Applicability of carbonate reference materials as matrix-matched standards for in-situ LA-ICPMS U-Pb dating of Sulphates

Recent developments on analytical capabilities in the field of in-situ laser ablation mass spectrometry (LA-ICPMS) have expanded the applications of U-Pb geochronometers in low-U minerals such as carbonates (Roberts et al. 2020) or garnets (Millonig et al., 2020). The rapid development of the technique requires well-characterized, matrix-matched reference materials, which are essential for ion probes or LA-ICPMS due to potential matrix effects. However, given the unavailability of standards for some minerals, the use of non-matrix-matched standards, i.e. reference materials that are different to the sample, have been also addressed (Piccione et al., 2019).

In this contribution, we explored the possibility of using carbonate reference materials for in-situ U-Pb dating of sulphates. For that purpose, we selected samples from the Messinian Salinity Crisis because their ages are well established by cyclostratigraphy and thus can be compared with ages obtained by LA-ICPMS analysis. Data was acquired using a RESOLution 193 nm ArF excimer laser coupled to a (I) sector field ICP-MS (ElementXR) or (II) multicollector ICP-MS (Neptune Plus).

The majority of the samples (27 out of 32) failed due to the elevated common-Pb content and low ²³⁸U/²⁰⁴Pb ratios. Nevertheless, five of the samples showed greater amounts of U and U/Pb ratios of up to 600; therefore, regression lines could be drawn and ages are calculated with 5-10 % of uncertainty. These ages obtained are within error of the cyclostratigraphic ages already published (Vasiliev et al., 2017).

 

Millonig et al., (2020) Earth Planet. Sci. Lett. 552, 116589; Piccione et al. (2019) Geosphere 15 (6), 1958– 1972; Roberts et al. (2020) Geochronology 2, 33–61; Vasiliev et al. (2017) Palaeogeogr. Palaeoclimatol. Palaeoecol. 471, 120-133.