HR: 1340h
AN: V43A-1109    [Abstracts]
TI: Modeling of Convection Driven "Weather" Patterns in Bushveld Type Magma Chambers via Computational Fluid Dynamics
AU: * Rice, A
EM: arice@amnh.org
AF: Dept of Earth and Planetary Sciences, American Museum of Natural History, 79th St and Central Park West, New York, NY 10024, United States
AB: Well established and well benchmarked multi-physics finite element codes which are commercially available (e.g., ANSYS, Inc) for modeling (amongst things) fluid flow are proving extremely useful in their application to problems in earth sciences. These codes incorporate the following physical processes: variable viscosity, phase change (e.g., freezing, melting), the impact of latent heat, assimilation, transport of suspended crystal load, porous media flow, chemical evolution, etc. These codes have seen extensive and successful application to fluid environments more complicated than or even similar to magmatic melts and have allowed 3D modeling… with much of their complexity… of the convective cooling and freezing history of magma chambers simulating the Bushveld Complex. Although constrained by much greater viscosities to appropriately diminished velocities, these models yield analogs similar to patterns seen in lakes, oceans and atmospheres: e.g., stratifications, currents, vortices, formation of clouds of crystals, precipitation, etc. The viscosities employed in the Bushveld models are taken to be strongly dependent on temperature (this implicitly includes particulate content and evolving chemistry, etc), increasing over eleven orders of magnitude during cooling. The initial stages of cooling are typified by highly turbulent flow which rapidly settles into more orderly and symmetric forms as the magma cools and "sets" on reaching approximately 65% crystal content. The inclusion of suspended load leads to the build up of stratifications within the model, the lowest in the chamber of primitive composition and the highest (i.e., at the top) of the most evolved composition. This is a natural consequence of the components of highest melting point crystallizing out first, followed by material of lower melting point, etc. Similar to ice crystals gathering along the boundaries of stratified layers in the atmosphere to form thin clouds, primocrysts will be driven by dispersive pressure into the shear zones that define the boundaries between stratifications. The final architecture of the chamber appears to be established quite early and then settles down to simmer and eventually stew in its own juices and any others that may flow in afterwards from surrounding country rock. These models replicate much of the features of the Bushveld Complex. This includes layering. Appeal to well known engineering derived relationships and established research in other disciplines dealing with stratification and layering in fluids supports the numerical inferences.
DE: 0545 Modeling (4255)
DE: 3299 General or miscellaneous
DE: 5480 Volcanism (6063, 8148, 8450)
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting