Isotopic signature of core-derived SiO2

Abstract

We apply an experimentally based thermodynamic model of Si+O saturation for the core to determine the saturation level of these elements under the conditions when the core formed. The model limits the bulk Si content of the core to between 0.4 and 3.1 wt% depending on the pressure, temperature, and oxygen content of the metal when it segregated from silicate. With knowledge of the core's Si content, the measured 30Si content of the silicate Earth, and the experimentally determined metal-silicate fractionation factor, we can calculate the core's δ30Si, which is between -0.92 to -1.36‰. SiO2 cycled through the core and then released into the mantle might be trapped in inclusions in diamond formed in the lower mantle. These would be characterized by significantly lighter δ30Si values of -1.12 ± 0.13‰ (1σ), compared to bulk silicate earth values of -0.29‰ and a potentially key indicator of mass transfer from the core to the mantle.