Melting of Alkali Aluminosilicate Systemsunder Hydrogen-Water Fluid Pressure, P = 2 kbarстатья
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Дата последнего поиска статьи во внешних источниках: 10 августа 2018 г.
Аннотация:The melting curves of albite and albite-quartz and albite-orthoclasequartz eutectics were studied
at a water-hydrogen fluid pressure of 2 kbar using high-pressure gas apparatuses. Instead of buffer reactions,
. hydrogen fugacity was directly controlled in the experiments using a specially designed cell with Ar-H2 mixtures,
in which hydrogen mole fraction, X(H2), ranged from 0 to 0.9. The addition of hydrogen to the watersaturated
systems considered resulted in the appearance of a distinct temperature minimum on the solidus
curves within a hydrogen fugacity range of 300-500 bar, when the melting temperature decreased relative to
the water-saturated solidus by 22OC for albite (Ab), 30°C for albite with quartz (Ab-Qtz), and 40°C for the haplogranite
(Ab-Or-Qtz) system. A further increase in hydrogen content in the mixtures raised the melting temperatures,
which attained the maximum values under pure hydrogen pressure. The results of NMR and photoelectron
spectroscopy of aluminosilicate and Na silicate glasses obtained under water and H20-H2 pressure
suggested different mechanisms for the dissolution of water and water-hydrogen fluids in magmatic melts. In
contrast to pure water, hydrogen-water fluid produced distinct depolymerization of aluminosilicate melts,
which caused the decrease of their solidus temperatures. In order to estimate the influence of hydrogen on the
formation of granitic melts, determine the redox conditions of granite magmatism, and compare the results
obtained here with published data obtained using buffer reactions in the Fe-O system, the magnetite-wiistite
and iron-wiistite buffer equilibria were investigated under the same parameters. These equilibria are regarded
as indicators of reducing conditions in natural and experimental processes. The experiments showed that the I hydrogen fugacities attained in the presence of water at the oxygen fugacities imposed by the buffer reactions
MW and W I are sufficiently high for the occurrence of hydrogen-oxide reactions and formation of mixed compounds.
As a result, the univariant buffer equilibria were transformed into divariant fields, and the stability of
magnetite, which is widespread in granites, expanded considerably to reducing conditions, up to AH2) =
1 I00 bar at 700OC and 2 kbar total pressure