The viscosities of partially molten materials undergoing diffusion creep

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• John Rudge (University of Cambridge)
• Thursday 14 February 2019, 11:30-12:30
• Open Plan Area, BP Institute, Madingley Rise CB3 0EZ.

If you have a question about this talk, please contact Catherine Pearson.

Partially molten materials resist shearing and compaction. This resistance is described by a fourth-rank effective viscosity tensor. When the tensor is isotropic, two scalars determine the resistance: an effective shear and an effective bulk viscosity. In this seminar, calculations are presented of the effective viscosity tensor during diffusion creep for a 3D tessellation of tetrakaidecahedrons (truncated octahedrons). The geometry of the melt is determined by assuming textural equilibrium. Two parameters control the effect of melt on the viscosity tensor: the porosity and the dihedral angle. Calculations for both Nabarro-Herring (volume diffusion) and Coble (surface diffusion) creep are presented. For Nabarro-Herring creep the bulk viscosity becomes singular as the porosity vanishes. This singularity is logarithmic, a weaker singularity than typically assumed in geodynamic models. The presence of a small amount of melt (0.1% porosity) causes the effective shear viscosity to approximately halve. For Coble creep, previous modelling work has argued that a very small amount of melt may lead to a substantial, factor of 5, drop in the shear viscosity. Here, a much smaller, factor of 1.4, drop is obtained.

This talk is part of the Institute for Energy and Environmental Flows (IEEF) series.

This talk is included in these lists:

• All Talks (aka the CURE list)
• Cambridge Energy Seminars
• Department of Earth Sciences seminars
• Institute for Energy and Environmental Flows (IEEF)
• NanoDTC Energy Materials Talks
• Open Plan Area, BP Institute, Madingley Rise CB3 0EZ
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