Simultaneous partitioning of silicon and oxygen into the Earth's core during early Earth differentiation

Abstract

[1] Silicon and oxygen are potential light elements in the Earth's core and may be involved in metal-silicate reactions at the present day core-mantle boundary. We have performed multianvil experiments at 25 GPa and 2770-3080 K to understand the simultaneous partitioning of these elements between liquid iron-rich metal and silicate melt. The presence of O in liquid Fe at high temperatures influences the partitioning of Si, causing more Si to partition into the metal than would be expected based on lower temperature measurements. Although Si and O are mutually exclusive in Fe metal at <3000 K, the level at which both element concentrations are similar in the liquid metal rises above 1 wt % at >3000 K. We have developed a thermodynamic model based on these experiments that accounts for the interaction between O and Si in the liquid metal. Comparison between this model and the previous results of diamond-anvil cell experiments up to 71 GPa indicates very little pressure dependence but a strong temperature dependence for O and Si partitioning. Our model predicts that subequal concentrations of Si and O, sufficient to explain the outer core density deficit, would have partitioned into core-forming metal if equilibration occurred between the metal and a magma ocean with a bulk silicate Earth composition at an average depth of~1200 km (~50 GPa and~3300 K). An O-and Sienriched buoyant layer may have developed at the top of the outer core as a result of subsequent equilibration with the overlying mantle. Citation: Tsuno K., D J. Frost, and D. C.Rubie, (2013), Simultaneous partitioning of silicon and oxygen into the Earth's core during early Earth differentiation, Geophys. Res. Lett., 40,[66][67][68][69][70][71]

High pressure metal–silicate partitioning of Ni, Co, V, Cr, Si, and O

“…interactions during the partitioning of these elements, in agreement with the findings of Tsuno et al (2013). For example, higher oxygen contents in the metal will cause more oxygen and more silicon to partition into the metal.…”

“…The metal-silicate partitioning of Ni, Co, V, Cr, Si, and O have been measured in 15 multianvil press experiments and five diamond anvil cell experiments up to 100 GPa and 5700 K. These new data were combined with literature data from 18 previous studies for a total of 179 experiments Chabot et al, 2005;Corgne et al, 2008;Geßmann and Rubie, 1998;Hillgren et al, 1996;Ito et al, 1995;Jana and Walker, 1997;Kegler et al, 2008;Mann et al, 2009;Ricolleau et al, 2011;Siebert et al, 2011Siebert et al, , 2012Siebert et al, , 2013Thibault and Walter, 1995;Tsuno et al, 2013;Wade and Wood, 2005) (Table A. The new parameterizations of these data can be used to learn about the conditions of core formation and the composition of the core. For a single effective pressure and temperature of core formation, we find that the Earth's Ni and Co distributions imply core-mantle equilibration at 54 ± 5 GPa and 3300-3400 K. Silicon and oxygen partitioning are also compatible with equilibration at these P-T conditions, which result in a core composition that is consistent with the core's measured density (8.5 ± 1.4 wt% Si,…”

“…For example, V and Cr are observed to become much more siderophile at higher P-T conditions, possibly due to interactions with oxygen in the metal . The low pressure partitioning behaviors of Si and O seem to suggest mutual incompatibility in metal due to the reducing conditions necessary to put Si in the metal (e.g., Malavergne et al, 2004), but higher P-T data reveal that Si and O also both become more siderophile at these conditions Siebert et al, 2012;Tsuno et al, 2013).…”

“…Metal-silicate reactions between liquid metal and liquid silicates at high P-T have been the subject of a large number of previous studies (e.g., Chabot and Agee, 2003;Chabot et al, 2005;Corgne et al, 2008;Cottrell et al, 2009;Geßmann and Rubie, 1998;Hillgren et al, 1996;Ito et al, 1995;Jana and Walker, 1997;Kegler et al, 2008;Agee, 1996, 2001;Mann et al, 2009;Ohtani et al, 1997;Ricolleau et al, 2011;Righter et al, 1997Righter et al, , 2010Righter et al, , 2011Siebert et al, 2011Siebert et al, , 2012Siebert et al, , 2013Thibault and Walter, 1995;Tsuno et al, 2013;Wade and Wood, 2005;Wood et al, 2009). These studies have produced a wide range of estimates of the effective pressure and temperature of core formation (see Rubie et al (2015b) for a recent review).…”

Core–Mantle Interactions

“…Recent experiments on partitioning of major elements between liquid iron and mantle minerals suggest that the core is currently undersaturated in Si and O (Asahara et al, 2007;Ozawa et al, 2008;Sakai et al, 2006;Siebert et al, 2012;Takafuji et al, 2005). For present-day estimates of temperature and bulk mantle composition, the equilibrium concentrations of Si and O in liquid iron should vastly exceed the concentrations required to explain the density deficit of the core relative to pure iron (Tsuno et al, 2013). Transfer of Si and O to the core can produce a buoyant layer at the top of the core (Ozawa et al, 2009), although the vertical extent of such a layer is potentially limited by diffusive transport through the mantle.…”