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 eq uation of diffusion and reaction on a spherical quartz grain with diam eter d and grain boundary width w, the flow law of pressure solution c reep is derived. As extreme cases, the flow law becomes: epsilon = (al pha upsilon(SiO2)(2) KDw)(upsilon(H2O)RTd(3))(-1)sigma for the diffusi on-controlled case and becomes: epsilon = (beta upsilon(SiO2)(2)K(+))( upsilon(H2O)RTd)(-1)sigma for the reaction-controlled case, where epsi lon is strain rate, sigma is deviatoric stress, upsilon is the molar v olume, 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 Barn es (1980) and the grain boundary diffusion coefficients estimated by N akashima (1995), the strain rate of pressure solution creep in metamor phic conditions for quartzose rocks is estimated as 10(-9 similar to 1 3), 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 durat ion of regional metamorphism, suggest rapid pressure solution and dewa tering in subduction zones followed by fluid-absent metamorphism.