THE POTENTIAL INFLUENCE OF RADIATIVE HEAT-TRANSFER ON THE FORMATION OF MEGAPLUMES IN THE LOWER MANTLE

Recent seismic tomographic models have revealed broad, low-velocity an omalies in the lower mantle beneath Africa and the central Pacific whi ch suggest a break in the symmetry between hot and cold regions in low er mantle dynamics. We have considered the possible impact from radiat ive heat transfer, which can be described by a nonlinear temperature-d ependent coefficient in the thermal conductivity, in 2D numerical simu lations. Results for Rayleigh numbers up to 10(6) show a strong stabil izing influence from radiative heat transfer on mantle upwellings and the production of extremely hot thermal anomalies in the interior. Thi s nonlinearity is responsible for producing a strong attractor in the mantle convective system, which greatly simplifies its time-dependent dynamics. The possible link of the simplified lower mantle time-depend ent dynamics with polar wander is discussed. The main point here is th at slow time dependence of the huge anomalies in the lower mantle can be the main mechanism controlling long-term rotational dynamics.