Solution behavior of reduced COH volatiles in silicate melts at high pressure and temperature

Mysen, Bjørn O.; Fogel, Marilyn L.; Morrill, Penny L.; Cody, George D.

doi:10.1016/j.gca.2008.12.016

Cited by 76 publications

(63 citation statements)

References 67 publications

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“…4). Previous studies (14)(15)(16) found methane as the only dissolved carbon species within the fO 2 range of our reduced experiments (fO 2 < IW−0.55), but these prior studies used Fe-free basaltic composition and obviously did not contain dissolved iron carbonyl. Therefore, carbon speciation is a function of melt composition as well as fO 2 .…”

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confidence: 76%

“…Previous experimental studies on the speciation of carbon in Fe-free silicate systems under reducing conditions or at fO 2 < IW show carbon is dissolved as methane (14)(15)(16). However, under more oxidizing conditions in basaltic melt compositions, carbon is dissolved as carbonate (17)(18)(19), and the transition in speciation from methane to carbonate has long been debated as either occurring at more reducing conditions than IW+1 (20,21) or at more oxidizing conditions (15).…”

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confidence: 98%

“…We found the reduced samples contain iron carbonyl [Fe(CO) 5 ], as well as minor methane (CH 4 ) in a few experiments, whereas the oxidized glasses have carbonate as the only dissolved carbon species. In the Raman spectra of the reduced glasses, peaks at 2,110 and 2,900 cm −1 are due to the CO vibrations associated with Fe(CO) 5 (30) and dissolved CH 4 (14), respectively ( Fig. 3 A and B).…”

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confidence: 99%

“…In addition, we observe a weak band at 3,370 cm −1 in FTIR spectra of reduced glasses (GG-24 and GG-25), which also display the 2,110-cm −1 Fe-carbonyl peak. Although the peak could arise from molecular H 2 O, recent studies have attributed peaks at 3,350 cm −1 (15), 3,310 cm −1 (14), and 3,290 cm −1 (32) to C-H stretching in alkyne groups. Another study (33) assigns peaks at 3,188, 3,293, and 3,377 cm −1 to N-H bonds.…”

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confidence: 99%

“…(B) High wavenumber region of Raman spectra shows dissolved water in all glasses at 3,550 cm −1 (36). Reduced glasses contain dissolved CH 4 (2,900 cm −1 ) (14), and GG-14 contains dissolved H 2 (4,100 cm −1 ) (38). (C ) FTIR spectra (normalized by glass thickness) show water dissolved at 3,550 cm −1 (37).…”

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confidence: 99%

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Degassing of reduced carbon from planetary basalts

Wetzel

Rutherford

Jacobsen

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Degassing of planetary interiors through surface volcanism plays an important role in the evolution of planetary bodies and atmospheres. On Earth, carbon dioxide and water are the primary volatile species in magmas. However, little is known about the speciation and degassing of carbon in magmas formed on other planets (i.e., Moon, Mars, Mercury), where the mantle oxidation state [oxygen fugacity (fO 2 )] is different from that of the Earth. Using experiments on a lunar basalt composition, we confirm that carbon dissolves as carbonate at an fO 2 higher than -0.55 relative to the iron wustite oxygen buffer (IW-0.55), whereas at a lower fO 2 , we discover that carbon is present mainly as iron pentacarbonyl and in smaller amounts as methane in the melt. The transition of carbon speciation in mantle-derived melts at fO 2 less than IW-0.55 is associated with a decrease in carbon solubility by a factor of 2. Thus, the fO 2 controls carbon speciation and solubility in mantle-derived melts even more than previous data indicate, and the degassing of reduced carbon from Fe-rich basalts on planetary bodies would produce methane-bearing, CO-rich early atmospheres with a strong greenhouse potential.hydrogen | iron carbonyl | magmatic volatiles | experimental petrology M agmas formed through igneous processes on parent bodies in the early solar system span 12 log units in oxidation state, from 6.3 log units of oxygen fugacity (fO 2 ) below the iron wustite oxygen buffer (IW) to 6 log units above the IW (IW−6.3 to IW+6) (1-4). Over the wide range of basalt fO 2 observed in these planetary bodies, thermodynamic data for the C-O-H gas system indicate that there are significant changes in gas phase speciation (5). These differences should be reflected in how volatiles are dissolved in magmas, but carbon speciation experiments for basaltic systems are limited, particularly at low fO 2 . The developing evidence for volatiles in magmas erupted on the Moon (6, 7) as well as on Earth (3,8), Mars (9-12), and Mercury (13) is a strong incentive to improve our understanding of C-O-H speciation and solubility in planetary basaltic magmas.Previous experimental studies on the speciation of carbon in Fe-free silicate systems under reducing conditions or at fO 2 < IW show carbon is dissolved as methane (14-16). However, under more oxidizing conditions in basaltic melt compositions, carbon is dissolved as carbonate (17)(18)(19), and the transition in speciation from methane to carbonate has long been debated as either occurring at more reducing conditions than IW+1 (20, 21) or at more oxidizing conditions (15). Another study (22) shows that a significant amount of C 4+ (carbonate) can be incorporated at extremely low fO 2 (IW−4.5) if Fe and alkalis are present in the melt. Additional experiments on Fe-bearing basalt are clearly required to resolve the conflicts in existing data. The results are important in understanding the residence time of carbon in the mantle and the rate of carbon degassing during the early evolution of terrestrial planets ...

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confidence: 76%

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confidence: 98%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Degassing of reduced carbon from planetary basalts

Wetzel

Rutherford

Jacobsen

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Hydrogen isotope fractionation and redox‐controlled solution mechanisms in silicate‐COH melt + fluid systems

Mysen

2015

JGR Solid Earth

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The behavior of volatiles in silicate‐COH melts and fluids and hydrogen isotope fractionation between melt and fluid were determined experimentally to advance our understanding of the role of volatiles in magmatic processes. Experiments were conducted in situ while the samples were at the desired temperature and pressure to 825°C and ~1.6 GPa and with variable redox conditions. Under oxidizing conditions, melt and fluid comprised CO2, CO3, HCO3, OH, H2O, and silicate components, whereas under reducing conditions, the species were CH4, H2, H2O, and silicate components. Temperature‐dependent hydrogen isotope exchange among structural entities within coexisting fluids and melts yields ΔH values near 14 and 24 kJ/mol and −5 and −1 kJ/mol under oxidizing and reducing conditions, respectively. This temperature (and probably pressure)‐dependent D/H fractionation is because of interaction between D and H and silicate and C‐bearing species in silicate‐saturated fluids and in COH fluid‐saturated melts. The temperature‐ and pressure‐dependent D/H fractionation factors suggest that partial melts in the presence of COH volatiles in the upper mantle can have δD values 100% or more lighter relative to coexisting silicate‐saturated fluid. This effect is greater under oxidizing than under reducing conditions. It is suggested that δD variations of upper mantle mid‐ocean ridge basalt (MORB) sources, inferred from the δD of MORB magmatic rocks, can be explained by variations in redox conditions during melting. Lower δD values of the MORB magma reflect more reducing conditions in the mantle source.

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A Low O/Si Ratio on the Surface of Mercury: Evidence for Silicon Smelting?

et al. 2017

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Data from the Gamma‐Ray Spectrometer (GRS) that flew on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft indicate that the O/Si weight ratio of Mercury's surface is 1.2 ± 0.1. This value is lower than any other celestial surface that has been measured by GRS and suggests that 12–20% of the surface materials on Mercury are composed of Si‐rich, Si‐Fe alloys. The origin of the metal is best explained by a combination of space weathering and graphite‐induced smelting. The smelting process would have been facilitated by interaction of graphite with boninitic and komatiitic parental liquids. Graphite entrained at depth would have reacted with FeO components dissolved in silicate melt, resulting in the production of up to 0.4–0.9 wt % CO from the reduction of FeO to Fe0—CO production that could have facilitated explosive volcanic processes on Mercury. Once the graphite‐entrained magmas erupted, the tenuous atmosphere on Mercury prevented the buildup of CO over the lavas. The partial pressure of CO would have been sufficiently low to facilitate reaction between graphite and SiO2 components in silicate melts to produce CO and metallic Si. Although exotic, Si‐rich metal as a primary smelting product is hypothesized on Mercury for three primary reasons: (1) low FeO abundances of parental magmas, (2) elevated abundances of graphite in the crust and regolith, and (3) the presence of only a tenuous atmosphere at the surface of the planet within the 3.5–4.1 Ga timespan over which the planet was resurfaced through volcanic processes.

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Solution behavior of reduced COH volatiles in silicate melts at high pressure and temperature

Cited by 76 publications

References 67 publications

Degassing of reduced carbon from planetary basalts

Degassing of reduced carbon from planetary basalts

Hydrogen isotope fractionation and redox‐controlled solution mechanisms in silicate‐COH melt + fluid systems

A Low O/Si Ratio on the Surface of Mercury: Evidence for Silicon Smelting?

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