Keywords:Lower mantle minerals, Lattice thermal conductivity , First-principles calculation
Determination of lattice thermal conductivity (κlat) of lower mantle (LM) minerals is a key to understanding the dynamics and evolution of the earth’s deep interior. Some recent experimental studies have shown that κlat of MgO and MgSiO3 bridgmanite (Brg) are substantially reduced by Fe incorporation (Manthilake et al., 2012; Goncharov et al., 2015; Ohta et al., 2017; Hsieh et al., 2017). In contrast, Okuda et al. (2017) reported a very different result on Brg with a marginal effect of Fe. Besides, the effect of Fe on MgSiO3 post-perovskite (PPv) has never been reported. Therefore, in this study, we investigate κlat of Fe-bearing LM minerals (ferropericlase (FP), Brg, and PPv) in the LM pressure and temperature conditions, based on the ab initio anharmonic lattice dynamics techniques with fully solving the phonon Boltzmann transport equation (Dekura and Tsuchiya, 2017) combined with the internally consistent LDA+U technique for more precisely describing the Fe-O bond (Wang et al., 2015). Calculations demonstrate strong negative solid solution effects of low-spin Fe on κlat of FP and high-spin Fe on κlat of Brg and PPv, as a linear decrease in logκlat of FP with increasing the Fe concentration. Our detailed analyses indicate that such strong effects occur primarily due to the substantial changes in harmonic properties and are found to be Brg > PPv > FP. The present results improve the conventional estimation of the effective LM conductivity (e.g., Stacey 1992). It is estimated to be ~2-3 Wm-1K-1 for the pyrolytic aggregate (FP + Brg) and ~4-5 Wm-1K-1 (FP+PPv) at 136 GPa and 4000 K, which are ~60-80% smaller than the conventional value of 10 Wm-1K-1.