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SUMMARY:The viscosities of partially molten materials undergoing diffusion
  creep - John Rudge (University of Cambridge)
DTSTART:20190214T113000Z
DTEND:20190214T123000Z
UID:TALK117328@talks.cam.ac.uk
CONTACT:Catherine Pearson
DESCRIPTION:Partially molten materials resist shearing and compaction. Thi
 s resistance \nis described by a fourth-rank effective viscosity tensor. W
 hen the tensor \nis isotropic\, two scalars determine the resistance: an e
 ffective shear and \nan effective bulk viscosity. In this seminar\, calcul
 ations are presented of \nthe effective viscosity tensor during diffusion 
 creep for a 3D tessellation of \ntetrakaidecahedrons (truncated octahedron
 s). The geometry of the melt is \ndetermined by assuming textural equilibr
 ium.  Two parameters \ncontrol the effect of melt on the viscosity tensor:
  the porosity and the \ndihedral angle. Calculations for both Nabarro-Herr
 ing (volume diffusion) \nand Coble (surface diffusion) creep are presented
 . For Nabarro-Herring \ncreep the bulk viscosity becomes singular as the p
 orosity vanishes. This \nsingularity is logarithmic\, a weaker singularity
  than typically assumed in \ngeodynamic models. The presence of a small am
 ount of melt (0.1% porosity) \ncauses the effective shear viscosity to app
 roximately halve. For Coble creep\, \nprevious modelling work has argued t
 hat a very small amount of melt may \nlead to a substantial\, factor of 5\
 , drop in the shear viscosity. Here\, a \nmuch smaller\, factor of 1.4\, d
 rop is obtained.\n
LOCATION:Open Plan Area\, BP Institute\, Madingley Rise CB3 0EZ
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