Microscopic mechanisms for heat transport in dense minerals (phonon scattering and photon attenuation) exhibit aspects of threshold behavior, discussed qualitatively here. For all minerals examined so-far using laser-flash analysis, the lattice component of the thermal conductivity of the mantle asymptotes to a constant above a critical temperature of ∼1500 K. Radiative transfer calculated from absorption spectra has thresholds in both grain-size and Fe content, and a rather complex dependence on temperature. These critical phenomena impact convection of the lower mantle, because the lattice contribution tends to destabilize the cold boundary layers, whereas radiative transfer mostly promotes stability in the lower mantle, unless the grains are large and Fe-rich, which makes convection chaotic and time-dependent. The specific behavior suggests that flow in the lower mantle is sluggish, whereas flow in the upper mantle-transition zone is time-dependent. The decrease in krad as Fe/(Fe + Mg) increases beyond ∼0.1 may be connected with formation of lower mantle, thermo-chemical plumes through positive feedback.
Bibliographical noteFunding Information:
Discussions in the CIDER 2004 workshop were helpful. AMH is supported by NSF-EAR-0132275 and 0207198. DAY is supported by the CSEDI and CMG programs in NSF-EAR. We thank M.A. Jellinek for helpful critical comments.
Copyright 2011 Elsevier B.V., All rights reserved.
- Lower mantle dynamics
- Radiative transfer
- Threshold phenomena
- Variable thermal conductivity