Determination of the second critical end point in silicate-H2O systems using high-pressure and high-temperature X-ray radiography

Slab melting versus slab dehydration in subduction-zone magmatism

“…Table 1. The stability fields of observed minerals (especially amphibole in the run S1176) in the recovered samples are consistent with previous studies (38,39) within the experimental uncertainties, indicating that our P-T calibrations (30) are reliable. When experimental P is below the second critical endpoint, and both aqueous fluid and hydrous silicate melt are present, round shapes can be observed in the radiographic images because of the differences in their interfacial tension.…”

“…No correction for the effect of P on the thermocouple electromotive force was applied. Detailed experimental methods and P-T calibrations have been reported elsewhere (30,35).…”

“…Because radiographic studies were done within a relatively short experimental duration, such as tens of minutes (30,35), the equilibrium was checked by conducting a series of long-duration constant-T quench experiments to see if we could reproduce quench textures of the aqueous fluids, hydrous melts, and SCFs, which were observed in the experimental products quenched after the radiography observations. Experiments were carried out using a Kawai-type multianvil high-P apparatus installed at the Earthquake Research Institute, University of Tokyo (58).…”

“…Under high-pressure (P) and high-temperature (T) conditions, it has been shown that the solubility of both water in silicate melt (13)(14)(15)(16) and silicate in aqueous fluid (13,(17)(18)(19)(20)(21)(22)(23)(24)(25) increases with increasing P. As a result, silicate melt and aqueous fluid in the interior of the Earth are expected to become SCF, and the hydrous solidus of the system can no longer be defined beyond a certain critical condition (26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36). This condition is called the second (or upper) critical endpoint (26) and is the point of intersection between the critical curve and hydrous solidus.…”

High-pressure experimental geosciences: state of the art and prospects

“…and by X-ray radiographic observations through multi-anvilp r e s sa s s e m b l i e sf o rfl u i d s / m a g m a s (Mibe et al, 2004) and for Fe-S/Fe-Si liquid alloys (Morard et al, 2008b). To get further insights into how P induces gap closure, structural information is required.…”