Stable strontium isotopic heterogeneity in the solar system from double-spike data

Abstract

Strontium isotopic anomalies in meteorites are important in assessing nucleosynthetic sources to, and measuring the timing of, early solar system processes. However, conventional use of a constant 88 Sr/ 86 Sr value in correcting for instrumental mass fractionation during analysis renders measurements ambiguous and removes information on mass-dependent fractionation variations. From doublespike techniques we obtain data for the four stable strontium isotopes free of this ambiguity, and report measurements from a range of meteoritic, lunar and terrestrial materials. The Earth, Moon, basaltic eucrites and feldspars from angrites (differentiated samples) follow a single mass-dependent fractionation line and have a common nucleosynthetic origin in terms of their strontium isotopes. In contrast, bulk rock CI, CV3, CM and CO chondrite samples serve to define another mass-dependent fractionation line, displaced by 94 ± 28 ppm to heavier 84 Sr/ 86 Sr and/or 88 Sr/ 86 Sr ratios than that for the differentiated samples. Our Sr-isotopic data are consistent with a primary contrast in early solar system composition between an outer zone of primitive, mostly undifferentiated, materials and an inner zone of (almost entirely) differentiated materials that accumulated to form the terrestrial planets.

Nucleosynthetic, radiogenic and stable strontium isotopic variations in fine- and coarse-grained refractory inclusions from Allende

“…3) Double-spike methodologies using TIMS (Dodson, 1963;Rudge et al, 2009;Neymark et al, 2014) have been used to measure absolute Sr isotopic ratios without recourse to internal or external normalisation (Patchett 1980a, b;Charlier et al, 2017). In the pioneering early work on Allende CAIs by Patchett (1980a, b), precisions of ~0.25 ‰ and ~0.5 ‰ were obtained for the 88 Sr/ 86 Sr and 84 Sr/ 86 Sr ratios, respectively, and only broad trends in massdependent fractionation could be determined.…”

“…In the pioneering early work on Allende CAIs by Patchett (1980a, b), precisions of ~0.25 ‰ and ~0.5 ‰ were obtained for the 88 Sr/ 86 Sr and 84 Sr/ 86 Sr ratios, respectively, and only broad trends in massdependent fractionation could be determined. The precision on the 84 Sr/ 86 Sr ratio was well below that needed to resolve any non-mass-dependent anomalies in the abundance of 84 Sr. With improvements in mass spectrometer technology and associated techniques, Charlier et al (2017) identified an offset mass-dependent fractionation line in three-isotope space ( 88/86 Sr vs  84/86 Sr). Relative to terrestrial and inner solar system materials, this offset was identified at the bulk meteorite scale in several undifferentiated primitive meteorites, including Allende, indicating the survival of small, yet resolvable, nucleosynthetic anomalies in these bulk meteorites.…”

“…Sr-isotopic mass spectrometry measurements were carried out using a Thermo-Fisher Triton TIMS instrument, also at VUW. Details of the analytical protocols, including double spiking, chemical separation and TIMS analysis are given in Charlier et al (2017) and summarised in the supplementary material. The TIMS measurements were carried out within a single analytical session over an approximately two-week period.…”

“…In Fig. 3, the data (Table 3) (Charlier et al, 2017) has an identical slope within error of -1.00 ± 0.21 (MSWD = 7.5) and has a similar (within error) x-intercept at δ 84/86 Sr = 0.094 ± 0.028 ‰. The slope value of the best fit line presented here corresponds to the theoretical expectation for mass-dependent fractionation which stipulates that the relative isotopic variations scale as the difference in the absolute masses of the isotopes involved; ( 84 Sr-86 Sr)/( 88 Sr-86 Sr)~-1.0.…”

Assessment of Nanosecond Laser Ablation Multi‐Collector Inductively Coupled Plasma‐Mass Spectrometry for Pb and Sr Isotopic Determination in Archaeological Glass: Mass Bias Correction Strategies and Results for Corning Glass Reference Materials

“…The isolation of Sr was carried out under class-10 clean laboratory conditions. Mass bias correction for Sr isotopic determination was achieved by internal correction using the stable 88 Sr/ 86 Sr ratio (8.375209) (Charlier et al 2017). Any contribution of the 87 Rb signal on 87 Sr was corrected using 85 Rb and the natural abundance of the Rb isotopes; correction for 84 Kr and 86 Kr on 84 Sr and 86 Sr, respectively, was based on monitoring of 83 Kr.…”