HR: 09:00h
AN: T21D-05    [Abstracts]
TI: Roles of Small-scale Convection, Crustal Heating, and Basal Motions in the Evolution of the Subcratonic Lithosphere
AU: * Zaranek, S E
EM:
AF: Brown University, Department of Geological Sciences, Box 1846, Providence, RI 02912 United States
AU: Parmentier, E
EM:
AF: Brown University, Department of Geological Sciences, Box 1846, Providence, RI 02912 United States
AU: Fischer, K M
EM:
AF: Brown University, Department of Geological Sciences, Box 1846, Providence, RI 02912 United States
AB: Using flux balance calculations and numerical evolution models, we address the influence of small-scale convection, crustal radioactive heating, and basal erosion and ablation on the evolution of the subcratonic lithosphere. Rather than modeling the formation of subcratonic lithosphere, our goal is to determine the relative importance of the various mechanisms that have been suggested to destabilize continental keels and to evaluate, more explicitly than previous studies, the effects that different rheological and compositional properties have on these mechanisms. Using 1D parameterized flux models consistent with previous numerical and laboratory fluid experiments, we explore the impact of viscosity beneath the keel (μ_R), activation energy and volume, and rate of crustal heating on the evolution of lithospheres. The μ_R needed to maintain a 100 km oceanic lithosphere or a 200-300 km thick continental lithosphere is reasonable when compared to the estimated viscosities for either diffusion or dislocation creep. Only the strong pressure-dependence of dislocation creep allows two equilibrium thermal thicknesses for the same μ_R. An unreasonable rate of crustal heating is necessary to allow the subcratonic lithosphere thicknesses to be determined by a purely conductive cooling. 2D numerical experiments are used to understand the effect that basal motions have on the thermal evolution of the lithosphere and the development and ability of edge-driven convection to erode the lithosphere. These 2D models indicate that, for reasonable values of plate velocities and activation energies, temperature structure in the middle of the keel is not significantly altered by the ablation or erosion of underlying motions of plate-driven flow. In the presence of edge-driven convection, plate motions actually decrease the rate of erosion. A limited range of 3D experiments are examined to understand the influence of assuming a 2D geometry.
DE: 8103 Continental cratons
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8125 Evolution of the Earth (0325)
SC: Tectonophysics [T]
MN: Fall Meeting 2005