High-precision Rb-Sr isotope analysis with Neoma MS/MS: Enhancing in situ geochronology by laser ablation

Abstract

The development of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) with tandem mass spectrometry (MS/MS) technology has brought significant advancements for in situ Rubidium‑strontium (Rb-Sr) geochronology, coupled with a laser ablation system (LA). This study investigates the potential of high-precision in situ Rb-Sr dating by the Neoma MS/MS instrument, using both solution and LA analysis, with a focus on optimizing instrumental parameters and the evaluating reference materials. We systematically assess the removal of Ar⁺, the influence of Focus Lens 2 voltage on Sr isotope analytical accuracy, and the effectiveness of reaction mode in eliminating isobaric interferences. Results of LA analyses demonstrate the capability of Neoma MS/MS to achieve high-precision in situ Rb-Sr isotope ratio measurements, with external precisions better than 1.9 % and 0.036 % relative standard deviation (RSD) for ⁸⁷Rb/⁸⁶Sr and ⁸⁷Sr/⁸⁶Sr ratios in standard glasses, respectively. The homogeneity of the Mica-Mg reference material is further assessed, with an inter-session RSD of 0.17 % for its Rb-Sr isochron age, demonstrating good age homogeneity across nine analytical sessions. Similarly, the natural ZMT04 muscovite yielded an inter-session RSD of 0.69 % for its Rb-Sr isochron age, and its Rb-Sr isochron age of 1778.8 ± 4.9 Ma (2 s, n = 180) is consistent with the reported Ar-Ar age (1772.2 ± 2.7 Ma, 2 s) within the uncertainty, confirming its suitability as a monitor reference material for Rb-Sr dating. These findings highlight the potential of the Neoma MS/MS in enhancing the precision of in situ Rb-Sr dating, for micro-scale investigations and revealing intricate age zonation patterns within individual minerals.