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

研制了一种内径34 mm的活塞缸高压测速仪，用于测量中、下地壳岩石的纵、横波速度。该仪器可以在25-400℃的温度范围内测量较大尺寸的岩心样品，长度为12mm，直径为14mm，最高可达1.0 Gpa。0.4 GPa以上的调性辉长岩测得的纵波速度几乎是恒定的。在1.0 GPa和室温条件下，SiO2含量为53.8 ~ 71.1 wt. %的辉长岩测得速度为6.6 ~ 5.9 km/sec， SiO2含量为43.2 ~ 47.7 wt. %的角闪岩测得速度为7.1 ~ 6.9 km/sec。将目前的结果与IBM弧北部的地震剖面进行比较（Suyehiro et al., 1996）表明，在7 - 12公里（约占弧地壳的30%）的范围内存在着调性中地壳（6.1-6.8公里/秒），覆盖在基性下地壳（7.1 - 7.3公里/秒的纵波速度）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).