Theoretical strain patterns in ductile zones simultaneously undergoing heterogeneous simple shear and bulk shortening

Structures observed in ductile shear zones show that deformation is continuous and strain is heterogeneous. This leads us to define a simple model for shear strain rate γ. When a shear zone simultaneously undergoes simple shearing and pure shearing (contraction or extension), the condition of continuity of deformation shows that γ must be a function of time. Integration of the deformation-rate equations yields the particle paths in the deforming body. From these we can determine, at any time and at any point in the body, the finite strain tensor (lengths and orientations of the axes of the finite strain ellipsoid); we can therefore define the finite strain trajectories and compare them with orientations of internal structures (schistosity, tension gashes). The particle paths also allow us to study the progressive deformation of passive strain markers.