Kinetic Fractionation Research Articles

Titanium-rich basaltic melts on the Moon modulated by reactive flow processes

The origin of titanium-rich basaltic magmatism on the Moon remains enigmatic. Ilmenite-bearing cumulates in the lunar mantle are often credited as the source, but their partial melts are not a compositional match and are too dense to enable eruption. Here we use petrological reaction experiments to show that partial melts of ilmenite-bearing cumulates react with olivine and orthopyroxene in the lunar mantle, shifting the melt composition to that of the high-Ti suite. New high-precision Mg isotope data confirm that high-Ti basalts have variable and isotopically light Mg isotope compositions that are inconsistent with equilibrium partial melting. We employ a diffusion model to demonstrate that kinetic isotope fractionation during reactive flow of partial melts derived from ilmenite-bearing cumulates can explain these anomalously light Mg isotope compositions, as well as the isotope composition of other elements such as Fe, Ca and Ti. Although this model does not fully replicate lunar melt–solid interaction, we suggest that titanium-rich magmas erupted on the surface of the Moon can be derived through partial melting of ilmenite-bearing cumulates, but melts undergo extensive modification of their elemental and isotopic composition through reactive flow in the lunar mantle. Reactive flow may therefore be the critical process that decreases melt density and allows high-Ti melts to erupt on the lunar surface.

Gallium isotope fractionation during precipitation of α-GaOOH from aqueous solution

Gallium (Ga) has two naturally-occurring stable isotopes: 69Ga (60.1%) and 71Ga (39.9%). Their isotopic ratios were employed as a potential proxy to trace the geochemical behavior of Ga and its analogue Al. Ga is also an important component of many semiconductors. When exposed to aqueous solutions, it may be dissolved and then precipitate as Ga-bearing crystals (e.g., GaOOH). Thus, the exploration of Ga isotope fractionation during α-GaOOH precipitation could be helpful for understanding geochemical behaviors of Ga and other metals (including Al and Fe) during oxyhydroxide precipitation. In this study, three series of precipitation experiments with variable initial aqueous Ga concentrations (about 9.2, 2.0, and 1.8 ppm) were carried out to determine Ga isotope fractionation factor during α-GaOOH precipitation at ∼20 °C and neutral pH as a function of time. The experimental results could be modeled using a Rayleigh precipitation process, in which fractionation factors between crystals and solution (Δ71Gasolid-solution) are between −0.28 and − 0.37‰, depending on the initial Ga concentration and type of matrix anion (Cl− vs. NO3−). This isotope fractionation is significantly smaller in magnitude than the values reported for Ga adsorption on goethite (−0.89‰) and calcite (−1.27‰). The isotope fractionation is mainly caused by the increase in GaO bond length from ∼1.84 Å in aqueous GaOH4— to ∼1.991 Å in α-GaOOH solid, with a simultaneous change of Ga coordination number from 4 to 6, although kinetic isotope fractionation may play an important role. Our study provides the first experimental evidence of significant Ga isotope fractionation during kinetic oxyhydroxide precipitation, and suggests that the measurable Ga isotope fractionation occurred at water-solid interface and during precipitations can be potentially used for tracing global geochemical cycling of Ga and its analogue Al and Fe.

Steady states and kinetic modelling of the acid-catalysed ethanolysis of glucose, cellulose, and corn cob to ethyl levulinate.

Ethyl levulinate is a promising advanced biofuel and platform chemical that can be derived from lignocellulosic biomass by ethanolysis processes. It can be blended with both diesel and gasoline and, thus, used in conventional engines and infrastructure. Previously, it has been shown that alkyl levulinate/alcohol/alkyl ether mixtures exhibit significantly enhanced fuel properties relative to any of the individual fuel components, particularly when blended with conventional hydrocarbon liquid fuels. Consequently, this study specifically quantifies the three primary components of the alcoholysis reaction mixture: ethyl levulinate, diethyl ether, and ethanol. The steady state and kinetic phase fractions of ethyl levulinate and diethyl ether produced from glucose, cellulose, and corn cob with 0.5-2 mass% sulphuric acid in ethanol are determined for 5, 10, and 20 mass% of feedstock at 150 °C. Knowledge of the steady state equilibrium mixture fraction is specifically targeted due to its importance in assessing commercial-scale production and in modelling analysis as: (i) it defines the maximum yield possible at a given condition, and (ii) it is equitable to the minimum free energy state. Maximum steady state yields (mass%) of ethyl levulinate of (46.6 ± 3.7), (50.2 ± 5.4), and (27.0 ± 1.9)% are determined for glucose, cellulose, and corn cob, respectively. The conversion of glucose and cellulose to ethyl levulinate in the presence of ethanol and sulphuric acid is shown to be a catalytic process, where the ethyl levulinate yield is not dependent on the acid concentration. For corn-cob biomass, in a new and contrasting finding, the ethyl levulinate yield is shown to strongly depend on the acid concentration. This effect is also observed in the fractions of diethyl ether formed, providing strong evidence that the hydrogen cation is not being replenished in the ethanolysis process and the overall reaction with corncob is not wholly catalytic. Thus, for the acid catalysed alcoholysis of lignocellulosic biomass, acid concentration must be scaled with feedstock concentration. The critical corn cob-to-acid ratio that maximises ethyl levulinate yields while minimizing the formation of undesired co-products (diethyl ether) is in the range 10-20 : 1 at 150 °C. A detailed, hierarchical, mass-conserved chemical kinetic model capable of accurately predicting the relative abundance of the three primary components of the ethanolysis reaction: ethyl levulinate, diethyl ether, and ethanol, from the biochemical composition of the feedstock, is elucidated and validated.

Climate monitoring in the Caumont cave and quarry system (northern France) reveal near oxygen isotopic equilibrium conditions for carbonate deposition

The study of modern cave deposits forming under near isotopic equilibrium conditions can potentially help disentangle the processes influencing the oxygen isotope system and suitability of stalagmites as archives of past hydrological or thermal changes. We used cave monitoring to evaluate the impact of kinetic isotope fractionation and assess the conditions under which modern cave carbonates form in the Caumont cave and quarry system, located in Normandy, northwest France. Over 20 months, we collected climatological data, dripwater, and modern carbonate samples at 2–4-week intervals at three different stations inside the Caumont cave and quarry system. We find highly stable (10.4 ± 0.3°C – 11.3 ± 0.1°C) temperature in the deeper sections of the Caumont cave and quarry system. The temporal dynamics of δ18Odrip indicates that the drip water composition in Caumont reflects the original (though subdued) signal of precipitation, rather than the impact the seasonal to interannual cave air temperature has on isotopic fractionation. The monitoring reveals that δ13C of modern carbonate is influenced by prior carbonate precipitation that occurs during the summer season when evapotranspiration can minimize effective infiltration. Comparison of δ18O from dripwater and modern calcite, precipitated on glass plates and collected every two to four weeks, reveals that modern calcite forms near oxygen isotope equilibrium. A Hendy test on modern carbonate deposited on a stalagmite-shaped glass flask over 20 months confirms this finding because neither does δ13C increase with distance from the apex, nor are δ13C and δ18O positively correlated. We conclude that the δ13C signal in speleothems reflect summer (and longer-term) prior carbonate precipitation in response to effective infiltration dynamics, and that the δ18O signal likely reflects annual to multi-annual changes in the composition of precipitation above the cave.

Complexation of Zr and Hf in fluoride-rich hydrothermal aqueous fluids and its significance for high field strength element fractionation

Zirconium and hafnium behave nearly identically in most geological processes due to their identical nominal ionic charge and similar radius. Some of the most pronounced exceptions from this rule are observed in fluoride-rich aqueous systems, suggesting that aqueous fluoride complexation may be involved in Zr/Hf fractionation. To understand the mechanisms causing this phenomenon, we investigated complexation of Zr4+ and Hf4+ in fluoride-rich (1.0 mol/kg HF) aqueous solutions at 40 MPa and 100–400 °C, using synchrotron X-ray absorption spectroscopy (X-ray absorption near edge structure and extended X-ray absorption fine structure) combined with classical and ab initio molecular dynamics simulations. The dominant experimentally observed complexes are [Zr(F,OH)4·2H2O]0 and [Hf(F,OH)4·2H2O]0, respectively. The first coordination shell comprises a distorted octahedron, with fluoride and hydroxide ligands at a similar mean radial distance (1.9–2.0 Å) from the central cation, and H2O ligands at a slightly greater distance (>2.1 Å). With increasing temperature, the H2O ligands move further out, causing first an increasing distortion of the octahedron and subsequently a partial transition to less hydrated complexes as a certain fraction of the H2O molecules move to the second shell at > 3 Å. As a consequence, the radial distance of the F- and OH– anions from the central cation, as well as the overall average radial distance of the first shell decreases due to decreased steric repulsion from the H2O ligands. Both experiments and simulations agree in that Hf forms slightly shorter bonds to its nearest neighbors than Zr. The results suggest two hypotheses for the mechanism of Zr/Hf fractionation during precipitation of minerals from fluoride-rich hydrothermal solutions: 1) The heavy twin (Hf) prefers the lower coordination (shorter bonds) and is thus less likely to enter into the higher coordination found in the solids. This mechanism would be analogous to equilibrium isotope fractionation. 2) The change of Hf into a higher coordination environment (e.g., from solution to solid) is slower because it forms stronger ligand-bonds than Zr. This would be analogous to reactive kinetic isotope fractionation. In either case mass dependent fractionation qualitatively matches the observations but mass independent effects on bond strength may also be significant. Quantitative investigations of these effects are needed and may also shed light on the currently still somewhat enigmatic fractionation behavior of Zr isotopes.

Kinetic Fractionation of Antimony Isotopes during Reduction by Sulfide

Kinetic Fractionation of Antimony Isotopes during Reduction by Sulfide

A New Method for Silicon Triple Isotope Analysis With Application to Siliceous Sponge Spicules

AbstractMultiple isotope ratios of elements disclose information on the fractionation mechanism that cannot be obtained from a single isotope ratio alone. We describe a laser fluorination technique in combination with gas source mass spectrometry for the measurement of triple Si isotope ratios with high precision that allows resolving ppm‐level variability in triple silicon isotope ratios (29Si/28Si, 30Si/28Si) Δ‘29Si due to purely mass‐dependent fractionation in Si isotopes. We demonstrate how the triple silicon isotope ratios can be used to characterize different mass‐dependent processes that fractionate silicon isotopes. We report new data on reference materials (NBS‐28 [RM8546], Diatomite, BigBatch) and on siliceous sponges. Our triple silicon isotope data resolve that kinetic fractionation, possibly related to breaking Si(OH)4 molecules, causes the low δ30Si of sponges. The data further suggest that the cause for fractionation may be the same for the groups of Demospongiae, Homoscleromorpha, and Hexactinellida and that triple silicon isotope ratios of sponges have potential as seawater silicon isotope proxy.

Petrogenesis of the Wushi carbonatites in the northwestern Tarim Basin: Implications to deep carbon recycling

Carbonatites are rarely exposed on the Earth's surface, and most of them are supposed to have been mantle-derived. However, in the most recent years, carbonatites with pronounced crustal signatures had also been recognized. Although carbonatites have attracted the attention of many researchers, their genesis remains controversial. In this study, we present a systematic C–O–Sr–Nd–Mg isotopic investigation on the carbonatites exposed in Wushi County located at the northwestern margin of the Tarim Basin to determine their petrogenesis. The Wushi carbonatites, containing the xenoliths of wall rocks, intruded into Precambrian sandstones as dykes. Carbonatites predominantly comprise calcite and accessory minerals, such as dolomite, apatite, mica and quartz, and thus are classified as calciocarbonatites. Trace element geochemistry indicates that the total rare earth element (REE) concentrations in Wushi carbonatites range from 13.6 to 57.3 ppm, with an average of 30.9 ppm. The chondrite-normalized REE patterns of the test samples indicate that light rare earth elements (LREE) in the samples have been enriched relative to their heavy rare earth elements (HREE) and that the LREE/HREE ratios vary from 6.0 to 9.1. The patterns also show negative Eu anomalies (δEu = 0.65–0.75) and weak negative Ce anomalies (δCe = 0.75–0.99). The primitive mantle-normalized trace element spider diagrams display the enrichment of large ion lithophile elements (LILE), such as Pb, Sr and Ba, and the strong depletion of high field strength elements (HFSE), such as Nb, Ta, Zr, Hf and Ti. The δ18OV-SMOW (15.9‰–18.2‰) and δ13CV-PDB (−2.97‰–3.36‰) values are more consistent with those of crust-derived carbonatites than with mantle-derived carbonatites. The values of δ18OV-SMOW and δ13CV-PDB are consistent with the high values of 87Sr/86Sr (0.7096–0.7110) and low values of 143Nd/144Nd (0.5118–0.5120). Typically, δ26Mg of the carbonatites (−1.76‰ to −1.27‰) is much lighter than the δ26Mg of the mantle (−0.25‰ ± 0.04‰) but heavier than the δ26Mg of sedimentary carbonates (−2.72‰ to −2.15‰) obtained from the neighbouring Western Tianshan orogenic belt. The light Mg isotope anomalies cannot be explained using secondary alteration, continental crustal contamination, kinetic isotope fractionation and fractional crystallization. Thus, these anomalies could be due to the isotope exchange reactions occurring between the oceanic crust and sedimentary carbonates during subduction. In this study, we propose a two-stage model to explain Wushi carbonatite formation based on its isotope characteristics. During the early stage of carbonatite formation, sedimentary carbonate rocks located along the northern margin of the Tarim Craton and oceanic crust were subducted into the deep mantle. Isotope exchange and carbonation occurred during subduction to form carbonated eclogite. In the second stage of carbonatite formation, the heat produced by the Permian mantle plume in the Tarim Basin melted the carbonated eclogite to produce carbonatite melt. Thus, the petrogenesis of the Wushi carbonatites revealed by the presence of multiple isotopes indicates that the carbonatite produced by carbonated eclogite in the deep mantle would exhibit typical crustal isotopic characteristics and provide new insights into deep carbon recycling.

13C-depleted methane pyrolyzed from contaminated Gale Crater sediment cores, Mars

This work re-interprets published SAM-EGA (Sample Analysis at Mars-Evolved Gas Analysis) geochemical data for twenty-four sediment cores sampled by the Curiosity rover. The samples were pyrolyzed at 35 °C/min in the range ∼ 100-850 °C. The amount of methane generated from carbonaceous matter in the cores and its stable carbon isotope ratio (δ13C-CH4) in selected cuts within the full temperature range were determined by tunable laser spectrometry (TLS cut). Chemometric analysis of five independent variables for eighteen of the cores identifies four genetic families in which three endmembers explain most data variance. One endmember is contamination by silylating agent (MTBSTFA) introduced unintentionally from wet-chemistry cups during flight and/or after landing of the rover. Five subsamples from the Cumberland (CB) core show a linear relationship between δ13C-CH4 and mean pyrolysis temperature (R2 = 0.77) within TLS cuts in the range 99-786 °C, which conforms with temperature-dependent kinetic theory. Based on dates of pyrolysis for the five CB samples, BSW (bisylylated water, a marker of MTBSTFA contamination) peaked on sol 281 and progressively decreased to sol 382. Linear regression of δ13C-CH4 versus BSW concentration (R2 = 0.98) yields δ13C-CH4 ∼ -70‰ for carbonaceous matter in uncontaminated CB core. Higher BSW yields systematically more negative δ13C-CH4 to the most negative value of −133‰ for CB1, which equates to an apparent fractionation of ∼98‰ from bulk MTBSTFA (δ13C = −35‰) to CB1 methane. Previous workers suggested that δ13C-CH4 from MTBSTFA could not be more than ∼5‰ depleted compared to bulk MTBSTFA. However, their SAM-like laboratory pyrolysis experiments for analogs of MTBSTFA yield δ13C-CH4 values that correspond only to gas trapped within the analyzed pyrolysis temperature cut (455-755 °C). Lower temperature TLS cuts for CB1 and CB2 (220-349 °C and 99-349 °C) trapped more 13C-depleted methane as reflected in their anomalous δ13C-CH4 of −133 and − 115‰, respectively. In addition, pyrolysis of MTBFTSA byproducts, residual solvent, and internal standards with Martian minerals, perchlorates, and sorption or desorption on clays may contribute to more negative δ13C-CH4 than expected from laboratory experiments that lack these components. It is not possible to determine bulk δ13C or δ13C-CH4 for the remaining two carbonaceous endmembers because of the effects of three factors: (1) Chemometric results by alternating least squares regression (ALS) define the relative contributions of endmembers based on five independent variables, not just δ13C-CH4. (2) Samples from distinct locations and stratigraphic ages are subject to variations in δ13C of deposited carbonaceous matter. (3) δ13C-CH4 values for samples from different TLS cuts differ due to temperature-dependent kinetic fractionation.

Fe and S isotopes variation of pyrite from hydrothermal mineralization in the Zijinshan region in Fujian Province, SE China

The Zijinshan district, Fujian Province, southeastern China, is a globally renowned CuAu orefield and hosts a wide variety of ore deposits within the Zijinshan granite complex and surrounding volcano-sedimentary rocks. We performed FeS isotope analysis on pyrite separates from the Zijinshan high-sulfidation epithermal deposit, Yueyang intermediate-sulfidation epithermal deposit, Wuziqilong transition-type (from high-sulfidation epithermal to porphyry) deposit, and Jintonghu porphyry CuMo deposit, aiming to understand the formation process of Fe-sulfides and the evolution of ore-forming fluids in different deposits. Pyrites from the Jintonghu porphyry CuMo deposit show variations in δ56Fe and δ34S from −0.15 ‰ to 0. 45 ‰, and from 1.81 ‰ to 2.70 ‰, respectively. In contrast, pyrites from epithermal-type deposits (i.e., Zijinshan, Yueyang, and Wuziqilong) show a negatively shifted Fe isotopic composition from −1.74 ‰ to 0.45 ‰. The combination of Fe isotopic data from the Jintonghu porphyry CuMo deposit with published minerals-fluid fractionation factors and the use of a Rayleigh fractionation model allowed us to determine the δ56Fe range of regional ore-forming fluids (−1.00 ‰ to −0.40 ‰), which is consistent with the previous “light fluid” hypothesis, suggesting that pyrite of porphyry CuMo deposits has isotopic compositions reflecting the isotopic value of the hydrothermal fluids. For the epithermal deposits, pyrite Fe isotopic composition is the result of a complex interaction of Rayleigh fractionation, rapid precipitation and kinetic fractionation, and δ56Fe values of the initial fluids is difficult to estimate. Integrating the Fe and S isotope data for pyrite of different genesis, we found that porphyry CuMo deposits (δ56Fe: −0.9 ‰ to 0.46 ‰; δ34S: −4.06 ‰ to 3.9 ‰) can be distinguished from a non-magmatic/low-temperature region, while the transitional area of which may be a porphyry-related hydrothermal deposit (i.e., epithermal deposit). In general, we suggest that the Fe and S isotopic signatures of pyrite can effectively distinguish porphyry-type deposits from their associated hydrothermal deposits.

Copper isotope fractionation by diffusion in a basaltic melt

Copper shows limited isotopic variation in equilibrated mantle-derived silicate rocks, but large isotopic fractionation during kinetic processes. For example, lunar and terrestrial samples that have experienced evaporation were found to have an isotopic fractionation of up to 12.5‰ in their 65Cu/63Cu ratios, while komatiites, lherzolites, mid-ocean ridge and ocean island basalts show negligible Cu isotope fractionation as a result of equilibrium partial melting and crystal fractionation. The contrast between the observed magnitudes of equilibrium and kinetic isotope fractionation for Cu calls for a better understanding of kinetic Cu isotope fractionation. One of the mechanisms for creating large kinetic isotopic fractionation even at magmatic temperatures is diffusion. In this study, we performed Cu isotopic measurements on Cu diffusion couple experiments to constrain the beta factor for Cu isotopic fractionation by diffusion. We demonstrate a Monte Carlo approach for the regression and error estimation of the measured isotope profiles, which yielded beta values of 0.16 ± 0.03 and 0.18 ± 0.03 for the two experimental charges measured. Our results are subsequently applied to a quantitative model for the evaporation of a molten sphere to discuss the role of diffusion in affecting the bulk Cu isotopic fractionation between liquid and vapor during evaporation. We apply the model to Cu evaporation experiments and tektite data to show that convection primarily governs mass transport for evaporation during tektite formation. In addition, we show that Cu isotopes can be used as a tool to test the role of kinetics during various magmatic processes such as magmatic sulfide ore deposit formation, porphyry-type ore deposit formation, and fluid-rock interactions.

Isotopic (δ13C, δ18O) Analysis of Small Amounts of Carbonate in Silicate Rocks by the Continuous Flow Isotope Ratio Mass Spectrometry Method

An experimental study of the main factors affecting the accuracy of oxygen and carbon isotopic analysis in carbonates dispersed in silicate matrix is carried out. Artificial 1, 2, 5, and 10% mixtures of quartz with carbonates with different isotopic parameters (KH-2, Ko, MCA-8) were analyzed by continuous flow isotope ratio mass spectrometry (CF IRMS). It is established that, in addition to the influence of the instrumental nonlinearity, the results are affected by two factors: trace amounts of CO2, constantly present in the system (the blank effect) and the presence of chemically neutral silicate particles (the matrix effect). The blank effect depends on the isotopic parameters of the sample and has very little influence on the estimated carbonate content in the rock. The matrix effect, on the contrary, strongly affects the estimated carbonate content, and produces the isotopic shift towards underestimated contents of heavy 13C and 18O isotopes. It is shown that this effect is related to the processes occurring near the CO2–acid–quartz interface, which are accompanied by kinetic fractionation of carbon and oxygen isotopes. Both effects are dependent on the amount of silicate matrix in the system and most clearly manifested during analysis of carbonate-poor rocks. When the carbonate content in the rock is about 1–2%, deviations from the true δ13C and δ18O values can reach the first ppm, while carbonate content obtained by chromatographic peak calibration can be underestimated by 20–40%.

Isotopic (δ13C, δ18O) Analysis of Small Amounts of Carbonate in Silicate Rocks by the Continuous Flow Isotope Ratio Mass Spectrometry Method

An experimental study of the main factors affecting the accuracy of oxygen and carbon isotopic analysis in carbonates dispersed in silicate matrix is carried out. Artificial 1, 2, 5, and 10% mixtures of quartz with carbonates with different isotopic parameters (KH-2, Ko, MCA-8) were analyzed by continuous flow isotope ratio mass spectrometry (CF IRMS). It is established that, in addition to the influence of the instrumental nonlinearity, the results are affected by two factors: trace amounts of CO2, constantly present in the system (the blank effect) and the presence of chemically neutral silicate particles (the matrix effect). The blank effect depends on the isotopic parameters of the sample and has very little influence on the estimated carbonate content in the rock. The matrix effect, on the contrary, strongly affects the estimated carbonate content, and produces the isotopic shift towards underestimated contents of heavy 13C and 18O isotopes. It is shown that this effect is related to the processes occurring near the CO2–acid–quartz interface, which are accompanied by kinetic fractionation of carbon and oxygen isotopes. Both effects are dependent on the amount of silicate matrix in the system and most clearly manifested during analysis of carbonate-poor rocks. When the carbonate content in the rock is about 1–2%, deviations from the true δ13C and δ18O values can reach the first ppm, while carbonate content obtained by chromatographic peak calibration can be underestimated by 20–40%.

Iron (hydr)oxide dynamic transformation-induced perfluorooctanoic acid transport and attenuation effect: Impacts of initial goethite and associated minerals content and groundwater type

Perfluorooctanoic acid (PFOA) has been widely utilized, leading to serious contamination. Iron (hydr)oxide transformation was varied in media. Whereas, dynamic transformation effect was extensively unclear. Here, iron (hydr)oxide dynamic transformation-induced PFOA transport and attenuation was investigated by emphasizing initial goethite (α-FeOOH) and associated minerals content and groundwater type based on the multi-process attenuation model. Results revealed that groundwater type did not affect the PFOA attenuation pathway. However, it controlled the iron (hydr)oxide dynamic transformation differences. PFOA transport behavior (retardation factor R from 2.61 to 1.91) was significantly affected by iron (hydr)oxide dynamic transformation. Iron (hydr)oxide transformation induced the greatest PFOA transport risk (R = 1.91, attenuation rate λ = 0.0001 min−1) in SO42− environment, where complex α-FeOOH, Fe3O4, and β-Fe2O3·H2O transformed to simplex β-FeOOH, leading to instantaneous (Kd) and kinetic (α) two-site sorption fraction change. Furthermore, the associated mineral Fe3O4 of goethite was crucial in PFOA attenuation (λ from 0.0001 to 0.0002 min−1). Fe3O4 released Fe2+ and the oxidation of Fe2+ to Fe3+ provided electrons, facilitating the formation of F–(CF2)7–COO· radicals, which played a key role in the following cycle attenuation process. This study provides a theoretical basis for understanding the interaction mechanism of PFOA and iron (hydr)oxide dynamic transformation under groundwater differences.

Enrichment of cobalt in the Xiarihamu Ni-Co sulfide deposit in the East Kunlun orogenic belt, Western China: Constraints from distribution of cobalt in sulfides and Fe and S isotopes of sulfides

The Xiarihamu Ni-Co sulfide deposit in the East Kunlun orogenic belt (EKOB), western China, is the largest magmatic Ni-Cu-(Co) sulfide deposit found in the orogenic belts worldwide. The geochemical behavior of Co during the evolution of sulfide melt is key to understand the enrichment process of Co in the Xiarihamu deposit, however remains unclear. In this study, the Co contents of sulfide inclusions enclosed within olivine and pyroxene and those of the sulfides interstitial to olivine and pyroxene in the Xiarihamu deposit were examinated by the Scanning Electron Microscopy (SEM) -Energy Dispersive Spectroscopy (EDS) and Electron Probe Microanalyzer (EPMA). The Fe and S isotopic compositions of the sulfides were measured in situ by LA-MC-ICPMS. The results show that Co contents increase from silicate to sulfide and arsenide minerals, and from chalcopyrite to pyrrhotite and pentlandite in the sulfides. High Co contents in pentlandite of pyroxenite (av. 2.79 %) and gabbro (av. 7.34 %) indicate that Co is enriched in the pentlandite of pyroxenite in different stage of magma. The pyrrhotite and pentlandite show positive correlation of Co with Fe and Ni, and suggested isomorphic substitution of Co for Fe and Ni. The δ56Fe values increase from pyrrhotite to pentlandite due to kinetic fractionation of Fe isotopes of Fe valent and bond length/strength, because pyrrhotite has longer bond and weaker bond strength of Fe-S than pentlandite, and display lighter Fe isotopic compositions. The δ56Fe values of pentlandite increase substantially from host peridotite to pyroxenite, which could be related to subsolidus fractional crystallization processes of monosulfide solid solution (MSS). The sulfide segregated and crystallized early from the MSS is richen in light Fe isotope. The sulfides in gabbro have high δ34S values, similar to δ34S of the sulfides in the country rocks of Proterozoic granitic gneiss, indicating a continuous addition of external sulfur into magma chamber. The δ34S and δ56Fe values of the sulfides approximately increase with increasing Co contents. Higher δ56Fe and δ34S values and Co contents of pentlandite in the pyroxenite suggest that the Co enrichment is mainly associated with sulfide saturation of magmas by crustal contamination.

Disorder effects in NbTiN superconducting resonators

Disordered superconducting materials like NbTiN possess a high kinetic inductance fraction and an adjustable critical temperature, making them a good choice for low-temperature detectors. Their energy gap (Δ), critical temperature (T c), and quasiparticle density of states (QDOS) distribution, however, deviate from the classical BCS theory due to the disorder effects. The Usadel equation, which takes account of elastic scattering, non-elastic scattering, and electro–phonon coupling, can be applied to explain and describe these deviations. This paper presents numerical simulations of the disorder effects based on the Usadel equation to investigate their effects on the Δ, T c, QDOS distribution, and complex conductivity of the NbTiN film. Furthermore, NbTiN superconducting resonators with coplanar waveguide (CPW) structures are fabricated and characterized at different temperatures to validate our numerical simulations. The pair-breaking parameter α and the critical temperature in the pure state TcP of our NbTiN film are determined from the experimental results and numerical simulations. This study has significant implications for the development of low-temperature detectors made of disordered superconducting materials.

High-temperature inter-mineral potassium isotope fractionation in ultrapotassic and granitic rocks: Implications for the potassium isotopic compositions of arc magmas

To constrain the mechanism and magnitude of inter-mineral K isotope fractionation during high-temperature magmatic processes, we conducted high-precision K isotope measurements on ultrapotassic and granitic rocks and mineral separates from the Qinling Orogenic Belt, China, as well as first-principles investigations of the corresponding K-bearing minerals. Our results show that the ultrapotassic rocks (−0.33 to −0.14‰) have considerably higher δ41K than the primitive mantle (−0.42 ± 0.08‰), confirming the previous conclusion that slab-derived fluids have contributed heavy K isotopic signatures to their mantle sources. Specifically, the K isotopic fractionation between biotite and microcline (Δ41Kbiotite-microcline = −0.11 to 0.05‰, with biotite and microcline ranging from −0.49 to −0.14‰ and − 0.48 to −0.12‰, respectively) agrees well with the calculated equilibrium isotopic fractionation scale. This evidence, together with the homogeneous mineral chemical compositions, suggests equilibrium K isotopic fractionation between biotite and microcline. Notably, amphiboles (δ41K ranging from −0.41 to 0.48‰) have heterogeneous K isotopic compositions and are generally heavier than coexisting microcline and biotite. In addition, the determined K isotopic fractionation between amphibole/plagioclase and microcline is inconsistent with the calculated results and is likely caused by the kinetic fractionation processes. To reveal the potential controls on the K isotopic compositions of arc magma, we utilized theoretical and measured K isotopic fractionation factors to model K isotopic fractionation behavior during amphibole crystallization. The results show that when Δ41Kamphibole-melt = 0.05‰, the fractional crystallization of amphibole shows negligible effect on the K isotopic composition of the residual melts. Even in the case of Δ41Kamphibole-melt = 0.24‰, fractional crystallization of amphibole exerts an insignificant control on the K isotopic composition of arc magma. Therefore, although amphibole may have heavier K isotopic compositions than the melts, its fractional crystallization may not distinctly decrease the K isotopic composition of residual melts.

Linking Significant Zr Isotopic Fractionation in Magmatic Zircons With Petrographic Textures

AbstractThe origin of crystal‐scale Zr isotopic variation remains enigmatic. Here, we report high‐precision Zr isotopic compositions of thin‐sectioned and hand‐picked zircon crystals from monzodiorites and K‐feldspar granites, which represent the mafic and felsic products of a differentiating magma. Our results reveal that zircons from both rock associations are dominated by a rim‐ward increase in the 94Zr/90Zr ratio and accompanied by ∼1‰ intracrystalline and intercrystalline variations, confirming the preferential incorporation of light Zr isotopes and thus kinetic isotopic fractionation during zircon growth. Notably, zircons enclosed by K‐feldspar in monzodiorites generally yield lower 94Zr/90Zr and higher Zr/Hf ratios than that of separated crystals, while in K‐feldspar granites, tiny zircons intergrown with apatite obtain higher 94Zr/90Zr but lower Zr/Hf ratios relative to that of sizable separates. The diversity in petrographic textures and sizes of zircon crystals, corresponding to their crystallization sequence, potentially accounts for some of the heterogeneity of Zr isotopes at the mineral scale.

Spatial variability of stable isotopes in river water over the Tibetan Plateau

AbstractEstimating isotopic changes of river water on the Tibetan Plateau (TP) remains highly uncertain due to variable water sources related with seasonality of atmospheric circulations and local kinetic fractionation. The in‐depth understanding of such changes is crucial for accurate palaeoaltimetry reconstruction and for river budget evaluation which related with surviving of one‐fifth of the world's population under accelerated warming. Here, we present a comprehensive river water isotopic composition dataset (δ18O, δD and d‐excess, 1852 samples) over the TP to systematically describe spatial distribution and explore possible controlling factors of isotopic data in theses rivers. Results showed that δ18O in river water range from −20.8‰ to −5.2‰ (latitudinally, 0.92‰ per degree), enriching northwardly in the seven exorheic river basins. The d‐excess values range from −19.7‰ to 20.5‰ with the pronounced low values in endorheic rivers basins. We identified that moisture sources and atmospheric transports leave significant signals in isotopic compositions of river water in the Upper Brahmaputra (UB), Upper Mekong (UM) and Upper Yangtze (UYA) basins, and local processes modify the isotopic signals mainly in the Upper Salween (US), Upper Indus (UI), Upper Yellow (UYE) and Endorheic Rivers (ER) basins. The δ18O‐elevation relationships are only established in the UB, UI and UYE with lapse rates of −4.4‰/km, −3.4‰/km and −3.5‰/km, respectively. We suggest that as changes of moisture sources and lapse rates in different basins, it is cautious to apply δ18O‐elevation lapse rates for palaeoaltimetry reconstruction. Our dataset will benefit regional studies of hydrological, biogeochemistry, palaeoaltimetry reconstruction and palaeoclimate.

The effect of bias current configuration on the performance of SQUID arrays

Designing superconducting electronic devices involves a careful study of all the elements in the circuit, including the superconducting bias leads. In this work, we introduce a theoretical model for two-dimensional (2D) superconducting quantum interference device (SQUID) arrays capable of simulating the voltage-to-magnetic flux response of devices with different bias current configurations. First, we compare uniformly biased and centre biased SQUID arrays by investigating the voltage versus magnetic flux response, maximum transfer function and voltage modulation depth. Then, we calculate the time-averaged fluxoid distributions for one-dimensional (1D) and 2D centre biased arrays. Finally, we study the performance of the two bias current configurations depending on array size, screening parameter, thermal noise strength and kinetic self-inductance fraction. Our calculations reveal: (i) centre biased 1D parallel SQUID arrays present an unusual voltage response caused by the asymmetric fluxoid distribution; (ii) the optimal transfer function of centre biased arrays strongly depends on the number of junctions in parallel; (iii) the performance of centre biased arrays approaches the uniform biased ones when the number of junctions in series exceeds those in parallel; (iv) while the screening parameter and the thermal noise strength clearly affect the device performance, the kinetic to self-inductance fraction seems to play only a secondary role.