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International audience; Mass-dependent K isotopic fractionations can be used to trace cosmochemical, geological, and biological processes such as evaporation/condensation, core formation, magmatic processes, weathering, and cellular metabolism. However, the application of stable K isotopes has been limited by major isobaric interferences from Ar, common on conventional multi-collector inductively-coupled-plasma mass-spectrometer (MC-ICP-MS), particularly for the low-K samples. Here, we present a set of high-precision K isotopic data acquired on terrestrial rocks, seawater, as well as a lunar meteorite using the recently released Nu Sapphire™ MC-ICP-MS that utilizes a collision cell to minimize Ar based interferences while maintaining remarkably high K sensitivity (≈ 2000 V/ppm). The influence of several parameters on the precision and accuracy of the K isotopic data has been evaluated, including total K concentration, K intensity mismatch between sample and standard, HNO3 molarity mismatch between sample and standard, and the presence of matrix elements. We found that the Nu Sapphire™ can be used to acquire precise and accurate data using as little as 125 ng of K, which represents an improvement by a factor 10 compared to what has been done on previous instruments. We present data for 23 previously analyzed samples; these data are highly consistent with literature values. On the other hand, accurate measurements are conditioned 1) to the close matching of sample and standard K intensities (a 1% mismatch creates a 0.02‰ offset on the 41K/39K ratio), and 2) to the absence of Ca (a Ca/K ratio of 1% creates a 0.069‰ offset on the 41K/39K ratio). In addition, Rb/K, Na/K, Ti/K and Cr/K ratio should also be maintained under 2.5% to avoid isotopic offset.We confirm the existence of significant mass-dependent K isotopic variations in terrestrial samples and that lunar rocks are isotopically heavier than terrestrial rocks. The incomparable sensitivity offered by the Nu Sapphire opens the possibility for high-precision K isotopic measurements across a wide range of samples for diverse applications.

Primitive chondrites have bulk compositions close to that of the solar photosphere, with however significant variations of elemental ratio relative to the solar composition, depending on the volatility of the elements considered. This is classically understood as indicating a primary geochemical signature due to the formation of the components of chondrites (refractory inclusions, chondrules and matrix), or of their precursors, through condensation of a gas of near solar composition, plus secondary variations due to processes such as (i) incomplete volatilization of presolar components, (ii) complex high-temperature exchanges between condensed phases and the nebular gas, and (iii) sorting and transport of grains in the accretion disk before accretion of chondrite parent bodies. Because most of the mass of chondrites is made by elements which condense at high temperatures, equilibrium condensation produces in general little isotopic fractionation for these elements. Silicon is however an exception with per mil level equilibrium isotopic fractionation at high temperature between the SiO gas and condensed silicates, allowing to use silicon isotopes in chondrites to constrain the origin of their components and to put at test scenarios of condensation. Individual components (chondrule fragments, isolated olivines in the matrix, and matrix fragments) of the carbonaceous chondrite Allende were separated and analysed at high-precision for their silicon isotopic composition. Large variations have been found among chondrules ( δ 30 Si from -0.86 ± 0.16‰ 2 s.e. to +0.04 ± 0.03‰ for 11 chondrules), isolated olivines ( δ 30 Si from -0.51 ± 0.12‰ 2 s.e. to +0.20 ± 0.10 ‰ for 12 olivines), and matrix ( δ 30 Si from -0.95 ± 0.08‰ 2 s.e. to -0.41 ± 0.01 ‰ for 17 matrix fragments). These variations distribute on both sides of the bulk δ 30 Si value of Allende (-0.43 ± 0.03‰ 2 s.e., Armytage et al., 2011 ; Pringle et al., 2013 , Pringle et al., 2014 ; Savage and Moynier, 2013 ). There is a global positive trend between δ 30 Si values and Mg/Fe ratio for chondrules and isolated olivines. This systematics appears in agreement with what can be modeled for producing Allende components, or their precursors, from fractionated condensation of a single gaseous reservoir having initially the silicon isotopic composition of bulk Allende. Mass balance taking into account the mean abundances and δ 30 Si values of Allende components is consistent with their accretion in the Allende parent body in the proportions produced by the condensation of the parent parcel of nebular gas. This supports complementarity between chondrules, olivines and matrix as being a primary feature. However, this conclusion cannot be definitive because of the uncertainties in defining mean δ 30 Si values for Allende components.

Variations in the abundances of moderately volatile elements (MVE) are one of the most fundamental geochemical differences between the terrestrial planets. Whether these variations are the consequence of nebular processes, planetary volatilization, differentiation or late accretion is still unresolved. The element mercury is the most volatile of the MVE and is a strongly chalcophile element. It is one of the few elements that exhibit large mass-dependent (MDF) and mass-independent (MIF) isotopic fractionations for both odd (odd-MIF, Δ 199 Hg and Δ 201 Hg) and even (even-MIF, Δ 200 Hg) Hg isotopes in nature, which is traditionally used to trace Hg biogeochemical cycling in surface environments. However, the Hg isotopic composition of Earth and meteorites is not well constrained. Here, we present Hg isotopic data for terrestrial basaltic, trachytic and granitic igneous samples. These rocks are isotopically lighter ( δ 202 Hg = −3.3 ± 0.9‰; 1 standard deviation) than sedimentary rocks that have previously been considered to represent the terrestrial Hg isotope composition ( δ 202 Hg = − 0.7 ± 0.5 ‰ ; 1 standard deviation). We show degassing during magma emplacement induces MIF that are consistent with kinetic fractionation in these samples. Also presented is a more complete dataset for chondritic (carbonaceous, ordinary and enstatite) meteorites, which are consistent with previous work for carbonaceous chondrites (positive odd-MIF) and ordinary chondrites (no MIF), and demonstrate that some enstatite chondrites exhibit positive odd-MIF, similar to carbonaceous chondrites. The terrestrial igneous rocks fall within the range of chondritic compositions for both MIF and MDF. Given the fact that planetary differentiation (core formation, evaporation) would contribute to Hg loss from the silicate portion of Earth and would likely fractionate Hg isotopes from chondritic compositions, we suggest that the budget of the mantle Hg is dominated by late accretion of chondritic materials to Earth, as also suggested for other volatile chalcophile elements (S, Se, Te). Considering the Hg isotopic signatures, materials with compositions similar to CO chondrites or ordinary chondrites are the most likely late accretion source candidates. Finally, eucrite meteorites, which are highly depleted in volatile elements, are isotopically heavier than chondrites and exhibit negative odd-MIF. The origin of volatile depletion in eucrites has been vigorously debated. We show that Δ 199 Hg versus Δ 201 Hg relationships point toward an equilibrium nuclear field shift effect, suggesting that volatile loss occurred during a magma ocean phase at the surface of the eucrite parent body, likely the asteroid 4-Vesta.

International audience; Stable isotope fractionation in magmatic systems depends on equilibrium isotope fractionation between different phases. However, current equilibrium stable isotope theory mostly assumes ideal crystal structures and simple chemical compositions, but it is unclear how the pressure and complex compositional variations in natural microscopic mineral structures affect inter-mineral stable isotope fractionation and thus control stable isotope fractionation in macroscopic magmatic systems. Here, we calculate the Casingle bondO and Mgsingle bondO bond lengths controlled by pressure and compositional variations of coexisting garnet (Grt) and clinopyroxene (Cpx) in the Roberts Victor eclogites from the Kaapvaal Craton and use these data as a proof of concept to interpret their inter-mineral Ca and Mg isotopic compositions (Δ44/40CaGrt-Cpx and Δ26MgGrt-Cpx). Our results show that the Casingle bondO difference between Grt and Cpx (ΔCasingle bondOGrt-Cpx) shows a significant increase with CaO content from 3.4 to 13.6 wt.% in Grt and with pressure from 2.9 to 6.9 GPa. ΔCasingle bondOGrt-Cpx has an excellent negative correlation with inter-mineral Ca isotope fractionation corrected for temperature effect (Δ44/40CaGrt-Cpx × T2/106), indicating that inter-mineral Ca isotope fractionation is controlled by pressure and compositional variations of the Grt through effects on the bond lengths. Inter-mineral Mg isotope fractionation corrected for temperature effect (Δ26MgGrt-Cpx × T2/106) in these eclogites shows a negative correlation with pressure but no obvious correlations with the mineral compositions, suggesting the dominant role of pressure effect in addition to temperature. The Mgsingle bondO bond length of Grt increases by about 0.02 Å with increasing CaO content in Grt of these eclogites, implying a mild compositional effect on inter-mineral Mg isotope fractionation. The results suggest that pressure and compositional variations in minerals control the equilibrium stable isotope fractionation between minerals. Utilizing the Ca isotope fractionation factor controlled by crystal chemistry of garnet, our modelling indicates that partial melting of eclogite in the mantle could not significantly fractionate Ca isotopes and, therefore, that low δ44/40Ca values in previously reported basalts cannot be attributed to the involvement of eclogite in their sources. This suggests that crystal chemistry exerts major controls on isotope fractionation in magmatic systems in addition to temperature.

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.

International audience; We report stable Zr isotope compositions of four common natural zircon grains: Penglai, 91500, GJ-1 and Mud Tank, and 22 whole rock reference materials which include fifteen magmatic rocks, one metamorphic rock, six sediments or sedimentary rocks. In addition, the isotopic calibration of the three Zr standard solutions used in different publications (IPGP-Zr, SRM3169, NIST) has been determined. The data are reported as δ94/90ZrIPGP-Zr, the permille deviation of the 94Zr/90Zr ratio relative to the IPGP-Zr standard solution. The isotopic offsets among the three Zr standard solutions are small (less than 0.033 ± 0.033‰). The isotopic composition of the zircons agrees well with previous in-situ measurements, validating the in-situ measurements. On the other hand, all the samples analyzed in this study show a large range of Zr isotope compositions of 0.602‰. This confirms the fairly large natural Zr isotopic variations. The general variation of δ94/90ZrIPGP-Zr with magmatic evolution of the various igneous samples is in agreement with previous studies, with the most magmatically evolved samples being the isotopically heavier. The two magmatic zircons are isotopically lighter compared to the magmatic rocks, which is in agreement with the enrichment of heavy isotope in the evolved samples. This is ultimately controlled by the crystallization of isotopically light zircons.

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Sulfides are the main host of platinum-group elements (PGE) in the mantle and the stability of sulfide controls PGE mobilization and enrichment. The enrichment of PGE in mantle melts is generally interpreted as the result of complete dissolution of sulfide during the high-degree melting. However, the mechanism by which PGE are transferred from sulfides to the melt is not well known. Here we show that in areas where sedimentary carbonate is recycled, PGE mobility in the mantle could be greatly increased by the transformation of sulfide into sulfate. Carbonatitic xenoliths from the Neogene Dalihu basalt in Inner Mongolia represent sedimentary carbonates recycled into the mantle, documented by limestone-like trace element patterns and high 87Sr/86Sr ratios. They also contain micro-diamonds and silicate minerals with chemical features of mantle peridotite, showing that they must have resided in the mantle. However, the carbonatitic xenoliths contain 1000 times more PGE than sedimentary carbonate, indicating the incorporation of mantle sulfide. Moreover, δ 34 Ssulfate values (9.6-10.2‰) are much lower than in the original limestone source (25-35‰), and higher Ni, Cu contents in the carbonate groundmass than in sedimentary carbonates suggest that sulfide had been transformed into sulfate. With the destruction of sulfide, PGE contained in sulfide was released into the carbonate melt, thus promoting their mobility in the mantle.

International audience; Carbonaceous chondrites are often considered potential contributors of water and other volatiles to terrestrial planets as most of them contain significant amounts of hydrous mineral phases. As such, carbonaceous chondrites are candidate building blocks for Earth, and elucidating their thermal histories is of direct importance for understanding the volatile element history of Earth and the terrestrial planets. A significant fraction of CM type carbonaceous chondrites are thermally metamorphosed or "heated" and have lost part of their water content. The origin and the timing of such heating events are still debated, as they could have occurred either in the first Myrs of the Solar System via short-lived radioactive heating, or later by impact induced heating and/or solar radiation. Since Rb is more volatile than Sr, and some heated CM chondrites are highly depleted in Rb, a dating system based on the radioactive decay of Rb-87 to( 87)Sr(lambda(87) Rb = 1.393 x 10(-11) yr(-1)) could be used to date the heating event relating to the fractionation of Rb and Sr. Here, we have leveraged the Rb-87/Sr-87 system to date the heating of five CM chondrites (PCA 02012, PCA 02010, PCA 91008, QUE 93005 and MIL 07675). We find that the heating events of all five meteorites occurred at least 3 Ga after the formation of the Solar System. Such timing excludes short-lived radioactive heating as the origin of thermal metamorphism in these meteorites, and relates such heating events to ages of collisional families of C-type asteroids.

Melting of recycled carbonate in the mantle explains the origin of carbonatitic magmas., The origin of carbonatites—igneous rocks with more than 50% of carbonate minerals—and whether they originate from a primary mantle source or from recycling of surface materials are still debated. Calcium isotopes have the potential to resolve the origin of carbonatites, since marine carbonates are enriched in the lighter isotopes of Ca compared to the mantle. Here, we report the Ca isotopic compositions for 74 carbonatites and associated silicate rocks from continental and oceanic settings, spanning from 3 billion years ago to the present day, together with O and C isotopic ratios for 37 samples. Calcium-, Mg-, and Fe-rich carbonatites have isotopically lighter Ca than mantle-derived rocks such as basalts and fall within the range of isotopically light Ca from ancient marine carbonates. This signature reflects the composition of the source, which is isotopically light and is consistent with recycling of surface carbonate materials into the mantle.

Introduction Alzheimer’s disease (AD) is neuropathologically marked by amyloid beta (Aβ) plaques and neurofibrillary tangles. Little is known about isotopic compositions of human AD brains. Here we study this in comparison with control subjects for copper and zinc. Methods We use mass-spectrometry methods, developed to study extraterrestrial materials, to compare the copper and zinc isotopic composition of 10 AD and 10 con- trol brains. Results Copper and zinc natural isotopic compositions of AD brains are statistically different compared to controls, and correlate with Braak stages. Discussion The distribution of natural copper and zinc isotopes in AD is not affected by the diet, but is a consequence of Aβ plaques and tau fibril accumulation. This is well predicted by the changes of the chemical bonding environment caused by the develop- ment of Aβ lesions and accumulation of tau proteins. Future work will involve testing whether these changes affect brain functions and are propagated to body fluids.

The Apollo 16 ‘Rusty Rock’ impact melt breccia 66095 is a volatile-rich sample, with the volatiles inherited through vapor condensation from an internal lunar source formed during thermo-magmatic evolution of the Moon. We report Cu and Fe isotope data for 66095 and find that bulk-rocks, residues and acid leaches span a relatively limited range of compositions (3.0 ± 1.3 wt.% FeO [range = 2.0–4.8 wt.%], 5.4 ± 3.1 ppm Cu [range = 3–12 ppm], average δ56Fe of 0.15 ± 0.05‰ [weighted mean = 0.156‰] and δ65Cu of 0.72 ± 0.14‰ [weighted mean = 0.78‰]). In contrast to the extreme enrichment of the light isotopes of Zn and heavy isotopes of Cl in 66095, δ65Cu and δ56Fe in the sample lie within the previously reported range for lunar mare basalts (0.92 ± 0.16‰ and 0.12 ± 0.02‰, respectively). The lack of extreme isotopic fractionation for Cu and Fe isotopes reflects compositions inherent to 66095, with condensation of a cooling gas from impact-generated fumarolic activity at temperatures too low to lead to the condensation of Cu and Fe in the sample, but higher than required to condense Zn. Together with thermodynamic models, these constraints suggest that the gas condensed within 66095 between 700 and 900 °C (assuming a pressure of 10−6 and an fO2 of IW-2). That the Cu and Fe isotopic compositions of sample 66095 are within the range of mare basalts removes the need for an exotic, volatile-enriched source. The enrichment in Tl, Br, Cd, Sn, Zn, Pb, Rb, Cs, Ga, B, Cl, Li relative to Bi, Se, Te, Ge, Cu, Ag, Sb, Mn, P, Cr and Fe in the ‘Rusty Rock’ is consistent with volcanic outgassing models and indicates that 66095 likely formed distal from the original source of the gas. The volatile-rich character of 66095 is consistent with impact-generated fumarolic activity in the region of the Cayley Plains, demonstrating that volatile-rich rocks can occur on the lunar surface from outgassing of a volatile-poor lunar interior. The ‘Rusty Rock’ indicates that the lunar interior is significantly depleted in volatile elements and compounds and that volatile-rich surface rocks likely formed through vapor condensation. Remote sensing studies have detected volatiles on the lunar surface, attributing them dominantly to solar wind. Based on the ‘Rusty Rock’, some of these surface volatiles may also originate from the Moon’s interior.

International audience; Tektites are glasses derived from near-surface continental crustal rocks that were molten and ejected from the Earths surface during hypervelocity meteorite impacts. They are among the driest terrestrial samples, although the exact mechanism of water loss and the behaviour of other volatile species during these processes are debated. Based on the difference in magnitude of the Cu and Zn isotopic fractionations in tektites, and the difference of diffusivity between these elements, it was suggested that volatile loss was diffusion-limited. Tin is potentially well suited to testing this model, as it has a lower diffusivity in silicate melts than both Cu and Zn, but a similar volatility to Zn. Here, we analysed the Sn stable isotopic composition in a suite of seven tektites, representing three of the four known tektite strewn fields, and for which Zn and Cu isotopes were previously reported. Tin is enriched in the heavier isotopes (>= 2,5 parts per thousand on the Sn-122/Sn-118 ratio) in tektites, correlated with the degree of Sn elemental depletion in their respective samples as well as with Cu and Zn isotope ratios, implying a common control. While the isotope fractionation of Sn, Cu and Zn is a result of volatility, the magnitude of isotope fractionation is strongly moderated by their relative rates of diffusion in the molten tektite droplets. An Australasian Muong Nong-type tektite analysed has the least Sn depletion and Sn isotope fractionation, consistent with these samples being more proximal to the source and experiencing a shorter time at high temperatures

International audience; Here were report on a laboratory study aiming to reproduce specificities of near-Earth Asteroid. We study how the elevated surface temperature, their surface roughness (rock or regolith), as well as observation geometry can affect the absorption features detected on asteroids. For that purpose, we selected a recent carbonaceous chondrite fall, the Mukundpura CM2 chondrite which fell in India in June 2017. Bidirectional reflectance spectroscopy was performed to analyze the effect of the geometrical configuration (incidence, emergence and azimuth angle) on the measurement. Our results show that reflectance spectra obtained under warm environment (NEA-like) tends to show shallower absorption bands compared to low-temperature conditions (MBA-like), but still detectable in our experiments under laboratory timescales. Irreversible alteration of the sample because of the warm environment (from room temperature to 250°C) has been detected as an increase of the spectral slope and a decrease of the band depths (at 0.7{\mu}m, 0.9{\mu}m and 2.7{\mu}m). Comparing the meteoritic chip and the powdered sample, we found that surface texture strongly affects the shape of the reflectance spectra of meteorites and thus of asteroids, where a dust-covered surface presents deeper absorption features. We found that all spectral parameters, such as the reflectance value, spectral slope and possible absorption bands are affected by the geometry of measurement. We observed the disappearance of the 0.7 {\mu}m absorption feature at phase angle larger than 120°, but the 3{\mu}m band remains detectable on all measured spectra.

Significance An impasse exists between chemical and astrophysical models that explore the accretion of the Solar System’s building blocks, the chondrites. To resolve this issue means to gain an understanding of the dimensions of mass transport in the early Solar System and, hence, a crucial insight into the volatile inventory of the terrestrial planets. Here, we use element volatility patterns of chondrules and their dust rims to show that these main constituents of chondrites are not complementary to each other and did not form in the same chemical reservoirs. We propose a unifying chondrule and matrix accretion model that necessitates significant mass transport in the protoplanetary disk and an inward flux of volatile-rich CI-like (Ivuna-type carbonaceous chondrite) dust., The so far unique role of our Solar System in the universe regarding its capacity for life raises fundamental questions about its formation history relative to exoplanetary systems. Central in this research is the accretion of asteroids and planets from a gas-rich circumstellar disk and the final distribution of their mass around the Sun. The key building blocks of the planets may be represented by chondrules, the main constituents of chondritic meteorites, which in turn are primitive fragments of planetary bodies. Chondrule formation mechanisms, as well as their subsequent storage and transport in the disk, are still poorly understood, and their origin and evolution can be probed through their link (i.e., complementary or noncomplementary) to fine-grained dust (matrix) that accreted together with chondrules. Here, we investigate the apparent chondrule–matrix complementarity by analyzing major, minor, and trace element compositions of chondrules and matrix in altered and relatively unaltered CV, CM, and CR (Vigarano-type, Mighei-type, and Renazzo-type) chondrites. We show that matrices of the most unaltered CM and CV chondrites are overall CI-like (Ivuna-type) (similar to solar composition) and do not reflect any volatile enrichment or elemental patterns complementary to chondrules, the exception being their Fe/Mg ratios. We propose to unify these contradictory data by invoking a chondrule formation model in which CI-like dust accreted to so-called armored chondrules, which are ubiquitous in many chondrites. Metal rims expelled during chondrule formation, but still attached to their host chondrule, interacted with the accreted matrix, thereby enriching the matrix in siderophile elements and generating an apparent complementarity.

International audience; Extraterrestrial materials have He and Ne isotopic compositions that are distinct from those of the Earth's surface. In order to track the extraterrestrial material accreted onto Earth during the Ediacaran period, we have analyzed the He and Ne isotopic composition of thirteen sedimentary rocks in the age range similar to 550-600 Ma, coming from the Huqf supergroup in Oman for which carbon and sulfur isotopic data have been characterized previously.He-3/He-4 ratios range between 0.006 +/- 0.003 and 0.27 +/- 0.01 RA, with RA being the atmospheric ratio. He-3/He-4 ratios show a positive relationship with He-3 contents ranging between 0.6 and 31x10(-13) cm(3) STP.g(-1). The He-3 contents are within the literature data for 3 to 480 Myr old samples with evidence of IDP 3He (IDP for interplanetary dust particles), suggesting that extraterrestrial He-3 is still retained in such old samples.Ne-20/Ne-22 ratios are close to or below the modern atmospheric ratio of 9.8 with the minimum value equal to 9.05 +/- 0.03. Ne-21/Ne-22 ratios show a high range of variation, going from 0.0345 +/- 0.0009 to 0.0935 +/- 0.0023. The Ne isotopic compositions follow a nucleogenic trend similar to that of crustal fluids from the literature and predicted continental crust. However, one sample (3404) shows an unusual Ne isotopic composition with a lower Ne-20/Ne-22 at similar Ne-21/Ne-22 compared to the other samples.Two hypotheses can explain this singular Ne isotopic composition. First, it could be the result of a particular nucleogenic trend due to the presence of F-bearing minerals in this sample. SEM-EDS elemental mapping showed that although F-and Ca-rich phases, which could correspond to fluorites, are present in sample 3404. However, their abundance of similar to 0.15% seems too low to explain the unusual Ne isotopic composition. However, due to the high uncertainty of the calculations, we cannot totally rule out this hypothesis. Alternatively, the singular Ne isotopic composition could be due to the presence of a Ne-A component, a component characterizing pre-solar diamonds contained in chondrites. This would indicate that a major object impacted the Earth at the time the sediment was forming, between similar to 600 and similar to 550 Ma, which is coherent with the estimated age range of the Acraman impact in Australia.

Calcium stable isotopes are mainly fractionated during low-temperature geochemical processes and have, therefore, the potential to trace weathering and incorporation of recycled carbonated material in the mantle. However, behavior of Ca isotopes during mantle processes over Earth's history is not well understood. In this study, we present Ca isotopic compositions of 27 spinifex-textured and olivine cumulate komatiites ranging in age from 2.41 to 3.55 Ga. The Ca isotopic composition of all spinifex textured komatiites analyzed is similar, with an average δ44/40Ca = 0.92 ± 0.16‰ (n = 7; 2SD) (permil deviation of the 44Ca/40Ca ratio from SRM915a). This value is identical, within error, to the previous estimates of the composition of the mantle. In contrast, olivine cumulates from the Weltevreden Formation in the Barberton Greenstone Belt are isotopically heavier compared to the rest of the komatiites studied. While igneous processes and sea-floor alteration unlikely account for this Ca isotopic signature, crystallization of an early crust from a global magma ocean is a possibility, in agreement with previously obtained O, Os, Nd, Hf isotopic data and trace elements systematics.

International audience; Chondrules are the main components of primitive meteorites and possibly the building blocks of planetary embryos and terrestrial planets. However, their ages and modes of formation are still highly debated. Here, we present high-precision Cr isotope data of nine chondrules from one of the more primitive chondrites, the CO3 chondrite Ornans. These chondrules define an external Mn-53-Cr-53 isochron, with an initial Mn-53/Mn-55 of (7.1 +/- 1.6) x 10(-6), corresponding to an age of 4567.6 +/- 1.3 Ma when anchored to the angrite D'Orbigny (U-corrected). This age is within error of the age of formation of calcium-aluminum-rich inclusions (CAIs). All chondrules show a wide range of epsilon Cr-54 values (+0.20 to +1.22) and a positive correlation between epsilon Cr-53 and epsilon Cr-54 values, suggesting mixing of different isotopic sources in the protoplanetary disk. This could reflect that silicate materials from the CAI-forming region (with complementary compositions to CAIs, i.e., low Mn/Cr and epsilon Cr-54) were transported to the accretion region of the CO chondrite parent body and mixed with CI-like material (high-Mn/Cr and epsilon Cr-54) during chondrule formation. Such mixing must have occurred prior to the formation of chondrule precursors. Furthermore, chondrules from chondrites with more CAIs (CV and CO) exhibit greater variability in epsilon Cr-54 than chondrules from chondrites formed later with fewer CAIs (e.g., CB and CR), suggesting that the accretion regions of the former received more material transported from the inner solar system than the latter. This dichotomy may indicate the CB and CR chondrites accreted at greater orbital distances than other chondrites

Context. When and where planetesimals form in a protoplanetary disk are highly debated questions. Streaming instability is considered the most promising mechanism, but the conditions for its onset are stringent. Disk studies show that the planet forming region is not turbulent because of the lack of ionization forming possibly dead zones (DZs). Aims. We investigate planetesimal formation in an evolving disk, including the DZ and thermal evolution. Methods. We used a 1D time-evolving stratified disk model with composite chemistry grains, gas and dust transport, and dust growth. Results. Accretion of planetesimals always develops in the DZ around the snow line, due to a combination of water recondensation and creation of dust traps caused by viscosity variations close to the DZ. The width of the planetesimal forming region depends on the disk metallicity. For Z = Z⊙, planetesimals form in a ring of about 1 au width, while for Z > 1.2 Z⊙ planetesimals form from the snow line up to the outer edge of the DZ ≃ 20 au. The efficiency of planetesimal formation in a disk with a DZ is due to the very low effective turbulence in the DZ and to the efficient piling up of material coming from farther away; this material accumulates in region of positive pressure gradients forming a dust trap due to viscosity variations. For Z = Z⊙ the disk is always dominated in terms of mass by pebbles, while for Z > 1.2 Z⊙ planetesimals are always more abundant than pebbles. If it is assumed that silicate dust is sticky and grows up to impact velocities ~10 m s−1, then planetesimals can form down to 0.1 au (close to the inner edge of the DZ). In conclusion the DZ seems to be a sweet spot for the formation of planetesimals: wide scale planetesimal formation is possible for Z > 1.2 Z⊙. If hot silicate dust is as sticky as ice, then it is also possible to form planetesimals well inside the snow line.

Alzheimer’s disease is associated with the production of Cu rich aβ fibrils. Because monitoring the changes in Cu level of organs has been proposed to follow the evolution of the disease, we analyzed the copper isotopic composition of serum and brain of APPswe/PSEN1dE9 transgenic mice, a model of Alzheimer’s disease, and wild-type (WT) controls. Serum composition of 3, 6, 9 and 12-month-old mice, as well as the composition of 9 brains of 12-month-old mice are reported. In WT mice, brains were ~1‰ isotopically heavier than serum, and the Cu isotopic composition of the serum was isotopically different between males and females. We propose that this effect of sex on the Cu isotopic budget of the serum may be related to a difference of Cu speciation and relative abundance of Cu carriers. Brains of APPswe/PSEN1dE9 mice were slightly lighter than brains of WT mice, while not statistically significant. This trend may reflect an increase of Cu(I) associated with the formation of Aβ fibrils. The Cu isotopic composition of the brains and serum were correlated, implying copper transport between these two reservoirs, in particular a transfer of Cu(I) from the brain to the serum. Altogether, these data suggest that Cu stable isotopic composition of body fluid may have the potential to be used as detection tools for the formation of Aβ fibrils in the brain, but further work has to be done.

International audience; The existence of mass-independent chromium isotope variability of nucleosynthetic origin in meteorites and their components provides a means to investigate potential genetic relationship between meteorites and planetary bodies. Moreover, chromium abundances are depleted in most surficial terrestrial rocks relative to chondrites such that Cr isotopes are a powerful tool to detect the contribution of various types of extra-terrestrial material in terrestrial impactites. This approach can thus be used to constrain the nature of the bolide resulting in breccia and melt rocks in terrestrial impact structures. Here, we report the Cr isotope composition of impact rocks from the ~0.57 Ma Lonar crater (India), which is the best-preserved impact structure excavated in basaltic target rocks. Results confirm the presence of a chondritic component in several bulk rock samples of up to 3%. The impactor that created the Lonar crater had a composition that was most likely similar to that of carbonaceous chondrites, possibly a CM-type chondrite.

Identifying extant materials that act as compositional proxies for Earth is key to understanding its accretion. Copper and sulfur are both moderately volatile elements; however, they display different geochemical behavior (e.g., phase affinities). Thus, individually and together, these elements provide constraints on the source material and conditions of Earth's accretion, as well as on the timing and evolution of volatile delivery to Earth. Here we present laser-heated diamond anvil cell experiments at pressures up to 81 GPa and temperatures up to 4,100 K aimed at characterizing Cu metal-silicate partitioning at conditions relevant to core-mantle differentiation in Earth. Partitioning results have been combined with literature results for S in Earth formation modeling to constrain accretion scenarios that can arrive at present-day mantle Cu and S contents. These modeling results indicate that the distribution of Cu and S in Earth may be the result of accretion largely from material(s) with Cu contents at or above chondritic values and S contents that are strongly depleted, such as that in bulk CH chondrites, and that the majority of Earth's mass (similar to 3/4) accreted incrementally via pebble and/or planetesimal accretion., Plain Language Summary Experiments wherein molten metal and silicate (rock-building) phases unmix themselves due to their physical properties, that is, metal-silicate partitioning, can be conducted at the high temperatures and pressures (HP-HT) that characterized Earth's differentiation into a core and mantle. The redistribution of elements between the metal and silicate phases-their partitioning-during this process can be measured and mathematically described, then placed into numerical models to better understand Earth's formation history. Here we have mathematically characterized the HP-HT partitioning of copper, combined this with results for sulfur from literature, and input these characterizations into numerical models that track their distribution between Earth's core and mantle as it grows to its present mass. Copper and sulfur were chosen because they display different sensitivities to the physical mechanisms that govern planetary formation, and we can leverage this to better understand Earth's formation and differentiation history. Our results indicate that similar to 75% of Earth's precursor materials grew incrementally from relatively small bits of material-on average similar to 0.1% of Earth's mass or less-that is most compositionally similar to meteorite classes that are made up of iron-rich metal and silicate solids (chondrules) that are depleted in easily vaporized (volatile) elements, especially sulfur.

This study investigates the analogy between basaltic and borosilicate glasses of nuclear interest, by focusing on mechanisms controlling glass dissolution under silica saturation conditions. These conditions are representative of a non- or slowly renewed contacting solution, favouring the formation of a potentially passivating silica rich gel layer and secondary phases. Laboratory batch experiments were performed with synthetic basaltic glass altered at 90 °C, at pH 7 in a saturated 29Si-doped aqueous solution for more than 600 days. Using elemental and isotopic solution analysis and solid characterizations by SEM, TEM and ToF-SIMS, we show that basaltic glass corrodes at an unexpectedly high and constant dissolution rate of 4 × 10−3 g m−2 d−1 associated with the absence of passivating gel. Our results highlight the fact that the dissolution rate is controlled by the hydrolysis of the glassy network, sustained by the precipitation of clay-type minerals and amorphous silica. When tested in similar conditions, the International Simple Glass (ISG), a six oxide borosilicate glasses of nuclear interest displays a much lower rate limited by water diffusion through a passivating layer. The different behavior of the two glasses is explained by their ability to form secondary crystalline phases at the expense of an amorphous passivating film.

Zinc is a moderately volatile and slightly siderophile element, and therefore provides information into the timing and conditions of volatile element delivery to Earth as well as the redistribution of these elements during planetary differentiation. Specifically, due to its similar volatility with S, it has been assumed that the Earth and its source material maintain the same relative abundances of these elements, and therefore the same S/Zn ratio. In this study, we have conducted Zn metal-silicate partitioning experiments at pressures up to 81 GPa and temperatures up to 4100 K in diamond anvil cells, for two distinct silicate compositions (one pyrolitic, one basaltic) and varying S contents in order to characterize Zn metal-silicate partitioning as a function of these variables. These results have been input into Earth formation models where various parametric controls have been evaluated–namely source material, impactor size and volatile delivery–to determine plausible sets of conditions that can generate present-day bulk silicate Earth (BSE) Zn and S abundances. Modelling results indicate that to arrive at present-day BSE contents for Zn and S, and with core S contents of ∼2 wt% or less, the Earth likely accreted heterogeneously – initially from a volatile-depleted source material compositionally akin to the metal and silicate chondrules of CH chondrites, with later delivery of more volatile-rich material.

The depletion pattern of volatile elements on Earth and other differentiated terrestrial bodies provides a unique insight as to the nature and origin of planetary building blocks. The processes responsible for the depletion of volatile elements range from the early incomplete condensation in the solar nebula to the late de-volatilization induced by heating and impacting during planetary accretion after the dispersion of the H2-rich nebular gas. Furthermore, as many volatile elements are also siderophile (metal-loving), it is often difficult to deconvolve the effect of volatility from core formation. With the notable exception of the Earth, all the differentiated terrestrial bodies for which we have samples have non-chondritic Mn/Na ratios, taken as a signature of post-nebular volatilization. The bulk silicate Earth (BSE) is unique in that its Mn/Na ratio is chondritic, which points to a nebular origin for the depletion; unless the Mn/Na in the BSE is not that of the bulk Earth (BE), and has been affected by core formation through the partitioning of Mn in Earth's core. Here we quantify the metal–silicate partitioning behavior of Mn at deep magma ocean pressure and temperature conditions directly applicable to core formation. The experiments show that Mn becomes more siderophile with increasing pressure and temperature. Modeling the partitioning of Mn during core formation by combining our results with previous data at lower P–T conditions, we show that the core likely contains a significant fraction (20 to 35%) of Earth's Mn budget. However, we show that the derived Mn/Na value of the bulk Earth still lies on the volatile-depleted end of a trend defined by chondritic meteorites in a Mn/Na vs Mn/Mg plot, which tend to higher Mn/Na with increasing volatile depletion. This suggests that the material that formed the Earth recorded similar chemical fractionation processes for moderately volatile elements as chondrites in the solar nebula, and experienced limited post nebular volatilization.

Direct analysis of the composition of Mars is possible through delivery of meteorites to Earth. Martian meteorites include ∼165 to 2400 Ma shergottites, originating from depleted to enriched mantle sources, and ∼1340 Ma nakhlites and chassignites, formed by low degree partial melting of a depleted mantle source. To date, no unified model has been proposed to explain the petrogenesis of these distinct rock types, despite their importance for understanding the formation and evolution of Mars. Here we report a coherent geochemical dataset for shergottites, nakhlites and chassignites revealing fundamental differences in sources. Shergottites have lower Nb/Y at a given Zr/Y than nakhlites or chassignites, a relationship nearly identical to terrestrial Hawaiian main shield and rejuvenated volcanism. Nakhlite and chassignite compositions are consistent with melting of hydrated and metasomatized depleted mantle lithosphere, whereas shergottite melts originate from deep mantle sources. Generation of martian magmas can be explained by temporally distinct melting episodes within and below dynamically supported and variably metasomatized lithosphere, by long-lived, static mantle plumes., A unified model for the formation of martian rock types is required to understand Mars’s formation and evolution. Here the authors show that nakhlite and chassignite meteorites originate from melting of metasomatized depleted mantle lithosphere, whereas shergottite melts originate from deep plume sources.

International audience; U-Pb geochronology requires knowledge of a precise and accurate value for the 238 U/ 235 U ratio of any mineral or material being dated by this method. It is now well established that the long-accepted value of 137.88 is not representative of most terrestrial materials and that the ratio is variant both between and within samples. As most samples used for chronology have insufficient amounts of U to determine a precise isotopic composition, the U-Pb geochronology community has informally adopted the recommended value of 137.818 ± 0.045 based on a single data set of 44 zircons by Hiess et al. (2012). To evaluate the robustness of this value and the true range of U isotopic compositions in U-bearing minerals, we have measured the U isotopic composition of 28 bulk zircon samples as well as several co-existing accessory minerals from rocks with a wide range of ages and geographical distributions. The 238 U/ 235 U ratio of 137.817 ± 0.031 represents the mid-point value of our data with an uncertainty that includes all 28 zircon populations analyzed and their respective uncertainties. This value is indistinguishable from the previously recommended value but with a smaller uncertainty that may reflect the refined analytical methods employed in our study. This result provides confidence to the U-Pb geochronology community that the value recommended by Hiess et al. (2012) is appropriate and that their stated uncertainty appears to be conservative. We find variability in the 238 U/ 235 U ratio of coexisting phases within single samples of up to 2.9 e-units (parts per 10,000). In addition, our range of U isotopic compositions for zircon is heavier than that reported for bulk continental crust in general and most granitoid intrusive rocks specifically. We attribute these observations to differences in the coordination environment of U in zircon and other U-bearing phases. With the amount of zircon formed in magmatic systems limited by the abundance of Zr, we estimate that the majority of U in granitoid rocks must reside in other phases with a bulk isotopic composition that represents a lighter complement to that of zircon.

Carbonaceous chondrites (CCs) may have been the carriers of water, volatile and moderately volatile elements to Earth. Investigating the abundances of these elements, their relative volatility, and isotopes of state-change tracer elements such as Zn, and linking these observations to water contents, provide vital information on the processes that govern the abundances and isotopic signatures of these species in CCs and other planetary bodies. Here we report Zn isotopic data for 28 CCs (20 CM, 6 CR, 1 C2-ung, and 1 CV3), as well as trace element data for Zn, In, Sn, Tl, Pb, and Bi in 16 samples (8 CM, 6 CR, 1 C2-ung, and 1 CV3), that display a range of elemental abundances from case-normative to intensely depleted. We use these data, water content data from literature and Zn isotopes to investigate volatile depletions and to discern between closed and open system heating. Trace element data have been used to construct relative volatility scales among the elements for the CM and CR chondrites. From least volatile to most, the scale in CM chondrites is Pb-Sn-Bi-In-Zn-Tl, and for CR chondrites it is Tl-Zn-Sn-Pb-Bi-In. These observations suggest that heated CM and CR chondrites underwent volatile loss under different conditions to one another and to that of the solar nebula, e.g. differing oxygen fugacities. Furthermore, the most water and volatile depleted samples are highly enriched in the heavy isotopes of Zn. Taken together, these lines of evidence strongly indicate that heated CM and CR chondrites incurred open system heating, stripping them of water and volatiles concomitantly, during post-accretionary shock impact(s)., Comment: 4 tables, 5 figures

International audience; The terrestrial planets are depleted in volatile elements with respect to chondritic meteorites, their possible building blocks. However, the timing, extent and origin of volatile depletion is debated. Zinc is a moderately volatile element (MVE), whose stable isotopic composition can distinguish when and where this depletion took place. Here, we report data for 40 ultramafic rocks comprising pristine upper mantle peridotites from the Balmuccia orogenic lherzolite massif and Archean komatiites that together define the Zn isotope composition of the Earth's primitive mantle. Peridotites and komatiites are shown to have indistinguishable Zn isotopic compositions of delta Zn-66 = + 0.16 +/- 0.06% (2SD), (with delta Zn-66 the per mille deviation of Zn-66/Zn-64 from the JMC-Lyon standard), implying a constant Zn isotope composition for the silicate Earth since 3.5 Ga. After accounting for Zn sequestration during core formation, the Earth falls on the volatile-depleted end of a carbonaceous chondrite array in delta Zn-66-Zn/Mg space, implying Earth avoided modification of its MVE budgets during late accretion (e.g. during a giant impact), in contrast to the Moon. The Moon deviates from the chondritic array in a manner consistent with evaporative loss of Zn, where its delta Zn-66 co-varies with Mn/Na, implying post-nebular volatile loss is more pronounced on smaller bodies. Should the giant impact deliver the Earth's volatile complement of Pb and Ag, it cannot account for the budget of lithophile MVEs (e.g. Zn, Rb, Mn), whose abundances reflect those of Earth's nebular building blocks. The Earth initially accreted from material that experienced chemical- and mass-dependent isotopic fractionation akin to carbonaceous chondrites, though volatile depletion was more pronounced on Earth.

International audience; The mechanisms driving the chemical complementarity between depleted MORB mantle (DMM) and continental crust (with an average 'andesitic' composition) remain unclear. By investigating Archean komatiites, and modern enriched (E) and normal (N) MORB samples, we demonstrate that partial melting of the mantle does not fractionate Ti isotopes, whereas intracrustal differentiation causes significant Ti isotopic fractionation between melts and minerals, specifically Fe-Ti oxides. Thus, Ti isotope ratios are tracers of these two magmatic regimes. N-MORB and late Archean (2.9-2.7 Ga) komatiites are depleted in the heavier Ti isotopes compared to E-MORB and middle Archean (3.5-3.3 Ga) komatiites. We show that the depletion in the heavier Ti isotopes of the DMM is due to mantle recycling of the isotopically light residues from the generation of felsic continental crust over 3.5-2.7 Ga. This process must have reached a steady state by ≈ 2.5 Ga, based on the uniform Ti isotopic composition of contemporary N-MORBs and late Archean komatiites. This change is likely due to a decrease in the mantle potential temperature related to the emergence of plate tectonics.

The abundance of moderately volatile elements, such as Zn and Ga, show variable depletion relative to CI between the Earth and primitive meteorite (chondrites) parent bodies. Furthermore, the first solar system solids, the calcium–aluminum-rich inclusions (CAIs), are surprisingly rich in volatile element considering that they formed under high temperatures. Here, we report the Ga elemental and isotopic composition of a wide variety of chondrites along with five individual CAIs to understand the origin of the volatile elements and to further characterize the enrichment of the volatile elements in high temperature condensates. The δ 71 Ga (permil deviation of the 71Ga/69Ga ratio from the Ga IPGP standard) of carbonaceous chondrites decreases in the order of CI > CM > CO > CV and is inversely correlated with the Al/Ga ratio. This implies that the Ga budget of the carbonaceous chondrites parent bodies were inherited from a two component mixing of a volatile rich reservoir enriched in heavy isotope of Ga and a volatile poor reservoir enriched in light isotope of Ga. Calcium–aluminum-rich inclusions are enriched in Ga and Zn compared to the bulk meteorite and are both highly isotopically fractionated with δ 71 Ga down to −3.56‰ and δ 66 Zn down to −0.74‰. The large enrichment in the light isotopes of Ga and Zn in the CAIs implies that the moderately volatile elements were introduced in the CAIs during condensation in the solar nebula as opposed to secondary processing in the meteorite parent body and supports a change in gas composition in which CAIs were formed.

International audience

The Moon is depleted in volatile elements compared to Earth. Gallium isotopes indicate a global-scale evaporation event., The distribution and isotopic composition of volatile elements in planetary materials holds a key to the characterization of the early solar system and the Moon’s formation. The Moon and Earth are chemically and isotopically very similar. However, the Moon is highly depleted in volatile elements and the origin of this depletion is still debated. We present gallium isotopic and elemental measurements in a large set of lunar samples to constrain the origin of this volatile depletion. We show that while Ga has a geochemical behavior different from zinc, both elements show a systematic enrichment in the heavier isotopes in lunar mare basalts and Mg-suite rocks compared to the silicate Earth, pointing to a global-scale depletion event. On the other hand, the ferroan anorthosites are isotopically heterogeneous, suggesting a secondary distribution of Ga at the surface of the Moon by volatilization and condensation. The isotopic difference of Ga between Earth and the Moon and the isotopic heterogeneity of the crustal ferroan anorthosites suggest that the volatile depletion occurred following the giant impact and during the lunar magma ocean phase. These results point toward a Moon that has lost its volatile elements during a whole-scale evaporation event and that is now relatively dry compared to Earth.

Isotopic variation for traditional elements (H, C, N, O and S) has been widely used in the past 40 years in Earth and planetary sciences to study many processes with an emphasis on environments where fluids are present (e.g., Valley and Cole 2011). More recent developments have allowed high-precision measurements of isotope ratios of what has been called non-traditional elements (i.e., Mg, Si, Fe, Zn, Cu, Mo), which are usually less fractionated than traditional elements by at least an order of magnitude (see this volume). These non-traditional stable isotopes can give insights on processes where fluids are not present (e.g., metal–silicate fractionation, e.g., Georg et al. 2007 and review by Poitrasson et al. 2017, this volume), evaporation processes during planetary formation (e.g., Paniello et al. 2012, Wang and Jacobsen 2016, and review by Moynier et al. 2017 this volume), igneous differentiation (e.g., Williams et al. 2009; Sossi et al. 2012; and review by Dauphas et al. 2017, this volume), and on biological processes (e.g., Walczyk and von Blanckenburg 2002, and review by Albarede et al. 2017 this volume). Among all these non-traditional isotopic systems, Mg isotopes are of major importance because (i) Mg is a major constituent of the silicate portion of planetary bodies, (ii) Mg has more than two isotopes (24Mg, 25Mg and 26Mg) allowing to study processes leading to various types of mass fractionation (Young et al. 2002; Young and Galy 2004; Davis et al. 2015) and (iii) 26Mg excesses produced by the radioactive decay of short-lived 26Al (T1/2=0.73 Ma) (Lee et al. 1976) are a key tool for early Solar system chronology (see reviews by Dauphas and Chaussidon 2011; Chaussidon and Liu 2015). Note that in addition, significant Mg isotopic …

International audience; X-ray emission in young stellar objects (YSOs) is orders of magnitude more intense than in main sequence stars(1,2), suggestive of cosmic ray irradiation of surrounding accretion disks. Protoplanetary disk irradiation has been detected around YSOs by the Herschel Space Observatory(3). In our Solar System, short-lived Be-10 (with a half-life of 1.39 Myr)(4), which cannot be produced by stellar nucleosynthesis, was discovered in the oldest Solar System solids, the calcium-aluminium-rich inclusions (CAIs)(5). The high 10Be abundance, as well as the detection of other tracers(6,7), suggest 10Be likely originates from cosmic ray irradiation caused by solar flares(8-10). Nevertheless, the nature of these flares (gradual or impulsive), the target (gas or dust), and the duration and location of irradiation remain unknown. Here we use the vanadium isotopic composition, together with the initial Be-10 abundance to quantify irradiation conditions in the early Solar System(11). For the initial Be-10 abundances recorded in most CAIs, V-50 excesses of a few per mil (%) relative to chondrites have been predicted(8,9). We report V-50 excesses in CAIs up to 4.4% that co-vary with Be-10 abundance. Their co-variation dictates that excess V-50 and Be-10 were synthesized through irradiation of refractory dust. Modelling of the production rate of V-50 and Be-10 demonstrates that the dust was exposed to solar cosmic rays produced by gradual flares for less than 300 years at approximate to 0.1 au from the protosun.

Age dating of meteorite inclusions suggests rapid formation of the building blocks of terrestrial planets within 1 My of the Sun., The most abundant components of primitive meteorites (chondrites) are millimeter-sized glassy spherical chondrules formed by transient melting events in the solar protoplanetary disk. Using Pb-Pb dates of 22 individual chondrules, we show that primary production of chondrules in the early solar system was restricted to the first million years after the formation of the Sun and that these existing chondrules were recycled for the remaining lifetime of the protoplanetary disk. This finding is consistent with a primary chondrule formation episode during the early high-mass accretion phase of the protoplanetary disk that transitions into a longer period of chondrule reworking. An abundance of chondrules at early times provides the precursor material required to drive the efficient and rapid formation of planetary objects via chondrule accretion.

International audience; We report a new method for precise analysis of gallium (Ga) isotopic composition in geological samples. The purification of Ga is achieved by a three-step ion exchange chromatography to remove matrix and interfering elements. The 71 Ga/ 69 Ga ratios are analyzed by multi-collector inductively-coupled-plasma mass-spectrometer (MC-ICP-MS). The external reproducibility of the measurements (0.05‰, 2 s.d.) was assessed by replicate analyses of the USGS BCR-2 and BHVO-2 standards. This newly developed technique was then used to investigate the extent of Ga isotopic fractionation during igneous processes by analyzing well-characterized samples from the Kilauea Iki lava lake, USA. These samples were formed in a closed system and have MgO contents ranging from 26.9 to 2.4 wt.%. We found that igneous processes do not fractionate Ga isotopes within the analytical uncertainty and that the Ga isotopic composition of mafic-ultramafic lavas can be used to estimate the composition of their mantle source. Twelve ocean island basalts, two mid-ocean-ridge basalts, one continental flood basalt and one komatiite have homogeneous and nearly identical Ga isotopic compositions within analytical uncertainties averaging 0.00 ± 0.06‰ (2 s.d.). This value represents the best estimate for the Ga isotopic composition of the bulk silicate Earth

Chemical fingerprints of impacts are usually compromised by extreme conditions in the impact plume, and the contribution of projectile matter to impactites does not often exceed a fraction of per cent. Here we use chromium and oxygen isotopes to identify the impactor and impact-plume processes for Zhamanshin astrobleme, Kazakhstan. ε54Cr values up to 1.54 in irghizites, part of the fallback ejecta, represent the 54Cr-rich extremity of the Solar System range and suggest a CI-like chondrite impactor. Δ17O values as low as −0.22‰ in irghizites, however, are incompatible with a CI-like impactor. We suggest that the observed 17O depletion in irghizites relative to the terrestrial range is caused by partial isotope exchange with atmospheric oxygen (Δ17O = −0.47‰) following material ejection. In contrast, combined Δ17O–ε54Cr data for central European tektites (distal ejecta) fall into the terrestrial range and neither impactor fingerprint nor oxygen isotope exchange with the atmosphere are indicated., Identifying the original impactor from craters remains challenging. Here, the authors use chromium and oxygen isotopes to indicate that the Zhamanshin astrobleme impactor was a carbonaceous chrondrite by demonstrating that depleted 17O values are due to exchange with atmospheric oxygen.

International audience; We measured Cu isotope compositions of 12 out of the 14 known IVB iron meteorites. Our results show that IVB iron meteorites display a very large range of δ65Cu values (−5.84‰ < δ65Cu < −0.24‰; defined as per mil deviation of the 65Cu/63Cu ratio from the NIST-976 standard). These Cu isotopic data display clear correlations with W, Pt, and Os isotope ratios, which are very sensitive to secondary neutron capture due to galactic cosmic ray (GCR) irradiation. This demonstrates that δ65Cu in IVB irons is majorly modified by neutron capture by the reaction 62Ni(n,γ)63Ni followed by beta decay to 63Cu. Using correlations with Pt and Os neutron dosimeters, we calculated a pre-exposure δ65Cu of −0.3 ± 0.8‰ (95% conf.) of IVB irons that agrees well with the Cu isotopic compositions of other iron meteorite groups and falls within the range of chondrites. This shows that the volatile depletion of the IVB parent body is not due to evaporation that should have enriched IVB irons in the heavy Cu isotopes.

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

High-precision stable Ba isotope ratios are reported in a variety of terrestrial samples, undifferentiated primitive meteorites, and calcium–aluminum-rich inclusions (CAIs) from the Allende chondrite. All whole-rock terrestrial and meteorite samples are isotopically indistinguishable at a 50 parts per million (ppm) level per atomic mass unit (amu). Three CAIs are isotopically light, with δ138/137Ba (permil deviation of the 138Ba/137Ba ratio from a terrestrial standard) values down to − 0.6‰ compared to whole-rock meteorites, whereas the matrix is enriched in heavy isotopes (δ138/137Ba: + 0.2‰). Similar light isotope enrichments in CAIs have been previously observed for Eu, Sr, and Ca, while for most other elements CAIs are enriched in the heavier isotopes (e.g. Mg, Fe). Kinetic isotopic fractionation is a possible explanation for the enrichment in the lightest isotopes, either by condensation from a vapor phase enriched in light isotopes by kinetic effects or by kinetic fractionation during non-equilibrium condensation of an undercooled gas as suggested for Ca isotopes. However, the common property of Ba, Eu, and Sr is that they all have a low first ionization potential. We suggest that electromagnetic sorting of ionized species in the early Solar System is a possible alternative mechanism to explain the depletion in heavy isotopes observed in refractory inclusions for those elements.

International audience

International audience; Ureilites displays  56 Fe values higher than average chondrite. 29-Segregation of Fe-sulfide melts explains the high  56 Fe values in ureilites. 30-Formation of a core can begin at very low degrees of melting through the circulation of a Fe-S melt 31 through a silicate mantle. 32 33 Earth and Planetary Science Letters, in press (11/3/15). 34 2 35 Abstract 36 37 Ureilite meteorites are achondrites that are debris of the mantle of a now disrupted 38 differentiated asteroid rich in carbon. They provide a unique opportunity to study the differentiation 39 processes of such a body. We analyzed the iron isotopic compositions of 30 samples from the Ureilite 40 Parent Body (UPB) including 29 unbrecciated ureilites and one ureilitic trachyandesite (ALM-A) 41 which is at present the sole large crustal sample of the UPB. The  56 Fe of the whole rocks fall within a 42 restricted range, from 0.01 to 0.11‰, with an average of +0.056 ± 0.008 ‰, which is significantly 43 higher than that of chondrites. We show that this difference can be ascribed to the segregation of S-44 rich metallic melts at low degrees of melting at a temperature close to the Fe-FeS eutectic, and 45 certainly before the onset of the melting of the silicates (< 1100 °C), in agreement with the marked S 46 depletions, and the siderophile element abundances of the ureilites. These results point to an efficient 47 segregation of S-rich metallic melts during the differentiation of small terrestrial bodies. 48 49

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.

International audience

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.

The Moon is depleted in volatile elements relative to the Earth and Mars. Low abundances of volatile elements, fractionated stable isotope ratios of S, Cl, K and Zn, highμ(238U/204Pb) and long-term Rb/Sr depletion are distinguishing features of the Moon, relative to the Earth. These geochemical characteristics indicate both inheritance of volatile-depleted materials that formed the Moon and planets and subsequent evaporative loss of volatile elements that occurred during lunar formation and differentiation. Models of volatile loss through localized eruptive degassing are not consistent with the available S, Cl, Zn and K isotopes and abundance data for the Moon. The most probable cause of volatile depletion is global-scale evaporation resulting from a giant impact or a magma ocean phase where inefficient volatile loss during magmatic convection led to the present distribution of volatile elements within mantle and crustal reservoirs. Problems exist for models of planetary volatile depletion following giant impact. Most critically, in this model, the volatile loss requires preferential delivery and retention of late-accreted volatiles to the Earth compared with the Moon. Different proportions of late-accreted mass are computed to explain present-day distributions of volatile and moderately volatile elements (e.g. Pb, Zn; 5 to >10%) relative to highly siderophile elements (approx. 0.5%) for the Earth. Models of early magma ocean phases may be more effective in explaining the volatile loss. Basaltic materials (e.g. eucrites and angrites) from highly differentiated airless asteroids are volatile-depleted, like the Moon, whereas the Earth and Mars have proportionally greater volatile contents. Parent-body size and the existence of early atmospheres are therefore likely to represent fundamental controls on planetary volatile retention or loss.

This paper reports the values of reduced partition function ratios (as 1000 ln β ) for Fe, Ni, Cu, and Zn bound to a number of inorganic and organic ligands. We used Density Functional Techniques to update the existing data and calculate ln β for new ligands. This work allows for the mass-dependent isotope fractionation to be predicted for various inorganic (hydrated cation, hydroxide, chloride, sulfate, sulfide, phosphate) and organic (citrate, amino acid) complexes of Fe, Ni, Cu, and Zn. Isotope fractionation among coexisting complexes of these metals was evaluated from the ln β values in a variety of geochemical and biological environments. The results provide a framework for interpretation of isotope fractionation observed in seawater and chemical sediments, in the roots and aerial parts of plants, and among the organs and body fluids of mammals.