Novel Methods for Concomitant Determination of the Stable Zr Isotope Composition, Lu-Hf Isotope Systematics and U-Pb Age of Individual Zircons

Abstract

The stable Zr isotope ratios in zircon yield a novel geochemical tracer that, together with the Lu-Hf and U-Pb radiogenic isotope systems, allows for a better understanding of the magmatic evolution of silicate melts. We present a solution-based procedure for coupled stable Zr, Lu-Hf and U-Pb isotope ratio determinations for individual zircons using a ⁹¹Zr-⁹⁶Zr tracer purified from Hf and a late-spiking protocol for Zr. This method yields high-precision Zr and Hf isotope results while maintaining low blank levels for U-Pb isotope and Lu/Hf ratio determinations. With a two-fold improvement on the precision relative to previous solution-based work, we report δ⁹⁴Zr_IPGP-Zr values (deviation of the ⁹⁴Zr/⁹⁰Zr ratio in the sample relative to the IPGP-Zr reference material) and associated intermediate precisions (2s) for the zircon reference materials 91500, Mud Tank, Plešovice and Penglai of -0.041 ± 0.015‰, 0.018 ± 0.013‰, 0.089 ± 0.020‰ and -0.117 ± 0.021‰, respectively. Furthermore, this method yields un-biased δ⁹⁴Zr_IPGP-Zr and ¹⁷⁶Hf/¹⁷⁷Hf results for 25-ng Zr and 0.56-ng Hf aliquots of the Mud Tank zircon with intermediate precisions (2s) of 0.027‰ and 1.7 ε (parts per ten thousand), respectively. Thus, the presented method is applicable for the analysis of extremely small and rare zircon grains.