Neutron-Poor Nickel Isotope Anomalies in Meteorites

Abstract

We present new, mass-independent, Ni isotope data for a range of bulk chondritic meteorites. The data are reported as E 60 Ni 58 61 , E 62 Ni 58 61 and E 64 Ni 58 61 or the parts per ten thousand deviations from a terrestrial reference, the NIST SRM 986 standard, of the 58 Ni/ 61 Ni internally normalised 60 Ni/ 61 Ni, 62 Ni/ 61 Ni and 64 Ni/ 61 Ni ratios. The chondrites show a range of 0.15, 0.29 and 0.84 in E 60 Ni 58 61 , E 62 Ni 58 61 and E 64 Ni 58 61 relative to a typical sample precision of 0.03, 0.05 and 0.08 (2 s.e.), respectively. The carbonaceous chondrites show the largest positive

The Isotope Geochemistry of Ni

“…This contrasts with material from the O-Ne zone required to account for a similarly constrained component in the Ti isotopic system. Steele et al (2012) Ni/ 58 Ni ratios >1000ε higher than terrestrial values (for these extreme ratios there is no internal normalisation) in X-grains believed to be derived from SNII sources. These Ni isotopic signatures suggest derivation from outer He/N and He/C zones of an SNII event, different to those inferred by Steele et al (2012) to be necessary to account for bulk isotopic variability.…”

“…Steele et al (2012) Ni/ 58 Ni ratios >1000ε higher than terrestrial values (for these extreme ratios there is no internal normalisation) in X-grains believed to be derived from SNII sources. These Ni isotopic signatures suggest derivation from outer He/N and He/C zones of an SNII event, different to those inferred by Steele et al (2012) to be necessary to account for bulk isotopic variability. As with other analyses of pre-solar SiC, these measurements bear striking testimony to the diversity of stellar sources that contribute to the bulk composition of the solar system, but do not identify a carrier for the signature that causes variability between different bulk, meteoritic objects (Steele and Boehnke, 2016).…”

“…Steele et al, 2012), but such mass-independent p3 variability does not have a significant impact on more typical mass-dependent determinations at the delta unit level (section 4.1).…”

“…4b) can also be reproduced by variable meteoritic values of 58 Ni/ 61 Ni, the p6 normalising isotope ratio. Indeed, from high-precision mass-dependent isotopic measurements (see section 4), Steele et al (2012) showed that variability in 58 Ni best explains all observations. This implies the source of this anomalous Ni is from the Si-S zone of a SNII.…”

“…4a) and with the inclusion of ε 64 Ni 61/58 data ( Fig. 4b) by Steele et al (2011Steele et al ( , 2012 and Dauphas (2012, 2014 (Fig. 4b).…”