水对Wadsleyite和Ringwoodite电导率的影响及地球动力学意义  

Influence of hydrogen on electrical conductivity of wadsleyite and ringwoodite with its geodynamics implications.

作　　者：黄晓葛[1] 白武明[1] XUYouSheng Shun-ichiroKarato 

机构地区：[1]中国科学院地质与地球物理研究所 [2]耶鲁大学地质与地球物理系

出　　处：《岩石学报》2005年第6期1743-1748,共6页Acta Petrologica Sinica

基　　金：中国国家自然科学基金(40204005;10299040);美国自然科学基金共同资助

摘　　要：在 Kawai-1000型多顶砧压机上,利用橄榄石相变人工合成地幔转换带矿物 wadsleyite 和 ringwoodite,其含水量从0.03wt%到2.0wt%变化不等。在压力14～16GPa,温度873K～1273K,通过 Mo:MoO_2固体反应控制氧逸度的条件下,利用阻抗谱分析方法,测量获得了这些样品的电导率。实验结果显示:wadsleyite 的电导率与 C_H^(0.66)呈正比,ringwoodite 的电导率与C_H^(0.69)呈正比,水极大地增强了样品的电导率;在我们的实验条件下,含水 wadsleyite 和 ringwoodite 样品的主要电荷载体是自由质子。另外,结合大地电磁反演获得的电导率结果和我们的实验数据,我们推断中国东北地区地幔转换带中的水含量约为0.1～0.3wt%,远远高于上地幔中的水含量,这或许表明在410km 处可能发生了部分熔融。The electrical conductivity of synthesized wadsleyite and ringwoodite containing different water contents from 0. 03wt% to 2.0wt% was investigated at a temperature range from 873K to 1273K under a confining pressure of 14 - 16GPa in 1000ton multi-anvil apparatus with the oxygen fugacity buffered by the Mo：MoO2 solid-state reaction. The results showed the electrical conductivity in these minerals depends strongly on water content but only weakly on temperature. The electrical conductivity is in proportion to CH^0.66for wadsleyite and CH^0.69 for ringwoodite. The dominant charge carrier in these minerals under the experimental conditions is free proton. By comparing our results with geophysically inferred conductivity, we infer that the water content in the mantle transition zone varies regionally, but its value in pacific back-arc region beneath northeastern China is estimated to be 0. 1 - 0. 3 wt%. These values significantly exceed estimated water content in the upper mantle, suggesting that partial melting likely occurs at -410km in this region.

关 键 词：水 电导率 地幔转换带 WADSLEYITE RINGWOODITE 

分 类 号：P589.1[天文地球—岩石学]