Geocheminar Winter-2018

he thermal conductivity of lower mantle minerals affects the heat flux across the core-mantle boundary and the dynamics of mantle convection. The pressure and temperature dependence of lattice thermal conductivity for dielectric materials, such as oxides and silicates in Earth’s mantle, can be well-explained by Debye theory and a thermal equation of state for the material. However, phase transitions in the lower mantle, such as the spin transition in ferropericlase, complicate extrapolation from lower pressures, and necessitate measurements of high pressure phases. As a method test, I present measurements of thermal conductivity of NaCl across the B1/B2 pressure-induced phase transition. I apply this technique to make measurements of ferropericlase, and show a significant decrease in thermal conductivity across the spin transition, in the pressure range of 40 – 60 GPa. Combining these results with previous measurements on iron-bearing bridgmanite, I construct a model of the depth dependence of lattice thermal conductivity for the lower mantle.