HR: 15:25h
AN: T23E-08 INVITED    [Abstracts]
TI: The influence of lower mantle viscosity on plate velocity time-dependence in numerical mantle convection models
AU: * Lowman, J P
EM: lowman@utsc.utoronto.ca
AF: University of Toronto, Department of Physical and Environmental Sciences, 1265 Military Trail, Toronto, ON M1C 1A4, Canada
AU: Gait, A D
EM: A.Gait@earth.leeds.ac.uk
AF: University of Leeds, School of Earth and Environment, Woodhouse Lane, Leeds, LS2 9JT, United Kingdom
AU: Gable, C W
EM: gable@lanl.gov
AF: Los Alamos National Laboratory, Hydrology, Geochemistry and Geology Group (EES-6), Los Alamos, NM 87545, United States
AB: Plate boundary locations, and therefore plate dimensions,can change significantly over time periods that are relatively short compared to the mantle overturn time-scale. However, the influence of plate geometry evolution on mantle convection has not been widely studied in 3D convection models. We examine the effect of mobile plate boundaries on the time-dependence of the mean surface velocity, individual plate velocities and heat flow in models featuring different mantle viscosity profiles.. The three-dimensional Cartesian geometry models feature evolving plate geometries, high Rayleigh numbers, periodic boundary conditions, and multiple plates with dynamically determined motion. Plate motion is determined by specifying that each plate move rigidly with a velocity that results in a net shear stress of zero at the base of the thick, viscously defined, lithosphere. This condition ensures that the specified plate motion neither drives nor resists the buoyancy driven flow. The time-dependent plate velocities determine the evolution of the plate geometry. Plate boundaries evolve as triple junctions and are moved with a velocity that is equal to the average of the velocity of the three surrounding plates. In a 3×3×1 solution domain geometry, we compare the time-dependence of the convection obtained in cases where plate geometry is able to evolve, with cases where the geometry remains fixed. We investigate time-dependence in three distinct viscosity stratification models. We compare the time-dependence of the plate velocities and mantle heat flux in these calculations and examine the consistency of the results in a pair of larger geometry calculations (obtained with 6×6×1 Cartesian geometry solution domains featuring a minimum of 9 plates).We find that an evolving plate geometry results in more rapid and more dramatic variations in all global measures of the vigor of the convection. However, the presence of a high viscosity lower mantle dampens the time-dependence of the convection, even over periods in which the plate geometry evolves considerably.
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8125 Evolution of the Earth (0325)
DE: 8155 Plate motions: general (3040)
DE: 8162 Rheology: mantle (8033)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting