10:15 AM - 10:30 AM
[SIT24-06] Experimental study of the effects of partial melting on anelasticity: toward quantitative interpretations of seismic high attenuation
Keywords:anelasticity, seismic high attenuation, partial melting, the effect of melt, melt network
We use polycrystalline aggregates made from borneol + diphenylamine binary eutectic system (eutectic or solidus temperature Tm = 316 K) as a partially molten rock analogue. This system has an equilibrium microstructure similar to that of olivine + basalt system (Takei, 2000, JGR). Samples used in this study have a few wt% diphenylamine. Above Tm, all diphenylamine grains disappear into the melt phase. In Yamauchi and Takei (2016), to prevent the rapid growth of borneol grains during the mechanical tests at supersolidus temperatures, testing samples were pre-annealed at the supersolidus temperature (T/Tm ≃ 1.03), cooled, and again partially molten to measure the melt effect without grain growth. In this previous experiment, quenched melt network remained even at T/Tm < 1. Therefore, the effect of microstructural change at T/Tm = 1 from dispersed diphenylamine grains to a connected melt network could not be examined. We have to improve the sample preparation method to clarify the effect of melt-network formation so that we can detect the existence/nonexistence of melt in the upper mantle by using the seismic data.
In this study, after partially melting a sample at supersolidus temperature (T/Tm ≃ 1.03) for grain growth, we kept the sample at just below the solidus (T/Tm ≃ 0.99) to promote the growth of diphenylamine grains from the quenched melt network. After 50-80 days, we successfully obtained a sample which is composed of large borneol grains and dispersed diphenylamine grains. We prepared two samples with melt fractions 4.5% and 3.7%. We will prepare an additional sample with different melt fraction. Using these samples, accurate measurements of elasticity at 1 MHz, anelasticity at 102-10-4 Hz, and viscosity will be performed at various temperatures from below to above the solidus temperature (T/Tm = 0.89 to 1.01). Data at T/Tm < 1 can be used to reproduce the subsolidus effect (due to grain-boundary premelting) captured in Yamauchi and Takei (2016). Data at T/Tm ≧ 1 can be used to clarify the melt effect. In the presentation, we will show these mechanical data and discuss seismological implications inferred from them.