HR: 11:35h
AN: T12B-06 INVITED    [Abstracts]
TI: Influence of anisotropic rheology on Rayleigh-Benard convection
AU: * Pouilloux, L
EM: pouilloux@ipgp.jussieu.fr
AF: Laboratoire Dynamique des Fluides geologiques - IPGP, 4 Place Jussieu, PARIS cedex 05, 75 252, France
AU: Kaminski, E
EM: kaminski@ipgp.jussieu.fr
AF: Laboratoire Dynamique des Fluides geologiques - IPGP, 4 Place Jussieu, PARIS cedex 05, 75 252, France
AU: Labrosse, S
EM: stephane.labrosse@ens-lyon.fr
AF: Laboratoire des Sciences de la Terre - ENS Lyon, 46 Allee d'Italie, Lyon, 69 007, France
AB: Dislocation creep, which is the dominant deformation mechanism in the upper mantle, results in a non-Newtonian anisotropic rheology. The implication of non-Newtonian rheology has been quite extensively studied in geodynamic models but the anisotropic aspect remains poorly in- vestigated. We propose to fill this gap by (1) introducing a simple mathematical description of anisotropic viscosity and (2) illustrating the link between plastic crystal deformation and bulk material rheology. The study relies on the two systems having highest symmetry, i.e. cubic and hexagonal being characterised by one and three anisotropic perturbation parameters, respectively. First-order implications of anisotropy are quantitatively explored as functions of these parameters. The effective rheology of the material is described as a function of the orientation of the crystals and of the imposed stress and the validity of the isotropic approximation is discussed. The model, applied to ringwoodite, a cubic crystal with spinel-type structure, predicts that the dynamics of the transition zone in the Earths mantle is going to be strongly affected by mechanical anisotropy. Similarly, the dynamics of materials having an hexagonal symmetry like in icy satellites and layered media is affected by anisotropy. Using linear stability analysis on Rayleigh-B?Šnard problem, we show how the critical Rayleigh number, the length scale of the first instability and the associated roll direction quantitatively depend on anisotropy.
DE: 8012 High strain deformation zones
DE: 8025 Mesoscopic fabrics
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8138 Lithospheric flexure
DE: 8160 Rheology: general (1236, 8032)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting