ABSTRACT

The isotopic compositions have been measured mass spectrometrically for xenon and krypton fractions released from a sample of thucholite from Besner Mine, Parry Sound, Ontario, Canada, in stepwise heating experiments. The relative abundances of the fissiogenic xenon and krypton isotopes released from the thucholite indicated that they are primarily the product of ²³⁸U spontaneous fission. A xenon fraction with an isotopic composition resembling that of the AVCC xenon was released at 400°C. In the case of krypton, the isotopic composition of a very large fraction of the total gas released at 250°C was closer to the AVCC krypton than to the atmospheric krypton. Small excesses of cosmic-ray-produced ¹²⁴Xe and ¹²⁶Xe appeared to be present in xenon fractions released at higher temperatures. A possible connection between the occurrence of a meteoritic rare gas component in terrestrial materials and the process of meteorite impact is discussed.