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Physics of mantle melting: two-phase flow, variable matrix viscosity and density effects

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MIMW02 - From the grain to the continuum: two phase dynamics of a partially molten, polycrystalline aggregate

In the introduction different partially molten regions within the earth's mantle will be identified. Then, the governing equations are introduced with emphasis on rheology, melt density, and solution strategies. The melt fraction and its geometrical distribution has an important influence on the shear and bulk viscosity of the matrix. A new semi-analytical model is introduced which may describe the geometrical distribution of the melt phase. Combined with a poro-elastic effective medium approach (Schmeling et al., 2012) effective shear and bulk viscosity can be estimated as a function of melt fraction. Models of 2D porosity waves are shown which use such effective viscosity laws. Another important quantity is the melt density which may be higher than the matrix density at transition zone depths. 1D models of a rising hot partially molten plume show that within a certain parameter regime standing porosity waves may develop. If there is time, I will briefly mention a simple mantle convection benchmark initiative with two-phase flow in its partially molten region. Schmeling, H., J.-P. Kruse, and G. Richard, 2012: Effective shear and bulk viscosity of partially molten rock based on elastic moduli theory of a fluid filled poroelastic medium. Geophys. J. Int., doi: 10.1111/j.1365-246X.2012.05596.x 

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