高温高压下上地幔岩石电导率实验研究

为了建立具有普遍适用性的上地幔电性结构，本文利用Kawai-1000t压机和Solartron IS-1260阻抗/增益-相位分析仪，在4.0~14.0 GPa、873~1673 K的条件下，采用交流阻抗谱法（频率范围10^-1~10⁶Hz）测量了不含水的地幔岩电导率.实验结果显示，岩石的电导率随温度升高而大幅度的增大；在较大的温度范围内岩石的导电机制发生了变化，中低温时为小极化子导电，此时激活焓为0.94 eV（±0.13）eV，激活体积为0.11（±0.92）cm³·mol^-1，高温时为和镁空穴相关的离子导电，此时激活焓为1.6~3.17 eV，激活体积为6.75（±7.43）cm³·mol^-1；本次测量的电导率比低压下岩石的电导率要高，比矿物的电导率也要高.用本次的实验结果回归计算得到Fennoscandian地区的上地幔的一维电导率剖面，发现200 km以上本次实验计算的结果和大地电磁测深的电导率剖面吻合的比较好，在200 km以下本次实验得到的要比野外测量的电导率稍稍高一点，可能是因为实验过程中没有完全避免水的影响.本次的实验结果比用有效均匀介质方法计算得到的pyrolite矿物模型的电导率要高出两个数量级，这样的结果显示只用一种矿物的电导率或是几种矿物理论计算的结果有一定的不合理性.

Experimental study on electrical conductivity of pyrolite at high temperature and high pressure

The purpose of this work was to construct a generally electrical structure of the upper mantle. The electrical conductivity of dry pyrolite was measured on Kawai-1000t multi-anvil apparatus and Solartron-1260 impedance/Gain-Phase analyzer in the conditions of 4.0~14.0 GPa, 873~1673 K and 10-1~106 Hz frequency ranges. The experimental results show that the electrical conductivity significantly increases with temperature. The conductive mechanism of pyrolite changes over a wide temperature range. When temperature is less than 1473 K, the small polaron model is the dominant conduction mechanism, activation energy ΔH and activation volume are 0.94 eV±0.13 eV and 0.11(±0.92) cm3·mol-1, respectively. When temperature is more than 1473 K, the ionic conduction is the dominant conduction mechanism, activation energy ΔH and activation volume are 1.6~3.17 eV and 6.75 (±7.43) cm3·mol-1, respectively. The electrical conductivity of pyrolite is higher than that of mantle minerals and the rock under low pressure. In shallow mantle above 200 km depth, the electrical conductivity profile obtained by the experiments is consistent with the result of magnetotelluric sounding. However, in deep mantle under 200 km depth, the experimental result is a little higher than that of field measurement, perhaps because of the presence of water in the samples. In addition, the results of this experiment are two orders of magnitude higher than the electrical conductivity calculated by the effective uniform medium method according to the pyrolite mineral model, which indicates that the results calculated using the electrical conductivity of only one or several minerals are not reasonable to some extent.