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

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