Abstract:Tectonic pseudotachylyte is rare glassy or aphanitic rock, which often occurs in fault zones. It is considered as a fossil record of rapid sliding of paleo-earthquakes. Formation of pseudotachylyte can effectively reduce the friction strength of rock or fault. Therefore, the study of pseudotachylyte is of great significance to understand the fault deformation and seismic genetic mechanism in deep crust. Although many studies have carried on pseudotachylyte, due to the rare occurring of natural pseudotachylyte and its complexity formation process, there are still many disputes and key scientific problems to be solved such as the structural characteristics, formation environment, and genetic mechanism of pseudotachylyte. The pseudotachylyte can be developed in different depth ranges of continental lithosphere, that is, a ductile deformation domain dominated by mylonite in the middle to lower crust and even the upper mantle (> 60 km), or a brittle deformation domain dominated by cataclastic rock in the middle to upper crust (< 12 km). More evidence shows that the pseudotachylyte form in the brittle—ductile transition domain of the fault zone, which is directly related to shallow seismic activity. It also means that there is a more complex coupling relationship between the brittle deformation of the middle—upper crust and the plastic deformation of the middle—lower crust. There is a long debate on the formation mechanisms of pseudotachylyte, which is caused by friction heating on the fault plane or only the rock comminution on the fault plane. It is believed that the dry environment is conducive to the formation of pseudotachylyte. Because the existence of fluid will reduce the effective normal stress of fault plane, which is not conducive to the accumulation of heat and the progress of friction melting. However, another view is suggested that the presence of fluid can reduce the melting temperature of minerals, which is conducive to fault friction melting and the formation of pseudotachylyte. This paper summarizes the formation mechanism, formation depth, fluid influence, influence on fault strength after formation, and preservation and failure mechanism of pseudotachylyte. Then it further to discuss the origin of amorphous materials in pseudotachylyte, the deformation mechanism of rocks under brittle—ductile transition zone, and the influence on continental crust strength and significance of unsteady rheology.