HR: 0830h
AN: T41C-0245    [PDF]
TI: On the Curvature of Oceanic Arcs
AU: * Morra, G
EM: morra@verleinix.ethz.ch
AF: ETH Zurich - Geophysics Institute, ETH Hoenggerberg, Zurich, 8093 Switzerland
AU: Regenauer-Lieb, K
EM: klaus.regenauer-lieb@csiro.au
AF: ETH Zurich - Geophysics Institute, ETH Hoenggerberg, Zurich, 8093 Switzerland
AU: Giardini, D
EM: giardini@seismo.ig.erdw.ethz.ch
AF: ETH Zurich - Geophysics Institute, ETH Hoenggerberg, Zurich, 8093 Switzerland
AB: The key feature of plate tectonics is the subduction of cold oceanic plates into a hot convective mantle. These subducting plates, as seen from the surface, mostly portray a distinct concave arc shape at the trench with respect to the leading edge of subduction. The origin of arc curvature is not yet understood. A common belief is that it is probably an effect of the Earth's sphericity. However, the spherical effect of the Earth creates convex, long-wavelength arc shapes. We thus investigate whether concave arc curvature can be explained by: (1) Exogenic feedback between the migrating lithosphere and the secondary induced mantle flow, (2) Endogenic heterogeneities within the lithosphere itself, e.g. owing to differences in cooling ages of the plate at the trench. Although both mechanisms create concave arcs, for isolate subduction systems, only the endogenic effects are sufficient to explain the magnitude of observed arc curvature. We compare our results to the Aleutian and Sandwich arcs. Our method is based on a novel 3-D numerical tool. We model the subduction process as a solid (lithosphere) - fluid (mantle) interaction. Two different numerical methods are used to solve for the constituents: Implicit Finite Element (FEM) for the lithosphere and Implicit Boundary Elements (BEM) for the mantle. The methods are chosen on the basis of a critical isotherm allowing a fluid mechanical approximation of the full continuum-mechanical problem above 1200 K. Thus the calculus of an approximate average drag effect is feasible through semi-analytical methods. This approach extends the 2-D setup of Funiciello et al., (JGR, 2003) into 3-D by adding the BEM solution. The BEM method builds on the stokeslet theory as a semi-analytical solution for the mantle drag. It shows that the drag mainly depends by the integration of the singularities at the lateral extremities of the slab.
UR: http://www.sg.geophys.ethz.ch/geodynamics/gabriele/
DE: 0903 Computational methods, potential fields
DE: 3210 Modeling
DE: 3230 Numerical solutions
DE: 3902 Creep and deformation
DE: 5120 Plasticity, diffusion, and creep
SC: Tectonophysics [T]
MN: 2003 Fall Meeting