Laboratory Electrical Conductivity Measurement of Mantle Minerals
Laboratory Electrical Conductivity Measurement of Mantle Minerals
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DOI：
10.1007/s10712-009-9084-0
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发表时间：
2010-03
影响因子：
4.6
通讯作者：
T. Yoshino
中科院分区：
文献类型：
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作者：
T. Yoshino
大地电磁测深和地磁测深估算的地幔电导率结构总体上显示，随着下地幔顶部深度的增加，电导率从10−4 ~ 10−2增加到100S/m。虽然下地幔的电导率变化不大，但从地球物理模拟的结果来看，下地幔底部可能存在一个高导电性层。地幔岩的电性受主要组成矿物的压力、温度和化学性质等热力学参数的控制。利用固体介质高压仪器，在高压和高温条件下进行了地幔矿物电导率的实验室测量。为了区分地幔矿物中的多种电荷输运机制，有必要在更宽的温度范围内测量其电导率。虽然每个实验室之间的数据尚未建立对应关系，但地幔矿物电导率的大致趋势几乎是相同的。大多数形成地幔的矿物相都表现出半导体性质。如果这些矿物含有铁，主要的传导机制是小的极化子传导（亚铁和铁之间的电子空穴跳跃）。橄榄石到高压相的相变由于结构的改变而提高了电导率。结果表明，沿绝热地热，电导率依次为橄榄石、瓦德利石和环伍德石。在660 km不连续处向后尖晶石的相变进一步增强了电导率。在下地幔中，由于铁的自旋转变，电导率在下地幔中部一度下降，然后在D″层条件下突然增加。地幔矿物中的杂质对载流子的形成、数量和迁移具有强烈的控制作用。在橄榄石和高压多晶等名义上无水的矿物中，氢可以通过质子传导来增强导电性。然而，质子传导与极化子小传导相比具有较低的激活焓，在高温下质子传导的贡献变小，与地幔条件相对应。地幔矿物中较高的铁含量极大地增强了地幔的导电性。这篇综述的重点是在实验实验室工作相当新的进展汇编及其解释。
Electrical conductivity structures of the Earth’s mantle estimated from the magnetotelluric and geomagnetic deep sounding methods generally show increase of conductivity from 10−4–10−2to 100S/m with increasing depth to the top of the lower mantle. Although conductivity does not vary significantly in the lower mantle, the possible existence of a highly conductive layer has been proposed at the base of the lower mantle from geophysical modeling. The electrical properties of mantle rocks are controlled by thermodynamic parameters such as pressure, temperature and chemistry of the main constituent minerals. Laboratory electrical conductivity measurements of mantle minerals have been conducted under high pressure and high temperature conditions using solid medium high-pressure apparatus. To distinguish several charge transport mechanisms in mantle minerals, it is necessary to measure the electrical conductivity in a wider temperature range. Although the correspondence of data has not been yet established between each laboratory, an outline tendency of electrical conductivity of the mantle minerals is almost the same. Most of mineral phases forming the Earth’s mantle exhibit semiconductive behavior. Dominant conduction mechanism is small polaron conduction (electron hole hopping between ferrous and ferric iron), if these minerals contain iron. The phase transition olivine to high-pressure phases enhances the conductivity due to structural changes. As a result, electrical conductivity increases in order of olivine, wadsleyite and ringwoodite along the adiabat geotherm. The phase transition to post-spinel at the 660 km discontinuity further can enhance the conductivity. In the lower mantle, the conductivity once might decrease in the middle of the lower mantle due to the iron spin transition and then abruptly increase at the condition of the D″ layer. The impurities in the mantle minerals strongly control the formation, number and mobility of charge carriers. Hydrogen in nominally anhydrous minerals such as olivine and high-pressure polymorphs can enhance the conductivity by the proton conduction. However, proton conduction has lower activation enthalpy compared with small polaron conduction, a contribution of proton conduction becomes smaller at high temperatures, corresponding to the mantle condition. Rather high iron content in mantle minerals largely enhances the conductivity of the mantle. This review focuses on a compilation of fairly new advances in experimental laboratory work together with their explanation.