Shear Zones: Kinematic Analysis

One class of kinematic criteria for ductile shear zones is based on mechanical heterogeneities introduced by minerals and mineral clasts more resistant than the enclosing matrix. Upon shearing, zones of pressure shadows and zones of pressure concentration develop around these clasts. As fluids and their solutes migrate from high pressure to low pressure zones, crystallisations develop in pressure shadows. The asymmetry of pressure shadows around a clast with respect to the shear plane depends on the sense of shear and as such can be used as kinematic criteria. On the top right sketch pressure shadows develop as a clast is dissolved. The rate of dissolution is faster for a sigma pressure shadows than for a delta pressure shadows.