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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2008 - 200912010 - 20111

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Autor: search.filters.author.Fueten, Frank

Resultados da Pesquisa

Agora exibindo 1 - 2 de 2
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    Complex fringes around magnetite porphyroclasts : growth and deformation history.
    (2011) Lagoeiro, Leonardo Evangelista; Barbosa, Paola Ferreira; Fueten, Frank
    Deformed strain fringes in iron formation rocks show complex quartz fiber patterns that grew alongside magnetite porphyroclasts embedded in a matrix of quartz and iron oxides during coaxial to non-coaxial deformation. These rocks have been deformed by a combination of processes involving microfracturing, pressure solution and dislocation glide at temperatures of approximately 300 °C. Detailed microstructural observation and crystallographic analysis show that quartz fiber growth is not controlled by the crystal faces. Quartz c-axis orientations of fibrous quartz indicate that these grains initially grew with their c-axes paralle to the fiber length. Late solid-state deformation of crystallized fibers comprised dislocation glide along basal plane and subsequent recrystallization. This produces aggregates of recrystallized grains consisting of equant to elongated quartz grains with straight and orthogonal grain boundaries.
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    Fluid-assisted grain boundary sliding in bedding-parallel quartz veins deformed under greenschist metamophic grade.
    (2008) Lagoeiro, Leonardo Evangelista; Fueten, Frank
    Iron formation rocks of Quadrilátero Ferrífero, Brazil, were deformed at greenschist facies. Quartz grains in bedding parallel veins were sheared and deformed by a combination of mechanisms assisted by aqueous fluids. Veins in the outcrop appear to be stretched parallel to the compositional layering. The overall vein shapes resemble those of boundinage and pinch and swell. In thin sections, veins show microstructures similar to those observed in hand samples, where domains of large quartz crystals are pulled apart for several millimeters. The voids between quartz fragments are filled with domains of polycrystalline quartz. The microstructural and orientation data show that the strain imposed on the vein as a rigid and competent layer was not accommodated in the quartz polycrystals exclusively by crystal plastic deformation or dynamic recrystallization. The new grains are strain-free, with straight boundaries and with weak to random crystallographic fabrics. We interpret these features to have resulted from a combination of processes, which included grain boundary sliding accomplished by solution transfer. We propose that the coeval operation of both mechanisms allows the aggregate to deform at higher strain rates without necking of the vein layer in a type of flow similar to those described in superplastic regimes.