here - ETH Zürich

feedback relations to the mechanical flow. Material properties are carried on tracer particlesthat are advected through the Eulerian mesh. Elasticity is implemented following the approachof Moresi et al. [3], which involves an adjustment of the viscosities, the addition of a forceterm, and storing stresses and their rotations on the tracers. Brittle materials deform followinga Mohr-Coulomb criterion. Brittle stress is kept at the yield value by iterating on an adjustedeffective viscosity [see for example 4]. The final effective viscosities are averaged in tracer toelement averaging schemes (harmonic, arithmetic or geometric) [5]. The top boundary of ourmodels can be a free surface on which simple surface processes models may be imposed. Thefree surface is obtained by small adjustments of the Eulerian mesh.We first show examples of simple models of upper crustal brittle deformation, elasticrecovery and viscous flow. We then build on these to derive simple models of ocean-continentsubduction, focussing on the near-surface behaviour.References[1] C., Cuvelier, A. Segal and A. A. van Steenhoven (1986), Finite element methods and Navier-Stokes equations, D. Reidel Publishing Company, Dordrecht, Holland, 483 pp.[2] D. Pelletier, A. Fortin and R. Camarero (1989), Are FEM solutions of incompressible flows reallyincompressible? (Or how simple flows can cause headaches!), Int. J. Num Meth. in Fluids 9, 99-112.[3] L. Moresi, F. Dufour and H.-B. Mühlhaus (2003), A Langrangian integration point finite elementmethod for large deformation modeling of viscoelastic geomaterials, J. Comp. Phys. 184, 476-497.[4] V. Lemiale, H.-B. Mühlhaus, L. Moresi and J. Stafford (2008), Shear banding analysis of plasticmodels formulated for incompressible viscous flows, Phys. Earth Planet. Int. 171, 177-186,doi:10.1016/j.pepi.2008.07.038[5] H. Schmeling, A. Y. Babeyko, A. Enns, C. Faccenna, F. Funiciello, T. Gerya, G. J. Golabek, S.Grigull, B. J. P. Kaus, G. Morra, S. M. Schmalholz and J. van Hunen (2008), A benchmarkcomparison of spontaneous subduction models—Towards a free surface, Phys. Earth Planet. Int.171, 198-223, doi:10.1016/j.pepi.2008.06.028Dynamics and implications of slab detachment due to ridge-trench collisionE.R. Burkett and M.I. BillenUC Davies, USAerburkett@ucdavis.eduThe approach of a buoyant spreading ridge to a subduction zone may lead to detachment of asubducted slab. Previous work has called upon the detachment process as an explanation forobserved ridge abandonment and slab-window related magmatism (e.g. in Baja CA/westernMexico), but such a scenario has not been tested using fully-dynamic numerical models. Weuse dynamic two-dimensional models including a non-Newtonian rheology to study theapproach of a spreading ridge to a subduction zone. In models exploring effects of subductedslab length, distance of the ridge from the trench, shear zone strength, and lithospheric yieldstrength, we find the following dynamics of ridge approach: (a) a decrease in subductionvelocity as the ridge approaches the trench, (b) a shrinking surface plate that maintains auniform subduction velocity, (c) ridge abandonment distances 100-275 km from the trench,and (d) slab gap distances 195-285 km from the trench. These results are consistent withobservations in Baja CA, where detachment of the Cocos slab may explain abandonment ofobserved segments of the East Pacific Rise 50-200 km outboard of the trench (Lonsdale,35