Melting Temperatures of Iron and MgO Using a New Flash Laser Heating Technique

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One of the major constraints on the temperature at the center of the Earth is the melting temperature of iron at the pressure conditions of the inner core boundary (ICB) (330 GPa, or 3.3 Mbar). Despite intensive research in this field over the last two decades, the data available from shock compression and laser-heated diamond cell experiments and from theory show considerable disagreement ranging from 4800 K to 7600 K for the ICB. Similarly ill constrained is the melting behavior of the lower mantle where one of its main components (Mg,Fe)O plays a key role for the upper bound of the melting temperature and the chemical composition of a possible partial melt. We have developed new techniques to improve the accuracy in melting experiments by combining pulsed laser-heating techniques in the diamond cell, recently developed in our laboratory, with new X-ray diffraction techniques. A more accurate knowledge of the temperature of the Earth's interior will have a profound impact on all geophysical research related to mantle geodynamics, thermal history models of the Earth, heat flux and radioactivity in the core and will put constraints on poorly known quantities such as thermal conductivity, viscosity and melting of the lowermost mantle. The technical improvements will provide new opportunities to research other physical and chemical processes in extreme environments. The development of new laser heating and synchrotron X-ray techniques will not only enlarge the scientific community in geophysics and geochemistry, but also in material science. In-situ structural and chemical analysis of matter at extreme high pressure and temperature conditions is essential for the scientific progress in these fields. Our work will help to reduce many of the previous technical problems and make these methods more easily accessible.