Simultaneous measurements of thermal conductivity and thermal diffusivity for garnet and olivine under high pressure

Thermal conductivity λ and thermal diffusivity κ have been measured simultaneously for garnet (Al₇₃Py₂₅Gr₁Sp₁) and olivine (Fo₉₃Fa₇) single crystals up to 8.3 GPa and 1100 K by using a pulse heating method. Anisotropy of thermal conduction is investigated along the three crystallographic axes, [1 0 0] [0 1 0], and [0 0 1] in olivine. The pressure dependence of κ, or dln κ /d P, is determined to be 0.03-0.04 GPa^-1 for the three crystallographic direction in olivine and 0.03 GPa^-1 for garnet, while dln λ /d P is determined to be ∼0.04 GPa^-1 for olivine and 0.03 GPa^-1 for garnet. The anisotropy in thermal diffusivity or thermal conductivity of olivine is clearly observed in the present experimental range of pressure and temperature. It is likely that the anisotropy in thermal conduction would be maintained throughout the olivine stability field in the mantle down to 410 km depth. Heat capacities of olivine and garnet are calculated from the present κ and λ. Both the present heat capacities of olivine and garnet are consistent with the previously reported values within 5%. Those obtained for the three crystallographic direction in olivine are also consistent with each other within 6%. Further, the effect of basalt-eclogite transition on heat transportation is discussed based on the present results for garnet. It implies that the eclogite layer of the slab transmits thermal energy more effectively than the upper basaltic layer.