The Hf isotopic composition of zircon reference material 91500

Ten new single zircon fragments, analyzed by solution chemistry and MC-ICP-MS, of the 91500 zircon standard show no evidence to support a recent claim based on in situ data that this reference material is heterogeneous in terms of its radiogenic Hf isotope composition and as a consequence should be abandoned as a reliable interlaboratory standard. Rather, the larger spread in Hf-176/Hf-177 among in situ data compared with solution chemistry data may reflect the uncertainties resulting from prominent isobaric interference corrections inherent to the in situ analytical protocol. The unweighted mean values of Hf-176/Hf-177 and Lu-176/Hf-177 measured for the ten zircon fragments of this study are 0.282313 +/- 0.000008 (2 sigma) and 0.000311 +/- 0.000136 (2 sigma), respectively. Pooling the mean Hf-176/Hf-177 of this work with those of published solution chemistry studies results in a value of 0.282308 +/- 0.000006 (2 sigma, relative to Hf-176/Hf-177 = 0.282163 for JMC-475), which is recommended here as the currently best estimate of the Hf isotopic composition of this standard. All published studies agree on a value of similar to 0.0003 for the corresponding Lu-176/Hf-177 ratio. (C) 2008 Elsevier B.V. All rights reserved.