(Table 1) 3He/4He and 4He/20Ne ratios of pore gases in sediment at DSDP Sites 84-568 and 90-594

Studies on He isotope ratios of gas and rock samples in various parts of the world have shown a close relation between the 3He/4He ratio and geotectonic features of the sampling area. Emission of primordial He is commonly found in gases and fluid in Cenozoic volcanic areas (mid-ocean ridges, hot spots, and subduction zones), whereas that of radiogenic He is predominant in continental areas. Thus, the 3He/4He ratio is considered a useful tool for evaluating a variety of geotectonic environments.