here - ETH Zürich

[7] J. Haruyama and 19 co-authors (2009), Long-lived volcanism on the Lunar farsiderevealed by SELENE Terrain Camera, Science, 323, 905-908[8] M. A. Wieczorek and M. Le Feuvre (2009), Did a large impact reorient the Moon?,Icarus, 200, 358-366Influence of density anomalies in the lower mantle on the geoidM. BeuchertInstitut für Geophysik, Goethe Universität Frankfurt, Germanybeuchert@geophysik.uni-frankfurt.deThe influence of the two near-equatorial, antipodal Large Low Shear Velocity Provinces(LLSVPs) in the lower mantle on global mantle dynamics is still a topic of major interest ingeodynamics. Whereas a qualitative correlation of the LLSVPs with observed residual (i.e.after subtraction of the geoid anomaly associated with subduction zones) positive geoidanomalies has been established, quantitative exploration of critical parameters like densityexcess, viscosity of the anomalies, lithosphere and lower mantle and their influence on theassociated geoid anomaly remains to be investigated in geodynamic simulations. We test theinfluence of variation of these parameters on the geoid in our dynamic two-dimensional FEMconvection model. In computation of the geoid, we include both the contribution of internaldensity variations and of surface and core-mantle boundary topography. We compare theresults obtained from our simulations with the geoid data acquired by the new geosatelliteGRACE and try to constrain realistic parameter ranges from this comparison.Simple subduction models with SulecS. Buiter 1 and S. Ellis 21 Geological Survey of Norway, Trondheim, Norway2 GNS Science, Lower Hutt, New Zealandsusanne.buiter@ngu.no, S.Ellis@gns.cri.nzModels of geodynamic processes on the scale of the upper crust to upper mantle putdemanding constraints on modelling software: codes should be able to handle viscous, elasticand brittle material behaviour, large deformations (even post-failure), free surface behaviour,and interactions between domains of highly variable material properties. We have developed atwo-dimensional finite-element code, Sulec, based on known techniques from literature,which gives us modelling flexibility in a stand-alone, non-commercial environment. Sulec ischaracterised by its ability to solve large-scale deformations for viscoelastic-plasticrheologies, with a free surface.Sulec solves the momentum equation under the condition of incompressibility. Thestructured mesh is built of quadrilateral elements that can vary in size. The elements are eitherlinear in velocity with constant pressure, or quadratic in velocity with linear pressure. Anaccurate pressure field is obtained through an iterative penalty (Uzawa) formulation [1, 2].Pressures are important not only for pressure-temperature-time paths that can be comparedwith observations, but the pressure-dependence of brittle behaviour in addition introduces34