Effects of interfacial energy on compaction creep by intergranular pressure solution: Theory versus experiments on a rock analog (NaNO3)

Abstract

Pressure solution plays an important role in compaction and lithification of sediments and fault gouges, but the effects of interfacial energy on this process are generally neglected. Here, microphysical models for densification of solid/liquid systems by pressure solution are derived, accounting for interfacial energy besides stress‐related driving forces. They predict that densification by pressure solution creep will slow down at very fine grain sizes, where opposing interfacial energy driving forces become important compared to applied stress, and will come to a halt below a certain “yield” stress. To test the models, uniaxial compaction creep experiments were performed at ambient conditions on granular NaNO3 aggregates (d = 8–250 μm, σeff = 0.0062–4.9 MPa). Though no significant creep occurred in dry or oil‐flooded material, rapid, grain‐size sensitive creep occurred in the presence of saturated NaNO3 solution. At high effective stresses (σeff > 0.025 MPa), wet‐compacted, coarser‐grained (d > 20 μm) samples showed compaction behavior roughly consistent with diffusion‐controlled pressure solution involving negligible interfacial energy effects. Creep rates in this regime imply an effective grain boundary diffusivity product of 5.7 × 10−19 m3/s. At low effective stress (σeff < 0.025 MPa), finer‐grained samples (d < 20 μm) showed a decrease in strain rate with decreasing grain size, reflecting a growing influence of interfacial energy‐related driving forces. This demonstrates a yield stress effect, broadly consistent with the predictions of the models incorporating interfacial energy and imply that compaction by pressure solution can be strongly inhibited in very fine‐grained materials, such as nanogouge in seismogenic faults.