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.