Tectonic evolution of convergent plate margins and its geological effects

Oceanic lithosphere is generated at divergent plate boundaries and disappears at convergent plate boundaries. Seafloor spreading and plate subduction together constitute the physical coupling and mass conservation relationships to the movement of lithospheres on Earth. Subduction zones are a key site for the transfer of both matter and energy at converging plate boundaries, and their study has been the hot spot and frontier of Earth system science since the development of plate tectonics theory. As far as the dynamic regime and geothermal gradient of convergent plate margins are concerned, they have different properties in different stages of the subduction zone evolution. In general, the early low-angle subduction leads to compressional tectonism dominated by low geothermal gradients at the plate interface, and the late high-angle subduction results in extensional tectonism dominated by high geothermal gradients at the plate interface and its hanging wall. Active rifts are produced along suture zones through not only slab rollback or slab breakoff in the terminal stage of oceanic subduction but also foundering and thinning of the lithosphere in the post-subduction stage. Due to the differences and changes in the geometric and thermobaric structures of convergent plate margins, a series of changes in the type of metamorphism and magmatism can occur in active and fossil subduction zones. Dehydration and melting of the subducting oceanic crust are prominent at subarc depths, giving rise to fluids that dissolve different concentrations of fluid-mobile incompatible elements. The subduction zone fluids at subarc depths would chemically react with the overlying mantle wedge peridotite, generating metasomatites as the mantle sources of mafic magmas in oceanic and continental arcs. However, these metasomatites did not partially melt immediately upon the fluid metasomatism to trigger arc magmatism, and they did not melt until they were heated by asthenospheric convection due to rollback of the subducting slab. Therefore, recognition of the changes in the dynamic regime and geothermal gradient of subduction zones in different stages of plate convergence not only provides insights into geodynamic mechanisms of the tectonic evolution from subduction zones to orogenic belts, but also places constraints on the formation and evolution of different types of metamorphic and magmatic rocks within the advanced framework of plate tectonics.