Deformation-enhanced fluid distribution in feldspar aggregates and implications for ductile shear zones

Experiments at 900 °C and 1.4 GPa show that the distribution of aqueous fluid in fine-grained feldspar aggregates changes from isolated pores under hydrostatic conditions to mostly wetted grain boundaries during deformation; the isolated pore distribution is rapidly regained during annealing following deformation. The deformation-enhanced fluid distribution causes a switch from dislocation creep to diffusion creep accompanied by a significant decrease in strength; it also increases the bulk transport rate through the aggregate by more than an order of magnitude. A change in fluid distribution is not observed in fine-grained quartz aggregates deformed at similar conditions. If deformation-enhanced fluid distribution occurs in naturally deformed feldspathic rocks, it could help to explain the localization of strain and enhancement of bulk transport in ductile shear zones.