SA01-A Proposed Zircon Reference Material for Microbeam U-Pb Age and Hf-O Isotopic Determination

摘要

A new natural zircon reference material SA01 is introduced for U-Pb geochronology as well as O and Hf isotope geochemistry by microbeam techniques. The zircon megacryst is homogeneous with respect to U-Pb, O and Hf isotopes based on a large number of measurements by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and secondary ion mass spectrometry (SIMS). Chemical abrasion isotope dilution thermal ionisation mass spectrometry (CA-ID-TIMS) U-Pb isotopic analyses produced a mean Pb-206/U-238 age of 535.08 +/- 0.32 Ma (2s, n = 10). Results of SIMS and LA-ICP-MS analyses on individual shards are consistent with the TIMS ages within uncertainty. The delta O-18 value determined by laser fluorination is 6.16 +/- 0.26 parts per thousand (2s, n = 14), and the mean Hf-176/Hf-177 ratio determined by solution MC-ICP-MS is 0.282293 +/- 0.000007 (2s, n = 30), which are in good agreement with the statistical mean of microbeam analyses. The megacryst is characterised by significant localised variations in Th/U ratio (0.328-4.269) and Li isotopic ratio (-5.5 to +7.9 parts per thousand); the latter makes it unsuitable as a lithium isotope reference material.