Anomalous Behavior of Viscosity and Electrical Conductivity of MgSiO₃ Melt at Mantle Conditions

Abstract

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 ∼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 ∼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 ∼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.

Insights into magma ocean dynamics from the transport properties of basaltic melt

“…4). Based on our results, the viscosity of basaltic magma at such mid-mantle conditions is ~0.027 Pa.s which is smaller than the viscosity of MgSiO 3 melt (0.048 Pa.s) at similar conditions 35,40 . The difference in viscosity could be due to the pressure difference induced by the different exchangecorrelation functionals used by the previous and present studies.…”

“…Most of the experimental studies that are confined to temperatures below 2100 K show the minima in the anomalous pressure dependence of viscosity around 5 GPa 29,31,36 . Although prior experiments on depolymerized melts indicated a continuous increase of viscosity with increasing pressure, more recent experiments reported a reduction in viscosity with increasing pressure in the depolymerized melts with pyroxene and peridotite compositions 10,26,35 .…”

“…The pressure dependence of viscosity is sensitive to the melt composition. Yet, there are disagreements between studies even for the same melt compositions 10,26,31,35,36 . Extrapolations of viscosity from experiments conducted at relatively low-pressures to higher pressures often add significant uncertainties due to pressure-induced changes to the atomistic scale structure of the melt and resulting changes in properties.…”

Deep potentials for materials science

“…A DP was developed to simulate liquid and glassy silica which proved to have satisfactory accuracy based upon a relatively small training dataset [143]. Other DPs were developed to calculate transport properties of silicate in the mantle [144][145][146]. DPs were also employed in large-scale calculations of thermodynamic, transport, and structural properties in different molten salts [149][150][151][152][153][154][155][156][157].…”

Deep Potentials for Materials Science

“…A DP was developed to simulate liquid and glassy silica which proved to have satisfactory accuracy based upon a relatively small training dataset [150]. Other DPs were developed to calculate transport properties of silicate in the mantle [151][152][153]. DPs were also employed in large-scale calculations of thermodynamic, transport, and structural properties in different molten salts [156][157][158][159][160][161][162][163][164].…”