The convection in the Earth's mantle was analyzed within the framework of model of thermal convection of non-uniform highly viscous fluid, with Rayleigh numbers in a range of 10⁵ - 10⁷. The role of low-density impurity was investigated. The following mechanism was considered: lowdensity substance is introduced from below as a result of processes in the liquid core of the Earth and then the light fraction is moving upward driven by buoyancy forces thus disturbing thermal convection flow. It was analyzed how penetration of the light fraction into bottom of the mantle and its upward moving to the outer surface of the mantle changes the thermal convection pattern. Numerical simulation demonstrates that thermal convection in the presence of light component may follow on three possible scenarios: Low-density impurity is floating up and forming a thin layer on the mantle surface. The impurity is moving down driven by thermal convection flow. An intermediate scenario when the floating up substance is separated into two domains with their further fixing by the cells of convection.

Mathematical modelling in actual problems of science and technics