Fábricas magnéticas y análisis cuantitativo de texturas mediante difracción neutrónica de tiempo de vuelo: ejemplos en tectonitas (NO del Macizo Ibérico, España)

Abstract

Crystallographic preferred orientation or texture is an intrinsic feature of crystalline matter. Texture determines physical properties of rocks, particularly anisotropy. Texture analysis should rely on quantitative methods, which provide 3D information of the aggregate. Neutron diffraction has notorious advantages because of high penetration in geomaterials, so large sample volume can be analyzed. Orientation distribution of crystals in the aggregate can be used to calculate physical properties of the rocks, like magnetic susceptibility, by averaging single crystal properties over the orientation distribution. Calculations of the anisotropy of magnetic susceptibility (AMS) have to be based on accurate correlation of the AMS single crystal data and crystal lattice. However, most of rock-forming minerals have low symmetry lattices (monoclinic-triclinic), consequently that correlation is complex. We can partially overcome those difficulties combining texture analysis, AMS simulation, and direct measurement of AMS. We present four examples of tectonites from NW Iberian Massif, where microstructural issues have been solved following that methodology.