Thermal diffusivity, thermal conductivity and heat capacity of serpentine (antigorite) under high pressure

Thermal diffusivity and thermal conductivity of serpentine (antigorite) were measured up to 8.5 GPa and 800 K in the Kawai-type high-pressure apparatus. Antigorite has thermal diffusivity of 0.90 × 10−6 m2 s−1 and thermal conductivity of 2.7 W m−1 K−1 at 5 GPa and 300 K, which are much lower than those of olivine. Furthermore, the pressure derivatives of thermal diffusivity and thermal conductivity are significantly smaller than those of olivine. The thermal properties of antigorite obtained in the present study imply existence of a thermal insulating layer in subduction zones. From the simultaneous measurement of both thermal diffusivity and thermal conductivity the heat capacity of antigorite was determined to be ≈1 × 103 J kg−1 K−1, and increased to ≈1.5 × 103 J kg−1 K−1 at ≈800 K under high pressure. The heat capacity was nearly independent of pressure, which indicates nearly temperature-independent thermal expansivity of antigorite. Its characteristics also were hypothesized in terms of lattice dynamics of hydrous minerals involving hydrogen atoms and hydroxyl groups.