Questions on the existence, persistence, and mechanical effects of a very small melt fraction in the asthenosphere

Holtzman, Benjamin K.

This paper integrates current questions in rock physics on the effects and behavior of very small melt fractions (<< 1%) in the asthenosphere. In experiment and theory, it has been shown that a very small melt fraction forming a connected network has a large effect on the diffusion creep shear viscosity, as well as in the anelastic behavior. Because small concentrations of volatiles, particularly H2O and CO2, significantly lower the peridotite solidus, a small melt fraction is expected in the asthenosphere. Even with connected networks, permeability will be low and surface tension will generate a strong force resisting complete draining of small melt fractions. The anelastic reduction of shear velocity due to melt could cause a ≥ 5% shear velocity contrast across the solidus, consistent with the contrast measured on features in the shallow suboceanic upper mantle that are often interpreted as the lithosphere-asthenosphere boundary.


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Geochemistry, Geophysics, Geosystems

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