Synthetic zircon doped with hafnium and rare earth elements: A reference material for in situ hafnium isotope analysis

A series of flux-grown synthetic zircon crystals doped with Hf and selected rare earth elements (REE) were produced for use as a potential reference material for Lu–Hf isotopic analysis of zircon by in situ laser ablation multi-collector inductively-coupled plasma mass spectrometry (LA-MC-ICPMS). The synthetic zircon crystals were doped such as to produce a large range of REE/Hf, allowing for a robust means of monitoring and correcting the sometimes large 176Yb and 176Lu isobaric interferences on the low-abundance 176Hf in natural zircon, as well as potential oxide interferences from Gd, Tb, and Dy. The synthetic zircon crystals have a homogeneous Hf isotopic composition, both within and between grains, as documented by solution MC-ICPMS analyses of Hf chemically separated from multiple fragments of zircon from three different syntheses, and 321 laser ablation MC-ICPMS analyses done in two different laboratories. An additional 110 in situ analyses of natural zircon crystals reveal identical behavior of natural and synthetic zircon during Hf isotope analysis by laser ablation. Hence, the synthetic zircon crystals provide a means of monitoring a wide range of Yb and Lu interferences (up to 50% of the total signal intensity at mass 176) during routine isotopic analysis for geological studies. They also may be helpful in developing improved laboratory protocols for accurate in situ Lu–Hf isotopic measurement of natural zircon. The present data illustrate the importance of the 176Yb interference correction on 176Hf, which can result in large biases if not properly applied to natural samples with their variable and often high 176Yb/177Hf. This study definitively shows that use of high-REE/Hf synthetic zircon standards for calibrating the Yb mass bias correction is more accurate than use of Yb-doped natural Hf solutions. Finally, the results of the present work suggest that synthetic minerals may prove useful as both in situ method development tools and isotopic reference materials.

Secondary electron image of rare earth element doped synthetic zircon crystals produced as reference materials for in situ lutetium–hafnium isotopic analysis.Figure optionsDownload as PowerPoint slideResearch highlights
► We produced synthetic zircon crystals doped with rare earth elements and hafnium.
► The zircons have a homogeneous Hf isotopic composition, within and between grains.
► Thus, the zircons represent a reference material for in situ Hf isotopic analysis.
► Synthetic minerals may generally prove useful as in situ isotopic reference material.