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 60 Fe

Abstract

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