Rheology of Rocks

1.1. Strategy and Techniques For a rock of given mineralogy and microstructure, the variables important in determining strength are pressure, temperature, strain, strain history, strain rate, pore fluid pressure, grain size, fugacities of water and other volatiles, and chemical activities of the mineral components. Although earth scientists may now duplicate pressures and temperatures appropriate to the mantle and core in modern high pressure apparatus, they still cannot study mechanical properties under truly natural conditions. Time scales in the Earth are too long, and length scales too large. Since exact deformation conditions cannot be duplicated in the laboratory, the experimenter’s strategy must involve determining the kinetic parameters of the appropriate processes at laboratory conditions and extrapolating to much lower strain rates [58]. Two convenient techniques are available to aid laboratory studies. Temperature and, hence, kinetic rates may be increased, or processes may be studied at smaller length scales [60]. Testing at high temperatures also imposes constraints. For example, maintaining chemical and phase stability and