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Article Dans Une Revue Earth and Planetary Science Letters Année : 2019

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

D. Freitas
Geeth Manthilake

Résumé

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 H 2 O under-saturated conditions. However, the residual mantle from partial melting atop the 410-km discontinuity may contain various possible amounts of water according to the initial mantle transition zone and melt concentrations. This residual H 2 O 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 H 2 O concentration of 50-200 ppm wt. Melting of the upwelling mantle transition zone with less than 1500 ppm wt. H 2 O produces residual peridotites with ∼ 200 ppm H 2 O 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 discontinuity. The hydrous partial melting at the top of the asthenosphere appears to be a consequence of H 2 O saturation in the upwelling residual peridotites.
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Dates et versions

hal-02455958 , version 1 (16-11-2020)

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D. Freitas, Geeth Manthilake. Electrical conductivity of hydrous silicate melts: Implications for the bottom-up hydration of Earth's upper mantle. Earth and Planetary Science Letters, 2019, 523, pp.115712. ⟨10.1016/j.epsl.2019.115712⟩. ⟨hal-02455958⟩
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