DOI: 10.1016/j.epsl.2018.07.030
Scopus记录号: 2-s2.0-85051044169
论文题名: Effects of core formation on the Hf–W isotopic composition of the Earth and dating of the Moon-forming impact
作者: Fischer R.A. ; Nimmo F.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2018
卷: 499 起始页码: 257
结束页码: 265
语种: 英语
英文关键词: core formation
; Hf–W
; isotopes
; partitioning
; tungsten anomaly
Scopus关键词: Commerce
; Geophysics
; Isotopes
; Oxygen
; Silicates
; Tungsten
; Core formation
; Earth's core formations
; Equilibration depths
; Evolution of oxygen
; Initial composition
; Isotopic composition
; Partition coefficient
; partitioning
; Moon
; accretion
; core-mantle boundary
; Earth
; hafnium
; isotopic composition
; Moon
; partition coefficient
; tungsten
英文摘要: Earth's core formation set the initial compositions of the core and mantle. Various aspects of core formation, such as the degree of metal–silicate equilibration, oxygen fugacity, and depth of equilibration, have significant consequences for the resulting compositions, yet are poorly constrained. The Hf–W isotopic system can provide unique constraints on these aspects relative to other geochemical or geophysical methods. Here we model the Hf–W isotopic evolution of the Earth, improving over previous studies by combining a large number of N-body simulations of planetary accretion with a core formation model that includes self-consistent evolution of oxygen fugacity and a partition coefficient of tungsten that evolves with changing pressure, temperature, composition, and oxygen fugacity. The effective average fraction of equilibrating metal is constrained to be k>0.2 for a range of equilibrating silicate masses (for canonical accretion scenarios), and is likely <0.55 if the Moon formed later than 65 Ma. These values of k typically correspond to an effective equilibration depth of ∼0.5–0.7× the evolving core–mantle boundary pressure as the planet grows. The average mass of equilibrating silicate was likely at least 3× the impactor's silicate mass. Equilibration temperature, initial fO2, initial differentiation time, semimajor axis, and planetary mass (above ∼0.9 M⊕) have no systematic effect on the 182W anomaly, or on fHf/W (except for fO2), when applying the constraint that the model must reproduce Earth's mantle W abundance. There are strong tradeoffs between the effects of k, equilibrating silicate mass, depth of equilibration, and timing of core formation, so the terrestrial Hf–W isotopic system should be interpreted with caution when used as a chronometer of Earth's core formation. Because of these strong tradeoffs, the Earth's tungsten anomaly can be reproduced for Moon-forming impact timescales spanning at least 10–175 Ma. Early Moon formation ages require a higher degree of metal–silicate equilibration to produce Earth's 182W anomaly. © 2018 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/109720
Appears in Collections: 影响、适应和脆弱性 气候变化事实与影响
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作者单位: Harvard University, Department of Earth and Planetary Sciences, United States; University of California Santa Cruz, Department of Earth and Planetary Science, United States; Smithsonian National Museum of Natural History, Department of Mineral Sciences, United States
Recommended Citation:
Fischer R.A.,Nimmo F.. Effects of core formation on the Hf–W isotopic composition of the Earth and dating of the Moon-forming impact[J]. Earth and Planetary Science Letters,2018-01-01,499