice cap (270 m a.s.l). Sampling along the cryoplanated plateau was carried out along a gradient extending inland from the margins of the Ice Cap; and sampling of the marine terraces was performed along a chronosequence under varying bird-nesting influence and age. The main pedogenetic processes observed in this area are marked phosphatization, melanization from the accumulation of organic matter, and cryoturbation. Soil development varies from weakly developed, shallow, stony and cryoturbated to well-developed and organic-rich, phosphate soils with colors ranging from grayish to brown. The mineralogical composition of the clay fraction contains secondary minerals, indicating the active role of chemical weathering. Ornithogenic soils have mature phosphate minerals such as vivianite and taranakite, as well as poorly crystalline leucophosphite. Intensively cryoturbated soils are underlain by permafrost and are classified as Typic Haploturbels; polygonal soils are widespread on the cryoplanated plateau. Areas without permafrost were classified as Typic Gelorthents. Phosphatization is a dominant soil-forming process in this area and is associated with past and present-day guano accumulation by bird nesting and has led to the the development of deeper Ornithogenic Haplorthels. The ornithogenic soils occur at different topographic levels on the cryplanated platform and marine terraces. High P concentrations can be used as a proxy of the past nesting birds' activities, with far-reaching implications, especially with regards to vegetation growth and microbial activity and diversity.
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    Polycrystals of “imperial” topaz from Minas Gerais state, Brazil.
    (2019) Araújo, Teodoro Gauzzi Rodrigues de; Silva, Gilberto Henrique Tavares Álvares da; Diniz, Rafael Silva; Graça, Leonardo Martins
    “Imperial” topaz is a gemstone variety that occurs in the Ouro Preto region (Minas Gerais state, Brazil). Polygonal sectors within the core and rims of topaz crystals, were optically observed but without consensual explanations about them. With the aid of optical microscopy, scanning electron microscopy-cathodoluminescence (SEM-CL), backscattered electrons (BSE) imaging, electron probe micro-analyser (EPMA) chemical analyses and electron backscatter diffraction (EBSD) maps, the present study intended to demonstrate the distinct crystallographic orientations within “imperial” topaz and relate the polygonal sectors with the compositional data. Cross-polarised transmitted-light photomicrographs show a well delimited and optically heterogeneous central rhombic area at (21 l) in the cores, and quadrant-like and alternated extinction areas at (200, (010) and (110) in the rims. Scanning electron microscopy-cathodoluminescence images show a central rhombic area heterogeneously luminescent in the core, and dark and homogeneous rims. Grey and completely homogeneous BSE images and EPMA results corroborate constant and homogeneous major composition of “imperial” topaz. Electron backscatter diffraction maps collected in the rim region show different areas and microstructural features instead of a uniform microstructure. The respective pole figures of orthorhombic system yielded multiple (001) poles disoriented in higher than 15° from each other. These results display numerous c-axes, suggesting distinct crystallographic orientations, and no reduction in the orthorhombic symmetry. Therefore, the presumed monocrystal of “imperial” topaz actually is a polycrystal.
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    Fingerprint e estudo cristaloquímico do topázio imperial da região de Ouro Preto (Minas Gerais, Brasil).
    (2018) Araújo, Teodoro Gauzzi Rodrigues de; Graça, Leonardo Martins; Lana, Cristiano de Carvalho; Graça, Leonardo Martins; Cipriano, Ricardo Augusto Scholz; Lagoeiro, Leonardo Evangelista; Romano, Antônio Wilson; Silva, Gilberto Henrique Tavares Álvares da
    O topázio imperial [Al2SiO4(F,OH)2] é uma variedade gemológica de ocorrência exclusiva na região de Ouro Preto (MG, Brasil). De modo a poder caracterizar o seu fingerprint, foram utilizadas técnicas como a microscopia electrônica de varredura com módulo de catodoluminescência (MEV-CL), microscopia óptica com módulo de catodoluminescência (MO-CL), espectroscopia de catodoluminescência, microssonda eletrônica (EPMA), ablação a laser com detecção por espectrometria de massas com plasma indutivamente acoplado (LA-ICP-MS) e espectroscopia Raman, em quarto amostras de topázio imperial. As imagens de MEV-CL de todas as amostras mostraram diferentes eventos de crescimento durante os processos de cristalização. Tal foi demonstrado pela existência de áreas rômbicas centrais com catodoluminescência (CL) heterogênea, e bordas escuras e com CL homogênea. As imagens de CL coloridas indicaram emissões homogêneas de cor azul a arroxeada em todas as amostras. Os espectros de CL indicaram a presença de duas faixas largas de emissão com um picos de baixa intensidade em ~417 nm, e de alta intensidade em 685, 698, 711 e 733 nm. Dados obtidos por EPMA quantificaram altos teores de OH, cuja razão XOH = OH / (OH+F) oscilou entre 0,35-0,43. Dados obtidos por LA-ICP-MS quantificaram altos teores de Cu e Zn nas áreas de alta luminescência (obtidas nas imagens de MEV-CL) sugerindo que ambos os elementos poderiam ser ativadores da CL no topázio imperial. Espectros de Raman e de CL indicaram altas emissões de Cr, corroboradas pelos altos teores de Cr obtidos por EPMA e LA-ICP-MS. Em todos os espectros Raman, os altos teores de Cr causaram altas intensidades de luminescência, originando a sobreposição das mesmas sobre os módulos vibracionais de estiramento do OH (~3.650 cm-1 ). Os elementos traços cujos teores permitiram caracterizar o fingerprint do topázio imperial foram Ti, V, Cr, Mn, Fe, Cu, Zn, Ga e Ge. De modo a caracterizar a dinâmica de cristalização e o fingerprint do topázio de ambientes geológicos distintos, seis amostras foram analisadas por MEV-CL e LA-ICP-MS: duas amostras geologicamente relacionadas a veios hidrotermais caulinizados da região de Ouro Preto (Brasil); duas a pegmatitos da Província Pegmatítica Oriental do Brasil (PPOB); uma a riolitos do Oeste dos Estados Unidos da América (EUA); e uma a veios hidrotermais carbonatados e a eventos metamórficos do Paquistão. As duas amostras da região de Ouro Preto demonstraram dois processos de cristalização bem distintos, comprovados pelas imagens de MEV-CL, onde foi possível observar um núcleo heterogêneo e bordas homogêneas. O fingerprint foi caracterizado pelos teores de Ca, Ti, V, Cr, Mn, Fe, Cu e Zn. As duas amostras da PPOB demostraram imagens de SEM-CL com luminescência escura e homogênea, implicando uma cristalização lenta e tardia, típica dos pegmatitos. O fingerprint foi caracterizado pelos teores de Li, Nb, ETRL (elementos terras raras leves), Ta e W, e de Ti, Nb e ETRP (elementos terras raras pesadas). A amostra do Oeste dos EUA demonstrou luminescência heterogênea com eventos de crescimento e de reabsorção, e zonas de crescimento bem preservadas, visíveis nas imagens de MEVCL. O fingerprint foi caracterizado pelos teores de Li, Ti, V, Mn, Nb, ETRL, Ta e W. A amostra do Paquistão demonstrou um processo de recristalização metamórfica, visível na luminescência incipiente e homogênea dada pelas imagens de MEV-CL. O fingerprint foi caracterizado pelos teores de Ca, Cr, V, Zn, ETRL, ETRP e W. Após conhecer o fingerprint e comparar os processos de cristalização das diferentes amostras de topázio, a relação entre estes processos e as possíveis implicações na gênese do topázio imperial continuaram por esclarecer. A partir de imagens de microscopia óptica (MO), MEV-CL e microscopia eletrônica com módulo de elétrons retroespalhados (BSE), e mapas de microscopia eletrônica com módulo de difração de elétrons retroespalhados (EBSD), foi possível estabelecer uma relação entre os setores poligonais e diferentes orientações cristalográficas em amostras de topázio imperial. As imagens obtidas por MO foi possível observar uma área rômbica central bem delimitada e opticamente heterogênea em (11l) no núcleo, e áreas com extinção semelhante a um quadrante e alternada em {100}, {010} e {110} nas bordas. As imagens obtidas por MEV-CL demonstraram as mesmas características já descritas nos parágrafos anteriores para o topázio imperial. As imagens obtidas por BSE eram homogêneas, refletindo a composição química homogênea e constante do topázio imperial em relação aos elementos maiores. Mapas obtidos por EBSD nas áreas de borda demonstraram cores e características microestruturais distintas ao invés de uniformidade. Nas figuras de pólo, foram obtidos múltiplos pólos com uma desorientação de mais que 15º entre si, segundo {001}. Estes resultados permitiram inferir a existência de múltiplos eixos c, implicando orientações cristalográficas distintas e uma não redução da simetria ortorrômbica do topázio imperial. Assim, foi igualmente possível afirmar que o presumido monocristal de topázio imperial é na verdade um policristal. Por fim, as imagens obtidas por MEV-CL, associadas aos dados obtidos por EBSD, permitiram corroborar que ocorreram dois processos de cristalização do topázio imperial durante a orogenia Brasiliana, entre 520-485 Ma: um processo de cristalização primária que resultou da atividade hidrotermal, e outro resultante de processos metamórficos de recristalização.
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    A cathodoluminescence-assisted LA‑ICP‑MS study of topaz from different geological settings.
    (2018) Araújo, Teodoro Gauzzi Rodrigues de; Graça, Leonardo Martins
    In this study, the crystallization dynamics and the fingerprints of two topaz crystals from the Ouro Preto region (Brazil), two from the Eastern Brazilian Pegmatite Province (EBPP), one from the Western part of the United States (US) and one from Pakistan were characterized. The combination of scanning electron microscope-cathodoluminescence (SEM-CL) and laser ablation inductively coupled plasma mass spectrometry (LA‑ICP‑MS) data allowed for the characterization of these samples. Samples from the Ouro Preto region showed primary crystallization and recrystallization processes, which were demonstrated by a CL-heterogeneous core and CL-homogeneous rims in the SEM-CL images. Their fingerprint was composed of Ca, Ti, V, Cr, Mn, Fe, Cu and Zn. Samples from the EBPP showed both dark and CL-homogeneous SEM-CL images, implying slow and late-stage crystallization, typical of pegmatites. Their fingerprints were composed of Li, Nb, LREE, Ta and W, and of Ti, Nb and HREE. A sample from a Western part of the US displayed CL-heterogeneity with growth and resorption events and well-preserved growth zones, which were noticeable through the SEM-CL images. Its fingerprint was composed of Li, Ti, V, Mn, Nb, LREE, Ta and W. A sample from Pakistan showed an evident metamorphic recrystallization process, which was visible by the incipient and CL-homogeneous luminescence given by the SEM-CL images. Its fingerprint was composed of Ca, Cr, V, Zn, LREE, HREE and W.
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    The fingerprint of imperial topaz from Ouro Preto region (Minas Gerais state, Brazil) based on cathodoluminescence properties and composition
    (2017) Araújo, Teodoro Gauzzi Rodrigues de; Graça, Leonardo Martins; Lagoeiro, Leonardo Evangelista; Mendes, Isolda Maria de Castro; Queiroga, Gláucia Nascimento
    A study of the cathodoluminescence (CL) properties of imperial topaz from Ouro Preto region (Minas Gerais state, Brazil) and its relation with trace-element composition was conducted, using scanning electron microscope cathodoluminescence (SEM-CL), optical microscope cathodoluminescence (OM-CL), cathodoluminescence-spectrometry (CL-spectrometry), electron microprobe analysis (EMPA), laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) and Raman spectrometry. Each analytical technique allowed characterization of the imperial topaz fingerprint. SEM-CL panchromatic images show different crystal growth and resorption events in imperial topaz crystals. Colour CL images indicate only blue to violet emissions. The CL-spectra indicate a broad emission band with low intensity peak at ∼417 nm and a broad emission band with high intensity and major peaks at 685, 698, 711 and 733 nm. The EMPA indicates high OH content, in which the OH/(OH + F) ratio ranges between 0.35–0.43 (0.72 ≤ OH ≤ 0.86 apfu). High Cu and Zn concentrations (LA-ICP-MS) were measured in the high luminescence areas of SEM-CL images, suggesting both elements as CL-activators in imperial topaz. Raman and CL-spectra indicate high Cr concentrations, corroborated by EMPA and LA-ICP-MS results. The high Cr caused strong luminescence intensities that enabled their superimposition over the OH stretching mode (∼3650 cm–1) of topaz in all Raman spectra. Among trace elements, the concentrations of Ti, V, Cr, Mn, Fe, Cu, Zn, Ga and Ge provide the fingerprint of imperial topaz.