High-precision Measurement of Hf Isotopic Reference Values for the U-Pb Geochronology Standard Zircons by Multi-collector Inductively Coupled Plasma-Mass Spectrometry

The Hf isotope ratios were determined by a Micromass Isoprobe multiple collector-inductively coupled plasma mass spectrometry (MC-ICP-MS) for two international zircon standards 91500 and Temora and one in-house zircon standard We-1. Zircons were digested by HF in high-pressure bombs. For the reason that Zr did not change Hf isotopic ratios in the simulative experiment, Hf was separated using a modified one-step ion-exchange chromatography reported by Arnard et al.. The overall recovery of Hf was better than 90%. Calibrated by an external standard solution JMC-475 Hf, 176Hf/ 177Hf ratios of these standard zircons were precisely determined. The average 176Hf/ 177Hf values of 91500 and Temora and We-1 were (0.282 310±0.000 034), (0.282 706±0.000 020) and ( 0.281 534±0.000 009), respectively. Considering that the Hf isotope results above consist of at least seven separated performances of aliquots for each zircon sample, the 176Hf/ 177Hf ratios of 91500, Temora and We-1 were homogeneous. These results have significant implications for testing the calibration method in zircon Hf isotopic determination by laser-ablation multiple collector-inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS).