Jilin zircon – a new natural reference material for microbeam U–Pb geochronology and Hf–O isotopic analysis

Abstract

Zircon U–Pb geochronology and Hf–O isotope composition provide important information on geological events. This matrix-matched reference material is routinely used to yield accurate and precise zircon U–Pb ages and Hf–O isotope ratios with in situ techniques. In this study, a new potential zircon reference material (Jilin) separated from gabbro diorite was introduced for microbeam U–Pb age and Hf–O isotope analysis. The obtained average U, Th, Pb, Lu and Hf concentrations were 439 ± 26 ppm (1 s), 378 ± 39 ppm (1 s), 67.6 ± 1.6 ppm (1 s), 54.6 ± 6.5 ppm (1 s), and 9135 ± 510 ppm (1 s) respectively. The chemical abrasion isotope dilution thermal ionization mass-spectrometry (CA-ID-TIMS) method yielded a Th-corrected weighted mean ²⁰⁶Pb/²³⁸U age of 117.63 ± 0.04 Ma (2 s, MSWD = 1.9). The homogeneity of U–Pb ages in Jilin zircon was also investigated in two independent secondary ion mass spectrometry (SIMS) laboratories and four different laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) laboratories. The obtained mean ²⁰⁶Pb/²³⁸U ages with SIMS and LA-ICP-MS were 116.8 ± 2.9 Ma and 117.8 ± 2.7 Ma, respectively, which are consistent with the CA-ID-TIMS value within the analytical uncertainties. The distribution of Hf isotopic composition was evaluated with LA-multicollector-ICP-MS (LA-MC-ICP-MS) and solution MC-ICP-MS. The results acquired in two LA-MC-ICP-MS laboratories were identical to the solution value with a mean ¹⁷⁶Hf/¹⁷⁷Hf ratio of 0.282926 ± 0.000014 (2SD, n = 17). The O isotope obtained with the laser fluorination method is also in agreement with the SIMS analysis with the recommended mean δ¹⁸O value of 6.05 ± 0.25‰ (2SD, n = 8). The results obtained with multianalytical techniques clearly indicate that the U–Pb age and Hf–O isotopic composition are homogenous in Jilin zircon grains. We propose the Jilin zircon as a potential reference material for the primary external calibration or monitoring of analytical validation for Mesozoic U–Pb geochronology and Hf–O isotopic measurements.