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Keywords:

  • Kawamoto Granodiorite;
  • secondary standard;
  • U–Pb dating;
  • zircon

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 238U–206Pb ages show good agreement, with an overall weighted average 238U–206Pb age of 33.0 ± 0.1 Ma (2σ). 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 ± 0.6 Ma (2σ). 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.