Search

A finite amplitude, numerical model of convective motions through a phase boundary is studied. The phase change is assumed to occur over a finite vertical transition zone in the fluid and thus a continuously stratified model is considered. The motions are driven by horizontal temperature gradients on the boundaries or super-critical vertical stratification. In the case of Rayleigh instability, the numerical results reproduce the neutral curve previously obtained in the analytic solution of the linearized problem. When the parameters of the problem are chosen to simulate the olivine-spinel transition in the upper mantle, the following results are obtained: (1) the vertical scale of motion is the entire depth of the fluid; (2) the horizontal scale is not significantly changed from the case of a single phase fluid; (3) the amplitude of the motion is not significantly changed, due to buoyancy changes at the phase boundary being offset by corresponding sources and sinks of latent heat; and (4) the phase boundary varies in depth by as much as 30 km when the vertical velocities are of the order of 10−1 cm yr−1.