Metal-Silicate Partitioning of Uranium at High Pressures and Temperatures

Chidester Bethany, University of Chicago, Chicago, United States, Kevin Righter, NASA Johnson Space Center, Astromaterials Acquisition and Curation Office, Houston, United States, Zia Rahman, NASA Johnson Space Center, Houston, TX, United States and Andrew Campbell, University of Chicago, Chicago, IL, United States
Abstract:
Uranium, along with the other long-lived radioactive elements Th and K, are important heat sources in the Earth, contributing as much as 50% of the total heat flux at the surface.[1] However, it is unknown whether these elements are also an important heat source in the core. Previous metal-silicate partitioning experiments of U have noted an increase in partition coefficient (D(U)) with decreasing oxygen fugacity and increasing S content. Regardless, they conclude that the partition coefficients are too low, even under the most extreme conditions, for U to be an important heat source in the Earth’s core. However, all of those experiments were conducted at relatively low pressures (<29 GPa) and moderate temperatures (<2700 K). We present metal-silicate partitioning experiments conducted in the diamond anvil cell at conditions more relevant to a basal magma ocean, 40-55 GPa in pressure and 3700-4900 K in temperature. Under relatively reducing conditions (ΔIW= -1.5 to -2.5, with 15-30 wt% Si in the metal) and with no sulfur present, we measure partition coefficients for U in the range of 0.01-0.1, significantly higher than has been previously reported. From these results, we are unable to rule out the possibility that U is a significant heat source in the core.

[1] Lay, et al. 2008. Nature Geo. 1, 25-32.

[2] Bouhifd, et al. 2013. GCA. 114, 13-28.

[3] Malavergne, et al. 2007. GCA. 71, 2637-2655.

[4] Wheeler, et al. 2006. GCA. 70, 1537-1547.

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