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

研制了一种内径为34 mm的活塞-圆柱体装置，用于高压测量中、下地壳岩石的P波和S波速度。这种新研制的仪器可以在25-400℃的温度范围内测量较大尺寸的岩心样品，长12 mm，直径14 mm，最高可达1 Gpa。对0.4 Gpa以上的英云闪长岩，测得的P波速度几乎是恒定的。SiO_2含量为53.8-71.1%的英云闪长岩和43.2-47.7%SiO_2的角闪辉长岩在1.0 Gpa和室温下测得的速度分别为6.6-5.9公里/秒和7.1-6.9公里/秒。与IBM弧北部地震剖面(Suyehiro等人，1996)的比较表明，在镁铁质下地壳(7.1-7.3公里/秒)之上存在7-12公里(约占弧壳的30%)的英云闪长岩中地壳(6.1-6.8公里/秒)。

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).