Lower-mantle material properties and convection models of multiscale plumes

We present the results of numerical mantle convection models demonstrating that dynamical effects induced by variable mantle viscosity, depth-dependent thermal expansivity, radiative thermal conductivity at the base of the mantle, the spinel to perov-skite phase change and the perovskite to post-perovskite phase transition in the deep mantle can result in multiscale mantle plumes: stable lower-mantle superplumes are followed by groups of small upper-mantle plumes. Both radiative thermal conductivity at the base of the lower mantle and a strongly decreasing thermal expansivity of perovskite in the lower mantle can help induce partially layered convection with intense shear heating under the transition zone, which creates a low-viscosity zone and allows for the production of secondary mantle plumes emanating from this zone. Large-scale upwellings in the lower mantle, which are induced mainly by both the style of lower-mantle viscosity stratification and decrease of thermal expansivity, control position of central upper- mantle plumes of each group as well as the upper-mantle plume-plume interactions.