In situ spectroscopic study of water speciation in the depolymerized Na 2 Si 2 O 5 melt

Chertkova, Nadezda; Yamashita, Shigeru

doi:10.1016/j.chemgeo.2015.05.012

Cited by 18 publications

(12 citation statements)

References 37 publications

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“…More problematic is the fact that the water speciation (the ratio between hydroxyl groups and molecular water) is highly temperature dependent and varies with the H 2 O content (Stolper, 1989;Silver et al, 1990;Shen and Keppler, 1995;Behrens, 1995, 2001;Zhang et al, 1997;Sowerby and Keppler, 1999;Ihinger et al, 1999;Kohn, 2000;Behrens and Nowak, 2003;Liu et al, 2004;Behrens and Yamashita, 2008;Chertkova and Yamashita, 2015). Thus the water speciation at magmatic temperatures is not preserved on quenching.…”

Section: Introductionmentioning

confidence: 99%

A comprehensive molecular dynamics simulation study of hydrous magmatic liquids

2020

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Despite its low abundance, water has a great influence on the geodynamics of the Earth's upper mantle. Indeed, water has the ability to modify the phase relations and to affect in a significant way the rheological properties of minerals and melts. However the mechanisms of water incorporation in silicate melts and the impact on the melt properties is still not fully understood. To improve our understanding of hydrous silicate melts, we have performed a series of molecular dynamics simulations to evaluate the H 2 O solubility, the liquid-vapour coexistence, the surface tension, the water speciation, the equation of state, the viscosity, the electrical conductivity, the diffusion of silicate elements and protonated species, as well as the melt structure of various magmatic liquids representative of the Earth's upper mantle (rhyolite, andesite, MORB, peridotite, and kimberlite). For that, we introduce a new force field for water, which is compatible with an accurate force field for silicates recently developed (Dufils et al., 2018). A comparison between MD calculations and experimental data (when they exist) shows that the MD simulations are reliable. Among all the results obtained in this study, the following points may be emphasized. (1) The solubility of water changes very little when the melt composition evolves from rhyolitic to andesitic and basaltic, but it is strongly enhanced in ultramafic melts. (2) When hydrous melt and aqueous fluid are coexisting with each other, the oxide content of the aqueous fluid increases rapidly with the pressure. (3) A consequence of point ( 2) is that water has a large influence on the surface tension, as the latter one drops by a factor of 2 4 when the water pressure increases from 1 bar to a few kbar. (4) Concerning the water speciation, an important point is that the MD simulation probes the liquid phase, when most of the experimental studies are dealing with glasses. Thus at magmatic temperatures the concentration in hydroxyl groups and the one in molecular water are crossing for a water content of about 15 wt%, a value much higher than 2 the one observed in glasses ( -4 wt%). ( 5) MD calculations show that the molar volume of the melt is a linear function of the water content, and so for all the chemical compositions investigated. Therefore the water partial molar volume () is virtually independent of total water content and of water speciation. A by-product of this result is that an ideal mixing rule between water and the silicate component leads to an accurate estimate of the melt molar volume. (6) At fixed T and P, the melt viscosity decreases with water content, more depolymerized the melt the smaller the influence of water on the viscosity. However, at the high temperatures investigated in this study (T 1673 K), the decrease in viscosity induced by water does not exceed one or two orders of magnitude, as compared with many orders of magnitude near the glass transition temperature. ( 7) The diffusivity of ions increases exponentially with water content. As for the prot...

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Section: Introductionmentioning

confidence: 99%

A comprehensive molecular dynamics simulation study of hydrous magmatic liquids

2020

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“…However, the environment of protons is still not well known in hydrous melts. Extending the knowledge acquired through Raman, NMR, and IR spectroscopic studies of hydrous glasses [ Scholze , ; Bartholomew et al ., ; Mysen et al ., ; Stolper , ; Mysen and Virgo , ; McMillan and Remmele , ; Kohn et al ., ], in situ studies of molten hydrous silicates confirm that water is present as molecular H 2 O (H 2 O mol ) that reacts with the melt oxygens to form hydroxyl groups [ Nowak and Behrens , ; Holtz et al ., ; Sowerby and Keppler , ; Behrens and Yamashita , ; Mysen , , ; Chertkova and Yamashita , ], following the equilibrium:

H_{2} O_{mol ((), melt)} + {O^{2 -}}_{(melt)} \Leftrightarrow {2 OH}^{-}_{(melt)} .

…”

Section: Introductionmentioning

confidence: 99%

“…Solid Earth,122,[4888][4889][4890][4891][4892][4893][4894][4895][4896][4897][4898][4899]doi:10.1002/ 2017JB014262. Behrens, 1995;Holtz et al, 1996;Sowerby and Keppler, 1999;Behrens and Yamashita, 2008;Mysen, 2009Mysen, , 2010Chertkova and Yamashita, 2015], following the equilibrium:…”

Section: Introductionunclassified

In situ study at high pressure and temperature of the environment of water in hydrous Na and Ca aluminosilicate melts and coexisting aqueous fluids

2017

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The bonding and speciation of water dissolved in Na silicate and Na and Ca aluminosilicate melts were inferred from in situ Raman spectroscopy of the samples, in hydrothermal diamond anvil cells, while at crustal temperature and pressure conditions. Raman data were also acquired on Na silicate and Na and Ca aluminosilicate glasses, quenched from hydrous melts equilibrated at high temperature and pressure in a piston cylinder apparatus. In the hydrous melts, temperature strongly influences O‐H stretching ν(O‐H) signals, reflecting its control on the bonding of protons between different molecular complexes. Pressure and melt composition effects are much smaller and difficult to discriminate with the present data. However, the chemical composition of the melt + fluid system influences the differences between the ν(O‐H) signals from the melts and the fluids and, hence, between their hydrogen partition functions. Quenching modifies the O‐H stretching signals: strong hydrogen bonds form in the glasses below the glass transition temperature Tg, and this phenomenon depends on glass composition. Therefore, glasses do not necessarily record the O‐H stretching signal shape in melts near Tg. The melt hydrogen partition function thus cannot be assessed with certainty using O‐H stretching vibration data from glasses. From the present results, the ratio of the hydrogen partition functions of hydrous silicate melts and aqueous fluids mostly depends on temperature and the bulk melt + fluid system chemical composition. This implies that the fractionation of hydrogen isotopes between magmas and aqueous fluids in water‐saturated magmatic systems with differences in temperature and bulk chemical composition will be different.

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“…With further increases in total water content, molecular water becomes the dominant species and the hydroxyl content levels off or may even decrease. The observed concentrations of hydroxyl and molecular water at different total water concentrations are well described by equations (1)- (3), although the appropriate solution model to describe the mixing of OH, H 2 O mol and O 0 in the melt is still not completely resolved (Silver and Stolper 1989;Silver et al 1990;Dixon et al 1995;Chertkova and Yamashita 2015), and the effect of quenching on the speciation of water in glasses versus high temperature melts is still debated (Stolper 1989;Dingwell and Webb 1990;Silver et al 1990;Dixon et al 1995;Sowerby and Keppler 1999;Withers et al 1999;Nowak and Behrens 2001;Lesne et al 2010). …”

Section: Speciation Of Water In Silicate Meltsmentioning

confidence: 99%

Solubility of water in lunar basalt at low pH2O

Newcombe

Brett

Beckett

et al. 2017

Geochimica et Cosmochimica Acta

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This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractWe report the solubility of water in Apollo 15 basaltic 'Yellow Glass' and an iron-free basaltic analog composition at 1 atm and 1350 °C. We equilibrated melts in a 1-atm furnace with flowing H 2 /CO 2 gas mixtures that spanned ~8 orders of magnitude in fO 2 (from three orders of magnitude more reducing than the iron-wüstite buffer, IW−3.0, to IW+4.8) and ~4 orders of magnitude in pH 2 /pH 2 O (from 0.003 to 24). Based on Fourier transform infrared spectroscopy (FTIR), our quenched experimental glasses contain 69-425 ppm total water (by weight). Our results demonstrate that under the conditions of our experiments: (1) hydroxyl is the only H-bearing species detected by FTIR; (2) the solubility of water is proportional to the square root of pH 2 O in the furnace atmosphere and is independent of fO 2 and pH 2 /pH 2 O; (3) the solubility of water is very similar in both melt compositions; (4) the concentration of H 2 in our iron-free experiments is <~4 ppm, even at oxygen fugacities as low as IW−2.3 and pH 2 /pH 2 O as high as 11; (5) Secondary ion mass spectrometry (SIMS) analyses of water in iron-rich glasses equilibrated under variable fO 2 conditions may be strongly influenced by matrix effects, even when the concentration of water in the glasses is low; and (6) Our results can be used to constrain the entrapment pressure of lunar melt inclusions and the partial pressures of water and molecular hydrogen in the carrier gas of the lunar pyroclastic glass beads. We find that the most water-rich melt inclusion of Hauri et al.(2011) would be in equilibrium with a vapor with pH 2 O ~3 bar and pH 2 ~8 bar. We constrain the partial pressures of water and molecular hydrogen in the carrier gas of the lunar pyroclastic glass beads to be 0.0005 bar and 0.0011 bar respectively. We calculate that batch degassing of lunar magmas containing initial volatile contents of 1200 ppm H 2 O (dissolved primarily as hydroxyl) and 4-64 ppm C would produce enough vapor to reach the critical vapor volume fraction thought to be required for magma 2 fragmentation (~65-75 vol. %) at a total pressure of ~5 bar (corresponding to a depth beneath the lunar surface of ~120 m). At a fragmentation pressure of ~5 bar, the calculated vapor composition is dominated by H 2 , supporting the hypothesis that H 2 , rather than CO, was the primary propellant of the lunar fire fountain eruptions. The results of our batch degassing model suggest that initial melt compositions with >~200 ppm C would be required for the vapor composition to be dominated by CO rather than H 2 at 65-75 % vesicularity.

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In situ spectroscopic study of water speciation in the depolymerized Na 2 Si 2 O 5 melt

Cited by 18 publications

References 37 publications

A comprehensive molecular dynamics simulation study of hydrous magmatic liquids

A comprehensive molecular dynamics simulation study of hydrous magmatic liquids

In situ study at high pressure and temperature of the environment of water in hydrous Na and Ca aluminosilicate melts and coexisting aqueous fluids

Solubility of water in lunar basalt at low pH2O

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