In situ LA-ICPMS U–Pb dating of sulfates: applicability of carbonate reference materials as matrix-matched standards

Abstract

Abstract. Recent developments in 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 or garnets. The rapid evolution of the technique relies on well-characterized matrix-matched reference materials. In this article, we explore the suitability of using carbonate as an “almost-matrix-matched reference material” for in situ U–Pb dating of sulfates. For such purpose, we have used the astrochronologically dated gypsum and anhydrite samples deposited during the Messinian Salinity Crisis (5.97–5.33 Ma) and compared these dates with the U–Pb ages obtained by LA-ICPMS. Although the majority of the samples failed due to the elevated common Pb content and low 238U/204Pb ratios, five of the samples showed a higher dispersion on U/Pb ratios. The obtained dates in four of these samples are comparable with the expected ages, while another gave an unexpected younger age, each of them with 6 %–11 % of uncertainty. The pit depth of the spots showed that the sulfates ablate similar to carbonates, so the offset due to the crater geometry mismatch or downhole fractionation can be assumed to be negligible. To sum up, the bias between the U–Pb and expected cyclostratigraphic ages, if any, is included in the uncertainty, and thus the results obtained here suggest that carbonate reference material is currently the best option for standardization of in situ U–Pb sulfate analyses.

Fossil record misconstrued: Sponge-like fabrics reflect incipient carbonate metamorphism

“…Uranium-lead age data of carbonate were collected on a ThermoFisher Element XR sector eld ICPMS coupled to a 193-nm ArF Excimer laser with a HelEx 2-volume cell (Analyte Excite+, Teledyne PhotonMachines) at the Laboratory for Environmental and Raw Materials Analysis (LERA), Karlsruhe Institute for Technology (Germany), and were slightly modi ed from 34 . The data were acquired in one analytical session in November 2023; see supplementary information le for analytical parameters (spot size, repetition rate, acquisition times, gas ows).…”

Multi-stage ultrahigh temperature metamorphism in the lower crust of the Kaapvaal craton recorded by U–Pb ages of garnet

“…are detailed in Appendix Table A1. The U-Pb analyses followed the procedure described in Beranoaguirre et al (2022). Soda-lime glass SRMNIST614 (Jochum et al 2011) was used as the primary reference material to correct for mass bias, inter-element fractionation and instrumental drift during the analytical session.…”