Abstract: Plate subduction is an important part of plate tectonic theory. Although there have been many numerical simulations of single-slab subduction, the mechanism of multi-plate interactions is still unclear and needs further study. In this paper, a two-dimensional geodynamic numerical model is established to study the dynamics of double-slab subduction with inward dipping and to explore the influence of subducting plate viscosity on the coupling interaction of multiple plates. The simulation results show that the difference in viscosity of the left and right subducting plates leads to the difference in the subduction velocity of the plates. The subducting plate with small viscosity sinks faster, enters the lower mantle first, folds periodically and stacks in the lower mantle. The subducting plate with high viscosity enters the lower mantle afterwards. It is obstructed by the mantle circulation with slab tip rollover and slips backward in the lower mantle. The difference in subduction speed and morphology between the left and right slabs also causes the overlying slab to move toward the side of the less viscous subducting plate, causing this side of the trench to retreat and the other side to advance. The results of this paper provide a dynamical explanation for the evolution of the complex tectonics in the Southeast Asian region. The India-Australia plate and the Pacific plate in the Southeast Asia region subducted in opposite directions, and the two plates interacted with each other to form a complex convergent subduction system, which caused the mantle upwelling and probably the origin of the Cenozoic magmatic rocks in the S outh China Sea region.

Key words: plate tectonics, double-slab Subduction with inward-dipping directions, plate viscosity, numerical simulation