Beginning of melting

Article Abstract:

The dehydration melting of tonalites, an assemblage of phlogopite, plagioclase and quartz, begins at 760 degree centigrade and 2 to 5 kbar. This temperature is lower than previously established temperature. As the pressure increases from 5 to 12 kbar, the melting point drops from 760 to 700 degree centigrade. At low temperatures, there is a vertical dehydration melting solidus curve which bends backward to lower temperature at high pressure. At 10 kbar or higher pressure, the phase contains melt, enstatite, clinopyroxene and potassium feldspar with or without amphibole.

Plagioclase, Quartz

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Composition of melts and solids

Article Abstract:

Melts of different compositions are formed by the dehydration melting of tonalites which ranges from granodiorite to granite. The composition of the melts depends on the composition of the starting material and the conditions of pressure and temperature used. At higher temperatures the melt is enriched in Al2O3, FeO and MgO. This data indicates that in the continental crusts, where the pressure and temperature conditions are similar to that used in the study, granitic melts and granulitic restites are formed by dehydration melting of tonalites.

Observations

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Liquidus temperatures and phase compositions in the system Qz-Ab-Or at 5 kbar and very low water activities

Article Abstract:

Research was conducted to determine the liquidus temperatures and phase relations in the system Qz-Ab-Or at 5 kbar and very low water activities. Crystallization and dissolution experiments were performed to derive the liquidus temperatures. Results showed that the Qz content of the eutectic composition in the system Qz-Or decreases as the water activity decreases, while no change occurred in the system Qz-Ab. The water activity has a greater effect on the eutectic temperatures in the system Qz-Ab than in the system Qz-Or.

Crystals

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