Quantitative texture analysis of slates: An insight into slate’s elastic properties and their contribution to the understanding of seismic wave reflections in anisotropic materials

Abstract

Slates are low-grade metamorphic rocks characterized by an alignment of the phyllosilicates, resulting in the development of a marked foliation. A consequence of this is a strong directional dependence of their elastic properties, which are tightly bound to their texture. The Rietveld analysis applied to synchrotron x-ray diffraction images of slates from the Truchas Syncline (NW Iberian Peninsula) will provide us with the orientation distribution function (ODF) of the principal minerals that constitute the rock. This textural analysis shows an exceptional alignment of phyllosilicates (muscovite and chlorite) in contrast with a poor orientation of other minerals such as quartz. In a later treatment of the data, the elastic properties of the slates, as well the variations of the seismic wave velocities, have been calculated from the ODF and the single crystal stiffness tensors. The results of both the elastic properties and the wave velocities can be used for the construction of models that allow to understand the reflections of seismic waves in markedly anisotropic materials, which is a matter of a great interest in the studies of the Earth’s lithosphere with seismic methods.

Keywords

• seismic anisotropy
• reflection coefficient
• crystal preferred orientation (OCP)
• slate
• stiffness tensor