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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

Photomicrographs of two basalts.Photomicrographs of two basalts analyzed in this study, with yellow crosses marking the locations of analyses. (A) Subhedral apatite grains (outlined in yellow for clarity) forming a cluster in Apollo 12039,42. (B) Euhedral to subhedral apatite grains in Apollo 12040,211 that show skeletal growth with hollow centers.
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Figure 1: Photomicrographs of two basalts.Photomicrographs of two basalts analyzed in this study, with yellow crosses marking the locations of analyses. (A) Subhedral apatite grains (outlined in yellow for clarity) forming a cluster in Apollo 12039,42. (B) Euhedral to subhedral apatite grains in Apollo 12040,211 that show skeletal growth with hollow centers.

Mentions: It has been difficult to reconcile interpretations based on H abundances and isotopic ratios with those based on Cl abundances and isotopic ratios, in part because there have been limited data on H and Cl abundances and isotopic compositions for the same materials. Here, we present measurements of H and Cl abundances as well as 37Cl/35Cl and D/H ratios in apatite crystals from a range of lunar basalts, where measurements are from the same thin sections and, when possible, in the same apatite crystals (for example, Fig. 1). We use these data to place constraints on the origin of the unusual chlorine isotopic composition of the Moon and to place that chlorine within the larger framework of lunar volatiles.


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)

Photomicrographs of two basalts.Photomicrographs of two basalts analyzed in this study, with yellow crosses marking the locations of analyses. (A) Subhedral apatite grains (outlined in yellow for clarity) forming a cluster in Apollo 12039,42. (B) Euhedral to subhedral apatite grains in Apollo 12040,211 that show skeletal growth with hollow centers.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 1: Photomicrographs of two basalts.Photomicrographs of two basalts analyzed in this study, with yellow crosses marking the locations of analyses. (A) Subhedral apatite grains (outlined in yellow for clarity) forming a cluster in Apollo 12039,42. (B) Euhedral to subhedral apatite grains in Apollo 12040,211 that show skeletal growth with hollow centers.
Mentions: It has been difficult to reconcile interpretations based on H abundances and isotopic ratios with those based on Cl abundances and isotopic ratios, in part because there have been limited data on H and Cl abundances and isotopic compositions for the same materials. Here, we present measurements of H and Cl abundances as well as 37Cl/35Cl and D/H ratios in apatite crystals from a range of lunar basalts, where measurements are from the same thin sections and, when possible, in the same apatite crystals (for example, Fig. 1). We use these data to place constraints on the origin of the unusual chlorine isotopic composition of the Moon and to place that chlorine within the larger framework of lunar volatiles.

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