Measurements of thermophysical properties of deep Earth materials under high pressure and high temperature

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Thermal diffusivity and thermal conductivity of major mantle candidate materials have been measured under pressures up to 8-10 GPa and temperatures to 1100 K, using a pulse-heating method of one-dimensional heat flow in a Kawai-type apparatus. The results show that the thermal conductivity or diffusivity of these major mantle minerals increases 3-4 % per 1 GPa, and that olivine likely preserves anisotropy in thermal diffusivity or conductivity throughout its stability in the mantle, i.e. down to 410 km depth. Garnet shows somewhat peculiar behavior of thermal conductivity or thermal diffusivity : their decrease by heating and increase by pressurizing are moderate compared to other dense oxides and olivine. Another major mantle material, pyroxene shows similar behavior of thermal conductivity or diffusivity to olivine. The present results of pressure dependence in thermal conductivity of diffusivity agree with previous experiments and theoretical predictions.As thermal diffusivity and t … More hermal conductivity are measured simultaneously, heat capacity is obtained by comparing these quantities. This study demonstrates a novel aspect of mineral physics : that the heat capacity of mantle materials under pressure could be determined experimentally. Heat capacities of olivine and garnet at room temperature are within 5 % of previously reported values. Moreover, the heat capacities for the three crystallographic directions in olivine are consistent within 6 %, which shows the adequacy of the present method for thermal diffusivity and conductivity. Under high pressures, heat capacities have slightly lower values to those at zero pressure. This is consistent with the identity of thermodynamics for changes in heat capacity under pressure.For future study, the pressure range will exceed 15 GPa, which is equivalent to those at the bottom of the upper mantle, and measurements of marked precision are hope to be performed with reduction of systematic errors probably derived from mechanical defect or deformation of the sample assembly by compression. Less