KINETICS OF PRESSURE SOLUTION CREEP IN QUARTZ - THEORETICAL CONSIDERATIONS

The kinetics of pressure solution creep are formulated using chemical potentials generalized to nonhydrostatic states. Solving a coupling equation of diffusion and reaction on a spherical quartz grain with diameter d and grain boundary width w, the flow law of pressure solution creep is derived. As extreme cases, the flow law becomes: epsilon = (alpha upsilon(SiO2)(2) KDw)(upsilon(H2O)RTd(3))(-1)sigma for the diffusion-controlled case and becomes: epsilon = (beta upsilon(SiO2)(2)K(+))(upsilon(H2O)RTd)(-1)sigma for the reaction-controlled case, where epsilon is strain rate, sigma is deviatoric stress, upsilon is the molar volume, D is the diffusion coefficient through a wet grain boundary, K is the equilibrium constant, k(+) is the rate constant of dissolution, R is the gas constant, T is temperature, and alpha and beta are shape factors. Using the reaction constants determined by Rimstidt and Barnes (1980) and the grain boundary diffusion coefficients estimated by Nakashima (1995), the strain rate of pressure solution creep in metamorphic conditions for quartzose rocks is estimated as 10(-9 similar to 13), 10(-8 similar to 11), and 10(-7 similar to 11) s(-1) at 150, 250, and 350 degrees C, respectively. These values, compared with the duration of regional metamorphism, suggest rapid pressure solution and dewatering in subduction zones followed by fluid-absent metamorphism.