1GPaにおけるマントル岩石中のH2O流体分布:Vs-Vp/Vsダイヤグラムによる検討

概要

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We investigate the distribution of H2O fluid in the olivine-pyroxene-H2O system produced by the dehydration of serpentinite, using P- and S-wave velocities measured simultaneously as a function of temperature at 1 GPa. Serpentine and brucite in serpentinite break down at high temperatures, and the rock sample consists of olivine, pyroxene, and H2O at～900℃ and 1 GPa. A Vs-Vp/Vs diagram is adapted to analyze the dehydration process from seismic velocity data. Employing Griineisen theory and third-order finite strain theory, we calculate elastic-wave velocities in a dry olivine-pyroxene solid. Then P- and S-velocities are estimated for various H2O fluid distributions (tubes, disks, and films) in the olivine-pyroxene-H2O system. At temperatures above complete dehydration of serpentinite, laboratory velocity data are reproduced using numerical calculations for triangular tubes of H2O fluid distribution. The results indicate that after dehydration is completed, elastic properties of serpentinite are estimated from those calculated for the olivine-pyroxene-H2O system.