Melting of albite and dehydration of brucite in H2O-NaCl fluids to 9 kbars and 700-900 degrees C: implications for partial melting and water activities during high pressure metamorphism

Article Abstract:

Congruent melting of albite occurs at 9 kbar in the presence of either H2O-NaCl fluids or H2O-CO2 fluids. The melting temperature of albite is higher in H2O-NaCl brines than in H2O-CO2 fluids. The results indicate that water activity controls the melting temperature at constant pressure. Water activity, in turn, decreases with rising fluid pressure up to 10 kbar. These observations suggest that saline aqueous brines play a major role in controlling the mineralogy, dehydration temperature and melting behavior of subduction zones.

Research, Observations, Phase transformations (Statistical physics), Phase transitions (Physics), Subduction zones (Geology), Subduction zones, Metamorphism (Geology)

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The breakdown of potassium feldspar at high water pressures

Article Abstract:

The breakdown of potassium feldspar at high-water pressures is studied by analyzing the reaction between sanidine and water to form sanidine hydrate. Potassium feldspar is a mineral found in the earth's crust and forms a wadeite type phase between 3 GPa at 700 degrees C and at 6 GPa at 1400 degrees C in the absence of water when it disintegrates. The study seeks to find out if sanidine hydrate helps in storing fluids in the lower crust or upper mantle if it has a large amount of water.

Analysis, Minerals (Geology), Feldspar, Rocks, Rock-forming minerals

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