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It is well-known that the equilibrium isotope fractionation of mercury (Hg) includes classical mass-dependent fractionations (MDFs) and nuclear volume effect (NVE) induced mass-independent fractionations (MIFs). However, the effect of the NVE on these kinetic processes is not known. The total fractionations (MDFs + NVE-induced MIFs) of several representative Hg-incorporated substances were selected and calculated with ab initio calculations in this work for both equilibrium and kinetic processes. NVE-induced MIFs were calculated with scaled contact electron densities at the nucleus through systematic evaluations of their accuracy and errors using the Gaussian09 and DIRAC19 packages (named the electron density scaling method). Additionally, the NVE-induced kinetic isotope effect (KIE) of Hg isotopes are also calculated with this method for several representative Hg oxidation reactions by chlorine species. Total KIEs for 202Hg/198Hg ranging from − 2.27‰ to 0.96‰ are obtained. Three anomalous 202Hg-enriched KIEs (δ202Hg/198Hg = 0.83‰, 0.94‰, and 0.96‰,) caused by the NVE are observed, which are quite different from the classical view (i.e., light isotopes react faster than the heavy ones). The electron density scaling method we developed in this study can provide an easier way to calculate the NVE-induced KIEs for heavy isotopes and serve to better understand the fractionation mechanisms of mercury isotope systems. [ABSTRACT FROM AUTHOR]

This benchmark provides the first rigorous test of a three-isotope system [12C, 13C, and 14C] subject to the combined effects of radioactive decay and both stable equilibrium and kinetic fractionation. We present a series of problems building in complexity based on the cycling of carbon in both organic and inorganic forms. The key components implement (1) equilibrium fractionation between multiple coexisting carbon species as a function of pH, (2) radioactive decay of radiocarbon with associated mass-dependent speciation demonstrating appropriate correction of the Δ14C value in agreement with reporting convention, and (3) kinetic stable isotope fractionation due to the oxidation of organic carbon to inorganic forms as a function of time and space in an open, through-flowing system. Participating RTM codes are CrunchTope, ToughReact, Hytec, and The Geochemist’s Workbench. Across all problem levels, simulation results from all RTMs demonstrate good agreement.

This research demonstrated the application of hydrochemical data and stable water isotopes of δ18O and δD (or delta 2H) for evaluating the relationship between surface water in Lake Bosumtwi and the underlying groundwater system. It aimed at determining the presence or absence of a hydraulic relationship and for evaluating the possible direction of flow at the interface between the two reservoirs. The study also estimated evaporative losses of infiltrating rainwater as it transits the unsaturated zone and provided important information on the hydrological processes prevailing in the area. The results of Q-Mode hierarchical cluster analysis (HCA) clearly differentiate the lake water from the groundwater based on their spatial relationship. These results indicated that groundwater recharge occurs on the hilltops of the crater, where it is slightly acidic with low levels of dissolved ions, characterised by short residence time and rapid unrestricted vertical infiltration and recharge. The groundwater becomes more mineralized with longer contact times and deeper circulation with the host rock, while it flows from the recharge areas towards the lake at lower elevations. Analyses of δ18O and δD showed a high evaporation rate on the lake surface (90%) with a significant evaporative enrichment, whereas groundwater showed no significant isotopic variations. Thus suggesting that the aquifers have been recharged by recent meteoric water that has undergone some evaporative enrichment since the study established an evaporation rate of water infiltrating the unsaturated zone ranging from 54 to 60%. Both reservoirs do not appear to be hydraulically connected, and where such a connection exists, it is expected to favour the lake. [ABSTRACT FROM AUTHOR]

To addresshow parent materials are affecting organic carbon dynamics in a soil profile, soils from a lithosequence comprising six parent lithologies under a rangeland ecosystem have been explored at three depth intervals for soil organic carbon (SOC) content and its 13C depth trends. Studied parent materials ranged from metamorphic (foliated: FM and non-foliated: NFM) to sedimentary (clastic carbonate: CCS) to plutonic (intermediate: IP, felsic: FP and intermediate felsic: IFP) geological contexts. The relationship between SOC concentration and its isotopic signatures to a depth of 50 cm in FM, NFM, FP and IFP profiles was well described by the kinetic fractionation of SOC during biodegradation. For CCS and IP lithologies, strong divergence from the Rayleigh equation was observed suggesting that the 13C enrichments in these soils resulted from both mixing different SOC pools and isotope fractionation related to the C mineralization. Results suggest that SOC across the lithosequence goes through different isotopic evolutions resulting from different 13C-enriched inputs and pedogenic properties as described by the extended Rayleigh equation (0 ≤ βC ≤ 0.80). These are presumably caused by the bedrock lithology implying that parent material affects C storage and dynamics. [ABSTRACT FROM AUTHOR]

Since 1971 water isotope measurements are being conducted by the Climate and Environmental Physics Division at the University of Bern on precipitation, river- and groundwater collected at several places within Switzerland. The water samples were stored in glass flasks for later analyses with improved instrumentation. Conventional isotope ratio measurements on precipitated water from all stations of the network are well correlated as expected. However, Δ17O as well as dex is anticorrelated to these isotope ratio. The combination of these parameters allow to investigate dependencies on temperature, turbulence factor, and humidity of these values as well as to look into the importance and relative contributions of kinetic to equilibrium fractionations. We used published temperature dependent fractionation factors in combination with a simple Rayleigh model approach to investigate the importance of the meteorological parameters on the isotope ratios. A direct comparison of measured and modeled isotope ratios for primary (δ17O, δ18O and (δD) as well as secondary isotope parameters (Δ17O and dex) is shown.

The feedback between CO 2 sources and sinks through chemical weathering is one of the important reasons why Earth has maintained a habitable climate for over four billion years. The lithium (Li) isotopic system is a promising tracer of silicate weathering, but the mechanisms causing its isotope fractionation during weathering remain ambiguous. Here, we performed batch experiments of Li adsorption to one of the common clay minerals -kaolinite in three sets, including the time-series, pH-dependent, and concentration-control sets. Our results demonstrate that the liquid-solid Li isotope fractionation reaches up to 36‰, with up to 99% initial Li being adsorbed on kaolinite. The magnitudes of Li adsorption and isotope fractionation increase with reaction time, and reach the steady-state after ∼1000 min. The magnitude of Li isotope fractionation increases with the adsorption ratio of Li, in positive relationships with solute pH and ionic strength. At constant solute pH = 8.5 and ionic strength of 0.001 M, the adsorption ratio and isotope fractionation of Li on kaolinite reach the maximum with the lowest initial Li concentration of 2 μM. In experiments, Li is removed by kaolinite as the inner-sphere and/or outer-sphere complexes, likely followed by structural occupation as supported by incomplete desorption. We model the Li isotope fractionation in all three sets, which can be best described by Rayleigh distillation models. In summary, significant Li isotope fractionation occurs following a kinetic law in closed-systems during adsorption on kaolinite. Adsorption-driven isotope fractionation conforms to a kinetic solid-liquid isotope fractionation factor α ∼ 0.992, consistent with theoretical ion-desolvation between complexed and dissolved ions (α = 0.9925, Hofmann et al., 2012). This study reveals a vital kinetic role of clay uptake in Li isotope fractionation during chemical weathering, suggesting rapid forward adsorption reaction versus relatively slow backward reaction. The dominance of the kinetic mechanism over the equilibrium mechanism further explains field observations from rivers worldwide. Given above, the outcome of this study calls for additional attention on low-temperature kinetic Li isotope fractionation at Earth's surface and further refinement of quantitative models using geological Li records to trace weathering and reconstruct climate. [ABSTRACT FROM AUTHOR]

The triple oxygen isotopes (16O, 17O, and 18O) are very useful in hydrological and climatological studies because of their sensitivity to environmental conditions. This review presents an overview of the published literature on the potential applications of 17O in hydrological studies. Dual-inlet isotope ratio mass spectrometry and laser absorption spectroscopy have been used to measure 17O, which provides information on atmospheric conditions at the moisture source and isotopic fractionations during transport and deposition processes. The variations of δ17O from the developed global meteoric water line, with a slope of 0.528, indicate the importance of regional or local effects on the 17O distribution. In polar regions, factors such as the supersaturation effect, intrusion of stratospheric vapor, post-depositional processes (local moisture recycling through sublimation), regional circulation patterns, sea ice concentration and local meteorological conditions determine the distribution of 17O-excess. Numerous studies have used these isotopes to detect the changes in the moisture source, mixing of different water vapor, evaporative loss in dry regions, re-evaporation of rain drops during warm precipitation and convective storms in low and mid-latitude waters. Owing to the large variation of the spatial scale of hydrological processes with their extent (i.e., whether the processes are local or regional), more studies based on isotopic composition of surface and subsurface water, convective precipitation, and water vapor, are required. In particular, in situ measurements are important for accurate simulations of atmospheric hydrological cycles by isotope-enabled general circulation models.

The Karakoram is a zone of Alpine -Karakoram Folded System and covers area between Eastern Hindu Kush, Pamir, Qiangtang Terrane and Kohistan-Ladakh Arc. Karakoram composed of sedimentary and crystalline complex from Precambrian to Pliocene age. The assessment of formation indicates the presence of geosyncline in Ordovician. Where occur weak Hurricane orogeny and develop rift in the Carboniferous - Permian time. This rift converts into Cimmerian Folded System which move towards Kirthar --Suleiman geosyncline. Therefore, Karakoram linked with Alpine-Himalayan folded Belt and experienced block fault tectonic processes. The presence of the coal, carboniferous shale, carbonate and clastic rocks in Northern Sedimentary Zone and crystallization and recrystallization processes in the Axial and the Southern zone allows to envisage potential of biotic and abiotic hydrocarbon in Karakoram. The palaeotectonic condition of development of Karakoram illustrates presence favourable environment of biotic and abiotic hydrocarbons in Karakoram. The sedimentary layers are source of biotic hydrocarbons. The abiotic hydrocarbons are result of geodynamic processes in upper mantle and upper crust. The semi --graben and graben structures can be a potential Oil and Gas Reservoirs. However geochemical studies will determine the total organic carbon, a factor to evaluate the volume of biotic hydrocarbons. The survey of zones of the crystalline and recrystallize rocks will elucidate the volume of the abiotic hydrocarbons in Karakoram. [ABSTRACT FROM AUTHOR]

The ratio of 3 He and 22 Ne varies throughout the mantle. This observation is surprising because 3 He and 22 Ne are not produced in the mantle, are highly incompatible during mantle melting, and are not recycled back into the mantle by subduction of oceanic sediment or basaltic crust. Our new compilation yields average 3 He/ 22 Ne ratios of 7.5 ± 1.2 and 3.5 ± 2.4 for mid-ocean ridge basalt (MORB) mantle and ocean island basalt (OIB) mantle sources respectively. The low 3 He/ 22 Ne of OIB mantle approaches planetary precursor 3 He/ 22 Ne values; ∼1 for chondrites and ∼1.5 for the solar nebula. The high 3 He/ 22 Ne of the MORB mantle is not similar to any planetary precursor, requiring a mechanism for fractionating He from Ne in the mantle and suggesting isolation of distinct mantle reservoirs throughout geologic time. New experimental results reported here demonstrate that He and Ne diffuse at rates differing by one or more orders of magnitude at relevant temperatures in mantle materials. We model the formation of a MORB mantle with an elevated 3 He/ 22 Ne ratio through kinetically modulated chemical exchange between dunite channel-hosted basaltic liquids and harzburgite wallrock beneath mid-ocean ridges. Over timescales relevant to mantle upwelling beneath spreading centers, He may diffuse tens to hundreds of meters into wallrock while Ne is effectively immobile, producing a mantle lithosphere regassed with respect to He and depleted with respect to Ne, with a net elevated 3 He/ 22 Ne. Subduction of high 3 He/ 22 Ne mantle lithosphere throughout geologic time would generate a MORB source with high 3 He/ 22 Ne. Mixing models suggest that to preserve a high 3 He/ 22 Ne reservoir, MORB mantle mixing timescales must be on the order of hundreds of millions of years or longer, that mantle convection has not been layered about the transition zone for most of geologic time, and that Earth's convecting mantle has lost at least 96% of its primordial volatile elements. The most depleted, highest 3 He/ 22 Ne mantle may be best preserved in the lower mantle where relatively high viscosities impede mechanical mixing. [ABSTRACT FROM AUTHOR]

Piston-cylinder experiments were run to determine the chemical diffusivities of 21 trace elements (Sc, V, Y, Zr, Nb, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Hf, Th and U) in hydrous rhyolitic melts at 1 GPa pressure and temperatures from 850 to 1250 °C. Diffusion couple glasses were doped with trace elements in low concentrations to characterize the diffusivities of all cations in a single experiment. Laser ablation ICP-MS was used to evaluate the trace element concentration gradients that developed in the silicate glasses. All calculated diffusion coefficients correspond to the temperature dependence D  =  D 0 exp (- E a / RT ). Rhyolite liquids contained either ∼4.1 wt% or ∼6.2 wt% dissolved H 2 O; separate Arrhenius relationships are produced for each melt composition. Trace element diffusivities in the melt with 6.2 wt% H 2 O are roughly two times higher than those in the less hydrous melt. Calculated trace element diffusion coefficients cover nearly two orders of magnitude at a given temperature. The high field strength elements are the slowest diffusers, followed by the transition metals and heavy rare earth elements. The light rare earth elements have the fastest diffusion rates in hydrous rhyolitic melt. The measured diffusion coefficients range down to values sufficiently low to preclude diffusive homogenization over geochemically realistic time scales in some cases. The substantial differences in the diffusivities of individual cations may result in fractionated trace element signatures in rhyolite melt pockets. A simple model is used to explore the potential for kinetic fractionation of REE during growth of an apatite crystal in a diffusive boundary layer locally saturated in P 2 O 5 . The faster-diffusing light REE are more efficiently transported away from the crystal interface than the slower-moving heavy REE. Diffusion effects will enrich the melt boundary layer in slow-moving HREE relative to the faster LREE. The kinetic fractionation of REE in the melt growth medium will result in a precipitated apatite crystal with a disequilibrium trace element composition. [ABSTRACT FROM AUTHOR]

Molecular diffusion is a key transport process for noble gases in water. Such diffusive transport is often thought to cause a mass-dependent fractionation of noble gas isotopes that is inversely proportional to the square root of the ratio of their atomic mass, referred to as the square root relation. Previous studies, challenged the commonly held assumption that the square root relation adequately describes the behaviour of noble gas isotopes diffusing through water. However, the effect of diffusion on noble gas isotopes has only been determined experimentally for He, Ne and Ar to date, whereas the extent of fractionation of Kr and Xe has not been measured. In the present study the fractionation of Kr and Xe isotopes diffusing through water immobilised by adding agar was quantified through measuring the respective isotope ratio after diffusing through the immobilised water. No fractionation of Kr and Xe isotopes was observed, even using high-precision noble gas analytics. These results complement our current understanding on isotopic fractionation of noble gases diffusing through water. Therefore this complete data set builds a robust basis to describe molecular diffusion of noble gases in water in a physical sound manner which is fundamental to assess the physical aspects of gas dynamics in aquatic systems. [ABSTRACT FROM AUTHOR]

The stable Cr isotope fractionation preserved in natural substances has been attributed predominantly to Cr(III)-Cr(VI) redox transformations. However, non-redox reaction pathways ( e.g. , ligand-promoted dissolution, ligand exchange, adsorption of Cr(III)) are liable to contribute to isotopic fractionation in natural systems given that soluble Cr(III)-ligands have been directly documented or modeled in several marine, continental, and hydrothermal environments. This study isolates the stable Cr isotope fractionation accompanying Cl-H 2 O ligand exchange during the transformation of three aqueous species in the Cr(III)-Cl-H 2 O system, [CrCl 2 (H 2 O) 4 ] + aq (abr. CrCl 2 + or S1), [CrCl(H 2 O) 5 ] 2+ aq (abr. CrCl 2+ or S2), and [Cr(H 2 O) 6 ] 3+ aq (abr. Cr 3+ or S3), at low pH (≤2). In dilute HCl (0.01 to 1 M), Cr 3+ is the kinetically favoured species and transformation of CrCl 2 + to CrCl 2+ to Cr 3+ via 2 steps of dechlorination/hydrolyzation begins immediately upon dissolution of a Cr(III)-Cl solid. Individual species are separated with cation exchange chromatography at different stages of transformation and inter- and intra-species (across an elution peak of one species) isotopic fractionation of up to 1 and 2‰ (δ 53/52 Cr), respectively, is documented. Comparison of peak elution characteristics with Cr-Cl-H-O isotopologue mass abundances suggests mass-dependent sorting of isotopologues alone cannot explain intra-species fractionation, supporting a previously published proposal that preferential adsorption of light Cr isotopes on the resin is driven by vibrational energy effects. The transformation of CrCl 2 + to CrCl 2+ is faster than CrCl 2+ to Cr 3+ and the rates of both transformations increase with solution pH. Preferential reaction of light Cr(III) isotopes into product species occurs during each transformation, consistent with closed-system, kinetic fractionation during Cl-H 2 O ligand exchange. Inter-species fractionation is assessed using time-series experiments beginning from the dissolution of two Cr(III)-Cl solids (dried NIST SRM979 standard and commercial CrCl 3 ·6H 2 O salt) in 0.01 M HCl (pH ≈ 2). The ε 53/52 Cr(CrCl 2+ / CrCl 2 + ) for the CrCl 2 + to CrCl 2+ reaction is −0.19‰ (SRM979) and −0.38‰ (salt) and the ε 53/52 Cr(Cr 3+ /CrCl 2+ ) for the CrCl 2+ to Cr 3+ reaction is consistent for both experiments at −0.49‰ (SRM979) and −0.51‰ (salt). Experiments where SRM979 is dissolved in 0.1 and 1 M HCl for a longer aging period provide preliminary evidence that the Cr 3+ /CrCl 2+ Cr(III) isotopic fractionation scales with HCl concentration (transformation rate). Chromium(III) dissolved in 6 M HCl and aged 5 months still yields an inter-species Cr isotope distribution that is apparently inherited from kinetic effects (light Cr isotopes in Cr 3+ ), attesting to the slow development of inter-species isotopic equilibrium, which instead predicts progressively heavier Cr isotopes from CrCl 2 + to CrCl 2+ to Cr 3+ . The kinetic Cr(III) isotopic fractionation documented herein is proposed to be relevant to understanding systems where aqueous Cr(III)-Cl species may be temporarily stable ( e.g. , metamorphic and hydrothermal systems or lateritic weathering). Further, the complexation of Cr(III) with other ligands ( e.g. , CO 3 2− , organics), combined with additional kinetic effects of Cr(III) potentially occurring in soils or sediment, must be explored prior to establishing the significance of empirical stable Cr isotope signatures in marine and continental environments. Further understanding of non-redox effects may lead to stable Cr isotopes developing as a proxy for system pH or ligand chemistry. [ABSTRACT FROM AUTHOR]

Significant magnesium and iron isotope fractionations were observed in an adjacent gabbro and granite profile from the Dabie Orogen, China. Chilled margin and granitic veins at the gabbro side and gabbro xenoliths in the granite indicate the two intrusions were emplaced simultaneously. The δ 26 Mg decreases from −0.28 ± 0.04‰ to −0.63 ± 0.08‰ and δ 56 Fe increases from −0.07 ± 0.03‰ to +0.25 ± 0.03‰ along a ∼16 cm traverse from the contact to the granite. Concentrations of major elements such as Al, Na, Ti and most trace elements also systematically change with distance to the contact. All the observations suggest that weathering, magma mixing, fluid exsolution, fractional crystallization and thermal diffusion are not the major processes responsible for the observed elemental and isotopic variations. Rather, the negatively correlated Mg and Fe isotopic compositions as well as co-variations of Mg and Fe isotopes with Mg# reflect Mg-Fe inter-diffusion driven isotope fractionation, with Mg diffusing from the chilled gabbro into the granitic melt and Fe oppositely. The diffusion modeling yields a characteristic diffusive transport distance of ∼6 cm. Consequently, the diffusion duration, during which the granite may have maintained a molten state, can be constrained to ∼2 My. The cooling rate of the granite is calculated to be 52–107 °C/My. Our study suggests diffusion profiles can be a powerful geospeedometry. The observed isotope fractionations also indicate that Mg-Fe inter-diffusion can produce large stable isotope fractionations at least on a decimeter scale, with implications for Mg and Fe isotope study of mantle xenoliths, mafic dikes, and inter-bedded lavas. [ABSTRACT FROM AUTHOR]

In this study we examine the behavior of stable Sr isotopes between strontianite [SrCO 3 ] and reactive fluid during mineral dissolution, precipitation, and at chemical equilibrium. Experiments were performed in batch reactors at 25 °C in 0.01 M NaCl solutions wherein the pH was adjusted by bubbling of a water saturated gas phase of pure CO 2 or atmospheric air. The equilibrium Sr isotope fractionation between strontianite and fluid after dissolution of the solid under 1 atm CO 2 atmosphere was estimated as Δ 88/86 Sr SrCO3-fluid = δ 88/86 Sr SrCO3 − δ 88/86 Sr fluid = −0.05 ± 0.01‰. On the other hand, during strontianite precipitation, an enrichment of the fluid phase in 88 Sr, the heavy isotopomer, was observed. The evolution of the δ 88/86 Sr fluid during strontianite precipitation can be modeled using a Rayleigh distillation approach and the estimated, kinetically driven, fractionation factor α SrCO3-fluid between solid and fluid is calculated to be 0.99985 ± 0.00003 corresponding to Δ 88/86 Sr SrCO3-fluid = −0.15‰. The obtained results further support that under chemical equilibrium conditions between solid and fluid a continuous exchange of isotopes occurs until the system approaches isotopic equilibrium. This isotopic exchange is not limited to the outer surface layer of the strontianite crystal, but extends to ∼7–8 unit cells below the crystal surface. The behavior of Sr isotopes in this study is in excellent agreement with the concept of dynamic equilibrium and it suggests that the time needed for achievement of chemical equilibrium is generally shorter compared to that for isotopic equilibrium. Thus it is suggested that in natural Sr-bearing carbonates an isotopic change may still occur close to thermodynamic equilibrium, despite no observable change in aqueous elemental concentrations. As such, a secondary and ongoing change of Sr isotope signals in carbonate minerals caused by isotopic re-equilibration with fluids has to be considered in order to use Sr isotopes as environmental proxies in aquatic environments. [ABSTRACT FROM AUTHOR]

Cassiterite (SnO 2) precipitates over a wide physicochemical range during magmatic-hydrothermal processes. Significant variations in chemical and Sn isotopic compositions of cassiterite have been increasingly reported from hydrothermal deposits worldwide. However, the mechanisms responsible for such notable changes in cassiterite geochemistry remain to be fully addressed. Toward this end, we investigated the chemical and Sn isotopic compositions of distinct generations of cassiterite from a highly-evolved magmatic-hydrothermal-metallogenic system (Xianghualing Sn polymetallic deposit, South China). Cassiterite is widespread in the albite granite, greisen, skarn, and sulfide ore of this deposit, covering most of the known cassiterite-bearing rock/ore types. Based on distinct morphologies and mineral paragenesis, three generations of the Xianghualing cassiterite are identified: (1) Cst 1 occurs in albite granite and greisen; (2) Cst 2 occurs in skarn; and (3) Cst 3 is present in sulfide ore. A lattice strain model indicates that inter-element compositional differences of cassiterite are dual-controlled by cassiterite element partition coefficients and melt/fluid compositions for sufficient and deficient elements, respectively. The variations in Zr, Hf, Nb, and Ta elements in cassiterite are recognized as thermo-indicators of the melt/fluid physicochemical conditions. Their concentrations are influenced by pre- and syn-precipitated Zr-Hf-Nb-Ta-enriched minerals that have a wide crystallization temperature range. Due to differentiations of multiple cationic valences, concentrations and interelement ratios of Sb, Fe, V, and U can be utilized to monitor the relative melt/fluid redox state of different cassiterite generations. Tin stable isotopic compositions are notably fractionated in the Xianghualing cassiterite samples, with δ amu Sn values relative to standard NIST 3161a ranging from − 0.16 ‰ to 0.19‰. By comparison with compiled Sn isotopes of other hydrothermal deposits, kinetic disequilibrium fractionation is proposed as the main control on cassiterite Sn isotopes fractionation. A Rayleigh fractionation model generates fractionation factors of 1.00010–1.00025, consistent with fractionation factors predicted by first principles calculations (1.00013 to 1.00037). Thus, progressive precipitation of Sn-enriched minerals due to the change of physicochemical conditions during magmatic-hydrothermal processes will cause lighter Sn isotopic compositions in residual melt/fluid. This study highlights that cassiterite chemical and Sn stable isotopes are novel indicators to magmatic-hydrothermal processes. • A mathematic method is proposed to normalize varied expressions of Sn isotopic data. • Lattice strain model predicts inter-elemental compositional differences of cassiterite. • Cassiterite chemical compositions could trace physicochemical conditions of melt/fluid. • Cassiterite Sn isotope fractionation mainly caused by kinetic disequilibrium fractionation. [ABSTRACT FROM AUTHOR]

Two independent analytical methods (kinetic and sequential extraction protocols) were used to understand the distribution, stability, and lability of Pb-sediment complexes in Indian continental shelf. The concentrations of sedimentary Pb varied from 12.0 ± 0.6 to 30.4 ± 0.1 mg·kg − 1 and 15.9 ± 0.3 to 36.7 ± 0.4 mg·kg − 1 in the western and eastern shelf of India respectively. The kinetic extraction study showed that higher proportion of labile Pb-complexes were present in the eastern shelf sediments (~ 24% of total Pb) than the western shelf sediments (~ 14% of total Pb). The sedimentary organic matter was found to regulate lability of sedimentary Pb complexes. The sequential extraction study suggested that Fe/Mn oxyhydroxide were the primary hosting phase for labile Pb complexes. This study showed that water soluble, exchangeable, carbonate/bicarbonate-Pb complexes in the sediments was labile. This study provides a better physicochemical description of stability or lability of Pb complexes in the coastal sediment of India. [ABSTRACT FROM AUTHOR]

Martian meteorites are the only samples available from the surface of Mars. Among them, olivine-phyric shergottites are basalts containing large zoned olivine crystals with highly magnesian cores (Fo 70–85) and rims richer in Fe (Fo 45–60). The Northwest Africa 1068 meteorite is one of the most primitive “enriched” shergottites (high initial 87 Sr/ 86 Sr and low initial ε 143 Nd). It contains olivine crystals as magnesian as Fo 77 and is a major source of information to constrain the composition of the parental melt, the composition and depth of the mantle source, and the cooling and crystallization history of one of the younger magmatic events on Mars (∼180 Ma). In this study, Fe-Mg isotope profiles analyzed in situ by femtosecond-laser ablation MC-ICP-MS are combined with compositional profiles of major and trace elements in olivine megacrysts. The cores of olivine megacrysts are enriched in light Fe isotopes ( δ 56 Fe IRMM-14 = −0.6 to −0.9‰) and heavy Mg isotopes ( δ 26 Mg DSM-3 = 0–0.2‰) relative to megacryst rims and to the bulk martian isotopic composition ( δ 56 Fe = 0 ± 0.05‰, δ 26 Mg = −0.27 ± 0.04‰). The flat forsterite profiles of megacryst cores associated with anti-correlated fractionation of Fe-Mg isotopes indicate that these elements have been rehomogenized by diffusion at high temperature. We present a 1-D model of simultaneous diffusion and crystal growth that reproduces the observed element and isotope profiles. The simulation results suggest that the cooling rate during megacryst core crystallization was slow (43 ± 21 °C/year), and consistent with pooling in a deep crustal magma chamber. The megacryst rims then crystallized 1–2 orders of magnitude faster during magma transport toward the shallower site of final emplacement. Megacryst cores had a forsterite content 3.2 ± 1.5 mol% higher than their current composition and some were in equilibrium with the whole-rock composition of NWA 1068 (Fo 80 ± 1.5). NWA 1068 composition is thus close to a primary melt (i.e. in equilibrium with the mantle) from which other enriched shergottites derived. [ABSTRACT FROM AUTHOR]

All physical process models and field observations are inherently imperfect, so there is a need to both (1) obtain measurements capable of constraining quantities of interest and (2) develop frameworks for assessment in which the desired processes and their uncertainties may be characterized. Incorporation of stable water isotopes into land surface schemes offers a complimentary approach to constrain hydrological processes such as evapotranspiration, and yields acute insight into the hydrological and biogeochemical behaviors of the domain. Here a stable water isotopic scheme in the National Center for Atmospheric Research's version 4 of the Community Land Model (CLM4) is presented. An overview of the isotopic methods is given. Isotopic model results are compared to available data sets on site-level and global scales for validation. Comparisons of site-level soil moisture and isotope ratios reveal that surface water does not percolate as deeply into the soil as observed in field measurements. The broad success of the new model provides confidence in its use for a range of climate and hydrological studies, while the sensitivity of simulation results to kinetic processes stands as a reminder that new theoretical development and refinement of kinetic effect parameterizations is needed to achieve further improvements. [ABSTRACT FROM AUTHOR]

Copper diffusion plays an important role in natural processes, such as metal transport during the formation of magmatic-hydrothermal porphyry-type ore deposits and Cu isotope fractionation during tektite formation. Copper diffusion data in natural silicate melts, however, are limited. In this study, chalcocite (Cu2S) 'dissolution' experiments were carried out using chalcocite-rhyolite diffusion 'couples' to study Cu (and S) diffusion in rhyolitic melts. Instead of chalcocite dissolution as initially expected, our experiments show that Cu is transferred from the chalcocite crystal to the rhyolitic melt, and Fe is transferred from the rhyolitic melt to chalcocite, whereas the S concentration profile in the rhyolitic melt is essentially flat. From the Cu and Fe exchange profiles in the rhyolitic melts, Cu diffusivities and Fe diffusivities are obtained and reported. Copper diffusivity in rhyolitic melts containing 0.10 to 5.95 wt% H2O at temperatures of 750 to 1391 °C and pressures of 0.5 to 1.0 GPa can be described as: which allows the estimation of an activation energy for diffusion in dry rhyolitic melts to be 96.8 ± 4.1 kJ/mol. In the above equation, diffusivity ( D) is in m2/s, T is the temperature in K, w is the H2O concentration in the rhyolitic melts in wt% and all errors reported are at 1σ level. Combining Cu diffusion data from this study and previous data in basaltic melt gives a general equation for Cu diffusivity in natural silicate melts: where Si+Al-H is the cation mole fraction of Si plus Al minus H in the silicate melt on a wet basis. Iron diffusivities obtained in this study, in anhydrous to 6 wt% H2O rhyolite, are combined with previous data to get a general equation for Fe diffusion in rhyolitic melts: Our data demonstrate that Cu diffusion is faster than H2O or Cl in rhyolitic melts containing 6 wt% water, which indicates that the scavenging and transport of Cu by a magmatic volatile phase during formation of porphyry-type ore deposits is not limited by diffusion of Cu. Based on our experimental data, Cu diffusivity is almost four orders of magnitude higher than Zn in anhydrous rhyolitic melts, which supports the explanation of more diffusive loss of Cu leading to more fractionated Cu isotopes than Zn isotopes in tektites. [ABSTRACT FROM AUTHOR]

We estimate the blank carbon mass over the course of a typical Ramped PyrOx (RPO) analysis (150–1000°C; 5°C×min–1) to be (3.7±0.6) μg C with an Fm value of 0.555±0.042 and a δ13C value of (–29.0±0.1) ‰ VPDB. Additionally, we provide equations for RPO Fm and δ13C blank corrections, including associated error propagation. By comparing RPO mass-weighted mean and independently measured bulk δ13C values for a compilation of environmental samples and standard reference materials (SRMs), we observe a small yet consistent 13C depletion within the RPO instrument (mean–bulk: μ=–0.8‰; ±1σ=0.9‰; n=66). In contrast, because they are fractionation-corrected by definition, mass-weighted mean Fm values accurately match bulk measurements (mean–bulk: μ=0.005; ±1σ=0.014; n=36). Lastly, we show there exists no significant intra-sample δ13C variability across carbonate SRM peaks, indicating minimal mass-dependent kinetic isotope fractionation during RPO analysis. These data are best explained by a difference in activation energy between 13C- and 12C-containing compounds (13–12∆E) of 0.3–1.8 J×mol–1, indicating that blank and mass-balance corrected RPO δ13C values accurately retain carbon source isotope signals to within 1–2‰. [ABSTRACT FROM PUBLISHER]

Stable Ca isotopes are an increasingly useful tool for understanding the sources and processes leading to the formation of magmatic rocks, yet Ca isotope fractionation during genesis of silicic continental crust is still poorly understood. Here, we present Ca, Sr, and Nd isotope, as well as major- and trace-element whole-rock geochemical data for A-, I-, and S-type granites (n = 30) from Australia/Tasmania, Canada, and France (δ 44 Ca BSE of -0.6‰ to +0.2‰) and compare them to phase-equilibrium models for partial-melting (pelite, greywacke, MORB, enriched Archean tholeiite) and crystallization (hydrous arc basalt, A-type granite) that incorporate novel ab-initio predictions for Ca isotope fractionation in epidote and K-feldspar. The ab-initio calculations predict that epidote has similar δ 44 Ca to anorthite and that K-feldspar is the isotopically lightest known silicate mineral at equilibrium (Δ 44 Ca kspar-melt of -0.4‰ at 1000 K). Our phase-equilibrium model results suggest that δ 44 Ca variations in all three granite types can be fully explained through magmatic processes, without necessarily requiring addition of isotopically exotic components (e.g., carbonate sediments). Heavy Ca isotope enrichments in A-type granites from the Lachlan Fold Belt, however, require isotopic disequilibrium between plagioclase and melt, which we use to constrain average plagioclase growth rates in these systems. This also serves to illustrate that whole-rock Ca isotope measurements can be used to estimate crystal growth rates, even in the absence of analyzable phenocrysts. In general, low Ca diffusivities and strong isotopic diffusivity ratios (D 44 /D 40) in low-H 2 O granitic magmas should lead to resolvable isotopic disequilibrium effects in plagioclase, even at relatively slow growth rates (e.g., > 0.03 cm/yr). Combining our data with those from previous studies, we demonstrate that average granitoids and upper continental crust (with newly estimated δ 44 Ca BSE of -0.25 ± 0.02‰, 2SE) have resolvable low δ 44 Ca compared to basalts and oceanic crust. Given that pressure has a major influence on Ca isotope fractionation across all of our models, this implies that melts feeding upper crustal granitoids dominantly evolve in the lower crust (10-14 kbar, through either partial-melting or fractional crystallization). This observation also suggests that heavier Ca isotopes are preferentially recycled back into the mantle through subduction and/or lower-crustal delamination events, but this is unlikely to have had a significant influence on the δ 44 Ca evolution of the upper mantle through geologic time. • Ca isotope variations in granites can be fully explained through magmatic processes. • Ab-initio (DFT) estimates suggest that K-feldspar concentrates light isotopes of Ca. • Crystal growth rates can be estimated using Ca isotopes + phase equilibrium models. • Upper crustal granitoids dominantly evolve in the lower crust (10-14 kbar). • Heavier Ca isotopes are preferentially recycled back into the mantle through time. [ABSTRACT FROM AUTHOR]

This study examines the behavior of Ba isotope fractionation between witherite and fluid during mineral dissolution, precipitation and at chemical equilibrium. Experiments were performed in batch reactors at 25 °C in 10 −2 M NaCl solution where the pH was adjusted by continuous bubbling of a water saturated gas phase of CO 2 or atmospheric air. During witherite dissolution no Ba isotope fractionation was observed between solid and fluid. In contrast, during witherite precipitation, caused by a pH increase, a preferential uptake of the lighter 134 Ba isotopomer in the solid phase was observed. In this case, the isotope fractionation factor α witherite-fluid is calculated to be 0.99993 ± 0.00004 (or Δ 137/134 Ba witherite-fluid ≈ −0.07 ± 0.04‰, 2 sd). The most interesting feature of this study, however, is that after the attainment of chemical equilibrium, the Ba isotope composition of the aqueous phase is progressively becoming lighter, indicating a continuous exchange of Ba 2+ ions between witherite and fluid. Mass balance calculations indicate that the detachment of Ba from the solid is not only restricted to the outer surface layer of the solid, but affects several (∼7 unit cells) subsurface layers of the crystal. This observation comes in excellent agreement with the concept of a dynamic system at chemical equilibrium in a mineral–fluid system, denoting that the time required for the achievement of isotopic equilibrium in the witherite–fluid system is longer compared to that observed for chemical equilibrium. Overall, these results indicate that the isotopic composition of Ba bearing carbonates in natural environments may be altered due to changes in fluid composition without a net dissolution/precipitation to be observed. [ABSTRACT FROM AUTHOR]

The chemical diffusivities of 25 trace elements (Sc, V, Rb, Sr, Y, Zr, Nb, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Hf, Ta, Th, and U) in basaltic melt were measured in diffusion couple experiments performed at 1 GPa pressure and temperatures from 1250 to 1500 °C. Trace element concentration gradients developed in the glasses were simultaneously characterized using laser ablation ICP/MS to create an internally consistent data set. A ratio-fitting technique was employed to accurately determine the relative diffusivities of the rare earth elements (REE). All diffusion coefficients conform to the expected Arrhenius relation D = D exp(− E /RT), where the constant log( D , m/s) ranges from −3.81 to −5.11 and E ranges from 161.73 to 223.81 kJ/mol. The slowest diffusivities are obtained for the high-field-strength elements; the fastest diffusivities are obtained for the low-field-strength elements. Trace element diffusion in MORB follows the compensation law, where log D is linearly correlated with E . Arrhenius parameters for diffusion of trivalent REE monotonically increase from La to Lu and are near-linear functions of bond strength (the variation in Arrhenius parameters means that the diffusivities decrease monotonically from La to Lu at a given T). The new data for trace element diffusion in basaltic melt can be used to explore the potential for diffusive fractionation of trace elements using kinetic models. Concentrations of the slower-diffusing heavy REE may be altered relative to those of the faster-diffusing light REE as a diffusive boundary layer develops in melt-melt and crystal-melt systems. The results indicate that diffusion in basalt can be an effective mechanism to fractionate trace elements from one another. [ABSTRACT FROM AUTHOR]

Recent studies suggest a potential role of diffusive transport of metals (e.g., Cu, Au, PGE) in the formation of magmatic sulfide deposits and porphyry-type deposits. However, diffusivities of these metals are poorly determined in natural silicate melts. In this study, diffusivities of copper in an anhydrous basaltic melt (<10 ppm H2O) were measured at temperatures from 1298 to 1581 °C, and pressures of 0.5, 1, and 1.5 GPa. Copper diffusivities in anhydrous basaltic melt at 1 GPa can be described as:. ... where DCubasalt is the diffusivity in m2/s, T is the temperature in K, and errors are given at 1s level. A fitting of all experimental data considering the pressure effect is:. ... where P is the pressure in GPa, which corresponds to a pre-exponential factor D0 = (1.25 ÷ 2.2)10-6 m²/s, an activation energy Ea = 101 ± 10 kJ/mol at P = 0, and an activation volume Va = (5.2 ± 2.0)10-6 m³/mol. The diffusivity of copper in basaltic melt is high compared to most other cations, similar to that of Na. The high copper diffusivity is consistent with the occurrence of copper mostly as Cu+ in silicate melts at or below NNO. Compared to the volatile species, copper diffusivity is generally smaller than water diffusivity, but about one order of magnitude higher than sulfur and chlorine diffusivities. Hence, Cu partitioning between a growing sulfide liquid drop and the surrounding silicate melt is roughly in equilibrium, whereas that between a growing fluid bubble and the surrounding melt can be out of equilibrium if the fluid is nearly pure H2O fluid. Our results are the first copper diffusion data in natural silicate melts, and can be applied to discuss natural processes such as copper transport and kinetic partitioning behavior in ore formation, as well as copper isotope fractionation caused by evaporation during tektite formation. [ABSTRACT FROM AUTHOR]

Revealing the potential of Ca isotopes in the research of travertine formation processes is the principal goal of this study. To achieve this, the hydrochemistry, travertine precipitation rates, and variations in Ca isotopic compositions (δ 44/40 Ca) of present-day endogenic (thermogenic) travertine in two different hydrodynamic systems (canal and pool) are studied at Baishuitai (Yunnan, SW China). In the canal, where the travertine precipitation is faster, δ 44/40 Ca values of both solution and travertine show a downstream increase, with Ca isotopic fractionation (Δ 44/40 Ca CaCO3-aq ) equal to ~− 1.6‰. Compared to the canal, Ca isotopic fractionation between travertine and aqueous Ca 2 + is smaller (Δ 44/40 Ca CaCO3-aq ≈ − 1.2‰) in the pools where travertine precipitation rates are lower. The spatial variations in δ 44/40 Ca values of solution and travertine are related to the amount of Ca removed from the solution when δ 44/40 Ca values of spring water remain stable. In addition, the results confirm the control of precipitation rates on Ca isotopic fractionation between calcite and parent aqueous Ca 2 + using natural samples. The observed negative correlation between Δ 44/40 Ca CaCO3-aq and travertine precipitation rates can be explained by the steady-state kinetic surface reaction model proposed by DePaolo (2011), with equilibrium and kinetic fractionation factors of α eq = 1.0000 ± 0.0001 and α f = 0.9983 ± 0.0002, respectively. An important consequence of this study is that Ca isotopes in travertine systems are good tools to have access to variations of δ 44/40 Ca aq , which are directly linked to the amount of precipitated Ca. This could then be useful for reconstructing past hydrodynamic conditions when applied to travertine core data. [ABSTRACT FROM AUTHOR]