Research ArticleGEOCHEMISTRY

The chlorine isotope fingerprint of the lunar magma ocean

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Science Advances  25 Sep 2015:
Vol. 1, no. 8, e1500380
DOI: 10.1126/sciadv.1500380

Figures

  • Fig. 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.

  • Fig. 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.

  • Fig. 3 δD versus H2O.

    δD versus H2O for new data (large symbols) and data from the literature (small symbols). Hollow symbols are multiple hydrogen abundance measurements plotted with bulk δD values. Data have been previously interpreted as representing mixing between a high-δD, high-H2O end member (possibly comets), and a low-δD, low-H2O end member (possibly solar wind), or evolution from or contamination with a material of chondritic composition (16, 24, 25, 33), though neither explanation explains all the data. Note the large number of analyses with δD values in the range for bulk chondrites (+750 to −200‰) (58).

  • Fig. 4 Plot of δD versus δ37Cl.

    Plot of δD versus δ37Cl for data generated in this study and those from previous studies (plotted as smaller symbols). Hollow symbols indicate in situ δ37Cl measurements plotted versus bulk or mean apatite δD from the literature. The presence of high δ37Cl apatite with low δD values is inconsistent with the prediction that elevated δ37Cl would accompany elevated δD, because both isotopes should shift toward higher δ values during degassing. The lack of correlation between δD and δ37Cl suggests that the two isotope systems are at least partially decoupled and that multiple processes may be at work.

  • Fig. 5 Bulk Th and La/Lu versus δ37Cl.

    (A and B) Measures of KREEP contribution, bulk rock Th abundance (A), and bulk rock La/Lu (B), as a function of δ37Cl, with trace element data from (43, 54, 59). Symbols are the same as those in previous figures. For all basalts, δ37Cl is strongly correlated with Th and La/Lu, suggesting that pure urKREEP would have δ37Cl ≥+30‰.

Tables

  • Table 1 New data generated for this study.
    SampleSectionGrainH2O (ppm)H2O 2σCl (ppm)Cl 2σδ37Clδ37Cl 2σδDδD 2σCategory
    100441210110529365104+93+93331High Ti basalt
    10044121a7282729211+63+95427High Ti basalt
    10044121b+64High Ti basalt
    10044121c12203030011+24+78123High Ti basalt
    1004464428772625010+113+53657High Ti basalt
    100446448421223976122+153High Ti basalt
    100446444a8262521910+123+60633High Ti basalt
    100446444b11552947916+123+70228High Ti basalt
    750555516042339814+83+62135High Ti basalt
    7505555212253548516+63+79426High Ti basalt
    7505555312413033412+143+96827High Ti basalt
    7505555414303441014+63+79426High Ti basalt
    7505555101+53High Ti basalt
    1203942419964392829+183+72030Low Ti basalt
    1203942623794747716+173+83031Low Ti basalt
    120394210+163Low Ti basalt
    120394211+173Low Ti basalt
    120394217a278495115736+173+72928Low Ti basalt
    120394217b29165766521+163+69828Low Ti basalt
    1204021111052115884489+173+9163Low Ti basalt
    120402114320268983+133+1484Low Ti basalt
    12040211516203388104+144−15026Low Ti basalt
    MIL 050351−42Low Ti basalt

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