Laboratory experiments on the Ne enrichments in terrestrial natural glasses

In order to study Ne diffusion into glasses, we measured noble gas concentrations in obsidian samples which were degassed in a vacuum at 800°C and subsequently heated in air at various temperatures and heating times. Neon was concentrated in samples which were kept at room temperature, indicating that Ne is easily diffused into obsidians from the atmosphere even at room temperature. We also measured noble gas concentrations in five size-separated fractions of the obsidian (ME1) (>250, 149-250, 74-149, 46-74 and <46 μm fractions) and in three size-separated fractions of tektite (TE6) (>250 and 149-250 μm fractions and powdered fraction) to examine the degassing effect on noble gases by crushing. The Ar and Kr concentrations, and especially the Ne concentration, show a gradual decrease with decreasing grain size of the obsidian samples. For the tektite samples, Ne concentration in the powdered fraction was about half of that in the >250 and 149-250 μm fractions. These results confirm that Ne in glasses mainly resides in vesicles in the glass.

Kayo Matsubara and Jun-ichi Matsuda