Determine the binodal curve shape for the phonolite–water system

Determine the precise shape of the binodal (liquid–vapor miscibility) curve of the phonolite–water system across relevant temperature and pressure conditions using high-temperature and high-pressure experiments, in order to assess the applicability of symmetric regular-solution approximations and evaluate conditions under which spinodal decomposition may occur in phonolitic melts.

Background

To assess whether spinodal decomposition can occur during decompression-induced vesiculation, the paper approximates hydrous magmas as symmetric regular solutions and computes binodal and spinodal curves from water solubility data. The analysis suggests spinodal decomposition is unlikely at pressures typical of continental crustal magmatic processes.

However, for alkali-rich phonolitic compositions, the second critical endpoint reportedly shifts to lower pressures and the symmetric approximation may fail, implying the binodal curve could be highly asymmetric. The authors note that the specific binodal curve for the phonolite–water system has not yet been empirically established, and its determination is necessary to understand phase separation mechanisms in such melts.