HR: 13:40h
AN: T32C-01    [PDF]
TI: Effects of Model Geometry on the Dynamics of Mantle Plumes
AU: * Zhong, S
EM: szhong@anquetil.colorado.edu
AF: University of Colorado, Dept. of Physics, Boulder, CO 80309 United States
AB: Mantle upwelling plumes are derived from thermal boundary layer instabilities at the bottom boundary of convective mantle. They play an important role in cooling the core and producing hot-spot volcanism. Most previous studies of plume dynamics have employed either 2D or 3D Cartesian models. In this study, we formulated models in Cartesian and spherical geometries to investigate the effects of model geometry on the plume dynamics. For each type of models, we explored a large parameter space of Rayleigh number and temperature-dependent viscosity. From the modeling, we determined scalings for the number and radius of plumes and spacing between plumes. We also determined the heat transferred through upwelling plumes or plume buoyancy flux. We found that plume dynamics are sensitive to model geometry. In 2D Cartesian models, the sensitivity of the number of plumes to Rayleigh number appears different from that in 3D models. This is mainly because that in the 2D models, upwelling plumes have a sheet-like structure, while they display quasi-cylindrical structure in the 3D models. For the same Rayleigh number, upwelling plumes are more vigorous in 3D spherical models than in 3D Cartesian models. This results from the fact that with different surface areas between the top and bottom boundaries in spherical models, the temperature difference across the bottom thermal boundary layer in spherical models needs to be significantly larger than that across the top thermal boundary layer and that in Cartesian models, leading to more unstable bottom thermal boundary layer in the spherical models. As a result, upwelling plumes in spherical models transfer a significantly larger fraction of the core-mantle heat flux than those in Cartesian models do.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8160 Rheology--general
SC: Tectonophysics [T]
MN: 2003 Fall Meeting