Current situation of research on the simulating experiments on the shear direction of asymmetry rotated porphyroclast in the ductile shear zone of mylonites. Geological Bulletin of China

Ductile shear zone is an important structural trace during the continental deformation process in deep-seated crust, it is an important research object for the reconstruction of the P-T condition, deformation geometry, kinematics and dynamics of the structural deformation. The shear direction is the most important and fundamental basis for the ductile shear zone research. Although, there are many indicators, because of the complexity of the deformation process, it is always difficult to define the shear direction, sometimes incompatible shear direction indicators can be observed within the same ductile shear zone. Asymmetry rotated porphyroclast system is considered as the most credible indicators to indicate the shear direction. In comparison with “mica-fish” and “domino” structure, porphyroclast system with tails is more dependable for shear direction recognition. Theoretical and simulating experiments have proved that evolution of porphyroclasts are influenced by various factors including shape, axis rate, initial orientation, matrix, viscosity of the particle/matrix interface, kinematic vorticity, intensity of shear strain, shear zone thickness and shorter axis ratio. With the help of understanding of development process, restricted conditions, influence factors of porphyroclast systems within the ductile shear zone, structural direction can be defined as to further probe into its related continental dynamic features.