Influencia de la microfábrica interna en el comportamiento tenso-deformacional de una fault gouge rica en arcilla

Abstract

Despite the high degree of deformation where it has been developed a marked macroscale tectonic fabric, the Alama de Murcia fault rock (clay rich fault gouge), presents important internal microfabric heterogeneities which will have relevant implication in the mechanical behavior of the fault rock. Optical and scanning electron microscopy (SEM) study reveals that, the more than 50 mts thick fault gouge is fundamentally of illite (mica) composition with small amount of quartz and calcite. The internal structure of the gouge is dominated by a laminar-discontinuous scaly clay type microfabric, characterized by the reorientation of the clay plates associated to the different small shear planes which are forming the complex feature of the gouge. Occasionally the platy like clays are covering and mantling the rigid crystals like quartz or carbonates, increasing the heterogeneity of the microfabirc. As a consequence the shear planes developed different surface features, ranging from a marked asymmetrical roughness to smooth or polished (slickenside) surfaces. This fact induced a remarkable difference on the mechanical behavior (stress-strian relationship) for the fault gouge, ranging from brittle behavior followed by strain softening, to ductile deformation with strain hardening at increasing strain. These differences have been observed under several CU triaxial tests conducted in core samples, in various orientations angle of the applied maximum stress (σ1) to the main macrofabric and for different (σ3 ).