Isotopic fractionation of Cu in tektites

Tektites are terrestrial natural glasses of up to a few centimeters in size that were produced during hypervelocity impacts on the Earth’s surface. It is well established that the chemical and isotopic composition of tektites is generally identical to that of the upper terrestrial continental crust. Tektites typically have very low water content, which has generally been explained by volatilization at high temperature; however, the exact mechanism is still debated. Because volatilization can fractionate isotopes, comparing the isotopic composition of volatile elements in tektites with those of their source rocks may help to understand the physical conditions during tektite formation.Interestingly, volatile chalcophile elements (e.g., Cd and Zn) seem to be the only elements for which isotopic fractionation is known so far in tektites. Here, we extend this study to Cu, another volatile chalcophile element. We have measured the Cu isotopic composition for 20 tektite samples from the four known different strewn fields. All of the tektites (except the Muong Nong-types) are enriched in the heavy isotopes of Cu (1.98 < δ65Cu < 6.99) in comparison to the terrestrial crust (δ65Cu ≈ 0) with no clear distinction between the different groups. The Muong Nong-type tektites and a Libyan Desert Glass sample are not fractionated (δ65Cu ≈ 0) in comparison to the terrestrial crust. To refine the Cu isotopic composition of the terrestrial crust, we also present data for three geological reference materials (δ65Cu ≈ 0).An increase of δ65Cu with decreasing Cu abundance probably reflects that the isotopic fractionation occurred by evaporation during heating. A simple Rayleigh distillation cannot explain the Cu isotopic data and we suggest that the isotopic fractionation is governed by a diffusion-limited regime. Copper is isotopically more fractionated than the more volatile element Zn (δ66/64Zn up to 2.49‰). This difference of behavior between Cu and Zn is predicted in a diffusion-limited regime, where the magnitude of the isotopic fractionation is regulated by the competition between the evaporative flux and the diffusive flux at the diffusion boundary layer. Due to the difference of ionic charge in silicates (Zn2+ vs. Cu+), Cu has a diffusion coefficient that is larger than that of Zn by at least two orders of magnitude. Therefore, the larger isotopic fractionation in Cu than in Zn in tektites is due to the significant difference in their respective chemical diffusivity

Mass-independent isotope fractionation of molybdenum and ruthenium and the origin of isotopic anomalies in Murchison

Dauphas et al.'s model for the nucleosynthetic origin of Mo and Ru anomalies in meteorites leaves the case of Murchison (CM2) unexplained.We explore the possibility that such a discrepancy is due to mass-independent effects controlled by nuclear field shift with, in particular, ‘‘staggering'' between odd and even masses.We first demonstrate the existence of such mass-independent fractionation of Mo and Ru isotopes by chemical exchange of Mo and Ru between DC18C6 crown ether and aqueous solutions. Our results fit the nuclear field shift theory of Bigeleisen. We then review the correlation between the mean-square charge radius (which controls the nuclear field shift) and the isotopic anomalies found in an Allende CAI and in Murchison. AlthoughMo and Ru in the Allende CAI show a clear indication of nucleosynthetic components, the mass-independent anomalies observed in Murchison show a strong correlation with the nuclear charge distribution. We therefore argue that some isotopic anomalies observed in meteorites may be due to nuclear field shift rather than nucleosynthetic processes. Such effects are temperature dependent and may represent either genuine nebular processes or analytical artifacts. This new interpretation may help assess the existence of anomalies due to the extinct isotopes 97Tc and 98Tc

Isotope fractionation of iron(III) in chemical exchange reactions using solvent extraction with crown ether

International audienceThis work reports on the chemical isotope fractionation of Fe(III) by a solvent extraction method with a crown ether of dicyclohexano-18-crown-6. The 56Fe/54Fe and 57Fe/54Fe ratios were analyzed by multiple-collector inductively coupled plasma mass spectrometry. We determined the dependence of the isotope enrichment factors () on the strength of HCl. The relative deviation of the 56Fe/54Fe ratios relative to the unprocessed material (104 56) increases from -15.3 to -6.3 with [HCl] increasing from 1.6 to 3.5 mol/L. Likewise, 104 57 increases from -22.8 to -9.6 under the same conditions. The correlation between 56 and 57 is mass dependent within the errors. The observed fractionation was broken down into the effects of competing extraction reactions and of a reaction between Fe(III) species (FeCl2+ and FeCl3) in the aqueous phase. We found that the isotope fractionation between the Fe(III) species is mass dependent, which we confirmed by calculating the reduced partition function ratios

A glimpse into the Roman finances of the Second Punic War through silver isotopes

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Zr isotope anomalies in chondrites and the presence of Nb-92 in the early solar system

The presence of Zr isotope anomalies in the early solar system is demonstrated with the identification of Zr-92 excesses and Zr-96. deficits in several chondrites and the CAI Allende inclusions. The isotopic composition of Zr in carbonaceous, enstatite, and ordinary chondrites, along with four SNC meteorites, was analyzed by plasma source mass spectrometry. Most chondrite samples show negative Zr-96 anomalies, which indicate the presence of a pre-solar nucleosynthetic component. Six of them also display a distinct negative Zr-92 anomaly, reaching down to -2.7 +/- 0.8 epsilon units for Forest Vale (H4). The CAI inclusions from Allende, which are among the oldest known igneous objects of the solar system and have the highest Zr/Nb ratios, also show negative epsilon Zr-92 Of -2.4 +/- 0.5. Although a substantial fraction of the Zr isotope variability may be due to pre-solar nucleosynthetic processes, part of the Zr-92 excess must result from the decay of the now extinct Nb-92. (C) 2000 Elsevier Science B.V. All rights reserved

Isotopic evidence of unaccounted for Fe and Cu erythropoietic pathways

International audienceDespite its potential importance for understanding perturbations in the Fe-Cu homeostatic pathways, the natural isotopic variability of these metals in the human body remains unexplored. We measured the Fe, Cu, and Zn isotope compositions of total blood, serum, and red blood cells of similar to 50 young blood donors by multiple-collector ICP-MS after separation and purification by anion exchange chromatography. Zinc shows much less overall isotopic variability than Fe and Cu, which indicates that isotope fractionation depends more on redox conditions than on ligand coordination. On average, Fe in erythrocytes is isotopically light with respect to serum, whereas Cu is heavy. Iron and Cu isotope compositions clearly separate erythrocytes of men and women. Fe and Cu from B-type men erythrocytes are visibly more fractionated than all the other blood types. Isotope compositions provide an original method for evaluating metal mass balance and homeostasis. Natural isotope variability shows that the current models of Fe and Cu erythropoiesis violate mass balance requirements. It unveils unsuspected major pathways for Fe, with erythropoietic production of isotopically heavy ferritin and hemosiderin, and for Cu, with isotopically light Cu being largely channeled into blood and lymphatic circulation rather than into superoxide dismutase-laden erythrocytes. Iron isotopes provide an intrinsic measuring rod of the erythropoietic yield, while Cu isotopes seem to gauge the relative activity of erythropoiesis and lymphatics

Lithium isotope fractionation during magma degassing: Constraints from silicic differentiates and natural gas condensates from Piton de la Fournaise volcano (Réunion Island)

International audienceRecent volcanic products from the Piton de la Fournaise Volcano, Reunion, show pronounced depletion or enrichment in lithium and significant isotopic fractionation related to degassing. (1) trachytic pumices from the April 2007 eruption show extreme Li depletion (90%) and isotopic fractionation (δ7Li of − 21‰). The depletion of water and volatiles (Cl, F, B, Cs) in these samples suggests that Li loss occurred in response to degassing, which most likely occurred as the small, isolated volume of magma underwent extensive differentiation near the surface. Because the pre-degassing composition is relatively well known, the composition of the degassed pumice constrains the partition coefficient to 60 &lt; DV–M &lt; 135 and the isotopic fractionation factor, αV–M, to 1.010 at magmatic temperatures. Unlike DV–M, αV–M does not depend on whether crystallization and degassing occurred successively or concomitantly. (2) basaltic samples from the interior wall of the long-lived 1998 Piton Kapor were extensively altered by acidic gas. They also show extreme Li depletion, but barely significant isotopic fractionation (δ7Li = + 4.5‰), suggesting that high-temperature leaching of Li by volcanic gas does not significantly fractionate Li isotopes. (3) high-temperature (400–325 °C) gas condensates formed during degassing of the thick lava flow of April 2007 display high Li contents (50–100 ppm), which are consistent with Li being as volatile as Zn and Sn. Their isotopically light Li signature (average of − 1.7‰) is consistent with their derivation from isotopically heavy vapor (+ 13.5‰) if the factor of isotopic fractionation between condensate and vapor is less than 0.985. A degassing-crystallization model accounts for the evolution of trace species, which, like lithium, are volatile but also moderately incompatible

Fe and Cu stable isotopes in archeological human bones and their relationship to sex

International audienceAccurate sex assignment of ancient human remains usually relies on the availability of coxal bones or well-preserved DNA. Iron (Fe) and copper (Cu) stable isotope compositions (56Fe/54Fe and 65Cu/63Cu, respectively) were recently measured in modern human blood, and an unexpected result was the discovery of a 56Fe-depletion and a 65Cu-enrichment in men's blood compared to women's blood. Bones, being pervasively irrigated by blood, are expected to retain the 56Fe/54Fe and 65Cu/63Cu signature of blood, which in turn is useful for determining the sex of ancient bones. Here, we report the 56Fe/54Fe, 65Cu/63Cu, and 66Zn/64Zn ratios from a suite of well-preserved phalanxes (n = 43) belonging to individuals buried in the 17th and 18th centuries at the necropolis of Saint-Laurent de Grenoble, France, and for which the sex was independently estimated from pelvic bone morphology. The metals were purified from the bone matrix by liquid chromatography on ion exchange resin and the isotope compositions were measured by multiple-collector inductively coupled plasma mass spectrometry. The results show that, as expected from literature data on blood, male bone iron is depleted in 56Fe and enriched in 65Cu relative to female. No sex difference is found in the 66Zn/64Zn ratios of bone. The concentration and isotopic data show no evidence of soil contamination. Four samples of five (77%) can be assigned their correct sex, a result comparable to sex assignment using Fe and Cu isotopes in blood (81%). Isotopic analysis of metals may therefore represent a valid method of sex assignment applicable to incomplete human remains