Complex flow structures in strongly chaotic time-dependent mantle convection

Large-scale numerical simulations of two-dimensional thermal convection have been conducted in the strong time-dependent regime for infinite Prandtl number fluids, as applied to the Earth's mantle. Both Newtonian and non-Newtonian (strain-rate proportional to the third power of the deviatoric stress) rheologies have been studied. Non-Newtonian plumes behave quite differently from Newtonian ones in that noticeable curvatures are developed in their ascent. The transition to the disconnected-plume regime take place at much lower Nusselt numbers for non-Newtonian rheology. For the Earth's mantle this would have strong implications, as the upper-mantle rheology is probably non-Newtonian. At high Rayleigh number, greater than 10⁷, convection with a single olivine to spinel phase transition becomes intermittently layered the effects of depth-dependent thermal expansivity and internal-heating are to increase the propensity toward layering. In an early Earth with a hotter temperature and greater amounts of radiogenic heating, mantle convection would have a greater tendency for layering. -from Authors