An inter‐laboratory evaluation of OD‐3 zircon for use as a secondary U–Pb dating standard

Abstract

Zircon OD-3 from the Paleogene Kawamoto Granodiorite (Mihara body) in Japan has been identified as a potential multi-grain secondary standard for U-Pb dating. We have carried out an inter-laboratory evaluation in order to evaluate possible heterogeneity amongst the OD-3 zircon grains. U-Pb ages were obtained using two analytical techniques (a sensitive high-resolution ion microprobe and a laser ablation-inductively coupled plasma-mass spectrometry) in eight laboratories. All the 238 U-206 Pb ages show good agreement, with an overall weighted average 238 U-206 Pb age of 33.0 Ϯ 0.1 Ma (2s). The U-Pb age results revealed no significant variation or heterogeneity in the U-Pb ages of the OD-3 grains. Twelve fission-track (FT) ages from three laboratories are also reported, and have a weighted average of 32.6 Ϯ 0.6 Ma (2s). Despite the different closure and annealing temperatures of the U-Pb and FT chronometers, respectively, the FT age is in good agreement with the U-Pb age. This suggests that the OD-3 zircon had a relatively fast cooling history and has not experienced later thermal annealing. The chronological dataset reported here clearly demonstrates that the OD-3 zircon could be a useful and reliable secondary standard for use during U-Pb dating studies of Cenozoic zircons.

Spatial U–Pb age distribution of plutonic rocks in the central Abukuma Plateau, northeastern Japan Arc

“…All discordant zircons and/or common-Pb detected zircons were removed from the calculation (Table A1; Table A1 Pb ages of concordant Plešovice zircon were, respectively, 337.9 ± 1.8 Ma and 338 ± 15 Ma (n = 18), consistent with reference data (337.13 ± 0.37 Ma, Sláma et al, 2008). The weighted-mean 238 U-206 Pb age of concordant OD-3 zircon was 32.98 ± 0.32 Ma (n = 11), consistent with reported data (33.0 ± 0.1 Ma, Iwano et al, 2013). Error-weighting and outlier rejection were done using software (Isoplot 4.15;Ludwig, 2008).…”

A trachyte–syenite core within a basaltic nest: filtering of primitive injections by a multi-stage magma plumbing system (Oki-Dōzen, south-west Japan)

“…The dating procedures were analogous to those described in Ito (2014) except that zircons were not polished and 40 μm laser beam with fluence of 4-6 J/cm 2 was used. The accuracy and precision of the age data were confirmed by analysis of standard OD-3 (Iwano et al 2013), which was also dated using unpolished zircons. Full details of the analytical results are presented in Electronic Appendix 3.…”

Molybdenum isotopes in hydrothermal manganese crust from the Ryukyu arc system: Implications for the source of molybdenum

“…The isotopic composition in the Nancy 91500 zircon crystal standard was measured to determine the isotope fractionation during the measurement. The zircon from the Kawamoto Granodiorite (OD-3; Iwano et al, 2013) was also measured to ensure the accuracy of measurements. The 238 U-206 Pb age of OD-3 during this study was 33.16 ± 1.52 Ma (n = 5, 2SD), and is consistent with the previous study (33.04 ± 0.10; Iwano et al, 2013).…”