Análisis cuantitativo de la textura de materiales policristalinos deformados mediante difracción neutrónicaimplicaciones reológicas para la corteza inferior

Abstract

Two samples of mylonitic-ultramylonitic ortogneisses collected along the Contín shear zone (Morais Complex, N Portugal) were investigated for crystal preferred orientation and seismic anisotropy. Neutron diffraction data obtained at the D1B beamline at ILL (Institute Laue-Langvin, Grenoble) were analyzed with the Rietveld method as implemented in the code MAUD, to obtain orientation distribution functions (ODF) of the principal phases (quartz, K-felsdpar, plagioclase, phlogopite, muscovite and riebeckite). Texture is compatible with the plastic deformation of the aggregates under medium to low-temperature conditions.Using preferred orientation data and single crystal elastic tensors, P and S-waves velocities and elastic anisotropy to seismic waves propagation have been calculated. We have explored the role of several factors controlling the elastic properties of rocks, particularly the role of strain state and mineral changes in a shear zone. Those factors have a direct impact on the medium impedance and consequently on the interphase reflectivity interphases. P-wave velocities, S-wave splitting and anisotropy increase with muscovite content.