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Highly conductivity anomalies have been extensively observed in the mid‒lower crust by geophysical surveys and are closely associated with major constituent minerals. We conducted a systematic conductivity study on dry and hydrous plagioclase solid solutions with different compositions to investigate the influence of hydrogen and sodium on the electrical conductivity at high temperature and high pressure. For dry samples, the discontinuous non‒linear variations of conductivity with temperature occurs at respective 673 K and ~873 K that is ascribed to the change of degree of Al/Si disorder. The distinct dependence of electrical conductivity and activation enthalpies on Na content was observed at moderate and high temperatures. For hydrous samples, the incorporation of water into plagioclase solid solutions pronouncedly enhanced the electrical conductivity, and the activation enthalpies are basically independent of water content and Na concentration. Therefore, we proposed that the dominant charge carriers in dry and hydrous plagioclase samples are Na ions and hydrogen, respectively. Both of them transport by a similar migration mechanism, i.e., via Frenkel defects, owing to the comparable activation enthalpies in hydrous and dry samples. The globally dry and hydrous conductivity−depth profiles for the continental crust were established based on the conductivity data of major constituent minerals in crust including plagioclase. The results show that crustal rocks themselves, even containing a substantial amount of water, unlikely account for the high conductivity layers in the mid‒lower crust observed by magnetotelluric surveys. The bulk conductivities of fluid−rock systems were further calculated, and indicates at least 1 vol.% of fluid with seawater salinity (3.5 wt%) is required to interpret the high conductivity anomalies in the mid‒lower crust.