Metal-silicate silicon isotopic fractionation and the composition of the bulk Earth

Abstract

The difference in the Si isotopic composition between the Earth and primitive meteorites had been used to constrain the amount of Si in the Earth's core. However, there is presently a debate on the magnitude of the isotopic fractionation between metal and silicates as function of temperature based on experimental data. Here, we use a natural sample, an enstatite meteorite, Itqyi, as a natural experiment to determine an independent Si isotopic fractionation factor between metal and silicate. We determined the temperature of equilibrium between metal and silicate as well as the Si isotopic composition between the phases. We find that the dependence of Si isotopes with *Manuscript Click here to view linked References temperature to be : Using this dependence of the  30 Si with temperature we estimate the bulk Earth  30 Si as a function of Si content of the core for different plausible conditions. Even when using the most extreme parameters, we show that the bulk Earth must be isotopically heavier than any chondrites groups. We therefore confirm that core formation alone cannot account for the isotopic difference between the Earth and primitive meteorites. We show that there is no correlation between  30 Si and the Mg/Si ratio suggesting that forsterite fractionation in the solar nebula may have had only a limited effect, if any.Our new results therefore confirm that volatility should have had a fundamental effect in shaping terrestrial planets chemical composition.

Tracing the origin and core formation of the enstatite achondrite parent bodies using Cr isotopes

“…Recently, Harries and Bischoff (2020) observed a new type of enstatite-rich differentiated meteorite clasts in Almahatta Sitta, which are believed to come from another asteroid with a size of ~500 km. These clasts also show petrological affinity to Itqiy, an EH7-anomalous meteorite, as they both underwent partial melting and are petrologically different from aubrites (Keil and Bischoff, 2008;Moynier et al, 2020;Patzer et al, 2001). The Cr isotope compositions of these different types of enstatite achondrites can be used to test their relationship to each other and to enstatite chondrites.…”

Formation of deep mantle heterogeneities through basal exsolution contaminated magma ocean

“…The addition of core exsolutions affects the Si isotopic compositions of the deep Earth. Core uid is depleted in heavy Si isotopes relative to the bulk silicate Earth (BSE) [48][49][50][51] . As a result, SiO 2 exsolved from the core has a light Si isotope composition with smaller than that of the BSE ( = − 0.29 ± 0.07‰) 52,53 by about 0.11‰-0.35‰ (Supplementary Information; Fig.…”

Effects of pebble accretion on the growth and composition of planetesimals in the inner Solar System

“…The amount of Si fractionated into the Earth's core is estimated to be between 2 wt% to 7 wt% based on geochemical and geophysical constraints (e.g. Badro et al 2007;Fitoussi et al 2009;Moynier et al 2020). The Earth's chemical composition is similar within uncertainties to the carbonaceous chondrites if more than 5 wt% of the Si is in the core.…”