Zirconium isotopic composition of zircon reference materials by laser ablation multi-collector inductively coupled plasma mass spectrometry

Zirconium isotopes have been suggested as a new geochemical fingerprint for tracing magmatic evolution and continental crust differentiation. In this study, we optimized the Zr isotope measurement by laser-ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC- ICP-MS) and reported stable Zr isotope compositions for different zircon reference materials (ZRMs). The RESOLution laser, coupled with MC-ICP-MS, yielded better results than the New Wave laser when comparing crater shape and depth indices, signal intensity, and isotopic ratio variations. The best working conditions for Zr isotope measurements were found to be with a laser spot size of 23 mm, a repetition rate of 2 Hz, and energy density of 3 J cm(-2) which resulted in a crater depth of similar to 8 mm. The Zr-90 intensities increased by a factor of 3.2, and the raw Zr-94/Zr-90 ratio remained constant within a broader range of sample gas flow rate with the addition of 8 mL min(-1) N-2 compared to the normal mode. Negligible interferences were identified from the gas blank and also from the different integrated cycles between the bracketing standard and samples. Using the above-mentioned parameters, we obtained a long-term delta Zr-94/90(GJ-1) stability of 0.08%, comparable with femtosecond laser-ablation (fsLA)-MC-ICP-MS methods. ZRMs (e.g., 91,500, Plesovice, Penglai, SA01, Tanz, and Ban-1) yielded homogeneous Zr isotope compositions, consistent with double spiked solution methods within error. Furthermore, zircon megacrysts of LKZ-1 and Cam-1, synthetical MUN-zircon with high Yb content, and MTUR1 zircon standard from carbonatite also had homogeneous Zr isotope compositions that indicate they could be used as tuning and monitoring standards. On the contrary, GHR1, Temora-2, Qinghu, and Jilin zircons were not ideal ZRMs for Zr isotope measurement. Zr isotope variations among homogeneous ZRMs (except Plesovice) further prove that Zr isotopes are a potentially powerful geochemical tracer. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

In this study, the Zr isotope measurement using laser-ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) was optimized, and stable Zr isotope compositions for different zircon reference materials (ZRMs) were reported. The RESOLution laser coupled with MC-ICP-MS outperformed the New Wave laser in terms of crater shape, depth indices, signal intensity, and isotopic ratio variations. The best working conditions for Zr isotope measurements were determined, and different ZRMs showed homogeneous Zr isotope compositions. The results indicate the potential of Zr isotopes as a powerful geochemical tracer.