5:15 PM - 6:30 PM
[SIT08-P09] Effects of chemical composition and melting on viscosity and electrical conductivity of synthesized lherzolite.
Keywords:viscosity, electrical conductivity, melt
We synthesized Fe-free lherzolite aggregates composed of forsterite (fo), enstatite (en), diopside (di) and anorthite (an) from Mg(OH)2, SiO2, CaCO3 powders with particle size of <50 nm and spinel powders with particle size of ~200nm. By changing the amount of spinel, we controlled fraction (φ) of incipient melt ranging from 0.005 to 0.06. Samples were sintered at temperature below solidus (~ 1230°C ) to prepare melt-free aggregates before experiments.
We found two types of chemical effects on subsolidus condition. The spinel-added samples exhibited about an order of magnitude lower viscosity compared to spinel-free samples. Fo + en + di and fo + en samples (Tasaka et al., 2013) exhibited the similar viscosity. Further, fo + en + spinel samples and fo + en + di + an samples exhibited the similar viscosity indicating that small amount of Al at grain boundaries or grain interior increases creep rate of the aggregates. Electrical conductivities of all diopside-bearing samples were higher than the conductivity of fo + en sample. No dependency of electron conductivity on grain size was detected for diopside-bearing samples indicating that Ca at grain interior of forsterite enhanced the electrical conductivity. During crossing solidus temperature, the samples with the lowest incipient melt fraction (φ = 0.005) showed a gradual decrease in viscosity and gradual increase in electrical conductivity whereas larger incipient melt fraction (φ = 0.04) samples showed step-wise decrease and increase in viscosity and electrical conductivity, respectively. The melt effect on viscosity could be expressed in empirical expression of η ∝ exp(αφ) where α = 69. This value is considerably larger than the value (α = 21) previously proposed from creep experiment of synthesized lherzolite aggregates using natural minerals, (Zimmerman and Kohlstedt, 2004).