摘要
大地电磁方法是地球物理电法的一个主要分支,目前已被广泛地用于深部地质构造的研究中.通过大地电磁方法获得地下介质电阻率(或电导率)参数的空间分布可为我们推断深部地质构造从电性的角度提供依据.而这种推断成立的基础主要建立在电性参数与其他物理参数之间广泛而深刻的内在联系上.其中,电性与温度之间的依赖关系因其在深部作用过程中所发挥的重要作用而被重视.本文从壳幔岩石的导电机制出发,指出在电解导电、电子导电、半导体导电以及熔融体导电四种导电机制中,上地幔附近的岩石以半导体导电为主,并给出了单一矿物在半导体导电条件下电导率与温度的依赖关系.进一步,利用Hashin Shtrikman(HS)边界条件得出了多相矿物体系构成的上地幔岩石的电导率上、下限值通用公式.在此基础上,结合通用的上地慢矿物组成模型以及岩石电性实验的结果,给出了通用的上地慢四相矿物体系组成岩石的电导率与温度的依赖关系.在本文最后,我们还对这一关系的应用范围及需要进一步研究的问题进行了讨论.
As a main branch of electromagnetic geophysical methods,Magnetotellurics (MT)has been broadly adopted for the study of tectonics in deep Earth.Various information about deep tectonic features can be inferred from the resistivity (or conductivity)values of underneath rocks obtained by MT method,giving the extensive and inherent relationships between electrical property and other physical properties of deep rocks.The temperature dependence of electrical conductivity plays an important role in the deep tectonic processes,and thus is broadly studied by various groups around the world.In this paper,by clarifying four different conduction mechanisms in the rocks of crust and upper mantle (electrolytic conduction,electronic conduction,semiconduction,and partial melts),we demonstrate that the semiconduction mechanism dominates in the upper mantle.The temperature dependence of electrical conductivity of single mantle mineral follows the Arrhenius behavior under this mechanism.Substituting the Arrhenius Equations for different upper mantle minerals into the Hashin-Shtrikman bounds,the temperature dependence of electrical conductivity of upper mantle mineral assemblage can be derived out.Combining with the results from electrical conductivity laboratory studies and the global upper mantle mineral composition model,a general model describing the temperature dependence of electrical conductivity of upper mantle rocks is obtained.A short discussion is made at the end of this paper to explain the applicability of this general model and point out the problems attention should be paid to when using this model.