Electrical conductivity of hydrous silicate melts: Implications for the bottom-up hydration of Earth's upper mantle

Abstract

The upwelling of the hydrous mantle transition zone triggers dehydration-induced partial melting atop the 410-km discontinuity. Here we investigate the electrical conductivity of hydrous silicate melts in the 200-400 km depth range and explore whether melting at the 410-km depths is responsible for the hydration of the upper mantle. Our experimental electrical conductivity data demonstrate that the mantle at 180-350 km depths is mostly melt free, confirming the H2O under-saturated conditions. However, the residual mantle from partial melting atop the 410km discontinuity may contain various possible amounts of water according to the initial mantle transition zone and melt concentrations. This residual H2O could contribute to the hydration of the upper mantle either through diffusion or material replacement by upwelling. Our calculations suggest that the diffusion may not be responsible for the hydration of the upper mantle to present H2O concentration of 50-200 ppm wt. Melting of the upwelling mantle transition zone with less than 1500 ppm wt. H2O produces residual peridotites with ~ 200 ppm H2O at the 410-km discontinuity. Continuous upwelling of such hydrous residues would gradually replace the dry upper mantle with depleted residual hydrous peridotites in less than 260 Ma. In this study, we propose a bottom-up hydration mechanism for the Earth's upper mantle driven by dehydration-melting at the 410-km

The Electrical Conductivity of Liebermannite: Implications for Water Transport Into the Earth's Lower Mantle

“…However, upon a decrease of temperature to 1000 K, at constant pressure, the sample is likely to transform to hiP liebermannite with monoclinic symmetry (Nishiyama et al, 2005). Upon structural transformation from lowP to hiP liebermannite, the electrical resistivity measurements of the sample do not indicate a discontinuous decrease of the electrical resistance, which indicates the release of free fluid phase or hydrous melting in the sample (Freitas & Manthilake, 2019). Assuming that the water incorporation into the liebermannite structure occurs at the highest temperature, this crucial observation suggests that the hiP liebermannite structure is capable of sequestering H + into octahedral sites as molecular H 2 O or ionic H 3 O + in its structure similar to the lowP liebermannite.…”

Effect of Water on the Thermal Properties of Olivine With Implications for Lunar Internal Temperature

“…Thus high water content helps decrease κ and promote heat retention in a positive feedback loop, contributing to thermal instability. Such a dynamic mantle hydration model based on the dehydration melting at 410‐km discontinuity has been proposed to account for the origin of partial melting in the upper mantle (Freitas & Manthilake, ).…”

Water Content of the Dehydration Melting Layer in the Topmost Lower Mantle

“…extrapolated from the dihedral angle in the olivine-silicate melt system (Freitas and Manthilake, 2019). With such a low dihedral angle (<10 o ), 0.5-1.3 vol.% of melt is sufficient to completely wet the grain boundaries of bridgmanite, which will substantially affect the dynamics at the topmost lower mantle.…”