Inference of high thermal transport in the lower mantle from laser-flash experiments and the damped harmonic oscillator model

Abstract Contact-free, laser-flash analysis (LFA) accurately (±2%) measures lattice thermal diffusivity ( D ) at high temperature ( T ). Conventional measurements of minerals underestimate D by ∼20% near 298 K due to interface resistance, although simultaneously existing direct radiative transfer artificially elevates D as T rises. Pressure ( P ) determinations possess these and other problems; however, reproduced values of ∂ D /∂ P agree the damped harmonic oscillator model. Models combined with new LFA data on perovskite compounds show that lattice thermal conductivity ( k lat ) is high and independent of T , increasing from 7.5 to 30 W/m K (±25%) across the lower mantle (LM) due to compression. Diffusive radiative transfer is estimated from a recent model: For expected fine grain-size, spectral characteristics do not play a strong role, indicating that k rad increases from ∼1 to ∼5 W/m K across the LM, estimated from olivine spectra. Although greater accuracy through improved measurements is needed, our results demonstrate that the LM is an efficient conductor of heat. Even a low, adiabatic temperature gradient can carry the power inferred to run the dynamo. Mantle convection may be limited to above 670 km.

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