レーザ加熱⁴⁰Ar/³⁹Ar年代測定による火山活動史の解明

• 宇都 浩三

  地質調査所地殻化学部同位体地学研究室

• 石塚 治

  地質調査所地殻化学部同位体地学研究室

書誌事項

タイトル別名

• Revealing volcanic history by the laser-heating ⁴⁰Ar/³⁹Ar dating method
• 企画総説 地球化学の新方法 レーザ加熱40Ar/39Ar年代測定による火山活動史の解明
• キカク ソウセツ チキュウ カガク ノ シン ホウホウ レーザ カネツ 40Ar 39Ar ネンダイ ソクテイ ニ ヨル カザン カツドウシ ノ カイメイ

抄録

The laser-heating ⁴⁰Ar/³⁹Ar dating method is now widely applied to the precise dating of a small amount of rocks and minerals. In this review paper, we first mention the principle of the dating method, and describe the analytical system established at the Geological Survey of Japan. We, then, emphasize the importance of determining the three-dimentional fast-neutron flux gradient within the irradiation capsule in order to obtain precise ⁴⁰Ar/³⁹Ar ages Reliable ages of standard minerals are also the key to the higher accuracy of ages of samples because the ⁴⁰Ar/³⁹Ar technique is a dating method relative to the age of a standard sample irradiated together with samples to be dated. GSJ mineral standard, SORI biotite, is considered to be accurate in age within a half percent comparing with other age standards elsewhere. Finally, preliminary studies are presented for the Tertiary volcanic rock and plagioclase phenocryst from a Quaternary tephra. Incremental laser-heating experiment for a Miocene lava from the Takashibiyama Formation was successful to obtain a reliable and precise age of its eruption. Totalfusion experiments were done for plagioclase separates from the Yabakei pyroclastic flow deposit. Each experiment by fusing 3-4 grains gave age with relatively large uncertainties of about 20%, but the weighted average of five runs gave an age of 0.92 ±0.09 Ma, which agrees with the K-Ar age of 0.99 ± 0.03 Ma for this deposit. Our case studies show that the laser-heating ⁴⁰Ar/³⁹Ar dating technique is a promising tool to reveal the history of volcanism.

収録刊行物

• 地球化学

  地球化学 33 (3), 141-154, 1999

  一般社団法人日本地球化学会

キーワード

• ⁴⁰Ar/³⁹Ar dating
• continuous laser
• laser heating
• microanalysis
• volcanic history

詳細情報

• CRID: 1390282680717956736
• NII論文ID: 110008679979
• NII書誌ID: AN00141280
• DOI: 10.14934/chikyukagaku.33.141
• ISSN: 21885923
• ISSN: 03864073
• NDL書誌ID: 4839954
• Web Site: https://ndlsearch.ndl.go.jp/books/R000000004-I4839954
• 本文言語コード: ja
• データソース種別:
  • JaLC
  • NDL
  • CiNii Articles
  • Crossref
• 抄録ライセンスフラグ: 使用不可