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Abstract Vanadium (V) isotopes have been hypothesized to record irradiation processes in the early solar system through production of the minor 50V isotope. However, because V only possesses two stable isotopes it is difficult to distinguish irradiation from other processes such as stable isotope fractionation and nucleosynthetic heterogeneity that could also cause V isotope variation. Here we perform the first detailed investigation of V isotopes in ordinary and carbonaceous chondrites to investigate the origin of any variation. We also perform a three-laboratory inter-calibration for chondrites, which confirms that the different chemical separation protocols do not induce V isotope analytical artifacts as long as samples are measured using medium resolution multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS). Vanadium isotope compositions (51V/50V) of carbonaceous chondrites correlate with previously reported nucleosynthetically derived excesses in 54Cr. Both 51V and 54Cr are the most neutron-rich of their respective elements, which may suggest that pre-solar grains rich in r-process isotopes is the primary cause of the V–Cr isotope correlation. Vanadium isotope ratios of ordinary chondrite groups and Earth form a weaker correlation with 54Cr that has a different slope than observed for carbonaceous chondrites. The offset between carbonaceous and non-carbonaceous meteorites in V–Cr isotope space is similar to differences also reported for chromium, titanium, oxygen, molybdenum and ruthenium isotopes, which has been inferred to reflect the presence in the early solar system of two physically separated reservoirs. The V isotope composition of Earth is heavier than any meteorite measured to date. Therefore, V isotopes support models of Earth accretion in which a significant portion of Earth was formed from material that is not present in our meteorite collections. Highlights • Vanadium isotopes in bulk carbonaceous chondrites correlate with ε 54 Cr. • Vanadium isotopes in bulk chondrites controlled by nucleosynthetic anomalies. • Parent body metamorphism does not affect vanadium isotopes in bulk meteorites. • Earth likely accreted primarily from material not found in our meteorite collection. [ABSTRACT FROM AUTHOR]

Elevated abundances of highly siderophile elements in Earth's mantle are thought to reflect the late accretion of primitive material after the cessation of core formation, but the origin of this material, and whether or not it can be linked to specific types of meteorites remain debated. Here, mass-dependent Ru isotopic data for chondrites and terrestrial peridotites are reported to evaluate the chemical nature and type of the late-accreted material. After correction for nucleosynthetic Ru isotope anomalies, enstatite, ordinary and carbonaceous chondrites all have indistinguishable mass-dependent Ru isotopic compositions. Thus, neither distinct formation conditions in the solar nebula nor parent body processes resulted in significant mass-dependent Ru isotope fractionation. All five terrestrial peridotites analyzed have mass-dependent Ru isotopic compositions that are indistinguishable from each other and from the composition of chondrites. The chondritic mass-dependent Ru isotopic composition of Earth's mantle is difficult to reconcile with prior suggestions that the late accretionary assemblage was a mixture of chondrites with a chemically evolved metal component. Although this mixture can reproduce the suprachondritic Ru/Ir inferred for Earth's mantle, it consistently predicts a heavy Ru isotopic composition of Earth's mantle with respect to chondrites. This is because metal components with elevated Ru/Ir are also enriched in heavy Ru isotopes, resulting from isotope fractionation during core crystallization. Thus, if late accretion involved impacts of differentiated protoplanetary bodies, then the projectile cores must have been either homogenized upon impact, or added to Earth's mantle completely, because otherwise Earth's mantle would have inherited a non-chondritic mass-dependent Ru isotopic composition from the unrepresentative sampling of core material. [ABSTRACT FROM AUTHOR]

When corrected for the effects of cosmic ray exposure, Mo and Ru nucleosynthetic isotope anomalies in iron meteorites from at least nine different parent bodies are strongly correlated in a manner consistent with variable depletion in s -process nucleosynthetic components. In contrast to prior studies, the new results show no significant deviations from a single correlation trend. In the refined Mo–Ru cosmic correlation, a distinction between the non-carbonaceous (NC) group and carbonaceous chondrite (CC) group is evident. Members of the NC group are characterized by isotope compositions reflective of variable s -process depletion. Members of the CC group analyzed here plot in a tight cluster and have the most s -process depleted Mo and Ru isotopic compositions, with Mo isotopes also slightly enriched in r - and possibly p -process contributions. This indicates that the nebular feeding zone of the NC group parent bodies was characterized by Mo and Ru with variable s -process contributions, but with the two elements always mixed in the same proportions. The CC parent bodies sampled here, by contrast, were derived from a nebular feeding zone that had been mixed to a uniform s -process depleted Mo–Ru isotopic composition. Six molybdenite samples, four glacial diamictites, and two ocean island basalts were analyzed to provide a preliminary constraint on the average Mo isotope composition of the bulk silicate Earth (BSE). Combined results yield an average μ 97 Mo value of +3 ± 6. This value, coupled with a previously reported μ 100 Ru value of +1 ± 7 for the BSE, indicates that the isotopic composition of the BSE falls precisely on the refined Mo–Ru cosmic correlation. The overlap of the BSE with the correlation implies that there was homogeneous accretion of siderophile elements for the final accretion of 10 to 20 wt% of Earth's mass. The only known cosmochemical materials with an isotopic match to the BSE, with regard to Mo and Ru, are some members of the IAB iron meteorite complex and enstatite chondrites. [ABSTRACT FROM AUTHOR]

The approximately chondritic relative, and comparatively high absolute mantle abundances of the highly siderophile elements (HSE), suggest that their concentrations in the bulk silicate Earth were primarily established during a final ∼0.5 to 1% of “late accretion” to the mantle, following the cessation of core segregation. Consequently, the isotopic composition of the HSE Ru in the mantle reflects an amalgamation of the isotopic compositions of late accretionary contributions to the silicate portion of the Earth. Among cosmochemical materials, Ru is characterized by considerable mass-independent isotopic variability, making it a powerful genetic tracer of Earth's late accretionary building blocks. To define the Ru isotopic composition of the oceanic mantle, the largest portion of the accessible mantle, we report Ru isotopic data for materials from one Archean and seven Phanerozoic oceanic mantle domains. A sample from a continental lithospheric mantle domain is also examined. All samples have identical Ru isotopic compositions, within analytical uncertainties, indicating that Ru isotopes are well mixed in the oceanic mantle, defining a μ 100 Ru value of 1.2 ± 7.2 (2SD). The only known meteorites with the same Ru isotopic composition are enstatite chondrites and, when corrected for the effects of cosmic ray exposure, members of the Main Group and sLL subgroup of the IAB iron meteorite complex which have a collective CRE corrected μ 100 Ru value of 0.9 ± 3.0 . This suggests that materials from the region(s) of the solar nebula sampled by these meteorites likely contributed the dominant portion of late accreted materials to Earth's mantle. [ABSTRACT FROM AUTHOR]

Abstract: The timing of sub-continental lithospheric mantle (SCLM) differentiation beneath Spitsbergen, western Svalbard, has been determined with spinel peridotite xenoliths using two complementary isotopic systems: Lu–Hf and Re–Os. The whole-rock Re–Os systematics (Re–Os errorchron, aluminochron, and Re-depletion age) define Paleoproterozoic/Neoarchean ages for isolation of the studied peridotites from the convecting mantle. We note that the age is independently supported by the Lu–Hf errorchron for the peridotite clinopyroxene grains, and average degree of melt depletion recorded in the samples. The obtained ages are indistinguishable from the oldest crustal ages reported in western Spitsbergen, implying that the mantle lithosphere in this area was stabilized at the same time as formation of the overlying crust. Our data suggest that the Spitsbergen lithosphere is unlikely to have undergone bulk lithospheric delamination since the tectonic transition from transpressional to transtensional which commenced in the Paleocene. We thus discount the delaminated and reactivated SCLM as a potential source for the Dupal-like enriched components in the Arctic upper mantle suggested by other studies. [ABSTRACT FROM AUTHOR]