Radiative heat transfer in a hydrous mantle transition zone

The structure and dynamics of Earth's interior depend crucially upon heat flow and thus upon the thermal conductivity of its constituents. We measured optical absorbance spectra of hydrous wadsleyite and hydrous ringwoodite at simultaneous high-pressure and high-temperature conditions up to 26GPa and 823K in order to determine their radiative conductivities and to study the potential influence of hydration in the transition zone on thermal conductivity of the mantle. We report radiative thermal conductivities of 1.5±0.2Wm^-1K^-1 for hydrous wadsleyite and 1.2±0.1Wm^-1K^-1 for hydrous ringwoodite at transition zone conditions. The analytically derived radiative thermal conductivities of anhydrous wadsleyite and ringwoodite are 40% and 33% higher, respectively. The total thermal conductivities, calculated from temperature- and pressure-dependent optical absorption measurements, maintain an energy transmission window in the infrared and visible spectral range at high pressures and temperatures. The results indicate that the mantle transition zone may contribute significantly to heat transfer in the mantle and demonstrate the importance of radiative heat transfer in controlling geodynamic processes in Earth's mantle.