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The chlorine isotope fingerprint of the lunar magma ocean.

Boyce JW, Treiman AH, Guan Y, Ma C, Eiler JM, Gross J, Greenwood JP, Stolper EM - Sci Adv (2015)

Bottom Line: The Moon contains chlorine that is isotopically unlike that of any other body yet studied in the Solar System, an observation that has been interpreted to support traditional models of the formation of a nominally hydrogen-free ("dry") Moon.Instead, (37)Cl/(35)Cl correlates positively with Cl abundance in apatite, as well as with whole-rock Th abundances and La/Lu ratios, suggesting that the high (37)Cl/(35)Cl in lunar basalts is inherited from urKREEP, the last dregs of the lunar magma ocean.These new data suggest that the high chlorine isotope ratios of lunar basalts result not from the degassing of their lavas but from degassing of the lunar magma ocean early in the Moon's history.

View Article: PubMed Central - PubMed

Affiliation: Division of Geological and Planetary Sciences, Caltech, 1200 East California Boulevard, Pasadena, CA 91125, USA. ; Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095-1567, USA.

ABSTRACT
The Moon contains chlorine that is isotopically unlike that of any other body yet studied in the Solar System, an observation that has been interpreted to support traditional models of the formation of a nominally hydrogen-free ("dry") Moon. We have analyzed abundances and isotopic compositions of Cl and H in lunar mare basalts, and find little evidence that anhydrous lava outgassing was important in generating chlorine isotope anomalies, because (37)Cl/(35)Cl ratios are not related to Cl abundance, H abundance, or D/H ratios in a manner consistent with the lava-outgassing hypothesis. Instead, (37)Cl/(35)Cl correlates positively with Cl abundance in apatite, as well as with whole-rock Th abundances and La/Lu ratios, suggesting that the high (37)Cl/(35)Cl in lunar basalts is inherited from urKREEP, the last dregs of the lunar magma ocean. These new data suggest that the high chlorine isotope ratios of lunar basalts result not from the degassing of their lavas but from degassing of the lunar magma ocean early in the Moon's history. Chlorine isotope variability is therefore an indicator of planetary magma ocean degassing, an important stage in the formation of terrestrial planets.

No MeSH data available.


Related in: MedlinePlus

Plots of Cl and H2O versus δ37Cl.(A and B) Plots of Cl (A) and H2O (B) concentrations versus δ37Cl values in apatite from the Moon. Each data point represents a single apatite grain in a rock, including data from the literature plotted as smaller symbols (11, 12, 33); magenta symbols are high-Ti basalts; blue symbols are low-Ti basalts; gray symbols are KREEP basalts. There are no statistically significant correlations observed for any of the sample types studied here. Elevated δ37Cl values are associated with both high H2O and high Cl concentrations: The former is inconsistent with the idea that elevated δ37Cl values are only associated with anhydrous conditions, and the latter is inconsistent with a simple, single-stage fractionation model.
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Figure 2: Plots of Cl and H2O versus δ37Cl.(A and B) Plots of Cl (A) and H2O (B) concentrations versus δ37Cl values in apatite from the Moon. Each data point represents a single apatite grain in a rock, including data from the literature plotted as smaller symbols (11, 12, 33); magenta symbols are high-Ti basalts; blue symbols are low-Ti basalts; gray symbols are KREEP basalts. There are no statistically significant correlations observed for any of the sample types studied here. Elevated δ37Cl values are associated with both high H2O and high Cl concentrations: The former is inconsistent with the idea that elevated δ37Cl values are only associated with anhydrous conditions, and the latter is inconsistent with a simple, single-stage fractionation model.

Mentions: Chlorine isotope ratios in the samples analyzed here range from δ37Cl = −4‰ in Miller Range (MIL) 05035 to +18‰ in 12039 (Fig. 2 and Table 1) and are consistent with the few previous analyses of δ37Cl in apatite from mare basalts, with the exception of MIL 05035: The δ37Cl for this sample (−4 ± 2‰) is among the lowest measured in any natural material from anywhere in the Solar System. Lunar apatites also display a wide range of D/H (Fig. 3), with δD values [reported as δD relative to Vienna standard mean ocean water (VSMOW)] of multispot grain averages ranging from −150 to +970‰. Of the basalts, 10044 has the greatest range in δ37Cl (+2 to +15‰), as well as in δD, from +540 to +950‰ (n = 6), where the latter are consistent with other analyses of 10044 (Fig. 3).


The chlorine isotope fingerprint of the lunar magma ocean.

Boyce JW, Treiman AH, Guan Y, Ma C, Eiler JM, Gross J, Greenwood JP, Stolper EM - Sci Adv (2015)

Plots of Cl and H2O versus δ37Cl.(A and B) Plots of Cl (A) and H2O (B) concentrations versus δ37Cl values in apatite from the Moon. Each data point represents a single apatite grain in a rock, including data from the literature plotted as smaller symbols (11, 12, 33); magenta symbols are high-Ti basalts; blue symbols are low-Ti basalts; gray symbols are KREEP basalts. There are no statistically significant correlations observed for any of the sample types studied here. Elevated δ37Cl values are associated with both high H2O and high Cl concentrations: The former is inconsistent with the idea that elevated δ37Cl values are only associated with anhydrous conditions, and the latter is inconsistent with a simple, single-stage fractionation model.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4643783&req=5

Figure 2: Plots of Cl and H2O versus δ37Cl.(A and B) Plots of Cl (A) and H2O (B) concentrations versus δ37Cl values in apatite from the Moon. Each data point represents a single apatite grain in a rock, including data from the literature plotted as smaller symbols (11, 12, 33); magenta symbols are high-Ti basalts; blue symbols are low-Ti basalts; gray symbols are KREEP basalts. There are no statistically significant correlations observed for any of the sample types studied here. Elevated δ37Cl values are associated with both high H2O and high Cl concentrations: The former is inconsistent with the idea that elevated δ37Cl values are only associated with anhydrous conditions, and the latter is inconsistent with a simple, single-stage fractionation model.
Mentions: Chlorine isotope ratios in the samples analyzed here range from δ37Cl = −4‰ in Miller Range (MIL) 05035 to +18‰ in 12039 (Fig. 2 and Table 1) and are consistent with the few previous analyses of δ37Cl in apatite from mare basalts, with the exception of MIL 05035: The δ37Cl for this sample (−4 ± 2‰) is among the lowest measured in any natural material from anywhere in the Solar System. Lunar apatites also display a wide range of D/H (Fig. 3), with δD values [reported as δD relative to Vienna standard mean ocean water (VSMOW)] of multispot grain averages ranging from −150 to +970‰. Of the basalts, 10044 has the greatest range in δ37Cl (+2 to +15‰), as well as in δD, from +540 to +950‰ (n = 6), where the latter are consistent with other analyses of 10044 (Fig. 3).

Bottom Line: The Moon contains chlorine that is isotopically unlike that of any other body yet studied in the Solar System, an observation that has been interpreted to support traditional models of the formation of a nominally hydrogen-free ("dry") Moon.Instead, (37)Cl/(35)Cl correlates positively with Cl abundance in apatite, as well as with whole-rock Th abundances and La/Lu ratios, suggesting that the high (37)Cl/(35)Cl in lunar basalts is inherited from urKREEP, the last dregs of the lunar magma ocean.These new data suggest that the high chlorine isotope ratios of lunar basalts result not from the degassing of their lavas but from degassing of the lunar magma ocean early in the Moon's history.

View Article: PubMed Central - PubMed

Affiliation: Division of Geological and Planetary Sciences, Caltech, 1200 East California Boulevard, Pasadena, CA 91125, USA. ; Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095-1567, USA.

ABSTRACT
The Moon contains chlorine that is isotopically unlike that of any other body yet studied in the Solar System, an observation that has been interpreted to support traditional models of the formation of a nominally hydrogen-free ("dry") Moon. We have analyzed abundances and isotopic compositions of Cl and H in lunar mare basalts, and find little evidence that anhydrous lava outgassing was important in generating chlorine isotope anomalies, because (37)Cl/(35)Cl ratios are not related to Cl abundance, H abundance, or D/H ratios in a manner consistent with the lava-outgassing hypothesis. Instead, (37)Cl/(35)Cl correlates positively with Cl abundance in apatite, as well as with whole-rock Th abundances and La/Lu ratios, suggesting that the high (37)Cl/(35)Cl in lunar basalts is inherited from urKREEP, the last dregs of the lunar magma ocean. These new data suggest that the high chlorine isotope ratios of lunar basalts result not from the degassing of their lavas but from degassing of the lunar magma ocean early in the Moon's history. Chlorine isotope variability is therefore an indicator of planetary magma ocean degassing, an important stage in the formation of terrestrial planets.

No MeSH data available.


Related in: MedlinePlus