HR: 15:30h
AN: V73B-06    [Abstracts]
TI: Synthetic zircon doped with Hf-Lu and Yb as potential reference materials for in situ microanalysis
AU: * Fisher, C M
AF: Department of Earth Sciences, Memorial University of Newfoundland, St. John's, NL A1B 3X5, Canada
AU: Hanchar, J M
AF: Department of Earth Sciences, Memorial University of Newfoundland, St. John's, NL A1B 3X5, Canada
AU: Lam, R
AF: MicroAnalysis Facility, Inco Innovation Centre (MAF-IIC), Memorial University of Newfoundland, St. John's, NL A1C 5S7, Canada
AB: Preliminary results are reported for a pilot study initiated to test the potential use of synthetic zircon (ZrSiO4) doped with hafnium (Hf) and varying amounts of ytterbium (Yb) and lutetium (Lu), as a Hf isotopic reference material for analysis of natural zircon crystals. The micron-scale Hf isotopic homogeneity in these (500-1000 microns) synthetic zircon crystals occurs at both the intra- and inter-grain scale levels. As such, these materials show high potential as standards for in situ microanalytical mass spectrometric techniques like secondary ion mass spectrometry (SIMS) and laser ablation-multicollector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS) of zircon. The isotopic homogeneity of these synthetic zircon crystals can be utilized to monitor the complex, and sometimes large corrections necessary for in situ microanalytical techniques, where a chemical separation to remove the significant isobaric inferences is not performed. The major obstacles in doing accurate in situ measurement of 176Hf/177Hf in zircon are the corrections for instrumental mass bias and the unavoidable 176Yb and 176Lu isobaric interference on 176Hf. To monitor the effectiveness of these corrections, a set of Hf + Yb +Lu doped synthetic zircon crystals were grown with 176Hf representing from 96% to 60% of the total 176 amu signal (176Yb/177Hf = 0.01-0.22, 176Lu/177Hf= 0.0004-0.0055), covering the range expected in natural zircon samples. Due to intrinsic chemical zoning in the large flux-grown synthetic zircon crystals, the Hf elemental concentrations vary by ~15% from core (mean 12000 ppm) to rim (mean 10000 ppm) and 176Yb/177Hf varies up to ~30% in some grains. This variation in Hf and Yb concentration allows a full range of possible zircon compositions to be monitored in an analytical session, with a single homogeneous Hf isotopic composition, thereby closely approximating the full range of natural zircon crystals that may be encountered in Hf tracer isotope studies of zircon.
DE: 1040 Radiogenic isotope geochemistry
DE: 1094 Instruments and techniques
DE: 3620 Mineral and crystal chemistry (1042)
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2009 Joint Assembly