Electrical conductivity of albite-(quartz)-water and albite-water-NaCl systems and its implication to the high conductivity anomalies in the continental crust

- EC of Ab-(Qtz)-H2O system shows a strong T and a weak fluid fraction dependence.
- EC of Ab-H2O-NaCl system increases with salinity and water volume fraction.
- Major mineral composition largely affects EC of the water- and brine-bearing systems.
- Ab-(Qtz)-H2O is applicable to explain the high EC anomalies in the crust at T<650 K.
- Low fluid fraction and salinity in Ab-H2O-NaCl can explain the EC anomaly of 0.1 S/m.

The electrical conductivities of albite-water, albite-quartz-water and albite-water-NaCl systems have been measured in terms of impedance spectroscopy at 1 GPa and 400-1000 K. The relationship between electrical conductivity and temperature in the albite-(quartz)-water system cannot be expressed by the Arrhenian formula, whereas that in the brine-bearing system follow the Arrhenian law showing small temperature dependence. The electrical conductivity of the albite-(quartz)-water samples decreased with decreasing temperature from 1000 to 800 K, then increased rapidly upon further cooling from 800 to around 550 K. The bulk conductivities of the albite-(quartz)-water system are consistent with variation of the total concentration of the dissolved electric charge carriers of H+, OH−, Na+, AlO2− and HSiO3− in aqueous fluid with temperature based on the thermal dynamic calibration. There is a small negative dependence of bulk conductivity on aqueous fluid fraction. Electrical conductivity of the albite-water-NaCl samples is higher than that of the albite-(quartz)-water samples, which shows the following features: (1) small dependence of conductivity on the temperature; (2) increase of electrical conductivity with the fluid fraction and the salinity. Our results suggest that the high conductivity anomalies of 10−1 S/m typically observed in the continental crust can be explained by the presence of albite and quartz with fluid fraction as low as 0.014 at temperatures lower than 650 K. In the case that the geotherm is higher than 650 K, the observed value of 10−1 S/m can be explained by the brine-bearing albite with a fluid fraction of 1 vol% if the salinity is similar to the seawater.