Further characterization of SA01 and SA02 zircon reference materials for Si and Zr isotopic compositions via femtosecond laser ablation MC-ICP-MS

Abstract

Here we present Si and Zr isotopic data of SA01 and SA02 zircons via multi-technique analytical methods to evaluate the suitability of the two zircon reference materials for in situ Si and Zr isotopic analysis using femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry (fs-LA-MC-ICP-MS). Precise and accurate Si and Zr isotopic compositions were determined by solution nebulization (SN) MC-ICP-MS. Fifteen SN-MC-ICP-MS Si isotopic measurements on two aliquots of SA01 zircon solutions gave consistent results with an average δ³⁰Si (relative to NBS28) value of −0.29 ± 0.08‰ (2SD), whereas a slight inter-grain offset was detected for the SA02 zircon with an average δ³⁰Si value of −0.25 ± 0.16‰ (2SD, n = 12). The mean δ^94/90Zr (relative to IPGP-Zr) values were 0.02 ± 0.03‰ (2SD, n = 9) and 0.02 ± 0.04‰ (2SD, n = 9) for SA01 and SA02 zircons, respectively. Extensive homogeneity test of both Si and Zr isotopic compositions was performed on SA01 and SA02 zircons by spot analysis with fs-LA-MC-ICP-MS. The Si and Zr isotopic results for SA01 zircon showed good agreement with our SN-MC-ICP-MS measurements, as did the Zr isotope results of SA02 zircon. In spite of the inter-grain offset in the Si isotopic composition revealed by SN-MC-ICP-MS, intra-grain homogeneity was confirmed for SA02 zircon by the LA-MC-ICP-MS method. In situ analyses of SA01 and SA02 zircons yielded mean δ³⁰Si values of −0.24 ± 0.10‰ (2SD, n = 143) and −0.26 ± 0.12‰ (2SD, n = 135), and mean δ^94/90Zr values of 0.03 ± 0.09‰ (2SD, n = 153) and 0.02 ± 0.09‰ (2SD, n = 153), respectively. Both solution and in situ dataset demonstrated the suitability of SA01 for calibrating in situ zircon Si and Zr isotopic analysis. We suggest that SA02 zircon is also a suitable reference material for micro-beam Zr isotopic analysis as well as a monitor for in situ Si isotopic analysis. Furthermore, an analytical approach using the spot mode of fs-LA is presented in this study. In situ Si and Zr isotopic analysis may benefit from it for improving spatial resolution and precision.