The Effective Rheology of Partially Molten Rocks: Numerical and Experimental Data
Abstract
We analyzed the mechanical and rheological behavior of a two-phase system consisting of rigid grains and an interconnecting viscous fluid. For this purpose we use 2D direct numerical simulations, i.e. the problem is solved on the spatial scale of individual grains. Effective properties of a two-phase particle suspension can be characterized by using the direct stress-strain rate relationship. On the basis of these results, we derived expressions for the effective viscosity for both Newtonian and non-Newtonian rheologies. We demonstrate that the effective rheology of the assemblage is non-Newtonian only if the fluid has a non-Newtonian rheology. At low porosity the strain rates within the fluid are locally up to three orders of magnitude higher than the overall applied background strain rate. This effect may explain the experimentally observed change in rheology from Newtonian to non-Newtonian rheology. Experimental studies indicate that melt-solid systems behave non-linearly for moderate to high strain rates. However, the experiments are controversial. In theory, 0D visco-elastic models can be used to extract the effective rheology from laboratory experiments. However, the effects of shear-heating and non-linear rheology of the assemblage may affect the results in a non-intuitive manner. For this reason, we compare a series of 2D finite strain grain-scale numerical simulations with a 0D rheology model. The 2D simulations employ an overall visco-elastic rheology, and the rheology of each phase is controlled independently. Rheologies can be either Newtonian or non-Newtonian, either constant temperature or temperature dependent viscosity according to Hess and Dingwell (1996) for the fluid phase - or - constant or power-law quartz-controlled rheology according to Ranalli (2002) for the solid phase. The simulations also account for shear heating. A 0D inversion model is developed that extracts effective material parameters from either synthetic or laboratory-derived stress-strain curves. A comparison with 2D numerical simulations indicates that non-Newtonian behaviour is important while the rheology of the solid phase has less influence on the system, a result that is in agreement with earlier findings. We are currently considering the relative importance of shear heating, non-Newtonian rheologies, elasticity and finite strain on the effective rheology of the assemblage, to better understand how rheological information can be extracted from 0D models. The results are applied to laboratory experiments on the effective rheology of partially molten rocks and have implications for volcanic eruptions and batholith emplacement.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.V51B1672D
- Keywords:
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- 3619 MINERALOGY AND PETROLOGY / Magma genesis and partial melting;
- 3902 MINERAL PHYSICS / Creep and deformation;
- 8033 STRUCTURAL GEOLOGY / Rheology: mantle;
- 8120 TECTONOPHYSICS / Dynamics of lithosphere and mantle: general