In situ study of magmatic processes: a new experimental approach

Abstract

We present an internally heated autoclave, modified in order to permit in situ studies at pressure up to 0.5 GPa and temperature up to 1000 °C. It is equipped with transparent sapphire windows, allowing the observation of the whole experiment along the horizontal axis. In the experimental cell, the sample is held between two thick transparent plates of sapphire or diamond, placed in the furnace cylinder. The experimental volume is about 0.01 cm³. Video records are made during the whole experiment. This tool is developed mainly to study the magmatic processes, as the working pressures and temperatures are appropriate for subvolcanic magma reservoirs. However, other applications are possible, such as the study of subsolidus phase equilibria as we have used well-known phase transitions, such as the system of AgI, to calibrate the apparatus with respect to pressure and temperature. The principle of the apparatus is detailed. Applications are presented, such as studies of melt inclusions at pressure and temperature and an in situ study of magma degassing through the investigation of nucleation and growth processes of gas bubbles in a silicate melt during decompression.

Keywords:

• In situ
• Transparent autoclave
• High pressure
• High temperature
• Phase transitions
• Melt inclusions studies
• Silicate melts
• Bubble growth
• Decompression

Acknowledgements

We would like to thank Gérard Hamel, Stéphane Lequien, Christian Bettoni, Pascal Lhénoret, Marc Billon, Francois Saillant, and Eddy Foy for their kind assistance. We acknowledge Rémi Champallier for his support during sample preparation. This work has been partly funded by the French Agency for Research (grant ANR-05-CATT-003, C. Martel).