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This work was supported by PhD funding to MM by the University of St Andrews School of Earth and Environmental Sciences and the Handsel scheme, as well as by NERC grant NE/R002134/1 to PS and NSF grant EAR-1321954 to RR and RG. Twenty-four composite samples of the fine-grained matrix of glacial diamictites deposited from the Mesoarchaean to Palaeozoic have been analysed for their silicon isotope composition and used to establish, for the first time, the long-term secular Si isotope record of the compositional evolution of upper continental crust (UCC). Diamictites with Archaean and Palaeoproterozoic Nd model ages show greater silicon isotope heterogeneity than those with younger model ages (irrespective of depositional age). We attribute the anomalously light Si isotope compositions of some diamictites with Archaean model ages to the presence of glacially milled banded iron formation (BIF), substantiated by the high iron content and Ge/Si in these samples. We infer that relatively heavy Si isotope signatures in some Palaeoproterozoic diamictites (all of which have Archaean Nd model ages) are due to contribution from tonalite-trondhjemite-granodiorites (TTGs), evidenced by the abundance of TTG clasts. By the Neoproterozoic (with model ages ranging from 2.3 to 1.8 Ga), diamictite Si isotope compositions exhibit a range comparable to modern UCC. This reduced variability through time is interpreted as reflecting the decreasing importance of BIF and TTG in post-Archaean continental crust. The secular evolution of Si isotopes in the diamictites offers an independent test of models for the emergence of stable cratons and the onset of horizontal mobile-lid tectonism. The early Archaean UCC was heterogeneous and incorporated significant amounts of isotopically light BIF, but following the late Archaean stabilisation of cratons, coupled with the oxygenation of the atmosphere that led to the reduced neoformation of BIF and diminishing quantities of TTGs, the UCC became increasingly homogeneous. This homogenisation likely occurred via reworking of preexisting crust, as evidenced by Archaean Nd model ages recorded in younger diamictites. Publisher PDF

This work was supported by NSF grants EAR-1447404 and EAR-1650033, and NERC grant NE/R002134/1. PS would also like to cite the support of a Carnegie Trust Research Incentive Grant, which helped the setup of various isotope techniques in the St Andrews Isotope Geochemistry (STAiG) laboratories. FM thanks the ERC under the European Community’s H2020 framework program/ERC grant agreement # 637503 (Pristine) and for the UnivEarthS Labex program (no. ANR-10-LABX-0023 and ANR-11-IDEX-0005-02). Parts of this work were supported by IPGP multidisciplinary program PARI, and by Region île-de-France SESAME Grant (no. 12015908). The silicon isotope composition of detrital quartz and zircon have the potential to inform us about secular changes to the silica cycle and weathering reactions on Earth. However, inferring source melt Si isotope composition from out-of-context minerals is hampered by the fact that, to-date, there is limited Si isotope equilibrium fractionation data for minerals. Here, we report experimental data to constrain Si isotope equilibrium fractionation between zircon and quartz, using two fundamentally different strategies, but with the same experimental design. First, zircon and quartz were hydrothermally synthesized from Zr(OH)4 and SiO2 at 1.5 GPa and temperatures of 725, 800, and 900 oC. The second experimental strategy utilized the three-isotope method; the starting materials consisted of natural zircon and isotopically-labelled SiO2. Three sets of hydrothermal time-series experiments were conducted at the same pressure and temperatures as the direct synthesis experiments. For all experiments, quartz and zircon were separated and 30Si/28Si and 29Si/28Si ratios were measured by solution multi-collector inductively coupled plasma mass spectrometry. The three-isotope method, which provides the best indicator of equilibrium fractionations, yields the following relationship: Δ30Si(qtz-zrc) = (0.53±0.14) × 106 /T2 where Δ30Si(qtz-zrc) is the relative difference in 30Si/28Si between quartz and zircon in permil, T is temperature in K, and the error is 2 s.e. This relationship can be used to calculate the fractionation between zircon and other phases, and to estimate the Si isotope composition of the melt from which a zircon crystallized. The results may be used to assess equilibrium-disequilibrium isotope fractionations between quartz and zircon and co-existing phases in igneous rocks. These data can also be applied to out-of-context zircon (and quartz) to estimate the isotope composition of the host rock. Zircons crystallizing from a melt derived from purely igneous sources – i.e., without the involvement of “weathered” material – are expected to display a δ30SiNBS-28 (permil deviation of the 30Si/28Si from the NBS-28 standard) range from -0.7 to -0.35‰. Deviations from this range indicate assimilation of non-igneous (i.e., sedimentary) material in the melt source. Postprint

FM acknowledge funding from ERC grant agreement No. 101001282 (METAL), the UnivEarthS Labex program (numbers: ANR-10-LABX-0023 and ANR-11-IDEX-0005-02), the IPGP multidisciplinary program PARI, the Region île-de-France SESAME Grants no. 12015908, EX047016, and the IdEx Université de Paris grant, ANR-18-IDEX-0001 and the DIM ACAV+. The source of and timing of delivery of the volatile elements to Earth is a question that is fundamental to understanding how our planet evolved. Here, we show that primitive meteorites have resolved mass-independent Zn isotope anomalies from the terrestrial reservoir. Carbonaceous chondrites (CC), likely originating from the outer Solar System are distinct from non-CC, and Earth is intermediate between these two components. Modelling based on these data indicates that around 30% of Earth's budget of Zn and other moderately volatile material derives from the participation of 6% of CC-like materials during Earth's accretion, with the remaining coming from NC meteorites. This implies that, despite the relatively minor mass of Earth thought to derive from CC-like material, the CC component of Earth was relatively and significantly volatile-enriched; this is in line with the observation that the terrestrial elemental abundance pattern of moderately volatile elements could be explained by a carbonaceous source, and with the carbonaceous chondrite-like isotopic budget of more volatile-rich material accreted later in Earth's accretion history (e.g. Hg, Se, N, noble gases). Publisher PDF

SF and the Si isotope measurements at STAiG were supported by NERC grant NE/R002134/1 to PS; PS would also like to cite the support of a Carnegie Trust Research Incentive Grant, which helped the setup of various isotope techniques in the St Andrews Isotope Geochemistry (STAiG) laboratories. C.D. Coath is thanked for laboratory support and the European Research Council is acknowledged for funding (ICY-LAB, grant agreement 678371). The use of silicon (Si) isotopes has led to major advances in our understanding of Si cycling in modern and past environments. This inter‐laboratory comparison exercise provides the community with the first set of soil and plant reference materials with an analytically challenging matrix containing organic material that is known to induce isotopic bias, for use as secondary reference materials in Si isotope measurement. Seven laboratories analysed four soil reference materials (GBW‐07401, GBW‐07404, GBW‐07407, TILL‐1) and one plant reference material (ERM‐CD281). Participating laboratories employed a range of chemical preparation methods and analytical setups but all analyses were performed by MC‐ICP‐MS. Irrespective of the chemical preparation method or analytical conditions, the results show excellent agreement among laboratories within 2s for at least three replicates. Data were combined together to calculate δ29Si and δ30Si mean values (relative to NBS 28) and their expanded uncertainties (U, coverage factor k = 2). The δ30Si values are as follow: GBW‐07401: ‐0.27 ± 0.06 ‰, GBW‐07404: ‐0.76 ± 0.12 ‰, GBW‐07407: ‐1.82 ± 0.17 ‰, TILL‐1: ‐0.16 ± 0.06 ‰ and ERM‐CD281: ‐0.28 ± 0.11 ‰. Also, a compilation of published data provides an up‐to‐date mean δ30Si for BHVO‐2 of ‐0.28 ± 0.08 ‰. Postprint

This research was supported by NERC award NE/L002590/1 to the IAPETUS DTP, and by NERC Standard Grant NE/J023485/2 to A.L.Z. The initiation of Cu isotope analysis at the University of St Andrews was aided significantly by a Carnegie Trust Research Incentive Grant awarded to P.S.S. The rise of oxygenic photosynthesis arguably represents the most important evolutionary step in Earth history. Recent studies, however, suggest that Earth’s pre-oxidative atmosphere was also heavily influenced by biological feedbacks. Most notably, recent geochemical records propose the existence of a hydrocarbon haze which periodically formed in response to enhanced biospheric methane fluxes. Copper isotopes provide a potential proxy for biological methane cycling; Cu is a bioessential trace metal and a key element in the aerobic oxidation of methane to carbon dioxide (methanotrophy). In addition, Cu isotopes are fractionated during biological uptake. Here, we present a high-resolution Cu isotope record measured in a suite of shales and carbonates from core GKF01, through the ~2.6–2.5 Ga Campbellrand-Malmani carbonate platform. Our data show a 0.85‰ range in Cu isotope composition and a negative excursion that predates the onset of a haze event. We interpret this excursion as representing a period of enhanced aerobic methane oxidation before the onset of the Great Oxidation Event. This places valuable time constraints on the evolution of this metabolism and firmly establishing Cu isotopes as a biomarker in Late Archaean rocks. Postprint

This work was supported by NASA grant NNX17AE84G (to R.M.). Magnesium isotopic measurements were supported by NSF grant EAR-17407706 (to F.-Z. T.). P.S. and the Si isotope measurements made at the St Andrews Isotope Group (STAiG) at the University of St Andrews were supported by NERC grant NE/R002134/1 a Carnegie Trust Research Incentive Grant. Evaporation experiments at Hokkaido University were supported by the Ministry of Education, Sports, Science, and Technology KAKENHI Grant (to S.T.). It is widely believed that the precursors of coarse-grained CAIs in chondrites are solar nebula condensates that were later reheated and melted to a high degree. Such melting under low-pressure conditions is expected to result in evaporation of moderately volatile magnesium and silicon and their mass-dependent isotopic fractionation. The evaporation of silicate melts has been extensively studied in vacuum laboratory experiments and a large experimental database on chemical and isotopic fractionations now exists. Nevertheless, it remains unclear if vacuum evaporation of CAI-like melts adequately describes the evaporation in the hydrogen-rich gas of the solar nebula. Here we report the results of a detailed experimental study on evaporation of a such melt at 1600°C in both vacuum and low-pressure hydrogen gas, using 1.5- and 2.5-mm diameter samples. The experiments show that although at 2×10−4 bar H2 magnesium and silicon evaporate ∼2.8 times faster than at 2×10−5 bar H2 and ∼45 times faster than in vacuum, their relative evaporation rates and isotopic fractionation factors remain the same. This means that the chemical and isotopic evolutions of all evaporation residues plot along a single evaporation trajectory regardless of experimental conditions (vacuum or low-PH2) and sample size. The independence of chemical and isotopic evaporation trajectories on PH2 of the surrounding gas imply that the existing extensive experimental database on vacuum evaporation of CAI-like materials can be safely used to model the evaporation under solar nebula conditions, taking into account the dependence of evaporation kinetics on PH2. The experimental data suggest that it would take less than 25 minutes at 1600°C to evaporate 15–50% of magnesium and 5–20% of silicon from a 2.5-mm diameter sample in a solar nebula with PH2∼2×10−4 bar and to enrich the residual melt in heavy magnesium and silicon isotopes up to δ25Mg ∼ 5–10‰ and δ29Si ∼ 2–4‰. The expected chemical and isotopic features are compatible to those typically observed in coarse-grained Type A and B CAIs. Evaporation for ∼1 hour will produce δ25Mg ∼30–35‰ and δ29Si ∼10–15‰, close to the values in highly fractionated Type F and FUN CAIs. These very short timescales suggest melting and evaporation of CAI precursors in very short dynamic heating events. The experimental results reported here provide a stringent test of proposed astrophysical models for the origin and evolution of CAIs. Postprint

The difference in the Si isotopic composition between the Earth and primitive meteorites had been used to constrain the amount of Si in the Earth's core. However, there is presently a debate on the magnitude of the isotopic fractionation between metal and silicates as function of temperature based on experimental data. Here, we use a natural sample, an enstatite meteorite, Itqyi, as a natural experiment to determine an independent Si isotopic fractionation factor between metal and silicate. We determined the temperature of equilibrium between metal and silicate as well as the Si isotopic composition between the phases. We find that the dependence of Si isotopes with temperature to be: Δ 30 Si silicate-metal = 7.6 ( ± 0.7 ) × 10 6 ( 1 S D ) T 2 Using this dependence of the δ30Si with temperature we estimate the bulk Earth δ30Si as a function of Si content of the core for different plausible conditions. Even when using the most extreme parameters, we show that the bulk Earth must be isotopically heavier than any chondrites groups. We therefore confirm that core formation alone cannot account for the isotopic difference between the Earth and primitive meteorites. We show that there is no correlation between δ30Si and the Mg/Si ratio suggesting that forsterite fractionation in the solar nebula may have had only a limited effect, if any. Our new results therefore confirm that volatility should have had a fundamental effect in shaping terrestrial planets chemical composition.

F.M. acknowledges funding from the European Research Council (ERC) under Horizon 2020 Framework Programme/ERC Grant Agreement 637503 (Pristine). F.M. and M.C. acknowledge the financial support of the UnivEarthS Labex Program at Sorbonne Paris Cité (Grants ANR-10-LABX-0023 and ANR-11-IDEX-0005-02). Parts of this work were supported by IPGP Plateau d’Analyse haute Résolution (PARI) and by Region Île-de-France Sesame Grant 12015908. Indirect evidence for the presence of a felsic continental crust, such as the elevated 49Ti/47Ti ratios in Archean shales, has been used to argue for ongoing subduction at that time and therefore plate tectonics. However, rocks of intermediate to felsic compositions can be produced in both plume and island arc settings. The fact that Ti behaves differently during magma differentiation in these two geological settings might result in contrasting isotopic signatures. Here, we demonstrate that, at a given SiO2 content, evolved plume rocks (tholeiitic) are more isotopically fractionated in Ti than differentiated island arc rocks (mainly calc-alkaline). We also show that the erosion of crustal rocks from whether plumes (mafic in average) or island arcs (intermediate in average) can all produce sediments having quite constant 49Ti/47Ti ratios being 0.1–0.3 per mille heavier than that of the mantle. This suggests that Ti isotopes are not a direct tracer for the SiO2 contents of crustal rocks. Ti isotopes in crustal sediments are still a potential proxy to identify the geodynamical settings for the formation of the crust but only if combined with additional SiO2 information. Postprint

This work was supported by NSF Grants EAR-1447404 and EAR-1650033. The ion microprobe facility at UCLA is partially supported by the Instrumentation and Facilities Program, Division of Earth Sciences, NSF (EAR-1339051 and EAR-1734856). The LA-ICP-MS instrument at the University of Rochester is partially supported by EAR-1545637. P.B. is supported by the University of Chicago Chamberlin Postdoctoral Fellowship. Hydrosphere interactions and alteration of the terrestrial crust likely played a critical role in shaping Earth’s surface, and in promoting prebiotic reactions leading to life, before 4.03 Ga (the Hadean Eon). The identity of aqueously altered material strongly depends on lithospheric cycling of abundant and water-soluble elements such as Si and O. However, direct constraints that define the character of Hadean sedimentary material are absent because samples from this earliest eon are limited to detrital zircons (ZrSiO4). Here we show that concurrent measurements of Si and O isotope ratios in Phanerozoic and detrital pre-3.0 Ga zircon constrain the composition of aqueously altered precursors incorporated into their source melts. Phanerozoic zircon from (S)edimentary-type rocks contain heterogeneous δ18O and δ30Si values consistent with assimilation of metapelitic material, distinct from the isotopic character of zircon from (I)gneous- and (A)norogenic-type rocks. The δ18O values of detrital Archean zircons are heterogeneous, although yield Si isotope compositions like mantle-derived zircon. Hadean crystals yield elevated δ18O values (vs. mantle zircon) and δ30Si values span almost the entire range observed for Phanerozoic samples. Coupled Si and O isotope data represent a constraint on Hadean weathering and sedimentary input into felsic melts including remelting of amphibolites possibly of basaltic origin, and fractional addition of chemical sediments, such as cherts and/or banded iron formations (BIFs) into source melts. That such sedimentary deposits were extensive enough to change the chemical signature of intracrustal melts suggests they may have been a suitable niche for (pre)biotic chemistry as early as 4.1 Ga. Postprint

Authors thank the McDonnell Center for the Space Sciences and the UK National Environment Research Council for their support. Funding for this work was provided in part by NERC grant NE/R002134/1. High-temperature equilibrium and kinetic stable isotope fractionation during partial melting, fractional crystallization, and other igneous differentiation processes has been observed in many isotope systems, but due to the relative nascence of high-precision analytical capabilities for K, it is still unclear whether igneous processes induce systematic and resolvable K isotope fractionation. In this study, we look to the natural laboratory of Hekla volcano in Iceland to investigate the behavior of K isotopes during magmatic differentiation of basalt to rhyolite. Using a novel MC-ICP-MS method, we analyzed 24 geochemically diverse samples from Hekla, including 7 basalts, 8 basaltic andesites, 3 andesites, 4 dacites, and 2 rhyolites, along with 2 additional samples from Burfell, Iceland, for comparison (1 basalt and 1 trachyte). We observed extremely limited variation of 41K/39K ratios throughout our suite of samples, which is not resolvable within the best current analytical uncertainty. The average value of all samples is δ41KNIST SRM3141a = −0.46 ± 0.07‰ (2sd). This value agrees with the Bulk Silicate Earth value previously defined by average global oceanic basalts in literature. The lack of variation throughout this suite of samples from a single volcano system indicates that K does not fractionate during magmatic differentiation (of basalt to rhyolite) through processes such as partial melting and fractional crystallization. This conclusion is important to the estimation of the Bulk Silicate Earth K isotope composition, to placing a more robust estimate on the composition bulk continental crust, and to fostering a better understanding of the behavior of K isotopes during differentiation of the terrestrial planets. Postprint

We thank the ERC under the European Community’s H2020 framework program/ERC grant agreement # 637503 (Pristine)) and for the UnivEarthS Labex program (no. ANR-10-LABX-0023 and ANR-11-IDEX-0005-02). Parts of this work were supported by IPGP multidisciplinary program PARI, and by Region île-de-France SESAME Grant (no. 12015908). High-precision double-spike Zr stable isotope measurements (expressed as δ94/90ZrIPGP-Zr, the permil deviation of the 94Zr/90Zr ratio from the IPGP-Zr standard) are presented for a range of ocean island basalts (OIB) and mid-ocean ridge basalts (MORB) to examine mass-dependent isotopic variations of zirconium in Earth. Ocean island basalts samples, spanning a range of radiogenic isotopic flavours (HIMU, EM) show a limited range in δ94/90ZrIPGP-Zr (0.046 ± 0.037 ‰; 2sd, n=13). Similarly, MORB samples with chondrite-normalized La/Sm of > 0.7 show a limited range in δ94/90ZrIPGP-Zr (0.053 ± 0.040 ‰; 2sd, n=8). In contrast, basaltic lavas from mantle sources that have undergone significant melt depletion, such as depleted normal MORB (N-MORB) show resolvable variations in δ94/90ZrIPGP-Zr, from -0.045 ± 0.018 to 0.074 ± 0.023 ‰. Highly evolved igneous differentiates (>65 wt% SiO2) from Hekla volcano in Iceland are isotopically heavier than less evolved igneous rocks, up to 0.53 ‰. These results suggest that both mantle melt depletion and extreme magmatic differentiation leads to resolvable mass-dependent Zr isotope fractionation. We find that this isotopic fractionation is most likely driven by incorporation of light isotopes of Zr within the 8-fold coordinated sites of zircons, driving residual melts, with a lower coordination chemistry, towards heavier values. Using a Rayleigh fractionation model, we suggest a αzircon-melt of 0.9995 based on the whole rock δ94/90ZrIPGP-Zr values of the samples from Hekla volcano (Iceland). Zirconium isotopic fractionation during melt-depletion of the mantle is less well-constrained, but may result from incongruent melting and incorporation of isotopically light Zr in the 8-fold coordinated M2 site of orthopyroxene. Based on these observations lavas originating from the effect of melt extraction from a depleted mantle source (N-MORB) or that underwent zircon saturation (SiO2 >65 wt%) are removed from the dataset to give an estimate of the primitive mantle Zr isotope composition of 0.048 ± 0.032 ‰; 2sd, n=48. These data show that major controls on Zr fractionation in the Earth result from partial melt extraction in the mantle and by zircon fractionation in differentiated melts. Conversely, fertile mantle is homogenous with respect to Zr isotopes. Zirconium mass-dependent fractionation effects can therefore be used to trace large-scale mantle melt depletion events and the effects of felsic crust formation. Publisher PDF

Silicon (Si) is the defining element of silicate reservoirs yet, despite its dominance in major Earth processes, there is still no clear understanding of how much is hosted in Earth's core, how the enriched continental crust forms or even if the crust is isotopically different from the mantle because of a long history of weathering, erosion and subduction. With the advent of multiple collector inductively coupled plasma mass spectrometry it has become relatively straightforward to explore small (100 ppm level) mass dependent variations in Si isotopic composition resulting from high temperature fractionation and to develop new isotopic fingerprints of magmatic processes and source regions. This paper reviews the technique developments, the new data and the veracity of current interpretations. Only a small Si isotopic effect is associated with basalt formation via mantle melting. However, there now is compelling evidence, based on a considerable number of samples (> 100), that the silicate Earth is isotopically fractionated by 100–200 ppm per amu to a heavy composition relative to that of chondrites and also all differentiated stony meteorites. This could reflect variability in the circumstellar disc, but this is not well supported by data for enstatite chondrites which are isotopically light. The most plausible current explanation is that Si is a light element in Earth's core and that differences in the bond stiffness between silicate- and metal-hosted Si resulted in substantial fractionation. Interestingly, the Moon has the same Si isotope composition as Earth's mantle, which is hard to explain unless the Moon's atoms were mainly derived from Earth. Differentiated magmatic sequences such as those of Hekla, Iceland display a systematic relationship between isotopic composition and Si content. More complex magmatic suites, such as I- and S-type granites, reveal a range of isotopic compositions not well correlated with chemical composition. Similar effects are found in lower crustal granulite facies xenoliths. Nonetheless the overall composition of the continental crust is only slightly heavy relative to the mantle; in fact the effect is barely resolvable. Therefore, the amounts of surface dissolved heavy Si removed to the mantle via weathering over time have been small or these losses have been balanced by subduction of isotopically light clay.

International audience; Core formation is the main differentiation event in the history of a planet. However, the chemical composition of planetary cores and the physicochemical conditions prevailing during core formation remain poorly understood. The asteroid 4-Vesta is the smallest extant planetary body known to have differentiated a metallic core. Howardite, Eucrite, Diogenite (HED) meteorites, which are thought to sample 4-Vesta, provide us with an opportunity to study core formation in planetary embryos. Partitioning of elements between the core and mantle of a planet fractionates their isotopes according to formation conditions. One such element, silicon, shows large isotopic fractionation between metal and silicate, and its partitioning into a metallic core is only possible under very distinctive conditions of pressure, oxygen fugacity and temperature. Therefore, the silicon isotope system is a powerful tracer with which to study core formation in planetary bodies. Here we show through high-precision measurement of Si stable isotopes that HED meteorites are significantly enriched in the heavier isotopes compared to chondrites. This is consistent with the core of 4-Vesta containing at least 1 wt% of Si, which in turn suggests that 4-Vesta's differentiation occurred under more reducing conditions (ΔIW∼−4) than those previously suggested from analysis of the distribution of moderately siderophile elements in HEDs.

The upper continental crust (UCC) is the major source of silicon (Si) to the oceans and yet its isotopic composition is not well constrained. In an effort to investigate the degree of heterogeneity and provide a robust estimate for the average Si isotopic composition of the UCC, a representative selection of well-characterised, continentally-derived clastic sediments have been analysed using high-precision MC-ICPMS. Analyses of loess samples define a narrow range of Si isotopic compositions (δ30Si = −0.28‰ to −0.15‰). This is thought to reflect the primary igneous mineralogy and predominance of mechanical weathering in the formation of such samples. The average loess δ30Si is −0.22 ± 0.07‰ (2 s.d.), identical to average granite and felsic igneous compositions. Therefore, minor chemical weathering does not resolvably affect bulk rock δ30Si, and loess is a good proxy for the Si isotopic composition of unweathered, crystalline, continental crust. The Si isotopic compositions of shales display much more variability (δ30Si = −0.82‰ to 0.00‰). Shale Si isotope compositions do not correlate well with canonical proxies for chemical weathering, such as CIA values, but do correlate negatively with insoluble element concentrations and Al/Si ratios. This implies that more intensive or prolonged chemical weathering of a sedimentary source, with attendant desilicification, is required before resolvable negative Si isotopic fractionation occurs. Shale δ30Si values that are more positive than those of felsic igneous rocks most likely indicate the presence of marine-derived silica in such samples. Using the data gathered in this study, combined with already published granite Si isotope analyses, a weighted average composition of δ30Si = −0.25 ± 0.16‰ (2 s.d.) for the UCC has been calculated.

The zinc stable isotope system has been successfully applied to many and varied fields in geochemistry, but to date it is still not completely clear how this isotope system is affected by igneous processes. In order to evaluate the potential application of Zn isotopes as a proxy for planetary differentiation and volatile history, it is important to constrain the magnitude of Zn isotopic fractionation induced by magmatic differentiation. In this study we present high-precision Zn isotope analyses of two sets of chemically diverse, cogenetic samples from Kilauea Iki lava lake, Hawaii, and Hekla volcano, Iceland, which both show clear evidence of having undergone variable and significant degrees of magmatic differentiation. The Kilauea Iki samples display small but resolvable variations in Zn isotope composition (0.26‰

Copper, a native metal found in ores, is the principal metal in bronze and brass. It is a reddish metal with a density of 8920 kg m−3. All of copper’s compounds tend to be brightly colored: for example, copper in hemocyanin imparts a blue color to blood of mollusks and crustaceans. Copper has three oxidation states, with electronic configurations of Cu([Ar]3 d 104 s 1), Cu+([Ar]3 d 10), and Cu2+([Ar]3 d 9). Cu does not react with aqueous hydrochloric or sulfuric acids, but is soluble in concentrated nitric acid due to its lesser tendency to be oxidized. Cu(I) exists as the colorless cuprous ion, Cu+. Cu(II) is found as the sky-blue cupric ion, Cu2+. The Cu+ ion is unstable, and tends to disproportionate to Cu and Cu2+. Nevertheless, Cu(I) forms compounds such as Cu2O. Cu(I) bonds more readily to carbon than Cu(II), hence Cu(I) has an extensive chemistry with organic compounds. In aqueous solutions, Cu2+ ion occurs as an aquacomplex. There is no clearly predominant structure among the four-, five-, and six-fold coordinated Cu(II) species (Chaboy et al. 2006). Hydrated Cu(II) ion has been represented as the hexaaqua complex Cu(H2O)62+, which shows the Jahn–Teller distortion effect (Sherman 2001; Bersuker 2006), whereby the two Cu–O distances of the vertical axial bond (Cu–Oax) are longer than four Cu–O distances in the equatorial plane (Cu–Oeq). The Jahn–Teller effect lowers the symmetry of Cu(H2O)62+ from octahedral Th to D2h. The sixfold coordination of hydrated Cu(II) species is questioned by a finding of fivefold coordination (Pasquarello et al. 2001; Chaboy et al. 2006; Little et al. 2014b …

JP was partly supported by NERC fellowship NE/H01313X/2. AB was supported by a Janet Watson Earth Science and Engineering Departmental PhD studentship and MW was supported in part by an undergraduate research opportunity award from Imperial College London. Trace element analyses were supported from US NSF Grant EAR-1456814 to TP. Stable thallium (Tl) isotopes are an extremely sensitive tracer for the addition of small amounts of sediments or materials altered at low temperatures to the source(s) of mantle-derived melts. The ability of Tl to trace such materials is due to the large concentration contrast between the mantle (Tl < 2 ng/g) and possible exotic inputs (Tl ~ 100 ng/g to > μg/g), which also often display fractionated Tl isotope compositions. However, the magnitude of Tl isotope fractionation induced by igneous processes alone has not been systematically assessed. Here, two suites of co-genetic magmas, spanning a large range of differentiation, from Hekla, Iceland, and Anatahan, in the Mariana arc, are used to assess the behavior of thallium and its stable isotope variations during magmatic processes. Thallium behaves as a near-perfectly incompatible lithophile element throughout magmatic evolution, mirroring elements such as Rb, Cs, and K. Lavas from Hekla have restricted Cs/Tl ratios and stable Tl isotope compositions, which overlap with mantle estimates. Lavas from subduction-related Anatahan volcano also have a restricted range in Tl isotope composition, which overlaps with Hekla and MORB, demonstrating that fractional crystallisation and partial melting does not fractionate stable Tl isotopes. Subduction environments display variable Cs/Tl, indicating that the subduction process commonly fractionates these two elements. The immunity of thallium stable isotopes to fractionation by magmatic processes coupled with its extreme sensitivity for tracing pelagic sediments, FeMn crusts and low temperature altered oceanic crust highlight its value in elucidating the nature of mantle sources of both oceanic basalts and arc lavas. Critically, meaningful interpretation of thallium isotope compositions need not be restricted to primitive lavas. Postprint

The silicon (Si) cycle is of great current interest but the isotopic composition of the continental crust has not been determined. Magmatic differentiation generates liquids with heavier Si and the lower crust, thought to be dominated by cumulates and restites, is predicted to have a light isotopic composition. This is borne out by the composition of many types of granite, which appear to have relative light Si for their silica content. Here we report the Si isotopic compositions of two granulite facies xenolith suites, from the Chudleigh and McBride volcanic provinces, Australia, providing new constraints on deep crustal processes and the average composition of the deep continental crust. The xenoliths display a range of isotopic compositions (δ30Si=−0.43‰ to −0.15‰) comparable to that measured previously for igneous rocks. The isotopic compositions of the McBride xenoliths reflect assimilation and fractional crystallisation (AFC) and/or partial melting processes. Silicon and O isotopes are correlated in the McBride suite and can be explained by AFC of various evolved parent melts. In contrast, the Chudleigh xenoliths have Si isotope compositions predominantly controlled by the specific mineralogy of individual cumulates. Using the xenolith data and a number of weighting methods, the Si isotope compositions of the lower and middle crust are calculated to be δ30Si=−0.29±0.04‰ (95% s.e.) and −0.23±0.04‰ (95% s.e.) respectively. These values are almost identical to the composition of the Bulk Silicate Earth, implying minimal isotope fractionation associated with continent formation and no light lower crustal reservoir.

Of the primitive meteorite groups, the enstatite chondrites are among the most chemically dissimilar to terrestrial, which should preclude them as major components of the proto-Earth. However, for many isotope systems (most notably oxygen), enstatite chondrites show very little variation away from terrestrial, hinting at a common origin. One isotope system which appears to differ from this trend is silicon, but no satisfactory explanation has been proposed as to why these meteorites should be significantly lighter than both the silicate Earth and other primitive meteorite groups. This study presents a comprehensive investigation into the Si isotope composition of enstatite chondrites and their differentiated counterparts, the aubrites, and confirms that these meteorites are, with respect to Si isotopes, the lightest macroscale solar system objects so far analysed. Crucially, the results show that EH chondrites are significantly lighter (δ30Si=−0.77±0.08‰) than EL chondrites (δ30Si=−0.59±0.09‰) and aubrites (δ30Si=−0.60±0.11‰). Silicon isotope analyses of the metal-free components of EH and EL reveal that these are identical, within error, to each other and with carbonaceous/ordinary chondrite bulk measurements (viz., δ30Si ∼−0.47), which is taken as evidence that Si isotope variation in the nebular gas is not the cause of the light Si isotope enrichment in enstatite chondrites. From this, one can infer that silicates condensing from the solar nebula over a wide range of compositions and, presumably, heliocentric distances have very similar Si isotope compositions. A statistically significant negative correlation between bulk δ30Si and Si content in enstatite chondrite kamacite indicates that the presence of isotopically light Si in the metal phase (as the result of formation under reducing conditions) is the principal cause of the bulk enrichment in lighter Si isotopes. Based on the Si isotope offset between enstatite meteorites and the silicate Earth, the extant enstatite meteorites cannot represent a significant proportion of the material that accreted to form the proto-Earth, as unfeasibly large amounts of Si would have to enter the core to satisfy mass balance equations. However, we posit that material enriched in refractory lithophile elements which condensed in the same region as E-chondrites, could still be an important component.

JP was funded by NERC postdoctoral fellowship NE/H01313X/2, with support of the Oxford laboratories from an Advanced ERC grant (NEWISOTOPEGEOSCIENCE) to ANH. PAS by an APA PhD scholarship and ANU Vice-Chancellor’s Scholarship. Recycling pathways of multivalent elements, that impact our understanding of diverse geological processes from ore formation to the rise of atmospheric oxygen, depend critically on the spatial and temporal variation of oxygen fugacity (fO2) in the Earth’s interior. Despite its importance, there is currently no consensus on the relative fO2 of the mantle source of mid-ocean ridge basalts compared to the sub-arc mantle, regions central to the mediation of crust-mantle mass balances. Here we present the first stable vanadium isotope measurements of arc lavas, complemented by non-arc lavas and two co-genetic suites of fractionating magmas, to explore the potential of V isotopes as a redox proxy. Vanadium isotopic compositions of arc and non-arc magmas with similar MgO overlap with one another. However, V isotopes display strikingly large, systematic variations of ~2 ‰ during magmatic differentiation in both arc and non-arc settings. Calculated bulk V Rayleigh fractionation factors (1000 lnαmin-melt of -0.4 to -0.5 ‰) are similar regardless of the oxidation state of the evolving magmatic system, which implies that V isotope fractionation is most influenced by differences in bonding environment between minerals and melt rather than changes in redox conditions. Thus, although subtle fO2 effects may be present, V isotopes are not a direct proxy for oxygen fugacity in magmatic systems. Publisher PDF

Thirty-five mafic and ultramafic rocks have been analysed for their silicon isotopic composition to very high precision with the aim of providing a robust average value for the silicate earth. This is of importance to studies using the difference between meteorite and terrestrial isotope composition to quantify silicon sequestration during core formation and, also, for understanding crustal processes. The δ 30 Si values of the samples are more limited than previously reported, ranging between just − 0.39 and − 0.23‰ despite significant variations in chemical and other isotopic compositions. A hint of a trend exists between δ 30 Si and both SiO 2 and Al 2 O 3 , which can be explained by concentration of the heavier isotopes in the melt as a function of silica polymerisation. Our best estimate for the δ 30 Si of the bulk silicate earth (BSE) is − 0.29 ± 0.08‰ (2 s.d.).

The silicon (Si) isotope compositions of 42 meteorite and terrestrial samples have been determined using MC-ICPMS with the aim of resolving the current debate over their compositions and the implications for core formation. No systematic δ30Si differences are resolved between chondrites (δ30Si=-0.49±0.15‰, 2σSD) and achondrites (δ30Si=-0.47±0.11‰, 2σSD), although enstatite chondrites are consistently lighter (δ30Si=-0.63±0.07‰, 2σSD) in comparison to other meteorite groups. The data reported here for meteorites and terrestrial samples display an average difference Δ30SiBSE-meteorite*=0.15±0.10‰, which is consistent within uncertainty with previous studies. No effect from sample heterogeneity, preparation, chemistry or mass spectrometry can be identified as responsible for the reported differences between current datasets. The heavier composition of the bulk silicate Earth is consistent with previous conclusions that Si partitioned into the metal phase during metal-silicate equilibration at the time of core formation. Fixing the temperature of core formation to the peridotite liquidus and using an appropriate metal silicate fractionation factor (ε∼0.89), the Δ30SiBSE-meteorite* value from this study indicates that the Earth core contains at least 2.5 and possibly up to 16.8wt% Si. © 2011 Elsevier Ltd.

Because weathering results in preferential incorporation of the lighter Si isotopes into clay minerals, the Si in magmas derived from (meta)sedimentary lithologies enriched in such phases should also be isotopically light, relative to melts derived from igneous sources. With the advent of new high precision techniques it should therefore be possible to resolve such differences. Hence, Si isotopes have to potential to distinguish between, and characterise, different magmatic source regions.To explore this, here we report the Si isotopic compositions of a suite of Phanerozoic I-, S- and A-type granites and mineral separates, as well as samples of associated country rock. The whole-rock data fall between δ 30Si=-0.40 and -0.11±0.04‰ (95%s.e.). This range is more limited than that defined by previous low precision measurements of granites, but is significantly broader than that displayed by more recent, high precision, measurements of high-Si extrusive igneous rocks. As predicted, S-type granites are, on average, isotopically lighter than I- and A-type samples, and negative correlations with alumina saturation index (ASI) values and initial 87Sr/ 86Sr provide evidence that Si isotope variations in granites can be explained by variable incorporation of an enriched sedimentary component. However, the relatively small isotopic perturbations and apparent degree of overlap between granite affinities suggest that Si isotopes are not as sensitive to sedimentary input, relative to more established proxies such as, for example, O isotopes. The average Si isotope value of all granites analysed in this study is δ 30Si=-0.23±0.15‰ (2s.d.), which is entirely consistent with a recently published estimate for the continental crust, based on an andesitic bulk composition and the well defined relationship between Si isotopes and magmatic fractionation. © 2012 Elsevier Ltd.

The study of silicon (Si) isotopes in ocean island basalts (OIB) has the potential to discern between different models for the origins of geochemical heterogeneities in the mantle. Relatively large (several per mil per atomic mass unit) Si isotope fractionation occurs in low-temperature environments during biochemical and geochemical precipitation of dissolved Si, where the precipitate is preferentially enriched in the lighter isotopes relative to the dissolved Si. In contrast, only a limited range (tenths of a per mil) of Si isotope fractionation has been observed from high-temperature igneous processes. Therefore, Si isotopes may be useful as tracers for the presence of crustal material within OIB mantle source regions that experienced relatively low-temperature surface processes in a manner similar to other stable isotope systems, such as oxygen. Characterizing the isotopic composition of the mantle is also of central importance to the use of the Si isotope system as a basis for comparisons with other planetary bodies (e.g., Moon, Mars, asteroids). Here we present the first comprehensive suite of high-precision Si isotope data obtained by MC-ICP-MS for a diverse suite of OIB. Samples originate from ocean islands in the Pacific, Atlantic, and Indian Ocean basins and include representative end-members for the EM-1, EM-2, and HIMU mantle components. On average, Si isotope compositions of OIB are in general agreement with previous estimates for the Si isotope composition of bulk silicate Earth. Nonetheless, some small systematic variations are present; specifically, most HIMU-type (Mangaia; Cape Verde; La Palma, Canary Islands) and Iceland OIB are enriched in the lighter isotopes of Si, consistent with recycled altered oceanic crust and lithospheric mantle in their mantle sources., Comment: 23 pages, 5 figures, 2 tables

The differentiation of Earth into a metallic core and silicate mantle left its signature on the chemical and isotopic composition of the bulk silicate Earth (BSE). This is seen in the depletion of siderophile (metal-loving) relative to lithophile (rock-loving) elements in Earth’s mantle as well as the silicon isotope offset between primitive meteorites (i.e. bulk Earth) and BSE, which is generally interpreted as a proof that Si is present in Earth’s core. Another putative light element in Earth’s core is sulphur; however, estimates of core S abundance vary significantly and, due to its volatile nature, no unequivocal S isotopic signature for core fractionation has thus far been detected. Here we present new high precision isotopic data for Cu, a chalcophile (sulphur-loving) element, which shows that Earth’s mantle is isotopically fractionated relative to bulk Earth. Results from high pressure equilibration experiments suggest that the sense of Cu isotopic fractionation between BSE and bulk Earth requires that a sulphide-rich liquid segregated from Earth’s mantle during differentiation, which likely entered the core. Such an early-stage removal of a sulphide-rich phase from the mantle presents a possible solution to the long-standing 1st terrestrial lead paradox. Publisher PDF

International audience; Inner solar system bodies, including the Earth, Moon, and asteroids, are depleted in volatile elements relative to chondrites. Hypotheses for this volatile element depletion include incomplete condensation fromthe solar nebula and volatile loss during energetic impacts. These processes are expected to each produce characteristic stable isotope signatures. However, processes of planetary differentiation may also modify the isotopic composition of geochemical reservoirs. Angrites are rare meteorites that crystallized only a few million years after calcium - aluminum-rich inclusions and exhibit extreme depletions in volatile elements relative to chondrites, making them ideal samples with which to study volatile element depletion in the early solar system. Here we present high-precision Si isotope data that show angrites are enriched in the heavy isotopes of Si relative to chondritic meteorites by 50-100 ppm/amu. Silicon is sufficiently volatile such that it may be isotopically fractionated during incomplete condensation or evaporative mass loss, but theoretical calculations and experimental results also predict isotope fractionation under specific conditions of metal-silicate differentiation. We show that the Si isotope composition of angrites cannot be explained by any plausible core formation scenario, but rather reflects isotope fractionation during impact-induced evaporation. Our results indicate planetesimals initially formed from volatile-rich material and were subsequently depleted in volatile elements during accretion.

Despite their unusual chemical composition, it is often proposed that the enstatite chondrites represent a significant component of Earth’s building materials, based on their terrestrial similarity for numerous isotope systems. In order to investigate a possible genetic relationship between the Fe isotope composition of enstatite chondrites and the Earth, we have analyzed 22 samples from different subgroups of the enstatite meteorites, including EH and EL chondrites, aubrites (main group and Shallowater) and the Happy Canyon impact melt. We have also analyzed the Fe isotopic compositions of separated (magnetic and non-magnetic) phases from both enstatite chondrites and achondrites. On average, EH3–5 chondrites (δ56Fe = 0.003 ± 0.042‰; 2 standard deviation; n = 9; including previous literature data) as well as EL3 chondrites (δ56Fe = 0.030 ± 0.038‰; 2 SD; n = 2) have identical and homogeneous Fe isotopic compositions, indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite. In contrast, EL6 chondrites display a larger range of isotopic compositions (−0.180‰ Enstatite achondrites (aubrites) also exhibit a relatively large range of Fe isotope compositions: all main group aubrites are enriched in the light Fe isotopes (δ56Fe = −0.170 ± 0.189‰; 2 SD; n = 6), while Shallowater is, isotopically, relatively heavy (δ56Fe = 0.045 ± 0.101‰; 2 SD; n = 4; number of chips). We take this variation to suggest that the main group aubrite parent body formed a discreet heavy Fe isotope-enriched core, whilst the Shallowater meteorite is most likely from a different parent body where core and silicate material remixed. This could be due to intensive impact-induced shearing stress, or the ultimate destruction of the Shallowater parent body. Analysis of separated enstatite meteorite mineral phases show that the magnetic phase (Fe metal) is systematically enriched in the heavier Fe isotopes when compared to non-magnetic phases (Fe hosted in troilite), which agrees with previous experimental observations and theoretical calculations. The difference between magnetic and non-magnetic phases from enstatite achondrites provides an equilibrium metal–sulfide Fe isotopic fractionation factor of Δ56Femetal–troilite = δ56Femetal − δ56Fetroilite of 0.129 ± 0.060‰ (2 SE) at 1060 ± 80 K, which confirms the predictions of previous theoretical calculations.

International audience; To examine the iron (Fe) isotopic heterogeneities of CI and ordinary chondrites, we have analyzed several large chips (approximately 1 g) from three CI chondrites and three ordinary chondrites (LL5, L5, and H5). The Fe isotope compositions of five different samples of Orgueil, one from Ivuna and one from Alais (CI chondrites), are highly homogeneous. This new dataset provides a δ56Fe average of 0.02 ± 0.04‰ (2SE, n = 7), which represents the best available value for the Fe isotopic composition of CI chondrites and probably the best estimate of the bulk solar system. We conclude that the homogeneity of CI chondrites reflects the initial Fe isotopic homogeneity of the well-mixed solar nebula. In contrast, larger (up to 0.26‰ in δ56Fe) isotopic variations have been found between separate approximately 1 g pieces of the same ordinary chondrite sample. The Fe isotope heterogeneities in ordinary chondrites appear to be controlled by the abundances of chondritic components, specifically chondrules, whose Fe isotope compositions have been fractionated by evaporation and recondensation during multiple heating events.

The Si isotopic composition of Earth’s mantle is thought to be homogeneous (δ 30 Si = −0.29 ± 0.08‰, 2 s.d.) and not greatly affected by partial melting and recycling. Previous analyses of evolved igneous material indicate that such rocks are isotopically heavy relative to the mantle. To understand this variation, it is necessary to investigate the degree of Si isotopic fractionation that takes place during magmatic differentiation. Here we report Si isotopic compositions of lavas from Hekla volcano, Iceland, which has formed in a region devoid of old, geochemically diverse crust. We show that Si isotopic composition varies linearly as a function of silica content, with more differentiated rocks possessing heavier isotopic compositions. Data for samples from the Afar Rift Zone, as well as various igneous USGS standards are collinear with the Hekla trend, providing evidence of a fundamental relationship between magmatic differentiation and Si isotopes. The effect of fractionation has been tested by studying cumulates from the Skaergaard Complex, which show that olivine and pyroxene are isotopically light, and plagioclase heavy, relative to the Si isotopic composition of the Earth’s mantle. Therefore, Si isotopes can be utilised to model the competing effects of mafic and felsic mineral fractionation in evolving silicate liquids and cumulates. At an average SiO 2 content of ∼60 wt.%, the predicted δ 30 Si value of the continental crust that should result from magmatic fractionation alone is −0.23 ± 0.05‰ (2 s.e.), barely heavier than the mantle. This is, at most, a maximum estimate, as this does not take into account weathered material whose formation drives the products toward lighter δ 30 Si values. Mass balance calculations suggest that removal of continental crust of this composition from the upper mantle will not affect the Si isotopic composition of the mantle.

International audience; LA-ICP-MS analysis of the chemical composition of biogenic carbonate has many applications in the environmental sciences but the characteristics of the material produced by the ablation process are largely unknown. To fill this gap, we have undertaken a study of the chemical and physical nature of particles produced by laser ablation of biogenic carbonates. SEM imaging suggests that laser ablation produces two distinct particle populations, one consisting of microsize particles and the other of nanosize particles. A 213 nm laser gives rise to a higher proportion of microsize particles than a 193 nm laser, probably because the 213 nm laser couples less completely with carbonate material. The microsize particles appear to form by photomechanical fracturing along lines of cleavage or weakness, rather than by hydrodynamic sputtering (as is generally observed for silicates). Chemical analysis of the carbonate particles suggests that little chemical fractionation of biogenic carbonates occurs during the ablation process or during transport to the plasma. This is supported by the constancy of the fractionation factor ([X/Ca](measured)/[X/Ca] true) during the course of an ablation of a carbonate standard. In contrast, changes in the fractionation factor during the first few seconds of ablation of the NIST 612 are observed for some elements. This difference in fractionation is likely to result from the different formation mechanisms of the microsize particles.

International audience; The presence or absence of variations in the mass-independent abundances of Si isotopes in bulk meteorites provides important clues concerning the evolution of the early solar system. No Si isotopic anomalies have been found within the level of analytical precision of 15 ppm in 29Si/28Si across a wide range of inner solar system materials, including terrestrial basalts, chondrites, and achondrites. A possible exception is the angrites, which may exhibit small excesses of 29Si. However, the general absence of anomalies suggests that primitive meteorites and differentiated planetesimals formed in a reservoir that was isotopically homogenous with respect to Si. Furthermore, the lack of resolvable anomalies in the calcium-aluminum-rich inclusion measured here suggests that any nucleosynthetic anomalies in Si isotopes were erased through mixing in the solar nebula prior to the formation of refractory solids. The homogeneity exhibited by Si isotopes may have implications for the distribution of Mg isotopes in the solar nebula. Based on supernova nucleosynthetic yield calculations, the expected magnitude of heavy-isotope overabundance is larger for Si than for Mg, suggesting that any potential Mg heterogeneity, if present, exists below the 15 ppm level.

This study has been funded through the Czech Science Foundation project 13-22351S. Paul Savage was supported by the Marie Curie IOF ‘Isovolc.’ Frederic Moynier is grateful to the European Research Council under the European Community's H2020 framework program/ERC grant agreement # 637503 (Pristine) and the Agence Nationale de la Recherche for a chaire d'Excellence Sorbonne Paris Cité (IDEX13C445), and for the UnivEarthS Labex program (ANR-10-LABX-0023 and ANR-11-IDEX-0005-02). Parts of this work were supported by IPGP multidisciplinary program PARI, and by Region Île-de-France SESAME Grant no. 12015908. Moldavites are tektites genetically related to the Ries impact structure, located in Central Europe, but the source materials and the processes related to the chemical fractionation of moldavites are not fully constrained. To further understand moldavite genesis, the Cu and Zn abundances and isotope compositions were measured in a suite of tektites from four different substrewn fields (South Bohemia, Moravia, Cheb Basin, Lusatia) and chemically diverse sediments from the surroundings of the Ries impact structure. Moldavites are slightly depleted in Zn (~10–20%) and distinctly depleted in Cu (>90%) relative to supposed sedimentary precursors. Moreover, the moldavites show a wide range in δ66Zn values between 1.7 and 3.7‰ (relative to JMC 3-0749 Lyon) and δ65Cu values between 1.6 and 12.5‰ (relative to NIST SRM 976) and are thus enriched in heavy isotopes relative to their possible parent sedimentary sources (δ66Zn = −0.07 to +0.64‰; δ65Cu = −0.4 to +0.7‰). In particular, the Cheb Basin moldavites show some of the highest δ65Cu values (up to 12.5‰) ever observed in natural samples. The relative magnitude of isotope fractionation for Cu and Zn seen here is opposite to oxygen-poor environments such as the Moon where Zn is significantly more isotopically fractionated than Cu. One possibility is that monovalent Cu diffuses faster than divalent Zn in the reduced melt and diffusion will not affect the extent of Zn isotope fractionation. These observations imply that the capability of forming a redox environment may aid in volatilizing some elements, accompanied by isotope fractionation, during the impact process. The greater extent of elemental depletion, coupled with isotope fractionation of more refractory Cu relative to Zn, may also hinge on the presence of carbonyl species of transition metals and electromagnetic charge, which could exist in the impact-induced high-velocity jet of vapor and melts. Postprint