The influence of water on the temperature of amphibole stability in melts

Abstract

-The influence of water concentration on the crystallization temperature of amphibole in a melt was analyzed theoretically using the model of an ideal melt. A general-type equation has been derived that can explain the presence of the isobaric temperature maximum at the amphibole stability curve by invoking the twofold influence of water on the equilibrium between amphibole and the melt: in accordance with the crystallization reaction, water increases the stability of amphibole, but at the same time it decreases the mole fractions of the other melt components that are taking part in the amphibole crystallization reaction, thereby decreasing the stability of amphibole. The pargasite-water-carbon dioxide system was used as an example to show that the model is a good fit to the experimental data. The data were used to obtain the coefficients in the equations that relate the constants of pargasite-melt and tremolite-melt equilibria to temperature and pressure.

Formation and Evolution of the Continental Crust

“…To stabilise hornblende in intermediate to felsic liquids requires the presence of at least 5% water (Allen and Boettcher, 1983;Maksimov, 2009). If we assume that 20% partial melting produced the parental magma of the granitic suite and that the melt was water-saturated, from mass balance we can calculate that the source would have contained at least 0.5% water.…”

New Constraints on the Main Mineralization Event Inferred from the Latest Discoveries in the Bor Metallogenetic Zone (BMZ, East Serbia)

“…The critical point of our interpretation is the fractionation of primary/parental basic to intermediate magmas, during which hornblende appears early in the crystallization sequence, likely in deep crustal levels (e.g., [65][66][67][68]). The stabilization field of hornblende in water-rich melts is enlarged at the expense of the stability of plagioclase [69][70][71]. As already mentioned above, this is an explanation of how evolved magmas acquire adakitic geochemical characteristics [57].…”

Petrogénesis y condiciones de cristalización del domo intracratérico del volcán Cerro Bravo, Colombia

“…Si se asume un peso específico de la corteza de 2,70 g/cm 3 (Ridolfi et al, 2010), es posible inferir con los resultados obtenidos para cada población de anfíbol, que estas dos poblaciones cristalizaron desde 13,2 hasta 4,6 km de profundidad (Ridolfi et al, 2010). Esto concuerda con los valores máximos esperados para magmas andesíticos, donde el anfíbol es inestable a temperaturas superiores a ~950°C y presiones inferiores a los 0,5 kba (~2 km de profundidad) (Maksimov, 2009).…”