Electrical Conductivity of Two‐Pyroxene Granulite Under High Pressure in Northern Margin of North China Craton

Abstract

AbstractElectrical conductivity of two‐pyroxene granulite, collected from the north margin of the North China craton, was measured at 1.0~2.0 GPa and 523~1173 K by using three different methods at the same time. The three methods are an impedance spectroscopy for a broad frequency range of 0.05 to 10−6 Hz, a single lower frequency (0.1 Hz) and the DC‐method. The experiments were carried out with a measurement system of electrical conductivity, which consisted of an YJ‐3000t multi‐anvil apparatus, a Solartron IS‐1260 Impedance/Gain‐Phase analyzer, an Agilent 34401A Multimeter and a computer. The experimental results indicate that within the range of experimental temperature and pressure, the electrical conductivity of two‐pyroxene granulite changes from 2.66×10−5 S·m−1 to 0.056 S·m−1, and hardly has a dependence on the given pressure. With increasing temperature, the electrical conductivity increases. The conductivity‐temperature relation follows an Arrhenius behavior. The pre‐exponential factor and activation energy of the Arrhenius formula are 8.95~17.9 S·m−1 and 0.569~0.605 eV, respectively. The comparison of the results obtained by the three methods indicates that the result measured by the impedance spectroscopy is always higher than that by 0.1 Hz single frequency and the result determined by the DC‐method is always the lowest. Nevertheless, the difference among the data points is less than 0.20 lg(S/m) other than two low‐temperature data points. Based on the experimental results, the regional crust model and the geothermal gradient, we constructed the profiles of conductivity versus depth. The comparison of the calculated results with the electrical structure of this area reveals that the electrical conductivity of twopyroxene granulite intersects the range of the electrical conductivity of the lower middle crust and the lowermost crust beneath this area. Combining with the conclusion of the in situ seismic velocity measurement and the seismic refraction profile, we can conclude that two‐pyroxene granulite could be a constituent of the lower crust in the northern margin of the North China craton.