HR: 18:00h
AN: T34A-07    [Abstracts]
TI: Modeling Pure Shear Porosity Instabilities in Compacting Porous Media: Implications for Melt Transport Beneath Mid-Ocean Ridges
AU: * Butler, S L
EM: sam.butler@usask.ca
AF: Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK S7N 5E2, Canada
AB: When a compacting porous layer, modeled as two interpenetrating viscous fluids, is subjected to an external stress, it has been shown that if the viscosity of the solid matrix decreases with porosity, that an instability occurs that results in localized regions of high and low porosity. This instability was first predicted theoretically for a pure shear external forcing (Stevenson, 1989). More recently the experiments of Holtzman et al. (2003) and the theoretical and numerical investigations of Katz et al. (2006) have demonstrated the instability for a compacting layer subjected to simple shear. In this contribution, I present a linear theory and numerical model results for a compacting layer subjected to pure shear. As in the simple shear case, bands of high and low porosity form that are parallel to the direction of maximum compression if the viscosity of the matrix is strain- rate independent. If viscosity depends on strain rate, then two sets of bands form at angles to the direction of maximum compression that increase with the degree of strain rate dependence. These bands are shown to form when the fluid is buoyant which induces oscillations and waves. Results for more complicated background shear stresses that more closely model deformations associated with large scale mantle convection between mid-ocean ridges will also be presented.
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
DE: 8434 Magma migration and fragmentation
SC: Tectonophysics [T]
MN: 2009 Joint Assembly