Research ArticlePLANETARY SCIENCE

Early formation of planetary building blocks inferred from Pb isotopic ages of chondrules

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Science Advances  09 Aug 2017:
Vol. 3, no. 8, e1700407
DOI: 10.1126/sciadv.1700407
  • Fig. 1 Absolute chronology of chondrule formation.

    (A) Pb-Pb dates for individual chondrules from NWA 5697 (L3.10), NWA 6043 (CR2), NWA 7655 (CR2), and Allende (CV3). The Allende chondrules and three chondrules from NWA 5697 were previously reported (6). The timing of CAI formation is accepted to be 4567.30 ± 0.16 Ma (6). The CB chondrules are interpreted as having formed from colliding planetesimals at 4562.49 ± 0.21 Ma (31). (B) Histogram depicting the Pb-Pb age distribution of individual chondrules (n = 22) relative to CAI formation. A full description of the methods used to collect the data reported in the paper is available in the Supplementary Materials.

  • Fig. 2 Lead isotope evolution diagrams.

    (A) Initial Pb isotopic compositions of individual chondrules. The initial Pb isotope compositions are defined by the intersection of the individual isochrons and a Pb evolution array anchored on the solar system initial Pb isotope composition defined by chondrules 2-C1 and C1, which record the most primitive initial Pb isotope compositions (see the Supplementary Materials for the calculation of uncertainties on initial Pb isotope compositions). Individual chondrule data points have been displaced to the left- and right-hand side of the solar system initial Pb array for clarity. (B) Initial 207Pb/206Pb compositions and age variation diagram. The (207Pb/206Pb)initial values are reported in per 10,000 deviations (ε unit) from the composition defined by chondrules 2-C1 and C1. The blue box reflects the range of ε(207Pb/206Pb)initial compositions of the >1-My chondrules back-calculated at 4566.8 Ma. The robustness of the ε(207Pb/206Pb)initial and age correlation, including the effect of point selection of the individual regressions, has been statistically evaluated using a Monte Carlo approach (see the Supplementary Materials).

  • Fig. 3 Histograms depicting the absolute and relative timing ages of chondrules from unequilibrated ordinary chondrites of low petrologic type (≤3.1) based on internal isochron relationships.

    (A) Pb-Pb dates of chondrules from the NWA 5697 ordinary chondrite (this study). (B) 26Al-26Mg ages of chondrules from Semarkona, LEW 86134, QUE 97008, and Bishunpur ordinary chondrites (6568). The relative 26Al-26Mg ages are calculated, assuming that the precursor material from which these chondrules formed had a reduced initial 26Al/27Al value corresponding to ~1.5 × 10−5 (33). Three chondrules record initial 26Al/27Al slightly higher than 1.5 × 10−5 but are within the analytical uncertainty of this estimate and, hence, have been assigned a T = 0 formation age for simplicity.

  • Table 1 Summary of Pb-Pb dates, petrology, μ values, and 238U/235U and Zn isotope compositions of individual chondrules.

    Pb isotope data for the Allende and three chondrules from NWA 5697 (C1, C2, and C3) were previously reported by Connelly et al. (6) and are included here for completeness. P, porphyritic; NP, nonporphyritic; I, type I; II, type II. The 238U/235U uncertainties are propagated in the final age uncertainties. The Pb-Pb isochrons for three chondrules (5-C1, 5-C4, and 1-C2) project back to a modern terrestrial composition, and thus, accurate μ values cannot be calculated for these objects. The zinc isotope compositions are reported in δ notation, which reflects the per thousand (‰) deviations of the 66Zn/64Zn of the sample from the JMC Lyon standard.

    ChondruleTexture and typePb-Pb age (Ma)μ238U/235Uδ66Zn (‰)
    NWA 5697
      5-C1NP, II4567.61 ± 0.54137.807 ± 0.033
      2-C1NP, I4567.57 ± 0.5633137.779 ± 0.022−0.38 ± 0.05
      5-C2NP, II4567.54 ± 0.5221137.756 ± 0.029−1.07 ± 0.05
      5-C10NP, II4567.41 ± 0.5738137.786 ± 0.013−1.41 ± 0.05
      C1NP, I4566.67 ± 0.4323137.786 ± 0.013
      D-C3P, II4566.58 ± 0.5751137.786 ± 0.013−1.12 ± 0.05
      5-C4P, II4566.56 ± 0.53137.786 ± 0.013−1.15 ± 0.05
      3-C5P, II4566.20 ± 0.6328137.807 ± 0.026
      C3NP, II4566.02 ± 0.26183137.786 ± 0.013
      11-C1NP, II4565.84 ± 0.7232137.779 ± 0.030
      C2P, I4564.71 ± 0.3063137.786 ± 0.013
      11-C2NP, II4564.65 ± 0.46108137.755 ± 0.025−2.20 ± 0.05
      3-C2P, II4563.64 ± 0.5194137.786 ± 0.013−1.13 ± 0.05
    NWA 6043
      1-C2P, I4567.26 ± 0.37137.786 ± 0.013
      2-C2P, II4565.06 ± 0.40104137.786 ± 0.013
      2-C4P, II4564.50 ± 0.7093137.786 ± 0.013
      0-C1P, II4563.24 ± 0.6258137.786 ± 0.013
    NWA 7655
      1-C7P, II4566.51 ± 0.372137.786 ± 0.013
      1-C2P, I4564.54 ± 0.3451137.786 ± 0.013
      1-C6P, II4564.27 ± 0.499137.786 ± 0.013
    Allende
      C30P, II4567.32 ± 0.4229137.786 ± 0.013
      C20P, II4566.24 ± 0.6326137.786 ± 0.013

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/8/e1700407/DC1

    Supplementary Materials and Methods

    Supplementary Text

    fig. S1. Representative individual Raman spectra of a matrix grain in NWA 5697.

    fig. S2. Spectral parameters of Raman bands of carbonaceous materials in chondrites.

    fig. S3. Combined x-ray elemental map of NWA 5697 chondrules.

    fig. S4. Combined x-ray elemental map of NWA 5697 chondrules.

    fig. S5. Combined x-ray elemental map of NWA 7655 chondrules.

    fig. S6. Combined x-ray elemental map of NWA 6043 chondrules.

    fig. S7. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 5-C1 chondrule.

    fig. S8. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 2-C1 chondrule.

    fig. S9. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 5-C2 chondrule.

    fig. S10. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 5-C10 chondrule.

    fig. S11. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 D-C3 chondrule.

    fig. S12. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 5-C4 chondrule.

    fig. S13. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 3-C5 chondrule.

    fig. S14. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 11-C1 chondrule.

    fig. S15. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 11-C2 chondrule.

    fig. S16. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 3-C2 chondrule.

    fig. S17. Pb-Pb isochron diagram of Pb isotope analyses of NWA 6043 1-C2 chondrule.

    fig. S18. Pb-Pb isochron diagram of Pb isotope analyses of NWA 6043 2-C2 chondrule.

    fig. S19. Pb-Pb isochron diagram of Pb isotope analyses of NWA 6043 2-C4 chondrule.

    fig. S20. Pb-Pb isochron diagram of Pb isotope analyses of NWA 6043 0-C1 chondrule.

    fig. S21. Pb-Pb isochron diagram of Pb isotope analyses of NWA 7655 1-C7 chondrule.

    fig. S22. Pb-Pb isochron diagram of Pb isotope analyses of NWA 7655 1-C2 chondrule.

    fig. S23. Pb-Pb isochron diagram of Pb isotope analyses of NWA 7655 1-C6 chondrule.

    fig. S24. IMP data plotted in 204Pb/206Pb versus 207Pb/206Pb diagrams.

    fig. S25. 238U/235U ratios of individual chondrules, bulk chondrites, and achondrites.

    fig. S26. 27Al/24Mg and ε(207Pb/206Pb)initial variation diagram.

    fig. S27. Age and μ value variation diagram.

    fig. S28. Age and ε(207Pb/206Pb)initial variation diagram for selected chondrules.

    table S1. Electron microprobe analyses of the NWA 5697, NWA 7655, and NWA 6043 chondrules studied.

    table S2. Pb isotopic data for NWA 5697, NWA 7655, and NWA 6043 chondrules studied.

    table S3. Uranium isotope compositions.

    table S4. Zinc isotope compositions of selected chondrules.

    table S5. IMP Pb analytical data for two chondrules.

    table S6. Summary of the chondrules investigated.

    table S7. Chondrule Pb-Pb ages corrected using different 238U/235U estimates.

    References (6996)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Materials and Methods
    • Supplementary Text
    • fig. S1. Representative individual Raman spectra of a matrix grain in NWA 5697.
    • fig. S2. Spectral parameters of Raman bands of carbonaceous materials in chondrites.
    • fig. S3. Combined x-ray elemental map of NWA 5697 chondrules.
    • fig. S4. Combined x-ray elemental map of NWA 5697 chondrules.
    • fig. S5. Combined x-ray elemental map of NWA 7655 chondrules.
    • fig. S6. Combined x-ray elemental map of NWA 6043 chondrules.
    • fig. S7. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 5-C1 chondrule.
    • fig. S8. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 2-C1 chondrule.
    • fig. S9. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 5-C2 chondrule.
    • fig. S10. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 5-C10 chondrule.
    • fig. S11. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 D-C3 chondrule.
    • fig. S12. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 5-C4 chondrule.
    • fig. S13. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 3-C5 chondrule.
    • fig. S14. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 11-C1 chondrule.
    • fig. S15. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 11-C2 chondrule.
    • fig. S16. Pb-Pb isochron diagram of Pb isotope analyses of NWA 5697 3-C2 chondrule.
    • fig. S17. Pb-Pb isochron diagram of Pb isotope analyses of NWA 6043 1-C2 chondrule.
    • fig. S18. Pb-Pb isochron diagram of Pb isotope analyses of NWA 6043 2-C2 chondrule.
    • fig. S19. Pb-Pb isochron diagram of Pb isotope analyses of NWA 6043 2-C4 chondrule.
    • fig. S20. Pb-Pb isochron diagram of Pb isotope analyses of NWA 6043 0-C1 chondrule.
    • fig. S21. Pb-Pb isochron diagram of Pb isotope analyses of NWA 7655 1-C7 chondrule.
    • fig. S22. Pb-Pb isochron diagram of Pb isotope analyses of NWA 7655 1-C2 chondrule.
    • fig. S23. Pb-Pb isochron diagram of Pb isotope analyses of NWA 7655 1-C6 chondrule.
    • fig. S24. IMP data plotted in 204Pb/206Pb versus 207Pb/206Pb diagrams.
    • fig. S25. 238U/235U ratios of individual chondrules, bulk chondrites, and achondrites.
    • fig. S26. 27Al/24Mg and ε(207Pb/206Pb)initial variation diagram.
    • fig. S27. Age and μ value variation diagram.
    • fig. S28. Age and ε(207Pb/206Pb)initial variation diagram for selected chondrules.
    • table S1. Electron microprobe analyses of the NWA 5697, NWA 7655, and NWA 6043 chondrules studied.
    • table S2. Pb isotopic data for NWA 5697, NWA 7655, and NWA 6043 chondrules studied.
    • table S3. Uranium isotope compositions.
    • table S4. Zinc isotope compositions of selected chondrules.
    • table S5. IMP Pb analytical data for two chondrules.
    • table S6. Summary of the chondrules investigated.
    • table S7. Chondrule Pb-Pb ages corrected using different 238U/235U estimates.
    • References (69–96)

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