Melting of β-quartz up to 2.0 GPa and thermodynamic optimization of the silica liquidus up to 6.0 GPa

Melting relations of p-quartz were experimentally determined at 1.0GPa(1900+/-20 degreesC), 1.5 GPa(2033+/-20 degreesC), and 2.OGPa (similar to2145+/-20degreesC) using anew high-pressure assembly in a piston-cylinder apparatus and substantial differences were found with data previously reported. The new melting data of p-quartz were combined and optimized with all available thermodynamic, volumetric, and phase equilibria data for beta-cristobalite, beta-quartz and coesite to produce a P-T liquidus diagram for silica valid up to 6.0 GPa. Using the now optimized thermodynamic parameters, the invariant point beta-cristobalite + beta-quartz + liquid and beta-quartz + coesite + liquid were determined to lie at 1687+/-17 degreesC and 0.457 GPa, and 2425 +/- 25 degreesC and 5.00 GPa, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.