同一ジルコン結晶を用いたフィッション・トラックとU-Pbダブル年代測定法の評価:−島根県川本花崗閃緑岩中の均質ジルコンを用いて−  [in Japanese] Evaluation of fission-track and U-Pb double dating method for identical zircon grains::Using homogeneous zircon grains in Kawamoto Granodiorite in Shimane prefecture, Japan  [in Japanese]

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Abstract

同一ジルコン粒子を用いたフィッション・トラック(FT)法とU-Pb法によるダブル年代測定した年代値の信頼性を評価した.試料にはFT年代が33 Ma,自発FT密度が10<sup>6</sup>〜10<sup>7</sup>/cm<sup>2</sup>の島根県川本花崗閃緑岩三原岩体のジルコン粒子(OD-3)を用いた.U-Pb年代分析は,Nd-YAG(λ=213 nm)レーザーアブレーションシステムを搭載したICP質量分析法を用い,ジルコンを47%HF溶液による洗浄あるいはKOH-NaOH共融液によるFTエッチングを施した後に行った.その結果,33 MaのコンコーディアU-Pb年代が得られた.これは化学処理されたジルコンには顕著なPb損失は生じず,そして同一ジルコン粒子のFTおよびU-Pbダブル年代測定が実行可能であることを示す.今回使用した川本花崗閃緑岩三原岩体のジルコン粒子(OD-3)は若いジルコンU-Pb年代測定の標準試料になりうる試料である.

Using the double-dating approach, we have conducted fission-track (FT) and U-Pb age dating on the same zircon grain to evaluate the reliability of the resulting age data. The zircon grains (OD-3) used for the investigation were collected from the Mihara Body of the Kawamoto Granodiorite, Shimane Prefecture, Japan. The zircon crystals yielded a FT age of 33 Ma, with a spontaneous FT density of 10<sup>6</sup>–10<sup>7</sup> cm<sup>2</sup>. The U-Pb age data were obtained using inductively coupled plasma-mass spectrometry (ICP-MS) combined with a frequency quintupled Nd-YAG (λ= 213 nm) laser ablation (LA) sample introduction system. The U-Pb age determinations on the zircon samples were performed after chemical leaching using 47% HF for 20 hrs at room temperature, or after FT etching using a KOH–NaOH eutectic solution for 20 hrs at 225 °C. The resulting U-Pb age of 33 Ma was concordant with the FT age data, suggesting that there was no significant loss of Pb during etching or chemical preparation, thus indicating the feasibility of FT and U-Pb double dating of single zircon grains. The results indicate that the zircon grains (OD-3) from the Kawamoto Granodiorite (Mihara Body) can become a new working standard for precise U-Pb age determinations of young zircons.

Journal

  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 118(6), 365-375, 2012

    The Geological Society of Japan

Codes

  • NII Article ID (NAID)
    130001915323
  • NII NACSIS-CAT ID (NCID)
    AN00141768
  • Text Lang
    JPN
  • ISSN
    0016-7630
  • NDL Article ID
    023879554
  • NDL Call No.
    Z15-174
  • Data Source
    NDL  J-STAGE 
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