Zircon S513 – A New Gem-Quality Reference Material for In Situ Microbeam U-Th-Pb, (U-Th)/He Geochronology and Hf-O Isotope Measurement

Abstract

A new gem-quality zircon reference material, S513, was developed for in situ microbeam U-Th-Pb, (U-Th)/He geochronology and Hf-O isotope measurement. The well-cut gem-quality zircon weighed 51.3 carats. Its U, Th, Pb and Hf mass fractions were 924 ± 64.6 μg g⁻¹ (2s), 89.6 ± 3.92 μg g⁻¹ (2s), 119 ± 5.20 μg g⁻¹ (2s) and 8259 ± 244 μg g⁻¹ (2s), respectively. Imaging results from LA-ICP-ToF-MS analysis showed homogeneous distribution of elements in S513. The Th-corrected weighted mean ²⁰⁶Pb/²³⁸U, ²⁰⁷Pb/²³⁵U and ²⁰⁷Pb/²⁰⁶Pb ratios of S513 zircon from eight ID-TIMS analyses are 0.090955 ± 0.000019 (2s, MSWD = 0.22, n = 8), 0.73873 ± 0.00023 (2s, MSWD = 0.19, n = 8) and 0.058934 ± 0.000008 (2s, MSWD = 0.35, n = 8), respectively. The Th-corrected weighted mean ²⁰⁶Pb/²³⁸U age obtained from chemical abrasion-isotope dilution-thermal ionisation mass spectrometry is 561.18 ± 0.63 Ma (n = 8, 95% conf., MSWD = 0.9), which is recommended as the best age estimate of S513. The weighted mean ²⁰⁶Pb/²³⁸U ages obtained from in situ microbeam analysis (i.e., LA-ICP-MS and SIMS) were 560.8 ± 5.8/10.2 Ma (2s, n = 260) and 562.4 ± 7.2/13.4 Ma (2s, n = 198). The measured weighted mean ²⁰⁸Pb/²³²Th age of S513 from LA analyses was 561.3 ± 3.3/11.7 Ma (2s, n = 86). The U-Pb and Th-Pb ages of S513 obtained with in situ methods showed good agreement with the CA-ID-TIMS results, respectively. The obtained (U-Th)/He age of S513 from thirty-seven aliquots analysed with U-Th isotope dilution method was 420.3 ± 7.6 Ma (2s, MSWD = 0.72). The recommended reference value of Hf isotope ratio was 0.281606 ± 0.000010 (2s, MSWD = 1.4, n = 12) according to the mean ¹⁷⁶Hf/¹⁷⁷Hf ratio acquired with solution MC-ICP-MS analysis. All the LA analyses yielded a mean ¹⁷⁶Hf/¹⁷⁷Hf ratio of 0.281605 ± 0.000008 (2s, MSWD = 0.53, n = 310), which was consistent with the reference value. Laser fluorination analyses yielded mean δ¹⁸O values of S513 were 11.71 ± 0.11‰ (2s, MSWD = 0.25, n = 5). The results obtained with multiple analytical methods show that zircon S513 is homogeneous to 8% (1s) or better for contents of Y, Nb, Ce, Gd, heavy REE, Ta, U, Th, Pb and Hf. Additionally, the homogeneity is observed at 0.12‰ (2s) for U-Pb ages, 1.8% (2s) for (U-Th)/He ages, 0.0036% (2s) for Hf isotopes, and 0.11‰ (2s) for O isotope ratios. Zircon S513 is proposed as a new potential primary calibration or quality control reference material for microbeam U-Th-Pb geochronology and Hf-O isotope measurement.