Nickel Nucleosynthetic Anomalies in Leachates of Carbonaceous Chondrites

Introduction: The numerous nucleosynthetic isotopic anomalies found in refractory inclusions, in presolar grains, and in special phases carried by chondrites suggest that the matter constituting the solar system results from a mixing between different sources. Recently, Ni nucleosynthetic anomalies have been found in various meteorites, including iron meteorites, ureilites, chondrites [e.g. 1-3], and building material of meteorites has been shown to come from at least 3 isotopically distinct reservoirs for Ni [3]. The carrier phases of the Ni isotope anomalies have however not been fully identified yet, despite a first study based on iron meteorites and chondrites [2]. Carbonaceous chondrites can be used to identify the nucleosynthetic sources of solar system material and to study stellar nucleosynthesis and formation of the solar system. Stepwise dissolution of carbonaceous chondrites is a powerful tool to characterize the finescale isotope heterogeneities of the solar system and to identify the presolar carrier phases of isotope anomalies. Acid leachates of these meteorites already display nucleosynthetic anomalies for Cr, K, Mo, Ba, Zr, Os [4-9]. Here we report Ni isotope analyses of leachates for the three primitive carbonaceous chondrites Allende, Murchison, and Orgueil with the aim of resolving the different nucleosynthetic components. Nickel is a suitable element for this purpose as Ni is overproduced by s-process when excesses of Ni and Ni witness nucleosynthesis in a neutron-rich environment. Besides, possible correlations between different isotopes or different elements in the same leachates potentially bring stronger and more precise constraints on the astrophysical setting where the nuclides have been produced. As an example, correlations between Fe, Ni and Zr have already been observed in CAIs [10] and Ni and Cr anomalies seem to be correlated in several types of meteorites [1].