The depletion of tungsten in the bulk silicate earth: Constraints on core formation

Newsom, H. E.; Sims, Kenneth W.W.; Noll, P. D.; Jaeger, W. L.; Maehr, S. A.; Beserra, T. B.

doi:10.1016/0016-7037(96)00029-4

Cited by 119 publications

(78 citation statements)

References 44 publications

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“…The terrestrial and lunar mantles have almost identical W isotope compositions (εW Moon = +2.1 ± 0.1 [19] and εW BSE = +1.9 ± 0.1 [117]) and Hf/W ratios ( f Moon,mantle = 25.7 ± 3.3 and f BSE = 25.4 ± 4.2; based on re-evaluation of literature estimates [120][121][122][123][124] and using the chondritic Th/W and U/W ratios of [125]). In the electronic supplementary material, we demonstrate by mass-balance that for a given impact scenario mathematical relationships exist between the observables f BSE , εW BSE , f Moon , εW Moon and the compositions of the proto-Earth and impactor mantles f impactor mantle , εW impactor mantle , f proto-Earth mantle , εW proto-Earth mantle (equations (23), (25), (39) and (41) figure 6 represent 500 outcomes of these Monte Carlo simulations).…”

Section: Hf-w In the Earth-moon-impactor Systemmentioning

confidence: 99%

Geochemical arguments for an Earth-like Moon-forming impactor

Dauphas

Burkhardt

Warren

et al. 2014

Phil. Trans. R. Soc. A.

125

101

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Geochemical evidence suggests that the material accreted by the Earth did not change in nature during Earth's accretion, presumably because the inner protoplanetary disc had uniform isotopic composition similar to enstatite chondrites, aubrites and ungrouped achondrite NWA 5363/5400. Enstatite meteorites and the Earth were derived from the same nebular reservoir but diverged in their chemical evolutions, so no chondrite sample in meteorite collections is representative of the Earth's building blocks. The similarity in isotopic composition (Δ 17 O, ε 50 Ti and ε 54 Cr) between lunar and terrestrial rocks is explained by the fact that the Moon-forming impactor came from the same region of the disc as other Earth-forming embryos, and therefore was similar in isotopic composition to the Earth. The heavy δ 30 Si values of the silicate Earth and the Moon relative to known chondrites may be due to fractionation in the solar nebula/protoplanetary disc rather than partitioning of silicon in Earth's core. An inversion method is presented to calculate the Hf/W ratios and ε 182 W values of the proto-Earth and impactor mantles for a given Moon-forming impact scenario. The similarity in tungsten isotopic composition between lunar and terrestrial rocks is a coincidence that can be explained in a canonical giant impact scenario if an early formed embryo (two-stage model age of 10–20 Myr) collided with the proto-Earth formed over a more protracted accretion history (two-stage model age of 30–40 Myr).

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Section: Hf-w In the Earth-moon-impactor Systemmentioning

confidence: 99%

Geochemical arguments for an Earth-like Moon-forming impactor

Dauphas

Burkhardt

Warren

et al. 2014

Phil. Trans. R. Soc. A.

125

101

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“…Mo lybdenum and W are diagnostic elements for un derstanding the formation of the Earth (Newsom and Palme, 1984;Newsom et al, 1996) and the redox conditions in the early solar nebula (Fegley and Palme, 1985;Kong and Ebihara, 1996a). In previous studies, Kong et al (1995) and Kong and Ebihara (1996b) Sixteen samples (G-1 to G-16) were prepared from a single bottle of JB-1 (split 3).…”

mentioning

confidence: 99%

Reproducibility of elemental concentrations for JB-1, a GSJ rock reference sample, with special reference to Mo, W and Ta.

Kong

Ebihara

1997

Geochem. J.

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“…1 (based on data from Newsom, 1990;McDonough and Sun, 1995;Newsom et al, 1996;comp. as well Walter et al, 2000), and exhibit two striking features. First, HSE are measurable in upper mantle samples, which is shocking given their extremely large metal/silicate partition coefficients at 1 atm.…”

Section: Introductionmentioning

confidence: 99%

Experimental study of platinum solubility in silicate melt to 14GPa and 2273K: Implications for accretion and core formation in Earth

Ertel

Walter

Drake

et al. 2006

Geochimica et Cosmochimica Acta

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We determined the solubility limit of Pt in molten haplo-basalt (1 atm anorthite-diopside eutectic composition) in piston-cylinder and multi-anvil experiments at pressures between 0.5 and 14 GPa and temperatures from 1698 to 2223 K. Experiments were internally buffered at $IW + 1. Pt concentrations in quenched-glass samples were measured by laser-ablation inductively coupled-plasma mass spectrometry (LA-ICPMS). This technique allows detection of small-scale heterogeneities in the run products while supplying threedimensional information about the distribution of Pt in the glass samples. Analytical variations in 195 Pt indicate that all experiments contain Pt nanonuggets after quenching. Averages of multiple, time-integrated spot analyses (corresponding to bulk analyses) typically have large standard deviations, and calculated Pt solubilities in silicate melt exhibit no statistically significant covariance with temperature or pressure. In contrast, averages of minimum 195 Pt signal levels show less inter-spot variation, and solubility shows significant covariance with pressure and temperature. We interpret these results to mean that nanonuggets are not quench particles, that is, they were not dissolved in the silicate melt, but were part of the equilibrium metal assemblage at run conditions. We assume that the average of minimum measured Pt abundances in multiple probe spots is representative of the actual solubility. The metal/silicate partition coefficients (D met/sil ) is the inverse of solubility, and we parameterize D met/sil in the data set by multivariate regression. The statistically robust regression shows that increasing both pressure and temperature causes D met/sil to decrease, that is, Pt becomes more soluble in silicate melt. D met/sil decreases by less than an order of magnitude at constant temperature from 1 to 14 GPa, whereas isobaric increase in temperature produces a more dramatic effect, with D met/sil decreasing by more than one order of magnitude between 1623 and 2223 K. The Pt abundance in the Earth's mantle requires that D met/sil is $1000 assuming core-mantle equilibration. Geochemical models for core formation in Earth based on moderately and slightly siderophile elements are generally consistent with equilibrium metal segregation at conditions generally in the range of 20-60 GPa and 2000-4000 K. Model extrapolations to these conditions show that the Pt abundance of the mantle can only be matched if oxygen fugacity is high ($IW) and if Pt mixes ideally in molten iron, both very unlikely conditions. For more realistic values of oxygen fugacity ($IW À 2) and experimentally-based constraints on non-ideal mixing, models show that D met/sil would be several orders of magnitude too high even at the most favorable conditions of pressure and temperature. These results suggest that the mantle Pt budget, and by implication other highly siderophile elements, was added by late addition of a 'late veneer' phase to the accreting proto-Earth.

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The depletion of tungsten in the bulk silicate earth: Constraints on core formation

Cited by 119 publications

References 44 publications

Geochemical arguments for an Earth-like Moon-forming impactor

Geochemical arguments for an Earth-like Moon-forming impactor

Reproducibility of elemental concentrations for JB-1, a GSJ rock reference sample, with special reference to Mo, W and Ta.

Experimental study of platinum solubility in silicate melt to 14GPa and 2273K: Implications for accretion and core formation in Earth

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