Late metal–silicate separation on the IAB parent asteroid: Constraints from combined W and Pt isotopes and thermal modelling

Hunt, A. C.; Cook, David L.; Lichtenberg, Tim; Reger, P.M.; Ek, Mattias; Golabek, Gregor J.; Schönbächler, Maria

doi:10.1016/j.epsl.2017.11.034

Cited by 36 publications

(64 citation statements)

References 63 publications

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“…as little as 0.1 to 0.3 million years after the formation of CAIs based on iron meteorites (Kruijer et al 2014). This time period is also within less than 2 Ma for silicate achondrite parent bodies and thus before the formation of most chondrules and the accretion of chondrite parent bodies (e.g., Hunt et al 2018). Widespread mafic magmas formed on various parent bodies within the first 3 to 5 Myr (Fig.…”

Section: Timescales Of Planetary Accretion and Differentiationmentioning

confidence: 80%

Accretion of the Earth—Missing Components?

2020

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Primitive meteorites preserve the chemical and isotopic composition of the first aggregates that formed from dust and gas in the solar nebula during the earliest stages of solar system evolution. Gradual increase in the size of solid bodies from dust to aggregates and then to planetesimals finally led to the formation of planets within a few to tens of million years after the start of condensation. Thus the rocky planets of the inner solar system are likely the result of the accumulation of numerous smaller primitive as well as differentiated bodies. The chemically most primitive known meteorites are chondrites and they consist mostly of metal and silicates. Chondritic meteorites are derived from distinct primitive planetary bodies that experienced only limited element fractionation during formation and subsequent differentiation. Different chondrite classes show distinct chemical and isotopic characteristics, which may reflect heterogeneities in the solar nebula and the slightly different pathways of their formation. To a first approximation the chemical composition of the bulk Earth bears great similarities to primitive meteorites. However, for some elements there are striking and significant differences. The Earth shows a much stronger depletion of the moderate to highly volatile elements compared to chondrites. In addition, mixing trends of specific isotopes reveal that the Earth is most enriched in s-process isotopes compared to all other analysed bulk solar system materials. It is currently not possible to fully define and quantify the different chemical and isotopic materials that formed the Earth, because a major component seems missing in the extant collections of extraterrestrial samples. Variations in nucleosynthetic isotope compositions as well as the strong depletion of moderately and strongly volatile elements points towards a source in the inner solar system for this missing material. It is conceivable that Venus and Mercury contain a much larger fraction of this

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Section: Timescales Of Planetary Accretion and Differentiationmentioning

confidence: 80%

Accretion of the Earth—Missing Components?

2020

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“…We first consider the aluminum partitioning behavior in a closed, isobaric (P = 0) system under increasing temperature. For consistency with earlier work (Tkalcec et al, 2013;Golabek et al, 2014;Lichtenberg et al, 2016a;Monteux et al, 2018;Lichtenberg et al, 2018;Hunt et al, 2018), we choose the lowest component melting point, T fsp m,0 = 1350 K, to conform with previous estimates of the silicate solidus. To test different partitioning behaviors, we vary the relative temperature difference between the melting points for the 26 Alhosting fsp and the pxn components, ∆T m = T Figure 2.…”

Section: Melting and Heat Source Partitioningmentioning

confidence: 99%

“…Planetesimals of this size are qualitatively representative of the interior evolution of planetesimals of R P 50 km as these are dominated by a relatively large adiabatic interior and a thin ( 10 km) conductive lid, whereas the relative dimensions of these domains vary significantly for planetesimal radii 50 km (cf. Castillo-Rogez and Young, 2017;Lichtenberg et al, 2018;Hunt et al, 2018). The computational domain includes 500 grid cells for a spatial resolution of 120 m. The surface boundary is T space = 290 K, similar to the temperature in the protoplanetary disk inside of the water snowline, while the center boundary is insulating, ∂T/∂z | z=0 = 0.…”

Section: Model Setup and Parameter Spacementioning

confidence: 99%

Magma ascent in planetesimals: Control by grain size

Lichtenberg

Keller

Katz

et al. 2019

Earth and Planetary Science Letters

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Rocky planetesimals in the early solar system melted internally and evolved chemically due to radiogenic heating from 26 Al. Here we quantify the parametric controls on magma genesis and transport using a coupled petrological and fluid mechanical model of reactive two-phase flow. We find the mean grain size of silicate minerals to be a key control on magma ascent. For grain sizes 1 mm, melt segregation produces distinct radial structure and chemical stratification. This stratification is most pronounced for bodies formed at around 1 Myr after formation of Ca,Al-rich inclusions. These findings suggest a link between the time and orbital location of planetesimal formation and their subsequent structural and chemical evolution. According to our models, the evolution of partially molten planetesimal interiors falls into two categories. In the magma ocean scenario, the whole interior of a planetesimal experiences nearly complete melting, which would result in turbulent convection and core-mantle differentiation by the rainfall mechanism. In the magma sill scenario, segregating melts gradually deplete the deep interior of the radiogenic heat source. In this case, magma may form melt-rich layers beneath a cool and stable lid, while core formation would proceed by percolation. Our findings suggest that grain sizes prevalent during the internal heating stage governed magma ascent in planetesimals. Regardless of whether evolution progresses toward a magma ocean or magma sill structure, our models predict that temperature inversions due to rapid 26 Al redistribution are limited to bodies formed earlier than ≈ 1 Myr after CAIs. We find that if grain size was 1 mm during peak internal melting, only elevated solid-melt density contrasts (such as found for the reducing conditions in enstatite chondrite compositions) would allow substantial melt segregation to occur.

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“…) and extra‐terrestrial (e.g., Akram and Schönbächler , Hunt et al . , , Kruijer and Kleine , Worsham et al . ) systems.…”

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Chemical Separation of Tungsten and Other Trace Elements for TIMS Isotope Ratio Measurements Using Organic Acids

Peters

Mundl‐Petermeier

Horan

et al. 2019

Geostandard Geoanalytic Res

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One requirement for isotope ratio measurement results with small measurement uncertainties is that the element of interest is effectively separated from the sample matrix. Efficient chemical separation of W from matrix components, especially Ti, can be challenging, particularly for large test portion masses (> 1 g). We present a new W separation procedure that takes advantage of the distinct complexation behaviour of Ti and W with citrate ligand in a moderately low pH, oxidising solution. This preparation procedure can reduce the Ti/W ratio of large (4–10 g) basaltic (i.e., high‐matrix) test portions by a factor of 105, relative to their original compositions, in a two‐step separation procedure. The procedure additionally provides a separate, well‐purified Mo fraction. We show that optimal separation requires precise selection of reagent concentrations and sample load. The procedure was employed to determine the μ182W composition of BHVO‐2 as −6.7 ± 4.2 (2 standard deviation, 2s). The principles derived from this method may prove useful for chemical separation of other elements used for geochemical and cosmochemical applications given an appropriate selection of organic acid. Future successful applications of this method may reveal that the use of organic acids as procedural reagents is a currently under‐utilised tool for efficient chemical separation protocols.

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Late metal–silicate separation on the IAB parent asteroid: Constraints from combined W and Pt isotopes and thermal modelling

Cited by 36 publications

References 63 publications

Accretion of the Earth—Missing Components?

Accretion of the Earth—Missing Components?

Magma ascent in planetesimals: Control by grain size

Chemical Separation of Tungsten and Other Trace Elements for TIMS Isotope Ratio Measurements Using Organic Acids

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