摘要
辉石岩往往具有较高的水含量和铁含量,对其高温高压条件下电导率的测定为探究岩石圈内部一些高电导率异常的贡献有重要意义.本文利用活塞圆筒压机在1~3 GPa和200~800℃条件下,采用交流阻抗谱法原位测量了2个天然辉石岩样品的电导率.测定结果表明:辉石岩电导率随温度升高而升高,激活焓ΔH范围在71~74 kJ·mol^(-1),其导电机制以质子传导为主;辉石岩电导率随压强的增大而轻微降低(实验误差范围内压强效应几乎可被忽略),相应的激活体积ΔV为约(0.63±0.10)cm^(3)·mol^(-1)到(2.25±0.22)cm^(3)·mol^(-1),ΔV与温度无明显的一致性关系,负压强效应可能与晶格畸变阻碍载流子迁移有关.辉石岩电导率随水含量、总铁含量和Fe^(3+)/ΣFe的增大而增大,根据实验数据推测富水富铁辉石岩在温度超过~900℃时电导率可超过0.01 S·m^(-1).辉石岩在大陆岩石圈地幔常以岩脉形式存在,一般与流体/熔体交代作用有关.考虑到交代作用可使古老大陆岩石圈地幔再次饱满化,富水富铁的辉石岩可用于解释大地电磁探测到的克拉通岩石圈内部0.01~0.1 S·m^(-1)的电导率异常.
Pyroxenite often has high water content and iron content.The measurement of its electrical conductivity under high-temperature and high-pressure conditions is of great significance for exploring the contribution of some high electrical conductivity anomalies in the lithosphere.This paper used a piston cylinder press to measure the electrical conductivity of two natural pyroxenite samples in situ by AC impedance spectroscopy under conditions of 1~3 GPa and 200~800℃.The results show that the electrical conductivity of pyroxenite increases with increasing temperature,with an activation enthalpy(ΔH)ranging from 71 to 74 kJ·mol^(-1),and the conduction mechanism is mainly proton conduction.The electrical conductivity of pyroxenite decreases slightly with increasing pressure(the effect of pressure is almost negligible within the experimental error range),with the corresponding activation volume(ΔV)ranging from approximately(0.63±0.10)cm^(3)·mol^(-1) to(2.25±0.22)cm^(3)·mol^(-1).There is no obvious correlation betweenΔV and temperature.The negative pressure effect may be related to lattice distortion hindering the migration of charge carriers.The electrical conductivity of pyroxenite increases with increasing water content,total iron content,and Fe^(3+)/ΣFe.Based on the experimental data,it is inferred that the electrical conductivity of water-rich and iron-rich pyroxenite can exceed 0.01 S·m^(-1) when the temperature exceeds approximately 900℃.Pyroxenite commonly occurs in the form of dikes in the continental lithospheric mantle and is generally associated with fluid/melt metasomatism.Considering that metasomatism can re-fertilize the ancient continental lithospheric mantle,water-rich and iron-rich pyroxenite can be used to explain the 0.01~0.1 S·m^(-1) electrical conductivity anomalies in the cratonic lithosphere imaged by magnetotelluric data.
作者
朱屹欣
徐义贤
杨晓志
费宏展
刘汉永
李满
ZHU YiXin;XU YiXian;YANG XiaoZhi;FEI HongZhan;LIU HanYong;LI Man(School of Earth Sciences,Zhejiang University,Hangzhou 310058,China;School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China)
出处
《地球物理学报》
北大核心
2025年第6期2112-2128,共17页
Chinese Journal of Geophysics
基金
国家自然科学基金项目(41830212,41974082)资助.
关键词
电导率
辉石岩
高温高压
压强效应
克拉通岩石圈
Electrical conductivity
Pyroxenite
High pressure and high temperature
Pressure effect
Cratonic lithosphere
