Thermal conductivity of lower mantle minerals is essential for controlling the rate of core heat loss and longterm
thermal evolution of the Earth, but it has been poorly constrained at the high pressures of the Earth's
lowermost mantle. We have newly developed an apparatus for measuring the thermal diffusivity using a pulsed
light heating thermoreflectance technique under high pressure in a diamond anvil cell. The new method enabled
us to determine the lattice thermal diffusivity of both MgSiO3 perovskite and post-perovskite, the main constituent
of the Earth's lower mantle, at room temperature and at high pressures up to 144 GPa greater than the
core-mantle boundary pressure. Lattice thermal conductivity of perovskite-dominant lowermost mantle assemblage
obtained in this study is about 11 W･m－1･K－1, while post-perovskite bearing rocks exhibit ～60 higher
conductivity. Such perovskite value is comparable to the conventionally assumed lowermost mantle conductivity
of 10 W･m－1･K－1.
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