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Iron isotopes are fractionated by multiple biological processes, which offers a novel opportunity to study iron homeostasis. The determination of Fe isotope composition in biological samples necessitates certified biological reference materials with known Fe isotopic signature in order to properly assess external reproducibility and data quality between laboratories. We report the most comprehensive study on the Fe isotopic composition for widely available international biological reference materials. They consist of different terrestrial and marine animal organs (bovine, porcine, tuna, and mussel) as well as apple leaves and human hair (ERC-CE464, NIST1515, ERM-DB001, ERM-BB186, ERM-BB184, ERM-CE196, BCR668, ERM-BB185, ERM-BB124). Previously measured Fe isotopic compositions were available for only two of these reference materials (ERC-CE464 tuna fish and ERM-BB186 pig kidney) and these literature data are in excellent agreement with our data. The Fe isotopic ratios are reported as the permil deviation of the 56Fe/54Fe ratio from the IRMM-014 standard. All reference materials present δ56Fe ranging from −2.27 to −0.35%0. Combined with existing data, our results suggest that animal models could provide useful analogues of the human body regarding the metabolic pathways affecting Fe isotopes, with many potential applications to medicine.

International audience; Earth's accretion history for volatile elements, and the origin of their depletions with respect to the Sun and primitive meteorites, continue to be debated. Two end-member scenarios propose either that volatile elements were delivered during the main phases of accretion and differentiation, or that the Earth accreted from materials largely devoid of volatiles with late addition of volatile-rich materials. Experiments evaluating the effect of metal-silicate equilibrium on elemental and isotopic distribution of volatile and siderophile elements such as Sn can help to distinguish between these scenarios. In this study, we have systematically investigated the relative influence of temperature, pressure, oxygen fugacity, and metal and silicate composition on the metal-silicate partioning behavior of Sn, from 2 to 20 GPa and 1,700 to 2,573 K, indicating that Sn siderophility noticeably decreases with temperature and S content of the metal but increases dramatically with pressure. A resolvable isotopic fractionation factor between metal and silicate suggests that core-mantle equilibrium temperatures (∼3,000 K) could potentially generate a Sn isotopic composition of the mantle lighter than the core by 150-200 ppm/amu. Core formation modeling shows that the volatiles were added during the last 10% of the accretion history. A final core containing 2.5 to 3.5 wt.% S is required. Furthermore, modeling of the BSE isotopic composition argues for a late Sn delivery on Earth with carbonaceous chondrite-like material as the most likely source of volatiles. Therefore, both elemental and isotopic approaches converge toward an identical volatile accretion scenario, involving a late volatile delivery.

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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.

International audience; The Earth has grown from chaotically mixed small dusts and gases to its present highly differentiated layered structure over the past 4.567 billion years. This differentiation has led to the formation of the atmosphere, hydrosphere, biosphere, crust, mantle, and core. The timing and mechanism for the formation and evolution of these different layers are still subjects of intense debate. This review brings together recent advances in using non-traditional stable isotopes to constrain major events and processes leading to the formation and differentiation of the Earth, including the Moon-forming giant impact, crust-mantle interactions, evolution of life, the rise of atmospheric oxygen, extreme paleoclimate changes, and cooling rate of magmas.

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

The potential complementarity between chondrules and matrix of chondrites, the Solar System's building blocks, is still a highly debated subject. Complementary superchrondritic compositions of chondrite matrices and subchondritic chondrules may point to formation of these components within the same reservoir or, alternatively, to mobilization of elements during secondary alteration on chondrite parent bodies. Zinc isotope fractionation through evaporation during chondrule formation may play an important role in identifying complementary relationships between chondrules and matrix and is additionally a mobile element during hydrothermal processes. In an effort to distinguish between primary Zn isotope fractionation during chondrule formation and secondary alteration, we here report the Zn isotope data of five chondrule cores, five corresponding igneous rims and two matrices of the relatively unaltered Leoville CV3.1 chondrite. The detail required for these analyses necessitated the development of an adjusted Zn isotope analyses protocol outlined in this study., Comment: in press

Moderately volatile elements show variable depletion in terrestrial planets compared to the Sun. Isotopic ratios can be used as a signature of the processes at the origin of this depletion. Using a new method, the Sn stable isotope composition and elemental abundance in 36 primitive meteorites (chondrites) have been characterised to high precision. Significant mass-dependent Sn isotope variations are found within chondrites. The widest isotopic range is observed for the ordinary chondrites (−1.1 ‰ to +0.5 ‰ in δ122/118Sn, representing the difference in the 122Sn/118Sn ratio of the sample relative to our in-house standard, Sn_IPGP), with the ordinary chondrite groups extending to lighter isotopic compositions in the order H > L > LL, while carbonaceous and enstatite chondrites are heavier and occupy narrower compositional ranges. Tin and Zn isotope and concentration data are strongly correlated, particularly in ordinary chondrites, from which both sets of data were obtained on the same rock powders. Given the difference in geochemical behaviour (Zn lithophile/chalcophile and Sn chalcophile/siderophile) of these elements, this suggests that the primary control on the isotope and abundance variations is volatility. Chondrite groups show variability increasing with petrographic types, suggesting a secondary control from parent-body metamorphism. The isotopic composition of the bulk silicate Earth (BSE; δ 122/118Sn = 0.49 ± 0.11 ‰) overlaps with the carbonaceous chondrites (δ 122/118Sn = 0.43 ± 0.12 ‰; excl. CR and CK). Despite isotopic similarities for almost all isotopic systems, EH chondrites have Sn isotope compositions that are distinct from the bulk silicate Earth (δ 122/118Sn = 0.18 ± 0.21 ‰). Therefore, an enstatite chondrite-like bulk Earth requires that isotopically light Sn was lost from the silicate Earth, possibly into the metallic core or a sulphide matte, or by evaporative loss from Earth or its precursors.

The circa 14 km diameter Pantasma circular structure in Oligocene volcanic rocks in Nicaragua is here studied for the first time to understand its origin. Geomorphology, field mapping, and petrographic and geochemical investigations all are consistent with an impact origin for the Pantasma structure. Observations supporting an impact origin include outward-dipping volcanic flows, the presence of former melt-bearing polymict breccia, impact glass (with lechatelierite and low H 2 O, 10 km found in the Americas south of N30 latitude, and provides further evidence that a significant number of impact craters may remain to be discovered in Central and South America., SCOPUS: ar.j, info:eu-repo/semantics/published

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Rocks from the lunar interior are depleted in moderately volatile elements (MVEs) compared to terrestrial rocks. Most MVEs are also enriched in their heavier isotopes compared to those in terrestrial rocks. Such elemental depletion and heavy isotope enrichments have been attributed to liquid–vapor exchange and vapor loss from the protolunar disk, incomplete accretion of MVEs during condensation of the Moon, and degassing of MVEs during lunar magma ocean crystallization. New Monte Carlo simulation results suggest that the lunar MVE depletion is consistent with evaporative loss at 1,670 ± 129 K and an oxygen fugacity +2.3 ± 2.1 log units above the fayalite-magnetite-quartz buffer. Here, we propose that these chemical and isotopic features could have resulted from the formation of the putative Procellarum basin early in the Moon’s history, during which nearside magma ocean melts would have been exposed at the surface, allowing equilibration with any primitive atmosphere together with MVE loss and isotopic fractionation. © 2021 National Academy of Sciences. ISSN:0027-8424 ISSN:1091-6490

The moderately volatile elements, Cu and Zn, are not strongly affected by magmatic differentiation [1, 2] and are important tracers of volatile depletion in planetary bodies, particularly low-mass, airless bodies [3]. New isotopic ratio and abundance measurements for both Cu and Zn are presented for eucrites to more fully understand volatile depletion processes that affected the parent-body of the howardite-eucrite-diogenite (HED) meteorites, the asteroid 4-Vesta. Zinc isotope ratios are reported for twenty-eight eucrite samples, which along with prior data [4] yield a range of δ66Zn from -1.8 to +6.3 ‰, excluding one outlier, PCA 82502 (δ66Zn = -7.8 ‰) and a Zn concentration range from 0.3 to 3.8 p.p.m. Heavy Zn isotopic ratios (positive δ66Zn compositions) in eucrites form a negative trend with Zn concentration, reflecting volatile depletion processes on Vesta that are similar to the Moon [5, 6]. Within the combined sample set, eleven eucrites have light Zn isotopic compositions from δ66Zn of -0.02 to -7.8 ‰, with the majority having more negative compositions than likely chondritic precursors (maximum δ66Zn of ~ -0.2 ‰ [7]). These samples are interpreted to reflect condensates formed subsequent to surface volatilization and outgassing, such as during impact bombardment. Measurements of Cu compositions are also reported for nineteen of the samples, yielding a range of δ65Cu from -1.6 to +0.9 ‰, and range of Cu concentrations from 0.2 to 2.8 p.p.m., with the exception of Stannern (Cu > 10 ppm). As with Zn, negative Cu isotopic ratios that are lighter than chondritic compositions (δ65Cu ~ -0.5 ‰ [8]) are attributed to recondensation that occurred following impact-induced vaporization (cf. [9]). Within the wide ranges of Zn and Cu isotopic compositions measured in eucrites, most samples cluster within ~ 0 ‰ < δ66Zn < +3 ‰ and ~ 0.2 ‰ < δ65Cu < +0.9 ‰. This range is interpreted to reflect volatile depletion processes similar to those that affected the Moon (BSM: δ66Zn +1.4 ± 0.5‰ [5, 6, 10, 11] and δ65Cu = +0.92 ± 0.16‰ [9-11]). The greater heterogeneity in eucrite Zn and Cu isotopic compositions compared to lunar samples can be attributed to the smaller size of the HED parent asteroid, which may have experienced more limited homogenization of these signatures following volatile depletion and for eucrites which have experienced complex impact addition and metamorphic processes. [1] Chen et al. (2013) EPSL, 369, 34-42. [2] Savage et al. (2015) Geochemical Perspective Letters, 1, 53-64. [3] Day and Moynier (2014) Philisophical Transactions of the Royal Society A, 372, p.20130259. [4] Paniello et al. (2012) GCA, 86, 76-87. [5] Paniello et al. (2012) Nature, 490, 376-379. [6] Kato et al. 2015 Nature Communications, 6, 1-4. [7] Luck et al. (2005) GCA 69, 5351-5363. [8] Luck et al. (2003) GCA, 67¸143-151. [9] Day et al. (2019) GCA, 266, 131-143. [10] Moynier et al. (2006) GCA, 70, 6103-6117. [11] Herzog et al. (2009) GCA, 73, 5884-5904.

Understanding the origin of chondritic components and their accretion pathways is critical to unravel the magnitude of mass transport in the protoplanetary disk, the accretionary history of the terrestrial planet region and, by extension, its prebiotic inventory. Here, we trace the heritage of pristine components from the relatively unaltered CV chondrite Leoville through their mass-independent Cr and mass-dependent Zn isotope compositions. Investigating these chondritic fractions in such detail reveals an onion-shell structure of chondrules, which is characterized by 54Cr- and 66Zn-poor cores surrounded by increasingly 54Cr- and 66Zn-rich igneous rims and an outer coating of fine-grained dust. This is interpreted as a progressive addition of 54Cr- and 66Zn-rich, CI-like material to the accretion region of these carbonaceous chondrites. Our findings show that the observed Cr isotopic range in chondrules from more altered CV chondrites is the result of chemical equilibration between chondrules and matrix during secondary alteration. The 54Cr-poor nature of the cores of Leoville chondrules implies formation in the inner Solar System and subsequent massive outward chondrule transport past the Jupiter barrier. At the same time, CI-like dust is transferred inwards. We propose that the accreting Earth acquired CI-like dust through this mechanism within the lifetime of the disk. This radial mixing of chondrules and matrix shows the limited capacity of Jupiter to act as an efficient barrier and maintain the proposed non-carbonaceous and carbonaceous chondrite dichotomy over time. Finally, also considering current astrophysical models, we explore both inner and outer Solar System origins for the CV chondrite parent body., accepted after peer-review

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.

The timing and origin of volatile elements accretion on Earth has been and continues to be key questions, despite intense research scrutiny. Two end-member scenarios are usually proposed in which (1) volatile elements were delivered during the main phases of Earth’s accretion and underwent subsequent core–mantle differentiation, or (2) Earth accreted from largely dry and volatile-depleted material, with late addition of volatile-rich material after differentiation. Studying the behaviour of elements that are both volatile and siderophile in a metal–silicate equilibrium can help discriminate between those two scenarios by deconvolving the effect of siderophile processes such as the Earth’s differentiation from the effect of volatile processes. We report high-pressure and high-temperature metal–silicate equilibrium experiments that are used to trace the behaviour of four moderately siderophile and volatile elements: Cd, Bi, Sb and Tl. Experiments were performed in piston cylinder and multianvil presses between 2 and 20 GPa, from 1700 to 2600 K, in order to study the partitioning behaviour of these elements, including the relative influence of pressure, temperature, oxygen fugacity (fO2), and composition. Our results indicate that Cd, Bi, Sb and Tl partitioning coefficients are largely controlled by changes in temperature, pressure, fO2 and the S content of the metal phase. The pressure effect on Tl and Bi partitioning is measured for the first time and improves significantly the knowledge of Bi and Tl behaviour during core formation. Core formation modelling was used to reconcile the experimental data with observed abundances for different accretion scenarios. Homogeneous accretion with full core–mantle equilibration induces a massive segregation of Bi, Sb and Tl in the core, preventing reproduction of observed present-day mantle abundances. We find that a scenario in which the volatile elements are accreted in the last 10–20 % of the Earth’s accretion is the most suitable accretion process that is able to explain the abundances of Cd, Bi, Sb and Tl in Earth’s mantle. Partial core–mantle equilibration is necessary to reproduce Bi and Tl abundances. Our partitioning data also suggests that a 0.5 % chondritic late veneer may account for the Bi abundance measured in the bulk silicate Earth. These observations corroborate a growing wealth of evidence in support of this schematic heterogeneous accretion pathway.

Prevailing models for the formation of the Moon invoke a giant impact between a planetary embryo and the proto-Earth \citep{Canup_2004, Cuk_Stewart_2012}. Despite similarities in the isotopic and chemical abundances of refractory elements compared to Earth's mantle, the Moon is depleted in volatiles \citep{Wolf_Anders_1980}. Current models favour devolatilisation via incomplete condensation of the proto-Moon in an Earth-Moon debris-disk \citep{Charnoz_Michaut_2015,Canup_2015,Lock_2018}. However the physics of this protolunar disk is poorly understood and thermal escape of gas is inhibited by the Earth's strong gravitational field \citep{Nakajima_Stevenson_2014}. Here we investigate a simple process, wherein the Earth's tidal pull promotes intense hydrodynamic escape from the liquid surface of a molten proto-Moon assembling at 3-6 Earth radii. Such tidally-driven atmospheric escape persisting for less than 1 Kyr at temperatures $\sim 1600-1700$ K reproduces the measured lunar depletion in K and Na., Comment: Accepted for publication in ICARUS

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.

Impact-induced oxidation of Mars’ crust by water >4.4 Ga ago likely supplied enough atmospheric H2 to attain a warm climate., Despite the abundant geomorphological evidence for surface liquid water on Mars during the Noachian epoch (>3.7 billion years ago), attaining a warm climate to sustain liquid water on Mars at the period of the faint young Sun is a long-standing question. Here, we show that melts of ancient mafic clasts from a martian regolith meteorite, NWA 7533, experienced substantial Fe-Ti oxide fractionation. This implies early, impact-induced, oxidation events that increased by five to six orders of magnitude the oxygen fugacity of impact melts from remelting of the crust. Oxygen isotopic compositions of sequentially crystallized phases from the clasts show that progressive oxidation was due to interaction with an 17O-rich water reservoir. Such an early oxidation of the crust by impacts in the presence of water may have supplied greenhouse gas H2 that caused an increase in surface temperature in a CO2-thick atmosphere.

Biometals play a critical role in both the healthy and diseased brain's functioning. They accumulate in the normal aging brain, and are inherent to neurodegenerative disorders and their associated pathologies. A prominent example of this is the brain accumulation of metals such as Ca, Fe and Cu (and more ambiguously, Zn) associated with Alzheimer's disease (AD). The natural stable isotope compositions of such metals have also shown utility in constraining biological mechanisms, and in differentiating between healthy and diseased states, sometimes prior to conventional methods. Here we have detailed the distribution of the biologically relevant elements Mg, P, K, Ca, Fe, Cu and Zn in brain regions of Göttingen minipigs ranging in age from three months to nearly six years, including control animals and both a single- and double-transgenic model of AD (PS1, APP/PS1). Moreover, we have characterized the Ca isotope composition of the brain for the first time. Concentration data track rises in brain biometals with age, namely for Fe and Cu, as observed in the normal ageing brain and in AD, and biometal data point to increased soluble amyloid beta (Aβ) load prior to AD plaque identification via brain imaging. Calcium isotope results define the brain as the isotopically lightest permanent reservoir in the body, indicating that brain Ca dyshomeostasis may induce measurable isotopic disturbances in accessible downstream reservoirs such as biofluids.

International audience

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.

Vaporisation fractionates elements and their isotopes between condensed phase(s) and the gas phase according to two end-member regimes; kinetic (Langmuir) or equilibrium (Knudsen). The fractionation factor of isotopes i and j of element E between gas and liquid, i/jE(αvap-liq), in the former case depends only on the molar masses of the evaporating species, (Mj/Mi)0.5, whereas, at equilibrium, the fractionation factor is ∼1 at high temperatures. The prevailing regime depends on the production rate of vapour species relative to their rate of transport away from the evaporating surface, for which an accurate theory is lacking. Here, we present results of Cu and Zn isotope fractionation during evaporation of ferrobasaltic melts in the FeO(T)-CaO-MgO-Al2O3-SiO2 (FCMAS) system in a 1 atm gas-mixing furnace at oxygen fugacities (fO2) from 10−8 bar to 10−0.68 bar (air) at temperatures between 1300 and 1500 °C. In air, the fractionation factors are 65/63Cu(αvap-liq) = 0.9972 ± 0.0001 and 66/64Zn(αvap-liq) = 0.9959 ± 0.0002, but increase under reducing conditions, at logfO2 = −8 for 65/63Cu(αvap-liq) (0.9979) and at −3, −5.5 and −8 for Zn, at which 66/64Zn(αvap-liq) = 0.9967, 0.9974 and 0.9978, respectively. This behaviour is caused by slow elemental diffusion through the silicate melt relative to the rate of evaporative loss, thereby depressing i/jE(αvap-liq). When evaporation rates far exceed those for diffusion in the melt, no isotopic fractionation develops in the condensed phase. To account for the 65/63Cu(αvap-liq) and 66/64Zn(αvap-liq) values observed in air, we develop a formalism for mass transfer applicable to any evaporating species over a range of pressures, gas compositions and flow regimes. For natural convection at 1 bar, diffusive transport through the gas is the rate-limiting step, where D(i,j)k is the diffusion rate of isotope i or j through a gas with mean molar mass Mk. Under these conditions i/jE(αvap-liq) is proportional to (Dik/Djk)2/3, and not (Dik/Djk) as previously proposed. Our model predicts i/jE(αvap-liq) in other experiments, and in nature, to a precision of ±0.0005 assuming ideality. The fractionation factors inferred for moderately volatile elements in lunar mare basalts (>0.9994) are inconsistent with a mass transport process, and instead reflect near-equilibrium conditions of vapour loss from the Moon. ISSN:0016-7037 ISSN:1872-9533

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.

We report on the mass-independent Cr isotope compositions of 11 main group ureilites and an ureilitic trachyandesite (ALM-A). The 54Cr/52Cr ratios for main group ureilites vary from −1.06±0.04 to −0.78±0.05 and averaged at −0.91±0.15 (2SD, N=18) including the data from literature. We argue that this variation reflects primitive mantle heterogeneities within the ureilite parent body (UPB). As such, this body did not experience a global-scale magma ocean, which is consistent with heterogeneous O isotope in ureilites. Furthermore, the ε54Cr values, Mn/Cr ratios, C isotope ratios, Mg# values, and Fe/Mn ratios in the olivine cores of ureilites are correlated with each other, which suggests the mixing of ureilite precursors from at least two reservoirs, rather than a smelting process or the oxidation from ice melting. All the ureilite samples (including the ALM-A) fall on a well-defined 53Mn–53Cr isochron corresponding to a 53Mn/55Mn ratio of (6.02 ± 1.59)×10−6, which translates to an age of 4566.7±1.5 Ma (within 2 Ma after calcium-aluminum-rich inclusions; CAIs) when anchored to the U-corrected Pb–Pb age for the D’Orbigny angrite. This old age indicates early partial melting on the UPB, consistent with the early accretion of the UPB (within 1 Ma after CAIs) predicted by thermal modeling. Furthermore, there is a 4∼5 Ma age difference between the external isochron in this study and internal isochron ages for the feldspathic clasts in polymict ureilites, which likely reflects an impact history during the early evolution of the UPB.

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.

International audience; We present here several laboratory analyses performed on the freshly fallen Mukundpura CM chondrite. Results of infrared transmission spectroscopy, thermogravimetry analysis and reflectance spectroscopy show that Mukundpura is mainly composed of phyllosilicates. The rare earth trace elements composition and ultrahigh resolution mass spectrometry of the soluble organic matter (SOM) give results consistent with CM chondrites. Finally, Raman spectroscopy shows no signs of thermal alteration of the meteorite. All the results agree that Mukundpura has been strongly altered by water on its parent body. Comparison of the results obtained on the meteorite with those of other chondrites of known petrologic types lead to the conclusion that Mukundpura is similar to CM1 chondrites, which differs from its original classification as a CM2.

Isotopic compositions of reservoirs in the Moon can be constrained from analysis of rocks generated during lunar magmatic differentiation. Mare basalts sample the largest lunar mantle volume, from olivine- and pyroxene-rich cumulates, whereas ferroan anorthosites and magnesian-suite rocks represent early crustal materials. Incompatible element enriched rocks, known as ‘KREEP,’ probably preserve evidence for the last highly differentiated melts. Here we show that mare basalts, including Apollo samples and meteorites, have remarkably consistent δ 66 Zn values ( + 1.4 ± 0.2 ‰ ) and Zn abundances (1.5 ± 0.4 ppm). Analyses of magnesian-suite rocks show them to be characterized by even heavier δ 66 Zn values (2.5 to 9.3‰) and low Zn concentrations. KREEP-rich impact melt breccia Sayh al Uhaymir 169 has a nearly identical Zn composition to mare basalts ( δ 66 Zn = 1.3 ‰ ) and a low Zn abundance (0.5 ppm). Much of this variation can be explained through progressive depletion of Zn and preferential loss of the light isotopes in response to evaporative fractionation processes during a lunar magma ocean. Samples with isotopically light Zn can be explained by either direct condensation or mixing and contamination processes at the lunar surface. The δ 66 Zn of Sayh al Uhaymir 169 is probably compromised by mixing processes of KREEP with mafic components. Correlations of Zn with Cl isotopes suggest that the urKREEP reservoir should be isotopically heavy with respect to Zn, like magnesian-suite rocks. Current models to explain how and when Zn and other volatile elements were lost from the Moon include nebular processes, prior to lunar formation, and planetary processes, either during giant impact, or magmatic differentiation. Our results provide unambiguous evidence for the latter process. Notwithstanding, with the currently available volatile stable isotope datasets, it is difficult to discount if the Moon lost its volatiles relative to Earth either during giant impact or exclusively from later magmatic differentiation. If the Moon did begin initially volatile-depleted, then the mare basalt δ 66 Zn value likely preserves the signature, and the Moon lost 96% of its Zn inventory relative to Earth and was also characterized by isotopically heavy Cl ( δ 37 Cl = ≥ 8 ‰ ). Alternative loss mechanisms, including erosive impact removing a steam atmosphere need to be examined in detail, but nebular processes of volatile loss do not appear necessary to explain lunar and terrestrial volatile inventories.

Zirconium isotopes have the potential to trace both magmatic differentiation and crustal evolution, as well as deep Earth processes. Zirconium is compatible in bridgmanite where it has a higher coordination number than in silicate melt, implying that Zr isotopes could be fractionated during magma ocean crystallisation. We report the Zr isotopic composition of 31 komatiites from around the globe, ranging in age from 2.41 to 3.55 Ga. The delta Zr-94/90 (per mille deviation of Zr-94/Zr-90 from IPGP-Zr standard) values for the komatiites are homogeneous at 0.030 +/- 0.049 parts per thousand (all errors are 2 s.d.), and consistent with associated basaltic rocks (0.048 +/- 0.032 parts per thousand). These results, identical within uncertainty of the bulk silicate Earth estimate from modern basalts, suggest that the mantle Zr isotope composition has been constant since at least 3.55 Ga. Combining the isotopic compositions of komatiites and basalts of all ages we suggest a conservative delta Zr-94/90 = 0.040 +/- 0.044 parts per thousand (n = 72) for the mantle composition. Several komatiite systems that we analysed in this study, including Schapenburg, Komati, and Weltevreden, have been previously argued to have isotope signatures consistent with magma ocean crystallisation processes. However, their Zr isotope compositions are indistinguishable from other komatiites, implying that bridgmanite crystallisation did not fractionate Zr isotopes to any measurable extent.