A combined rapid-quench and H2-membrane setup for internally heated pressure vessels: Description and application for water solubility in basaltic melts

Abstract

This study presents improvements of internally heated pressure vessels to realize high-pressure experiments at controlled f O₂ in low-viscosity systems such as basaltic ones. The new design is a combination of two experimental techniques: a hydrogen sensor membrane made of platinum to measure f H₂ , and therefore f O₂ , and a rapid-quench system to avoid crystallization of low-viscosity melts during quench. The experimental setup has been tested successfully at temperatures up to 1250 °C and pressures up to 500 MPa. Basaltic melts containing up to 9.38 wt% water can be quenched as bubble-free and crystal-free glasses. The improvements allow synthesis of hydrated glass or partly crystallized samples with a large volume (for further studies) and to perform routine phase-equilibrium studies in basaltic systems at geologically relevant conditions. We used the new technique to determine the effect of f O₂ on water solubility in a melt with MORB composition. The results show that there is a small but significant decrease of water solubility with decreasing f O₂ from MnO-Mn 3 O 4 to QFM buffer conditions in the pressure range 50-200 MPa. Kinetic problems in crystallization experiments in basaltic systems and the duration necessary to attain equilibrium Fe 2+ /Fe 3+ ratio in the charge are discussed.