ABSTRACT

The contents and the isotopic compositions have been measured mass-spectrometrically for neon, argon, krypton and xenon released from four specimens of granites in stepwise-heating experiments. These rocks contained appreciable amounts of ⁴⁰Ar from the decay of ⁴⁰K and ^131-136Xe from the ²³⁸U spontaneous fission. The contents of neon, argon (excluding ⁴⁰Ar), krypton and xenon in these granites were considerably lower than the estimated rare gas contents of rocks reported by BROWN (1949), except for the Red Rock granite, which contained an abnormally large amount of xenon. The Ne/Xe, Ar/Xe and Kr/Xe ratios in the Red Rock granite were abnormal in that they resembled the relative abundances in meteorites. Moreover, a large fraction of the total xenon released from the Red Rock granite appeared to be a mixture of AVCC xenon and the atmospheric xenon. The Red Rock granite is from the Sudbury structure, Ontario, Canada, which is believed to have been formed by the impact of an asteroid in an event that formed a crater 30 miles in diameter 1, 720 million years ago.