Depth‐Profiling Determinations of Rare Earth Element Abundances and U‐Pb Ages from Zircon Crystals Using Sensitivity‐Enhanced Inductively Coupled Plasma‐Time of Flight‐Mass Spectrometry

Abstract

Depth‐profiling measurements of both the abundances of rare earth elements (REEs) and U‐Pb ages from zircons were conducted using a time‐of‐flight based inductively coupled plasma‐mass spectrometer (ICP‐ToF‐MS) coupled with laser ablation sampling. To improve ion transmission, a dry plasma cone from Nu Instruments was applied to the ICP‐ToF‐MS system employed. The signal‐to‐noise ratios for the analytes were further improved using a multiple spot‐laser ablation (msLA) protocol. Moreover, constructing a ‘moat’ around an analysis area obviated the risk of mixing of particles released from different layers. With the technique developed here, reproducible analyses of REE abundances and U‐Pb ages for three reference material zircons (91500, Plešovice and OD‐3) were performed for sampling depths in the range 0.59–0.66 μm. The present technique was also applied to zircon samples collected from the Himalayan orogen. The combination of REE abundances and U‐Pb isotopic ratios suggested that the discordant trend in U‐Pb isotopic ratios observed in this study was mainly due to mixing among three components in grains (thin outer layer, inner rim and core). The geochemical data obtained demonstrate that the combination of the msLA technique and ICP‐ToF‐MS system is a powerful tool to decode the multiple thermal events contributing to sample formation.

Development of an In SituU‐Th Disequilibrium Dating Method Utilising Multiple‐Spot Femtosecond Laser Ablation‐CRC‐ICP‐MS

“…With the msLA-CRC-ICP-MS technique used in this study, the overall useful yield was approximately 0.07% for 238 U. This resulting useful yield enhanced by using the dry plasma cones (Nakazato et al 2022) was nearly half of LA-SF-ICP-MS (Guillong et al 2016). It should be noted that the typical useful yield achieved by conventional LA-ICP-MS systems equipped with low repetition rate-LA and quadrupole-ICP-MS is an order of magnitude lower than that of LA-SF-ICP-MS systems.…”

“…This resulting useful yield enhanced by using the dry plasma cones (Nakazato et al . 2022) was nearly half of LA‐SF‐ICP‐MS (Guillong et al . 2016).…”

“…Comparison of the elemental sensitivity achieved between the two cones revealed that a nearly threefold enhancement was achieved for the elements with mid‐ to heavy‐mass ranges (from REE to U) (Nakazato et al . 2022).…”

“…The dry plasma cone used in this study was designed to suppress the expansion of the ion beams at the expansion region (Douglas and French 1988), and thus ion transmission through the two orifices (sampler and skimmer orifices) could be improved. Comparison of the elemental sensitivity achieved between the two cones revealed that a nearly threefold enhancement was achieved for the elements with mid-to heavy-mass ranges (from REE to U) (Nakazato et al 2022).…”

Atomic spectrometry update – a review of advances in environmental analysis

“…Such rocks oen do not contain minerals such as zircon or K-bearing phases, thus limiting the application of more conventional dating techniques. Isochrons were generated by combining LA-SF-ICP-MS measurements of the host ilmenite (low in U and Th mass fractions) with those of numerous inclusions (higher U and Th mass fractions) with a large spread of 238 U/ 232 Th ratios. Estimates of age overlapped within the uncertainty of published ages.…”