Uranium valence change in silicate melts at the highly reducing conditions of the Early Earth

The distribution of heat-producing trace elements including uranium (U) and thorium (Th) between a silicate and metal melt is a key parameter to reconstruct the formation history of the Earth’s core, its composition and initial heat budget. The main objective of this study is to unambiguously investigate the valance of U and Th contained in silicate glasses (600 ppm) synthesized previously at Early Earth's conditions (highly reducing). This knowledge is crucial to interpret their experimentally observed silicate-metal melt distribution behaviors and to deduce their abundances in the Earth’s core. U and Th valence can only be determined unambiguously from High-energy-resolution-fluorescence (HERFD) X-ray Near Edge Absorption Spectroscopy measurements at the M4 edges, which remain challenging at these high dilution levels. ID26 and BM20 are the few instruments in Europe allowing acquiring such data also thanks to the significant flux increase of the ESRF-EBS.