UM MODELO PARA A EVOLUÇÃO MICROESTRUTURAL DOS MINÉRIOS DE FERRO DO QUADRILÁTERO FERRÍFERO. PARTE II – TRAMA, TEXTURA E ANISOTROPIA DE SUSCEPTIBILIDADE MAGNÉTICA

Abstract

Low strain itabirite still displays primary features similar to jaspilites such as sedimentary layeringand a porous granoblastic fabric composed of martite with magnetite relics and hematite Due tosynmetamorphic deformation this mineralogy recrystallizes in specularite producing a variety of fabrics,textures and anisotropy of the magnetic susceptibility (AMS) depending mainly on the strain conditions.Folded ores usually display a foliation parallel to the banding due to flexural slip and an axial planeschistosity that results in a lepidogranoblastic fabric. The stereogram of the {11.0} texture is a singlemaximum parallel to the intersection lineation. The AMS is low and its ellipsoid is triaxial. Increasingstrain and shearing transposes and obliterates the primary banding, resulting in iron ore mylonites withlepidoblastic (S-tectonites) or nematoblastic (L-tectonites) fabrics probably depending on the shape of thestrain ellipsoid.The stereogram of the {11.0} texture of schistose ores is typically a girdle parallel to foliation. AMSintensity is high with oblate shape. Stereograms of the texture of lineated ores display a single maximumparallel to the stretch lineation. AMS is low to moderate with prolate shape. Secondary recrystallizationand grain growth does not affect the lattice preferred orientation.