2-PHASE NATURAL-CONVECTION - IMPLICATIONS FOR CRYSTAL SETTLING IN MAGMA CHAMBERS

Crystal settling is no longer thought to be the most likely mechanism operating in the formation of layered igneous intrusions. The main objection raised against its feasibility is the prediction that crystal settling velocities are likely to be orders of magnitude smaller than convective velocities, and that vigorous convection would therefore keep crystals well mixed within the interior of a magma chamber. In previous theoretical and numerical investigations of crystal settling, no account has been taken of compositional buoyancy gradients created by the interpenetration of crystals and melt. This paper includes these effects. The results of two-dimensional numerical simulations show that parameter regimes exist in which effective crystal settling occurs in infinite Prandtl number, thermally convecting, two-phase fluids even for small ratios of settling to convective velocity.