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Iron and Nickel Isotopes in IID and IVB Iron Meteorites: Evidence for Admixture of an SN II Component and Implications for the Initial Abundance of 60Fe

We measured Fe and Ni isotopes in 13 iron meteorites from magmatic groups IID and IVB. Resolvable deficits (≈−0.14) are observed in ε 60Ni in both groups. Small deficits (≈−0.08) are also evident in ε 56Fe but not in the most neutron-rich isotope of Fe (58Fe). Relative to terrestrial material, the observed ε iFe values are consistent with the presence of a small excesses of material in the parent bodies of IID and IVB irons that was produced in a type II supernova. The ε 60Ni and ε 56Fe values are uncorrelated in both groups. This is consistent with a nucleosynthetic origin of the ε 56Fe deficits, whereas the ε 60Ni deficits are best explained as radiogenic in nature due to the former presence of live 60Fe (t 1/2 = 2.62 Ma) in the early solar system. The 60Ni deficits correspond to 60Fe/56Fe ratios of ≈3 × 10−7 at the time of core formation on the IID and IVB parent bodies. These data, in conjunction with previously published 182Hf–182W core formation ages, are used to estimate a solar system initial 60Fe/56Fe = (6.4 ± 2.0) × 10−7 for the formation region of carbonaceous chondrites.