Characterization of the potential reference material SA02 for micro-beam U-Pb geochronology and Hf-O isotopic composition analysis of zircon

In the present work, a natural zircon megacryst SA02 (the exact provenance unknown) is investigated as a new potential reference material for U-Pb geochronology and Hf-O isotopic composition analysis via micro-beam methods. The precise and accurate U-Pb age is determined by the chemical abrasion isotope dilution thermal ionization mass-spectrometry (CA-ID-TIMS) method. The resultant mean Pb-206/U-238 date is 535.10 +/- 0.24 Ma (2s, n = 2), interpreted as the crystallization age of the zircon megacryst. The mean ID-TIMS Pb-206/U-238 date of 533.7 +/- 3.7 Ma (2s, n = 8) is recommended as the working value for micro-beam analyses when using untreated SA02 zircon grains as the primary reference material. Pb-206/U-238 dates of 533.0 +/- 6.2 Ma (2s, n = 57) and 534 +/- 8 Ma (2s, n = 101) obtained by secondary ion mass spectrometry (SIMS) and laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) respectively are reproducible and in agreement with the results of ID-TIMS within < 0.3% relative analytical errors. Solution data of Hf isotope compositions measured by multi-collector ICP-MS (MC-ICP-MS) from SA02 zircon yield a mean Hf-176/Hf-177 of 0.282287 +/- 0.000016 (2s, n = 31), which is recommended as a reference value for microbeam analysis. Hf isotope analyses by LA-MC-ICP-MS yield homogeneous Hf isotopic compositions with a mean Hf-176/Hf-177 of 0.282289 +/- 0.000033 (2s, n = 142) identical to the solution value. The mean delta O-18 value measured by laser fluorination is 6.03 +/- 0.28 parts per thousand (2s, n = 13), which is consistent with the result of SIMS analysis.

Automated summary

In this study, a natural zircon megacryst SA02 was investigated as a potential reference material for U-Pb geochronology and Hf-O isotopic composition analysis. The results obtained by different methods showed consistent and reliable age data.