Influence of fluid composition on the elastic properties of sandstone and quartzite at high temperature and pressure in application to the problem of crustal waveguides

Recent geophysical studies have revealed zones with anomalously low seismic velocities and increased electric conductivity in the middle part of the Earth’s crust. It is suggested that these zones can probably be related with the variations in the porosity and permeability of the rocks and the presence of fluids, and that they can explain the existence of crustal waveguides. In order to verify this model, we carried out an experimental study. Among the studied metamorphic processes, the acid metasomatose most completely explains the silicification of rocks. The present work considers the physico-chemical causes of the redeposition of quartz from the solutions, the influence of the pH of the solutions on the mass transfer and deposition of quartz during silicification, and alteration of the physical properties of the rocks. Silicification leads to the increase in density, change in microtexture, and cementation of rocks. It also causes the change in seismic velocities in the Earth’s crust.