Enhanced pressure solution creep rates induced by clay particles: Experimental evidence in salt aggregates

Pressure solution is responsible for mechano-chemical compaction of sediments in the upper crust (2-10 km). This process also controls porosity variations in a fault gouge after an earthquake. We present experimental results from chemical compaction of aggregates of halite mixed with clays. It is shown that clay particles (1-5 micron) greatly enhance the deformation by pressure solution in salt aggregates (100-200 micron), the strain rates being 50 % to 200 % faster in samples containing 10 % clays than for clay-free samples. Even the presence of 1 % clay increases the strain rate significantly. We propose that clay particles enhance pressure solution creep because these microscopic minerals are trapped within the salt particle contacts where they allow faster diffusion of solutes from the particle contacts to the pore space and inhibit grain boundary formation.