Tectonic Slickensides and Fault Gouge as Markers of Mechanical Instability in Fault Zones of Different Depth Levels

Issues of the influence of rock composition and depth level of dynamic mobility on its geomechanical regime are considered with a number of natural examples from noncoeval terrigenous, metamorphic, and magmatic complexes and geostructural positions by studying fault gouge and films of slickensides. The features of rock material alteration in weakly lithified strata of the near-surface part of the crust and in consolidated rock and mineral varieties of a slightly deeper level in the transition zone from aseismic to seismogenic behavior of faults are assessed. The article demonstrates the consequences of mechanochemical alteration of rocks of different composition, changes in the thermodynamic parameters of metamorphic reactions, their volumetric effects and thermal energy orientation, as well as the influence of mineral-phase and structural-textural rearrangements on the mechanical instability of the displacement zone, its strengthening or weakening during dynamic development. The structural and material markers of stable, aseismic slip along the fault and unstable seismogenic displacement are characterized.