Navegando por Autor "Morales, Luiz Fernando Grafulha"
Agora exibindo 1 - 2 de 2
Resultados por página
Opções de Ordenação
Item Crystallographic fabric development along a folded polycrystalline hematite.(2008) Morales, Luiz Fernando Grafulha; Lagoeiro, Leonardo Evangelista; Endo, IssamuDetailed analyses of microstructures and crystallographic preferred orientations (CPOs) of hematite rocks were conducted in samples of polycrystalline hematite around a tight fold in the Quadrilátero Ferrífero region, southeastern Brazil. Grain size is dominantly very fine in all samples (z15–30 mm), with a slight increase toward the hinge. Grain aspect ratio increases substantially toward the hinge, from an average of 2 in the limb to 9 in the hinge. Distribution patterns of [0001] axes and poles of planes {1010}, {1120} and {1014} suggest that intracrystalline slip operate on the basal plane along the direction. The distribution of the poles of prismatic planes parallel to the foliation of reference frame indicate that the all the symmetric -slip directions of hematite crystals were equally efficient during activation of basal intracrystalline slip. Increasing aspect ratio is accompanied by CPO intensification toward the hinge, where intensification was aided during deformation by bulk rotation of the hematitic plates and possibly by some grain boundary sliding. Such CPO intensification with the increase of aspect ratio toward the hinge is used to infer that the fold developed by flexural flow.Item First results on the LPO-derived seismic properties of iron ores from the Quadrilátero Ferrífero region, southeastern Brazil.(2008) Morales, Luiz Fernando Grafulha; Lagoeiro, Leonardo Evangelista; Endo, IssamuDeterminations of the LPO-derived seismic properties of iron ores were carried out in five samples with contrasting mineralogy (hematite, magnetite and quartz) and deformed in different conditions. All the samples are seismically quasi-isotropic or weakly anisotropic, which reflect (i) an absent or weak crystallographic preferred orientation (CPO) in some samples; (ii) the high modal content of magnetite, (iii) the relatively weak anisotropy of elastic stiffness of hematite single crystal. Such variables induce a low anisotropic seismic behavior even in high strained iron ores with strong preferred orientation of hematite. A plane of seismic transversal isotropy parallel to the foliation of the aggregates is developed in hematite ± magnetite aggregates and in itabirites with strong CPO of hematites. In these high strained aggregates, some relationships between the crystallographic axes of hematite and the propagation velocities can be observed. The magnitudes of P and S-wave velocities derived of hematite CPO are lower than the values experimentally determined in iron ores. Such a difference probably reflects other microstructural variable which were not taken into account in the present contribution (e.g. shape preferred orientation).