CHAOTIC, SUBDUCTION-LIKE DOWNFLOWS IN A SPHERICAL MODEL OF CONVECTION IN THE EARTHS MANTLE

NUMERICAL models of three-dimensional, nonlinear, thermal convection of very viscous fluids have recently been developed in rectangular1-4 and spherical5-12 geometries as analogues of convection in the Earth's mantle. Here we describe model calculations for a compressible fluid in a three-dimensional spherical shell with 80% of the surface heat flow generated within the model mantle, in agreement with estimates for the Earth's mantle13. The Rayleigh number and the numerical resolution for these calculations are greater than those of our previous studies9,10 of internally heated convection in a spherical shell. Our numerical solutions are strongly chaotic, with surface planforms dominated by long curvilinear downflows reminiscent of the descending slabs in the Earth's mantle. Although analogy to the Earth's mantle is necessarily imperfect, owing to, for example, the absence of variable viscosity and rheology - and hence of lithospheric plates - our results suggest that descending slabs play an important part in driving mantle convection, and that their chaotic evolution may influence the spatial and temporal behaviour of plates and thus the dispersal and aggregation of continents. © 1990 Nature Publishing Group.