A mechanistic model for compaction of granular aggregates moderated by pressure solution

Abstract

A model is presented for the compaction of granular aggregates that accommodates the serial processes of grain‐contact dissolution, grain‐boundary diffusion, and precipitation at the pore wall. The progress of compaction and the evolution of the mass concentration of the pore fluids may be followed with time, for arbitrary mean stress, fluid pressure, and temperature conditions, for hydraulically open or closed systems, and accommodating arbitrary switching in dominant processes, from dissolution, to diffusion, to precipitation. Hindcast comparisons for compaction of quartz sands [ Elias and Hajash , 1992 ] show excellent agreement for rates of change of porosity, the asymptotic long‐term porosity, and for the development of silica concentrations in the pore fluid with time. Predictions may be extended to hydraulically open systems where flushing by meteoric fluids affects the compaction response. For basins at depths to a few kilometers, at effective stresses of 35 MPa, and temperatures in the range 75°–300°C, rates of porosity reduction and ultimate magnitudes of porosity reduction increase with increased temperature. Ultimate porosities asymptote to the order of 15% (300°C) to 25% (75°C) at the completion of dissolution‐mediated compaction and durations are accelerated from a few centuries to a fraction of a year as the temperature is increased. Where the system is hydraulically open, flushing elevates the final porosity, has little effect on evolving strain in these precipitation‐controlled systems, and depresses pore fluid concentrations. These effects are greatest at lower temperatures.