THE ROLE OF SILICA PRECIPITATION KINETICS IN DETERMINING THE RATE OF QUARTZ PRESSURE SOLUTION

Traditionally, models of intergranular pressure solution have assumed that grain boundary diffusion, probably through an absorbed water layer, is the rate-limiting process (Weyl, 1959; Rutter, 1976). However, observations by Heald (1956, 1965) and experiments by Cecil and Heald (1971) show that the presence of clays may strongly inhibit the growth of secondary quartz. Under these circumstances, silica precipitation kinetics may also be important in determining the pressure solution rate. A model of quartz pressure solution including the rate of silica precipitation kinetics is developed, and strain rate equations are derived for a compacting sediment. Laboratory data for the precipitation constant k}, for quartz, indicate that precipitation kinetics should not be important in determining the rate of pressure solution in clean quartz sand. However, an estimate of the in situ value of k} for the Dogger Beta formation, made from the data of Fuchtbauer (1983), suggest's that in a geological setting, k} may be much smaller than under laboratory conditions. In consequence, it is asserted that silica precipitation kinetics may influence the rate of quartz pressure solution when secondary quartz growth is inhibited.