TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 61 (No. 8), pp. 1003-1011, 2009

Argon retentivity of carbonaceous materials: feasibility of kerogen as a carrier phase of Q-noble gases in primitive meteorites

Takahito Osawa1, Norie Hirao2, Nobuyori Takeda3, and Yuji Baba2

1Neutron Imaging and Activation Analysis Group, Quantum Beam Science Directorate, Japan Atomic Energy Agency (JAEA), Tokai-mura, Naka-Gun, Ibaraki, 319-1195, Japan
2Surface Chemistry Research Group, Synchrotron Radiation Research Unit, Quantum Beam Science Directorate,Japan Atomic Energy Agency (JAEA), Tokai-mura, Naka-Gun, Ibaraki, 319-1195, Japan
3JAPEX Research Center, Japan Petroleum Exploration Co. Ltd., Hamada 1-2-1, Mihama-ku, Chiba, 261-0025, Japan

(Received January 9, 2009; Revised March 19, 2009; Accepted May 27, 2009; Online published October 19, 2009)

Abstract: Extremely large amounts of heavy noble gases are concentrated in phase Q, which seems to be a carbonaceous phase analogous to terrestrial Type III kerogen. Phase Q must have very high noble gas retentivity based on the presence of such extremely large amounts of heavy noble gases in a very minor fraction of the meteorite. To verify that kerogen is a carrier phase of Q-noble gases, X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) using synchrotron radiation were carried on for kerogens (coals) and carbon allotropes that had been bombarded by 3-keV Ar ions, and the Ar retentivities of the two materials were compared. This comparison of the estimated Ar concentrations in the target materials revealed that carbon allotropes (graphite, fullerene, carbon nanotube, and diamond) have a much higher Ar retentivity than kerogens. This unexpected result clearly shows that the terrestrial kerogens tested in our study are not suitable as a carrier phase of Ar and, consequently, that phase Q may not be similar to the terrestrial kerogen tested. If heavy noble gases are really concentrated in carbonaceous components of primitive meteorites, phase Q may have a more ordered structure than terrestrial kerogen based on the fact that the greatest difference between terrestrial kerogen and carbon allotropes is the degree of order of the molecular structure.
Key words: Noble gas, XAS, XPS, kerogen, phase Q, ion implantation, diamond, graphite.

Corresponding author E-mail: osawa.takahito@jaea.go.jp

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