Research ArticleSPACE SCIENCES

Refining lunar impact chronology through high spatial resolution 40Ar/39Ar dating of impact melts

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Science Advances  12 Feb 2015:
Vol. 1, no. 1, e1400050
DOI: 10.1126/sciadv.1400050
  • Fig. 1 BSE image mosaics and x-ray elemental maps of the studied sections of 77115 and 73217.

    White dashed lines mark the lithologic boundaries of domains 1, 2, and 3 in the sections of 73217 (B to D). (A) BSE mosaic of 77115,121 with the locations and dimensions of UVLAMP melt analyses shown as red circles. (B) BSE mosaic of 73217,83 with the locations and dimensions of UVLAMP melt analyses in domains 1 (yellow), 2 (blue), and 3 (red). The coarse-grained region in the upper right is a gabbroic granulite. (C) Combined x-ray elemental map of Al-Mg-Fe (R-G-B) in 73217,84 (the thin section facing 73217,83). Plagioclase grains are generally red, pyroxenes and olivines are green, and ilmenite is blue; the black elongate grain in domain 2 is quartz. (D) X-ray elemental map of K in 73217,84; arrows denote the apparent enrichment of K in domain 3. See the text for descriptions of domains labeled 1a, 1b, 2, and 3 in (B) to (D). Scale bars, 1 mm.

  • Fig. 2 UVLAMP 40Ar/39Ar results for 77115,121.

    (A) Summed PDP of melt dates (red) with individual dates depicted as small red circles above. The gray region represents the range of dates obtained for clasts in 77115,121. (B) Isotope correlation plot of 40Ar/36Ar versus 39Ar/36Ar and linear regression (dashed line) for melt analyses in 77115,121. The inset figure is an enlarged plot of the boxed region near the origin. The data have been corrected for the presence of nucleogenic and cosmogenic isotopes (see Materials and Methods for details). Error ellipses and uncertainties are all 2σ.

  • Fig. 3 UVLAMP 40Ar/39Ar results for 73217,83.

    (A) Summed PDP of the dates for the three melt domains with individual dates depicted as small colored circles above (yellow, domain 1; blue, domain 2; red, domain 3). Vertical gray bars indicate ranges of two populations of clast dates from 73217,83. The vertical dashed lines indicate U/Pb dates for zircons and phosphates from another section of 73217 interpreted by Grange et al. (2) to represent impact melting events. (B to D) Isotope correlation plots of 40Ar/36Ar versus 39Ar/36Ar with linear regressions shown as dashed lines. Inset figures are enlarged plots of the boxed regions in their parent figures. The data have been corrected for the presence of nucleogenic and cosmogenic isotopes (see Materials and Methods for details). Error ellipses and uncertainties are all 2σ. (B) Isotope correlation plot for analyses in domain 1. (C) Isotope correlation plot of domain 2 analyses. Note: The one analysis that was rejected as an outlier is not shown (see the text for details). It would plot below the regressed line, up and to the right outside of the present bounds. (D) Isotope correlation plot of domain 3 data. Points shown as dark red ellipses were selected from mode 3A of the PDP (see the text for details) and regressed (upper line) to constrain the upper bound of the range of apparent ages measured for domain 3. Points shown as light red ellipses were selected from mode 3B of the PDP and regressed (lower line) to constrain the lower bound of the range of apparent ages for domain 3. The locations of the analyses that constitute modes 3A and 3B are shown in fig. S2. All other data are shown as unfilled ellipses.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/ content/full/1/1/e1400050/DC1

    Materials and Methods

    Fig. S1. BSE image mosaic of 77115,121,1 with UVLAMP analysis locations.

    Fig. S2. BSE image mosaic of 73217,83,1 with UVLAMP analysis locations.

    Table S1. Recalculated literature data.

    Table S2. UVLAMP 40Ar/39Ar data for 77115,121,1.

    Table S3. UVLAMP 40Ar/39Ar data for 73217,83,1.

    Table S4. Irradiation history for 77115,121 and 73217,83, PP20 age monitor, and flux monitors.

    References (5062)

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. BSE image mosaic of 77115,121,1 with UVLAMP analysis locations.
    • Fig. S2. BSE image mosaic of 73217,83,1 with UVLAMP analysis locations.
    • Table S1. Recalculated literature data.
    • Table S4. Irradiation history for 77115,121 and 73217,83, PP20 age monitor, and flux monitors.
    • References (50–62)

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    Other Supplementary Material for this manuscript includes the following:

    • Table S2. UVLAMP 40Ar/39 data for 77115,121,1.
    • Table S3. UVLAMP 40Ar/39 data for 73217,83,1.

    Files in this Data Supplement:

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