The Chlorine Isotope Composition of the Moon and Implications for an Anhydrous Mantle

Sharp, Z. D.; Shearer, C. K.; McKeegan, Kevin D.; Barnes, Jaime D.; Wang, Y. Q.

doi:10.1126/science.1192606

Cited by 216 publications

(218 citation statements)

References 26 publications

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“…In particular, direct measurements of water in incompletely degassed, primitive lunar glasses made in several laboratories have shown that water concentrations are similar to those observed in magmas from Earth's depleted upper mantle (Saal et al 2008;Chen et al 2015;Hauri et al 2015;Wetzel et al 2015) and that the isotopic composition of this water is approximately chondritic (Friedman et al 1974;Saal et al 2013;Barnes et al 2014;Füri et al 2014;Tartèse et al 2014). Although these results and their generality to the Moon as a whole are not universally accepted (Sharp et al 2010;Greenwood et al 2011;Albarède et al 2015), these observations have been interpreted as signifying a common origin for terrestrial and lunar water ). The incorporation of water into the Moon in concentrations similar to those of the Earth is seemingly at odds with the widely held view of the origin of the Moon as the result of an impact between the early Earth and a Mars-sized impactor (e.g., Canup and Asphaug 2001;Pahlevan and Stevenson 2007).…”

Section: Introductionmentioning

confidence: 95%

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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Section: Introductionmentioning

confidence: 95%

Solubility of water in lunar basalt at low pH2O

Newcombe

Brett

Beckett

et al. 2017

Geochimica et Cosmochimica Acta

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“…Chlorine isotopes have been strongly fractionated in some lunar materials (−1 to +24 ), leading Sharp et al [32] to suggest a mechanism of volatilization of Cl as metal halides (e.g. NaCl, ZnCl 2 , FeCl 2 ), loss of Cl during basalt eruption on the lunar surface and, consequently, an essentially anhydrous lunar interior.…”

Section: (B) Chlorinementioning

confidence: 99%

“…where X is the heavier mass isotope ( 34 S, 37 Cl, 41 K, 66 Zn) and Y is the lighter mass isotope ( 32 S, 35 Cl, 39 [53,54,56], for (b) from [32,[57][58][59], for (c) from [31] and for (d) from [34,37].…”

Section: Isotopic Fractionation Of Moderately Volatile Elements In Comentioning

confidence: 99%

“…Volatilization of Cl on the Moon is possible because of the low calculated H/Cl ratio for lunar basalts and from the presence of metal halides on the surface coatings of lunar pyroclastic glass beads [63]. Sharp et al [32] presented Cl isotope and abundance data for bulk rock analyses of lunar mare basalts, regolith materials and lunar pyroclastic glass beads by gas-source mass spectrometry, as well as Cl isotope analyses of apatites performed by secondary ionization mass spectrometry. Lunar regolith components (+5.6 to +16 and 8-117 ppm Cl) are enriched in 37 Cl relative to mare basalts (0 to +4.2 and 5-25 ppm Cl) and apatites within mare basalts and KREEP-rich (potassium-rare earth elements-phosphorus) rocks (lunar sample no.…”

Section: (B) Chlorinementioning

confidence: 99%

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Evaporative fractionation of volatile stable isotopes and their bearing on the origin of the Moon

Day

Moynier

2014

Phil. Trans. R. Soc. A.

109

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The Moon is depleted in volatile elements relative to the Earth and Mars. Low abundances of volatile elements, fractionated stable isotope ratios of S, Cl, K and Zn, high μ ( 238 U/ 204 Pb) and long-term Rb/Sr depletion are distinguishing features of the Moon, relative to the Earth. These geochemical characteristics indicate both inheritance of volatile-depleted materials that formed the Moon and planets and subsequent evaporative loss of volatile elements that occurred during lunar formation and differentiation. Models of volatile loss through localized eruptive degassing are not consistent with the available S, Cl, Zn and K isotopes and abundance data for the Moon. The most probable cause of volatile depletion is global-scale evaporation resulting from a giant impact or a magma ocean phase where inefficient volatile loss during magmatic convection led to the present distribution of volatile elements within mantle and crustal reservoirs. Problems exist for models of planetary volatile depletion following giant impact. Most critically, in this model, the volatile loss requires preferential delivery and retention of late-accreted volatiles to the Earth compared with the Moon. Different proportions of late-accreted mass are computed to explain present-day distributions of volatile and moderately volatile elements (e.g. Pb, Zn; 5 to >10%) relative to highly siderophile elements (approx. 0.5%) for the Earth. Models of early magma ocean phases may be more effective in explaining the volatile loss. Basaltic materials (e.g. eucrites and angrites) from highly differentiated airless asteroids are volatile-depleted, like the Moon, whereas the Earth and Mars have proportionally greater volatile contents. Parent-body size and the existence of early atmospheres are therefore likely to represent fundamental controls on planetary volatile retention or loss.

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“…Of the Apollo 12 basalt suite, 12040 is considered one of the slowestcooled samples 21 , suggesting the magma of 12040 may have underwent extensive degassing of water. Significant degassing of water has recently been suggested for 12040 based on Cl isotope composition of apatite 22 . Apatite grain fragments in the late-stage matrix regions of breccia samples 12013 and 14305,94 were also found to have very low water.…”

mentioning

confidence: 99%

Hydrogen isotope ratios in lunar rocks indicate delivery of cometary water to the Moon

et al. 2011

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Hydrogen isotope ratios in lunar rocks and the delivery of cometary water to the MoonWater plays a critical role in the evolution of planetary bodies 1 , and determination of the amount and sources of lunar water has profound implications for our understanding of the history of the Earth-Moon system. During the Apollo program, the lunar samples were found to be devoid of indigeneous water 2,3 . The severe depletion of lunar volatiles 4 , including water, has long been seen as strong support for the giant-impact origin of the Moon 5 . Recent studies have found water in lunar volcanic glasses 6 and in lunar apatite 7-9 , but the sources of lunar water have not been determined. Here we report ion microprobe measurements of water and hydrogen isotopes in the hydrous mineral apatite, found in crystalline lunar mare basalts and highlands rocks collected during the Apollo missions. We find significant water in apatite from both mare and highlands rocks, indicating a role for water during all phases of the Moon's magmatic history. Variations of hydrogen isotope ratios in apatite suggest the lunar mantle, solar wind protons, and comets as possible sources for water in lunar rocks and imply a significant delivery of cometary water to the Earth-Moon system shortly after the Moon-forming impact.

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The Chlorine Isotope Composition of the Moon and Implications for an Anhydrous Mantle

Cited by 216 publications

References 26 publications

Solubility of water in lunar basalt at low pH2O

Solubility of water in lunar basalt at low pH2O

Evaporative fractionation of volatile stable isotopes and their bearing on the origin of the Moon

Hydrogen isotope ratios in lunar rocks indicate delivery of cometary water to the Moon

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