La esquistosidad en las pizarrasun estudio al SEM

Abstract

Scanning electron microscopy is used to provide microstructural information at greater resolution, than is possible by optical microscopy in fine grained rocks, like slates. Primary cleavage in low and very low metamorphic slates, presents differents microstructural features depending on previous sedimentary fabric and on its location in folds. Slates exhibit a slaty cleavage if there is no preferred orientation parallel to bedding. Crenulation cleavage is characteristic mainly in the hinges areas, in slates with a well defined preferred orientation parallel to bedding. Slaty cleavage is defined by the orientation of phyllosilicates in narrow domains, cleavage lamellae, bounfing microlithons with grains oriented at random. The cleavage lamellae are thin parallel or anastomosing seams, that can be continuous or discontinuous through the domain. Crenulation cleavage is characterized by microfolding of phyllosilicates and it presents an incipient differentiation. In the slates studied, three mechanisms contribute to cleavage development: mechanical rotation, crystallisation of oriented phyllosilicates and pressure solution.