THEORETICAL CONSIDERATIONS OF SHEAR DEFORMATION IN ROCKS,

Strength of rock material depends on pressure, temperature, rate and duration of stress application, type of stress, solutions, anisotropy, past strain history, crystal perfection and composition. Failure of materials at high temperatures and pressures occurs by uniform flow, which involves the four distinct mechanisms of translation gliding, twin gliding, recrystallization and cataclasis. Increases in temperature, pressure and the presence of solutions favor translation gliding, twin gliding and recrystallization, whereas low temperatures and pressures favor cataclasis. The AFCRL experimental rock deformation program yields data on the behavior of rock materials of lower crust-upper mantle composition under geophysically realistic conditions of high pressure and temperature. Experimental variables, temperature, pressure and rate of strain, are derived from calibration equations based on observable physical variables. Mechanical behavior of the samples adduces in terms of two physical models the Coulomb-Navier substance expressing brittle behavior and the Bingham substance expressing ductile behavior. The nature of failure in shear experiments yields information on the origin of deep earthquakes, and the catalytic effect of shearing stresses may induce new high pressure polymorphs. Author