Kinematics of ductile shear zones with deformable or mobile walls

Shear zones are important phenomena in the Earth’s middle and lower crust and are of great interest to structural geologists. Models involving rigid boundaries moving parallel to themselves are extended here to include the case where (i) walls are deformable and (ii) mobile rigid walls approach each other. These models are combined with Couette and Poiseuille flow to define a broad range of kinematic possibilities. Deformable wall models lead to smooth transitions from deformed to undeformed materials as well as with the zone transitions to gentler and more spread out deformation. Mobile walls, on the other hand, lead to shear zones where shear sense can change along a shear zone boundary.