Helium Isotope Ratios of Pore Gases in Deep-Sea Sediments, Leg 128

Abstract

He ratio of 1.393 × IQr 6 ) to 0.840 R atm , and from 0.41 to 4.5, respectively. Helium in the samples can be explained by the mixing between atmospheric helium dissolved in bottom water of the Japan Sea and crustal helium in the sediment. The sedimentary helium is enriched in mantle-derived 3 He compared with those from the Japan Trench and the Nankai Trough. This suggests that the basement of the Japan Sea has relatively large remnants of mantle-derived helium compared with that of the Pacific. Major chemical compositions of the samples are methane and nitrogen. There is a positive correlation between methane content and helium content corrected for air component. Based on the ^erHe-ZC^He diagram, the major part of methane can be attributed to crustal and/or organic origin.

Elemental and Isotopic Abundance of Noble Gases in Formation Fluids Recovered In Situ from the Chile Triple Junction

“…Data from the Chile Triple Junction are shown by squares and are designated by letters that correspond to the samples indicated in Table 2. Data from ODP Site 583 in the Nankai Trough (circles, from Sano and Wakita, 1985), Site 584 in the Japan Trench (crosses, Sano and Wakita, 1985) and from the Japan Sea (+ signs, Sano et al, 1992) are included for comparison. The data for the sample from Core 859A-8X (G) is very uncertain; the high gas content of this sample resulted in large errors during sampling and analysis (see text).…”