Loss of solar He and Ne from IDPS in subducting sediments: Diffusion and the effect of phase changes

Three samples of a magnetic fraction of Pacific Ocean sediment were heated to 500 °C, 800 °C, and 950 °C, respectively, for two hours in a vacuum furnace in the same condition as that for the diffusion experiment. The run products as well as an unheated sample were examined with an x‐ray diffraction method. The results show that (1) major magnetic mineral was magnetite for all the samples, (2) no peaks of hematite, wustite, nor metallic iron were observed, (3) however, magnetite in the unheated sample had been partly oxidized to form maghemite, which has essentially the same crystal structure as that of magnetite. These observations suggest that the effect of phase changes, if present, would be negligibly small in the diffusion experiment. The present results further support the reliability of the diffusion data obtained in the previous study and support the conclusion that solar He and Ne would be lost from subducting slabs at shallow depths.