The Cu isotopic composition of iron meteorites

Abstract

Abstract– High‐precision Cu isotopic compositions have been measured for the metal phase of 29 iron meteorites from various groups and for four terrestrial standards. The data are reported as the δ 65 Cu permil deviation of the 65 Cu/ 63 Cu ratio relative to the NIST SRM 976 standard. Terrestrial mantle rocks have a very narrow range of variations and scatter around zero. In contrast, iron meteorites show δ 65 Cu approximately 2.3‰ variations. Different groups of iron meteorites have distinct δ 65 Cu values. Nonmagmatic IAB‐IIICD iron meteorites have similar δ 65 Cu (0.03 ± 0.08 and 0.12 ± 0.10, respectively), close to terrestrial values (approximately 0). The other group of nonmagmatic irons, IIE, is isotopically distinct (−0.69 ± 0.15). IVB is the iron meteorite group with the strongest elemental depletion in Cu and samples in this group are enriched in the lighter isotope (δ 65 Cu down to −2.26‰). Evaporation should have produced an enrichment in 65 Cu over 63 Cu (δ 65 Cu >0) and can therefore be ruled out as a mechanism for volatile loss in IVB meteorites. In silicate‐bearing iron meteorites, Δ 17 O correlates with δ 65 Cu. This correlation between nonmass‐dependent and mass‐dependent parameters suggests that the Cu isotopic composition of iron meteorites has not been modified by planetary differentiation to a large extent. Therefore, Cu isotopic ratios can be used to confirm genetic links. Cu isotopes thus confirm genetic relationships between groups of iron meteorites (e.g., IAB and IIICD; IIIE and IIIAB); and between iron meteorites and chondrites (e.g., IIE and H chondrites). Several genetic connections between iron meteorites groups are confirmed by Cu isotopes, (e.g., IAB and IIICD; IIIE and IIIAB); and between iron meteorites and chondrites (e.g., IIE and H chondrites).