Magnitude of stable iron isotope fractionation limited by multiple stages of terrestrial core formation

Abstract

One proposed mechanism for generating iron isotopic differences between planetary mantles and chondrites is metal-silicate equilibration during terrestrial core formation. Prior studies of this isotopic fractionation effect employ single-stage core formation models that are inconsistent with reproducing the siderophile element budget of the Earth's mantle. Here, we model iron isotopic evolution of the Earth's mantle in a multistage core formation scenario that is consistent with dynamic models of planet formation and reproduces the geochemistry of the bulk silicate Earth, specifically the refractory moderately siderophile elements. We find that multiple stages of core formation rebalance the fractionating effect of metal-silicate equilibration for the iron isotopic system, comparable to or smaller than typical analytical uncertainties in mantle rocks. Ultimately, this rebalancing effect - coupled with stochastic accretion and differentiation histories which further complicate planetary formation processes - makes it unlikely that isotopic fractionation during metal-silicate equilibration is the primary mechanism responsible for the iron isotopic composition of the Earth's mantle.

Accepted for publication in Geochimica et Cosmochimica Acta, 17 pages, 7 figures

References in corpus (16)

• Building Terrestrial Planets
• Highly Siderophile Elements in the Earth's Mantle as a Clock for the Moon-forming Impact
• Close-in planetesimal formation by pile-up of drifting pebbles
• Highly siderophile elements were stripped from Earth's mantle by iron sulfide segregation
• Lunar and Terrestrial Planet Formation in the Grand Tack Scenario
• Terrestrial planet formation from lost inner solar system material
• The early instability scenario: terrestrial planet formation during the giant planet instability, and the effect of collisional fragmentation
• Formation, stratification, and mixing of the cores of Earth and Venus
• Scaling laws for the geometry of an impact-induced magma ocean
• The Metal-Silicate Partitioning of Carbon During Earth's Accretion and its Distribution in the Early Solar System
• Metal-silicate partitioning of W and Mo and the role of carbon in controlling their abundances in the Bulk Silicate Earth
• Comparisons of the core and mantle compositions of earth analogs from different terrestrial planet formation scenarios
• Terrestrial planet and asteroid belt formation by Jupiter-Saturn chaotic excitation
• Constraining the Origin of Mars via Simulations of Multi-Stage Core Formation
• The effect of collisional erosion on the composition of Earth-analog planets in Grand Tack models: Implications for the formation of the Earth
• Early Solar System Turbulence Constrained by High Oxidation States of the Oldest Non-Carbonaceous Planetesimals