Anomalous Ne enrichment in obsidians and Darwin glass: Diffusion of noble gases in silica-rich glasses

Abstract

We have determined noble gas concentrations in seven obsidians and a Darwin glass by stepwise heating. The pattern of noble gases relative to air showed that Ne was enriched in most of the obsidians and Darwin glass. The release temperatures of Ne were 400–500°C. The occurrence of Ne excess in Darwin glass and related impact glasses can be explained by diffusion into the glass from the atmosphere. Diffusion coefficients and activation energies of noble gases in obsidians and a Darwin glass were determined. It is also conceivable that the anomalously high Ne Ar ratios observed in some submarine glasses are from sea water or atmosphere rather than derived from the mantle.