Planetary and meteoritic Mg/Si and d30Si variations inherited from solar nebula chemistry

Abstract

The bulk chemical compositions of planets are uncertain, even for major elements such as Mg and Si. This is due to the fact that the samples available for study all originate from relatively shallow depths. Comparison of the stable isotope compositions of planets and meteorites can help overcome this limitation. Specifically, the non-chondritic Si isotope composition of the Earth's mantle was interpreted to reflect the presence of Si in the core, which can also explain its low density relative to pure Fe-Ni alloy. However, we have found that angrite meteorites display a heavy Si isotope composition similar to the lunar and terrestrial mantles. Because core formation in the angrite parent-body (APB) occurred under oxidizing conditions at relatively low pressure and temperature, significant incorporation of Si in the core is ruled out as an explanation for this heavy Si isotope signature. Instead, we show that equilibrium isotopic fractionation between gaseous SiO and solid forsterite at 1370 K in the solar nebula could have produced the observed Si isotope variations. Nebular fractionation of forsterite should be accompanied by correlated variations between the Si isotopic composition and Mg/Si ratio following a slope of 1, which is observed in meteorites. Consideration of this nebular process leads to a revised Si concentration in the Earth's core of 3.6 (+6.0/-3.6) wt% and provides estimates of Mg/Si ratios of bulk planetary bodies.

Accepted in Earth and Planetary Science Letters, 40 pages, 8 figures, 2 tables

References in corpus (5)

• Abundance, distribution, and origin of 60Fe in the solar protoplanetary disk
• A perspective from extinct radionuclides on a Young Stellar Object: The Sun and its accretion disk
• Differentiation of Vesta: Implications for a shallow magma ocean
• Low 60Fe abundance in Semarkona and Sahara 99555
• Small Planetesimals in a Massive Disk Formed Mars

Cited by in corpus (28)

• The composition of Mars
• Near-equilibrium isotope fractionation during planetesimal evaporation
• Vapor drainage in the protolunar disk as the cause for the depletion in volatile elements of the Moon
• Thermodynamics of Element Volatility and its Application to Planetary Processes
• The Volatility Trend of Protosolar and Terrestrial Elemental Abundances
• Bayesian Inference on the Isotopic Building Blocks of Mars and Earth
• Subsolar Al/Si and Mg/Si ratios of non-carbonaceous chondrites reveal planetesimal formation during early condensation in the protoplanetary disk
• The cool and distant formation of Mars
• Stochastic accretion of the Earth
• Potassium Isotope Compositions of Carbonaceous and Ordinary Chondrites: Implications on the Origin of Volatile Depletion in the Early Solar System
• Evidence for depletion of heavy silicon isotopes at comet 67P/Churyumov-Gerasimenko
• Earth and Mars -- distinct inner Solar System products
• Potassium Isotopic Compositions of Enstatite Meteorites
• Modification of the composition and density of Mercury from late accretion
• Eta-Earth Revisited II: Deriving a Maximum Number of Earth-like Habitats in the Galactic Disk
• Effects of pebble accretion on the growth and composition of planetesimals in the inner Solar System
• Presolar grain dynamics: creating nucleosynthetic variations through a combination of drag and viscous evolution
• Quantitative estimates of impact induced crustal erosion during accretion and its influence on the Sm/Nd ratio of the Earth
• Composition, Structure and Origin of the Moon
• The cosmochemistry of planetary systems
• Effect of Equation of State and Cutoff Density in Smoothed Particle Hydrodynamics Simulations of the Moon-Forming Giant Impact
• Accretion regions of meteorite parent bodies inferred from a two-endmember isotopic mixing model
• Dynamic evolution of major element chemistry in protoplanetary disks and its implications for chondrite formation
• Variable refractory lithophile element compositions of planetary building blocks: insights from components of enstatite chondrites
• The Limited Role of the Streaming Instability During Moon and Exomoon Formation
• Physicochemical Controls on the Compositions of the Earth and Planets
• Spatial distribution of isotopes and compositional mixing in the inner protoplanetary disk
• Coupling dynamical accretion and chemical differentiation: A unified framework for the diversity of Earth and Mars