Evidence for Live Iron-60 in Semarkona and Chervony Kut: a Nanosims Study

Introduction: One of the most debated subjects in meteoritics is the time scale of events that occurred during the early history of the solar system. Chronometers based on short lived nuclides, such as Al, Mn, Fe, Pd, I, Sm, were extensively studied during the last decades. Some of them were shown to afford chronological resolutions on the order of a few Ma to less than one Ma [e.g. 1,2]. This considerably helped resolving the sequence of events that occurred since the formation of the first solid objects. Considering the high iron and aluminum contents of meteorites, special attention was devoted to Fe and Al, as they would have been the most powerful heat sources for inducing planetary melting and differentiation. The search for Ni isotopic anomalies produced by the decay of short lived Fe (T1⁄2 = 1.5 Ma) had been successful in the eucrite Chervony Kut [3]. Correlated with the Fe/Ni ratio, Ni excesses were found for several bulk samples. A large 5‰ excess was measured in a "troilite", which, however, does not follow the trend of the bulk samples. While this evidence shows that Fe was alive in the early solar system, the apparent mobility of Ni between the major phases of this meteorite limits the usefulness of the Fe-Ni system as a chronometer. In this report we present an in situ NanoSIMS study of the Fe-Ni system in iron sulfides in the Chervony Kut (CK) eucrite and in the Semarkona (LL3.0) ordinary chondrite. We chose CK to perform a follow-up study on a micro-scale on this highly Ni depleted planetary differentiate [4]. Semarkona was selected because it is a highly unequilibrated chondrite where a disturbance of the Fe-Ni system during parent body processing is assumed to be minimal.