Anomalous Behavior of Viscosity and Electrical Conductivity of MgSiO3 Melt at Mantle Conditions
HY Luo and BB Karki and DB Ghosh and HM Bao, GEOPHYSICAL RESEARCH LETTERS, 48, e2021GL093573 (2021).
Silicate melts have served as transport agents in the chemical and thermal evolution of Earth. Molecular dynamics simulations based on a deep neural network potential trained by ab initio data show that the viscosity of MgSiO3 melt decreases with increasing pressure at low pressures (up to similar to 6 GPa) before it starts to increase with further compression. The melt electrical conductivity also behaves anomalously; first increasing and then decreasing with pressure. The melt accumulation implied by the viscosity turnover at similar to 23 GPa along mantle liquidus offers an explanation for the low-velocity zone at the 660-km discontinuity. The increase in electrical conductivity up to similar to 50 GPa may contribute to the steep rise of Earth's electrical conductivity profiles derived from magnetotelluric observations. Our results also suggest that small fraction of melts could give rise to detectable bulk conductivity in deeper parts of the mantle.
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