Radiative Thermal Conductivity of Upper Mantle and Transition Zone Minerals

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Structure and dynamics of our planet's interior depend crucially upon heat flow and thus upon the thermal conductivity of its constituents. Temperature- and pressure-dependent thermal conductivity of Earth's mantle materials, such as olivine, is an important parameter for geodynamic models of mantle convection. Thermal conductivity variations affect models of lithospheric geotherms, subduction dynamics, and the structure of lithospheric slabs. Does the mantle transition zone between a depth of 410 and 660 km act as a heat flux regulator within the Earth's upper and lower mantle? Thermal conductivities of upper mantle and transition zone minerals are poorly constrained, and there is little experimental data on the radiative part of thermal conductivity, especially at the high pressures and temperatures that exist in those regions. This experimental study aims to complement continually evolving theoretical frameworks, extend ongoing projects to all major constituents of the Earth's mantle and indirectly measure temperature-pressure variation of radiative thermal conductivity using in-situ optical spectroscopy as powerful tool. A primary goal of the project is to further our understanding of a major driving force of nature - heat flow within the Earth. This project builds upon recent in-situ optical measurements, for the first time at simultaneous high-pressure and high-temperature, studying two major transition zone phases, hydrous wadsleyite and hydrous ringwoodite. We reported large radiative thermal conductivities, which reveal an energy transmission 'window' in the infrared and visible spectral range. We found that the mantle transition zone may contribute significantly to radiative heat transfer, and we confirmed predictions that hydration may enhance radiative heat flux. The current project will extend those studies to olivine, majorite, and phase D. In addition, we plan to systematically study the effect of compositional changes (such as iron and water concentrations) on thermal conductivity properties of olivine and it's high-pressure polymorphs wadsleyite and ringwoodite. This research is of highly collaborative nature, and will take advantage of the expertise and facilities of laboratories across the nation, as well as internationally, in particular the Geophysical Laboratory of the Carnegie Institution of Washington (optical measurements), the Earth and Planetary Science and Civil and Environmental Engineering departments at Northwestern University (spectroscopy) and the Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences (syntheses). This work will illuminate a fundamentally interdisciplinary topic of deep concern to a broad audience, including mineral physicists, seismologists, geodynamicist, geochemists, and planetary scientists. Our study will provide a valuable learning experience for undergraduate students, as well as important data, which will contribute to our knowledge of heat transfer in the Earth?s interior and will help to improve geophysical models of heat flux in the Earth.