Exposure age and terrestrial age of the paired meteorites Yamato-82192 and -82193 from the moon

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Abstract

The isotopic abundances of the noble gases in the lunar meteorites Yamato-82192 and -82193 were investigated with emphasis on the determination of the exposure history and the terrestrial age. Both meteorites contain low amounts of solar wind trapped noble gases indicating that the breccia grains resided for a very brief period of time on the lunar surface compared to typical lunar soil. Strong gas losses are reflected by the extremely low concentrations of He. Identical exposure histories are derived for both meteorites confirming earlier suggestions that they represent a paired fall. The investigated samples experienced a shallow shielding to cosmic rays of less than 25g/cm^2. From the activity of cosmogenic radionuclides we conclude that the meteoroid spent at least 5Ma of its most recent exposure history in free space. Assuming excavation on the Moon from a depth completely shielded from cosmic rays and propulsion into Earth orbit by the same impact event we calculate a Moon-Earth transit time, i. e. an exposure age in free space at 4π exposure geometry of 11±2Ma. The terrestrial age of the Y-82192/3 meteorite is 70000 to 80000 years which is typical for the meteorites collected in the Yamato Mountains.

The isotopic abundances of the noble gases in the lunar meteorites Yamato-82192 and -82193 were investigated with emphasis on the determination of the exposure history and the terrestrial age. Both meteorites contain low amounts of solar wind trapped noble gases indicating that the breccia grains resided for a very brief period of time on the lunar surface compared to typical lunar soil. Strong gas losses are reflected by the extremely low concentrations of He. Identical exposure histories are derived for both meteorites confirming earlier suggestions that they represent a paired fall. The investigated samples experienced a shallow shielding to cosmic rays of less than 25g/cm^2. From the activity of cosmogenic radionuclides we conclude that the meteoroid spent at least 5Ma of its most recent exposure history in free space. Assuming excavation on the Moon from a depth completely shielded from cosmic rays and propulsion into Earth orbit by the same impact event we calculate a Moon-Earth transit time, i. e. an exposure age in free space at 4π exposure geometry of 11±2Ma. The terrestrial age of the Y-82192/3 meteorite is 70000 to 80000 years which is typical for the meteorites collected in the Yamato Mountains.

Journal

  • Proceedings of the NIPR Symposium on Antarctic Meteorites

    Proceedings of the NIPR Symposium on Antarctic Meteorites 1, 135-141, 1988-03

    National Institute of Polar Research

Codes

  • NII Article ID (NAID)
    110000029859
  • NII NACSIS-CAT ID (NCID)
    AA10784627
  • Text Lang
    ENG
  • Article Type
    Departmental Bulletin Paper
  • ISSN
    09145621
  • Data Source
    NII-ELS  IR 
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