HR: 10:35h
AN: S11G-02    [PDF]
TI: Stability of Subduction Zones in Numerical Models of Mantle Convection With Plate Tectonics
AU: * Quere, S
EM: squere@sca.uqam.ca
AF: Universite du Quebec A Montreal, Centre GEOTOP, C.P. 8888, Succ. Centre-Ville, Montreal, QC H3C 3P8 Canada
AU: * Quere, S
EM: squere@sca.uqam.ca
AF: Dept. of Earth Sciences, University of Western Ontario, London, ON N6A 5B7 Canada
AU: Forte, A
EM: forte.alessandro@uqam.ca
AF: Universite du Quebec A Montreal, Centre GEOTOP, C.P. 8888, Succ. Centre-Ville, Montreal, QC H3C 3P8 Canada
AU: Forte, A
EM: forte.alessandro@uqam.ca
AF: Dept. of Earth Sciences, University of Western Ontario, London, ON N6A 5B7 Canada
AB: During geological time, the Earth's surface has been marked by several cycles of opening-closing of oceans and collision-breakup of continents related to mantle dynamics and location of subduction zones.\\indent Here we present a 3-D spherical model of mantle convection which incorporates surface surface tectonic plates which are dynamically coupled to the buoyancy-driven mantle flow. The formalism used to take into account the plates is the same as the one used by Monnereau and Qu\'er\'e (2001). These time-dependent convection models reveal a cyclical re-organization of the subduction zones, alternating between two stable configurations. The principal input to this convection model is a multi-layer viscosity profile, with a low-viscosity channel at the bottom of the upper mantle, inferred by Forte and Mitrovica (2003) from simultaneous inversions of convection and glacial isostatic adjustment (GIA) data.\\indent In these numerical convection simulations, the cycling between the two stable subduction zone configurations is characterized by a period between 500 and 700 Ma. This periodic behaviour is manifested in a relatively restricted range of model parameter space. For example, we have also used the same viscosity profile with differing internal and bottom heating inputs and we found that the cyclical behaviour was suppressed or entirely absent. For these alternative heating configurations, the convection simulations instead yielded a classical polygonal cell pattern usually obtained in free-slip models with upwellings surrounded by cold downwellings. It appears that the configuration of the mantle (e.g., relative importance between internal and bottom heating at the core-mantle boundary) plays a role in determining the appearance of steady, periodic variations in subduction zone configuration. Oscillations in bottom heat flux will enable the convective process to cycle back and forth between its two stable plate subduction patterns. We speculate that geological inferences of periodic variations in subduction zone configuration may provide a possible constraint on the style of mantle convection and in particular on viscosity structure and/or heating configuration. \\
DE: 1213 Earth's interior--dynamics (8115, 8120)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8150 Plate boundary--general (3040)
SC: Seismology [S]
MN: 2003 Fall Meeting