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Convergence of Ni and Co metal–silicate partition coefficients in the deep magma-ocean and coupled silicon–oxygen solubility in iron melts at high pressures

DOI: 10.1016/j.epsl.2011.05.006 DOI Help

Authors: M. A. Bouhifd (University of Oxford) , A. P. Jephcoat (Diamond Light Source)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Earth And Planetary Science Letters , VOL 307 , PAGES 341 - 348

State: Published (Approved)
Published: July 2011

Abstract: Models for a deep magma ocean have gained wide acceptance although with variations in the specific conditions at which core formation may have taken place. Preliminary high-pressure studies produced results consistent with metal-silicate equilibration at the base of a magma ocean that would have extended to as much as 60 GPa (corresponding to a depth of ~ 2000 km), > 2000 K and an oxygen fugacity two orders of magnitude below iron-wüstite (IW) buffer. However, up to now the magma models are based on extrapolations of low pressure (< 25 GPa) partition coefficient data that cannot be extrapolated to higher pressures. In this work, metal-silicate partitioning experiments were performed for pressures up to ~ 52 GPa and ~ 3500 K to investigate the behaviour of Ni and Co during terrestrial core formation using Laser-Heated Diamond-Anvil Cell (LHDAC) techniques. Our experimental results show that Ni and Co partitioning coefficients converge and remain similar above 30 GPa to the maximum pressure reached. In the range 30-52 GPa the data account for the relative depletions of Ni and Co (e.g., the chondritic Ni/Co ratio) confirming evidence for a deep-magma ocean. The present results suggest a wide interval of pressure where the siderophile elements can match their mantle concentrations. We also show that both the solubilities of oxygen and silicon in molten Fe-rich alloy increase with increasing pressure. The experimental partition coefficient of Si (DSi) together with DNi and DCo all match the theoretical partition coefficients required for an equilibrium core-mantle differentiation at pressures above 30 GPa and for temperatures between 3000 and 3500 K.

Journal Keywords: Earth's core; siderophile elements; light elements; metal–silicate segregation; magma ocean; laser-heated diamond-anvil cell

Subject Areas: Environment


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