【摘要】 利用超声波脉冲反射法和透射-反射联合法,测量了压力在0.4~2.0GPa条件下7种岩石熔融玻璃的纵波波速(vp)和横波波速(vs),并在恒压2.0GPa下,在0~1 000℃和0~730℃温度范围内,分别测量了纵波波速和横波波速随温度的变化。结果显示,室温下随着压力的升高,大多数玻璃的vp和全部玻璃的vs异常地降低。异常的波速-压力关系与玻璃中SiO2的含量密切相关,随着SiO2的质量分数从87%降低到52%,玻璃的纵波波速和横波波速对于压力的导数(vp/p和vs/p)分别从-0.159和-0.114μm/(s·Pa)升高到0.050和-0.001μm/(s·Pa)。分析认为,玻璃的波速随压力升高而降低的原因主要与玻璃中SiO2所具有的敞型结构有关。在2.0GPa压力下,玻璃的波速首先随温度升高而缓慢降低,当达到600~700℃后,开始快速下降,设此温度为玻璃的转变温度Tg。根据实验测得的玄武岩玻璃波速,结合上地幔二辉橄榄岩的弹性性质,推测若在上地幔岩石中存在体积分数大于20%的玄武岩质非晶质体,上地幔便可能形成地震波低速层。更多还原

【Abstract】 Measurements of compressional and shear wave velocities(vp and vs)under pressure from 0.4to 2.0GPa were performed on seven types of synthetic glasses,including basalt,andesite,dacite,amphibolite,pyroxenite,rhyolite and gneiss.At confining pressure of 2.0GPa,the wave velocities were also measured as functions of temperature up to 1000℃for compressional wave velocity(vp)and up to 730℃for shear wave velocity(vs).At room temperature,the wave velocities of the glasses decrease anomalously with pressure,as a result of the open structure of SiO2 in silica-rich glasses.With varying SiO2 mass fraction in the glasses from 87%to 52%,vp /pincreases from-0.159to 0.050μm/(s·Pa),andvs /pincreases from-0.114to-0.001μm/(s·Pa).At 2.0GPa,vp and vs of the glasses decrease slowly first up to 600-700℃,indicating the glass transition temperatures(Tg),and then decrease rapidly.Based on the elastic properties of basalt glass and mantle rocks,it is concluded that the basalt glass with volume fraction of about 20%in matrix can cause the low velocity zone in upper mantle.更多还原