Determination of the zirconium isotopic composition of the new isotopic standard NRC ZIRC-1 using MC-ICP-MS

High precision analytical methods for 'non-traditional' stable isotopes rely upon standards for normalizing isotopic ratios, correcting instrumental mass fractionation, and comparing data between different laboratories. Zirconium isotope measurements are a new and rapidly expanding field, displaying potential for tracing the history of magmatic differentiation, as well as the formation and evolution of crustal reservoirs. However, previous studies have reported Zr isotopic data relative to different Zr standards, with the IPGP-Zr standard being most commonly used. This situation hinders direct inter-laboratory comparison thereby enlarging uncertainties when converting the data. Here the Zr isotopic composition of a new, commercially available isotopic standard ZIRC-1 is systematically calibrated relative to IPGP-Zr through a collaborative approach between two different laboratories using sample-standard bracketing and double spike methods. Moreover, the Zr isotopic composition of the certified reference materials BHVO-2 and AGV-2, alongside the widely studied Allende chondrite, is reported to ensure the robustness of our data and allow for future inter-laboratory data comparison. Consistent results are obtained from the two laboratories and the average delta Zr-94(IPGP_Zr) (the permil deviation of the Zr-94/Zr-90 of the sample from the IPGP-Zr standard) of ZIRC-1 is -0.220 +/- 0.006 parts per thousand (2SD, n = 7). The delta Zr-91(IPGP_Zr), delta Zr-92(IPGP_Zr), delta Zr-94(IPGP_Zr) and delta Zr-96(IPGP_Zr) values of ZIRC-1 follow a mass-dependent relationship. The delta Zr-94(IPGP_Zr) and delta Zr-94(ZIRC-1) values of the CV3 carbonaceous chondrite Allende are -0.041 +/- 0.021 parts per thousand and 0.179 +/- 0.022 parts per thousand (2SD, n = 7), respectively, and lower than those of bulk Earth, which has delta Zr-94(IPGP_Zr) and delta Zr-94(ZIRC-1) values of 0.041 +/- 0.041 parts per thousand and 0.261 +/- 0.041 parts per thousand respectively, according to the reference of Tian et al. (2021). The BHVO-2 and AGV-2 aliquots analyzed along with ZIRC-1 show agreement with literature data, demonstrating that the data from this study are accurate. The renormalized delta values of all other Zr isotopic standards are listed, allowing for further inter-laboratory comparison.