He and Ne isotopic studies on the extraterrestrial material in deep-sea sediments

Elemental abundances and isotopic compositions of He and Ne were determined by stepwise heating for a magnetic separate of deep-sea sediments and its 3 M HCl resistant fractions. High 3He/4He ratios (2 - 3 x 10-4) and solar 20Ne/22Ne ratios (12-14) were observed in all temperature fractions for these samples. The major release temperatures of 4He were at 1,000 C, whereas 20Ne at 1,200 C. These results suggest that solar He and Ne are tightly trapped inside the grains with nearly uniform isotopic ratios. The magnetic separate lost about 75% of its 3He against 37% weight loss during the 3 M HCl treatment, indicating that solar He and Ne are relatively enriched in the fine fraction and/or on the surface of magnetite grains. It is likely that the solar wind with its high energy tail is reponsible for the extraterrestrial noble gases in deep-sea sediments. Alternatively, solar wind He and Ne were redistributed in the magnetite during atmospheric entry and tightly trapped inside the grains