0.6～2.0 GPa压力下部分熔融角闪辉长岩的纵波波速

摘要

With ultrasonic wave transmission-reflection combined method,measurement of compressional wave velocities (vp) of bojite was carried out up to 1 085℃ at the pressure of 0.6 GPa,1.0 GPa and 2.0 GPa respectively.Based on investigating the partially molten products,the authors calculated the vp of bojite at different pressures and temperatures with volume percentages and elastic parameters of minerals and melt.The calculations show the same vp-t correlations with experiment runs,which indicate that at first vp decreases slowly with increasing temperature,and then decreases quickly above about 800℃ to 900℃ at different pressures.The investigations of the products indicate that bojite is dehydrated and partially molten when the temperature is higher than 812℃ at 0.6 GPa,865℃ at 1.0 GPa and 919℃ at 2.0 GPa respectively.It is believed that partial melting is responsible for quick decrease of vp at high temperature.There is more quick decrease of vp of bojite when volume percentages of melt are lower than about 2％.It is thus held that water and melt with low viscosity result in the sharp decrease of vp,because it is easy for them to move into the microfissures in nature rock at the beginning of dehydration and partial melting.%利用超声波透射-反射法,测量了0.6～2.0 GPa、最高1 085℃条件下角闪辉长岩的纵波波速(vp),详细统计了部分熔融阶段实验产物组分的体积百分含量,利用矿物含量和弹性参数,计算了角闪辉长岩的纵波波速.实验测量和理论计算显示了较一致的vp-t关系,即高压下角闪辉长岩的vp随温度升高先缓慢降低,在温度约800～900℃后转而大幅下降.实验产物显示,样品在温度达812℃(0.6 GPa)、865℃(1.0 GPa)和919℃(2.0 GPa)后发生矿物脱水和部分熔融,熔体含量随温度升高显著增加.熔体是导致高温阶段岩石vp快速降低的主要原因.在初熔阶段vp随熔体增加而降低尤为显著,可能是初熔时矿物脱水生成的自由水及含水量高的熔体,以微细熔体薄膜浸润矿物边界或裂隙所导致.