A model for C–O–H fluid in the Earth’s mantle

Zhang, Chi; Duan, Zhenhao

doi:10.1016/j.gca.2009.01.021

Cited by 184 publications

(140 citation statements)

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“…The chemical composition of planetary ices and possible chemical reactions within deep interiors of these planets are critical for understanding their thermal, magnetic and electrical properties 3 , and represent necessary input information for theoretical modelling 4 . Also, the behaviour of hydrocarbons as a part of reduced carbon-oxygen-hydrogen fluid within the deep Earth is of particular interest as oxygen fugacity below the wustitemagnetite buffer is likely to shift fluid phase composition from CO 2 -H 2 O to CH 4 -H 2 O in the simplest modelling [5][6][7][8] . However, phase relations in the C-H system are poorly understood even at relatively low pressures.…”

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confidence: 99%

“…However, phase relations in the C-H system are poorly understood even at relatively low pressures. For example, the results of methane melting curve measurements are contradictory and report only up Thermodynamic modelling of C-H systems 7,15 , as well as ab initio molecular dynamic (MD) computations 12,14 , show the rise of stability of heavier hydrocarbons with increasing pressure and temperature. According to MD, methane dissociates to molecular hydrogen and diamond at pressures of 4300 GPa and at temperatures of 44,000 K (ref.…”

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confidence: 99%

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Carbon precipitation from heavy hydrocarbon fluid in deep planetary interiors

Lobanov

Chen

et al. 2013

Nat Commun

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The phase diagram of the carbon-hydrogen system is of great importance to planetary sciences, as hydrocarbons comprise a significant part of icy giant planets and are involved in reduced carbon-oxygen-hydrogen fluid in the deep Earth. Here we use resistively-and laser-heated diamond anvil cells to measure methane melting and chemical reactivity up to 80 GPa and 2,000 K. We show that methane melts congruently below 40 GPa. Hydrogen and elementary carbon appear at temperatures of 41,200 K, whereas heavier alkanes and unsaturated hydrocarbons (424 GPa) form in melts of 41,500 K. The phase composition of carbon-hydrogen fluid evolves towards heavy hydrocarbons at pressures and temperatures representative of Earth's lower mantle. We argue that reduced mantle fluids precipitate diamond upon re-equilibration to lighter species in the upwelling mantle. Likewise, our findings suggest that geophysical models of Uranus and Neptune require reassessment because chemical reactivity of planetary ices is underestimated.

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confidence: 99%

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Carbon precipitation from heavy hydrocarbon fluid in deep planetary interiors

Lobanov

Chen

et al. 2013

Nat Commun

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“…The H-C-O vapor in our experiments contains negligible N, and, under the conditions of our experiments, CH 4 can also be neglected (Deines et al 1974;Zhang and Duan 2009). However, our most reducing experimental glasses were equilibrated with atmospheres containing >90% H 2 , so the possible dissolution of H as molecular hydrogen must be considered.…”

Section: The Potential Role Of Other H-bearing Species In Lunar Meltsmentioning

confidence: 68%

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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“…This ratio of CH 4 to CO degassing will change depending on the depth of degassing. At greater pressures, a reduced atmosphere will be CH 4 -rich, but it will change to being CO-rich at shallower depths (43). For the crust formation conditions assumed, an oxidized Martian melt would produce a thicker atmosphere than a reduced melt, but both oxidized and reduced melts would degas more carbon than previously reported (21,29).…”

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confidence: 84%

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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A model for C–O–H fluid in the Earth’s mantle

Cited by 184 publications

References 69 publications

Carbon precipitation from heavy hydrocarbon fluid in deep planetary interiors

Carbon precipitation from heavy hydrocarbon fluid in deep planetary interiors

Solubility of water in lunar basalt at low pH2O

Degassing of reduced carbon from planetary basalts

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