Constraints on compaction rate and equilibrium in the pressure solution creep of quartz aggregates and fractures: Controls of aqueous concentration

A relationship is developed to examine dissolution precipitation creep in crustal rocks with implicit coupling of the dissolution-diffusion-precipitation system and without requiring the iterative solution of a linear equation system. Implicit control is maintained over aqueous silica concentrations within hydrated solid contacts and in open pore space. For arbitrary conditions of temperature, pressure, and mechanical stress, the simple equation system conforms to a polynomial solution for aqueous concentrations set within a small iterative compaction scheme. Equilibrium (long-term) pressure solution compaction, previously ill constrained, is explored with two alternate methods: (1) a modified form of critical stress and (2) rate-controlled growth of diffusion limiting cement at the periphery of solid contacts. Predictions are compared to previous experimental results that allow compaction equilibrium to be achieved. Only the modified critical stress is capable of reproducing these results. In this case the agreement is strong across a range of conditions (400 degrees C-500 degrees C, 20-150 MPa, and 3-120 mu m mean particle diameter). Compaction rates are overestimated in very early times in a manner suggesting the importance of plastic flow during this period. Predictions are also compared to concentration independent simplifications at general conditions of 350 degrees C and 50 MPa. Compared to the implicit coupling, these methods represent the mean behavior, slightly underestimating rates in dissolution control and slightly overestimating in diffusion control. Aqueous concentration is influential in either regime. The solution is applicable to open and closed systems, is extended to systems with boundary influx, and may be applied to granular media or fractures, differing only in the method defining evolving contact geometry.