Densified glasses as structural proxies for high-pressure melts: Configurational compressibility of silicate melts retained in quenched and decompressed glasses

Abstract

The structures of high-pressure magmatic liquids have often been inferred from spectroscopic studies on quenched and decompressed glasses. However, it has not been completely veriied whether the structures of quenched and decompressed glasses are representative of the structure of their corresponding liquids at the glass transition temperature and synthesis pressure. Here, we provide quantitative evidence for the retention of pressure-induced conigurational changes upon isobaric quench and isothermal decompression for synthesis pressures up to 3.5 GPa. We use the degree of densiication and elastic compressibility of permanently densiied glasses, together with thermo-elastic data from the literature, to calculate the density of the melt at the glass transition temperature and synthesis pressure. The derived densities agree with those derived directly from the thermal equations of state of the melts. This observation indicates that, at least up to 3.5 GPa, the densiied structure of the melt is preserved in the glass upon quenching and decompression; this validates past and future structural studies of high-pressure melts based on studies of quenched and decompressed glasses.

A NMR and molecular dynamics study of CO2-bearing basaltic melts and glasses

“…In other words, the aluminosilicate network molecular structure in the high temperature melt can be straightforwardly approximated through the determination of the aluminosilicate network molecular structure in the glass which recorded the aluminosilicate network molecular structure of the melt at the glass transition temperature. This result is consistent with the recent work by Malfait et al (2014) who demonstrated that the structure densification of the melt is preserved in the glass upon quenching. Malfait et al (2014) showed that this observation holds true for pressure up to 3.5 GPa.…”

“…This result is consistent with the recent work by Malfait et al (2014) who demonstrated that the structure densification of the melt is preserved in the glass upon quenching. Malfait et al (2014) showed that this observation holds true for pressure up to 3.5 GPa. In the present work, we might extend this observation to higher pressure and to CO 2 -bearing aluminosilicate glasses and melts.…”

“…Although those recent studies (Sanloup et al, 2013;Malfait et al, 2014) comfort our conclusions suggesting that the aluminosilicate network structure recorded in the glass is close to the aluminosilicate network structure recorded in the melt, it is commonly assumed that the molecular structure in the high temperature melt is different from the molecular structure of the equivalent glass owing to the increase in structural disorder with increasing temperature (Dubinsky and Stebbins, 2006). Several hypotheses can be formulated to explain the aluminosilicate network of the glass being very close to its high temperature counterpart.…”

Density of magmas at depth

“…However, if the glass is heated up to the glass transition temperature, then the pressure behavior is similar. Having a similar structure to that of melts, relaxed glasses are thus good analogues for their bulk properties, and quenched glasses from high P -T melts may preserve the densification as suggested by Malfait et al (2014c). : Tracking densification of melts structure through the evolution of the first sharp diffraction peak (FSDP).…”

Nonlinear effects of hydration on high-pressure sound velocities of rhyolitic glasses

“…shown that quenched glasses retain the local structure of their corresponding liquids (Seifert et al 1981;Malfait et al 2014), which has been commonly used as justification for the analogue approach.…”