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

A CO2 laser-heated diamond anvil cell was used for performing argon so lubility experiments in silicate melts. This technique allowed solubil ity experiments to be carried out at much higher pressures than in a p iston-cylinder-type apparatus. When the beam of the CO2 laser is focus ed on the silicate sample, argon, acting as a pressure-transmitting me dium, melts by conductive heating from the molten sample and can disse rve 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 cont ents increase up to nearly 5 wt% at 5 GPa and decrease below 1% at hig her pressures. This behaviour is interpreted as resulting from a profo und 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.