Research ArticlePLANETARY SCIENCE

Aluminum-26 chronology of dust coagulation and early solar system evolution

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Science Advances  11 Sep 2019:
Vol. 5, no. 9, eaaw3350
DOI: 10.1126/sciadv.aaw3350
  • Fig. 1 Distribution of 26Al/27Al in 18 ALHA77307 CAIs.

    (Top) Inferred 26Al/27Al ratios are plotted against the associated ∆26Mg0* (errors 2σ) obtained from the isochron plots. Each symbol indicates one inclusion. The solid red square represents 26Al/27Al = (5.2 ± 0.1) × 10−5 and ∆26Mg0* = (−0.13 to −0.014‰) inferred from large CV3 CAIs (using both bulk-sample and internal isochron methods). (Bottom) Black solid curve stands for the probability density plot calculated on the basis of the 26Al/27Al ratios acquired in this study. The probability curve based on the data of bulk and internal isochron-derived 26Al/27Al from CM SHIBs and one hibonite-grossite–rich inclusion (gray curve) is shown for comparison. The band formed by two gray dashed lines represents 26Al/27Al = (5.2 ± 0.1) × 10−5.

  • Fig. 2 Multi-CAI isochrons.

    (A) Five CAIs that make up the 5.4 × 10−5 peak in the probability density plot (Fig. 1) form a well-defined isochron (χ2 = 1.1), the slope of which corresponds to 26Al/27Al = (5.40 ± 0.13) × 10−5. (B) Six CAIs under the 4.9 × 10−5 peak are characterized by tightly constrained 26Al/27Al = (4.89 ± 0.10) × 10−5, albeit with some scatter (χ2 = 4.3). The intercept is broadly consistent with the chondritic value within errors. All errors are 2σ.

  • Fig. 3 CAIs devoid of resolved excesses in 26Mg that could be attributed to the decay of 26Al.

    Instead, ∆26Mg* appears to be slightly heterogeneous even within a single grain. A line corresponding to 26Al/27Al = 5.2 × 10−5 is shown for reference. All errors are 2σ.

  • Fig. 4 The true initial 26Mg/24Mg (≡∆26Mg0,i*) of individual CAI, calculated from isochron-derived 26Al/27Al and ∆26Mg0*, and bulk 27Al/24Mg estimated by using scanning electron microscopy–energy-dispersive x-ray spectroscopy.

    A gray arrow is drawn from each CAI data point to the 26Al/27Al ratio of 5.4 × 10−5 (defined as “t0,” the vertical solid line), with the slope determined from the CAI’s present-day bulk 27Al/24Mg, which is the number shown in a black square. The small orange rectangle stands for 26Al/27Al = (5.40 ± 0.13) × 10−5 and ∆26Mg0* = (−0.14 ± 0.03‰). (Inset) A blow-up of the area where arrows intersect the vertical solid line, showing the distribution of back-calculated ∆26Mg0,i* in the form of a probability density plot. The horizontal orange bar represents ∆26Mg0,i* = (−0.14 ± 0.03). Most of the values cluster at ∆26Mg0,i* = −0.4‰ with a full width at half maximum (FWHM) (~2.3σ) of ±0.3‰.

  • Table 1 Inferred 26Al/27Al ratios, initial Δ26Mg0*, and goodness of fit for 18 26Al-bearing ALHA77307 CAIs.

    Uncertainties are 2σ. hib, hibonite; pv, perovskite; sp, spinel; mel, melilite; di, diopside rim; and fo, forsteritic olivine.

    SampleMinerals26Al/27Al (±2σ)26Mg0*
    (‰, ±2σ)
    Reduced χ2
    019hib(4.86 ± 0.42) × 10−50.05 ± 0.260.3
    021hib-pv-sp(0.80 ± 1.65) × 10−50.87 ± 0.442.0
    070sp-pv-di-ol(5.12 ± 0.67) × 10−5−0.13 ± 0.090.7
    073hib-pv-sp(4.85 ± 0.32) × 10−50.12 ± 0.1010
    074hib-pv-sp(5.37 ± 0.29) × 10−5−0.21 ± 0.501.9
    095hib-sp(4.94 ± 0.21) × 10−5−0.06 ± 0.271.0
    117hib-pv-sp-di(3.76 ± 0.37) × 10−50.86 ± 0.276.7
    119hib-pv-sp-di(5.46 ± 0.35) × 10−5−0.16 ± 0.140.4
    147hib-sp-di(5.73 ± 1.20) × 10−5−0.05 ± 0.431.2
    148hib-sp-di(3.34 ± 0.37) × 10−50.46 ± 0.339.4
    155hib-sp(1.72 ± 0.81) × 10−51.57 ± 0.4622.3
    164hib-sp-di(4.68 ± 0.39) × 10−5−0.04 ± 0.241.8
    165sp-di-fo(4.32 ± 0.62) × 10−5−0.01 ± 0.040.9
    212sp-pv-di(4.53 ± 0.80) × 10−5−0.11 ± 0.110.4
    222hib-sp(2.44 ± 0.44) × 10−50.26 ± 0.320.2
    229sp-pv-mel-di-ol(5.59 ± 0.91) × 10−5−0.15 ± 0.131.4
    230hib-pv-sp-mel(4.48 ± 0.19) × 10−50.33 ± 0.313.8
    230SWhib-pv-sp-mel(3.01 ± 0.79) × 10−51.77 ± 0.810.7

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/9/eaaw3350/DC1

    Supplementary Materials and Methods

    Fig. S1. Individual internal 26Al isochrons obtained in 18 26Al-bearing inclusions.

    Fig. S2. Example of IMF characterized in one analysis session.

    Table S1. Magnesium isotopic compositions of 22 inclusions analyzed in this study.

    Table S2. Relative sensitivity factors determined on standards with known 27Al/24Mg in three analysis sessions.

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Materials and Methods
    • Fig. S1. Individual internal 26Al isochrons obtained in 18 26Al-bearing inclusions.
    • Fig. S2. Example of IMF characterized in one analysis session.
    • Table S1. Magnesium isotopic compositions of 22 inclusions analyzed in this study.
    • Table S2. Relative sensitivity factors determined on standards with known 27Al/24Mg in three analysis sessions.

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