Natural variations in the rhenium isotopic composition of meteorites

Abstract

Rhenium is an important element with which to test hypotheses of isotope variation. Historically, it has been difficult to precisely correct the instrumental mass bias in thermal ionization mass spectrometry. We used W as an internal standard to correct mass bias on the MC‐ICP‐MS, and obtained the first precise δ187Re values (~±0.02‰, 2SE) for iron meteorites and chondritic metal. Relative to metal from H chondrites, IVB irons are systematically higher in δ187Re by ~0.14 ‰. δ187Re for other irons are similar to H chondritic metal, although some individual samples show significant isotope fractionation. Since 185Re has a high neutron capture cross section, the effect of galactic cosmic‐ray (GCR) irradiation on δ187Re was examined using correlations with Pt isotopes. The pre‐GCR irradiation δ187Re for IVB irons is lower, but the difference in δ187Re between IVB irons and other meteoritic metal remains. Nuclear volume‐dependent fractionation for Re is about the right magnitude near the melting point of iron, but because of the refractory and compatible character of Re, a compelling explanation in terms of mass‐dependent fractionation is elusive. The magnitude of a nucleosynthetic s‐process deficit for Re estimated from Mo and Ru isotopes is essentially unresolvable. Since thermal processing reduced nucleosynthetic effects in Pd, it is conceivable that Re isotopic variations larger than those in Mo and Ru may be present in IVBs since Re is more refractory than Mo and Ru. Thus, the Re isotopic difference between IVBs and other irons or chondritic metal remains unexplained.

Defining the Potential of Nanoscale Re‐Os Isotope Systematics Using Atom Probe Microscopy

“…), with only small variations of < 0.14‰ observed (Liu et al . ). So, although 187 Os has a lower mass fraction, 187 Re, 185 Re and 187 Re should be used to deconvolve the isobaric interference to produce a ‘real’ fraction of 187 Os.…”

“…As these mass fractions are used in radiometric dating (Naldrett and Libby 1948, Geiss et al 1958, they cannot be assumed to have standard values. However, Re isotopic relative fractions are relatively consistent across a range of geological and meteoritic samples (Luck et al 1980, Anders and Grevesse 1989, Walczyk and Heumann 1993, Lodders 2003, Meija et al 2016b, with only small variations of < 0.14‰ observed (Liu et al 2017). So, although 187 Os has a lower mass fraction, 187 Re,185 Re and 187 Re should be used to deconvolve the isobaric interference to produce a 'real' fraction of 187 Os.…”

Galactic cosmic ray effects on iron and nickel isotopes in iron meteorites

“…Because they are nonmass-dependent, GCR effects may masquerade as nucleosynthetic isotopic variations and/or may obscure the true age of samples. In the case of iron meteorites, GCR effects have been reported for various stable isotopes, including Ru (Fischer-G€ odde et al 2015), Os (e.g., Walker 2012;Wittig et al 2013), Pt (e.g., Kruijer et al 2013;Wittig et al 2013;Hunt et al 2017), Re (Liu et al 2017), Cr (Liu et al 2019), and Cu (Chen et al 2016). Effects from GCRs have also been shown to affect chronometers in iron meteorites, including 107 Pd-107 Ag (Matthes et al 2015) and 182 Hf-182 W (e.g., Markowski et al 2006;Kruijer et al 2013;Hunt et al 2018).…”

Rhenium elemental and isotopic variations at magmatic temperatures

“…There is a growing dataset of Re isotopic compositions of seawater and river waters (Dickson et al, 2020;Dellinger et al, 2021). However, due partly to analytical challenges, few δ 187 Re measurements exist on igneous materials, limited to meteorites (Liu et al, 2017) and standard reference materials (Dellinger et al, 2020). No studies have investigated the behaviour of Re isotopes during magmatic processes on Earth.…”