高温高压下岩石电导率不同测量方法的实验对比——以二辉橄榄岩为例

摘要

In order to compare different methods (impedance spectroscopy, single-frequency method and DCmethod), the lherzolite collected from Damaping was used for electrical conductivity measurement under high pressures and high temperatures (1.0GPa and 500～900℃, 2. 0GPa and 500～950℃) using a YJ3000t cubic-anvil apparatus. The experimental results indicate that within the range of experimental temperatures and pressures, the electrical conductivity of lherzolite changes between 8.65 × 10-7 s/m and 2.09 × 10-3 s/m; lnσ and 1/T well match to the Arrhenius relationship. The values of pre-exponential factor change between 1.36 s/m and 37.89 s/m and the activation energy values between 0. 74～1.0leV.The electrical conductivity of lherzolite shows strong positive dependence of temperature, but little dependence of pressure. Comparison of the results from three methods shows that impedance spectroscopy is the highest one and the DC-method＇s is lowest one, but the discrepancy of lna among them is negligible (＜3％). In the end, we compared our experimental results with the data derived from magnetotelluric measurements. Coupled our results with electromagnetic data from the sampling area, the electrical conductivities vs depth diagram based on our experiment data shows that the electrical conductivities of lherzolite at the corresponding depth intersects with that of the upper mantle in the lithosphere of the northern margin of the North China Craton. Therefore, it can be concluded that lherzolite is likely the predominant constituent of the upper mantle rocks in the North China Craton.%利用YJ-3000t紧装式六面顶压机,在1.0GPa、500～900℃和2.0GPa、500～950℃的实验条件下,同时采用交流阻抗谱法(AC0.05～10-6Hz)、直流法(DC)和单频交流法(0.1Hz)三种方法对采自河北大麻坪玄武岩中的尖晶石二辉橄榄岩进行了电导率的实验测量.实验结果表明:在实验的温度和压力范围内,二辉橄榄岩的电导率在8.65×10-7～2.09×10-3s/m之间变化,lnσ与1/T之间符合Arrenhius关系,指前因子在1.36～37.89 s/m之间变化,活化能在0.74～1.01eV之间变化;二辉橄榄岩的电导率随着温度的升高而增大,但压力对电导率无明显影响;三种方法所得的lnσ差别很小(＜3%),其中阻抗谱法所得结果最大,直流法所得结果最小.最后依据实验所得的二辉橄榄岩电导率与温度的关系建立电导率-深度曲线图,将所得结果与样品采集区的大地电磁测量结果进行了比较,发现在相应深度下的二辉橄榄岩电导率与华北北缘岩石圈地幔电导率值的范围相交,由此我们推断二辉橄榄岩可能是华北克拉通岩石圈上地幔的主要组成岩石.