HR: 14:25h
AN: T52E-04    [PDF]
TI: Texture Evolution and Visco-Elasticity in Mantle Convection
AU: * Mulhaus, H M
EM: muhlhaus@quakes.uq.edu.au
AF: The University of Queensland, St Lucia, Brisbane, QLD QLD Australia
AU: Moresi, L
EM: louis.moresi@sci.monash.edu.au
AF: School of Mathematical Sciences, Monash University, Melbourne, PO Box 28M Australia
AB: A novel class of nonlinear, visco-elastic rheologies has recently been developed by Mhlhaus et al (see web page). The theory has originally been developed for the simulation of large deformation processes including folding and kinking in multi-layered visco-elastic rock . The orientation of the layer surfaces or slip planes in the context of crystallographic slip is determined by the normal vector-the so called director-of these surfaces. Here the model is generalized to include thermal effects; it is shown that in 2D steady states the director is given by the gradient of the flow potential. The model is applied to anisotropic simple shear where the directors are initially parallel to the shear direction. The relative effects of textural hardening and thermal softening are demonstrated. Turning to natural convection we compare the time evolution and approximately steady states of isotropic and anisotropic convection for a Rayleigh number Ra =5.64 x 10E5. The isotropic case has a simple steady state solution, whereas the orthotropic convection model produces a continuously evolving patterning in the core of the convection cell which makes only a near-steady condition possible. The direct simulation of anisotropic mantle flow has been a very specialized area with very few publications since the original paper of Christensen (Geophys.J.R.astr. Soc. 91;711-736) In general it has instead been assumed that the instantaneous flow patterns predicted by convection simulations can be mapped immediately to seismic anisotropy. However, the results of Simons et al http://quake.mit.edu/~fjsimons/azimuthal.html and many others show the observations to be far more advanced than this simplistic modeling assumption. Advanced models should include feedback processes between large-scale flow, director miss-alignment and the drive towards flow alignment. A step in this direction is illustrated in finite element simulations of anisotropic simple shear and anisotropic natural convection.
UR: http://www.ned.dem.csiro.au/research/solidmech/Publications/
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8150 Plate boundary--general (3040)
DE: 8155 Plate motions--general
DE: 8160 Rheology--general
SC: Tectonophysics [T]
MN: 2003 Fall Meeting