レーザ加熱<sup>40</sup>Ar/<sup>39</sup>Ar年代測定による火山活動史の解明  [in Japanese] Revealing volcanic history by the laser-heating <sup>40</sup>Ar/<sup>39</sup>Ar dating method  [in Japanese]

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Author(s)

    • 宇都 浩三 UTO Kozo
    • 地質調査所地殻化学部同位体地学研究室 Isotope Geoscience Section, Geochemistry Department, Geological Survey of Japan
    • 石塚 治 ISHIZUKA Osamu
    • 地質調査所地殻化学部同位体地学研究室 Isotope Geoscience Section, Geochemistry Department, Geological Survey of Japan

Abstract

The laser-heating <sup>40</sup>Ar/<sup>39</sup>Ar 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 <sup>40</sup>Ar/<sup>39</sup>Ar ages Reliable ages of standard minerals are also the key to the higher accuracy of ages of samples because the <sup>40</sup>Ar/<sup>39</sup>Ar 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 <sup>40</sup>Ar/<sup>39</sup>Ar dating technique is a promising tool to reveal the history of volcanism.

Journal

  • Chikyukagaku

    Chikyukagaku 33(3), 141-154, 1999

    The Geochemical Society of Japan

References:  38

Cited by:  4

Codes

  • NII Article ID (NAID)
    110008679979
  • NII NACSIS-CAT ID (NCID)
    AN00141280
  • Text Lang
    JPN
  • Article Type
    Journal Article
  • ISSN
    0386-4073
  • NDL Article ID
    4839954
  • NDL Source Classification
    ZM41(科学技術--地球科学)
  • NDL Call No.
    Z15-645
  • Data Source
    CJP  CJPref  NDL  NII-ELS  J-STAGE 
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