Convection and Crystallization in Magma Chambers

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The crust-magma interface in basaltic lava lakes occurs at a crystallinity of about 55%, which marks the transition from rigid, albeit partially molten, crust to viscous magmatic suspension. Most of the original temperature contrast between the magma and its enclosure occurs within this crust with the remainder occurring within a few meters of the advancing solidification front (i.e. crust/magma interface). The potential bouyancy available for large scale convection is thus limited by this reduced temperature contrast and length scale. The ensuing Rayleigh number is about 1010 times smaller than previously thought. The overall style of convection is not one of turbulence. The PI will investigate the dynamic and petrologic evolution of a sheet-like magmatic body cooling from either only the top or from both the top and bottom. The overall theme extends present and previous investigations by B. Marsh, G. Brandeis, and C. Jaupart. The critical issue of investigation is the dynamic interplay between crystallization attending advancement of the crust-magma interface and small scale convection in the suspension zone, just inward of the advancing crust.