Influence of contiguity on seismic velocities of partially molten aggregates
نویسنده
چکیده
[1] The microstructure of partially molten rocks plays a key role in determining their physical properties. The area fraction of intergranular contact, contiguity, governs the establishment of a skeletal framework of solid grains and controls the effective elastic moduli of the aggregate. This work presents a theoretical calculation of steady state grain shape, contiguity, effective elastic moduli, and S and P wave velocities for a partially molten aggregate containing an approximate melt volume fraction of 0.09. The steady state microstructure is controlled by surface tension gradients arising from interaction among adjacent grains in a close-packed aggregate. The ratio of viscosity between the grains and the melt, as well as the capillary number, strongly influence the contiguity. For an aggregate with a high viscosity ratio, surface tension-driven faceting is suppressed due to the large viscous resistance of the grains, leading to a small contiguity. Both VS and VP decrease in a nonlinear fashion with an increasing viscosity ratio for all capillary numbers. When extrapolated to the conditions similar to the core-mantle boundary, a 3:1 ratio of shear to P wave velocity reduction can be explained by a melt volume fraction of 0.15.
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