Element and isotope composition of light noble gas in marine ferromanganese nodules

The authors have measured element and isotope compositions of He and Ar gases in 10 nodules dredged from Mariana Trough (opening back-arc basin) and the Ogasawara region on the Hakuho Maru Cruise. After being washed with distilled water, samples were dried and preheated in vacuo at 150°C in a gas extraction system for two days to reduce surface air contamination. Each sample was placed in a doublewalled tantalum crucible with a surrounding tantalum heater and extracted gases at 1700°C . Gas purification was carried out by the two-stage Ti/Zr getter. The He-Ne and Ar fractions were separated by use of charcoal traps held at -196°C. The noble gas isotopes were analysed by a single focusing mass spectrometer (6-60-SGA, Nuclide Co.). A resolving power of ~600 at 1% peak height was attained to separate 3He from H3 + HD.