HR: 14:10h
AN: T32C-03    [PDF]
TI: Conversion of Poloidal Energy in the Mantle to Toroidal Motions of Surface Plates - A Numerical Investigation
AU: * Dong, F
EM: feidong@uiuc.edu
AF: Department of Theoretical and Applied Mechanics, 216 Talbot Lab University of Illinois, Urbana, IL 61801 United States
AU: Hsui, A T
EM: hsui@uiuc.edu
AF: Department of Geology, 245 NHB University of Illinois, Urbana, IL 61801 United States
AU: Riahi, D N
EM: d-riahi@uiuc.edu
AF: Department of Theoretical and Applied Mechanics, 216 Talbot Lab University of Illinois, Urbana, IL 61801 United States
AB: Equal partition of poloidal and toroidal energies of surface plates has been reported by many investigators. It has also been pointed out that convection within a constant viscosity mantle is unable to produce toroidal motions at the surface. Thus, surface plate rotation remains a problem of considerable interests in the theory of plate tectonics. Several investigators have suggested subsequently that lateral viscosity variations can excite toroidal motions. Because mantle viscosity is strongly temperature-dependent and lateral temperature variation is the main driving mechanism of mantle dynamics, a source to produce toroidal energies appears readily available in the mantle. Unfortunately, numerical simulations of convection with strong temperature-dependent viscosity show that the amount of toroidal energy produced can only reach about 20% of the poloidal energy using a viscosity contrast of 5 orders of magnitude. Simulations with greater viscosity contrasts are computationally difficult at present. Here, instead of treating the mantle and the lithosphere as a single system, we decide to model the lithosphere as a rigid lid resting on a dynamic mantle. We seek to study the interactions between a circular solid top and a cylindrical impinging plume. In addition, we also wish to examine the effects of a solid lid with bottom topographic variations to the generation of rotational motions at the surface. Our results indicate that rotational torques of a rigid lid is dependent on the separation between the center of mass of the lid and the stagnation point of the impinging plume. If a plume impinges at the center of mass of a rigid lid and if the lid possesses a plane of symmetry that goes through its center of mass, no net torque is produced. Thus, as long as up-welling and down-going currents of the mantle occur away from the center of mass of a surface plate, net torques can be realized to produce plate rotation and show toroidal motions at the surface.
DE: 3210 Modeling
DE: 3230 Numerical solutions
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8155 Plate motions--general
SC: Tectonophysics [T]
MN: 2003 Fall Meeting