Low Fe Abundance in Semarkona and Sahara 99555

Iron-60 (t1/2= 2.62Myr) is a short-lived nuclide that can help constrain the astrophysical context of Solar System formation and date early Solar System events. A high abundance of Fe(Fe/Fe ≈ 4 × 10) was reported by in situ techniques in some chondrules from the LL3.00 Semarkona meteorite, which was taken as evidence that a supernova exploded in the vicinity of the birthplace of the Sun. However, our previous multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) measurements of a wide range of meteoritic materials, including chondrules, showed that Fe was present in the early Solar System at a much lower level (Fe/Fe≈ 10). The reason for the discrepancy is unknown but only two Semarkona chondrules were measured by MC-ICPMS and these had Fe/Ni ratios below ∼2× chondritic. Here, we show that the initial Fe/Fe ratio in Semarkona chondrules with Fe/Ni ratios up to ∼24× chondritic is (5.39± 3.27) × 10. We also establish the initial Fe/Fe ratio at the time of crystallization of the Sahara 99555 angrite, a chronological anchor, to be (1.97± 0.77) × 10. These results demonstrate that the initial abundance of Fe at Solar System birth was low, corresponding to an initial Fe/Fe ratio of (1.01± 0.27) × 10.