Tungsten-182 in the upper continental crust: Evidence from glacial diamictites

Mundl, Andrea; Walker, Richard J.; Reimink, Jesse; Rudnick, Roberta L.; Gaschnig, Richard M.

doi:10.1016/j.chemgeo.2018.07.036

Cited by 43 publications

(32 citation statements)

References 49 publications

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“…However, the reason these effects are either absent or too small to be observed for the metal fractions measured by TIMS is unclear. Differences in bulk composition (i.e., metal vs. silicate-oxide matrices) of the samples are unlikely to be the cause, as previously reported 183 W values for terrestrial, silicate-oxide dominated samples also measured by TIMS appear to be free from these effects (e.g., Mundl et al, 2018). We speculate that it could be due to different column dimensions for the two procedures, or different abundances of W in metals vs. nonmagnetic and slightly magnetic fractions, or the formation of hydrides within the plasma, as proposed by Breton and Quitté (2014).…”

Section: Hafnium and W Abundances 182 Hf-182 W Isotopic Compositionsmentioning

confidence: 85%

“…Archer et al (2017) compared the results of samples measured using the two procedures detailed above, and reported that the 182 W and 183 W isotopic compositions were identical within uncertainties. Mundl et al (2018) also compared data for NIST steel standard 129c processed using these two procedures, and found that the 182 W and 183 W isotopic compositions were also in agreement within uncertainties.…”

Section: Separation and Purification Of W For Isotopic Compositions-mmentioning

confidence: 96%

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Siderophile element constraints on the thermal history of the H chondrite parent body

Archer

Walker

Tino

et al. 2019

Geochimica et Cosmochimica Acta

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The abundances of highly siderophile elements (HSE: Re, Os, Ir, Ru, Pt, Pd), as well as 187 Re-187 Os and 182 Hf-182 W isotopic systematics were determined for separated metal, slightly magnetic, and nonmagnetic fractions from seven H4 to H6 ordinary chondrites. The HSE are too abundant in nonmagnetic fractions to reflect metal-silicate equilibration. The disequilibrium was likely a primary feature, as 187 Re-187 Os data indicate only minor open-system behavior of the HSE in the slightly and non-magnetic fractions. 182 Hf-182 W data for slightly magnetic and nonmagnetic fractions define precise isochrons for most meteorites that range from 5.2 ± 1.6 Ma to 15.2 ± 1.0 Ma after calcium aluminum inclusion (CAI) formation. By contrast, 182 W model ages for the metal fractions are typically 2-5 Ma older than the slope-derived isochron ages for their respective, slightly magnetic and nonmagnetic fractions, with model ages ranging from 1.4 ± 0.8 Ma to 12.6 ± 0.9 Ma after CAI formation. This indicates that the W present in the silicates and oxides was not fully equilibrated with the metal when diffusive transport among components ceased, consistent with the HSE data. Further, the W isotopic compositions of size-sorted metal fractions from some of the H chondrites also differ, indicating disequilibrium among some metal grains. The chemical/isotopic disequilibrium of siderophile elements among H chondrite components is likely the result of inefficient diffusion of siderophile elements from silicates and oxides to some metal and/or localized equilibration as H chondrites cooled towards their respective Hf-W closure temperatures. The tendency of 182 Hf-182 W isochron ages to young from H5 to H6 chondrites may indicate derivation of these meteorites from a slowly cooled, undisturbed, concentrically-zoned parent body, consistent with models that have been commonly invoked for H chondrites. Overlap of isochron ages for H4 and H5 chondrites, by contrast, appear to be more consistent with shallow impact disruption models.

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Section: Hafnium and W Abundances 182 Hf-182 W Isotopic Compositionsmentioning

confidence: 85%

Section: Separation and Purification Of W For Isotopic Compositions-mmentioning

confidence: 96%

Siderophile element constraints on the thermal history of the H chondrite parent body

Archer

Walker

Tino

et al. 2019

Geochimica et Cosmochimica Acta

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“…Transparent green diamonds are samples where ages have not been reliably determined using U‐Pb zircon methods. Note that all negative μ 182 W values from the Archean, including diamictite analyses, come from South Africa and may be a locally derived signal (Mundl et al, 2018). Inset shows the same plot with only felsic rocks and diamictites.…”

Section: Discussionmentioning

confidence: 99%

Tungsten Isotope Composition of Archean Crustal Reservoirs and Implications for Terrestrial μ¹⁸²W Evolution

Reimink

Mundl‐Petermeier

Carlson

et al. 2020

Geochem Geophys Geosyst

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The evolution of Earth's major geochemical reservoirs over ~4.5 × 109 years remains a matter of intense study. Geochemical tools in the form of short‐lived radionuclide isotope ratios (142Nd/144Nd and 182W/184W) have expanded our understanding of the geochemical variability in both the modern and ancient Earth. Here, we present 142Nd/144Nd and 182W/184W data from a suite of rocks from the Slave craton that formed over a 1.1 × 109 year time span in the Archean. The rocks have consistently high 182W/184W, yet 142Nd/144Nd that is lower than bulk mantle and increased over time. The declining variability in 142Nd/144Nd with time likely reflects the homogenization of compositional heterogeneities in the silicate Earth that were initially created by differentiation events that occurred prior to 4.2 Ga. The elevated 182W/184W recorded in the Slave samples help refine models for the broader W‐isotope evolution of the silicate Earth. Globally, the Archean mantle that formed continental crust was dominated by 182W/184W elevated by some 10–15 ppm compared to the value for the modern upper mantle. The Slave craton lacks significant volumes of komatiite yet has elevated 182W/184W until 2.9 Ga. This observation, combined with the presence of other komatiite suites that have low 182W/184W, suggests that deep‐seated sources contributed low 182W/184W in the Archean Earth. The regional variability in 182W/184W may be explained by invoking chemical and/or isotopic exchange between a well‐mixed silicate Earth and the core or a portion of the lower mantle whose W‐isotope composition has been influenced by interaction with the core.

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“…Mundl et al . ), requires a Ti/W < 1. The use of oxidising organic acid solutions on anion exchange resins has previously been employed to chemically separate Ti from W (Kleine et al .…”

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confidence: 99%

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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Tungsten-182 in the upper continental crust: Evidence from glacial diamictites

Cited by 43 publications

References 49 publications

Siderophile element constraints on the thermal history of the H chondrite parent body

Siderophile element constraints on the thermal history of the H chondrite parent body

Tungsten Isotope Composition of Archean Crustal Reservoirs and Implications for Terrestrial μ¹⁸²W Evolution

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

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Tungsten-182 in the upper continental crust: Evidence from glacial diamictites

Cited by 43 publications

References 49 publications

Siderophile element constraints on the thermal history of the H chondrite parent body

Siderophile element constraints on the thermal history of the H chondrite parent body

Tungsten Isotope Composition of Archean Crustal Reservoirs and Implications for Terrestrial μ182W Evolution

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

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Product

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Tungsten Isotope Composition of Archean Crustal Reservoirs and Implications for Terrestrial μ¹⁸²W Evolution