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

Contact-free, laser-flash analysis (LFA) accurately (+/- 2%) measures lattice thermal diffusivity (D) at high temperature (T). Conventional measurements of minerals underestimate D by similar to 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 partial derivative D/partial derivative 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 30W/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 similar to 1 to similar 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. (C) 2008 Elsevier B.V. All rights reserved.