The Effect of Deformation on Grain Boundary Wetness in Partially Molten Peridotite
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The spatial distribution of the melt phase can affect many properties of partially molten rocks, including viscosity and seismic wave velocity. A good way to quantify this distribution is the grain boundary wetness, the fraction of total grain boundaries that are in contact with melt. This goal of this study was to quantify the effect of deformation on grain boundary wetness. We analyzed three prepared samples consisting of olivine and 3%, 7% or 15% of a basalt melt phase, which were equilibrated at 1250°C, 300 MPa of confining stress and <50 MPa of differential stress. We describe a process developed to calculate the grain boundary wetness from prepared SEM images of the samples. We find an expected dependence of wetness on porosity. The effect of deformation was not consistent across all three samples: the two higher melt fraction samples show greater wetness before deformation, while the 3% melt sample showed no effect. This result does not agree with experiments on an organic analog material, which indicated that deformation increases wetness. If viscosity increases with wetness, the results of this study indicate that partially molten peridotite strengthen with deformation, which would have important implications for mantle dynamics. Some researchers have proposed that if you deform a sample of partially molten peridotite it will in fact raise the grain boundary wetness Takei [private communication, 2004]. This statement is bold because if you raise the wetness of the sample then the viscosity goes down thereby making the specimen weaker. Our results show that deformation does not have a consistent discernible effect on grain boundary wetness in partially molten peridotite.
Schneider, Stephen E. (2006). The Effect of Deformation on Grain Boundary Wetness in Partially Molten Peridotite. Available electronically from