PROBLEMS OF NUMERICAL MODELING OF LARGE-SCALE MANTLE CONVECTION IN THE SUBDUCTION ZONE

The article provides a review of modern models of large-scale mantle convection in the zone of a heavy cold oceanic plate (slab) subduction into the upper mantle. The formal approximation of the upper mantle for the present case is an incompressible Newtonian fluid with variable viscosity. It is assumed that the plate subduction is preceded by the stage of regime formation for thermo-gravitational convection in the mantle, which is caused by temperature and buoyancy of the lightweight hot substance. Important in this situation is the problem of quantitative formal modeling of phase transitions in the plate itself, as a result of which it becomes compacted due to thermal compression, removal of a part of lightweight mobile components of its original sediments and, consequently, overall weighting of the residual components of its material. It is also important to take into account the impact of mantle currents on the plate, which leads to its geometric distortion. Emphasis should also be placed on representing this plate/slab as an object of numerical modeling, since in the case of its representation as a thin elastic plate, adopted by Gustav Kirchhoff, the current hypotheses of normal remaining normal to the deformed middle surface of the plate and an unchanging thickness are violated. The aim of the work is to construct a large-scale 2D numerical model of mantle convection in the subduction zone, which takes into account the thermal gravity regime for the upper mantle and the plate, initiated by plate subduction, the influence thereon of mantle flows (mantle wind), and phase transitions in the plate. Based on smoothed particles hydrodynamics (SPH), there was constructed a computational scheme of the slab dynamics. To verify the model, there have been performed a number of computational experiments, the results of which are generally consistent with the seismotomographically identified structure of mantle flows in the subduction zone. Thus, the model appears to show fragmentary nature of the process of subduction being due to the interaction between the subducting plate and the part that remains on the surface, which leads to deformation of the descending plate.