Noble gas mass spectrometry

The method for the isotopic analysis of trace noble gas is described briefly, and the theoretical background of the application to earth science is discussed. Furthermore, the measured results of 3He/4He ratio in volcanic gases and hot spring gases from various areas in Japan, and 3He/4He and 40Ar/36Ar ratios in mantle-origi nated rocks and minerals are presented. The examples of the application of these results to the field of earth science are introduced. The magma activity which is specific to the considered volcano is identified from the decrease in 3He/4He ratio with the process of volcanic activity. The possibility of earthquake prediction by the measurement of 3He/4He ratio is suggested from the measured results of 3He/4He ratio in the gas sampled from an earthquake fault. The isotopes of He and Ar in a diamond were analyzed, and from these results, the isotope composition in mantle when the diamond had been formed was estimated. The mantle model that the mantle is constituted from upper depleted mantle and lower fertile mantle is explained, based on the results of the analysis of He and Ar isotopes in various volcanic eruptions. (Yoshitake, I.)