A kinematic model for deformation within brittle shear zones

Textural analysis of fault gouge indicates that displacement of particles within brittle shear zones occurs by three different modes: synthetic Riedel shears, antithetic Riedel shears, and shearing particulate flow. A kinematic model is developed which incorporates these three slip modes and constrains the combined deformation to be simple shear parallel to the shear zone boundaries. Penetrative fabric (P-foliation and shape preferred orientation of survivor grains) commonly observed in foliated fault gouge is assumed to be a result of the shearing particulate flow only. The model, which relates penetrative fabric orientation to the relative shear rates on Riedel shears and shearing particulate flow, reconciles inclined P-foliation and high (γ>10) shear strain.