Melting relations of NaAlSi_3O_8 to 30 Kb in the presence of H_2O:CO_2 = 50:50 vapor

Abstract

Synthetic albite was reacted with oxalic acid dihydrate under oxidizing conditions in an internally-heated pressure vessel from 1 to 4 kb and in a piston-cylinder apparatus from 10 to 30 kb. Breakdown of the oxalic acid in subsolidus runs produced a vapor with H_2O:CO_2 = 50:50 in moles (X^v_(H_2O) = 0.5, neglecting solubility of solids in the vapor). The curve determined for the beginning of melting under these conditions defines a contour on the divariant solidus surface for the system NaAlSi_3O_8-H_2O-CO_2 for X^v_(H_2O) = 0.5, between the published limits for X^v_(H_2O) = 1.0 and X^v_(H_2O) = O. Addition of 50 mole percent of relatively insoluble CO_2 to NaAlSi_3O_8-H_2O at 15 kb total pressure raises the solidus temperature from 660° to 830°C. The results give no indication of increased solubility of CO_2 in NaAlSi_3O_8 liquids at pressures above 15 kb, in contrast with published results for a basalt liquid.

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