Elastic velocity measurement of lower crustal rocks at high P-T conditions

本文介绍了一种内径为34 mm的活塞-圆筒装置，用于中低地壳岩石P波和S波速度的高压测量。该装置能在25-400℃温度范围内测量1.0GPa的长12 mm、直径14 mm的较大岩心样品，在0.4GPa以上测得的英云闪长岩-辉长岩的纵波速度几乎为常数。在1.0 GPa和室温下，对质量分数为53.8-71.1 wt. %的SiO2和角闪石辉长岩的43.2-47.7 wt. % SiO2的速度为7.1- 6.9km/sec。本结果与IBM弧北方地震剖面的比较（Suyehiro等人，1996年）表明存在英云闪长质中地壳（6.1-6.8 km/sec），范围为7 km至12 km（约占弧壳的30%），覆盖在镁铁质下地壳（7.1 - 7.3 km/sec P波速度）上。

A piston-cylinder apparatus with 34 mm internal diameter was developed for high pressure measurement of P- and S wave velocities of lower to middle crustal rocks. This newly developed apparatus makes possible to measure relatively large size core sample, 12 mm in length and14 mm in diameter up to 1.0 Gpa in a temperature range of 25-400℃.Measured P-wave velocities for tonalitic-gabbroic rocks above 0.4 GPa are nearly constant. Measured velocities are 6.6-5.9 km/sec at 1.0 GPa and room temperature for tonalite-quartz gabbros with 53.8-71.1 wt. % SiO2 and those measured for hornblende gabbros with 43.2-47.7 wt. % Si02 are 7.1-6.9 km/sec. Comparison of the present results with the seismic profile of the northern IBM arc (Suyehiro et al., 1996) suggests a presence of tonalitic mid-crust (6.1-6.8 km/sec) ranging from 7 km to 12 km (about 30 % of the arc crust) overlying a mafic lower crust ( 7.1 - 7.3 km/sec P-wave velocities).