A review on the numerical geodynamic modeling of continental subduction, collision and exhumation

Continental subduction and collision normally follows oceanic subduction, with the remarkable event of formation and exhu- mation of high- to ultra-high-pressure （HP-UHP） metamorphic rocks. Based on the summary of numerical geodynamic models six modes of continental convergence have been identified： pure shear thickening, folding and buckling, one-sided steep sub- duction, flat subduction, two-sided subduction, and subducting slab break-off. In addition, the exhumation of HP-UHP rocks can be formulated into eight modes： thrust fault exhumation, buckling exhumation, material circulation, overpressure model, exhumation of a coherent crustal slice, episodic ductile extrusion, slab break-off induced eduction, and exhumation through fractured overriding lithosphere. During the transition from subduction to exhumation, the weakening and detachment of sub- ducted continental crust are prerequisites. However, the dominant weakening mechanisms and their roles in the subduction channel are poorly constrained. To a first degree approximation, the mechanism of continental subduction and exhumation can be treated as a subduction channel flow model, which incorporates the competing effects of downward Couette （subduction） flow and upward Poiseuille （exhumation） flow in the subduction channel. However, the （de-）hydration effect plays significant roles in the deformation of subduction channel and overriding lithosphere, which thereby result in very different modes from the simple subduction channel flow. Three-dimensionality is another important issue with highlighting the along-strike differ- ential modes of continental subduction, collision and exhumation in the same continental convergence belt.