Optimisation of LA‐ICP‐MS/MS Rb‐Sr Dating of Micas with Non‐Matrix‐Matched Reference Materials

Abstract

The recent development of LA‐ICP‐MS/MS techniques enables in situ Rb‐Sr dating of micas, but there is not yet a matrix‐matched reference material (RM). In this contribution we optimised laser conditions and developed a new data reduction approach for Rb‐Sr dating of micas with non‐matrix‐matched RMs Mica‐Mg‐NP and NIST SRM 612. This was achieved by systematically investigating the effects of laser ablation settings, data reduction methods and the selection of the RMs on the Rb‐Sr dating quality of a 306 ± 1 Ma hydrothermal muscovite. We then tested this approach using twelve mica samples with known ages from 306 to 1.4 Ma. The results show that this technique can achieve accuracy of 2.5% or better, and precision of ~1–3% for micas > 15 Ma. The dating accuracy (> 9%) and precision (> 21%) decrease for micas younger than 5 Ma due to the short radiogenic accumulation time. This technique provides a way to date many types of mineral deposits and rocks, with a relatively high spatial resolution (down to 38 μm), a fast turnaround time and a higher closure temperature for muscovite than the Ar‐Ar system, which makes it a powerful tool in geochronological studies.