Performing such viscosity measurements requires the use of special PHYSICS AND CHEMISTRY OF HARD CONDENSED heating elements, which should be both highly refractory to support MATTER, EARTH SCIENCES the high temperatures needed to melt the silicate sample entirely, and SYNCHROTRON SOLEIL HIGHLIGHTS 2020 highly transparent to record clear X-ray radiographies. The lack of such a heating element has limited the viscosity measurement of silicate melts to pressures lower than 13 GPa until present. Now, experiments PSICHE BEAMLINE to /home/webapps/asp_fr/data/asp/publications/synchrotron-soleil/synchrotron-soleil-2020/soleil-highlights-2020-hd-ss-tc30 GPa were made possible by the recent development of an electrical conductor made of boron-doped diamond with melting point Associated publication of /home/webapps/asp_fr/data/asp/publications/synchrotron-soleil/synchrotron-soleil-2020/soleil-highlights-2020-hd-ss-tc5000 K [4]. As a result, the present study successfully investigated the viscosity of silicate melts with compositions similar to major mantle Formation of bridgmanite-enriched minerals, namely forsterite (MgSiO, Fo), enstatite (MgSiO, En), layer at the top lower-mantle during and diopside (CaMgSiO, Di) up to the conditions of the Earth’s lower2 4 3 magma ocean solidification. 2 6 mantle. A very interesting result is a very low melt viscosity, in the order L. Xie, A. Yoneda, D. Yamazaki, of 0.01 Pa.s, comparable to water. G. Manthilake, Y. Higo, Y. Tange, N. Guignot, A. King, M. Scheel & MODELLING AND CONCLUSION D. Andrault. Based on our new viscosity data, we modeled the progressive solidification Nature Communications, 11: of the magma-ocean. Results show an homogeneous crystallization art.n° 548 (2020). in the deep lower mantle, due to the dominant entraining forces in a highly turbulent magma-ocean. Upon cooling, a sedimentation of crystal References grains is calculated when the bottom of the magma-ocean reaches a [1] W. B. Tonks & H. J. Melosh, depth around 1000 km, which induces fractional crystallization of the J. Geophys. Res., Planets, 98, magma-ocean (Figure 2). This effect should also take place later when 5319 (1993). the upper mantle finally crystallizes. Our results show unambiguously [2] J. Monteux et al., Earth Planet. that mantle heterogeneities were induced very early in the Earth’s history Sci. Lett, 448, 140 (2016). and some of these heterogeneities seem to have remained in the mantle [3] V. Solomatov, Treatise Geophys. until present despite the continuous persistence of mantle convection. Second Ed., 9, 81 (2015). [4] L. Xie et al., Rev. Sci. Instrum., FIGURE 2 88, 093904 (2017). Corresponding author Longjian Xie Institute for Planetary Materials, Okayama University, Misasa, Tottori 682-0193, Japan Bayrisches Geoinstitut, University of Bayreuth, Bayreuth 95440, Germany Earth and Planetary Laboratory, Carnegie Institute for Science, Washington DC 20015-1305, USA Longjian.Xie@uni-bayreuth.de Captions FIGURE 1: Path of a rhenium sphere falling in liquid forsterite at /home/webapps/asp_fr/data/asp/publications/synchrotron-soleil/synchrotron-soleil-2020/soleil-highlights-2020-hd-ss-tc2873 K and /home/webapps/asp_fr/data/asp/publications/synchrotron-soleil/synchrotron-soleil-2020/soleil-highlights-2020-hd-ss-tc24 GPa. FIGURE 2: A conceptual drawing of Earth’s mantle after magma ocean solidification. Bdg: bridgmanite. 73