高温高压下地幔岩和苦橄质榴辉岩的电导率实验  

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

作　　者：王欣欣[1,2] 黄晓葛[1] 白武明[1] 

机构地区：[1]中国科学院地质与地球物理研究所地球与行星物理重点实验室,北京100029 [2]中国科学院大学,北京100049

出　　处：《地球物理学报》2016年第2期624-632,共9页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(41174074)资助

摘　　要：为了探讨地幔岩模型和苦橄质榴辉岩模型在上地幔存在的合理性,建立上地幔的电性结构,本文利用YJ-3000t紧装式六面顶压机和Solartron IS-1260阻抗/增益-相位分析仪,在1.0-4.0GPa、700-1150℃的条件下,采用交流阻抗谱法（频率范围10-1-106 Hz）分别测量了地幔岩和苦橄质榴辉岩的电导率.实验结果表明：随着温度的升高,地幔岩和苦橄质榴辉岩的电导率大幅增加;随着压力的增大,地幔岩的电导率略有增加,活化体积ΔV为-4.73cm3·mol-1,而苦橄质榴辉岩的电导率几乎没有变化,活化体积ΔV为-0.11cm3·mol-1;在电性方面,用苦橄质榴辉岩来表示深部的物质较为合理,地幔岩解释浅部可能更恰当,但浅部物质的分布不均匀,电导率随深度的变化主要受控于温度的影响,其次才是成分.Measurements of electrical conductivity for rocks and minerals at high temperature and high pressure provide a powerful tool to acquire information about chemical and mineralogical composition of the Earth′s interior.Based on physical properties of minerals and rocks such as density,and elastic-wave velocity,Ringwood and Anderson Bass proposed two competing mineralogical models of the mantle：pyrolite model and piclogite model.In order to investigate electrical structure of the upper mantle and the rationality of these two models,the electrical conductivities were measured using YJ-3000tmulti-anvil apparatus and Solartron-1260impedance/GainPhase analyzer under conditions of 1.0-4.0GPa,700-1150℃and 10-1-106 Hz frequency ranges.The experimental results show that the electrical conductivities significantly increase with temperature.The linear relationship between Lgσand 1/Tindicates that they follow an Arrhenius formula and the small polaron model is the dominant conduction mechanism.The pre-exponential factorσ0 and the activation energy ΔU have been obtained in the setting range.They are respectively 68.08-248.09S·m-1 and 1.14 eV for pyrolite;17.99-77.46S·m-1 and 1.01 eV for piclogite.With increasing pressure,the electrical conductivities of pyrolite slightly increase,while those of piclogite almost do not change.If pressure effects on conductivity of pyrolite and piclogite are expressed as the activation volumeΔVin the Arrhenius equation,they yield values of order of magnitude-4.73cm3·mol-1 and-0.11cm3·mol-1,respectively.So far,researchers have not yet formed a unified understanding about the reason of positive and negativeΔV.The conductivity-depth profiles have been established by using our experimental results and geothermal gradients.Comparing our results with the previous electromagnetic data beneath the different regions in the mantle,the reasonability of the pyrolite model and the piclogite model are discussed.In the aspect of conductivity,the piclogite model is more reasonable for explaining

关 键 词：电导率 地幔岩 苦橄质榴辉岩 高温高压 

分 类 号：P312[天文地球—固体地球物理学]