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 exhumation 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 subduction, 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 subducted 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 differential modes of continental subduction, collision and exhumation in the same continental convergence belt.