Abstract: The conductivity of serpentine has been experimentally measured at pressure of 200 MPa to 1100 MPa and temperature of 100°C to 1100°C. The results show that within the pressure range of 1 GPa, the dehydration occurs at 650°C to 700°C for serpentine and dehydration causes the increase of conductivity. The mechanism of the conductivity increase is the free water associated with dissolution of surrounding materials. Serpentine is one of the important water-bearing minerals. What depth can it be brought to during subducting of plate? It depends on the P-T conditions of its dehydration and the thermal structure of subduction belt. The emergency of free water can also lead to the occurrence of partial melting or melting at lower temperature. This may explain the genesis of island-arc-magma and the source of volcanic thermotube. The changes of volume and energy during dehydration of serpentine may be one of the important causes for deep seismicity.

Key words: Electric conductivity, High pressure and high temperature test, Serpentine