Behavior and properties of water in silicate melts under deep mantle conditions

Abstract Water (H2O) as one of the most abundant fluids present in Earth plays crucial role in the generation and transport of magmas in the interior. Though hydrous silicate melts have been studied extensively, the experimental data are confined to relatively low pressures and the computational res...

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Autores principales:	Bijaya B. Karki, Dipta B. Ghosh, Shun-ichiro Karato
Formato:	article
Lenguaje:	EN
Publicado:	Nature Portfolio 2021
Materias:	Medicine R Science Q
Acceso en línea:	https://doaj.org/article/4397679b33fe40ef9b60a247df11fee0
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spelling	oai:doaj.org-article:4397679b33fe40ef9b60a247df11fee02021-12-02T15:52:55ZBehavior and properties of water in silicate melts under deep mantle conditions10.1038/s41598-021-90124-72045-2322https://doaj.org/article/4397679b33fe40ef9b60a247df11fee02021-05-01T00:00:00Zhttps://doi.org/10.1038/s41598-021-90124-7https://doaj.org/toc/2045-2322Abstract Water (H2O) as one of the most abundant fluids present in Earth plays crucial role in the generation and transport of magmas in the interior. Though hydrous silicate melts have been studied extensively, the experimental data are confined to relatively low pressures and the computational results are still rare. Moreover, these studies imply large differences in the way water influences the physical properties of silicate magmas, such as density and electrical conductivity. Here, we investigate the equation of state, speciation, and transport properties of water dissolved in Mg1−x Fe x SiO3 and Mg2(1−x)Fe2x SiO4 melts (for x = 0 and 0.25) as well as in its bulk (pure) fluid state over the entire mantle pressure regime at 2000–4000 K using first-principles molecular dynamics. The simulation results allow us to constrain the partial molar volume of the water component in melts along with the molar volume of pure water. The predicted volume of silicate melt + water solution is negative at low pressures and becomes almost zero above 15 GPa. Consequently, the hydrous component tends to lower the melt density to similar extent over much of the mantle pressure regime irrespective of composition. Our results also show that hydrogen diffuses fast in silicate melts and enhances the melt electrical conductivity in a way that differs from electrical conduction in the bulk water. The speciation of the water component varies considerably from the bulk water structure as well. Water is dissolved in melts mostly as hydroxyls at low pressure and as –O–H–O–, –O–H–O–H– and other extended species with increasing pressure. On the other hand, the pure water behaves as a molecular fluid below 15 GPa, gradually becoming a dissociated fluid with further compression. On the basis of modeled density and conductivity results, we suggest that partial melts containing a few percent of water may be gravitationally trapped both above and below the upper mantle-transition region. Moreover, such hydrous melts can give rise to detectable electrical conductance by means of electromagnetic sounding observations.Bijaya B. KarkiDipta B. GhoshShun-ichiro KaratoNature PortfolioarticleMedicineRScienceQENScientific Reports, Vol 11, Iss 1, Pp 1-13 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Medicine R Science Q
spellingShingle	Medicine R Science Q Bijaya B. Karki Dipta B. Ghosh Shun-ichiro Karato Behavior and properties of water in silicate melts under deep mantle conditions
description	Abstract Water (H2O) as one of the most abundant fluids present in Earth plays crucial role in the generation and transport of magmas in the interior. Though hydrous silicate melts have been studied extensively, the experimental data are confined to relatively low pressures and the computational results are still rare. Moreover, these studies imply large differences in the way water influences the physical properties of silicate magmas, such as density and electrical conductivity. Here, we investigate the equation of state, speciation, and transport properties of water dissolved in Mg1−x Fe x SiO3 and Mg2(1−x)Fe2x SiO4 melts (for x = 0 and 0.25) as well as in its bulk (pure) fluid state over the entire mantle pressure regime at 2000–4000 K using first-principles molecular dynamics. The simulation results allow us to constrain the partial molar volume of the water component in melts along with the molar volume of pure water. The predicted volume of silicate melt + water solution is negative at low pressures and becomes almost zero above 15 GPa. Consequently, the hydrous component tends to lower the melt density to similar extent over much of the mantle pressure regime irrespective of composition. Our results also show that hydrogen diffuses fast in silicate melts and enhances the melt electrical conductivity in a way that differs from electrical conduction in the bulk water. The speciation of the water component varies considerably from the bulk water structure as well. Water is dissolved in melts mostly as hydroxyls at low pressure and as –O–H–O–, –O–H–O–H– and other extended species with increasing pressure. On the other hand, the pure water behaves as a molecular fluid below 15 GPa, gradually becoming a dissociated fluid with further compression. On the basis of modeled density and conductivity results, we suggest that partial melts containing a few percent of water may be gravitationally trapped both above and below the upper mantle-transition region. Moreover, such hydrous melts can give rise to detectable electrical conductance by means of electromagnetic sounding observations.
format	article
author	Bijaya B. Karki Dipta B. Ghosh Shun-ichiro Karato
author_facet	Bijaya B. Karki Dipta B. Ghosh Shun-ichiro Karato
author_sort	Bijaya B. Karki
title	Behavior and properties of water in silicate melts under deep mantle conditions
title_short	Behavior and properties of water in silicate melts under deep mantle conditions
title_full	Behavior and properties of water in silicate melts under deep mantle conditions
title_fullStr	Behavior and properties of water in silicate melts under deep mantle conditions
title_full_unstemmed	Behavior and properties of water in silicate melts under deep mantle conditions
title_sort	behavior and properties of water in silicate melts under deep mantle conditions
publisher	Nature Portfolio
publishDate	2021
url	https://doaj.org/article/4397679b33fe40ef9b60a247df11fee0
work_keys_str_mv	AT bijayabkarki behaviorandpropertiesofwaterinsilicatemeltsunderdeepmantleconditions AT diptabghosh behaviorandpropertiesofwaterinsilicatemeltsunderdeepmantleconditions AT shunichirokarato behaviorandpropertiesofwaterinsilicatemeltsunderdeepmantleconditions
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Behavior and properties of water in silicate melts under deep mantle conditions

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