ARGON SOLUBILITY IN SILICATE MELTS AT VERY HIGH PRESSURES. EXPERIMENTAL SET-UP AND PRELIMINARY RESULTS FOR SILICA AND ANORTHITE MELTS

Abstract

A CO2 laser-heated diamond anvil cell was used for performing argon solubility experiments in silicate melts. This technique allowed solubility experiments to be carried out at much higher pressures than in a piston-cylinder-type apparatus. When the beam of the CO2 laser is focused on the silicate sample, argon, acting as a pressure-transmitting medium, melts by conductive heating from the molten sample and can dissolve into the melt. Preliminary results for argon solubility in silica and anorthite melts up to 10 GPa are presented. In anorthite melt, the Ar content levels up at 0.5 wt% above 5 GPa. For silica melt, Ar contents increase up to nearly 5 wt% at 5 GPa and decrease below 1% at higher pressures. This behaviour is interpreted as resulting from a profound change in the structure of the melt above 5 GPa, probably related to an increase in the proportion of 4- and 3-membered SiO4 rings.