High-precision strontium isotope analysis of geological samples by thermal ionisation mass spectrometry

We present a method for the efficient separation of Sr from geological materials followed by high-precision measurement of Sr isotopes by thermal ionisation mass spectrometry (TIMS). These analyses focus on high-precision measurements of the low abundance isotope 84Sr (0.56%), which is of high interest for cosmochemical applications. The robust dataset obtained through the analysis of a range of basalts and anorthosites sheds light on a number of issues regarding Sr isotopic analyses. Specifically, concerns that analytical artefacts may produce a spurious signal on 84Sr have been investigated. The external reproducibility, based on replicate measurements of the basalt standard BCR-2, for ε84Sr is ±0.36 (2SD), and is ±0.51 (2SD) for repeated analyses of NIST SRM-987. In contrast with the static measurements of previous work (Andreasen and Sharma, 2007; Moynier et al., 2012; Paton et al., 2013; Brennecka et al., 2013), our dynamic data reveal no 84Sr variations in terrestrial rocks or standard material. The dataset indicates that, by the analytical procedure employed, 84Sr variations in extra-terrestrial material larger than ~0.5ε are resolvable.