3C-O2-1625 PDF
Highly sensitive and simultaneous determination of halogens and noble gases in mantle rocks using noble gas mass spectrometry after neutron irradiation
Neutron irradiation in a nuclear reactor converts halogens to noble gas proxy isotopes. Trace amount of halogens can be determined by noble gas mass spectrometry after neutron irradiation. The detection limits of this technique are several orders of magnitude lower than those of conventional methods applied in geochemistry. At subduction zones, two plates collide with each other and one plate goes down beneath the other along the trench. The subducted plate is called a slab and carries water into the mantle. Halogens and noble gases are expected as sensitive tracers of the slab-derived fluids in the mantle. Fluid inclusions within minerals of mantle xenoliths provide the best medium to investigate slab-derived fluids. In order to investigate how far the influence of slab-derived fluids extends into the mantle, we analyzed the halogens and noble gases within mantle xenoliths from the Western-Pacific subduction zones and intraplate settings. The mantle xenoliths from the subduction zones show similar signatures to those of marine sedimentary pore fluids. This indicates that slab-derived fluids significantly extend into the mantle beneath subduction zones, although the influence of slab-derived fluids is getting smaller with distance from the trench.