Trace element composition, texture, cathodoluminescence, Raman scattering, LA–ICP–MS U–Pb dating, and Lu–Hf isotopic composition of zircon Bai-1-2023 from sands of the Peschanaya Bay complex of Lake Baikal as a potential Early Proterozoic age standard

The search for and substantiation of geochronological standards, as well as their interlaboratory testing, are current tasks in the field of analytical geochemistry. Zircon Bai-1-2023 from the sands of the bays of Lake Baikal (“Peschanaya Bay”), a product of the destruction of rapakivi granites of the Primorsky Complex of the Western Cis-Baikal region, has been proposed by the Institute of the Earth’s Crust SB RAS as a U–Pb geochronological standard. Results . This paper presents the results of an interlaboratory, “blind” U–Pb and Lu–Hf isotope study of more than 100 Bai-1-2023 zircon grains. Grain composition, texture, and homogeneity were analyzed by the methods of microprobe and LA–ICP–MS analysis, local Raman and cathodoluminescence spectroscopy. The results were compared with those obtained for international reference materials of zircon Mud Tank, 91500, Temora-2, GJ–1, and Plesovice. For 25 grains (37 LA–ICP– MS determination rounds), two statistically isolated, concordant age populations of 1871 ± 8.1 and 1781 ± 5.7 Ma were identified; for most points, the discordance parameter for 207 Pb/ 206 Pb and 206 Pb/ 238 U ages was less than 5–6%; for single ones – 10–17%. One population showed an age close to IR-TIMS dating (1859 ± 16 and 1853.6 ± 6.5 Ma). The presence of two populations is not accompanied by clearly distinguishable changes in the composition of zircon grains and their texture, cores, shells, and cracks. LA–ICP–MS data were obtained for 176 Hf/ 177 Hf and 176 Lu/ 177 Hf isotope ratios. The parameter ε Hf (t) and the model age of the source T DM were calculated as follows ε Hf (t) = –13.7 ÷ –6.5 and T DM = 2.5– 2.7 Ga. For zircon grains, significant variations in the position of the vibrational mode ν 3 (SiO 4 ) (1003.4– 1006.6 cm -1 ) and its width FWHM (4.8–9.8 cm -1 ), as well as the values of accumulated autoradiation and equivalent doses – (0.64–2.47) and (0.20– 0.52)·10 18 α-decay/g, respectively, were established. Bai-1-2023 zircon was shown to correspond to II–III stages of the mineral disorder. Cathodoluminescence brightness of zircon grains varied by more than an order of magnitude. In the spectra, a number of broad bands A i , B i , C i in the near UV, blue–green, and yellow regions were distinguished. The position of points for Bai-1-2023 zircon on the triple A i –B i –C i discrimination diagram was analyzed. Spectroscopic properties of Bai-1-2023 zircon and the degree of its radiation damage were shown to overlap the properties of the reference materials 91500 → Temora-2→ GJ–1 → Plesovice. Conclusions. Zircon Bai-1-2023 can be recommended as a secondary age reference material for verifying the accuracy of LA–ICP–MS analysis.