HR: 0800h
AN: U11A-0013    [Abstracts]
TI: Evolution of Plate Tectonics From Hadean to the Modern Geodynamic Regime According to 3D Spherical Models With Self-Consistently Generated Plates
AU: * van Heck, H
EM: hvanheck@erdw.ethz.ch
AF: ETH Zurich, Schafmattstrasse 30, Zurich, 8093, Switzerland
AU: Tackley, P
EM: ptackley@ethz.ch
AF: ETH Zurich, Schafmattstrasse 30, Zurich, 8093, Switzerland
AB: It has been proposed that the plate tectonic style has changed from the Hadean to the modern geodynamic regime. In the past decade, several studies have documented the effectiveness of plastic yielding in causing a basic approximation of plate tectonic behavior in mantle convection models with strongly temperature dependent viscosity, strong enough to form a rigid lid in the absence of yielding. The vast majority of such research to date has been in either two-dimensional, or three-dimensional cartesian geometry. In our recently-presented study, the planforms of self consistent tectonic plates in three-dimensional spherical geometry were calculated and compared to the outcome of similar calculations in which a three dimensional cartesian geometry was used, as in Tackley (2000). Several diagnostics are used to analyze how successful each model is in producing tectonic plates. In general, the observed structures in spherical geometry are consistent with the structures observed in cartesian geometry, but two previously unobserved planforms are found. At low lithospheric yield stresses one great circle downwelling formed, with fragmented oceanic plates at both hemispheres. At intermediate yield stresses two hemispherical plates formed, separated by a spreading centre and a downwelling. Here, new calculations are presented that study the evolution of the tectonic mode and planforms in time as the Earth cools, by decreasing the internal heating rate with time according to the decay of K, U and Th and by decreasing the temperature at the CMB according to a parameterized core model. The influences of these two effects are separated by comparing to calculations where the heat flux across the CMB is set to zero. We study the proposed transitions in tectonic mode (e.g. changes in plate size, rigid lid convection to tectonic plates, smoothly evolving plates to more episodic, time dependent, tectonics) as a function of yield stress envelope. The results are compared to analytical scalings for boundary regimes as well as scalings for heat flux.
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 5475 Tectonics (8149)
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Union [U]
MN: 2007 Fall Meeting