OU-9: A Potential Reference Material with High ⁸⁷Rb/⁸⁶Sr and ⁸⁷Sr/⁸⁶Sr for Data Quality Control and Method Validation in ID-MS Rb-Sr Geochronology

The use of ID-MS (ID-TIMS/MC-ICP-MS) techniques to characterise reference materials (RM) with high Rb/Sr and 87Sr/86Sr for in situ LA-ICP-MS-MS Rb-Sr geochronology is highly important. However, there is a lack of well-characterised RMs with high Rb/Sr and 87Sr/86Sr ratios to effectively monitor data quality for ID-TIMS/MC-ICP-MS Rb-Sr geochronology. In this study, a pegmatite RM, OU-9, was comprehensively characterised using ID-TIMS/MC-ICP-MS techniques. Measurements undertaken on OU-9 yielded mass fractions of 2494 ± 22 μg g-1 for Rb, 36.05 ± 0.25 μg g-1 for Sr, as well as isotope ratios of 832.4 ± 5.2 for 87Rb/86Sr and 32.60 ± 0.19 for 87Sr/86Sr. Despite the presence of inhomogeneity within and between RM sachets, regarding Rb-Sr isotope systematics at sampling scales of ~ 10 mg and even 0.2 g, 87Rb/86Sr and 87Sr/86Sr values derived from the analyses align well along the reference isochron. This alignment yields a model age of ~ 2650 Ma with an initial 87Sr/86Sr of ~ 1.2. We advocate that OU-9 could serve as a potential RM for ID-TIMS/MC-ICP-MS Rb-Sr data quality control for materials characterised by high 87Rb/86Sr and 87Sr/86Sr ratios. The data quality of individual measurement results can be assessed based on their fit to the correlation line.