大陆下地壳高电导率的起源:矿物中的结构水

The Possible Effect of Hydrogen on the High Electrical Conductivity in the Lower Continental Crust

大地电磁学的测定结果显示，大陆下地壳可能具有异常高的电导率（10^-4～10^-2S／m）。认识这种异常现象的起源，对于更好地理解地球内部的结构和一些典型的地质学过程具有重要的意义。虽然目前有多种机制试图对大陆下地壳高电导率现象进行解释，但是争论依然激烈，已有的模型（含水矿物模型、孔隙流体模型、颗粒边界石墨膜模型和正空穴电子对模型等）都不能提供令人信服的答案。对安徽女山下地壳麻粒岩包体中的主要组成矿物（斜长石、斜方辉石、单斜辉石）的Micro-FTIR分析表明：这三种矿物普遍含有结构水，含量分别可以高至～1700×10^-6、-1600×10^-6和～2400×10^-6。麻粒岩中结构水的存在可能会对大陆下地壳的电导率分布产生重要的影响，从而可能为认识其起源提供一个新的解释方法。

Magnetolluric measurements show that the lower continental crust has remarkably high electrical conductivity which is about 10^-4- 10^-2 S/re. Tracing the origin of this phenomenon will have important implications to understand the structure and some typical geological processes in the interior of the Earth. Many mechanisms, among which the most probable candidates are models of hydrous minerals, interconnected saline pore fluids, interconnected grain boundary films of graphite and positive hole pairs, were presented for the explaination. However, none of them is totally reasonable and controversy still exists. Micro-FTIR analysis performed on minerals （plagioclase, clinopyroxene and orthopyroxene） in granulite xenoliths from Nushan demonstrated that all these minerals contained water incorporated in the structure as OH with the content （H20 wt. ） up to - 1700 × 10^-6 for plagioclase, -1600 × 10^-6 for orthopyroxene and -2400 ×10^-6 for clinopyroxene, respectively. The water （hydrogen） may have dramatic effect on the electrical conductivity of the lower continental crust and thus provides a more possible explanation.