Other
Scientific paper
Jul 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008e%26psl.272..330r&link_type=abstract
Earth and Planetary Science Letters, Volume 272, Issue 1-2, p. 330-338.
Other
38
Scientific paper
We report small but significant variations in the 58Ni/61Ni-normalised 60Ni/61Ni and 62Ni/61Ni ratios (expressed as ɛ60Ni and ɛ62Ni) of bulk iron and chondritic meteorites. Carbonaceous chondrites have variable, positive ɛ62Ni (0.05 to 0.25), whereas ordinary chondrites have negative ɛ62Ni (- 0.04 to - 0.09). The Ni isotope compositions of iron meteorites overlap with those of chondrites, and define an array with negative slope in the ɛ60Ni versus ɛ62Ni diagram. The Ni isotope compositions of the volatile-depleted Group IVB irons are similar to those of the refractory CO, CV carbonaceous chondrites, whereas the other common magmatic iron groups have Ni isotope compositions similar to ordinary chondrites. Only enstatite chondrites have identical Ni isotope compositions to Earth and so appear to represent the most appropriate terrestrial building material. Differences in ɛ62Ni reflect distinct nucleosynthetic components in precursor solids that have been variably mixed, but some of the ɛ60Ni variability could reflect a radiogenic component from the decay of 60Fe. Comparison of the ɛ60Ni of iron and chondritic meteorites with the same ɛ62Ni allows us to place upper limits on the 60Fe/56Fe of planetesimals during core segregation. We estimate that carbonaceous chondrites had initial 60Fe/56Fe < 1 × 10- 7. Our data place less good constraints on initial 60Fe/56Fe ratios of ordinary chondrites but our results are not incompatible with values as high as 3 × 10- 7 as determined by in-situ measurements. We suggest that the Ni isotope variations and apparently heterogeneous initial 60Fe/56Fe results from physical sorting within the protosolar nebula of different phases (silicate, metal and sulphide) that carry different isotopic signatures.
Coath Christopher D.
Elliott Tim
Regelous Marcel
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